workmanship and design practices for electronic equipment.compressed

OP 2230

SECOND REVISION

WORKMANSHIP AND DESIGN PRACTICES

FOR

ELECTRONIC EQUIPMENT

This publication supersedes OP 2230 (First Revision) dated 22 April 1959.

PUBLISHED BY DIRECTION OF

THE CHIEF OF THE BUREAU OF NAVAL WEAPONS

1 DECEMBER 1962

TK

FOREWORD

Ordnance Pamphlet 2230 has been prepared as a guide for the design andconstruction of military electrical and electronic equipment. Informationcontained herein should not be construed as a specification, but as a guide indesigning for reliable performance and ease of manufacture, inspection, operation, maintenance, and repair of equipments.This publication is intended primarily for engineers and technicians whomust translate circuit designs or breadboard models into a product design,and those who must manufacture or inspect the final products in accordancewith the applicable detail performance specifications.Because of the great variety of electronic equipments and the many factorswhich influence individual design considerations, only recommended basicpractices of general application are included.Comments for the improvement of this publication are invited. Recommended additions, corrections, or deletions should be addressed to theBureau of Naval Weapons, RREN-4, Department of the Navy, Washington25, D.C.

DEPOSITED BY THEUNITED 9TATC~ -r *..rr

CONTENTS

1. PERSONNEL PROTECTION

1 . 0 GENERAL

1.1 DESIGN OBJECTIVES1.1.1 Operating Personnel1.1.2 Maintenance Personnel

1.2 ELECTRIC SHOCK

1 . 3 PREVENTION OF ELECTRIC SHOCK1.3.1 Warnings1.3.2 Fusing1.3.3 Grounding1.3.4 Power Lines1.3.5 Main Power Switch1.3.6 Panel- Mounted Parts1.3.7 Parts Safety1.3.8 Shields and Guards1.3.9 Discharging Devices1.3.10 Interlocks

1 . 4 MECHANICAL AND OTHER HAZARDS

2. OPERATION AND MAINTENANCE

2.0 GENERAL

2.1 OPERATIONAL FEATURES2.1.1 Visual Indicators2.1.2 Controls2.1.3 Console Design and Panel Layout2.1.4 Lighting Applications

2.2 MAINTENANCE FEATURES2.2.1 Testing2.2.2 Assembly Slides2.2.3 Replacing Subassemblies2.2.4 Replacing Parts

in

OP 2230

3. ASSEMBLY DESIGN

3.0 GENERAL

3.1 HEAT TRANSFER3.1.1 Parts3.1.2 Cases and Cabinets3.1.3 Liquid Filling and Potting

3.2 SHOCK, VIBRATION, AND INCLINATION3 .2.1 Shock Loads3.2.2 Vibration3.2.3 Inclination3.2.4 General Practice3.2.5 General Design3.2.6 Resilient Mountings3.2.7 Resilient Structures3.2.8 Component Mounting3.2.9 Modes of Vibration3.2.10 Workmanship

3 . 3 SUBASSE MB LIES3.3.1 Types3.3.2 Connectors3.3.3 Clamping and Supporting

3.4 ENCLOSURES3.4.1 Types

3.5 CLIMATIC PROTECTION3.5.1 Humidity3.5.2 Temperature3.5.3 Wind, Ice, and Dust

3.6 RADIO FREQUENCY INTERFERENCE3.6.1 Radiated Noise3.6.2 Conducted Noise3.6.3 Types of Shields

3.7 AUTOMATIC PROCESSES3.7.1 Prefabricated Circuits3.7.2 Automatic Assembly

3.8 MINIATURIZATION3.8.1 Dense Packaging3.8.2 Micromodules3.8.3 Microelectronics3.8.4 Related Devices3.8.5 Utilization

iv

CONTENTS

3.9 BIBLIOGRAPHY

4. STRUCTURAL DESIGN

4.0 GENERAL

4.1 FABRICATING PROCESSES4.1.1 Sheet Metal Working4.1.2 Machining4.1.3 Forging4.1.4 Casting4.1.5 Extruding4.1.6 Plastic Molding

4.2 STRUCTURAL TECHNIQUES4.2.1 Bracing4.2.2 Gusseting4.2.3 Ribbing4.2.4 Laminates4.2.5 Rigidizing

4.3 MECHANICAL PARTS4.3.1 Handles4.3.2 Bails4.3.3 Lifting Devices4.3.4 Mechanical Safety Devices4.3.5 Gears4.3.6 Bearings4.3.7 Shafts4.3.8 Doors4.3.9 Slides4.3.10 Latches4.3.11 Gaskets4.3.12 Springs

