aviation electronics technician - basic material/navedtra 14028.pdfas an aviation electronics...

NONRESIDENTTRAININGCOURSE

Aviation Electronics Technician - Basic

NAVEDTRA 14028

DISTRIBUTION STATEMENT A
: Approved for public release; distribution is unlimited.

PREFACE

About this course:

This is a self-study course. By studying this course, you can improve your professional/military knowledge, as well as prepare for the Navywide advancement-in-rate examination. It contains subject matter about day-to-day occupational knowledge and skill requirements and includes text, tables, and illustrations to help you understand the information. An additional important feature of this course is its references to usefulinformation to be found in other publications. The well-prepared Sailor will take the time to look up the additional information.

History of the course:

• Jun 1991: Original edition released. • Mar 2003: Minor revision released.

Published byNAVAL EDUCATION AND TRAINING

PROFESSIONAL DEVELOPMENTAND TECHNOLOGY CENTER

NAVSUP Logistics Tracking Number0504-LP-022-3690

TABLE OF CONTENTS

CHAPTER PAGE

1. Physics ................................................................................................................... 1-1

2. Infrared, Lasers, and Fiber Optics.......................................................................... 2-1

3. Analog Fundamentals............................................................................................. 3-1

4. Digital Computers .................................................................................................. 4-1This chapter has been deleted. For information on number systems, logic, anddigital computers, refer to Nonresident Training Course (NRTC) NavyElectricity and Electronics Training Series (NEETS), Module 13, NAVEDTRA 14185, and Module 22, NAVEDTRA 14194.

5. Aviation Systems Fundamentals and Support Equipment ..................................... 5-1

6. Avionics Maintenance............................................................................................ 6-1

7. Avionic Drawings, Schematics, Handtools, and Materials .................................... 7-1

8. Test Equipment ...................................................................................................... 8-1

9. Safety and Security ................................................................................................ 9-1

APPENDIX

I. Glossary ................................................................................................................. AI-1

II. Symbols, Formulas, and Measurements................................................................. AII-1

CHAPTER 1

PHYSICS

As a Navy technician, you deal with complexmachines and equipment. You are expected tounderstand, operate, service, and maintain thesemachines and equipment and to instruct newpersonnel. No matter how complex a machine oritem of equipment, its action is based on theapplication of a few basic principles of physics.To understand, maintain, and repair the equip-ment and machinery necessary to operate shipsand aircraft, you must understand these basicprinciples.

The physicist finds and defines problemsand searches for their solutions. Studyingphysics teaches a person to be curious aboutthe physical world and provides a means ofsatisfying that curiosity. The principles ofphysics apply to the other sciences. Physicsis a basic branch of science and deals withmatter, motion, force, and energy. It dealswith the phenomena that arise because mattermoves, exerts force, and possesses energy,and it is the foundation for the laws governingthese phenomena. Physics is closely associatedwith chemistry and depends heavily uponmathematics for many of its theories andexplanations.

BASIC CONCEPTS

In the study of physics, specific wordsand terms have specific meanings that mustbe understood. If you don’t understand theexact meaning of a particular term, you won’tunderstand the principles involved in the useof that term. Once the term is understood,however, you can understand many principles.The first part of this chapter defines some of thephysical terms and briefly discusses some of theparticular principles that concern technicalpersonnel.

MEASUREMENT

Learning Objective: Identify units ofmeasurement for magnitude, direction,and time.

Measurement is an important consideration inall branches of science. To evaluate results, youmust often answer the questions “how much, howfar, how many, how often, or in what direction.”As scientific investigations become more complex,measurements must become more accurate, andnew methods must be developed to measure newthings.

Measurements may be classed in threebroad categories—magnitude, direction, andtime. These categories are broken down intoseveral types, each with its own standardunits of measurement. Measurements of direc-tion and time are fairly well standardizedand have few subdivisions. Magnitude, onthe other hand, is an extremely complexmeasurement category having many classes andsubdivisions.

The unit of measurement is just as im-portant as the number that precedes it, andboth are necessary to give an accurate descrip-tion. The two units of measurement mostcommonly used are the metric and the English.Metric units are usually used to express scientificobservations, where the basic unit of distanceis the meter (m), the mass is the kilogram(kg), and of time is the second (s). Thisis called the meter-kilogram-second (mks)system. Another widely used metric system usesthe centimeter (cm) as the basic unit of distance,the gram (g) as the basic unit of mass, andthe second (s) as the basic unit of time,and is called the centimeter-gram-second (cgs)system. The English system uses the foot fordistance, the pound avoirdupois (weight) for

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mass, and the second for time, and is calledthe foot-pound-second (fps) system. Refer totable 1-1 for other frequently used units ofmeasurement.

Q1. What are the three broad categories ofmeasurement?

Q2. What unit of measurement is used toexpress scientific measurements?

Units of Distance

As an aviation electronics technician, you willuse both the English and the metric systems ofmeasurement. For example, radar range is usuallyexpressed in the English system as yards or miles,while wavelength is most often expressed in themetric system, with the meter as the basic unit.

METRIC UNITS OF LENGTH.— Metricunits of length are based on the standard meter.

In 1960, the 11th General Conference on Weightsand Measures adopted an atomic standard forthe meter: The meter is the length equal to1,650,763.73 wavelengths in a vacuum of theradiation corresponding to the transition betweenthe levels and of an atom of krypton 86.

When large distances are measured, use thekilometer (km), which is 1,000 meters (m)(1 kilometer = 1,000 meters). For smaller measure-ments, the meter is divided into smaller units. Onemeter equals 100 centimeters (1 m = 100 cm), and1 centimeter equals 10 millimeters (1 cm = 10 mm),so 1 meter equals 1,000 millimeters (1 m = 1,000mm). The table in appendix 3 lists other prefixesused with basic units.

The micrometer (pm) is smaller than themillimeter. It is often the unit used to state thewavelength of light. The micrometer is one-thousandth of a millimeter or one-millionth of ameter, the nanometer is one-thousandth of amicrometer, and picometer is one-thousandth ofa nanometer or one-millionth of a micrometer.

Table 1-1.-Frequently Used Units of Measurement

ENGLISH SYSTEM METRIC SYSTEM GENERAL

acre angstrom ELECTRICALBtu (British thermal calorie ampere

unit) dyne coulombbushel erg decibeldram gram faradfoot hectare henrygallon hertz mho (siemens)hertz hour ohmhorsepower joule volthour liter wattinch meter LIGHTknot metric ton (1 ,000 candlemil kg) candelamile micrometer lambertminute micron lumenounce minute MAGNETICpeck newton gausspint quintal gilbertpound second maxwellquart stere relsecondslugton (short, 2,000 lb

long, 2,240 lb)yard

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ENGLISH UNITS OF LENGTH.— Thecommon units of distance in the English systemof measurement are inches, feet, yards, and miles,where 1 foot equals 12 inches (1 ft = 12 in.), 1yard equals 3 feet (1 yd = 3 ft = 36 in.), and 1mile equals 1,760 yards (1 mile = 1,760 yd= 5,280 ft = 63,360 in.). The nautical mile is6,076.115 feet. The mil is one-thousandth of aninch.

In 1866 the United States, by an act ofCongress, defined the yard to be 3600/3937part of a standard meter, or in decimal formapproximately 0.9144 meter. Therefore, you canmake conversions between the other systemsby properly multiplying or dividing. Someapproximate conversions are listed in table 1-2.

Q3. Match the element being measured with them e t r i c t e r m u s e d t o e x p r e s s t h emeasurement.

1. Distance a. Kilogram2. Time b. Second3. Mass c. Meter

Q4. What is the English equivalent of 1 meter?

Units of Mass, Weight, and Force

The measure of the quantity of matter that abody contains is called mass. The mass of a bodydoes not change. It may be compressed to asmaller volume or expanded by heat, but thequantity of matter remains the same.

The metric unit of mass is based on the gram,since it is equal to the mass of 1 cubic centimeterof pure water at a temperature of 4° Celsius. Forpractical purposes, this is correct. The U.S.Bureau of Standards has one iridium cylinder,which is identical to the standard kilogram (1,000gram) cylinder of platinum preserved at theInternational Bureau of Weights and Measures,near Paris. The standard pound (lb) is the massequal to 0.4536 kilogram or 453.6 grams.

The mass of a body is constant no matterwhere the body is located. The weight of a bodyis the force with which it is attracted toward theearth. The body’s weight is slightly higher at thepoles than at the equator, and becomes less as thebody moves away from the earth’s surface.

Grams, kilograms, and pounds are used asunits of mass. These units are also used to describethe weight of a body by comparing the body’sweight to the weight of a standard mass unit.Normally, when an object is described as weighing1 pound, it means the object has the same pullof gravity that amass of 1 pound would have nearthe earth’s surface at sea level. At sea level, thenumerical values of weight and mass of a givenobject are equal, when expressed in the sameunits.

Sometimes, the slug is used as the unit of mass.This is the mass that weights 32 pounds at sealevel. At sea level, a mass of 1 gram exerts adownward force of 980 dynes because of gravity,and 1 kilogram exerts a downward force of 9.8newtons. Since 1 kg = 1,000 g, a kilogram exertsa force of 1,000 x 980 dynes, or 980,000 dynes,

Table 1-2.-Conversion Factors for Units of Length

NOTE: When a number is multiplied by a power of ten, the decimal point is moved the number of placesrepresented by the power. A negative power moves the decimal point to the left; a positive power movesit to the right. Thus, 84 x 10-2= .84, and 84 x 10-2 = 8,400. Simply stated, a power of ten merely movesthe decimal point left or right.

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which is equal to 9.8 newtons. Therefore, 1newton equals 100,000 dynes.

The newton can be equated to the Englishsystem as follows: 1 newton equals 0.2247 pound-force, or 1 pound-force equals 4.448 newtons.

Its easy to convert between the weight unitsof the metric system since you only have to movethe decimal point through a conversion of 1000:1.For example, 1,000 mg = 1.000 g, 1,000 g= 1.000 kg, and 1,000 kg = 1.000 metric ton. Itsharder to convert between weight units of theEnglish system since the pound is divided into 16ounces and the ounce into 16 drams. The shortton is 2,000 pounds, while the long ton is 2,240pounds. (Note: The metric ton is fairly close tothe long ton; it converts to 2,205 pounds.)

fundamental units of the two systems are notcombined. For example, if force is given inpounds and distance in meters, one or the othermust be changed before combining them to getwork units.

SPEED AND VELOCITY.— One example ofa derived unit is the knot, a unit of speed. Thisunit combines the nautical mile as the unit ofdistance and the hour as the unit of time. It isderived by dividing the distance traveled by thetime required for that travel. For example, if aship traveled at a constant rate for 15 minutes(0.25 hr) and moved a distance of 6 nautical miles,its speed would be 6/0.25 or 24 knots (kn). Therate of travel (speed) may also be used to solve

Q5.

Q6.

for distance traveled when time is known. If theWhat is the difference between the mass of above ship traveled 24 knots for 3 hours, it woulda body and the weight of a body? move 72 nautical miles. Likewise, the time

required for moving a certain distance mayWhat is meant when a person is described be determined when the speed is known. Aas weighing 195 pounds? movement of 36 nautical miles by a ship traveling

at 24 knots would require 1 hour and 30 minutesDerived Units

Units based on combinations of two or threefundamental units are sometimes expressed assome combination of these units. The watt (unitof power) can be written as the joule (unit ofwork) per second. The joule could be expressedas newtons (force) times meters (distance), andthe watt then becomes newton-meters per second.Likewise, the unit of horsepower could beexpressed in foot-pounds per second. Althoughthere are conversion factors between derived unitsof the English system and the metric system,

(36/24 = 1.5 hr, or or hr 30 min).Speed is often expressed as two fundamental

units such as miles per hour; kilometers per hour;or feet, inches, meters or centimeters per minuteor per second. Conversion is a matter of replacingone unit by its equivalent in another unit. Forexample, a speed of 60 miles per hour (60 mph)is converted to feet per second by replacing themile with 5,280 feet and the hour with 3,600seconds. Therefore, a speed of 60 mph = 60(5,280 ft/3,600 s) = 88 feet per second.

Table 1-3 gives the conversion factors betweenmeters per second (m/s), feet per second (ft/s),

ANSWERS FOR REVIEW QUESTIONS Q1. THROUGH Q4.

A1. a. Magnitudeb. Directionc. Time

A2. Metric unit of measurement

A3. ELEMENT METRIC TERM

1. Distance c. Meters2. Time a. Seconds3. Mass c. Kilograms

A4. Approximately 1 yard

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kilometers per hour (km/hr), miles per hour(mi/hr), and knots.

The terms speed and velocity are sometimesinterchanged. However, velocity is a vectorquantity; that is, it is speed in a given direction.For example, a car may move around a circularpath with a constant speed while its velocity iscontinuously changing. When a body moves withconstant speed along a straight line whosedirection is specified, it is customary to speak ofits velocity (which is numerically equal to itsspeed). When a body moves along a curved pathor along a straight path with no reference beingmade to direction, it is proper to speak of itsspeed.

WORK AND ENERGY.— Units of work andenergy, also derived units, are the product of theunits of force and distance. In the cgs system, theerg is the work done by a force of 1 dyne actingthrough a distance of 1 centimeter. The joule isthe unit of work in the mks system where 1 newtonacts through a distance of 1 meter. Since 1 newtonequals 100,000 dynes and 1 meter equals 100centimeters, the joule is equal to 10 million ergs.

In the English system, the unit foot-pound isdefined as the work done in lifting 1 pound adistance of 1 foot against the force of gravity. Forexample, the work done in lifting a mass of 5pounds vertically 4 feet is 20 foot-pounds (5 lbx 4 fg = 20 ft-lb). (Do not confuse this foot-poundwith the one used to measure torque. ) Since 1pound-force equals 4.448 newtons, and 1 footequals 0.3048 meter, 1 foot-pound is approxi-mately 1.356 joules.

The calorie is the heat energy required to raisethe temperature of 1 gram of water 10 Celsius.The British thermal unit (Btu) is the heat energyrequired to raise the temperature of 1 pound ofwater 10 Fahrenheit, and it is equivalent to 252calories (and, incidentally, to 777.8 foot-poundsof mechanical energy).

POWER.— All units of power includemeasurements of force, distance, and timebecause power equals work (which is force timesdistance) divided by time. The watt is the unit ofpower frequently used with electrical units, andit is also the rate of doing 1 joule of work in 1second. Therefore, if a force of 5 newtons actsthrough a distance of 12 meters in 3 seconds, thepower required is 20 watts, or

If the same work is done in 2 seconds, 30 wattsare required.

The horsepower is a larger unit of power. Itis equal to 550 foot-pounds per second, or 746watts; therefore, 1 foot-pound per second is746/550 watts. or about 1.356 watts.

OTHER UNITS.— Magnitude measurementis complex. Consider a few examples of measure-ment dealing with magnitude: weight, distance,temperature, voltage, size, loudness, andbrightness. Then consider measurements based oncombinations of magnitude: density (weight perunit volume), pressure (force per unit area),thermal expansion (increase in size per degreechange in temperature), and so forth. Also,measurements combine categories. The flow ofliquids is measured in volume per unit of time,speed is measured in distance per unit of time,rotation is measured in revolutions per units oftime (second, minute, etc.), and frequency isexpressed in cycles per second (hertz).

The importance of measurement and theselection of the proper unit of measurementcannot be overemphasized. Several systems ofmeasurement further complicate matters. Forexample, distance may be measured in feet or inmeters; weight, in pounds or in kilograms;capacity, in quarts or in liters; temperature, in

Table 1-3.-Conversion Factors for Speed and Velocity

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degrees Fahrenheit, Celsius, or Rankine, or inKelvin units; density, in pounds per cubic foot orin grams per cubic centimeter; and angles, indegrees or in radians.

Q7.

Q8.

Q9.

Q10.

How are derived units constructed?

Speed and velocity are sometimes used usif they meant the same thing. What is thedifference between speed and velocity?

What term is defined as the work done inlifting 1 pound a distance of 1 foot againstthe force of gravity?

List the measurements included in the unitsof power.

MATTER AND ENERGY

Learning Objective: Identify generalphysics laws and general properties ofmatter, density and specific gravity, pres-sure and total force, and kinetic energy.

Matter is defined as anything that occupiesspace and has weight or mass. In its natural state,matter is a solid, a liquid, or a gas. All matteris composed of small particles called moleculesand atoms. Matter may be changed or combinedby various methods—physical, chemical, ornuclear. Matter has many properties; propertiespossessed by all forms of matter are called generalproperties, while those properties possessed onlyby certain classes of matter are referred to asspecial properties.

Energy is defined as the capacity for doingwork. It is classified in many ways; but in thistraining manual (TRAMAN), energy is classifiedas mechanical, chemical, radiant, heat, light,sound, electrical, or magnetic. Energy is con-stantly being exchanged from one object toanother and from one form to another.

Law of Conservation

Matter may be converted from one form toanother with no change in the total amount ofmatter. Energy may also be changed in form withno resultant change in the total quantity of energy.In addition, although the total amount of matterand energy remains constant, matter can beconverted into energy or energy into matter. Thisstatement is known as the law of conservation forenergy and matter. The basic mathematicalequation that shows the relationship betweenmatter and energy is where E representsenergy, m represents mass, and c represents thevelocity of light.

From this equation, you can see that thedestruction of matter creates energy, and that thecreation of matter requires expenditure of energy.You can also see that a given quantity of matteris the equivalent of some amount of energy. Incommon usage it is usually stated that matterpossesses energy.

General Properties of Matter

All forms of matter possess certain properties.In the basic definition, matter occupies space andhas mass (inertia). Those terms represent most,if not all, of the general properties of matter.

SPACE.— The amount of space occupied by,or enclosed within, the bounding surfaces of abody is called volume. In the study of physics,this concept is modified somewhat to be com-pletely accurate. You know that matter is a solid,a liquid, or a gas, and each has its own specialproperties. Liquids and solids tend to retaintheir volume when physically moved from onecontainer to another, while gases tend to assumethe volume of the container.

All matter is composed of atoms and mole-cules. These particles are composed of still smallerparticles separated from each other by empty

ANSWERS FOR REVIEW QUESTIONS A5. AND A6.

A5. The mass of- the body is the measure of the quantity of matterthat the body contains, and it does not change. The weight ofa body is the force that attracts toward earth.

A6. The person has the same pull of gravity that a mass of 195 wouldhave when located near sea level.

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space. This idea is used to explain two generalproperties of matter—impenetrability andporosity.

Two objects cannot occupy the same space atthe same time; this is known as the impenetrabilityof matter. The actual space occupied by theindividual subatomic particles cannot be occupiedby any other matter. The impenetrability ofmatter may, at first glance, seem invalid when acup of salt is poured into a cup of water, as theresult is considerably less than two cups of saltwater. However, matter has an additional generalproperty called porosity, which explains thisapparent loss of volume: The water simplyoccupies space between particles of salt. Porosityis present in all material, but to a wide range ordegree. Generally, gases are extremely porous andliquids only slightly so; solids vary over a widerange, from the sponge to the steel ball.

INERTIA.— Every object tends to maintaina uniform state of motion. A body at rest neverstarts to move by itself; a body in motion willmaintain its speed and direction unless it is causedto change. To cause a body to change from itscondition of uniform motion, a push or a pullmust be exerted on it. This requirement is due tothat general property of all matter known asinertia. The greater the tendency of a body tomaintain uniform motion, the greater its inertia.The quantitative measure of inertia is the massof the body.

Acceleration.— Any change in the state ofmotion of a body is known as acceleration. Inother words, acceleration is the rate of change inthe motion of a body and may represent eitheran increase or a decrease in speed and/or a changein the direction of motion.

The amount of acceleration is stated as thechange of velocity divided by the time requiredto make the change. For example, if a cartraveling 15 mph increased its speed to 45 mphin 4 seconds, the 30-mph increase divided by 4seconds gives 7.5 miles per hour per second as itsacceleration. By converting the 30 mph to 44 feetper second, you could express the acceleration as11 feet per second per second or as

Force.— Force is the action or effect on a bodythat tends to change the state of motion of thebody acted upon. A force tends to move a bodyat rest; it tends to increase or decrease the speedof a moving body; or it tends to change the body’sdirection of motion. The application of a force

to a body does not necessarily result in a changein the state of motion; it may only tend to causesuch a change.

A force is any push or pull that acts on a body.Water in a can exerts a force on the sides andbottom of the can. A tugboat exerts a push or apull (force) on a barge. A man leaning against abulkhead exerts a force on the bulkhead. In theseexamples, a physical object is exerting the forceand is in direct contact with the body upon whichthe force is being exerted. Forces of this type arecalled contact forces.

Other forces act through empty space withouthaving contact and, at times, without seeming tohave any mass associated with them. The forceof gravity exerted on a body by the earth (weight)is an example of a force acting on a body throughempty space. Such a force is known as an action-at-a-distance force. Electric and magnetic forcesare other examples of action-at-a-distance forces.The space through which these action-at-a-distance forces are effective is called a force field.

Force is a vector quantity; that is, it has bothdirection and magnitude. A force is completelydescribed when its magnitude, direction, and pointof application are given. In a force vectordiagram, the starting point of the line representsthe point of application of the force.

Any given body, at any given time, is subjectedto many forces. In many cases, all of these forcesmay be combined into a single resultant force thatis used to determine the total effect on the body.Because of its extremely large mass, the earthexerts such a large gravitational attraction that itis practical to ignore all other attractions and usethe earth’s gravitational attraction as the resultant.

Gravitational attraction is exerted by eachbody on the other. When there is a greatdifference in the mass of two bodies, we think ofthe force as being exerted by the larger mass onthe smaller mass. Therefore, it is commonly statedthat the earth exerts a gravitational force ofattraction on a body. The gravitational attractionexerted by the earth is called gravity.

The gravitational force exerted by the earthon an object is called the weight of that objectand is expressed in force units. In the Englishsystem, force is expressed in pounds. If an objectis attracted by a gravitational force of 160 pounds,the object weighs 160 pounds. The gravitationalforce between two objects decreases as thedistance between them increases; therefore, anobject weighs less a mile above the surface of the

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ocean than it weighs at sea level, and it weighsmore a mile below sea level.

Q11.

Q12.

Q13.

Q14.

Q15.

Q16.

What relationship is defined by theequation mc2?

Name the concept of the statement “Twoobjects can’t occupy the same space at thesame time.”

What action must be applied to an objectto overcome inertia?

What is meant by the term acceleration?

Why is force considered a vector quantity?

In the English system of measurement, whatforce is expressed in pounds?

Density and Specific Gravity

The density of a substance is its weight per unitvolume. A cubic foot of water weighs 62.4pounds; the density of water is 62.4 pounds percubic foot. (In the metric system, the density ofwater is 1 gram per cubic centimeter.)

The specific gravity (sp gr) of a substance isthe ratio of the density of the substance to thedensity of water and is expressed by the equation

weight of substancespecific gravity = weight of equal volume of water

.

Specific gravity is not expressed in units ofmeasurement, but as a pure number. For example,

if a substance has a specific gravity of 4, 1 cubicfoot of the substance weighs 4 times as much asa cubic foot of water, 62.4 times 4 = 249.6pounds. In metric units, 1 cubic centimeter of asubstance with a specific gravity of 4 weighs 1times 4, or 4 grams. (Note that in the metricsystem of units, the specific gravity of a substancehas the same numerical value as its density.)

Specific gravity and density are independentof the size of the sample under consideration anddepend only upon the substance of the sample.See table 1-4 for typical values of specific gravityfor various substances.

Table 1-4.-Typical Values of Specific Gravity

SUBSTANCESPECIFICGRAVITY

Aluminum 2.7Brass 8.6Copper 8.9Gold 19.3Ice 0.92Iron 7.8Lead 11.3Platinum 21.3Silver 10.5Steel 7.8Mercury 13.6Ethyl alcohol 0.81Water 1.00


A7.

A8.

A9.

They are based on combinations of two or three fundamentalunits expressed as some combination of these units. For example,the watt could be written as a joule per second.

Velocity is a vector quantity; it is speed in a given direction, whilespeed is a body moving along a path with no reference being madeto direction.

Foot-pound

A10. a. Forceb. Distancec. Time

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A great deal of ingenuity is often needed tomeasure the volume of irregularly shaped bodies.Sometimes it is practical to divide a body into aseries of regularly shaped parts, then apply therule that the total volume is equal to the sum ofthe volumes of all individual parts. Figure 1-1shows another method of measuring the volumeof small irregular bodies. The volume of waterdisplaced by a body submerged in water is equalto the volume of the body.

A somewhat similar consideration is possiblefor floating bodies. A floating body displaces itsown weight of liquid. This statement may beproved by filling a container to the brim withliquid, then gently lowering the body to thesurface of the liquid and catching the liquid thatflows over the brim. Weigh the liquid displacedand the original body and prove the truth of thestatement.

Pressure and Total Force

Pressure and force, while related topics, arenot the same thing. A weight of 10 pounds restingon a table exerts a force of 10 pounds. However,the shape of the weight determines the effect ofthe weight. If the weight consists of a thin sheetof steel resting on a flat surface, the effect is quitedifferent from the effect of the same sheet of steelresting on a sharp corner.

Pressure is the distribution of a force withrespect to the area over which that force isdistributed. Pressure is defined as the force perunit of area, or P = F/A. A flat pan of water witha bottom area of 24 square inches and a totalweight of 72 pounds exerts a total force of 72pounds, or a pressure of 72/24 or 3 pounds persquare inch, on a flat table. If the pan is balancedon a block with a surface area of 1 square inch,the pressure is 72/1 or 72 pounds per square inch.

Figure 1-1.-Measuring the volume of an irregular object.

An aluminum pan with a thin bottom is suitablefor use on a flat surface, but may be damagedif placed on the small block.

This concept explains why a sharp knife cutsmore easily than a dull one. The smaller areaconcentrates the applied force (increases thepressure) and penetrates more easily. Forhydraulic applications, the relationship betweenpressure and force is the basic principle ofoperation. In enclosed liquids under pressure, thepressure is equal at every point on the surfacesof the enclosing container; therefore, the force ona given surface is dependent on the area.

Kinetic Energy

Moving bodies possess energy because they arecapable of doing work. The energy of mass inmotion is called kinetic energy, and may beexpressed by the equation

kinetic energy = 1/2

where m represents the mass of the body, and vis the velocity of its motion.

When the moving body is stopped, it loses itskinetic energy. The energy is not destroyed, butis merely converted into other forms of energy,such as heat and potential energy. Remember,bodies at rest also possess energy by virtue of theirposition. You will learn more about kinetic energyand potential energy later in this chapter.

Q17.

Q18.

Q19.

How is the density of a substancedescribed?

How is the specific gravity of a substancedescribed?

Moving bodies have energy because theycan do work. What term describes theenergy of mass in motion?

STRUCTURE OF MATTER

Learning Objective: Identify the variouselements, compounds, and states of matteras they affect the structure of matter.

All matter is composed of atoms, and atomsare composed of smaller subatomic particles.The subatomic particles of major interest inelementary physics are the electron, the proton,

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and the neutron. They may be consideredelectrical in nature, with the proton representinga positive charge, the electron representing anegative charge, and the neutron being neutral(neither positive nor negative). The compositionof matter follows a consistent pattern for allatoms; however, the detailed arrangement ofsubatomic particles is different for each distinctsubstance. The combination and the arrangement

the mass is contained in the nucleus. Normally,any change in the composition of the atominvolves a change in the number or arrangementof the electrons (due to their smaller mass,electrons are more easily repositioned thanprotons). A most notable exception is in the fieldof nuclear physics, or nucleonics. In chemistry andin general physics (including electricity andelectronics), the electron complement is usually

of the subatomic particles determine the dis- dealttinguishing chemical and physical characteristicsof a substance. Q20.

The protons and the neutrons of an atom areclosely packed together in the atom’s nucleus(core), and the electrons revolve around the Q21.nucleus. Atoms are normally considered to beelectrically neutral; that is, they normally containan equal number of electrons and protons. This Q22.condition is not present all the time. Atoms that

with.

What gives a substance its distinguishingcharacteristics?

List the three subatomic particles of theatom.

What is a balanced atom?

contain an equal number of electrons and protons ELEMENTSare called balanced atoms; those with an excess(too many) or a deficiency (too few) of electrons The word element means any of about 100are called negative and positive ions. substances that make up the basic substances of

The proton and the neutron have approxi- all matter. Two or more elements may combinemately the same mass, approximately 1,836 times chemically to form a compound, and anythe mass of an electron. In any atom, nearly all combination that does not result in a chemical


A11. The law of conservation for energy and matter which states that“Although the total amount of matter and energy remainsconstant, matter can be converted into energy or energy intomatter.”

A12. Impenetrability of matter.

A13. A push or pull that exerts a force on the body.

A14. An increase or decrease in speed and/or a change in directionof motion.

A15. Because it has both direction and magnitude.

A16. The gravitational force exerted by the earth on the body, knownas weight of that body, expressed in force units.

A17. It is its weight per unit volume.

A18. It is the ratio of the density of the substance to the density ofwater.

A19. Kinetic energy.

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reaction between the different elements is called amixture. The atom is the smallest unit that exhibitsthe distinguishing characteristics of an element. Anatom of any one element differs from an atom ofany other element in the number of protons in thenucleus. All atoms of a given element contain thesame number of protons. Therefore, the numberof protons in the nucleus determines the type ofmatter. Elements are frequently tabulatedaccording to the number of protons they contain.The number of protons in the nucleus of the atomis referred to as the atomic number of the element.

Nucleus

The study of the nucleus of the atom, knownas nucleonics or nuclear physics, is the subject ofextensive modern investigation. Experimentsusually involve the bombardment of the nucleusof an atom, using various types of nuclearparticles. By doing this, the composition of thenucleus is changed, usually resulting in the releaseof energy. The change to the nucleus may occuras an increase or a decrease in the number ofprotons and/or neutrons.

If the number of protons is changed, the atomhas become an atom of a different element. Thisprocess, called transmutation, is the processsought by the alchemists of the Middle Ages intheir attempts to change various metals into gold.Scientists of that period believed transmutationcould be accomplished by chemical means, givingimpetus to the development of chemistry.

If, on the other hand, only the number ofneutrons in the nucleus is changed, the atomremains an atom of the same element. Althoughall of the atoms of any particular element havethe same number of protons (atomic number),atoms of certain elements may contain variousnumbers of neutrons. Normally, an atom ofhydrogen (the sole exception to the rule that allatoms are composed of three kinds of subatomicparticles) contains a single proton and a singleelectron, but no neutrons. However, somehydrogen atoms do contain a neutron. Such atoms(although they are atoms of hydrogen) are knownas deuterium, or heavy hydrogen. (They are calledheavy because the addition of the neutron hasapproximately doubled the weight of the atom. )The atomic weight of an atom is an indication ofthe total number of protons and neutrons in theatomic nucleus.

Atoms of the same element but with differentatomic weights are called isotopes. Nearly allelements have several isotopes; some are common,and some are rare. A few of the isotopes occurring

naturally and most of those produced by nuclearbombardment are radioactive or have unstablenuclei. These unstable isotopes undergo aspontaneous nuclear bombardment, whicheventually results in either a new element or adifferent isotope of the same element. The rateof spontaneous radioactive decay is measured byhalf-life. Half-life is the time required forone-half the atoms of a sample of radioactivematerial to change (by spontaneous radioactivedecay) into a different substance. Uranium, aftera few billion years and several substance changes,becomes lead.

Electron Shells

The physical and chemical characteristics ofan element are determined by the number anddistribution of electrons in the atoms of thatelement. The electrons are arranged in successivegroups of electron shells around the nucleus. Eachshell can contain no more than a specific numberof electrons. An inert element (one of the few gaselements that do not combine chemically with anyother element) is a substance in which the outerelectron shell of each atom is completely filled.In all other elements, one or more electrons aremissing from the outer shell. An atom with onlyone or two electrons in its outer shell can be madeto give up those electrons. An atom whose outershell needs only one or two electrons to becompletely filled can accept electrons fromanother element that has one or two extras.

The concept of needed or extra electrons arisesfrom the basic fact that all atoms have a tendencytoward filling their outer shell. An atom whoseouter shell has only two electrons may have tocollect six additional ones (no easy task, from anenergy standpoint) to have the eight required forthat shell to be full. Or, and this is easier froman energy standpoint, the two electrons in theouter shell can be given up, and the full shell nextto it serves as the new outer shell. In chemicalterminology, this concept is called valence, whichis the prime determining factor in predictingchemical combinations.

Q23. How is the atomic number of an elementdetermined?

Q24. How is the atomic weight of an elementdetermined?

Q25. The outer electron shell of each atom of anelement is completely filled. What type ofelement is this?

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COMPOUNDS AND MIXTURES ions stick together to form a molecule of thecompound sodium chloride.

Under certain conditions, two or moreelements are brought together and unitedchemically to form a compound. The result-ing substance may differ widely from itscomponent elements. For example, ordinarydrinking water is formed by the chemicalunion of two gases—hydrogen and oxygen.When a compound is produced, two or moreatoms of the combining elements join chemicallyto form the molecule that is typical of the newcompound. The molecule is the smallest unit thatexhibits the distinguishing characteristics of acompound.

The combination of sodium and chlorine toform the chemical compound sodium chloride(common table salt) is a typical example of theformation of molecules. Sodium is a highlycaustic, poisonous metal whose atom con-tains 11 electrons. Its outer shell consistsof one electron (a valence of +1). Chlorineis a highly poisonous gas whose atom has17 electrons, but it lacks a single electron(a valence of –1) to fill its outer shell. When theatom of sodium gives up its extra electron, itbecomes a positively charged ion. (It has lost aunit of negative charge.) The chlorine atom,having taken on this unit of negative charge(electron) to fill its outer shell, becomes a negativeion. Since opposite electric charges attract, the

Common Table Salt

NOTE: The attracting force that holds theions together in the molecular form isknown as the valence bond, a term that isfrequently encountered in the study oftransistors.

In the chemical combination of sodiumchloride, there is no change in the nucleus of eitheratom; the only change is in the distribution ofelectrons between the outer shells of the atoms.Also, the total number of electrons has notchanged, although there has been a slight redistri-bution. Therefore, the molecule is electricallyneutral and has no resultant electrical charge.


A20. The combination and arrangement of the subatomic parti-cles.

A21. Electron, proton, and neutron.

A22. An atom that contains an equal number of protons andneutrons.

A23. By the number of protons in its nucleus.

A24. By the number of protons and neutrons in its nucleus.

A25. Inert.

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Not all chemical combinations of atoms areon a one-for-one basis. In the case of drinkingwater, two atoms of hydrogen (each with a valenceof +1) combine with a single atom of oxygen(valence of –2) to form a single molecule of water.Some of the more complex chemical compoundsconsist of many elements, with various numbersof atoms of each. All molecules, like all atoms,are normally considered to be electrically neutral.There are some exceptions to this rule, however,specific cases of interest are the chemical activityin batteries.

Elements or compounds may be physicallycombined without necessarily undergoing anychemical change. Grains of finely powdered ironand sulfur stirred and shaken together retain theirown identity as iron or sulfur. Salt dissolved inwater is not a compound; it is merely salt dissolvedin water. Each chemical substance retains itschemical identity, even though it may undergo aphysical change. This is the typical characteristicof a mixture.

Q26. Name the smallest unit that exhibits thedistinguishing characteristics of a compound.

Q27. In forming a compound, what part of theatom changes?

STATES OF MATTER

Matter is classified and grouped in many ways.One such classification is according to theirnatural state—solid, liquid, or gas. This classi-fication is important because of the commoncharacteristics possessed by substances in onegroup that distinguish them from substances inthe other groups. However, the usefulness of theclassification is limited because most substancescan assume any of the three forms.

The molecules of all matter are in constantmotion; this motion determines the state ofmatter. The moving molecular particles in allmatter possess kinetic energy of motion. The totalof kinetic energy is considered the equivalent ofthe quantity of heat in a sample of the substance.When heat is added, the energy level is increased,and molecular agitation (motion) is increased.When heat is removed, the energy level decreases,and molecular motion diminishes.

In solids, the molecular motion is restrictedby the rigidity of the crystalline structure ofthe material. In liquids, molecular motion issomewhat less restricted, and the substance as a

whole is permitted to flow. In gases, molecularmotion is almost entirely random; the moleculesare free to move in any direction and are almostconstantly colliding with each other and thesurfaces of the container.

Solids

A solid tends to retain its size and shape. Anychange in these values requires the exchange ofenergy. The common properties of a solid arecohesion and adhesion, tensile strength, ductility,malleability, hardness, brittleness, and elasticity.Ductility is a measure of the ease with which thematerial can be drawn into a wire. Malleabilityrefers to the ability of some materials to assumenew shape when pounded. Hardness and brittlenessare self-explanatory terms. The remainingproperties are discussed in the followingparagraphs.

COHESION AND ADHESION.— Cohesionis the molecular attraction between like particlesthroughout a body, or the force that holds anysubstance or body together. Adhesion is themolecular attraction existing between surfaces ofbodies in contact, or the force that causes unlikematerials to stick together.

Different materials possess different degreesof cohesion and adhesion. In general, solid bodiesare highly cohesive but only slightly adhesive.Fluids (liquids and gases) are usually highlyadhesive but only slightly cohesive. Generally, amaterial having one of these properties to a highdegree will possess the other property to arelatively low degree.

TENSILE STRENGTH.— The cohesionbetween the molecules of a solid explains theproperty called tensile strength. This is a measureof the resistance of a solid to being pulled apart.Steel possesses this property to a high degree andis very useful in structural work. When a breakdoes occur, the pieces of the solid cannot be stuckback together because pressing them together doesnot bring the molecules into close enough contactto restore the molecular force of cohesion.However, melting the edges of the break (welding)allows the molecules on both sides of the breakto flow together. This brings them once again intothe close contact required for cohesion.

ELASTICITY.— If a substance will springback to its original form after being deformed,

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it has the property of elasticity. This property isdesirable in materials to be used as springs. Steeland bronze are examples of materials that exhibitthis property.

All solids, liquids, and gases have elasticity ofcompression to some degree. The closeness of themolecules in solids and liquids makes them hardto compress, but gases are easily compressedbecause the molecules are farther apart.

Liquids

The outstanding characteristic of a liquid isits tendency to retain its own volume whileassuming the shape of its container, A liquid isconsidered almost completely flexible and highlyfluid.

Liquids are practically incompressible.Applied pressure is transmitted through theminstantaneously, equally, and undiminished to allpoints on the enclosing surfaces. The hydraulicsystem is an example of liquids used in aircraft.The system is used to increase or decrease inputforces, providing an action similar to that ofmechanical advantage in mechanical systems. Thefluidity of the hydraulic liquid permits placementof the component parts of the system at widelyseparated points when necessary. A hydraulicpower unit can transmit energy around cornersand bends without the use of complicated gearsand levers. The system operates with a minimumof slack and friction, which are often excessivein mechanical linkages. Uniform action isobtained without vibration, and the operationof the system remains largely unaffected byvariations in load.

Gases

The most notable characteristics of a gas areits tendency to assume not only the shape but alsothe volume of its container, and the definiterelationship that exists between the volume,pressure, and temperature of a confined gas.

The ability of a gas to assume the shape andvolume of its container is the result of itsextremely active molecular particles, which arefree to move in any direction. Cohesion betweengas molecules is extremely small, so the moleculestend to separate and distribute themselvesuniformly throughout the volume of the con-tainer. In an unpressurized container of liquid,pressure is exerted on the bottom and the sidesof the container up to the level of the liquid. Ina container of gas, however, the pressure is alsoexerted against the top surface, and the pressureis equal at all points on the enclosing surfaces.

The relationship of the volume, pressure, andtemperature of confined gas is explained byBoyle’s law, Charles’ law, and the general law forgases.

Many laboratory experiments based on theselaws make use of the ideas of standard pressureand standard temperature. These are not naturalstandards, but are standard values selected forconvenience in laboratory usage. Standard valuesare generally used at the beginning of anexperiment or when a temperature or a pressureis to be held constant. Standard temperature is0°C, the temperature at which pure ice melts.Standard pressure is the pressure exerted by acolumn of mercury 760 millimeters high. In manypractical uses, these standards must be changedto other systems of measurement.

All calculations based on the laws of gasesmake use of absolute temperature and pressure.These topics require a somewhat more detailedexplanation.

GAS PRESSURE.— Gas pressure is indicatedin either of two ways—absolute pressure or gaugepressure. Since the pressure of an absolutevacuum is zero, any pressure measured withrespect to this reference is referred to as absolutepressure. In this TRAMAN, this value representsthe actual pressure exerted by the confined gas.

At sea level the average atmospheric pressureis approximately 14.7 pounds per square inch

ANSWERS FOR REVIEW QUESTIONS Q26. AND Q27.

A26. Molecule.

A27. The electron outer shell only. There is no change in the nucleusof either atom, and the total number of electron ’s hasn’t changed,they’ve been rearranged.

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(psi). This pressure would, in a mercurialbarometer, support a column of mercury 760millimeters in height. Normal atmosphericpressure is the standard pressure. However, theactual pressure at sea level varies considerably;and the pressure at any given altitude may differfrom that at sea level. Therefore, it is necessaryto take into consideration the actual atmosphericpressure when converting absolute pressure togauge pressure (or vice versa).

When a pressure is expressed as the differencebetween its absolute value and that of thelocal atmospheric pressure, the measurement isdesignated gauge pressure and is usually expressedin pounds per square inch gauge (psig). Gaugepressure is converted to absolute pressure byadding the local atmospheric pressure to the gaugepressure.

ABSOLUTE ZERO.— Absolute zero, one ofthe fundamental constants of physics, is usuallyexpressed as –273°C. It is used to study the kinetictheory of gases. According to kinetic theory, ifthe heat energy of a given gas sample wereprogressively reduced, molecular motion wouldcease at some temperature. If accuratelydetermined, this temperature could then be takenas a natural reference, or a true absolute zerovalue.

Experiments with hydrogen indicate that if agas were cooled to –273.16°C (use -273°C formost calculations), all molecular motion wouldcease and no additional heat could be extractedfrom the substance. At this point, both the volumeand the pressure of gas would shrink to zero.When temperatures are measured with respect tothe absolute zero reference, they are expressed inthe absolute, or Kelvin, scale. Therefore, absolutezero may be expressed either as OK or as –273°C.

BOYLE’S LAW.— The English scientist,Robert Boyle, was among the first to study whathe called the springiness of air. By directmeasurement, he discovered that when thetemperature of an enclosed sample of gas was keptconstant and the pressure was doubled, thevolume was reduced to half the former value.Conversely, when the applied pressure wasdecreased, the volume was increased. From theseobservations, he concluded that for a constanttemperature, the product of the volume andpressure of an enclosed gas remains constant.Boyle’s law (fig. 1-2, view A) is normally stated:“The volume of an enclosed dry gas varies

Figure 1-2.-The general gas law.

inversely with its pressure, provided the tempera-ture remains constant.”

CHARLES’ LAW.— The French scientist,Jacques Charles, provided the foundation for themodern kinetic theory of gases. He found that allgases expand and contract in direct proportion tothe change in the absolute temperature, providedthe pressure is held constant (fig. 1-2, view B).

Any change in the temperature of a gas causesa corresponding change in volume; therefore, ifa given sample of a gas were heated while confinedwithin a given volume, the pressure wouldincrease. In actual experiments, the increase inpressure was approximately 1/273 of the 0°Cpressure for each 1°C increase. Because of thisfact, it is normal practice to state this relationshipin terms of absolute temperature. The equation(fig. 1-2, view C) means that with a constantvolume, the absolute pressure of a gas variesdirectly with the absolute temperature.

GENERAL GAS LAW.— Look at figure 1-2.The facts about gases covered in the precedingsections are summed up and shown in this figure.Boyle’s law is shown in view A of the figure, whilethe effects of temperature changes on pressure andvolume (Charles’ law) are shown in views B andC, respectively.

By combining Boyle’s and Charles’ laws, youcan derive a single expression that states all theinformation contained in both laws. This

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expression is the general gas equation (fig. 1-2,view D).

NOTE: The capital P and T signifyabsolute pressure and temperature, respec-tively.

Refer to figure 1-2 again. Here, you can seethat the three equations are special cases of thegeneral equation. If the temperature remainsconstant, equals and both are eliminatedfrom the general formula, it reduces to the formshown in view A. When the volume remainsconstant, equals thereby reducing thegeneral equation to the form given in view B.Similarly, is equated to for constantpressure, and the equation then takes the formgiven in view C.

The general gas law applies only when one ofthe three measurements remains constant. Whena gas is compressed, the work of compression isdone upon the gas. Work energy is converted toheat energy in the gas so that dynamic heating ofthe gas takes place. Experiments show that whenair at 0°C is compressed in a nonconductingcylinder to half its original volume, its rise intemperature is 90°C, and when compressed toone-tenth, its rise is 429°C.

The general gas law applies with exactness onlyto ideal gases in which the molecules are assumedto be perfectly elastic. However, it describes thebehavior of actual gases with sufficient accuracyfor most practical purposes.

Q28.

Q29.

Q30.

Q31.

Q32.

Q33.

Q34.

List the states of matter.

List the common properties of solids.

List the advantages of liquids as applied toaviation.

What is one of the main uses of absolutezero?

List the absolute zero points on the Kelvinand Celsius scales.

Name the person who formulated thefollowing conclusion: “For a constanttemperature, the product of the volumeand pressure of an enclosed gas remainsconstant.”

Charles’ law states that ________________.

MECHANICS

Learning Objective: Identify terms andrecognize concepts involved with themechanics of force, mass, and motion.

Mechanics is the branch of physics that dealswith the ideas of force, mass, and motion.Normally considered the fundamental branch ofphysics, it deals with matter. Many of itsprinciples and ideas may be seen, measured, andtested. All of the other branches of physics arealso concerned with force, mass, and motion; soif you understand this section, you will understandlater sections of this chapter.

FORCE, MASS, AND MOTION

Each particle in a body is acted upon bygravitational force. In every body, there is onepoint at which a single force, equal to thegravitational force and directed upward, wouldsustain the body in a condition of rest. This pointis known as the center of gravity (cg). It representsthe point at which the entire mass of the bodyappears to be concentrated. The gravitationaleffect is measured from the center of gravity. Insymmetrical objects of uniform mass, this is thegeometrical center. In the case of the earth, thecenter of gravity is near the center of the earth.

When considering the motion of a body, thepath followed by the center of gravity is“described.” The natural tendency of a movingbody is to move so that the center of gravitytravels in a straight line. Movement of this typeis called linear motion. However, some movingbodies do not move in a straight line, but movein an arc or a circular path. Circular motion fallsinto two general classes—rotation and revolution.

Objects come in many different shapes, andto discuss rotary and revolutionary motion, thelocation of the center of gravity with respect tothe body must be considered. As you read thefollowing section, refer to figure 1-3.

In view A, the center of gravity of a ballcoincides with the physical center of the ball. Inthe flat washer (view B), the center of gravity doesnot coincide with any part of the object but islocated at the center of the hollow space insidethe ring. In irregularly shaped bodies, the centerof gravity may be difficult to locate exactly.

Look at figure 1-4. If the body is completelyfree to rotate, the center of rotation coincides withthe center of gravity. However, the body may berestricted so that rotation is about some point

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Figure 1-3.-Center of gravity in various bodies.

other than the center of gravity. In this event, thecenter of gravity revolves around the center ofrotation. The gyro rotor (view A) rotates aboutits axis, and the ball (view B) revolves about apoint at the center of its path.

Q35.

Q36.

Q37.

Q38.

Name the branch of physics that deals withforce, mass, and motion.

Describe the point of an object that is itscenter of gravity.

List the two classes of circular motion.

Generally, a gyro rotor (a) revolves or (b)rotates about its axis.

MASSES IN MOTION

Learning Objective: Identify factors thataffect masses in motion.

Motion is defined as the act or process ofchanging place or position. The state of motion

Figure 1-4.-Center of gravity and center of rotation.

refers to the amount and the type of motionpossessed by a body at some definite instant (orduring some interval of time). A body at rest isnot changing in place or position; it is said to havezero motion, or to be motionless.

The natural tendency of any body at rest isto remain at rest. A moving body tends tocontinue moving in a straight line with no changein speed or direction. A body that obeys thisnatural tendency is said to be in uniform motion.

Any change in the speed or direction ofmotion of a body is known as acceleration andrequires the application of some force. Theacceleration of a body is directly proportional tothe force causing that acceleration; accelerationdepends also upon the mass of the body. Thegreater mass of a lead ball makes it harder to movethan a wood ball of the same diameter. A woodball moves farther with the same push.

These observations indicate a connectionbetween force, mass, and acceleration. Theyindicate that the acceleration of a body is directlyproportional to the force exerted on that body andinversely proportional to the mass of that body.In mathematical form, this relationship may beexpressed as

or, as it is more commonly stated: “Force is equalto the product of the mass and acceleration( F = m a ) . ”

Acceleration Due to Gravity

The small letter g represents the accelerationof a body in free fall, neglecting any friction. Thiscan happen only in a vacuum. At sea level nearthe equator, g has the approximate values of

in the fps system, in the cgssystem, and in the mks system. Theabsolute units of mass of a body may bedetermined when its weight is known. To solvefor m in the formula W = mg, you transpose theformula so

When you use the formula stated in Newton’ssecond law of motion (force equals mass timesacceleration [F = ma]) to find what force is

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needed to give a 1-ton car an acceleration of

In the metric system, the newton is the forcethat causes a mass of 1 kg to be accelerated

Since g = a 1-kg mass exertsa force of 9.8 newtons due to gravity. A newtonis equal to 0.224 lb.

The dyne is the force that causes a mass of1 g to be accelerated Therefore, a massof 1 g exerts a force of 980 dynes due to gravity.

An accelerating force applied to the center ofgravity to accelerate a body with no rotation iscalled a translational force. The force applied tocause a body to rotate about a point is called atorque force,

Laws of Motion

Among the most important discoveries intheoretical physics are the three fundamental laws


A28. a. Solidb. Liquidc . Gas

A29. a. Cohesion and adhesionb. Tensile strengthc. Ductilityd. Malleabilitye. Hardnessf. Brittlenessg. Elasticity

A30. a. Component parts of a system can be placed at separatedpoints

b. Hydraulic energy is transmitted around corners without gearsand levers

A31. To study the kinetic theory of gases.

A32. a. 0 Kelvinb. -273° Celsius

A33. Boyle.

A34. “All gases expand and contract in direct proportion to the changein the absolute temperature, pro vialed the pressure is heldconstant.”

A35. Mechanics.

A36. The point where a single force, equal to the gravitational forceand directed up, sustains the body at rest.

A37. Rotation and revolution.

A38. Rotates about its axis.

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of motion attributed to Newton. These laws havebeen used to explain topics earlier in this chapter.In this section, they are restated and consolidatedto clarify and summarize the discussion regardingmechanical physics.

1. Every body tends to maintain a state ofuniform motion unless a force is applied to changethe speed or direction of motion.

2. The acceleration of a body is directlyproportional to the magnitude of the applied forceand inversely proportional to the mass of thebody; acceleration is in the direction of the appliedforce.

3. For every force applied to a body, the bodyexerts an equal force in the opposite direction.

Momentum

Every moving body tends to maintain uniformmotion. Quantitative measurement of thistendency is proportional to the mass of the body,and also to its velocity (momentum = massx velocity). This explains why heavy objects inmotion at a given speed are harder to stop thanlighter objects. It also explains why it is easier tostop a body moving at low speed than it is to stopthe same body moving at high speed.

Q39. What type of force is an accelerating forceapplied to the center of gravity of a bodyso that the body is accelerated with norotation?

WORK, POWER, AND ENERGY

Learning Objective: Perform calculationsinvolving kinetic energy, work, power, andmechanical advantage.

As defined earlier, energy is the capacity fordoing work. In mechanical physics, work involvesthe idea of a mass in motion, and is usuallyregarded as the product of the applied force andthe distance through which the mass is moved(work = force x distance). For example, if a manraises a weight of 100 pounds to a height of 10feet, he accomplishes 1,000 foot-pounds of work.The amount of work accomplished is the sameregardless of the time involved. However, the rateof doing the work may vary.

The rate of doing work (called power) i sdefined as the work accomplished per unit of time(power = work/time). In the example cited above,if the work is accomplished in 10 seconds, power

is being expended at the rate of 100 foot-poundsper second; if it takes 5 minutes (300 seconds),the rate is approximately 3.3 foot-pounds persecond.

In the English system of measurements, theunit of mechanical power is called horsepower,and is the equivalent of 33,000 foot-pounds perminute, or 550 foot-pounds per second. Sinceenergy converts from one form to another, thework and power measurements based on theconversion of energy must also be readilyconvertible. For example, the electrical unit ofpower is the watt. Electrical energy may beconverted into mechanical energy; therefore,electrical power must be convertible intomechanical power. One horsepower is themechanical equivalent of 746 watts of electricalpower and is capable of doing the same amountof work in the same time.

Doing work always involves a change in thetype of energy, but does not change the totalquantity of energy. Thus, energy applied to anobject may produce work, changing the com-position of the energy possessed by the object.

Potential Energy

A body has potential energy if it is able to dowork. A wound clock spring and a cylinder ofcompressed gas both possess potential energysince they can do work in returning to theiruncompressed condition. Also, a weight raisedabove the earth has potential energy since it cando work by returning to the ground. Potentialenergy results when work has been done againsta restoring force. The water in a reservoir abovea hydroelectric plant has potential energy,regardless of whether the water was placed thereby work applied via a pump or by the work doneby the sun to lift moisture from the sea and placeit in the reservoir as rain.

Kinetic Energy

The ability of a body to do work through itsmotion is called its kinetic energy. A rotatingwheel on a machine has kinetic energy of rotation.A car moving along the highway has kineticenergy of translation.

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For a given mass (m) moving in a straight linewit h a velocity (v), the kinetic energy is determinedby

For example; The kinetic energy of a 3,200-lbcar traveling at 30 miles per hour can be foundby expressing the 3,200 lb as 100 slugs and the30 mph as 44 feet per second. Inserting thesevalues into the formula gives

kinetic energy = ½ x 100 x 44 x 44= 96,800 foot-pounds of

energy. This amount of kinetic energy is the resultof applying 96,800 foot-pounds of work (plus thatto overcome friction) to the car to get it travelingat the rate of 44 feet per second. The same amountof energy could do the work of lifting the 3,200pounds vertically a distance of 30.25 feet; it couldhave been potential energy if the car had been atrest on an incline and then allowed to coast to apoint which is vertically 30.25 feet below itsstarting point (again neglecting friction).

Efficiency

If there is no change in the quantity of matter,energy is convertible with no gain or loss.However, the energy resulting from a given actionmay not be in the desired form; it may not evenbe usable in its resultant form. In all branches ofphysics, this concept is known as efficiency.

Energy expended is always greater than energyrecovered. An automobile in motion possesses aquantity of kinetic energy that depends on its massand velocity. To stop the car, this energy isconverted into potential energy. When the car

stops, its potential energy is less than thekinetic energy it possessed while in motion. Thedifference, or the energy used, was converted intoheat by the brakes. The heat serves no usefulpurpose, so the recovered energy is less than theexpended energy; therefore, the system is less than100-percent efficient in converting kinetic topotential energy.

Normally, the term efficiency is used inconnection with work and power considerationsto show the ratio of the input to the output work,power, or energy, It is always expressed as adecimal or as a percentage less than unity.

Friction

In mechanical physics, the most commoncause for the loss of efficiency is friction.Whenever one object is slid or rolled over another,irregularities in the contacting surfaces interlockand cause an opposition to the force beingexerted. Even rubbing two smooth pieces of icetogether produces friction. Friction also exists inthe contact of air with all exposed parts of anaircraft in flight.

When a nail is struck with a hammer, theenergy of the hammer is transferred to the nail,and the nail is driven into a board. The depth ofpenetration depends on the momentum of thehammer, the size and shape of the nail, and thehardness of the wood. The larger or fuller the nailand the harder the wood, the greater the friction;therefore, the lower the efficiency and the lesserthe depth of penetration, but the greater theheating of the nail.

Friction is always present in movingmachinery, which is why the useful work done bythe machine is never as great as the energy applied.Work accomplished in overcoming friction isusually not recoverable. Friction is minimized bydecreasing the number of contacting points, bymaking the contacting areas as small and assmooth as possible, by the use of bearings, or bythe use of lubricants.

There are two kinds of friction—sliding androlling, with rolling friction usually of lowermagnitude. Therefore, most machines are builtso rolling friction is present rather than sliding

ANSWER FOR REVIEW QUESTION Q39.

A39. A translational force.

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friction. The ball bearing and the roller bearingare used to replace sliding friction with rollingfriction. The common (or friction) bearing useslubricants applied to surfaces that areas smoothas possible. Many new types of machines use self-lubricating bearings to minimize friction andmaximize efficiency.

Q40.

Q41.

Q42.

Q43.

Q44.

How much power is being expended if aman lifts 50 pounds 5 feet to put it on ashelf in 15 seconds?

When does an object have potential energy?

What is lost whenever energy is expended?

What is the most common reason forefficiency loss in mechanical physics?

What type of bearing is used in many typesof machinery to minimize friction andmaximize efficiency?

Mechanical Advantage

The concept of mechanical advantage is oneof the great discoveries of science. It permits anincrease in force through a distance and representsthe basic principle involved in levers, block-and-tackle systems, screws, hydraulic mechanisms, andother work-saving devices. Actually, these devicesdo not save work; they just let humans do tasksthat are beyond their capability. For example,normally, a human couldn’t lift the rear end ofa truck to change a tire; but with a jack, blockand tackle, or lever, the human can do the job.

Mechanical advantage is usually consideredwith respect to work. Work represents theapplication of a force through a distance to movean object through a distance. Therefore, you cansee that two forces are involved, each with anappropriate distance. This is shown by the simplelever (fig. 1-5).

If there is perfect efficiency, the work input is equal to the work output If

distances and are equal, a force of 10pounds must be applied at the source tocounteract a weight of 10 pounds at the load.

When the fulcrum is moved nearer the load,less force is required to balance the same load.This is a mechanical advantage of force. If the

Figure 1-5.-Mechanical advantage.

force is applied to raise the load 1 foot, the sourcemust be moved through a distance greater than1 foot. Therefore, the mechanical advantage offorce represents a mechanical disadvantage ofdistance. When the fulcrum is moved nearer thesource, these conditions are reversed.

Since the input work equals the output work(assuming no losses), the mechanical advantagemay be stated as a ratio of the force or of thedistances. Actually, friction results in energy lossand decreased efficiency, thereby requiring aneven greater input to do the same work.

REVOLVING BODIES

Learning Objective: Recognize themechanics involved in revolving bodies andidentify the forces that act on such bodies.

Revolving bodies represent masses in motion;therefore, they possess all the characteristics (andobey all the laws) associated with moving bodies.Since they possess a specific type of motion, theyhave special properties and factors.

Revolving bodies travel in a constantlychanging direction, so they must be constantlysubjected to an accelerating force. Momentumtends to produce linear motion, but this isprevented by application of a force that restrainsthe object. The force that prevents the object fromcontinuing in a straight line is known as centripetalforce. According to Newton’s third law ofmotion, the centripetal force is opposed by anequal force that tends to produce linear motion.This second force is known as centrifugal force.

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The two forces, their relationships, and theireffects are shown in figure 1-6.

The forces involved in revolving bodies maybe demonstrated by using a ball and string. Tiea slip knot in the center of a 10-foot length ofstring to shorten the line to 5 feet. Then, attacha rubber ball to one end of the string. Holdingthe other end of the string, whirl the ball slowlyin a circle. At this point in the experiment, youcan tell that the ball exerts a force against yourhand (through the string). As you keep the ballin its circular path, your hand exerts a force

Figure 1-6.-Forces on revolving bodies.

(through the string) on the ball. As you revolvethe ball at a higher speed, the forces increase, butthe ball continues in a circular path.

At some rotational speed, the forces areenough to overcome inertial friction, and the knotslips. At this time, stabilize the velocity of rotation(keep the rotational velocity constant). Let’sanalyze what has happened. When the knot slips,the ball is temporarily unrestrained and is free toassume linear motion in the direction of travel atthat instant (tangent to the circle at theinstantaneous position, which is shown infig. 1-6). The ball travels in a straight line untilthe string reaches its full length. During this time,no force is exerted on or by the hand. As soonas all the slack is taken up, there is a sharp jerk;an accelerating force is exerted to change thedirection of motion from its linear path intoa circular rotation. The ball again assumesrotational motion, but with an increase in radius.

The ball does not make as many revolutionsin the same time (rotational velocity is decreased),but it does maintain its former linear velocity.(The kinetic energy and the momentum of the ballhave not changed.) Since the change in directionis less abrupt with a large radius than with a smallone, less accelerating force is required, and thehand will feel less force. Accelerate the ball to thesame rotational velocity it had just before the knotslipped. The linear velocity of the ball becomesmuch greater than before; the centripetal andcentrifugal forces are much greater, also,

In this experiment, your hand is fixed at apoint that represents the center of rotation. This


A40. a. First, solve for amount of work being done:work = force x distance, orwork = 50 x 5 = 225 foot-pounds of work

b. Next, solve for power expanded to do the work:power = work/time, orpower = 225/15 = 15 foot-pounds per second

A41. When it can do work, such as a wound clock spring or a cylinderof compressed gas.

A42. Efficiency.

A43. Friction.

A44. Self-lubricating bearings.

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assumption, while not exactly correct, does notaffect the general conclusions you can draw fromthe experiment. For practical purposes, the twoforces are equal at all points along the string atany given time, and the magnitude of each forceis equal at all points along the string.

The above example and explanation canbe summarized by the following mathematicalrelationship:

force =mass x velocity2

radius

where velocity represents the linear velocity of theball.

This relationship describes the following factsabout forces acting on revolving bodies:

The centripetal and the centrifugal forcesare equal in magnitude and opposite in direction.

Each force is directly proportional to themass of the body and inversely proportional tothe radius of rotation.

Each force is also proportional to thesquare of the velocity.

In revolving or rotating bodies, all particlesof matter not on the axis of rotation are subjectedto the forces just described. The statement is truewhether the motion is through a complete circle,or merely around a curve. An aircraft tends toskid when changing course, and an automobiletends to take curves on two wheels. The sharperthe curve (smaller radius) or the higher thevelocity, the greater the tendency to skid.

Q45.

Q46.

Q47.

Name the principle that allows man to accom-plish work that he normally could not do.

What force prevents a revolving objectfrom continuing along a straight line?

When an object is revolving, what forcetries to oppose centripetal force?

WAVE PARAMETERS

Learning Objectives: Identify the factorsinvolved in wave motion and recognizevarious types of waves to include transversewaves, waves in water, and standing waves.Identify the terms used to describe waveparameters. Recognize the properties thataffect reflection, refraction, and diffrac-tion. Identify the applications of theDoppler effect.

The term wave parameter is a general term,and it applies to all types of waves—water, radio,sound, light, and heat. All types of waves exhibitsome common characteristics, such as trans-mission, reflection, refraction, and absorption.

TERMS USED IN WAVE PARAMETERS

Before you read the section on wave param-eters, its helpful to understand the terminologyused in the discussion. The terms included in thissection will help you as you read about waveparameters.

Propagation. A travel of waves through oralong a medium.

Velocity. The velocity of propagation is therate at which the disturbance transverses themedium, or the velocity with which the crest ofthe wave moves along. The velocity of the wavemust not be confused with the speed of a particle,which is always less than the velocity of the wave.The velocity of the wave depends both on the typeof wave and the nature of the medium.

Frequency. The frequency of any periodicmotion is the number of complete variations perunit of time. With waves, the time unit is thesecond, and the frequency unit is the hertz (Hz).A hertz is the number of complete cycles persecond; therefore, it is the number of completewaves that pass a given point each second.

Period. The period of a wave is the timerequired to complete a full cycle. Therefore, theperiod and the frequency of a given wave arereciprocals of each other. The period of a wavecan be expressed mathematically as follows:

If a sound wave has a frequency of 400 Hz,its period is 1/400, or 0.0025 second. If successivecrests of a water wave pass a given point each 5seconds, the frequency of the wave is 1/5 or 0.2Hz.

Wavelength. Wavelength, shown by thesymbol (Greek lambda), is the distance, alongthe direction of propagation of the wave, betweentwo successive points in the medium that are atprecisely the same state of disturbance. In a waterwave, this is the distance between two adjacent

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crests. Wavelength depends on both the frequencyof the wave and the velocity of propagation ofthe wave in a given medium. Wavelength isexpressed mathematically as follows:

velocitywavelength =

frequency .

Wavelength must be given in compatible units;which means that if frequency is in waves persecond (in hertz), then velocity must be in distanceunits per second (feet per second or meters persecond). Also, if velocity is given in feet persecond, wavelength is given in feet; if velocity isgiven in meters per second, wavelength is givenin meters.

WAVE MOTION

Energy is transferred progressively from pointto point in a medium by a disturbance that mayhave the form of an elastic deformation, avariation of pressure, electric or magneticintensity, electric potential, or temperature. Thisdisturbance advances with a finite velocitythrough a medium. Energy is transferred from onepoint to another without the passage of matterbetween the two points (although in some casesparticles of matter do move to and fro aroundtheir equilibrium position). A single disturbanceinduced into the medium is called a wave pulse,and a series of waves produced by continuousvariations is called a train of waves or wavetrain.

Transverse Waves

In the description of any periodic wave, thewave is a transverse wave if the disturbancetakes place at right angles to the direction ofpropagation. You can see this motion by fasteningone end of a hemp line to a stanchion, and movingits free end up and down with a simple periodicmotion. The motion of the waves will be alongthe length of the line, but each particle of the linemoves at right angles to its length.

Electromagnetic waves do not involve movingparticles of matter; they rely on electric andmagnetic force fields. The variations of thesefields are also at right angles to the direction ofwave movement; therefore, electromagnetic wavesare transverse waves. Also, the variations ofelectric-field intensity and those of magnetic-fieldintensity are at right angles to each other as wellas to the direction of propagation of the wave.For example, if an electromagnetic wave is movingtoward the north and is horizontally polarized,the variations of the electric-field intensity areeast-west horizontal to the earth’s surface, whilevariations in the magnetic-field intensity arevertical. Electromagnetic waves are known asradio waves, heat rays, light rays, etc., dependingon their frequency.

Longitudinal Waves

Longitudinal waves are waves in which thedisturbance takes place in the direction ofpropagation. The compressional waves thatconstitute sound, such as those set up in air bya vibrating tuning fork, are longitudinal waves.As you read this section, look at figure 1-7. Whenstruck, the tuning fork sets up a vibrating motion.As the tine moves in an outward direction, theair immediately in front of the tine is compressedso that its momentary pressure is raised above thatof other points in the surrounding medium.Because air is elastic, this disturbance istransmitted progressively in an outward directionas a compression wave. When the tine returns andmoves in the inward direction, the air in front ofthe tine is rarefied so that its momentary pressureis reduced below that at other points in thesurrounding medium. This disturbance is alsopropagated, but in the form of a rarefaction(expansion) wave, and follows the compressionwave through the medium.

The compression and expansion waves are alsocalled longitudinal waves because the particles ofmatter of the medium move back and forthlongitudinally in the direction of wave travel.


A45. Mechanical advantage.

A46. Centripetal force.

A47. Centrifugal force.

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Figure 1-7.-Compression and expansion wave propagation.

Waves in Water

The wave motion of the surface of water isa combination of both transverse and longitudinalwaves. The particles of water move in circles orin ellipses. You can see this motion by placing asmall cork on the surface of the water andobserving it from the side. The cork will be carriedupward and in the direction of the wave motionas the crest of the wave approaches. After the crest

has passed, the cork falls and is then carriedbackward.

Standing Waves

Standing waves are produced by two wavetrains of the same type and of equal frequencytraveling in opposite directions in the samemedium, whether the medium be solid, liquid, orgas. Look at figure 1-8. It shows the formation

Figure 1-8.-Formation of a standing wave.

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of a standing wave represented by the solid curvedline. The points A and N along the horizontal axisof the graph are fixed points within the mediumand are stationary or standing. Points N are thelocations within the medium where the amplitudeof the standing wave is always medium and arecalled nodes. Successive nodes are a half-wavelength apart. Halfway between the nodes arethe antinodes (or loops), represented by points Aon the graph. The standing wave reaches itsmaximum amplitude at point A (a quarter-wavelength from a node). The dotted curved linerepresents a wave train traveling from left to right,and the dashed curved line represents an equalwave train traveling from right to left, as theywould appear if each were the only wave withinthe medium. As they meet, they combine witheach other to form a standing wave (shown bythe solid curved line); they cease to exist in theiroriginal form.

In the top drawing, the crests of the twoidentical component waves are approaching eachother and coincide at points A. At this time, thestanding wave will increase to a maximumamplitude equal to the sum of the two com-ponents.

Look at the lower drawing in figure 1-8. Afteran interval of time, the crests of the componentwaves pass each other, and the standing wavedecreases until it becomes zero at the time the twocomponent waves exactly neutralize each other.After this, the standing wave will increase inamplitude in the opposite direction from that inthe drawings. You can see that the points ofmaximum variation of the standing wave are notmoving, and that at points N the standing waveis always at zero. At points N, the magnitudes ofthe two component waves are the same and theirdeviations are opposite; therefore, at points N,the standing wave is always zero.

Q48.

Q49.

Q50.

What are the characteristics that all typesof waves have in common?

Energy is transferred in a medium by adisturbance that may have an elasticdeformation, a pressure variation, anelectric or magnetic intensity, an electricpotential, or temperature. Continuousvariations induced in to a medium is knownas a

Electromagnetic waves are what types ofwaves?

Q51.

Q52.

Air is elastic; therefore, a disturbance istransmitted progressively out ward as acompression wave. What type of wavesbehave in this manner?

How are standing waves produced?

REFLECTION

Lines drawn from the source of waves toindicate the path along which the waves travel arecalled rays. Often, these lines are used inillustrations to show wave propagation. Whenseveral rays are drawn from a nearby source, theyare shown diverging from the source; rays drawnfrom a distant source are usually shown as beingmore nearly parallel.

A wavefront is a surface on which the phaseof the wave has the same value at all points ata given instant. Wavefronts near the source aresharply curved. As their distance from the sourceincreases, they become more nearly flat.

Within a uniform medium, a ray travels in astraight line. Only at the boundary of two media,or in an area where the velocity of propagationof the wave within the medium changes, do therays change their direct ion.

When an advancing wavefront meets a mediumof different characteristics, some of its energy isreflected back into the initial medium, and someof it is transmitted into the second medium. Inthe second medium, it continues at a differentvelocity or is absorbed by the medium. In somecases, all three processes (reflection, absorption,and transmission) may occur to some degree.

As you read this paragraph, look at figure 1-9.Reflected waves are waves that are neither

Figure 1-9.-Reflection of a wave.

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transmitted nor absorbed; they are thrown backfrom the surface of the medium they meet. If aray is directed against a reflecting surface, the raystriking the surface is called the incident ray, andthe ray that bounces back is the reflected ray. Animaginary line perpendicular to the reflectingsurface at the point of impact of the incident rayis called the normal. The angle between theincident ray and the normal is called the angle ofincidence. The angle between the reflected ray andthe normal is the called the angle of reflection.

The law of reflection states that “The angleof incidence is equal to the angle of reflection.”If the surface of the medium contacted by theincident rays of the wave is smooth and polished(a mirror), each reflected ray is thrown back atthe same angle as the incident ray. The path ofthe ray reflected from the surface forms an angleexactly equal to the one formed by the path ofthe ray in reaching the medium, therefore,conforming to the law of reflection.

The amount of incident wave energy reflectedfrom a surface depends on the nature of thesurface and the angle at which the wave strikesthe surface. The amount of wave energy reflectedincreases as the angle of incidence increases. Itis greatest when the ray is nearly parallel to thesurface. When the incident ray is perpendicularto the surface, more of the wave energy istransmitted into the substance and less is reflected.At any angle of incidence, a mirror reflects almostall of the wave energy, and a dull black surfacereflects very little. Waves that are reflected directlyback

Q53.

Q54.

Q55.

. .toward the source cause standing waves.

A ray is traveling through a medium in astraight line. What would cause the ray tochange its direction?

What happens when a wave is directedagainst a reflecting surface?

“The angle of incidence is equal to the angleof reflection.” What is meant by thisstatement?

REFRACTION

When a wave passes from one medium intoa medium having a different velocity of propaga-tion for the wave, and if the ray is notperpendicular to the boundary between the twomedia, the wave changes direction or bends. Thisis called refraction. Look at figure 1-10. Youshould refer to it as you read the section on

Figure 1-10.-Refraction of a wave.

refraction. The ray striking the boundary is theincident ray, and the imaginary line perpendicularto the boundary is the normal. The angle betweenthe normal and the path of the ray through thesecond medium is the angle of refraction.

A light ray is shown from points A to B infigure 1-10. This is the incident ray. As it nearsthe boundary between the air and the top of theglass plate, it bends toward the normal and takesthe path BC through the glass. You can see thatit becomes the refracted ray from the top surfaceand the incident ray to the lower surface. Theangle formed by the ray and the normal to thelower surface is the second angle of incidence. Asthe ray passes from the glass to the air, it is againrefracted, this time away from the normal, andtakes the path CD.

Refraction follows a general rule: When a raypasses from one medium into another having alower velocity of propagation for the waves,refraction is toward the normal, so the angle ofrefraction (r) is smaller than the angle of incidence(i); when a ray passes into a medium having ahigher velocity of propagation for the waves,refraction is away from the normal, so the angleof refraction (r1) is larger than the angle ofincidence (i1). The angle of refraction depends ontwo factors: (1) the angle of incidence and (2) theindex of refraction. The index of refraction is theratio of the velocities of the waves within the twomedia. The greater the angle of incidence, thegreater the bending; the greater the differencebetween the velocities of propagation in the twomedia, the greater the bending.

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When the two surfaces of glass are parallel,a ray leaving the glass is parallel to a ray enteringthe glass. The distance between these two paths(between lines AE and CD in fig. 1-10) is calledlateral displacement. Lateral displacement is zerowhen the incident ray is directed along t he normal,and increases as the angle of incidence increases.Lateral displacement is greater in thicker glassthan in thin.

A boundary between two media does notalways have a sharp point of transition, such asfrom the surface of glass to air. Air layers abovethe earth’s surface have different temperaturesthat cause refraction of sound waves. Thermal

Variations in the ionosphere cause refraction ofradio waves and light rays.

You already know that when a waveencounters a medium having a higher velocity ofpropagation, refraction is away from the normal,and the angle of refraction is larger than the angleof incidence. When the angle of incidence isincreased to the angle at which the refracted waveis 90° to the normal (parallel with the boundary),the angle of incidence is called the critical angleof refraction. Any angle of incidence larger thanthis results in total reflection of the incident wave.The size of the critical angle of refraction dependson the index of refraction of the two media; thelarger the index of refraction, the smaller the

layers in the ocean also cause refraction. critical angle of refraction.


A48. a. Transmissionb. Reflectionc. Refractiond. Absorption

A49. Wave train. This is a series of waves produced by continuousvariations.

A50. They are transverse waves because the disturbance takes placeat right angles to the direction of propagation.

A51. Longitudinal waves. They behave this way because thedisturbance takes place in the direction of propagation. The wavesmove back and forth in the direction of wave travel.

A52. They are produced by two wave trains of the same type and equalfrequency traveling in opposite directions in the same medium.As two waves traveling in opposite directions meet, they combinewith each other, and they cease to exist in their originalform.

A53. It would change its direction if it reached the boundary of a mediaor if it reached an area within the media where the velocity ofpropagation of the wave changes.

A54. The wave is thrown back from the surface. The ray that strikesthe surface is the incident ray and the ray the bounces back isthe reflected ray.

A55. The path of a ray reflected from a surface forms an angle thatis exactly equal to the one formed by the path of the ray reachingthe medium (law of reflection).

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DIFFRACTION

Diffraction (fig. 1-11.) is the bending of thepath of waves when the wavefront is limited by anobstruction. This is very easy to observe in waterwaves. Generally, the lower frequency wavesdiffract more than those at higher frequency. Youcan hear the diffraction in sound waves bylistening to music from an outdoor source. Then,step behind a solid obstruction, such as a brickwall. The high notes, having less diffraction, seem

reduced in loudness more than the low notes.Broadcast band radio waves often travel over tothe opposite side of a mountain from their sourcebecause of diffraction. Higher frequency TVsignals from the same city might not be detectedon the opposite side of the same mountain.

DOPPLER EFFECT

When there is relative motion between thesource of a wave and a detector of that wave, the

Figure 1-11.-Diffraction.

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frequency at the detector position differs from thefrequency at the source. If the distance betweenthe source and the detector is decreasing, morewavefronts are encountered per second than whenthe distance is constant. This results in anapparent increase in the transmitted frequency.Conversely, if the separation is increasing, fewerwaves are encountered. There is an apparentdecrease in transmitted frequency.

The pitch of the whistle on a fast-moving trainsounds higher as the train is coming toward youthan when the train is going away. Though thewhistle is generating sound waves of constantfrequency, and they travel through the air at thesame velocity in all directions, the distancebetween the approaching train and the listener isdecreasing. Each wave has less distance to travelto reach the observer than the wave preceding it;the waves arrive with shorter intervals of timebetween them.

These changes in frequency are called theDoppler effect. The Doppler effect affects theoperation of equipment used to detect andmeasure wave energy. The amount of change inthe frequency varies directly with the relativevelocities of the source and detector and inverselywith the velocity of propagation of the wavewithin the medium. The Doppler effect isimportant when dealing with wave propagationapplicable to sonar equipment operation, radarsearch, target detection, fire control, andnavigation.

Q56.

Q57.

Q58.

Q59.

As a wave passes from one medium intoanother, what causes refraction?

What are the two factors that determine theangle of refraction?

What causes diffraction?

What is the cause of the Doppler effect?

HEAT

Learning Objective: Recognize the charac-teristics of heat and identify the ways inwhich heat is transferred.

Heat is a form of energy; it is readilyexchangeable with, or convertible into, otherforms of energy. For example, when a piece oflead is struck a sharp blow with a hammer, partof the kinetic energy of the hammer is converted

into heat. In the core of a transformer, electricaland magnetic energy are exchanged; but due tohysteresis and eddy currents, some of the energyis lost as heat. These are some examples of theunwanted conversions. There are, however, manyinstances when heat production is desirable, andmany devices are used to produce heat.

Some of the characteristics heat possessesmake it important to the technician. A knowledgeof the nature and behavior of heat will help youunderstand the operation of some types ofelectronics equipment. This knowledge will alsohelp you determine the cause of nonoperation orfaulty operation of equipment.

NATURE OF HEAT

There are several theories about the nature ofheat. The two theories most commonly includedin discussions about the nature of heat are thekinetic theory and the radiant energy theory.

The basis of the kinetic theory assumes thatthe quantity of heat contained in a body isrepresented by the total kinetic energy possessedby the molecules of the body.

The radiation theory treats radio waves, heat,and light as the same general form of energy,differing primarily in frequency. Heat is con-sidered as a form of electromagnetic energyinvolving a specific band of frequencies fallingbetween the radio-wave and light-wave portionsof the electromagnetic spectrum.

A common method of producing heat energyis the burning process. Burning is a chemicalprocess in which fuel unites with oxygen, andusually produces a flame. The amount of heatliberated per unit mass or per unit volume duringcomplete burning is known as the heat ofcombustion of a substance. Each fuel producesa given amount of heat per unit quantity burned.

TRANSFER OF HEAT

There are three methods of heat transfer—conduction, convection, and radiation. Inaddition to these, a phenomenon called absorp-tion is related to the radiation method.

Conduction

The metal handle of a hot pot will burn yourhand while a plastic or wooden handle remainsrelatively cool to touch, even though it is in directcontact with the pot. This phenomenon is dueto a property of matter known as thermalconductivity.

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All materials conduct heat to some degree.When heat is applied to a body, the molecules atthe point of application become violently agitated,strike the molecules next to them, and causeincreased agitation. The process continues untilthe heat energy is distributed evenly throughoutthe material. Aluminum and copper are used forcooking pots because they conduct heat veryreadily to the food being cooked. Generally,metals are the best conductors of heat.

Among solids, there is an wide range ofthermal conductivity. In the original example, themetal handle transmits heat from the pot to thehand, with the possibility of burns. The woodenor plastic handle does not conduct heat very well,so the hand is given some protection. Materialsthat are extremely poor conductors are calledinsulators; they are used to reduce heat transfer.Some examples of insulators are the wood handleof soldering irons, the finely spun glass or rockwool insulation in houses, and the tape or ribbonwrapping used on steam pipes.

Liquids are generally poor conductors of heat.Look at figure 1-12. The ice in the bottom of thetest tube has not yet melted, although the waterat the top is boiling. Water is such a poorconductor of heat that the rate of heating waterat the top of the tube is not sufficient to causerapid melting of the ice at the bottom.

Since thermal conduction is a process by whichmolecular energy is passed on by actual contact,gases are the poorest conductors of heat becausetheir molecules are far apart and molecularcontact is not pronounced. A double-pane

Figure 1-12.-Water is a poor conductor of heat.

window with an air space between the panes isa fair insulator.

Q60.

Q61.

Q62.

Q63.

In the radiation theory, heat is generallytreated the same way as several forms ofenergy. List these forms.

List the three methods of heat transfer.

Wood handles are used on soldering ironsbecause they are ______________________ .

In what state is matter the poorestconductor of heat?

Convection

Convection is the process by which heat istransferred by movement of a hot fluid. Forexample, an electron tube gets hotter and hotteruntil the air surrounding it begins to move. Themotion of the air is upward because heated airexpands in volume and is forced upward by thedenser cool air surrounding it. The upwardmotion of the heated air carries the heat awayfrom the hot tube by convection. Using aventilating fan to move the air around a hotobject is a fast method of transferring heat byconvection. The rate of cooling of a hot vacuumtube is increased by using copper fins to conductheat away from the hot tube. The fins providelarge surfaces against which cool air can be blown.

A convection process may take place in aliquid as well as in a gas; for example, atransformer in an oil bath. The hot oil is less dense(has less weight per unit volume) and rises, whilethe cool oil falls, is heated, and rises in turn. Whenthe circulation of gas or liquid is not rapid enoughto remove sufficient heat, use fans or pumps toaccelerate the motion of the cooling material. Insome installations, pumps are used to circulatewater or oil to help cool large equipment. Inairborne installations, electric fans and blowersare used to aid convection.

Radiation

Conduction and convection do not accountfor all of the phenomena associated with heattransfer. For example, heating through convectioncan’t occur in front of an open fire because theair currents are moving toward the fire. Heatingcan’t occur through conduction because theconductivity of the air is very low, and the coolercurrents of air moving toward the fire would

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overcome the transfer of heat outward. Therefore,heat must travel across space by some means otherthan conduction and convection.

Conduction and convection take place onlythrough molecular contact within some medium;therefore, heat from the sun reaches the earth bysome other method. (Outer space is an almostperfect vacuum.) The third method of heattransfer is known as radiation.

The term radiation refers to the continualemission of energy from the surface of all bodies.This energy is known as radiant energy. Radiantenergy is in the form of electromagnetic waves andis identical in nature to light waves, radio waves,and X-rays, except for a difference in wavelength.Sunlight is radiant heat energy that travels a greatdistance through space to reach the earth. Theseelectromagnetic heat waves are absorbed whenthey come in contact with nontransparent bodies.The motion of the molecules in the body increases,

as indicated by an increase in the temperature ofthe body.

The differences between conduction, con-vection, and radiation are discussed below,

Conduction and convection are extremelyslow, while radiation takes place with the speedof light. You can see this at the time of an eclipseof the sun when heat from the sun is shut off atthe same time as light is shut out.

Radiant heat may pass through a mediumwithout heating it. For example, the air inside agreenhouse may be much warmer than the glassthrough which the sun’s rays pass.

Conducted or convected heat may travelin roundabout routes, while radiant heat alwaystravels in a straight line. For example, radiationis cut off when a screen is placed between thesource of heat and the body to be protected.


A56. As a wave travels through one medium it is traveling at a specificvelocity of propagation. When it reaches a new medium, thevelocity of propagation changes. If the ray is not perpendicularto the boundary between the two media, the ray will changedirection and bend. This is known as refraction.

A57. a. The angle of incidenceb. The index of refraction

A58. Diffraction occurs when the path of waves is bent because ofan obstruction.

A59. The relative motion between the source of a wave and a detectorof that wave. The frequency of the wave at the detector positiondiffers from the frequency of the wave at the source.

A60. a. Radio wavesb. Heatc. Light

A61. a. Conductionb. Convectionc. Radiation

A62. Poor conductors of heat

A63. Gas

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Absorption

The sun, a fire, and an electric light bulb allradiate energy, but a body need not glow to giveoff heat. A kettle of hot water or a hot solderingiron radiates heat. If the surface is polished orlight in color, less heat is radiated. Bodies thatdo not reflect are good radiators and goodabsorbers. Bodies that do reflect are poorradiators and poor absorbers. This is the reasonwhite clothing is worn in the summer. A practicalexample of heat control is the Thermos bottle. Theflask itself is made of two walls of silvered glasswith a vacuum between them. The vacuumprevents the loss of heat by conduction andconvection, and the silver coating reduces the lossof heat by radiation.

The silver-colored paint on the radiators inheating systems is used as decoration; it actuallydecreases the efficiency of heat transfer. The mosteffective color for heat transfer is dull black; dullblack is the ideal absorber and also the bestradiator.

Temperature Conversion

There are many systems of temperaturemeasurement, and often you need to convert fromone to the other. The four most common scales(fig. 1-13) used today are the Fahrenheit (F),Celsius (C), Kelvin (K), and Rankine (R) scales.

FAHRENHEIT SCALE.— The scale familiarto most Americans is the Fahrenheit scale. Its zeropoint approximates the temperature produced bymixing equal quantities (by weight) of snow andcommon salt.

Under standard atmospheric pressure, theboiling point of water is 212° above zero, and thefreezing point is 32° above zero. Each degreerepresents an equal division, and there are 180such divisions between freezing and boiling.

CELSIUS SCALE.— This scale, formerlycalled the Centigrade scale, uses the freezing point

Q64. Convection is the process of heat transferby means of a hot fluid. Name the aid usedin airborne installations to aid convection.

Q65. For an object to become a good absorberof heat, it is normally painted _________.

TEMPERATURE

Learning Objectives: Convert Fahrenheitand Celsius temperatures. Recognize theimportance of and identify the principlesof thermal expansion. Identify the purposeand use of various types of thermometers.

If an object is hot when touched, it has a hightemperature; if it is cold when touched, it has alow temperature. In other words, temperature isused as a measure of the hotness or coldness ofan object. The hotness and coldness of an objectare relative. For example, on a cold day, metalsseem colder to the touch than nonmetals becausethey conduct heat away from the body morerapidly. When you leave a warm room to gooutside, the outside air seems cooler than it reallyis. When you come from the outside cold into awarm room, the room seems warmer than it reallyis. The temperature a person feels depends on thestate of his/her body.

Figure 1-13.-Comparison of the four common temperaturescales.

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and boiling point of water under standardatmospheric pressure at fixed points of 0 and 100with 100 equal divisions between. These 100divisions represent the same difference intemperature as 180 divisions of the Fahrenheitscale, creating a ratio of 100 to 180. The ratio of100/180 reduces to 5/9, which means a changeof 1°F is equal to a change of 5/9°C. A changeof 5° on the Celsius scale is equal to a change of9° on the Fahrenheit scale. Because 0 on theCelsius scale corresponds to 32° on the Fahrenheitscale, a difference in reference points existsbetween the two scales. (See figure 1-13.)

The Celsius scale is used with most scientificmeasurements. In your work, you will need toconvert Fahrenheit temperatures to their Celsiusequivalents. To convert from the Fahrenheit scaleto the Celsius scale, you subtract 32° from thetemperature and multiply the result by 5/9. Forexample, to convert 68° Fahrenheit to Celsius,you would perform the following calculations:

To convert from the Celsius scale to theFahrenheit scale, you reverse the process. Multiplythe reading on the Celsius thermometer by 9/5and add 32 to the result.

Another method of temperature conversion isbased on the fact that the Fahrenheit and Celsiusscales both register the same temperature at –40°;that is, –40°F is equivalent to –40°C. Thismethod of conversion is known as the 40 rule, andyou can use the following steps:

Step 1. Add 40 to the temperature that is to beconverted. Do this whether the giventemperature is Fahrenheit or Celsius.

Step 2.

Step 3.

For

Multiply the result by 9/5 when changingCelsius to Fahrenheit; multiply by 5/9when changing Fahrenheit to Celsius.

Subtract 40 from the result of step 2. Thisis the answer.

example, to convert 100°C to theFahrenheit scale using the 40 rule, performfollowing calculations:

100 + 40 = 140

140 x 9/5 = 252

252 – 40 = 212°F.

Remember, always ADD 40 first, then MULTI-PLY, then SUBTRACT 40, regardless of thedirection of the conversion.

It is important that all technicians be able toread thermometers and to convert from one scaleto the other. In some types of electronicequipment, thermometers are provided as a checkon operating temperatures. Thermometers arealso used to check the temperature of a chargingbattery.

KELVIN SCALE.— The Kelvin scale wasadopted in 1967. It is defined as 1/273.16 of thethermodynamic temperature of the triple point ofwater. The Kelvin scale is also known as anabsolute scale. Its zero point is the temperatureat which all molecular motion would cease andno additional heat could be extracted from thesubstance. It is referred to as absolute zerotemperature, which is –273.16°C [commonlyused as –273°C (fig. 1-13) for most calculations].The spacing between degrees is the same as forthe Celsius scale; conversion from the Celsius scaleto the Kelvin scale is made by adding 273 to theCelsius temperature.


A64. Fans and blowers

A65. Dull black

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RANKINE SCALE.— The Rankine scalehas the same spacing between degrees as theFahrenheit scale. Its zero point corresponds to0 Kelvin (absolute zero). This point is calculatedas the equivalent of –459.69°F; usually, –460°Fis used for calculations. To convert Fahrenheitto Rankine, add 460 to the Fahrenheit tempera-ture.

Since Rankine and Kelvin both have the samezero point, conversion between the two scalesrequires no addition or subtraction. Rankinetemperature is equal to 9/5 times the Kelvintemperature, and Kelvin temperature is equal to5/9 of the Rankine temperature.

Thermal Expansion

Nearly all substances expand, or increase insize, when their temperature increases. Railroadtracks are laid with small gaps between thesections to prevent buckling when the temperatureincreases in summer. Concrete pavement hasstrips of soft material inserted at intervals toprevent buckling when the sun heats the roadway.A steel building or bridge is put together withred-hot rivets so that when the rivets cool theywill shrink, and the separate pieces will be pulledtogether very tightly.

As a substance is expanded by heat, theweight per unit volume decreases. This decreaseoccurs because the weight of the substanceremains the same while the volume is increasedby the application of heat. Therefore, you cansee that density decreases with an increase intemperature.

Experiments show that for a given change intemperature, the change in length or volume isdifferent for each substance. For example, a givenchange in temperature causes a piece of copperto expand nearly twice as much as a piece of glassof the same size and shape. For this reason, theconnecting wires into an electronic tube are notmade of copper; they are made of a metal thatexpands at the same rate as glass. If the metal doesnot expand at the same rate as the glass, thevacuum in the tube is broken by air leaking pastthe wires in the glass stem.

The amount that a unit length of anysubstance expands for a 1-degree rise in

temperature is known as the coefficient of linearexpansion for that substance. The temperaturescale used must be specified.

To estimate the expansion of any object,such as a steel rail, you must know threethings about it—its length, the rise in tempera-ture to which it is subjected, and its rate orcoefficient of expansion. Expansion is expressedas follows:

expansion = coefficient x length x rise intemperature, or

In this equation, k represents the coefficient ofexpansion for the particular substance (in someinstances, the Greek letter alpha is used toindicate the coefficient of linear expansion), lrepresents the length, and minus is thedifference of the two temperatures.

Use the formula shown above to solve thefollowing problem:

If a steel rod measures exactly 9 feet at 21°C,what is its length at 55°C? The coefficient oflinear expansion for steel is

e = 0.000011 x 9 x 34

e = 0.003366

This amount, when added to the original lengthof the rod, makes the rod 9.003366 feet long.(Since the temperature has increased, the rod islonger by the amount of e. If the temperature hadbeen lowered, the rod would have become shorterby a corresponding amount.)

The increase in the length of the rod isrelatively small; but if the rod were placed whereit could not expand freely, there would bea tremendous force exerted due to thermalexpansion. Thermal expansion is considered whendesigning ships,machinery.

buildings, and all forms of

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Table 1-5.-Linear Expansion Coefficients

SUBSTANCECOEFFICIENT OF

LINEAR EXPANSION

Aluminum 24 x

Brass 19 x

Copper 17 x

Glass 4 to 9 x

Kovar 4 to 9 x

Lead 28 x

Iron, Steel 11 x

Quartz 0.4 x

Zinc 26 x

Figure 1-15.-Thermostat.Refer to table 1-5 for a list of the coefficients

of linear expansion (approximate values) of somesubstances per °C.

A practical application for the difference inthe coefficients of linear expansion is thethermostat. This instrument is made of two stripsof different metals fastened together. When thetemperature changes, the strip bends because ofthe unequal expansion of the metals (fig. 1-14).Thermostats (fig. 1-15) are used in overload relaysfor motors, in temperature-sensitive switches, andin electric ovens.

The coefficient of surface or area expansionis approximately twice the coefficient of linearexpansion. The coefficient of volume expansionis approximately three times the coefficient oflinear expansion. It is an interesting fact that ina plate containing a hole, the area of the hole

Figure 1-14.-Compound bar.

expands at the same rate as the surroundingmaterial. In the case of a volume of air enclosedby a thin solid wall, the volume of air expandsat the same rate as that of a solid body made ofthe same material as the walls.

Thermometers

The measurement of temperature is known asthermometry. Many modern thermometers useliquids in sealed containers. The best liquids touse in the construction of thermometers arealcohol and mercury because they have lowfreezing points.

LIQUID THERMOMETERS.— The commonlaboratory thermometer is constructed so itindicates a change of 10 in temperature. A bulbis blown at one end of a piece of glass tubinghaving a small bore. Then, the tube and bulb arefilled with a liquid. During this process, thetemperature of both the liquid and the tube arekept at a point higher than the thermometer willreach in normal usage. The glass tube is sealed,and the thermometer is allowed to cool. Duringthe cooling process, the liquid falls away from thetop of the tube and creates a vacuum in thethermometer. The thermometer is marked byplacing it in melting ice, The height of the cooledliquid column is marked as the 0°C point.

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Next, the thermometer is placed in steam at apressure of 76 centimeters of mercury, and a markis made at the point to which the liquid insiderises. The space between these two marks is thendivided into 100 equal parts (degrees on theCelsius thermometer). This type of thermometeris used in laboratory work and in testing electricalequipment.

SOLID THERMOMETERS.— Because therange of all liquid thermometers is limited, othermethods of thermometry are necessary. Mostliquids freeze at temperatures between 0°C and–200°C. At the upper end of the temperaturerange, high heat levels are encountered. Here, theuse of liquid thermometers is limited by the highvapor pressures of the liquids. The resistancethermometer and the thermocouple are among themost widely used solid thermometers.

The resistance thermometer makes use of thefact that the electrical resistance of metalschanges as the temperature changes. This type ofthermometer is usually constructed of platinumwire wound on a mica form and enclosed in athin-walled silver tube. It is extremely accuratefrom the lowest temperature to the melting pointof the unit.

The thermocouple (fig. 1-16) is an electriccircuit. Its operation is based on the principle thatwhen two unlike metals are joined and thejunction is at a different temperature from theremainder of the circuit, an electromotive forceis produced. The electromotive force is measuredwith great accuracy by a galvanometers. Thermo-couples can be located wherever measurement ofthe temperature is important and wires run to agalvanometers located at any convenient point. Bymeans of a rotary selector switch, you can useone galvanometers to read the temperatures ofthermocouples at any of a number of widelyseparated points.

Figure 1-16.-Thermocouple.

The principle of the compound bar (fig. 1-14)is also used in thermometers. The bar may be inthe shape of a spiral or a helix so, within a givenenclosure, a greater length of the compound barmay be used. This increases the movement of thefree end per degree of temperature change. Also,the indicating pointer may be joined to the movingend of the compound bar by means of distancemultiplying linkage to make the thermometereasier to read. Often this linkage is arranged togive circular movement to the pointer.

MEASUREMENT OF HEAT

Learning Objective: Recognize the meansof heat measurement in terms of itsmechanical equivalent and specific heat.

A unit of heat may be defined as the heatnecessary to produce some agreed-on standard ofchange. There are three such units in commonuse—the British thermal unit (Btu), the gram-calorie, and the kilogram-calorie.

1. One Btu is the quantity of heat necessaryto raise the temperature of 1 pound of water 1°F.

2. One gram-calorie (small calorie) is thequantity of heat necessary to raise 1 gram of water1°c .

3. One kilogram-calorie (large calorie) is thequantity of heat necessary to raise 1 kilogram ofwater 1°C. One kilogram-calorie equals 1,000gram-calories.

NOTE: The large calorie is used in relationto food energy and for measuring com-paratively large amounts of heat. In thisTRAMAN, the term calorie means gram-calorie.

The terms quantity of heat and temperatureare commonly misused. The distinction betweenthem should be understood clearly. For example,two identical pans, containing different amountsof water of the same temperature, are placed overidentical gas burner flames for the same lengthof time. At the end of that time, the smalleramount of water reaches a higher temperature.Equal amounts of heat have been supplied; but,the increases in temperatures are not equal. Inanother example, the water in both pans is thesame temperature (80°F), and both pans areheated to the boiling point. More heat must besupplied to the larger amount of water. Thetemperature rises are the same for both pans, but

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the quantities of heat necessary to make thetemperature rise are different.

Mechanical Equivalent

Mechanical energy is usually expressed in ergs,joules, or foot-pounds. Energy in the form of heatis expressed in calories or in Btu; 4.186 joulesequals 1 gram-calorie; and 778 foot-pounds equals1 Btu. The following equation is used to convertfrom the English system to the metric system:

1 Btu =

Specific Heat

Substances differ

252 calories.

from one another in thedifferent quantities of heat they require to producethe same temperature change in a given mass ofsubstance. The thermal capacity of a substanceis the calories of heat needed, per gram mass, toincrease the temperature 1°C. The specific heatof a substance is the ratio of its thermal capacityto the thermal capacity of water at 15°C. Specificheat is expressed as a number that has no unitsof measurement and applies to both the Englishand the metric systems.

Water has a high heat capacity. Large bodiesof water on the earth stabilize the air and thesurface temperature of the earth. A great quantityof heat is required to change the temperature ofa large lake or river. Therefore, when thetemperature of the air falls below the temperatureof bodies of water, they give off large quantitiesof heat to the air. This process keeps theatmospheric temperature at the surface of theearth from changing very rapidly.

Table 1-6 gives the specific heats of severalcommon substances. To find the heat required toraise the temperature of a substance, multiply itsmass by the rise in temperature times its specificheat.

For example, it takes 1,000 Btu to raise thetemperature of 100 pounds of water 10°F, butonly 31 Btu to raise 100 pounds of lead 10°F.

CHANGE OF STATE

Learning Objective: Identify the way heatchanges the state of matter, to includefusion and vaporization.

A thermometer placed in melting snowbehaves strangely. The temperature of the snowrises slowly until it reaches 0°C. Then, provided

Table 1-6.-Specific Heats of Some Common Substances

Hydrogen (at constant pressure). . . . . 3.409

Water at 4°C . . . . . . . . . . . . . . . . . . . . . 1.0049

Water at 15°C . . . . . . . . . . . . . . . . . . . 1.0000

Water at 30°C . . . . . . . . . . . . . . . . . . . . 0.9971

Ice at 0°C . . . . . . . . . . . . . . . . . . . . . . . .0.502

Steam at 100°C . . . . . . . . . . . . . . . . . . . 0.421

Air (at constant pressure) . . . . . . . . . . 0.237

Aluminum . . . . . . . . . . . . . . . . . . . . . . .0.217

Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.160

Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0.114

Copper . . . . . . . . . . . . . . . . . . . . . . . . . ..0.093

Brass, zinc . . . . . . . . . . . . . . . . . . . . ..0.092

Silver . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.057

Tin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.056

Mercury . . . . . . . . . . . . . . . . . . . . . . . .0.033

Gold, lead . . . . . . . . . . . . . . . . . . . . . . . .0.031

the mixture is stirred constantly, it remains at thatpoint until all the snow has changed to water.When all the snow has melted, the temperatureagain begins to rise. A definite amount of heatis required to change the snow to water at the sametemperature. This heat is required to change thewater from crystal form to liquid form.

Heat of Fusion

Eighty gram-calories of heat are required tochange 1 gram of ice at 0°C to water at 0°C. InEnglish units, the heat required to change 1 poundof ice at 32°F to water at 32°F is 144 Btu. Thesevalues (80 gram-calories and 144 Btu) are calledthe heat of fusion of water. The heat used to meltthe ice represents the work done to produce thechange of state. Since 80 calories are required tochange a gram of ice to water at 0°C, when a gramof water is frozen, it gives up 80 calories.

Many substances behave very much like water.At a given pressure, they have a definite heat offusion and an exact melting point. However, there

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are many materials that don’t change from aliquid to a solid state at one temperature. Forexample, molasses gets thicker and thicker as thetemperature decreases, but there is no exacttemperature where the change of state occurs.Wax, celluloid, and glass are other substances thatdo not change from a liquid to a solid state at anyparticular temperature. In fact, measurements ofglass thickness at the bottom of windows inancient cathedrals tend to indicate that the glassis still flowing at an extremely slow rate. Mosttypes of solder used in electronics maintenancealso tend to become mushy before melting.

Heat of Vaporization

Damp clothing dries more rapidly under a hotflat iron than under a cold one. A pool of waterevaporates more rapidly in the sun than in theshade. Therefore, heat has something to do withevaporation. The process of changing a liquid toa vapor is similar to what occurs when a solidmelts.

If a given quantity of water is heated until itevaporates [changes to a gas (vapor)], more heatis used than is necessary to raise the same amountof water to the boiling point. For example, 540calories are required to change 1 gram of waterto vapor at a temperature of 100°C. It takes 972Btu to change 1 pound of water at 212°F to watervapor (steam) at 212°F. The amount of heatnecessary for this change is called the heat ofvaporization of water. Over five times as muchheat is required to change a given amount of waterto vapor than to raise the same amount of waterfrom the freezing point to the boiling point.

When water is heated, some vapor formsbefore the boiling point is reached. As the watermolecules take up more and more energy fromthe heating source, their kinetic energy increases.The motion that results from the high kineticenergy of the water molecules causes a pressure,which is called the vapor pressure. As the velocityof the molecules increases, the vapor pressureincreases. The boiling point of a liquid is thetemperature at which the vapor pressure equalsthe external or atmospheric pressure. At normalatmospheric pressure at sea level, the boiling pointof water is 100°C or 212°F.

NOTE: At sea level, atmospheric pressureis normally 29.92 inches of mercury.

While the water is below the boiling point, anumber of molecules acquire enough kinetic

energy to break away from the liquid state intoa vapor. For this reason, some evaporation slowlytakes place below the boiling point. At or abovethe boiling point, large numbers of molecules haveenough energy to change from liquid to vapor,and the evaporation takes place much morerapidly.

If the molecules of water are changing to watervapor in an open space, the air currents carry themaway quickly. In a closed container, they becomecrowded and some of them bounce back into theliquid as a result of collisions. When as manymolecules are returning to the liquid state as areleaving it, the vapor is saturated. Experimentsshow that saturated vapor in a closed containerexerts a pressure and has a given density at everytemperature.

Q66.

Q67.

Q68.

Q69.

Q70.

Q71.

Convert 96°F to the Celsius scale.

List the four types of scales.

What principle is involved in temperature-sensitive switches?

What type of thermometer is usually usedin the laboratory? In aircraft?

What other principle is used to constructa thermometer?

What effect does the heat of fusion haveon solder?

LIGHT

Learning Objective: Recognize the charac-teristics of light and identify colors in thefrequency spectrum.

The exact nature of light is not fully under-stood, although men have been studying thesubject for centuries. There are scientificphenomena that are explained only by the wavetheory, and other phenomena that are explainedby the particle or corpuscular theory. Gradually,physicists have accepted a theory about light thatcombines these two views; light is a form ofelectromagnetic radiation. As such, light andsimilar forms of radiation are made up of movingelectric and magnetic forces.

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CHARACTERISTICS

Light waves travel in straight lines. When theymeet another substance, they are transmitted,reflected, or absorbed. Substances that permitclear vision through them and transmit almost allthe light falling upon them are transparent.Substances that allow part of the light to pass butappear clouded and impair vision substantially arecalled translucent. Substances that transmit nolight are called opaque.

Objects that are not light sources are visiblebecause they reflect part of the light reaching themfrom some luminous source. If light is neithertransmitted nor reflected, it is absorbed or takenup by the medium. When light strikes a substance,some absorption and reflection always takes place.No substance completely transmits, reflects, orabsorbs all the light that reaches its surface.

Luminous Intensity andIntensity of Illumination

Luminous intensify refers to the total lightproduced by a source. Intensity of illuminationdescribes the amount of light received per unitarea at a distance from the source. The followingterms are generally used when describing luminousintensity and intensity of illumination.

Candlepower. This is the luminous intensityexpressed in candelas. A candela is the luminous

intensity in the perpendicular direction of asurface of 1/600,000 square meter of a black bodyat the temperature of freezing platinum under apressure of 101,325 newtons per square meter.

Footcandle. The intensity of illumination ofa surface (illuminance) is directly proportional tothe luminous intensity of the light source. It isinversely proportional to the square of thedistance between the light source and the surface,Look at figure 1-17. It shows how an experimentcan prove the inverse square law of light.

Place a card 1 foot from a light source. Thelight striking the card is of a certain intensity.Next, move the card 2 feet away. You can see thatthe intensity of light decreases with the square ofthe distance (2 x 2, or 4 times) and is one-fourthas bright. Now, move the card 3 feet away fromthe light; the light is now one-ninth as intense asit was when the light was 1 foot from the card.If you move the card 4 feet away from the lightsource, the light is one-sixteenth as intense.

The footcandle is one unit of measuring theintensity of incident light using the formula:

Illumination in footcandles =candlepower of source.

(distance in

A surface 1 foot from a 1-candlepower source hasan illumination of 1 footcandle; but, if the surfaceis moved to a distance of 4 feet, a 16-candlepowersource is required for the same illumination.


A 6 6 .

A67. a. Celsiusb. Fahrenheitc. Kelvind. Rankine

A68. Coefficient of linear expansion.

A69. The liquid thermometer is usually used in the laboratory whitethe solid thermometer is used in aircraft.

A70. The principle of the compound bar.

A71. It causes it to become mushy before it melts; that is, it flowsat a very slow rate.

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The inverse square law of light holds true forundirected light only. For light that is directed,the rate its intensity diminishes depends on therate of divergence of the beam.

Lumen. This unit is the amount of lightflowing through a solid angle of 1 radian froma standard candle. The following example helpsexplain the term lumen. If a light source of 1candlepower is placed in the center of a spherewith a radius of 1 foot, it illuminates every pointon the surface of the sphere at an intensity of1 footcandle. Every square foot of the surfacereceives 1 lumen of light. The total surface of thesphere is found by the formula If the radiusof a sphere is 1 foot, the area is 4 x 3.1416 x 12

= 12.5664 square feet. Therefore, a source of 1candlepower emits 12.5664 lumens.

The output of light bulbs is given either incandlepower or in lumens. Since the light bulbmay not distribute the light equally in alldirections, the lumen is most frequently used.Light bulb manufacturers measure the lightoutput in all directions and specify its total outputin lumens. When the total output in lumens isknown, the average candlepower is computed bydividing the total output in lumens by (12.5664).

Lux. The lux is the illumination given to asurface 1 meter away from a 1-candlepower sourceand is sometimes called a meter-candle.

Phot. The phot is the illumination given toa surface 1 centimeter away from a 1-candlepowersource and is sometimes called a centimeter-candle.

Luminance. Luminance (or brightness) refersto the light a surface gives off in the direction ofthe observer. The lambert is the unit of luminanceequal to the uniform luminance of a perfectlydiffusing surface that emits or reflects light at therate of 1 lumen per square centimeter. For aperfectly reflecting and perfectly diffusing surface,the number of lamberts is equal to the numberof phots (incident light).

Q72.

Q73.

Q74.

Q75.

Q76.

List the effects on light waves when theymeet a substance.

What is meant by the term luminousintensity?

What is meant by the term intensity ofillumination?

What is measured by the footcandle?

What term is usually used to describe theoutput of a light bulb?

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Reflection

Light waves obey the law of reflection the same way as other types of waves.Optical devices that reflect light are generally classed as mirrors. They area polished opaque surface, or they are a specially coated glass. Glass mirrorsrefract as well as reflect; however, if the glass is of good quality and notexcessively thick, the refraction causes no trouble. The following discussionis based on the mirror.

Basically, the reflector is used to change thedirection of a light beam. The angle of thereflected light is changed to a greater or lesserdegree by changing the angle at which the incidentlight impinges upon the mirror.

Changing direction.

The reflector is also used to focus a beam oflight. The focusing action of a concave mirror isindicated. The point of focus may be made anyconvenient distance from the reflector by properselection of the arc of curvature of the mirror;the sharper the curvature, the shorter the focallength.

Focusing a beam.

The reflector can be used to intensify theillumination of an area. The flashlight is anexample of this application. You can see that thelight source (bulb) is located approximately at theprincipal focus point, and that all rays reflectedfrom the surface are parallel. You can also seethat the reflector does not concentrate all the rays,and some are transmitted without being reflectedand are not included in the principal beam.

Illuminating an area.

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Refraction

As light passes through a transparent substance, it travels in a straightline. When it passes into or out of that substance, it is refracted like otherwaves. Refraction of light occurs because light travels at different velocitiesin different transparent media. To make it easier to predict the outcome ofspecific applications, many transparent substances have been tested forrefractive effectiveness. The ratio of the speed of light in air to its speed ineach transparent substance is called the index of refraction for that substance.For example, light travels about one and one-half times as fast in air as itdoes in glass, so the index of refraction of glass is about 1.5. When the lawof refraction is used in connection with light, a denser medium refers to amedium with a higher index of refraction.

Refraction through a piece of plate glass isshown in figure 1-18. The ray of light strikes theglass plate at an oblique angle along path AB. Ifit were to continue in a straight line, it wouldemerge from the plate at point N. But accordingto the law of refraction, it is bent toward thenormal RS and emerges from the glass at pointC. As it enters the air, the ray does not continueon its path, but is bent away from the normal XY,and leaves along the path CD in the air.

If the two surfaces of the glass are parallel,the ray leaving the glass is parallel to the rayentering the glass. The displacement depends uponthe thickness of the glass plate, the angle of entryinto it, and the index of refraction for the glass.

All rays striking the glass at any angle otherthan perpendicular are refracted in the samemanner. In the case of a perpendicular ray, norefraction takes place, and the ray continues

Figure 1-18.-The law of refraction.

through the glass and into the air in a straight line.

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.

.

.

.

PRISMS.— When a ray of light passes through a flat sheet of glass, itemerges parallel to the incident ray. This is true only when the two surfacesof the glass are parallel. When the two surfaces are not parallel, as in a prism(fig. 1-19), the ray is refracted differently at each surface of the glass anddoes not emerge parallel to the incident ray.

View A shows that both refractions are in thesame direction. The ray coming out of the prismis not parallel to the ray going into it, followingthe law of refraction. When the ray entered theprism, it was bent toward the normal; and whenit emerged, it was bent away from the normal.You can see that the deviation is the result of thetwo normals not being parallel.

If two triangular prisms are placed base tobase (view B), parallel incident rays passingthrough them are refracted and intersect. The rayspassing through different parts of the prisms donot intersect at the same point. With two prisms,there are only four refracting surfaces. The lightrays from different points on the same plane arenot refracted to a point on the same plane behindthe prism. They emerge from the prisms andintersect at different points along an extendedcommon baseline, as you can see by looking atpoints A, B, and C in view B.

Parallel incident light rays falling upon twoprisms apex to apex (view C) are spread apart.The upper prism refracts light rays toward itsbase, and the lower prism refracts light raystoward its base. The two sets of rays diverge.

Figure 1-19.-Passage of light through a prism.

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POSITIVE LENSES.— A positive (convergent) (fig. 1-20) lens acts liketwo prisms base to base, with their surfaces rounded off into a curve. Raysthat strike the upper half of the lens bend downward, and rays that strikethe lower half bend upward.

A good lens causes all wavelengths within eachray to cross at the same point behind the lens.When the incident ray of light enters the densermedium (the lens), it bends toward the normal.When it passes through the lens into the less densemedium (the air), it bends away from the normal.

View B shows the refraction of only one rayof light; but all rays passing through a positivelens behave in the same way. All incident lightrays, either parallel or slightly diverging, convergeto a point after passing through a positive lens.

The only ray of light that can pass througha lens without bending is the ray that strikes thefirst surface of the lens at a right angle,perpendicular or normal to the surface. It passesthrough that surface without bending and strikesthe second surface at the same angle. It leaves thelens without bending. This ray is shown in view B.

The terms positive lens and convergent lensare synonymous; either of them may be used todescribe the action of a lens that focuses (bringsto a point of convergence) all light rays passingthrough it. All simple positive lenses are easy toidentify since they are thicker in the center thanat the edges. The three most common types ofsimple positive lenses are shown in view C.

Figure 1-20.-Positive lenses.

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NEGATIVE LENSES.— Look back at figure1-19, view C. Here you can see the refraction oflight rays by two prisms apex to apex. If the prismsurfaces are rounded, the result is a negative(divergent) lens, A negative lens is called adivergent lens, since it does not focus the rays oflight passing through it. Light rays passingthrough a negative lens diverge or spread apart(fig. 1-21, view A).

Look at View B. Here, the law of refractionto one ray of light passing through a negative lens

is shown. However, just as in a positive lens, aray of light passing through the center of anegative lens is not affected by refraction andpasses through without bending.

Three simple negative lenses are shown in viewC. They are often referred to as concave lensesand are identified by their concave surfaces. Thesimple negative lenses are thicker at the edgesthan at the center. They are generally used,in conjunction with simple positive lenses, toassist in the formation of a sharper image by

Figure 1-21.-Negative lenses.

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eliminating or subduing various defects presentin an uncorrected simple positive lens.

Q77. What are the principle uses of reflectors?

Q78. What happens when light passes througha transparent substance?

Q79. List the objects that act as refractors.

FREQUENCIES AND COLOR

The electromagnetic waves that produce thesensation of light are all very high frequency(VHF) waves, which means that they have veryshort wavelengths. These wavelengths aremeasured in nanometers (billionths of meters, or

meters). By looking at figure 1-22, you cansee that light with a wavelength of 700 nanometersis red and that a light with a wavelength of 500nanometers is blue-green. The information in thisfigure is not exactly correct as the color of lightdepends on its frequency, not its wavelength.

Wavelength varies, depending on the mediumthe wave is in. When a wave producing the colorred is in air, its wavelength is 700 nanometers.

When the same wave is in another medium, itswavelength is other than 700 nanometers. Whenred light that has been traveling in air enters glass,it loses speed and its wavelength becomes shorteror compressed, but it continues to be red. Thecolor of light depends on frequency and not onwavelength. (Note: The color scale in figure 1-22is based on the wavelengths in air.)

All color-component wavelengths of the visiblespectrum are present in equal amounts in whitelight. Variations in composition of the componentwavelengths result in other characteristic colors.For example, when a beam of white light is passedthrough a prism (fig. 1-22), it is refracted anddispersed into its component wavelengths. The eyereacts differently to each of these wavelengths,seeing the various colors making up the visiblespectrum. The visible spectrum is recorded as amixture of red, orange, yellow, green, blue,indigo, and violet. You can see that white lightresults when the primaries (red, green, and blue)are mixed together in overlapping beams of light.

NOTE: These are not the primaries usedin mixing pigments.

Figure 1-22.-Electromagnetic wavelengths and the refraction of light.

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The complementary or secondary colors(magenta, yellow, and cyan) are shown by mixingany two of the primary colors in overlappingbeams of light. For example, red and green lightmixed in equal intensities make yellow light; greenand blue mixed together produce blue-green(cyan) light; and blue and red light correctly mixedproduces magenta (purplish red).

Q80. Name the primary colors of light fre-quencies.

Q81. If you mix the primary colors together,what is the result?

CONDUCTION MEDIA ANDVELOCITY OF TRANSMISSION

In a uniform medium under given physicalconditions, sound travels at a definite speed. Insome substances, the velocity of sound is higherthan in others. Even in the same medium, whentemperature conditions differ, the velocity ofsound varies. Density and elasticity of a mediumare basic physical properties that govern thevelocity of sound.

You can calculate the velocity of com-pressional waves in centimeters per second whenthe elasticity and density of the medium are givenin units by using the formula

SOUND

Learning Objectives: Recognize the charac-teristics of sound and travel. Identify thesound conduction media and recognize itseffects on the velocity of sound trans-mission.

Normally, the term sound refers to hearing.When used in physics, sound refers to a particulartype of wave motion. It deals with the generation,propagation, transmission, characteristics, andeffects of sound waves.

BASIC CONSIDERATIONS

One example of the generation and propaga-tion of sound waves is the tuning fork (discussedearlier in this chapter). Any object that movesrapidly to and fro or vibrates rapidly, disturbingthe surrounding medium, may become a soundsource, Sound requires three components—asource, a medium for transmission, and adetector. As widely different as sound sourcesmay be, the waves they produce have certain basiccharacteristics.

WAVE MOTION

Sound waves are longitudinal-type waves thatrely on a physical medium for propagation andtransmission. Since the waves are transmitted bythe compression and rarefaction of particles ofmatter in the medium, they cannot be transmittedthrough a vacuum. Sound waves are similar toother types of waves because they can be reflected,absorbed, or refracted. Sound waves are alsosubject to the Doppler effect.

The major differences between sound waves,heat, and light waves are the frequencies, thenature of the waves, and the velocities of wavetravel.

The elasticity of most liquids and solids is muchgreater than gases, and the velocity of sound isfaster in them in spite of their larger densities. Thecoefficient of elasticity for water is 15,230 timesthat of air, while water has only 773 times thedensity of air. Because of this, sound travels overfour times faster in water than it does in air.

Some velocities of sound are given in table 1-7;these velocities correspond closely to those

Table 1-7.-Comparison of Velocity of Sound in VariousMedia

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calculated by using the formula. Compare thevelocity of sound in lead and water. Lead has adensity that is eleven times greater than water, yetthe velocity of sound is only slightly less in leadthan in water. The density of steel is over twicethat of aluminum, but steel is more elastic. If youcompare the velocity of sound in steel andaluminum, you will find that the velocity is almostthe same in the two metals.

The elasticities of most gases at equal pressures

This amounts to about a 2-foot-per-secondincrease for each °C rise in temperature, andabout a 1.1-foot-per-second increase for each °Frise in temperature. Since air temperature isusually lower at high altitudes, the velocity ofsound is also lower at these altitudes.

For a fixed temperature, the velocity of soundis constant for any medium, and is independentof both the frequency and the amplitude of thesound waves.

are the same, so the velocity of sound-throughgases is inversely proportional to the square root Q82.of their densities. For example, the density of airis almost 16 times that of hydrogen; therefore,the velocity of sound in air is slightly more than Q83.one/fourth the velocity of sound in hydrogen. Inthe other direction, air has a density of slightlyless than two-thirds the density of carbon dioxide;therefore, the velocity of sound in air is approxi- Q84.mately 1.25 times the velocity of sound in carbondioxide. (See table 1-7 for actual values.)

The velocity of sound in a gas, such as air, isindependent of pressure. When pressure is increased,the density and elasticity both increase at the same Q85.ratio. Consequently, the velocity is constant so longas the temperature is not changed. But if the temp-

List the three components that are requiredby sound.

List the two properties of a medium thatgovern the velocity of sound as it passesthrough the medium.

Sound travels faster in liquids and solidsthan in gases even though liquids and gasesare more dense. Why will sound travelfaster in water than it does in air?

The velocity of sound is lower at highaltitudes. Explain why this is so.

erature is raised (pressure being constant), densiy CHARACTERISTICSdiminishes, and the velocity of sound increases.If absolute values for temperature (Kelvin or Learning Objective: Identify the pitch,Rankine) are used, the velocities of sound in air quality, and intensity of sound.are related to air temperatures by the relation

Many words describe sounds, such as whistle,scream, rumble, and hum. Most of these wordsdescribe noises, not musical tones. Musical tones

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are based on the regularity of the vibrations, thedegree of damping, and the ability of the ear torecognize components having a musical sequence.

The ear can distinguish tones that are differentin pitch, intensity, or quality. Each of thesecharacteristics is associated with one of theproperties of the vibrating source or of the wavesthat the source produces.

Pitch is determined by the number ofvibrations per second.

Intensity is determined by the amplitudeof the wave motion.

Quality is determined by the number ofovertones (harmonics) that the wave con-tains.

A sound wave is best described by itsfrequency rather than by its velocity or wavelengthbecause both velocity and wavelength changewhen the temperature of the air changes.

Pitch

The term pitch describes the frequency of asound. The recognizable difference between thetones produced by two different keys on a pianois a difference in pitch. The pitch of a sound isproportional to the number of compressions andrarefaction received per second, which, in turn,is determined by the vibration frequency of thesounding source. Sound waves vary in length; along wavelength sounds as if its pitch is low, whilea short wavelength sounds is if its pitch is high.

Pitch is usually measured by comparison witha standard. The standard tone may be producedby a tuning fork of known frequency or by a sirenwhose frequency is computed for a particularspeed of rotation. When the speed is regulated,the pitch of the siren is made equal to that of thetone being measured. The ear can determine thisequality directly if the two sources are soundedalternately, or by the elimination of beats byregulating the speed of the siren if the two sourcesare sounded together.

NOTE: If a sound is below 15 hertz orabove 20,000 hertz, it is not normally heardby the human ear. The frequency rangeover which sound is heard is known as theaudible range, and the sounds heard areknown as sonics. Sounds below 15 hertzare subsonics; those above 20,000 hertz areultrasonics.

On the musical scale, pitch refers to thestandard frequency of a given note on the scale.In a few cases, 256 Hz is used for the keynote,sometimes called middle C. For scientificpurposes, the A string of the violin is tuned to440 Hz. The note one octave higher than the firsthas a frequency twice that of the first, and onean octave lower is one-half the frequency of thefirst. For example, if middle C on a piano is tunedto 256 Hz, the C an octave higher is 512 Hz, andone octave lower is 128 Hz. A pitch change from55 Hz to 110 Hz is of just as much consequenceas the change from 440 Hz to 880 Hz.

Quality

Most sounds and musical notes are not puretones. They are mixtures of tones of differentfrequencies. The tones produced by most sourcesare composite waves in which the sound of lowestpitch (the fundamental tone) is accompanied byseveral harmonics or overtones. These harmonicshave frequencies that are two, three, four, or moretimes that of the fundamental frequency. Thequality of a tone depends on the number ofovertones present and on their frequencies andintensities relative to the fundamental tone. It isthis characteristic of difference in quality thatdistinguishes tones of like pitch and intensity whensounded on different types of musical instruments(piano, organ, violin, and so forth).

Intensity

When a bell rings, the sound waves spread outin all directions, and the sound is heard in alldirections. When a bell is struck lightly, thevibrations are of small amplitude, and the soundis weak. A stronger blow produces vibrations ofgreater amplitude, and the sound is louder.Therefore, the amplitude of the air vibrations isgreater when the amplitude of the vibrations ofthe source is increased, and the loudness of thesound depends on the amplitude of the vibrationsof the sound waves. As the distance from thesource increases, the energy in each wave spreadsout, and the sound becomes weaker.

The intensity of sound in the energy per unitarea per second. In a sound wave of simpleharmonic motion, the energy is half kinetic andhalf potential; half is due to the speed of theparticles, and half is due to the compression andrarefaction of the medium. These two energies are90 degrees out of phase at any instant; that is,when the speed of particle motion is at a

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maximum, the pressure is normal. When thepressure is at a maximum or a minimum, thespeed of the particles is zero.

Loudness is a subjective measurement thatdepends primarily on the sound pressure,frequency, and waveform of the stimulus.Intensity of sound is an objective measurementof the sound power being delivered, and it isusually measured as the power flowing througha unit area perpendicular to the direction of thewaves. One such method specifies microwattflowing through an area of 1 square centimeter,One microwatt is equivalent to 10 ergs per secondor joules per second.

At any distance from a point source of sound,the intensity of the wave varies inversely as thesquare of the distance from the source. As a soundwave advances, variations in pressure occur at allpoints in the transmitting medium. The greaterthe pressure variations, the more intense the soundwave. Intensity is proportional to the square ofthe pressure variation, regardless of frequency;therefore, when pressure changes are measured,intensities of sounds having different frequenciescan be compared directly.

MEASUREMENT OF SOUND

Learning Objective: Identify means ofsound measurement to include sound units,intensity level, acoustical pressure, andpower ratio.

The range of sound that the human ear candetect varies with the individual. The normalrange extends from about 20 to 20,000 vibrationsper second. In the faintest audibles speech sounds,the intensity at the ear is about At the threshold of feeling, the maximumintensity that the ear perceives as sound is about1 0-4 watts/cm 2.

The human ear is a nonlinear unit thatfunctions on a logarithmic basis. Its threshold ofaudibility is reached when intensity is reduced tosuch a low level that auditory sensation ceases.On the other hand, the threshold of feeling isreached when intensity is increased to such a highlevel that sound produces the sensation of feelingand becomes painful. By applying this procedureover a wide frequency range, data is used to plottwo curves—one for the lower limit of audibilityand the other for the maximum auditory response(fig. 1-23). Below the lower curve, the human earcannot hear the sound. Above the upper curve,the sensation is one of feeling rather than ofhearing; that is, the sensation of sound is maskedby pain. The area between the two curves showsthe pressure ranges for auditory response atvarious frequencies.

Sound Units

The loudness of sound is not measured by thesame type of scale used to measure length. Unitsof sound measurement vary logarithmically withthe amplitude of the sound variations. These units

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Figure 1-23.-Field of audibility.

are the bel and decibel,

NOTE: When the logarithmic base is not indicated, it is assumed to be 10.

If P2 is greater than P1, the decibel value ispositive and represents a gain in power. If P2 isless than P1, the decibel value is negative andrepresents a loss in power.

Intensity Level

An arbitrary zero reference level is used toaccurately describe the loudness of varioussounds. This zero reference level is the soundproduced by 10-16 watts per square centimeter ofsurface area facing the source. This levelapproximates the least sound perceptible to theear and is usually called the threshold ofaudibility. The sensation experienced by the ear

when subjected to a noise of 40 decibels above thereference level would be 10,000 times as great aswhen subjected to a sound that is barelyperceptible.

Acoustical Pressure

Typical values of sound levels in decibels and thecorresponding intensity levels are summarized intable 1-8. The values in this table are based on anarbitrarily chosen zero reference level. Note thatfor each tenfold increase in power, the intensity ofthe sound increases 10 decibels. The powerintensity doubles for each 3-decibel rise in soundintensity.

Q86. List the three characteristics of sound.

Q87. What two terms describe the range of soundthe human ear can distinguish?

Q88. How do sound units vary with amplitude ofvariations?

Q89. The units of sound measurement are the beland the decibel. They vary logarithmically withthe amplitude of the sound variations. To what dothe bel and the decibel refer?

Q90. In sound-system engineering, what ratio doesdB express?

Q91. What is the arbitrary zero reference levelused to describe the loudness of sounds?

Table 1-8.-Values of Sound Levels

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which refer to thedifference between sounds of unequal intensity orsound levels. The decibel (one-tenth of a bel) is theminimum change of sound level perceptible to thehuman ear. A sound for which the power is 10times as great as that of another sound leveldiffers in power level by 1 bel, or 10 decibels. Forexample, 5 decibels may represent almost anyvolume of sound, depending on the intensity of thereference level on which the ratio is based. Insound-system engineering, decibels (dB) are usedto express the ratio between electrical powers orbetween acoustical powers, If the amounts ofpower to be compared are P1 and P2, the ratio indecibels is

dB = 10 x log (P2)___ . (P1)

Power Ratio

The decibel is used to express an electricalpower ratio, such as the gain of an amplifier, theoutput of a microphone, or the power in a circuitcompared to an arbitrarily chosen reference powerlevel. The value of decibels is often computedfrom the voltage ratio or the current ratio squared.These values are proportional to the power ratiofor equal values of resistance. If the resistancesare not equal, a correction must be made. To findthe number of decibels from the voltage ratio,assuming that the resistances are equal, substitute

for P in the basic equation:

To find the number of decibels from thecurrent ratio, assuming that the resistances areequal, substitute 12 for P in the basic equation:

The power level of an electrical signal is oftenexpressed in decibels above or below a power levelof 0.001 watt (1 milliwatt) as

where, dBm is the power level above 1 milliwattin decibels, and P is the power in watts.

The volume level of an electrical signalcomprising speech, music, or other complex tonesis measured by a specially calibrated voltmetercalled a volume indicator. The volume levels readwith this indicator are read in v units (vu), thenumber being numerically equal to the numberof decibels above or below the reference volumelevel. Zero vu represents a power of 1 milliwattdissipated in an arbitrarily chosen load resistanceof 600 ohms, which corresponds to a voltage of0.7746 volt. Therefore, when the vu meter is con-nected to a 600-ohm load, vu readings in decibelsare used as a direct measure of power above orbelow 1 milliwatt. For any other value ofresistance, the following correction must be addedto the vu reading to obtain the correct vu value:

where vu is the actual volume level, and R is theactual load, or resistance, across which the vumeasurement is made.

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NOTE: If the volume levels are indicatedin units other than vu, the meter cali-bration, or reference level, must be statedwith the decibel value.

ACOUSTICS

Learning Objective: Identify factors thataffect acoustics to include echo, reverbera-tion, interference, and resonance.

Acoustics is the science of sound, includingits propagation, transmission, and effect. Theperformance of an announcing system or soundsystem, when used in a room or enclosed space,depends on the acoustical characteristics of theenclosure. Sound originating in an enclosed spaceis partly reflected and partly absorbed byenclosing surfaces such as walls, ceilings, andfloors. This action introduces echoes andreverberations, which may seriously impair thequality or character of the sound.

Light is often thought of first wheneverreflection is discussed; however, reflection isequally common in other waves. As an example,echoes are caused by reflection of sound waves.

Echo

An echo is the repetition of a sound causedby the reflections of sound waves. For example,when a surface of a room reflects sound, thereflected sound appears as a distinct echo and isheard an appreciable interval later than the directsound. If the surface is concave, it may have afocusing effect and concentrate the reflectedsound energy at one locality. Such a reflectionmay be several levels higher in intensity than thedirect sound, and its arrival at a later time maybe particularly disturbing. This condition iscorrected by

covering the offending surface with absorbingmaterial to reduce the intensity of the reflectedsound;

changing the contour of the offending surfaceand thus send the reflected sound in anotherdirection;

changing the position of the loudspeaker; or

varying the amplitude or the pitch of thesignal.

Q92.

Q93.

Q94.

Name some of the uses of the decibel as itis used to express an electrical power ratio.

What type of acoustical disturbance causesan echo?

A loudspeaker is being used in a fairly largeroom and is producing considerable echothat limits the usefulness of the speaker.List four ways that the effects of echo canbe corrected or modified.

Reverberation

Reverberation is the persistence of sound dueto the multiple reflection of sound waves betweenseveral surfaces of an enclosure. It is one of themost common acoustical defects of a largeenclosure. Its duration varies directly with the timeinterval between reflections (the size of theenclosure) and inversely with the absorbingefficiency of the reflecting surfaces. The result isan overlapping of the original sound and itsimages. If excessive, reverberation causesconfusion, making speech unintelligible.

The hangar deck of an aircraft carrier is anexample of an extremely reverberant area. Thevolume is large, and the hard steel interior surfacesoffer very little absorption. If a single loudspeakeris mounted in a hangar deck, you can understandspeech when you are standing directly in front ofthe loudspeaker. As you move away from theloudspeaker or if you move in a direction thatincreases the angle between you and theloudspeaker’s sound axis, intelligibility decreasesrapidly. Sound from a loudspeaker in areverberant space (such as a hangar deck) iscomposed of direct sound that reaches the listenerwithout any reflection and indirect sound that isreceived with at least one reflection.

Intelligibility, under these conditions, is relatedto the ratio of direct sound to indirect sound. Asthe listener moves away from the loudspeaker, theratio of direct sound to indirect sound at thelistener’s position decreases, and intelligibilitydecreases correspondingly. Therefore, in a highlyreverberant space, intelligibility decreases withdistance from the loudspeaker.

To prevent sound from becoming unintelli-gible, install several speakers in an area.This action prevents the sound from becomingunintelligible in a highly reverberant space. Thepower requirements remain the same; one 25-wattspeaker is replaced by five speakers, each

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consuming 5 watts. This would greatly increasethe direct-to-indirect sound ratio.

Interference

Two sound waves moving through the samemedium at the same time advance independently,each producing the same disturbance as if it werealone. The resultant of the two waves is obtainedby adding the ordinates (instantaneous magni-tudes) of the component waves algebraically,

Two sound waves of the same frequency, inphase with each other, and moving in the samedirection are additive. The resultant wave is inphase with, and has an amplitude equal to, thesum of the component waves.

Two sound waves of the same frequency, inphase opposition, and moving in the samedirection are subtractive. If the component waveshave equal amplitudes, the resultant wave is zero.This addition or subtraction of waves is oftencalled interference.

Two sound waves of slightly differentfrequency that move in the same direction producea beat note. For example, two waves originatefrom two vibrating sources at the same point, andthe frequency of one wave is 1 vibration persecond greater than the other one at a particularinstant. The sources produce additive dis-turbances at some points and subtractivedisturbances at other points on the relativepositions of the waves. These changes continueas long as the sources are kept vibrating. Theresultant wave has a periodic variation in intensityat a frequency equal to the difference between theoriginal frequencies of the component waves. The

difference frequency, referred to as the beatfrequency, produces a type of pulsatinginterference particularly noticeable in soundwaves. The effect of beat frequency (beats)produces alternately loud and soft pulses orthrobs. The effect is most pronounced when thecomponent waves have equal amplitudes.

Resonance

Resonance, or sympathetic vibration, is acommon problem encountered in acoustics. It ismore serious than some other problems becausethe possibility exists for damage to equipment.Reverberation and resonance are frequentlyconfused, but they are distinctly different innature. Reverberation is a result of the reflectionof sound waves and of the interaction betweenthe direct and reflected sound. Only a singlesource is involved. In resonance, however, theoffending object becomes a sound source undercertain conditions. This may be explained by thefollowing example.

Assume that the natural frequency of vibra-tion of a steel shaft, weighted on one end and heldfirmly on the other, is 25 vibrations per second.Suppose, that with the system at rest, a soundwave produces a force that acts on the shaft witha to-and-fro motion 125 times per second. Thisforce sets the system to vibrating at 125 vibrationsper second. These vibrations are of smallamplitude because the rod and weight are tryingto vibrate at their natural rate of only 25vibrations per second. During part of the time,the system is resisting the driving force. The

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motion of the system in this case is called a forcedvibration.

If the force is slowed from 125 vibrations persecond to the shaft’s natural frequency of 25vibrations per second, the amplitude of vibrationbecomes very large. The amplitude builds up toa point where the driving force is enough toovercome the inertia of the system. When theseconditions exist, the system is said to be inresonance with the driving force, and sound wavesare produced by this vibration.

A common example of resonance is found ina crystal oscillator circuit. When an alternatingvoltage is applied to a crystal that has the samemechanical (resonant) frequency as the appliedvoltage, it vibrates, and only a small applied

voltage is needed to sustain vibration. In turn, thecrystal generates a relatively large voltage at itsresonant frequency.

Q95. What is the effect of excessive reverberationin a large area when a loudspeaker is beingused?

Q96. Describe action that can be taken to lessenor eliminate reverberation in a large area,such as a hangar deck.

Q97. Describe the effect of beat frequency.

Q98. Why is resonance potentially a seriousproblem?

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.

.

CHAPTER 2

INFRARED, LASERS, AND FIBER OPTICS

In this chapter, you will learn about infrared,lasers, cryogenics, and fiber optics. The basicoperations of these systems are also discussed.For information about the safety precautionsyou must follow, look at chapter 9 of thisTRAMAN.

INFRARED

Learning Objective: Identify infraredadvantages and remote sensing types.

Infrared radiation (IR) is important in missileguidance, target detection, fire control, com-munications, and mapping. Like radar, IRequipment was developed and used by the militaryduring World War II. In some military appli-cations, IR has advantages over radar. When usedfor communications, IR is usually less susceptibleto detection and interference than visible light.Also, infrared equipment is usually less complexthan radar equipment used for similar tasks.

Another advantage of infrared equipment isremote sensing, which is the process of detectingor sensing infrared radiation from a target withoutbeing in physical contact with that target. WhileIR detection systems are passive, both active andpassive systems are used for remote sensing.

Active systems send a signal to the target andreceive a return signal. Radar sets are examplesof active systems. Passive systems detect a signalor disturbance starting at the target. The signalmay be either target emission or another source.Photography, using natural light, is an exampleof a passive system. Now, with an idea of someadvantages of using infrared, lets get into someof the basics. To help you understand infrared,lasers, and fiber optics, the electromagneticspectrum and infrared radiation are covered in thenext section of the TRAMAN.

ELECTROMAGNETIC SPECTRUM

Learning Objective: Recognize the charac-teristics of the electromagnetic spectrum toinclude the characteristics of the infraredfrequency range.

The term infrared is a Latin word meaningbeyond the red. Humans only see a small part ofthe entire electromagnetic spectrum. However,other parts of the spectrum contain usefulinformation. The infrared spectrum is a smallportion of the entire electromagnetic spectrum.IR radiation is a form of electromagnetic energy.IR waves have certain characteristics similar tothose of light and RF waves. These characteristicsinclude reflection, refraction, absorption, andspeed of transmission. IR waves differ from light,RF, and other electromagnetic waves only inwavelength and frequency of oscillation.

The IR frequency range is from about 300gigahertz (109 Hz) to 400 tetrahertz (1012 Hz). Itsplace in the electromagnetic spectrum (fig. 2-1)is between visible light and the microwave regionused for high-definition radars. The IR region ofthe electromagnetic spectrum lies betweenwavelengths of 0.72 and 1,000 micrometers(approximately). Discussion of the IR region isusually in terms of wavelength rather thanfrequency.

NOTE: Formerly, the micron (10-6 meter)symbol µ expressed measurements ofwavelength in the electromagneticspectrum. In 1967, the 13th GeneralConference of Weights and Measuresabolished the micron and its symbol. Thisunit is now called the micrometer, symbolµm.

The IR portion of the electromagneticspectrum is frequently divided into three bands.

1. Near infrared (NIR), which extends fromthe visible region out to around 1.5 µm

2-1

Figure 2-1.-Electromagnetic spectrum.

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2. Intermediate infrared (IIR), which extendsfrom 1.5 to 5.6 µm

3. Far infrared (FIR), which extends from5.6 µm to the microwave frequencies

Some confusion exists because the infraredrange of wavelengths is so close to the visible rangein the electromagnetic spectrum. Thus, it is notuncommon to hear references to infrared light.

Infrared radiation is also known as thermalor heat radiation. All materials emit radiation inthe IR region of the electromagnetic spectrum. Inaddition to emitting this radiation, a solid objectsubjected to IR radiation undergoes an increasein temperature, absorbs heat, and then reradiatesit. For example, when an aircraft is parked in thesun on a runway, it gets hotter and hotter. It alsoradiates more and more IR radiation. The aircraftretains heat after the sun sets and continues toradiate that heat. Infrared systems detect thepresence of an aircraft on a runway even after theaircraft is moved. This happens because the areaof the runway that was directly below the aircraftis cooler than the surrounding runway. You cansee how the military might use IR radiation. Heatdiffers from IR waves in much the same way thatelectricity differs from radio waves.

Q1.

Q2.

Q3.

Q4.

Q5.

List some of the advantages of IR overradar.

Define remote sensing.

List the similar characteristics of infraredand light.

What frequencies of the electromagneticspectrum are considered to be in the IRfrequency range?

Name the three IR bands of the electro-magnetic spectrum.

INFRARED RADIATION

Learning Objectives: Identify the advan-tages of IR detection systems. Identify thecharacteristics of emissivity and the effectsof atmospheric attenuation. Identify thetypes of optical devices used in IR systems.

All objects above absolute zero (0 K or–273 °C or –460 °F) emit infrared radiation.Radiation emits from any given object over a wide

2-3

range of wavelengths, but it reaches a peak atone particular wavelength. This wavelength hasmilitary applications. Detection of IR energydepends on the contrast between the IR radiationfrom the source under consideration and IRradiation emitted by the background. A coldobject with a warm background has as good atarget definition as does a warm object with a coldbackground.

There are several advantages in using IR fortarget detection. Some of these are as follows:

IR systems are passive.

Complete jamming is difficult. (AlthoughIR systems are sometimes confused.)

Military targets are usually good sourcesof IR.

IR systems are smaller, lighter, lesscomplex, and less expensive than othercomparable systems.

IR systems have a high target resolution.

EMISSIVITY

One useful concept about IR is the blackbodyconcept. A blackbody is an object that absorbsall radiation incident on it. Conversely, theradiation emitted by a blackbody is the maximumfor any given temperature. Therefore, a black-body is a perfect absorber and radiator of IR atall temperatures and wavelengths.

All matter whose temperature is above–273°C (absolute zero) emits IR radiation, Theamount of the IR radiation emitted is a functionof heat. Theoretically, a perfect emitter is ablackbody with an emissivity of 1. Realistically,the best emissivity is somewhere around .98. Theemissivity of various objects is measured on a scaleof 0 to 1.

The total energy emitted by an object at allwavelengths directly depends on its temperature,If the temperature of a body increases 10 times,the IR radiation emitted by the body increases10,000 times. If you plot the energy and itswavelengths emitted by a blackbody on a graph,

Figure 2-2.-Blackbody radiation.

shill-shaped curve results (fig. 2-2). By lookingat this graph, you can see that the energy emittedby short wavelengths is low. As the wavelengthsget longer, the amount of energy increases up toa peak amount. After reaching the peak, theenergy emitted by the body drops off sharply witha further increase in wavelength.

Emissivity is the ratio of the total radiationemitted by any object at any temperature (T) tothe total radiation emitted by an ideal blackbodyat the same temperature. Emissivity is used tocompare the radiation emitted by an actual

radiator (source) with that of a perfect radiator.The emissivity of any object depends on theamount of energy its surface can absorb. If thesurface absorbs most of the IR striking it, it emitsa relatively high amount of radiation, and theemissivity of the object is comparatively large. Ifthe surface reflects most of the incident radiation,the object has a relatively small emissivity. Bydefinition, a blackbody has an emissivity of unity.Therefore, any other body (surface) has anemissivity of less than 1. Table 2-1 shows theemissivity of various surfaces.

Table 2-1.-Emissivities of Various Surfaces

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The basic laws that describe the characteristicsof IR were first developed for blackbody radiation(the ideal case). Then they were modified todescribe radiation from any source.

Temperature is the most important parameterin determining the IR characteristics of any body.As the temperature of an object changes, twospecific changes in the IR characteristics takeplace:

1. the wavelength where peak radiation occursshifts, and

2. the total energy radiated varies with thefourth power of the temperature.

There are two laws that describe the relation-ship between these IR characteristics.

1. Wein’s displacement law. This law statesthat “‘the wavelength at which maximum radiationoccurs (Am) is inversely proportional to theabsolute temperature of the body.” This law canbe expressed by the formula

Figure 2-3.-The wavelength of the peak radiation from ablackbody in relation to its temperature.

where wavelength is in micrometers, and the con-stant (K) has a value (for a blackbody) of about2,900. For example, a block of ice emits peakenergy at about 10 µm and a jet aircraft engineemits peak energy at about 3.5 µm (fig. 2-3).

2. Stefan-Boltzmann law. This law states that“radiation intensity (E) is directly proportionalto the fourth power of the absolute temperature. ”The law can be expressed by the formula

where E has dimensions of power per unit areas,and (sigma) is the proportionality constant.

Thus, if the temperature of an object isdoubled, radiation from the object will be 16 timesas much.

The Stefan-Boltzmann law can be modifiedto include the emissivity factor, and total radiationcan be computed from the formula

where (epsilon) is the emissivity factor of theradiating surface.

Figure 2-4 shows the distribution of energyradiated from a blackbody at various tempera-tures. A blackbody at a temperature of 300K(81°F) (not shown) radiates 46 milliwatts of powerper square centimeter of its surface. A paintedsurface, such as the skin of a commercial airliner,at the same absolute temperature radiates 41milliwatts per square centimeter. If the aluminumaircraft skin weren’t painted, the emissivity factorwould be considerably smaller, and the radiationwould be less than 4 milliwatts of power persquare centimeter.

Figure 2-4.-IR distribution curves for a blackbody atvarious temperatures.

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IR from a source covers a good part of thespectrum, but the maximum radiation occurs atsome specific wavelength. For example, IR fromjet and rocket engine exhaust plumes is primarilydue to molecular excitation of water vaporand carbon dioxide, which are characteristicby-products of combustion. This molecularradiation peaks at 2.77pm (due to carbon dioxidealone). However, in a practical situation it is easierto get more radiation from the hot tail pipe andother heated surfaces.

ATMOSPHERIC ATTENUATION

In military applications, the IR transmittingmedium is often the atmosphere. The effect ofatmospheric attenuation on transmission is a veryimportant factor in considering the overalleffectiveness of the systems. There are twoprimary causes of atmospheric attenuation:

1. scattering by suspended particles (solids),and

2. absorption by free molecules in theatmosphere.

These two attenuations are additive, but absorp-tion is the more important.

The amount of scattering caused by particlesdepends on the relationship between the wave-length of the radiated energy and the size of theparticles. When the wavelength is considerablyshorter than the dimensions of the particles,scattering is essentially independent of wave-length. Usually this relationship is the case in theIR spectrum. Therefore, attenuation caused byscattering can be measured at one wavelengthand applied over a relatively wide band ofwavelengths. However, this technique does notwork with attenuation caused by molecularabsorption.

The amount of molecular absorption is closelyassociated with wavelength. The two substancesin the atmosphere that absorb the most radiationare water vapor and carbon dioxide. In bothsubstances, there are several wavelength bands inwhich absorption is relatively high. Molecularresonance causes this condition. (Each moleculehas a natural frequency of vibration, or resonantfrequency.) The resonant frequencies of thesemolecules are in the infrared region. Theirstructure is such that this natural vibration createsan oscillation of the electric charge in themolecules, increasing the absorption. At low

Table 2-2.-Wavelength Limits of IR Transmission Windowsin the Atmosphere

altitudes, this absorption is so great in somewavelength bands that the percentage of radiationtransmitted drops rapidly to zero. This is due todenser atmosphere at low altitudes. Between theseabsorption bands are transmission bands in whichthe atmospheric attenuation is not as great. Thesetransmission bands, known as windows, containwavelengths as shown in table 2-2.

The atmosphere is not a very good transmitterof infrared radiation because of the absorptionproperties of C02, H2O, and O3. Figure 2-5shows the transmission spectrum characteristicsof the atmosphere. You can see that the besttransmission is between 3 µm and 5 µm andbetween 8 µm and 14 µm. The range between thesefrequencies is a window, Infrared imaging devicesoperate in one of the two windows, usually the8 µm and 14 µm. The absorption bands are muchnarrower at high altitudes because of the thinneratmosphere. Therefore, the absorption bands areof lesser consideration in the design of high-altitude IR systems.

Figure 2-5.-Transmission spectrum of the atmosphere.

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OPTICAL DEVICES

Optical devices are used in front-end optics togather and focus the infrared radiation upon thedetector. They can be used because of thesimilarity between infrared and visible light.Figure 2-6 shows a simple optical system forgathering and focusing IR radiation. The entiresystem lies within a protective housing to protectthe detector and the optical system from theweather. The dome is a continuation of theprotective housing and must be able to pass IRradiation easily.

Many of the materials commonly used invisible light optics can’t be used in IR imagingsystems because these materials are opaque at IRfrequencies. The optical materials used in IRimaging systems should have most of thefollowing qualities:

Be transparent at the wavelengths on whichthe system is operating.

Be opaque to other wavelengths.

Have a zero coefficient of thermalexpansion to prevent deformation andstress problems in optical components(parts).

Have high surface hardness to preventscratching the optical surfaces.

Figure 2-6.-Simple IR optical arrangement.

Have high mechanical strength to allow theuse of thin lenses (high-ratio diameter tothickness).

Have low volubility with water to pre-vent damage to optical components byatmospheric moisture.

Be compatible with antireflection coatingsto prevent separation of the coating fromthe optical component.

Although none of the materials now used forIR optics have all of these qualities, silicon,germanium, zinc selenide, zinc sulfide, andIRTRAN have many of them. The actual materialused for IR optics depends on the material’s bestcharacteristics and their application.

Typical materials for making domes includeglass, quartz, synthetic sapphires, germanium,and silicon. The transmission coefficient of theoptical material is an important factor in thedesign of IR equipment. Glass and quartz aresatisfactory material for NIR, and generally forIIR, Figure 2-7 shows that glass, quartz, andsynthetic sapphires have excellent transmissioncharacteristics in the visible and near infraredregions. They cut off sharply in the intermediateinfrared region. Optical glass is completely opaqueto wavelengths longer than 3 µm, quartz cuts offat 4 µm, and synthetic sapphire loses its

Figure 2-7.-Wavelength versus transmission coefficient.

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transparency at wavelengths greater than 6 pm.Germanium and silicon are semiconductormaterials that are opaque to visible light andtransparent to IR throughout most of the near andintermediate infrared regions.

FIR requires a completely different type ofoptics. Single crystals of silver chloride, rolled flat,are satisfactory windows for the transmission ofFIR. Single crystals of sodium chloride (rock salt),cut and ground into a lens or window, is excellentfor FIR. However, rock salt is highly soluble inwater; therefore, it must be protected fromatmospheric moisture. This characteristic makesrock salt impractical for use as an IR domematerial.

There are some problems involved in designingIR optical systems. The material used must matchthe wavelength to which the detector will respond.Optical materials are physically weak, and manydamage easily by high temperature and thermalshock. Pressure and chemical reactions willchange the properties of some optical materials.

Heat is another problem. When any part ofthe IR optical system becomes heated by theenergy it absorbs, the energy reradiates atwavelengths other than those of the originalradiation. If the detector is sensitive to these newwavelengths, this closer source will obscure thetarget or cause ghost images.

Surface reflections and attenuation by thematerial cause attenuation in optical materials.Surface reflections may be overcome by anti-reflection coatings. Attenuation by the materialis the more serious problem.

IR systems often have a chopping reticle(chopper) in the principal focal plane. Thechopper generally is a rotating disc with some clearand some opaque areas. Although a chopper isnot absolutely necessary in a search system, it hasseveral useful properties. The chopping ratefurnishes a conveniently high carrier frequencyfor the electronic amplifiers, and the reticlepattern can operate as a discriminator or filter.Manufacturers can design this filter for thetypes of background expected to provide betterdifferentiation between target and background.

Optical filters in IR instruments isolatecertain wavelength regions of interest, such asatmospheric windows, and screen out undesiredwavelengths. There are three general types offilters:

1. Those that pass short waves.2. Those that pass a particular band of waves.3. Those that pass long waves.

Q6. List the advantages in using IR for targetdetection.

Q7. What is the blackbody concept?

Q8. Of all the parameters in determining IRcharacteristics, which one is the mostimportant, and why?

Q9. What is the primary factor that affects theIR transmitting medium and its primarycause?

Q10. Absorption is the major cause ofattenuation in IR system design. Whathappens at higher altitudes?

Q11. List the problems involved when designingIR optical systems.

Q12. Optical filters isolate certain wavelengthsand screen out undesired wavelengths.What are the three general types of filters?

DETECTORS

Learning Objective: Identify the charac-teristics of detectors to include thermaldetectors.

The most critical component of any IR systemis the detector (or sensor), which detects andconverts IR into an electrical signal. Thecharacteristics of the atmosphere and of the source(if it is a military target) cannot change. Opticalmaterials are somewhat standard, as are displaydevices and control circuits. Research anddevelopment have resulted in some very goodall-around detectors, but selecting the properdetector for a particular application must be donecarefully. Many variables confront the selectionprocess. These variables and the characteristicsof the radiation involved determine the selectionof the detector.

DETECTOR CHARACTERISTICS

The detector is the most important componentof the IR imaging system. There are many typesof detectors, each having a distinct set ofoperating characteristics. Bolometers, Golay cells,mercury-doped germanium, lead sulfide, andphototubes are the most commonly used types ofdetectors. Two ways to characterize detectors is

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by their optical configuration or by the energy-matter interaction process. Two classes ofdetectors include the photoelectric and thermal.There are two types of optical configurations—elemental and imaging.

1. Elemental detectors. Elemental detectorsaverage the portion of the image of the outsidescene falling on the detector into a single signal.To detect the existence of a signal in the field ofview, the detector builds up the picture bysequentially scanning the scene. The elementaldetector requires time to develop the imagebecause the entire scene requires scanning.

2. Imaging detectors. Imaging detectors yieldthe image directly. An imaging detector is like amyriad of point detectors. Each of the detectorsrespond to a discrete point on the image.Therefore, the imaging detector produces theentire image instantaneously. A good example ofan imaging detector is photographic film.

To compare the relative merits of differentdetectors in different situations, you must knowseveral parameters of detector operation. Theseparameters make it possible to discuss thecharacteristics of a particular detector in termsapplicable to any detector.

Responsivity

When IR strikes either the photoelectric orthermal detector, a change takes place in thedetector material, causing an electrical outputsignal. The responsivity (R) of the detector is theamount of output signal that each unit of inputradiation intensity produces. Responsivity isexpressed by the following ratio:

where R is generally given in volts per watt.Many factors influence responsivity such as

detector and source temperatures, detector area,detector time constant, and spectral distributionof the radiation.

Spectral Response

One important influence on the responsivityof a detector is the change in detector sensitivitywith the change in the wavelength of receivedradiation. The spectral limit of responsivity is thewavelength, where the value of responsivity is half

that of its maximum value. Spectral response isa nonlinear characteristic. Therefore, you mustknow its value for each wavelength considered.Any discussion of values must include details ofthe conditions involved.

Time Constant

In any IR scanning system, the time constantof the detector must be such that the detector canfully respond before the radiation intensitychanges. The time constant is the time requiredfor the detector to develop 63 percent of itsmaximum output signal. The maximum scanningrate depends on this time constant.

Noise Equivalent Power (NEP)

Noise exists in any circuit that carries current.Most outside noises can be reduced or eliminatedby shielding and proper design. However, thermalnoise is an ever-present problem.

Power supplies used with IR detectors requireextremely good filtering. Since the IR radiationreceived by the detector is very small, noise of anyappreciable amount could be enough to generateweak IR signals or cause false targets. IR systemsgenerate many different types of noise. The mostimportant of these are—

current noise, caused by bias currentswithin the detector, and

Johnson (thermal) noise, caused bythermal fluctuations in the detectormaterial.

At low bias voltages, current noise isnegligible, and the output noise consists almostentirely of Johnson noise. The current noiseincreases linearly with bias voltage and mayeventually become the primary source of noise.

NOTE: In modern IR systems, cryogeniccooling of the detector reduces much of theJohnson noise.

Another useful and important detectorparameter is the noise equivalent power (NEP) ofa detector. NEP is the radiation power (in watts)that must strike a detector to produce a signalresponse equal to the noise output over a referencebandwidth. Thus, a signal-to-noise ratio is equalto 1.

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When comparing two different IR detectors,the one with the lower NEP has the higher usefulsensitivity. Since this use of NEP may beconfusing, another parameter, defectivity may beeasier to use. Detectivity is simply the reciprocalof the given NEP of a detector. Thus, the higherdefectivity a cell has, the higher its useful output.For example, a detector with an NEP of4.0 x 10-9 has a defectivity of

The best IR detector would have the greatestpossible spectral response within the frequencyband of interest, and the lowest possible NEP (orhighest possible defectivity). A properly chosendetector might have a maximum range of 90 miles,with a signal-to-noise ratio of 5, from a 1-square-meter target at 300K. This range is equivalent toan ability to detect IR emitted by a cubic inch ofice at 3 miles.

Energy-Matter Interaction

There are two basic types of energy-matterinteraction. They are the photon effect(photoelectric effect) and the thermal effect.

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PHOTON EFFECT.— In the photon effectenergy-matter interaction, the photons of theradiant energy interact directly with the electronsin the detector material. Usually, detectors usingthe photon effect use semiconductor material.There are three specific types of photon effectdetection.

The three major types of photodetectors arethe photoconductive, photovoltaic, and photo-emissive types. The signal-to-noise ratio of eachof these detectors is the limiting factor indetermining its effectiveness.

1. Photoconductive. Photoconductivity is themost widely used photon effect. It is also knownas the internal photoelectric effect. (See fig. 2-8.)Radiant energy changes the electrical conductivityof the detector material. An electrical circuitmeasures the change in the conductivity.

The photoconductor contains a semiconductorcrystal that absorbs the photon energy from theradiation, which strikes the surface of thecrystal. This changes the crystal’s resistance orconductivity. Several different materials are usedfor this type of detector, including lead sulfide,lead telluride, lead selenide, and cadmium sulfide.Gold-doped germanium is a good detectormaterial. However, there are some difficultiessuch as long time constants.

2. Photovoltaic effect. In the photovoltaiceffect (fig. 2-9), the radiant signal causes apotential difference across a PN junction. The

Figure 2-8.-Photoconductive detector circuit and graphicsymbols.

Figure 2-9.-Photovoltaic effect and graphic symbol.

photocurrent (current generated by light) adds tothe dark current (current that flows with noradiant input). The total current is proportionalto the amount of light that falls on the detector.

The photovoltaic effect uses a photovoltaic cellsimilar to a solar cell. This is a semiconductor witha high-resistance, photosensitive barrier betweentwo layers. When exposed to IR, a potentialdifference builds up across the two layers of thecell.

3. Photoemissive. The photoemissive effect(fig. 2-10) is also the external photoelectric effect.The action of the radiation causes the emissionof an electron from the surface of the photo-cathode in the surrounding space.

Figure 2-10.-Photoemissive effect and graphic symbol.

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The photoemissive cell’s cathode is exposedto IR and causes electronic emission. The numberof emitted electrons depends on the intensity ofthe IR striking the cathode.

THERMAL EFFECT. —The thermal effecttype of energy-matter interaction involves theabsorption of radiant energy in the detector. Thisresults in a temperature increase in the detectorelement. You detect the radiation by monitoringthe temperature increase in the detector. Both theelemental and imaging forms of detectors use thethermal effect.

THERMAL DETECTORS

Thermal detection is the sensing of the changein temperature of the detector material as a resultof IR striking its surface. There are three differenttypes of sensing elements employed in modernthermal detectors.

1. The thermopile, a series combination ofseveral thermocouples

2. The bolometer, which senses changes inresistance of the detector material

3. The pneumatic cell, which uses theexpansion of a gas as an indicator

Thermocouple

One of the basic heat detectors is thethermocouple. When applying heat to the junctionof two dissimilar metals such as iron and copper,a measurable voltage is generated between them.Figure 2-11 shows a basic thermocouple.

The voltage difference across the thermo-couple is small. However, you can increase thesensitivity to a point where the thermocouple

becomes useful as an IR detector. You can obtainan increase in sensitivity by connecting or stackingseveral thermocouples in series, forming athermopile. The complete thermopile action is likeconnecting several flashlight cells in series; theoutput of each thermocouple adds to the outputof the others. For example, 10 thermocouples,with individual outputs of 0.001 volt, have a totaloutput of 0.01 volt when connected in series.

The effective sensitivity increases further bymounting a thermopile at the focal point of aparabolic reflector. When using this method, thereflector focuses the IR from the target onto thethermopile.

Bolometer

A bolometer is a very sensitive device whoseresistance will vary, depending on the IRexposure. There are two main classes ofbolometers—the barretter and the thermistor.

A barretter is a variable resistor made of ashort length of very fine wire (usually platinum)that has a positive temperature coefficient ofresistance. (A substance has a positive temperaturecoefficient if its resistance increases with an

Figure 2-11.-Thermocouple.

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Figure 2-12.-Various thermistors.

Figure 2-13.-Comparison of thermistor and barrettersensitivity.

increase in temperature. It has a negativecoefficient if its resistance decreases with anincrease in temperature.)

A thermistor is a variable resistor made ofsemiconductor material, such as an oxide ofmanganese, nickel, cobalt, selenium, or copper.The thermistor has a negative temperaturecoefficient of resistance. A thermistor is usuallyin the form of a bead, disc, rod, or flake, as shownin figure 2-12. The mixing of various proportionsof the heat-sensitive materials provide specificcharacteristics of resistance versus temperaturenecessary for target detection.

Figure 2-13 shows changes in resistance that atypical thermistor can produce compared to thosein a barretter. Note the thermistor has the steepertemperature coefficient of resistance curve. There-fore, it is the more sensitive of the two sensors.

One simple type of infrared detector consistsof two thin strips of platinum that form two armsof a Wheatstone bridge. To increase the thermal

Figure 2-14.-Infrared detecting device.

sensitivity of the strips, one strip is black on oneside. The blackened surface absorbs the IR. Asthe strip absorbs heat, its resistance changes andunbalances the bridge. The imbalance causes achange in current produced by an external voltageapplied to the input terminals of the bridge.

The infrared detecting device (fig. 2-14) is likethe one discussed in the previous paragraph. Itconsists of four nickel strips supported bymounting bars that have electrical leads attachedto them. A silvered parabolic reflector (mirror)focuses the IR on the nickel strips. The changeof resistance in the strips causes an unbalancedcondition in the bridge circuit, producing anoutput signal.

Pneumatic Cell

Another unique infrared detector is the Golaydetector (pneumatic cell), shown in figure 2-15.

Figure 2-15.-Golay detector.

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This detector is actually a miniature heat engine.IR energy entering the window causes expansionof a volume of gas located between the reflectingdiaphragm and the window. The lamp at the afterend of the detector emits a light beam. The lensfocuses the beam that passes through the grid andonto the reflecting diaphragm.

Changes in the amount of infrared energyentering the window cause changes in the shapeof the diaphragm. This causes its light-reflectiveproperties to vary accordingly, modulating itslight output. The light reflected from thediaphragm passes back through the grid, whichintensifies the variations of the reflected light.After passing through the grid, some of the light(reflected by the diaphragm) strikes the mirror.This light reflects to a photocell of high sensitivity(not shown in the figure). The modulated outputof the photocell is a voltage proportional to theintensity of the IR entering the window.

The Golay detector has the most rapidresponse of any infrared detector, but it canoperate only when intermittently receiving radiantheat. An optical chopper can interrupt the flowof IR to the cell periodically. Another advantageof the Golay detector is its extremely widebandwidth, making it a good choice for use in IRspectrum analysis.

Q13.

Q14.

Q15.

Q16.

Q17.

Q18.

Q19.

Q20.

What is the most critical component of anyIR system?

List the most common types of detectors.

Define responsivity as it relates to thedetector.

What are two of the most important typesof noise generated by an IR system?

Name the two basic types of energy-matterinteraction.

What are the three major types of photo-detectors?

Three different types of sensing elementsare used in modern thermal detectors. Whatare they?

The Golay detector has the most rapidresponse of any infrared detector, but itrequires an optical chopper. Why does itneed the optical chopper?

APPLICATIONS

Learning Objective: Identfy military appli-cations to include homing techniques,imaging system component operation, andconfigurations.

The number of military and industrial appli-cations of IR has grown in recent years. Acomplete discussion of all applications is beyondthe scope of this manual, but some IR systemsand concepts applicable to military situations arediscussed in the following paragraphs.

During World War II, infrared found its firstmilitary use in a snooperscope device. This deviceworked in total darkness, and outlined enemytroops by the heat radiated from their bodies. Arifle with a sniperscope made it possible to see atarget in total darkness and to fire with normalaccuracy at a target.

Since IR is invisible but behaves much likevisible light (that is, it can be reflected andcontrolled in a beam pattern), it served as a meansof communication for specific wartime purposes.Development of equipment to receive the invisiblelight was the base for design and successful useof some important weapons. Infrared used forshort-range communication between sea-levelstations, such as ships, affords excellent security.Line-of-sight limitations of IR rays and their rapidattenuation at sea level provides security for short-range communications. Military use of infraredfor communications requires a powerful sourceand a sensitive receiver for detecting themodulated source. Such sources and receivers areavailable for near infrared energy.

Photography uses infrared because it iseffective against camouflaged targets. Nightphotography, using infrared, can produce a bettervisual presentation of terrain than the bestmapping radar.

Navigation also uses infrared. Ground speedindicators are available that can compete withDoppler radar. Anticollision circuits using IR areundergoing experiments.

Image-forming devices, thermal or shipdetection devices, and infrared radar are alsousing IR. The portable infrared detector (PID) isa passive far infrared (FIR) equipment fordetecting personnel, vehicles, tanks, small boats,and ships. It detects the difference in temperaturebetween a body and its immediate backgroundand provides an audible signal output. A largerFIR system for ship detection is the stabilized shipdetector (SSD). This system provides a permanent

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record of the true bearing of all targets detectedwithin the angle scanned. Infrared radar uses apulsed IR source and receives reflected IR energyas in microwave radar.

Infrared has excellent application to guidedmissiles. Military targets, such as ships, factories,and aircraft, are normally warmer than theirsurroundings. Detection of these targets is fromthe heat they radiate. Heat radiated at lowertemperatures is particularly important in passivedetection of surface targets. There is noeconomical way for the enemy to camouflageself-radiated heat.

The Felix bomb was the first guided missileto use IR. Its automatic guidance system was aninfrared homing device in the nose of the bomb.The Felix bomb was reliable and adequate foroperational use. World War II ended before itcould be used under combat conditions. However,this bomb opened the way to a new and differentmethod of guidance, infrared homing.

A homing guidance system controls the flightpath of a missile by a device in the missile thatreacts to some distinguishing feature of the target.Homing guidance systems are the most accurateof all guidance systems. There are three types ofhoming systems; they are subdivided by the sourceof target radiation.

1.

2.

3.

Active homing—Both the source thatilluminates the target and the receiver thatdetects the echoes are within the missile.Semiactive homing—The target illumina-tion is from some source outside themissile, and the missile receiver uses thetarget reflections.Passive homing—The missile receiverdetects the natural radiation of the target.

Active and semiactive types of homing systemstypically use radar or lasers. Passive types useheat, light, or in some cases, a radio or radarsignal for homing.

The Sidewinder is probably the most simpleand economical guided missile. It contains aninfrared homing system and can destroy high-performance aircraft flying at any altitude fromsea level to about 50,000 feet.

While it is unlikely that IR will ever entirelyreplace radar, IR has certain advantages overradar. You can expect that radar and IR will beused together in fire control, guidance, and searchapplications.

INFRARED IMAGING SYSTEMS

An infrared imaging system consists ofdetectors, a scene disection system, front-endoptics, a refrigeration system (if required), andan image processing system.

Detectors

You have learned about imaging detectors.Now, you will learn how imaging detectors areused in IR imaging systems. Detectors convert theIR radiation signal into an electrical signal forprocessing into information used by an operator.Detectors have many different configurations fortheir use in IR imaging systems.

DETECTOR ARRAY.— The detector (ele-ment) needs only a small portion of the imagescene to achieve maximum resolution. You canform an array by grouping several detectorelements (fig. 2-16, view A). This array has closelypacked elements in a regular pattern. Thus, theimage of the scene spreads across the array likea picture or a mosaic with no scanning. Eachdetector element views a small portion of the totalscene. The disadvantage of this type of system isthat each detector element requires a supporting

Figure 2-16.-Detector arrays.

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electronic circuit to process the information thatit provides. Also, each detector element requiresa preamplifier to boost the signal to a useful level.

SINGLE DETECTOR.— Another methodthat provides the operator with information is thesingle scanning detector (fig. 2-16, view B). Here,there is one detector requiring one set ofsupporting circuitry. In this type of system, thescanning of the image is across the detector so thatthe detector can see the whole image. An opticalsystem supplies the scanning. This type of systemis adequate if real-time information is notimportant, or if the object of interest is stationaryor not moving quickly.

Scene Disection System

The scene disection system scans the sceneimage. There are many types of scanning—oneassociated with each type of detector array. Asingle detector with one fast scan axis and oneslow scan can scan the scene rapidly in the

horizontal direction and slowly in the verticaldirection.

A vertical linear array is scanned rapidly inthe horizontal direction. One detector elementscans one line of the image. In the linear array,there is a space one element wide between eachelement. The scan is one axis with an interlace.After each horizontal scan, the mechanism shiftsthe image upward or downward one detectorelement width. This allows the next scan to coverany of the missed lines.

Each system has an optimum configurationof detector array and image disection. If thenumber of elements in the detector array areincreased, the system becomes more complicated.The cost of the system increases, and the reliabilityof the system decreases. If you decrease thenumber of detectors, you reduce the amount ofinformation that you can process. A compromisebetween increasing the number of elements(increased cost) and decreasing the number ofelements (reduced information) is to use a lineararray scanned in one direction only. Each detector

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scans one line of the scene image. This reducesthe complexity of the electronics and increases theamount of information you can process. Thus,the viewing size of the scene and the detail of thescene increase.

There are many types of mechanisms you canuse to scan the scene. When scanning using twoaxes, you must synchronize the two scanningmotions. The electronic signal that controls thesampling of the detectors must also synchronizewith the scanning motions.

Front End Optics

The front end optics collect the incomingradiant energy and focus the image at the detec-tors. The optics may be reflective or refractive,or a combination of both. Many systems offer azoom capability, allowing a continuous changein amplification of the image without changingthe focus. Spectral filters restrict the wavelengthof light entering the system. This preventsunwanted wavelengths of light from reaching thedetector and interfering with the imaging process.

Refrigeration System

Many types of infrared detectors require lowtemperatures to operate properly. A refrigerationsystem in imaging systems provide the necessaryoperating temperatures. The two types of detectorcooling are the open cycle and closed cycle types.

The open cycle type of cooling provides areservoir of liquified cryogenic gas. The liquidtravels to the detector, where it reverts to a gas.As it changes from a liquid to a gas, it absorbs

a lot of heat from the surrounding area and thedetector.

The closed cycle type of cooling compressesthe gas, and the heat generated by the compressionis radiated away by the use of a heat exchanger.The gas then returns to the compressor, and thecycle repeats itself.

Image Processing Systems

The image processing system converts the datacollected by the detectors into a video display.Multiplexing of the data from the detectors allowshandling by one set of electronics. Then furtherprocessing ensures the information coming fromthe detectors is in the correct order of serialtransference to the video display. At this point,the addition of any other display informationtakes place.

Other image processing systems amplify the sig-nals from the detectors and send them to an LEDdisplay. Others optically amplify by photomuhi-plier tubes and project on a phosphorescent screen.

INFRARED IMAGING SYSTEMCONFIGURATIONS

Presently, the Navy uses several IR imagingsystem configurations. They are the direct viewparallel scan linear system, the serial scan parallelvideo two-dimensional array system, and the serialscan standard video system.

Direct View Parallel Scan Linear System

The direct view parallel scan linear system (fig.2-17) is the simplest type of infrared imaging

Figure 2-17.-Direct view parallel scan linear system.

2-17

system. The scene image enters the system through Serial Scan Parallel Videothe infrared lens. Then, it strikes a double-sided Two-Dimensional Array Systemscan mirror. The image scans across a lineardetector array. Preamplifiers amplify the signals Figure 2-18, view A, shows a serial scanfrom the detectors. Then, the signals are sent to parallel video two-dimensional array system. Athe LED drivers, which lie in a linear array. Light two-dimensional array of detectors is coupled onefrom the LED array scans across the field of view for one to a similar array of LED. The scan mirrorof an ordinary eyepiece directly from the second operates in two dimensions. This system offersside of the scan mirror, or it is viewed on a the same options of direct viewing or CRT viewingcathode-ray tube (CRT). as found in the one-dimensional array.

Figure 2-18.-Serial scan video systems.

2-18

Serial Scan Standard Video System

Figure 2-18, view B, shows a serial scanstandard video system. Scanning of the incomingimage is done in two dimensions by a scan mirrorand an interlace mirror. The interlace mirror shiftsthe image one detector element width. This isusing a linear detector array. Preamplifiersamplify the information from each detector.Then, it is sent to the delay circuitry for changinginto serial form. This circuitry samples eachdetector at the appropriate time for correct lengthof time, resulting in a serial output to the videoprocessor.

ELEMENTS OF A SCANNINGINFRARED IMAGING SYSTEM

Refer to figure 2-19 while you read about theelements of a scanning infrared imaging system.

The observer views the system output andinterprets the information while operating thecontrols. The system control interfaces betweenthe operator and system, allowing the operatorto control the system.

The stabilization and pointing gimbals providea stabilized platform from which the imagingsystem operates. It isolates the system fromvibration and sudden motions of the aircraft.Also, it provides a pointing capability for theimaging system.

The collecting optics and filters collect thelight (thermal radiation) originating from thetarget. Special filters or optical components thattransmit only the desired wavelengths filter anyunwanted wavelengths of radiation. The opticalcomponents focus the scene image on the detectorarray.

The optomechanical scanner scans the sceneimage across the detector array in a process calledscene disection. The optomechanical scannerincludes a mirror(s) or prism(s) with the mechani-cal drive controlled by a scan synchronizer.

The scan encoders convert mechanicalinformation about the motion of the scanner toelectronic signals. These encoders synchronize thescanner motion with the image generation of thevideo monitor. This information then goes to thescan synchronizer.

The scan synchronizer controls the motion ofthe scanner. It interacts with the video process tosynchronize the scanner with the display imagegeneration.

The detector assembly contains the detectorarray that converts the optical signal from thetarget to an electrical signal. The detector coolerprovides cooling for the detector assembly, ifrequired. The detector bias and preamplifiercircuits supply voltage or current for operatingthe detectors. They scan the detectors at theappropriate times, and they amplify the signal

Figure 2-19.-Forward looking infrared (FLIR) set

2-19

block diagram.

from the detectors before further processing. Theyalso convert the output of the detectors into aserial form.

The video processor converts the detectorinformation into the format necessary for thevideo monitor. It adds any additional informationfor the observer, if needed. The video monitor,usually a CRT, provides information to theoperator.

The built-in test (BIT) locates and reports thenature of failures in the system.

Q21.

Q22.

Q23.

Q24.

Q25.

Q26.

There are many uses for infrared, includingshort-range communication, navigation,and anticollision circuit experimentation.Why is infrared used in photography?

Name the three types of homing systemsclassified by their source of radiation.

List some of the components of a typicalinfrared imaging system.

What is the purpose of front end optics?

Why do some infrared imaging systemsneed refrigeration systems?

N a m e s o m e o f t h e e l e m e n t s a n dcomponents of a scanning infrared imagingsystem.

INTRODUCTION TO CRYOGENICS

Learning Objective: Identify cryogeniccharacteristics.

Cryogenics is the science that involves thestudy of very low temperatures. The wordcryogenic comes from the Greek root cryo orkyros, which means icy cold or relating to thecold .

Cryogenic temperatures extend from – 150°Cdownward to –273°C (absolute zero). Under suchextreme temperatures, many metals become brittleand shatter, atmospheric gases turn into liquids,electrical resistance disappears in some materials,and current flows indefinitely without loss (superconductivity).

Heat is a form of energy, and cold is theabsence of heat. When a system cools, heat flowsout of the system. Therefore, you might say coldis physical manifestation of a lack of energy. Thetemperatures of a system are an internal feature

of the system; therefore, cold can relate to a lowinternal energy of a system.

Many modern systems require cryogenictemperatures to operate properly, imaging systemsbeing one of these. The detectors of the imagingsystem require cooling for maximum efficiency.Therefore, you need some sort of refrigerationsystem to provide these low temperatures. If youare to understand the operating principles of arefrigeration system, you must understandthermodynamics. Before you begin the followingsection, refer to figure 2-20. This figure illustratesa numerical scale that you can use to measuredegrees of hot and cold.

When bodies at different temperatures meetin thermal contact, heat flows from the body atthe higher temperature to the body at the lowertemperature. The flow of heat stops when the twobodies are at the same temperature (thermalequilibrium).

IDEAL GAS LAW

Nearly all thermodynamic systems have aworking fluid of some type. To explain the idealgas law, we use a theoretical fluid (gas, dependingupon temperature), and this fluid is the ideal gas.The assumptions about the nature of this idealgas are as follows:

The molecules that make up ideal gas arevery hard, small spheres whose volume youmay disregard when comparedvolume of the gas as a whole.

Figure 2-20.-Absolute temperature scale.

to the

2-20

The molecules do not interact with each PHASE CHANGESother, only with the walls of the container;they do so by elastic collision (a moleculeleaves the wall at the same speed it wastraveling before the collision).

Real gas behaves like ideal gas, especially atlow pressures. However, real gas differs fromideal gas in the following ways. The molecules ofa real gas are large enough that their volume doesmatter when calculating gas volumes, and themolecules do collide with each other.

Matter exists in three states: gas, liquid, andsolid. For matter to change from a solid to a liquidor from a liquid to a gas, it must absorb a largeamount of energy. The reverse is also true. Fusionis the process by which a solid changes to a liquid.Vaporization is the process by which a liquidchanges to a gas. This process is a good vehiclefor heat transfer. It is the basic theory behindrefrigeration.

LAWS OF THERMODYNAMICSENERGY

Energy is the driving force of the universe.You can make the following assumptions aboutenergy:

Energy is the fuel required to make thingshappen.

No system can operate without a transferof energy.

Heat is a form of energy.

A system has an internal energy (whichincludes all potential and kinetic energiesof the system or molecules of a gas).

A closed system conserves energy,although it may change energy states(potential to kinetic).

ENERGY AND THE IDEAL GAS

In the ideal gas, energy is in the form of kineticenergy of the molecules. When the internal energyof the gas increases, the molecules move faster;therefore, they have a higher kinetic energy. Ifthe mass of the molecules is low, the moleculesmove faster. Therefore, the higher the tempera-ture of the ideal gas, the higher its internal energyand the faster the molecules move.

Molecular motion (movement of moleculeswithin a mass) also produces the phenomenonof pressure. As the molecules move about acontainer, they collide with the walls, exerting aforce on the walls. The hotter the gas, the fasterthe molecules collide with the walls; thus, thehigher the pressure.

The four laws contained in this section dealwith thermodynamics, They are basic to thetheory of refrigeration and cryogenic systems.

1. The Zeorth law of thermodynamics statesthat “when two systems of the same temperatureare in thermal contact, no heat will flow.”

Heat will flow between two systems when onesystem is at a higher temperature than the other.In this case, heat will flow away from the highertemperature.

There are three types of heat flow: convection,conduction, and radiation (fig. 2-21). Convectionis the transfer of heat through macroscopicmovement of material. (Macroscopic meaninglarge or visible as opposed to microscopic [smallor invisible].) Conduction is the transfer of heatthrough materials when there is no macroscopicmotion, as in the heat flow in metals. The rate

Figure 2-21.-Heat flow, conduction, convection, andradiation.

2-21

of heat flow depends upon the following physicalsituations:

a. The higher the temperature gradient,the greater the rate of heat flow (the temperaturegradient is equal to the difference in temperaturesdivided by the distance over which the heat mustflow).

b. The larger the area across which theheat is flowing, the higher the rate of heat flow.

c. The shorter the distance the heat mustflow, the higher the rate of heat flow.

Radiation is the transfer of energy by electro-magnetic radiation. All bodies that have atemperature greater than 0 K give off electro-magnetic radiation. The higher the temperature,the greater the amount of radiation emitted.

2. The first law of thermodynamics states that“the change in the internal energy of a system isequal to the heat introduced into the system minusthe energy expended by the system when it doeswork on the environ merit.”

3. The second law of thermodynamics statesthat “a cyclic process must transfer heat from ahot reservoir if it is to convert heat into energy.”Also, work must be done to transfer heat from

4. The third law of thermodynamics statesthat “it is not possible by any procedure, nomatter how idealized, to reduce the temperatureof any system to absolute zero in a finite numberof steps.”

Absolute zero is a limit that you can onlyapproach and never achieve. The lowest tempera-ture that has ever been attained is .00002 K. Thecloser that a system gets to 0 K, the harder it isto get heat from the system.

PRINCIPLES OF REFRIGERATION

Refer to figure 2-22 during the followingdiscussion. The working fluid used in the systemis (Freon). The compressor (A) deliversgas at high temperature and pressure to the coils(B). Water or air cooling removes the heat fromthe gas in (B), resulting in condensation of thegas into a liquid. The liquid flows by forcethrough a small orifice (C) and expands as it leavesthe orifice. It leaves the valve as a mixture ofliquid and vapor at a lower temperature. Themixture of liquid and vapor now enters the coil(D), and heat from the surrounding area suppliedto the working fluid converts the remaining liquidto a gas. The gas enters the compressor, and the

a cold reservoir to a hot reservoir. cycle-repeats.

2-22

Q27.

Q28.

Q29.

Q30.

Q31.

Figure 2-22.-Common refrigeration cycle.

Define cyrogenics and identify its tempera-ture range.

What happens when bodies of differenttemperatures meet in thermal contact?

Energy is the driving force of the universe.What assumptions can you make aboutenergy?

Name the three types of heat flow.

How does heat flow through radiation?

LASERS

Learning Objectives: Identify the principlesof optics and lasers to include terms,theory, and the partical theory of light.Recognize the purpose of Q-switching andidentify solid-state laser types.

A laser is a device that produces or amplifiesultraviolet, visible, or infrared radiation. This isdone by a process of controlled stimulatedemission. The word laser is an acronym for lightamplification by stimulated emission of radiation.The first lasers were used for surveying becausethey accurately measured distance. Later, laserswere used by the military. The initial militaryapplication of the laser was for fire control. Todirect gunfire, the range to and the direction ofthe target must be determined. This is done bythe laser system. Then, the data gathered by the

laser system is used to direct the weapon system.Currently, the technology exists for laserdesignation of the target for laser-guidedmunitions. Military laser systems have both arange-finding capability for conventionalmunitions and a designation for laser-guidedmunitions.

TERMS

There are several terms that you may finduseful when dealing with lasers. These are watts,irradiance, joules, and radiant exposure.

Watts. A watt is a unit of power associatedwith light energy.

Irradiance. Irradiance is the amount of powerper unit area, watt/cm2. Energy cannot be createdor destroyed. In a vacuum, the amount of energythat is available at the output of the laser is thesame amount of energy contained within the beamat some point downrange. However, since lasersare not normally used in a vacuum, some energyis lost downrange. Figure 2-23 shows a typicallaser beam. The amount of energy available within

Figure 2-23.-Irradiance.

2-23

the sampling area is considerably less than theamount of energy available in the beam. Forexample, a 0.1-watt laser output might have 0.04watt measured within a 1-square-centimeter (cm2)sampling area. In this example, the irradiance is0.04 watt/cm2.

Joule. A joule is a unit of energy. It is thenumber of watts being delivered during a shortperiod of time (1 watt per second).

NOTE: The output of a continuous-wave(CW) laser is normally given in watts whilethe output of a pulsed laser is normallygiven in joules.

Radiant exposure. Radiant exposure is theamount of energy per unit area, J/cm2 .

PRINCIPALS OF OPTICS AND LASERS

NOTE: Before reading this section, youshould review the information on lightfound in chapter 1.

The theory of lasers was published around1956. Along with the theory, a study wasreviewed. In the study, methods of extending therange of lasers were looked at using various solidsand gases as the method of range extension. Itwas from this study that laser theory evolved. Thefirst laser was built in 1960 by Hughes ResearchLaboratories.

A simplified solid-state laser currently used bythe military is shown in figure 2-24. The elementsof the laser are the material, pump source, optical

Figure 2-24.-Typical solid-state laser.

2-24

cavity (amplifying and modifying the emission),and the output radiation.

The electrons in the atoms of the laser materialnormally reside in a steady-state lower energylevel. When energy is added to the atom, theelectrons are raised to a higher energy level. Theflash lamp (fig. 2-24) is the device used in thesolid-state laser to add energy to the atoms. Whenenergy is added to the electrons, they are in anunstable condition. They stay in this condition fora short time and then spontaneously return totheir steady-state lower energy level. Thetransition of the electrons from the higher energylevel to the lower energy level releases energy inthe form of photons of light. The emitted lightrays travel back and forth in the optical cavitythrough the lasing material between the100-percent reflecting mirror and the 99-percentreflecting mirror. The photons collide with otherexcited electrons in the laser material, therebystimulating the emission of other photons of light.The light energy is amplified in this manner untilsufficient energy is built up to be transmittedthrough the 99-percent reflecting mirror. Thisaction is termed lasing. The equipment thataccomplishes lasing is the laser.

Find the Q-switch shown in figure 2-24. It isused to provide pulses of extremely shortduration. One type of Q-switching is provided bya rotating prism. Only at the point of rotationwhere there is a clear optical path is light energyallowed to pass. Another type of Q-switchingdevice is a normally opaque electro-optical devicesuch as a Pockels cell. At the time of voltageapplication, the Pockels cell becomes transparentto light. A complete optical path is formed thatallows the transmission of light.

The construction of the gas laser is slightlydifferent from that of the solid-state laser. A glasstube filled with gas is placed in the optical path.This tube replaces the lasing material and flashlamp in the solid-state laser. A voltage (theexternal energy source) is applied to the tube. Thelight emitted from this type of laser is normallycontinuous wave rather than pulsed.

Light from a conventional light source isextremely broadband. It emits several wavelengthsacross the electromagnetic spectrum. But, if youplace a filter that allows only a very narrow bandof wavelengths (such as a red filter) in front ofa broadband light source, only red light exits thefilter. An analogy can be made between the lightfrom the filter and the light from the laser, withone exception—there is only a single wavelengthemitted from the laser.

The wavelength (or color) of light emittedfrom the laser depends on the type of materialused in the laser. For example, if a Nd:YAGcrystal is used as the material in the laser, thelaser emits light with a wavelength of 1.064micrometers. Look at figure 2-25. It shows yousome of the types of material that are used forlasing and the wavelengths that are emitted bylasers using these materials. Note that somematerials and gases emit more than one wave-length. In these cases, the wavelength of the lightemitted depends on the optical configuration ofthe laser.

Light from a conventional light sourcediverges or spreads quite rapidly. If you hold asheet of paper near a 100-watt light bulb, theentire sheet is illuminated. Figure 2-26 shows thedivergence (amount of beam spread) from aconventional light source. On the other hand, laserlight has a very narrow beam divergence. If a sheetof paper is held the same distance from the laseras it was from the conventional light source, thelaser light has a very narrow beam divergence; itshows a very small point of light (fig. 2-27). Thelaser light beam has a very narrow beamdivergence. For example, if the paper were placeddouble the distance from the original point, thespot would be twice the size of the one firstdescribed. If a paper were held three times thedistance, a spot three times the original size wouldbe seen.

Materials reflect, absorb, or transmit lightrays. Reflection of light can be shown by usinga mirror. If light rays strike a mirror, almost allof the energy incident on the mirror is reflected.Refer to figure 2-28. This figure shows how aplastic or glass surface acts on an incident lightray, The amount of energy transmitted, absorbed,and reflected equals the amount of energy incidenton the surface of the material.

A surface is termed specular when the sizesof surface imperfections and variations are muchsmaller than the wavelength of the incident opticalradiation. A surface is termed diffuse whensurface irregularities are randomly oriented andmuch larger than the incident optical radiation.In the intermediate region of the laser section ofthe electromagnetic spectrum, it is sometimesnecessary to regard the diffuse and specularcomponents separately.

If light is incident upon an interface thatseparates two transmitting media (such as anair-glass interface), some light is transmitted whilesome is reflected, and no energy is absorbed atthe interface. Since no energy is absorbed at the

2-25

Figure 2-25.-Laser electromagnetic spectrum.

2-26

Figure 2-26.-Divergence of a conventional light source.

interface, T + R = 1.00; where T and R are thefractions of the incident beam intensity that aretransmitted and reflected.

T and R are the transmission and reflectioncoefficients, respectively. These coefficientsdepend not only upon the wavelength of theradiation, but they also depend upon the angleof incidence of the beam. The amount of theincident light beam that is reflected and theamount that passes through the material(transmitted) also depends upon the polarization(aligning the light to certain directions) of the lightbeam.

The angle that an incident ray of radiationformed with the normal to the surface determinesthe angle of refraction and the angle of reflection(the angle of reflection equals the angle of

Figure 2-27.-Divergence of a laser source.

incidence). The relationship between the angle ofincidence and the angle of refraction isn sine = n´ sine where n and n´ are theincidence of refraction of the media that theincident and transmitted rays move through,respectively.

A flat specular surface does not change thedivergence of the incident light beam significantly.However, a curved surface may change thedivergence, The amount of change in thedivergence depends upon the curvature of thesurface and the beam size incident to the surface.

Figure 2-28.-Light ray incident on a glass surface.

2-27

Figure 2-29.-Specular reflectors.

Figure 2-30.-Diffused reflectors.

In figure 2-29, the reflection of an incident laserbeam is shown on the two surfaces. (The divergenceand curvature of the reflector have been exagger-ated.) You should note that the value of irradiancemeasured at a specific range from the reflectoris less after reflection from the curved surface thanwhen a beam is reflected from a flat surface.

A diffuse surface is a surface that reflects theincident laser beam in all directions. Thebeampath is not maintained when the laser beamstrikes it. Whether a surface is a diffuse reflectoror a specular reflector depends upon the wave-length of the incident laser beam. A surface wouldbe a diffuse reflector for a visible laser beam,while it might be a specular reflector for aninfrared laser beam, such as CO2. Look atfigure 2-30. It shows the effect of different curva-tures of diffuse reflectors on incident laser beams.

Q32.

Q33.

Q34.

Q35.

Describe the basic principle of a laser.

What determines the wavelength (or color)of light emitted by a laser?

Some terms are useful in dealing with lasers.These include watts, joules, and irradiance.What is meant by irradiance?

What is meant by a diffuse surface?

LASER THEORY

To understand laser and infrared operation,you must understand wave propagation, thecomponent parts of waves, and wave interaction.

Wave Propagation

Wave propagation is the travel of a wavethrough a medium. Refer to figure 2-31. Here a

Figure 2-31.-Parts of waves.

2-28

plain wave is shown, and you can see that thepropagation (direction of travel) is perpendicularto the lines of the crest. Another type of wave isa spherical wave that propagates outward like thatwhich a pebble causes when it is thrown into apond.

Wave Optics

When light strikes an object or a medium, itis either reflected or absorbed. Wave opticsinvolve the reflection or absorption of waves.

REFLECTION.— Refer to figure 2-32. Thisfigure illustrates light reflection and refraction.As an incident wave strikes a reflective surface,it is reflected from the surface. If the reflectivesurface is smooth, the angle of reflection equalsthe angle of incidence.

REFRACTION.— Again, refer to figure 2-32.When light passes through a transparent medium,it is bent or refracted. The term index of refractionrefers to the amount that the light is bent or theangle of refraction. The higher the index ofrefraction, the more the light is bent. The index

of refraction is a function of wavelength of theincident light. Since different colors have differentwavelengths, they have a different index ofrefraction.

DIFFUSION.— Earlier, you saw how light isreflected when it strikes a smooth surface. Whenthe same type of beam strikes a rough surface,the light is scattered. The term used to describethis scattering is diffusion. Diffusion allows youto see nonluminous objects.

Lens Optics

Lenses are used extensively in laser andinfrared system operation. Therefore, you needto understand lens optics before you can under-stand the system. A lens is defined as a piece oftransparent material with two opposite refractingsurfaces. Converging and diverging lenses are thetwo categories of lenses. Within these categories,there are three basic types of lenses—convex,concave, and meniscus (fig. 2-33), The converginglenses are thin at the edge and thick in the middle,while the diverging lenses are thick at the edgesand thin in the middle.

Figure 2-32.-Reflection and refraction. Figure 2-33.-Types of lenses.

2-29

THIN CONVERGING LENS.— A thinconverging lens is shown in figure 2-34. Lightrays traveling parallel to the axis of a thinconvex lens are refracted so that they convergeat a point called the focal point of the lens.The distance from the center of the lens tothe focal point is the focal length of thelens.

THIN DIVERGING LENS.— A thin diverg-ing lens is shown in figure 2-35. In the case of athin diverging lens, light rays that travel parallelto the axis of the concave lens are refracted sothat they diverge at a point known as the focus.The distance from the center of the lens to thefocus is known as the focal length. Since the focusis on the viewing side of the lens, it is considerednegative.

Particle Theory of Light

Light, and all other forms of electromagneticradiation, is energy. Light is composed of particlescalled photons, which are bundles of masslessenergy.

PHOTOELECTRIC EFFECT.— In 1887,Heinrich Hertz discovered that metals ejectelectrons when illuminated. This discovery gaverise to the particle theory of light. Thephotoelectric effect is shown in figure 2-36. Thefollowing conclusions can be drawn about thenature of light:

The number of photoelectrons ejected isproportional to the intensity of light; thatis, the more intense the light, the greaterthe number of photoelectrons ejected.

Figure 2-34.-Thin converging lenses.

2-30

Figure 2-35.-Thin diverging lenses.

Figure 2-36.-Photoelectric effect.

2-31

Maximum kinetic energy (Kmax) is afunction of the frequency of incident light.

Photoelectrons are ejected instantaneously,regardless of the intensity of the incidentlight.

The surface of the specific metal has athreshold frequency; that is, the thresholdis the minimum frequency of light thatcauses photoelectrons to be ejected.

PHOTON THEORY OF LIGHT.— Thephoton theory of light was announced by Einsteinin 1905. This theory explains the photoelectriceffect and adds to the understanding of thephotoelectric effect in the following ways:

A beam of light is a stream of photons.The intensity of the beam is proportional to thenumber of photons in the beam. If one photonknocks out one electron, the photoelectrons willbe proportional to the intensity of the beam.

The energy created in the collision of thephotons is transferred instantaneously.

Stimulated Emissions

Lasers operate by stimulated emission. Referto figure 2-37 while you read this section. Anexcited atom is struck by a photon. The energyof the incident photon is equal to the transitionenergy of the excited atom, and the excited atomtriggers or stimulates an emission from atomnumber two. The output produced by thestimulation is emitted instantaneously uponimpact, and it is considered an amplified output.

Refer to figure 2-38. The laser rod and theflash lamp are placed at the foci of the ellipticalmirror (fig. 2-38, view A). The elliptical mirrorcan be focused on the laser rod and also the flashlamp. The flash lamp is fixed (fig. 2-38, view B).The photons from the lamp enter the laser tube,causing the tube to go to a high state (excited).The input light signal hits the excited atoms ofthe laser rod, causing stimulated emissions (fig.2-38, view C). Finally, the amplified signal leavesthe laser tube (fig. 2-38, view D).

Q-Switching

As you can see by looking at figure 2-39,uncontrolled laser output consists of a series of

Figure 2-37.-Stimulated emission.

2-32

Figure 2-38.-Light amplification.

Figure 2-39.-Typical laser output.

2-33

Figure 2-40.-—Pockels cell.

Figure 2-41.-Laser pulse comparison.

2-34

sharp spikes with random heights and randomintervals. Normally, this type of output isunusable. Some method of control is needed toregulate or change this output into a single pulseof demand, and quality switching (Q-switching)meets this need.

There are many ways to provide Q-switching,from simple mechanical methods to more elabo-rate electronic methods. The type of Q-switchingdiscussed in this chapter is the Pockels cell.

POCKELS CELL.— The Pockels cell is a typeof electro-optic Q-switch (fig. 2-40). The Pockelscell is placed between the laser rod and the mirror(fig. 2-40). This cell is composed of lithiumniobium

POCKELS CELL WITH ZERO VOLTAGEAPPLIED.— When light from the laser strikes thefirst calcite prism, the calcite prism splits the lightinto ordinary o and extraordinary e beams, whichare diverged slightly. These beams strike thesecond prism where they are bent or divergedagain. They leave this prism in parallel and strikea mirror, which reflects them 100 percent. Thelight stays inside the Pockels cell; thus, there iszero output.

POCKELS CELL WITH 5 KV APPLIED.—Look at figure 2-40, views A and B. Once again,the light from the laser strikes the first calciteprism. Again, it splits and becomes the o beamand e beam. These two beams strike the lithiumniobium with the voltage applied, and it becomesbirefringent. (Birefringent means to refract thelight in different directions.) The outputs fromthe lithium are the e beam and the o beam, rotatedby 90°. This causes the beams to interchange orbecome each other. The new o beam strikes thesecond prism where it is refracted sharply to hitthe Porro prism, which reflects it sharply backinto the optical path to provide the feedback thatcauses sustained optical oscillations (powerbuildup). The Pockels cell is the device that allowsthese oscillations to build until a threshold isreached. Then the laser fires (fig. 2-41).

Solid-State Lasers

The demand for lasers with diverse appli-cations caused the development of many types oflasers. Most lasers are grouped into fivecategories—solid state, gas, ion, chemical, anddye. Solid-state lasers were developed first andwere most widely used for military applications.For this reason, solid-state lasers are the typediscussed in this chapter.

CRYSTALLINE LASERS.— Crystallinelasers are widely used. Two materials are used inthese lasers: the matrix substance (host) and animpurity (dopant). The host is an inert, opticallytransparent crystalline substance. The mainpurpose of the host is to lattice sites (honeycombarrangement) occupied by the dopant. Thesubstances commonly used as the host includesapphires, yttrium aluminum garnet (YAG),fluorite, glass, calcium tungstate, and calciummolybdate. Dopants are ions of rare earthmetals, with the exception of chromium. Themost commonly used dopants are chromium,neodymium, holmium, erbium, uranium, andsamarium.

RUBY LASERS.— The host material for rubylasers is sapphire crystalline alumina. The dopantis triply ionized chromium, which gives a charac-teristic red color. Although natural rubies couldbe used in lasers, their use is rare because largenatural rubies with uniform color are rare.Synthetic crystals can be grown to a desired sizewith no flaws and uniform color.

NEODYMIUM YAG LASER.— Normally,the YAG laser is used as a continuous-wave (CW)laser. The YAG is the host for the trivalentneodymium ion dopant. The neodymiumgives the YAG a pale, reddish-purple color. Thelaser rod is produced synthetically, as is the rubylaser. The major difference between the ruby andYAG laser is the output wavelength.

SEMICONDUCTOR DIODE LASERS.— Asemiconductor functions somewhere in betweena metal (conductor) and a nonmetal (insulator).At high temperatures, the semiconductor has lowresistance; while at very low temperatures (nearabsolute zero), it has extremely high resistance.An example of a semiconductor diode laser isshown in figure 2-42. The semiconductor diode

Figure 2-42.-Diode laser.

2-35

is made by sandwiching a diode between twometal conductors that are polished to providefeedback. The semiconductor diode laser hasseveral advantages when compared to other typesof lasers.

They are more efficient.

They have a wider bandwidth.

They are faster and do not requireQ-switching.

Military Applications

Target designation and range-finding are twoof the military applications of lasers.

TARGET DESIGNATION.— Target desig-nation is provided by a laser fixed on a target.A beam is reflected from the target and producesa small, bright spot. Then, a laser-guided bomb,shell, or missile can home in on the spot. Toprevent the enemy from jamming the signal, acoded pulse repetition rate is added.

RANGE-FINDING.— When used for range-finding, a laser fires a pulse of light that is pointedat a target. When the pulse is fired, a clock starts.The pulse strikes that target and is reflected. Whenthe returning pulse is detected, the clock stops.Because the speed of light is known, this systemis accurate to within 1 foot at a range of 2 miles.

Q36.

Q37.

Q38.

Q39.

Q40.

Explain wave optics.

Name two categories of lenses.

What is the particle theory of light?

What is meant by stimulated emission (fig.2-37)?

List the five categories in which most lasersare grouped.

DETECTING-RANGING SET (DRS)AN/AAS-33A

Learning Objectives: Identify major com-ponents and functions of the AN/AAS-33A.Identify the system shop replaceable assem-blies (SRAs) and recognize their functions.

The Detecting-Ranging Set (DRS) AN/AAS-33A is part of the A-6E integratedweapons system. The DRS provides three electro-optical sensors and associated controls andindicators to enhance the all-weather capabilityof the weapons system to detect, recognize, andidentify targets accurately.

NOTE: While reading this section, youshould refer to table 2-3 for a listing of thecomponents and associated assemblies ofthe AN/AAS-33A. The physical locationof the AN/AAS-33A within the aircraftcan be seen by referring to figures 2-43through 2-48.

The three sensors are housed in a 20-inch, fullygimballed turret and are collectively known as thereceiver group (RG). This group is installed in theaircraft underneath the radome, forward of thenosewheel. The three sensors are the laser rangefinder/designator (LRD), forward air controller(FAC) receiver, and forward looking infrared(FLIR) receiver. The LRD is also known as thelaser receiver-transmitter. The LRD functions asa range finder and target designator. It providesrange-to-target data to the ballistic computer setand designated targets for laser-guided bombs(LGBs). The FAC receiver is used as an aid forthe bombardier/navigator (B/N) in locating atarget designated by an external laser source froma ground observer or another aircraft. A lasersource can serve as the offset aimpoint in thesolution of a computer-controlled bombingattack. The FLIR receiver is a passive sensor thatis used to detect targets of interest by their emittedinfrared radiation. The infrared radiation signalsare processed and a real-time, television-like imageis displayed on the FLIR indicator.

The SRAs consist of turret-stabilized platform,FLIR receiver, laser range finder designator,forward air controller receiver, reciprocatingcompressor, electronic control amplifier,generator processor, signal processor, infraredindicator, detecting ranging set control, powersupply, and cable assembly.

TURRET STABILIZEDPLATFORM (TSP)

The turret stabilized platform (TSP) consistsof a two-axis turret and a vernier two-axis gimbalthat provides azimuth coverage of –195° andelevation coverage of +20° to +180°. A turretstow position of 0° azimuth and –210° elevation

2-36

Table 2-3.-AN/AAS-33A Components

I IREF

NOMENCLATUREPLACARD OR

DES COMMON NAME

Components

89A1

89A2

89A3

89A4

89A5

89A6

89A7

89A8

89A9

89A10

02A2

02A3

02A11

03A2

14A10

23A1

Receiver Group 0R-203/AAS-33A orOR-203A/AAS-33A

Major SRAs:

1. Forward Looking Infrared Receiver

2. Laser rangefinder/Designator or LaserReceiver-Transmitter (LRT)

3. Forward Air Controller Receiver

4. Turret Stabilized Platform

Reciprocating Compressor HD-1032/AAS-33A

Power Supply PP-7417/AAS-33A

Generator Processor 0-1761/AAS-33A

Signal Processor CV-3460/AAS-33A

Electronic Control Amplifier AM-6959A/AAS-33A

Infrared Indicator IP-1301/AAS-33A

Detecting-ranging Set Control C-10301/AAS-33A

Temperature Control C-10358/AAS-33A

Cable Assembly W1 of AN/AAS-33A

3-Way, 2-Position, DRS Solenoid SelectorValve

Receiver group (RG)

FLIR receiver

Laser rangefinder designator (LRD) orlaser receiver-transmitter (LRT)

FAC receiver

Turret stabilized platform (TSP)

Compressor

Low voltage power supply (LVPS)

Laser transceiver electronics (LTE)

Laser receiver electronics (LRE)

Electronic control amplifier (ECA)

Forward looking infrared indicator(FLIR)

DRS control panel

—

Pulse forming network cable (PFN cable)

Solenoid selector valve

Associated Assemblies

Nosewheel Well Circuit Breaker Box(Forward)

Bombardier/Navigator Circuit BreakerPanel

Nosewheel Well Circuit Breaker Panel (Aft)

Top Deck Relay Box

Temperature Control Box

Caution Dim and Test Light Assembly

Nosewheel well circuit breaker panel(FWD)

CB panel (NWW) (Aft)

—

Caution lights panel

2-37

Table 2-3.—AN/AAS-33A Components—Continued

REF NOMENCLATUREPLACARD OR

DES COMMON NAME

Associated Assemblies—Continued

50A1 Ballistics Computer CP-985/ASQ-133 or Ballistics computerCP-1391/ASQ-155A

50A3 Computer Control C-9535/ASQ-155 Pedestal control unit (PCU)

50A10 Analog-to-Digital/Digital-to-Analog A/D converterConverter CV-3163/ASQ-155

61A1 Mission Recorder Electronics Unit Electronics unitMX-9276/USH-17(V)

61A3 Mission Recorder Control Panel C-9071/ MISSION RECORDER control panelUSH-17(V)

75A4 Power Supply PP-6574/APQ-148 Low-voltage power supply (LVPS)

75A12 Analog Display Indicator IP-722D/ ADIAVA-1 or IP-722F/AVA-1

75A15 Fault Locating Indicator ID-1933/APQ-156 BIT panel

75A16 Pilot’s Control Box PCB

S67 Nose Gear Down and Locked Switch —

S6030 Right Main Gear Weight-on-Wheels —Switch


A36. Wave optics involve the reflection or absorption of waves. Lightstrikes an object or medium and is either reflected or absorbed.

A37. Converging and diverging.

A38. The particle theory of light states that “light is composed ofparticles called photons, which are bundles of massless energy.”

A39. The energy of the incident photon in figure 2-37 is equal to thetransition energy of the excited atom; the excited atom triggersor stimulates an emission from atom two.

A40. Solid state, gas, ion, chemical, and dye.

2-38

Figure 2-43 .-Outside view A-6E.

protects the three optical windows of the lowerball when the receiver group is not in the on-targetmode of operation. A hydraulic motor connectedto the aircraft hydraulic system provides powerfor turret outer azimuth drive. The elevationaxis and inner gimbal drives are powered elec-trically.

FLIR RECEIVER

The FLIR receiver provides infrared targetdetection and recognition capability. It hasa continuous optical zoom ratio capabilityof 5 to 1 (5x). A counterbalance weight movesin an opposing motion to the zoom to maintaina balance when the FLIR is installed in theTSP.

LASER RANGE FINDERDESIGNATOR (LRD)

The LRD provides target ranging and desig-nating capability. It contains separate telescopesfor its transmitter and receiver, which viewthrough a common window on the TSP. Com-puter control of range-finding and target desig-nation modes is provided.

FORWARD AIR CONTROLLER (FAC)RECEIVER

The FAC receiver provides position infor-mation of acquired targets that are illuminatedby remotely operated ground or airborne laserdesignators. It receives the laser energy througha separate window on the TSP. A four-quadrant

2-39

Figure 2-44.-Aft view with pallets extended and radome raised.

detector generates the position signals, which areprocessed to locate the position of a target symboldisplayed on the FLIR indicator.

RECIPROCATING COMPRESSORHD-1032/AAS-33A

The HD-1032/AAS-33A compressor is apiston device that is driven by a 115-volt ac,400-Hz, three-phase induction motor that is anintegral part of the compressor assembly. Thecompressor provides helium pressure pulses forthe required cooling for the detectors.

ELECTRONIC CONTROL AMPLIFIER(ECA) AM-6959/AAS-33A

The ECA contains the electronics circuits thatprovide the capability to accurately position or

show the receiver group up to 1 radian/sec inresponse to input signals from the ballisticcomputer.

GENERATOR PROCESSOR1761/AAS-33A

The generator processor is also known as thelaser transceiver electronics (LTE). It providesprecise timing signals and a high-voltage firingpulse to the LRD. All mode commands and powerfor the laser subsystem interface with the rest ofthe DRS through LTE.

SIGNAL PROCESSORCU-3460/AAS-33A

The signal processor is also known as the laserreceiver electronics (LRE). It processes four video

2-40

Figure 2-45.-View looking inboard and aft with pallets stowed.

signals from the FAC receiver, which are propor-tional to the position of a designated target in theFAC receiver field of view.

INFRARED INDICATORIP-130/AAS-33A

The infrared indicator (fig. 2-48, view A)presents a high-resolution video display of theinfrared scene in real-time on an 8-inch diagonalCRT. In-flight video tape recordings can be madeand played back on the infrared indicator. Sixstatus lights on the front panel provide the B/Nwith the operating status of the DRS subsystem.

DETECTING-RANGING SET (DRS)CONTROL C-10301/AAS-33A

The DRS control panel (fig. 2-48, view B)provides on/off power and mode command

control logic for FLIR, stabilization, laser, andFAC subsystem operation. It also has controls forthe FLIR indicator and FLIR subsystem. TheDRS control panel also houses the BIT interfacecircuits between the aircraft BIT panel and theDRS WRAs.

POWER SUPPLY PP-7417/AAS-33A

The low-voltage power supply (LVPS)generates the low voltage necessary to operate theentire DRS system.

CABLE ASSEMBLY WI (PFN CABLE)

The PFN cable conducts the pulse-formingnetwork voltage from the LTE to the receivergroup.

2-41

FIBER OPTICS

Learning Objectives: Describe fiber opticsto include a basic system, advantages, andfiber construction. Describe light trans-mission, fiber types, cables, and coupling.

Fiber optics has revolutionized the telephoneindustry and will become the preferred norm ofaviation and electronics technology. You won’tsee the cumbersome myriad of wires, connections,and cabling we have today. Weight will bereduced, and capabilities will be increased. As anAviation Electronics Technician, you should seefiber optic technology in the near future.

Fiber optics is not new. In the mid 1800s,William Wheeler patented a device for piping lightfrom room to room, Alexander Graham Bells’photophone could reproduce voices throughdetection of the amount of light received from amodulated light source. In the last decade, apractical means of sending light has evolved—in

Figure 2-46.-Receiver group. the form of glass fibers.

Figure 2-47.-Cockpit.

2-42

BASIC SYSTEM

Figure 2-48.-FLIR indicator and control panel.

The principles of fiber optics follow the basicproperties of light, as discussed in chapter 1, andinclude refraction and reflection. Light travelingwithin a fiber obeys the laws of propagation. Fiberoptics is the technique of sending data in the formof light through long, thin, flexible fibers of glass,plastic, or other transparent materials. A basicfiber optic system (fig. 2-49) consists of atransmitter, a fiber medium, and a receiver. Thetransmitter converts electrical signals into currentto drive a light source for injection into a fiber.The fiber or fibers guide(s) the light to a lightdetector that converts the light back into anelectrical signal. The receiver is a low-noise andlarge-voltage gain receiver that provides furtherprocessing.

ADVANTAGES OF FIBER OPTICSYSTEMS

There are many advantages of using fiberoptics over systems in use today. Some of theseadvantages are shown below:

Fiber optics can be used in flammableareas because light, not an electrical pulse,is the energy sent.

Figure 2-49.-Basic fiber optic system block.

2-43

Fiber optic systems are immune to radiofrequency interference (RFI), electro-motive interference (EMI), and noisecaused by lightning and cross talk.

Fiber optic systems are immune toelectromagnetic pulse effects induced bynuclear explosions.

Fiber optics aren’t affected by moisture ortemperature changes.

Fiber optic systems are easy to repair.

Fiber optic systems have very high datatransmission rates.

Fiber optic devices are small andlightweight.

OPTICAL FIBER CONSTRUCTION

A typical fiber is a transparent, dielectriccylinder (core) enclosed within a second trans-parent dielectric cylinder (cladding). The core andcladding are enclosed by insulation (fig 2-50). Thedielectric cylinders consist of various opticalglasses and plastics. The cladding, which has arelatively low index of refraction, encloses thecore, which has a very high index of refraction.The cladding contains most of the transmitted

light within the core. This low index prevents lightleakage and increases efficiency. The insulationprotects a single fiber or several fibers from stressand the environment.

LIGHT TRANSMISSION

The light injected into a fiber travels in a seriesof reflections from wall to wall between the coreand cladding. The reflections depend on the coneof acceptance and resulting angles of refractionand reflection propagation (fig 2-50). The coneof acceptance is the area in front of the fiber thatdetermines the angle of light waves it will accept.The acceptance angle is the half-angle of the coneof acceptance. The light enters the core andrefracts to the interface of the core and cladding.The light reflects at the same angle of impact. Thelight, reflecting from wall to wall, continues atthe same angle to the end of the fiber at thedetector. Like the physics of light, the maximumcritical angle is that angle that, when surpassed,won’t reflect; in this case, it is lost in the claddingof the fiber. As long as the light wave is at a lesserangle than the maximum critical angle of the fiber(as determined by the function of the fibers’ coreand cladding indexes of refraction), light willtravel to the receiver.

TYPES OF OPTICAL FIBERS

There are two types of optical fibers. Thestep-index type has large differences in the core

Figure 2-50.-Transmission of light in a fiber.

2-44

and cladding indexes of refraction. When heldconstant, these differences cause light to reflectfrom the interface back through the core to itsopposite wall.

The graded-index type has a decreasing corerefractive index as the radial distance from thecore increases. This causes the light rays tocontinuously refocus as they travel down the fiber.These types operate in either single-mode or multi-mode operation. Single-mode operation acceptsa specific wavelength, otherwise large attenuationwill result. The multi-mode type operates over arange of wavelengths with minimum signal loss.(See fig. 2-51.)

PROPERTIES OF OPTICAL CABLES

Optical cables are affected by many physicalproperties, Some of these are discussed in thefollowing section.

Numerical Index

The numerical index of optical cables dealswith the sine of the angle of acceptance. Thenumerical aperature (NA) or numerical index canbe found using the formula shown below:

where i = acceptance angle, n1 = Core Index ofRefraction, and n2 = Cladding Index ofRefraction.

The acceptance angle is a measure of thenumerical aperature (NA) or numerical indexof a fiber. This lets the manufacturer selectthe proper fiber for the desired specific lightwaves and for optimum power coupling. NAis a measure of the light capture angle (half-acceptance angle). It describes the max core angleof light rays that will be reflected down the fiberby total reflection.

The refractive index (Index of Refraction) ofa material is the ratio of the speed of light in avacuum to the speed of light in the material.Review chapter 1 for more information onrefraction if you don’t understand this section.The higher the refractive index of a material, thelower the velocity of light through the material.Also, there will be more refraction or bending ofthe light when it enters the material.

If NA increases, angle i must have increased,and the fiber sees more light. NA can never begreater than 1.0; normal values are low (0.2 and0.6).

Dispersion

Dispersion is the spreading or widening of lightwaves due to the refractive index of the materialand the wavelength of the light traveling in thefiber. There are two types of dispersion—intermodal and intramodal.

Intermodal (multi-mode) dispersion. Inter-modal dispersion is the propagation (travel) ofrays of the same wavelength along different pathsthrough the fiber. These wavelength rays arriveat the receiving end at different times.

Figure 2-51.-Types of optical fibers.

2-45

Intramodal dispersion.is due to variations of thethe core and cladding.