4.4 FASTENING TECHNIQUES4.4.1 Welding4.4.2 Soldering and Brazing4.4.3 Riveting4.4.4 Threaded Fasteners4.4.5 Stapling4.4.6 Miscellaneous Fasteners4.4.7 Cementing

4.5 BIBLIOGRAPHY

OP 2230

5. PROTECTIVE COATINGS

5.0 NEED FOR COATINGS

5.1 SURFACE PREPARATION5.1.1 Cleaning Methods5.1.2 Hydrogen Embr ittlement

5.2 COATINGS5.2.1 Metallic Coatings5.2.2 Conversion Coatings5.2.3 Painted Coatings5.2.4 Metalizing Nonmetallic Materials5.2.5 Other Coatings

5.3 IMPREGNATION, ENCAPSULATION, POTTINGAND EMBEDDING5.3.1 Impregnation5.3.2 Encapsulation5.3.3 Potting and Embedding

5.4 PRESERVATIVES

5.5 SELECTION OF COATINGS

5.6 DISSIMILAR METALS IN CONTACT5.6.1 Galvanic Corrosion5.6.2 Similar and Dissimilar Metals5.6.3 Protection of Faying Surfaces

5.7 BIBLIOGRAPHY

VI

CONTENTS

6. ELECTRICAL AND ELECTRONIC PARTS

6.0 GENERAL

6.1 SELECTION CRITERIA6.1.1 Standard Parts6.1.2 Interchangeability6.1.3 Reliability6.1.4 Repairability of Components6.1.5 Nuclear Radiation Effects

6.2 USE OF ADVANCED- DESIGN ITEMS

6.3 LOCATION OF PARTS6.3.1 Heat Transfer6.3.2 Circuit Considerations6.3.3 Clearances6.3.4 Accessibility

6.4 MOUNTING OF PARTS6.4.1 Lead-Supported Parts6.4.2 Body-Supported Parts6.4.3 Plug-In Mountings6.4.4 Standoff Mountings

6.5 MARKING OF PARTS6.5.1 Reference Designations and

Part Identification6.5.2 Location of Markings6.5.3 Marking Processes

6 . 6 BIBLIOGRAPHY

vii

OP 2230

7. WIRING AND CABLING

7.0 GENERAL

7.1 SELECTION OF CONDUCTORS7.1.1 Types and Uses7.1.2 Size7.1.3 Insulation

7.2 CODING OF CONDUCTORS7.2.1 Color Codes7.2.2 Identification Tags7.2.3 Coding of Noninsulated Leads

7.3 WIRING PROCEDURE7.3.1 Routing and Dressing7.3.2 Harnessing and Cabling7.3.3 Preparing Connections7.3.4 Permanent Wire Connections7.3.5 Solders and Fluxes7.3.6 Soldering Methods7.3.7 Hand Soldering7.3.8 Wiring Protection7.3.9 Separable Connectors

8 . MATERIALS

8.0 GENERAL

8.1 PROPERTIES AND USES8.1.1 Metals8.1.2 Nonmetals

8.2 SELECTION OF MATERIALS8.2.1 General8.2.2 Moisture, Fungus, and Corrosion

Resistance

8.3 SPECIFYING MATERIALS

INDEX

viii

Chapter I

PERSONNEL PROTECTION

1.0 GENERALDesign of any equipment mustembody features to protect personnelfrom electrical and mechanicalhazards; also, from those dangerswhich may arise from fire, elevatedoperating temperatures, and toxicfumes .There are various methods ofincorporating adequate safeguards forpersonnel, many of these methodsbeing implicit in routine designprocedures. However, certainprocedures, design practices, andrelated information are of suchimportance as to warrant specialattention.

1.1 DESIGN OBJECTIVESIn the design, attention must begiven to the protection of bothoperating and maintenance personnel.Personnel aboard ship are frequentlyrequired to operate and maintainequipment on an inherently unstabledeck .Operating personnel must not beexposed to any mechanical orelectrical hazards, nor shouldoperation of the equipment necessitateany unusual precautions; in particular,all parts accessible during normaloperations should be reliably grounded.Maximum safeguards must beprovided inside the equipment toprotect maintenance personnelworking on energized circuits .

1.1.1 Operating PersonnelOperating personnel must be safeguarded from dangerous voltages,excessive temperatures, andmechanical hazards which may causephysical injury during either normaloperation or malfunctioning of theequipment .