Attenuation

Intramodal dispersionindex of refraction of

Attenuation is the loss or reduction inamplitude of the energy transmitted. These lossesare due to differences of refractive indexes andimperfections in fiber materials. Also, man-madescratches or dirt and light scattering within thefiber cause unwanted losses. Efforts to reducethese losses include the forming of the followingstandard parameters:

Bandwidth parameters. Bandwidth param-eters include attenuation curves, whichprovide all designers the ability to chosethe best fiber. These parameters are plottedin decibels per kilometer (dB/km). Theymeasure the efficiency of the fiber as acomparison of light transmission to lightloss through a fiber.

Rise time parameters. These parameters setspeed requirements for operation.

Fiber strength parameters. Theseparameters set tensile strength standardsto help reduce flaws and microcracks in thefiber.

FIBER COUPLING

One important aspect of a fiber system is theconnection between the fiber and the other parts.The coupling efficiency is the ratio of poweraccepted by the fiber to the power emitted by thesource

Coupling efficiency increases with the square ofthe NA (numerical aperature) and decreases withsource and fiber mismatches. Optical powercoupled into the fiber is a function of the radianceof the source and the NA.

Q41.

Q42.

Q43.

Q44.

Q45.

A basic fiber optic system consists of atransmitter, a fiber medium, and a receiver.Describe the basic technique of fiber optics.

List the advantages of fiber optic systems.

By what means does light travel through afiber optic?

What is the difference between single-modeand multi-mode operation?

Attenuation is the loss or reduction ofenergy transmitted. Efforts to reduce theselosses include the forming of standardparameters. What are these parameters?

2-46

(THIS PAGE IS INTENTIONALLY LEFT BLANK.)

2-47


A41. Fiber optics is the technique of sending data, in the form of light,through long, thin, flexible fibers of glass, plastic, or othertransparent materials.

A42. (a) Usable in flammable areas(b) Immune to noises generated by RFI, EMI, lightning, and

cross talk(c) Immune to electromagnetic pulse effects(d) Not affected by moisture or temperature changes(e) Easy to repair(f) Very high transmission rates(g) Small size and lightweight

A43. The light injected into a fiber travels in a series of reflectionsfrom wall to wall between core and cladding. The reflectionsdepend on the cone of acceptance and resulting angles ofrefraction and reflection propagation.

A44. Single-mode types accept a specific wavelength, otherwise, largeattenuation results. Multi-mode types operate over a range ofwavelengths, with minimum signal loss.

A45. (a) Bandwidth parameters provide designers the ability to choosethe best fiber.

(b) Rise time parameters set the speed requirements for fiberoperation.

(c) Fiber strength parameters set tensile strength requirementsto help reduce flaws and microcracks in the fiber.

2-48

CHAPTER 3

ANALOG FUNDAMENTALS

A computer is a device that performsmathematical calculations on input data to yieldnew and generally more useful results. The firstcomputer, an abacus, was used by the ancientGreeks and Remans. The abacus is a simple kindof manually operated device using sliding beads.If operated according to definite rules, you canperform addition and subtraction very rapidly.

The development of the computer probablycontributed more to the advancement of today’sweapons systems than any other single factor.Without the use of such complex machines, thesolution of today’s weapon control problemwould be impossible.

NOTE: You should remember that themethods presented in this chapter are basic.Many variations of these methods arefound in equipment.

Analog computers are used for situationswhere continually varying solutions are needed forproblems whose factors are continuously varying.Generally, these factors are physical quantities,such as velocity, direction, or range. Such physicalquantities are conveniently represented by degreesof shaft rotation, magnitude or phase of a voltage,or the speed and direction of movement of somemechanical part. The varying instantaneoussummation, or simultaneous solution, of outputsfrom all the computing parts is the computer’soutput.

The accuracy of an analog computer isdetermined by the percentage of errors of thedevices used, multiplied by the maximum quantityof the input variables.

The computer’s output is applied as needed,depending on the purpose of the computer. Forexample, in a fire control computer, the computeroutput positions a weapon-sighting reticle inrelation to the direction of flight. As the pilotmaneuvers to keep an enemy target within thereticle, the weapons are properly aimed. In abombing computer, the computer output releases

bombs at the proper time and drives indicatorsthat give the aircraft’s position at all times inlatitude and longitude.

To understand analog computers, you needa review of synchros and various types of servosystems. The particular type of servo system orsynchro (such as electromechanical, electro-hydraulic, hydraulic amplidyne, or pneumatic)depends on the type of load for which it wasdesigned.

Synchros are used primarily for rapid andaccurate transmission of information betweenequipment and stations. Speed and accuracy arethe key fundamentals of synchros in their role inthe operation of a weapons, communications,underwater detection, and navigation systemsused in the Navy. Synchros are fast but weak; theyneed the help of a servo. Servos are powerful.They move heavy loads accurately and may beremotely controlled with great precision bysynchro devices. This combination is unbeatable,and it is the foundation for analog computationand performance in many systems.

You will not read about any specific servosystem in this chapter. Instead, you are introducedto the basic systems, their essential components,and how each functions. If you want specificdetails on the theory and operation of a particularsystem, refer to the technical manuals for thatsystem. In addition, you should review the basictheory of synchros and servomechanisms as dis-cussed in module 15 of the Navy Electricity andElectronics Training Series (NEETS), NAVEDTRA14187. After this review, you will be ready for thisdiscussion of basic servomechanisms and their pur-

Q1.

Q2.

pose in analog computation.

Analog computers are used for situationswhere continually varying solutions areneeded for problems whose factors, suchas velocity, direction, or range, areconstantly changing. Is this statement trueor false?

Describe the primary use of synchros.

3-1

BASIC SERVOMECHANISMS

Learning Objective: Identify various typesof servo systems and components includingalignment and characteristics.

The essential components of a servo-mechanism are a data transmission system, servocontrol amplifier, and servomotor. These com-ponents are shown in the block diagram infigure 3-1, and are discussed in the followingparagraphs.

The four functions of the data transmissionsystem are to—

1.2.

3.

4.

measure the servo output,transmit or feedback the signal, which isproportional to the output, to the errordetector (a differential device for com-paring two signals),compare the input signal with the feedbacksignal, andtransmit to the servo amplifier a signal thatis proportional to the difference betweenthe input and output signals.

The signal obtained by comparing the servoinput and output is called the servo error,represented by the symbol E. In figure 3-1, youcan see that the servo error (E) is the difference

Figure 3-1.-Simplified block diagram of a servomechanism.

between the input and the output Thisis stated mathematically as

In many servo systems, the servo input andoutput devices are remotely located from eachother and from the servo amplifier. Because ofthis, some means is required to transmit theoutput information back to the device receivingthe input command and transmitting the servoerror to the servo amplifier. This system oftransmission, as well as the comparing device(error detector), is part of the data transmissionsystem. The servo amplifier receives the errorsignal from the error detector. Next, it sufficientlyamplifies the signal to cause the output device toposition the servo load to the commandedposition. Finally, the servo amplifier transmits theamplified signal to the servomotor.

The servomotor positions the servo load. Itmust be capable of positioning the load within aresponse time based on the requirements of thesystem.

ERROR DETECTORS

The error detector compares the input with theservomechanism output in the data transmissionsystem. The error detector is a mechanical or anelectrical device. In aircraft weapons systems,most error detectors are electrical devices becausethey are adapted to widely separated or remotelyinstalled components. Most electrical devices areeither potentiometer (resistive) or magneticdevices.

Electrical error detectors are either ac or dcdevices, depending on the requirements of theservo system. An ac device compares the two inputsignals. Then it produces an error signal withthe phase and amplitude to indicate both thedirection and the amount of control necessary toaccomplish correspondence. In a dc device, thepolarity of the output error signal determines thedirection of the correction necessary.

3-2

Error detectors are used in gyrostabilizedplatforms and rate gyros. In stabilized platforms,synchros are attached to gimbals. Any movementof the platform around the gyro axes is detectedby the synchro, and the error voltage is sent tothe appropriate servo system.

In rate gyros, an E-transformer is used todetect gyro precession. The E-transformer issensitive to slight changes, but its movement islimited to a small amount. It is used withconstrained gyros.

POTENTIOMETER

Potentiometer error detector systems are usedwhere the input and output of the servo-mechanism have limited motion. These systemshave the following advantages:

High accuracy.

Small size.

Either a dc or an ac voltage may beobtained as the output.

Disadvantages of potentiometer error detectorsystems include the following:

Limited motion.

A life problem that results from wear ofthe brush on the potentiometer wire.

A

The potentiometer voltage output changesin discrete steps as the brush moves fromwire to wire.

Some potentiometers require a high drivetorque to rotate the wiper contact.

balanced potentiometer error detector isshown in figure 3-2. The purpose of this circuitis to give an output error voltage proportional tothe difference between the input and outputsignals. In the following paragraphs, you willlearn how the potentiometer error detector works.Refer to figure 3-2 as you read the followingparagraphs.

The command input shaft is mechanicallylinked to R1, and the load is mechanically linkedto R2. An electrical source of 115 volts ac isapplied across both potentiometers.

When the input and output shafts are in thesame angular position, they are in corre-spondence, and there is no output error voltage.If the input shaft is rotated, the wiper contact ofR1 is moved. This action causes an error voltageto be developed and applied to the controlamplifier. The error voltage is the difference ofthe voltages at the wiper contacts of R1 and R2.The amplifier output causes the motor to rotateboth the load and the wiper contact of R2 untilboth voltages are equal. When this occurs, thereis no output error voltage.

In figure 3-2, both R1 and R2 are showngrouped together. In actual practice, thepotentiometers may be remotely located fromeach other. R2, the output potentiometer, maybe located at the output shaft or load. The remotelocation of one of the components does notremove it as part of the error detector.

Figure 3-2.-Balanced potentiometer error detector system.

3-3

E-Transformer

The E-transformer (fig. 3-3) is a type ofmagnetic device that is used as an error detector.It is used in systems that do not require the errordetector to move through large angles.

The primary excitation voltage is applied tocoil A on the center leg of the laminated core. Thecoupling between coil A and the secondarywindings (coils B and C) is controlled by thearmature, which is displaced linearly by the inputsignal. When the armature is positioned so thecoupling between the windings is balanced (null),the output voltage is minimum. The outputvoltage is minimum because of the series opposingconnections of the secondary windings. The phaseof the output voltage on either side of the voltagenull differs by 180 degrees. The amplitude can bemade proportional to the displacement of thearmature from its null voltage position. This errordetector is small and accurate, but it permits onlylimited input motion.

Control Transformers

Synchros have relatively high accuracy, lownoise level, reasonably small driving torques,and long life. These qualities also apply tosynchro control transformers. The synchrocontrol transformer has an unlimited rotationangle. Both the input and output to the synchrocontrol transformer may rotate through unlimitedangles. However, synchro control transformersare large, consume large amounts of power,and the output supplied to the servo controlamplifier is always ac modulated with the servoerror.

Figure 3-3.-E-transformer error detector.

Alternating current may be used to representthe value of a function if the following conditionsare met:

1.

2.

The frequency of the ac is greater thanthe maximum frequency response of themeasuring devices used.

If negative values of the variables areallowed, the devices must be phasesensitive.

Look at figure 3-4. It shows a dc signaland the same function represented by an acvoltage. The instantaneous value of the acsignal does not indicate the value of thefunction. However, the average value of the acsignal is used to represent the value of a function.For example, if the ac signal is the input to aservomotor, the motor must not attempt to followevery variation of the ac signal; it must follow theaverage value. Following the average value isessential because a negative ac signal does notexist. But, negative values can be indicated by achange in the phase of the signal. Look atfigure 3-4. During the period when the dcsignal is positive, the positive peaks of theac signal correspond to the positive peaksof the ac reference. During the period whenthe dc signal is negative, the positive peaksof the ac signal correspond to the negativepeaks of the reference signal; that is, thesignal is 180 degrees out of phase with thereference. There are ac servomotors that rotatein one direction when the input signal is in phase

Figure 3-4.-AC modulated with servo error.

3-4

with a reference voltage and in the other directionwhen the signal is out of phase with the referencevoltage.

A synchro data transmission system is madeup of a synchro transmitter, a synchro controltransformer, and, at times, a differentialtransmitter. The synchro transmitter transformsthe motion of its shaft into electrical signalsfor transmission to the synchro control trans-former, which makes up the error detector(fig. 3-5).

The stator of the transmitter consists of threecoils spaced 120 electrical degrees apart. Thevoltage induced into the stator windings is afunction of the transmitter rotor position. Thesevoltages are applied to the three similar statorwindings of the synchro control transformer. Thevoltage induced in the rotor of the synchro controltransformer depends on the relative position ofthis rotor with respect to the direction of the statorflux.

Look at figure 3-6. The variation of thesynchro control transformer output voltageis a function of the rotor position relativeto an assumed stator flux direction. Thereare two positions of the rotor, 180 degrees apart.Only the one whose output voltage is zero willcorrespond to the stable operating position of theservo.

Figure 3-6.-Induced voltage in synchro control transformerrotor.

Figure 3-5.-The control transformer as an error detector.

3-5

When a synchro differential transmitter (fig.3-7) is used for additional inputs to the servosystem, it is connected between the synchrotransmitter and the synchro control transformer.When the synchro differential rotor is in line withits stator windings, the differential transmitter actsas a one-to-one ratio transformer. The voltagesapplied to the synchro control transformer are thesame as the voltages from the synchro transmitter.If the synchro differential transmitter rotor isdisplaced by a second input, the voltages for thesynchro transmitter to the control transformer aremodified. The synchro differential transmittermodifies the voltages by the amount and directionof its rotor displacement. Thus, the two inputsare algebraically added and fed to the synchrocontrol transformer as a single input.

Flux Gate

A flux gate element is used to drive or excitea control transformer. It is usually used incompass systems. The flux gate operates on theprinciple of using the earth’s magnetic field toproduce a second harmonic current flow in theelement. This, in turn, produces a voltage in thestator windings of the control transformer thatis in direct proportion to the earth’s magneticnorth. It is desirable to use the horizontalcomponent of the earth’s field only. Therefore,a gyro is used to hold the element level with theearth’s surface, or the element is suspended bya spring and uses the properties of a pendulumto maintain a horizontal position. The assemblyis rigidly mounted to the aircraft and turns in anazimuth as the aircraft turns.

Q3.

Q4.

Q5.

Q6.

Q7.

Within a servomechanism, what is thefunction of the data transmission system?

What determines whether an ac or dcelectrical error detector is used in aparticular servo system?

List the advantages of potentiometer errordetector systems.

Describe the E-transformer and explainwhere it can be used.

What means are used to indicate negativevalues from ac signals from a synchrocontrol transformer?

MULTIPLE-SPEED DATATRANSMISSION SYSTEMS

The static accuracy (accuracy of load control)of a servomechanism is limited by the accuracyof the data transmission system. The accuracy ofthis system is increased by using a multiple-speeddata transmission system along with a one-speedsystem. The error-detector elements of themultiple-speed transmission system rotate at somemultiple of the shaft being controlled. Theelements of the one-speed transmission operateone-to-one with respect to the controlled shaft.

Figure 3-8 shows a diagram of a multiple- anda one-speed system. This is called a dual-speed

Figure 3-7.-Synchro differential transmitter used for additional input.

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Figure 3-8.-Dual-speed data transmission

system because it can transmit data at twodifferent speeds. If the input shaft of this systemturns through 1 degree, the one-speed transmitteris rotated 1 degree, and the multiple-speed unitis rotated 10 degrees. The synchro controltransformer associated with each of thesetransmitters is geared in similar ratios with respectto the servo output shaft. A 1-degree errorbetween the position of the input and outputshafts produces a relative rotor displacement of1 degree in the one-speed synchros and 10 degreesin the multiple-speed synchros. If the relationshipbetween the rotor displacement and outputvoltage is linear, the error signal in the multiple-speed system is 10 times that of the one-speedsystem. This amplification of the error signal inthe data transmission link reduces the signalamplification required in the servo controller. Ifthe synchro has an inherent error of 0.1 degreewith respect to its own shaft, the consequent servoerror introduced by a one-speed data transmissionsystem is of corresponding value. However, theconsequent servo error introduced by a 10-speeddata transmission system is only one-tenth asgreat, or 0.01 degree.

The multiple-speed error detector does havea disadvantage. It might fall out of step andsynchronize in a position different than the correctone by an integral number of revolutions of themultiple-speed synchro. Look at figure 3-8. If the

system.

output shaft were held fixed and the inputshaft rotated 36 degrees, the 10-speed synchrotransmitter would turn one complete revolution.The error signal from the multiple-speed errordetector would be zero. If the output shaft werereleased, the system would operate in a stablefashion with a 36-degree error between theinput and output shafts. A one-speed errordetector, along with the multiple-speed detector,is used to prevent this ambiguous synchronization.An error signal selector circuit may switchcontrol of the servo to the one-speed datatransmission system. However, this only occurswhenever the servo error becomes large enoughto permit the multiple-speed system to synchronizefalsely.

The simplest device to control an error-selectorcircuit is shown in figure 3-8. It is a single-pole,double-throw relay actuated by the output of theone-speed error detector. The relay is shown inthe de-energized position. When the output of theone-speed synchro is high, the relay is energized,and the one-speed circuit controls the servomotor.When the output is low, the relay opens and the10-speed synchro controls the circuit. Remember,the synchro output is high when there is a largeerror.

The relationship of the coarse (one-speed)synchro output and the fine (10-speed) synchro

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output is shown in figure 3-9, view A. The shadedareas represent the area where control is switchedfrom the one-speed circuit to the 10-speed circuit.With the selector circuit shown, it is possible tohave a single ambiguous synchronizing point. Thispoint is at the 180-degree position of the one-speed(coarse) synchro. At this point, the one-speed(coarse) synchro and 10-speed (fine) shafts arenulled (but 180 degrees out of phase), and controlswitches to the one-speed circuit.

The false synchronization position iseliminated by driving the multiple-speed synchro

at any odd multiple of the one-speed synchro. Thephase relationship of a one-speed and seven-speedsystem is shown in figure 3-9, view B. Althoughthere is still a null of both synchros at the180-degree position of the one-speed synchro,their outputs are in phase. This position isunstable, and the servo will not remain at thispoint.

The system shown in figure 3-8 is not used inoperating equipment because of the load the relayplaces on the one-speed synchro. In actualpractice, an electronic circuit (operated by synchro

Figure 3-9.-Phase relationships of fine and coarse synchro voltages; (A) 1-speed and 10-speed: (B) 1-speed and 7-speed.


A3. The data transmission system measures the servo output,transmits or feedbacks the signal, compares input signal withfeedback, and transmits the differerrce signal to the servoamplifier.

A4. Electrical error detectors are either ac or dc devices, dependingon the requirements of the servo system.

A5. Potentiometer error detector systems are used where the inputand output of a servomechanism has limited motion. Thesesystems have the following advantages:

a. High accuracy.b. Small size.c. Either a dc or ac voltage may be obtained as the output.

A6. The E-transformer is a type of magnetic device that is used asan error detector in systems that do not require the error detectorto move through large angles.

A7. A negative ac signal does not exist; but, negative values can beindicated by a change in phase of the ac signal.

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voltages) could use and control the relays.However, the outputs of the synchros are fed toan electronic circuit biased so that the fine synchrovoltage is not used when the coarse synchrovoltage is high. This method does not require arelay.

The disadvantage of the multiple-speed errordetector is the need for an additional synchrosystem and switching circuit to avoid falsesynchronization. The increased servo accuracythat results from amplifying the error signal andthe effective reduction of the inherent synchroerrors accounts for use of multiple-speed datatransmission systems.

SERVO CONTROL AMPLIFIERS

Earlier, you learned that the output of an errordetector (error voltage) is fed to a servo controlamplifier. This signal is small in amplitude andrequires amplification to actuate a prime mover.In addition to amplification, the servo controlamplifier might transfer the error signal intosuitable form for controlling the servomotor oroutput member. It may also have the specialcharacteristics needed to obtain a stable, fast, andaccurate operation.

Electronic and magnetic servo amplifiers areused in aircraft weapons systems. The operationof electronic amplifiers and their circuits iscovered in NEETS, module 8, NAVEDTRA14180.

Servo amplifiers have the basic characteristicsof amplifiers. They also have the following neededcriteria:

A flat gain versus frequency response fora frequency well beyond the frequencyrange used

A minimum of phase shift with a changein level of input signal (zero phase shift isdesired, but a small amount can betolerated, if constant)

A low output impedance

A low noise level

Servo amplifiers use either ac or dc amplifiers,or a combination of both. The application of dcamplifiers is limited by problems such as drift andprovisions for special bias voltages needed incascaded states. Drift, a variation in outputvoltage with no change in input voltage, is causedby a change in supply voltage or a change in valueof a component. Therefore, many servo amplifiersuse ac amplifiers for voltage amplification.

MODULATORS

Ac amplifiers amplify error signals better thandc amplifiers. They do not need well-regulatedpower supplies and costly precision components.But, some aircraft weapons systems do use a dcvoltage for an error signal. The dc error voltageis changed to an ac signal by a modulator(sometimes called a chopper). Modulator circuitsused in servo control amplifiers are phasesensitive. They produce an ac output signal whoseamplitude is proportional to the dc input signal,and their phase indicates polarity.

Vibrator Modulators

A modulator is either an electromechanicalvibrator (fig. 3-10) or an electronic circuit. An ac

Figure 3-10.-A vibrator modulator.

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supply voltage is used to vibrate the contacts ofthe vibrator in synchronism with the supplyvoltage. The dc error voltage is applied to thecenter contact. The reference voltage causes thecenter arm to contact point A during the first halfcycle and point B during the second half cycle.Then, the output is shown by waveform B if theerror voltage is positive, and by waveform C whenthe error voltage is negative.

Electronic Modulator

The electronic modulator circuit (fig. 3-11) isa diode-ring modulator. It works by causing achanging current to flow through one-half of theprimary transformer (T2) and then through theother half at a rate of 400 hertz. Each half cycleof changing current produces a half cycle ofsinusoidal output voltage. The phase of the outputvoltage compared to the 400-hertz carrier dependson the direction of current through each primaryhalf.

When the dc control voltage is positive, diodesCR1 and CR4 are forward biased. When the dccontrol voltage is negative, diodes CR2 and CR3are forward biased. Therefore, when two of thediodes are forward biased by the dc controlvoltage, the other two are reverse biased and cutoff. As long as the instantaneous amplitude ofthe carrier voltage is less than the dc controlvoltage, the cutoff diodes remain reverse biased.The current flows through one of the conductingdiodes and through one of the half windings.

Figure 3-11.-An electronic mudulator.

If the amplitude of carrier voltage exceeds thedc control voltage, one of the reverse-biaseddiodes becomes forward biased, and the diodeconducts. This interrupts the current flowingthrough the half winding, and the output voltageamplitude is clipped at the value it had when thecurrent was interrupted.

The capacitor connected across the primaryof T2 filters any high-frequency componentsassociated with the clipped half-cycle of the sinewave so that a nearly sinusoidal output half cycleoccurs. The output’s amplitude is nearly equal tothe output voltage at the time of clipping.

The capacitor operates by coupling the high-frequency components of the clipped voltagethrough the nonconducting half windings. Thehigh-frequency components are canceled becausethey produce currents that flow in oppositedirections in both halves of the center-tappedprimary windings; they produce magnetic fieldsthat cancel each other.

The amplitude of each half cycle of the400-hertz carrier voltage is modulated by the dccontrol voltage. The polarity of the controlvoltage determines the phase of the modulatedcarrier voltage output relative to the unmodulatedcarrier voltage input. This is the result of thedirection of current flow through the halfwinding. The direction depends on which diodeis forward biased as a result of the polarity of thedc control voltage.

Q8.

Q9.

Q10.

Q11.

The static accuracy of a servomechanismis limited by

List the basic components of a dual-speeddata transmission system.

S e r v o a m p l i f i e r s h a v e t h e b a s i ccharacteristics of amplifiers. They also meetwhat additional criteria?

What are the two types of modulators usedin servo control amplifiers? Describe theirfunction.

PHASE DETECTORS

You have learned that an ac amplifier hasadvantages over a dc amplifier, a dc error voltagecan be changed into an ac signal, and the ac signalcan be amplified and applied to an ac servomotor.Some systems, however, use dc servomotors,which require the ac signal be converted to dc.To do this, a phase detector (sometimes knownas a demodulator) is used.

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Bridge Phase Detectors

Look at figure 3-12 as you read this section.It shows a phase detector using a bridge circuit.With no error input signal and only the referencevoltage applied, CR1 and CR2 conduct in serieswhen point C is on its positive half cycle. Whenpoint C is on its negative half cycle, CR3 and CR4conduct in series. If the drops across the diodesand resistances are equal, points A and B are atground potential on both half cycles, and theoutput voltage is zero.

An error signal is applied to the bridge inphase with the referenced voltage, and points Aand C are both on their positive half cycles.Electron flow is from point G on the referencetransformer T2 to point D, through CR2 to pointA, from point A to the center tap on T1, and toE through to G. On the next half cycle, bothpoints A and C change polarity, and the electronflow is from point G to point C, through CR3to point B, through T1 to the center tap, to theright to point E, and through to ground,developing a negative dc output voltage.

If the error signal is applied out of phase withthe reference voltage and positive at points A andD, electron flow is from point G up through The flow continues left to the center tap of T1,down to point B, through CR4, down to pointD, and left to point G. On the next half cycle,both points A and D change polarity. Therefore,electron flow is from G up through to thecenter tap of T1, up to point A, through CR1 topoint C, and right to the center tap to point G.On both half cycles of the error and referencevoltages, electron flow is up through developing a positive voltage output at point E.In both cases, the magnitude of the dc producedat point E depends on the amplitude of the acerror signal. The polarity of the dc signal dependson the phase of the ac error signal. filters thepulses and provides smooth dc.

Triode Phase Detectors

A triode phase detector (fig. 3-13) uses NPNtransistors and provides amplification of the errorsignal in addition to phase detection. In thiscircuit, the collectors of the transistors aresupplied with the ac reference voltage so that thecollector voltages are in phase. In this explanation,no error signal is present at T2. When thecollectors of Q1 and Q2 are positive, the twotransistors conduct equally. The collector currentthat flows sets up magnetic fields in the dc motor

Figure 3-12.-Bridge phase detector.

Figure 3-13.-Triode phase detector.

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exciter windings that are equal and opposite;therefore, the fields cancel and produce no output.When the collector voltages are on a negativehalf cycle, C1 and C2 discharge through theirrespective exciter windings to maintain a constantdc through the windings.

An error signal is introduced into the primaryof T2 with a phase relationship that causes thebase of Q1 to be positive at the same instant thatthe collector of Q2 is positive. When this occurs,the following conditions exist:

On this half cycle, the conduction of Q1is increased above its no-error-signal condition.

The heavier collector current causes astronger field to be created in the upper exciterwinding.

At this same instant, the base of Q2 is ona negative half cycle, and its average conductionis reduced to a level below that of its no-error-signal condition.

The lower level of collector current causesa weaker field to be produced in the lower exciterwinding.

Since the magnetic fields produced in theexciter windings are no longer of equal amplitude,they no longer cancel each other.

The exciter produces an output voltage ofa polarity controlled by the polarity of theresultant field and of an amplitude controlled bythe relative strength of this resultant field.

The exciter output causes the propermechanical actions necessary to reduce theamplitude of the error to zero.

As the error signal is reduced to zero, thecurrent conduction through Q1 and Q2 is againbalanced. Also, the exciter fields are equaland opposite, canceling each other, reducingthe exciter output to zero, and stopping themechanical action. Resistors R1 and R2 preventexcessive base current when the error angle islarge.

SPECIAL AMPLIFIER CIRCUITS

You have already learned how a servo controlamplifier can change a dc error signal to an acsignal. You have also learned that an ac error


A8. The static accuracy (accuracy of load control) of aservomechanism is limited by the accuracy of the datatransmission system.

A9. Look at figure 3-8, which shows a diagram of a multiple- andone-speed system. This is called a dual-speed system because itcan transmit data at two different speeds.

A10. Servo amplifiers have the following criteria:

a. A flat gain versus frequency response for a frequency wellbeyond the frequency range used.

b. A minimum of phase shift with a change in level of inputsignal (zero phase shift is desired, but a small amount canbe tolerated, if constant).

c. A low output impedance.d. A low noise level.

A11. A modulator is either an electromechanical vibrator or anelectronic circuit used to convert a dc error voltage to an ac signal,whose amplitude is proportional to the dc input signal, and whosephase indicates polarity.

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signal may be detected to supply a dc voltage toa servomotor or controller. In the followingparagraphs, you will learn about other specialamplifier circuits.

Two-Stage DC Servo Control Amplifier

If more power is required by the servomotorthan the servo amplifier (fig. 3-14) can supply,a push-pull dc amplifier is inserted between thephase-sensitive transistors and the servomotor.Refer to the schematic diagram shown in figure3-14. The output of the phase detector transistorsis now taken across the parallel RC networks inthe collector circuit.

The bias source (Ecc) for the dc amplifier isconnected with its positive terminal on the baseside. This positive voltage subtracts from thehighly negative voltage across the capacitor. Anegative voltage results that allows the transistorto operate on the l inear portion of itscharacteristic curve.

When there is no signal input from the errordetector, the collector currents of the phase-sensitive rectifiers are equal. The outputs of Q1and Q2 are applied to the base of Q3 and Q4,respectively. Equal output from Q1 and Q2 causesequal currents to flow in Q3 and Q4. With R5 andR6 equal in resistance and current, the voltageacross the motor is zero. Consequently, the motordoes not turn.

Now, you are going to analyze a signal outputfrom the error detector. Assume that the errorsignal makes the base of Q1 positive and the baseof Q2 negative. The collector current of Q1increases, and the collector current of Q2decreases. An increasing collector current in Q1increases the charge on capacitor C1. Conversely,

a decreasing collector current in Q2 decreases thecharge on capacitor C2. As a result of the changein error signal, the voltage on the base of Q3 isnow more negative that the voltage on the baseof Q4. This increased negative voltage on the baseof Q3 decreases its collector current, and thevoltage e3 decreases. The decreased negativevoltage on the base of Q4 increases its collectorcurrent, and the voltage e4 increases. As a result,a voltage difference appears across the motorarmature, and the motor rotates. When the outputsignal from the error detector reverses in phase,the sequence of events causes the motor to reverseits direction of rotation.

Magnetic Amplifiers as ServoControl Amplifiers

The servomotor used with the magneticamplifier (fig. 3-15) is of an ac type. The

Figure 3-15.-Magnetic amplifier servo control amplifier.

Figure 3-14.-Two-stage dc servo control amplifier.

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uncontrolled phase is connected in parallelwith transformer T1 by using a phase-shiftingcapacitor, or it is connected to a different phaseof a multiphase system. The controlled phase isenergized by the magnetic amplifier, and its phaserelationship is determined by the polarity of thedc error voltage.

The magnetic amplifier consists of a trans-former (T1) and two saturable reactors, eachhaving three windings. Note that the dc biascurrent flows through a winding of each reactor,and the windings are connected in series aiding.This bias current is supplied by a dc bias powersource. A dc error current also flows through awinding in each reactor; however, these windingsare connected in series opposing.

The reactors Z1 and Z2 are equally andpartially saturated by the dc bias current when nodc error signal is applied. The reactance of Z1 andZ2 are now equal, resulting in points B and Dbeing at equal potential. There is no current flowthrough the controlled phase winding.

If an error signal is applied causing the currentto further saturate Z2, the reactance of its acwinding is decreased. This current through Z1tends to cancel the effect of the dc bias currentand increase the reactance of its ac winding.Within the operating limits of the circuit, thechange in reactance is proportional to theamplitude of the error signal. Hence, point D isnow effectively connected to point C, causingmotor rotation. Reversing the polarity of the errorsignal causes the direction of rotation to reversesince point D is effectively connected to point A.

The basic magnetic servo amplifier discussedabove has a response of approximately 6 to 20hertz. In some applications, this delay is excessive,creating too much error. This error is reduced toabout 1 hertz by use of special push-pull circuits.

Amplifier Integrator

A servo system in a steady-state condition willhave a constant positional displacement betweeninput and output, which is called the error. Theonly way to reduce this error is to increase thedrive torque. Therefore, a new signal is introducedthat is related to the error. The error isnot changing; it isn’t a derivative signal orproportional to the error. If it were, it woulddecrease as the error decreases, and a newcondition would be met without removing theerror. The only way to reduce the error is toproduce a signal proportional to the integral ofthe error. Then, if a torque proportional to the

time integral of the error is added to the normaltorque that is proportional to the error, the erroris eventually reduced to zero. An amplifierintegrator circuit is used for this purpose.

A simple and commonly used integrator(fig, 3-16) consists of two circuit elements—aresistor and a capacitor. The voltage across thecapacitor is proportional to the integral of thecharging current. The formula to find the voltageacross a capacitor is

For any given capacitor (C), the voltage dependsdirectly on the charge (Q), which is the imbalanceof electrons on the two capacitor plates. Theamount of the charge depends on the current flowand the time that the flow exists.

Because the voltage is proportional to theintegral of the charging current, the RC circuitcan be used as an integrator. The capacitor voltageis the integrator output. A charging current mustbe supplied that is proportional to the inputinformation. The resistor is used to produce theproportional current from an input signal voltage

At the instant this voltage is applied, thecurrent becomes

This condition, unfortunately, does notcontinue. As the capacitor becomes charged, thecapacitor voltage opposes the charging current.This makes the charging current less proportionalto the input signal, which results in an error inthe output. The ideal output, for a constant inputsignal, is a steadily increasing output. This steadyincrease is attained only when the signal voltageis first applied, and the capacitor is notappreciably charged.

Figure 3-16.-Simple integrator.

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One way to fix this error in the RC integratoris to use a circuit with a long-time constant. Thistype of circuit delays the charging of the capacitor,which results in a more accurate integration ofan input signal. The ideal output is a perfecttriangular wave. Although a long-time constantproduces more accurate results, it also providesa much lower output for the same input signal.Better integration is possible by using a high-gain,feedback amplifier.

An amplifier integrator is shown in figure3-17. This circuit arrangement has a high-gainamplifier known as the Miller integrator. Theamplifier produces an output that is not limitedby the input signal. Also, the amplifier suppliesany energy that is required in the output. Thefunction of the input signal is to control thecharging current.

The operation can be explained if you makethe following assumptions:

There is a constant input, as shown infigure 3-17, view A.

At the start, the initial condition is

The capacitor is discharged.

Figure 3-17.-Amplifier integrator.

The positive voltage to be integrated isapplied. The capacitor charges with a polarity asshown, since electrons are attracted from the leftplate. The charging path is shown in figure 3-17,view B.

A voltage measured at the amplifier input tends to rise in the positive direction since thispoint is directly coupled to However, this risetends to be opposed by the degenerative feedbackvoltage from the output. The output will be

where A stands for the amplifier gain.The minus sign indicates that the output polarityor phase is opposite to the input. The outputchanges A times faster or steeper than Theoutput voltage is negative and helps charge thecapacitor.

For a certain input voltage, the chargingcurrent is limited to a particular value that tendsto keep practically zero. If the current exceedsthis value, decreases a small amount becauseof the increased voltage drop across R. The decreases, and the charging current decreases tothe original value. If the initial charging currentdecreases, the opposite action occurs. Therefore,the value of the charging current is stabilized toa specific value proportional to the input voltage.This eliminates the error caused by and thecharging current does not remain proportional inthe fundamental RC integrator.

The constant charging current must beproduced by despite the fact that the steadilyincreasing capacitor voltage opposes the chargingcurrent. To do this, must steadily increase. Thissteady increase in is exactly the integratoroutput voltage desired for a constant signal input.Similar action is produced for a condition wherethe input signal suddenly becomes negative.Polarities are the reverse of those described in theabove paragraph.

Remember, simple examples are used forexplanation. The desired result is produced fora more complicated signal input. If wereremoved, little or no effect would be producedon the output that existed at that instant, sincethe amplifier output would oppose the tendencyfor the capacitor to discharge.

The limits for are determined by theamplifier and not by or the range of Theoutput range is designed to produce an increasingoutput for any probable input amplitude andperiod of application. The exception to this is anintegrator designed to function as a limiter.

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Q12. What is the purpose of phase detectors?

Q13. A simple and commonly used integratorconsists of what two circuit elements?

OUTPUT DEVICES

The output of the servo control amplifier isfed to an output device. This device suppliestorque, power, and dynamic characteristicsneeded to position the servo load. Ideally, thepower device requires small power from thecontrol amplifier, accelerates rapidly, is small andlight, lasts, has small time lags, and has anadequate speed range. In aircraft weaponssystems, the electric motor is often used as anoutput device. However electromagnetic clutches,hydraulic devices, and pneumatic devices are alsoused.

Electric Motors

Electric motors are used to drive the servo loadin aircraft weapons systems. The type of electricmotor used in a particular piece of equipment isdetermined by the following power factors—typeof power available, output power, speed range,inertia, and electrical noise.

ALTERNATING-CURRENT MOTORS.—Alternating-current motors are used in low-powerservo applications. They are simple and reliable.The commutator’s don’t spark, and they respondrapidly. Their disadvantage is their narrow speedrange. For the theory of operation of acmotors, you should refer to NEETS, module 5,NAVEDTRA 14177.

The two-phase induction motor is a widelyused ac servomotor. The stator of the motorconsists of two similar windings positioned at rightangles to each other. The rotor is wound withshort-circuited turns of wire, or it is a squirrel-cage rotor. The squirrel-cage rotor is the typemore frequently used. It is made up of heavyconducting bars that are set into armature slots,and the bars are shorted by conducting rings atthe ends.

The ac voltages applied to the two statorwindings must be 90 degrees out of phase to causethe rotor to turn. The direction of rotation isdetermined by the phase relationship of the statorwindings, which is determined by the servo errordetector. One phase is connected directly to oneof the stator windings. The other phase is usedto energize an error detector. The resulting error

voltage is either in phase or 180 degrees out ofphase with the signal applied to the error detector.This causes the controlled phase to either lead orlag the uncontrolled phase by 90 degrees.

Most induction motors have low startingtorque and high torque at high speed. For servoapplications, high starting torque is needed forthe system to have a low time lag. This may bedone by increasing the armature resistance withthe use of material such as zinc for the conductingbars. The increased torque at low speed resultsin decreased torque at high speed. However,increased stability of the servo system is adesirable result of the change.

Split-phase ac motors are similar to the two-phase induction motor. The difference is thephase-shifting network used to shift the phase ofthe voltage supplied to one of the windings by 90degrees. This is usually done by connecting acapacitor in series with the uncontrolled windingof the stator. Direction of rotation and reversalis accomplished in the same way as in the two-phase motor.

Other types of ac motors may be used withan ac power supply, including the shaded pole,universal, and repulsion motors. Many methodsof getting rotation reversal are used in thesemotors. However, they are not normally foundin aircraft weapons systems.

DIRECT-CURRENT MOTORS.— Direct-current motors have the following advantagesover ac motors—higher starting torque, reversingtorque, and less weight for equal power.

Series motors are characterized by their highstarting torque and poor speed regulation with achange in torque. Higher torque is obtained onreversal of direction with a series motor. However,it is a unidirectional motor and requires specialswitching circuits to get bidirectional charac-teristics. This is normally done by switching eitherthe armature or field connections, but not both.

The split-series motor is a variation of theseries motor that has bidirectional characteristics.The motor has two field windings on its frame,but only one is used for each direction of rotation.This reduces the number of relay contacts neededfor reversing by one-half. This double windingreduces the torque capabilities of the motor ascompared to a straight-series motor wound on thesame frame.

The most frequently used dc servomotor is theshunt motor. Its direction of motion is controlledby varying the direction of flow of either the

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armature or field current. The uncontrolledcurrent is usually maintained constant to preservea linear relationship between the motor outputtorque and the voltage or current input. Usually,the field windings are two diffentially wound coilsthat make it easier for the servo control amplifierto control the direction of the field current. Thefield current is usually controlled with receiving-type vacuum tubes. The larger armature currentsrequire thyratrons or generators as currentregulators, but they are not normally found inaircraft weapons systems.

Magnetic Clutches

Any device that uses an electrical signal tocontrol the coupling of torque from an input shaftto an output shaft is a magnetic clutch. Thiscoupling is accomplished by the contact betweenfriction surfaces or by the action of one or moremagnetic fields. A magnetic clutch is used onlyto couple the input torque to the output shaft.This makes it capable of controlling large amountsof power and torque when compared to its sizeand weight. The magnetic clutch is used with alarge flywheel driven at high speed by a smallmotor. This allows the flywheel to give very largeacceleration to the load when the magnetic clutchis energized.

There are two distinct types of magneticclutches. Some transmit torque by physicalcontract of frictional surfaces. Others use theaction of magnetic flux produced by two sets ofcoils, or one set of coils and induced eddy currentsthat result from rotating the one set of coils neara conducting surface. The eddy current type ofclutch offers smoother operation and has nowear problem due to friction. Both types havesuitable control characteristics and are found inservomechanisms.

Hydraulic Devices

Hydraulic components used in servo-mechanisms are frequently found in aircraftweapons systems. Hydraulic power devices, suchas motors and associated control valves, have anadvantage of a response that is much faster thanthe best electric motors and equal to that of amagnetic clutch system. They also require aminimum of maintenance, are accurate, and arewell adapted to heavy loads.

The following are the essential components ofa hydraulic system:

A source of high-pressure oil and a sumpto receive discharge oil

A control valve and means of using anactuating signal

An actuator (motor or cylinder)

NOTE: The theory of operation ofhydraulic systems is discussed in FluidPower, NAVEDTRA 14105 (series).

The source of high-pressure oil serves as asource of power to operate the actuator. However,this source is controlled by the control valve. Thevalve is actuated by the output from the servocontrol amplifier. This control is normallyaccomplished by feeding the error signal to asolenoid-controlled valve. The actuator is usuallyan axial motor that is reversible and of the variablespeed type. Some applications may use a cylinder,where linear motion is required for positioning.

Q14. The output of the servo control amplifieris fed to an output device to provide thetorque, power, and dynamic characteristicsneeded to position the servo load. List thesedevices and describe their function.

Q15. Why are alternating-current motorsfrequently used in low-power servo applica-tions?

Q16. Describe a magnetic clutch.

SERVOMECHANISM OSCILLATION

Learning Objectives: Describe servo-mechanism oscillation. Identify proceduresfor correction and control to includedamping, integral control, gain, phase, andbalance.

Servomechanisms are used in aircraft weaponssystems. They perform various functions andmeet certain performance requirements. Theserequirements involve speed of response andaccuracy and the way the system responds incarrying out its command functions. All systemscontain certain errors, the problem is to keep themwithin allowable limits.

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You already know that the servomotor mustdevelop sufficient torque and power to positionthe load in a minimum of time. The servomotorand its connected load have sufficient inertia todrive the load past the point of commandposition. This overshooting results in an oppositeerror voltage, reversing the direction of rotationof the servomotor and the load. Again, theservomotor tries to correct the error, and again,it overshoots the point of correspondence. Eachreversal requires less correction until the systemis in correspondence. The time required for theoscillations to die out determines the transientresponse of the system, and is reduced by usingdamping.

DAMPING

Damping reduces the amplitude and durationof oscillations that exist in a system. The simplestform of damping is viscous damping, which is theapplication of friction to the output load or shaftproportional to the output velocity. The amountof friction applied to the system is critical andmaterially affects the results of the system.When just enough friction is applied to preventovershoot, the system is critically damped. Whenthe friction is greater than needed for criticaldamping, the system is overdamped; whendamping is slightly less than critical, the systemis slightly underdamped. A slightly underdamped

system is usually the desired condition. Theapplication of friction absorbs power from themotor, which is dissipated in the form of heat.

A pure, viscous damper would absorb anexcessive amount of power from the system. Asystem that has some of the characteristics of aviscous damper with somewhat less power loss isactually used. Two types of systems are discussedin this section—a dry friction clutch to couple aweighted flywheel to the output drive shaft andan eddy current damper.

Remember, the damper using a dry frictionclutch coupled to a weighted flywheel to theoutput drive shaft has somewhat less power lossthan a pure, viscous damper. A flywheel has theproperty of inertia. But, since the flywheel iscoupled to the output shaft with a friction clutch,any rapid change in velocity of the output membercauses the clutch to slip. This effectively dis-connects the flywheel instantaneously, yetallows sufficient power to be coupled to theflywheel to overcome its inertia. As the inertia isgradually overcome, the flywheel gains speed andapproaches the velocity of the output member.As the point of correspondence is neared and theerror signal is reduced, the inertia of the flywheelgives up power to the system. This causes the loadto increase its overshoot. When the system triesto correct for the overshoot, the inertia of theflywheel adds to the output load, reducing theeffect of the correcting signal. The effect dampens


A12. Some systems use dc servomotors, which require the ac signalbe converted to dc. To do this, a phase detector (sometimesknown as a demodulator) is used.

A13. A simple integrator circuit consists of a resistor and a capacitor,as shown in figure 3-16.

A14. Electric motors drive the servo load in aircraft weapons systems;magnetic clutches couple input torque to the output shaft;and hydraulic components are much faster than the bestelectric motors and equal to that of a magnetic clutchsystem.

A15. They are simple, reliable, have no commutator sparking, andprovide rapid response.

A16. Any device that uses an electrical signal to control the couplingof torque from an input shaft to an output shaft.

3-18

the oscillations in the system, reducing its transittime.

The eddy current damper uses the interactionof induced eddy currents and a permanent magnetfield to couple the output shaft to a weightedflywheel. Look at figure 3-18. The solid line showsthe action of the load without damping. Note thetime required to reach a steady-state conditionwithout damping. With damping, this time isreduced, although the initial overshoot isincreased. You can also see that a viscousdamper effectively reduces transient oscillations,but it produces an undesired steady-stateerror.

How well the load is controlled is a measureof the steady-state performance of a servo system.If the load is moved to an exact given position,then the servo system has a perfect steady-stateperformance. If the load is not moved to the exactposition, then the system is not perfect, and thedifference in error is known as the steady-stateerror. Steady-state error is either one or both ofthe following—a velocity lag or a position error.Velocity error is the steady-state error due toviscous drag during velocity operation. Positionerror is the difference in position between the loadand the position order given to the servo system.Since the friction damper absorbs power from thesystem, its use is normally limited to smallservomechanisms.

Error-rate damping overcomes the disad-vantages of viscous dampers. Error-rate dampingworks by introducing a voltage that is propor-tional to the rate of change of the error signal.The voltage is fed to the servo control amplifierand combined with the error signal.

Look at figure 3-19. You can see theeffect of error-rate damping on the torqueoutput of the servomotor. Curve A shows thetorque that results from the error voltage; curveB shows the torque that results from theerror-rate damper; and curve C shows theresultant of curves A and B.

You should note that the torque that resultsfrom the damper increases the total torque as longas the error component is increasing. Once theerror component starts to decrease, the error-ratedamper produces a torque in an oppositedirection. This reduces the transit time of thesystem.

Figure 3-18.-Effect of friction damper.

Figure 3-19.-Torque variations using error-rate damping.

3-19

Normally, two methods are used to generatean error-rate voltage in aircraft weaponssystems—the tachometer and electrical net-works.

The tachometer error-rate damper isessentially a generator, which has an outputvoltage proportional to its shaft speed. Thetachometer is connected to the shaft of the outputmember, giving a voltage proportional to itsspeed. Look at figure 3-20. Here, you can see thatthe output voltage is fed to a network thatmodifies this voltage so it is proportional to achange in input voltage. The voltage is fed backto the servo control amplifier and added with theerror signal.

Electrical networks used for error-ratedamping are a combination of resistors andcapacitors used to form an RC differentiatingnetwork. These networks, sometimes referred toas phase advance or lead networks, vary in design,depending on the type of error signal.

NOTE: For a detailed explanation of RCcircuits, refer to Navy Electricity and ElectronicsTraining Series (NEETS), module 2, NAVED-TRA 14174.

In practice, networks are limited to the dc type(fig. 3-20) because a small change in frequencyof the power source causes unstable results. A dcnetwork may be used in an ac system through theuse of a demodulator (detector) before thenetwork. However, the output of the networkmust be modulated for use in the remainder ofthe ac system. Like the tachometer, the outputof the network is fed to the servo controlamplifier.

INTEGRAL CONTROL

Servomechanisms used in aircraft weaponssystems are sometimes required to follow an inputfunction whose magnitude changes at a constantrate with time. The antenna system tracking atarget is such a system. If the input is the angleof a shaft, the velocity of the shaft is constantfor a substantial percentage of time. Theservomechanism is required to respond to this typeof input with substantially zero error. The errorthat characterizes the servo response to a constantvelocity input is known as the velocity error.

An integral control is used to correct a velocityerror or an inaccuracy due to a steady-state error.The integral control modifies the error voltage sothe signal fed to the servo control amplifier is afunction of both the amplitude and time durationof the error signal. A variable voltage divider isused to do this because its output increases withtime for a constant input. As in all voltagedividers, the output is the only portion of the inputthat effectively reduces the amplitude of the errorsignal. To compensate for the loss of amplitude,additional amplification is used, either in the formof a preamplifier or a higher gain servo controlamplifier. When the overall gain of the system isincreased to give a normal output for transienterror signals, small velocity or steady-state errorsignals of long duration result in an increasedoutput to the servomotor because of the actionof the integral control.

The integral control (fig. 3-21) consists of acombination of resistors and capacitors connectedto make an integrator circuit for a dc error signal.The value of the components is such that thecapacitor does not have sufficient time to changewith fluctuations in error voltage. Only thatportion of the transient error signal developedacross R1 is impressed on the amplifier. But, ifthere is a velocity error or steady-state error oflonger duration, the capacitor (C1) charges. Thisincreases the amplitude of the amplifier input.

Figure 3-20.-Error-rate stabilization network. Figure 3-21.-Integral stabilization network.

3-20

Networks shown in figure 2-21 are not limited todc systems. A demodulator may be used beforethe integrator, and its output modulated for easieramplification.

GAIN, PHASE, AND BALANCE

The overall system gain has an importanteffect on the servomechanism response charac-teristics. It is one of the more easily adjustableparameters in electronics servo controllers.Increasing the system gain reduces the systemvelocity errors and steady-state errors that resultfrom restraining torques on the servo load ormisalignment in the system. An increase in systemgain increases the speed of response to transientinputs. However, excessive gain always decreasesthe rate at which oscillatory transients disappear.Continued increase in the system gain producesinstability.

Servo systems using push-pull amplifiers mustbe balanced to ensure equal torque in bothdirections of the servomotor. You should checkthis adjustment periodically because a change inthe value of a component causes an unbalancedoutput. You balance it by adjusting the systemfor zero output with no signal applied.

A phase control is included in some servosystems using ac motors. The two windings of theac servomotor are energized by ac signals that are90 degrees apart. A phasing adjustment isnormally included in the system to compensatefor any phase shift in the amplifier circuit. (Anuncorrected phase shift causes unstable operation

of the system.) This adjustment may be locatedin the control amplifier or, in the case of asplit-phase motor, it may be in the uncontrolledwinding.

Q17.

Q18.

Q19.

Q20.

Q21.

Q22.

Describe servomechanism oscillation.

Name the level of damping that is thedesired condition.

A servo system has a perfect steady-stateperformance. What is meant by thisstatement?

Normally, what two methods are used togenerate an error-rate voltage in aircraftweapon systems?

Describe the purpose of an integral control.

What is the effect of increasing system gainon servomechanism response characteristics?

ZEROING SYNCHRO UNITS

Learning Objective: Recognize zeroingprocedures for synchro and servo systems.

So far, you have learned that it is importantfor servo systems to be accurate. In any servo-mechanism using synchro units, it is importantthat the units are zeroed electrically. As you readthe rest of this section, refer to figure 3-22.

I

Figure 3-22.-Synchro electrical zero positions.

3-21

Look at figure 3-22, view A. For a synchrotransmitter or receiver to be in a position ofelectrical zero, the following conditions must bemet:

The rotor must be aligned with S2.

The voltage between S1 and S3 must bezero.

The phase of the voltage at S2 must be thesame as the phase of the voltage at R1.

The most common methods of zeroingsynchro transmitters and receivers are the Figure 3-23.-Electrical lock method of zeroing a synchro.electrical lock and ac voltmeter methods. Themethod used to zero a synchro depends on howthe synchro is used. positions itself in the zero position. After the

The electrical lock method is used if the rotor synchro is zeroed, the pointer is adjusted tois free to turn. This is done by connecting S1 and indicate zero.S3 to R2 using a jumper wire and connecting S2 The majority of synchros used in aviationto R1 (fig. 3-23). When power is applied, the rotor weapons systems have their rotor gears driven or


A17. The servomotor and load have sufficient inertia to drive the loadpast the point of command resulting in overshoot and an oppositeerror voltage that reverses the direction, again overshooting thepoint of correspondence. Each reversal requires less correctionuntil the system is in correspondence.

A18. The desired level of damping is slightly underdamped.

A19. How well the load is controlled is a measure of the steady-stateperformance of a servo system. If the load is moved to an exactposition, the servo system has a perfect steady-state performance.

A20. The tachometer and electrical networks. The tachometer error-rate damper is essentially a generator having an output voltageproportional to its shaft speed, and the electrical networks area combination of resistors and capacitors used to form an RCdifferentiating net work.

A21. Integral control corrects a velocity error or an inaccuracy causedby a steady-state error.

A22. Increasing system gain reduces the system velocity errors andthose steady-state errors that result from restraining torques onthe servo load or misalignment in the system. Also, it increasesthe speed of response to transient inputs and decreases the rateat which oscillatory transients disappear. Continued increase insystem gain produces instability.

3-22

mechanically coupled to a driving member. Inthese cases, the ac voltmeter method is used tozero the synchro. The synchro is zeroed byrotating the stator or housing until its electricalzero is reached. Before zeroing the synchro, youmust set the mechanical unit that positions thesynchro to its indexing or zeroing position. To dothis, align the unit to this index, and install itsindexing pins in the holes that are provided. Thepoints hold the unit to its index and keep it frommoving.

The ac voltmeter method is used to zero thesynchro by connecting the meter and jumper wires(fig. 3-24, view A). Rotate the energized synchrountil a zero reading is obtained on the voltmeter.Since rotor positions of 0 and 180 degrees producethe zero reading, you must determine if the phaseof S2 is the same as R1. Make the connectionsshown in figure 3-24, view B. If the properpolarity relationship exists, the voltmeter indicatesless than the excitation voltage being applied to

Figure 3-24.-Ac voltmeter method of electrically zeroingsynchro receiver or transmitter.

the rotor. If the indication is greater than the rotorexcitation voltage, the rotor or stator must berotated 180 degrees and the previous stepperformed again.

DIFFERENTIAL TRANSMITTER

When the three windings of the rotor are incorrespondence with their respective statorwindings and their respective voltages are inphase, the synchro differential transmitter orreceiver is in the electrical zero position (fig. 3-22,view B). The differential transmitter synchro isnormally used to insert a correction into a synchrosystem; therefore, it is usually driven eitherdirectly or through a gear train. Before you zerothe differential transmitter synchro, zero the unitwhose position the differential synchro transmitsfirst. After doing this, connect the differentialsynchro, as shown in figure 3-25, view A. Turnthe synchro in its mounting until the voltmetershows a minimum indication. Then, make theconnections shown in figure 3-25, view B.Again, turn the synchro slightly in its mountinguntil a minimum voltage is indicated by thevoltmeter.

DIFFERENTIAL RECEIVER

Look at figure 3-22, view B. It shows theelectrical zero for a differential receiver. To zeroa differential receiver synchro, you make the

Figure 3-25.-Electrically zeroing a differential transmitter.

3-23

connections shown in figure 3-26. As soon as thepower is applied to the synchro, the rotor assumesa position of electrical zero. Then, set the dial tozero, and reconnect the unit to the circuit.

CONTROL TRANSFORMER

The synchro control transformer is normallyzeroed by using the ac voltmeter method.Remember, the electrical zero position of thecontrol transformer is 90 degrees from that of areceiver. This must occur because the rotorwinding must be perpendicular to the stator’sresulting magnetic field to have a zero output (fig.3-22, view C). Make the coarse adjustment byconnecting the meter and unit as shown in figure3-27, view A. Rotate the rotor to give a minimumor null reading on the voltmeter. The finaladjustment is made when you connect the unit,as shown in figure 3-27, view B, and displace therotor a few degrees in both directions to determinethe null or electrical zero position. Once the zeroposition is determined, the unit is locked.

Now that you have a better understanding ofservo systems, you are ready to learn about analogcomputation and analog computer functions.

Q23.

Q24.

Q25.

Q26.

Q27.

What conditions must be met for a synchrotransmitter or receiver to be in a positionof electrical zero?

Name the most common methods used tozero synchros.

Under what condition should you use theelectrical lock method?

What action should you take before youzero the differential transmitter synchro?

How does the electrical zero position of acontrol transformer differ from that of areceiver?

Figure 3-26.-Electrically zeroing a differential synchroreceiver.

Figure 3-27.-Electrically zeroing a control transformersynchro.

COMPUTER CLASSIFICATION

Learning Objective: Recognize computerclassifications and identify various compu-tations of an analog computer.

Computers are classified as either digital oranalog. They are further classified by theirconstruction—electronic, electromechanical, ormechanical.

Electronic computers use electrical units, suchas resistance, electrical impulses, voltageamplitude and phase, and other electrical units,to represent physical quantities. Computers of thistype usually contain electronic and magneticamplifiers, phase detectors, modulators, anddemodulators.

Electromechanical computers representnumbers of variables in both electrical andmechanical units. A typical application may useboth electrical and mechanical inputs to aservomechanism, and may have a mechanicaloutput.

Mechanical computers use mechanicalquantities to represent the input and outputvalues. They normally contain devices that add,subtract, multiply, or divide by means of gearratios, shaft rotations, etc. Mechanical-computingdevices are discussed in Basic Machines,NAVEDTRA 14037.

Complex and accurate computers are used inaviation weapons systems. These computers arenot normally of any one type, but contain somefeatures of all types. Their classification is based

3-24

on the predominant type of computing devicefound in the equipment.

COMPUTATION PRINCIPLES

Learning Objective: Identify linear functionsof a computer and solve given mathematicalproblems.

An airborne analog computer must fulfill anumber of requirements, including the following:

1. It must possess sufficient accuracy to solvea problem within the required limits.

2. It must be constructed so that it canwithstand the stresses of airborne use and stillrequire a minimum of maintenance.

From the maintenance standpoint, the analogcomputer should use as many similar componentsas practical, keeping the number of spare partsto a minimum. This requires the rearrangementof equations from their simplest form to ones thatare more complicated. Many computers have beendesigned around equation rearrangement.

EQUATION REARRANGEMENT

The equation below represents a typicalproblem to be solved within a computer.

Where, the dependent variable J is a mathematicalquantity determined by the independent variableR (present range of airborne target), is the timeof flight of the projectile, and is the futurerange of the target. The quantity J has nosignificant meaning other than that it representsthe term

— in the above equation.

One method of solving this problem requires theuse of a servo system.

Remember, the operation of a servomechanismdepends on its ability to compare two quantitiesand feed an error signal to its output device. This,in turn, causes the error signal to be canceled. Theservo system gives a continuous solution to theproblem if the formula is rearranged to give a zero

output. By multiplying both sides of the aboveequation by

and transposing, the equation can be written asfollows:

Another example of equation rearrangementinvolves the use of logarithms. A computerproblem may involve the multiplication anddivision of several quantities. Refer again to theequation

It can be arranged as follows:

= + –

The logarithm of each quantity is foundelectronically by using specially designednetworks. When the equation has been changedinto the logarithmic form, the computation isdone by simplified addition and subtraction of thequantities. Magnetic amplifiers are suited forsolutions of this type.

Frequently, the results of logarithmic compu-tation are used in the logarithmic form. However,the antilogarithm is also found by using a networkgiving an answer to the problem in the same formin which it was originally stated.

IMPLICIT SOLUTION

The use of computers to solve complexproblems does not always afford a direct solutionto all parts of the problem. Thus, the solution maybe based on indirect or implicit methods.

Implicit problem solving may accomplishsubtraction by means of addition, division bymeans of multiplication, the extraction of a squareroot by means of squaring, and differentiationby means of integration. The following is a

3-25

comparison of explicit and implicit methods ofproblem solving:

EXPLICIT IMPLICIT

Subtraction . . . . c = a – b c + b = a

Square root . . . . c =

Division . . . . . .c = a/b c b = a

The implicit function technique is usedfrequently in airborne computers. Many times theimplicit method is more accurate or moreconvenient, based on the information availableto the computer. Servomechanisms and amplifiersthat use negative and positive feedback are wellsuited for implicit operations.

QUANTITY REPRESENTATION

Representation of quantity is that physicalquantity used by an analog computer to representa specific input quantity. For example, a specificquantity, such as the range from the gun platformto the target aircraft, is identified with a dc voltagefed to the analog computer for the solution of theproblem.

IDENTITY OPERATIONS

An identity operation is defined as a n y

quantity represented. Examples of identityoperations arc changes in scale factor, voltagelevel, and impedance.

Change in Scale Factor

In an analog computer, the scale factor is theratio of the analog unit to the equation unit, or

the scale factor =analog units

equation units (physical)

Any change in analog units without acorresponding change in equation units results ina change in scale factor. For example, a 10-voltpositive dc signal is selected to represent a rangeof 1,000 yards.

Scale factor =+10 volts

1,000 yards

= 0.01 volt per yard.

If the 10-volt signal is fed through a dc amplifierhaving a voltage gain of 10, the analog unit is nowequal to 100 volts. The scale factor is as follows:

Scale factor =+100 volts1,000 yards

= 0.1 volt per yard.

Therefore, the scale factor was changed by theoperation that does not change the mathematical action of the amplifier.


A23. Refer to figure 2-22. Conditions required for a synchro trans-mitter or receiver to be at electrical zero include the following:

a. Rotor aligned with S2.b. Voltage between S1 and S3 is zero.c. Phase of voltage at S2 must be same as that at R1.

A24. The ac voltmeter and the electrical lock methods are used to zerosynchros.

A25. Use the electrical lock method if the rotor is free to turn.

A26. You should zero the unit whose position the differential synchrotransmits first.

A27. The electrical zero position of the control transformer is 90 degreesfrom that of a receiver since the rotor winding must be perpendicularto the stators, resulting in a magnetic field having a zero output.

3-26

When the multiplier is less than one, simplenet works of resistance, capacitance, or inductanceare normally used. When the constant ofmultiplication is greater than one, amplifierswhose gain has been accurately calibrated areused.

Change of Voltage Level

Computers, such as those that use additionand subtraction, must frequently change or shiftthe voltage level or reference to a level that isusable by subsequent components or units. Anexample of a shift in voltage level is found in adirect-coupled amplifier, where the equipment islimited by the output of the dc supply for theamplifier.

Change of Impedance

A change in output impedance may berequired to match the various sections of acomputer. This may be accomplished by the useof networks and, in some cases, the use of cathodeor emitter followers or other amplifiers usingfeedback.

Q28.

Q29.

Q30.

Q31.

Q32.

Q33.

List the three construction classes of analogand digital computers.

The rearrangement of equations from theirsimplest form to more complex forms isrequired in computers from a maintenancestandpoint. What is the reason for thisrearrangement?

Solving a subtraction problem byaddition involves what technique?

Define quantity representation.

Define identity operations.

Determine the scale factor forsignal representing 300 yards.

using

a +15-volt

MATHEMATICAL FUNCTIONS

Learning Objective: Recognize linear andnonlinear functions of analog computers.

In this section of the TRAMAN, linear andnonlinear functions are discussed. The discussionincludes linear and nonlinear mathematical

functions as they are used as analog computationdevices.

LINEAR FUNCTIONS

Learning Objective: Identify summation,multiplication, and division as linearfunctions of analog computers.

In mathematics, a linear function is one thatcan be shown by a straight line on rectangularcoordinate graph paper. Linear functions includeoperations that involve summation (addition andsubtraction), multiplication, and division. Theydo not include operations involving squares,square roots, trigonometric functions, andlogarithms (nonlinear functions).

Summation

Summation is accomplished by using elec-trical, mechanical, or electromechanical devices.Voltages are added, motions are added, orvoltages and motions may be combined to givean output proportional to their input.

ELECTRICAL SUMMATION.— To simplifythe presentation, both electrical and electronicsumming devices are discussed under this heading.The first device is the series circuit in which theoutput voltage is the series addition of the inputvoltages E1 and E2.

(1)

Only one of the input voltages can be grounded.Any others must be isolated from ground. Thisis shown in figure 3-28. Note that the secondaryof the transformer is not grounded, while thevoltage E1 is from a grounded source. Isolating

Figure 3-28.-Series addition.

3-27

transformers must be carefully designed tominimize capacitive coupling from primary tosecondary winding, which would cause phase shiftvariations.

Series adding is used when voltage sources areinductive units (such as synchros, tachometers,and resolvers) already isolated from ground.Series summation is also used when the attenua-tion of parallel summation networks cannot betolerated.

When subtracting two ac voltages by theelectrical summation method, they should be180 degrees out of phase for correct results.Combining voltages that are not in phase or 180degrees out of phase results in a quadraturevoltage, causing an error in the output.

If dc voltages are to be added in series,transformers cannot be used. A separate dc powersupply is required for each term or input to obtainisolated sources of voltage.

A parallel resistance network can be used toelectrically produce the algebraic sum of severalinput voltages. Voltages E1 and E2 are connectedin series with two resistors R1 and R2 and

Figure 3-29.-Parallel summation network.

terminated at a common junction, as shown infigure 3-29. The voltage is not the actual sumof the input voltages, but is proportional to thatsum.

Using the values given in figure 3-29, you canprove that the output voltage is proportionalto the inputs. If the voltage feeds into aninfinite impedance, there is no load current. Thecircuit is now considered a series circuit. For more


A28. Computers are classified as either digital or analog. They arefurther classified by their construction, as electronic,electromechanical, or mechanical.

A29. Use of as many similar components as practical, keeping thenumber of spare parts to a minimum.

A30. Implicit problem solving allows using addition to accomplishsubtraction. For example,

Explicit Implicit

c = a – b c + b = a

The implicit function technique is used frequently in airbornecomputers.

A31. Quantity representation is that physical quantity used by ananalog computer to represent a specific input quantity, such asa dc voltage whose value represents a range.

A32. Identity operation is any operation that does not change themathematical quantity represented.

+15 voltsA33. Scale factor = 300 yards = .05 volt per yard.

3-28

information about electrical summation, youshould refer to Naval Electricity and ElectronicsTraining Series (NEETS), module 15, Principlesof Synchros, Servos, and Gyros, NAVEDTRA14187. Therefore,

I1 = 12. (2)

Then, since all branches are parallel,

E1 + I1R1 = E2 – I2R2 = (3)

Solving for the currents in each part of equation(3) and substituting the results into equation (2),

Solving equation (4) for

or, by further simplication,

(4)

(5)

(6)

Therefore, an expression for voltage wasobtained in terms of the sum of the two inputvoltages and their respective series resistors.

The voltage was obtained by assuming avery high-impedance load. If a grid resistor is included, the voltage is determined by

As you know, the voltage output is notthe actual sum of the input voltages, but isproportional to that sum. The following exampleillustrates this proportionality:

E1 = 50 volts E2 = 100 volts

R1 = 1 megohm R2 = 1 megohm

Then, using equation (5),

If were the actual sum of the input voltages,the voltage output would be 150 volts. However,this difference in actual sum and proportionalvoltage is compensated for by a change in scalefactor. When a difference between two terms isrequired (subtracted), a negative voltage is usedto represent the quantity being subtracted. Boththe negative and positive voltages are fed to theparallel resistance network.

Scale Factor.— Although addition is a sum-mation of voltages, the computer’s real job is toadd physical units, such as feet per second ordegrees per minute. The proper application ofscale factors makes the addition of the physicalunits of an equation possible. The followingtransformation formula is used for this purpose:

Equation units x scale factor = analog units.

When the physical inputs to the analogcomputer are represented by voltages, the finalsolution in the proper units is found by dividingthe summed voltages by the output scale factor.If the voltages E1 and E2 in figure 3-30 werechosen to represent 1,000 feet each, the scalefactor for the input voltages would be 1 volt per10 feet, and should be written as 1 volt/10 feet.

Figure 3-30.-Scale factors assigned tosummation networks.

parallel resistor

3-29

If the output physical units are to equal thesum of the input physical units, the scale factorat the output must be 1 volt/20 feet. Using thetransformation formula, you can find the sum ofthe physical units as follows:

2,000 feet x = 100 volts.

In the examples you have seen, the input scalefactors were identical. Consider the operation ofthe summing circuit (fig. 3-3 1) if the input scalefactors are different. In the equation,

= D1 + D2, D1 has a scale factor of 1 volt/10feet, and D2 is represented by the scale factor1 volt/5 feet. Since the physical units per volt ofthe scale factors must add directly, the outputscale factor is 1 volt/15 feet. This result isobtained in terms of units per volt (reciprocal ofscale factor) for the addition operation. Directaddition of the scale factors for D1 and D2 doesnot result in the desired addition of physical unitsbecause the scale factor definition places thephysical units in the denominator.

Look at figure 3-31. Here you can see that thecorrect answer for is 2,000 feet. If the analogunit at the output is known and the output scalefactor is known, what values of R1 and R2 supplythe answer? The analog unit is obtained bysubstituting in the following formula:

analog unit = equation unit x scale factor

= 2,000 feet x

= 133 volts.

Figure 3-31.-Addition with unequal scale factors.

Refer back to equation (6). You can see thatR1 cannot equal R2 as in the previous example.You can select one resistance value arbitrarily;consequently, R1 may be set equal to 100,000ohms, a typical value. Substituting known valuesin equation (6) and solving for R2

R2 = 200,000 ohms.

As an AT, you will not be expected to computecomponent sizes or scale factors. However, byunderstanding scale factors, you will understandwhat is done in each stage of a computer.

Electronic Amplifiers Used for Isolation.—In analog computers, it is not always possible toapply the output of parallel resistor summationnetworks directly to subsequent circuits withoutgetting nonlinear results because of loading.Loading is avoided by using an isolation amplifierwith a high-impedance input and a low-impedanceoutput between the summation network outputand the succeeding computer component.

Since the signal magnitude is the computedquantity, the gain of these isolation amplifiersmust be maintained quite accurately. The gain ofany amplifier, of course, is affected by such thingsas a weak tube or transistor, a shift in powersupply voltage, temperature changes, etc. The useof negative feedback is quite effective in solvingthis problem. Since a large amount of negativefeedback is required if the full advantage offeedback stabilization is to be obtained, high-gainamplifiers are needed in such circuits. The gainof the amplifier itself does not affect the overallcircuit gain because of the negative feedback.Figure 3-32 shows the basic circuit using anisolation amplifier.

Figure 3-32.-Basic isolation amplifier circuit.

3-30

As you read the rest of this section, refer tofigure 3-32. The amplifier output is fed back tothe summing point G at the input of the amplifierthrough the feedback resistance Since the gainof the amplifier is extremely high, the voltage

at the summing point G is nearly zero.(Remember that the value of any fraction whosedenominator is extremely large approaches zero.)Therefore, the current through is negligible.Assuming the amplifier input does not drawcurrent (normally a good assumption) and theamplifier gain is high (that is, 1/A is much lessthan 1), the current through equals minus thatthrough by Kirchhoff’s current law at point G,

This equation can be rearranged to obtain anexpression for gain as follows:

This is the basic equation that describes theoperation of any circuit having a high-gainamplifier with negative feedback. It is well worthr e m e m b e r i n g .

If = the circuit gain is unity, and thecircuit is effective as a precision isolation device.The loading that this circuit presents to its drivingcircuit is essentially since the voltage at pointG is essentially zero.

If the amplifier gain deteriorates with age,there is some point at which the approximateexpression for circuit gain no longer holds. Amore exact expression showing the effect ofamplifier gain is

You can use this equation to show that evenif the amplifier gain is designed to be only 100,a reduction in gain to about 50 percent is requiredto reduce the circuit gain by 1 percent.

Summing Amplifiers.— High-gain dc ampli-fiers are used in many applications where isolationcharacteristics are needed. A typical applicationis in summing circuits, where loading effects areserious. When used in this way, they are connectedas shown in figure 3-33. The entire circuit,including the electrical summing network, thehigh-gain amplifier, and the feedback loop, isknown as a summing amplifier.

Figure 3-33.-Summing amplifier schematic.

Remember that the overall gain of thefeedback amplifier circuit is determined by theratio of feedback impedance to total inputimpedance. When this ratio is 1 (both impedancesequal), the gain of the amplifier circuit is unity.The circuit algebraically adds all the inputvoltages.

Realistically, the number of inputs to asumming amplifier is limited by amplifiersaturation. A typical summing amplifier inputvoltage range is from –50 volts to +50 volts andan output voltage range from –100 volts to +100volts. This means that the total input voltagecannot exceed ±50 volts. The individual voltageinputs and gains must provide a total output thatdoes not exceed ±100 volts. When theseconditions are exceeded, amplifier saturationoccurs and further linear amplification isimpossible.

Operational Amplifiers.— Almost any mathe-matical operation can be performed by suitablemechanical and electronic devices. Some of theseoperations have already been discussed. Others,including the calculus operations of differentiationand integration, are discussed later in thischapter. The use of high-gain dc amplifiersis commonplace in the performance of thesemathematical operations, therefore, the termoperational amplifiers. This term, usedthroughout the remainder of this chapter, meansany high-gain dc amplifier that uses negativefeedback.

Ideally, dc amplifiers used in operationalamplifiers can produce an output voltage that isan exact magnified version of the input voltage,but exactly 180 degrees out of phase with theinput. For a number of reasons, practicalamplifiers fail to perform in this ideal manner.

The usual operational amplifier consists ofthree cascaded dc-amplifier stages with a

3-31

combined open loop gain of 50,000, or 92 dB. Theclosed loop gain (that is, the gain obtained whena feedback resistor that is equal in value to theinput resistance is connected between the outputplate and the input grid) is unity.

At the high gains used in these amplifiers, anyspurious voltage variations in the dc-amplifierstages may produce a considerable amount ofundesired variation or drift in the amplifier outputvoltage. Drift shows up as a voltage imbalanceappearing at the amplifier output terminals inaddition to the correct output voltage. When itoccurs in computer applications, this imbalanceproduces errors in the computation.

There are four main causes of drift:

1.2.

3.4.

Power supply voltage variationFilament voltage variation or transistorbias variationVarying resistance valuesVarying vacuum tube characteristics ortransistor parameters

Other operational amplifier errors are causedby seemingly insignificant currents and voltages,such as leakage currents, voltage drops in groundloops, and grid currents. The resulting currentsare in the order of fractions of a microampere.Yet, these currents flow through the inputresistors. A current of 0.1 microampere flowingthrough a 1-megohm resistor will generate anerror voltage of 0.1 volt.

Look at figure 3-34. If an assumed 0.2-volt,grid-voltage change is produced by a filament-voltage change, an output-voltage change of 200volts is obtained, even though the input signalvoltage is zero. By means of a similar analysis,you can show that plate or collector supplyvoltage changes and cathode or emitter emissionvariations all tend to increase the output voltageimbalance, and that they produce the most seriouseffects when they occur in the first stage.

The main cause of drift in transistorized dcamplifiers is changes in transistor parameterscaused by temperature variations. The mostwidely used drift reduction circuit is the

Figure 3-34.-Amplification of three stages of gain.

differential amplifier (fig. 3-35). As the nameimplies, the output voltage (taken betweencollectors) is equal to the difference between thetwo input voltages. Any output variations causedby drift voltages are canceled because bothtransistors are almost equally affected, and thedifference voltage between collectors remainsconstant.

The circuit (fig. 3-35) can be used either withtwo inputs or with one input having a fixed bias.In either case, collector current drawn by onetransistor affects that drawn by the other becauseof the common emitter resistor. For moreinformation on differential amplifiers, refer toNavy Electricity and Electronics Training Series(NEETS), module 8, Introduction to Amplifiers,NAVEDTRA 14180.

For example, an increase in the collectorcurrent of transistor Q1 increases the emittervoltage of transistor Q2. However, the base-to-emitter voltage of transistor Q2 is decreased (ifthe base voltage is held constant) since thedifference between the base voltage and emittervoltage appears there. Consequently, the basecurrent of transistor Q2 decreases, and thecollector voltage increases. Since the collectorvoltage of transistor Q1 decreases, the differencevoltage becomes greater.

The differential amplifier provides a gaindetermined by the current gain of each stage. Asone collector voltage is reduced, the othercollector voltage is increased. The differencebetween the two collectors is much greater thanthe difference between the two input voltages

Figure 3-35.-Basic differential amplifier.

3-32

because of the current gain of the two transistors.The high value of emitter resistance and voltagealso provides a very high input impedance.

The potentiometer in the emitter circuit is usedto adjust the circuit output voltage when no inputis present. By varying the emitter voltages of thetwo transistors, it is possible to select the valuesof quiescent base currents.

As you have already learned, most operationalamplifiers consist of a basic three-stage dcamplifier. Multiple stages are used to obtain highgain. An odd number of stages is used to obtainthe required reversal of polarity between theinput and output voltages. (Remember, negativefeedback is used in the operational amplifier.)

Figure 3-36 shows a schematic of a three-stage,dc amplifier that consists of two differentialamplifiers and a conventional amplifier. Negativefeedback is used within the amplifier to providestable gains over a wide range of frequencies.Negative feedback occurs when a portion of theoutput voltage is fed back to transistor Q2. Thebase current caused by this voltage is amplifiedand affects the emitter voltage of Q1. The voltagefed back to Q2 is in phase with the input voltageto Q1. Q1 and Q2 form a difference amplifier,and the amplifier’s output is an amplified versionof the algebraic difference between the base inputsignals at Q1 and Q2. The feedback voltage toQ2 causes a feedback current that subtracts from,or partly cancels the effect of, the input voltageto the base of Q1. You can see that although Q2’sfeedback voltage is exactly in phase with Q1’sinput voltage, it has a negative feedback effect.

In negative feedback circuits, a fixed portionof the output voltage is fed back to the input andused to cancel out a portion of the input voltage

Figure 3-36.-A three-stage, dc amplifier.

or current. In some ways the feedback circuit(fig. 3-36), consisting of R1 and R2, is like thecollect or-to-base negative feedback.

The feedback and the output voltage of theoverall amplifier must be exactly in phase withthe input voltage and current to function properly.Unfortunately, the input capacitances of eachstage introduce time delays or phase shifts. Thesephase shifts depend on the frequency componentsof the signal passing through the amplifier.Without some form of compensation, distortionis produced as a result of the summation of twocurrent waveforms that are not exactly in phase.The resistor capacitor network applying basecurrent to transistor Q5 provides the extra phaseshift required to make the output voltage exactlyin phase with the input voltage and current.

ELECTROMECHANICAL SUMMATION.—If the inputs or outputs of a summing operationcannot be physically brought together, a synchrosystem is used. A chain of three synchro unitsconsisting of a synchro transmitter, a synchrodifferential transmitter, and a synchro receiveradds or subtracts shaft rotations. If an outputvoltage rather than a shaft rotation is needed, thesynchro receiver is replaced with a synchro controltransformer. Gear ratios are added between theinput shaft and the differential transmitter rotorto introduce coefficients. The accuracy of asynchro summing system is increased by using atwo-speed, synchro transmission system.

Multiplication

Multiplication is a mathematical operationperformed by computers using the followingdevices:

Electronically by transistor amplifiers,electron-tube amplifiers, or by magneticamplifiers

Electromechanically by potentiometers

Mechanically by multipliers

ELECTRONIC METHODS.— Every linearamplifier is a multiplier. The dc amplifierpreviously discussed had a voltage gain of 100.In this section, you will hear about a high-gain,operational amplifier with a gain of 25,000. Thecomplete high-gain, operational amplifier is

3-33

shown in figure 3-37. The maximum allowableoutput voltage is ±5 volts. Since the circuitvoltage gain is 25,000, the input signal should notexceed ±0.0002 volt (0.2 millivolt).

When the amplifier is used as an operationalamplifier, the following restrictions are observed:

The input signal times the gain withfeedback should never produce an output greaterthan 5 volts.

The input resistor is small compared to theinput resistance of the operational amplifier. Thislimits the value to about 5K (one-tenth of theinput resistance). The feedback resistor can be anydesired value.

The input resistance of the following stagemust be 1,500 ohms or more.

As you read this section, look at figure 3-37.The input stage is composed of transistor Q1 andis a grounded collector amplifier. The voltagedivider in the collector circuit provides a smallnegative voltage for the collector of the transistor.This voltage, approximately –0.8 volt, allows theoutput of the stage to assume small negativevalues. The input voltage varies from zero to±0.0002 volt. As a result, the output voltage ofthe first stage is in this range.

The second stage consists of transistor Q2,which is a common emitter amplifier. The 33-ohm

resistor in the emitter circuit is part of the biasnetwork for the stage; that is, the voltage dividernetwork causes the emitter junction to be positivewith respect to the base. This results in the flowof a small bias current. Also, the 33-ohm resistorcauses a negative feedback to occur in the secondstage. Although this feedback reduces stage gain,it also provides wide frequency response andreduces noise, drift, and other undesirable effects.

Transistors Q3 and Q4 form the third stageand the output stage. Both are high gain, commonemitter amplifiers. Emitter resistors are used toprovide self-bias. Positive feedback is used inthese stages to offset the negative feedbackintroduced by the emitter resistors. The positivefeedback is obtained by feeding a portion of thevoltage developed across the collector resistors tothe emitter. The emitter of the output stage alsoreceives a bias voltage through the series resistorfrom the positive voltage supply.

A block diagram of the high-gain operationalamplifier is shown in figure 3-38. By looking atthis block diagram, you can see the feedbackpaths. Note that a single capacitor (C1) is usedfor phase shift correction. In addition, a specialpositive feedback path is provided for the higherfrequency components of the input signal. Theoutput of the third stage is in phase withthe input because the input stage does notinvert the signal.

Figure 3-37.-A high-gain operational amplifier.

3-34

Figure 3-38.-Block diagram of a high-gain operationalamplifier.

External feedback resistors are also shown inthe block diagram. The gain, with feedback, canbe varied from 1 (input resistor of 4.7K andfeedback resistance of 4.7K) to 10 (input resistorof 4.7K and feedback resistance of 47K). Highergains are obtained by using higher values offeedback resistance. In most analog computerapplications, a gain of 10 is sufficient. Feedbackin amplifiers is discussed in detail in NavyElectricity and Electronics Training Series(NEETS), module 8, Introduction to Amplifiers,NAVEDTRA 14180.

Electron tube amplifiers are also capable ofsolving multiplication problems involving twovariables as represented by the equation

= kxy.

Figure 3-39 shows a typical triode multiplicationcircuit. One variable input is applied as grid bias(preferably a dc voltage), which establishes thegain of the stage. The other variable input isapplied to the grid of the tube.

The output is a proportional quantity equalto the grid signal modified by the gain, which is

Figure 3-39.-Variable-gains tube as a multiplier circuit.

proportional to the variable bias voltage. Thiscircuit is limited in scope and accuracy due tovariations in tube characteristics, contactpotential, plate and filament supply changes, etc.

An improved multiplying circuit is shown infigure 3-40, view A. Its operation is like the circuitshown in figure 3-39 except that it uses twoseparate grids. The voltage gain of the stage iscontrolled by the voltage on grid 3 (shown by thecurve in figure 3-40, view B).

The gain of the amplifier is proportional tothe voltage and may be expressed as follows:

A =

If the output voltage is directly proportionalto the input signal is

=

Substituting for A, the equation reads

=

The output is a proportional quantity as indicatedby the constant k.

Figure 3-40 .-A multielectrode tube used as a multiplier.

3-35

NOTE: In discussions of amplification asrelated to computers, it is common toemphasize that an odd number of ampli-fiers inverts the signal. This is interpretedmathematically by use of a negative sign;the symbol A (for amplification factor) isoften written as –A.

Magnetic amplifiers are also used to multiplyone factor by another. The saturable core reactorelement in a magnetic amplifier makes themagnetic amplifier easily adaptable for multi-plying operations. Its amplification is madeproportional to a bias current over a limited range.However, accuracy is limited by variations inmagnetic characteristics and winding resistancedue to temperature variations.

ELECTROMECHANICAL METHODS.—Other than synchros, some of the electro-mechanical devices used for multiplication arepotentiometers and precision variable autotrans-formers (usually known by the trade nameVariac).

Precision potentiometers are frequently usedas multipliers in aviation fire control equipmentbecause they are accurate, rugged, simplyconstructed, and inexpensive. They are equallywell suited for ac or dc applications. Figure 3-41shows a typical potentiometer-type multipliercircuit.

The voltage occurring between the wiper andone end of the potentiometer is in reality theproduct of multiplying two quantities:

=

One quantity is the voltage impressed across theresistor element, and the other is the position ofthe wiper. When is 100 volts and is100 percent, is equal to 100 volts. If is

50 percent of full-shaft rotation, is equal to50 volts. Such close correspondence is achievedonly if the potentiometer is a precision device withlinear resistance.

A grounded center tap on the potentiometerwinding permits either positive or negative output,depending on the polarity of the input voltage andthe position of the wiper shaft. The potentiometermultiplier actually multiplies a quantity by afactor of less than one. This presents no problembecause the scale factor is adjusted to give thedesired output.

Autotransformer multiplication is identicalwith potentiometer multiplication with oneexception—the input must be an ac voltage. Theinput impedance of an autotransformer is high,and its regulation under load variations is verygood due to the low dc resistance of the winding.The low output impedance of the variableautotransformer lets you connect it directly toother transformers, potentiometers, or inductiveresolvers without intervening isolation amplifiers.

Division

Instrumentation of division problems in anexplicit form is generally difficult to perform.However, division is done by taking the reciprocaloft he divisor and multiplying it by the dividend.This allows the use of less complex multiplicationdevices, a method normally found in avionicsequipments.

ELECTROMECHANICAL DIVIDERS.— Arheostat, or a potentiometer connected as arheostat in a voltage divider circuit, provides ameans of dividing a voltage by a shaft position.The voltage divider is an extremely simple methodof dividing. The input voltage is applied to oneend of the rheostat; the second input is the shaftposition of the rheostat. Figure 3-42 shows theoperation of a rheostat divider network.

Figure 3-41.-Potentiometer-type multiplier circuit. Figure 3-42.-Rheostat divider network.

3-36

Since the shaft position of the movable contactcontrols the series resistance, current is a quotientof voltage divided by the circuit resistance. Thequotient can be obtained as a voltage across thefixed resistor R2, in series with the rheostat. Asin any analog system of division, the divisorcannot go to zero since the quotient would thenbecome infinity. R2 limits the current, and itsvalue establishes the range of the divisor.

A voltage, is made proportional to oneinput, and the resistance R1 + R2 is proportionalto the second input.

The current

The output voltage

example, consider the equation for determiningangular velocity.

= radians per second

where S is linear velocity in feet per second, andD is the slant range with limits from 600 to 6,000feet.

The value of R2 represents the minimum rangeof 600 feet and R1 + R2 represents 6,000 feet.Therefore,

A value for R2 is selected that will producereasonable current limits over the range of If has a range from +100 to –100 volts, andthe maximum current drawn is 10 mA, R2becomes 10,000 ohms. R1 will then vary from 0to 90,000 ohms as D goes from 600 to 6,000 feet.

at maximum speed and minimum range is as

or

Substituting K for the constant for the variable R1:

value of R2, and

The term K affects only as a scale factorchange. It affects only as a shift in value. For

follows:

When D = 6,000 feet, maximum speed producesan angular velocity output represented by anoutput voltage of

Since range cannot have a negative value, thismethod is only suitable when the divisor has thesame polarity at all times.

Division can also be done using a servo-mechanism (fig. 3-43). The system has two

Figure 3-43.-Division with a servomechanism.

3-37

electrical inputs, whose amplitude and polarity aredetermined in other units. The voltage (Y) is feddirectly to the error detector. The voltage (Z) ismultiplied by the shaft position (X). The product(XZ) is fed to the error detector and comparedwith the input (Y). As in any servo system, theerror voltage drives the servomotor in thedirection that will cancel the error voltage, givinga zero output.

Servomechanisms are often used for implicitdivision in computers. Division is usually repre-sented by the equation

However, in order to use a servomechanism, theequation is arranged as

Y – X Z = 0 .

The instrumentation of the equation is shownin figure 3-43.

ELECTRONIC DIVIDERS.— Electronicdivision can be performed by inserting a vacuumtube in place of the variable resistor in a rheostatdivider network. The plate resistance of the tubeis varied by the voltage applied to the control grid.

Figure 3-44 shows the circuit of an electronicdivider. The cathode resistor, performsthe same function as R2 in figure 3-42. Asin other electronic circuits, the circuit mustbe operated within limits determined by itscomponents.

Figure 3-44.-Electronic divider circuit.

Q34.

Q35.

Q36.

Q37.

Q38.

Q39.

In mathematics, a linear function is graphedas a straight line. What mathematicaloperations are included in linear opera-tions?

The proper application of scale factorsmakes the addition of physical units of anequation possible. What is the transforma-tion formula for this?

Describe the components that comprise atypical summing amplifier?

What is/are the purpose(s) of using an oddnumber of multiple stages in operationalamplifiers?

List some electromechanical methods usedfor multiplication.

State the equation a servomechanism woulduse in performing implicit division in acomputer.

NONLINEAR FUNCTIONS

Learning Objective: Identify power androots, trigometric functions, and loga-rithms as nonlinear functions of analogcomputers.

Instrumentation of various mathematicaloperations, such as raising a term to a power orextracting a root of a term, is discussed in thissection. It also includes a discussion about thegeneration of trigonometric functions.

Most nonlinear operations are performed bymechanical, electromechanical, and electronicdevices. However, one type of device is moreadaptable to a particular operation than another.Nonlinear mathematical operations are alsoperformed by special applications of the lineardevices previously discussed. For example, a termmay be raised to the second power by simplymultiplying it by itself, using some type of linearmultiplier.

Power and Roots

A variety of methods is used in aviation firecontrol equipment for solving problems involvingpowers and roots. The most common method useselectromechanical principles.

The solution of an armament control problemrequires the use of devices capable of raising terms

3-38

to a power. In most cases, the term is raised to thesecond power (squared). There are several electroniccircuits that can perform this operation. The simplestcircuit is a modified multiplying circuit previouslydiscussed and shown in figure 3-40. By applying theinput value to both grids 1 and 3, the output voltageis proportional to the square of the input.

Another electronic circuit capable of squaring isthe squaring amplifier. It consists of a paraphaseamplifier, with its output driving push-pull triodeamplifiers. Its output is also proportional to thesquare of the input, requiring a change in scalefactor.

A common electromechanical method of raising aterm to a power is by successive multiplication withpotentiometer multipliers (fig. 3-41).

When the equation is y = kx2, gangedpotentiometers are used, provided that x is a commonshaft position of the potentiometers. This circuit isshown in figure 3-45. The variable (x) may be raisedsuccessively to higher powers by repeating thiscircuit with additional potentiometers.

The voltage (ex) at the variable tap of R1 isproportional to x at all times. The voltage at the tapof R1 is fed through an isolating circuit to R2. The

voltage to R2 is equal to ex. This voltage is againmultiplied by x, and the output voltage at thevariable tap of R2 is equal to x times ex, or ex2.

Using the values shown in figure 3-45, thesquaring process is explained mathematically asfollows: The fixed voltage e corresponds to theconstant k, in the expression y = kx. Placing the twoforms of the equation side by side for comparison,

y = kx2 eo = ex2 = [ex](x)

y = 100(0.50)2 eo = [(100)(0.50)](0.50)

y = 25 eo = 25

The mechanization of these equations, in termsof percentage of travel by the potentiometer wipers, isdescribed as follows: If the control of thepotentiometers (x) were calibrated in equal units from0 to 10, then 5 on the dial would represent 50 percentof total travel, and 50 percent of El would appear atthe wiper of R1. With this 50 volts applied to R2 andthe wiper of R2 at 50 percent of the travel, 25 percent(50 percent x 50 percent) of E1 will appear at thewiper of R2. If, in this case, the output meter iscalibrated to read 0 = 100 volts, then it will read 25.In effect, we have squared the number 5.

Figure 3-45.-Powers by successive multiplication.

3-39

The power to which a quantity can be raisedis limited by the practical limits of voltageavailable to R1.

The root of a term maybe extracted by eitherelectromechanical or electronic devices. In fact,any multiplying or integrating device capable ofraising a term to a power and also capable ofproducing inverse functions is capable ofproducing roots. However, extracting roots isusually accomplished by electromechanicaldevices.

An electromechanical device for extracting theroot of a term or number is the servomechanismfeedback loop that uses ganged potentiometers,as shown in figure 3-46. The equation y = may be written as x – = 0 by raising both sidesto the nth power and transposing the y term. Nowthe equation is in the required form for servo-mechanism instrumentation. Square root is solvedby multiplying the output quantity by itself andusing this value as the feedback term. The outputof the square root device is in the form of a shaftposition.

Figure 3-46.-Square root servomechanism.

all-mechanical devices. Electronic networksconsisting of R and C are sometimes used toperform some trigonometric functions, such asvector addition.

The trigonometric functions most often usedin avionics equipment are sines and cosines ofangles. However, the four remaining functions

Q40.

Q41.

may be computed based on the sine and cosine.A squaring amplifier consists of what other If you are not familiar with trigonometry,circuits? you should study Mathematics, volume 2,

NAVEDTRA 10071-B.The root of a term may be extracted bywhat types of devices? INDUCTIVE RESOLVER.— This is one of

the most common ac electromechanical devicesTrigonometric Functions used to generate trigonometric functions. It is

basically a right triangle solver, using windingsTrigonometric processes are carried out to represent the sides and magnetic flux to

with inductive resolvers, potentiometers, or represent the hypotenuse. The shaft rotation

3-40

Figure 3-47.-Inductive resolver diagram.

corresponds to one of the angles of thetriangle that is to be solved.

The construction is very similar to that of asynchro except that both the rotor and stator havetwo windings oriented 90 degrees from each other,as shown in figure 3-47. Their primary use is toresolve a voltage into two components at rightangles or to combine two component voltages intotheir vector sum.

When a rotor winding is parallel to one statorwinding, the device acts as a one-to-one trans-former. As the rotor winding is rotated, thevoltage induced depends on the sine of the angleof rotation times the applied voltage.

Figure 3-49.-Inductive resolver with two-phase winding.

right

Figure 3-48.-Inductive resolver action.

Figure 3-48 shows the action of the inductiveresolver for three positions.

If the second rotor winding (R2) (fig. 3-49) isat right angles to the first winding, its output willcorrespond to the cosine of the rotation angle,since

Resolvers are low-impedance devices. Isolationor booster amplifiers are generally used as drivingcircuits if the inductive resolver input signaloriginates in a high-impedance source, such as apotentiometer. Isolation amplifiers have a lowoutput impedance and can correct for anyundesirable phase shift developed in the resolver.Since inductive resolvers operate only with acvoltages, they cannot be used in dc analogcomputers.

Some operations require that the computer becapable of transforming data from a polar(fig. 3-50) to a rectangular coordinate system. Ifthe position of a point or object is defined by avector, the polar dimensions of the vector maybe converted to rectangular coordinates. Thevector quantity, distance r and angle may beresolved into horizontal and vertical distances,x and y respectively, with a two-phase inductive

Figure 3-50.-Polar to rectangular transformation.

3-41

resolver. By feeding a voltage representing thedistance r into the stator winding and rotating therotor shaft through an angle corresponding to voltages representing x and y are produced at therotor windings.

POTENTIOMETERS.— Sine and cosinepotentiometers are special devices used to selecta voltage indicative of either the sine or cosineof an angle. Output voltages proportional to theproduct of the input voltage and either the sineor cosine of the angle through which the shaft isrotated can be obtained from the speciallydesigned potentiometers.

Logarithms

The application of logarithms to performmultiplication and division was briefly discussedearlier in this chapter. By studying the logarithmicprocesses in Mathematics, volume 2, NAVEDTRA10071-B, you can see that logarithms are alsouseful in raising a term to a power or extractinga root of a term. In this section, the primaryconcern is with computing devices for obtainingthe logarithm of a term.

Under some conditions, diodes and contactrectifiers have nearly exponential variation ofcurrent with voltage or logarithmic variation ofvoltage with current. However, the operatinglimits of a single diode are surpassed by therequirements of most armament controlcomputers. This limitation makes the use ofcircuits, such as the one shown in figure 3-51,necessary to produce logarithmic functions,

The purpose of this circuit is to produce anoutput voltage that is proportional to thelogarithm of the input current. By looking atfigure 3-51, you can see that R2, R4, and R6 forma voltage divider network. The cathode of each recti-fier is connected through a resistor to some pointon the voltage divider. This effectively acts as bias,causing each rectifier to be cut off until its anode

Figure 3-51.-Typical logarithmic shaping net work.

As the input current is applied, current flowis up through R1, producing an output voltageproportional to the current (E = IR). As thecurrent, hence the voltage drop across R1,becomes great enough, the positive voltage at thetop of R1 becomes great enough to bring CR1 intoconduction. As soon as CR1 conducts, it effec-tively places R3 in parallel with R1, lowering thetotal resistance and producing less voltage dropfor a given increase in input current. This accountsfor the bend in the curve at point a. The circuitresponse curve shows how the slope is successivelyreduced as additional rectifiers come into conduc-tion. Note that an increased number of rectifierscould result in a more perfect curve. However,the circuit shown provides an output well withinthe tolerances required for airborne computers,

There are several means available to obtain theantilogarithm of a quantity. This is done eitherby using an exponential characteristic directly orby using a feedback loop. Implicit methods mayalso be used, such as taking the derivative of theterm in order to eliminate the logarithm in the

reaches a potential higher than its cathode. equation.

3-42

Q42.

Q43.

What is the primary use of an inductiveresolver?

Logarithm applications include multipli-cation and division, but also include whatother applications?

CALCULUS

Learning Objective: Recognize the variouscomponents of calculus as used in analogcomputers.

Calculus is a branch of mathematics that dealswith the rate of change of a function and withthe inverse process. The inverse process is thedetermination of a function from its rate ofchange. The process of determining the rate ofchange of one variable with respect to another isknown as differentiation or differential calculus.The process of determining the sum of manyminute quantities is known as integration orintegral calculus.

DIFFERENTIATION

Before going into the actual process ofdifferentiation, you need to know the terminologyused in the process. Consider the equationx = f(y). You should read it as x equals a functionof y. If the derivative of x is taken with respectto y, then it would be written as

which, in notation form, is

You should note that the prime indicates the firstderivative of the function. When the derivativeis a time derivative, it is common practice toshorten the symbol even more, especially fordiagrams. For example, dx/dt (where t representstime) is often shortened to x (note the dot overthe x).

Although y represents any variable, you aregenerally interested in the derivative with respectto time. The derivative of a quantity with respectto time can be thought of as the time rate of

Figure 3-52.-Graphic representation of the derivative of avoltage.

change of that quantity, For example, for motionalong a straight line, the derivative of the distancetraversed with respect to time is the velocity orthe time rate of change of distance. Similarly, thederivative of a voltage with respect to time is thetime rate of change of that voltage. Figure 3-52is a graphic representation of the derivative of avoltage. If a voltage is changing at a constantrate (fig. 3-52, view A), then the derivative ofthat voltage has a constant value (fig. 3-52, viewB).

Electronic Methods

The rate at which an input voltage is changingis obtained from a simple series-connected resistorand capacitor circuit (fig. 3-53, view A). Noticethat the output voltage of this circuit appearsacross the resistor. With the proper values of Rand C to provide a short RC time constant andwith a square-wave input voltage the outputvoltage is that shown in figure 3-53, view B.

Figure 3-53.-Simple differentiating circuit.

3-43

When the rate of change of is greatest andwhen the rate of change of is zero, the output

tends toward zero. The derivative of atriangular wave or a sawtooth wave is shown infigure 3-53, view C. These facts show that theoutput voltage is approximately equal to the timerate of change (derivative) of the input voltage.

The primary disadvantage of the simpledifferentiating circuit is the time required for theoutput voltage to become equal to the derivativeof the input voltage. Shortening the RC timeconstant to decrease this time decreases theamplitude of the output voltage. Also, you shouldbe aware that the higher the output amplitude,the less the output resembles the derivative of theinput voltage. Thus, for good discrimination, asmall output voltage is required.

A feedback amplifier differentiator is shownin figure 3-54. This type of differentiator worksbetter than the simple differentiator circuit. Itsoutput voltage approximates the derivative ofthe input voltage in a much shorter time andwith greater accuracy. However, the use of adifferentiator circuit using a feedback amplifieris limited to those situations where introductionof electronic noise is not a serious problem. Thedifferentiator circuit acts as a high-pass filter, andthis causes amplification of circuit noise andintroduces instability in the amplifier. In a circuitwhere noise is already a problem, differentiationmust be accomplished by setting up an implicitfunction; this allows indirect differentiation byoperating in reverse and using integrators.

The following discussion involves the applica-tion of a feedback amplifier. You should alreadyunderstand the theory of negative feedbackamplifiers. If, for some reason, you do notunderstand this theory, study module 8 of theNavy Electricity and Electronics Training Series(NEETS).

Figure 3-54.-Differentiating circuit using a feedbackamplifier.

Before beginning the discussion about theoperation of the differentiator amplifier circuit,the following conditions are established:

The amplifier must be biased to operatenear the center of its linear range and not drawany grid current when operating within itsspecified limits.

The grid voltage is near ground potentialand changes only a very small amount when theinput signal varies. This occurs because thefeedback voltage tends to prevent any change ingrid voltage.

Since the grid voltage remains almostconstant, any change in plate voltage due to aninput signal appears almost entirely across thefeedback resistor, causing a corresponding changein current through it. Therefore, the outputvoltage is given by the formula = In this formula, is the change in plate voltageresulting from an input signal applied to the grid,

3-44

is the change in current flowing through thefeedback resistor, and is the feedback resistor.

The formula can be restated simply byremembering that a differentiator produces anoutput only when there is a change in the inputvoltage. The amplitude of the output voltage (at)is equal to the change in feedback current (accomponent), multiplied by the resistance of thefeedback resistor. The negative sign serves toemphasize the fact that a polarity inversion isintroduced by the amplifier.

Refer to figure 3-54. Consider the action ofthe circuit with a constantly changing voltageapplied. For explanation purposes, consider aback-to-back sawtooth that is starting downwardfrom its apex. As the negative-going signal startsdownward, electrons from the grid side of C1 startto flow through (electrons are attracted to thehigher potential of the plate), causing the gridvoltage to drop. This action reduces plate current,causing a rise in plate voltage. A portion of theplate voltage increase is fed back to the grid,causing it to rise in potential. However, since thefeedback voltage is only a small portion of theplate signal, the grid cannot come back to itsinitial voltage. The grid and plate will reach a stateof equilibrium almost instantly, and will remainbalanced as long as the current through isconstant. With an input voltage that is linear, thedischarge current of C1 remains constant through

until the input reverses its direction.Since the plate is the source of the output,

watch its action closely. Remember that theoutput is only the ac component of the platevoltage. When the input signal started downward,the plate voltage shot up and leveled offinstantaneously, and it remained at this level untilthe input signal reversed its direction. Thisproduced a square-wave output that is oppositein polarity to the input. The other half-cycle willproduce a similar output. Therefore, the outputis a voltage waveform indicative of the rate ofchange of the input voltage. In the fire controlcomputer, this input voltage may represent aninput variable such as range, and the outputvoltage may represent range rate or velocity.

Electromechanical Methods

When the derivative of a voltage is desired,a generator driven by a servomechanism is used.In this case, the servo transforms the voltage tobe differentiated into a corresponding shaftposition. A generator that is driven by the servoshaft produces an output voltage proportional to

Figure 3-55 .-Electromechanical differentiator.

the speed of the motor. The rate generator voltageis a derivative of the rotor displacement withrespect to time or a measure of the rate of rotorrotation. (See figure 3-55. )

The derivative range is limited by the responseof the servomechanism. A system having movingparts with appreciable inertia cannot respondsatisfactorily to a voltage step function where theslope is infinite.

INTEGRATION

Integration is the process of summing up aninfinite number of minute quantities. In thesolution of the armament control problem,integration is usually the summing of certainquantities in respect to time. For example, takingthe integral of velocity between certain limits oftime will give the distance traveled.

The process of integration is like determiningthe area under a curve. In the case of a stepfunction input, the curve may be considered asa rectangle having one side variable with time.Look at figure 3-56, view A. The solid curve Y1

Figure 3-56.-Integration of area.

3-45

shows the velocity at any time—in this case, aconstant velocity. The distance traveled is equalto the velocity multiplied by the time. With properscale values, the distance is given by the numericalarea under this (rectangular) curve; that is,area = height (or velocity) multiplied by length(or time).

On the distance-time diagram (fig. 3-56, viewA), the sloping line X1 shows the total distancetraveled at any instant of time, The larger the stepinput, the steeper the slope of the line in thedistance-time diagram.

The distance traveled, X, must continue toincrease as long as there is a positive value ofvelocity, Y. When X is represented by a voltage,there are limitations on its maximum value dueto circuitry to be used.

The integral of a dc voltage is a voltage withconstant slope, as shown in figure 3-57. Normally,there is no need for integrating dc voltages, butthis effect is identical to the voltage wave for stepinputs.

A simple integrator is shown in figure 3-58,view A. Here, a square-wave voltage is appliedto the input, and the output voltage appears acrossthe capacitor. During the positive portions of theinput voltage, the output voltage is the sum ofall the positive quantities, which results in anincreasing voltage. During the negative portionsof the input voltage, the output voltage is the sumof all of the negative quantities in the input, whichresults in a decreasing voltage. Look at thewaveforms in figure 3-58, view B. Compare themwit h the output of the simple differentiator circuit.The integrator output and the differentiatoroutput combined equal the instantaneous inputvoltage, except for circuit losses.

For further details on simple integratorcircuits, review the discussion of this topic in theNavy Electricity and Electronics Training Series(NEETS), module 9.

Figure 3-57.-Graphical representation of integration of avoltage.

Figure 3-58.-Simple integrating circuit.

An integrating amplifier circuit using afeedback amplifier is shown in figure 3-59. Thiscircuit is very similar to the differentiatingamplifier circuit previously discussed. However,you should note that the negative feedback iscoupled by a large coupling capacitor. Thiscapacitor, along with the input resistor and loadresistor, performs the integration. The amplifierfunctions only to improve its response andlinearity. The input circuit also uses an isolationresistor to allow the amplifier input to bemaintained at an almost constant potential whenan input signal is applied.

The output is based on the rate of charge, ordischarge, of the feedback capacitor. Theamplifier functions to maintain the charge, ordischarge, of the integrating capacitor in the mostlinear portion of the RC curve. The net effect isthat the capacitor voltage does not oppose theinput voltage, and the capacitor-charging currentis a direct function of the input signal voltage.

Figure 3-59.-A common integrating circuit.

3-46

Q44.

Q45.

Q46.

Q47.

Describe the process of differentiation andintegration.

What calculus processing circuit is limitedto use where electronic noise is not a seriousproblem?

What calculus circuit allows indirectdifferentiation by operating in reverse?

What components of an integratingamplifier use a feedback amplifier?

GROUPED OPERATIONS

Learning Objective: Identify the groupedoperations of an analog computer andproblems encountered in computation.

So far, you have learned about computingdevices for performing various mathematicaloperations. Now, you are ready to learn aboutseveral instruments or devices grouped togetherfor the solution of a problem. The groupingdiscussed will not make up a workable computer;it will show you that by grouping devices, thesolution of more complex equations can occur.You should remember that this grouping mayinvolve only a small portion of a completecomputer.

PROBLEMS ENCOUNTERED

When various devices are selected to carry outa grouped operation, certain problems are almostcertain to develop. Such problems are present evenin grouping the simplest devices. Here again, thisinformation is presented not to help you designa computer but to help you understand morecomplex computers.

Change of Representation

If two or more computing devices are con-nected, the use of two or more methods ofrepresentation is frequently required. The outputof the first device may not have the samerepresentation as required by the input of thesecond device. An example might be the multi-plication of two voltages by a potentiometer-typemultiplier. To multiply successfully, one of thevoltages would have to be represented by a shaftrotation.

Scale Factor

Another problem that must be consideredwhen grouping two or more devices is that of scalefactor. As you have learned, a change of scalefactor takes place any time the device producesa proportional output. Such devices includethose that perform the operations of adding,multiplying, dividing, etc.

Impedance Matching

When the output of one electronic circuit isfed to another, the input impedance of the secondcircuit or stage may affect the operation of thefirst. Therefore, it is important that the inputimpedance of the second circuit be matched to theoutput impedance of the driving stage. Amismatch may result in an error in the computer,making the complete computer inaccurate. Twodevices often used between two computing circuitsare the emitter-follower and impedance-matchingtransformers. Impedance matching in the use ofelectrical components, such as resolvers andcontrol transformers, must also be considered.

Speed of Computation

The speed of response of a device is importantin a grouped operation. Some devices have ashorter response time than others. For example,a device with a minimum speed of computationtime, when required to function longer thanthe minimum time, may lose a considerablepercentage of its accuracy. The overall accuracyof a group of devices could be reduced below thedesired tolerance due to one device requiring alonger time to function than the rest of the group.The speed of response is an importantregard to the stability of computersfeedback.

TYPICAL EQUATION SOLUTION

factor inthat use

In the solution of a navigation problem, it isnecessary to find the hypotenuse of a right trianglewhen the length of the two sides is given.Navigation computers normally use ground rangeor horizontal range because ground range ratesare more constant than slant range rates.However, to minimize the possibility of error, youconvert computed ground range into slant rangefor comparison with observed radar range. This

3-47

requires a constant solution from the followingequation:

where

r = slant range

H = altitude

R = ground range

A block diagram of a squaring-type trianglesolver is shown in figure 3-60. The quantities Hand R are squared and summed. The summedquantity + is fed to a device that extractsthe square root, giving an output equal to r.

Figure 3-60.-Block diagram of right triangle solver.

A simplified circuit capable of performing theabove operation is shown in figure 3-61. Thequantities H, R, and r are represented by theirrespective shaft positions. Ganged potentiometersare used for squaring each quantity. A voltageproportional to + appears across R4 andis fed to a feedback amplifier. Here the signal isamplified, and the scale factor is corrected beforebeing fed to the difference amplifier.

Potentiometers R15 and R16 are squaringpotentiometers, with the output being a voltageproportional to This signal is also amplifiedand fed to the difference amplifier. If the voltage

is equal to the voltage + the outputfrom the difference amplifier is zero, and theposition of the r shaft is indicative of

However, if there is a difference in the two inputs,the output signal fed to the servo amplifier willcause the servomotor to rotate in a direction toreduce the difference voltage, thus correcting theoutput r.

Remember, this example is only one of manypossible ways of solving for the values in a righttriangle. It is included only to show you that thedevices discussed earlier in this chapter may begrouped for the solution of more complexequations.

There are many applications of the analog-type computer in naval aviation. The trend in thedevelopment of today’s weapons systems is

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Figure 3-61.-Schematic diagram of a

toward computers known as hybrids. These Q48.computers are a combination of both analog- anddigital-computing devices. This arrangement willprobably remain for some time since many of theinput and output services must be analog. Input Q49.devices of the analog type are required to receivethe data from a radar set, airspeed probe, or ashaft position because this type of data is analog Q50.in nature.

right triangle solver.

When grouping various devices to carry outa grouped operation, what type problemscan develop?

Describe the problem of impedancematching.

Name two devices used between two com-puting circuits for impedance matching.

3-49

CHAPTER 4

DIGITAL COMPUTERS

4-1

This chapter has been deleted. For information on digital computers, refer to Nonresident Training Course (NRTC) Navy Electricity and Electronics TrainingSeries (NEETS) Module 22, NAVEDTRA 14194. For information on numbersystems and logic, refer to Nonresident Training Course (NRTC) Navy Electricityand Electronics Training Series (NEETS) Module 13, NAVEDTRA 14185.

CHAPTER 5

AVIATION SYSTEMS FUNDAMENTALS ANDSUPPORT EQUIPMENT

Aviation Electronics Technicians (ATs)operate and maintain complex electronic installa-tions in modern naval aircraft. To do this,the AT must know aircraft systems and supportequipment (SE). Therefore, you, as an AT, mustalso understand the systems and SE of a typicalaircraft, such as the power generation equipment,the conversion units, the power control, regu-lation, and protection devices, and the generalpower distribution systems.

AVIATION SYSTEMSFUNDAMENTALS

Learning Objective: Identify systems char-acteristics for communications, navigation,radar, ECM, and ASW systems.

In this chapter, you are introduced to a fewequipments you may be responsible for main-taining. It includes coverage of displays, radar,IFF, air navigation, communications and datalink, ECM, ESM, weapons control, and ASWacoustic and recorder systems. The AviationElectronics Technician 2 (Organizational),NAVEDTRA 14030, and Aviation ElectronicsTechnician 2 (Intermediate), NAVEDTRA 14029,contain a more in-depth coverage of thesesubjects. The specific maintenance instructionsmanuals (MIMs) contain in-depth information onspecific systems and equipment.

DISPLAYS

Learning Objective: Identify various typesof displays used in aviation systems.

To understand the basic fundamentals of anydisplay system, you need to know the operationof cathode-ray tubes (CRTs), amplifiers, powersupplies, and other solid-state devices. For moreinformation about CRTs and related circuitry,you should refer to Navy Electricity and

Electronics Training Series (NEETS), modules 6,7, 8, 16, 18, and 21 for help in understandingelectronics and troubleshooting many differenttypes of display systems.

Display systems can range from a simplemonitor to a highly sophisticated head-up display(HUD). They include radar and loran indicatorsas well as most systems that use a CRT or visualdisplay. Most display systems contain a CRT andassociated circuitry to present informationusing a PPI-scan, A-scan and/or graphics,alphanumerics, and conies generation. The nextsection of this chapter contains information aboutsome typical radar indicators. The various typesand operational principles of radar indicators,such as the A-scope, B-scope, and PPI-scope, arediscussed in NEETS, module 18.

A-Scope

Figure 5-1 shows a simplified block diagramand scan presentation of a typical A-scope. TheA-scope is only included to show you how scopeswork. Then, the more advanced types arediscussed.

In the operation of the A-scope, an initialtrigger pulse from the timer is applied to both theradar transmitter and the one-shot (monostable)multivibrator. The one-shot multivibratorgenerates the following:

A negative gate pulse that is fed to therange marker generator and the rangesweep generators

A positive gate pulse that is fed to thecontrol grid of the CRT

The gate pulse to the range marker generatorcauses a series of equally spaced range marks tobe generated. These range marks are added to thereceiver output signal in the video mixer. Theoutput of the video mixer is applied betweenground and one vertical-deflection plate of the

5-1

Figure 5-1.-Typical A-scope block diagram and scan presentation.

CRT. The other vertical-deflection plate is connected tothe vertical-centering control.

The negative gate pulse fed to the range sweepgenerator causes a nearly linear sawtooth sweepvoltage to be generated. The different timing capacitorsin the one-shot multivibrator and in the range sweepgenerator are connected to a common range switch.Therefore, when the operating range is changed, theRC time constants of both circuits are simultaneouslychanged.

When the duration of the negative gate pulse ischanged, the duration of the sawtooth sweep voltage ischanged; but, the amplitude of the sweep voltage isunchanged. Therefore, at different operating ranges,the scanning spot travels about the same distanceacross the A-scope screen. However, the speed of the

scanning spot increases as the range setting isdecreased.

The sawtooth output of the range sweep generatoris amplified by the range sweep amplifier. Then, it isapplied to the paraphase amplifier (phase splitter). Theparaphase amplifier outputs the sawtooth sweepvoltage in push-pull fashion to the horizontal-deflectionplates of the CRT. This reduces defocusing of theelectron beam.

The positive gate pulse applied to the control gridof the CRT intensifies the electron beam during thesweep time, displaying the output of the video mixer onthe A-scope screen. When the positive gate pulse isremoved, blanking results (the electron beam is cutoff).

5-2

Clamping circuits are frequently used with A-scopes. They keep the display properly positioneddespite changes in the average (de) value of thesweep or signal voltages. Remember, clampers holdone part of the signal waveform at a constant voltagelevel. In some A-scopes, expanded sweep circuits areused. These circuits let a small section of the sweepexpand to cover the A-scope screen. Thus, moreaccurate range measurements are made.

B-Scan

The B-scan represents a compromise betweenthe extremes of simple and complex circuitry. Whenradar requirements call for simple circuitry andconstruction, the B-scan is used. In the B-scan, threevariables are possible:

1. Range (a function of time)

2. Azimuth (a function of antenna rotation)

3. Intelligence received by the radar orassociated equipment

B-scan circuitry involves the simplest circuitryconstruct ion of any two-dimensional presentation,yet it presents information as a reasonably faithfulreplica of the area scanned by the antenna (fig. 5-2).It works best under conditions where the antennascans a sector of less than 180 degrees. However, itcan be used in a situation where a 360-degree area isscanned.

Range is usually presented vertically by the useof a conventional sweep circuit. Azimuth is Presentedhorizontally by the use of a potentiometermechanically connected to the antenna. Theintelligence is presented on the indicator by intensity-modulating the sweep. The antenna scanning speedis approximately one scan per second, and the sweepspeed is at the PRF rate; therefore, the intelligencehas range and bearing.

C-Scope

C-scopes (fig. 5-3) present data on the bearingand elevation of targets. C-type indicators may

Figure 5-3.-C-scope presentation.

Figure 5-2.-B-scan presentation.

5-3

Figure 5-4.—PPI presentation.

5-4

sometimes be used in aircraft interception. LikeB-scopes, C-scopes provide a rectangular displayon their screens. However, in C-scopes, thevertical axis represents elevation and the hori-zontal axis represents bearing. Thus, in aviationfire control radar, targets may appear on eitherside of both the horizontal and vertical axes.

To get a rectangular display on the screen ofa C-scope, both horizontal and vertical-sweepgenerators are used. Since the sweep frequenciesare relatively low, potentiometers (like theazimuth sweep potentiometer of the B-scope)are generally used. These potentiometers areconnected to the radar antenna,

When the antenna turns sideways, thescanning spot on the C-scope screen is deflectedhorizontally. When the antenna is tilted up ordown, the scanning spot is deflected vertically.Echo signals, applied to the control grid (orcathode) of the CRT during the sweep period,cause the brightness of portions of the horizontaltrace to be increased. The position of a bright spotindicates the elevation and bearing of a target.

Targets at different ranges, but with the samebearing and elevation, appear as a single spot ona C-scope. Targets of this kind cannot bedistinguished individually on the C-scope. For thisreason, an indicator that presents range data isgenerally used along with a C-scope. Once therange of a particular target is determined, a rangegate pulse (rectangular pulse) is applied to theC-scope. This intensifies the electron beam onlyfor the duration of the range gate pulse. Thus,only the desired target echo appears on theC-scope; all other signals are blanked out. By thismeans, the bearing and elevation of a particulartarget at a specific range is determined.

PPI-Scope

P-type indicators, known as plan-positionindicators (PPI or PPI-scopes), are used to presentthe range and bearing data of targets. Like B- andC-scopes, PPI-scopes generally use CRTs withlong-persistence screens.

The PPI presentation is practically an exactreplica of the region scanned by the radarantenna. Distance along the radial sweep linerepresents target range. Rotation of the radialsweep line, synchronized with the antenna’srotation, produces a circular display.

When echo signals are applied to the controlgrid (or cathode) of the PPI CRT during thesweep period, the brightness of portions of theradial sweep line is increased, Like the B-scope,an increase in the brightness of portions of the

PPI radial sweep line results in a maplike picture.Figure 5-4 shows a typical PPI presentation.

E-Scan (RHI)

The range-height indicator (RHI) (fig. 5-5) isanother type of scan used to present range andheight information. The RHI is also known as anE-scan. The E-scan is a modification of theB-scan on which an echo appears as a brightspot. The range is indicated by the horizontalcoordinate and the elevation (height) by thevertical coordinate. This type of scan is used indirecting aircraft during ground- and carrier-controlled approaches and in fire-control systemsfor terrain clearance.

Miscellaneous Presentations

Many other types of radar indicators are used.Often, more than one type of presentation isincorporated into one indicator. Most indicatorsin aviation fire control radar use two or moreelectron guns—one gun is used to develop aB-type presentation, and the other to develop thevarious elements of an attack presentation. Theseelements may consist of an elevation strobe,artificial horizon, steering information,acquisition circle, and range circle. Some of thesystems and equipment that use displays includeradar, IFF, and fire control.

RADAR

Learning Objectives: Identify the characteris-tics of radar to include range, resolution,azimuth, and accuracy. Recognize the factorsthat affect radar performance. Identify thecomponents of a pulse-modulated radar,and recognize the functions of thecomponents within the system.

Figure 5-5.-E-scan presentation.

5-5

The word radar applies to electronicequipment used to detect the presence of objects.Radar determines an object’s direction, altitude,and range by using reflected radio waves.

Characteristics of Radar

The characteristics of radar discussed in thissection include the range, azimuth, resolution, andaccuracy. Also, some of the factors that affectradar performance are discussed.

RANGE.– Radar measurement of range, ordistance, is possible because radiated radio-frequency (RF) energy travels through space ina straight line at a constant speed. However, thestraight path and constant speed are alteredslightly by varying atmospheric and weatherconditions.

Velocity. – RF energy travels at the speed oflight, about 186,000 statute miles per second,162,000 nautical miles per second, or 300 millionmeters per second. Radar timing is expressed inmicroseconds; the speed of radar waves is givenas 328 yards or 984 feet per microsecond. Onenautical mile is equal to about 6,080 feet. Thismeans that it takes RF energy about 6.18microseconds to travel 1 nautical mile.

Range Measurement.– The pulse-type radarset determines range by measuring the time it takesfor the emitted pulse to travel to the target andreturn. (This is known as the elapsed time.) Sincetwo-way travel is used in range measurement, theelapsed time for the pulse to leave the antenna,travel to the target, and return takes a total timeof 12.36 microseconds per nautical mile. Therange, in nautical miles, of an object is found—

1.

2.

by measuring the time that elapses duringa round trip of the radar pulse (inmicroseconds), andthen dividing this quantity by 12.36.

Mathematically,

The minimum range of a pulse radar isdetermined by adding the time of the transmittedpulse, or pulsewidth (PW), to the recovery timeof the duplexer and the receiver. Recovery timeis the time required for the receiver to become

operative after the transmitter has fired. To findthe minimum range (in yards) at which a targetis detected—

1. add the PW (in microseconds) to therecovery time,

2. divide the result of step 1 by 2, and3. multiply the result of step 2 by 328 yards.

Mathematically,

= (PW + recovery time) x 164 yd.

Targets closer than this range are not seen. Thereceiver is inoperative for the time necessary fora signal to travel this distance.

The maximum range of any pulse radardepends upon the transmitted power, PRF, andreceiver sensitivity. The peak power of thetransmitted pulse determines the maximum rangethat the pulse can travel to a target and return inusable echo strength. There must be enough timeallowed between transmitted pulses for an echoto return from a target located at the maximumrange of the system.

AZIMUTH.– The azimuth (bearing) of atarget is its clockwise angular displacement in thehorizontal plane with respect to true north. Thisangle is measured with respect to the aircraftheading. In this case, it is relative bearing. Theangle is measured from true north, giving truebearing, if the installation contains azimuthstabilization equipment. The angle is measuredby using the directional characteristics of aunidirectional antenna. Then the position of theantenna is determined when the strongest echoreturns from the target.

RESOLUTION.– The range resolution of apulse radar is the minimum resolvable separation,in range, of two targets on the same bearing,Range resolution is a function of the width of thetransmitted pulse. The type and size of the targetsand the characteristics of the receiver andindicator also affect resolution. With a well-designed radar, sharply defined targets on thesame bearing are easy to resolve. Their rangesdiffer by the distance the pulse travels in one-halfof the time of the pulsewidth (164 yards permicrosecond of PW). If a radar set has apulsewidth of 5 microseconds, the targets must

5-6

be separated by more than 820 yards before theycould appear as two pips on the scope. Theformulas for range resolution and minimum targetseparation are given below:

range resolution = PW x 328 yd

minimum target separation = PW x 164 yd

Azimuth resolution is the ability to separatetargets at the same range but on differentbearings. Azimuth resolution is a function of theantenna beamwidth and the range of the targets.The antenna beamwidth is the angular distancebetween the half-power points of an antenna’sradiation pattern. Two targets at the same rangeappear as one target instead of two. They mustbe separated by at least one beamwidth todistinguish between them. Strong multiple targetsappearing as one target are resolved in azimuth(bearing) by reducing the gain of the receiver.

ACCURACY.– The accuracy of a radar is ameasure of its ability to determine the correctrange and bearing of a target. To determine thedegree of accuracy in azimuth, the effectivebeamwidth is narrowed. On a PPI scope, the echobegins to appear when energy in the edge of thebeam first strikes the target. The echo is strongestas the axis of the beam crosses the target. The echo

continues to appear on the scope as long as anypart of the beam strikes the target. The targetappears wider on the PPI than it actually is. Therelative accuracy of the presentation depends onthe width of the radar beam and range of thetarget.

The true range of a target is the actualdistance between the target and the radar set(fig. 5-6). In airborne radar, the true range iscalled slant range. The term slant range indicatesthat the range measurement includes the effect ofa difference in altitude.

The hor izonta l range of a target is astraight-line distance (fig. 5-6) along an imaginaryline parallel to the earth’s surface. This conceptis important. An airborne target, or the observer’saircraft, only needs to travel the distancerepresented by its horizontal range to reach aposition directly over its target. For example, anaircraft at a slant range of 10 miles at an altitudeof 36,000 feet above the radar observer’s aircrafthas a horizontal range of 8 miles.

The timing sequence of a radar range-indicating device starts at the same instant thatthe transmitter starts operation. Therefore, withairborne surface-search radar, the first targets seenare those directly beneath the aircraft. However,

Figure 5-6.-Slant range versus horizontal range.

5-7

on the PPI scope, there is a hole in the middle of thepicture (fig. 5-7), with a minimum radiuscorresponding to the altitude of the aircraft. The holeis known as the altitude ring. Objects directlybeneath the aircraft appear on the scope at a distanceequal to the distance between the aircraft andground.

Factors Affecting Radar

Many factors affect radar performance; theprincipal one is maintenance. Keeping theequipment operating at peak efficiency affects theoverall capabilities and limitations of the radar. Asecond factor is the radar operator’s knowledge of

the equipment. This knowledge must include themaximum and minimum ranges at which theoperator can expect to pick up various targets, therange and bearing accuracy of the gear, and therange and bearing resolution. If the radar is a heightfinder, the operator must know the altitudedetermination accuracy and the altitude resolution.Some of the factors that affect radar are coveredbelow. For more detailed information, you shouldrefer to the maintenance instruction manual (MIM)for each radar.

PEAK POWER.—The peak power of a radar isits useful power. The range capabilities of the radarincrease with an increase in peak power.

Figure 5-7.-Effect of altitude on radar. (A) Radar tilted down; (B) radar with zero tilt.

5-8

Doubling the peak power increases the rangecapabilities by about 25 percent.

PULSEWIDTH.– The longer the pulsewidth,the greater the range capabilities of the radarbecause of the greater amount of RF energy sentout in each pulse. In addition, because narrowbandpass receivers are used, the noise level isreduced. Remember though, an increase in pulse-width increases the minimum range and reducesthe range resolution capabilities of the system.

BEAMWIDTH.– The beamwidth is indegrees between the half-power points in theradiation pattern. The effective beamwidth of aradar is not a constant quantity, The receiver gain(sensitivity) and the size and range of the targetaffect it. The narrower the beamwidth, the greaterthe concentration of energy. The more concentratedthe beam, the greater the range capabilities fora given amount of transmitted power.

RECEIVER SENSITIVITY.– The sensitivityof a receiver is a measure of the ability of thereceiver to amplify a very weak signal. Increasingthe receiver sensitivity increases both the detectionrange of the radar and the radar’s ability to detectsmaller targets. However, sensitive receivers areeasier to jam, and interference shows on the scopemore easily.

INDICATORS.– The choice of the type ofscope used to display weak pips adds to thecapabilities of the radar. A deflection-modulatedA-scope would be more sensitive to weak echoesthan the intensity-modulated PPI. A weak targetis seen on the A-scope before it can be detectedon the PPI.

ANTENNA ROTATION.– The more slowlythe antenna rotates, the greater the detection rangeof the radar. Therefore, an antenna that is notrotating has the greatest range in the direction itis pointing. For tactical reasons, antennas arerotated. Pointing the antenna beam at the targetmomentarily allows you to gain informationabout the composition of a target.

Q1.

Q2.

The A-scope’s positive gate pulse goes tothe control grid of the CRT, causing theelectron beam to

What type of display works best underconditions where the antenna scans a sectorof less than 180 degrees?

Q3.

Q4.

Q5.

Q6.

Q7.

The PPI scope provides what type ofpresentation?

List the factors that affect the maximumrange of pulse radars.

What are the characteristics of radar?

Define azimuth resolution.

Why does a long pulse width increase ordecrease the range capabilities of a radar?

Functional Components ofPulse-Modulated Radar

The functional breakdown of a pulse-modulated radar can be divided into six essentialparts

1.

2.

3.

4.

(fig, 5-8).

The synchronizer (also known as the timeror keyer) supplies the synchronizing signalsthat time the transmitted pulses and theindicator. It also coordinates otherassociated circuits.The transmitter generates the RF energy inthe form of short, powerful pulses.The antenna system takes the RF energyfrom the transmitter, radiates it in a highlydirectional beam, receives any returningechoes, and passes these echoes to thereceiver.The receiver amplifies the weak RF pulsesreturned by the target and reproduces themas video pulses, which are applied to theindicator.

Figure 5-8.-Functional block diagram of a funda-mental radar system.

5-9

5.

6.

The indicator produces a visual indicationof the echo pulses in a manner thatfurnishes the required information.

The power supply provides the electricalpower for the radar set.

The physical configuration of radar systemsdiffer. However, the fundamental characteristicsremain the same. Radar also works with theidentification friend or foe (IFF) system.Normally, the IFF antenna is mounted on andshares the radar antenna, and its information isdisplayed on the same radar scope.

IDENTIFICATION FRIENDOR FOE (IFF)

Learning Objective: Recognize IFF theoryof operation to include interrogation andtransponder functions.

Identification friend or foe (IFF) wasdeveloped because of the destructive power ofmodern weapon systems and the speed of theirdelivery. You cannot wait to identify a detectedradar target. Figure 5-9 shows a typical IFFsystem. It consists of an interrogator unit, a codersynchronizer unit, a search radar unit, and a

Figure 5-9.-IFF system block diagram.

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transponder unit. The interrogator, synchronizer,and radar units make up the challenging station.The transponder unit is the responder station. Bylooking at figure 5-9, you can see that thechallenging station can be a ground station, a ship,or another aircraft. The responder station isnormally an aircraft.

There are five modes of IFF operation usedby the air traffic control radar beacon system(ATCRBS) and naval aircraft–mode 1, mode 2,mode 3/A, mode C, and mode 4. In addition,there is a test mode used only by the aircrafttransponder as a self-check of the transponderequipment.

Modes 1 and 2 are used exclusively by themilitary as tactical modes for target identification.Mode 3/A is used at military and civilian airtraffic control stations. Mode C is used with anexternal pressure altitude digitizer to report theaircraft’s altitude to an ATCRBS. Mode 4 is amilitary encrypted mode, which is controlled byan external computer. The operation of mode 4is classified. Only interrogators and transpondersusing the same encrypted codes can respond.

NAVIGATION

Learning Objectives: Recognize the naviga-tion-related terms and definitions basicto inertial navigation system operation.Recognize the operating principles andcharacteristics of the inertial navigationsystem, to include Schuler loops andtuning. Recognize components and operat-ing principles and features of airbornenavigation systems used by the Navy.

Navigation is the procedure by which youmove from one point to another point. Airnavigation is the process of directing themovement of an aircraft from one point toanother. The function of air navigation is to locatepositions and measure distance and time along theintended direction of flight.

Terms

As you read about air navigation, you mustunderstand the terms that are being used. In thispart of the TRAMAN, you will learn about someof these terms.

Position. Position is a point defined by statedor implied coordinates. One basic problem ofnavigation is to fix a position. If navigators do

not know where they are, they can’t directthe movement of the aircraft to its intendeddestination.

Direction. Direction is the position of onepoint in space relative to another, withoutreference to the distance between them. Directionmay be either three-dimensional or two-dimensional. For example, the direction of SanFrancisco from New York is approximately west(two-dimensional). However, the direction of anaircraft from an observer on the ground may bewest and 20° above the horizontal (three-dimensional). Direction is not itself an angle, butit is often measured in terms of its angular distancefrom a reference direction.

Course. Course is the intended horizontaldirection of travel. For example, the direction ofNAS Jacksonville from NAS Pensacola is east.This should be the intended direction of flight.

Heading. Heading is the horizontal directionin which an aircraft is pointing. Heading is theactual orientation of the aircraft’s longitudinalaxis at any instant. The term heading includes thefollowing:

True heading uses the direction of thegeographic North Pole as the reference.

Magnetic heading uses the direction of theearth’s magnetic field at that location asthe reference.

Compass heading differs from magneticheading by the amount of magneticdeviation.

Magnetic heading differs from true headingby the amount of magnetic variation at thatlocation. Compass heading differs from trueheading by the amount of compass error(deviation ± variation).

Bearing. Bearing is the horizontal direction ofone terrestrial point from another. Bearings canbe expressed by two terms—true north or thedirection in which the aircraft is pointing. If truenorth is the reference direction, the bearing is atrue bearing. If the reference direction is theheading of the aircraft, the bearing is a relativebearing. If you get a bearing by radio, it is a radiobearing; if visual, it is a visual bearing. You canaccurately describe the direction between two

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objects on or near the surface of the earth bysaying: THE (RADIO, VISUAL) BEARING OFA FROM B IS X ± (RELATIVE/TRUE).

Distance. Distance is the separation betweentwo points. To measure distance, you measure thelength of a line joining the two points. This seemsunderstandable enough. However, suppose thatthe two points are on opposite sides of a baseball.How do you draw the line? Does it run throughthe center of the ball or around the surface? Ifaround the surface, what path does the linefollow? You must qualify the term distance usedin navigation to show how to measure thedistance. The shortest distance on the earth’ssurface from NAS San Diego to Sydney,Australia, is 6,530 miles. If you travel viaHonolulu and Guam, a frequently used route, itis 8,602 miles. You can express the length of achosen line in various units, such as miles,kilometers, or yards.

Time. Time has many definitions. The twodefinitions used with navigation are—

1. the hour of the day, and2. an elapsed interval.

The first appoints a definite instant, as takeofftime is 0215. The second definition appoints aninterval, such as time of flight, 2 hours 15 minutes.

Poles. The earth’s geographic poles are theextremities of the earth’s axis of rotation. As theearth rotates, a man on the surface facing thedirection of rotation has the North Pole on hisleft. East is in front of him, the South Pole is onhis right, and west is behind him.

The earth has some of the properties of a barmagnet. The magnetic poles are the regions nearthe ends of the magnet. This is where the highestconcentration of magnetic lines of force exist.However, the earth’s magnetic poles are not atthe geographic poles, nor are they opposite eachother.

Great circles and small circles. The intersectionof a sphere and a plane is a circle. The intersectionis a great circle if the plane passes through thecenter of the sphere. It is a small circle if it doesnot.

Parallels and meridians. Look at figure 5-10.Here, the earth’s equator is a great circle. If a

Figure 5-10.-The equator is a great circle whose plane isperpendicular to the polar axis.

second plane (fig. 5-11) passes through the earthparallel to the equator, its intersection is a smallcircle. If the small circles are perpendicular, thenall points on the small circle are equidistant fromthe equator; that is, the circles are parallel to theequator. Such small circles, together with theequator, are parallels. Parallels are onecomponent of a system of geographical coordi-nates,

Planes that pass through the earth’s poles(fig. 5-12) form great circles. Great circles throughthe poles of the earth are meridians. All meridiansare perpendicular to the equator. Meridians formthe second part of a system of geographicalcoordinates. These coordinates are commonlyused by navigators.

Latitude and longitude. Look at figure5-13. You can identify any point on earthby the intersection of a parallel and a meridian.It is the same as an address at the cornerof Fourteenth Street and Seventh Avenue.

Figure 5-11.-The plane of a parallel is parallel to theequator.

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Figure 5-12.-Great circle through the poles form meridians.

You just use different names for identifying theparallels and meridians. Latitude is the north-south geographical coordinate and longitude is theeast-west geographical coordinate.

Longitude is described as being east or westof Greenwich, England. This longitude atGreenwich is the Prime Meridian of 0°, thestarting point. Longitude extends 180° east andwest of the Prime Meridian, and it is broken downinto degrees, minutes, and seconds.

A degree is divided into smaller units. Howeverthe common method of subdividing the degrees isby—

1. degrees—60 minutes (60'), and

2. minutes—60 seconds (60").

To convert minutes or seconds into decimals ofdegrees, divide by 6. Thus, 15°30' = 15.5°, and15°30'24" = 15°30.4'.

Variation. The earth’s true (geographic) polesand its magnetic poles are not at the samelocations. Lines of magnetic force are not generallystraight because of irregu-lar iron deposits nearthe earth’s surface. Since a compass needle alignsto the lines of force at its location, it may not pointto true or magnetic north. When connectedtogether, lines connecting the locations on theearth where the compass does point to true northform an irregular line. This is the agonic line. Atother locations, the angle between the direction oftrue north and the direction of the earth’smagnetic field is the location’s variation. Linesconnecting locations having the samevariation are known as isogonic lines. Theearth’s field direction may not be the same asthe direction of the magnetic poles. This sameangle is also often called the angle of declina-tion. You label variation (or declination) eastor west as the magnetic field direction

Figure 5-13.-Longitude and latitude.

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Figure 5-14.-Easterly magnetic variation.

is east or west, respectively, of true north.(See figures 5-14 and 5-15.)

Deviation. Deviation is the error in a magneticcompass caused by nearby magnetic influences.These influences may relate to magnetic materialin the structure of the aircraft and to electrical(electronic) circuits. They deflect a compass needlefrom its normal alignment with the earth’smagnetic field. These deflections are expressed asdegrees. The deflection is east or west as thecompass points east or west, respectively, of theearth’s magnetic lines of force. Deviation varieswith the heading of the aircraft. Figure 5-16 showsone reason for this deviation.

Compass error. The net result of bothvariation and deviation is the compass error. If

Figure 5-15.-Westerly magnetic variation.

Figure 5-16.-Deviation changes with heading.

variation and deviation have the same name (eastor west), you add to get compass error. If theyhave different names, subtract the smaller fromthe larger. Give the difference given as the nameof the larger. (See fig. 5-17.) Label variation anddeviation plus (+) if west, and minus (–) if east.

Example 1.

Given:

Required:

Solution:

Variation 7° west (W), deviation 2°west (W).

Compass error.

7°W + 2°W = 9°W. To fly a truecourse of 135°, this aircraft over thisspot on the earth would fly a compassheading of 144°.

Example 2.

Given: Variation (–)2°, deviation (+)5°.

Required: Compass error.

Solution: (–)2° + 5° = (+)3°.

Magnetic dip. At the magnetic poles, thedirection of the earth’s magnetic field is vertical(perpendicular to the earth’s surface). Along theaclinic line (sometimes called the magnetic

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Figure 5-17.-Effect of compass error.

equator) roughly half way between the poles, thefield’s direction is parallel to the earth’s surface(horizontal). The difference between the directionof the earth’s field and the horizontal at anylocation is the magnetic dip. The magnetic dipvaries from very small angles near the equator tovery large angles near the poles. You can measurethe angles with a dip needle, which is a magneticneedle free to turn about a horizontal axis. A lineconnecting all locations having equal dip anglesis an isoclinic line.

Dead reckoning. Dead reckoning is the processof determining a position from the record of apreviously known position, course, speed, andtime traveled. To be accurate, every change ofcourse and speed during the flight is considered.It does not matter whether the pilot or the air mass(wind) through which the aircraft is flying makesthe changes.

Radar navigation. Modern radar is a valuableaid to navigation. Some radars present a maplikedisplay of the terrain around the aircraft on thescreen of a CRT. This lets the pilot go beyondsome of the limitations of visual observations.

Radar transponders are devices that do notoperate until interrogated or triggered into action

by a signal from another radar transmitter.Then, they transmit their own signal, which theinterrogating radar receives. These are used bothas fixed navigational aids, such as radar beaconstations, and as airborne identification friend orfoe (IFF) systems.

Doppler radar detects and shows actualground speed and drift of an aircraft, regardlessof wind speed or direction.

Radar altimeters give the actual distance fromthe aircraft to the surface below, The surfacebelow can be a body of water or land mass farabove sea level.

Radio navigation. Radio navigational aidsvary from a fairly simple direction-finding receiverto complex systems using special transmittingstations. These special stations make it possibleto fix the position of an aircraft with considerableaccuracy. The usable range varies accordingto its intended use, and also with weather andionospheric conditions. Beacon stations associatedwith an instrument landing system (ILS) areusually of low power. Long-range air navigation(loran) stations have a range extending to 1,400miles under favorable conditions. AviationElectronics Technicians (ATs) maintain theairborne portions of radio and radar systems.

Celestial navigation. Celestial navigation is themethod of fixing the position of the aircraftrelative to celestial bodies. Since the earth isconstantly revolving, an accurate time device isnecessary. In celestial navigation, three referencesare needed. The navigator tries, wheneverpossible, to select three bodies about 120 degreesapart in azimuth. This results in lines of positionthat cross cleanly and minimizes the effects of aconstant error in the observations.

Inertial navigation. An inertial navigationsystem (INS) is a dead-reckoning device that iscompletely self-contained. It is independent of itsoperating environment, such as wind, visibility,or aircraft attitude. It does not radiate or receiveRF energy; therefore, it is not affected bycountermeasures. An INS makes use of thephysical laws of motion that Newton describedthree centuries ago.

Air Navigation

Air navigation is the process of determiningthe geographical position and maintaining the

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desired direction of an aircraft relative to theearth’s surface. Certain conditions are unique toair navigation and have a special impact on thenavigator.

Continued motion. If necessary, a ship orland vehicle can stop and resolve any uncertaintyof motion or wait for more favorable conditions.Most aircraft must keep going.

Limited endurance. Most aircraft canremain aloft for only a relatively short time,usually a matter of hours.

Greater speed. Navigation of high-speedaircraft requires detailed flight planning, navi-gation methods, and procedures that are quickand accurate.

Effect of weather. Visibility affects theavailability of landmarks. Wind directly affectsthe position of aircraft. Changes of atmosphericpressure and temperature affect the heightmeasurement of aircraft using barometricaltimeters.

The primary problem in air navigation is todetermine the direction necessary to accomplishthe intended flight, to locate positions, and tomeasure distance and time as means to that end.The following equipments are used in airbornenavigation.

HORIZONTAL SITUATION INDICATOR(HSI).— Aircraft, such as the P-3, use thehorizontal situation indicator to provide the pilotwith a visual indication of the navigationalsituation of the aircraft.

BEARING-DISTANCE-HEADING INDI-CATOR (BDHI).— The BDHI is used withvarious navigation systems and providesinformation according to the mode selected. Someaircraft have more than one BDHI (fig. 5-18),wit h separate select switches for each instrument.The distance counter numerals may be in a verticalrow or horizontal.

The lubber index is a fixed reference mark atthe top of the instrument face. The compass card(read under the lubber index) shows the aircraftheading (either true or magnetic, depending on

Figure 5-18.-Bearing-distance-heading indicator.

the mode used). Two pointers, a single bar anda double bar, can indicate the following:

Bearing to a ground electronic station

Bearing to destination

Aircraft ground track

Aircraft drift angle

Heading error

The BDHI select switch selects the availablecombinations of these indications in a givenaircraft configuration.

ATTITUDE HEADING REFERENCESYSTEM (AHRS).— The AN/ASN-50 attitudeheading reference system (fig. 5-19) generates andprovides continuous roll, pitch, and headingsignals. These signals go to the aircraft attitudeindicator and other avionics equipment. Errorsignals develop in the displacement gyroscope asa result of displacement of synchro sensing devicesfrom their null position. A remote compasstransmitter supplies additional heading informa-tion to the system. For detailed information onthe AN/ASN-50 system, you should refer toReference Al t i tude Heading, N A V A I R05-35LAA-1.

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Q8.

Q9.

Q10.

Q11.

Q12.

Q13.

Figure 5-19.-Attitude heading reference system.

List the units in an IFF that make up the Q14.challenging station.

A point that is defined by stated or implied Q15.coordinates is known as a .

Q16.

The intended horizontal direction of travelis known as . Q17.

In what two reference directions can youexpress bearings?

Q18.

The east/west geographical coordinate isknown as . Q19.

You measure longitude 180° east or westfrom what point? Q20.

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The angle between true north and thedirection of the earth’s magnetic field isknown as .

How do you label variation?

Magnetic influences cause what type oferror in magnetic compasses?

The net result of both variation anddeviation is known as .

You can determine a position from the recordof a previously known position, course,speed, and time traveled by what process?

What navigation system makes use of thephysical laws of motion that Newtondescribed three centuries ago?

Describe navigation.

Inertial Navigation System

The inertial navigation system (INS) issometimes maintained by personnel in theAviation Electronics Technician (AT) rating.Some squadrons have an integrated weapons team(IWT). It is composed of the threeavionics/armament division (work center 200)ratings—AT, AO, and AE.

Navigation is defined as the process ofdirecting a vehicle from one point to another.Navigation can be divided into two basiccategories—position fixing and dead reckoning.

In position fixing, you determine positionrelative to positions of known objects such as starsand landmarks. The most common example ofnavigation by position fixing is celestial navi-gation. Loran is another example of navigationby periodic position fixes. Except for INS,

navigation systems rely on some information thatis external to the vehicle to solve its navigationalproblem.

Dead reckoning, the second category, is theprocess of estimating your position from thefollowing known information:

Previous position

Course

Speed

Time elapsed

Two examples of navigation by dead reckoningare Doppler radar and inertial navigation systems.

BASIC PRINCIPLES.– The operatingprinciple of the inertial navigation system (INS)


A8. The interrogator, synchronizer, and radar.

A9. Position.

A10. Course.

A11. True north or the direction the aircraft is pointing.

A12. Longitude.

A13. Prime Meridian, 0 degree in Greenwich, England.

A14. Variation.

A15. You label variation east or west as the magnetic field directionis east or west, respectively, of true north.

A16. Deviation.

A17. Compass error.

A18. Dead reckoning.

A19. Inertial navigation.

A20. Air navigation is the process of determining the geographicalposition and maintaining the desired direction of an aircraftrelative to the earth’s surface.

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is Newton’s first law of motion. This law states“Every body continues in its state of rest, or ofuniform motion in a straight line, unless it iscompelled to change that state by forces impressedon it.” In laymans terms, this law says that a bodyat rest t ends to remain at rest. It also says a bodyin motion tends to remain in motion, unless actedupon by an outside force.

The full meaning of Newton’s first law is noteasy to visualize in the earth’s reference frame.An inertial reference system can be defined as anonrotating coordinate frame. It can be eitherstationary or moving linearly at a uniform speedin which there are no inherent forces such asgravity.

A true inertial system can exist only in emptyspace, far from any mass. A reference systemattached to the earth can closely approximate aninertial system. For this system to work, you mustbalance the gravitational force on a body by asecond force. For example, an object sliding ona flat, frictionless plane on the earth’s surfacemoves in a nearly straight line. The object willhave a nearly constant speed.

Newton’s second law of motion is asimportant as his first law in an inertial navigationsystem because the inertial navigation systemworks on Newton’s second law. Newton’s secondlaw of motion states “Acceleration is proportionalto the resultant force and is in the same directionas this force.” Written mathematically—

where,

F = force

m = mass

a = acceleration

The physical quality in the equation thatpertains to the inertial navigation system isacceleration. You can derive velocity and displace-ment from acceleration.

Differentiation is the process of investigatingor comparing how one physical property varieswith respect to another. Integration, the reverseof differentiation, is the process of summing allrate of changes that occur within the limits underinvestigation.

The inertial navigation system is an integratingsystem. Yet, before integration can be done, itmust first have a rate of change. Therefore, theinertial navigation system is a detector and anintegrator. It first detects changes of motion. Itthen integrates these changes of motion with timeto arrive at velocity, and again with time to arriveat displacement.

DOPPLER RADAR PRINCIPLES.–Doppler radar uses continuous-wave (CW) radio-frequency (RF) transmission along with theDoppler effect. Pulse-type radar determines thedistance to the target by measuring the periodbetween transmission of a pulse and receipt of thereflected pulse. The CW Doppler radar sensesvelocity by measuring a proportional shift infrequency of the reflected signal. This frequencyshift is the Doppler effect.

Airborne Navigation Systems

The airborne navigation systems now in useare classified as either self-contained or ground-referenced.

A self-contained system is complete in itself.It does not depend on the transmission of datafrom a ground installation. Some self-containedsystems, such as search radar and Doppler radar,do require transmission of energy from theaircraft. Other self-contained systems, such as theinertial system and celestial-referenced aids, arecompletely passive in operation; they do notradiate energy from the aircraft.

Ground-referenced aids include all aids thatdepend on transmission of energy from theground.

THE IDEAL SYSTEM.– Every navigationsystem has certain advantages and disadvantages.An ideal system would not have to contend withadvantages of one system over another. Suchan ideal system would have the followingcharacteristics:

Ground information. The system indicatesthe ground position of the aircraft.

Global coverage. The system positions andsteers the aircraft accurately and reliably any placein the world,

Self-contained. The system does not relyon ground transmissions of any kind.

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Passive operation. The system does notbetray the position of the parent aircraft bytransmitting signals of any kind.

Immune to countermeasures. The systemis not susceptible to countermeasures of any type.

Useless to enemy. The system does notprovide navigational aid or intelligence of anykind to enemy forces.

Flexible. The system is flexible. The systemtracks the aircraft, even when unplanned devia-tions are made from the preflight course. Thesystem also operates at any altitude and at anyspeed within the capability of the aircraft.

ADF .– Radio beacons t r a n s m i t anondirectional signal that is easily identified asa specific station. If an aircraft has automaticdirection finding (ADF) equipment, the directionof the beacon from the aircraft can be determined.Most low-frequency, direction-finding equipmentreceives any frequency between 100 and 1750 kHz.

UHF/DF.– Some aircraft are equipped withautomatic direction finders in the UHF frequencyrange (225.00 to 399.95 megahertz), which useloop and sensing (antennas) to give bearinginformation. Operation of the direction finder iscontrolled from the UHF radio panel. It is usedto obtain a bearing to other aircraft and toemergency locator beacons that operate on 243.0MHz and 282.0 MHz.

VOR/ILS.– The VHF omnidirectional range(VOR) is a radio aid that has practically eliminatedinterference due to atmospheric conditions. VORstations operate between 108.00 and 117.95 MHz.Station identifiers for VOR navaids are given incode or voice or by alternating code and voicetransmission. The VOR provides an infinitenumber of courses or radials from the station. TheVOR also provides instrument landing system(ILS) capability. The transmission principle of theVOR is based on creating a phase differencebetween two signals.

RMI.– The RMI is a bearing indicator,usually with two pointers and a movable compassrose. The compass rose rotates as the aircraftturns, indicating the compass heading of theaircraft under the top of the index at all times.Therefore, all bearings taken from an RMI aremagnetic.

BDHI.– The BDHI is similar to the RMIin that a pointer provides magnetic bearinginformation. Additional information concerningthe BDHI is contained in the TACAN section.

HSI.– The HSI gives the pilot a visualindication of the navigational situation of theaircraft.

Tactical Air Navigation System (TACAN)

The tactical air navigation (TACAN) systemprovides the crew with information needed forprecise positioning within 200 nautical miles. Aswith VOR, TACAN provides an infinite numberof radials radiating outward from the station.In addition, distance measuring equipment(DME) provides continuous slant-range distanceinformation.

TACAN operates in the UHF band and has126 channels available in the X-mode pulsecode. Pulse coding gives ground equipment thecapability of an additional 126 channels in theY mode. The station identifier is usually trans-mitted at 37.5-second intervals in internationalMorse code. Airborne DME transmits on 1025 to1150 MHz; associated ground-to-air frequenciesare in the 962 to 1024 MHz and 1151 to 1213 MHzranges. Channels are separated at 1-MHz intervalsin these bands.

TACAN DME is designed to provide rangeinformation to a maximum distance of 200 to 300nmi, depending on aircraft equipment.

The air-to-air (A/A) function is provided togive distance information between two aircraft,working in the same manner as a regular ground-based TACAN station. Some sets provide onlyDME information. Newer sets provide bothdistance and bearing information to other aircraft.To obtain useful information, the A/A functionshould be selected by both aircraft with a63-channel frequency separation, In addition,each aircraft must have the same mode (X or Y)selected. If one aircraft sets A/A channel 4 andthe other sets A/A channel 67 in the X band,useful information should be obtained.

TACAN bearing is presented on an RMI(bearing), a BDHI, and a HSI (bearing andDME). The BDHI and HSI combine an RMI witha distance or range indicator, which saves spaceby displaying TACAN information on a singleinstrument.

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Long Range Navigation (Loran)

The name loran is derived from the words longrange navigation, which describes the hyperbolicsystem of electronic navigation, It provides linesof position over the surface of the earth. Overwater, usable loran signals can be received atranges up to 2,800 miles.

The loran system consists of a series ofsynchronized chain (set) of radio transmittingstations. These stations broadcast pulse signalssimilar to those used in radar with a constant timeinterval between them. The transmitting stationsare the foci. The aircraft has a combination radioreceiver and time difference measuring device. Themeasurements made by this equipment are usedto make entries in tables or charts that identifythe hyperbola on which the receiver is located.

The loran receiver is similar to an ordinaryradio receiver, except that it has no speaker. Theoutput of the receiver is fed to a loran baseindicator. The base indicator is an electronicdevice capable of measuring the time differencebetween the receptions of the master andsecondary signals with high precision. Thisindicator measures the time difference by one ofthe following methods:

1.

2.

3.

Using a CRT to provide a visual displayof the incoming signals. By visuallyaligning these signals, a reading of the timedifference measurement is obtained.Automatically, by the loran set. It providesreadings of the time difference.Integrating with a computer to displaylatitude and longitude.

Readings obtained by these methods areplotted on a loran plotting chart, or, in the caseof direct latitude/longitude readouts, they areplotted on any chart.

OMEGA Navigation System

Loran has significantly improved navigationover water and is very accurate up to 800 nmi.At distances over 1,000 nmi, sky waves must beused. Sky wave use causes a loss in positionaccuracy. Omega is an accurate long-range systemthat overcomes these problems.

The very low frequency (VLF) used by Omegatransmitters increases range. To get an accuratefix, a navigator obtains simultaneous signals fromthree different Omega stations. There are onlyeight Omega stations worldwide; yet, they provideworldwide coverage (fig. 5-20). These eight

Figure 5-20.-Omega transmitter locations.

stations actually operate at 10 to 13 kHz and usea signal phase difference rather than a time-of-arrival signal.

Omega transmitting stations operate in theinternationally allocated very low frequency(VLF) navigational band between 10 and 14 kHz.The VLF lets Omega provide navigational signalsat much longer ranges than other ground-basednavigational systems. The eight transmittingstations provide worldwide coverage with aninherent potential fixing accuracy of 2 to 4nautical miles 95 percent of the time.

Navigational Computer Systems

When automatic sensing devices are tied intoa navigation computer system, the navigator isautomatically provided current readings of presentlatitude and longitude, ground speed, andheading. The navigation computer system easesthe navigator’s workload and frees him or her tomake the decisions that are beyond the capabilityof computers.

To handle the many flight conditions at thespeed of sound or faster, the navigator usesautomatic navigation computers. The navigational

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computer system consists of the following com- handle, the navigator simultaneously changes theponents: position of the cross hairs and the corresponding

coordinate measurements (east-west and north-The data-gathering units (sensors) such as south) being fed to the navigation computers. Theradar, Doppler, INS, LORAN, and function is completed almost instantaneously.TACAN When the navigator positions the cross hairs

on a given return, the computers determine theComputer units where the computations distance between the aircraft and the return. Ifand comparisons are made the coordinates of the return have been set in the

computer, the computer can maintain a runningNavigation panels containing the dials and account of the aircraft latitude and longitude.controls that give the navigator a system-monitoring and control capability

SENSORS.– Sensors are data-gathering unitssuch as radar, Doppler, INS, LORAN, andTACAN.

Radar.– When a radar set is incorporated intothe computer system, movable electronic crosshairs are displayed on the radarscope so that rangeand direction of radar returns are measured andinserted into the computer (fig. 5-21). The crosshairs consist of a variable range mark and avariable azimuth mark. They are maneuvered witha cross hair control handle. On the radarscope,they resemble a single fixed-range mark and aheading mark. By moving the cross hair control

Doppler.– Doppler radar’s contribution to thecomputer system is ground speed and drift angle.These two outputs are put to several uses in thecomputer system. Doppler ground speeds is usedto drive the present position latitude and longitudecounters. Doppler outputs are used in platformleveling and in checking inertial ground speed inan inertial system. Doppler radar is an essentialpart of many navigation computer systems.

INS.– The INS is used to feed velocityinformation into the computers. Once the inertialsensor is leveled and in operation, it is used tocontinually update the present position counters.

Loran.– Loran fits in well with an automaticcomputer system. Some computer systems have

Figure 5-21.-Radar cross hairs.

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the coordinates of loran stations stored in them.During flight, the navigator selects the stations,and the computer does the rest. Fixing isautomatic and occurs in the same way that thenavigator takes a celestial fix. An assumedposition is determined by the computers; then, theloran position is applied to this assumed position.A series of credibility checks and approximationsare applied automatically to the computer. Theresult is an accurate loran fix. When the computerfunctions in the loran mode, continuous presentposition and ground speed information is stillavailable.

TACAN.– TACAN can easily be added to acomputer system. Since the TACAN output isgiven in the form of a range and bearing, thecomputers only need the coordinates of theTACAN station being used. This data is set intothe computer before the mission begins. Somecorrections must be applied to TACAN outputsto increase accuracy. The bearings received fromTACAN are magnetic; therefore, the computermust have an accurate magnetic variation valueat all times. This is usually built into the computer.TACAN range output is expressed in slant range.The computer applies absolute altitude above thestation to the slant range to produce exact groundrange.

COMPUTER UNITS.– The two basic typesof navigation computers are the analog and thedigital computer.

graphic replica of the problem to be solved isconstructed to find the answer, The analogcomputer is generally larger than the digitalcomputer because many components must beadded to solve a wide variety of problems. Theanalog computer has one main advantage—it isnot as sensitive to temperature and pressurechanges as the digital system.

Digital.– The digital computer is generallylighter and more compact than the analog system.In some cases, the digital computer weighsless than 100 pounds. It computes navigationproblems in the same way as the analog computer.It is unnecessary to design a digital computerexpressly for the navigation problems it is to solve.Properly programmed, the same computer couldbe used in fields other than navigation. This ispossible because the digital computer deals strictlywith numbers. This requires that all inputs bechanged to a numerical value before they are sentto the computer. Likewise, all outputs must beconverted back to terms that are meaningful tothe navigator.

NAVIGATION PANELS.– The navigationpanels make up the greatest part of the computersystem visible to the navigator. Panel appearanceand operation vary with each computer system.The multitude of counters, dials, switches,buttons, control knobs, and selectors give thenavigator maximum use and control of thesystem. Selectors that determine which sensors areused and which readouts are given let the

Analog.– An analog computer is comparable navigator switch from one mode of operation toto the navigator’s handheld computer because a another, as shown in figure 5-22.

Figure 5-22.-Typical control display unit.

5-23

The computer system helps the navigator.Most modern computers have limits built intothem so they will not accept unreasonableinformation. For instance, if the coordinates ofa fix point are set 1 degree of latitude inerror, the computer rejects the fix becausethe information is totally incompatible withinformation already in the computer. A rapidchange in ground speed from a sensor might berejected and that sensor output no longer usedbecause it would be considered unreliable.

So far in this discussion, only basic navigationhas been considered. A sophisticated computersystem can solve ballistic problems and auto-matically release bombs and missiles. If the systemis installed on a transport-type aircraft, cargo dropsand notification of bailout time to paratroops canbe controlled by the navigation computer.

Q21.

Q22.

Q23.

Q24.

Q25.

Q26.

Q27.

Q28.

Q29.

Describe differentiation.

Define a self-contained navigation system.

State the transmission principle of the VOR.

What is the frequency range of thetransmitted airborne TACAN DME?

With the addition of X and Y modes to theTACAN system, what total number ofchannels are available?

Loran determines the difference bymeasuring time intervals between the arrivalof the first signal and the arrival of a secondsignal. What type of measurements can beused?

State the basic reason for incorporating thenavigational computer in aircraft.

List the data-gathering units of a typicalnavigational computer system.

What other uses can the sophisticatedcomputer system provide?

COMMUNICATIONS AND DATA LINK

Learning Objectives: Identify communica-tions and data link systems and recognizetheir purpose. Recognize the interfacestructure between, and the operatingfeatures of participating units of a datalink system.

Radio communications is a highly sophisti-cated field of electronics. Even small Navy aircrafthave the capability to come up on the commonlyused communication circuits. Some common

circuits include ship-to-ship, ship-to-air, air-to-air,air-to-ground, and ship-to-shore.

Telecommunications refers to communica-tions over a distance. It includes any transmission,emission, or reception of signs, signals, writings,images, or sounds. It also includes intelligenceproduced by visual means, oral means, wire,radio, or other electromagnetic systems.Electrical, visual, and sound telecommunicationsare all used in the Navy. The basic equipment usedto communicate are the transmitter and receiver,

Transmitters and receivers each perform twobasic functions. The transmitter generates a radio-frequency (RF) signal of sufficient power at thedesired frequency and has a means of varying (ormodulating) the basic frequency so it can carryan intelligible signal. The receiver selects thedesired RF signal you want to receive and rejectsall unwanted RF signals. In addition, the receiverdetects the intelligence of the signal and amplifiesthe weak incoming signal to overcome the lossesthe signal suffers in its travel through space.

Navy Frequency Band Use

Table 5-1 shows the radio-frequency (RF)spectrum broken down into bands used by the

Table 5-1.-Radio-Frequency Spectrum

FREQUENCY DESCRIPTION

30 GHZ—300 GHZ extremely high frequency

3 GHZ—30 GHZ superhigh frequency

300 MHZ—3 GHZ ultrahigh frequency

30 MHZ—300 MHZ very high frequency

3 MHZ—30 MHZ high frequency

300 KHZ—3 MHZ medium frequency

30 KHZ—300 KHZ low frequency

3 KHZ–30 KHZ very low frequency

300 HZ—3 KHZ voice frequency

up to 300 HZ extremely low frequency

5-24

military. Propagation of radio waves varies widelyat different frequencies. Frequencies andequipment are chosen to meet the communicationsapplication desired. The frequency bands ofparticular interest to the Aviation ElectronicsTechnician (AT) are discussed in the followingparagraphs. For information on the other bands,refer to Navy Electricity and Electronics TrainingSeries (NEETS), module 17, Radio-FrequencyCommunications Principles.

MEDIUM-FREQUENCY (MF) BAND COM-MUNICATIONS.– The medium-frequency (MF)band of the radio-frequency spectrum includes theinternational distress frequencies (500 kHz andabout 484 kHz). Only the upper and lower endsof the MF band have naval use. Frequencies inthe lower portion of the MF band (300 to 500 Hz)are normally used for ground-wave transmission.They provide for transmission over moderatelylong distances over water and for moderate toshort distances over land. Transmission in theupper MF band is generally limited to short-rangecommunications (400 miles or less).

HIGH-FREQUENCY (HF) COMMUNICA-TIONS.– Successful transmission of HF signalsover long distances depends on the refraction ofradio waves by layers of the ionosphere. Ultra-violet radiation from the sun determines the heightand density of these layers. They vary significantlywith the time of day, season of the year, and the11-year cycle of sunspot activity.

Naval communications within the HF bandfall into groups of four general types of services.They include point-to-point, ship-to-shore,ground-to-air, and fleet broadcast. All of theseservices, except the fleet broadcast service,normally operate with two-way communications.Some of these services involve ships and aircraftthat present special problems because of theirphysical characteristics and mobility. These specialproblems of HF performance are at least partiallyoffset by powerful transmitters and sensitivereceiving systems at the ship/shore terminals.

VERY-HIGH-FREQUENCY (VHF) ANDABOVE COMMUNICATIONS.– Normally,frequencies above 30 megahertz are not subjectto refraction (bending) by the atmosphere, andground-wave range is minimal. This normallylimits the use of this frequency spectrum to lineof sight. However, you can increase range throughtropospheric scatter techniques, Some com-munications using VHF and above frequencies use

a technique called forward propagation bytropospheric scatter.

Certain atmospheric and ionospheric con-ditions can also extend the normal line-of-sightrange. Frequencies at the lower end of this bandare capable of overcoming the shielding effectsof hills and structures to some degree. However,as the frequency increases, the problem becomesmore prominent. Reception is notably free fromatmospheric and man-made static. The very-high-frequency (VHF) and ultra-high-frequency (UHF)bands are within the line-of-sight transmissionbands.

Amplitude-Modulated Systems

Amplitude modulation (AM) is a method usedto vary the amplitude of an electromagnetic carrierfrequency according to the intelligence carried bythe carrier. The carrier frequency is a radio-frequency (RF) wave suitable for modulation bythe intelligence to be transmitted. One form ofamplitude modulation is to interrupt the carrierusing a prearranged code.

The on-off keying of a continuous-wave (CW)carrier (fig. 5-23) frequency is one way tomodulate a carrier. The intervals of time whena carrier is present or absent carries the desiredintelligence. As applied to a continuouslyoscillating RF source, on-off keying is known asCW signaling, or as an interrupted continuouswave (ICW).

The primary disadvantages of AM modulationare susceptibility to noise interference and theinefficiency of the transmitter. To overcome thesusceptibility to noise interference, anglemodulation was developed.

Angle Modulation

Angle modulation is modulation in which theangle of a sine-wave carrier is varied by a

Figure 5-23.-Continuous-wave modulation.

5-25

modulating wave, Frequency modulation (FM) signals from 190 kHz to 550 kHz and from 2 MHzand phase modulation (PM) are two types of angle to 25 MHz, in five frequency bands, A mechanicalmodulation. In FM, the modulating signal causes type counter, located on the front panel of thethe carrier frequency to vary. These variations are receiver (fig. 5-24), shows the frequency, in MHz,controlled by both the frequency and amplitude of received signals. It can receive signals that areof the modulating wave. In PM, the phase of the of the amplitude modulated (AM), unmodulatedcarrier is controlled by the modulating wave form.

In frequency modulation (FM), an audiosignal is used to shift the frequency of an oscillatorat an audio rate. Frequency-shift key (FSK) is thesimplest form of FM, and it is similar to CWkeying in AM transmissions.

For more information on AM, FM, and pulsemodulation principles, refer to Navy Electricityand Electronics Training Series (NEETS), module12, Modulation Principles, N A V E D T R A14184.

General-Purpose Receiver

A typical general-purpose receiver, consistingof a receiver and its mounting, is a super-heterodyne receiver. It is capable of receiving RF Figure 5-24.-Megahertz frequency indicator.


A21. Differentiation is the process of investigating or comparing ho wone physical property varies with respect to another.

A22. A self-contained system is complete in itself; it does not dependon the transmission of data from ground installations.

A23. The VOR transmission principle is based on creating a phasedifference between two signals.

A24. 1025 MHz to 1150 MHz.

A25. 126 channels in X and 126 channels in Y, 252 total channelsavailable.

A26. CRT display, automatically by the loran set, integrating with thecomputer.

A27. To handle the many flight conditions at the speed of sound orabove.

A28. Radar, Doppler, INS, loran, and TACAN.

A29. Solving of ballistic problems, automatic release of bombs andmissiles, cargo drops, and notification of bailout times are justa few.

5-26

continuous wave (CW), or frequency shift keyed(FSK) types.

HF Transceiver

The typical HF transceiver transmits andreceives communications in the high-frequency(HF) band and can operate on a frequency rangefrom 2.0 to 29.999 MHz. The set may include aradio receiver-transmitter (RT), radio set control,and mounting. The RT unit is usually of modularconstruction and easy to maintain. In additionto the set components, the complete aircraftinstallation may require a headset, microphone,key, antenna coupler, and antenna.

VHF Transceivers

The main purpose of VHF transceivers isto provide two-way communications betweenaircraft, ships, and shore stations. They normallyoperate within the frequency range of 116 MHzto 149.95 MHz. Some VHF transceivers are dualpurpose. Their receivers also work with the VHFomnidirectional rapid range (VOR) navigationsystems. When used for this purpose, thefrequency range of the receiver extends to cover108 MHz to 151.95 MHz.

UHF Transceivers

There are two main types of UHF trans-ceivers—frequency modulated (FM) and ampli-tude modulated (AM). Typical FM UHFtransceivers operate between 225.0 MHz to 399.9MHz, with channels spaced 100 kHz apart.Typical AM UHF transceivers operate between225.0 MHz to 399.975 MHz, with a fixed guardfrequency of 243. MHz.

Intercommunications Systems

All aircraft intercommunication systemsperform essentially the same basic functions. Theydeliver audio to one or more selected stations onboard the aircraft to permit crew members tospeak to each other. They also provide controlof the communication facilities so variousmembers of the crew may receive incoming radiomessages or transmit messages with the aircrafttransmitters. It is also necessary for theintercommunication system to contain facilitiesfor operating recording equipment. This lets youmake permanent records of the various receptionsand transmissions occurring during flight.

Communication Antennas

An antenna is a special type of electrical circuitintentionally designed to radiate and/or receiveelectromagnetic energy. In an ordinary circuit, theinductance (L), capacitance (C), and resistance (R)properties lump together and are constant.Therefore, the electromagnetic field is confinedto the circuit where it performs useful work. Inan antenna, the L, C, and R properties spread out,and the electromagnetic field tends to escape orradiate. It is this radiated field that provides thelink between a transmitter and receiver.

While the simplest type of antenna is thebidirectional dipole, limitations in directivity,frequency bandpass, and gain somewhat restrictits use. Other dipole configurations such as theram’s horn and the corner reflector are for specialapplications.

Although the crossed dipole, the whip, thetop-loaded vertical, or the J antennas are in use,the ground plane antenna is probably the mostpopular. This is especially true when reception ortransmission must be equally effective in alldirections (omnidirectional), For much higherfrequencies, the biconical or the disc horn is anexcellent antenna.

The log periodic, helical, and flat-spiralantennas have an extremely wide (as high as 20: 1)operating frequency range.

When space is not a controlling factor, therhombic and the V type provide high gainand directivity. They can be unidirectional byterminating the ends of the legs with a non-inductive resistor. The V can be unidirectional byuse of another V spaced an odd number of quarterwavelengths behind the original. Typical legs forthe rhombic are three to four wavelengths; for theV type, legs of eight wavelengths are notuncommon.

The parabolic antenna can produce high gainand excellent directivity. Although screen mesh,or even a grid or rod, provides increased stabilitywhere wind resistance is a design factor, thereflector element generally consists of a solidsurface. Physically, the reflector should be severalwavelengths in diameter. The radiating elementmay be a dipole, a horn, or other suitableradiator. Mounting a hemispherical reflector infront of the dipole may increase gain providingits surface area does not appreciably shadow therear parabolic reflector.

5-27

Data Link System Interfacingand Operation

The data link system is a communications linkthat provides computer-to-computer exchange ofinformation. A typical link may include tacticalASW data between an aircraft and other partici-pating units (PUS) and reporting units (RU) viaRF transmission. Data link transmission includescommunication and navigation information, voicecommunications, secure (coded) voice communi-cations, sonobuoy information, and computerdata.

A data link system is an integrated communi-cations system that uses the functions andcomponents of various communications systemsto provide the data link capability. A modern datalink system has the following components installedon the aircraft.

A general-purpose digital computer(GPDC)

A switching logic unit (SLU)

A data terminal set (DTS)

An integrated radio control (IRC)

A secure data keyer

A communication system (HF and UHFradio equipment discussed earlier)

ELECTRONIC COUNTERMEASURES(ECM), ELECTRONIC SUPPORTMEASURES (ESM), AND WEAPONCONTROL

Learning Objectives: State the meaning andpurpose of the two basic categories ofECM—electronic and nonelectronic.Identify various types of deception andjamming devices used in ECM andrecognize their characteristics. Describe theweapon control fundamentals to includethe primary problem, ballistics, andtrajectory.

The purpose of ECM equipment is to detect,analyze, locate, and degrade the use of an enemy’selectronic warfare equipment. To do this, theNavy uses two basic categories of airborne ECMsystems—passive ECM (PECM) or ESM andelectronic and nonelectronic ECM (designed to

jam or block an electronics system). Because ECMequipment is classified, no in-depth theory orcircuitry is discussed in this TRAMAN.

ESM Indicator Units

ESM operations are not directly detectable bythe enemy because they do not transmit. Thepurpose of ESM equipment is to detect (receive),plot (locate), and analyze the signal characteristicsof a suspected enemy’s communications, navi-gation, and radar equipments. To do this, an ESMsystem must have receivers that cover the entirefrequency spectrum and a direction-finder (DF)type of antenna system. They also requireindicators with circuitry to analyze and displaythe various signal characteristics. You may knowESM as passive electronic countermeasures(PECM). The terms PECM and ESM a r esynonymous.

ESM indicators give the operator a visualpicture or digital readout of the received signal,let the operator analyze and determine therequired signal characteristics, and plot thelocation of the transmitting station. There arethree basic classes of indicators—panoramicadapters, digital display indicators, and pulseanalyzers.

Electronic Countermeasures (ECM)

The design of defensive ECM equipment isprimarily to protect a single aircraft from anenemy radar. This equipment is also referred toas a deceptive ECM system because it deceivesrather than jams a radar system. The two basiccategories of ECM equipment are electronic andnonelectronic ECM.

ELECTRONIC ECM EQUIPMENT.–Various types of electronic ECM equipmentsdeceive various types of radars, such as search,fire-control, etc. The method of deception (suchas time delay for search radar and frequencyshifting for fire-control radar) may vary, but theoperating concept is the same. For example, todeceive a threat radar signal, false informationis injected, and the signal is retransmitted withincreased power.

The ECM equipment receives the threat radarsignal, amplifies it, detects the pulse, delays thepulse a few seconds, and retransmits the pulse.Some ECM equipment not only injects timedelays, but transmits multiple pulses that showup as multiple targets on a radar’s indicator.

5-28

Regardless of the type of deception used, thethreat radar cannot plot the correct location ofthe aircraft. Fire-control radar will not be ableto “lock-on” the aircraft,

ACTIVE ECM/JAMMING.– Active ECM isa term given to ECM electronic equipmentdesigned to jam communications, navigation, andradar receivers. These jammers are high-power,noise-modulated transmitters that transmitrandom noise over a given band of frequencies.This high-powered noise overdrives (jams) thereceiver of the target equipment and makes ituseless. In threat radar, the jammer signal willcause the indicator to blossom. It blossomsbecause the jammer’s powerful noise signaloverdrives the radar receiver’s circuits. When theradar receiver’s circuits are overdriven, thereceiver puts out a constant video signal for anarea where the noise signal is stronger than thereceiver’s maximum sensitivity. In this way,one ECM jammer can protect (hide) a group ofaircraft over a large area.

NONELECTRONIC ECM.– Another meansof deceiving a threat radar is by using chaff. Chaffis the general name given to packaged strips ofmetal foil that resembles confetti. When chaffejects from an aircraft, it disperses into the airand causes multiple echo signals (targets) on theradar’s indicator. The metal foil is cut to thecorrect wavelength of the radar transmittingfrequency, so it will reflect maximum echo signalsback to the radar receiver.

Weapon Control Fundamentals

The primary problem of aircraft weaponssystems is to accurately determine the correctposition and attitude in which to place theaircraft. Correct positioning of the aircraft givesreasonable assurance of a hit on the target. Nomatter how difficult or how simple the problem,two terms are always present in the solution ofthe problem—ballistics and trajectory.

Ballistics refers to the science of the motionof projectiles. It is a study of all the various forces,both controllable and uncontrollable, that governthe movements of projectiles.

The study of ballistics includes two branches—interior and exterior. The study of interior

ballistics involves the movement of projectilesinside a gun barrel or bore. The study of exteriorballistics involves the motion of the projectile infree air after it leaves the bore of the gun or thelauncher.

Exterior ballistics is the branch of ballisticswith which you are concerned. To understandexterior ballistics, you must fully understand theterm trajectory. Trajectory is the curve a projectiledescribes in space as it travels to the target.

For guns, trajectory is from the muzzle tothe first point of impact.

For rockets and missiles, the actual ballistictrajectory is that portion of the distanceto the target under free flight (after burntime).

For bombs, the trajectory is from the timeof release to the time of impact.

Weapons Systems Concept

As aircraft altitudes increased and speedsreached the supersonic regions, the ability of theattacking aircraft to perform its mission becamemore difficult. To engage a target at supersonicspeeds was impossible when depending only onthe operator for accuracy. The result of solvingthese problems was the current aircraft—acompletely integrated machine. Each of theseparate systems are subsystems interconnectedand dependent, to some extent, on each of theothers. For example, the navigation systemdepends on the radar system; and the automaticflight control system depends on a computer. Thecomputer depends on both the radar and naviga-tion systems for proper operation. A weaponssystem includes the following:

Units that detect, locate, and identify thetarget.

Units that direct or control the deliveryunit or the weapon, or both.

Units that deliver or initiate delivery of theweapon to the target.

Units that destroy the target when incontact with it or near it; these units areusually termed weapons.

5-29

Q30.

Q31.

Q32.

Q33.

Q34.

Q35.

Q36.

Q37.

ASW

To what NEETS module should you referfor information on radio frequency com-munications principles?

What two transmission bands are containedwithin the line-of-sight transmission band?

What is meant by the statement “someVHF transceivers are dual purpose?”

To what NEETS module should you referfor more information on AM, FM, andpulse modulation principles?

What type of communications antenna isexcellent for higher frequencies?

What term is given to electronic ECMequipment designed to jam communica-tions, navigation, and radar receivers?

Describe ballistics.

Define trajectory.

ACOUSTIC AND RECORDERSYSTEMS

Learning Objectives: Recognize the operat-ing principles of magnetic anomaly detec-tion (MAD). Recognize the classification,specifications, and operating principles ofsonobuoys currently in use. Recognize thefunctions of and the relationship betweencomponents comprising magnetic taperecorder systems used on Navy ASWaircraft.

The most feasible method of detecting asubmerged submarine was to detect its disturbanceof the local magnetic field of the earth. Thedevelopment of the sonobuoy has made it possibleto detect submarines using sound-ranging equip-ment (sonar) by aircraft.

Principles of Magnetic Detection

Light, radar, and sound energy cannot passfrom air into water and return to the air in anydegree that is usable for airborne detection.However, the lines of force in the earth’s magneticfield pass through the surface of the oceanessentially undeviated and undiminished instrength. The change of medium from water toair or air navigation has little or no effect onmagnetic lines of force. Consequently, detection

of an object under the water can occur from aposition in the air above it if the object hasmagnetic properties that distort the earth’smagnetic field. A submarine has sufficient ferrousmass and electrical equipment to cause a detect-able distortion (anomaly) in the earth’s field.Detection of this anomaly is the function ofmagnetic anomaly detection (MAD) equipment.

The maximum range of submarine detectionis a function of both the intensity of its magneticanomaly and the sensitivity of the detector.

NOTE: A magnetometer is the detector inMAD equipment.

A submarine’s magnetic moment (magneticintensity) determines the intensity of the anomaly.The magnetic moment depends mainly on thesubmarine’s alignment in the earth’s field, its size,its detected latitude, and the degree of itspermanent magnetization.

ANOMALY STRENGTH.– A submarine’sanomaly is usually so small that MAD equipmentmust be capable of detecting a distortion of aboutone part in 60,000. This is because the directionof alignment of the earth’s magnetic lines of forcerarely change by more than one-half of 1 degreein a submarine anomaly.

COMPENSATION.– Regardless of itssource, strength, or direction, any magnetic fieldmay be defined in three axial coordinates. Thatis, it must act through any or all of three possibledirections—longitudinal, lateral (transverse),or vertical—in relation to the magnetometerdetector.

Compensation for magnetic noises is necessaryto provide a magnetically clean environment. Thisensures the detecting system will not be limitedto the magnetic signal associated with the aircraftitself.

Under ideal conditions, all magnetic fieldsacting on the magnetometer head are completelycounterbalanced. In this state, the effect on themagnetometer is the same as if there are nomagnetic fields at all. This state exists only whenthe following ideal conditions exist:

1.

2.

3.

The aircraft is flying a steady course (nomaneuvers) through a magnetically quietgeographic area.Electric or electronic circuits remain eitheron or off during compensation.Direct current of the proper intensity anddirection flow through the compensationcoils, so all stray fields are balanced.

5-30

To approximate these conditions, the com-pensation of MAD equipment usually occurs inflight, well at sea. In this way, the equipmentcompensation occurs under operating conditions,which closely resemble those of actual ASWsearch flights.

Sonobuoys and Associated Receiversand Recorders

Sonobuoys are aircraft-deployed, expendablesonar sets that contain a VHF radio transmitterto relay acoustic information to the deployingaircraft. The detection, localization, andidentification of potentially hostile submarines isthe primary mission of the U.S. Navy airborneantisubmarine warfare (ASW) forces. The ASWcapability of the fleet and the Navy operationalreadiness to deal with the submarine threatcritically depends on sonobuoys. Sonobuoysdetect underwater sounds, such as submarinenoise and fish sounds. These audio frequency(AF) signals modulate an oscillator in the RFtransmitter portion of the sonobuoy. The outputof the transmitter is an FM-modulated, VHFsignal that is transmitted from the sonobuoyantenna. The signal is received by the aircraft thatdropped the sonobuoy. This signal is detected andprocessed by a sonobuoy receiver. By analyzingthe detected sounds, the ASW operator candetermine various characteristics (such aspropeller shaft speed) of the detected submarine.The use of several sonobuoys operating ondifferent VHF frequencies in a tactical pattern letsthe ASW operator localize, track, and classify asubmerged submarine.

Sonobuoys may be grouped into three cate-gories—passive, active, and special-purpose.Passive sonobuoys are used in LOFAR andDIFAR systems. Active sonobuoys are used inCASS and DICASS systems, and special-purposesonobuoys (BTS and DLC) are used for missionsother than ASW.

PASSIVE SONOBUOY.– The passivesonobuoy is a listen-only sonobuoy. The basicacoustic sensing system that uses the passivesonobuoy for detection and classification is thelow-frequency analysis and recording (LOFAR)system.

LOFAR System. In the LOFAR system,sounds emitted by the submarine are detected by

a hydrophone from a passive omnidirectionalsonobuoy. Data on the frequency and amplitudeof these sounds are then transmitted by thesonobuoy antenna to a receiving station. Atthis station, normally located on board thedeployment aircraft, the sound data is analyzed,processed, displayed, and recorded, The basicLOFAR display plots the frequency of the soundwaves against the intensity of their acoustic energyand against the duration of the sound emission.This data can be displayed on a video screen andprinted out. The data is also recorded on magnetictape for storage and retrieval when desired.

DIFAR System. The directional low-frequencyanalysis and recording (DIFAR) system is animproved passive acoustic sensing system. Usingthe passive directional sonobuoy, DIFAR operatesby detecting directional information, and then itfrequency multiplexes the information (data) tothe acoustic data transmitted by the sonobuoy tothe deployment aircraft. This informationundergoes processing by the aircraft’s acousticanalysis equipment to compute a bearing anddisplay it. Subsequent bearing information fromthe sonobuoy can pinpoint, by triangulation, thelocation of the sound or signal source.

ACTIVE SONOBUOY.– The active sono-buoy is either self-timed or commendable. Theself-timed sonobuoy generates a sonar pulse at afixed pulse length and interval. The commandablesonobuoy generates a sonar pulse, as determinedby a UHF command signal from the controllingaircraft.

An active sonobuoy uses a transducer toradiate a sonar (sound) pulse that is reflected fromthe hull of the submarine. The time between theping (sound pulse) and the echo return to thesonobuoy is measured. Taking into account theDoppler effect on the pulse frequency, thistime-measurement data helps to calculate bothrange and speed of the submarine relative to thesonobuoy.

CASS sonobuoys. The command activesonobuoy system (CASS) allows the sonobuoy toremain silent until it receives a command signalfrom the aircraft to radiate a sound pulse. Thistechnique allows the aircraft to surprise thesubmarine.

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DICASS sonobuoy. A CASS sonobuoy,equipped with a directional hydrophone, is adirectional commandable sonobuoy (DICASS).A DICASS sonobuoy lets the aircraft acousticanalysis equipment determine both range andbearing to the target with a single sonobuoy.DICASS sonobuoys are replacing the older ROand CASS sonobuoys.

SPECIAL-PURPOSE SONOBUOYS.–Currently there are two categories of special-purpose sonobuoys in use by the fleet—thebathythermobuoy (BTS), and the Down-LinkCommunication (DLC) special-purpose sonobuoys.These sonobuoys are NOT for use in sub-marine detection or localization.

Bathythermobuoy. The bathythermobuoy(BTS) measures the water temperature versusdepth. The time of descent of a temperature probedetermines the water depth. Once the BTS entersthe water, this probe (fig. 5-25) descendsautomatically at a constant 5 feet per second.

The probe uses a thermistor, a temperature-dependent electronic component, to measure thetemperature. The electrical output of the probegoes to a voltage-controlled oscillator, whoseoutput signal frequency modulates the sonobuoytransmitter. The frequency of the transmit signal,which is recovered at the sonobuoy receiver in theaircraft, is linearly proportional to watertemperature. The water temperature and depthare recorded on graph paper that is visible to theASW operator.

DLC. The down-link communition (DLC)buoys are for communication between air-craft and submarines. The DLC buoy is not com-manded and provides down-link communicationsonly by a preselected code.

Sonobuoy Receivers

The sonobuoy receiver has many functions.It receives RF signals from deployed sonobuoys,


A30. Module 17.

A31. UHF and VHF.

A32. Module 12, Modulation Principles.

A33. Their receivers also work with VHF and VOR.

A34. The biconical or disc horn.

A35. Active ECM.

A36. The science of motion of projectiles.

A37. The curve of a projectile describes in space as it travels to thetarget.

5-32

Figure 5-25.-Bathythermograph sonobuoy deployment.

detects intelligence on the signals, providesintelligence to various onboard equipment foracoustic analysis and recording and for navigatingor navigation purposes.

SONOBUOY RECEIVER SET.– One com-monly used sonobuoy receiver set includes 31radio receivers that receive FM-modulated signalsin the VHF range. Thus, simultaneous reception,demodulation (detection), and audio output of upto 31 RF channels are possible. These channelsmay each be any one of 31 preselected channels.Each audio output provides two levels—highaudio and standard audio.

The equipment is primarily for (but not limitedto) installation in either fixed- or rotary-wingaircraft. Although capable of being an inde-pendent operating unit, normally, the equipmentis used with some combination of several typesof sonobuoys and a signal processor.

Newer sonobuoy receiver groups provide thecapability of simultaneously receiving 20sonobuoy signals. To accomplish this they use20 subassemblies. Each subassembly may beindependently and automatically tuned to any1 of 99 sonobuoy RF channels now in use, andthose that are in development for futuredeployment.

5-33

SONAR COMPUTER-RECORDER GROUP.–The sonar computer-recorder group (DIFARsystem) analyzes, records, and generates apermanent printed display of the passive andactive sonobuoy signals processed by the receiversystem. This display can provide information foridentifying and locating the source of thesound. The system uses low-frequency analysis,directional-frequency analysis, broadband-frequency analysis, directional listening, andactive ranging or Doppler techniques to detect,classify, and localize the underwater target,

The four basic modes of operation of theDIFAR system are as follows:

1.

2.

3.

4.

OMNISEARCH—omnidirectional signalfrom a passive buoy with NO directionalcapabilitiesALI-LOFAR—integrated omnisearchd i s p l a y u s i n g a d i r e c t i o n a l o rnondirectional passive buoyDIFAR—directional frequency analysisand recording—will give a bearing to thetarget using directional buoysRange—gives the range in yards to thetarget using an active range only buoy

Magnetic Recorders

Magnetic recorders are used throughout theNavy in various forms and types. They may bea simple audio recorder or the most complex datarecorder; however, all of them provide a handy,compact means of storing and retrieving largeamounts of information.

OPERATION OF A MAGNETIC RE-CORDER.– Operation of a magnetic recorderinvolves three basic processes—recording,reproducing, and erasing. In analog systems,reproducing is playback or play. In digitalsystems, record is write, and reproducing is readback or read. Keep in mind that analog recordingand digital recording refer to recording techniquesand not to the information recorded.

DIGITAL RECORDING.– The basicdifference between analog and digital recordingis in the method and degree of magnetizing of therecording media. For analog recording, linearityand low distortion are the primary requirements.However, for digital recording (as in most digitalsystems) there are only two states—0 or 1, ONor OFF, TRUE or FALSE, or whatever namesare convenient.

ERASING.– The term erasing refers to anelectromagnetic process, or demagnetizingprocedure, that removes signals previouslyrecorded without affecting the magnetic tape inany other way. The action is a realignment (orpolarizing) of the oxide particles on the tape soall modulation (recorded data) is removed,making it possible to reuse the same tape.

Q38.

Q39.

Q40.

Q41.

Q42.

What two factors determine the maximumdetection range of a submarine?

What is the purpose of compensation?

What recorder system plots the frequencyof the sound waves against the intensity oftheir acoustic energy and duration of thesound emission from an omnidirectionalpassive sonobuoy?

List the types of sonobuoys.

List the four basic modes of the DIFARsystem.

SUPPORT EQUIPMENT

Learning Objective: Identify varioussupport equipment, including aircraftpower generation, conversion, control,regulation, and protection equipment.

Support equipment has become as importantto the assigned mission of naval aviation activitiesas the aircraft itself. Many different types ofsupport equipment are required for handling,servicing, loading, testing, and maintainingaircraft. Although your rating is not responsiblefor the upkeep and maintenance of supportequipment, you, as a user, must have a basicknowledge of the equipment’s capacity andoperation.

You must understand the capabilities andlimitations of the auxiliary power sourcesprovided for use in ground servicing andmaintenance of aircraft. You must observe andenforce all safety precautions and regulationsconcerning the use of the units,

You must also know the requirements forcooling the various electronic equipment while onthe ground. You must be familiar with the sourcesof auxiliary air and cooling, and you must knowthe capabilities and limitations of the variouscooling units.

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This chapter discusses these topics. In mostsections, the discussion is general. In a fewinstances, details are presented as they pertain tospecific items of equipment. Coverage of theequipment is limited to those expected to be incommon usage during the life of this trainingmanual.

AIRCRAFT POWER

The electrical power system of an aircraftconsists of the power source and its associatedcontrols, the generation system and its associatedcontrols and regulation, the conversion units, thefeeder and distribution system and its componentparts, and the various protective devices usedthroughout the installation.

As part of the overall effort to standardizeaircraft and electronic installations, the supply anddistribution of power offered a logical startingpoint. The first step was to standardize the supplyvoltages and power frequencies and to usegenerators that would provide the requiredpower. Later in the standardization program, thegeneration of dc power was discontinued, and theprimary power became exclusively ac. The dcrequirement was supplied through transformer-rectifiers. This reduced the number of voltagesgenerated, reduced the number of rotary devices,and allowed the use of smaller conductors in thedistribution system. The result was a drasticdecrease in the total weight of a given installation,which, in turn, permitted a more complexinstallation for a given weight allowance.

To be of any real value, a partial listing of theconsiderations involved in any discussion ofaircraft electrical systems must include thefollowing items:

1. A main generating source refers to allgenerator units driven by a specified engine; thus,a single-engine aircraft can have only one mainsource.

2. Multiengine aircraft may have a maingenerating subsystem for each engine. This is theusual practice, but it is not universally followed.

3. Adequate frequency regulation andstability in ac generation systems require somemethod of speed control of the generator’s rotordrive mechanisms.

4. Provisions must be made to ensure thatadequate power is available in each mode ofoperation. In the event of failure of the aircraftengine or its associated generation system, themaximum amount of power that can be produced

is decreased. In the case of single-engine aircraft,this automatically constitutes an emergencysituation.

5. The failure of a single generator or enginein a multiple installation does not constitute thesame degree of emergency as the same failure ina single-engine installation. Although somerestrictions are placed on operational capabilities,some degree of safety may usually be maintainedwith the remaining engines and generators.

6. Provisions should be made to enable useof external power sources for starting the engineswhile on the ground and for ground operationwithout using the aircraft engines. The aircraftelectrical system must include provisions toprevent applying both internally generated powerand externally furnished power to the system atthe same time.

Aircraft Electrical Systems

The electrical system of each model aircrafthas some features peculiar to it alone, while otherfeatures are common to most models. In thissect ion, you are presented with a generaldiscussion of the electrical system of a typicalaircraft.

SOURCE OF POWER.— The basic source ofpower for the electrical system is the aircraftengine. An ac generator requires a constantrotational speed to produce a constant frequencyoutput. In most modern aircraft, a constant-speeddrive (CSD) unit is inserted between the aircraftengine and the ac generator for this purpose.

GENERATION SYSTEM.— The heart of theelectrical generation system is the constant-speed,wye-connected ac generator. This unit normallyproduces a three-phase output voltage of about120/208 volts at 400 Hz, which is subsequentlyregulated to 115/200 volts. The basic theory ofac generators is discussed in Navy Electricity andElectronics Training Series (NEETS), module 5.

DC Generator.— In most older aircraft, allelectrical power was generated as dc voltage. Inmost of the newer aircraft, no dc voltage isgenerated. The dc requirements are met bytransforming and rectifying the ac. In someoperational aircraft presently in service, however,the main power generation system provides bothac and dc voltages from a common unit. In otheraircraft models, a separate generator is used toprovide the dc power required for operation of

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the dc components. This method is not commonin airborne applications because of the limitednumber of engines available. The basic theory ofdc power generators is presented in NEETS,module 5.

Emergency Generators.— In the event offailure or shutdown of the aircraft engines ormain generators, the electrical system becomesinoperative. The aircraft must have electricalpower to maintain adequate flight control. Allnaval aircraft incorporate an auxiliary oremergency generator that operates independentlyof the aircraft engine.

System Voltage Regulation

Voltage regulators are incorporated in allelectrical generation systems. Although similar inbasic purpose, the configuration and details ofoperation vary with each type. A typical solid-state voltage regulator may consist of a sensingcircuit with input rectifiers, a temperature-compensated Zener diode reference and error-detecting bridge, and a three-stage transistoramplifier. The output of the bridge circuit is avoltage inversely proportional to the differencebetween the generator voltage and the regulatorset voltage, and it is referred to as the error signal.

External Power

All aircraft have provisions for application ofelectrical power from an external source forstarting the aircraft engines and/or for groundservicing and maintenance without operating theengines. This power, while not generated withinthe aircraft, is part of the overall electrical systemof the aircraft. All aspects must be compatible

with the power generated within the aircraft.Under no circumstances may the internal andexternal power be used at the same time. This isone of the functions of the distribution system,which is discussed briefly in the following text,The equipment used to supply power in theexternal mode of the electrical system is discussedbriefly in a later portion of this chapter.

Distribution Systems

Once the electrical power has been generatedand some of it transformed, it must be distributedto the various components and equipment whereit is to be used. In a simple system, withcomparatively few equipment and requiring onlya single form of electrical power, a simpledistribution system could be used. In modernnaval aircraft, however, with the complexelectrical and electronic installations requiringmany forms of power, an extremely complexdistribution system is required.

Each model aircraft has different electricalrequirements; therefore, each distribution systemmust differ from all others under individualrequirements. The major area of differencebetween distribution systems of different modelaircraft lies in the switching arrangement used tochange electrical loads from one source to anotherin the event of a malfunction.

Power Conversion Devices

In most naval aircraft, the main electricalpower generation system produces three-phase acpower at 400 Hz. All aircraft require various levelsand quantities of dc power. In many instances,ac power of a different frequency is also required.In these cases, various devices are needed to


A38. Its magnetic anomaly and the sensitivity of the detector.

A39. To provide a magnetically clean environment and ensure thedetecting system will not be limited by the aircraft itself.

A40. LOFAR and DIFAR.

A41. Passive, active, CASS, DICASS, and special purpose.

A42. Omnisearch, ALI-LOFAR, DIFAR, and range.

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convert the power from the forms generated intothe forms required for the specific application.A few important conversion devices are discussedbriefly in the following paragraphs.

TRANSFORMER-RECTIFIERS.— The mostcommon conversion device for changing ac to dcis the transformer-rectifier. The three-phase,115-volt ac is reduced in a step-down transformer,and then rectified to produce the 28-volt dcrequired for operation of various relays, lights,instruments, and mechanical devices. Specifictransformer-rectifier units are discussed in theelectrical section of the maintenance instructionsmanual (MIM) for each model aircraft. Thefundamental theory of transformers is discussedin NEETS, module 2.

INVERTERS.— An inverter is a rotatingelectromechanical device used to convert low-voltage dc into ac. It consists essentially of aspeed-governed dc motor, an armature and brushassembly, and a permanent magnet inductor-typeac generator all within a single unit. The armatureand the permanent magnet rotor are usuallymounted on a common shaft.

The inverter’s output frequency and voltageshould be checked periodically to assure that theyare within prescribed limits. Should adjustmentbe required, the electrical shop is notified, sinceadjustment of inverters is a responsibility of theAE rating.

FREQUENCY CHANGERS.— When ac volt-ages of a frequency different from that producedby the main generator are required, suitablemotor-generator combinations are used. Mainelectrical power frequency is usually 400 Hz,Many aircraft provide a 60-Hz source for testequipment and an 800-Hz source for certaininstruments or components.

Q43. To what NEETS module should your referfor information on ac generators?

Q44. What is the purpose of external power?

Q45. List some power conversion devices.

CIRCUIT PROTECTIONAND CONTROL

The electrical system of an aircraft is protectedfrom damage and failure by fuses, currentlimiters, and circuit breakers. Control and

distribution of power are accomplished by the useof switches and relays. Each of these componentsis available in many styles and sizes, some ofwhich are ideally suited for use in aircraft, whileothers are limited to use in shop installations. Inthe following section, you will be presented witha brief discussion of these components.

Fuses

Fuses provide a controlled, intentionallyweakened link in an electrical circuit. They serveas safety devices in the event of undesiredoverloads. Fuse sizes are available with ratings aslow as a few milliamperes to several hundredamperes. Fuses of most ratings are available fornormal, slow-acting, or fast-acting operation.

A fuse is a heat-sensitive, heat-operateddevice. When operated at the rated current, itconsumes electrical power, and then dissipates thispower in the form of heat. Under normaloperating conditions, the dissipated heat is notsufficient to cause the fuse to open (blow).However, when the fuse is operated above thenormal current rating, the overload currentgenerates additional heat, which melts the fusibleelement.

1. Voltage rating. A fuse can be operated atany circuit voltage if it is mounted in a sufficientlywell-insulated holder (as long as the fusibleelement is able to open without suffering arcdamage). When a fuse blows due to excessivecurrent, the full-circuit voltage appears across theopen fuse. If inductance is present in the circuit,a surge is generated that may cause a destructivearc to be formed within the fuse. Under theseconditions, intense heat and pressure develop, andthe fuse may literally explode.

2. Blow-time characteristics. The blow-timecharacteristics of a fuse depend on the percent ofrated current and thermal inertia of the fuse.Overload currents (currents larger than themaximum value for which the fuse is rated), whenflowing through a fuse, heat the element beyondnormal capacity. After a period of time, thefusible element opens.

Fuse elements with a large thermal inertiaincrease the length of time before blowing. Fusescontaining such elements are known as slow-acting, slow-blow, or time-delay fuses. Slow-acting fuses are constructed with a compoundelement—a thermal cutout and a fusible link thatmelts on short circuits on very high overloads.

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Small, light fuse elements reduce the thermalinertia; therefore, they are faster acting. This typeof fuse is known as a fast-acting fuse and isused principally for the protection of sensitiveinstruments.

In the selection of blow-time characteristics,both the steady state and the transient or surgecurrents are considered. If currents of 200 to 400percent above normal can be tolerated for periodsof 1 to 10 seconds, a slow-acting fuse is specified.If the circuit requires immediate protection forany current above normal, a fast-acting fuse isspecified. If the current must be limited to 200percent of the rating for periods less than1 second, then a normal or medium blow-timecharacteristic is specified. (See fig. 5-26.)

When possible, a fuse should be operated atabout 75 percent of its rated value. This providesa good balance between protection and reliability.

3. Vibration resistance. Fuse protection forequipment subject to vibration can be providedby special vibration-resistant construction. Thistype of fuse has a spring formation, with winglikeextensions that bear on the inside wall of the glassbody to decrease vibration of the fuse element.For slow-acting fuses, a different construction isused. This construction consists of a compoundspring and link structure. On moderate overloads,as the compound element reaches the meltingpoint, the spring pulls away from the link, whileon short circuits, the link fails.

Figure 5-26.-Blow-time characteristics of fuses.

4. Identification coding. Fuses and theircorresponding fuse holders are numberedaccording to a standardized system for easyidentification. The numbering system is shownand explained in figure 5-27.

5. Fuse holders. The most common class offuse holders used in Navy equipment is the post-type holder, shown in figure 5-28. It may be ascrew in or a bayonet type. Both of these typesare securely mounted to the chassis or front panelof the equipment. The purpose of the holder isthe same, regardless of type—to hold the fusesecurely with good electrical connection andphysical stability for protection from mechanicalvibration and electrical short circuit.

You should use care to ensure that the fuse isof a physical size compatible with the holder. Fusesthat are undersized allow physical movement andarcing. This results in a blown fuse, erratic opera-tion, or damaged holder. Fuses that are too largemay cause cracking or breaking of the holder.Force should never be applied to either the fuseor the holder, since most are fragile devices.

Post-type fuse holders are normally seriesconnected in the line, with the end connection tothe power source and the center connection to theload. When connected in this fashion, theequipment is protected in the event of a brokenholder. A short circuit from a fuse holder tochassis ground will result in a blown fuse andexcessive current will not flow. Reversedconnections will not furnish this protection.Connection is normally made by solder, althoughsome fuse holders are connected by the use of ascrew or lug method.

Current Limiters

Devices somewhat similar to fuses, calledcurrent limiters, are used in aircraft circuits thatcarry high currents. (See fig. 5-28.) The currentlimiter consists of a copper link of carefullypredetermined sections. The sections melt when


A43. Module 5.

A44. Starting aircraft engines and/or ground servicing andmaintenance.

A45. Transformer-rectifier, inverter, and frequency changer.

5-38

Figure 5-27.-Identification coding: (A) fuses; (B) fuse holders.

Figure 5-28.-Example of aircraft fuses and holders.

abnormally high currents start to flow. Themelting sections have a high-arc resistance to keepthe circuit current within the capacity of thelimiter. If the excessive current is only a temporarysurge, the melting ceases, and the circuit continuesto operate as if no abnormal current had beenpresent. Repeated applications of excessivecurrent or uninterrupted application for a periodof several seconds melt through the sections andcause the limiter to function in the same manneras a fuse.

Circuit Breakers

In modern naval aircraft, circuit breakers havereplaced fuses as the circuit protection devices formost of the wires and cables making up theelectrical system. The circuit breaker is designed

to open the circuit under short-circuit or overloadconditions without injury to itself. Thus, itperforms the same function as the fuse, but it hasthe advantage of being reset and used again.Circuit breakers are rated in amperes and volts.

There are three basic types of circuitbreakers—thermal, magnetic, and thermomag-netic. The following discussion is slanted towardthe thermal type, because this type is more widelyused. Circuit breakers are divided into threecategories—the push-button reset type, the toggletype, and the automatic reset type (sometimescalled a circuit protector).

The push-button reset type (fig. 5-29) consistsof a bimetallic, thermally actuated, spring-loaded

Figure 5-29.-Thermal circuit breaker.

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device that connects two electrical contacts whenset. An excessive current through the device causesan uneven expansion of the bimetallic mechanism(thermal release). This action releases a triggerescapement and permits the spring-loading toseparate the contact members.

A visual indication of the automatic openingis provided by causing the push button to moveto an easily noticed “tripped” position. In thisposition, the button is fully extended and the whitering on the button is showing. This type of push-button breaker has a pullout feature that permitsmanual opening of the circuit.

Another type of circuit breaker uses a togglelever instead of the push button. It operates inthe same manner as the push-button reset-typebreaker, except that the tripped condition isindicated by the toggle lever being in the OFFposition. This type of circuit breaker has theapparent advantage of also being used as a switch.

Manual resetting of the circuit breaker maybe accomplished by means of the actuator (eitherpush button or toggle lever) whenever thebimetallic thermal element cools sufficiently forthe trigger to engage its latching mechanism.In connection with resetting, there are twoclassifications for circuit breakers—trip-free andnontrip-free.

In the trip-free class, the contacts cannot bekept closed by holding the actuator in the closed(or reset) position as long as an overload conditionpersists, which would otherwise cause normaltripping.

The nontrip-free circuit breakers can beprevented (by the operator’s action) fromtripping, even though a tripping condition exists.This should be done only in an emergency. Sincethis action is apt to change the calibration, thebreaker should be replaced as soon as conditionspermit. This type of breaker is no longer beinginstalled in new aircraft, but it is still found onsome older models.

A disk type of thermal circuit breaker is shownin figure 5-30. This breaker consists of aconductive, snap-acting bimetallic disk that

Figure 5-30.-Disk type of thermal circuit breaker.

bridges two electrical contacts. When the disk isheated by the excess current through it, it snapsto the reverse position, opening the contacts andbreaking the circuit. In circuit breakers having lowratings, a resistance wire is inserted. Currentthrough this wire provides the heat necessary tosnap the disk. These breakers are reset by pressinga button that restores the disk to its originalposition. When circuit breakers of this type areclosed, they cannot be reopened manually. Theyare also nonindicating; that is, the position of thebreak (open or closed) cannot be determined byvisual inspection.

The automatic reset type of circuit breaker issimilar to the bimetallic-disk type just described,except that it has no reset push button. It resetsitself automatically. After a short time, when thedisk has cooled sufficiently, it will bend back andclose the circuit, resetting itself. If a constantoverload exists, the breaker will intermittentlybreak the circuit.

Another type of circuit breaker is the switchtoggle variety, which is based on magnetic insteadof thermal operation. This type can be made toopen almost instantly when more than the ratedcurrent flows in the circuit. An electromagnet isplaced in series with the spring-loaded contacts.The contacts are mounted so that an armature actsas a latch to hold them closed. When an excesscurrent flows, the armature is pulled toward theelectromagnet, releasing the contacts and openingthe circuit. To reset the circuit breaker, thecontacts are closed manually, and the spring-loaded armature returns to its normal position.

MOBILE ELECTRIC POWER PLANTS

The electrical power requirements for startingand servicing modern aircraft are extremely high.Even in aircraft equipped with batteries, and withthe batteries fully charged, the capacity is notsufficient to withstand the heavy load of startingan aircraft engine or the power drain of prolongedoperational ground checks.

CAUTION

Batteries are not to be used to start aircraftreciprocating engines except in an extremeemergency. The purpose of an aircraftbattery is to operate specific instrumentsand radios in case of a loss of aircraftgenerator power.

Aircraft are being manufactured that have nointernal source of electrical power unless the

5-40

engines are operating. This presents problemswhen electrical power is required to performmaintenance. Running the aircraft engines toprovide electrical power for maintenance purposesis also poor practice. There is the danger ofturning propellers, jet intake and exhaust blast,or the expense of operating high-powered enginesfor long periods when only electrical power isrequired. To make maintenance easier and toprovide instrumentation for monitoring engineperformance during starts, an external source ofelectrical power is necessary.

Although the AT is not responsible for theupkeep and maintenance of mobile electric powerplants (MEPPs), you must have a basic knowledgeof their capacity and operation. On all of themobile electric power plants described in thischapter, the ac frequency is automaticallycontrolled by a governor that controls the speedof the power plant. The voltage is controlled bya voltage regulator. If the power plant does notregulate to the proper speed (frequency), it mustbe serviced by the support-equipment work center.

The term mobile electric power plant (MEPP)is limited to portable units not installed aboardthe aircraft. The units may be self-propelled,towable, or merely transportable. They may bepowered by diesel fuel, jet fuel, gasoline, orelectricity.

Identification of MEPPs

There are four categories of MEPPs—(1) self-propelled vehicular, (2) gasoline- or diesel-enginedriven trailer-mounted, (3) electrically driventrailer-mounted, and (4) gasoline-/diesel-engineor electrically driven dolly/skid-mounted. Thesepower plants are further identified by prefix lettersNA, NB, and NC, These letters indicate the typeof power available from the unit as follows:

NA—dc output power only

NB—ac output power only

NC—ac/dc output power

The NC-2A is discussed here. For informationon other MEPPS, you should refer to specificMIMs.

The NC-2A (fig. 5-31) is a self-propelleddiesel-engine-powered unit. It is front-axle driven,steered by the two rear wheels, and easilymaneuverable in congested areas. The front axleis driven by a 28-volt dc, reversible, variable-speedmotor, capable of propelling the unit up to 14mph on level terrain, and has a turning radius ofapproximately 11 feet.

Figure 5-31.-MEPP NC-2A.

This unit supplies 30 kVA, 120/208-volt,400-Hz, three-phase power for servicing, starting,and maintaining jet aircraft. A dc generatorproduces 28 volts up to 500 amperes.

Mobile Motor-Generator Sets

Mobile motor-generator sets (MMGs) performthe same function as the mobile electric powerplants. However, they are not self-contained andrequire an external source of electrical power foroperation. The MMGs are primarily used inhangars on shore stations or on the hangar decksof aircraft carriers where running an internalcombustion engine is not practical, and whereexternal power is readily available. Only theMMG-1A is described in this section. Forinformation about other MMGs, refer to theapplicable publications.

The MMG-1A (fig. 5-32) is a small, compact,trailer-mounted, electric-motor-driven generator

Figure 5-32.-MMG-1A.

5-41

set, used to provide 115/200-volt, three-phase,400-Hz ac power for ground maintenance,calibration, and support for various types ofaircraft systems and equipment. Operation oft heunit requires a three-phase, 60-Hz, 220- or440-volt ac external power source. The unit mustbe towed or manually moved.

Additional Support Equipment

Other power systems and support equipmentsavailable to the AT include the deck-edge powersystem, the flight-line distribution system, andground-cooling equipment.

DECK-EDGE POWER.— The primary func-tion of the deck-edge electrical power systeminstalled on aircraft carriers is to provide a readilyaccessible source of servicing and starting powerto aircraft at almost all locations on the carrier’sflight and hangar decks.

FLIGHT-LINE ELECTRICAL DISTRIBU-TION SYSTEM.— The flight -line electrical distri-bution system (FLEDS) is an electrical distributionsystem for servicing aircraft on the flight line.Figure 5-33 shows the major parts of the FLEDS.It consists of three-way junction boxes, inter-connecting ramps, aircraft service point castings,and aircraft connector plug assemblies. The totalsystem capability is 24 aircraft. (See fig. 5-33.)Each service point can service one aircraft with115/200-volt, three-phase, 400-Hz power,

The FLEDS accepts power from a mobile elec-trical power plant (MEPP) capable of supplying115/200-volt, three-phase, 400-Hz power. Poweris applied at the junction boxes and branches intothe service point castings to the aircraft connectorplug assemblies. The cables connecting the junc-tion boxes, service point castings, and aircraftconnector plugs are installed underneath theinterconnecting ramps for protection.

Figure 5-33.-FLEDS.

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GROUND-COOLING EQUIPMENT.— Thepurpose and need for ground cooling varies. Aprimary reason for using ground-coolingequipment is that electronic equipment produceslarge quantities of heat. This heat must bedissipated or the equipment could get so hot thatthe equipment would be damaged and a firehazard would be created.

When a large quantity of air is required forcooling, a common source for this air is theaircraft’s ventilation system. Line maintenance,ground operational checks, and functional checksare usually performed without the aircraft’soperating ventilation system since this system isdriven by the aircraft engines. Therefore, asubstitute air supply must be provided for the airdistribution system. The mobile air-conditioner(fig. 5-34) was designed for this purpose. Mobileair-conditioners include the NR-2B, NR-5C, andNR-10A. For information about these air-conditioners, refer to the applicable MIM.

Additional SE information can be found inspecific MIMs and Airman, NAVEDTRA 14014.OPNAVINST 4790.2 (series) has established thesupport equipment operator/organizationalmaintenance program. This program emphasizesand formalizes the responsibilities and proceduresrequired in connection with the operation ofsupport equipment (SE). (Support equipment isalso referred to as ground support equipment

Figure 5-34.-NR-2B mobile air-conditioning unit.

[GSE], and you may see this terminology andabbreviation used in many publications.) Duringrecent years, the improper use of SE has resultedin far too many ground-handling accidents,excessive repair and replacement costs amountingto millions of dollars annually, and reducedoperational readiness. Investigation has shown themajor reasons for improper use of this equipmentto be lack of effective training for the individualswho operate and maintain the equipment. Also,the lack of effective supervision and leadership bythe officers, chief petty officers, and pettyofficers/noncommissioned officers directlyresponsible for such operation and maintenance atthe various activities contribute to the problem.

CAUTION

An SE operator’s license, OPNAV Form4790/102, is required of all personnel whooperate SE regardless of rate or rating.

It is emphasized that the SE training program isintended to teach support-equipment operationand organizational-level maintenance only. Thistraining does not qualify the individual to operateequipment on the aircraft.

Q46. What components protect an aircraft electrical system?

Q47. At what potential should a fuse be operated? For what reason?

Q48. What advantage does a circuit breaker have have over a fuse?

Q49. List the three basic types of circuit breakers.

Q50. MEPP refers to what types of units? How are these units powered?

Q51. What MEPPs identification would indicate dc output power, as output power, and ac/dc output power, respectively?

Q52. What is the difference between an MEPP and an MMG?

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A46.

A47.

A48.

A49.

A50.

A51.

A52.

Fuses, current limiters, and circuit breakers.

At about 75 percent of its rated value, it provides a good balancebetween protection and reliability.

They can be reset and used again.

Thermal, magnetic, and thermomagnetic.

Portable units not installed aboard aircraft; they are poweredby either diesel fuel, jet fuel, gasoline, or electricity.

NA, NB, and NC.

MMGs are not self-contained and require an external electricalpower source for operation.

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CHAPTER 6

AVIONICS MAINTENANCE

In today’s high-speed aircraft, the avionicssystems must always be in top operating conditionto ensure the aircraft can complete its mission.The effectiveness of the avionics systems dependson your ability to maintain them. You are onlyas good as the handtools and publications you useand your knowledge of general and specificmaintenance procedures. This chapter coversgeneral maintenance procedures and relatedinformation that apply to most avionics systemsfound in aircraft today.