Design must minimize thepossibility of operator's clothingbecoming caught or entangled inthe equipment. Handles and knobsshould be so arranged that clothingwill not catch; corners should berounded; and potentials greaterthan 70 volts must be physicallyshielded or removed by the actionof interlock switches .Some of these precautions areparticularly important. In militaryservice it may become necessaryfor the operator to rapidly manipulate or abandon the equipment.There is also the ever-presentpossibility that despite safetyregulations, operating personnelmay attempt to service equipmentin a non- approved manner.

1.1.2 Maintenance PersonnelSafeguarding the maintenanceman is more difficult; tests andrepairs must often be made withmuch of the apparatus exposed.It may be necessary to short outinterlock switches and to removecovers which shield high voltagesor moving machinery .Every effort should be made in

the design to protect maintenancepersonnel against contact withdangerous voltages in unexpectedplaces. Controls for adjustment andpoints of access for lubrication shouldbe located away from high voltageand moving parts. Danger signsimprinted next to dangerous partsor on protective covers should beused to alert maintenance personnel.

1.2 ELECTRIC SHOCKPotentials exceeding 70 volts areconsidered to be possible electricshock hazards , Research reveals

1 - 1

OP 2230

that most deaths result from contactwith the relatively low potentialsranging from 70 to 500 volts, althoughunder extraordinary circumstances,even lower potentials can cause injury.Many severe injuries are caused

not by electric shock directly, but bythe reflex action and consequent bodyimpact with nearby objects.Some contact with electric potentialscan be expected where maintenancepersonnel are by the very nature oftheir duties exposed to live terminals.Both shocks and burns, however, canbe minimized by greater care indesign, and by a better understandingof electrical characteristics .Three factors determine theseverity of electric shock: (1) Quantityof current flowing through the body:(2) Path of current through the body,and (3) Duration of time current flowsthrough the body.The most important variable iscurrent. Amperage depends not onlyon voltage, but also on resistance ofthe circuit through the body, which inturn depends on whether points ofcontact are wet or dry. In cases onrecord, potentials below 10 voltshave proved fatal when points ofcontact have pierced the skin.Sufficient current passing throughany part of the body will cause severeburns and hemorrhages . However,

relatively small currents cancause death if the path includesthe heart or lungs . Electricburns are usually of two types,those produced by heat of the arcwhich occurs when the body touchesa high-voltage circuit, and thosecaused by passage of electric currentthrough skin and tissue.

1.3 PREVENTION OF ELECTRICSHOCK

1.3.1 WarningsWarning signs marked "CAUTION-HIGH VOLTAGE," or "CAUTIONVOLTS," should be placed in proml-nent positions on safety covers,access doors, and inside equipmentwherever danger may be encountered. These signs should be sodurable, easily read and so placedthat dust or other foreign depositswill not in time obscure the warnings.However, since signs are not physicalbarriers, they should be relied upononly if no other method of protectionis feasible .

1.3.2 FusingAll leads from the primaryservice lines should be protectedby fuses. Fusing of circuitsshould be such that rupture orremoval of a fuse will not cause

Current Values (Milliamperes)

0 - 11 - 44-2121 - 4040 - up

Effects

PerceptionSurpriseReflex actionMuscular inhibitionRespiratory block

PROBABLE EFFECTS OF SHOCK

1 - 2


malfunction or damage to otherelements in the circuit.Fuses should be connected to theload side of the main power switch.Holders for branch-line fuses shouldbe such that when correctly wired,fuses can be changed without thehazard of accidental shock. At leastone of the fuse-holder connectionsshould be normally inaccessible tobodily contact, and this terminalshould be connected to the supply;the accessible terminal should beconnected to the load. The followingillustration shows the correctmanner of wiring the instrumenttype of fuse holder to preventaccidental contact with theenergized terminal.

\LOAD

FUZE HOLDER WIRING

Provisions for storage of sparefuses should be made at anaccessible location.

1.3.3 GroundingVarious grounding techniques

used to protect personnel fromdangerous voltages in equipment.All enclosures, exposed parts,

are

and chassis should be maintained atground potential.Specifications for the reductionof electrical noise interferenceshould be consulted to determine themaximum permissible resistance ofa grounding system. Reliable groundingsystems should be incorporated in allelectronic equipment. Enclosuresand chassis should not be used aselectric conductors to complete acircuit because of possible inter-circuit interference .