MAINTENANCE CATEGORIES

Learning Objective: Identify the mainte-nance categories and recognize the pro-cedures for each.

The maintenance performed on the equipmentfalls into the following two broad categories:

1.

2.

In

Preventive maintenance, which is actionstaken to reduce or eliminate failure andprolong the useful life of the equipments.Corrective maintenance, which is actionstaken when a part or component has failedand the equipment is out of service.

maintenance work of any kind, you willneed two basic kinds of knowledge. First, youmust have specific information that applies to theparticular equipment you are repairing or keepingin good condition. Second, you must haveand be able to use certain general skills andknowledges that apply to many kinds of equip-ment and types of work assignments.

Specific information consists of special pro-cedures and processes and detailed step-by-stepdirections. This information is approved bythe proper authority and recommended for aparticular piece of equipment. Information isavailable in publications or checkoff lists from theNaval Air Systems Command (NAVAIRSYSCOM),

type commanders, or other authorized sources.The general maintenance skills and proceduresare not available in equipment manuals. Theseskills must be learned during on-the-job training.

PREVENTIVE MAINTENANCE

Maintenance performed to reduce the likeli-hood of future troubles or malfunctions ispreventive maintenance. This form of mainte-nance consists mainly of visually checking theequipment before and during operation, cleaningthe equipment and the various components,lubricating, and performing periodic inspections.

Visual Checks

Before you apply power to equipment, visuallycheck equipment for loose leads, improperconnections, and damaged or broken compo-nents. This type of check applies particularlyto new equipment, equipment returned fromoverhaul, and preserved equipment. Also, itapplies to equipment stored for long periods, andequipment that has been exposed to the weather.A close visual inspection of O-rings, gaskets, andother types of seals is necessary when theequipment under check is a pressurized com-ponent. This visual inspection often reveals easilycorrectable discrepancies with a minimum amountof labor and parts. Such discrepancies, if leftuncorrected, might result in a major maintenanceproblem.

Cleaning

Cleaning the equipment and various com-ponents consists of removing dust, grease, andother foreign matter from the covers, chassis, andoperating parts. Cleaning includes removingcorrosion, fungus, and all other types of matterthat could cause operating failure of the equip-ment. The methods used to clean the various partsand units will vary, but usually a vacuum cleaner

6-1

is good for removing the loose dust and foreignmatter. Other types of foreign matter can bewiped off using a clean, lint-free cloth.

If you need to remove grease or otherpetroleum deposits, moisten the cloth withalcohol, dry-cleaning solvent, or some otherapproved degreaser. After removing the grease,wipe the part dry and clean before you applypower to the equipment.

NOTE: For more specific details oncorrosion removal, you should referto Avionics Cleaning and CorrosionPrevention/Control, NAVAIR 16-1-540.

Lubrication

Lubrication of electronic equipment consistsof lubricating the mechanical parts that work withthe electronic equipment. Equipment, such asunsealed bearings, antenna drives, and waveguiderot sting joints, may require lubrication as directedby the maintenance instructions manual (MIM)for the equipment. Using the correct specificationnumber is very important because the viscosity ofa lubricant changes with a change in operatingtemperature. High operating temperatures causelubricants to become thin, while low operatingtemperatures cause lubricants to thicken orharden. Therefore, the lubricant for a particularjob depends on operating characteristics andtemperature. You should pay particular attentionto equipment lubrication for aircraft that fly athigh altitudes. At high altitudes, aircraft requirea special lubricant that will not harden. Thisreduces any physical overload on the drive motorsand shafts and any electrical overload on thecircuits involved.

CORRECTIVE MAINTENANCE

When finding defective parts or unsatisfactoryoperation occurs, you must analyze the equip-ment, determine the defective part or parts, andreplace or repair. In general, the most effectivemethod for this analysis is a logical step-by-steptroubleshooting procedure.

TROUBLESHOOTING

Learning Objectives: Identify correcttroubleshooting techniques; recognize theprocedures used to determine malfunctionsin aircraft systems and equipment; andidentify color coding for electroniccomponents.

Most of your maintenance time is spenttroubleshooting the equipment within thesquadron’s aircraft. Your job is to maintainseveral units and systems. Many systems arecomplex and might seem, at first glance, to bebeyond your ability to maintain. However, themost complex job usually becomes much simplerif it is broken down into successive steps. Anymaintenance job should be performed in thefollowing order:

1. Analyze the symptom2. Detect and isolate the trouble3. Correct the trouble and test the work

Remember, you should follow the six-steptroubleshooting procedure found in NavyElectricity and Electronics Training Series(NEETS), module 16, Introduction to TestEquipment, NAVEDTRA 14188.

AIRCRAFT PROCEDURES

In troubleshooting, there is no substitute forcommon sense. Most beginners make a commonmistake; they remove major units from theaircraft unnecessarily. The first step you shouldtake when receiving a discrepancy is to determineif the equipment in question is actually faulty.Very often, a preliminary check of the system willshow a faulty control box, frayed or brokenwiring, or corroded or wet connectors. In somecases, you may find someone using an improperoperating procedure—especially with newequipment. (Improper operating procedures areespecially common when the reported discrepancyinvolves new equipment or when operatingpersonnel are undergoing indoctrination.)

If there is no power present at the input to theequipment, you may assume (temporarily) thatthe set is not broken. You should check allapplicable switch positions, circuit breakers, fuses,and other common problems. Then, check forpower at the electrical bus that feeds theequipment. Check the tightness of connectionsand the physical condition of interconnectingcables. Using the wiring diagrams in the applicablemanuals, you should check at successive tie pointsand splices for continuity, short circuits, orgrounds.

If a circuit breaker trips or if a fuse blows,it indicates a circuit malfunction. Turn off powerto the circuit containing the open, and do notreapply power until you locate and correct themalfunction. The most common causes of tripped

6-2

or blown circuit protectors are short circuits,faulty grounds, or overload conditions. However,circuit protectors sometime fail because of age orother conditions. If, after a thorough check, thereis no clear reason for the failure, reset the breakeror replace the fuse. Make sure the replacementfuse is the proper size and type, then reapply thepower.

The analysis may not indicate the existence ofa short circuit, faulty ground, or overloadcondition. If the equipment still does not operate,you should continue to take measurements withpower applied. Observe all safety precautions.Systematically take these measurements atprogressive checkpoints. Particular faults that caninterrupt current through a circuit include brokenwiring, loose or faulty terminal or plug con-nections, faulty relays or switches, and uncoupledsplices. Be alert for these conditions!

Sometimes, you cannot determine thedefective unit while its still installed in the aircraft.You may need to turn off the power and replaceunits, one at a time, with units that operateproperly. After replacing each unit, reapply powerand check the system for proper operation. If thesystem operates normally, you have found thefaulty unit. You may then take the bad unit tothe shop for corrective maintenance. At this stageof the overall maintenance process, you shouldtry to determine the reason for the failure of theunit. It is possible the new unit may also becomedamaged if the basic cause has not been corrected.

After you have removed the defective unit andfurther analyzed it, reinstall all other items of theoriginal installation and safety wire. Then,perform a complete operational check. During theoperational check, readjust or calibrate asnecessary. This should be done before clearing thediscrepancy on the original VIDS/MAF.

The rules shown here are a guide you can usewhen making the tests described in this section.

1. Always connect an ammeter in series.

2. Always connect a voltmeter in parallel.

3. N e v e r connect an ohmmeter to anenergize circuit.

4. Select the highest range first, and thenswitch to lower ranges, as needed.

5. When using an ohmmeter, select a scalethat will result in a midscale reading.

6. Do not leave the selector switch of amultimeter in the resistance position when themeter is not in use. The leads may short togetherand discharge the internal battery. There is lesschance of damaging the meter if you leave it ona high ac voltage setting or in the OFF position.Meters that have an OFF position dampen theswing of the needle by connecting the metermovement as a generator. This prevents the needlefrom swinging wildly when moving the meter.

7. View the meter from directly in front toeliminate parallax.

8. Observe polarity when measuring dcvoltage or direct current.

9. Do not place meters in the presence ofstrong magnetic fields.

10. Never try to measure the resistance of ameter or a circuit with a meter in it. The highcurrent required for ohmmeter operation maydamage the meter. This also applies to circuitswith low-filament current tubes and some typesof semiconductors.

11. When measuring high resistance, becareful not to touch the test lead tips or the circuit.Your body resistance will shunt the circuit andcause an erroneous reading.

12. Connect the ground lead of the meter firstwhen making voltage measurements. Work withone hand whenever possible.

Continuity Test

Open circuits are circuits that interrupt currentflow, either from a broken wire, defective switch,or any other means that stops current flow. Tocheck for opens (or to see if the circuit is completeor continuous) you conduct a continuity test.

An ohmmeter, which contains its ownbatteries, is an excellent tool to use when youperform a continuity test. (In an emergency, aflashlight can function as a continuity tester.)Normally, you make continuity checks in circuitswhere the resistance is very low (such as theresistance of a copper conductor). A very high orinfinite resistance indicates an open circuit. Sucha condition would be an open conductor.

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Look at figure 6-1. It shows a continuity test ofa cable. When using an ohmmeter, make sure youdisconnect both connectors and connect theohmmeter in series with the conductor under test.The power must be off. When you are checkingconductors A, B, and C, the current from theohmmeter flows through plug No. 2, theconductor, and plug No. 1. From this plug, itpasses through the jumper to the chassis groundand to the aircraft’s structure. The structureserves as the return path of the current to thechassis of unit 2, completing the circuit to theohmmeter. The ohmmeter will indicate a lowresistance.

Checking conductor D (fig. 6-1) reveals anopen. The ohmmeter indicates maximumresistance because current cannot flow. With anopen circuit, the ohmmeter needle is all the way tothe left, since it is a series-type ohmmeter (readsright to left).

You cannot use the aircraft structure as thereturn path; use one of the other conductors. Forexample, to check D (fig. 6-1), connect a jumperfrom pin D to pin A of plug 1 and the ohmmeterleads to pins D and A of plug 2. By the process ofelimination, this technique will also reveal theopen in the circuit.

Grounded Circuit Test

Grounded circuits may be caused from eitherdirect or indirect contact between some con-ducting part of the circuit and the

metallicframework of the aircraft. Grounds mayhave many causes. Perhaps the most commoncause of a ground is frayed wire insulation thatallows the bare wire to come into contact with themetal ground.

Grounds are usually indicated by blown fusesor tripped circuit breakers. Blown fuses or trippedcircuit breakers, however, may also result from ashort other than a ground. A high-resistanceground may also occur where enough current doesnot flow to rupture the fuse or open the circuitbreaker.

Ohmmeters provide a good test for grounds.You may also use other continuity testers. Bymeasuring the resistance to ground at any point ina circuit, you can determine if the point is atground potential. Look at figure 6-1 again. Itshows a way to test a cable for grounds. If youremove the jumper from pin D of plug No. 1, a testfor grounds can be made for each conductor of thecable. This is done by connecting one meter lead toground and the other to each of the pins of one ofthe plugs. A low-resistance reading on theohmmeter indicates a grounded pin. You mustremove both plugs from their units. If you removeonly one plug, a false indication is possible. Thisfalse indication occurs because the other conductorreceives a ground through the unit.

Short Test

A short-circuit test is a test to determinewhether two conductors have accidentally touched

Figure 6-1.-Continuity test.

6-4

each other, directly or through another conductingelement. Two conductors with frayed insulationmay touch and cause a short. Too much solderon one pin of a connector may short it to anadjacent pin. In a short circuit, sufficient currentmay flow to blow a fuse or open a circuit breaker.However, it is entirely possible to have a shortbetween two cables carrying signals and not blowa fuse.

The device used to check for a short is theohmmeter. By measuring the resistance betweentwo conductors, you may detect a short betweenthem. A low-resistance reading usually indicatesa short. Look at figure 6-1. You may perform ashort test by removing the jumper and discon-necting both plugs. This is done by measuringthe resistance between the two suspected con-ductors.

Shorts can occur in many components, suchas transformers, motor windings, and capacitors.The major method for testing such componentsis to take a resistance measurement and thencompare the indicated resistance with theresistance given on schematics or in maintenancemanuals. You may also make comparisons withidentical operational equipment.

Voltage Test

You make voltage tests with the powerapplied. Therefore, you must follow theprescribed safety precautions to prevent injuryto yourself and others or damage to the equip-ment. Making voltage tests is an importantpart of maintenance work. It lets you isolatediscrepancies to major components, and youcan use these tests in the maintenance ofsubassemblies, units, and circuits. Beforechecking a circuit voltage, you should checkthe voltage of the power source to makesure normal voltage is being input to thecircuit.

COLOR CODING

As an AT, you need to know the dif-ferent color codes that identify resistors,capacitors, wiring, and other components.Resistor color codes (fig. 6-2) lets you quicklyidentify size (in ohms) and tolerances. You canuse color codes, along with MIL-STD-199C(which contains a complete part numberbreakdown), to identify or find suitablereplacements.

Figure 6-2.-Resistor color codes.

6-5

Capacitor color coding is one of two methods number is stamped on the capacitor. For moreused to identify capacitors. Figures 6-3, 6-4, 6-5, information on capacitor identification, youand 6-6 are several examples of capacitor color should refer to NEETS, module 19, NAVEDTRAcoding for different styles of capacitor. The other 14191, and specific military standards and speci-method is the typographical method where a fications.

Figure 6-3.-Six-dot color code for mica and molded paper capacitors.

6-6

Figure 6-4.-Six-band color code for tubular paper dielectric capacitors.

6-7

Figure 6-5.-Ceramic capacitor color code.

6-8

Figure 6-6.-Mica capacitor color code.

6-9

Semiconductor diodes and transformers alsohave color-coding identification. See figures 6-7and 6-8.

BENCH PROCEDURES

The visible condition of a unit is usually thefirst check in any troubleshooting process. Ifcertain parts are obviously not in good condition,correct them before you resume testing. Suchfaults include burned parts, loose, disconnected,dented, broken, or otherwise obviously faultyparts. Check the visible condition of a unit beforeinstalling and connecting the unit at the test bench.

The sense of smell can help pinpoint certaintroubles. A part that overheats usually gives off

an odor that is sometimes readily detectable.However, location of a burned part does notnecessarily reveal the cause of the trouble.

To determine the cause of the trouble, youshould refer to the MIM for the given equipment.The MIM is a source of valuable information forperforming maintenance on electronic equipment.(Few technicians are so thoroughly familiar withan electronic unit that they do not have to use theMIM when performing maintenance.)

Signal Tracing

Signal tracing is one method used in trouble-shooting. It is a good method for tracing signalsin RF receivers and audio amplifiers. However,

Figure 6-7.-Semiconductor diode markings and color-code system.

6-10

Figure 6-8.-Color codes for transformers.

in radar, the frequencies are higher, the methodsof signal application differ, and the output in thefinal stage is video (viewed). The applicable MIMcontains detailed procedures for testing most unitsor circuits.

Signal tracing is a very effective method forlocating defective stages in many types ofelectronic sets. It is especially useful when

servicing equipment that normally contains nobuilt-in meters. In signal tracing, a signal voltage(similar to that present under operating con-ditions) from a signal generator is input to thecircuit in question. The signals that result are thenchecked at various points in the stage, using ahigh-impedance test instrument. The particulartest equipment, such as a vacuum tube voltmeter,an oscilloscope, or an output meter, depends oncircuit application and other parameters, asappropriate. (The test instrument should havehigh impedance so that it will not change theoperation of the circuit under test.)

When using the signal-tracing to measure acsignals, you should make sure the test instrumentsare adequately isolated from any dc potentialpresent in the circuit. Some test instruments havespecial ac probes that incorporate a capacitor inseries with the input. Before using any item of testequipment, you must know the characteristics andproper use of the test equipment as well as theequipment under test.

By using the signal-tracing method, you canmeasure the signal gain or loss of amplifiers.You can also locate the points of origin ofdistortion, hum, noise, and oscillation that occurin the amplifiers.

The gain measurement is a good example ofan important method in signal tracing. By thisprocedure, you can quickly isolate a discrepancyto the defective stage. A signal generator, withthe output attenuator calibrated to microvolt,and an output meter can measure gain. It ishelpful to have data on the normal gain of thevarious stages of the device. You can find this datain the MIM for the receiver under test.

To measure gain, you connect the outputmeter across the headset (or the voice coil of aspeaker) or across the secondary of the outputtransformer. Connect the output of the signalgenerator to the grid circuit of the stage under test.Then, adjust the attenuator of the signal generatoruntil the output meter reads a value appropriateto serve as a reference figure. After adjustment,connect the output of the signal generator to theoutput of the stage under test (or to the input ofthe next stage). Adjust the attenuator untilregistering the same reference value on the outputmeter. To determine the gain of the stage, dividethe second value of the signal (taken from thecalibrated attenuator) by the value of the signalapplied to the input of the stage. For example,suppose the signal generator supplies a voltage of400 microvolt to the grid of an IF amplifier. Thisvoltage causes the output meter to indicate some

6-11

value you can use as a reference. When thegenerator signal is input to the following grid,the signal strength must be increased (4,000microvolt) to cause the output meter to indicatethe same reference value. The gain of the stageis equal to

that is,

If similar measurements made in the remainingstages of the receiver reveal one stage in whichthe gain is lower than normal or is zero, a faultystage is indicated. Then, you can check that stagethoroughly by measuring voltage or resistance orby replacing parts until you find the defective one.

Test Probe Substitution

Do not use a test equipment probe withequipment other than that for which it is designed.Errors may result. Any differences in the internalresistance of the probe and input circuitry of theequipment make substitution impossible withoutcalibration. For example, the internal resistanceof a 10:1 probe is usually nine times higher thanthe input circuitry of the equipment. You shouldnote that 2:1, 50:1, and 100:1 probes are alsoavailable.

Use the test probe that is designed for theequipment. Do not use a probe that is notspecifically designed for the equipment under test.An improper test probe may not have sufficientcapacitive adjustment to preserve the waveshapeof the observed signal.

Voltage Checks

You should make voltage measurements atvarious points in the stage suspected of beingfaulty. Compare the observed voltage values withthe normal voltage values given in the MIM.When making voltage checks for comparison witha chart, you should use a voltmeter with theproper ohms-per-volt rating (sensitivity). Alwaysconnect voltmeters in shunt with the circuitelements under test. This results in circuit loading.(For an explanation of circuit loading, refer toNEETS, module 3, NAVEDTRA 172-03-00-79.)The sensitivity of the test instrument must be the

same as that of the instrument used in making thereadings on the chart. This ensures the loadingeffect will be the same in both cases, and yourmeter readings should be reliable. Remember, ifthe meter sensitivity is too low, the loading effectmay be so severe that it will prevent properoperation of an otherwise normally functioningcircuit.

By comparing observed voltages with thevoltages given in the MIM, you can often isolatethe defect. Voltage checks are most effective whenapplied within a single stage after you have madechecks to localize the defect. This is true becausemodern electronic equipment is complex, andrequires time to check all the voltages present inall the stages.

Some electronic sets have built-in meters orplugs for front panel application of meters. Thesemeters usually work with a selector switch andread voltage or current values at set points.Normally, you can isolate a defective stage in thismanner.

After isolating the defective stage, it becomesa matter of point-to-point checking to isolate thefault within the stage itself. A voltmeter willpinpoint the trouble, but it often becomesnecessary to use an ohmmeter to determine theexact cause of trouble; for example, shortedcapacitors, open resistors or transformers, or awire grounded to chassis.

Resistance Checks

Like voltage measurement, resistance checksare most effective after you isolate the trouble toa particular stage. After isolating the trouble, theohmmeter is a very useful instrument, and oftenquickly leads you, the technician, to the cause ofthe trouble. Resistance checks are made likevoltage checks, except you must remove powerfrom the set. You measure resistance and compareyour readings to the normal values given in themaintenance publications. Reliance on resistancemeasurement alone is too time-consuming to beefficient.

NOTE: To prevent damage to theohmmeter, always be sure there are novoltages present in the equipment beforebeginning the resistance checks. Turn offthe power switches, discharge the powersupply and other large capacitors, andbleed off any other residual charges in theset. Also observe proper precautions whenconnecting or disconnecting the ohmmeteracross large inductors.

6-12

The ohmmeter method of checking electrolyticcapacitor serves as an example of how to makea routine resistance check. You make a resistancemeasurement on the discharged capacitor usingthe high resistance range of the ohmmeter. Whenyou first apply the ohmmeter leads across thecapacitor, the meter pointer rises quickly and thendrops back to indicate high resistance. Now, ifyou reverse the test leads and reapply them, themeter pointer rises again, even higher than before,and again drops to a high value of resistance. Thebattery of the ohmmeter charges the capacitor andcauses the meter to deflect. When reversing theleads, the voltage in the capacitor adds to theapplied voltage, resulting in a greater deflectionthan at first.

WARNING

Do not leave the ohmmeter connectedacross an electrolytic capacitor for anylength of time. Electrolytic capacitors arepolarity sensitive, and reverse polarity ofvoltage (even from an ohmmeter) maycause excessive current, which could resultin overheating and possible explosion ofthe capacitor.

If the capacitor is open-circuited, no deflectionwill occur. If the capacitor is short-circuited, theohmmeter indicates zero ohms. The resistancevalues registered in the normal electrolyticcapacitor result from the slight current leakagebetween the electrodes. Because the electrolyticcapacitor is a polarized device, the resistance isgreater in one direction than the other.

If a capacitor indicates a short circuit, youmust disconnect one end of it from the circuit.Then, take another resistance reading to determineif the capacitor is actually at fault.

Unless the ohmmeter has a very high resistancescale, you will not be able to see any meterdeflection when you are checking small capacitors.Even a scale of R x 10,000 is not enough for verysmall capacitors. The smaller the capacitor, theless leakage across the plates; therefore, the moreresistance.

When making resistance checks, you need todetermine what circuits connect to the check-points. The MIM indicates the proper resistanceat various checkpoints throughout the set. Also,the MIM contains a complete schematic of the set,as well as a circuit schematic of the stage under

test. The schematics may set up conditions forperforming voltage and resistance measurements.These conditions may include the positions ofswitches and control knobs, relays energized orde-energized, and tubes in sockets. Theseconditions duplicate the initial measurementconditions with which you are comparing yourreadings. Typical instructions might read “Powerswitch OFF—all controls on the control box fullCCW (counterclockwise).” By following theseinstructions, you should get accurate values tocompare with the specified values. Otherwise, youmay get incorrect values.

Defective Components

Before you replace a defective part, determineif such an operation is within your activity’scapability. The maintenance that you can performis a function of your activity’s assigned level ofmaintenance. Because electronic equipment iscomplex and compact, the trend in the Navy istoward replacement of subassemblies instead ofindividual parts. This trend stems from thenecessity of exact parts replacement and thedifficulty of working in small spaces. Even theamount of solder used on a connection isimportant. However, there are many parts thatyou may replace at any level of maintenance. Thegeneral rule is to replace any defective part withan exact duplicate.

You should refer to the specific MIM, IPB,and supply publications to help get information(such as stock number and description) about aparticular part. The publication that you will usemost often when ordering parts for the particularequipment under repair is the illustrated partsbreakdown (IPB). For an explanation on how touse the IPB, you should refer to AviationMaintenance Ratings Fundamentals, NAV-EDTRA 14318.

If it becomes necessary to substitute parts, youneed to make sure the substitute part is a properreplacement. When replacing resistors, you mustconsider ohmic value, wattage rating, tolerance,physical dimensions, and type of construction. Ifyou are replacing capacitors, you must considerphysical dimensions, capacity, tolerance, tempera-ture coefficient, and voltage rating. Plugs andconnectors almost always have to be exact becauseit is difficult to find items of this type that areinterchangeable. Familiarity with the IPB is adefinite asset to the technician who mustdetermine exactly what part to order.

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Checking After Repair

No repair job is complete until you reinstallthe repaired unit or component and actually checkto see that it is operating properly. The componentmust be bench checked after correcting thetrouble. Before completely reassembling thecomponent, you should make any alignment oradjustments that are necessary for the properoperation of the component. After reassembly ofthe component, replace dust and shielding covers,install the component in the outer case (andpressurize, if necessary), and perform a finalbench operational check. Often, when installinga shield or plate, it touches a bare wire or othercontact and makes the component inoperative orcauses substandard operation. It is much betterto discover such a fault at the bench than in theaircraft.

After installing the component in the aircraftand properly securing it for flight, you must giveit a final operational test. You cannot assume thatbecause the component operated properly on thebench it will do so in the aircraft. The mostimportant test is an operational check under exactoperating conditions. When the componentperforms properly in the aircraft and is secure,you may sign off the discrepancy sheet (VIDS/MAF). This signature indicates that the electroniccomponent should operate properly under normalflight conditions.

Figure 6-9 summarizes the troubleshootinginformation described in the precedingparagraphs. The directions given in blocks 1through 5 are steps for locating a trouble. Thedirections given in blocks 6 and 7 are steps inrepairing the set and should always occur.However, steps 2, 3,4, and/or 5 may sometimesbe eliminated.

Q1.

Q2.

Q3.

Q4.

Q5.

What are the two broad categories ofmaintenance?

Describe preventive maintenance.

What is the first step you should take whenreceiving a discrepancy?

Describe the use of continuity tests.

Describe the major method for testingshorts in transformers, motor windings,and capacitors.

Q6.

Q7.

What is the proper color code fora 100-ohm resistor with a 10-percenttolerance?

What must you consider when substitutinga resistor to ensure it is a proper sub-stitution?

REPAIR INFORMATION

Learning Objective: Describe repairtechniques for soldering microelectronics,including modules, maintenance aids, andprinted circuits (construction, repairtechniques, and parts replacement).

The trend toward replaceable units has led toseveral new methods of construction of electronicequipment. Two examples of replaceable units aremicroelectronic and printed circuits. These circuitdesigns provide speed and economy of manu-facture and speed and ease of maintenance, as wellas for saving space and weight.

NOTE: Only certified microminiaturecomponent repair (MMCR) personnel areauthorized to make microelectronicrepairs.

Figure 6-9.-Troubleshooting procedures.

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SOLDERING

Soldering operations are a vital part ofelectronics maintenance procedures. Soldering isa manual skill that all personnel assignedelectronics maintenance shop duties must learn.Practice is necessary to develop proficiency in thetechniques of soldering. However, practice servesno useful purpose unless it is based on anunderstanding of basic principles, For a discussionon soldering materials and practices, you shouldrefer to NEETS, module 4, NAVEDTRA14176.

MICROELECTRONIC MAINTENANCE

Microelectronic technology by itself does notsolve the maintenance problem. In spite of theincreased reliability, failures still occur. When theydo, the faulty items must be isolated and repairedor replaced.

With the discrete miniature component(transistor, resistor, capacitor, etc.), you can testindividual circuit elements. Thus, you candetermine the cause of failure, and repair it byreplacing the faulty component.

With the integrated circuit, you cannot replacean individual part because the unit exists only asa complete functional element. The maintenanceprocess then becomes a matter of isolation andreplacement of the defective chip, flat-pack,board, or module.

Modules

Modular assemblies are mechanically morerugged than conventional circuits. However,they are susceptible to damage from improperhandling, electrical overload, or overheating.Techniques used to maintain and service modulesare similar to those used for conventional circuits,but they require somewhat more care in execution.The small size and close spacing of the partswithin the modular assembly require smaller toolsthan those used for conventional maintenance.Additional devices and maintenance aids help withthe precision needed for such close work.

Many components are susceptible to damagefrom various causes, especially maintenance.Component damage during maintenance usuallyresults from excess heat during repair, reversedpolarity of ohmmeters while checking for con-tinuity, excessive voltage application or signalstrength during testing, rough handling, or use ofthe wrong tools or materials.

Do not loosen connections, disconnect parts,insert or remove transistors, or change modularunits with the power on or while the circuit isunder test. A loose connection of any type causesan inductive kickback, which may damage thecomponent.

You should remove any capacitive chargefrom parts, tools, or test equipment beforeconnecting them to any modular unit. Connecta grounding clip from the item to the modularchassis before you make any other contact. Whendisconnecting the equipment, you should removethe grounding clip last.

Damage easily occurs to transistor leads,printed circuit boards, etc., as well as manyminiature components, during handling, stowage,or shipping. You should always observe properprecautions. If you use adequate care and propertechniques, you can repair these miniaturecomponents.

Maintenance Aids

To maintain microcircuits, you need specialdevices to extend your vision, aid your reach, andact as a third hand. The special tools and devicesyou use will depend on the equipment you areservicing and on the maintenance operationsinvolved. Many of the tools and devices discussedin this section are useful in all maintenanceactivities, while others have limited applicability.Keep the assortment of tools to the minimumrequired for effective and efficient maintenanceof assigned equipment.

Many dental tools, no longer usable for theiroriginal purpose, make excellent tools for youruse. These tools include various knives forscraping protective coatings and excess solder,brushes for cleaning, probes, and mirrors forinspecting crowded spaces. Drills and drill bits areuseful when making small repairs. You can usetweezers and surgical hemostats to grasp and holdsmall parts. They also provide good heat shuntsfor soldering, but their effectiveness is limited. (Amore desirable heat shunt is described later in thissection.) Hypodermic syringes can be used to oilhard-to-reach points.

You should use a pin vise when drillingthrough plastic or Bakelite, or when drillingthrough the copper-ribbon conductor strips onprinted circuit boards. You may also use it whencleaning solder from hollow receptacles andterminals. In addition, the pin vise can hold manysizes and shapes of hooks and probes made fromspring wire. These attachments are useful when

6-15

you are inspecting and servicing equipment andcomponents in confined spaces.

A magnifying device is essential for inspectingminute parts. If the magnifier is on a stand, youwill have both hands free for other tasks.

When you work on a removed printed circuitor terminal board, the item must remain still. Youcan use a module holder or module jig for thispurpose. The jig provides support and preventsflexing or slipping. Securing the jig to theworktable leaves both of your hands free to workon the board.

For any resoldering operation, mount the partso the terminals point out and down. Place thesoldering iron under the terminals so the solderflows away from the joint. To resolder the joint,invert the part.

Some technicians use a drawer or box with awhite cloth to catch (trap) any small parts droppedduring maintenance. (See fig. 6-10.)

NOTE: This procedure is no longerrecommended since the cloth and/or boxmay contain an electrostatic charge. Thestatic charge may damage solid-statecomponents when they fall on the cloth.Ensure you and your fellow workers DONOT use this unless approved by proper

Figure 6-10.-Trap for catching small dropped parts.

For further information on procedures tofollow when resoldering components, refer toAssembly Electronics Repair, Standard Mainte-nance Practices, NAVAIR 01-1A-23.

PRINTED CIRCUITS

The trend toward replaceable units has led toseveral new methods of construction of electronicequipment. An example of such a unit is theprinted circuit. This type of circuit provides forspeed and economy of manufacture and speed andease of maintenance, as well as for saving space

authority. and weight.


A1. Preventive and corrective maintenance.

A2. Preventive maintenance is maintenance performed to reduce thelikelihood of future troubles or malfunctions.

A3. Determine if the equipment in question is actually faulty.

A4. To check for opens or to see if a circuit is complete or continuous.

A5. The major method for testing these components is to takeresistance measurements and compare them with schematics,MIMs, or identical operational equipment.

A6. 1st Digit: Brown; 2nd digit: Black; Multiplier: Brown; Tolerance:Silver; see figure 6-2.

A7. You must consider ohmic value, wattage rating, tolerance,physical dimensions, and type of construction.

6-16

Circuit Construction

One method of manufacturing a printedcircuit is the photoetching process. During thisprocess, a plastic or phenolic sheet is coated with athin layer of copper. A light-sensitive enamel coversthe copper coating. A template of the circuit that willeventually appear on the plastic sheet is placed overit. Then, the entire sheet is exposed to light. The areaof the exposed copper reacts to the light. This area isthen removed by an etching process. The enamel onthe unexposed circuit protects the unexposed copperfrom the etching bath that removes the exposed

copper. After the etching bath, the enamel is removedfrom the printed circuit. This leaves the surfaces in acondition for soldering of parts and connections.

Some manufacturers use machinery to mountstandard parts like capacitors, resistors, andtransistor sockets—further speeding manufacture.These circuits operate as well as conventional circuitsand are as easily repairable.

Look at figure 6-11, which shows an improvedtype of construction, from the troubleshooter’sstandpoint. This construction is a removablesubassembly, known as a module. Modules areremovable and have many internal and external

222.255Figure 6-11.—Electronic module construction.

6-17

test points to make troubleshooting easier. Themodules are built of standard parts that are easilyreplaceable. Most test racks have plug extensionsthat permit raising any module, making all partsaccessible for checking and repairing. The moduleis not expendable, but it is easy to repair, sinceall the parts are of conventional design. Miniatureand subminiature parts are so common in today’selectronic equipment that they are considered tobe conventional.

Soldering Repair Techniques

Soldering techniques used to repair the printedcircuit board differ from those used on theconventionally wired circuits. You can repairprinted circuits with a little care and commonsense. If a printed circuit becomes broken, repairit by placing a short length of bare copper wireacross the break and soldering both ends to theprint. If the break is small, simply flow solderacross it (fig, 6-12). When you perform theseoperations, you do not apply too much heat anddon’t let solder flow to other printed areas.

The phenolic boards used for printed circuitsare similar to the phenolic strips used forconventional terminal strips and mountingboards. There has been no difficulty in solderingto the metal connectors on these terminal stripsand mounting boards, so there should be nonein soldering printed circuits. In rare cases whereexcessive heat causes separation of printedconductors from the phenolic board, jumper wiresare used for repair (fig. 6-13).

Figure 6-12.-Repairing breaks in foil.

Figure 6-13.-Repairing raised portion of foil.

NOTE: The repair procedures describedabove will result in satisfactory INTERIMrepairs. Normally, however, you will turnmost faulty printed circuit boards requiringrepair in to a certified repair facility—either to a miniature component repair(MCR) facility or to a certified micro-miniature component repair (MMCR)facility.

Parts Replacement

Removing (resoldering) a part from a printedcircuit board without damaging the printed circuitor the associated parts requires precision and skill.When it is necessary to unsolder a component,you will probably use a pencil iron and specialtips. Figure 6-14, view A, shows how to use specialtips to unsolder multiple terminals. It is possibleto unsolder boards using a jury rig (view B). Aground lead connected from the tip of thesoldering iron to the frame or chassis preventsdamage to transistors and other parts due toleakage current in the soldering iron. Often it ismore convenient, and always safer, to remove themodule and work on it on an insulated surface.

The general procedure recommended forremoving soldered parts is applicable to mostconnections. A chassis-holding jig holds theprinted circuit boards. Position the board so theterminals to be unsoldered are facing out anddown. Place the tip of a hot pencil soldering ironunder and against the terminal. The solder willflow to the soldering tip, and you may removeit from the tip by wiping it. Remove sufficient

6-18

Figure 6-14.-Unsoldering multiple terminals.

solder from each of the terminals to free the part.When the terminals are loose, lift the part fromthe board. The part should NEVER be pried orforced loose. Any attempt to force a part loosemay result in a broken or separated printed circuitpanel. If the terminals do not pass easily throughtheir holes, chances are that some solder stillremains. After removing the leads, remove anysolder left in the terminal hole by applying thesoldering iron to the hole just long enough tosoften the solder. Then, poke the softened solderout with a toothpick, scribe, or small brush.

You should use these special tips wheneverpossible. Use slotted tiplets to simultaneously meltsolder and straighten bent leads, tabs, or smallwires against the board or terminal.

Parts such as resistors and small capacitors areeasier to remove if you cut them first to free theirleads. It requires much less heat to remove a partif the leads are free. Sometimes it is inconvenientto remove a board for access to the wiring side.However, it is usually possible to cut the leads ofsmall resistors and capacitors so a small portionof the lead is accessible. You can then solder thenew part to the old leads. See figure 6-15.

The bar tiplet will remove straight-linemultiterminal parts quickly and efficiently, as

shown in figure 6-14, view A. You can also do

Figure 6-15.-Replacement of a resistor on a printed circuitboard.

this by heating each solder connection andbrushing away the melted solder. If you use thelatter method, be careful that loose solder doesnot stick to other parts or to the printed panel,where it may cause a short.

You can also improvise a tip that will coverall the connections simultaneously, as shown infigure 6-14, view B. If you use this method, makesure that the tool contacts only the terminals youneed to unsolder and nothing else. Do not allowthe tool to remain in contact for too long a periodof time.

The cup tiplet (fig. 6-14, view C), the triangletiplet, and the hollow cube tiplet are specialdesigns used to withdraw solder from circular ortriangular-mounted parts in one operation. Ifthese tools are not available, you can improvisea tip by shaping it to cover the terminals, as shownin view D. The same procedures and precautionsgiven for unsoldering straight-line terminals applyhere.

Most printed circuit board components can beremoved by following the methods just described.However, if an unfamiliar situation occurs, spendsome time and think about the best way to removethe part. Planning saves you time.

In some cases, excess solder at a printed circuitconnection makes removal difficult. You may findthe following method helpful: Coat a piece ofclean copper braid (such as a ground strap orlength of coaxial shield) with a noncorrosivesolder flux and apply it to the connection. Heatingthe braid with a soldering iron causes the excesssolder to transfer to the braid. Be careful not tooverheat the braid.

6-19

The proper methods of solder removal andapplication are shown in figure 6-16, views A, B,and C. View A shows the correct and incorrectmethods of solder application. The correctmethod for removing solder from a componentwithout damaging the printed wiring circuits is

Figure 6-16.-Soldering techniques.

shown in view B, View C shows the correctmethod of applying solder to a replacedcomponent.

Resistors

One of the most important considerationswhen replacing a resistor is the wattage value ofthe resistor. The wattage rating is a measure ofthe ability of the resistor to dissipate heat. Thewattage value is a function of the dimensions ofthe resistor.

The selection of a resistor with a safe wattagevalue is based on a consideration of the workingconditions of the resistor in the circuit. Consider,for example, the replacement of an 850-ohmresistor with one of equal ohmic value but witha tolerance of ±20 percent. Suppose the normalvoltage existing across the resistor is 40 volts.Because of the 20-percent tolerance, the actualresistance of the replacement may be as much as1,020 ohms or as little as 680 ohms. If the resistorwith the lesser value is chosen (the moreunfavorable from a heat-dissipating standpoint),the power that may be developed in the resistorunder circuit conditions is found as follows:

To allow a sufficient safety margin, a resistorshould be capable of dissipating from 1.5 to 2times the power it will actually meet. In the aboveexample, this value is not more than 4.7 watts.Since a 5-watt resistor is the next standard sizeabove the 4.7-watt value, this is a desirablewattage rating for the replacement.

Under emergency conditions, you may needto combine resistors in series or in parallel to geta desired resistance value. When doing this, youshould avoid a voltage distribution (or currentdistribution) that would cause any low-wattageresistor in the combination to dissipate anexcessive amount of heat. Suppose, for example,that you combine two 10-watt resistors of 1-ohmvalue with a 2-watt resistor of 10-ohm value ina series circuit with 12 volts applied. The totalwattage now being dissipated by the 10-ohm,2-watt resistor would be 10 watts, a value far morethan its capabilities. Therefore, you must consider

6-20

2

each resistor in the combination and select awattage value based on the voltage that willdevelop across the individual unit.

Q8.

Q9.

Q10.

Who can make microelectronic repairs?

Describe the causes of component damageduring maintenance.

What manual should you refer to forfurther information on procedures fordesoldering components?

AIRCRAFT AND EQUIPMENTWIRING

Learning Objective: Identify the purposeand use of various components whenwiring aircraft and equipment.

Aircraft wiring is identified by a system ofnumbers and letters stamped on each wire. TheMIM for the aircraft or equipment gives thenumber of each wire used in electronic equipmentcabling. If you need to trace and repair a wire inan aircraft, refer to the MIM to determine therouting of the wire.

You can find the wiring data for all electricaland electronic systems in each model aircraft inthe wiring data section of the applicable MIM.The diagrams are prepared separately for eachcircuit. They provide all data necessary tounderstand the construction of each circuit, totrace each circuit within the system, and to makecontinuity and resistance checks. They alsoprovide specific troubleshooting performance dataon inoperative or malfunctioning circuits. Theschematic diagrams for circuits and relatedcomponents are in those volumes of the MIM thatspecifically cover a system or systems.

CONNECTORS

When you inspect major units, inspect theirconnectors. During this inspection, separate themating parts of the connectors and examine thecontacts for corrosion. If corrosion is present,clean the surfaces with a brush or clean rag anda noncorrosive solvent. Inspect the coupling ringfor battered threads, and replace it if the threadsare not in good condition. When attaching ordetaching the connector, be careful not to damagethe coupling or bend the coupling nut.

If the connector does not contain a moisture-proofing compound, inspect the conductors wherethey are soldered to the pin contacts. Short circuitsoften occur because a frayed strand of oneconductor touches the solder cup of anotherconductor within the plug. In this case, you mayclip the frayed strand. You should check to seethat all soldered connections are adequate and thatno cold solder joints exist.

Connectors do not require lubrication exceptthe coupling ring threads. Occasionally, theyshould receive a light coat of antiseize compoundto ensure smooth operation.

At times, operating conditions demand thatordinary electrical connectors receive a moisture-proofing treatment. Moistureproofing reducesfailure of electrical connectors and reinforces thewires at the connectors against failure caused byvibration and lateral pressure. Both of thesefailures fatigue the wire at the solder cup. Thebasis of moistureproofing is the application of asealing compound.

Sealing compound also protects electricconnectors from corrosion and contamination byexcluding metallic particles, moisture, and aircraftliquids. As a result of its improved dielectriccharacteristics, sealing compound reduces thechance of arcover between pins at the back ofelectric connectors.

The sealant is available in kit form throughthe normal supply channels. Sealing (or potting)is not necessary on environmentproof E con-nectors or connectors located in areas where thetemperature exceeds 200°F. The sealingcompound deteriorates after long exposure toambient temperatures above 200°F.

For detailed instructions on how to performsealing operations, refer to current electronicmaterial changes and to Installation Practices forAircraft Electrical and Electronic Wiring,NAVAIR 01-1A-505. A summary of the pro-cedures that you should follow when sealing aconnector is as follows:

1. Prepare a used connector by removingexisting sealants and by cleaning. The cleaningsolvent used must clean thoroughly, evaporatequickly, and leave no residue. Remove all sleevingfrom the wires. Resolder loose or poorly solderedconnections, and add a length of wire about 9inches long to each unused pin. The purpose ofsoldering a short length of wire to each spare pinis to allow for circuit growth. Use a stiff-bristlebrush to remove any excess rosin from around the

6-21

pins. Now, repeat the cleaning, and then separatethe wires evenly.

2. Thoroughly mix the accelerator and basecompound (fig. 6-17). The ratio of accelerator tobase compound is critical; therefore, you mustadd the entire quantity of accelerator furnishedto the base compound.

3. Place the plugs or receptacles on a table,arranging them so gravity will draw the sealer tothe bottom of the plug. Box receptacles of plugswithout back shells require fittings with a moldmade of masking tape, cellophane tape, or itsequivalent (fig. 6-18, view A). This will retain the

Figure 6-17.-Combining accelerator with base compound.

Figure 6-18.-(A) Making a mold from masking tape;(B) finished potted plug.

sealant during the curing process. If using the backshell, apply a slight amount of oil to the innersurface to prevent the compound from adheringto it.

4. Use a spatula, putty knife, or paddle toapply the compound. Ensure good packingaround the base of the pins. When potting,completely fill the part, or at least fill it to a pointwhere you can cover about three-eighths inch ofinsulated wire. Now, allow the compound to cure.


A8.

A9.

A10.

Only certified microminiature component repair (MMCR) personnel.

Component damage during maintenance usually results fromexcess heat during repair, reversed polarity of ohmmeters whilechecking for continuity, excessive voltage application or signalstrength during testing, rough handling, or using the wrong toolsor materials.

Assembly Electronics Repair, Standard Maintenance Practices,NAVAIR 01-1A-23.

6-22

The normal curing time is about 24 hours.Temperature affects the curing time.

Sometimes you may need to seal the entireconnector assembly (plug and receptacle) toprevent fluid from entering or collecting betweenthe two parts. You may fit a rubber O-ring overthe barrel of the plug. This will provide a sealwhen connecting the two parts securely. Ifproperly installed, this seal prevents moist airfrom entering during variations in temperature,altitude, or barometric pressure on the ground.Rubber packing O-rings are available for thispurpose through normal supply channels.Examine O-rings every time you disassemble theconnecter because O-rings age during service. Ifyou find that the O-rings have deteriorated,replace them.

CONDUCTORS AND TERMINALS

Although printed circuits and microelectroniccomponents are used in contemporary electronicequipment, conductors are still important asa signal- or current-carrying device. In thisdiscussion, the term conductor refers to both wireand cable. As a significant part of operatingequipment, conductors deserve appropriateattention.

Wire

When you are replacing wire, consult the MIMfor the particular aircraft or equipment, sinceit normally lists the wire used. When thisinformation is not available from the MIM, youmust determine the correct conductor needed forthe job. The three major selection factors (indescending order of importance) are size,insulation, and the characteristics required tosatisfy the specific environment in which the wiremust function.

CONDUCTOR SIZE.— For dc applications,the allowable voltage drop and current-carryingcapacity govern the choice of size. At radiofrequencies, the skin effect and inductance maybecome a controlling factor. Although normally(except in inductors or RF transformers) theseparameters are not considered. Therefore, wiresize is basically a function of the current or theallowable resistance, except when this results ina very small conductor size.

Small conductors are difficult to handle andbreak easily when soldered or from vibration. UsingNo. 22 or No. 24 American Wire Gage (AWG)

wire for general circuit wiring lessens theseproblems. Also, you should use at least No. 20AWG wire for connecting tube filaments inparallel. Only use solid wire for short jumperconnections, not exceeding 3 inches in length.However, you may use longer runs of solid wirewhen connecting parts that are solidly mountedand not subject to vibration. Clamps or dress lugsare recommended for long leads. In other words,use stranded copper wire whenever possible.Under extreme conditions of vibration or in areasthat require high flexibility, maintenanceprocedures may specify the use of oxygen-freecopper. Copper-clad steel is another possibilityfor applications requiring greater strength andrigidity.

INSULATION.— A wide variety of insulatingmaterial is available, which makes its specificationparticularly important. Since each type of insula-tion has its peculiar characteristics, no single typeis always suitable for general usage. The majorinsulation requirements include the following:

Good dielectric strength

High insulation resistance (internal andsurface)

Wide temperature range (with highsoftening and low brittle points)

Flexibility

Color stability

Resistance to abrasions, crushing,moisture, fungus, burning, radiation, oil,and acids

Insulation requirements for electronic, asopposed to power, applications are somewhatmore exacting because of the higher frequenciesand impedances and often higher voltagesinvolved. Insulation resistance and dielectricstrength are the prime considerations, although,for RF application the figure of merit, Q, becomesimportant.

Some of the insulations used for general-hookup wire include lacquered cotton, high-temperature rubber, butadiene styrene copolymers,fiber glass, nylon, and vinyl. Also, polyvinylchloride, cellulose acetate, polystyrene, poly-ethylene, and various silicon-treated materials areused as general hookup wire. The recommended

6-23

insulation wall thickness for all wiring within theconfines of an enclosure or with mechanicalprotection is less than 0.013 inch. Exposed wiringor wiring that is subject to wear or abrasionrequires heavier insulation.

ENVIRONMENT.— You must considerenvironmental factors such as temperature,humidity, altitude, vibration, radiation, fungus,contaminants, and corrosive elements whenselecting conductors. These requirements are partof the specification for the equipment where thewire is to be used.

Terminals

Since most aircraft have stranded wires, youuse terminal lugs to hold the strands together andmake it easier to fasten wires to terminal studs.The types of terminals used in electrical wiringare either of the soldered or crimped. Terminalsused in repair work must be the size and typespecified on the electrical wiring diagram for theparticular models. You may use soldered- andcrimped-type terminals interchangeably, but bothmust have the same amperage capacity and thesame size hole in the lug.

The increased use of crimp-on terminals is, toa large degree, due to the limitations of solderedterminals. The quality of soldered connectionsdepends upon the operator’s skill. Such factorsas temperature, flux, cleanliness, oxides, andinsulation damage caused by heat contribute todefective connections,

The crimp-on solderless terminals requirerelatively little operator skill. Another advantageis that the use of a crimping tool eliminates thenecessity of supplying power to a soldering iron.This allows installing terminals in an aircraft witha minimum of time and effort. The connectionsare made more rapidly, are cleaner, and are moreuniform. Because of the pressures exerted and thematerials used, the crimped connection or splice(when properly made) has an electrical resistancethat is less than that of an equivalent length ofwire.

The basic types of terminals are shown infigure 6-19. View A shows the straight type, viewB the right-angle type, view C the flag type, andview D the splice type. There are also variationsof these types. Variations may include the use ofa slot instead of a terminal hole, three- and four-way splice-type connectors, and others.

Since present-day aircraft have both copperand aluminum wiring, both copper and aluminum

Figure 6-19.-Types of solderless terminals.

terminals are necessary. There are various sizeterminal and stud holes for each of the differentwire sizes. A further refinement of the solderlessterminals is the insulated type, where insulationencloses the barrel of the terminal. The crimpingprocess compresses the insulation along with theterminal barrel, but does not damage it in theprocess. This eliminates the need for taping ortying an insulating sleeve over the joint.

Cable Splicing

A cable splice (other than one made with thecrimp-on splice or connector) is an emergencymeasure only. You may or may not use solder,as the condition warrants. However, the spliceshould give a good electrical and mechanical jointwithout solder. Tape the splice enough to provideinsulation equivalent to that in the rest of thecable. You must make permanent repairs as soonas possible.

You should refer to NAVAIR 01-1A-505 fordetailed information about attaching cableterminals, forming terminals for emergencyuse, and repairing damaged or broken cables,including fiber optic cables.

Terminal Blocks and Junction Boxes

Terminal blocks are an insulating material thatsupports and insulates a series of terminals fromeach other and from ground. They give you ameans of installing terminals within junctionboxes and distribution panels.

Two methods of attaching cable terminals toterminal blocks are shown in figure 6-20. View Ashows one of the standard nonlocking nutmethods. In this installation method, lockwashersare used. The preferred method is shown in

6-24

Figure 6-21.-Cable clamps.

Figure 6-20.-Installation of cable terminals on terminalblock.

view B. Here, an anchor nut (or self-locking nut)and the lockwasher are used for additionalsecurity. The use of anchor nuts is especiallydesirable in areas of high vibration. In bothinstallation methods, you must use a flat washer,as shown in the drawing.

Junction boxes are used to hold electricalterminals or other equipment, such as relays andtransformers. Individual junction boxes arenamed according to their function, location, orequipment with which they work. Junction boxesusually have a drain hole (except boxes labeledvaportight) located at the lowest point. This allowswater, oil, condensate, or other liquids to drainout.

Insulating Sleeving

Electronic maintenance operations in manyaviation activities use insulating sleeving(commonly called spaghetti) or shrink tubing.You will use sleeving when fabricating cableconnectors and connections to relays and terminalstrips. Crimped or soldered terminal lugs or splicesand tie points on terminal strips or terminalboards also require insulating sleeving.

Support Clamps

Clamps provide support for open wiring andserve as (or in addition to) lacing on open wiring.They usually come with a rubber cushion. Whenused with shielded conduit, the clamps are of thebonded type (fig. 6-21, view A); that is, theyprovide for electrical contact between the clampand conduit. Unbended clips provide for thesupport of open wiring.

To support long runs (lengths) of cablebetween panels, you should use either a strap-typeclamp (view B) or a clamp of the type shown inview C. The preferred method of supportingcables for all types of runs is with the type shownin view C. When using the strap-type clamps, youshould make sure they hold the cables firmly awayfrom lines, surface control cables, pulleys, andall movable parts of the aircraft. Use these clampsas an emergency measure only.

When cables pass through lightening holes, theinstallation should conform to the examplesshown in figure 6-22. You should route the cable

Figure 6-22.-Routing cables through lightening holes.

6-25

clear of the edges of the lightening hole to avoidany chance of chafing the insulation.

Replacing Wiring

When you install or replace wire or wirebundles, make sure there is no excessive slackbetween cable clamps. Normally, there should beno more than a one-half inch deflection withnormal hand pressure. However, you should allowsufficient slack at each end of the wire or wirebundles for the following reasons:

To allow easy removal and connection ofplugs

To allow replacement of terminals twotimes

To prevent mechanical strain on the wires

To permit free movement of shock- andvibration-mounted equipment

To allow movement of equipment formaintenance

Normally, bends in individual wires shouldhave a minimum bend radius of 10 times thediameter of the bundles. However, where the wirehas suitable support at each end of the bend, aminimum bend radius of three times the diameterof the bundle is acceptable.

Never bend coaxial cable to a radius smallerthan six times its outside diameter. Damage willresult. Route coaxial cables as directly as possible,avoiding any unnecessary bends.

Wires passing through a bulkhead requiresupport at each hole by a cable clamp. If theclearance between the wires and the edge of thehole is less than one-fourth inch, you should usea suitable grommet in the hole. See figure 6-23.

You must maintain a minimum clearance of3 inches between wiring and control cables. If thiscannot be done, install guards to prevent thewiring from contacting the control cables. Whenthe wiring must be parallel to plumbing carryingflammable fluids or oxygen, maintain as muchseparation as possible. Support the wiring so itcannot come closer than one-half inch to theplumbing. Never support any wire or wire bundlefrom a plumbing line that carries combustibleliquids or oxygen.

Install cable clamps so the mounting screwsare above the wire bundle (fig. 6-24). Otherwise,

Figure 6-23.-Cable clamp and grommet at bulkhead hole.

the weight of the cable may bend and break theclamp. It is also desirable that the back of theclamp rest against a structural member, ifpractical. Be careful not to pinch wires in the cableclamp.

TYING AND LACING WIRE GROUPSAND BUNDLES.— A wire group is two or morewires tied or laced together to give identity to anindividual system. A wire bundle is two or morewires or groups tied or laced together to provide

Figure 6-24.-Safe angles for cable clamps.

6-26

easier maintenance. Wire groups and bundlesshould be laced or tied together. This makes iteasier to install, maintain, and inspect them. Also,it keeps the cables neatly secured in groups andbundles to help avoid damage from chafing orequipment operation.

Tying is the securing together of a group orbundle wires by individual pieces of cord tiedaround the group or bundle at regular intervals.

Lacing is the securing together of wires insideenclosures by a continuous piece of cord, formingloops at regular intervals around the wire groupor bundle.

Wherever possible, you should use a narrow,flat, nonadhesive tape for lacing and tying. Youmay use round cord; however, it has a tendencyto cut into wire insulation. Therefore, it is not thepreferred method. Use cotton, linen, nylon, orglass-fiber cord or tape, according to thetemperature requirements. Prewax cotton or linencord or tape to make it moisture- and fungus-resistant. Nylon cord or tape may be waxed orunwaxed. Glass-fiber cord or tape is usually notwaxed.

PRECAUTIONS FOR LACING ANDTYING WIRE GROUPS.— When lacing or tyingwire groups and bundles, use the followingprecautions:

1. Lace or tie bundles tightly enough toprevent slipping, but not so tightly that the cordcuts into or deforms the insulation. This appliesespecially to coaxial cable, which has a softdielectric insulation between the inner and outerconductors.

2. Do not place ties on that part of a wiregroup or bundle located inside a conduit.

3. Lace wire groups or bundles only insideenclosures, such as junction boxes. Use doublecord on groups or bundles larger than 1 inch indiameter. Use single or double cord for groupsor bundles 1 inch or less in diameter.

NOTE: Coaxial cables can be damagedfrom lacing materials or methods of lacingor tying wire bundles that cause aconcentrated force on the cable insulation.Elastic lacing materials, small-diameterlacing cord, and excessive tighteningdeform the innerconductor insulation,which may result in short circuits orimpedance changes. Flat, nylon, braided,waxed lacing tape is recommended forcoaxial cables.

Figure 6-25.-Single-cord lacing.

PROCEDURES FOR LACING WITH ASINGLE CORD.— The procedures you shoulduse to lace a wire group or bundle with a singlecord are as follows:

1. Start the lacing at the thick end of the wiregroup or bundle with a knot consisting of a clovehitch with an extra loop. See figure 6-25.

2. At regular intervals along the wire groupor bundle and at each point where a wire or wiregroup branches off, continue the lacing with halfhitches. Space half hitches so the group or bundleis neat and securely held.

3. End the lacing with a knot consisting of aclove hitch with an extra loop.

4. Trim the free ends of the lacing cord tothree-eighths inch minimum.

PROCEDURES FOR LACING WITH ADOUBLE CORD.— The procedures you shoulduse to lace a wire group or bundle with a doublecord are as follows:

1. Start the lacing at the thick end of the wiregroup or bundle with a bowline on a bight. Seefigure 6-26.

Figure 6-26.-Double-cord lacing.

6-27

2. At regular intervals along the wire groupor bundle and at each point where a wire groupbranches off, continue the lacing with half hitches,holding both cords together. Space half hitchesso the group or bundle is neat and securely held.

3. End the lacing with a knot consisting of ahalf hitch, using one cord clockwise and the othercounterclockwise, and then tie the cord ends witha square knot.


PROCEDURES FOR LACING A BRANCH-ING WIRE GROUP.— The procedures youshould use to lace a wire group that branches offthe main wire bundle are as follows:

1. Start the branch-off by lacing with astarting knot located on the main bundle just pastthe branch-off point. See figure 6-27. When usingsingle-cord lacing, make the starting knot the sameas regular single-cord lacing. When using double-cord lacing, use the double-cord lacing startingknot.

2. End the lacing with the regular knot usedin single- and double-cord lacing.


Figure 6-27.-Lacing a branch-off.

TYING WIRE GROUPS WHEN SUP-PORTS ARE MORE THAN 12 INCHES.—Tie all wire groups or bundles (fig. 6-28)when supports are more than 12 inches apart.Space the ties so they are 12 inches or less

Figure 6-28.-Tying groups or bundles.

6-28

apart. To make a tie, you should perform thefollowing:

1. Wrap cord around wire group or bundle,as shown in figure 6-28, view A.

2. Make a clove hitch, followed by a squareknot with an extra loop.

3. Trim free ends of cord to three-eighths inchminimum.

When tying sleeves to wire groups or wirebundles, make the ties the same as for wire groupsand bundles.

USING TAPE.— When it is permissible to usetape, you should use the following method:

1. Wrap tape around the wire group or bundlethree times, with a two-thirds overlap for eachturn. See figure 6-28, view B.

2. Heat-seal the loose tape end with the sideof a soldering iron heating element. Do not usetape to secure wire groups or bundles that requirefrequent maintenance.

SELF-CLINCHING CABLE STRAPS

Self-clinching cable straps are adjustable,lightweight, flat nylon strips. They have moldedribs or serrations on the inside surface to grip thewire. You may use them instead of individual cordties for quickly securing wire groups or bundles.The straps are of two types—a plain cable strapand one that has a flat surface for identificationof cables.

CAUTION

Do not use nylon cable straps over wirebundles containing coaxial cable. Do notuse straps in areas where failure of thestrap would allow the strap to fall intomovable parts.

Installing self-clinching cable straps is donewith a military standard handtool (fig. 6-28, viewC). An illustration of the working parts of the toolis shown in figure 6-28, view D. You should followthe manufacturer’s instructions when using the tool.

WARNING

Use proper tools and make sure the strapis cut flush with the eye of the strap. Thisprevents painful cuts and scratches causedby protruding strap ends. Do not useplastic cable straps in high-temperatureareas (above 250°F).

BONDING

A bond is any fixed union between twometallic objects that results in electricalconductivity between them. Such a union resultseither from physical contact between conductivesurfaces of the objects or from the addition ofa firm electrical connection between them.Aircraft electrical bonding is the process by whichthe necessary electrical conductivity between thecomponent and metallic parts of the aircraft isgotten. An isolated conducting part of an objectis one that is physically separate (by interveninginsulation) from the aircraft structure and fromother conductors bonded to the structure. Abonding connector provides the necessaryelectrical conductivity between metallic parts inan aircraft where electrical contact is insufficient.Examples of bonding connectors are bondingjumpers and bonding clamps. See figure 6-29.

Figure 6-29.-Bonding methods.

6-29

An aircraft can become highly charged withstatic electricity while in flight. In an improperlybonded aircraft, all metal parts will not have thesame amount of charge, and a difference ofpotential will exist between various metal surfaces.Charges flowing through paths of variableresistance, such as moving control surfaces, willproduce electrical disturbances (noise) in the radioreceiver. If the resistance between isolated metalsurfaces is large enough, charges can accumulateuntil the potential difference becomes sufficientlyhigh to cause a spark, creating a fire hazard. Iflightning strikes an aircraft, a good conductingpath is necessary for the heavy current. Thisreduces severe arcs and sparks, which woulddamage the aircraft and possibly injure itsoccupants.

The aircraft structure is also the ground forthe radio. For the radio to function properly, aproper balance between the aircraft structure andantenna is required. This means the surface areaof the ground must be constant. Control surfaces,for example, may at times become partiallyinsulated from the remaining structure becauseof a film of lubricant on the hinges. This willaffect radio operation if the condition is not takencare of by bonding.

Bonding also provides the necessary low-resistance return path for single-wire electricalsystems. This low-resistance return path also aidsthe effectiveness of the shielding and provides ameans of bringing the entire aircraft to the earth’sground potential.

In summary, aircraft are electrically bondedfor the following reasons:

To reduce radio and radar interferences byequalizing static charges that accumulate

To eliminate a fire hazard by preventingstatic charges from accumulating betweentwo isolated members and creating a spark

To reduce lightning damage to the aircraftand injury to its occupants

To provide the proper ground for properfunctioning of the aircraft radio

To provide a low-resistance return path forsingle-wire electrical systems

To aid in the effectiveness of the shielding

To provide a means of bringing the entireaircraft to the earth’s potential, andkeeping it that way while it is grounded tothe earth

Bonding connections are made so vibration,expansion or contraction, or relative movementincidental to normal service use will not break thebonding connections. Bondings should not loosento such an extent that the resistance will varyduring the movement. The bonding of mostconcern is the bonding jumpers that go acrossshock mounts used to support electronic equip-ment.

A primary aim of bonding is to provide anelectrical path of low dc resistance and low RFimpedance. Therefore, the jumper should be agood conductor of ample size for the current-carrying capacity, have low resistance, and be asshort as possible. If practical, you should bondparts directly to the basic aircraft structure ratherthan through other bonded parts. Install bondingjumpers so they do not interfere with theoperation of movable components of the aircraft.

Contact of dissimilar metals in the presenceof an electrolyte, such as salt water, produces anelectric action (battery action) that causes a pittingin one of the metals. The intensity of this electricaction varies with the kinds of metals. Frequently,bonding involves the direct contact of dissimilarmetals. In such cases, the metals used produce aminimum amount of corrosion. The connectionsare also made so that if corrosion does occur, itwill be in replaceable elements, such as jumpers,washers, or separators, rather than the bondedor bonding members. Thus, use washers made ofthe same material as the structural member againstthe structural member. Also, use washers of thesame material as the bonded member that is incontact with that item.

Self-tapping screws should not be used forbonding purposes, nor should jumpers becompression-fastened through plywood or othernonmetallic material. When performing a bondingoperation, you should remove contact surfacefilms before assembly, and then refinish thecompleted assembly with a suitable protectivefinish.

For more detailed information about bonding,you should refer to Installation Practices, AircraftElectric and Electronic Wiring, N A V A I R01-1A-505.

SHOCK MOUNTS

Electronic equipment is sensitive to mechanicalshock and vibration. Therefore, units of electronicequipment are normally shock mounted toprovide some protection against in-flight vibrationand against launching and landing shock. The

6-30

specific type of prescribed shock mount will bein the MIM for the specific aircraft, and youshould not use a substitute.

Shock mounts require periodic inspections.Replace any defective mounts as soon as possible.In the inspection, you should check for chemicaldecay of the shock-absorbing material, stiffnessand resiliency of the material, and overall rigidityof the mount. If the mount is too still or too rigid,it may not provide adequate protection againstthe shock of launching and landing. If it is notstiff or rigid enough, it may permit prolongedvibration following an initial shock. Whendetermining the limits of rigidity and resiliency,you should consider the weight of the mountedunit as well as the possible amounts of positiveand negative acceleration the unit may receive.

Shock-absorbing materials commonly used inshock mounts are usually electrical insulators. Forsafety, each electronic unit mounted in thismanner is electrically bonded to a structuralmember of the aircraft (fig. 6-29, view B.) Theinspection of the shock mounts should include thebonding straps. Replace or redo any defective orineffective bonds as soon as possible.

SAFETY WIRING

Some equipment parts require a positive safetylocking device. The use of safety wire is oneaccepted method of providing this safety measure.Two of the most common reasons for safetywiring nuts, bolts, screws, and connector parts are

1. to prevent them from coming loose due toaircraft vibration, and

2. to prevent accidental engagement of aguarded switch.

You will learn about some of the methods ofapplying safety wire in the following paragraphs.

The most common method of safetying nuts,bolts, and screws is the double-twist method. Youcan do this by hand or with special safety wirepliers. (See figure 6-30, view A.) If you make thetwists by hand, make the final few twists usingpliers so there is enough tension to secure the endsof the wire properly. The safety wire shouldalways be installed and twisted so that the looparound the head stays down and does not tendto come up over the bolt head. When you twistthe wires together, be extremely careful to ensurethey are tight, but do not overstress them to thepoint where they will break under a slight loador vibration. You should always use new safety

Figure 6-30.-Safety wiring nuts, bolts, and screws.

wire on every job. Be careful to use pliers onlyon the ends of the wire so you don’t nick the wire.If safety wire becomes nicked, discard it and usea new piece. After you make the final twists withpliers, cut off the nicked loose ends and bend theend of the wire around the bolt or screw head.This will protect personnel from the sharp ends.

You may use the single wire method of safetywiring (fig. 6-30, view B) on small screws in aclosely spaced area provided the screws form aclosed geometrical pattern. Note that anyloosening tendencies will pull against the tensionof the wire. Never back off or overtorque to alignholes for safety wiring.

Safety wire electric connectors only whenspecified on engineering drawings or whenexperience has shown that the connector will notstay tight. Electric connectors are usually safetywired in engine nacelles, in areas of high vibration,and in locations not readily accessible for periodicmaintenance inspection.

When you must safety wire electrical con-nectors, you should use 0.032-inch-diameter safetywire wherever possible. On small parts with holes0.045 inch nominal diameter or smaller, use0.020-inch-diameter safety wire. Sometimes the

6-31

connector to be safety wired does not have a wirehole. If there is no wire hole, remove the couplingnut and drill a No. 56 (0.045-inch-diameter) holediagonally through the edge of the nut. Figure6-31 shows a properly safety-wired connector.

An example of safety wiring a guarded switchis shown in figure 6-32. You can see that the wireis not twisted tightly. Use very soft wire; the wiremay be either aluminum or copper. This soft wire(called shear wire) lets the operator break the wireeasily when necessary to engage the switch,

Q11.

Q12.

Q13.

Q14.

Q15.

Q16.

Q17.

To what NAVAIR manual should you referfor detailed instructions on potting orsealing operations?

What are the three major factors toconsider when you have to determine thecorrect conductor you need for a job?

When may you use a cable splice (other thanone made with the crimp-on splice or con-nector) and to what manual should you refer?

Why should you install cable clamps so thescrews are above a wire bundle?

Describe the difference between a wiregroup and wire bundle.

When should you NOT use nylon cablestraps?

Describe the primary aim of bonding.

Figure 6-31.-Safety wiring a connector.

Figure 6-32.-Shear wire on a switch guard.

ENVIRONMENTAL PROBLEMS

Learning Objective: Recognize the variousenvironmental effects on electronic equip-ment and the methods used to combatthese effects.

The complexity of avionics equipment andenvironmental conditions are among the chiefcauses of equipment failure. For these reasons,you need to know how environmental conditionsaffect the equipment. Some of the environmentalfactors that affect the design characteristicsof equipment include temperature, humidity,pressure, abrasive conditions, and shock, vibra-tion, and acceleration.

TEMPERATURE

Research has resulted in the development ofcomponent parts that are able to withstandoperation under extreme temperatures. Extremelylow temperatures cause brittleness in metal andloss of flexibility in rubber, insulation, and similarmaterials. Extremely high temperatures causedeformity and decay of these items.

Most internal component parts cannot with-stand extreme temperatures. Because equipmentis normally in confined spaces aboard aircraft, thegenerated heat causes the temperature to rise;therefore, many units have fans installed toincrease the air circulation. This reduces thetemperature within the unit. Most new models ofaircraft use an electronic equipment compartmentconcept. Also, blast air from outside the aircraft

6-32

ABRASIVE CONDITIONSor from the aircraft’s air-conditioning system mayprovide cooling.

HUMIDITY

Humidity is a term that defines the measureof water content in the air. Humidity is a possiblecause of avionics equipment or componentfailure. High humidity (a high water content inthe air) provides a possible environment forcorrosion and fungus growth. Humid air cancause short circuiting between points of highpotential.

In certain cases, the removal of heat fromequipment requires the use of external air. If thisexternal air has a high moisture content, coolingmay occur using one of two methods. First, thehigh-humidity air may go through an air jacketthat surrounds the equipment. In this case, theheat is removed without allowing the humid airto come in contact with the internal equipmentcomponents. Second, when the internal equip-ment components require direct air for heatremoval, the direct air passes through silica-gelcrystals (a desiccant), removing the moisture fromthe air.

PRESSURIZATION

When operating high-voltage electrical equip-ment at high altitudes, there is always the problemof arcing. At high altitudes, arcing is caused bythe reduced dielectric strength of the air as itbecomes thinner. The pressurized equipment casereduces the possibility of arcing. All componentsinside the case are subjected to pressurization,which reduces the chance of arcing. In radaroperation at high altitudes, the waveguides andparts of the antenna are also pressurized.

Pressurization is usually not a big maintenanceproblem, but occasionally it can cause trouble.The problems that do arise in the pressurizationsystem are usually the result of poor scheduledmaintenance. For a trouble-free pressure system,all seals and gaskets (located at the points ofseparation, waveguide joints, and case covers)must undergo careful installation to provide anairtight seal. When pressurization troubles dooccur, they may be difficult to detect, since a verysmall leak may make the system inoperable.Before you try to pressurize a system to check forleakage, consult the MIM for the amount of safepressure for that system. If excessive pressure isapplied, it could possibly rupture the seals orgaskets or cause mechanical damage to parts ofthe equipment.

Sand, dust, and other substances that areabrasive affect many components. Normally,these components are not sealed off fromatmospheric conditions. In some cases, theabrasive material may form even though theunit is sealed. This material may come fromgenerators, motors, and dynamotors that usebrushes. Also, the protective coating may wearoff a part by the movement of the abrasivematerial in the cooling air. Removing theprotective coating may allow the unprotectedmetal to corrode.

Modern aircraft configurations use air-conditioning systems to cool avionics equipments.The external air cools the heat exchanger, whilethe internal air that removes heat from theequipment may be pressurized. The use of thepressurized air for equipment heat removalreduces the undesired environmental effects oftemperature, humidity, arcover, and abrasiveconditions.

SHOCK, VIBRATION, ANDACCELERATION

Since acceleration effects are directly pro-portional to mass, the smaller the object, the lessthe mass and inertia, all other factors being equal.The extended use of miniaturized components onprinted circuits will, to some extent, counteractthe trouble due to increased accelerations andshocks.

Vibration effects are directly proportionalto the resonant mechanical frequency of theequipment. Shock and vibration effects arereduced by locating the heavier components asclosely as possible to the mounting points toreduce the length of the moment arm.

The decision to mount entire equipmentson shock and vibration mounts or to mounteach component individually depends on theoverall mass. Using vibration mounts forcomponents and then mounting the entire chassison shock mounts would probably amplify anyvibration.

Q18. What causes arcing at high altitudes?

Q19. How do we reduce the possibility of arcing?

6-33

ELECTROSTATIC DISCHARGE(ESD)

Learning Objective: Recognize the hazardsto ESD-sensitive devices, to include properhandling and packaging techniques.

The sensitivity of electronic devices and com-ponents to electrostatic discharge (ESD) has recentlybecome clear through use, testing, and failureanalysis. The construction and design features ofcurrent microtechnology have resulted in devicesbeing destroyed or damaged by ESD voltages aslow as 20 volts. The trend is toward greater-com-plexity, increased packaging density, and thinnerdielectrics between active elements. This trend willresult in devices even more sensitive to ESD.

Various devices and components are suscepti-ble to damage by electrostatic voltage levelscommonly generated in production, test, opera-tion, and by maintenance personnel. These devicesand components include the following:

Thick and thin film resistors, chips andhybrid devices, and crystals

All subassemblies, assemblies, and equipmentcontaining these components/devices withoutadequate protective circuitry are ESD-sensitive(ESDS).

You can protect ESDS items by implementingsimple, low-cost ESD controls. Lack of imple-mentation has resulted in high repair costs,excessive equipment downtime, and reducedequipment effectiveness.

The operational characteristics of a systemmay not normally show these failures. However,under internal built-in test monitoring in adigital application, they become pronounced. Forexample, the system functions normally on theground; but, when placed in an operationalenvironment, a damaged PN junction mightfurther degrade, causing its failure. Normalexamination of these parts will not detect the

All microelectronic and most damage unless you use a curve tracer to measuresemiconductor devices, except for various the signal rise and fall times or check the partspower diodes and transistors for reverse leakage current.


A11. You should refer to the current electronic material changes andto Installation Practices, Aircraft Electric and Electronic Wiring,NAVAIR 01-1A-505.

A12. Conductor size, insulation, and the environment for the conductor.

A13. As an emergency measure only. You must make permanentrepairs as soon as possible. For detailed information, you shouldrefer to NAVAIR 01-1A-505.

A14. The weight of the cable may bend and break the clamp.

A15. A wire group is two or more wires tied or laced together to giveidentity to an individual system. A wire bundle is two or morewires or groups tied or laced together to provide easier maintenance.

A16. Do not use nylon cable straps over wire bundles containingcoaxial cable or in areas where failure of the strap would allowthe strap to fall into moveable parts.

A17. The primary aim of bonding is to provide an electrical path oflow dc resistance and low RF impedance.

A18. At high altitudes, arcing is caused by the reduced dielectricstrength of the air as it becomes thinner.

A19. Pressurization of the equipment case.

6-34

STATIC ELECTRICITY

Static electricity is electrical energy at rest.Some substances readily give up electrons whileothers accumulate excessive electrons. When twosubstances are rubbed together, separated, or flowrelative to one another (such as a gas or liquidover a solid), one substance becomes negativelycharged and the other positively charged. Anelectrostatic field or lines of force radiate betweena charged object to an object at a differentelectrostatic potential (such as more or lesselectrons) or ground. Objects entering this fieldwill receive a charge by induction.

The capacitance of the charged object relativeto another object or ground also has an effect onthe field. If the capacitance is reduced, there isan inverse linear increase in voltage, since thecharge must be conserved. As the capacitancedecreases, the voltage increases until a dischargeoccurs via an arc.

CAUSES OF STATIC ELECTRICITY

Generation of static electricity on an objectby rubbing is known as the triboelectric effect.Table 6-1 lists substances in the triboelectric series.

The size of an electrostatic charge on twodifferent materials is proportional to theseparation of the two materials. Typical primecharge generators commonly encountered in amanufacturing facility are shown in table 6-2.

Electrostatic voltage levels generated bynonconductors can be extremely high. However,air slowly dissipates the charge to a nearbyconductor or ground. The more moisture in theair the faster a charge dissipates. Table 6-3 showstypical measured charges generated by personnelin a manufacturing facility. You can see that thegenerated voltage decreases with an increase inhumidity levels of the surrounding air.

NOTE: The triboelectric series is arrangedin an order so that when any twosubstances in the list contact one anotherand are separated, the substance higher onthe list assumes a positive charge.

EFFECTS OF STATIC ELECTRICITY

The effects of ESD are not always recognized.Failures due to ESD are often misanalyzed asbeing caused by electrical overstress due totransients other than static. Many failures, oftenclassified as other, random, unknown, infant

Table 6-1.-Triboelectric Series

POSITIVE (+)

ACETATEGLASSHUMAN HAIRNYLONWOOLFURALUMINUMPOLYESTERPAPERCOTTONWOODSTEELACETATE FIBERNICKEL, COPPER, SILVERBRASS – STAINLESS STEELRUBBERACRYLICPOLYSTYRENE FOAMPOLYURETHANE FOAMSARANPOLYETHYLENEPOLYPROPYLENEPVC (VINYL)KEL FTEFLON

NEGATIVE (–)

NOTE: THE TRIBOELECTRIC SERIESIS ARRANGED IN SUCH ANORDER THAT WHEN ANY TWOSUBSTANCES IN THE LIST CON-TACT ONE ANOTHER ANDARE SEPARATED, THE SUB-STANCE HIGHER ON THELIST ASSUMES A POSITIVECHARGE.

mortality, manufacturing defect, etc., are actuallycaused by ESD. Misclassification of the defect isoften caused by not performing failure analysisto the proper depth.

COMPONENT SUSCEPTIBILITY

All solid-state devices (all microcircuits andmost semiconductors), except for various power

6-35

Table 6-2.-Typical Charge Generators

WORK SURFACES FORMICA (WAXED OR HIGHLY RESISTIVE) FINISHED WOOD SYNTHETIC MATS

FLOORS WAX FINISHED VINYL

CLOTHES COMMON CLEAN ROOM SMOCKS PERSONNEL GARMENTS (ALL TEXTILES

EXCEPT VIRGIN COTTON) NONCONDUCTIVE SHOES

CHAIRS FINISHED WOOD VINYL FIBERGLASS

PACKAGING AND HANDLING COMMON POLYETHYLENE — BAGS,WRAPS, ENVELOPES

COMMON BUBBLE PACK, FOAM COMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALS

ASSEMBLY, CLEANING, SPRAY CLEANERSTEST AND REPAIR AREAS COMMON SOLDER SUCKERS

COMMON SOLDER IRONS SOLVENT BRUSHING (SYNTHETIC BRISTLES) CLEANING, DRYING TEMPERATURE CHAMBERS

Table 6-3.-Typical Measured Electrostatic Voltages

VOLTAGE LEVELS @ RELATIVE HUMIDITYMEANS OF STATIC GENERATION

LOW-10-20% HIGH-65-90%

WALKING ACROSS CARPET 35,000 1,500

WALKING OVER VINYL FLOOR 12,000 250

WORKER AT BENCH 6,000 100

VINYL ENVELOPES FOR WORK 7,000 600INSTRUCTIONS

COMMON POLY BAG PICKED UP 20,000 1,200FROM BENCH

WORK CHAIR PADDED WITH 18,000 1,500URETHANE FOAM

6-36

transistors and diodes, are susceptible to damageby discharging electrostatic voltages. Thedischarge may occur across their terminals or bysubjecting these devices to electrostatic fields.

LATENT FAILURE MECHANISMS

ESD overstress can produce a dielectricbreakdown of a self-healing nature when thecurrent is unlimited. When this occurs, the devicemay retest good. However, it contains a hole inthe gate oxide. With use, metal will eventuallymigrate through the puncture, resulting in ashorting of this oxide layer.

Another structure mechanism involves highlylimited current dielectric breakdown from whichno apparent damage is done. However, thisreduces the voltage at which subsequentbreakdown occurs to as low as one-third of theoriginal breakdown value. ESD damage can resultin a lowered damage threshold at which asubsequent lower voltage ESD will cause furtherdegradation or a functional failure.

ESD ELIMINATION

The heart of an ESD control program is theESD-protected work area and ESD-groundedwork station. When you handle an ESD-sensitive(ESDS) device outside of its ESD protectivepackaging, you need to provide a means ofreducing generated electrostatic voltages below thelevels at which the item is sensitive. The greaterthe margin between the level at which thegenerated voltages are limited and the ESDS itemsensitivity level, the greaterprotecting that item.

PRIME GENERATORS

Look at table 6-2. It

the probability of

lists ESD primegenerators. All common plastics and other primegenerators of static electricity should be prohibitedin the ESD-protected work area. Carpeting shouldalso be prohibited. If you must use carpet, itshould be of a permanently anti-static type.Perform weekly static voltage monitoring wherecarpeting is in use.

CAUTION

Anti-static cushioning material isacceptable; however, the items cited needto be of conductive material to preventdamage or destruction of ESDS devices.

PERSONAL APPAREL ANDGROUNDING

An essential part of the ESD program isgrounding personnel and their apparel when theyhandle ESDS material. Means of doing this aredescribed in this section.

Smocks

Personnel handling ESDS items should wearlong-sleeve ESD-protective smocks, short-sleeveshirts or blouses, and ESD-protective gauntletsbanded to the bare wrist and extending towardthe elbow. If these items are not available, useother anti-static material (such as cotton) that willcover sections of the body that could contact anESDS item during handling.

Personnel Ground Straps

Personnel ground straps should have aminimum resistance of 250,000 ohms. Based onlimiting leakage currents to personnel to 5milliamperes, this resistance protects personnelfrom shock from voltages up to 125 volts RMS.The wrist, leg, or ankle bracelet end of the groundstrap should have some metal contact with theskin. Bracelets made completely of carbon-impregnated plastic may burnish around the areain contact with the skin, resulting in too high animpedance to ground.

ESD-PROTECTIVE MATERIALS

There are two basic types of ESD-protectivematerials-conductive and anti-static. Conductivematerials protect ESD devices from staticdischarges and electromagnetic fields. Anti-staticmaterial is a nonstatic generating material. Otherthan not generating static, anti-static materialoffers no other protection to an ESD device.

CONDUCTIVE ESD-PROTECTIVEMATERIALS

Conductive ESD-protective materials consistof metal, metal-coated, and metal-impregnatedmaterials (such as carbon particle impregnated,conductive mesh or wire encased in plastic). Themost common conductive materials used for ESDprotection are steel, aluminum, and carbon-impregnated polyethylene and nylon. The lattertwo are opaque, black, flexible, heat sealable,electrically conductive plastics. These plastics are

6-37

composed of carbon particles, impregnated in theplastic, which provides volume conductivitythroughout the material.

ANTI-STATIC ESD PROTECTIVEMATERIALS

Anti-static materials are normally plasticmaterials (such as polyethylene, polyolefin,polyurethane, nylon) that are impregnated withan anti-static substance. This anti-static substancemigrates to the surface and combines with thehumidity in the air to form a conductive sweatlayer on the surface. This layer is invisible and,although highly resistive, is conductive enough toprevent the buildup of electrostatic charges bytriboelectric (or rubbing) methods in normalhandling. Simply stated, the primary asset of ananti-static material is that it will not generate acharge on its surface. However, this materialwon’t protect an enclosed ESD device if it comesinto contact with a charged surface.

Anti-static material is tinted pink, a symbolof its being anti-static. Anti-static materials areused for inner-wrap packaging. However, anti-static trays, vials, carriers, boxes, etc., are notused unless components and/or assemblies arewrapped in conductive packaging.

HYBRID ESD-PROTECTIVE BAGS

Hybrid ESD-protective bags area laminate ofdifferent ESD-protective materials. They aremade from conductive and anti-static materials.The hybrid ESD-protective bag provides theadvantages of both types of materials in a singlebag.

ESDS DEVICE HANDLING

The following are general guidelines that youshould follow when handling ESDS devices:

Ground all containers, tools, test equip-ment, and fixtures used in ESD-protective areasbefore and/or during use, either directly or bycontact with a grounded surface.

Avoid physical activities around ESDSitems that are friction-producing; for example,removing or putting on smocks, wiping feet,sliding objects over surfaces, etc.

Wear cotton smocks and/or other anti-static treated clothing.

Avoid the use or presence of plastics,synthetic textiles, rubber, finished wood, vinyls,and other static-generating materials, especiallywhen handling ESDS out of their ESD-protectivepackaging.

Place the ESD protective material con-taining the ESD item on a grounded work benchsurface to remove any charge before opening thepackaging material.

Attach personnel grounding to groundthemselves before removing ESDS items fromtheir protective packaging.

Remove ESDS items from ESD-protectivepackaging with fingers or metal grasping tool onlyafter grounding, and place on the ESD-groundedwork bench surface.

Make periodic electrostatic measurementsat all ESD-protected areas. This assures the ESD-protective properties of the work station and allequipment contained there have not degraded.

Perform periodic continuity checks ofpersonnel ground straps (between skin contact andground connection), ESD-grounded work stationsurfaces, conductive floor mats, and otherconnections to ground. Perform this check witha megohmmeter to make sure grounding resistivityrequirements are met.

ESDS DEVICE PACKAGING

Before an ESDS item leaves an ESD-protectedarea, package the item in one of the followingESD-protective materials:

Ensure shorting bars, c l i p s , o rnoncorrective conductive materials are insertedcorrectly in or on all terminals or connectors.

Package ESD items in an inner wrap oftype II material and an outer wrap of type Imaterial that conform to MIL-B-81705. You mayuse a laminated bag if it meets the requirementsof M-B-81705. Cushion-wrap the item withelectrostatic-free material conforming to PPP-C-1842, type III, style A. Place the cushioned iteminto a barrier bag made from MIL-C-131 andheat-seal closed, using method 1A-8. Place thewrapped, cushioned, or pouched ESDS item inbags conforming to MIL-B-117, type I, class F,style I. Mark the packaged unit with the ESDsymbol and caution (fig. 6-33).

6-38

Figure 6-33.-ESDS markings.

TESTING/REPAIR

Before you work on ESDS items, make sureyou meet the following precautions/procedures:

Ground the work area, equipment, andwrist strap assembly.

Attach the wrist strap and place metaltools, card extractors, test fixtures, etc., on agrounded bench surface.

Place conductive container on the benchtop. Remove the component/assembly frompackaging. Remove shorting devices, if present.Handle components by their bodies and lay themon the conductive work surface or test fixtures.

Test through the connector or tabs only.

Do not probe assemblies with testequipment.

After testing, replace shorting devices andprotective packaging.

Do not use a Simpson Model 260 orequivalent to test parts or assemblies. You mustuse a high input impedance meter such as a Fluke8000A multimeter.

Do not permit or perform dielectricstrength tests.

Q20.

Q21.

Q22.

Q23.

ESD-sensitive devices can be damaged byelectrostatic voltages as low as ___________

When handling ESDS devices, personneland their apparel should be connected to

What is the minimum resistance forpersonnel ground straps?

What color is a symbol of material that isantistatic?

ELECTRICAL/ELECTRONIC NOISE

Learning Objective: Recognize the typesand effects of radio noise, includingnatural and man-made interference.

6-39

The electrical noise generated within a radioor radar receiver is not the same as the electricalnoise generated external to the receiver thatcouples into the receiver. The internally generatednoise is the result of circuit deficiencies in thereceiver itself. Normally, replacing the defectivecomponents in the receiver or replacing the entirereceiver will eliminate internally generated noise.Externally produced electrical noise enters thereceiver by various means. The noise causesinterference in and poor reception by the receiver.

In early naval aircraft, electrical noiseinterference was not a major problem becausethere were fewer external sources of electricalnoise. Receiver sensitivities were low, and theaircraft control components were manual. Intoday’s aircraft, there are considerably moresources of externally generated electrical noise.The aircraft now contains many receivers withhigher sensitivities, and the aircraft controls arefrom various electrical and/or mechanical devices.These devices include control surface drivemotors, fuel and hydraulic boost pumps, acinverters, and cabin pressurization systems. Inaddition, pulsed electronic transmitters, such astacan, radar, and IFF, can be sources of electricalnoise interference. Listening to electrical noiseinterference in the output of a radio receiver cancause nervous fatigue in aircrew personnel.Electrical noise may also reduce the performance(sensitivity) of the receiver. For these reasons,electrical noise must be kept at the lowest possiblelevel.

TYPES AND EFFECTS OF RECEIVERNOISE INTERFERENCE

There are two types of electrical noiseinterference that enter aircraft receivers—naturalinterference and man-made interference.

Natural Interference

The three types of natural electrical noise thatcause radio interference are atmospheric static,precipitation static, and cosmic noise.

ATMOSPHERIC STATIC.— Atmosphericstatic is the result of the electrical breakdownbetween masses (clouds) of oppositely chargedparticles in the atmosphere. An extremely largeelectrical breakdown between two clouds orbetween the clouds and ground causes lightning.Atmospheric static is completely random innature. Both its rate of recurrence and intensityof individual discharges are random. Atmosphericstatic produces irregular popping and cracklingin audio outputs and grass (noise floor) on visualoutput devices. Its effects range from minorannoyance to complete loss of a receiver’susefulness. The intensity of atmospheric inter-ference is seldom crippling at frequencies from2 MHz to 30 MHz, but it can be annoying. Above30 MHz, the noise intensity decreases to a verylow level. At frequencies below 2 MHz, naturalstatic is the main limiting factor on usable receiversensitivity.

The intensity of atmospheric static varies withlocation, season, weather, time of day, andthe receiver’s tuned frequency. It is strongestat the lower latitudes, during the summer,during weather squalls, and at the lower radiofrequencies. Many schemes are available forreducing the effect of atmospheric static.However, the best technique is to avoid thosefrequencies associated with intense static, ifpossible.

PRECIPITATION STATIC.— Precipitationstatic is a type of interference that occurs duringdust, snow, or rain storms. The main cause ofprecipitation static is the corona discharge ofhigh-voltage charges from various points on the


A20. 20 volts.

A21. Ground.

A22. 250,000 ohms.

A23. Pink.

6-40

airframe. These charges may reach severalhundred thousand volts before discharge occurs.The charge can build up in two ways. First, anelectrostatic field existing between two oppositelycharged thunderclouds induces bipolar charges onthe surfaces of the aircraft as it passes throughthe charged clouds. Second, a high unipolarcharge on the entire airframe occurs fromfrictional charging. This occurs from collision ofatmospheric particles (low altitudes) or fine iceparticles (high altitudes) with the aircraft’ssurface. The effects of corona discharge vary withtemperature. The effects increase as altitude andairspeed increase. Doubling airspeed increases theeffect by a factor of about 8; tripling airspeedincreases the effect by a factor of about 27.

The effect of precipitation static is a loudhissing or frying noise in the audio output of acommunication receiver. A grassy indication mayalso appear on a visual output device, such as aradar receiver. The radio frequency rangesaffected by ‘precipitation static are nearly thesame as for atmospheric static. When present,precipitation interference is severe and oftendisables all receivers tuned to the low- andmedium-frequency bands.

COSMIC NOISE.— Cosmic noise usuallyaffects the UHF band and above. However, itoccasionally affects receivers operating atfrequencies as low as 10 MHz. Cosmic noise iscaused by radiation of stars. Its effect is normallyunnoticed. However, at peaks of cosmic activity,cosmic-noise interference could be a limitingfactor in the sensitivity of navigational andheight-finder radar receivers.

Man-Made Interference

The general categories of man-made inter-ference are tied to their spectrum of influence,such as broadband and narrow band.

BROADBAND INTERFERENCE.— Broad-band interference occurs when the current flowin a circuit is interrupted or varies radically froma sinusoidal rate. A current whose waveform isa sine wave can interfere at only a singlefrequency. Any other waveform containsharmonics of the basic sinewave frequency. Thesteeper the rise or fall of current, the higher theupper harmonic frequency will be. A perfectrectangular pulse contains an infinite number ofodd harmonics of the frequency represented byits pulse recurrence rate. Typical types of electrical

6-41

disturbances that generate broadband interferenceare electrical impulses, electrical pulses, andrandom noise signals.

In this chapter, the term impulse describes anelectrical disturbance. An impulse may be aswitching transient that is an incidental productof the operation of an electrical or electronicdevice. The impulse recurrence rate may or maynot be regular. The term pulse describes anintentional, timed, momentary flow of energyproduced by an electronic device. The pulserecurrence rate is usually regular.

Switching transients or impulses result fromthe make or break of an electrical current. Theyare extremely sharp pulses. The duration and peakvalue of these pulses depend on the amount ofcurrent and the characteristics of the opening orclosing circuit. The effects are sharp clicks in theaudio output of a receiver and sharp spikes onan oscilloscope trace. The isolated occasionaloccurrence of a switching transient has little orno significance. However, when repeated oftenenough and with enough regularity, switchingtransients are capable of creating intolerableinterference to audio and video circuits. Theydegrade receiver performance. Typical sources ofsustained switching transients are ignition timingsystems, commutators of dc motors andgenerators, and pulsed navigational lighting.

Pulse interference is normally from pulsedelectronic equipment. This type of interferencepresents a popping or buzzing in the audio outputdevice and noise spikes on an oscilloscope. Theinterference level depends on the pulse severity,repetition frequency, and regularity of occurrence.Pulse interference can trigger beacons and IFFequipment and cause false target indications onradar screens. In certain types of navigationalbeacons, these pulses cause loss of reliability.

Random noise consists of impulses that are ofirregular shape, amplitude, duration, andrecurrence rate. Normally, the source of therandom noise is an intermittent contact betweenbrush and commutator bar or slip ring. Anothersource can be an imperfect contact or poorisolation between two surfaces.

NARROW BAND INTERFERENCE.—Narrow band interference is almost always fromoscillators or power amplifiers in receivers andtransmitters. In a receiver, the cause is usually apoorly shielded local oscillator stage. In atransmitter, several of the stages could be at fault.The interference could be at the transmitteroperating frequency, a harmonic of its operating

frequency, or at some false frequency. Amultichannel transmitter that uses crystal-bankfrequency synthesizing circuits can produceinterference at any of the frequencies present inthe synthesizer. Narrow-band interference in areceiver can range from an annoying heterodynewhistle in the audio output to the completeblocking of received signals. Narrow-bandinterference affects single frequencies or spots offrequencies in the tuning range of the affectedreceiver.

SOURCES OF ELECTRICAL NOISE

Learning Objective: Recognize the varioussources of electrical noise and the operatingcharacteristics of each.

Any circuit or device that carries a varyingelectrical current is a potential source of receiverinterference. The value of the interference voltage

depends on the amount of voltage change. Thefrequency coverage depends on the abruptness ofthe change. The main sources of man-madeinterference in aircraft include rotating electricalmachines, switching devices, pulsed electronicequipment, propellers systems, receiver oscillators,nonlinear elements, and ac power lines.

Rotating Electrical Machines

Rotating electrical machines are a majorsource of receiver interference because of themany electric motors used in the aircraft. Rotatingelectrical machines used in aircraft are ofthree general classes—dc motors, ac motors andgenerators, and inverters.

DC MOTORS.—Modern aircraft use many dcmotors as flight control actuators, armamentactuators, and flight accessories. Most electronicequipment on the aircraft includes one or moredc motor for driving cycling mechanisms, com-pressor pumps, air circulators, and antennamechanisms. Each of these motors can generatevoltages capable of causing radio interference overa wide band of frequencies. The following is alist of the types of interfering voltages generatedby dc motors:

1. Switching transients generated as the brushmoves from one commutator bar toanother (commutation interference)

2. Random transients produced by varyingcontact between the brush and the com-mutator (sliding contact interference)

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3. Audio-frequency hum (commutator ripple)4. Radio frequency and static charges built up

on the shaft and the rotor assembly

The dc motors used in aircraft systems are ofthree general types—series-wound motors, shunt-wound motors, and permanent-magnet (PM)motors. The field windings of both series- andshunt-wound motors afford some filter actionagainst transient voltages generated by thebrushes. The PM motor’s lack of such inherentfiltering makes it a very common source ofinterference. The size of a dc motor has littlebearing upon its interference generating charac-teristics. The smallest motor aboard the aircraftcan be the worst offender.

AC GENERATORS AND MOTORS.—Theoutput of an ideal ac generator is a pure sinewave, A pure sine-wave voltage is incapableof producing interference except at its basicfrequency. However, a pure waveform is difficultto produce, particularly in a small ac generator.Nearly all types of ac generators used in navalaircraft are potential sources of interferenceat frequencies other than the output powerfrequency. Interference voltages come from thefollowing sources:

Harmonics of the power frequency.Normally, the harmonics are due to a poorwaveform.

Commutation interference. This conditionstarts in a series-wound motor.

Sliding-contact interference. Thiscondition starts in an alternator and in aseries-wound motor.

Normally, an ac motor without brushes doesnot create interference.

INVERTERS.— An inverter is a dc motorwith armature taps brought out to slip rings tosupply an ac voltage. The ac output contains someof the interference voltages generated at the dcend as well as the brush interference at the ac endof the inverter.

Switching Devices

A switching device makes abrupt changes inelectrical circuits. Such changes are accompaniedby transients capable of interfering with radio

operation and other types of electronic receivers.The simple manual switch (occasionally operated)is of little concern as a source of interference.Examples of switching devices (frequentlyoperated) capable of causing interference are therelay and the thyratron.

RELAYS.— A relay is an electromagneticremote-control switch. Its main purpose is toswitch high-current, high-voltage, or other criticalcircuits. The relay is used almost exclusively forcontrolling large amounts of power with relativelysmall amounts of power. Therefore, the relayis always a potential source of interference,especially so if the relay controls an inductivecircuit. Relay-starting circuits are also possibleinterference sources. Even though the actuatingcurrents are small, the inductances of theactuating coils are usually quite high. It is notunusual for the control circuit of a relay toproduce more interference than the controlledcircuit.

THYRATRONS.— A thyratron is a gas-filled,grid-controlled, electronic switching tube usedmainly in radar modulators. The current in athyratron is either on or off; there is noin-between. The time required to turn a thyratronON is only a few microseconds. Therefore, thecurrent waveform in a thyratron circuit always hasa sharp leading edge. As a result, the waveformis rich in radio interference energy. The voltageand peak power in a radar modulator are usuallyvery high. The waveforms are intentionally sharpand flat as possible. These factors are essentialfor proper radar operation, but they do increasethe production of interference energy.

Pulsed Electronic Equipment

Pulse interference is from pulsed electronicequipment. Types of systems that fall within thiscategory include radar, beacons, transponders,and coded-pulse equipment.

RADAR.— In radar equipment, rangeresolution depends largely on the sharpness of theleading and trailing edges of the pulse. The idealpulse is a perfect square wave. Target definitionalso depends on the narrowness of the pulse.Both the steepness and narrowness of a pulsedetermine the number and amplitudes ofharmonic frequencies. The better the shape of aradar pulse, the better the radar is working, andthe greater the interference it can produce. Most

of the interference is from frequencies other thanthose leaving the radar antenna, except in receiversoperating within the radar band.

Radar interference at frequencies below theantenna frequency severely affects all receivers inuse. Principal sources of such interference are themodulator, pulse cables, and transmitter.

CODED-PULSE EQUIPMENT, BEACONS,AND TRANSPONDERS.— This group includesIFF, beacons, tacan, teletype, and other coded-pulse equipment. The interference energyproduced by this group is the same as thatproduced by radar-pulsing circuits. The effects ofthis interference energy are smaller because theequipment is usually self-contained in one shieldedcase, and uses lower pulse power. However, theeffects also increase because the radiatingfrequencies are lower. This permits fundamentalfrequencies and harmonics to fall withinfrequency bands used by other equipment. Eachpiece of equipment is capable of producinginterference outside the aircraft where otherreceiver antennas may pick it up.

Propeller Systems

Propeller systems, whether hydraulic orelectric, are potent generators of radio inter-ference. The sources of interference includepropeller pitch control motors and solenoids,governors and associated relays, synchronizersand associated relays, deicing timers and relays,and inverters for system operation.

Propeller control equipment generates clicksand transients as often as 10 per second.The audio frequency envelope of commutatorinterference varies from about 20 to 1000 Hz. Thepropeller deicing timer generates intense impulsesat a maximum rate of about 4 impulses perminute.

Values of current in the propeller system arerelatively high. Therefore, the interferencevoltages generated are severe. They are capableof producing moderate interference at frequenciesbelow 100 kHz and at frequencies above 1 MHz.However, the interference voltages can causesevere interference at intermediate frequencies.

Receiver Oscillators

Either directly or through frequency multi-pliers or synthesizers, the local oscillator in asuperheterodyne receiver generates an RF signalat a given frequency. The local oscillator signal

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mixes with another RF signal to produce anintermediate frequency (IF) signal. Depending onreceiver design, the frequency of the localoscillator signal is either above or below thefrequency of the RF signal by a frequency equalto the IF.

The amount of interference leaving thereceiver through its antenna is roughly pro-portional to the ratio of the tuned input frequencyto the intermediate frequency. For any tuningband on the receiver, oscillator leakage is highestat the low end of the band. Also, the lower theintermediate frequency, the greater the leakagechance.

Although the receiver antenna is the principaloutlet of oscillator leakage, leakage can occurfrom other points. Any path capable ofintroducing interference into a receiver is alsocapable of carrying internally generatedinterference out of the receiver. The paths of entryare discussed more fully later in this chapter.

O s c i l l a t o r l e a k a g e f r o m a s i n g l ecommunications receiver in an aircraft is not likelyto be a direct source of interference. However,oscillator leakage is a direct source in very largeaircraft using two or more frequencies in the sameband simultaneously. However, high-orderharmonics of the oscillator frequency can becometroublesome in the VHF band and above.

Oscillator leakage from a swept-tuningreceiver can produce interference in any receiveraboard the aircraft. This is done directly (onharmonics) or by nonlinear mixing, as shown inthe following example:

Receiver A, operating at a frequency of2100 kHz, with an IF of 500 kHz, hasoscillator leakage at 2600 kHz (or 1600kHz).

Receiver B, operating at 150 MHz, withan IF of 10 MHz, has oscillator leakageat 160 MHz (or 140 MHz).

Receiver C, sweeping a frequency bandfrom 200 to 300 MHz, with an IF of 30MHz, has oscillator leakage across theband 170 to 270 MHz (or 230 to 330 MHz).

Each receiver can interfere with the otherreceivers at the oscillator frequency and itsharmonics. In addition, with the presence of anonlinear detector, the leakage signals from the

three receivers can be mixed and interfere withthe following frequencies:

Receiver A and B, after nonlinear mixing,can produce interference at 160 ±2.6 MHz.

Receivers A and C can similarly produceinterference at any frequency from 200±2.6 to 300 ±2.6 MHz; receivers B andC between 200 ±60 to 300 ±160 MHz.

Nonlinear Elements

A nonlinear element is a conductor, semi-conductor, or solid-state device whose resistanceor impedance varies with the voltage appliedacross it. Therefore, the resultant voltage is notproportional to the original applied voltage.Typical examples of nonlinear elements aremetallic oxides, certain nonconducting crystalstructures, semiconductor devices, and electrontubes. Nonlinear elements that could cause radiointerference in aircraft systems are overdrivensemiconductors and vacuum tubes, oxidized orcorroded joints, cold-solder joints, and unsoundwelds.

In the presence of a strong signal, a nonlinearelement acts like a detector or mixer. It pro-duces sum and difference frequencies and anyharmonics from the signal applied to it. Thesefalse frequencies are called external crossmodulation. These frequencies (sum, difference,and harmonics) can cause interference problemswhen the combined product of their field strengthsexceeds 1 millivolt.

A common example of this action is the entryof a strong off-frequency RF voltage into themixer stage of a superheterodyne receiver. By thetime the interfering signal has passed through thepreselector stages of the receiver, it has undergonedistortion by clipping. Therefore, the interferingsignal is essentially a rectangular wave that is richin harmonics. Frequency components of the wavebeat both above and below the local oscillatorfrequency and its harmonics. This producessignals at the output of the mixer that areacceptable to the IF amplifier.

Power Lines

Alternating current power sources arebroadband sources of receiver interference. Eventhough they are conducting a nearly sinusoidalwaveform, ac signals on power lines are capableof interfering with audio signals in receivers. In

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such cases, only the power-line frequency appears.However, where multiple sources of ac power arepresent, these signals are capable of mixing in thesame manner as receiver radiation. Sum anddifference frequencies appear.

In ac-powered equipment, ac hum can appearat the power frequency or at the rectificationripple frequency. The rectification ripplefrequency is twice the power frequency times thenumber of phases. Normally, aircraft systems useonly single- and three-phase sources at a nominal400 Hz. Full-wave rectification with single-phase,400-Hz power gives a ripple frequency of 800 Hz;a three-phase source yields 2400 Hz. This rippleproduces interference that varies from simpleannoyance to complete unreliability of equipment,depending on its severity and its coupling tosusceptible elements.

INTERFERENCE COUPLING

Learning Objective: Identify the varioustypes of electrical interference caused bycoupling, and recognize means used toreduce the interference.

Openings in the outer shields of equipment arenecessary for the entrance of power leads, controlleads, mechanical linkages, ventilation, andantenna leads. Interference entering theseopenings is amplified by various amounts,depending on the point of entry into theequipment’s circuits. Coupling between the entrypath and the sensitive points of the receiver canbe in any form.

Conductive Coupling

Interference often couples from its source toa receiver by metallic conduction. Normally, thisis done by way of mutual impedance, as shownin figure 6-34. In the figure, A is the power source,B the receiver, and C the interference source. The

Figure 6-34.-Path of conducted interference.

interference is maximum at the interference source(C) and decreases rapidly to a relatively low valueat battery (A) because of the very low impedanceof the battery. The size of the arrows indicate thatthe nearer the power tap of the receiver (B) is tothe interference source (C), the greater theamplitude of interfering current in the BC loop.

Inductive-Magnetic Coupling

Every current-carrying conductor is within amagnetic field whose intensity variations arefaithful reproductions of variations in the currentin the conductor. When another parallel con-ductor is cut by the lines of force of this field,the conductor has a current induced into it. Theamplitude of the induced current depends on thefollowing factors:

The strength of the current in the firstconductor

The nearness of the conductors to eachother

The angle between the conductors

The length through which the conductorsare exposed to each other

The amount of the variation in the current thatdirectly affects variation in the magnetic fieldsurrounding the conductor depends on the natureof the current. When the conductor is a powerlead to an electric motor, all the frequenciesand amplitudes associated with broadbandinterference are present in the magnetic field.When the lead is an ac power lead, a strongsinusoidal magnetic field is present. When the leadis carrying switched or pulsed currents, extremelycomplex broadband variations are present. Asthe magnetic field cuts across a neighboringconductor, a voltage replica of its variation isinduced into the neighboring wire. This causes acurrent to flow in the neighboring wire. When theneighboring wire leads to a sensitive point in asusceptible receiver, serious interference with thatreceiver’s operation can result. Similarly, a wirecarrying a steady pure dc current of high valuesets up a magnetic field. This field is capable ofaffecting the operation of equipment that uses theearth’s magnetic field.

Shielding a conductor against magneticinduction is both difficult and impractical.Nonferrous shielding materials have little or no

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effect upon a magnetic field. Magnetic shieldingthat is effective at low frequencies is too heavyand bulky.

In aircraft wiring, the effect of induction fieldsmust be reduced. This can be done by using theproper spacing and coupling angle between wires.The degree of magnetic coupling diminishesrapidly with distance. Interference coupling is leastwhen the space between active and passive leadsis at a maximum, and when the angle between theleads approaches a right angle.

Inductive-Capacitive Coupling

Capacitive (electric) fields are voltage fields.Their effects depend on the amount of capacitanceexisting between exposed portions of noisy circuitsand noise-free circuits. The power transfercapabilities are directly proportional to frequency.Thus, high-frequency components couple moreeasily to other circuits. Capacitive coupling isrelatively easy to shield out by placing a groundedconducting surface between the interfering sourceand the sensitive conductor.

Coupling by Radiation

Almost any wire in an aircraft system can, atsome particular frequency, act like an antennathrough a portion of its length. Inside an airframe,however, this occurs only at very high frequencies.At high frequencies, all internal leads normallyhave good shielding against pickup of moderatelevels of radiated energy. Perhaps the only casesof true inside-the-aircraft radiation at HF andbelow occur with unshielded or inadequatelyshielded transmitter antenna leads.

Complex Coupling

Complex coupling involves more than onetype of interference (conduction, induction, orradiation). When more than one coupling occurssimultaneously, we need corrective actions, suchas bonding, shielding, or filtering. Sometimes thecorrective action for one type of coupling canincrease the coupling capabilities of another typeof coupling. The result may be an increase inthe transfer of interference. For example, anunbended, unfiltered dc motor can transferinterference to a sensitive element by conduction,inductive coupling, capacitive coupling, and byradiation. Some frequencies are only transmittedby one form of coupling, and some frequenciesby others. At still other frequencies, all methods

of transmission are equally effective. On a motor,bonding almost always eliminates radiation fromthe motor shell. It also increases the intensity inone of the other methods of transmission, usuallyby conduction. The external placement of a low-pass filter or a capacitor usually reduces theintensity of conducted interference. At the sametime, it may increase the radiation and inductionfields. This occurs because the filter appears tointerference voltages to be a low-impedance pathacross the line. Relatively high interferencecurrents then flow in the loop formed between thesource and the filter. For complex couplingproblems, multiple solutions may be necessary toprevent the interference.

RADIO INTERFERENCE REDUCTIONCOMPONENTS

Learning Objective: Recognize variousmethods and components used to reduceradio interference caused by electricalnoise.

Radio interference reduction at the source mayinclude, to varying degrees, one or more of thefollowing methods—short circuiting, dissipation,open circuiting, or a combination of all three.

Using discrete components will normallyachieve interference reduction at the source. Theuse of capacitors, resistors, and inductors are toshort circuit, dissipate, and open circuit theinterference, respectively.

Capacitors

Short circuiting of interference is done byusing capacitors connected across the source. Theperfect capacitor looks like an open circuit to dcor the power frequency, and progressively as ashort circuit to ac as the frequency increases.

FUNCTION.— The function of a capacitor inradio interference filtering is to provide alow-impedance radio-frequency path across thesource. When the reactance of the capacitor islower than the impedance of the power lines tothe source, high-frequency voltages see thecapacitor as a shorter path to ground. Thecapacitor charges to the line voltage. It then tendsto absorb transient rises in the line voltage andto provide energy for canceling transient dropsin the line voltage.

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LIMITATIONS.— The efficiency of a perfectcapacitor in bypassing radio interference increasesin direct proportion to the frequency of theinterfering voltage. Its efficiency is also indirect proportion to the capacitance of thecapacitor. All capacitors have both inductanceand resistance. Any lead for connecting thecapacitor has inductance and resistance as a directfunction of lead length and an inverse functionof lead diameter. Some resistance is inherent inthe capacitor itself in the form of dielectricleakage. Some inductance is inherent in thecapacitor. Inherent inductance is usually pro-portional to the capacitance.

The effect of the inherent resistance in ahigh-grade capacitor is negligible as far as itsfiltering action ability. The inherent inductanceplus the lead inductance seriously affects thefrequency range over which the capacitor is useful.The bypass value of a capacitor with inductancein series varies with frequency.

At frequencies where inductive reactance ismuch less than capacitive reactance, the capacitorlooks very much like a pure capacitance. As thefrequency approaches a frequency at which theinductive reactance is equal to the capacitive react-ance, the net series reactance becomes smaller. Thiscontinues until reaching its resonant frequency, apoint of zero impedance. At this point, maximumbypass action occurs. At frequencies above the

resonant frequency, the inductive reactancebecomes greater than the capacitive reactance. Thecapacitor then exhibits a net inductive reactancewhose value increases with frequency. At frequenciesmuch higher than the resonant frequency, thevalue of the capacitor as a bypass becomes lost.

The size of the capacitor and the length of theleads control the frequency at which the reversalof reactance occurs. For instance, the installationof a very large capacitor frequently requires theuse of long leads. As an example of the influenceof lead length upon the bypass value of acapacitor, the following data is presented for atypical 4-microfarad capacitor whose inherentinductance is 0.0129 henrys.

Lead Length Crossover Frequency

1 inch 0.47 MHz

2 inches 0.41 MHz

3 inches 0.34 MHz

4 inches 0.30 MHz

6 inches 0.25 MHz

You can see that for the 4-µF capacitor, eachadditional inch of lead causes the capacitance-inductance crossover point to decrease.

By looking at figure 6-35, you can see thecapacitance-to-inductance crossover frequencies

Figure 6-35.-Crossover frequency of a 0.05-microfarad capacitor with various lead lengths.

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for various lead lengths of a 0.05 µF capacitor.Notice the difference in the crossover frequenciesfor the 3-inch lead of the 4-microfarad capacitorand the 3-inch lead of the 0.05-µF capacitor infigure 6-35.

COAXIAL FEEDTHROUGH CAPACI-TORS.— Coaxial feedthrough capacitors areavailable with capacitances from 0.00005 to about2µF. These capacitors work well up to frequenciesseveral times those at which capacitors with leadsbecome useless.

The curves shown in figure 6-36 compare thebypass value of a feedthrough capacitor of 0.05µF with that of a theoretically perfect capacitorof the same capacitance. The feedthroughcapacitor differs from the capacitor with leads.The feedthrough capacitor forms a part of boththe filtered circuit and the shield used to isolatethe filtered source. Lead length has been reducedto zero. The center conductor of the feedthrough

capacitor must carry all the current of the filteredsource, and it must have an adequate currentrating to prevent dc loss or power frequencyinsertion loss. Figure 6-37 shows the internalconstructions of feedthrough and conventionalcapacitors. Notice the differences in the two types.

SELECTION OF CAPACITORS.— Theselection of capacitors for filtering circuits inaircraft depends on characteristics such as physicalsize, high temperature and humidity tolerances,and physical ruggedness. The capacitors shouldhave at least twice the voltage rating of the circuitto be filtered. When installing capacitors useminimum lead length.

APPLICATION OF CAPACITIVE FIL-TERS.— Bypass every circuit carrying anunintentionally varying voltage or current capableof causing radio interference to ground by usingsuitable capacitors. When variations cause

Figure 6-36.-Crossover frequency of a 0.05-microfarad feedthrough capacitor.

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Figure 6-40.-Capacitive filtering of a servomotor.

Figure 6-37.-Internal construction of feedthrough andconventional capacitors.

Figure 6-38.-Capacitive filtering of a reversible dc seriesmotor.

interference at both high and low frequencies,chose and install a capacitor that provides anadequate insertion loss at the lowest interferedfrequency. The overall capacitance required at lowfrequency may provide inadequate insertion lossat high frequencies. Therefore, you may need tobridge the capacitor in the shortest and most directmanner possible by a second capacitor.

Install a capacitive filter as near as possibleto the actual source of interference. Hold leadlength to an absolute minimum for two reasons.First, the lead to the capacitor carries interferencethat must not radiate. Second, the lead hasinductance that tends to lower the maximumfrequency for which the capacitor is an effectivebypass.

When possible, a filter capacitor should beinstalled to make use of any element of the filteredcircuit that provides a better filtering action.Figures 6-38, 6-39, and 6-40 show the proper useof filter capacitors.

CAPACITIVE FILTERING IN AN ACCIRCUIT.— Radio interference from slip ring acmotors and generators is transient noise causedby sliding contacts plus high-frequency energyfrom other internal sources. For this reason,

Figure 6-39.-Capacitive filtering of a three-phase attenuator.

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filtering should attempt to reduce HF and VHFnoise components. This requires the use of low-capacitance, high-grade capacitors. Whereverpossible use feedthrough capacitors. Capacitancesshould be chosen low enough in value to representa high impedance at the power frequency and toavoid resonance with the internal inductances ofthe filtered unit. Voltage ratings should be at leasttwice the peak voltage across the capacitors.

In a four-wire electrical system, the neutrallead carries all three phases. A large quantity ofthe third harmonic of the power frequency ispresent. This frequency must be considered insetting capacitance limits and in filtering the returnlead. Normal values of capacitance for filtering400-Hz leads vary from 0.05 to 0.1 µF.

CAPACITIVE FILTERING OF SWITCHINGDEVICES.— Normally, a capacitor should not beused by itself as a filter on a switch in a dc system.In the open position, the capacitor bridging theswitch assumes a charge equal to the line voltage.When the switch closes, the capacitor dischargesat such a rapid rate that it generates a transient.The transient interference value exceeds thatcaused by the opening of the unfiltered circuit.The capacitor across a switch should have enoughseries resistance to provide a slow discharge whenthe switch shorts the capacitor.

Resistive-Capacitive Filters

A resistive-capacitive (RC) filter is an effectivearc and transient absorber. The RC filter reducesinterference in two ways—by changing thewaveform of transients and by dissipatingtransient energy. Figure 6-41 shows how an RCfilter is connected across a switch.

Without the RC filter, the voltage appearingacross the switch at the instant the switch opensis equal to the line voltage plus an inductivevoltage of the same polarity. The amplitude of

Figure 6-41.-An RC filter connected across a switch.

the inductive surge depends upon the inductanceof the line and the amplitude of the closed-circuitcurrent.

When the sum of the voltages appearing acrossthe switch is large enough, arcing occurs. Whenthe capacitance is large enough, the capacitorabsorbs enough transient energy to reduce thevoltage below arcing value. During the chargingtime of the capacitor, the resistor is passingcurrent and dissipating some of the transientenergy.

For maximum absorption of the circuitopening transients, resistance should be small andcapacitance should be large. Good representativevalues are R = 1/5 load resistance and C = 0.25 µF.

Figure 6-42 shows two RC filters used toabsorb the transient interference resulting fromthe opening of a relay field. In circuit A, the valueof should provide a low resistance path toground less than the line impedance and highenough to lower the Q sufficiently. The capacitorshould be at least 0.25 µF, with a voltage ratingseveral times the line voltage. Circuit B has theadvantage of reducing the capacitor and coil leadsto absolute minimum and reducing the relay fieldcurrent. It also has the disadvantage of carryingthe dc coil current. Normal values of eachresistance in circuit B is 5 percent of the dcresistance of the coil. The capacitor is normally0.25 µF. Circuit B serves as both a damping loadand a high-loss transmission line.

Inductive-Capacitive Filters

Filtering radio interference is done through aninductor inserted in series with the ac powersource. The inductor offers little impedance to theac or power-line frequency and an increasing highimpedance to transient interference as frequencyincreases. Combinations of inductance andcapacitance are widely used to reduce bothbroadband and narrow-band interference.

Filters used to reduce radio interferencetransmissions are available in the Navy supplysystem. The filters come in a large variety of typesand sizes. Filters are classified as to theirfrequency characteristics—low-pass, high-pass,bandpass, and band-reject filters. Also, you candistinguish filter classes by their applications, suchas power-line, antenna, and audio filters. The typemost often used in aircraft is the low-pass, power-line filter.

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Figure 6-42.-Methods for using RC filters in relay circuits.

LOW-PASS FILTERS.— A low-pass filter inan aircraft filters power leads coming from inter-ference sources. The filter prevents the transmissionof interference voltages into the wiring harness.It also blocks transmission or reception of radio-frequency energy above a specified frequency.

The ideal low-pass filter has no insertion lossat frequencies below its cutoff frequency, but hasan infinite insertion loss at all higher frequencies.Practical filters fall short of the ideal in threeways. First, a filter of acceptable physical size andweight has some insertion loss, even under dcconditions. Second, because of the lack of a pureinductor, the change from low to high impedanceis gradual instead of abrupt. Third, the impedanceis held to a finite value for the same reason.Figure 6-43 compares the insertion loss of a typical

Figure 6-43.-Insertion-loss curve of a commercial low-passpower-line filter.

low-pass filter with that of the hypothetical idealfilter.

Figure 6-44 shows the arrangement and typicalparameters of a low-pass filter having a designcut off frequency of 100 kHz. Inductor L mustcarry load current. It must be wound of wire largeenough that its dc insertion loss is negligible.Therefore, maximum current is one parameter forrating filters. The capacitors C1 and C2 mustwithstand the line voltage. Therefore, maximumvoltage is another parameter for rating filters.

At frequencies immediately below cutoff, thefilter looks capacitive to both the generator andthe load. Inductive reactance has very littleinfluence, and no filtering action takes place.However, at frequencies above cutoff, the seriesreactance of coil L becomes increasingly higher.The series reactance of coil L is limited only bythe resistance of the coil and its distributedcapacitance. Coil L then functions as a high-frequency disconnect. The bypass values of bothC1 and C2 become increasingly higher, and arelimited only by the inductance of the capacitors

Figure 6-44-Low-pass filter circuit.

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and their leads. As a result of these two actions,high-frequency isolation between points A and Boccurs.

HIGH-PASS FILTERS.— In most radiotransmitters operating at high frequencies (HF)and above, the master oscillator generates a signalat a submultiple of the output frequency. The useof one or more frequency multipliers raises thebasic oscillator frequency to the desired outputfrequency. At the input to the antenna, anoverdriven output amplifier may output theoutput frequency and harmonics of the outputfrequency. A high-pass filter is very effectivein preventing the undesired harmonics fromradiating or reaching the antenna.

High-pass filters are also useful for isolatinga high-frequency receiver from the influence ofenergy of signals of lower frequencies. Figure 6-45shows the use of a typical high-pass filter to reduceradio-noise interference. In symmetrical high-passfilter sections (Zin = Zout), the series combinationof Cl and L should resonate at 2 times the desiredcutoff frequency. The L/C ratio that is chosenshould have a square root equal to the terminalimpedance.

BANDPASS FILTERS.— Bandpass filtersprovide a very high impedance above and belowa desired band of frequencies. They also providea very low impedance to frequencies within thatband. Bandpass filters find their greatestapplication in (1) decoupling the receiver fromshock and overload by transmitters operatingabove and below the receiver pass band, and (2)multiplexing or decoupling two or more receiversor transmitters using the same antenna.

A bandpass filter can have many forms andconfigurations, depending on its application. Forfiltering antennas, a bandpass filter normally

Figure 6-45.-Schematic diagram of a high-pass filter.

consists of one or more high-pass filter sectionsfollowed by one or more low-pass filter sections.The section configuration is normally selected sothe upper limit of the pass band approaches orexceeds twice the frequency of the lower limit ofthe pass band. Figure 6-46 shows typical arrange-ments for bandpass filters.

BAND-REJECTION FILTERS.— A band-rejection (band-stop) filter rejects or blocks a bandof frequencies from passing. This filter allows allfrequencies above and below this band to passwith little or no attenuation.

The band-stop filter circuit consists ofinductive and capacitive networks combined andconnected to form a definite frequency responsecharacteristic. The band-stop filter’s designattenuates a specific frequency band and permitsthe passage of all frequencies not within a specificband. The frequency range over which attenuationor poor transmission of signals occurs is theattenuation band. The frequency range over whichthe passage of signals readily occurs is thebandpass. The lowest frequency at which theattenuation of a signal starts to increase rapidlyis the lower cutoff frequency (f1). The highestfrequency at which the attenuation of a signalstarts to increase rapidly is the upper cutofffrequency (f2) . The basic configurationarrangement or assembly of the band-reject filterelements are the L- or half-section, the T-section,

Figure 6-46.-Examples of bandpass filter circuits.

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and the Pi-section configurations. (See figure6-47.) For a more in-depth discussion on thevarious filters discussed in this chapter, youshould refer to Installation Practices for Electricaland Electronic Wiring, NAVSHIPS 0967-000-0120,section 4.

Figure 6-47.-Examples of band-reject filter circuits.

Q24.

Q25.

Q26.

Q27.

Q28.

Q29.

Q30.

Q31.

Q32.

Q33.

Q34.

Name the two types of electrical noiseinterference that enter aircraft receivers.

Of the three types of natural interference,which is caused by radiation of stars?

Why are rotating electrical machines amajor source of receiver interference?

Does the size of an electric dc motordetermine its interference capability?

Name the types of equipment that can causepulse interference.

Describe rectification ripple frequency.

In aircraft wiring, the effect of inductionfields is reduced by using proper spacingand coupling angle between wires. When isinterference coupling at its least?

What methods may be used to reduce radiointerference at the source?

Capacitors and capacitive filter circuitsmake good filters for reducing and elimi-nating noise. What characteristics are usedin selecting capacitors for filtering circuitsin aircraft?

How does an RC filter reduce interference?

How can you distinguish filter classes?

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CHAPTER 7

AVIONIC DRAWINGS, SCHEMATICS,HANDTOOLS, AND MATERIALS

The theory of operation of avionic equipmentis a small part of the knowledge you need tosuccessfully perform maintenance on theseequipments. You need to know how to use avionicdrawings, schematics, handtools, and material.

As an AT, you use many publications toproperly maintain a weapons system. Theweapons systems in modern-day aircraft areso complex that maintenance is difficult orimpossible without the use of technical publi-cations. Just the list of the electronics equipmentinstalled in modern-day aircraft is quite long. Itis impossible for you to be thoroughly familiarwith all the various types of electronics equipmentpresently in use. However, with a good generalbackground of electronic principles and circuittheory and a little study, you can become familiarwith any specific system or test equipment.

The material presented in this chapter includesgeneral and specific types of publications anddrawings, illustrations, diagrams, charts, andtables. It also includes identification of handtoolsand materials common to the Aviation ElectronicsTechnician.

DRAWINGS AND SCHEMATICS

Learning Objective: Recognize types ofand uses for various avionics-relatedsymbols, diagrams, illustrations, charts,and tables.

Nearly all technical manuals make extensiveuse of drawings and diagrams. As an AT, you willuse these drawings and diagrams in nearly everyphase of your work. You will use them in thelocation and identification of units and com-ponents, troubleshooting, signal and/or circuittracing, installation, calibration and adjustment,testing, operation, and evaluation. You will alsouse these figures when you study the operatingprinciples of circuits and equipments.

No one particular type of illustration issuitable for all applications; therefore, manydifferent types exist. Several different types ofillustrations are discussed in the followingparagraphs. Each type has its own advantages anddisadvantages.

NOTE: Blueprint Reading and Sketching,NAVEDTRA 14040, provides many de-tails on the construction of illustrationsand drawings. You should review thatmanual before continuing the study ofthis chapter. The Navy Electricity andElectronics Training Series (NEETS),module 4, contains additional informationon drawings and schematics.

ILLUSTRATIONS

Illustrations present the idea of a text visually;therefore, they are used in many forms. A fewof these are the photograph, line drawing, shadedsketch, blueprint, etc. However, you will learnabout some of the more common illustrations,such as pictorial, cutaway view, location anddimension, and assembly drawings in this chapter.

Pictorial

Pictorial illustrations normally show physicalappearance. They may present details on location,size, construction, physical relationships of sizeand location, or parts arrangement. Pictorialillustrations appear throughout all types ofmanuals, and you can use them to locate andidentify systems, equipments, components, orparts. You will use them to install, inspect, service,operate, adjust, calibrate, troubleshoot, andrepair equipment.

A pictorial illustration may be an accurate,detailed representation or a generalized indication,depending on its purpose. They may bephotographs, halftone or shaded sketches, or linedrawings.

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Cutaway View

A cutaway view is an illustration used to showsome detail of construction that would beextremely difficult or impossible to show byconventional pictorial views. It is often usedin connection with discussions of physicalconstruction and the operation of mechanicaldevices. You will frequently find them in assemblydiagrams and in construction details.

Location and Dimension

Location diagrams show physical positionrelationships, and they may or may not besufficiently detailed to show physical appearance.They are primarily used for familiarization, andare commonly found in flight manuals or NavalAir Training and Operating Procedures Standard-ization (NATOPS) manuals. Location diagramsare also contained in the general information andservicing section of maintenance instructionmanuals (MIMs), illustrated parts breakdown(IPB) manuals (fig. 7-1), and in the operation andmaintenance instruction manuals for equipments.

Dimension diagrams show physical size anddistance. They are useful in planning the layoutof bench stations, making equipment installations,or packing materials for reshipment. They arefrequently used in the general information sectionsof technical manuals and in those sectionscovering equipment familiarization, installation,and shipment. They are also found in change-typetechnical directives.

Sometimes, location and/or dimensiondiagrams are combined with other types ofillustrations, giving additional details withoutincreasing the number of illustrations.

Assembly Diagrams

Assembly diagrams, as the name implies,provide details of construction that you use toassemble parts into a unit. They are also used toexplain the operating procedures of mechanicalor electromechanical devices.

BLOCK DIAGRAMS

Block diagrams present a generalized explana-tion of overall functional operation. They do not

show physical shape, size, or location. They rangefrom the very simple to very complex, dependingon the type of equipment, the quantity and qualityof details, and the purpose of the information.Nearly all manuals that deal with basic or detailedoperational theory contain block diagrams. Themore complex the equipment, the more probablethe need for block diagrams.

Manuals for many electromechanical devices,as well as electrical or mechanical systems, containblock diagram descriptions. By using this type ofdiagram, you can increase your understanding offunctional relationships and operations.

Symbols

Since block diagrams provide a generalanalysis of functional operation, symbolsrepresent individual circuits or functionalcomponents. To use block diagrams success-fully, you must recognize the symbols andunderstand their meanings and limitations.Appendix II of this manual contains many of thecommon symbols found on block diagrams. Asyou read this chapter, you should refer to thisappendix.

Signal Flow Diagram

One special type of block diagram is the signalflow diagram or signal flow chart. It is usuallyassociated with overall operation of complicatedsystems, such as fire control computers, ASWsystems, aircraft control or power distributionsystems, or search or navigation radar systems.The signal flow diagram includes all featuresnormally associated with block diagrams. Inaddition, it includes considerable detail on signalpaths, signal wave shapes, timing sequences, andrelationships and magnitudes of potentials,signals, and frequencies.

WIRING DIAGRAMS

The wiring diagram presents detailed circuitryinformation on electrical and electronics systems.A master wiring diagram is a single diagram thatshows all the wiring in a complete system or inan aircraft. Usually, this diagram is too large touse. It is normally broken down into logicalfunctional sections, each of which maybe further

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Figure 7-1.-IPB sample figure, radar control panal installation and stick assembly.

7-3

subdivided into circuit diagrams. When a diagramof a system is broken down into individual circuitdiagrams, each circuit is presented in greaterdetail. The increased detail lets you trace, test, andmaintain circuits more easily.

Wiring diagrams fall into two basic classes—chassis wiring and interconnecting diagrams. Eachclass has specific purposes and many variationsin appearance (depending on application).Wiring diagrams are not normally used indiscussions of the operational theory of specificcircuits.

Figure 7-2.-Wiring

View A of figure 7-2 is an example of one typeof chassis wiring diagram commonly used. Thisdrawing shows the physical layout of the unit, andall component parts and interconnecting tiepoints. Each part has a reference designationnumber, thus enabling use of the IPB to determinevalues and other data. The values of resistors,capacitors, or other components are normally noton wiring diagrams. However, the polarity ofsemiconductor diodes and the polarized capacitorare on wiring diagrams. Also, the lead numbersforfor

the transistor (Q101) in figure 7-2 areconvenience. Since this specific diagram

diagrams. (A) Chassis wiring; (B) interconnection wiring; (C) sealed component parts layout;board connections.

(D) terminal

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shows physical layout and dimensional detailsfor mounting holes, it could also functionas an assembly drawing and an installationdrawing.

View B of figure 7-2 shows the reverse sideof the same mounting board. It also shows thewiring interconnections to other components.However, it does not show actual positioningof circuit components, and wire bundles arerepresented by single lines, with the separate wiresentering at an angle.(The angle indicates thedirection to follow in tracing the circuit to locatethe other end of the wire.)

The wire identification coding on this diagramconsists of a three-part designation. See figure 7-2,view B, (3-T101-3). The first part (3) is a number

Figure 7-3.-Example of wire identification coding usingcircuit function letter coding.

representing the color code of the wire accordingto military specification. (Many other chassiswiring diagrams designate color coding byabbreviations of the actual colors.) The second(T101) is the reference part designation numberof the item to which the wire is connected. Thelast (3) is the designation of the specific terminalto which the wire connects.

View C of figure 7-2, while not a wiringdiagram, illustrates a method commonly used toshow some functional aspect of sealed or specialcomponents. View D of figure 7-2 shows severalmethods used to indicate connections at terminalstrips.

Normally, wiring diagrams are the majorcontent of the last volume of a MIM set, and thelast section of most other maintenance manuals.This volume, or section, contains wiring diagramsfor all electrical and electronic systems of theaircraft. The diagrams are prepared separately foreach circuit and provide all data necessary for thefollowing:

To understand the construction of eachcircuit

To trace each circuit within the system tomake continuity and resistance checks

To perform specific troubleshootingon inoperative or malfunctioning cir-cuits

Aircraft Wire Identification Coding

To make maintenance easier, all aircraft wiringthat appears on the wiring diagrams are exactlyas marked in the aircraft. Identification of eachwire is coded by a combination of letters andnumbers imprinted on the wire at prescribedintervals along its entire run. Look at figure 7-3as you read this section, which explains the codesused in aircraft wiring installation.

The unit number (shown in dashed outline) isonly when there is more than one given unitinstalled in an identical manner in the sameaircraft. The wiring concerned with the first suchunit is labeled prefix 1. Corresponding wires forthe second unit have exactly the same designation,except they carry prefix 2.

7-5

The circuit function letter identifies the basicfunction of the unit. Look at table 7-1. Note thatcircuit function R, S, and T wiring may bear asecond letter to designate the functionalbreakdown of the circuit.

On new aircraft, the equipment identificationcode replaces the circuit function letters R, S, T,and Y. The equipment identification code is thepart of the AN nomenclature following thediagonal (/), excluding the hyphen (-) and suffixletters. For example, wires of an AN/APS-115(V)unit will have an equipment identification codeof APS115. Those of an AN/ARC-52A unit willuse ARC52 (fig. 7-4), and those of an AN/MX-94unit use MX94 as there equipment identificationcodes.

Each wire within a given circuit function grouphas a separate wire number. Wires that havesegments of splices, plug and receptacle con-nectors, terminal strip tie points, etc., have a lettersegment designation. Passage through a switch,relay, circuit breaker, etc., requires assignmentof a new number.

Wire size numbers identify the size of the wireor cable, but are not on coaxial cables. Wire sizenumbers are replaced by a dash and codeddesignator when part of a thermocouple arrange-ment.

A suffix is added to designate the phase (orground) in three-phase ac power wiring. Athermocouple has a suffix that denotes the metalelement involved.

For further information on aircraft wiringcodes, you should refer to Installation Practices,Aircraft Electric and Electronic Wiring, NAVAIR01-1A-505.

Cable Construction

Cable construction diagrams present detailsabout the fabrication and construction of cables.These details usually include designation of thetype connectors or terminals, identification ofwires for each terminal, and method of connectingwire to terminal. The details also include pottingrequirements, length of wires, lacing or sleevingspecifications, and any other specifications orspecial considerations.

Cable Routing

Diagrams of major systems usually includean isometric shadow outline of the aircraft,showing the approximate location of equip-ment components and the physical routing of

Table 7-1.-Wiring Circuit Function Code

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Figure 7-4.-Example of wire identification coding (circuit function letters R, S, T, and Y) using equipment identification coding.

interconnecting cables. A cable, regardless of thenumber of conductors, is represented by a singleline on an isometric wiring diagram. No attemptis made to show individual connections atequipment units or in connection boxes. Anisometric drawing shows, at a glance, a pictureof the layout of the entire system.

SCHEMATIC DIAGRAMS

The major purpose of the schematic diagramis to show the electrical operation of a particularsystem. The system schematic is not drawn toscale, and the diagram shows none of the actualconstruction details of the system unless theconstruction details are essential to understandingcircuit operation.

Schematic diagrams differ from blockdiagrams because they present more detail abouteach circuit. While the block diagram deals withfunctional units of the system, the schematicdiagram shows each part that contributes to thefunctional operation of the circuit.

Simplified Schematic

In large or complex equipments, a completeschematic diagram may be too large for practicaluse. For this reason, most technical manualspresent partial or simplified schematics forindividual circuits or units.

Simplified schematic diagrams normally leaveout parts and connections that are not essentialto understanding circuit operation. In studyingor troubleshooting equipment, you will frequentlymake and use simplified drawings. In these

cases, you should include only those items thatcontribute to the purpose of the drawing, and youneed to be careful to include all such items.Many techniques for simplifying schematics arepresented in this TRAMAN, and you will see themas you read the course. Pay special attention tothose techniques maintenance personnel finduseful. They are important tools in your work.

Electromechanical Drawings

Electromechanical devices such as synchros,gyros, accelerometers, autotune systems, andanalog computing elements are quite common inavionics systems. Neither an electrical drawing nora mechanical drawing is adequate for a completeunderstanding of these units. You might beconfused if you only use these two drawings.Therefore, you need to use a drawing thatcombines the two—using some aspects of eachtype. Electromechanical drawings are usuallysimplified both electrically and mechanically, andusually show only those items essential to theoperation.

CHARTS AND TABLES

Charts and tables present factual data in aclear, concise form. Many types of charts andtables are used in all types of technicalpublications. In this discussion, a chart containsinformation in lists, pictures, tables, or diagrams.A table is one type of chart that presents or listsinformation in a very condensed form.

Tables are valuable when presenting the samegeneral type of information about many items.

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The list of details for the items maybe in columns. Q2.The columns are arranged so that by reading acrossthem, you find details about a specific item, whilereading down presents a comparison of items about Q3.

a specific detail. One very common and useful tableof this type is found in the IPB (fig. 7-5). For moredetail about using information in publications and Q4.IPBs, you should refer to Aviation MaintenanceRating Fundamentals, NAVEDTRA 14022.

Q5.

Q1. In what publication can you find moreinformation about illustrations, drawings, Q6.and schematics?

Describe some uses for dimensiondiagrams.

What type of diagram presents detailedcircuitry information on electrical andelectronic systems?

List the two basic classes of wiringdiagrams.

In what publication can you find more infor-mation on aircraft wire identification codes?

Describe the major purpose of a schematicdiagram.

Figure 7-5.-IPB sample.

7-8

HANDTOOLS

Learning Objective: Identify commonhandtools used in avionics maintenance,including their proper operation and care.

Tools are a costly investment. Therefore, youneed to take care of them and use then correctly.There is something about a good tool that helpsthe technician turn out good work. This fact morethan justifies the slightly higher cost of qualitytools. Even more important, low quality toolsbecome defective sooner, and can result ininjury to the user or damage to the equipment.In the same manner, by properly using qualitymaterials, the quality of any maintenance taskis improved and chances of new failures arereduced.

In this TRAMAN, the term handtools refersto small, portable or fixed-power tools, as wellas those normally classified as nonpoweredhandtools. Handtools are tools commonly avail-able in electronics maintenance shops or used byelectronics maintenance personnel during work onaircraft.

SAFETY, USE, AND CAREOF HANDTOOLS

Carelessness is the greatest menace in anyshop. It comes from the technician; the machinealone cannot inflict injury. Lack of care causesmost of the accidents in electrical and electronicsshops today. Remember, all moving machineryis potentially dangerous! Do not lean against anymachine that is in motion, or that may be startedin motion by anyone else. Treat a machine withrespect and there is no need to fear it. Do not starta machine until you know how it operates andunderstand the safety precautions you are tofollow.

Information about accident prevention iscontained in chapter 9 of this TRAMAN. Youshould refer to it frequently. Other sources ofinformation on the use and care of handtools canbe found in Airman, NAVEDTRA 14014, andTools and Their Uses, NAVEDTRA 14256.Since these manuals are basic to all aviationratings, the material they cover is not containedhere. If you have not done so, you shouldreview this material before proceeding with thismanual.

The safe use of tools cannot be over-emphasized. The following two safety precautionsare basic to most situations when using tools:

1.

2.

Use the proper tool for its designedfunction, and use it in the proper manner.Maintain all tools in proper working orderand in a safe condition. Sharpen or replacedull cutting tools. Replace broken ordefective tools. Protect tools from damagewhile in use or storage.

When you use tools and/or materials, arrangethem so you can reach them easily, and so theywon’t interfere with your work. This arrangementincreases efficiency as well as safety.

You should inventory tools before starting ajob. After completing a job, you should clean andinspect the tools. Next, inventory the tools again.Finally, return the tools to their proper storageplace. If any tool is missing, you must report itimmediately to maintenance control. Refer toOPAVINST 4790.2 (series) and your localprocedures for specific procedures and guidance.

GENERAL TOOL PROCEDURES

The basic manuals provide a lot of informa-tion about commonly used general tools. In thissection, you will read about procedures youshould or should not follow.

You should never use a center punch onextremely hard metals, or use it to remove boltsby force. If you do, you will dull the point. Neveruse a pin punch as a starting punch; a hard blowmay cause the slim shank to break. Always usethe largest starting and pin punch that will fit thehole. When using punches, do not strike aglancing blow because the punch may break, andbroken pin punches are difficult to remove.

Do not hammer on a screwdriver. If anobstruction is in the slot, apply a driving forcewith the heel of the hand or remove theobstruction with a file. Never use a screwdriveras a pry bar, lever, or chisel. Do not use pliersor wrenches on a screwdriver to increase torque.

When using a grinding wheel, make sure thatthe guard is in place. If you must use the wheelwith the guard removed, stand to one side to avoidflying particles of emery or metal. Use safetygoggles when using a grinding wheel to grindscrewdriver blades or any metal object. Use the

7-9

rest stand when possible, but ensure that the restis close to the grinding wheel.

WARNING

NEVER use the grinding wheel onnonferrous metals. When used with thistype of material, the grinding wheel could,in effect, explode. This could result inserious injury to or death of personnel.

When drilling, you should never use your handto hold the work being drilled. Use a vise or aclamp. The same idea applies when you aresoldering, filing, or sawing.

You should always use the right type ofscrewdriver. If you use a Reed and Princescrewdriver on Phillips head screws (or vice versa),you may ruin the tool. Also, using the wrongscrewdriver may round out the screwhead, makingit difficult to remove the screw. Do not use thescrewdrivers interchangeably. In general, Reedand Prince screws are used for airframe structuralapplications, while Phillips screws are usually usedin component assemblies.

Figure 7-6 shows the difference between thetwo screwdrivers. The Phillips screwdriver hasflukes that are about 30 degrees with a blunt end.However, the Reed and Prince has 45-degreeflukes and a sharper, pointed end. The Phillipsscrew has beveled walls between the slots, while

Figure 7-6.-Matching cross-slot screws and drivers.

In addition, the Phillips screw is not as deep asthe Reed and Prince.

Use the following methods to identify the rightscrewdriver for the job.

If the screwdriver stands up unassisted whenthe point is put in the head of a verticalscrew, it is probably the proper one.

The outline of the end of a Reed andPrince screwdriver is approximately a rightangle, as seen in figure 7-6.

The best way is to know the descriptionsthe Reed and Prince has straight, pointed walls. of both types.

7-10


A1. Blueprint Reading and Sketching, NA VEDTRA 14040, and NEETS module 4.

A2. Dimension diagrams are useful in layout of bench stations, making equipment installations, or packing materials and equipment for reshipment.

A3. A wiring diagram.

A4. Chassis wiring and interconnecting diagrams.

A5. Installation Practices, Aircraft Electric and Electronic Wiring NAVAIR 01-IA-505.

A6. The major purpose of a schematic diagram is to show the electrical operation of a particular system.

Remember, if you use the right tool, you will become magnetized and transfer this magneticsave time and avoid trouble. condition.

Q7. What training manuals contain informationAlso, use nonmagnetic tools in tuning RF

on handtools, their use, and care?circuits, which are susceptible to frequencychanges resulting from the introduction of newmagnetic fields (or the distortion of the existingmagnetic fields). Many RF circuits are slug tuned

SPECIAL TOOLS

Learning Objective: Identify specializedtools used by AT personnel to includeproper use and purpose.

The manufacturers of aircraft, engines, andrelated equipment furnish a wide variety of specialtools. These tools are listed in special allowancelists. Their use is explained in the maintenance orservice instructions manuals covering the specificaircraft, engine, or item of equipment for whichthey were designed. Other tools are peculiarto the maintenance of electronic equipment.Although the following discussion is not complete,it represents some of the special tools mostcommonly used in aircraft electronics mainte-nance work.

NONMAGNETIC TOOLS

Tools made of nonmagnetic materials areavailable through normal supply channels. Theyare primarily used when performing specificmaintenance functions on certain classes ofequipment or components. These tools areexpensive tools. They are normally made ofberyllium-copper or plastic, and they are not asrugged as steel tools, and are more easilydamaged. If you use them for their intendedpurpose, you will prolong their useful life andincrease their usefulness. In addition to possibledamage of the tool itself, improper use of thesetools could allow them to transfer foreign particlesto locations where they could cause problems. Ineither case, the results could be of considerableinconvenience to you. Some of the general usesof nonmagnetic tools are described in thefollowing paragraphs.

Always use nonmagnetic tools near magne-trons and other components containing perma-nent magnets. Magnetic tools may attract withenough force to cause damage to the magnet orinjury to the technician. The tool could also

to avoid this potential trouble.

A good general maintenance practice to followis to wipe the tools before and after use. This isespecially true for nonmagnetic tools. Use alint-free cloth, dampened with a suitable cleaningsolvent for this purpose.

INSULATED TOOLS

Safety considerations require you to useinsulated tools whenever the danger of electricalshock or short circuit exists. Many types ofinsulated tools are available directly throughsupply channels. You should obtain these toolsand use them whenever available. However, manytypes of insulated tools are not readily available(or are available only at considerable addedexpense). If essential, procure these tools ormodify conventional tools. Insulated sleeving maybe put on the handles of pliers and wrenches andon the shanks of screwdrivers. Use tools modifiedin this manner for low-voltage circuits onlybecause of the limitations of the insulatingmaterials. For use on higher voltages, specialinsulating handles are available for many of thecommon types of tools.

At times, you will need to use tools that aremade of insulating material, rather than justhaving an insulating handle. In these instances,you should requisition the tools through normalsupply channels.

TORQUE WRENCHES

Sometimes, for engineering reasons, a specifictorque must be applied to a nut or bolt head. Insuch cases, you must use a torque wrench. Thetorque wrench is a precision tool, consisting ofa torque-indicating unit and an appropriateadapter or attachments. It measures the amountof turning or twisting force you are applying toa nut, bolt, or screw.

7-11

The three most commonly used torquewrenches are the deflecting-beam, dial-indicating,and micrometer-setting types (fig. 7-7). Whenusing deflecting-beam and dial-indicating torquewrenches, you read the torque visually froma dial or scale mounted on the handle of thewrench.

The most accurate and reliable torque wrenchis the micrometer-setting type. The next mostaccurate and reliable is the dial-indicating type.The least accurate and reliable is the deflecting-beam type. You should not use the deflecting-beam type (because of the high probabilityof operator error) unless it is absolutelynecessary.

To use the micrometer-setting torque wrench,unlock the grip and adjust the handle to thedesired setting on the micrometer-type scale, andthen relock the grip. Install the required socketor adapter to the square drive of the handle. Placethe wrench assembly on the nut or bolt and pullin a clockwise direction with a smooth, steadymotion. (A fast or jerky motion results in animproperly torqued unit. ) When the appliedtorque reaches the torque value indicated on the

handle setting, the handle automatically releasesor “breaks” and moves freely for a short distance.The release and free travel is easy to feel, sothere is no doubt when the torquing process iscomplete.

To make sure the correct amount of torqueis gotten on fasteners, all torque handlesrequire periodic testing under the metrologyprogram.

You should take the following precautionswhen using torque wrenches.

Always ensure proper calibration.

Do not use the torque wrench as ahammer.

When using the micrometer-setting type,do not move the setting handle below thelowest torque setting. However, youshould place it at its lowest setting beforereturning it to storage.

Do not use the torque wrench to applygreater amounts of torque than its ratedcapacity.

Figure 7-7.-Torque wrenches.

ANSWER FOR REVIEW QUESTION Q7.

A7. TRAMAN, NAVEDTRA 12000, and Tools and Their Uses,NAVEDTRA 14256.

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• Do not use the torque wrench to break loose bolts.

• Never store a torque wrench in a toolbox or in an area that may cause damage to it.

• Do not drop the wrench because it will affectits accuracy.

RELAY TOOLS

You may damage or ruin relay tools if you usesandpaper or emery cloth to clean the contactpoints. Use of abrasives as a cleaner causes thecent acts to bend. Trying to straighten them withlong-nose pliers causes further damage, eventuallyrequiring replacement of the relays. You can avoidthe whole problem by using a burnishing tool toclean dirty contact points. Figure 7-8, view A,shows the use of a burnishing tool on a relay.Burnishing tools are available through normalsupply channels. Before using this tool, you shouldclean it thoroughly with alcohol; do not touch thetool surface with your fingers before use.Burnishing burned and pitted contacts will notrepair them. You must replace burned and pittedcontacts.

Another tool useful in relay maintenance is apoint bender (fig. 7-8, view B). It can help tostraighten bent relay contacts. You can make thistool locally using a 0.12-inch diameter rod stock,shaping it as shown in figure 7-8.

WIRE AND CABLE TOOLS

An innovation in electrical connectors is thetaper pin electrical connector for aircraft. Thetaper pin works on the principle of driving a taperwedge into a tapered hole, and depends on frictionto keep the pin in the hole. The taper pinconnector makes a very good electrical andmechanical connection because of the high metal-to- metal contact pressure developed during thedriving action of the insertion tool. Taper pins letyou make circuit changes quickly and easilywithout using a soldering iron. Tests show thatvibration and corrosion over time can improve theelectrical continuity and increase the mechanicalpulling force required to remove a taper pin.Another advantage of taper pins is theaccessibility of test points for voltage and circuitcontinuity checks.

Figure 7-8.-View A, burnishing tool; view B, pointbender.

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You use a special tool (fig. 7-9) to properlyinsert the taper pin into a terminal block socket.Internally, the insertion tool has a calibrateddriving spring, a calibrated pull test spring, anda taper pin captive key.

The driving spring adjusts to apply the properdriving impact to the pin. The pull test springadjusts to apply the correct pull force on thepin to check for proper pin insertion. Thecaptive key ensures that each taper pin has a100-percent pull test before removing the toolfrom the pin. You need to rotate the removal leverto remove the taper pin from the terminal blocksocket,

It is important that you properly insert thetaper pin into the terminal block sockets. By doingthis, you maintain the reliability of the system.Pushing the pins into the sockets with your fingersor pliers will not make them stay. You must drivethem in with the insertion tool. The tool must becalibrated for you to apply the proper pressure.When inserting the taper pins, hold the insertiontool at right angles to the terminal block. Then,push it straight toward the terminal block, withouttwisting the tool. (The pins are very sensitive totwists, which could cause a faulty connection ora broken pin.) By installing the pin correctly, youcan install and remove a taper pin as many as 25times before you must replace it. If you properlyinstall the taper pin, it will pass the pull test ofthe insertion tool. Always replace bent or brokenpins.

Three different sizes of taper pins are used toterminate wires from size 16 through size 22. Thesizes are identified by color coding-the insulating

sleeves. A crimping tool is used to attach thetaper pin to the wire. The taper pin crimpingtool is similar to other wire terminal crimpingtools.

DIAGONAL PLIERS

Diagonal pliers are described briefly in Toolsand Their Uses, NAVEDTRA 14256. The fol-lowing discussion describes a modification todiagonal pliers when they are used to maintainequipment aboard aircraft.

The diagonal pliers (fig. 7-10, view A) havebeen modified by adding potting compound to thejaws. This prevents loss of small pieces of wireinto the equipment when you are cutting wire. Thepotting compound also lets you cut the wirewithout holding onto the piece being cut away.(Figure 7-10, view B, shows the diagonals beforemodification.) If you do not have a pair of thesemodified diagonal pliers, make your own byadding potting compound. Before applying thepotting compound, clean the diagonals withsolvent; then secure the handles with a rubberband (fig. 7-10, view C), and apply the compound.Let the compound dry for 24 hours. You canseperate the jaws by slicing them apart with asingle-edged razor blade.

SAFETY WIRING PLIERS

When you install equipment in aircraft, it isnecessary to lockwire (usually referred to as safetywire) certain parts of the installation. You canlockwire parts faster and more neatly by usingspecial pliers. Use these pliers with extreme care.

Figure 7-9.-Taper pin insertion and removal tool.

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Figure 7-10.-Diagonal pliers. View A, compound; View B, without compound; View C, apply compound.

The wire must be installed snugly, but not so tightthat any part of the wire is overstressed. Theappropriate MIM normally prescribes the properrouting of the twisted wire for the particularinstallation.

Safety wiring pliers (wire twister) (fig. 7-11)are three-way pliers that hold, twist, and cut. Theyreduce the time used in twisting safety wire on nutsand bolts. To use them, grip the wire between thetwo diagonal jaws, and the thumb will bring thelocking sleeve into place. A pull on the knob twirlsthe twister, making uniform twists in the wire.You may push the spiral rod back into the twisterwithout unlocking it, which lets you pull on the

knob again and gives a tighter twist to the wire.Squeezing the handle unlocks the twister, and thewire can be cut to the desired length with the sidecutter. You should occasionally lubricate thespiral of the twister.

WIRE AND CABLE STRIPPERS

Nearly all wire and cable used as electricalconductors have some type of insulation cover.To make electrical connections with the wire, youmust remove a part of this insulation, leaving theend of the wire bare. You should use a wire andcable stripping tool similar to the one shown infigure 7-12 when stripping electrical cable.

Figure 7-11.-Safety wiring pliers.

Figure 7-12.-Wire and cable stripper.

7-15

Although several variations of this basic toolare available, the most efficient and effective typeis shown in figure 7-12. Its operation is extremelysimple: You insert the end of the wire in theproper direction to the depth you need stripped.Position the wire so it rests in the proper groovefor that size wire and squeeze. The tool functionsin three steps as follows:

1. The cable gripping jaws close, clamping theinsulated wire firmly in place. You must insert thewire so the jaws clamp the main section of thewire rather than the end to be stripped.

2. The insulation cutting jaws close, cutting theinsulation. If the wire is not inserted in a groove,the conductor will also be cut. If the wire is posi-tioned onto too small a groove, you may cut someof the strands. If the groove is too large, theinsulation will not be completely cut. Inserted intothe correct groove, the insulation will be cut neatlyand completely, and the wire will not be damaged.

3. The two sets of jaws separate, removing theclipped insulation from the end of the wire.

CRIMPING TOOLS

The two types of crimping tools described inthis section are the MS 25037-1 and the MS3191-3.

Type MS 25037-1

The standard tool issued for crimping less terminals is MS 25037-1. It is used withstandard insulated copper terminal lugs manu-factured according to MS 25036. The standardtool uses a double jaw to hold the terminal lugor splice. One side of the jaw applies crimpingaction to fasten the terminal to the bare wire wheninserting the terminal, as shown in figure 7-13,view A. When using the tool correctly, a deepcrimp is made in the B area of terminal lugs andsplices (fig. 7-13, view C). This also makes ashallow crimp to the portion of the terminal orsplice that extends over the insulation of the wire(fig. 7-13. view C, area A). This clamping actioncomes from a recessed portion in the other sideof the divided jaw. A guard, which should be inthe position shown when crimping terminals,helps to properly position the terminal. However,the guard must be moved out of the way whenusing the tool for crimping splices.

The MS 25037-1 tool should be checkedoccasionally. A No. 36 (0.106) drill rod should notbe able to enter the smaller (red or blue) nest whenthe tool is fully closed. If it does enter, have thetool repaired.

Figure 7-13.-Crimping tool MS 25037-1.

7-16

Instruction in the proper crimping procedureshould be given to all who need to make solderlessterminal connections. Installation Practices, AircraftElectric and Electronic Wiring, NAVAIR 01-1A-505,contains detailed procedures for using manysolderless connector tools.

Type MS 3191-3

MS 3191-3 is the latest standard crimping tooldesigned specifically for use with MS 3191 contactsfor electrical connectors. It features interchangeableheads that fit various size terminals. You may use itwith the turret (fig. 7-14, view A) for normal use orwithout the turret (fig. 7-14, view B) for eyeballcrimping (when material alignment does not allowuse of the turret).

Before you use the tool, you must select thecorrect position on the positioner head and also onthe indentor gap selector plate. To release the turret

for indexing, press the trigger and the spring-loadedturret snaps out to its indexing position. Select thedesired position from the color-coded nameplate, androtate the turret to align the selected positioner withthe index. Depress the turret until flush, and itautomatically locks into place. To prevent furtherindexing, insert the lockwire through the hole in thetrigger.

To crimp a terminal, select the proper size andtype terminal. Insert the prepared wire into thecontact pocket until the wire seats on the bottom. Thewire should be visible through the inspection hole,and the insulation should enter the contact insulationsupport. Then, insert the contact and wire into theterminal crimping tool, making sure that the contactseats properly in the positioner. Close the crimpingtool handles to crimp the contact and wire. At thecompletion of the stroke, the ratchet releases, andyou can open the handles and remove the crimpedcontact from the tool.

Figure 7-14.-Crimping tool MS 3191-3.

7-17

Inspect the crimped terminal and wire. Thewire must be visible through the inspection hole.The insulation must be inside the insulationsupport. The crimping indents must be positionedbetween the inspection hole and the front of theinsulation support. The contact must not bend.The crimped contact is now ready to be installedinto a connector.

For eyeball crimping, remove the headassembly from the tool. Select the proper wire sizeand move the thumb button until the pointeraligns with the selected wire size on the indentorgap selector plate. Holding the contact in thecrimping tool, slowly close the handles. At thesame time, position the contact so the indentersare positioned midway on the contact barrel.Insert the wire, making sure it bottoms in thecontact, and then close the handles fully. Afterreleasing the handles, remove and inspect thecrimped contact. The contact must not befractured, and the conductor must be visible inthe inspection hole.

SOLDERING GUNS, IRONS, AND TIPS

The soldering tools for aviation maintenanceactivities come in many sizes and models. Theymay be of the gun type or of the common irontype. Soldering irons come in a wide range ofwattage ratings and may operate on 28 volts dcor 115 volts ac.

The soldering iron most commonly used inavionics maintenance is the pencil soldering iron(fig. 7-15). You should use this tool and its specialtips when the applied heat must remain low. Theseoperations include all cases involving transistors,printed circuit repair, miniaturized components,and so forth.

Because of its rapid heating and cooling, thesoldering gun has gained great popularity in recentyears. It is especially useful when maintaining andtroubleshooting work where only a small partof your time is spent actually soldering. Acontinuously hot iron oxidizes rapidly and isdifficult to keep clean.

A transformer in the gun supplies about 1 voltat high current to a loop of copper that serves asthe tip. It heats to soldering temperature in 3 to5 seconds, and it will heat to as high as 1,000°Fif left on longer than 30 seconds. Because itoperates for short periods, very little oxidationoccurs. Thus, it is one of the easiest soldering toolsto keep well tinned. (Tinned refers to the tin alloyprotective coating on soldering tips.) However,this tip is pure copper with no plating, so pittingoccurs easily. Offsetting this disadvantage,however, is the low cost of replacement tips. Youshould NEVER use a soldering gun when workingon solid-state equipment. Serious damage todiodes, transistors, and other solid-state com-ponents can result from the strong electromagneticfield surrounding the tip of the soldering gun.

To get the best results from a soldering gunor iron, keep the tip free of oxide and scale. Mosttechnicians wipe the tip on a cloth, and then fileand retin as necessary.

A faster way to clean the tip is the dampsponge method. Keep a dampened cellulosesponge in a container, such as a soap dish or metalashtray. (The sponge is more effective than thecloth in keeping the tip clean, and it presents nosafety problems.) The damp sponge preventssplattering that sometimes occurs when wiping theheated tips off in the usual way. It will also absorbparticles that can injure your face. The sponge

Figure 7-15.-Pencil iron with special tips.

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eliminates oxide and scale, which keeps filing andretinning to a minimum.

A time-controlled resistance soldering set(fig. 7-16) is especially useful for soldering cablesof-AN plugs and similar connectors, even thesmallest types. The set consists of a transformerthat supplies 3 or 6 volts at high current tostainless steel or carbon tips. The transformer isturned ON by a foot switch and OFF by anelectronic timer. You can adjust the timer for aslong as 3 seconds of soldering time.

When in use, adjust the double-tip probes ofthe soldering unit to straddle the connector cupto be soldered. One pulse of current heats it fortinning and, after inserting the wire, a secondpulse of current completes the job. Since thesoldering tips are hot only during the brief periodof actual soldering, your chances of burning thewire insulation and melting connector inserts areless.

MECHANICAL FINGERS

You use mechanical fingers to reach andretrieve small articles that fall into places you can’treach. This tool can be used to start nuts or boltsin difficult areas. Mechanical fingers (fig. 7-17)have a tube containing flat springs that extendfrom the end of the tube to form clawlike fingers,much like the screw holder of a screwdriver. Thesprings are attached to a rod that extends fromthe outer end of the tube. A plate is attached tothe end of the tube, and a similar plate is attachedto the end of the rod. A coil spring placed

Figure 7-16.-Resistance soldering unit.

Figure 7-17.-Mechanical fingers.

around the rod between the two plates holdsthem apart and retracts the fingers into thetube.

When you grasp the bottom plate betweenyour fingers, and you apply enough thumbpressure to the top plate to compress the spring,the tool fingers will extend from the tube in agrasping position. See figure 7-17, view A. Whenyou release the thumb pressure, the tool fingersretract into the tube as far as the object they holdwill allow. There is enough pressure on the objectto hold it securely. Some mechanical fingers havea flexible end on the tube to let you use them inclose quarters or around obstructions.

NOTE: You should not use mechanicalfingers as a substitute for wrenches orpliers. The fingers are made of thin sheetmetal and are easily damaged by over-loading.

7-19

STEEL SCALE

The steel scale (fig. 7-18) is a measuring devicemost technicians keep in their toolbox. It has grad-uated divisions of one-eighth and one-sixteenthinch on one side and one thirty-second and onesixty-fourth inch on the other side. The steel scalemost commonly used is 12 inches long. You shouldtake measurements with the steel scale by holdingit on its edge on the surface of the object you wantto measure. This will prevent you from makingerrors that might be caused by the thickness of thescale. Such thickness causes the graduations to bea slight distance away from the surface of theobject. Read measurements at the graduation thatcoincides with the distance you are measuring.

FLASHLIGHT

Your toolbox should contain a standard Navyvaporproof two-cell flashlight. You will use itduring all phases of maintenance. Installed in bothends of the flashlight are rubber seals that keepout all vapors. You should inspect the flashlightperiodically for the installation of these seals, thespare bulb, and the blue lens. (The spare bulb,lenses, and filters should be available in the end cap.)

NOTE: Do not throw away any filters; youmay need them for night operations.

INSPECTION MIRROR

There are several types of inspection mirrorsused in aircraft maintenance. The mirror comes

Figure 7-18.-Steel scale.

Figure 7-19.-Typical inspection mirror.

in a variety of sizes and may be round orrectangular. The mirror connects to the end ofa rod and may be rigid or adjustable (fig. 7-19).

The inspection mirror helps you make detailedinspections where you cannot directly see theinspection area. By angling the mirror, and usinga flashlight, it is possible to inspect most areas.

CANNON PLUG PLIERS

Figure 7-20 shows a set of special pliers youshould use to remove electrical connectors whenthey are on so tight that you cannot remove themby hand. These pliers, when properly used,will prevent damaging or destroying electricalconnectors.

FIBER OPTICS

Special tools for fiber optic equipment andcable repair include optical time-domain reflec-tometers, optical multimeter, optical ohmeters,optical power meters, radiometer/photometer, andautomatic test equipment. Furthur informationis available in NEETS, module 21, NAVEDTRA14193, and Installation Practices, Aircraft Electricand Electronic Wiring, NA 01-1A-505.

Q8.

Q9.

You should use nonmagnetic tools whentuning RF circuits susceptible to frequencychanges. How do some RF circuits avoidthis potential frequency change problem?

List the three common types of torquewrenches in order of their accuracy andreliability from most to least.

Figure 7-20.-Cannon plug pliers.

7-20

Q10.

Q11.

Q12.

Q13.

What special tool will hold, twist, and cut?

Describe the MS 3191-3 crimping tool.

What is the most common soldering ironused in avionics maintenance?

Where can you find the special tools forfiber optic repair?

AIRCRAFT HARDWARE ANDCONSUMABLE MATERIALS

Learning Objective: Identify aircrafthardware and consumable materials, andrecognize their use in the maintenance ofintegral aircraft parts and substitution ofparts.

As a technician, you should have knowledgeof certain items of hardware and consumablematerial. Hardware and material are used forinstalling equipment and repairing installedequipment. You should always use the properparts and material. The applicable MIMs specifyitems of hardware and material necessary foraircraft maintenance. If you find you must makesubstitutions, make sure that the substituted itemis satisfactory.

MOUNTING PARTS

The same mounting parts that were removedfrom an installation should not always be usedwhen you reinstall equipment. Before reinstalling

the same items, inspect them to make sure thatthey are the specified parts and that they are notdefective or damaged. You must also determineif instructions forbid their reuse. If not forbidden,then, and only then, reinstall the removed parts.

Information on the use of mounting parts,such as screws. nuts. bolts, and washers, is of ageneral nature. You should follow establisheddoctrine for their use. A valuable source ofdetailed information is Aircraft StructuralHardware for Aircraft Repair, NAVAIR 01-1A-8.

TURNLOCK FASTENERS

Turnlock fasteners secure inspection plates,doors, and other removable panels on aircraft.Turnlock fasteners are also referred to by suchterms as quick-opening, quick-action, and stresspanel fasteners. The most desirable feature ofthese fasteners is that they let you quickly andeasily remove access panels for inspection andservicing purposes.

Turnlock fasteners are manufactured andsupplied by a number of manufacturers undervarious trade names. Some of the more commonlyused fasteners are the Camloc stress panel fastenerand the Airloc fastener. For a discussion of otherturnlock fasteners, you should refer to Airman,NAVEDTRA 14014.

Camloc Stress Panel Fasteners

The Camloc stress panel fastener (fig. 7-21)is a high-strength, quick-release, rotary-type

Figure 7-21.-Camloc stress panel fasteners.

7-21

fastener. You may find them on flat or curvedinside or outside panels. The fastener may haveeither a flush or a nonflush stud. The studs areheld in the panel with flat or cone-shaped washers,the latter being used with flush fasteners indimpled holes.

You can tell this fastener from screws by thedeep No. 2 Phillips recess in the stud head andby the bushing in which the stud is installed. Athreaded insert in the receptacle provides anadjustable locking device. As you insert the studand turn it counterclockwise one-half turn ormore, it screws out the insert enough to permitthe stud key to engage the insert cam when youturn it clockwise. Rotating the stud clockwiseone-fourth turn engages the insert, and continuedrotation screws the insert in, tightening thefastener. Turning the stud one-fourth turncounterclockwise will then release the stud, butit will not screw the insert out far enough to permitreengagement in installation. It is necessary toturn the stud at least one-half turn counter-clockwise to reset the insert.

To unlock the stress panel fastener and resetit in the same operation, you should use aNo. 2 Phillips screwdriver to turn the studcounterclockwise one-half turn or more. Do notturn the stud past the stop.

CAUTION

Do not use a power screwdriver on this

To lock the stress panel fastener, you shoulduse a No. 2 Phillips screwdriver. Push the studin, and turn clockwise until you feel increasedtorque; then continue turning until the fasteneris tight.

When installing a large panel, it may benecessary to engage all the fasteners beforetightening them. This is done by pushing each studin and turning it clockwise one-fourth turn. Thestud should engage the receptacle, but it shouldremain loose. If the stud does not engage, it willpop out, indicating that the insert must be resetby turning the stud counterclockwise one-half turnor more.

Airloc Fastener

The Airloc fastener consists of a stud, a studcross pin, and a receptacle (fig. 7-22). The studis attached to the access cover and is held in placeby the cross pin. The receptacle is riveted to theaccess cover frame. A quarter turn of thestud (clockwise) locks the fastener in place.Turning the stud counterclockwise unlocks thefastener.

THREADED FASTENERS

fastener. text.

For a discussion of threaded fasteners, referto Airman, NAVEDTRA 14014. However, a briefdiscussion of Torq-set screws is included in this

7-22

Figure 7-22.-Airloc fastener.

Torq-Set Screws

Torq-set machine screws (offset cross-slotdrive) have begun to appear in new equipment. Theirmain advantage is that you can apply more torque toits head while tightening or loosening. You can applymore torque than any other screw of comparable sizeand material without damaging the head of thescrew. Torq-set machine screws are similar inappearance to the more familiar Phillips machinescrews. Look at figure 7-23. Here, you can see thedifference between the Phillips machine screw andthe Torq-set machine screw. Using a Phillipsscrewdriver could easily damage a Torq-setscrewhead, making it difficult, if not impossible, toremove the screw, even if the proper tool is laterused.

Figure 7-23.-Comparison of Phillips and Torq-set screwheads.

7-23

Torque Information

You should use torque tables, such as shownin table 7-2, as a guide in tightening nuts, bolts,and screws whenever specific torque values are notcalled out in maintenance procedures. Using theproper torque allows the structure to develop itsdesigned strength and greatly reduces the chanceof failure due to fatigue.

Threads must be free from grease or oil.Lubrication changes the torque value and resultsin overtorquing.

When using castellated nuts, you shouldtighten them to the lower torque limit; thencontinue tightening until the cotter pin hole alignswith slots in the nut. Do not back off the nut toalign the hole.

When you need to tighten from the bolt head,use the high side of the torque range. If necessary,the maximum allowable tightening torque may beused.

When using corrosion-resistant steel bolts,lubricate them with an antiseize compound.

Table 7-2.-Torque Values in Inch-Pounds

7-24

Corrosion-resistant steel bolts and nuts must beused together. Use shear nut torque values whentightening these bolts.

CONNECTORS

In the discussion that follows, the wordconnector is used in a general sense. It appliesequally well to connectors designated by ANnumbers and those designated by MS numbers.

Electrical connectors are designed to providea detachable means of coupling between majorcomponents of electrical and electronic equip-ment. These connectors can withstand the extremeoperating conditions imposed by airborne service.They must make and hold electrical contactwithout excessive voltage drop despite extremevibration, rapid shifts in temperature, and greatchanges in altitude.

These connectors vary widely in design andapplication. Each connector consists of a plugassembly and a receptacle assembly. The twoassemblies connect by a coupling nut, and eachconsists of an aluminum shell containing aninsulating insert that holds the current-carryingcontacts. The plug usually attaches to a cable endand is the part of the connector on which thecoupling nut mounts. The receptacle is the halfof the connector to which the plug is connected,and is usually mounted on a part of the equip-ment.

There are wide variations in shell type, design,size, layout of contacts, and style of insert. Figure7-24 shows six types of connector shells.

The shells of MS connectors come in eighttypes, each for a particular kind of application.A letter designation in the MS number will indicatethe shell design, as in MS 3106E, where E is theshell indicator. The shell indicators are as follows:

A Solid shell

B Split shell

C Pressurized

D Sealed construction

E Environment resistant

F Vibration resistant

H Flame barrier shell

K Fireproof construction

Solid-shell connectors are used where nospecial requirements, such as fireproofing ormoistureproofing, must be met. The rear shellsare made from a single piece of aluminum.

Split-shell connectors allow maximumaccessibility to soldered connections. The rearshell has two halves, either of which you may

Figure 7-24.-Connector shells.

7-25

Figure 7-25.-Exploded view of a split-shell connector.

Figure 7-26.-Exploded view of a 90-degree angle connector.

7-26

remove. Figure 7-25 shows an exploded view ofone type of split-shell connector.

Pressurized connectors provide a pressure-tight feed-through for wires that pass throughwalls or bulkheads of pressurized compartmentsin high-altitude aircraft. The contacts are usuallymolded into the insulator, and the shell is spunover the assembly to seal the bond.

Sealed connectors are used in equipment thatis sealed and operated under gas pressure. Theseconnectors include a glass-to-metal seal and haveeither special rubber inserts or a cementingcompound applied to the insert.

Vibration-resistant connectors are used inequipment that is subject to intense vibrations ininstallations on or near reciprocating engines.

Fireproof connectors are made under specifi-cations that require the connector to maintaineffective electrical service for a limited time evenwhen exposed to fire. The inserts are made of aceramic material, and special crimp-type contactsare used.

Moisture-resistant connectors consist of acombination of the features of the solid-shell, thepressurized, and the vibration-resistant types.Figure 7-26 shows the component parts of thiskind of connector.

Each connector has an identification symbolcalled the MS part number. This symbol indicatesthe shell type, the shell design, the size, the inserttype, the insert style, and the insert position. Anexample is the designator MS 3100-A-16-11 PX.

The letters MS form the prefix. The number3100 indicates the shell type and identifies theconnector as one of the types shown in figure 7-24,

The letter A indicates a solid-shell connector.The number 16 is the shell size.

The number 11 is a designation of the insertpin arrangement used in the connector. A chartshowing various pin arrangements is available inInstallation Practices, Aircraft Electric andElectronic Wiring, NA 01-1A-505.

The letter P means the insert is a pin, or male,insert. (The letter S indicates it is a socket, orfemale, insert.)

The concluding letter, X, is a designation ofthe insert position. Connectors specially designedfor a particular application sometimes havenonstandard contact, or insert, positions. Fourpositions of the inserts are employed, and theseare lettered W, X, Y, and Z. Each letter refersto an angle by which the insert is rotated fromthe standard position. When the standard positionis employed, there is no letter at the end of theMS designation.

Figure 7-27 shows three common types ofsubminiature connectors. Since these connectorsare the wire-connected type, they have no flangesfor mounting. However, the receptacle shown inview C can be mounted with nuts and lockwashers. They are used on miniature instruments,switches, transformers, amplifiers, and relays.

The subminiature connectors described andshown in figure 7-27 have not proven sufficientlysatisfactory and are not being used in new aircraftdesigns. Their use is limited to those aircraft inwhich they were initially installed.

The miniature connectors (MS 311X and 313Xseries) are intended to supersede these sub-miniature connectors. The miniature connectorsdiffer from the types just described in theirmethod of coupling and contact sizes. They willhave two types of quick-disconnect couplings—axial and bayonet.

A reduction in size of contacts, from 0.062-to 0.040-inch diameter, allows a greater numberof contacts per unit area, The miniature con-nectors with smaller contacts rated at 7.5 ampereshave found increased use in aircraft ac power,where the majority of the circuits are lowpower and low current. All these connectorsare environment-resisting class E. Hermetic

Figure 7-27.-Subminiature connectors.

7-27

Figure 7-28.-Several typical coaxial connectors.

7-28

receptacles and connectors suitable for potting arealso provided in this series.

Figure 7-28 shows how coaxial connectors aredivided into series. Each series consists of plugs,panel jacks, receptacles, and straight and right-angle adapters.

Series UHF connectors are low-cost, general-purpose connectors of nonconstant impedance.The small and large coaxial types are for usewith small and medium size coaxial cables inapplications where line imbalance or increasedstanding wave ratio is not important. Whereimpedance matching is necessary, you should useC, N, or BNC series connectors. Both small andlarge series UHF connectors can be weather-proofed for outdoor use, but most are non-weatherproof.

Series N connectors are the most popularconstant impedance connectors for medium sizecoaxial cables. They can be used up throughmicrowave frequencies with minimum lineimbalance or increase in standing-wave ratio.Although series N 50-ohm and 70-ohm connectorsdo not mate, 70-ohm cables may be used with50-ohm series N connectors where impedancematching is not critical. Series N connectors arecompletely weatherproof.

Series C connectors are similar to 50-ohmseries N connectors. They are used with the samecables, are weatherproof, and are for frequenciesup through microwave. Series C connectors aremechanically and electrically superior to seriesN connectors. Series C connectors feature quick-connect and quick-disconnect bayonet-lockcouplings and an improved cable-clampingmechanism for better cable grip with minimum

cable indentation. These connectors are intendedfor use up to 1,500 volts,

Series BNC connectors (fig. 7-29) are com-monly used on small coaxial cables. Theyincorporate quick-connect and quick-disconnectbayonet-lock couplings and are weatherproof.Besides regular and modified low-voltage typesof nonconstant impedance, improved series BNCconnectors are available that have a constant50-ohm impedance and yield excellent electricalperformance up to 10,000 megahertz.

Series HN connectors are weatherproof, high-voltage connectors of constant impedance for usewith 50-ohm RF cables.

Series LC connectors are high-voltage (5 ,000volts peak), 50-ohm, weatherproof connectorsdesigned for applications involving the trans-mission of large amounts of RF power.

Series BN connectors are small, lightweightconnectors (of nonconstant impedance) designedfor use with the same coaxial cables that use BNCconnectors. BN connectors are not recommendedfor applications at frequencies over 200 megahertzunless electrical requirements of the circuit are notcritical. You may use them at peak voltages upto 250 volts.

Series LT connectors are very similar inappearance to series LC; however, series LTconnectors differ not only in cable accom-modation but also in weight—they are lighter thanseries LC connectors. Series LT connectors arelarge, 50-ohm, 5,000-volt connectors for use withRG-117/U cable.

Series TNC connectors are basically identicalwith series BNC connectors. The major differenceis that TNC connectors have a threaded type ofcoupling instead of the bayonet-lock coupling.

Figure 7-29.-Exploded view of a standard BNC connector.

7-29

E

Consequently, TNC connectors are usuallypreferred in applications that are subject toextreme vibration.

Series TPS connectors are weatherproofand designed to produce minimum electricaldiscontinuities in small size 50-ohm coaxial cableup to a frequency of 10,000 megahertz. Theconnectors are rated at 1,500 volts RMS at sealevel. Their use is governed by the temperaturelimitations of their associated cables.

Series SM connectors are nonweatherprooffittings for coaxial cables of one-fourth-inchoverall diameter and smaller. You may use themwhere electrical matching is not a concern. TheSM connectors are smaller and contain fewer partsthan the BNC series. The SM series uses a femalecenter-conductor contact on plugs and a malecenter-conductor contact on jacks and receptacles.However, for consistency in cataloging and usage,a plug is still regarded as having a male matingend and a receptacle or jack as female. The SMseries is not meant to replace the BNC seriesexcept for internal equipment connections whereweatherproofing is not a concern.

The pulse connectors are designed for high-voltage pulse or dc applications. They are nearlyall weatherproof and available in three types—rubber insert, ceramic insert, and triaxial. Therubber-insert pulse connectors have a peak voltagerating of 5,000 volts at an altitude of 50,000 feet.They are designed principally for use with cableshaving an insulated neoprene layer under thebraid, such as RG-77/U and RG-78/U.

You may use pulse connectors with cableshaving a conducting rubber under the braids(such as RG-25/U, RG-26/U, and RG-64/U).However, you must take special care in assemblingthe connectors. The ceramic-insert pulse con-nectors are available in small (type A) and large(type B) sizes. Type A connectors are designed foruse with the 8,000-volt RG-25/U and RG-26/Ucables, and type B with the 15,000-volt RG-27/Uand RG-28/U cables. (Use special care whenassembling connectors. ) Pulse connectors tend toleak noise that may interfere with communicationsequipment. Triaxial connectors are for trans-mission line applications where requirementsdictate maximum RF shielding and minimumnoise radiation. They are commercially availablein sizes of the same diameter as the BNC seriesand C series (and possibly others). Some militaryequipment use these connectors and some within-series adapters are commercially available.

SKL connectors were originally designed toprovide a connection to a klystron tube. However,

newer klystrons are coming with BNC connectors.Various design modifications now providegeneral-purpose cable-to-cable connectors andadapters.

Miniature connectors have a gold finish, havescrew-type coupling, and contain a high-voltagedielectric. They have a nominal impedance of 50ohms, a sea-level breakdown voltage of 1,500volts RMS, a practical frequency limit of 10,000megahertz, and will operate up to 200°C.

WIRE

Although printed circuits and microelectroniccomponents are widlely used in today’s electronicequipment, wire is still important as a signalor current-carrying device. Since most navalequipment is of conventional construction, andcomplete conversion to the new forms of con-ducting components has not occurred, traditionalwire conductors are used and will continue to beused for some time to come. This means that whenwire is requisitioned, either for installation orrepair, you should select it carefully. The threemajor factors involved in this selection, indescending order of importance, are—

1. size,2. insulation, and3. the characteristics required to satisfy

specific environments in which the wiremust function.

COAXIAL CABLES

Flexible coaxial cables (sometimes called RDcables) are a special type of cable used for carryingvideo and RF signals, cathode-ray tube sweepcurrents and voltages, trigger range marks,blanking pulses, and other signals for radarreceivers, transmitters, and indicators. Thesecables are constructed with special considerationsfor shielding, impedance, capacitance, andattenuation. All of these factors are important inmany circuits. Coaxial cables have neitherinduction nor radiation losses. These lines havelow attenuation even at very high frequencies, andare used as high as 3,000 MHz.

The name coaxial is derived from theconstruction. The inner and outer conductorshave a common axis or coaxis. These cablesconsist of an inner conductor, a dielectricinsulator, an outer conductor, and an outercovering. The inner conductor is usually made ofcopper—plain, tinned, or silver coated. The

7-30

dielectric insulation is usually polyethylene,although other materials are used. The outerconductor is made of a single or double braid ofplain, tinned, or silver-coated copper. The outerconductor is covered by a protective jacket. Thisjacket serves both to weatherproof the outerconductor and to protect it from mechanicalabuse.

Flexible coaxial cables are classified in fourgroups—general purpose, high temperature,pulse, and special characteristics. The general-purpose cables consist of various sizes of cablesas just described. The high-temperature cable isbasically the same but usually has a dielectric andouter covering designed to withstand increasedtemperatures. Pulse cables have the ability towithstand high voltages because of conductorspacing and the type of dielectric used in theirconstruction. The special characteristics cables aremade of various materials and sizes of innerconductor, outer conductor, dielectic, and outercovering. By varying these parts, the capacitance,impedance, shielding, attenuation, voltage rating,and ability to withstand weather and abuse arevaried to fit the required qualities.

With the exception of the special charac-teristics type, coaxial cables have an impedanceof 50 to 75 ohms. The impedance of the specialcharacteristics type is often much higher; forexample, the RG-65A/U, which has an approxi-mate impedance of 950 ohms and is used as a highimpedance video cable. When replacing a coaxialcable, you should use the correct replacement,otherwise most of the advantages of coaxial cablesare lost.

At frequencies near 3,000 MHz, flexiblecoaxial cables have appreciable losses. At thesefrequencies, rigid coaxial cables are used with airas the dielectric. The inner conductor is supportedby ceramic or polystyrene beads.

FIBER OPTIC CABLES

You can repair fiber optic cables using thespecial tools for fiber optic cable repair and theprocedures in Installation Practices, AircraftElectric and Electronic Wiring, NA 01-1A-505.

SUBSTITUTION OF PARTS

If the specified parts cannot be obtained, atemporary installation may be made using suitablesubstitute parts, and these parts should bereplaced with the proper items as soon as they canbe obtained. When making parts substitutions,

give special attention to the following con-siderations:

1. Corrosion. The chemical or metalliccomposition of the part must be such that its usedoes not contribute appreciably to the danger ofcorrosion,

2. Strength. The strength of the substitute partmust be the same as or greater than the prescribedstrength. When determining the strength, giveconsideration to the tensile, compression, and/orshear strength, as applicable to the specific use.

3. Size. Substitute bolts and screws should bethe same size as the prescribed item. If adetachable nut is to be used, a different threadmay be tolerated; if a threaded hole or an anchornut is involved, the thread must be the same asthe one prescribed. In all cases, washers must havethe same inner diameter as the prescribed item,but a different outer diameter or thickness maysometimes be permitted.

4. Length. Substitute screws or bolts musthave a length that is sufficient for the particularinstallation, but they must not be so long that theyare in the path of any moving part. They mustnot be in contact with other aircraft items suchas electrical wiring, hydraulic lines, and so forth.

5. Magnetic properties. Specific areas of theaircraft (for example, vicinity of such items as themagnetic compass, magnetic anomaly detectionequipment, radio direction finder, or gyros)should not be changed in a manner that may causethe magnetic fields of the area to becomedistorted. In these areas, any substitute part mustpossess the same magnetic properties andcharacteristics as the one prescribed.

6. Style. Most items of mounting hardwareare available in various styles. It is usually easyto find screws and bolts that are identical in allrespects except for the type of head. These partsare preferred as substitutes, provided they possessall the required special features.

7. Special features. If a bolt is to be torquedto a given value, a torque wrench that is usablewith that type of part and has the proper torquerange must be available. If lockwiring is required,the part must have suitable provisions.

8. Lubrication or coating. If specific instruc-tions call for lubrication or coating of the parts,they must be followed for the substitute part aswell as for the prescribed part. If no lubricationis permitted, the substitute part is not to belubricated.

7-31

SOLDER

Two types of solder are available, the tin-leadalloy known as soft solder and the so-called hardor silver solder. Soft solder alloys permit the useof lower soldering temperatures; therefore, theyare recommended for electronic applications.Where a joint of greater strength is required, silversolder is used.

Most solder alloys do not liquify immediatelyas the temperature is increased. Ordinarily, theychange from the solid state to a plastic orsemiliquid, and finally become completely liquid.Most tin-lead solders enter the plastic state at358°F, and become totally liquid at varioustemperatures, depending upon the individualsolder composition. A combination of 63 percenttin and 37 percent lead has the best melting point(361°F) for the tin-lead group. However, sinceit changes from solid to liquid without anintervening plastic state, it is susceptible tofracture from slight vibration while cooling.(Solder is commonly referred to as 70/30, 60/40,and so on. This is the tin-lead content. )

FLUXES

All common metals are covered with anonmetallic film, usually an oxide of the material,that prevents them from making the intimatecontact so necessary for a good electricalconnection. The purpose of a flux is to removethe oxide from the surfaces to be soldered, notto clean them. Flux cannot replace good cleaningmethods in preparing surfaces for soldering.Without a clean, intimate contact, poor solderingtechniques may result in a mechanically weak,high-resistance joint, a so-called rosin joint in thecase of rosin-base flux. Solder fluxes may bedivided into three general groups—rosin, organic,and chloride (sometimes called acid).

The residue from the rosin-base fluxes isnoncorrosive and electrically nonconductive,making them highly acceptable for use in militaryelectronic equipment. The organic and chloridetypes are seldom used (sometimes even prohibited)because of their corrosiveness. Only rosin-baseflux is recommended for electronic applications.

Activated or intensified rosin-alcohol fluxesare permitted if they are noncorrosive. Fordetails, you should consult applicable militaryspecifications.

Organic fluxes consist of mild organic acidsand bases. These fluxes are almost as active asthe organic salts, but their period of activity isbrief due to their susceptibility to thermaldecomposition. This limits corrosion; therefore,they may be used in applications where thesoldered assembly lends itself to residue removal.

Chloride fluxes are not recommended forelectronic applications.

POTTING COMPOUND

Most electrical connectors and some relaysused in aircraft are potted to prevent corrosion,contamination, or arc-over between pins andterminals. Because of temperature variationsthroughout the aircraft, two different pottingcompounds are used. You can tell which one wasused by its color. The tan compound is used wherethe temperature under operating conditions doesnot exceed 87.8°C (190°F). The red compoundis used where the temperature is higher. If itbecomes necessary to replace or repot a relay orconnector, the potting compound that is usedshould have the same temperature range (color)as the original material. Care should also be takento duplicate the shape of the original potting sothat no installation problems will occur.

Q14.

Q15.

Q16.

Q17.

Q18.

Q19.

Q20.

When can you reinstall removed mountingparts?

What is the main advantage of Torq-setscrews?

If maintenance procedures do not call outspecific torque requirement, how can youdetermine the proper torque for tightening?

Each e lec tr i cal connector has anidentification symbol called the MS partnumber. What information can you obtainfrom this number?

Describe the difference between a BNC andTNC connector.

List the three major factors in wireselection.

What considerations should you pay specialattention to when making part substitu-tions?

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7-33

CHAPTER 8

TEST EQUIPMENT

The operational theory of equipment is onlyone part of the knowledges you need to maintainavionics equipment. You also need a knowledgeof avionics drawings, schematics, and testequipment.

You use many publications to properlymaintain a weapons system in modern-day aircraftbecause they are so complex. Just the list of theelectronics equipment installed in modern-dayaircraft is lengthy. It is impossible for eachindividual to know all the various types ofelectronics equipment presently in use. However,with a good general background on electronicprinciples and circuit theory and a little study,you, the Aviation Electronics Technician, canrapidly become familiar with any specific systemor test equipment.

In this chapter, you will learn about somecommon test equipment used by AviationElectronic Technicians (ATs). This informationis in addition to modules 3 and 16 of the NavyElectronic and Electricity Training Series(NEETS) on test equipments. Review and referto the NEETS modules as necessary for additionalinformation about the test equipment describedin this chapter. No in-depth theory beyond thatnecessary to describe the operation of the test setunder discussion is included here. When you usea piece of test equipment with which you are notfamiliar, always use the appropriate instructionmanual. These publications contain detailedand specific information about the particularequipment.

CARE AND USE OF AVIONICSSUPPORT EQUIPMENT

Learning Objective: Identify the propercare and use of avionics support equipmentto include calibration, repair, and handlingrequirements.

All electronic maintenance shops have andrequire many pieces of test equipment to maintaindifferent types of electronic units. However, thereare very few spare test sets. When a test setbecomes inoperative, shop maintenance suffers.Therefore, each person should use the testequipment properly and only for its designedpurpose. Protect the equipment from physicalharm that may result from dropping, falling, orany other careless misuse, and always observeproper operating techniques.

One of the chief causes of test set failure iscarelessness. The user can be careless in anoperating procedure or in handling the set.Improper range selection for the measuredquantity is the most common mistake in anoperating procedure. Such an error might be totry to measure 250 volts on the 50-volt scale ofa meter. If you aren’t sure about proper use ofa test set, refer to the manual issued with the set.

Improper handling causes damage to testequipment. Often, technicians place test sets nearthe edge of the bench where they can be easilyknocked or pulled off. Read the instructions forproper handling and operating procedures, andthink when you use a piece of equipment. Referto NEETS, modules 3 and 16, for furtherinformation on test equipment operation andtheory.

CALIBRATION

Test sets require checks to determine if theyare within operating tolerances. Some test sets areused as frequency standards and require periodiccalibration. You should always follow the recom-mendations of the manual or pamphlet issued withthe set, unless current instructions change thoserecommendations.

Normally, personnel in an intermediate-levelmaintenance shop perform calibration usingspecial-purpose calibration equipment. Personnelat the organizational level of maintenance seldomcalibrate test equipment.

8-1

REPAIR

The using activity normally makes any minorrepair of test sets not requiring calibration.Repairs are usually limited to the replacement oftest leads and fuses. Before you make any repair,consult current instructions on repair of testequipment.

Personnel assigned to an intermediate-levelmaintenance activity repair test equipment on awider scale. Repair can vary from the replacementof circuit components to modules, depending onthe authorized level of repair. However, most testequipment work at this level consists of calibratingequipment.

HANDLING PRECAUTIONS

Some equipments require special handling;however, several precautions apply to testequipments in general. Rough handling, moisture,and dust all affect the useful life of testequipment. For example, bumping or droppinga test instrument can destroy the calibration ofa meter or short circuit the elements of anelectronic tube within the instrument. Creasingor denting coaxial test cables alter theirattenuating effect, affecting the accuracy of anyRF measurements made with these cables. Toreduce the danger of corrosion to untreated parts,always store test equipment in a dry place whennot in use. Excessive dust and grime inside a testequipment affect its accuracy. Be sure all assemblyscrews that hold the case of the test equipmentin place are tight and secure. As an addedprecaution, place all dust covers on testequipments when they are not in use.

Meters are the most delicate part of testequipments. To make sure the meter maintainsits accuracy, you should follow these additionalprecautions:

1.

2.

3.

Make certain the amplitude of the inputsignal under test is within the range of themeter.Keep meters as far away as possible fromstrong magnets.When servicing an item of electronicequipment that contains a meter, dis-connect the meter from the circuit beforemaking resistance or continuity tests. Thisprecaution should prevent the possibilityof burning out the meter.

The instruction manuals that come with apiece of equipment contain the procedures forproperly stowing test equipment cables and otheraccessories. Read these manuals carefully andfollow the equipment instructions. Improperstowage of accessories could change cable charac-teristics and cause intermittent shorts in cables andleads. Improper stowage causes unreliable testequipment indications.

Q1.

Q2.

Q3.

Q4.

Name one of the chief causes of test setfailure.

Although test equipment is repaired at theintermediate-level maintenance activity,most work performed at this level on testequipment consists of

What is the most delicate part of a pieceof test equipment?

List the basic measuring parameters ofelectronic equipment.

MEASURING INSTRUMENTS

Learning Objective: Recognize types anduses of measuring equipment to includeelectronic meters, frequency measurement,and power measurement.

In this chapter, the term measuringinstruments includes only the class of testequipments that measure the basic parameters ofan electronic equipment. The basic parametersare voltage, current, resistance, power, andfrequency.

METER OPERATION

There must be some source of power availableto operate a meter. Some meters use batteriesinstalled in the meter case as a power source;others may use an electrical power cord pluggedinto a power receptacle. A vacuum tube voltmeter(VTVM) is an example of the second type. Thepower to operate some meters (such as meggers)is self-produced by manual operation of ahandcrank.

Most meters provide the means to measuremore than one electrical quantity; these aremultimeter. Before discussing any one particulartype of meter, a brief review of each of the basicmeters is necessary. For more details refer toNEETS, modules 3 and 16.

8-2

Ammeter

The amplitude of current flow through thebasic meter mechanism limits it to measuring afixed range of only a fraction of an ampere. Acurrent shunt overcomes this limitation andprotects the mechanism. The current shunt isactually a resistance of low value, permitting theinstrument to serve as a dc ammeter that canmeasure relatively large direct currents.

The current distribution between metermovement and shunt is inversely proportional totheir individual resistances. Thus, the shunt,which has less resistance, carries most of thecurrent. Since the meter coil carries only asmall portion of the circuit current, it canindicate relatively large values of circuit current.The instrument provides a variety of currentranges by the use of shunts of different values.Figure 8-1 shows a simplified schematic diagramof an ammeter section taken from a typicalvolt-ohm-milliammeter (VOM).

Ohmmeter

The midscale deflection of an ohmmeteroccurs when the current drawn by the meter isone-half the value of the current at full-scale (zeroohms) deflection. This condition exists when themeasured resistance is equal to the total metercircuit resistance. Analysis of the circuit infigure 8-2 shows that full-scale deflection occurswhen shorting the meter probes together. Lessthan full-scale deflection occurs when theresistance to be measured, Rx, is connectedinto the circuit. If the meter now reads one-halfof its former current, the total circuit resistance

Figure 8-1.-Simplified schematic diagram of an ammeter.

Figure 8-2.-Series-type ohmmeter basic circuit.

has doubled. This indicates that RX is equal to thetotal meter circuit resistance.

Since the ohms-calibrated scale is nonlinear,the midscale portion represents the most accurateportion of the scale. The usable range extends withreasonable accuracy on the high end to 10 timesthe midscale reading. However, on the low endit decreases to one-tenth of the midscale reading.

To extend the range of an ohmmeter, theproper values of shunt and series resistors andbattery voltages are connected into the circuit. Theproper values let you read the meter full scale withthe test leads shorted. Figure 8-3 shows a

Figure 8-3.-Simplified schematic diagram of an ohmmeter.

8-3

simplified schematic diagram of an ohmmetersection taken from a typical VOM.

Voltmeter

Adding a voltage-multiplying resistor makesthe basic meter mechanism suitable for use whenmeasuring dc voltages. The voltage-multiplyingresistor is placed in series with the coil (fig. 8-4)and limits the flow of current to a safe value.

Since the value of the resistor is constant forany given application, the flow of current throughthe coil is proportional to the voltage undermeasurement. By properly calibrating the dial, theinstrument indicates voltage. However, it isactually the current that activates the meter. Theuse of different values of multiplying resistorsestablishes the voltage ranges of the instrument.

MULTIMETER

Much of the work that you do using a VOMcan be done with a multimeter. The namemultimeter comes from multiple meter, which isexactly what a multimeter is. It is an ohmmeter,a dc and an ac milliammeter, and a voltmeter. Atypical multimeter is shown in figure 8-5.

Figure 8-5.-Typical multimeter.

In many shops, you might use a portable,battery-operated multimeter such as a TS-352,USM-311, Simpson 260, or Simpson 160 for fielduse (troubleshooting in the aircraft, for instance).As an AT, however, you will often need a moresensitive meter—one that gives more accuratereadings and has wider ranges.

Often, equipment schematics and wiringdiagrams specify that voltages indicated at testpoints were obtained with a meter of a certainsensitivity, such as a 20,000-ohms-per-volt meter.

Figure 8-4.-Simplified schematic diagram of a dc voltmeter. You should use a meter with the same sensitivity

8-4

in repairing that equipment to obtain accuratereadings because of circuit loading.

NOTE: For a review of the basic theoryand operation of the multimeter, refer toNEETS, module 3.

MILLIOHMMETER

One of the most common and troublesomeproblems is finding the exact location of a shortcircuit in a power distribution circuit involvingmany parallel paths. This and several trouble-shooting problems are easier to solve with amilliohmmeter.

A milliohmmeter is a low-range ohmmeterthat can measure resistances in the milliohmrange or less. The AN/USM-21A is a typicalmilliohmmeter used in the fleet. It can measureresistances in the range of 10 milliohms or less.Most ohmmeters read zero at such a low value.

When using a milliohmmeter, you mayencounter several problems. These problemsinclude stray circuit resistances, such as contactresistance, test lead resistance, and switchingresistance. In the conventional low-rangeohmmeters, the primary problem is in the contactresistance at the test probes. The design of theAN/USM-21A overcomes the contact resistanceproblem.

MEGOHMMETER (MEGGER)

The megohmmeter, commonly called themegger, is an instrument that applies a highvoltage to the component under test and measuresthe current leakage of the insulation. This lets youcheck a capacitor or an insulated cable for leakage

under much higher voltages than an ohmmetercan supply. The megger consists of a hand-drivendc generator and an indicating meter. It measuresresistances of many megohms.

There are various resistance ratings of meggerswith full-scale values as low as 5 megohms andas high as 10,000 megohms. Figure 8-6 shows thescale of a 100-megohm, 500-volt megger. Noticethat the upper limit is infinity and that the upperend of the scale is also crowded. The first scalemarking below infinity represents the highestaccurate value the instrument can provide. Thus,if the pointer goes to infinity while you are makinga test, it means that the resistance is higher thanthe range of the set.

There are also various voltage ratings ofmeggers, such as 100, 500, 750, 1,000, and 2,500.The most common type is the one with a 500-voltrating. This voltage rating refers to the maximumoutput voltage of the megger. The output voltagedepends on the turning speed of the crank andarmature. When the megger’s armature rotationreaches a predetermined speed, a slip clutchmaintains the armature at a constant speed. Thevoltage rating is important. If too high a voltageis applied, it will cause even a good componentto break down. Therefore, do not use a 500-voltmegger to test a capacitor rated at 100 volts.

You can use meggers to test the insulationresistance of conductors that may be shorting orbreaking down under high voltage. In somesituations, you can use meggers in the preventionof unnecessary breakdowns. You could maintaina record of insulation resistance of powerand high-voltage cables, motor and generatorwindings, and transmission lines. These recordsreflect fluctuations in resistance and help

Figure 8-6.-Scale of a 100-megohm, 500-volt megger.

8-5

determine when to replace the components toprevent a breakdown.

Meggers are used for testing capacitors whosepeak voltages are not below the output of themegger. They are also used for testing forhigh-resistance grounds or leakage on devices suchas antennas and insulators.

The following are precautions you should takewhen using meggers:

1. When you are making a megger test, do notenergize the equipment. Disconnect it entirelyfrom the system before testing.

2. Observe all safety rules in preparingequipment for test and in testing, especially whentesting installed high-voltage apparatus.

3. Use well-insulated test leads, especiallywhen using high-range meggers. Check the leadsafter connecting them to the megger and beforeconnecting them to the component under test.Operate the megger and make sure there is no leakbetween the leads. The reading should be infinity.Check the leads by touching the test ends of theleads together while turning the crank slowly. Thereading should be about zero. If the indicationreads differently, you may have a faulty lead ora loose connection.

4. When using high-range meggers, takeproper precautions against electric shock. Thereis enough capacitance in most electrical equip-ment to store up energy from the meggergenerator to give a very disagreeable and evendangerous electric shock. Because there is a highprotective resistance in the megger, its open circuitvoltage is not as dangerous as it would otherwisebe; still, be careful.

5. Discharge equipment having considerablecapacitance before and after megger tests. Thisshould help you avoid receiving a dangerousshock. You can do this by grounding or shortcircuiting the terminals of the equipment undertest.

The AN/PSM-25, shown in figure 8-7, is acommon megger used through the fleet. For moreinformation on meggers, refer to NEETS, module16.

ELECTRONIC METERS

Electronic meters and nonelectronic meters areused for the same purposes; however, they dohave some differences. In the electronic multi-meter and corresponding nonelectric measuringdevices, the current- and resistance-measuring

Figure 8-7.-AN/PMS-25 megger.

circuits function in the same way. However, whenan electronic multimeter is used to measurevoltage, an amplifier is involved. Therefore, theelectronic meter requires calibration before it isused. The proper calibration and use of theinstruments vary slightly, according to model.You should refer to the operation instructionmanual for the specific details of each model.

The ordinary voltmeter cannot be accuratelyused to make voltage measurements in high-impedance circuits. For example, you need tomeasure the plate voltage of a pentode amplifier.(See fig. 8-8.) When you connect the meterbetween the plate and cathode of the electrontube, the meter resistance is in parallel withthe effective plate resistance Thus, the plateresistance is lowered. The effective plate resistanceis in series with the plate load resistor andthis series circuit appears across the supply voltage

as a voltage divider. Since the overall

8-6

Figure 8-8.—Loading effect created by meterresistance.

resistance is now lower, the current through RL willincrease. This causes the voltage drop across RL to alsoincrease, and the voltage drop across Reff will decrease.The result is an incorrect indication of plate voltageand is called the loading effect. The lower thesensitivity of the meter, the greater the loading effectand the higher the incorrect indication (error) will be.

A meter having a sensitivity of 20,000 ohms pervolt and a 250-volt maximum scale reading wouldintroduce an error of about 1 percent. However, incircuits with very high impedances, even a meter witha 20,000-ohm-per-volt sensitivity would impose toomuch of a load on the circuit.

VACUUM TUBE VOLTMETER

Another limitation of the ac, rectifier-typevoltmeter is the shunting effect at high frequencies ofthe relatively large capacitance of the meter’s rectifier.This shunting effect may be greatly reduced byreplacing the usual metallic oxide rectifier with a diodeelectron tube. The output of the diode goes to the gridof an amplifier, in which the plate circuit contains thedc meter. Such a device is an electron tube voltmeter ora vacuum tube voltmeter (VTVM). Voltagemeasurements are extremely accurate with this type ofmeter, even at frequencies up to 500 megahertz andsometimes higher. The VTVM model that is useddetermines its frequency limitation.

The input impedance of a VTVM is large;therefore, the current drawn from the circuit voltagebeing measured is small and in most cases negligible.The main purpose of a VTVM is to reduce the loadingeffect by taking advantage of the VTVM’s extremely

high input impedance. The TS-505 multimeter containsa VTVM, and it is used extensively in electronicsmaintenance.

You should refer to figure 8-9 as you read thissection. The VTVM measures dc voltages from 0.05 voltto 1,000 volts (in nine ranges) and ac voltages from0.05 volt to 250 volts rms (in seven ranges) atfrequencies from 30 Hz to 1 MHz. Using the RFadapter with the dc voltage measurement circuit letsyou measure RF voltages from 0.05 volt to 40 volts rmsat frequencies from 500 kHz to 500 MHz. You maymeasure resistances from 1 ohm to 1,000 megohms.

Figure 8-9.—TS-505 multimeter front panel.

8-7

The accuracy of this meter is ±5 percent fordc voltages and ±6 percent for ac and RFvoltages. The meter movement requires 1 mA forfull-scale deflection. The input impedance to themeter is 6 megohms at audio frequencies, 40megohms on the 1,000-volt dc range, and 20megohms on all other ranges. The power require-ment is 98 to 132 volts, single phase, 50 to1,000 Hz, at about 21 volt-amperes.

The removable cover of the TS-505 containsaccessories such as alligator clips, an RF adapter,and miniature probe tips. The miniature tips slipover the regular tips for work in confined areas.

Operating Controls

The following are the controls you use whenoperating the meter (fig. 8-9):

FUNCTION switch—Selects the type ofmultimeter operation desired and turns themultimeter on or off.

RANGE switch—Selects the variousvoltage or resistance measurement ranges.

ZERO ADJ. control—Controls thepointer of the indicating meter. Use it toset the meter pointer at zero on the +DC,–DC, AC, or OHM scale, or at midscaleon the ±DC scale.

OHMS ADJ. control—Controls thepointer of the indicating meter. Use it toset the meter pointer at on the OHMSscale when the FUNCTION switch is seton OHMS position.

Meter—Indicates the value of voltage orresistance measured.

AC LINE cord—Connects the multimeterto the ac power source.

COMMON probe—Connects the groundor common circuit of the multimeter to theequipment under test.

DC probe—Connects the equipment undertest to the dc measuring circuit of themultimeter

OHMS probe—Connects the equipmentunder test to the ohmmeter circuit of themultimeter

AC probe—Connects the equipment undertest to the ac measuring circuits of themultimeter.

Pilot light indicator—Lights when poweris applied to the multi meter.

Techniques for Use

The TS-505 multimeter is not difficult tooperate. However, do not try to use thisinstrument unless you have studied the technicalmanual that contains the operating procedures,or unless you have received instruction in itsproper use from your shop supervisor. There aretwo peculiarities of this meter that you need toknow about.

1. It must warm up before it gives accuratereadings. This usually takes about 10minutes. During this period, the meterpointer may drift rapidly. This is normal.

2. You cannot read voltage measurementsdirectly off the meter scale when thefunction switch is in the ±DC position.The purpose of the ±DC position (zerocenter scale) is to determine the polarity ofan unknown dc voltage. It also indicatesa zero dc voltage input to the multimeter

CAUTION

The maximum input dc voltage to themultimeter when in the ±DC position isone-half of the range switch voltagesetting.

The major difference between any VTVM anda conventional multimeter is that the VTVM usesa vacuum tube in its input. For a detailedexplanation of the circuitry of the TS-505 VTVM,consult the manufacturer’s manual or theoperation and service instruction manual.

PHASE ANGLE VOLTMETER

The overall accuracy of many electronicequipments is determined by measuring phaseangles. In the past, the phase shift or phase anglesbetween signals were measured by observingpatterns on an oscilloscope. It was hard todetermine small angles and difficult to translatevarious points into angles and sines of angles usingthis method. Also, using oscilloscope patterns is

8-8

a limiting factor if one of the signals containsharmonic distortion or noise.

In any complex waveform containing afundamental frequency and harmonics, measuringphase shifts presents problems. In most applica-tions, the primary interest is the phase relationshipof the fundamental frequency, regardless of thephase relationship of any harmonics that arepresent. Therefore, one requirement of a phase-measuring device is its ability to measure the phasedifference between two discrete frequencies,regardless of the phase and amplitude of othercomponents of the waveform.

Figure 8-10 shows the basic block diagram ofa phase angle voltmeter. There are two inputs—the signal and the reference. Each channelcontains a filter that passes only the funda-mental frequency and highly attenuates allother frequencies. Each channel has a variableamplitude control and amplifiers to increase thevariety of signals that you can check.

A calibrated phase shifter is inserted into onechannel. That channel signal can then be phase

shifted to correspond to the other channel. Thephase detector detects this and indicates it on themeter.

The calibrated phase shifter is a switch (whoseposition corresponds to the 0-degree, 90-degree,180-degree, and 270-degree phase shift) and apotentiometer (whose dial is calibrated from 0 to90 degrees). The total phase shift is the sum ofthe two readings.

The phase detector is a balanced diode, bridge-type demodular. Its output is proportional to thesignal frequency amplitude times the cosine of theangle of phase difference between the signal inputand the reference input.

If the shifted reference input is in phase or 180degrees out of phase with the signal input, theoutput from the phase detector is proportional tothe signal input amplitude. The cosine of the angleis unity. If the shifted reference input is 90 degreesor 270 degrees from the signal input, the phasedetector output will be zero (the cosine of theangle is zero).

The point at which the two signals are in phaseor 180 degrees out of phase is the point of

Figure 8-10.-Phase angle voltmeter block diagram.

8-9

maximum deflection on the meter. The difference Q 8 .between the in-phase and the 180-degree out-of-phase points is in the direction in which theneedle swings—not the distance it swings. Uponapproaching the point of maximum deflection,the rate of change of the meter reading decreasesbecause the cosine has a small rate of change near0 degrees. This makes it difficult to read the exactpoint of maximum deflection.

The cosine’s maximum rate of change occursas it approaches 90 degrees (and thus gives a betterindication on the meter). Therefore, mostcommercial voltmeters are set to determine thepoint at which the signals are 90 degrees out ofphase, known as quadrature. However, thisrequires converting the phase shifter reading soit shows the correct amount of phase shift ratherthan 90 degrees more or less than the actualamount.

Different manufacturers use different methodsto determine the signal quadrant, which leads tosome confusion. Also, manufacturers differ onwhether the final reading is a leading or a laggingphase shift. This means that you, the technician,must know the phase angle voltmeter you areusing.

The Navy has several phase angle voltmetersand each operates differently. You cannot assumethat the method you use to determine the phaseangle on one type of meter is the method youshould use to determine it on another. Also, youcannot assume that because one meter gives aleading angle between signal and referencewaveforms, another meter will also give a leadingphase shift.

Q9.

Q10.

Q5.

Q6.

Q7.

What is the most accurate portion of theohmmeter scale, and why?

When repairing equipment, you shoulduse a meter with the same sensitivityas specified in schematics and wiringdiagrams. What is the reason for doingthis?

Name the piece of test equipment thatconsists of a hand-driven dc genera-tor, applies a high voltage to the com-ponent under test, and measures currentleakage.

Loading effect is the result of a meter’ssensitivity, and it causes incorrect voltageindications. What relationship existsbetween a meter’s sensitivity and its loadingeffect?

What is the major difference between aVTVM and a conventional multimeter?

A phase angle voltmeter is used todetermine the overall accuracy of electronicequipment by measuring phase angles.What is actually measured by the phaseangle voltmeter?

DIFFERENTIAL VOLTMETER

The differential voltmeter is a reliableprecision piece of test equipment. Its generalfunction is to compare an unknown voltage withan internal reference voltage and to indicate thedifference in their values. A common differentialvoltmeter is the 883A (fig. 8-11), manufacturedby the John Fluke Co. The Fluke 883A has manycapabilities and uses. You may use it as

1.

2.

3.

a conventional transistor voltmeter formeasuring voltages from 0 volt to 1,100volts dc,

a differential voltmeter for precision (0.01percent of input voltage) measurement ofdc voltages in this range, or as

an accurate ac vo l tmeter and amegohmmeter for measuring resistancefrom 10 megohms to 11,000 megohms.

The Fluke Model 883A is accurate enough forprecision work in calibration laboratories yetrugged enough for general shop use. For moreinformation on the Fluke Model 883A, youshould refer to NEETS, module 16.

FREQUENCY MEASUREMENT

Often, frequency measurements are anessential part of preventive and correctivemaintenance for electronic equipment. You mayhave to determine rotation frequencies of somemechanical devices. For example, you have to

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Figure 8-11.-Fluke Model 883A differential voltmeter.

check the output frequency of electric powergenerators when starting the engine and duringpreventive maintenance routines. Equipment thatoperates in the audio-frequency range requiresadjusting to operate at the correct frequencies.Accurate tuning of radio transmitters to theirassigned frequencies provides reliable com-munications. Tuning also avoids interfering withradio circuits operating on other frequencies.Radar sets also require proper tuning to getsatisfactory performance.

A stroboscope can measure the rotationfrequency of rotating machinery such as radarantennas, servomotors, and other types of electric

motors. Stroboscopic methods compare the rateof one mechanical rotation or vibration withanother or with the frequency of a varying sourceof illumination. Tachometers can also measurethe rotation frequency of armatures in electricmotors, dynamotors, and engine-drivengenerators.

Vibrating-reed, tuned-circuit, or moving-diskmeters directly measure the electrical outputfrequency of ac power generators. The vibrating-reed device is the simplest frequency meter, andit is rugged enough to mount directly on generatorcontrol panels. You may also use it to check theline voltage in the shop to be sure the proper

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frequency is available to the equipment and/ortest sets.

Frequency Meters

The term frequency meter refers to an itemof test equipment used to indicate the frequencyof an external signal. Although some frequencymeters generate signals having a basic frequency,you should not confuse them with test equipmentknown as signal generators. The frequency metermeasures the frequency of a signal developed inan external circuit.

Some frequency meters generate a signalfrequency; others do not. Those that don’tgenerate an internal frequency are known aswavemeters. There are two basic types ofwavemeters—reaction and absorption. Frequencymeters that do generate an internal frequency mayuse either electronic or mechanical oscillation asthe frequency generator.

Measurement Methods

Youin theparison

may make frequencyaudio-frequency rangemethod or by using a

measurementsby the com-direct-reading

frequency meter. You may make frequencycomparisons by use of a calibrated audio-frequency signal generator with either anoscilloscope or a modulator and a zero-beatindicator device. Instruments using seriesfrequency-selective electrical networks, bridge testsets having null indicators, or counting-typefrequency meters can make direct-readingfrequency measurements.

Since the wavemeter is relatively insensitive,it is very useful in determining the fundamentalfrequency in a circuit generating multipleharmonics. You may check the calibration of testequipment that measures signals in this frequencyrange by comparing them with standard frequencysignals broadcast by the National Bureau ofStandards.

The signal frequencies of radar equipment thatoperate in the UHF and SHF ranges can bemeasured by resonant cavity-type wavemeters,resonant coaxial line-type wavemeters, orLecher-wire devices. When properly calibrated,resonant cavity and resonant coaxial linewavemeters are more accurate. They also havebetter stability than wavemeters used formeasurements in the LF to VHF range. Thesefrequency-measuring instruments often come aspart of communication and electronic equipment,but they are also available as general-purpose testsets.

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Heterodyne Meters

Heterodyne frequency meters are available inseveral varieties. Although they all function in thesame general manner, some differences exist inhow they accomplish their purpose.

Test instruments of this class generate a signalwithin the test set. This signal mixes with a signalfrom the equipment under test to obtain a beatfrequency. The frequency of one signal is thenchanged to obtain a zero beat. The beat frequencyis the difference frequency that results fromheterodyning two signals. A zero beat results whenheterodyning two signals of the same frequency.You may determine the frequency of the unitunder test by reading the frequency indicator ofthe test set.

A heterodyne frequency meter (fig. 8-12)usually consists of the following parts:

A heterodyne oscillator

An RF harmonic amplifier

A crystal-controlled oscillator

A

A

mixer or detector

modulator

An AF output amplifier

A means for indicating frequency

Most models come with a set of calibrationcharts giving the dial readings for the frequencieslisted and a table of the crystal harmonics. Thetable and charts give complete and accuratefrequency coverage over the set’s range. Somemodels indicate the frequency directly ondials.

The crystal-controlled oscillator operates at afixed frequency. However, it is also capable ofemitting various harmonic frequencies of thecrystal for use as check frequencies. Thesecheckpoints provide a measure for adjusting theheterodyne oscillator, thus ensuring more accurateoperation. Provisions are usually made within thecrystal-controlled oscillator for precise adjustmentto its assigned fundamental frequency.

Figure 8-12.-Crystal-calibrated heterodyne frequency meter block diagram.