BOLTED LUG

SPOT WELDED LUG

A terminal spot welded to thechassis provides a reliable groundconnector. For aluminum chassiswhere welding is not feasible, aterminal properly secured by amachine screw, lockwasher, and nutis satisfactory.A grounding lug should not beincluded as part of a "pile-up" thatincludes any material subject tocold-flow. The machine screw used

1 r 3

OP 2230

should be of sufficient size so thateventual relaxation will not resultin a poor connection. A lockwasheris necessary to maintain a secureconnection. All nonconductivefinishes of the contacting surfacesshould be removed prior to insertingthe screw. In no event shouldriveted elements be used forgrounding since these cannot bedepended upon for reliable electricalconnections .The common ground of eachchassis should connect to a through-bolt, mounted on the enclosure andclearly marked "ENCLOSUREGROUND," which in turn shouldconnect to an external, safetyground strap.

CABINET GROUNDING SYSTEM

For best design, the externalground conductor should befabricated from suitably plated,flexible copper strap, capable ofcarrying at least twice the currentrequired for the equipment.Electronic test equipment must befurnished with a grounding pigtail atthe end of the line cord. Signalgenerators, vacuum tube voltmeters,amplifiers, oscilloscopes, and tube

testers are among the devices soequipped. These leads are to beused for safety grounding purposes.Thus , in the event that a faultinside the portable instrument shouldconnect a dangerous voltage to themetal housing, the dangerous currentis bypassed to ground without endangeringthe operator .The power supply lines aboardship are not grounded. For suchpurposes as reducing of interference,these leads may be bypassedthrough capacitors to ground, butthe total current, including leakage,which the capacitor is likely topermit, must not exceed 5 milli-amperes .

1.3.4 Power LinesDesigners are often inclined to

confine their safety considerationsto high- voltage apparatus. However,it is important that considerableattention be devoted to the hazardsof power lines. Fires, severeshocks, and serious burns are knownto result from personnel contacting,short-circuiting, or grounding theincoming lines .

1.3.5 Main Power SwitchEach equipment should be furnishedwith a clearly labeled main powerswitch which will remove allpower from the equipment byopening all leads from the primarypower service connections.Main power switches should beequipped with safety devices thatafford protection against possibleheavy arcing . Barriers which shieldfuses and conducting metal parts, anddevices that prevent opening theswitch box with the switch closed,should be provided as protection forpersonnel. Switches incorporatingsuch safeguards are standardized,commercially obtainable equipment.

1 - 4

PERSONNEL, PROTECTION

1.3.6 Panel-Mounted PartsPanel-mounted parts , especiallyjacks, are occasionally employedin power circuits for the insertionof meters, output lines, test

apparatus, and other supplementaryequipment. Such items should beconnected to the grounded leg ofthe monitored circuit, rather thanin the ungrounded, high-voltage line.

VOLTAGE RANGE

70350

350 volts500 volts500 voltsand up

SUITABLE PROTECTIVE MEASURES

Interlocks aloneBarriers and interlocksEnclosures, warnings, and interlocks

1.3.7 Parts SafetyElectric parts and circuits should

be designed to minimize arcing inswitches, relays, and other make-or-break apparatus . Fast-actionswitches are usually employed.Switches used in dc circuits employmagnetic arc blowouts and capacitors across the contacts.Only explosion- proof switchingdevices should be employed wherethere is any possibility thatequipment will be operated in anatmosphere of explosive gas or vapor.The design of explosion- proofequipment is covered by militaryspecifications .Protective devices should beincorporated in the design for allparts carrying hazardous voltages.Wherever possible, such componentsshould be mounted beneath the chassis.Ventilation requirements must alwaysbe considered.When it is impracticable to mountparts below the chassis and thusreduce the hazard to maintenancepersonnel when replacing above-chassis parts, protective housingshaving ventilating holes or louversshould be provided. If housingscannot be used, exposed terminalsof the parts should be oriented

away from the direction of easycontact. These expedients lessenthe possibility of accidentalshock and arcing.

1.3.8 Shields and GuardsSafety enclosure covers should

be anchored by means of screwsor screwdriver-operated locksand should be plainly marked bywarnings .Hinged covers, doors, andwithdrawable chassis should becounter-balanced or provided withother means to retain them intheir open position, thus preventingaccidental closing due to shipmovement.Terminal boards carryinghazardous voltages above 500volts should be protected bymeans of a cover provided withholes for the insertion of testprobes. Terminal numbersshould be plainly marked on theexternal side of the cover . Withthis arrangement, it is possibleto check circuits that areenergized.High-voltage meters should

be recessed and two shatterproof windows used.