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Wavemeters

Wavemeters are calibrated, resonant circuitsused to measure frequency. Although not asaccurate as heterodyne frequency meters, wave-meters are comparatively simple and easy to carry.

You may see any type of resonant circuit inwavemeter applications. The exact kind of circuitdepends on the frequency range for which themeter is intended. Resonant circuits consisting ofcoils and capacitors are used with low-frequencywavemeters. VHF and microwave instrumentshave butterfly circuits, adjustable transmissionline sections, and resonant cavities.

There are three basic kinds of wavemeters—the absorption, the reaction, and the transmissiontypes.

The absorption wavemeter consists of thebasic resonant circuit, a rectifier, and a meter forindicating the amount of current induced into thewavemeter. In use, this type of wavemeter looselycouples to the measured circuit. Then, you adjustthe resonant circuit of the wavemeter until thecurrent meter shows a maximum deflection. Youdetermine the frequency of the circuit under testfrom the calibrated dial of the wavemeter.

The reaction wavemeter gets its name fromhaving to be adjusted until a marked reaction

occurs in the circuit being measured. For example,the wavemeter is loosely coupled to the grid circuitof an oscillator, and the tuning circuit of thewavemeter is adjusted until it is in resonance withthe oscillator frequency. The setting of thewavemeter dial is made by observing the grid-current meter in the oscillator. At resonance, thewavemeter circuit takes energy from the oscillator,causing the grid current to dip sharply. Thefrequency of the oscillator is then determinedfrom the calibrated dial of the wavemeter. Thistype is commonly referred to as a grid-dip meter.

The transmission wavemeter is an adjustablecoupling link. When inserted between a source ofradio-frequency energy and an indicator, energyis transmitted. However, energy to the indicatoronly occurs when the wavemeter is tuned to thefrequency of the source. Transmission wavemetersare commonly used to measure microwavefrequencies. Units of this type are also found inecho boxes. The additional provisions for echoboxes permit additional testing functions.

Many types of wavemeters are used forvarious functions. The cavity-type wavemeter(fig. 8-13) is the type most commonly used formeasuring microwave frequencies; therefore, it isthe one covered in this chapter. The deviceemploys a resonant cavity that effectively acts as

Figure 8-13.-Typical cavity wavemeter.

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a high-Q, LC tank circuit. The resonant frequencyof the cavity varies by means of a plunger,which mechanically connects to a micrometermechanism. Movement of the plunger into thecavity reduces the cavity size and increases theresonant frequency. Conversely, an increase in thesize of the cavity (made by withdrawing theplunger) lowers the resonant frequency. Themicrowave energy from the equipment under testgoes into the wavemeter through one of twoinputs—A or D. The crystal rectifier then detects(rectifies) the signal, and the current meter (M)indicates the rectified current. You can use thecavity wavemeter as either a transmission-type oran absorption-type wavemeter.

When used as a transmission wavemeter, theunknown signal couples into the circuit throughthe A input. When the cavity is tuned to theresonant frequency of the signal, energy is coupledthrough coupling loop B into the cavity and outthrough loop C to the crystal rectifier. It isrectified, and current flow resulting from thisrectification is indicated on the meter. Atfrequencies off resonance, little or no currentflows in the detector, and the meter reading issmall. Vary the micrometer and attached plungeruntil you get a maximum meter reading. Comparethe resulting micrometer setting with a calibrationchart supplied with the wavemeter to determinethe unknown frequency.

When the unknown signal is relatively weak,such as the signal from a klystron oscillator, thewavemeter functions as an absorption wavemeter.Connect the instrument at the D input. The RFloop C then acts as an injection loop to the cavity.When the cavity is tuned to the resonant frequencyof the klystron, the cavity absorbs maximumenergy and the meter will dip. This indicates areduction of current. When the cavity is not atthe resonant frequency of the klystron, the currentmeter will indicate high current. Therefore, tunethe cavity for a minimum reading, or dip, in themeter, and determine the resonant frequency fromthe micrometer setting and the calibration chart.

Potentiometer R1 adjusts the sensitivity of themeter from the front panel of the instrument. J1is a video jack for observing video waveforms witha test oscilloscope.

A directional antenna is used with theinstrument for making relative field strengthmeasurements of radiated signals for use inmeasuring the frequency of radar transmitters.This setup is also used for constructing radiationpatterns of transmitting antennas.

In radiation pattern measurements connect thedirectional antenna to the wavemeter input andtune the instrument to the frequency of the systemunder test. The cavity will then lock on thisfrequency by an automatic frequency control(AFC) system. For reliable results, the outputsignal must be continuous and constant. This isnecessary for any variation in the meter readingcaused directly by a change in the actual fieldstrength. That is the signal field strength when theposition of the wavemeter changes with respectto the transmitting antenna. After establishing areference level on the meter, change the positionof the wavemeter by moving it around theradiating antenna, maintaining a fixed distancefrom it. To determine the field pattern, record thewavemeter readings at various positions aroundthe transmitting equipment on polar graph paper.

COUNTER-TYPE FREQUENCY METER

The counter type of frequency meter is ahigh-speed electronic counter, with an accurate,crystal-controlled time base. This type ofcombination provides a frequency meter thatautomatically counts and displays the number ofevents (hertz) occurring in a precise interval, Thefrequency meter itself does not generate anysignal, it merely counts the recurring pulses fedto it.

The Hewlett-Packard Model 5245L electroniccounter (figs. 8-14 and 8-15) is a high-frequencygeneral-purpose electronic counter. The Model5245L measures frequencies from 0 to 50 MHz,periods from 1 µsec to 10 seconds, and periodaverages from 10 to 100,000 periods. Also, it canmeasure the ratio of two frequencies and themultiplied ratio of two frequencies. The Model5245L provides the following additional features:

Decade scaling to for any frequencyto 50 MHz

Standard output frequencies from 0.1 Hzto 10 MHz, in decade steps

Four-line, binary-coded-decimal (BCD)output to drive digital recorder (Hewlett-Packard Model 562A), digital-to-analogconverter (Hewlett-Packard Model580A/581A), remote readout, or dataprocessing equipment

Remote control by external contact closure

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Figure 8-14.-Model 5245L electronic counter front panel.

8-16

Figure 8-15.—Model 5245L electronic counter rear panel.

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Display storage that permits readingdisplay while making a new count

Eight-digit display using rectangular(narrow) digital display tubes, with decimalpoint position and measurement unitsdisplayed automatically

Operation with plug-in units that extendthe basic range and performance of thecounter

The Model 5245L features solid-state design,low-power consumption, small size (5 1/4-inchpanel height), light weight (32 pounds), easyconversion for rack mounting, and modular plug-in circuit boards for simplified maintenance. Toincrease the range of measurement, five plug-inunits (not shown) are available.

The Model 5245L measures frequency, periodaverage, ratio of two frequencies, and totalevents. A FUNCTION selector switch selectsmeasurement function, and a TIME BASEselector switch selects time base or multiplier. ASAMPLE RATE control selects the sampling rate,and a SENSITIVITY control adjusts instrumentsensitivity.

Direct readout is available in both PERIODand FREQUENCY functions with measurementunits displayed and with decimal point auto-matically positioned. In the MANUAL functionthe display is a direct read. The decimal point willnot light. Note that the only difference betweenratio and period measurements is the use of anexternal frequency instead of the internal 1-MHzoscillator.

Two factors determine the basic counteraccuracy, One factor is the aging rate of the1-MHz crystal standard in the time base, whichis less than 2 parts in per week. A secondfactor is the inherent error of ±1 count presentin all counters of this type. This error is due tophasing between the timing pulse that operates theelectronic gate and the pulses that pass throughthe gate to the counters. The chart in figure 8-16shows the errors possible for frequency or periodmeasurements,

The three factors contributing to the accuracyof period measurements are as follows:

1.

2.3.

The aging rate of the l-MHz standard,which is less than 2 parts in per weekThe ambiguity of the ±1 countThe ± trigger error (for one period, anda signal-to-noise ratio of 40 dB, this triggererror is 0.3 percent at rated sensitivity)

Figure 8-16.-Model 5245L electronic counter measurementaccuracy.

Frequencies of 0.1 Hz to 1 MHz are availablein decade steps at the TIME BASE EXTconnector as selected by the TIME BASE switch.This output is subject to the following restrictions,

Frequencies of 0.1 Hz through 10 MHz areavailable in decade steps at the rear-panelOUTPUT connector as selected by the rear-panelOUTPUT switch. This output is subject to thefollowing restrictions.

All frequencies are available one at a timein the MANUAL function without interruption.1 kHz is continuously available for all functionsexcept 100K PERIOD AVERAGE. The 10 kHzto 10 MHz is continuously available in allfunctions.

NOTE: The accuracy and stability of theseoutputs are the same as those of the timebase oscillator.

The Hewlett-Packard Model 525 1A frequencyconverter extends the frequency range of theModel 5245L to 100 MHz. The Model 5251Amixes a selected 10-MHz harmonic (between 20and 90 MHz) with the input signal. The resultingdifference-frequency signal receives amplificationand goes to the basic counter for counting anddisplay. Because the selected 10-MHz harmonic

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is from a harmonic generator driven by a 10-MHzoutput from the basic counter, the stability andaccuracy of the basic counter remains.

The Hewlett-Packard Model 5253B frequencyconverter extends the frequency range of theModel 5245L to 512 MHz. To retain the stabilityand basic accuracy, multiply a 10-MHz signal,from the counter’s internal time base, to aknown harmonic frequency. When this harmonicfrequency mixes with the input signal frequency,the difference frequency that results is within therange of the basic counter, and the counterdisplays the difference frequency.

The Hewlett-Packard Model 5254A frequencyconverter provides the Model 5254L with afrequency range from 300 to 3,000 MHz. Toretain the stability and accuracy of the basiccounter, use a 50-MHz multiple of the crystal-oscillator signal from the counter to beat withthe measured signal. The difference frequencyproduced is within the display range of the basiccounter. The converter has an indicator that aidsin frequency selection and indicates the outputlevel to the counter. The required input signal levelis 50 mV rms to 1 V rms. The input connectoris a type N female.

The Hewlett-Packard Model 5261A videoamplifier unit extends the sensitivity of the Model5245L to 1.0 millivolt over the frequency rangeof 10 Hz to 50 MHz. Input impedance increasesto 1 megohm and can increase to 10 megohms byusing an accessory 10:1 divider probe (Hewlett-Packard 10003A) for signals greater than 10 mV.A 50-ohm output is used for oscilloscope moni-toring of the amplified signal.

The Hewlett-Packard Model 5262A timeinterval unit provides start and stop pulses. Thesepulses start by electrical inputs to the main countgate in the Model 5245L, enabling it to make timemeasurements. Time intervals from 1 microsecondto 108 seconds are measured with a resolution of0.1 microsecond. Basic counter accuracy remainswhen the signal counted is from the internaloscillator.

Q11.

Q12.

Q13.

Describe the general function of adifferential voltmeter.

What item of test equipment is used toindicate the frequency of an external signal?

List the parts of most heterodyne frequencymeters.

Q14.

Q15.

Q16.

Q17.

Wavemeters are calibrated resonant circuitsused to measure frequency. List the threebasic kinds of wavemeters.

Of the three basic wavemeters, which oneis commonly used to measure microwavefrequencies?

The counter frequency meter is a high-speedelectronic counter, with an accurate, crystal-controlled time base. What does thiscombination provide?

What does the Model 5245L counterfrequency meter measure?

POWER MEASUREMENTS

You must check the power consumption andthe input and output signal power levels ofelectronic equipment. It is easy to determine dcpower; the unit of power (the watt, P) is theproduct of the potential in volts (E) and thecurrent (I) in amperes, or, P = IE. You can takea few basic circuit measurements and compute thepower using Ohm’s law.

It is not as easy to determine ac power. Tomake ac power measurements, you must considerthe phase angle of the voltage and current.Measurement is further complicated by thefrequency limitations of various power meters. Ifthere is no phase difference, compute ac powerin the same manner as dc power—by determiningthe average value of the product of the voltageand current.

Electric power at a line frequency of approxi-mately 60 Hz is directly measured by a dyna-mometer type of wattmeter. This type of meterindicates the actual power. Therefore, the phaseangle of the voltage and current does not haveto be determined. Normally, the exact powerconsumption of equipment is not necessary formaintenance, and a current measurement isenough to decide whether the power consumptionis within reasonable limits.

Many ac voltmeters have scales calibrated indecibels (dB) or volume units. Such metersare used to make measurements where directindication in decibels is desired. Remember, theseare voltmeters and that power measurements arenot meaningful unless the circuit impedance isknown. The topic of decibels is discussed inchapter 1 of Aviation Electronics Technician 3,NAVEDTRA 14028, NEETS, modules 11 and 16,and in the Electronics Installation & Maintenance

8-19

Book Test Methods and Practices, NAVSHIPS 0967-LP-000-0130. For more information on decibels, refer to these publications.

At radio frequencies below the UHF range, power is usually determined by voltage, current, and impedance measurements. One common method used to determine the output power of RF oscillators and radio transmitters consists of connecting a known resistance to the equipment output terminals. After measuring the current flow through the resistance, you then calculate the power as the product of I2R. Since the power is proportional to the current squared, the meter scale can indicate power units directly. A thermocouple ammeter is used to measure RF current. The resistor used to replace the normal load is of special design. It has to have low reactance and the ability to dissipate the required amount of power. Some common names for such resistors are dummy loads or dummyantennas.

In the UHF and SHF portions of the RF spectrum, it is more difficult to accurately measure voltage, current, and impedance. These basic measurements may change greatly at slightly different points in a circuit. Also, small changes in the placement of parts near the tuned circuits may affect their measurements. Test instruments that convert RF power to another form of energy, such as light or heat, can

measure the power output of microwave radio or radar transmitters indirectly. One method measures the heating effect of a resistor load on a stream of passing air. To achieve accurate measurement of large magnitude power, you can measure the temperature change of a water load. The most common type of power meter for use in this frequency range uses a bolometer. The bolometer is a loading device that undergoes changes of resistance as changes in the power dissipation occur. Measure the resistance before and after applying RF power; the change in resistance determines the power.

The Model 432A power meter operates with Hewlett Packard (HP) temperature-compensated thermistor mounts, such as the 8478B and 478A coaxial and 486A waveguide series. The frequency range of the 432A with these mounts in 50-ohm coaxial systems is 10 MHz to 18 GHz. Its frequency range in waveguide systems is 2.6 GHz to 40 GHz. Full-scale power ranges are 10 microwatts to 10 milliwatts (-20 dBm to +10 dBm). The total measurement capacity of the instrument is divided into seven ranges, selected by a front-panel RANGE switch (fig. 8-17).

The COARSE ZERO and FINE ZERO controls zero the meter. Zero carry-over from the most sensitive range to the other six ranges is within ±0.5 percent. When setting the RANGE

A11. Its general function is to compare an unknown voltage with an internal reference voltage and to indicate the difference in their values.

A12. Frequency meter.

A13. A heterodyne oscillator, RF harmonic amplifier, crystal-controlled oscillator, a mixer or detector, a modulator, an AF output amplifier, and a means for indicating frequency.

A14. Absorption, reaction, and transmission.

A15. Transmission.

A16. A frequency meter that automatically counts and displays the number of events (hertz) occurring in a precise interval.

A17. Frequency, period average, ratio of two frequencies, and total events.

8-20

8-21

Figure 8-17.—Model 432A power meter front panel.

switch to COARSE ZERO, the meter indicatesthermistor bridge unbalance. Adjust the front panelCOARSE ZERO adjust for initial bridge balance. Forbest results, FINE ZERO the 432A on the particularmeter range in use.

The CALIBRATION FACTOR switch providesdiscrete amounts of compensation for measurementuncertainties related to standing wave ratio (SWR) andthermistor mount efficiency. The calibration factor valuepermits direct meter reading of the RF power deliveredto an impedance equal to the characteristic impedance(ZO) of the transmission line between the thermistormount and the RF source. The label of each 8478B, 478Aor 486A thermistor mount contains calibration factorvalues.

The MOUNT RESISTANCE switch on the frontpanel compensates for three types of thermistor mounts.You can use Model 486A waveguide mounts by settingthe MOUNT RESISTANCE switch to 100 or 200Ω,depending on the thermistor mount. The 200Ω positionis for use with Models 478A and 8478B thermistormounts.

The rear panel baby N connector (BNC) labeledRECORDER (fig. 8-18) provides an output voltage that is

Figure 8-18.-Model 432A power meter rear panel.

linearly proportional to the meter current. One volt fedinto an open circuit equals full-scale meter deflection.This voltage develops across a 1-kilohm resistor.Therefore, when a recorder with a 1-kilohm inputimpedance is connected to the RECORDER output,about 0.5 volt will equal full-scale deflection. Thisloading of the RECORDER output has no effect on theaccuracy of the 432A panel meter.

You may connect a digital voltmeter to the rearpanel RECORDER output for more resolution of powermeter readings. When connecting a voltmeter with aninput impedance greater than 1 megohm to theRECORDER output, 1 volt equals full-scale deflection.

The 432A has two calibration jacks (VRF and VCOMP)on the rear panel. You can use them for precision powermeasurements. Instrument error can be reduced from ±1percent to ±0.2 percent of reading +5 µW. This dependson the care taken when measuring and on the accuracyof auxiliary equipment.

Some factors affect the overall accuracy of powermeasurement. The major sources of error are mismatcherror, RF losses, and instrumentation error.

In a practical measurement situation, both thesource and thermistor mount have SWR, and the

source seldom matches the thermistor mountunless using a tuner. The amount of mismatch lossin any measurement depends on the total SWRpresent. The actual thermistor mount impedance,the electrical length of the line, and thecharacteristic impedance of the line willdetermine the impedance that the source sees.

In general, neither the source nor thethermistor mount has impedance, and theactual impedances are only reflection coefficients,mismatch losses, or SWR. The power deliveredto the thermistor mount, hence the mismatch loss,can only be described as being somewhere betweentwo limits. The uncertainty of power measurementdue to mismatch loss increases with SWR. Limitsof mismatch loss are generally determined bymeans of a chart. To determine the totalmismatch loss uncertainty in power measurement,algebraically add the thermistor mount losses tothe uncertainty caused by source and thermistormount match.

RF losses account for the power entering thethermistor mount but not being dissipated in thedetection thermistor element. Such losses may bein the walls of a waveguide mount or in the centerconductor of a coaxial mount. Losses may alsobe from the capacitor dielectric, poor connectionswithin the mount, or be due to radiation.

The degree of inability of the instrument tomeasure the substitution power supplied to thethermistor mount is called power meter accuracyor instrumentation error. Instrumentation errorof the Model 432A is ±1 percent of full scale,0°C to +55°C.

Calibration factor and effective efficiencyare correction factors for improving powermeasurement accuracy. Both factors are markedon every HP thermistor mount. The calibrationfactor compensates for thermistor mount VSWRand RF losses whenever connecting the thermistormount to an RF source without a tuner. Effectiveefficiency compensates for thermistor mount RFlosses when using a tuner in the measurementsystem.

Set the 432A CALIBRATION FACTORselector to the appropriate factor indication onthe thermistor mount. This resulting powerindicates the power that would go from the sourceto a load impedance equal to The calibrationfactor does not compensate for source VSWR orfor multiple reflections between the source andthe thermistor mount.

You can minimize mismatch between thesource and the thermistor mount without a tuner.Insert a low SWR precision attenuator in the

transmission line between the thermistor mountand the source. Since the mount impedance (andcorresponding SWR) deviates significantly onlyat the high and low ends of a microwave band,it is unnecessary to use a tuner. A tuner or othereffective means of reducing mismatch error isrecommended when the source SWR is high orwhen more accuracy is necessary.

The HP Model 478A coaxial thermistor mount(fig. 8-19) is designed for use with HP Models 431and 432 power meters. It can measure microwavepower from 1 µW to 10 µW. The mount designminimizes adverse effects from environmentaltemperature changes during measurement. Forincreased measurement accuracy, effectiveefficiency and calibration factor are measured foreach mount and at selected frequencies across theoperating range. The results are marked on thelabel of the instrument. The Model 478A operatesover the 10-MHz to 10-GHz frequency range.Throughout the range, the mount terminates thecoaxial input in a 50-ohm impedance and has aSWR of not more than 1.75 without externaltuning.

Each mount contains two matched series pairsof thermistors, which cancel the effects ofdrift with ambient temperature change. Thermalstability is accomplished by mounting the leadsof all four thermistors on a common thermalconductor to ensure a common thermal environ-ment. This conductor is thermally insulated fromthe main body of the mount. The thermalinsulation makes sure thermal noise or shocksapplied externally to the mount, such as those

Figure 8-19.-Model 478A thermistor mount.

8-22

from handling the mount manually, cannotsignificantly disturb the thermistor. The thermalimmunity lets the thermistors be used to measuremicrowave power down to the microwatt region.

Q18. By what method is dc power determined?

Q19. You use a resistor that is specially designedto dissipate the required amount of powerand replace normal loads. List the two typesof resistors used for this purpose.

Q20. List the major sources of error that affectthe overall accuracy of power measure-ments.

SEMICONDUCTOR TESTERS

Since semiconductors have replaced vacuumtubes, the testing of semiconductors is vital. Inthis section, three basic types of equipment arediscussed—the Huntron Tracker 1000, HuntronTracker 2000, and the Automatic TransistorAnalyzer Model 900 in-circuit transistor tester.

Huntron Tracker 1000

You will test components with HuntronTracker 1000 using a two-terminal system, wheretwo test leads attach to the leads of the componentunder test. The 1000 tests components in-circuit,even when there are several components inparallel. The following types of devices are testedusing the Huntron Tracker 1000:

Semiconductor diodes

Bipolar and field effect transistors

Bipolar and MOS integrated circuits (bothanalog and digital)

Resistors, capacitors, and inductors

The 1000 is used on boards and systems withALL voltage sources in a power-off condition. A0.25 ampere signal fuse (F1) connects in series withthe channel A and B test terminals. Accidentallycontacting test leads to active voltage sources (forexample, line voltage, powered-up boards orsystems, charged high-voltage capacitors, etc.)may cause this fuse to open, making replacementnecessary. When the signal fuse blows, the displayshows open circuit signatures, even with the testleads shorted together.

CAUTION

The device to be tested must have all powerturned off and have all high-voltagecapacitors discharged before connectingthe 1000 to the device.

The line fuse (F2) should only open when thereis an internal failure inside the instrument.Therefore, you should always locate and correctthe problem before replacing F2.

The front panel of the 1000 makes functionselection easy. The 1000 uses interlocking push-button switches for range selection. A toggleswitch is used for channel selection, and integralLED indicators show the active functions.

The CRT displays the signatures of the partsunder test. The display has a graticule consistingof a horizontal axis that represents voltage, anda vertical axis that represents current. Thehorizontal axis is divided into eight divisions,which lets you estimate the voltage at whichsignature changes occur. This is mainly useful indetermining semiconductor junction voltagesunder either forward or reverse bias.

Push in the power on/off switch. The 1000should come on line with the power LEDilluminated.

Before you can analyze signatures on theCRT, you must focus the 1000. To do this, turnthe intensity control to a comfortable level. Now,adjust the focus control (back panel) for thenarrowest possible trace. Aligning the trace isimportant in determining the voltages at whichchanges in the signature occur. With a short circuiton channel A, adjust the horizontal control untilthe vertical trace is even with the vertical axis.Open channel A and adjust the vertical controluntil the horizontal trace is even with thehorizontal axis. Once set, you should not have toadjust these controls during normal operation.

Turn the power off by pushing the powerswitch in. When you turn the power on again, thesame intensity setting will be present.

The 1000 has three impedance ranges—low,medium, and high. To select these ranges, pressthe appropriate button on the front panel. Alwaysstart with the medium range; then you can adjustfor other ranges. If the signature on the CRT isclose to an open (horizontal trace), try the nexthigher range for a more descriptive signature. Ifthe signature is close to a short (vertical trace),try the next lower range.

There are two channels (channel A andchannel B) that you can select by moving the

8-23

toggle switch to the desired position. When usinga single channel, plug the red probe into thecorresponding channel test terminal. Then plugthe black probe into the common test terminal.When testing, connect the red probe to thepositive terminal of the device (that is, anode, +V,etc.). Connect the black probe to the negativeterminal of the device (that is, cathode, ground,and so forth.). By following this procedure, thesignature will appear in the correct position onthe CRT display.

The alternate mode of the 1000 provide-sautomatic switching back and forth betweenchannel A and channel B. This allows easycomparison between two devices or the same pointon two circuit boards. You select the alternatemode by moving the toggle switch to the ALTposition. The alternate mode is useful whencomparing a known good device with the samedevice whose quality is unknown.

The signal section applies the test signal acrosstwo terminals of the device under test. The testsignal causes current to flow through the deviceand a voltage drop across its terminals. Thecurrent flow causes a vertical deflection of the

signature on the CRT display. The voltage acrossthe device causes a horizontal deflection of thesignature on the CRT display. The combinedeffect produces the current-voltage signature ofthe device on the CRT display.

An open circuit has zero current flowingthrough the terminals and a maximum voltageacross the terminals. In the LOW range, adiagonal signature from the upper right to thelower left of the CRT (fig. 8-20, view A)represents an open circuit. In the HIGH andMEDIUM ranges, an open circuit shows as ahorizontal trace from the left to the right (fig.8-20, view B). When you short the terminalstogether, the maximum current flows through theterminals, and the voltage at the terminals is zero.A vertical trace from the top to the bottom of theCRT graticule in all ranges shows this short (fig.8-20, view C).

The CRT deflection drivers boost the low-leveloutputs from the signal section to the highervoltage levels needed by the deflection plates inthe CRT. The HORIZONTAL and VERTICALcontrols on the front panel adjust the position ofthe trace on the CRT display.

288XFigure 8-20.-Circuit signatures: View A—Low-range open circuit; view B—medium- and high-range open circuit; and

view C—all ranges short circuit.

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You use three other CRT controls to adjustthe brightness and clarity of the trace—INTENSITY, FOCUS, and ASTIGMATISM.The front panel intensity control is the primarymeans of adjusting the visual characteristics ofthe trace. The focus control is on the back paneland is operator adjustable. The astigmatism trimpot is inside the 1000 on the main printed circuitboard. The pot is factory adjusted to the correctsetting.

Huntron Tracker 2000

The Huntron Tracker 2000 (fig. 8-21) is aversatile troubleshooting tool having the followingfeatures:

Multiple test signal frequencies (50/60 Hz,400 Hz, 2000 Hz)

Four impedance ranges (low, medium 1,medium 2, high)

Automatic range scanning

Range control: high lockout

Adjustable rate of channeland/or range scanning

alteration

Dual polarity pulse generator for dynamictesting of three terminal devices

LED indicators for all functions

Dual channel capability for easycomparison

Large CRT display with easy to operatecontrols

GENERAL OPERATION.— You will testcomponents using the 2000 t wo-terminal system.It also has a three-terminal system when using thebuilt-in pulse generator. When using this system,you place two test leads on the leads of thecomponent under test. The 2000 tests componentsin-circuit, even when there are several parts inparallel.

Use the 2000 only on boards and systems withall voltage sources in a power-off condition. A0.25 ampere signal fuse connects in series with thechannels A and B test terminals. Accidentalcontact of the test leads to active voltage sources,such as line voltage, powered-up boards orsystems, and charged high-voltage capacitors maycause this fuse to open, making replacementnecessary. When the signal fuse blows, the 2000displays short circuit signatures even with the testleads open.

CAUTION

The device under test must have all powerturned off and all high-voltage capacitorsdischarged before connecting the 2000 tothe device.

288XFigure 8-21.-Huntron Tracker 2000.

8-25

Table 8-1.-Front Panel Controls and Connectors

288X

8-26

Figure 8-22.-Front panel.288X

The line fuse should only open when there isan internal failure inside the instrument. Alwayslocate the problem and correct it before replacingthis fuse.

Front Panel.—The front panel of the 2000makes function selection easy. All push buttonsare the momentary action type. Integral LEDindicators show which functions are active. Lookat figure 8-22 and table 8-1 for details about eachitem on the front panel.

Back Panel.— Secondary controls andconnectors are located on the back panel (fig. 8-23and table 8-2). Figure 8-23.-Back panel.

Table 8-2.-Back Panel Controls and Connectors

288X

288X

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CRT Display.— The signature of the partunder test is displayed on the CRT. The displayhas a graticule consisting of a horizontal axis thatrepresents voltage, and a vertical axis thatrepresents current. The axes divide the display intofour quadrants. Each quadrant displays differentportions of the signatures.

Quadrant 1 displays positive voltage (+V)and positive current (+I).

Quadrant 2 displays negative voltage (-V)and positive current (+I).

Quadrant 3 displays negative voltage (-V)and negative current (–I).

Quadrant 4 displays positive voltage (+V)and negative current (–I).

The horizontal axis divides into eight divisions,which allows the operator to estimate the voltageat which changes in the signature occur. This isuseful in determining semiconductor junctionvoltages under either forward or reverse bias.

OPERATION OF PANEL FEATURES.—The following section explains how to use thefront and back panel features.

Turn the power/intensity knob clockwise. The2000 comes on with the LEDs for power,channel A, 50/60 Hz, low range, and pulse/DCilluminated.

Focusing the 2000 display is an important partof analyzing the test signatures. First you adjustthe intensity control to a comfortable level. Then,adjust the focus control (back panel) for thenarrowest possible trace.

Aligning the trace is important in determiningwhich quadrants the portions of a signature arein. With a short circuit on channel A adjust thetrace rotation control until the trace is parallel tothe vertical axis. Adjust the horizontal controluntil the vertical trace is even with the vertical axis.Open channel A and adjust the vertical controluntil the horizontal trace is even with thehorizontal axis. Once set, you should not have toreadjust these settings during normal operation.

Range Selection.— The 2000 has fourimpedance ranges—low, medium 1, medium 2,and high. You select these ranges by pressing theappropriate button on the front panel. Start withone of the medium ranges; that is, medium 1 ormedium 2. If the signature on the CRT display

is close to an open (horizontal trace), select thenext higher range for a more descriptive signature,If the signature is close to a short (vertical trace),select the next lower range.

The high lockout feature, when activated,prevents the instrument from entering the highrange. This feature works in either the manual orauto mode.

The auto feature scans through the fourranges—three with the HIGH LOCKOUTactivated at a speed set by the RATE control. Thisfeature allows you to see the signature of a partin different ranges while freeing your hands tohold the test leads.

Channel Selection.— There are two channelson the 2000-channel A and channel B. You selecta channel by pressing the appropriate front panelbutton. When using a single channel, plug the redprobe into the corresponding channel testterminal. Plug the black probe into the commontest terminal. When testing, connect the red probeto the positive terminal of the device; that is,anode, +V, etc. Connect the black probe to thenegative terminal of the device; that is, cathode,ground, and so forth. Following this procedureshould assure that the signature appears in thecorrect quadrants of the CRT display.

The ALT mode is a useful feature of the 2000.It lets you compare a known good device with adevice of unknown quality. In this test mode, youuse common test leads to connect two equivalentpoints on the boards to the common test terminal.The ALT mode of the 2000 allows you toautomatically switch back and forth betweenchannel A and channel B so you can easilycompare two devices. You may also compare thesame points on two circuit boards. Select the ALTmode by pressing the ALT button on the frontpanel. You may vary the alternation frequencyby using the RATE control.

NOTE: The black probe plugs into thechannel B test terminal.

When using the alternate and auto featuressimultaneously, each channel is displayed beforethe range changes. Figure 8-24 shows the sequenceof these changes.

Frequency Selection.— The 2000 has three testsignal frequencies—50/60 Hz, 400 Hz and2000 Hz. You can select these by pressing theappropriate button on the front panel. In mostcases, you should start with the 50/60 Hz test

8-28

signal.

288XFigure 8-24.-Auto/alternate sequence.

Use the other two frequencies to view smallamounts of capacitance or large amounts ofinductance.

Pulse Generator.— The built-in pulsegenerator of the 2000 allows dynamic, in-circuittesting of certain devices in their active mode. Inaddition to using the red and black probes, youuse the pulse generator. The output of the pulsegenerator connects to the control input of thedevice under test with one of the blue micro clipsprovided. The pulse generator has two outputs,G1 and G2, so you can test three terminal devicesin the alternate mode.

A variety of output waveforms is availableusing the pulse generator selector buttons. Firstselect the pulse mode or the dc mode using thePULSE/DC button.

In the pulse mode, the LED flashes at aslow rate.

In dc mode, the LED is continuously on.

Then select the polarity of output desired usingthe positive (+) and negative (–) buttons. All threebuttons function in a push-on/push-off mode,and only interact with each other to avoid theNOT ALLOWED state.

After selecting the specific output type, set theexact output using the LEVEL and WIDTHcontrols. The LEVEL control varies the magni-tude of output amplitude from zero to 5 volts(peak or dc). During pulse mode, the WIDTHcontrol adjusts the duty cycle of the pulse outputfrom a low duty cycle to 50 percent maximum(square wave). The start of a pulse is triggeredby the appropriate zero crossing of the test signal.This results in the pulse frequency being equal tothe selected test signal frequency. The WIDTH

control setting that selects the duty cycledetermines the end of a pulse. The WIDTHcontrol has no effect when in the dc mode.

Troubleshooting Tips

You will use the Huntron Tracker 1000 andthe Huntron Tracker 2000 to test various typesof devices and circuits. Some troubleshooting tipsare given in this section.

Perform most tests using the medium orlow range.

Use the high range only for testing at ahigh impedance point, or if higher testvoltages are required (that is, to test theZener region of a 40-volt device).

Sometimes, component defects are moreobvious in one range than another. If asuspect device appears normal for onerange, try the other ranges.

Use the low range when testing a singlebipolar junction, such as a diode, a base-emitter junction, or a base-collectorjunction. It offers the best signature.

Use a higher range to check for reverse biasleakage.

When performing in-circuit testing, do adirect comparison to a known good circuit.

The 1000 test leads are not insulated at thetips, Be sure to make good contact to thedevice(s) under test. (NOTE: This tippertains to the 1000 only.)

When you troubleshoot, try relating the failuremode of the circuit under test to the type ofdefect the 1000 shows. For example, expect acatastrophic printed circuit board failure to havea dramatic signature difference from that of anormal device of the same type. A marginallyoperating or intermittent board may have a failedpart that shows only a small pattern differencefrom normal.

If you cannot relate a system failure to aspecific area of the printed circuit board, beginby examining the signatures at the connector pins.This method of troubleshooting shows all theinputs and outputs. It will often lead directly tothe failing area of the board.

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Devices made by different manufacturers,especially digital integrated circuits, are likely toproduce slightly different signatures. This isnormal and may not show a failed device.

Remember, leakage current doubles with every10-degree Celsius rise in temperature. Leakagecurrent shows up as a rounded transition (wherethe signatures show the change from zero currentflow to current flow) or by causing curvature atother points in the signatures. Leakage currentcauses curvatures due to its nonlinearity.

Never begin the testing of an integrated circuitusing the low range. If you initially use the lowrange, confusion can result from the inability ofthis range to display the various junctions. Alwaysbegin testing using the medium range. If thesignature is a vertical line, switch to the low range.Here you can check for a short or low impedance(less than 500 ohms). Switch to the low range ifthe device is suspect and appears normal in themedium range. This will reveal a defective inputprotection diode not evident when using themedium range.

NOTE: The 2000 test leads are conductiveonly at the tips. Be sure to make goodcontact with the device(s) under test.

When testing analog devices or circuits, usethe low range. Analog circuits contain many moresingle junctions. Defects in these junctions showmore easily when using the low range. Also, the54-ohm internal impedance in the low rangemakes it less likely that parts in parallel with thedevice under test will sufficiently load the testerto alter the signature.

When testing an op amp in-circuit, compareit directly to a known good circuit. This is becausethe many different feedback paths associated withop amps can cause an almost infinite number ofsignatures.

Often when checking a Zener diode in-circuit,it will not be possible to examine the Zener regiondue to circuit leakage. If you must see the Zenerregion under this condition, unsolder one side ofthe diode to eliminate the loading effects of thecircuit.

HUNTRON TRACKER 1000.— Bipolarintegrated circuits containing internal shortsproduce a resistive signature (a straight line). Thisline begins in the 10 o’clock to 11 o’clock position.It ends in the 4 o’clock to 5 o’clock position onthe display when using the low range. This typeof signature is always characteristic of a shorted

integrated circuit. It results from a resistive valueof 4 to 10 ohms, typical of a shorted integratedcircuit. A shorted diode, capacitor, or transistorjunction always produces a vertical (12 o’clock)straight line using the low range.

HUNTRON TRACKER 2000.— Bipolarintegrated circuits containing internal shortsproduce a resistive signature (a straight line)beginning in the 1 o’clock to 2 o’clock position.This signature ends in the 7 o’clock to 8 o’clockposition when using the low range. This type ofsignature is characteristic of a shorted integratedcircuit. This results from a resistive value of 4 to10 ohms. A shorted diode, capacitor, transistorjunction, etc., always produces a vertical (12o’clock) straight line when using the low range.

Automatic Transistor Analyzer Model 900

You can use this instrument to test bipolartransistors and diodes in any one of three differentmodes. Two modes, the VIS and SND, can beused either in-circuit or out-of-circuit.

In the VIS mode, red and green lightsflashing in or out of phase with the amber lightshow the condition of the device under test.

In the SND mode, the Sonalert™ alsoindicates good devices by beeping out of phasewith the amber light. The intent of the SND modeis to permit the operator to perform in-circuit testson transistors or diodes without having to lookat the light display.

The third mode is the METER mode. Youcan only use this for out-of-circuit testing. In theMETER mode, you may measure Beta, and material identity. Also, you can measureemitter base voltage, base current (Ib), andcollector current (Ic). There are four ranges forthe Beta mode—one for small signal transistors,two ranges for medium-power transistors, and onefor large-power transistors.

In the VIS mode and the SND mode, themaximum voltage, current and signal levelsapplied to the device under test are within safelimits. Therefore, the device under test will receiveno damage nor will any adjacent circuitry.

This instrument will test transistors and diodesin-circuit in the VIS or SND mode if the totaldynamic shunt impedances across the junctionsare not less than 270 ohms. Also, the total

8-30

dynamic shunt for the emitter to collector mustnot be less than 25 ohms. If such should occur,the test set will give the indication for a SHORT.

The 8-inch meter, which reads from left toright, has two scales marked 0-10 and 0-50. The0-10 range is used in the leakage collector currentand Vbe (IDENT) modes. The 0-50 range is usedin the BETA modes. Notice a mark on the meterjust short of half-scale with the nomenclatureGERMANIUM and SILICON. This mark is thereference in the IDENT mode. As the metermarkings show, those readings below the markshow the device material is germanium. Thereadings above the mark show the device is silicon.On the slanting horizontal panel immediately infront of the meter face are the appropriate testsockets and two push-button switches. One switchis ZERO and the other BETA. On the verticalfront panel immediately below the push-buttonswitches are knobs marked ADJ and CAL. At thetop center is the POLARITY switch marked PNPand NPN. In the center of the vertical front panelis the RANGE switch, the FUNCTION switch,and the Sonalert™. Near the bottom of thevertical front panel are the probe jacks. The slideswitch for turning the instrument on and off isalso in this location.

VIS MODE: TRANSISTOR.— To testtransistors with the visual indication only, turnthe FUNCTION switch to the XSTR-VIS mode.The amber light should flash at about a 1-secondrate. Insert the transistor under test in the propersocket.

In this mode, you perform two tests on thetransistor. The amber light shows the performanceof each test. When the amber light is out, this isthe EB-BC test mode. When the amber light ison, this is the emitter-collector test mode. The testshows good transistors by one pair of similarlycolored lights (green for NPN and red for PNP)when the amber light is off. When the amberlight is on, no lights show good transistors. Theleft-hand lights show the condition of thebase-collector. The absence of one or all lights inthe EB-BC test mode shows an open or opens.The occurrence of both a red and a green lighton either side in the EB-BC test mode shows ashort.

For more information about the Model 900tracker, refer to the Maintenance Manual, AllLevels for Automatic Transistor Analyzer Model900, ST810-AD-0PI-010, for patterns other thanthose just discussed. There are 96 possible patternslisted,

VIS MODE: DIODE.— You cannot properlytest diodes in the XSTER mode. To test a diode,insert the diode in the proper socket and turn theFUNCTION switch to the DIODE/VIS mode. Ifthe diode is good, a pair of green lights will flashout of phase with the amber. If a pair of red lightsflash out of phase with the amber light, thediode is either installed improperly or markedimproperly. If the diode has a short, additionallights will flash out of phase with the amber. Nolights will flash in phase with the amber.

You cannot properly test transistors in theDIODE mode. When testing transistors, only onetransistor should be in the test socket at one time.Do not leave any diodes in the diode socket whiletesting transistors. When testing diodes, do notleave transistors in the transistors sockets. If youdo not observe these precautions and the devicesleft in the socket are defective, incorrect lightindications will occur. These indications maymislead the operator into believing the deviceunder test is defective.

WARNING

Unit being tested must be disconnectedfrom ac outlet, and all capacitors capableof storing electricity should be discharged.

IN-CIRCUIT TESTING.— When testingdiodes in-circuit, attach the emitter lead to theanode of the diode. Attach the collector lead tothe cathode. When testing transistors, attach theleads to the right terminals as shown by theschematic. If the operator happens to fasten theleads to the transistor in the wrong order, anerroneous display will result. However, if thetransistor is good, the instrument will give a goodindication. The indication will be for the transistorof the opposite type. A good NPN improperlyconnected will give good PNP indications and viceversa. If the device is bad, the instrument will givea bad indication. You cannot make a qualitativeanalysis of the kind of failure unless you attachthe proper leads to the correct terminals.

To ensure the instrument will show the correcttype of transistor (PNP or NPN), you mustidentify the base lead. Use the following procedureto identify the base lead:

1. Disconnect the lead to the emitter terminalon the instrument. Only the light repre-senting the emitter junction should go out.

2. Reconnect the emitter lead.

8-31

3.

4.

5.

Disconnect the lead to the collectorterminal of the instrument. Only the lightrepresenting the collector junction shouldgo out.Should both lights go out during the tests,the connections are incorrect.Rearrange the leads on the transistor andperform-the tests again. You should nowsee the proper results.

There are six possible combinations forthe connection of these leads. Four of thesecombinations are incorrect. These will cause theinstrument to give an incorrect indication as totransistor type (PNP or NPN). The other twocombinations will give proper indications, but youstill may not know which leads are the emitter andcollector terminals. You will know whether thetransistor is good and whether it is an NPN ora PNP transistor. If you must know which leadsare the emitter and collector terminals, it ispossible to find out after identifying the base leadusing the meter mode for Beta.

SND Mode.— In either the XSTR/SND modeor DIODE/SND mode, light patterns showinggood devices will have an accompanying beepingsound from the Sonalert™. The beeping will beout of phase with the amber light.

METER Mode.— Before testing a transistorin any of the METER modes, you should test thetransistor in one of the visual modes. This willtell you whether the transistor is an NPN or aPNP. After determining this, put the POLARITYswitch in the proper position to agree with theindication in the visual mode.

Beta.— To test the Beta of the transistor, setthe FUNCTION switch to the BETA position.Next, set the RANGE switch to the appropriateposition according to the power capability of thetransistor under test. After the RANGE switchis in the proper position, operate the push-buttonswitch marked ZERO. Now adjust the ADJ knobfor a zero reading on the meter. Next, actuate thepush-button switch marked BETA and adjust theCAL knob for full-scale deflection, Release theBETA push-button switch; now the Beta of thedevice will show on the meter. Take care inselecting the Beta range to test the transistor. Itis possible to damage small signal transistorsshould you try to test them in the 2 mA Ib(LG. PWR. XSTR) mode.

Leakage: or To test a transistor for or set the FUNCTION switch on the

proper position. Next, set the RANGE switch tothe 100 mA position. Then push the switchmarked ZERO and adjust the ADJ knob for azero reading on the meter. Now release the ZERObutton. Set the RANGE switch on the lowestleakage range, which will still permit less thanfull-scale deflection on the meter. You may nowread the leakage directly off the meter. Read the

first and then Use this order because themeter will read down scale when switching from

to Also, you can increase the metersensitivity. However, if you read first andthen switch to the meter will read up scale.It is now possible to peg the meter. Although themeter has protection, avoid undue abuse.

Material Identity: Transistor.— To use thisinstrument in the IDENTITY mode, set theFUNCTION switch to IDENT. Check the ZEROADJUST on the meter as mentioned before. Aftersetting the ZERO, release the ZERO push button.Now note whether the needle reads above orbelow the mark on the meter face just short ofhalf scale, If the meter reads below the mark, thedevice is a germanium transistor. If it readsabove the mark, it is a silicon transistor. Thisinformation can be extremely useful when tryingto substitute transistors.

Leakage: Diode. — To test the reverse leakageof diodes, install the diode in the diode socket.You now determine whether the diode is good bytesting the device in the visual mode. Once youdetermine that the diode is good, place thePOLARITY switch to NPN. Turn the FUNC-TION switch to the mode, and set theRANGE switch to 100 mA. Now check to see thatthe meter is at zero, as mentioned before. Afterzeroing the meter, set the RANGE switch on thelowest range possible that still permits less thanfull-scale deflection on the meter. Read theleakage on this range.

Material Identity: Diode.— To test the materialidentity of a diode with the diode properlyinstalled in the socket, place the POLARITYswitch in the PNP position (zero the meter) andthe FUNCTION switch in the IDENT position.Using the leads, short the base and collectorterminals together. The meter will show eithergermanium or silicon as described before in theIDENT mode for transistors.

8-32

CAUTION

Do not identity test transistor material withthe base and collector leads shortedtogether. This may create an erroneousreading.

Model 109 Probe

The Model 109 probe, used with the Model900 tester, is easy to use, having one-handoperation. It automatically adjusts to any spacingbetween one-thirty second inch to five-eighthsinch. You can rotate each probe point in a full360-degree circle. The points are individuallyspring loaded for proper contact. You can connectthe probe to three printed circuit boardterminations. The probe has the extremely lowcontact resistance of less than .005 ohm. The useof the probe eliminates unsoldering while makingin-circuit tests of transistors, diodes, ICs, andother components. Finally, the retractable cordstretches to a full 12 feet.

DESCRIPTION.— The Model 109 three-pointprobe speeds servicing of printed circuitassemblies that have transistors, diodes, and mostother board-mounted components. You can makeinstant connections to three points on a printedcircuit board. You will make rapid evaluation oftransistors using the Model 109 probe withthe Model 900 automatic transistor analyzerin-circuit. You can accomplish a complete test ofall stages in a piece of electronic equipment in amatter of minutes. You can also use the Model109 to make temporary component substitutionson the printed circuit board.

OPERATION.— Connect the leads of theModel 109 probe to an appropriate piece of testequipment. Determine the connection points onthe printed circuit board to connect to the testequipment. Apply the Model 109 probe points tothe circuit board. Press the probe toward theboard to ensure a good connection. The Model109 probe green point is slightly shorter than theyellow and blue probe points. This allowsconnection of the collector and emitter before thebase to provide maximum ease of use.

The Model 109 probe is a valuable aid whenmaking resistance and voltage measurementsusing a conventional VOM or VTVM. Use theyellow and blue probe points as the negative andpositive meter feeds. You can make rapidevaluations of entire circuits faster than with any

other method because each point pierces throughconventional resist coatings and solder residues.

Q21.

Q22.

Q23.

Q24.

Q25.

The Huntron Trackers 1000 and 2000 arefor use on circuit boards and systems withall voltage sources in what condition?

What mode on the automatic transistoranalyzer Model 900 has the Sonalert™?

What type signal display does the HuntronTrackers 1000 and 2000 show when thesignal fuse is open and the test leads shortedtogether?

When using the Huntron Tracker 2000, whymust you make good contact with the testleads?

What is the minimum total shunt im-pedance across the junction of the diodeor transistor under test using the automatictransistor analyzer Model 900 to ensure agood test reading?

SIGNAL GENERATORS

Learning Objective: Recognize charac-teristics and identify the uses of signalgenerators to include frequency-modulatedand pulse-modulated signal generators.

Standard sources of RF energy are used tomaintain airborne electronic equipment. Theseenergy sources are called signal generators. Theprincipal function of the signal generator is toproduce an alternating voltage of the desiredfrequency and amplitude. The generated signalmay be modulated or unmodulated, dependingon the test or measurement in question. Whenusing the signal generator, the output signalcouples into the circuit under test. You trace itsprogress through the equipment by using ahigh-impedance device such as a VTVM or anoscilloscope.

RF SIGNAL GENERATORS

Radio-frequency signal generators comprise arather large and very useful class of testequipment. Because of the extremely widefrequency range in the RF region of the spectrum,many signal generators, with different RF ranges

8-33

as well as other instrument refinements, areavailable.

FREQUENCY-MODULATED RFSIGNAL GENERATORS

Many types of frequency-modulated (FM)signal generators are available for your use;however, some are used for special applications.The following discussion of FM generatorsprovides basic information that applies to mostFM generators.

An FM signal is one in which the outputfrequency varies above and below a centerfrequency. The overall frequency variation isknown as the frequency swing (or deviation). Therate at which this swing recurs is controllable atany audio- or video-frequency rate for which thegenerator is capable. The frequency change ofthe output is accomplished by the mechanicalvariation of either the capacitance or inductanceof the oscillator circuit or by the use of a reactancetube connected to the oscillator circuit. In thelatter case, changes of the voltage impressed onthe grid of the reactance tube change the amountof reactance introduced into the oscillator-tunedcircuit. As a result, it causes the output frequencyto change. The frequency of the signal on the gridof the reactance tube thereby controls the rate offrequency deviation. The amplitude of the signalvoltage controls the amount of the deviation.

A sweep generator is a form of an FM signalgenerator. Its carrier deviation is adjustable bya sweep-width control. The sweep generatordiffers from the ordinary FM signal generatorbecause it maintains the rate of carrier deviationat a fixed frequency. The voltage used to effectthe deviation is either a sine wave or a sawtoothwaveform. You use an oscilloscope to observe thepatterns formed when the passband of interest is

swept by this type of generator. The oscilloscopetime base must use (or be synchronized with) thesame waveform used to produce the deviation.The horizontal (or time) axis of the patternrepresents the instantaneous frequency of thegenerator output. The vertical axis shows theresponse characteristic of the circuit under test foreach frequency. Sweep generators are widely usedfor observing the response characteristics and thevisual alignment of tuned circuits. The sweepgenerator is used to check the bandwidth of IFamplifiers used in radar receivers.

Deviation of the carrier may occur eitherelectromechanically or electronically. The electro-mechanical method consists of mechanicallyvarying the capacitance or the inductance of theoscillator tank circuit, causing the frequency tovary accordingly. The electronic method makesuse of a reactance-tube modulator.

A sweep generator produces patterns con-taining a considerable number of instantaneousfrequencies. Marker signals, which are super-imposed on the trace, are introduced. Thesesignals orient passband characteristics (or centerfrequency) of the circuit under test with respectto frequency. The circuit that produces the markersignals may be an integral part of the instrument,or the marker signals may come from an externalsource.

Most modern frequency-swept signal genera-tors use a reactance-tube method of modulation.Modulation of this type results in greaterflexibility. Also, the equipment is lighter and morecompact than rotating capacitor equipment.

The reactance tube and its associated com-ponents are connected across the tank circuit ofthe oscillator in the signal generator. Often,the ac power line, which provides an excellentoscilloscope-synchronizing medium, couples tothe grid of the reactance tube to control the rate

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of the sweep. The reactance-tube modulator hasan advantage over electromechanical modulatorsbecause it can be excited by an external variableAF signal generator. The electromechanicalmodulator is usually limited to single-frequencyoperations.

PULSE-MODULATED RF SIGNALGENERATORS

A pulse-modulated (PM) RF signal generatoris similar to the conventional RF signal generator.It differs in its output, which consists of RF energyin the form of pulses that occur at an audio rate.The generator controls can vary the pulsewidth(duration of each pulse) and the repetition rate(number of pulses per second). The PM generatoris commonly used to check receiver performanceof many radar systems that have a pulse-typeemission.

A conventional oscillator circuit generates aconstant RF carrier to produce pulse-modulatedRF signals. This energy goes to the grid of a mixerstage, which has at the same time impressed onits suppressor grid a square wave generated in a

separate circuit. The positive half-cycles of thesquare wave allow the mixer tube to conduct, andthe negative half-cycles cut the tube off. Duringthe conducting intervals, the RF signal on thecontrol grid varies the plate current. Therefore,pulses of RF current, corresponding to the positivehalf-cycles of the square wave, appear in themixer plate circuit. The pulses normally go toone or more amplifier stages. Controls in thesquare wave circuit vary pulse time and repetitionrate.

The Model 628A SHF signal generator(fig. 8-25) is a general-purpose broadband signalgenerator that produces RF output voltages from15 GHz to 21 GHz. A single control determinesthe output frequency, which is directly read ona dial calibrated to an accuracy of ±1 percent orbetter.

The 628A signal generator has some versatilemodulation characteristics. It is possible tofrequency modulate, square-wave modulate, orpulse modulate the output by internally orexternally generated signals. The 628A alsoprovides synchronizing pulses for use withexternal equipment.

Figure 8-25.-Model 628A SHF signal generator front panel.

8-35

In addition to producing an accurate andcontrollable RF signal, you can use the 628Asignal

Q26.

Q27.

Q28.

Q29.

generator to

test pulse systems,

measure sensitivity and selectivity ofamplifiers, receivers, and other tunedsystems,

measure signal-to-noise ratio of RF signals,

make slotted line measurements,

investigate microwave impedances andother transmission line characteristics,

measure frequency response of microwavesystems, and

determine resonant frequency and Q ofwaveguide cavities.

What is the principal function of the signalgenerator?

While various types of FM signal generatorsare available, many are restricted to specialapplications. What type is used for generalapplications?

Most frequency-swept signal generators usea reactance-tube method of modulation.What is the reason for this?

What is a common application for pulse-modulated generators?

SIGNAL ANALYZERS

Learning Objective: Identify signalanalyzers to include signal analysis andwaveform measurements including Oscope, synchroscope, spectrum analyzers,and distortion analyzers.

Signal analyzers, while used in many differentsituations, are normally used for one purpose—to check the response of an equipment undersimulated conditions of specific operations.

WAVEFORM MEASUREMENT

Waveform measurements are made by observ-ing displays of voltage and current variations

with respect to time or by harmonic analysisof complex signals. Waveform displays areparticularly valuable for adjusting and testingpulse-generator, pulse-former, and pulse-amplifiercircuits. The waveform visual display is also usefulfor determining signal distortion, phase shift,modulation factor, frequency, and peak-to-peakvoltage.

You can use harmonic analysis test sets todetermine the energy distribution in electricalsignals. Frequency-selective circuits separate thesignals into narrow frequency bands. The energyin each band is indicated by a meter or displayedon a CRT. By connecting a group of frequency-selective circuits in parallel, you can manually orautomatically tune a single frequency-selectivecircuit. You can also use a heterodyne method(using a sweep generator and fixed-tuned circuit)to select electrical power present in a narrowfrequency band.

OSCILLOSCOPE

An oscilloscope or O scope is an electronic testset that displays information on the face of itsCRT. There are many ways you can use anoscilloscope; however, its primary use is introubleshooting and aligning electronic equip-ment. You do this by observing and analyzingwaveform shape, amplitude, and duration. Themaintenance instruction manual (MIM) for theparticular equipment specifies the waveformsthat you should see at the various test pointsthroughout the equipment. Waveforms at any oneselected test point may differ, depending onwhether the operation of the equipment is normalor abnormal.

Figure 8-26 is a typical display you may seeon a cathode-ray oscilloscope. This illustrationshows the instantaneous voltage of the waveplotted against time. The elapsed time equates tothe horizontal distance (view A), from left toright, across the etched grid (graph) placed overthe face of the tube. The amplitude of the waveis the vertical measure (view B) on the graph.

The oscilloscope also provides picture changesin quantities other than voltages in electric circuits.If an electric current waveform is of interest, youcan usually send the current through a small seriesresistor and look at the voltage wave across theresistor with the oscilloscope. There are alsosuitable transducers that change other quantitiessuch as temperature, pressure, speed, andacceleration into voltage for display on theoscilloscope.

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Figure 8-26.-Typical waveform display: (A) measure-ment of elapsed time; (B) measurement of voltagedifference.

Interpreting the Display

As you read this paragraph, look at figure8-26. Find the elapsed time between two pointson the graph (view A, points A and B). Multiplythe horizontal distance between these points inmajor graduated divisions by the setting of theTIME/DIV (time per division) control. Thiscontrol sets the horizontal sweep rate of theoscilloscope. The distance between points A andB is 4.5 major divisions. If the TIME/DIV controlis set at 100 microseconds per division, thenthe elapsed time between points A and B is4.5 x 100 = 450 microseconds. In general,elapsed time = horizontal distance (in divi-sions) x TIME/DIV setting.

If you are using the MULTIPLIER controlwith the TIME/DIV control, multiply the aboveresult by the setting of the MULTIPLIER. If aMAGNIFIER is in operation, divide the result bythe amount of magnification.

Again, look at figure 8-26. To find the voltagedifference (view B, points A and B) between anytwo points on the graph, multiply the verticaldistance between these points (in major graduateddivisions) by the setting of the VOLTS/DIVcontrol. This control sets the vertical deflectionfactor, or sensitivity, of the oscilloscope. Thevertical distance between points A and B is

4.0 divisions. If using the VOLTS/DIV controlat 0.5 volt per division, then the voltagedifference between points A and B must be4.0 x 0.5 = 2.0 volts.

You can express the quantity called pulserepetition rate (or pulse repetition frequency) forperiodic pulses as the number of pulses per unitof time. For example, 10 pulses per secondand 50 pulses per microsecond. In using theoscilloscope to measure the frequency orrepetition rate of periodic waveforms, you readthe horizontal distance in major divisions betweencorresponding points on two succeeding wavesfirst. This is the horizontal distance occupied byone cycle of the wave. Multiply this by the settingof the TIME/DIV control in seconds, milli-seconds, or microseconds. Determine thereciprocal of this product; that is, divide 1 by theproduct. The result is the desired frequency orrepetition rate.

Square waves, rather than other forms ofwaves, are usually used to test equipment. Byusing square waves, you can see more than justa defect’s presence; you can see the nature of thedefect. The nature of the defect is suggested bythe kind of distortion that occurs on a squarewave. By observing the square wave response,you, the technician, can easily tell whether thetransmission of low or high frequencies isaffected. However, this observation is not so clearwith regard to frequency with waves other thansquare waves.

Linear devices that give identical responses tosquare wave inputs generally give responsessimilar to each other when other waveforms areinput to them.

Information Contained in a Square Wave

A periodic wave contains the followingcomponents:

1. A fundamental wave, which is a sine wavehaving a frequency equal to the repetitionfrequency of the square wave.

2. An infinite series of odd harmonics—sinewaves having frequencies that are equal towhole numbers multiplied by the funda-mental frequency. The harmonics mustbe in phase and in amplitude to thefundamental.

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Waveform D of figure 8-27 depicts a periodicrectangular wave (square wave). With the squarewave, the only harmonics present are the oddharmonics (those whose frequencies are equal tothe fundamental frequency multiplied by oddwhole numbers). The strengths of the harmonicsvary in inverse proportion to the frequencies ofthe harmonics, the fifth harmonic being one-fifthas strong as the fundamental, for example. Figure8-27 suggests a way in which these waves combineto make up a square wave.

By looking at the four curves shown in figure8-27, you can see that

1. curve A is the fundamental sine wave,2. curve B is the sum of the fundamental and

third harmonic,3. curve C is the sum of the fundamental plus

third and fifth harmonics, and4. waveform D is the ultimate square wave.

You can see by looking at figure 8-27 that thefirst few harmonics combine with the fundamentalto provide an approach to an actual square wave.

Figure 8-27-Addition of harmonics to a fundamentalwaveform.

Additional harmonics, of higher frequencies,would cause the leading edge of the wave to risemore rapidly. This will produce a sharper cornerbetween the leading edge and the top of the wave.It would require an infinite range of harmonicsto produce a truly vertical leading edge and anactual sharp corner. Although this situation isphysically impossible to produce, waves can begenerated that are very close to this ideal. (Thesame considerations apply to the falling edge ofthe waveform and to the following corner.)

You can find information about the amplitudeand phase relationships of the higher harmonicswithin the leading-edge steepness and in thesharpness of the corner.

If low-frequency components (fundamentaland the first few harmonics) are not present inthe proper amounts and in the correct phaserelationships, the flat top of the square wave isaffected. Refer to figure 8-28. View A shows the

Figure 8-28.-Information found in a square wave.

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location of the low- and high-frequency low-frequency components have lagging phaseinformation in a square wave. Low-frequency angles and are accentuated.defects appear in the form of slope or generalcurvature in the top (views B and C). In view B,

Oscilloscope Block Diagram

the low-frequency components have leading phase Figure 8-29 is a block diagram of a typicalangles and are attenuated. In view C, the oscilloscope, omitting power supplies. The

Figure 8-29.-Typical oscilloscope block diagram.

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waveform (A) is input into the vertical amplifierinput. The calibrated VOLTS/DIV control setsthe gain of this amplifier. The push-pull outputs(B and C) of the vertical amplifier go through adelay line to the vertical deflection plates of thecat bode-ray tube.

The time base generator or sweep generatordevelops a sawtooth wave (E) that is a horizontaldeflection voltage. The rising or positive-goingpart of this sawtooth, called the runup portionof the wave, is linear. It rises through a givennumber of volts during each unit of time. Thisrate of rise is set by the calibrated TIME/DIVcontrol. The sawtooth voltage goes to the timebase amplifier. This amplifier supplies two outputsawtooth waveforms (G and J) simultaneously—one of them positive-going, like the input, andthe other negative-going. The positive-goingsawtooth goes to the right horizontal deflectionplate of the CRT, and the negative-going sawtoothgoes to the left deflection plate. As a result, thecathode-ray beam sweeps horizontally to the rightthrough a given number of graduated divisionsduring each unit of time. The TIME/DIVCONTROL establishes the sweep rate.

To maintain a stable display on the CRTscreen, each horizontal sweep must start at thesame point on the waveform. To accomplish this,a sample of the displayed waveform goes to atrigger circuit, which gives a negative outputvoltage spike (D) at some selected point on thedisplayed waveform. This triggering spike startsthe rising portion of the time base sawtooth. Asfar as the display is concerned, then, triggeringis synonymous with the starting of the horizontalsweep of the trace at the left side of the grid.

The rectangular unblanking wave (F) isderived from the time base generator goes to thegrid of the CRT. The duration of the positive partof this rectangular wave corresponds with theduration of the positive-going or rising part of thetime base output. The beam is switched on duringits left-to-right travel and switched off during itsright-to-left retrace.

Often, the leading edge of the displayedwaveform actuates the trigger circuit. However,it may be desirable to observe this leading edgeon the screen—and the triggering and unblankingoperations require a measurable time (P), oftenabout 0.15 microsecond. To see the leading edge,a delay (Q) of about 0.25 microsecond isintroduced by the delay line in the verticaldeflection channel. The delay occurs after thepoint where the sample of the vertical signal istapped off and fed to the trigger circuit.

The purpose of the delay line is to retard theapplication of the observed waveform to thevertical deflection plates. This occurs until thetrigger and time base circuits have had anopportunity to begin the unblanking and hori-zontal sweep operations. This permits viewing theentire desired waveform—even though the leadingedge of that waveform was used to trigger thehorizontal sweep. If the delay line were not used,only that portion of the waveform following theinstant (T) in waveform (B) could be seen.

Oscilloscope Probe

The input circuit to the vertical amplifier(fig. 8-30) of an oscilloscope can be simulated bya high resistance (R) shunted by a small shuntcapacitance (C).

In some applications, even this high resistanceand small capacitance can produce undesirableloading on the circuit whose waveforms are beingexamined by means oft he oscilloscope. Loadingcan cause the oscilloscope presentations to bedifferent from the waveforms that would bepresent with the oscilloscope disconnected. Useof a passive probe reduces this resistive-capacitiveloading on the circuit under investigation.

The probe (fig. 8-31) includes a resistor shunted by a capacitor This combination isconnected in series with the inner conductor ofthe cable to the oscilloscope input. The result isthat when connecting the probe to the circuitunder investigation, a new effective loadingcapacitance smaller than the original capacitance(C) and a new effective loading resistance largerthan the original resistance (R) occurs. Thus,the probe reduces the loading effect of theoscilloscope input circuit on the circuit underinvestigation.

A second effect of the probe is to reduce theamount of signal voltage applied directly to the

Figure 8-30.-Oscilloscope vertical amplifier input circuit.

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Figure 8-31.-Oscilloscope vertical amplifier using a passive probe input.

oscilloscope input connection for a given amountof original signal voltage. This occurs because ofthe voltage-divider action of and R. This effectis taken into account in the attenuation ratiomarked on the probe. Thus, if the probe is a10 x ATTEN, all oscilloscope voltage indicationsmust be multiplied by 10.

If an oscilloscope equipped with a probe isused to look at a square wave, and the probecapacitor is too small, some of the high-frequency components of the square wave arebypassed around the oscilloscope input terminalsby the input capacitance (C). Thus, the steepnessof the leading edge of the displayed square wave(fig. 8-32, view A) is reduced.

If the probe capacitor is adjusted to the correctvalue, a compensating amount of high-frequencyinformation is bypassed around the probe resistor

Figure 8-32 .-Effects of probe adjustment.

(fig. 8-31). To makeup for the loss throughC (fig. 8-31), the leading edge of the displayedsquare wave is restored to its original steepness(fig. 8-32, view B). If (fig. 8-31) is made toolarge, the high-frequency response of the circuitis overcompensated and applies too much high-frequency information to the oscilloscope inputconnection. This results in an overshoot in thedisplayed waveform (fig. 8-32, view C) that wasnot present in the original waveform. (fig.8-31) is adjusted to its correct value by using theprobe to display the square wave generated by thevoltage calibrator, which is a part of theoscilloscope. Adjustment is made to display asquare wave with as flat a top as possible.

You must check the probe adjustmentwhenever you use a probe with an oscilloscopeor a plug-in preamplifier. This is especiallyimportant if the previous use was with an inputcapacitance different from that of the instrumentto which you are now connecting the probe.

NOTE: As indicated in figure 8-31, theattenuation achieved is a result of R as wellas Though you may swap probes withother types of oscilloscopes, the calibrationmay be in error even though the waveformdistortion may adjust out.

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SYNCHROSCOPE

The synchroscope is an adaptation of theoscilloscope. Its normal use is for radarapplications. A trace occurs only with an inputtrigger, as contrasted with the continuoussawtooth sweep provided by the oscilloscope.Synchroscope circuits are similar to oscilloscopecircuits, with the exception of the signal and thesweep channels. Figure 8-33 shows these circuitsin block diagram form.

The signal channel of a typical synchroscopeincludes an input circuit that is usually in the formof a 72-ohm adjustable-step attenuator. Variousdegrees of attenuation are available, and thecalibrated dial indicates how much attenuation ispresent. The attenuator makes sure all signals,regardless of amplitude, produce about the sameinput level to the amplifier section.

Following the attenuator is an artificial delayline. This low-pass filter has a cutoff frequencyhigher than the highest passed frequency and animpedance of 72 ohms. The delay line terminatesinto a 72-ohm gain control. One purpose of thedelay line is to delay presentation of the observedsignal. The delay lasts until an undelayed portionof the input signal initiates the sweep trace.Without the delay line, the initial portion of thewaveform would not appear on the trace. Thiswould occur because a certain amount of time isnecessary for the input signal voltage to rise tothe level needed to trigger the sweep circuit. Withthe delay line in use, the signal does not reach the

amplifier until one-half microsecond after thetrace starts. As a result, you can see the entirepulse. A secondary purpose of the delay line isto provide, by reflection, a series of accuratelyspaced pulses suitable for calibration of short timeintervals.

A switch causes a mismatch in the terminationof the delay line, causing the secondary purpose.When a sharp pulse is input into the line, a seriesof reflections occurs similar to those shown infigure 8-34. Since the time required for a pulseto travel down the line and back is 1 microsecond,a series of pulses occurring 1 microsecond apartoccur. Each successive pulse is smaller because ofthe losses in the delay line, but enough pulses arevisible for most high-speed calibration purposes.

The gain control feeds a wideband or videoamplifier, which connects to the vertical deflectionplates. In addition, an external connection isprovided to the vertical plates.

The horizontal circuit consists of a sync switchfor either internal or external sync, a syncamplifier with a gain control, and a start-stopsweep generator. The sweep generator will notdevelop a sweep voltage until it receives a pulseof enough amplitude. The duration of the sweep,or sweep speed, is adjustable from a very fewmicroseconds to about 250 microseconds. Thesweep generator connects to a conventionalhorizontal amplifier. Since the trace is triggeredby the input signal, the synchroscope may be usedto observe nonperiodic pulses; for example, the

Figure 8-33.-Typical synchroscope block diagram.

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Figure 8-34 .-Pulse reflection on a mismatched line.

nonperiodic pulses occurring in a radar systemwith an unstable PRF generator.

In later designs, provisions are commonlymade for calibration of input voltages and sweeptime. Voltage calibration is made by comparingthe unknown voltage with a variable-voltage pulseof known value, generated internally. Thecalibrating pulse is adjusted so it is equal inamplitude to the unknown voltage. You can thenread the value from the dial that controls thecalibrating pulse. Sweep time calibration occurswith the help of marker pulses produced byaccurately adjusted tuned circuits. The markerpulses appear on the trace as a series of bright dotsspaced at intervals chosen by the operator. In atypical synchroscope, you may select markerintervals of 0.2, 1, 10, 100, and 500 microseconds,depending on the time duration of the pulse undertest.

Q30.

Q31.

Q32.

Q33.

Signal analyzers can be used in manyapplications. It is used for what function?

What determination can you make byobserving the square wave response?

Look at figure 8-28. At what point on asquare wave does low- and high-frequencyinformation appear?

An oscilloscope probe reduces the loadingeffect of the O-scope input circuit on thecircuit under test. What is the secondpurpose of the probe?

Q34. The synchroscope is an adaption of the—oscilloscope. What is the difference of thetrace on the synchroscope and oscilloscope?

SPECTRUM ANALYZER

When a radio-frequency carrier wave ismodulated by keying, speech or music, or pulses,the resulting wave contains many frequencies. Theoriginal carrier is present, together with twogroups of new frequencies (sideband com-ponents). One group of sidebands is displaced infrequency below the carrier. The other group isdisplaced above the carrier. The distribution ofthese frequencies, when shown on a graph ofvoltage or power against frequency, is called thespectrum of the wave.

A spectrum analyzer is a device used to exhibitthe spectrum of modulated waves in the radio-frequency range and the microwave region. Inprinciple, the spectrum analyzer operates bytuning through the frequency region in question,using a narrow band receiver. A cathode-rayoscilloscope usually measures the output of thereceiver, and the plot on the screen is a graph ofvoltage versus frequency. The device is essentiallya superheterodyne receiver with a very narrow-band intermediate frequency amplifier section.The local oscillator frequency varies between twovalues at a linear rate. The frequency-controlgenerator governs the frequency of the localoscillator. It also produces the horizontal sweepvoltage for the CRT deflection plates. (See

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Figure 8-35.-Typical spectrum analyzer block diagram.

fig. 8-35.) As a result, each position of the beamcorresponds to a definite frequency value, and thedisplay is a graph in which the X-axis is interpretedin terms of frequency.

The output of the receiver detector is amplifiedand goes to the vertical deflection plates. Thebeam deflects vertically by an amount pro-portional to the voltage developed in the detector(and amplifier).

The signal for analysis goes into the mixerstage of the receiver. The local oscillator changesin frequency at a linear rate, beating with eachof the signal frequency components in succession

to form the intermediate frequency of thenarrowband amplifier. The output of the IFamplifier is detected, amplified, and applied tothe vertical deflection plates.

Spectrum analyzers designed for analysis ofmicrowave signals have klystron tubes in the localoscillator stage. Analyzers adapted for lowerfrequency RF signals use triode oscillators thatvary through reactance-tube modulators.

Spectrum analyzers are the main tool forstudying the output of pulse-radar transmittertubes, such as magnetrons. In this kind ofanalysis, unwanted effects, such as frequency

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Figure 8-36.-Frequency spectra.

modulation of the carrier, are easy to detect. Inpure amplitude modulation of a carrier wave bya square pulse, the spectrum is symmetrical aboutthe carrier frequency. Lack of symmetry indicatesthe presence of frequency modulation. Look atview A of figure 8-36. It shows a spectrumrepresenting the ideal condition. Views B and Cshow examples of undesirable magnetron spectra.These forms indicate trouble in the modulator,the tuning system, or in the magnetron tube itself.

The best definition of carrier frequency is thecenter frequency in a symmetrical spectrum (fig.8-36, view A). Some analyzers use this principleas a means of carrier frequency measurement. Asharply resonant circuit in the receiver acts as atrap to prevent an extremely narrow range offrequencies from appearing in the output of theIF amplifier. The result of its use is a gap thatappears in the display, and the gap correspondsto the resonant frequency of the trap. Theadjustment of the trap is calibrated in frequency,and the circuit can be adjusted to make the gap

occur in the center of the spectrum. You can thenread the frequency of the carrier from thecalibration of the trap.

For more information about spectrumanalyzers, refer to NEETS, module 16. Inaddition, the EIMB Test Methods and Practices,NAVSHIPS 0967-LP-000-0130, contains detaileddiscussions of spectrum analysis techniques.

Echo BOX

The echo box is for use in field testing,troubleshooting, and adjusting pulsed-type radarsystems. Although simple in construction andoperation, it has many applications. If properlyused within its design limitations, the echo boxcan frequently eliminate the need for a complextest setup and an elaborate step-by-step testingprocedure. The echo box uses passive circuitry,which does not require any external power otherthan the radar set whose signal is under analysis.External power requirement is a critical factorwith most other test sets.

The echo box is similar in operation to a tunedcavity frequency meter; however, it has differentcapabilities. The tuned cavity frequency meter canmeasure the frequency of CW or pulsed RFsignals in the microwave range. The echo box,however, has no practical application in the testingor analysis of CW equipment signals. Figure 8-37indicates the basic functional elements of a typicalecho box.

Energy from the radar transmitter goesthrough the directional couplers to the resonant

Figure 8-37.-Typical echo box functional circuit.

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cavity. When the cavity length is properlyadjusted, resonant oscillations are set up by eachsuccessive pulse of microwave energy. Maximumamplitude of oscillation occurs when the cavityis tuned precisely to the signal frequency. Thecrystal diode detects these cavity oscillations andindicates them on the meter as an average dccurrent. The amplitude of oscillation and theaverage current reading are proportional to thetransmitter power output. Oscillations in thetuned cavity also couple back to the radar setunder test, where they are processed as an echosignal. This signal, when viewed on the indicatorCRT, permits analysis of the radar pulse andpresents an indication of the general operatingcondition of the radar set.

Since energy builds up in the cavity, saturationof the cavity is possible. If saturation does occur,distortion of the waveform and erroneous valuesof the measurements result. If the directionalcouplers do not prevent cavity saturation, theremust be some additional attenuation.

Analysis of the displayed waveform canprovide a fairly complete functional analysis ofthe operational condition of a radar set. Amongthe most important factors it can determine arefrequency and bandwidth, power and frequencyspectra, sensitivity, pulsewidth and condition, andrecovery time. Analysis of the waveform can alsoprove helpful in locating the cause of malfunctionswithin the radar set.

You need to remember, however, that the echobox presents only relative (rather than absolute)values of power and sensitivity and only roughvalues of frequency. These quantities are not asaccurate as the corresponding values obtained byusing a spectrum analyzer. The primary value ofthe echo box lies in its regular usage. For maxi-mum benefit, you must compare the values froma given test to corresponding values from a teston a radar set you know is operating properly.

In general, however, the echo box is anextremely valuable instrument. When used in acontinuing maintenance program, it lets theoperator maintain the equipment in peakoperating condition. Also, it gives indications ofdeterioration before actual malfunctions occur.

Distortion Analyzer

The Hewlett-Packard Model 332A distortionanalyzer (fig. 8-38) is a solid-state instrument formeasuring distortion and ac voltages. The Model332A includes a high-impedance AM detector thatoperates from 500 kHz to greater than 65 MHz.

Distortion levels of 0.1 percent to 100 percentfull scale are measured in seven ranges for anyfundamental frequency of 5 Hz to 600 kHz.Harmonics are indicated up to 3 MHz. The highsensitivity of these instruments requires only 0.3V rms for the 100 percent set level reference. TheOUTPUT connectors provide a low distortionoutput for monitoring with an oscilloscope, atrue rms voltmeter, or a wave analyzer. Theinstruments are capable of an isolation voltage of400 volts above chassis ground.

You can also use the transistorized voltmetercontained in the Model 332A separately forgeneral-purpose voltage and gain measurements.The voltmeter has a frequency range of 5 Hz to3 MHz (20 Hz to 500 kHz for the 300 µV range),and a voltage range of 300 µV to 300 V rms fullscale.

The AM detector is a broadband dc restoringpeak detector consisting of a semiconductor diodeand filter circuit. AM distortion levels as low as0.3 percent can be measured on a 3 V to 8 V rmscarrier modulated 30 percent in the standardbroadcast band. Also, lower than 1 percentdistortion can be measured at the same level ofthe carrier up to 65 MHz.

The Model 332A distortion analyzer has twomodes of operation—the distortion mode and thevoltmeter mode. Total harmonic distortionmeasurements from 5 Hz to 600 kHz are possible.The distortion mode can indicate harmonics upto 3 MHz. Distortion measurement accuracy isdetermined by the overall effect of harmonicfrequency measurement accuracy, eliminationcharacteristics, distortion introduced by theinstrument, and meter accuracy. In the voltmetermode, the transistorized voltmeter provides a full-scale sensitivity of 300 µV rms (residual noise <25µV). The voltmeter frequency range is 5 Hz to 3MHz (20 Hz to 500 kHz on the 300 µV range).

The distortion measurement accuracy of the332A is a result of the sharp eliminationcharacteristic of the rejection amplifier circuit andthe low level of distortion introduced by theinstrument. The fundamental reject ion is at least80 dB, which is small compared to the distortionintroduced by the instrument. Thus, low-levelharmonic content in the input signal can bemeasured accurately. You can use the 332A witha wave analyzer for extremely sensitive (>80 dBdown in the audio-frequency range) measurementsof odd harmonics.

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ON switch turns instrument ac power on. Pilot lamp glows when instrument is turned ON.NORM-RF DET switch selects front panel INPUT connectors or rear panel RF INPUT connector.INPUT terminals provide connections for input signals.FUNCTION selector selects mode of operation of the instrument.MECHANICAL ZERO ADJUST mechanically zero-sets meter before turning instrument on.DISTORTION/VOLTMETER indicates distortion level and voltage levels of input signals.SENSITIVITY selector provides 0 to 50 dB attenuation of input signal in 10 dB steps in SET LEVEL and DISTORTIONpositions of FUNCTION selector.SENSITIVITY VERNIER control provides fine adjustment of attenuation level selected by SENSITIVITY selector.METER RANGE selector selects full-scale range of meter in percentage, dB, and rms volts.FREQUENCY RANGE selector selects frequency range to correspond to fundamental frequency of input signal.COARSE BALANCE control provides coarse adjustment for balancing the Wien bridge circuit.FINE BALANCE control provides a vernier adjustment for balancing the Wien bridge circuit.Frequency vernier control provides fine adjustment of FREQUENCY dial.FREQUENCY dial selects fundamental frequency of input signal.OUTPUT connectors provide means of monitoring the output of the meter circuit with an oscilloscope, a true rms voltmeter,or a wave analyzer.RF INPUT connector provides input connection for AM RF carrier input signal.FUSE provides protection for instrument circuits.LINE VOLTAGE (115 V/230 V) switch sets instrument to operate from 115 V or 230 V ac.AC power connector provides input connections for ac power.BATTERY VOLTAGE (+28 to +50 VDC and –28 to –50 VDC) terminals provide connections for external batteries.

Figure 8-38.-Model 332A distortion analyzer front and rear panels.

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Q35. Describe what factors a spectrum analyzerexhibits.

Q36. Describe the purpose of the echo box.

Q37. What limitation should you consider whenyou use the echo box?

REFLECTOMETRY TEST SETS

Learning Objectives: Recognize the basictheories of time- and frequency-domainreflectometry. Recognize the characteristicsof resistive and reactive loads. RecognizeTDR displays and identify range andresolution and the uses of analyzingterminations. Identify the advantages anddisadvantages of FDR as compared toTDR testers. Recognize the purpose anduse of FDR testers.

Reflectometry test sets have many uses. Theyare primarily used to help the organizationalmaintenance technician verify and troubleshootaircraft wiring, transmission lines, waveguides,and antenna systems. However, the intermediatemaintenance technician can use reflectometry testsets to verify cable connectors, determine testcable impedances, and troubleshoot test equip-ment. There are two types of reflectometry testsets currently used by the Navy—time-domainreflectometer (TDR) and frequency-domainreflectometer (FDR) testers.

TIME-DOMAIN REFLECTOMETRY(TDR) TEST SETS

You will use time-domain reflectometer (TDR)test sets to check and troubleshoot aircraft wiring,transmission lines, and antenna systems forshorts, opens, crimps, bad couplings, etc. To dothis, you will monitor TDR reflected waveforms.TDRs operate on the same principle as radar; thatis, they send pulses of energy into a system to seewhat, if anything, is reflected. Like standingwaves on an antenna line, if nothing is reflected,the impedance of the transmission line is uniformand properly terminated. However, if crimps,opens, bad couplings, and so forth, are present,a discontinuity exists, and in-phase or out-of-phase pulses return to the TDR test set. Thesereflections occur on its CRT as positive, negative,or simply fast-rising voltages, which show theknown causes usually at fault. Impedances greater

than 50 ohms appear to the TDR as in phase,while those less than 50 ohms appear out of phase.These are respectively classified (traditionally) asinductive and capacitive faults, which areexplained by the basic equation: = where L = inductance, C = capacitance, andZ = impedance.

TDR Basics

The TDR analysis begins with the insertion ofa step or pulse of energy (referred to as theincident signal into a system or cable. Then, atthe point of insertion, you see the energy reflectedby the system or cable under test. Figure 8-39shows the typical TDR analysis. The output ofthe pulse generator is, a step signal with a rise timeof about 110 picosecond. This signal (incidentsignal) goes through a sampling tee to the CRTof the sampling oscilloscope and to the systemunder test via a termination connector. Theequivalent bandwidth of the CRT deflectioncircuits provides a system rise time of about 140picosecond. This allows the TDR to giveresolution (detect faults) as close as one-half inchapart. The reflected signal from the system undertest reenters the TDR test set and returns via thesampling tee to the sampling oscilloscope CRTalong with the incident signal. By comparing themagnitude, duration, and shape of the reflectedsignal, you can determine the nature of theimpedance variation in the system under test.

RESISTIVE LOADS.— With a pure resistiveload on the output of the TDR, and a step signalapplied, a signal whose amplitude is a functionof the resistance (fig. 8-40) appears on the CRT.If the line terminates in its characteristicimpedance (fig. 8-40), there is no reflectedsignal. The signal on the CRT will remain flat.However, if the impedance at the terminationis greater or less than then reflections(standing-wave ratio [SWR]) exist. The amplitudeof the reflected signal is proportional to the valueof If is greater than (50 the reflectedsignal is in phase with the incident signal, and,when applied to the CRT, the reflected signal addsto the incident signal. If is less than thereflected signal is out of phase with the incidentsignal. When applied to the CRT, the reflectedsignal subtracts from the incident signal. Thedotted lines in figure 8-40 represent variouscomposite signals (incident ± reflected) that youwould observe for various values of The timefrom the start of the incident (step) signal to the

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Figure 8-39.-Typical TDR analysis.

Figure 8-40.-Step signal-height variations resulting from different resistive loads.

step created by the reflected signal represents twice cable. This moves the reflections away from thethe distance to the discontinuity; that is, the time leading edge of the step (start of the incidentit took the incident step to reach the discontinuity signal) and prevents overshoot and ringing fromand return. Most TDRs are calibrated to read this appearing on the CRT signal.time in feet or inches to the discontinuity.

You should separate the system under test REACTIVE LOADS.— The waveform offrom the TDR test set by 8 inches of 50-ohm reactive loads (fig. 8-41) depends on the time

Figure 8-41.-TDR reactive load characteristics (time constant = 1).

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constant formed by the load and the 50-ohmsource. The series RL network (fig. 8-41, view A)appears as an open the instant the step voltagereaches it. This is because the inductor L offersmaximum impedance to the change in currentcaused by the step voltage. Therefore, thereflected signal is in phase with the step voltageand is additive. This explains the sharp rise involtage. However, as soon as the inductorsaturates, the only opposition to current is resistorR. Since L saturates at a nonlinear rate, thevoltage drops at a nonlinear rate from the peakof the spike to the same level as the flat portionof the step voltage. At this time, the only loadseen by the line is the 50-ohm resistor, whichequals the characteristic impedance of the line.The reflections cease until the next step appearsat the termination. Then, the cycle repeats itself.

To understand the wave shape shown in figure8-41, view B, you need to remember that Lappears as an open to the fast-rising step voltagethe instant it is felt at the termination. However,as the inductor saturates, it offers less and lessopposition to current until it completely saturates(0 ohm). Since the inductor is parallel to R, thetermination is a short, and the reflected wave is180 degrees out of phase with the incident wave.Since L saturates at a nonlinear rate, the voltagedeclines at a nonlinear rate. Views C and D offigure 8-41 show a similar analysis of thetransmission lines with the RC terminations.

The analysis of these different types ofdiscontinuities explains the usefulness of the TDR.Through proper analysis of the discontinuities,you can determine whether they are resistive,inductive, or capacitive and whether it is in seriesor parallel with the load.

TDR in Practice

TDR discontinuities have clear separations intime on the CRT. You can easily see the mismatchcaused by a connector even if another baddiscontinuity is present elsewhere in the system.By using the analysis explained before, you canestablish which connector is troublesome andin what way. Once you determine that adiscontinuity appears in a waveform, it is simpleto locate it in the system. You can save time bycalibrating the system so 1 centimeter on thehorizontal axis equals a certain number of feetfor the transmission system under test. Thelimiting factor is the system rise time, and anyclosely spaced discontinuities will appear as asingle discontinuity.

The finite rise time also limits the size of thedistinguishable reactive impedance response. Forexample, a small shunt capacity in a 50-ohmsystem causes the waveform to depart from theideal response (fig. 8-42).

The maximum observable line length is afunction of the repetition rate chosen. This ratedetermines the duration of the pulse after its rise.For example, a 200-kHz repetition rate permitsthe use of TDR devices with up to 1,000 feet ofair dielectric cable or 670 feet of polyethylenedielectric coaxial cable. A system’s velocityconstant determines the speed at which a wavetravels through a transmission system. Awave travels faster through air than throughpolyethylene. This explains the difference inmaximum checkable lengths of coaxial cable usinga particular repetition rate on the TDR. Thelonger the cable, the lower the repetition rate mustbe.

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Figure 8-42.-Small shunt capacity in system degrades idealresponse.

Range and Resolution

Assuming that the total impedance equals50 ohms, you may measure a resistance between0.025 ohm and 100 kilohms. Because the heightof the reflection is directly proportional to theresistance, you may determine the resistance byusing a precalculated transparent overlay.

One common use of the TDR is in analyzinga coaxial cable. The amount of impedancevariation that is detectable in a long section ofcable is a function of the flatness of the top ofthe incident step. If this step is flat within ±0.5percent, it can detect an impedance variation of0.5 ohm along the cable, corresponding to a1 percent check on cable impedance. Thus,irregularities in cable makeup resulting fromvariations in the braiding process or tightness ofthe insulating jacket show up clearly.

Analyzing Terminations

A departure from 50 ohms in a terminationor cable connector can cause some problems. Forexample, large reflections in a pulse system or alarge voltage standing-wave ratio (VSWR) canoccur in a system that carries primarily sinusoidalsignals. Because of human errors in the assembly

process, even the best connectors will causereflections or a varying VSWR. Therefore,expensive connectors do not ensure freedom fromunwanted reflections. However, the TDR helpsyou locate unacceptable connectors by rapidlyshowing where the mismatches are and how badthey are. The TDR also indicates if theseconnectors are resistive, capacitive, or inductiveand whether series or shunt. Figure 8-43 showsa step being propagated from a section ofRG9A/U into a load. The connector on the loadand the cable are the general radio type 874. Itshows four different cases with varying loads.These cases show how you can analyze theconnection and the load by using the TDR. Withdifferent connectors and loads, the smallmismatches (discontinuities) take on different

Figure 8-43.-Waveforms resulting from the use of differentloads. Horizontal scale 0.4 µsec/cm; vertical scale0.5 percent/cm.

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impedance characteristics and the reflected signalschange. This change also appears in the waveshape viewed on the oscilloscope. You cancompare these signals with those of a normalsystem by using an overlay showing the patternof a normal system.

The most convenient method to make precisemeasurements of cable impedance is to connecta section of air dielectric line (with preciselydetermined impedance) between the cable and theTDR. The step height through the air dielectricline section sets the 50-ohm level. You note anyvariations from this level in the test cable andcalculate the impedance of the cable (fig. 8-44).

In this test, the impedance level of the test line is

where (Greek letter rho) is the reflectioncoefficient of the reflected mismatch, If thechange in amplitude shows to be +0.03, then

The impedance of a long section of coaxialcable would be exactly if there were no linelosses. However, most cables have a small seriesloss and a negligible shunt loss. This seriesresistance adds to causing the impedance level(as observed at one end of a cable) to increasewhen adding longer sections of cable. The slopeon the step height that results from the increasingimpedance is evident in figure 8-45.

There are other applications in which the TDRmethod of analysis is effective, includingcomponent characteristic analysis, antennaanalysis, and aircraft wiring checks. You can placethe components in an appropriate jig and use theTDR method to determine their shunt capacityand series inductance (fig. 8-46).

Investigation of antennas reveals that the TDRpattern is not simple, but instead presents a

Figure 8-44.-Oscillograph of step from air dielectric lineinto test cable.

Figure 8-45.-Trace of cable shows construction irregularitiesand increasing series resistance.

complex reactive profile (fig. 8-47). Once youdetermine the proper profile for a particu-lar antenna, you can detect any improperconstruction details and determine the propercorrective action.

FREQUENCY-DOMAINREFLECTOMETRY (FDR) TEST SETS

Frequency-domain reflectometry (FDR) is afast, simple, and reliable technique developed to

Figure 8-46.-Resistor checked for shunt capacityspecial jig.

Figure 8-47.-Scope trace of antenna

with

reactive profile.

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locate defects in microwave cables and waveguidesystems connecting receivers, transmitters, andantennas. Like the TDR, the FDR tester permitsdirect readout of cable distance, in feet, to thediscontinuity (impedance fault). This system hasan impressive record of reliability, reduced servicetime, and improved service standards. Because theFDR checks cables at their actual operatingfrequencies, discontinuities outside those fre-quencies do not affect the test. When measure-ments indicate a fault, you can precisely determineits location (in terms of distance in feet from thepoint of test). Therefore, you can make repairsquickly and efficiently.

FDR vice TDR

Until FDR testers, TDR was used as theprimary test of cables; a system that has severallimitations. For example, TDR measurementscover a spectrum determined by its pulse charac-teristics; therefore, it detects all discontinuities,including those outside the operating frequencyrange, which do not affect a system’s operation.With the FDR, however, the analysis is within theactual operating frequency band of the microwave

system, which assures proper system performanceat the operating frequencies.

While the FDR works in waveguides andband-limited systems (including transmissionnetworks that contain filters), the TDR cannotwork in such systems. The TDR requires atransmission line that passes the whole spectrumfrom the fundamental frequency (2 MHz to5 MHz) to the highest harmonic (15 GHz).Waveguides that act as high-pass filters cannottransmit TDR pulses. Similarly, the TDR cannotsee through low-pass or bandpass filters becausethey eliminate the low-frequency harmonics andappear to display a discontinuity on the TDR’sCRT.

FDR Testing

The FDR identifies defective systems byinjecting an RF signal into a system and usinginsertion-loss (attenuation in the line) and return-loss (VSWR) measurements. These measurementshelp to classify the system under test as good orin need of repair. There are various test setupconfigurations to measure these losses, based onthe particular FDR equipment. Figure 8-48

Figure 8-48.-Typical setup for VSWR and insertion performance.

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represents a typical test setup for VSWR andinsertion-loss monitoring. Such a test configura-tion provides simultaneous measurement of thelosses.

If the input and output connectors of thedevice under test are accessible, an insertion-losscheck verifies input to output performance acrossthe band. For insertion-loss measurement, thenetwork analyzer (fig. 8-48) (using its B and REFchannels) indicates the ratio of output signal toinput signal directly in dB. For tests of long cableswhose ends are accessible, the FDR allowsmeasurements from a connector end as far as2,000 feet from the tester. In some tested systems,however, either the input or output connector maybe inaccessible. For such systems, a return-lossmeasurement made on the accessible connectorprovides a total system check. For return-lossmeasurements, the network analyzer (using theA and REF channels) indicates (measures) theratio of reflected power to incident power directlyin dB. Incident power is the output of the RFsweep oscillator unit. Figure 8-48 shows how thesignals in each case are sampled via directionalcouplers.

Comparison of each measured signal with theincident power of the RF oscillator suppliesautomatic compensation for any swept-sourcepower variations across the band. This gives a truegraph of performance in dB versus frequency onthe network analyzer CRT. Figure 8-49 shows anexample of insertion-loss measurement on thenetwork analyzer CRT. In this example, a loss ofless than 10 dB is acceptable (as determined fromprevious tests of a good system). The cable,

however, needs repair because a fault(discontinuity) is present, which produces aninsertion loss greater than 35 dB at a frequencyof 3.56 GHz.

Figure 8-50 shows a return-loss measurementfor the same cable. Here, a loss of 11 dB(as determined from a good system), whichcorresponds to a VSWR of 1.8, is acceptable. At3.56 GHz, however, the return loss on the CRTindicates 5 dB, which corresponds to a VSWR of3.6, and it is unacceptable.

The dual-channel network analyzer in figure8-48 permits the display of both measurementssimultaneously, and both verify the discontinuityin the system cable under test. Single-channel FDRtesters require individual test setups for measuringinsertion and return losses and comparison of theindividual graphs.

DETERMINING CABLE LENGTHS ORDISTANCE TO FAULTS.— To determine cablelength or fault (discontinuity) location measure-ments (fig. 8-51), a waveguide or a coaxial tee isadded in the test setup. You then calibrate theFDR test setup with a calibration cable (providedwith FDR set) to establish a known 0-footreference on the CRT display, Then connect thesystem cable to the tee. The resulting CRT displayof the network analyzer consists of a stationarypattern containing a series of half-dome ripples.A count of the total number of these ripplesindicates the number of feet from the cable endto the fault, as shown in figure 8-52. The FDRdisplay is from the cable that needs repairs (figs.8-50 and 8-51). Multiply the 5 2/3 ripples by the

Figure 8-49.-Insertion-loss display.

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Figure 8-50.-Return-loss display.

Figure 8-51.-Test setup for fault location measurement.

calibration factor of 2 feet per ripple (CRT to the same tee junction, discontinuities and/orcalibrated that way). You can see that the locationof the fault is 11 1/3 feet from the cable endconnector (5 2/3 x 2 = 11 1/3 ft). Figure 8-53shows a dual-channel display of the cable aftercompleting the repairs. The insertion loss is lessthan 10 dB and the return loss is greater than 11dB, indicating proper performance of the systemcable.

DETAILED FDR ANALYSIS.— With thesweep oscillator output, the transmission systemunder test, and the crystal detector all connected

Figure 8-52.-Measuring a cable fault.

termination mismatches in the system reflect someof the incident power. The reflected powercombines with the incident signal at the crystaldetector, resulting in a changing phase relation-ship that depends on both distance to thediscontinuity and signal frequency. As thefrequency is swept, it changes the number ofwavelengths that occupy the fixed path from thetee to the point of reflection and back. The display

Figure 8-53.-Dual-channel display of a repaired cable.

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shows amplitude ripples that result from thesumming of the incident and reflected signals.This relationship changes with frequency. Figure8-54 shows how the magnitude of the vector sumof these signals, which is the signal level detectedfor display, varies with frequency.

The resulting display of the varying-magnitudedetected signal is actually a logarithmic SWRpresentation. The ripple peaks are adjacentVSWR maxima that occur during the sweep. Theyoccur at each frequency in which the round-triplength of the reflected wave path from the sourceto the defect has changed by one wavelength. Thenumber of ripples appearing across the full widthof the display is a measure of the distancefrom the discontinuity to the crystal detector.Therefore, a direct readout of fault distance isavailable when the swept source operates over asweep width (AF). The sweep width is chosen toprovide a display calibration (in terms of ripplesper foot) compatible with the length of thetransmission system under test.

In a coaxial system, the distance to adiscontinuity, which may be a fault or the cableend, is represented by the equation

Where D is the distance to the fault or cableend in feet,

492 is the half wavelength in feet of a 1-MHzwave in free space transmission,

K is the propagation constant that relates thepropagation velocity in the coaxial system tothe velocity in free space,

N is the number of ripples observed in thedisplay, and

AF is the swept-frequency excursion (sweepwidth) of the signal source in MHz.

You should note that for any type of cable,AF can be selected to equal 492K. The distancein feet is equal to the number of ripples (includingthe fractional ripples) shown in the display.

Figure 8-54.-Magnitude of the vector sum.

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In waveguide systems, the distance down thewaveguide to the fault is represented by the sameequation, with K as the

relation is the wavelength in free space

and g is the wavelength in the waveguide) at thefrequency of measurement.

Q38.

Q39.

Q40.

Q41.

Q42.

Q43.

Q44.

Q45.

Describe some of the main uses for theTDR.

Describe the basics of TDR.

While you can determine different types ofdiscontinuities with the TDR, what else canyou determine through proper analysis?

What factor determines the speed at whicha wave travels through a transmissionsystem?

By what method does using a TDR help youlocate an unacceptable connector?

While TDR and FDR provide similarmeasurements, the FDR eliminates whatlimitation of the TDR?

Describe the means by which the FDRidentifies defective systems.

When determining cable lengths or distanceto faults, what means do you use todetermine the number of feet from the cableend to the fault?

VAST STATION

Learning Objective: Identify features,components, and operating procedures ofa typical ATE VAST station.

U.S. Navy aircraft carriers and shoreinstallations are equipped with automatic testequipments (ATEs), such as the Versatile AvionicsShop Test (VAST) station, AN/USM-247(V), andthe Hybrid Automatic Test System (HATS),AN/USM-403. The VAST and HATS deal withthe continually changing field of avionics testing.The use of these computerized ATEs hassignificantly reduced the space requirements ofspecial- and manual-support test equipments, Thediscussion contained in this chapter deals with theVAST station.

TYPICAL VAST STATION

In its basic form, a VAST station is assembledfrom an inventory of functional building blocks.These building blocks furnish all the necessarystimuli and have the measurement capability tocheck current naval avionics equipment. As newequipment is developed and introduced, the teststation configuration may be modified. As itbecomes necessary, new building blocks furnishnew parameters or greater precision to existingcapabilities.

A typical VAST station (fig. 8-55) consists ofa computer subsystem, a data transfer unit

Figure 8-55.-Typical carrier-based VAST station.

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(DTU), and a stimulus and measurement sectioncontaining functional building blocks configuredto meet the intended test application.

A computer subsystem controls the teststation, which executes test programs to assureaccurate and satisfactory testing. The computersubsystem includes a general-purpose digitalcomputer that executes test routines and hasdiagnostic and computational capabilities. Also,this subsystem processes data and furnishes apermanent record of test results. Two magnetictape transports provide rapid access to avionicstest programs and immediate availability of VASTself-check programs.

The data transfer unit (DTU) (fig. 8-56) servesas the operator-machine interface. It synchronizesinstructions and data flow between the computer

and the functional building blocks. Also, itcontains the display and control panels.

The operator communicates with the com-puter and the stimulus and measurement sectionof the VAST system by using the DTU controlpanel, which has the keyboard and mode selectkey. The test station may be operated inthree modes—manual, semiautomatic, or fullyautomatic.

The DTU contains a maintenance panel thatmonitors station auto-check results and indicatesbuilding block faults. Transmission of instructionsfrom the control computer is on a request/acknowledge basis. Essentially, the stimulus andmeasurement section controls the response rate.This allows instructions to be transmitted atan asynchronous rate, corresponding to the

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Figure 8-56.-Data transfer unit (DTU).

maximum frequency at which a given buildingblock or avionics unit can respond. Therefore,there is no requirement for immediate programstorage in the DTU.

FEATURES OF A VAST STATION

A VAST station may have as many as 14 racksof stimulus and measurement building blocks(fig. 8-57). Large station configurations maycontain as many as 17 core building blocks. Corebuilding blocks are designated as a result ofhigh-use factors or because they are needed forself-test requirements. Building blocks not in thecore category are usually selected to meet thespecific test requirements of shop operations oravionics equipment on board ship. In general, thelocation of such peripheral building blocks isflexible. To maintain standardization betweenVAST stations, the effects of building blockinterconnection cable losses and switches have toremain within predictable limits; this is thepurpose of the core concept.

Ease of maintenance is the main objective ofthe VAST station designed. In addition to themodularized design of VAST building blocks,there are three levels of fault detection, whichensure rapid confidence tests and easy faultlocation. The three levels of detection areauto-check. self-check, and self-test.

Fault detection may be initially made throughauto-check. The auto-check is inherent in the logicand control design of the test station and includes

Figure 8-57.-VAST station with building blocks.

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verification of instructions and fault monitoring.Auto-check is carried out on a continuous basisduring station operation and, when a fault occurs,testing is interrupted.

The second level of VAST fault detection isself-check. Self-check is a programmed sequencethat is initiated by the VAST operator throughthe DTU keyboard. Self-check may be eitherinternal or at the system level. Internal self-checkmeasures the ability of a building block toperform against its own internal standards.System self-check requires the use of two or morebuilding blocks in a test configuration selected toisolate faults within the test setup.

The self-check philosophy used to verify theoperation of VAST is based upon confirmationof key system elements first. Then, these elementsare used to check the remaining building blocks.Fundamental core building blocks are checked bymeans of internal standards. Once satisfactoryperformance is assured, their capabilities areused to check the remaining building blocks,The checkout of noncore building blocks isaccomplished by using any combination(s) of coremeasurement and stimulus building blocks.

The final level of VAST fault detection isself-test. This is a series of test programs used tolocate faults within a building block. If a buildingblock has been found to contain a malfunctionas a result of a self-check routine, then self-testprograms are conducted. This is done by removingthe faulty building block from the VAST rack andby connecting it to the test station in the samemanner as if it were a unit under test.

Avionics equipment must be designed to beadaptable to automatic testing to assure optimumsupport by VAST. Moreover, test programs mustbe prepared that are compatible with VASTperformance characteristics.

VAST-TO-UUT INTERCONNECTINGDEVICE

Included in the program design is the all-important interconnecting device design. In itssimplest form, the interconnecting device consistsof an adapter cable, which connects the unit undertest (UUT) to the VAST interface. In some cases,however, it is necessary to introduce, as part ofthe electrical interface in the interconnectingdevice, passive and active circuits to changeimpedance levels or to amplify low signals,Ordinarily, this is not required if avionics

equipment has been designed within the require-ments of VAST. Often, passive circuit functionsare obtained through the use of standard plug-inmodules.

The last element of the test program is theinstruction booklet or microfilm strip. Thiselement details all the steps to follow when youtest any given unit, from initial procedures, suchas hookup and clearing operations, down to thefinal stages of disconnect and UUT closeout.

OPERATION OF A VAST STATION

In the typical VAST test procedure, ease ofoperation in the actual testing becomes apparent,The initial setup of the weapon replaceableassembly, including removal of dust covers,cooling provisions, and connections to interfacedevice, may be made off station to minimizedisruptions of station operators. Final connectionsbetween the VAST station’s interface panel andthe UUT are made in a few moments at thestation.

The operator begins testing by selecting thecode that initiates the test program. Before poweror stimulus is applied to the UUT, continuity testsare run to make sure the proper test program hasbeen selected and no condition exists that willdamage the VAST station or the UUT once activetests are started. If everything checks out, thetesting proceeds automatically, The operator onlyhas to respond to instructions that appear on theCRT display. The program will not stop until afault is encountered or a program halt is reached.

The purpose of programmed halts is to allowmanual intervention during the course of testingto make adjustments and observations. When theidentification of faults and the operator’sinstructions are required (such as interpreting acomplex waveform), the operator may be referredto the test program instructions. Upon completionof the test program, the CRT display indicatescloseout procedures.

A VAST station is completely autonomousand normally operated under computer controlin a fully automatic mode, stopping only aspreviously mentioned. Of course, the operator canselect any one of the semiautomatic modes or amanual mode.

The semiautomatic modes include a one-group, one-test, and one-step mode. Theseauxiliary modes permit detailed observation ofvarious test sequences, and they are useful

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in performing work-around procedures inreconciling differences in equipment and programmode status and in the verification of repairs.

In the manual mode, the test station iscompletely off-line with respect to the computer.Instructions are introduced by the operatorthrough the keyboard on a one-word-at-a-timebasis. (See fig. 8-58.) Although the manual modeis never used for avionics testing, it is usefulfor debugging new programs, integrating newbuilding blocks into the station, and performingself-check operations on some of the buildingblocks.

Q46. List the elements of a typical VASTstation.

Q47. List the three levels of detection that ensurerapid confidence tests and easy faultdetection.

Q48. What is the purpose of programmed halts? Figure 8-58.-Typical VAST control panel.

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CHAPTER 9

SAFETY AND SECURITY

As you strive to advance, the responsibilitieswill increase at each paygrade. As an airman youstart developing your character and attitudes. Itis at this level, you should start preparing for yourfuture responsibilities for safety and security. Thischapter should give you a good start in the rightdirection for a positive accident-preventionattitude and proper security posture.

MISHAP PREVENTION

Learning Objectives: Identify mishap pre-vention responsibilities to include super-visor’s role, hazard identification, training,and general mishap prevention. Recognizeaviation mishap prevention to includetechniques, machinery, electrical equip-ment, volatile fluids, general hazards, andmaintenance hazards.

The procedures and information withinthis chapter are for training purposes only.They do not replace local safety proceduresand should not be considered as, or takeprecedence over, established procedureswithin NAVOSH program manuals. Youmust use commonsense and becomefamiliar with current NAVOSH safetyprocedures and information to assist youin your safety awareness and mishapprevention efforts.

Why is mishap prevention necessary? Theproduct of the Navy is national defense.Therefore, the quality of our performance mustbe better than that of any competitor. The Navy’sbusiness is deadly serious, is conducted byprofessionals, and is restricted by limitedresources. It allows no room for waste! Mishaps

produce waste. Therefore, when mishaps arereduced, waste is reduced, and readiness isimproved.

A mishap is an unplanned event that resultsin injuries to personnel, fatalities, or damageto material. Mishaps can and must be prevented.In the Navy, mishap prevention is everyone’sjob. Mishap prevention is the process of elimi-nating mishap-producing causes before a mishapoccurs.

A near-mishap is an mishap that almosthappened. It is an occurrence that, except forlocation or timely action, would have resulted inproperty damage and/or injury to personnel.While the near-mishap does not cause damage toequipment, material, or personal injury, it doesserve notice that a hazardous condition exists thatcould result in a future mishap. The near-mishapis significant because it serves as a warning. If youignore any condition that caused a near-mishap,you are inviting a mishap.