1 - 5

OP 2230

WINDOWSMETER

/

HIGH VOLTAGE PANEL METER

Housings, cabinets, or coversmay require perforations to provideair circulation. The area of aperforation should be limited tothat of a 1/2-inch square or roundhole. High-voltage componentswithin should be set back farenough to prevent accidentalcontact. If this cannot be done,the size of the openings shouldbe reduced.Where access to rotating oroscillating parts is required forservicing, it may be desirable toequip the protective covers orhousings with safety switches orinterlocks .

1.3.9 Discharging DevicesSince high-grade filter capacitorscan store lethal charges overrelatively long periods of time,adequate discharging devices mustbe incorporated in all medium-and high-voltage power supplies .Such devices should be usedwherever the time constant

of capacitors and associatedcircuitry exceeds 5 seconds; theyshould be positive acting, reliable,and should be automatically actuatedwhenever the enclosure is opened.

SHORTING BAR

*//

'/DOOR

SHORTING BAR ACTUATION

Shorting bars should be actuatedeither by mechanical release orby an electrical solenoid when thecover is opened.Good insurance is provided by

the automatic charge- drainingaction of a bleeder resistor,permanently connected across theoutput terminals of a dc powersupply. Although bleeder currentis an added load on the power supply,the system should be designed tocarry this slightly additional load.Bleeder resistance should be thelowest value, without presentingexcessive loading, through whichthe capacitors can discharge quicklyafter the power is switched off.However, in circuits wherelarge high-voltage capacitorsmust be Operated without adequate

1 - 6


bleeding; as in high-voltage radarapparatus, capacitors must bedischarged by automatic devicesas described previously . Forhigh-voltage capacitors, discharging devices should be equippedwith large resistors rated at 200watts, 10,000 ohms, to limitdischarge current and thepossibility of damage.

1.3.10 InterlocksInterlock switches are used toremove power during maintenanceand repair operations . Each coverand door providing access topotentials greater than 70 voltsshould be equipped with interlocks .Some interlock systems functionalso to ground capacitors, asdescribed in 1.3.9, when theenclosure is opened.An interlock switch isordinarily wired in series with oneof the primary service leads to thepower supply unit. It is usuallyactuated by the movable accesscover; thus breaking the circuitwhen the enclosure is entered.Where more than one interlock switch is used, they arewired in series. Thus, oneswitch may be installed on theaccess door of an operatingsubassembly; another, on thedust cover of the power supply.The selection of a type ofinterlock switch must be basedupon its reliable operation. Theso-called self-aligning switchappears most reliable, but inactual usage the type shown,although it contains movingparts, has proven mostsatisfactory .

DOOR OPEN

JDOOR CLOSED

DOOR INTERLOCK SWITCH

Since electronic equipment mustoften be serviced with the power on,a switch enabling maintenancepersonnel to bypass the interlocksystem should be mounted insidethe equipment. The switch shouldbe so located that reclosing of theaccess door or cover automaticallyrestores interlock protection. Alsoto be provided are a panel- mountedvisual indicator, such as a neonlamp, and a suitable name plateto warn personnel when interlockprotection is removed.

A"Battle-Short" switch orterminals for connection of anexternal switch should also beprovided to render all interlocksinoperative. It differs from theswitch used to bypass the interlocksystem for maintenance purposesin that the panel-mounted orremotely controlled "Battle-Short"switch is designated for emergency

1 - 7

OP 2230

use only. The circuit consists ofa single switch, wired in parallelwith the interlock system. Closingthe "Battle-Short" switch places ashort circuit across all interlockswitches, thus assuring incomingpower regardless of accidentalopening of interlock switches .

1.4 MECHANICAL AND OTHERHAZARDS

To minimize the possibility ofphysical injury, all enclosureedges and corners should berounded to maximum practicalradii. This is especially importantfor front-top edges, front-sideedges, and enclosure, door, andpanel corners .Thin edges should be avoided andchassis construction should besuch that the chassis may becarried without danger of cuttingthe hands on the edges .To prevent hazardous protrusions

on panel surfaces, flathead screwsshould be used wherever sufficientpanel thickness is available;otherwise, panhead screws shouldbe used.All accessible surfaces should

be smooth. Surfaces that cannotbe reasonably machined to asmooth finish should be coveredor coated to prevent the possibilityof skin abrasion. Small projections ,in areas where the rapid removalof plug-in units may cause injuryto the hands , must not be leftuncovered.Recessed mountings arerecommended for small projectingparts such as toggle switches andsmall knobs located on front panels.