RESPONSIBILITIES

Mishaps are preventable. Each person mustbecome a mishap prevention specialist. Mishapprevention is based on recognizing and eliminatinghazards through training, inspections, and anawareness of safety. These actions must becomehabit. In any environment, personal habitsdetermine the chance of an mishap occurring. Forthese reasons, you must maintain high standardsof cleanliness and neatness. Insist on goodhousekeeping practices and hold frequentinspections (formal and informal). Mishapprevention is a responsibility of the entire chainof command. Hazardous conditions should bereported, and supervisory personnel should takecorrective action. When a mishap occurs, it isinvestigated, and the cause determined bypersonnel in the chain of command. Lessons

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learned from mishaps are used to prevent theirrecurrence.

NOTE: OPNAVINST 5100.1 (series) andOPNAVINST 5100.23 (series) containdetailed information about safety pro-grams for afloat and ashore commands. Asa supervisor, you need to be familiar withapplicable sections of these instructions.

NOTE: One of your responsibilities as asupervisor is to report hazardous situationsto the chain of command. For informationon the procedures for reporting possiblehazardous situations that may affectpersonnel Navy-wide, you should referto OPNAVINST 5102.1 (series) andOPNAVINST 3750.6 (series).

The proper use of tools eliminates unsafe acts.All tools and equipment should conform to Navystandards for quality and type. You should usethem only in the intended manner, Keep yourtools in good repair. Replace all damaged, worn,or nonworking tools. When a job is completedor when work is interrupted, account for all yourtools and return them to their toolbox or the toolissue room.

NOTE: Review the Naval AviationMaintenance Program, OPNAVINST4790.2 (series) for the latest tool controlprogram procedures. Also, information onthe use, care, and selection of general toolsis contained in the rate training manual,Tools and Their Uses, N A V E D T R A14256.

A Navy ship holds a great potential formishaps. Fuel, ammunition, high temperatures,electrical circuits, steel decks, salt water, ladders,voids, and machinery create conditions that couldcause mishaps. Navy personnel must learn to livesafely within this hazardous environment by beingaware of its elements.

People cause mishaps. Since people causemishaps, mishap prevention must be directed atpeople. As an individual, you can prevent mishapsif you recognize factors that cause mishaps andif you are motivated to carry out corrective action.

The Navy Safety Center has found that 88percent of all mishaps are caused by human error.Unsafe conditions are the direct cause of only10 percent. Most mishaps are caused by people;they are not the result of uncontrolled events or

acts of God. If the principal cause is the humanbeing, then people can prevent mishaps throughproper knowledge, hazard awareness, and cor-rective action.

The mishap prevention program is the sum ofall actions taken to reduce mishap damage toequipment and/or injury to personnel. It includesthe establishment, maintenance, and enforcementof mishap prevention standards and practices. Italso consists of mishap prevention training andeducation, supervision of operations, maintenanceand repair, and mishap investigation andreporting. You cannot separate or isolate mishapprevention from other activities.

SUPERVISOR’S ROLE

One key to a successful mishap-preventionprogram is a safety-minded supervisor. As a pettyofficer, you must know your work area, yourpeople, and the materials with which you work.You can take action to prevent mishaps by makingsure personnel develop and use safe workinghabits. If you understand the principles of mishapprevention, you can prevent mishaps. Insist onsafe practices at all times, recognize hazardousmethods and procedures, and take corrective(mishap preventive) measures. Experience hasshown that a lack of knowledge or skill is thesingle biggest cause of mishaps—people doingsomething they do not know how to do. Whena person is taught the RIGHT way to do a job,it is impossible not to teach him the SAFE way.This is why your increasing responsibilities forconducting on-the-job training and supervisingsubordinates is important.

MISHAP-PREVENTION TRAINING

Mishap-prevention training begins when youfirst join the Navy. It begins during indoctrinationand continues with orientation and on-the-jobtraining. Doing a job properly requiresknowledge, and you need to pass this knowledgeto the less experienced worker. You must motivatethis worker.

One way to prevent mishaps is to use thewritten operating procedures. You can use theseto train your subordinates and to prevent mishaps.Another important way to prevent mishaps is touse the proper protective device and equipment.This element of mishap prevention is importantin any procedure related to a piece of equipmentor system. Following correct procedures preventsmishaps.

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As a petty officer, you must be aware ofhazards. Hazard awareness is important when youconsider the shipboard environment. As asupervisor or worker, you must apply yourpersonal experience and improve your awarenessof hazards to promote mishap prevention.Supervisors must also correct any hazardoussituation they discover. Further, they arechallenged with teaching these abilities tosubordinates.

The commanding officer establishes themishap prevention program, according toOPNAVINST 5100.23 (series) and OPNAVINST5100.19 (series), and gives it direction; but thesupervisors make it work. They make it workthrough supervision and personnel management.Supervisors assess individual qualifications,provide guidance, and develop proper attitudes(pride in a job well done). Supervisors areresponsible for identifying and correctingdiscrepancies; they are the most qualified to trainothers to recognize unsafe work practices.

GENERAL MISHAP PREVENTION

Some general rules for mishap prevention arelisted in the following paragraphs. These rulesapply to personnel in all types of activities, andyou should strictly observe them because they aredirectly related to your work or duty.

Report any condition, equipment, ormaterial that is considered to be unsafe.

Warn personnel of known hazards or theirfailure to observe mishap preventiontechniques.

Wear or use the required, approvedprotective clothing or equipment.

Report any injury or evidence of impairedhealth occurring in the course of work orduty.

Exercise reasonable, appropriate cautionif any unforeseen hazard occurs.

The mishap-prevention techniques in thischapter are not intended to replace informationgiven in instructions or maintenance manuals. If,at any time, you are not sure of the steps andprocedures to follow, ask your leading pettyofficer.

AVIATION MISHAP PREVENTION

In this section, the term aviation mishapprevention covers all functions and operationsdealing with aircraft. Also, it refers to materialsand equipment used with aircraft, hangars,parking areas and ramps, and flight lines andtaxiways. (Note: See OPNAVINST 4790.2 [series]and OPNAVINST 3750.6 [series] for detailedmaintenance and safety information.)

Hazards

The following are some of the major hazardspresent in aviation activities:

Fire or explosion due to applying externalor internal power to an aircraft that is in somestate of malfunction or disrepair. Also, aircraftundergoing maintenance or modification, orcreating explosive vapors, or that containselectrical short circuits.

Personal injuries sustained by falling fromaircraft or workstands, being burned or blownabout by jet blast or prop wash. Also, injuriescaused by people being struck by objects blownabout by jet blast or prop wash, being sucked intojet intakes, or being struck by propeller or rotorblades.

Personnel being run down or run overbecause they are not alert when aircraft are taxiingor ground equipment vehicles are moving.

Explosion of aircraft batteries causedby improper charging methods or to currentoverloading on ground tests within an aircraft.

Injuries caused by encounters withtie-down lines, pad eyes, chocks, protruding partsof aircraft or other equipment, or other itemsabout a deck or ramp. These injuries are especiallycommon during the hours of darkness.

Canopy, ejection seat, ordnance, and other“wrong switch at the wrong time” type ofmishaps.

Misuse of and abuse to flight safety equip-ment, parachutes, “Mae Wests,” life rafts, etc.

Mishaps caused by careless workers, wholeave tools or other materials in aircraft bilges,engine nacelles, intake or exhaust ducts, ormovable parts of aircraft structures.

9-3

Techniques

Many mishap-prevention techniques are of ageneral nature and apply to all types of aircraft.However, others vary in specific details betweenspecific models. Because your duties will bearound aircraft, you need to know both generaland specific mishap-prevention techniques orprocedures. The mishap-prevention techniqueshere are not a complete listing. They are a guideto show the types of mishap-prevention items thatmust be part of the mishap-prevention educationand training programs of all aviation activities.

Place appropriate warning signs in oraround aircraft or work areas whenever andwherever a hazardous condition is known orthought to exist. Enforce strict attention andadherence to the signs.

Observe and enforce smoking regulationsand prohibitions. Since explosive vapors may beignited from any source of open flame or fromelectrical arcing, these conditions are subject tothe same restrictions as smoking.

Radio and radar transmitters should notbe trained on potentially explosive areas or onpersonnel. They should not be operated nearflammable or explosive materials or vapors.

Do not disconnect or remove storagebatteries or electric cables from their circuits inany enclosed space without first ventilating thespace to remove accumulated vapors. Open allswitches and disable electric power beforedisconnecting batteries or electric cables.

Store combustible waste materials, such asrags, in covered metal containers. Never discardused waste and rags near aircraft; put them intoplainly marked metal containers. Dispose of wasteproperly, according to local regulations.

Aircraft should be parked with parkingbrakes set, chocks in place, and tie-downsinstalled.

During jet engine run-up, foreign objectsmay be drawn into the intake ducts, causingdamage to the engine compressor section andcreating a danger of flying debris from the exhaustsection. During maintenance procedures involvingengine operation, carefully inspect the intakeducts and surrounding areas to ensure the absence

of foreign objects. Ensure all engine air intakesafety screens are properly installed. Parkingareas, turnup areas, taxiways, and runways mustbe kept clean and free of stones, hardware, andother foreign objects.

MACHINERY

When working with, on, or around machinery,you need to watch out for moving parts. Neverreach into the path of moving parts of a machine,either with your hands or with any other item.Always follow prescribed procedures in makingadjustments on operating machinery. If possible,make the adjustments with the machinery shutdown. Never wear loose, baggy, or ill-fittingclothes in the immediate vicinity of machinery.Remove rags, papers, and all items from pockets.Remove ties, wristwatches, rings, and all jewelry.Button shirt sleeves and make sure dog tags areinside the undershirt or remove them. Wearrequired eye and ear protection.

ELECTRICAL EQUIPMENT

In addition to the danger of a person’s beinggrabbed or struck by moving parts, electricalequipments also present the danger of fire,explosion, electrical shock, and burns.

Never operate electrical equipment in areaswhere explosive vapors are present or suspectedunless the equipment is explosionproof. Whenworking with, on, or around electrical equipment,you should avoid contact with power circuits.Work on energized circuits or electrical equipmentrequires the commanding officer’s permission andspecial precautions. Use adequate protectivematerials and be extremely careful. Adequateprotective material includes rubber gloves,insulated tools, and insulated matting etc. Neverwork on electrical equipment when standing inwater, when perspiring heavily, or when in contactwith metal decks or other metallic structuresor equipment. When preparing to work onde-energized electrical circuits, make sure thepower switch is off the unit tagged out or lockedout. Then, use a grounding probe to eliminate anyresidual charge that may exist in the circuit.

These precautions apply to low-voltage equip-ments and high-voltage equipments. Remember,in connection with electrical shock and burns, thatit is the current that does the damage, not thevoltage.

9-4

HAZARDOUS MATERIALS

Hazardous materials include flammables,compressed gases, aerosols, corrosives, andoxidizers. These materials may be hazardousto workers’ health, a safety hazard, and anenvironmental hazard. For special precautionson handling, storage, and use and disposalof hazardous materials, you should refer toOPNAVINST 5100.23 (series), OPNAVINST5100,19 (series), and the item material safety datasheet (MSDS),

Explosive Vapors

When stored in a closed space, fuels, alcohol,painting materials and supplies, insulatingvarnish, certain cleaning supplies, and manyindustrial gases produce potentially explosivevapors. The hazards relating to these materialsare associated with the flash point of theliquids. The flash point of a liquid is thelowest temperature at which the liquid givesoff vapors that accumulate near the surfacein sufficient quantity to form a combustiblemixture with the air. Although liquid oxygen doesnot have a flash point, it has the same explosiveeffect.

Different fluids have different flash points.You should know the particular characteristics ofany volatile liquids with which you work. Youshould know the flash point and also theconcentration that constitutes (makes up) acombustible mixture. You can find this informa-tion on the MSDS.

Adequate ventilation dilutes or dispersesaccumulated vapors. When working in areaswhere volatile fluids are being used, make surethe space is ventilated before you operate electricalequipment. The smell of gasoline or otherflammable or explosive vapors is not a reliableindicator of flammability.

Toxic Vapors

Some liquids produce vapors that are harmfulto personnel. Many materials are either prohibitedor their use is rigidly limited. Generally, theprecautions are listed on the container and theMSDS, You must adhere to and enforce theseprecautions at all times.

To prevent mishaps, all personnel shouldknow the hazards involved in the use of allmaterials. Personnel should properly handle, storeand dispose of the hazardous materials they use.These actions are attained by training. Also,personnel should use the MSDS.

CONFINED SPACES

When personnel are working in confined orenclosed spaces, the spaces must be gas free. Thisincludes oxygen for normal breathing, cooling toprevent heat stress, and air movement andexchange to prevent accumulations of hazardousgases or vapors. Personnel also require anadditional or alternate source of ventilation orrespiratory protection if there is an emergency.Whenever workers are to be sent into a confinedspace for any reason, make advance provisionsfor their rescue in case there is a mishap oremergency, according to OSHA regulations.These provisions should include the use of safetylines for locating the workers and for retrievingthem from the space. Make sure you cancommunicate with workers inside the space so theexisting conditions (both inside and outside thespace) may be made known to the concernedpersonnel. One person (acting as tender) mustkeep a constant check on the condition of thespace and the workers. This person should beprepared to sound the alarm for additional helpor to give assistance to the workers in the confinedor enclosed spaces, as required. Personnel whoenter a confined space and personnel tending aworker must be trained in confined space hazardsand rescue procedures.

Vapors and gases tend to collect in confinedand enclosed spaces, so the spaces must becertified as being gas free before entering.Personnel should maintain constant communica-tion with the tender, and inform the tender of anyabnormal conditions that exist.

Equipment used by personnel working inconfined or enclosed spaces is a matter ofconsiderable importance. Enough light should beprovided so the workers can clearly see what theyare doing. The light should be insulated so thatit does not present a shock or explosive hazard.Protective clothing may be required if vapors orgases exist or are suspected to exist within thespace. When the space is tested by the gas-freeengineer, restrictions and protective equipmentrequirements are determined.

9-5

Q1.

Q2.

Q3.

Q4.

Q5.

What is the benefit of reducing mishaps inthe workplace?

What type of mishap serves notice that acondition exists that could cause a mishapin the future?

What is the cause of 88 percent of allmishaps?

Working with 10 w-voltage equipment is justas dangerous as working with high-voltageequipment because

List the types of materials considered to behazardous materials.

GENERAL HAZARDS

In addition to the specific hazards encounteredin electronic maintenance, there are obviousdangers involved in falling, tripping, slipping, orcollision. However, you are concerned with othergeneral classes of hazards. You have learnedabout some of the dangers from fire and explosionand the hazards of working with materials thatproduce vapors. You will also learn abouthazards present when working with chemicals orradioactive materials.

Fire and Explosion

Although fire andassociated with one

explosion are frequentlyanother, they can exist

separately. Basic Military Requirements, NAV-EDTRA 14325, contains detailed coverage onfire and explosion. Other sources of informationabout fire and explosion danger include Seaman,NAVEDTRA 14067, Airman, NAVEDTRA14014, Military Requirements for Petty OfficerThird Class, NAVEDTRA 14504, and MilitaryRequirements for Petty Officer Second Class,NAVEDTRA 14504, Ship Firefighting, NSTM555, OPNAVINST 5100.19 (series), OPNAV-INST 5100.23 (series), EIMB SE-000-31M-100,and NA 16-1-529, section 3.

FIRE.— A general discussion of the nature offire, the classes of fires, fire-fighting systems andequipment, protective clothing and equipment,and fire prevention is contained in Basic MilitaryRequirements, NAVEDTRA 14325. Generalinformation on aircraft crash rescue and firefighting is found in Airman, NAVEDTRA 14014.Specific details relating to fire-fighting and rescue

procedures for a particular model aircraft maybefound in the technical manuals for that modelaircraft. Take special precautions if a fire is inan enclosed space, and follow local regulations,which will give the appropriate procedures. Thefollowing section contains some actions thatshould be taken.

In the case of electrical fires, take thefollowing steps:

1. Use carbon dioxide. Do not touchenergized circuits with the fire extinguisherdischarge horn. When possible, leave the CO2

bottle in contact with the deck. Discharge it inshort, intermittent burst. Direct the carbondioxide at the base of the flame. Here, it servestwo purposes—(1) it cools the area, and (2) itdecreases the percentage of oxygen present at thefire. However, for major fires of any type inconfined spaces, the excessive use of carbondioxide may be dangerous because it decreases theoxygen content of the air.

2. If CO2 is not available, use dry chemicalPurple K (PKP) extinguisher.

3. De-energize all electrical circuits that mayinterfere with the proper control or extinguishingof the fire or that may constitute a hazard to thefire fighters.

4. Call the fire department or damage controlcentral. This should be done even if it is a smallfire that can be easily controlled or extinguised.This is a precautionary measure that coversunforeseen complications or miscalculations.

5. Try to control or extinguish the fire ifpossible, using the appropriate fire extinguisherand fire-fighting procedure.

6. Make a full report on the fire to theappropriate authority. The fire marshal hascomplete information about the proper forms andreports and should be contacted for assistance ifneeded. However, this does not relieve the persondiscovering the fire from responsibility in thismatter.

7 . Overhaul o f a l l f i res should beaccomplished by a trained fire-fighting team.

The following actions should not be takenwhen fighting electrical fires:

1. Using water to fight an electrical fire caninjure personnel because water conductselectricity. Also, water can damage equipmentbecause of its corrosive properties when used onmetals.

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2. Do not use foam-type fire extinguishers onelectrical fires because foam is a good electricalconductor.

3. Do not inhale smoke from fires. Smoke cancontain toxic gases, which, if inhaled, could causeserious injury or death.

EXPLOSION.— Fire may cause an explosion,explosion may cause a fire, or the two may beunrelated. Explosion may result from chemicalaction, heat, mechanical malfunction, or othercauses. An explosion is generally accompanied bya loud noise and a sudden buildup of pressure.Several types of explosions are of interest to youas a technician when you perform your normalduties.

1. The accumulation of combustible gases orvapors from fire or from evaporating liquidsrepresents a potential hazard. A spark, an increasein heat, or certain chemical combinations maytrigger an explosion.

2. An explosion in the presence of fire mayresult in the rapid spread of that fire. An explosionin the presence of combustible materials maycause a fire to start.

3. An explosion may result in flying debris,which will act as shrapnel and may cause severepersonnel injuries. In the event of a severeexplosion, nearby personnel may suffer from theconcussion effect of the blast.

There are many explosion hazards besidesfire-caused accumulation of combustible vaporsand the accumulation of combustible gases neara fire or electric spark. A few of these arediscussed in the following paragraphs.

Pressurized equipment and aerosols aresusceptible to explosion in the event of excessivepressurization or a mechanical failure of any partof the pressurized system. If an explosion occurs,the major hazards of the explosion are thecreation of shrapnel and the increased danger ofarcing in the absence of the pressurization.Implosion, like explosion, results in the creationof shrapnel, frequently with toxic materialscoating the splinters. The rapid collapse of glassvacuum tubes is an example of an implosion thatis of prime concern to electronics personnel.

Explosive ordnance devices are sometimesinstalled on aircraft or placed adjacent to theaircraft before loading. Accidental operation ofswitches may result in the firing of these devices.When operating any equipment in the aircraft,you must be constantly aware of any electrically

initiated ordnance devices in the vicinity of theaircraft and must observe all precautions thatapply to the situation. When missiles or weaponsare aboard, only fully qualified personnel shouldbe permitted to operate any electronic equipmentin the aircraft. A definite possibility of detonationof ordnance devices by radiated RF energy is alsoknown to exist. This hazard is discussed later inthe chapter under RF radiation hazards.

Air Contaminants

The term air contaminants refers to vapors,gases, dust, mist, or fumes, especially those thatmay be toxic or hazardous, They may result fromfire, evaporating liquids or solids, chemical action,or air displacement in confined or poorlyventilated spaces. They may be easily detectable,or almost impossible to detect. They mayrepresent a single hazard, or they may representa combination of several distinct hazards.

FUELS.— The vapors from nearly allhydrocarbon fuels present hazards of fire andexplosion. In addition, they are toxic. If breathedin heavy concentration or for prolonged periods,they may result in permanent damage to therespiratory system, loss of consciousness,paralysis, and/or death. For these reasons, thereare numerous mishap-prevention regulations anddetailed procedures regarding fuels and fuelingoperations. In general the most important of theseregulations require rigid enforcement of theNO SMOKING rules, adequate ventilation,restrictions on the use of electrical equipment, useof special equipment, and the presence of mannedfire-fighting equipment.

PAINT SUPPLIES AND MATERIALS.—Most paints, thinners, and many other paintsupplies emit vapors that are both flammable andtoxic. Regulations require that these items bestored in closed containers in a noncombustibleenclosure isolated from living, working, orordinary stowage spaces. Aboard ship, they mustbe stowed in approved flammable storage. Useof the material is restricted to well-ventilatedareas, and in many cases, personal protectiveequipment (PPE) and clothing are required.

BATTERY GASES.— In the standard lead-acid storage battery, explosive gases are generatedby chemical action. When charging, the batteryreleases hydrogen. Hydrogen, a highly com-bustible gas, is violently explosive when in strong

9-7

concentration. The newer nickel-cadmiumbatteries do not present this hazard, but dopresent other hazards that are covered in a laterdiscussion. Battery lockers are subject to verystrict mishap-prevention regulations with specialemphasis on smoking restrictions and ventilationrequirements.

MISCELLANEOUS MATERIALS.— Manyother general classes of materials containsubstances that produce hazardous vapors orgases. You should only use them according tospecified procedures, Some of these classes arecleaning materials, insecticides, preservatives,solvents, adhesives, and finishes.

Other air contaminants, such as dust and smallparticles from grinding operations present similarhazards and require similar precautions. Fumesare condensed metal particles from welding orcutting operations. When working in areas wherefumes are present, you should take requiredspecial precautions and respiratory protection.

Chemical Warfare Agents

The subject of chemical warfare, its agents,treatments, and preventive measures, is treatedin detail in other TRAMANs. Among thesemanuals are Basic Military Requirements,NAVEDTRA 14325, Military Requirements forPetty Officer Third Class, NAVEDTRA 14504,and Military Requirements for Petty OfficerSecond Class, NAVEDTRA 14504.

Radioactivity

The use of radioactive materials is commonthroughout the Navy, particularly in the elec-tronics field. Common radioactive materials

familiar to most technicians include luminousdials on watches, various instruments, CRTs,and the luminescent markings on equipment.Radioactive material is intentionally added tomany special-purpose electron tubes. The materialproduces a continuous supply of ionized particlesto ensure the tube always ionizes at the samevoltage. The principal radioactive materials inthese tubes include certain isotopes of carbon,cesium, cobalt, nickel, and radium. These tubesare usually TR and ATR tubes, glow lamps andcold-cathode tubes, and certain spark gap tubes.With proper precautions and procedures, thesematerials present no serious hazard. However,with careless or improper treatment, the hazardmay become very serious.

Radioactive materials emit rays (known asionizing radiations) that can cause changes inliving tissue, with subsequent injury to the body.The amount of change, and therefore theseriousness of the injury, increases with theamount of radiation absorbed. The absorption ofradiation is cumulative, and the repair of damagedtissue is slow. Therefore, the hazard level is basedon the total amount of radiation absorbed andthe rate of absorption. For more detailedinformation, refer to OPNAVINST 5100.23(series) and OPNAVINST 5100.19 (series).

A primary handling hazard would occur ifradioactive substances enter the bloodstream.These substances may enter through a cut or anabrasion or through slivers of glass from brokentubes penetrating the skin. This type of injury maybe quite serious, even if only minute quantitiesof radioactive materials were injected. Thematerials injected are carried throughout the bodyby the bloodstream. They tend to accumulate incertain organs or parts of the body. In addition

9-8

to the radiation effects, they also cause a type ofpoisoning similar to chemical poisoning.

A wound containing a radioactive particlerequires treatment by a medical officer as soonas possible, regardless of the size of the wound.The hazard of allowing radioactive particles toremain in a wound cannot be ignored.

There are no known antidotes for radiationpoisoning caused by radioactive particles remain-ing in the body. Treatment of radiation sicknessis complicated and lengthy. Even with the bestmedical attention, the results are often incon-clusive. However, progress continues in this field,and close liaison with the medical departmentensures you receive the latest first-aid proceduresand medical treatment.

Inhalation of minute particles of radioactivedust can cause coating of the mucous membranes,which results in poisoning and increased radiationeffects. Once lodged in the nasal passages orthroat, these particles are difficult to remove.They are even more difficult to remove from thelungs.

Contamination of the skin by radioactivematerials may produce radiation burns resemblingthe temporary redness of a mild sunburn. Insevere cases, a serious burn, which destroys theskin, will occur. All such cases should be reportedto the medical authorities immediately. Withproper medical care, complete recovery usuallyoccurs, except in extreme cases involving severeburns over an extensive area. This type of injuryis rare.

DETECTION.— Radioactive radiation iscompletely undetectable through the use of thehuman senses; detection relies upon the use ofspecial equipment. The methods of detection andthe types of radioactivity detectors are discussedin Basic Military Requirements, NAVEDTRA14325. The following areas and/or conditionsrequire monitoring:

Periodically, monitor storage areascontaining instruments, equipments, or tubes withradioactive materials to make sure the radiationlevel does not exceed allowable limits. Specifically,monitor the air intake and exhaust screens orfilters before cleaning.

Monitor all areas that surround brokentubes containing radioactive material or flakingradioactive paint or markings to help locate allthe radioactive material. These areas shouldbe monitored again after decontamination to

determine the effectiveness of the proceduresused.

Monitor personnel whenever contact withradioactive materials is suspected or afterparticipating in decontamination activities.

PRECAUTIONS.— Observe the followingmishap-prevention practices to minimize thehazard presented by radioactive materials.

Tubes or instruments should not beremoved from cartons until immediately beforeactual installation. This serves two purposes—(1)to prevent mishapal breakage and (2) to avoid thepossibility of concentrating several radioactivesources in a small volume (which would increasethe effective intensity of radiation).

When removing a radioactive componentfrom equipment, place it in an appropriate cartonto prevent breakage.

Never carry items containing radioactivematerials in your pocket or elsewhere in a mannerthat lets flaking or breakage occur.

Exercise extreme care whenever handlingradioactive items, especially during installation orremoval from equipment.

Never break tubes intentionally. However,if they do break, do not let contaminated materialcontact any part of your body at any time. Avoidbreathing any dust or vapor (such as radon gas,a highly radioactive substance) released by brokentubes. Locate all broken pieces immediately andisolate the area until the broken pieces have beenremoved or declared nonradioactive by testingwith an adequate radiation-sensitive device.

Do not bring food or drink into acontaminated area or near any radioactivematerial.

Personnel who have handled radioactivematerial in any way should remove contaminatedclothing immediately after leaving a contaminatedarea. They should wash their hands and armsthoroughly with soap and water, especially beforeeating, drinking, or smoking.

If you receive a wound from a sharpradioactive object, report to medical authoritiesfor treatment as soon as possible.

9-9

DECONTAMINATION AND DISPOSAL.—When cleaning a contaminated area, you shouldwear rubber or plastic gloves. Remove largefragments of a broken tube by using tools, suchas forceps, if they are available. You can removethe remaining particles by using a vacuum cleanerwith a HEPA-filter collecting bag or by using awet cloth to wipe across the area. (If tubes arebroken frequently, select the best type ofcollecting bags.)

If you use a wet cloth, make one stroke at atime, and fold the cloth in half after each stroke,always using a clean side. When the cloth becomestoo small, discard it and continue with a cleanpiece. Be careful not to rub the radioactiveparticles into the surface by using a back-and-forth motion. Seal all used cleaning debris, cloths,and bags in a container, such as a plastic bag,heavily waxed paper, or a glass jar, Then, placeit in a steel can for disposal, according to localdisposal guidelines.

Radioactive waste materials and HEPA-filterbags should not be disposed of individually.Collect them in a designated steel container witha tight-fitting lid, suitably marked, until you havea reasonable quantity for disposal. Mark allradioactive material containers with the radiationsymbol (fig. 9-1). The symbol is printed inmagenta (a purplish red) on a yellow background.

Dispose of radioactive waste in proper con-tainers according to current regulations andinstructions of the Nuclear Regulatory Com-mission.

Figure 9-1.-Radiation symbol.

Q6.

Q7.

Q8.

Q9.

Q10.

What training manuals contain informationon fire and explosion?

What is the primary hazard you will meetwhen handling radioactive materials?

List some of the general hazards.

What is an excellent reference fordetermining flash points and concentrationlevels of combustible mixtures?

List the minor hazards associated with anexplosion of pressurized equipment.

MAINTENANCE HAZARDS

Everyone who works with electronic equip-ment must be alert to the hazards of theirequipment and be capable of giving first aid. Theinstallation, operation, and maintenance ofelectronic equipment requires enforcement of astern mishap-prevention code. Carelessness on thepart of the operator or the maintenance techniciancan result in serious injury or death. Mishapinvestigations usually show that mishaps arepreventable by following simple mishap-prevention techniques and procedures with whichthe personnel involved should have been familiar.

Because you work with electronic equipment,you should read and follow the mishap-preventionpractices and procedures contained in applicablesafety directives, manuals, other publications,and in equipment technical manuals. Readthe material before you work on electronicequipment. It is your responsibility to identify,report, and eliminate any unsafe condition andunsafe acts that could cause a mishap.

General Precautions

You should take time to consider and usemishap-prevention techniques when working onelectronic circuits and equipment. Carefully studythe schematics and wiring diagrams of the entiresystem, noting what circuits must be de-energizedand tagged or locked out in addition to themain power supply. Remember that electronicequipments frequently have more than one sourceof power. Be sure that ALL power sources arede-energized before servicing the equipment. Do

9-10

not service any equipment with the power onunless it is necessary.

Remember, de-energizing main supply circuitsby opening supply switches will not necessarily killall circuits in a given piece of equipment. An oftenneglected or ignored source of danger is the inputsto electronic equipment from other sources,such as synchros, remote control circuits, etc.Sometimes neglect and ignorance can be tragic.For example, turning off the antenna safety switchdisables the antenna, but it may not turn off orlockout the antenna synchro voltages from othersources. Moreover, the rescue of a victim shockedby a remote power input is often difficult becauseof the time required to find the power source andturn it off. Therefore, turn off ALL power inputsbefore working on equipment.

Remember that the 115-volt power supplyvoltage is not a low, relatively harmless voltage.This voltage source is the cause of more deathsin the Navy than any other.

Do not work with high-voltage circuits byyourself. Another person (safety observer),qualified in first aid for electrical shock, shouldbe present at all times. The person should alsoknow the circuits and switches controlling theequipment. They should de-energize the circuitimmediately if anything unforeseen happens.

Always be aware of the nearness to high-voltage lines or circuits. Use rubber gloves, whereapplicable, and stand on approved matting. Notall so-called rubber mats are good insulators.

Do not use equipment containing metal parts,such as brushes and brooms, in an area within4 feet of high-voltage circuits or any electric wiringhaving exposed surfaces.

Inform remote stations as to the circuit onwhich you are working.

Keep clothing, hands, and feet dry if at allpossible. When it is necessary to work in wet ordamp locations, use a dry platform or woodenstool to sit or stand on. Place a rubber mat orother nonconductive material on top of the wood.Use insulated tools and insulated flashlights of themolded type when working on exposed parts.

Do not wear loose or flapping clothes. The useof thin-soled shoes with metal plates or hobnails

is prohibited. Safety shoes with nonconductingsoles should be worn if available. Flammablearticles, such as celluloid cap visors, should notbe worn.

When working on electronic or electricalapparatus, remove all rings, wristwatches,bracelets, ID chains and tags, and similar metalitems. Care should be taken that the clothing doesnot contain exposed zippers, metal buttons, or anyother type of metal fastener.

Do not work on energized circuits unlessabsolutely necessary. Be sure to take time totagout or lock out (or block out) the switch. Locksfor this purpose should be readily available.

Use one hand when turning switches on or off.Keep the doors to the switch and fuse boxes closedexcept when working inside or replacing fuses.Use a fuse puller to remove cartridge fuses afterfirst making certain that the circuit is dead.

Secure and tag all supply switches or cutoutswitches from which power could possibly be fedin the OPEN position. The tag should read‘‘THIS CIRCUIT WAS ORDERED OPEN FORREPAIRS AND SHALL NOT BE CLOSEDEXCEPT BY DIRECT ORDER OF. . . .” (theperson making, or directly in charge of, repairs).See OPNAVINST 3120.32 (series) and localinstructions to ensure proper tagging and securingof electrical and electronic equipment.

Never short out, or tamper with, an interlockswitch.

Provide warning signs and suitable guards toprevent personnel from coming into mishapalcontact with high voltages.

Avoid reaching into enclosures except whenabsolutely necessary. If you do have to reach intoan enclosure, use rubber gloves or mats to preventaccidental contact with the enclosure.

Do not use bare hands to remove hot tubesfrom their sockets. Use insulated gloves or a tubepuller.

Use only rubber or insulated hose on air linesfor blowing out equipment. Use no more than 10PSI to avoid damage to the insulation and/orcomponents. Use only moisture-free air. Neverturn compressed air on yourself or others, sinceit could cause serious injury.

9-11

Use a shorting probe (fig. 9-2) to discharge allhigh-voltage charges. Before touching a capacitoror any part of a circuit that is known or likelyto be connected to a capacitor (whether the circuitis de-energized or disconnected entirely), short-circuit the terminals to make sure that anycapacitor is completely discharged.

Degree of Shock

The amount of current that may pass throughthe body without danger depends on theindividual and the current quantity, type, andpath. It also depends on the length of time thecurrent passes through the body. Body resistancevaries from 1,000 to 500,000 ohms for unbroken,dry skin. Moisture lowers body resistance and dryskin increases it. Breaks, cuts, or burns maylower body resistance to 200 ohms. A current of1 milliampere can be felt. Five milliamperes isabout the highest current safe for the averagebody. If the palm of your hand makes contactwith the conductor, a current of about 12milliamperes will cause the hand muscles tocontract. This current will freeze your hand to theconductor. Such shock may or may not causeserious damage, depending on contact time andpersonal physical condition, particularly thecondition of the heart. A current of 25milliamperes can be fatal.

Generally, currents between 100 and 200milliamperes are lethal. Ventricular fibrillation ofthe heart occurs when the current through thebody approaches 100 milliamperes. Ventricularfibrillation is the uncoordinated actions of the

ventricles of the walls of the heart. This, in turn,causes the loss of the pumping action of the heart,Fibrillation is usually fatal because peoplequalified to administer appropriate treatment arenot available to administer treatment soonenough.

If currents of 200 milliamperes or higher passthrough the body, severe burns and uncon-sciousness result. Generally, in these cases theheart will not fibrillate, but it will stop. It maybe started again by closed-chest heart massage.If breathing has also stopped, the heart mayspontaneously restart if cardiopulmonaryresuscitation (CPR) brings the blood oxygensupply to a high enough level. In any case, ifbreathing has stopped, CPR should be startedimmediately.

When a person receives an electrical shock andis unconscious, it is impossible to tell how muchcurrent caused the unconsciousness. CPR mustbe started immediately if breathing has stoppedand continued until the person is breathingnormally or until otherwise directed by medicalauthority.

Special Components

Several components common to aviationelectronic maintenance present hazards orpotential hazards. The following paragraphspresent a brief summary of some of the moreimportant of these components and their hazards.

SELENIUM RECTIFIERS.— When seleniumrectifiers burn out, selenium dioxide gas causes

9-12

Figure 9-2.-Shorting probe.

an overpowering stench. Do not breathe these permitting absorption of some of the seleniumpoisonous gases. If a rectifier burns out, you compound.should de-energize the equipment immediatelyand ventilate the compartment. Allow the POLYCHLORINATED BIPHENYL (PCB).–damaged rectifier to cool before attempting any PCB is a toxic, environmental contaminant thatrepairs. If possible, move the defective equipment was commonly used in older transformers. Otheroutdoors. Do not touch or handle the defective material and equipment that contain PCBs shouldrectifier while it is hot. A skin burn might result, be adequately marked with appropriate warning

9-13

labels (fig, 9-3). PCB contaminants require special the installation and removal process. The weighthandling precautions. You should refer to and clumsiness of the battery can cause backNAVSEA-S9593-A1-MAN-010 and local instruc- injury or muscle strain; common sense and routinetions. attention to detail minimize this hazard. All

rechargeable storage batteries should be chargedBATTERIES.— Battery hazards are most in strict accordance with the manufacturer’s

common during the charging process and during recommendations.

Figure 9-3.-PCB warning labels.

9-14

Lead-Acid.— Lead-acid storage batteriespresent hazards of acid burn, explosion, andback and muscle strain. Prevent burns bythe proper use of goggles and a face shield,rubber gloves, rubber aprons, and rubber bootswith nonslip soles. Wear protective clothingwhenever you are refilling, checking, trans-porting, or charging batteries. Explosion mayresult from accumulation of hydrogen gas duringthe charging operation. Proper ventilation andstrict enforcement of the NO SMOKING rules aremandatory.

Nickel-Cadmium.— The electrolyte used innickel-cadmium (NiCad) batteries is potassiumhydroxide (KOH), a highly corrosive alkalinesolution, which should be handled with the samedegree of caution as sulfuric acid. If KOH issprayed on any material, wash it immediately withliberal quantities of water and neutralize theaffected area with vinegar or a weak solution ofacetic acid.

An extremely violent explosion will occur ifKOH is added to a lead-acid battery or if sulfuricacid is added to a NiCad battery. Although thereis no valid excuse for such an occurrence, it canhappen. Clearly mark all battery electrolytecontainers and keep them in different stage areas,if possible, when they aren’t in use.

Mercury Cell.— Under certain conditions,mercury dry cells or batteries may explode. Themost common cause of explosion is overloadingthe battery (with the subsequent heating andignition of hydrogen gas within the cell). Theloading capacity of the battery decreases as thebattery discharges. When a mercury cell (or anycell within a mercury battery) has discharged to70 percent of its nominal voltage, the cell orbattery should be replaced. Discharged mercurybatteries should never be stored. Follow disposalinstructions contained in OPNAVINST 5190.1(series).

Lithium Batteries.— Never puncture,incinerate, or recharge lithium batteries. Beforelithium batteries are shipped or stored, theterminals should be covered with an insulatingmaterial to prevent short circuits. These batteriesshould be stored in a ventilated and cool fireproofarea. Make sure you use eye and skin protectionwhen working with wet lithium batteries. For

other precautions on lithium batteries, refer toOPNAVINST 5100.19 (series).

CATHODE-RAY TUBES.— Use extremecaution when handling a cathode-ray tube (CRT).The glass envelope encloses a high vacuum;because of the large surface area, the envelope issubjected to considerable total force due toatmospheric pressure.

The trend toward the use of larger CRTsincreases the hazard of implosion. The tubes arenot considered hazardous if handled properly.However, if they are struck, scratched, dropped,or handled improperly in any way, they may causesevere injury or death.

When handling, installing, or removing aCRT, be extremely careful to avoid contactbetween the tube and any sharp or hard object.Wear suitable gloves to protect your hands. Weargoggles, which protect your eyes from flying glassparticles if there is an implosion. The gogglesshould provide both side and front protection andshould have clear lenses that can withstand a rigidimpact. Insert the tube carefully into the socket,using only moderate pressure. Do not jiggle thetube. Never hold it by the narrow neck. Do notstand directly in front of the face of the tube.Accidental implosion may cause the electron gunor other parts to be propelled directly forwardwith sufficient velocity to cause severe injury.When the tube must be set down, it is importantthat the face be placed gently on a thick, clean,soft padding.

In addition to the hazard of implosion, roughhandling may also cause displacement of theelectrodes within the tube and result in faultyoperation or nonoperation of the tube.

The chemical coating material on the face ofthe tube may be extremely toxic. When disposingof a broken tube, you should use protectivedevices and procedures to ensure that none of thiscompound gets on the hands or into the skin.Dispose of the material according to instructionscontained in OPNAVINST 5090.1 (series).

Before discarding a CRT, you must eliminatethe danger of implosion. While wearing PPE,place the defective tube facedown in an emptyCRT carton or special container. Carefully breakoff the location pin from the tube base. Using asmall screwdriver, pliers, or a probe, break off

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the tip of the glass vacuum seal. (See fig. 9-4.)With the vacuum seal broken, pressure inside andoutside the tube will equalize, and the danger ofimplosion is removed. However, all other hazardsstill remain. Before you dispose of a CRTor remove danger of implosion, check localhazardous waste disposal procedures.

DIELECTRIC MATERIALS.— The use ofmicrowave energy causes an increase in powerlevels, which raises several problems. One problemis the use of certain dielectric materials innew environments without previous applicationexperience. In several cases, personnel wereexposed to potentially toxic agents as a directresult of the introduction of new substances, Forexample, using sulfur hexafluoride as a gasdielectric to increase the power-handling capabilityof waveguides. In its pure state, this gas isessentially inert and nontoxic. However, whenarc-over occurs in a waveguide filled with the gas,decomposition products constitute a toxic gashazard. These toxic gases, which include fluorine,are colorless and odorless. While they may notirritate the skin, they may cause extreme lungirritation and hemorrhaging.

Arcing may take place periodically in thewaveguide until the system fails completely, or atleast until system performance drops below anacceptable minimum level. If you open thewaveguide while making repairs on the system,you may release these highly toxic gases. Whenopening a waveguide pressurized with sulfurhexafluoride, use an approved acid gas respirator.Perform this type of work in a well-ventilatedarea. If toxic hazards exist from a mishap, clearthe area of all toxic hazards before allowing otherpersonnel to enter the area.

As toxicological or other informationregarding safety matters becomes available,

Figure 9-4.-Construction of a CRT base.

precautionary measures and protective devices aredeveloped, distributed, and issued. If you don’tknow whether a new material or substance ishazard free, take precautionary measures as ifdefinite hazards were known to exist.

RF RADIATION

Electromagnetic radiation (nonionizing radia-tion) is not visible, Its presence must be detectedand measured by instruments or approximated bymathematical calculations. Radiated beams ofhigh-power RF energy present a health hazard andcontribute to mishaps. In general, the health-hazard and mishap-contributing factors fall intothe ordnance, personnel, fuel, and miscellaneousareas. The Naval Medical Command, Naval AirSystems Command, and Naval Sea SystemsCommand are responsible for establishing health-hazard and mishap-prevention precautionsregarding electromagnetic radiation. For moreinformation on RF hazards, refer to Radio-Frequency Hazards Manual, NAVSEA OP3565/NAVAIR-16-1-529, and Electronics Installa-tion and Maintenance Book— Test Methods andPractices, NAVSEA 0976-LP-000-0130, andOPNAVINST 5100.19 (series).

The energy striking an object in an electro-magnetic field may be reflected, transmitted, orabsorbed; only the absorbed energy constitutesa hazard. The hazard resulting from a focusedconcentration of such energy, like any hazard,can be controlled if personnel understand theconditions and take precautionary measures.

Ordnance Hazards

The problem of hazards of electromagneticradiation to ordnance (HERO) is acute. Thenumber and variety of electrically explosivedevices are increasing rapidly. For example,some current operational weapons contain morethan 76 electro-explosive devices. Continuingdevelopment efforts are directed toward reducingweight and space requirements, lowering powerrequirements, assuring positive response, andincreasing mishap-prevention characteristicsand reliability. These goals are not alwayscomplementary.

At the same time, the power of communica-tions and radar-transmitting equipment isconstantly increasing and the frequency spectrumbroadened. The airborne Navy uses the radio-frequency spectrum from 10 kHz to about20 GHz. Transmitter power outputs extend to

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10 kilowatts at communications frequencies, andpeak power outputs extend to approximately 5megawatts at radar frequencies. These trendsproduce situations that are in direct conflict witheach other. On the one hand, transmitters andtheir antennas have only one purpose—to radiateelectromagnetic energy. The initiating elements ofordnance devices need only be supplied with theproper amount of electrical energy for anexplosion to take place. Therefore, certainprecautions are required for mishap preventionand to ensure reliable performance of ordnanceitems.

To meet the growing need for new proceduresto reduce the hazard to ordnance equipment fromRF radiation, the Naval Air Systems Commandsponsors tests. These tests, coordinated withstudies made by other agencies, have providednew guidelines and restrictions for handlingelectrically initiated ordnance equipment.

The basic problem in determining suscepti-bility of an ordnance system to RF radiation liesin the evaluation of the antenna-like couplings;specifically, the couplings that exist betweenilluminating fields and the electro-explosivedevices in the system. RF energy may enter aweapon as a wave radiated though a hole or crackin the weapon skin, or it may be conducted intothe weapon by the firing leads or other wiresleading into the weapon.

The exact chances of such firing of electro-explosive devices are quite unpredictable. The typeof occurrence depends upon several variables.These variables may be frequency, field strength,positional and directional orientation, environment,and metallic or personnel contacts with theordnance or aircraft. The most susceptible timefor this type of mishap is during ordnanceassembly/disassembly and loading/unloadingoperations or during testing in electromagneticfields. The most likely effects of prematureactuation are dudding, reduction of the reliabilityof the device, or propellant ignition. In extremecases, there is a definite possibility of warheaddetonation.

Some specific mishap-prevention techniquesthat the AT must observe with respect to theseweapons and ordnance devices include thefollowing:

Turn off all RF transmitters duringweapons-handling operations in the area.

Observe all local and general mishap-prevention techniques and HERO restric-tions.

Maintain radio and radar silence duringassembly/disassembly, loading/unloading,or testing operations.

Avoid illumination of ordnance devices byhigh-power RF transmitters.

The HERO problem is a complex one. Thehazard and the solution is a function of thefollowing factors:

1.2.3.4.

In

Frequency and field strengthGeometrical configurationOrientationThe antenna characteristics of the weaponor weapon-aircraft and weapon-launchercombinations

general, the path by which energy isintroduced to the electro-explosive devices is notreadily definable. For more specific information,refer to NAVAIR 16-1-529.

Personnel Hazards

Development of RF systems with high-powertransmitting tubes and high-gain antennas hasincreased the hazard to personnel in the vicinityof these elements. Harmful effects of over-exposure to RF radiation are associated with theaverage power of the absorbed radiation. Theeffects are thermal in nature and are observed asan increase in overall body temperature or as atemperature rise in certain sensitive organs of thebody. The only known nonthermal effects onpersonnel are due to power density valuesconsiderably greater than the power densitiesnormally associated with present RF transmittingsystems.

The Naval Medical Command has establishedsafe limits based on the power density ofthe radiation beam and the exposure time ofthe human body in the radiation field. [SeeOPNAVINST 5100.2 (series) and OPNAVINST5100.19 (series).] All areas in which the RF levelsexceed the safe limits are considered hazardous.The Naval Sea Systems Command is responsiblefor determining hazardous shipboard areas,posting or marking these areas, and for decreasingthe hazard to personnel from RF radiation.Calculations and power density measurements areused to establish the distances from radarantennas within which it is not biologically safefor personnel to enter. This information is thenused to determine if and where hazardous areas

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exist. All hazardous areas subject to entry bypersonnel are posted with warning signs, and theship’s intercommunication system is used to warnpersonnel when the radars are operating.

Personnel must be protected from RF radia-tion; however, blanket restrictions on antennaradiation are not possible. Maintenance andcheckout procedures must take place and can bedone by taking the following precautions:

Do not visually inspect feed horns, openends of wave guides, and openings emitting RFelectromagnetic energy unless the equipment isdefinitely secured for the purpose of such aninspection.

Park aircraft having high-power radar ororient their antennas so that the beam is directedaway from personnel working areas.

Observe RF-hazard warning signs and deckmarkings (fig. 9-5), which point out the existenceof RF radiation hazards in a specific location orarea.

Either continuously rotate while radiatingantennas that normally rotate or train the beamto a known safe bearing.

Train and elevate nonrotating antennasaway from inhabited areas, hangars, shop spaces,ships, piers, etc., while radiating.

Where a poss ib i l i ty o f mishapaloverexposure might still exist, have someonestationed within view of the antenna to warnpersonnel of the hazard. However, have them staywell out of the beam and in communication withthe operator while the antenna is radiating.

Radiation-hazard warning signs should beavailable. You must use them not only where theymust be permanently posted but also where theymay temporarily restrict access to hazardousareas.

Table 9-1 generalizes the relationshipbetween transmitter power and safe distance forpersonal exposure of 1 hour or more. It is thusapplicable to many types of transmitters.Guidelines and specifics can be found in NAVAIR16-1-529.

Table 9-1.-Transmission Power Versus Safe Distance

Fuel Hazards

The increase in radiated RF energy fromhigher power communications and radar equip-ments has increased the potential hazard ofRF-induced ignition of volatile fuel-air mixtures.This flammable condition is normally present onlyclose to aircraft fuel vents, open fuel inlets, orspilled fuel, or during over-the-wing fuelingoperations. Ignition of fuel vapors in air hasoccurred; however, the probability of ignitionwith normal refueling conditions is remote.

Ignition of gasoline vapors caused by RF-induced arcs is rare because ALL of the followingconditions must exist:

1.

2.

3.

a flammable fuel-air mixture must bepresent within the range of the inducedarcing,the arc must contain a sufficient amountof energy to cause ignition, andthe gap across which the arc occurs mustbe a certain minimum distance and mustcontain a sufficient amount of theflammable mixture to ignite.

The possibility that these conditions wouldoccur at the same time is remote; but since thepossibility does exist, radars should not beoperated within 100 feet of a fueling operation.For specific fuel-hazard information, refer toNAVAIR 16-1-529.

Miscellaneous Aspects

Photoflash bulbs, fluorescent lamps, and neonglow lamps can be activated by electromagneticenergy from radar sets. Although this doesn’t

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Figure 9-5.-RF hazard warnings.

happen often, personnel should be warned of the exposed to radiation. With some high-power radarpresence of any high-power radar operating in the sets, steel wool ignites with a violent explosion.area and of the hazards involved. The presence of oils and spilled fuels in the vicinity

In a similar manner, steel wool may be set of aircraft constitutes a serious hazard. Thisafire, or metallic chips may produce sparks when makes good housekeeping procedures essential.

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Keep in mind that you, the technician, are thekey to mishap prevention. Be alert at all times andbe safe. No job is so important that you have tobe unsafe.

Q11.

Q12.

Q13.

Q14.

Q15.

Q16.

Q17.

When a selenium rectifier burns out,selenium dioxide gas is liberated. Whatsteps should be taken when a seleniumrectifier does burn out?

When used as a gas dielectric in a wave-guide, what causes sulfur hexafluoride tobecome toxic?

List some of the danger sources oftenneglected when de-energizing electronicequipment.

Who should you contact if you find a circuittagged out for repairs?

When are battery hazards most common?

Before discarding a CRT, you musteliminate the danger of implosion. What doyou do first?

What times are most susceptible to HEROmishaps?

LASER SAFETY

Learning Objective: Recognize biologicaleffects of laser radiations, and identify

laser safety responsibilities assigned tovarious commands and personnel.

The following text discusses the proceduresand precautions to follow during laser operationto prevent injury to personnel and damage tomaterial by laser radiation. The biologicaleffects of laser radiation are described, and thedescriptions and sources of protective devices aregiven. Because the Navy uses laser systems, rangeofficers and safety personnel must know lasersafety procedures.

BIOLOGICAL EFFECTS OF LASERRADIATION

The electromagnetic spectrum (fig. 9-6)includes radiated energy ranging from gammarays to dc electricity. The type of emitted energydepends upon the wavelength of the radiation.The optical radiation of the electromagneticspectrum includes infrared, visible light, andultraviolet; it is known as light.

The initial physical effects of laser radiationare thermal, photochemical, or thermal acoustic.The initial physical trauma of exposure is followedby a biological reaction of the tissue itself. Thelasting effects of this damage range from completerecovery to severe injury with little or no recovery.

The skin can be damaged by exposure to laserradiation. The large surface area makes itsusceptible to radiation exposure; therefore,

Figure 9-6.-Electromagnetic spectrum.

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caution should be taken to protect your skin ifyou may be exposed to laser radiation. The eyeis the one organ of the body that is affecteddirectly by optical radiation because it has nonatural protection, and its function is to collectand concentrate light. For information aboutmedical and health considerations, refer toOPNAVINST 5100.23 (series) and OPNAVINST5100.19 (series).

General Precautions

Most injuries from laser radiation occur in thelaboratory or intermediate maintenance activity.These injuries usually happen because personneldo not wear the proper eye protection. Controlmeasures must be taken to make sure thatpersonnel use the correct protection for the highestclass of laser in operation.

Eye Protection

In any situation where you may be exposedto laser radiation at levels that can cause eyedamage, eye protection must be worn! Todetermine when eye protection is required and

what type should be selected, you must know thefollowing factors:

The laser wavelengths

The maximum intensity of the beam at theeye of the observer

The maximum permissible exposure(MPE) for that wavelength

The optical density (OD) required of thefilter to reduce the intensity-below MPElevels

The characteristic of a protective device thatreduces the energy in a laser beam to a safe levelis the optical density (OD) of the device.

Laser protective devices are available frommany sources. Some devices are available throughnormal supply channels. Other devices areavailable from commercial sources only. Therecommended protective densities, devices, andtheir sources for typical laser protective devicescurrently in the Navy inventory are shown intable 9-2.

Table 9-2.-Protection Densities, Devices, and Sources

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When assigned to a laser system, ensure that LASER SAFETY RESPONSIBILITIESyou obtain and observe all additional precautionslisted in the applicable maintenance instructions The safety responsibilities for the variousmanual. To minimize the danger of laser devices, commands and personnel are discussed in theyou should always follow these general practices: following paragraphs.

1.

2.3.

4.

5.

6.

7.

8.

9.

10.

11.

Use laser equipment properly.Know laser hazards.Ensure research laboratory areas andmaintenance shops are closed areas.Wear goggles or filter-type goggles whenworking with lasers.

Do NOT look directly at an operatinglaser or its reflection in any type ofoperation.

Avoid all contact between the skin and thelaser beam.

Report any concern or anxiety aboutpossible or existing exposure to laserradiation to appropriate medicalpersonnel.

Do NOT look directly at the pump source.

Use countdown procedures.

Ensure a minimum of two people arepresent whenever the laser is operating.

Identify laser areas properly by posting

Space and Naval WarfareSystems Command

Space and Naval Warfare Systems Commandis the lead agency for laser safety in the Navy. Itexercises technical direction over laser safety bothafloat and ashore [See SPAWARINST 5100.12(series)]. The command is responsible for directingand coordinating the following:

The establishment of Navy laser safetydesign standards, documentation, andoperational guidance

Surveys, reviews, and measurements andsafety certification of laser target areas,laser systems, and installations

Reviews of laser systems by the Navy LaserSafety Review Board (LSRB)

The development of laser protectivewarning signs (figs. 9-7 and 9-8). devices -

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Figure 9-7.-Examples of laser classes 2 through 4 warning labels.

Figure 9-8.-Laser maintenance area warning signs.

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Naval

An inventory of all military-exempt lasersand class IIIb and class IV lasersNavy-wide

The Navy participation in all triservice andinteragency laser safety matters andsupport of the Naval Medical Command(NAVMEDCOM) with regard to laserradiation health medical surveillance

Support the Chief of Naval Education andTraining (CNET) with regard to laserradiation safety training

Medical Command(NAVMEDCOM)

The medical aspects of laser safety are theresponsibility of the Naval Medical Command.These responsibilities are as follows:

Recommend and issue maximum permissi-ble exposure limits.

Establish medical surveillance programsand evaluate suspected laser overexposurelimits.

Conduct research on the biological effectsof laser radiation.

Conduct laser health surveys ashore andafloat.

Provide technical assistance and adviceconcerning laser radiation health hazards.

Commanding Officer

The commanding officer of a ship or navalshore station is responsible for the safety ofthe personnel under his/her command. Thecommanding officer should take action to ensurethat personnel performing or supervising laseroperations are qualified and certified. Also, thecommanding officer should require personnel ofother agencies, including contract personnel, toconduct their activities according to safety ruleswhen they are on board. Commanding officersalso have the authority to impose and enforcemore stringent safety rules than those imposed byhigher authority. If no safety rule or regulationexists that applies to a given situation, thecommanding officer should submit this require-ment to the Space and Naval Warfare SystemsCommand.

Laser System Safety Officer (LSSO)

The LSSO establishes and chairs a local lasersafety committee, This committee assists theLSSO in the above responsibilities if warrantedby the potential hazards of the local operations.

Supervisory Personnel

Laser and laser system supervisors areresponsible for normal installation planning,operational procedures, employee training, andmishap investigation. These supervisors shouldmaintain a log of all laser firings including thedate, time, and location (and any abnormaloccurrences of the firing[s]).

Operating Personnel

All laser operating personnel should under-stand the potential hazards of laser operations.Also, personnel who operate lasers should befamiliar with normal and emergency proceduresand personal protective equipment.

RECOMMENDED READING ONSAFETY AND MISHAP

PREVENTION

You have been referred to many publicationsin this chapter. These publications will give youmore detailed information on safety and mishapprevention. For specific information, you shouldrefer to the following publications.

Naval Aviation Maintenance Program,OPNAVINST 4790.2 (series)

The Naval Aviation Safety Program,OPNAVINST 3750.6 (series)

Navy Occupational Safety and Health(NAVOSH) Program Manual, OPNAV-INST 5100.23 (series)

Navy Occupational Safety and Health(NAVOSH) Program Manual for ForcesAfloat, OPNAVINST 5100.19 (series)

DOD Hazardous Materials InformationSystem, Hazardous Item Listing, DOD6050: 5-L (series), Material Safety DataSheet (MSDS)

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Electronics Installation and MaintenanceBook–General (EIMB), SE000-00-EIM-100

Navy Laser Hazards Prevention Program,SPAWARINST 5100.12 (series)

Q18.

Q19.

Q20.

List the laser factors necessary todetermine when eye protection isrequired and what type of pro-tection.

What command is the lead agencyfor laser safety in the Navy?

What command conducts laserhealth surveys ashore and afloat?

SECURITY OF CLASSIFIEDMATERIAL

Learning Objectives: Recognize the use andlimitations of each category of securityclassification; identify safekeeping,storage, access to, and control of classifiedmatter policies. Recognize the purpose andscope of each type of security investigation.Identify policies, procedures, and responsi-bilities pertaining to the handling anddisclosure of classified material. Recognizethe procedures required for reporting theloss, possible compromise, or mishandlingof classified material. Identify means usedto transmit each category of classifiedmaterial. Recognize the methods ofdestruction of classified material, andidentify the records of destruction.

History indicates that most wars are carefullyplanned long before the first shot is fired. Duringso-called peaceful periods, nations collect andevaluate all types of intelligence material frompotential enemies. In peacetime, people tend torelax, and security is sometimes ignored. Thistendency makes it easier for a potential enemy togather information concerning our capabilitiesand intentions.

The term security is defined as a protectedcondition of classified information that preventsunauthorized persons from obtaining informationof director indirect military value. This conditionis the result of establishing and maintainingprotective measures that ensures information issafe.

A simple security principle is used within theDepartment of Defense. Only personnel who havethe proper clearance and who have a need to knoware permitted possession or knowledge ofclassified information. It is the possessor of thematerial that has the responsibility of determiningwhether a person’s duties involve a need to knowor whether that person is authorized to receiveclassified material.

The regulations and guidance for classifyingand safeguarding classified information are foundin the Department of the Navy Informationand Personnel Security Program Regulation,OPNAVINST 5510.1 (series). This instruction isthe basic Department of the Navy regulationgoverning the Information and Personnel SecurityProgram. In OPNAVINST 5510.1 (series), youwill also find policy and guidance from theDepartment of Defense (DOD) InformationSecurity Program Regulation, DODINST 5200.1(series) and DOD Personnel Security ProgramRegulation, DODINST 5200.2 (series). Informa-tion from DOD INST 5200.1 (series) pertains toall Department of Defense personnel. Informationin this instruction pertains to all military andcivilian personnel and to all activities ofDepartment of the Navy.

CLASSIFICATION DESIGNATIONS

Official information that requires protectionin the interest of national security must beclassified under one of three designations—TopSecret, Secret, and Confidential.

1. Top Secret. Use of the classification TopSecret is limited to defense information ormaterial that requires the highest degree ofprotection. Top Secret is applied only toinformation or material the unauthorizeddisclosure of which could result in exceptionallygrave damage to the national security and could

lead to a break in diplomatic relations,armed attack on the United States orits allies, or a war, and

compromise national defense plans orscientific or technologicaldevelopments vital to the nationalsecurity.

2. Secret. Use of the classification Secret islimited to defense information or material whoseunauthorized disclosure could result in seriousdamage to the national security and could

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jeopardize the international relations ofthe United States,

endanger the effectiveness of aprogram or policy vital to the nationaldefense,

compromise important military ordefense plans or scientific or techno-logical developments important tonational defense, and

reveal important intelligence opera-tions.

3. Confidential. Use of the classificationConfidential is limited to defense information ormaterial the unauthorized disclosure of whichcould result in damage to the national security.An example is the unauthorized disclosure oftechnical information used for maintenance andinspection of classified munitions of war.

CUSTODY

The custody of classified material is extremelyimportant. In this section, a brief discussion onclassified material storage, custody, and access ispresented.

Storage

Commanding officers are directly responsiblefor safeguarding all classified information withintheir commands. They are responsible forestablishing measures for the inspection of safestorage containers and areas where classifiedmaterial is kept to ensure compliance with securityregulations. The term commanding officer isintended to include competent authority,commander, o f f i c e r i n charge, naval

representative, director, inspector, and any othertitle assigned to an individual (military or civilian)who, through position or status, is qualified toassume responsibility y and make decisions.

In keeping with the Navy’s security principleof need to know, combinations to locks ofclassified containers should only be known tothose whose official duties demand access to thecontainer. Also, a record of combinations mustbe sealed in an envelope and kept on file by aperson designated by the commanding officer.

When selecting combinations for locks, youshould avoid using personal data, such as birthdates and serial numbers. You should also avoidusing multiples of numbers and simple ascendingor descending arithmetic series. A combinationshould never be used for more than one containerin any one classified material control center orsecondary control point.

When securing dial combination locks, youshould rotate the dial at least four complete turnsin the same direction. The drawers of safes andcabinets should be checked to assure they are heldfirmly in the locked position.

The combination to a security container ischanged when the container is placed in use afterprocurement, whenever an individual knowing thecombination no longer requires access, andwhenever the combination is compromised or thesecurity container is discovered unlocked andunattended. In addition, the combination mustbe changed at least annually and reset to standardcombinations if taken out of service.

Custodians

Custodians of classified material are responsi-ble for providing protection and accountabilityfor that material at all times. They should lockclassified material in appropriate securityequipment whenever the material is not in use or

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under direct surveillance of authorized persons.Never remove classified material from workingareas for the purpose of working on such materialduring off-duty hours or for any other purposethat involves personal convenience.

EMERGENCY PLANNING.— Plans must bedeveloped by each command for the protection,removal, or destruction of classified material incase of natural disaster, civil disturbance, orenemy action. Such plans establish detailedprocedures and responsibilities for the protectionof classified material so that it does not fall intounauthorized hands. Such plans must also indicatewhat material is to be guarded, removed, ordestroyed. An adequate emergency plan providesfor guarding the material; removing the classifiedmaterial from the area; complete destruction ofthe classified material on a phased, priority basis;or any combination of these actions. However,reducing the amount of classified material onhand and maintaining only current and necessarymaterial can be the most effective step towardplanning for an emergency situation. Emergencyplans should provide for the protection ofclassified information in a manner that willminimize the risks of loss of life or injury topersonnel.

ACCOUNTABILITY.— Except for publicationscontaining a distribution list by copy number, allcopies of Top Secret documents must be seriallynumbered at the time of origination, in thefollowing manner: Copy No. of copies.

Top Secret documents must contain a list ofeffective pages; this list should include a Recordof Page Checks. When this is impractical, as incorrespondence or messages, the pages must benumbered as follows: Page pages.

Commanding officers establish administrativeprocedures for recording all Secret materialoriginated and received. They maintain areceipting system for all Secret material distributedor routed to activities outside their commands.As a general rule, Secret materials are also seriallynumbered.

Access and Dissemination

Personnel whose work requires access toclassified material must have an appropriateclearance. The standards for the various levels ofclearances are different, but they all follow a basicformat for both civilian and military personnel.Essentially, the standards are that no person is

permitted knowledge of, possession of, or accessto classified material solely by virtue of rank,position, or security clearance. Clearance servesto indicate that the persons concerned are eligiblefor access to classified material if required by theirofficial duties. No person is granted a securityclearance unless it has been determined that theclearance is in keeping with the interests ofnational security.

ELIGIBILITY STANDARDS.— Any personauthorized access to classified information isconsidered to be loyal and to possess goodcharacter, integrity, trustworthiness, and habitsand associations that indicate discretion orgood judgment in the handling of classifiedinformation. The ultimate determination ofwhether the granting of a clearance is in keepingwith the interests of national security must be anoverall determination based on all availableinformation. Some of the significant personalsecurity factors, both past and present, that areinvestigated and considered before a clearance isgranted includes the following:

Any criminal, infamous, dishonest, ornotoriously disgraceful conduct

Habitual excessive

Drug abuse

Sexual perversion

use of intoxicants

Any excessive indebtedness, recurringfinancial difficulties, unexplainedaffluence, or repetitive absences withoutleave that furnish reason to believe that theindividual may act contrary to the bestinterests of national security

SECURITY CLEARANCE.— A personalsecurity clearance requires an administrativeinvestigation by competent authority and certifiesthat the person is eligible for access to classifiedmaterial of the same or lower category as theclearance being granted. Security clearances areof two types:

1. Final clearance—one granted uponcompletion of the required investigation

2. Interim clearance—a temporary eligibilityfor access to classified information basedon a lesser investigative requirement

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An interim clearance is issued only when thedelay of waiting for the completion of theinvestigation required for a final clearance wouldbe harmful to the national interest. When interimclearance procedures are used, the investigationrequired for a final clearance must be initiated.A final clearance is executed upon the satisfactorycompletion of the investigation, unless suchclearance is no longer required.

REQUIREMENTS FOR SECURITYCLEARANCE.— The clearance requirementslisted below are solely for military personnel.

Top Secret.— The investigative requirementsfor access to Top Secret material are as follows:

Final clearance—a background investiga-tion (BI) or special background investi-gation (SBI).

Interim clearance—a satisfactorycompletion of a national agency check ifthe BI or SBI has been requested.

Secret.— For access to Secret material, a finalclearance requires a specific type of nationalagency check, depending on the individual’semployment status. An interim clearance may beissued to personnel if the necessary nationalagency check has been requested.

Confidential.— A final clearance requires anational agency check, depending on theindividual’s employment status. An interimclearance may be granted if the national agencycheck has been requested.

PERSONNEL SECURITYINVESTIGATIONS

The following are categories of personnelsecurity investigations. The NAC and backgroundinvestigations are described in this section. Referto OPNAVINST 5510.1 (series) for specificdetails.

1. A national agency check (NAC)2. A national agency check with written

inquiries (NACI)3. A DOD national agency check plus written

inquiries (DNACI)4. A background investigation (BI)5. A special background investigation (SBI)6. A periodic reinvestigation (PR)

A National Agency Check (NAC)

A national agency check (NAC) consists of acheck with various federal agencies by DefenseInvestigative Service (DIS) for pertinent facts thathave a bearing on the loyalty and trustworthinessof the individual. The initial NAC conducted oninductees and first-term enlistees does not includea detailed technical fingerprint search, and it isreferred to as an ENT NAC.

A National Agency Check With WrittenInquiries (NACI)

NACI consists of a national agency check(described above) by the Office of PersonnelManagement (OPM) on civilian employees andwritten inquiries sent to law enforcement agencies,former employees, references, schools attended,and so forth, for pertinent facts having a bearingon the individual’s suitability for federalemployment.

A Background Investigation

A background investigation conducted forclearance purposes is designed to developinformation on whether the access to classifiedinformation by the person being investigated isclearly consistent with the interest of nationalsecurity. In this investigation, inquiry is made onthe loyalty and trustworthiness of the individual.It normally covers the most recent 5 years of theperson’s life or from the date of that person’s 18thbirthday, whichever is the shorter period. At leastthe last 2 years is covered, except that noinvestigation is conducted before a person’s 16thbirthday. When derogatory information isdeveloped in the course of any investigation, theinvestigation is extended to any part of theindividual’s life necessary to substantiate ordisprove the information and to develop adequateinformation upon which to base a securitydetermination.

SECURITY MANAGEMENTPROCEDURES

Each command develops written securityprocedures to meet the requirements of securityregulations. These procedures specify what is tobe done, who is to do it, and who is to superviseit. They are rewritten, as required, when changesin Navy security regulations occur or whenchanges in the command’s assigned functions

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occur. These procedures include requirements forany special or extraordinary control measures thatneed to be observed to provide the required degreeof circulation control. This is especially truewhenever automatic data-processing equipmentis used to process any classified information orwhen any printing, duplicating, or reproducingof classified material is accomplished at the localcommand.

Security Manager

The commanding officer is assisted in fulfillinghis/her responsibility for the security of classifiedmaterial by the security manager. The securitymanager serves as the commanding officer’s directrepresentative in all cases concerning security. Thesecurity manager ensures that the proper securityclearances are obtained and coordinates a securityorientation, education, and training program forthe protection of classified information.

Disclosures

Classified material is issued to all agencies ofthe executive branch of the government. Ifrequests come from Department of Defenseactivities, the need to know maybe judged on theface of the request. When the need to know is notdiscernible from the scope of the requester’sactivities, classified material is sent via thedepartmental headquarters of the requestingactivity for a determination of the requester’s needto know and capability to handle classifiedmaterial.

The authority for disclosure of classifiedmilitary information to foreign governments hasbeen centralized in the Navy Office of TechnologyTransfer and Security Assistance. Accordingly,no command, office, agency, or individual in theDepartment of the Navy may disclose classifiedinformation, direct the disclosure of it, or permitthe disclosure of it by oral, visual, writtencommunications, or by any other means to foreigngovernments or international organizations unlesssuch disclosure has been specifically authorizedin writing. OPNAVINST R5510.48 (series) con-tains specifics and guidance for proper authori-zation authority.

VIOLATIONS AND COMPROMISES

Violations and compromises of classifiedmaterial occur all too regularly. The followinginformation is a brief outline of procedures

necessary for reporting and investigating theseoccurrences.

Security Violations

Any person who has knowledge of a loss orpossible compromise of classified matter mustreport the fact immediately to the securitymanager or commanding officer. Any violationof regulations that pertains to the safeguardingof classified material but does not result incompromise (or the material is not subject tocompromise) is acted upon by the individual’scommanding officer without reference to higherauthority. The fact that a security violationhas occurred may, at the discretion of thecommanding officer, be considered sufficientjustification for some form of formal disciplinaryaction.

If a classified material storage container isfound unlocked in the absence of assignedpersonnel, report such information immediatelyto the senior duty officer. Guard the containeruntil the duty officer arrives at the location of theunlocked container. The duty officer inspects theclassified material involved, locks the container,and makes a security violation report to thecommanding officer. If the duty officer believesthat classified information has been compromised,the duty officer must require the personresponsible for the container to return to theassigned ship or station to make a definiteinspection report. Appropriate further actionmust be taken by the commanding officer orhigher authority. In addition, change thecombination.

Commanding officers who receive classifiedmaterial that shows improper handling by thesending activity must promptly notify thatactivity’s commanding officer. For example,security violations involving improper mailing,shipping, wrapping, packaging, or transmissionof classified material, or failure to mark oraddress inner wrappings or envelopes properlyshould be promptly reported.

If classified information is compromisedbecause it appears in a newspaper, magazine,book, pamphlet, radio or television broadcast,etc., a report is made to the Chief of NavalOperations (CNO). This report fully identifieswhat information is considered classified, thenews media concerned (title, date, issue, volume,page, column, station, program, etc.), and thereporter or author involved. The report cites thoseportions of the magazine, book, etc., that reveal

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the classified information. If known, the level ofclassification and original classifying authority isestablished.

If lost classified material is found and thematerial has definitely been compromised, thecompromise must be reported to all personnelnotified of the loss.

Preliminary Inquiry

When a command receives a report of acompromise and does not have the custodialresponsibility for the material compromised, thenthe command takes the following actions:

1.

2.

3.4.

Accurately identifies the information ormaterial involvedDetermines the circumstances of possiblecompromiseIdentifies all witnesses to the eventTentatively establishes the degree ofprobabi l i ty o f compromise

This information is sent to the commandhaving custodial responsibility as quickly aspossible. If the command having custodialresponsibility cannot be determined, thecommand initially notified will, to the extentfeasible, conduct the preliminary inquiry and anysubsequent investigation.

The responsible custodial command conductsa preliminary inquiry if it receives a report ofcompromise or suspected compromise. If theinquiry finds a suspected compromise but minimalrisk and no significant command securityweakness, the formal disciplinary action is notrequired. If the next higher commander in thechain agrees, no further action may be necessary,

If a compromise is confirmed, and probabilityof damage to national security may exist,significant activity weakness is revealed, orpunitive action is appropriate, a JAG manualinvestigation is started. A report of the pre-liminary inquiry is sent to the originator. Also,information copies of the preliminary inquiry aresent to the custodial command’s chain ofcommand and the Chief of Naval Operations(CNO).

Investigations

In the Department of the Navy, all investiga-tions are in the form of a Judge Advocate General

(JAG) manual investigation. The JAG manualinvestigation includes the following:

1. A complete identification of each item ofclassified material involved.

2. A complete identification of all theindividuals mentioned in the report.

3. Findings of fact in the form of achronology of the circumstances relating to theevent.

4 . A f ind ing o f fac t or op in ion , asappropriate, establishing a time frame duringwhich the material was subjected to compromise.

5 . A f inding o f fac t or op in ion , asappropriate, as to the person or personsresponsible, if individual culpability is indicated.

6 . A f inding o f fac t or op in ion (asappropriate) as to the probability of compromise.If, during the course of investigation, thedetermination is made that compromise did notoccur, the investigation may be terminated. If theinvestigation is terminated, the recipients of thereport of initial inquiry must be so advised, witha brief statement supporting the determination.

7. By reference, enclosure, or finding of fact,affirmation of notification of the originators ofthe material involved.

8. Recommendation as to remedial action tobe taken to prevent recurrence.

9. Recommendation (when required by theappointing order) as to disciplinary action.

This report of investigation is forwarded tothe CNO via the chain of command. It includesapproval or disapproval of the proceedings,measures taken to prevent a recurrence, and anydisciplinary action taken or recommended.

TRANSMISSION OF CLASSIFIEDMATERIAL

When material leaves the originator and is sentto the addressees, it is transmitted. Whether it goesby courier, by radio, or by mail, if it is classified,it has to be safeguarded.

Top Secret material is transmitted by directpersonal contact of officials concerned, ArmedForces Courier Service, or electrical means inencrypted form. Top Secret material is NOTtransmitted through the United States postalsystem or any foreign postal system.

Secret material is transmitted in any of themeans approved for transmittal of Top Secretmaterial and by United States registered mail.

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Confidential material is transmitted by anymeans approved for the transmission of Secretmaterial and by U.S. Postal Service certified orfirst-class mail within U.S. boundaries. U.S.Postal Service registered mail is used for allNATO, SEATO, and CENTO Confidentialmaterial; all FPO or APO addressees; and anyother addresses when the originator is not surewhether their location is within U.S. boundaries.

DESTRUCTION OF CLASSIFIEDMATERIAL

When a command’s classified material is nolonger required, it is not allowed to accumulate.It is either turned in to the appropriate office ordestroyed.

Methods of Destruction

Classified material is destroyed in the presenceof appropriate e cleared officials. It is burned,melted, chemically decomposed, pulped, pul-verized, shredded, or mutilated so it can’t berecognized or reconstructed.

During emergency situations at sea, classifiedmaterial is jettisoned at depths of 1,000 fathomsor more. If it is not possible to jettison thematerial in water 1,000 fathoms deep and if timedoes not permit other means of emergencydestruction, the material should be jettisonedto prevent its easy capture. When shipboardemergency destruction plans include jettisoning,document sinking (weighted) bags should beavailable. If a vessel is to be sunk throughintentional scuttling or is sinking due to hostileaction, classified material should be locked insecurity filing cabinets or vaults and allowed tosink with the vessel, rather than being jettisoned.

As a last resort, and when none of the methodspreviously mentioned can be used, the use of othermethods, such as dousing the classified materialwith a flammable liquid and burning it, is usedas an alternate to certain loss.

Records

Records of destruction are not required forConfidential documents. Records of destructionare required for Top Secret and Secret material.They are dated and signed by two officials thatwitness the actual destruction; however, if the

classified material is placed in burn bags, thedestruction record is signed by the witnessingofficials at the time the material was placed in theburn bags. The record of destruction is retainedfor 2 years. Persons witnessing the destruction ofclassified material must

1. have a security clearance at least as highas the category of material being destroyed, andbe thoroughly familiar with the regulationsand procedures for safeguarding classifiedinformation;

2. observe the complete destruction ofclassified documents;

3. check residue to determine that destructionis complete and reconstruction is impossible; and

4. take precautions to prevent classifiedmaterial or burning portions of classified materialfrom being carried away by wind or draft.

Q21. What instruction contains regulations,references, and guidance for classifying andsafeguarding classified information?

Q22. List the three classification designations ofofficial information that requires protectionin the interest of national security.

Q23. When is the combination of a securitycontainer changed?

Q24. What are the two types of personnelsecurity clearances?

Q25. List the categories of personnel securityinvestigations.

Q26. Describe the time frame involved in anormal background investigation coverageof an individual’s life.

Q27. What Navy office has been established asthe centralized authority for disclosure ofclassified information to foreign govern-ments?

Q28. Which classified material designationswould require records of destruction?

Q29. Describe the requirements of personnelwitnessing the destruction of classifiedmaterial.

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APPENDIX I

GLOSSARY

ABSORPTION—Loss of energy that is turnedinto heat.

ABSORPTION FREQUENCY METER(WAVEMETER)—A frequency-measuring deviceincorporating a variable-tuned circuit that absorbsa small portion of the radiated energy undermeasurement.

ACCESS TIME—In computers, the timeinterval between the calling for information froma computer unit and the instant that such infor-mation is delivered.

ACCUMULATOR—A computer unit whereinnumbers are accumulated. Usually an accumulatorholds one number in storage; when a secondnumber is entered, the accumulator adds the twonumbers and retains the sum in storage.

ACOUSTIC—Pertaining to sound or thestudy of sound.

ACTIVE SONAR—An apparatus that radiatesand receives information from returning echoes.

ADDER—An electronic circuit capable ofproviding the sum of two numbers enteredtherein.

ADDRESS—In computers, an identifyingnumber or numbers or a particular group ofsymbols that identifies a particular storagelocation.

ADF—Automatic direction finding. Anautomatic radio compass that automatically aimsa directional antenna to show the direction of thelocation of a transmitter. The ADF is normallyused for homing purposes, but it can be used inconjunction with the magnetic compass to provideline-of-position information.

ADP—Acoustic data processor.

AMBIENT CONDITIONS—Physical condi-tions of the immediate environment; may pertainto temperature, humidity, pressure, etc.

AMBIENT NOISE—The naturally occurringnoise in the sea and the noise resulting from man’sactivity, but excluding self-noise and reverberation.

ANALOG COMPUTER—A type of computerthat provides a continuous solution of amathematical problem with continuously changinginputs. Inputs and outputs are represented byphysical quantities that may be easily generatedor controlled.

AND GATE—A logic circuit having multipleinputs and a single output, so designed that theoutput is energized when (and only when) everyinput is in the prescribed signal state.

ANTENNA—Also aerial, A conductor orsystem of conductors that radiates or interceptsenergy in the form of electromagnetic waves.

ANTIJAMMING—A function of a radar setto reduce or eliminate enemy jamming of electro-magnetic waves, which hinder the usefulness ofspecific segments of the radio spectrum.

A-SCAN (A-DISPLAY)—In radar, a displayin which targets appear as vertical displacementsfrom a line representing the time base. Targetdistance is represented by the horizontal distancefrom one end of the time base. Amplitude of thevertical deflection is a function of the signalintensity.

ASW—Antisubmarine warfare. Operationsconducted against submarines, their supportingforces, and bases.

ASWOC—ASW operations center.

ASYMMETRIC—Not symmetrical; withoutsymmetry.

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AVB—Avionic Bulletin.

AVC—Avionic Change.

AZIMUTH—Angular position or bearing ina horizontal plane, usually measured clockwisefrom true north. Azimuth and bearing are oftenused synonymously.

BALLISTICS—The term that refers to thescience of the motion of projectiles or bombs.

BAND—The radio frequencies existing betweentwo definite limits and used for a definite purpose;for example, standard broadcast band extendingfrom 550 to 1600 kHz.

BANDWIDTH—The total frequency width ofa channel or band of frequencies.

BATHYTHERMOGRAPH—A recordingthermometer for obtaining a permanent graphicalrecord of water temperature in degrees Fahrenheitat different water depths, in feet, as it is loweredor dropped into the ocean.

BEACON—Compared to a lighthouse. Aradio or radar signal station that provides naviga-tion and interrogation information for ships andaircraft.

BEAMWIDTH—The width of an electro-magnetic beam, measured in degrees on an arcthat lies in a plane along the axis of propagation,between points of equal field strength. It maybemeasured in the horizontal or vertical plane.

BEARING—The angular position of anobject with respect to a reference point or line.If the reference point is true north, the bearingis the true bearing; if the reference is NOT truenorth, then the bearing is a relative bearing. Ifmagnetic north (vice true north) is used as thereference, the bearing then becomes a magneticbearing. Also, the direction of the line of sight,from a radar antenna to a target, measured indegrees. See also AZIMUTH.

BIAS—In vacuum tubes, the difference ofpotential between the control grid and thecathode; in transistors, the difference of potentialbetween the base and emitter and between the baseand collector; in magnetic amplifiers; the level offlux density in the core under no-signal conditions.

BIDIRECTIONAL COUPLER—A waveguidedevice having two outputs, which sample andpresent a signal at one output that is largely afunction of the wave traveling in one direction,while the signal at the other output is largely afunction of the wave traveling in the oppositedirection.

BLACKBODY—An ideal body that absorbsall incident light and therefore appears perfectlyblack at all wavelengths. The radiation emittedfrom such a body when it is hot is called black-body radiation. The spectral energy density ofblackbody radiation is the theoretical maximumfor a body in thermal equilibrium.

BLANKING—The process of applying negativevoltage to the control grid of the cathode-ray tubeto cut off the electron beam during the retraceor flyback period.

BOLOMETER—A small resistive elementused in the measurement of low and medium RFpower. It is characterized by a large temperaturecoefficient of resistance that is capable of beingproperly matched to a transmission line.

BOTTOM BOUNCE—That form of sonarsound transmission in which sound rays strike theocean bottom in deep water at steep angles andare reflected back to the surface and returned,which allows the obtaining of target informationat long distances.

BRIDGE CIRCUIT—The electrical bridgecircuit is a term referring to any one of a varietyof electric circuit networks, one branch of which,the “bridge” proper, connects two points of equalpotential, and hence carries no current when thecircuit is properly adjusted or balanced.

B-SCAN (B-DISPLAY)—In radar, a rec-tangular display in which targets appear asilluminated areas, with bearing indicated by thehorizontal coordinate and distance by the verticalcoordinate.

CAGING (GYRO)—The act of holding a gyroso that it cannot precess and change its attitudewith respect to the body containing it.

CAVITATION—The formation of localcavities (bubbles) in a liquid as a result ofthe reduction of total pressure. This pressurereduction may result from a negative pressure

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produced by rarefaction or from the reduction ofpressure by hydrodynamic flow, such as isproduced by high-speed movement of an under-water propeller.

CAVITY RESONATOR—A hollow, metalliccavity in which electromagnetic oscillation canexist when the cavity is properly excited.

CCTV—Closed circuit television. The applica-tion of television where reception is limited bybroadcasting on specific frequencies and/or byconnecting the receivers directly to the televisioncamera via coaxial cables.

CHARACTERISTIC (ITERATIVE) IMPED-ANCE— The apparent load presented to a source;in electronics, the characteristic impedance at anyfrequency range is approximately equal to theratio of the inductance to the capacitance.

CIC—Combat information center. The tacticalcommand center of the ship.

CLEARING PULSE—In computers, a pulsethat is employed for clearing or resetting a circuitto its predetermined initial state.

COMPARATOR—A circuit that comparestwo signals or values, and indicates agreement orvariance between them.

COMPOSITE VIDEO—The total video signal,consisting of picture information, blanking pulses,and sync pulses.

COMPRESSION—In wave motion, the forcingtogether of the medium’s molecules. See alsoRAREFACTION.

COMPUTER—A mechanism or device thatperforms mathematical operations. See alsoANALOG COMPUTER and DIGITAL COM-PUTER.

COMPUTER CODE (ALSO CALLED ACOMPUTER LANGUAGE)—The code bywhich data are represented within a computersystem; for example, binary coded decimal.

COMPUTER PROGRAM—A series ofinstructions or statements prepared in a formacceptable to the computer.

CONTROL CIRCUITS—In computers, thosecircuits involved in the carrying out of theprogram instructions.

COUNTERMEASURES—Devices and/ortechniques intended to impair the operationaleffectiveness of enemy activity.

COUNTING CIRCUIT—A circuit thatreceives uniform pulses representing units to becounted and produces a voltage in proportion totheir frequency.

CRT—Cathode-ray tube.

DC RESTORER—A circuit used to reinsertthe dc component of the video signal lost duringamplification.

DEGREES OF FREEDOM (GYRO)—A termapplied to gyros to describe the number ofvariable angles required to specify the position ofthe rotor spin axis relative to the case.

DETECTORS, INFRARED—Thermal devicesfor observing and measuring infrared radiation,such as the bolometer, radiomicrometer, thermo-pile, pneumatic cell, photocell, photographicplate, and photoconductive cell.

DIFAR—Directional frequency analyzing andrecording. An ASW technique used in pinpointingsubmerged contacts.

DIFFERENTIAL—A mechanical computingdevice used to add or subtract two quantities.

DIFFUSION—The spreading out of energy orparticles from a high concentration to a low con-centration, due to random velocity and scattering.

DIGITAL COMPUTER—A type of com-puter in which quantities are represented innumerical form and which is generally made tosolve complex mathematical problems by use ofthe fundamental processes of addition, sub-traction, multiplication, and division. Its accuracyis limited only by the number of significant figuresprovided.

DIPPING SONAR—Used by helicopters.Lowered from the helicopter for searching andretracted for flight.

DIRECTIONAL COUPLER—A device usedto extract a portion of the RF energy movingin a given direction in a transmission line orwaveguide. Energy moving in the opposite direc-tion is rejected. See also BIDIRECTIONALCOUPLER.

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DIRECTION FINDER (DF)—VHF/UHFnavigation aid operated by personnel on theground to furnish azimuth information to aircraft.

DISCRIMINATOR—A dual-input circuit inwhich the output is dependent on the variationof one input from the other input or from anapplied standard.

DISTORTION—The production of an outputwaveform that is not a true reproduction of theinput waveform. Distortion may consist ofirregularities in amplitude, frequency, phase, etc.

DIURNAL—Having a recurring daily cycle.

DIVERGENCE—Energy loss caused byspreading in all directions.

DOPPLER EFFECT—An apparent change inthe frequency of a sound wave or electromagneticwave reaching a receiver when there is relativemotion between the source and the receiver.

DRIFT—Net change in characteristics ofelectronic components or parameters, resultingfrom external or incidental conditions.

DRUM—In computers, a cylinder coated witha material capable of being magnetized so thatit can be employed for the retention of informa-tion in storage functions.

DUPLEXER—A switch or tube that permitsthe use of a single antenna for both transmissionand reception. The dual function of the duplexeris to prevent absorption of transmitter energy bythe receiver system (thereby protecting thereceiver) and to prevent absorption of anyappreciable portion of the received echo signal bythe transmitter.

ECHO—That portion of the energy reflectedto the receiver from the target.

ECHO BOX—A high-Q resonant cavity usedwith microwave radar sets to provide artificialtargets for radar testing and for tuning the receiverto the transmitter. The echo box stores RF energyduring the transmitted-pulse interval, andreradiates it through the same antenna for a shorttime following the pulse.

ECM—Electronic countermeasures. Themeans by which enemy electronic devices are

nullified and, at the same time, intelligence isgathered concerning the nature of the enemyradiations. ACTIVE ECM implies jamming/deceptive techniques to degrade enemy equipmentor operator functions. PASSIVE ECM entails theuse of receiving (only) equipment to detect, locate,analyze, and evaluate enemy radiations and radioemissions.

ELECTRONIC SWITCH—A circuit thatcauses a start and stop action or a switchingaction by electronic means.

ELECTROSTRICTION—That property ofcertain ceramic materials that, after having apermanent operating bias established, causes thesematerials to vary slightly in length when they areplaced in an electric field.

EQUIVALENT CIRCUIT—A diagrammaticarrangement of component parts, representing insimplified form the effects of a more complicatedcircuit, to permit easier analysis.

ERASING HEAD—A device that removesstored data from the surface of a magnetic storagematerial.

ESM—Electronic warfare support measures.Concerns electronic emissions and counter-measures.

E-TRANSFORMER—A magnetic devicewith an E configuration, used as an errordetector.

EW—Electronic warfare. Tactical use ofelectronics to prevent or reduce the enemy’seffective use of radiated electromagnetic energy,and the actions taken to assure the effective useof ours. See also ECM.

FEEDBACK—The return of a portion ofthe output of a circuit stage to the input of thatstage or a preceding stage, such that there iseither an increase (regeneration) or a reduction(degeneration) in amplification, depending onthe relative phase of the returned signal withthe input.

FERRITE—A hard and brittle crystallinesubstance made from a mixture of powderedmaterials, including iron oxides; it has specialmagnetic properties of particular value incomputers and in many other applications.

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FIDELITY—The extent to which a system, ora portion of a system, accurately reproduces atits output the essential characteristics of the signalthat is impressed upon its input.

FLIR—Foward Looking InfraRed system.

FREE GYRO—A gyro so gimbaled that it canassume and maintain any attitude in space. A freegyro has two degrees of freedom; torque cannotbe applied to the rotor of a truly free gyro.

FREQUENCY—The number of hertz (cyclesper second) of an alternating current.

FULL ADDER—An adder circuit that cancomplete the adding procedure involving the carryprocess, as distinguished from the half adder,which is not capable of accepting a previous carry.

GATING CIRCUIT (GATE)—A circuit usedto activate (or deactivate) another circuit bypermitting (or prohibiting) operation duringselected periods of time.

GIMBAL—A frame in which the gyro wheelspins and that allows the gyro wheel to havecertain freedom of movement. It permits the gyrorotor to incline freely and retain that positionwhen the support is tipped or repositioned.

GRADIENT—The nature of the sound-transmission curve (negative, positive, isothermal,etc.) as used in sonar applications. See alsoISOTHERM and THERMOCLINE.

GRADIENT, NEGATIVE—When the temper-ature of the water decreases with depth, it has anegative temperature gradient.

GRADIENT, POSITIVE—When the temper-ature of the water increases with depth, it has apositive temperature gradient.

GYROSCOPES—A wheel or disk so mountedas to spin rapidly about one axis and be free tomove about one or both of the two axes mutuallyperpendicular to the axis of spin.

HALF ADDER—A partial adding circuit thatis not capable of accepting a previous carry. Itmust be combined with another half adder anda circuit capable of performing the carry functionto form a full adder.

HERO—Hazardous electromagnetic radiationto ordnance.

HERTZ—A unit of frequency equal to 1 cycleper second.

HETERODYNE—To mix two alternatingcurrents of different frequencies in the samecircuit; they are alternately additive and sub-tractive, thus producing two beat frequencies,which are the sum of, and difference between, thetwo original frequencies.

HORIZONTAL PLANE—A horizontal planeis tangent to the surface of the earth. Visualizethis condition by laying a playing card on anorange. The card represents the horizontal plane;the orange symbolizes the earth; and the point ofcontact between the two is the point of tangency.Every plane parallel to the horizontal plane islikewise a horizontal plane.

HYDROPHORE—An acoustic device thatreceives and converts underwater sound energyinto electrical energy.

HYSTERESIS—A lagging of the magneticflux in a magnetic material behind the magnetizingforce that is producing it.

INFRARED—Invisible waves in that portionof the electromagnetic spectrum lying betweenvisible light and radio frequencies, and having apenetrating heating effect.

INHIBITORY PULSE—A pulse that acts toinhibit or suppress another signal from goingthrough a logic circuit and appearing at theoutput.

INPUT-OUTPUT EQUIPMENT—A devicethat provides the means of communicationbetween the computer and external equipment.The device accepts new data, sends it into thecomputer for processing, receives the results, andtransforms the data into usable form. In manycases it is also referred to as peripheral equipment.

INSTRUCTION—in computer programming,a set of identifying characters or a computer“word” that is designed to cause the computerto perform specific operations.

INTEGRATING CIRCUIT—A circuit whoseoutput voltage is proportional to the product ofthe instantaneous applied input voltages and theirdurations.

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INTEGRATOR—A computing device usedfor summing up an infinite number of minutequantities.

INTELLIGENCE—The message or informa-tion conveyed, as by a modulated radio wave.

INTERFACE—A concept involving thespecification of the interconnection between twoequipments or systems. The specifications includethe type, quantity, and function of signals to beinterchanged via those circuits. A device thatconverts or translates any type of informationfrom one given medium into signals of anothergiven medium; for example, electrical signals tofluidic signals, fluidic signals to electronic signals,etc.

IR—InfraRed.

ISOTHERM—Aequal temperature.

line connecting points of

ISOTHERMAL LAYER—A layer of waterin which there is no appreciable change oftemperature with depth.

ISOVELOCITY LAYER—A layer of waterin which there is no appreciable change of soundvelocity with depth.

KINEMATIC LEAD—The lead required toscore a hit on a specified target due to relativemotion between target and gun platform.

KNEE (OF A CURVE)—An abrupt changein direction between two fairly straight segmentsof a curve.

LAYER DEPTH—The depth from the surfaceof the seato the top of the first significant negativethermocline.

LAYER EFFECT—Partial protection fromecho ranging and listening detection when belowlayer depth.

LOGIC CIRCUITS—Digital computer circuitsused to store information signals and/or toperform logical operations on those signals.

LOOP ANTENNA—One or more completeturns of wire used with a radio receiver. Alsoused with direction-finding equipment.

LOS—Line of sight. The straight-line distancefrom ship to horizon. Represents radio and radarVHF and UHF transmission range limits undernormal conditions.

MAD—Magnetic anomaly detection. Thedetection of slight distortions in the earth’smagnetic field. In the U.S. Navy, it is usedexclusively by aircraft.

MAGNETIC FIELD—The region in space inwhich a magnetic force exists, caused by apermanent magnet or as a result of currentflowing in a conductor.

MAGNETOSTRICTION—That property ofcertain ferro-type materials that causes them tovary slightly in length when they are in analternating magnetic field.

MAGNETRON—A microwave oscillator thatuses an electron tube (consisting of a cathode andan anode), a strong axial magnetic field, andresonant cavities.

MAGNETRON ARCING—Internal breakdownbetween cathode and anode of a magnetron,usually resulting from presence of gas. Occursduring the breaking-in or “seasoning” period andagain at the end of the useful life. Occasionalarcing is common, especially in high-powermagnetrons.

MAGNETRON PULLING—The frequencyshift of a magnetron resulting from a mismatchat the output. It is caused by such factors as faultyrotating joints, reflections from objects near theantenna, etc.

MAGNETRON PUSHING—The frequencyshift of a magnetron resulting from faulty opera-tion of the modulator. It may result from animproperly shaped pulse or from interaction ofthe pulse with the magnetic field.

MASTER CLOCK—The timed and synchro-nized generators that comprise the source and timereference for computer signals.

MEMORY UNIT—In computers, a device usedfor storing data for possible use in computation.

MICROFICHE—A film negative card (fiche)developed for many purposes throughout theNavy wherever microfilming is used to reduceamounts of paper documents.

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MICROMETER—A unit of length equal to10-6 meter, Formerly a micron.

MICRON—See MICROMETER.

MICROWAVES—A term commonly used toindicate electromagnetic waves in the frequencyrange between 1,000 and 300,000 megahertz (30 cmto 1 mm).

MILLIAMMETER—An ammeter that mea-sures current in thousandths of an ampere.

MODULATION—The process of varying theamplitude or frequency of a carrier wave in accord-ance with other signals to convey intelligence. Themodulating signal may be an audiofrequencysignal, a video signal (as in television), or evenelectrical pulses or tones to operate relays.

MODULE—In electronic terminology, agroup or cluster of circuits/components usuallymounted together on a “board” or “potted”together in a lump.

MONOPULSE—A method of antenna lobingthat permits information to be obtained on targetrange, bearing, and elevation from a single pulse(as distinguished from sequential lobing).

NOISE—Any undesired disturbance withinthe useful frequency band; also, that part of themodulation of a received signal (or an electricalor electronic signal within a circuit) representingan undesirable effect of transient conditions.

NOT CIRCUIT—In computers, a circuit inwhich the output signal does not have the samepolarity as the input signal. A phase inverter.

NULL—A point or position where a variable-strength signal is at its minimum value (or zero).

OFF-LINE EQUIPMENT—Peripheral com-puter equipment that can operate independentlyof the main computer for such operations astranscribing punch card information to magnetictape, or magnetic tape to printed form.

OMNIDIRECTIONAL—Going out in alldirections as the radiation pattern of a singledipole antenna.

ON-LINE EQUIPMENT—Computer equip-ment, due to configuration or design, that requiresthe use of the central processing unit of thecomputer.

OR GATE—A logic circuit having multipleinputs and a single output, so designed that theoutput is energized when any one or more of theinputs are in the prescribed signal state.

PARALLEL MODE—In computer opera-tion, the handling of a group of numbers or othersymbols simultaneously.

PARAMETERS—In electronics, the design oroperating characteristics of a circuit or device.

PASSIVE SONAR—An apparatus that receivesenergy generated from another source.

PERIPHERAL EQUIPMENT—Either on-lineor off-line auxiliary equipment supporting theoperations, but is not a part of the computer itself.These machines may consist of card readers, cardpunches, magnetic tape feeds, and high-speedprinters.

PHOTON—A quantum of electromagneticenergy. The equation hv, where h is Plank’sconstant and v is the frequency associated withthe photon.

PICKOFF—In gyros, a sensing device thatmeasures the angle of the spin axis with respectto its reference, and provides an error signal thatindicates the direction and (in most cases) themagnitude of the displacement.

PIEZOELECTRIC EFFECT—Effect of pro-ducing a voltage by placing stress, either bycompression, expansion, or twisting, on a crystaland, conversely, producing a stress in a crystalby applying a voltage to it.

PIPS—Popular term for bright spots on aCRT display such as a radar or sonar screen.

POLARIZATION—In electronics, a term usedin specifying the direction of the electric vectorin a linearly polarized electromagnetic wave asradiated from a transmitting antenna, or as pickedup by a receiving antenna.

POTENTIOMETER—A variable voltagedivider; a resistor that has a variable contact armso that any portion of the potential appliedbetween its ends may be selected.

PPI SCAN (PPI DISPLAY)—A cathode-raytube presentation in which the signal appears on arotating radial line. Distance is indicated radially,and bearing as an angle.

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PRECESSION—The reaction of a gyro to anapplied torque, which causes the gyro to tilt itselfat right angles to the direction of the appliedtorque in such a manner that the direction of spinof the gyro rotor will be in the same direction asthe applied torque.

PROGRAM—A complete plan for the solutionof a problem, including the complete sequence ofmachine instructions and routines necessary tosolve the problem by an electronic computer.

PROPAGATION—Extending the action of,transmitting, carrying forward as in space or timeor through a medium (as the propagation ofsound, light, or radio waves).

PSEUDO—Term meaning false or fake.

PULSE—A momentary sharp surge ofelectrical voltage or current.

PULSE DURATION—The time intervalbetween the leading and trailing edges of each ofa particular group of pulses; the instantaneousvalues of these are often used in a specificrelation to the peak pulse amplitude to determinepower output.

PULSE INTERVAL—The time intervalbetween the leading edges of successive pulses ina sequence.

PULSE SEPARATION—The time intervalbetween the trailing edge of one pulse and theleading edge of the next pulse.

PULSE TRAIN—A series of pulses passedthrough a circuit as control or information signals.

RADIAN—In a circle, the angle includedwithin an arc equal to the radius of the circle. Acomplete circle contains radians. One radianequals 57.3 degrees and 1 degree equals 0.01745radian.

RANGE—The distance of an object from anobserver.

RAREFACTION—In wave motion, when thevibration is inward, a rrrarefaction or region ofreduced pressure is produced.

RASTER—The illuminated rectangular areascanned by the electron beam in a picturetube/CRT.

RATE GYRO—A gyro with 1 degree offreedom, which has an elastic restraint, with orwithout a damper, and whose output will beproportional to the rate of the applied torque.

REFLECTION, SOUND—Sound rays trans-mitted in the sea eventually reach either thesurface or the bottom. Since these boundaries areabrupt and very different in sound transmittingproperties from the water, sound energy along aray path striking these boundaries will be returned(reflected) to the water.

REFRACTION, SOUND—The bending orcurving of a sound ray that results when the raypasses from a region of one sound velocity to aregion of a different velocity. The amount of raybending depends on the amount of differencebetween sound velocities.

REGISTER—A specific computer unit thatstores a single computer word.

RELATIVE BEARING—A bearing takenwhen the heading of a ship serves as the referenceline. See also BEARING.

RELATIVE MOTION—The apparent move-ment of an object in relation to another object.

RESONANT CAVITY—A space, normallyenclosed by an electrically conductive surface, inwhich oscillatory electromagnetic energy is stored,and whose resonant frequency is determinedprimarily by the geometry of the enclosure.

REVERBERATION—A succession of echoescaused by reflections of sounds. In the ocean itis caused by irregularities in the ocean bottom,surface, and suspended matter (as fish). Underthese conditions, an emitted pulse may be receivedas a muffed echo due to sound interference.

RHEOSTAT—A variable resistor that has onefixed terminal and a moveable contact, Potenti-ometers may be used as rheostats, but a rheostatcannot be used as a potentiometer becauseconnections cannot be made to both ends of theresistance element.

RIGIDITY—In gyros, the characteristics ofa spinning body that causes it to oppose allattempts to tilt it away from the axis in which itis spinning.

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RING TIME—In radar, the time during whichthe output of an echo box remains above apredetermined level; used in measuring theperformance of radar equipment.

SAR—Search and rescue.

SCALE FACTOR—A quantity used tointroduce a change according to a fixed ratio orscale; a proportionality constant.

SCANNING SONAR—Sonar that transmitssound pulses in all directions simultaneously.

SCATTERING—Reflection losses from par-ticles suspended in the water.

SENSO—Sensor operator (SO). Operates theASW platforms acoustic and nonacoustic sensorsystems.

SENSOR—A component that senses variablesand produces a signal therefrom. Temperature,sound, heat, and light sensors are some examples.

SEQUENTIAL LOBING—Successively shiftingthe radar beam about the scanner centerlinethrough a particular pattern; differs frommonopulse.

SERIAL OPERATION-In computers, thesequential handling of a group of numbers orsymbols.

SHIFT REGISTER—In computers, a circuitthat will shift a digit or a group of digits eitherto the left or to the right; it is of particularimportance in some multiplication and divisionprocesses, and in sequential storage of pulsetrains.

SHOT EFFECT—Noise voltages developed asa result of the random nature of electron flow invacuum tubes, or the random flow of eitherprimary or secondary carriers in transistors.

SLEW—To change the position of anindicator mark on a CRT display by varying thetime relationship of the mark with respect to thestart of the sweep.

SOFTWARE—Pertains to the programs androutines used with computers. The totality ofprograms and routines used to extend thecapabilities of computers. In contrast to HARD-WARE, which is the construction parts(mechanical, electrical, and electronic elements)of the computer.

SONAR—Acronym for SOund NavigationAnd Ranging. Apparatus or technique of obtaininginformation regarding objects or events under-water.

SONIC—Within the audible range of thehuman ear.

SONOBUOY—Small floating buoy with anattached hydrophore and a radio transmitter thatrelays underwater sounds picked up by thehydrophone to ASW units.

SONOBUOY RECEIVER SYSTEM (SRX)–An FM radio receiver system used exclusively forsonobuoy RF signal reception and processing.

SONOBUOY REFERENCE SYSTEM (SRS)–The system used to determine the position ofdeployed sonobuoys relative to aircraft position.

SOUND CHANNEL—Condition when twolayers of water with near equal temperaturesproduce a sound channel. Sound between the twolayers is refracted by the layers, stays betweenthem, and travels for great distances.

SYNC—A short form of the word synchroniz-ing, which means to cause two elements of asystem to coincide in speed, frequency, relativeposition, or time.

TACCO—Tactical coordinator.

THERMAL NOISE—A very low-level noiseproduced by molecular movement in the sea.

THERMISTOR-A solid-state, semiconductingdevice whose resistance varies with temperature.

THERMISTOR-A bolometer characterizedby a decrease of resistance as the temperaturerises. See also BOLOMETER.

THERMOCLINE-The layer in the sea wherethe temperature decreases continuously withdepth. Usually the decrease (gradient) is greaterthan 2.7°F per 165 feet in depth.

TORQUE—A force tending to cause rotationalmotion; the product of the force applied times thedistance from the force to the axis of rotation.

TRANSDUCER—A device that convertssignals received in one medium into outputs insome other medium; for example, electrical inputsto fluidic outputs, or mechanical motion intoelectrical quantities.

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TRIGGERING—Starting an action in anothercircuit, which then operates for a time under itsown control.

TRUE BEARING—A bearing given in relationto true geographic north. See also BEARING.

TUMBLE (GYRO)—To subject a gyro to atorque so that it presents a precession violentenough to cause the gyro rotor to spin end overend.

VELOCITY—A vector quantity that includesboth magnitude (speed) and direction in relationto a given frame of reference.

VERTICAL PLANE—A vertical plane isperpendicular to the horizontal plane, and is thereference from which bearings are measured.Relative bearing, for example, is measured in thehorizontal plane clockwise from the vertical planethrough own ship’s centerline to the vertical planethrough the line of sight. The system of planesmakes possible the design and construction ofmechanical and electronic equipment to solve thefire control problem. These lines and planes areimaginary extensions of some characteristic of the

ship or target, or of the relation in space betweenthem.

WAVEGUIDE—Metal tubes or dielectriccylinders capable of propagating electromagneticwaves through their interiors. The dimensions ofthese devices are determined by the frequencyto be propagated. Metal guides are usuallyrectangular or circular in cross section; theymay be evacuated, air filled, or gas filled, andmay or may not be pressurized. Dielectric guidesconsist of solid dielectric cylinders surrounded byair.

WAVELENGTH—The distance traveled bya wave during the time interval of one completecycle, It is equal to the velocity divided by thefrequency.

WAVE PROPAGATION—The radiation, asfrom an antenna, of RF energy into space, or ofsound energy into a conducting medium.

WORD—In computers, a particular numberof characters handled as a unit by the computerand having a specific meaning with respect to thecomputation process.

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APPENDIX II

SYMBOLS, FORMULAS, ANDMEASUREMENTS

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SYMBOLS(SEE ANSI/IEEE STD Y32.2-1975 AND 315A-1986)

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FORMULAS

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BRIDGE CIRCUIT CONVERSION FORMULAS

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Comparison of Units in Electric and Magnetic Circuits

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U.S. CUSTOMARY AND METRIC SYSTEMUNITS OF MEASUREMENTS

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GREEK ALPHABET

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