RECESSED CONTROLS

Care should be taken whendesigning equipment to preventpersonnel from accidentallycontacting rotating or oscillatingparts such as gears, couplings,levers, cams, latches, or heavysolenoid equipment. Moving partsshould be enclosed or shieldedby protective guards whereverpossible. Where such protectionis not possible, warning signsmust be furnished.The cathode-ray tube is aspecial hazard in view of the highvoltages that must be applied andthe physical damage that mayresult from implosion. If thetube is accidentally nicked orscratched, resultant implosionmay not occur until days later.The face of such a tube must

be safeguarded by a shatterproofglass or heavy plastic shieldfirmly attached to the panel.Signs warning personnel that the

1 - 8


neck of the tube is easily brokenand must be handled with cautionshould be posted inside theequipment .In their normal installedpositions, chassis should besecurely retained in enclosures .Stops should be provided onchassis slides to preventinadvertent removal. Provision forfirmly holding the chassis handleswhile releasing the equipmentfrom the cabinet should also beincorporated. In the tilt-upposition, a secure latch shouldsupport the equipment firmlydespite conditions of shock,vibration, or inclination.Suitable handles or similarprovisions should be furnishedfor removing chassis from enclosures. Bails or other suitablemeans should be provided toprotect parts when the chassisis removed and inverted forservicing. These serve also toprotect the hands as the chassisis placed on the service bench.

Where access is providedto rotating, oscillating, or anyother hazardous mechanisms,the cover or apparatus shouldbear a warning such as:

CAUTION - KEEP CLEAR OFROTATING PARTS

All reasonable precautionsshould be taken to minimize fire,high temperature, and toxichazards. In particular , anycapacitors, inductors, or motorsinvolving fire hazards should beenclosed by a noncombustiblematerial having minimum openingsAs stated previously, elevatedoperating temperatures, andventilation requirements areprimary considerations inpersonnel protection. Sincemany equipments are installedin confined spaces, materialsthat may produce toxic fumesmust not be employed. Finishedequipment should be carefullychecked for verification of protective features in the design.

1 - 9

Chapter 2

OPERATION AND MAINTENANCE

2.0 GENERALEquipment for military use must

be designed to facilitate operationand maintenance, and thus decrease"down-time" and minimize over-allmanpower and training costs.Realistically designed operatingfeatures simplify control of theequipment, and well-plannedmaintenance features permit faultsto be rapidly located and defectiveparts to be easily repaired or-replaced.

2.1 OPERATIONAL FEATURESThe following general recommendations are presented as anaid in the selection of operationaldevices. Specific applicationssometimes require exceptions tothese rules, however, and itmay be wise to consult thehuman- engineer ing specialistwhen in doubt .

2.1.1 Visual IndicatorsFor a few discrete conditions(qualitative), use an indicator.which presents large differencesin position, brightness or color.The use of two or more variablesis recommended, such as colorand position, as in the trafficlight.For precise numerical values

(quantitative) with no need forinterpolation between numbersor for rate or directional

information, use a counter. Ascale indicator, however, ismore efficient when such valuesare to be "set into" theequipment.For numerical value plusorientation (check reading) intime, space, magnitude, orrate, use a scalar type ofindicator . Avoid multiplepointers on a single pivot whenpossible. One pointer plusand adjacent counter is bestwhen scale expansion isnecessary.

OFF

VISUAL INDICATORS

2 - 1

OP 2230

Once the type of indicator hasbeen chosen, and the amount andaccuracy of the information to bedisplayed have been determined,then it is necessary to considerthe factors which contribute to the

legibility of the indicator. Thesize of detail, form of numeralsand pointers, and illuminationall affect the efficiency withwhich an operator uses the visualdisplay .

CHECKLIST FOR A GOOD INDICTTOR

CAN THE INSTRUMENT BE READ QUICKLY IN THE MANNERREQUIRED (THAT IS, QUANTITATIVE, QUALITATIVE, OR CHECKREADING) ?

CAN THE INSTRUMENT BE READ ACCURATELY WITHIN THENEEDS OF THE OPERATOR (PREFERABLY NO MORE ACCURATELY)?

IS THE INSTRUMENT DESIGN FREE OF FEATURES WHICH MIGHTPRODUCE AMBIGUITY OR INVITE GROSS READING ERRORS?

ARE THE CHANGES IN INDICATION EASY TO CHECK?

IS THE INFORMATION PRESENTED IN THE MOST MEANINGFULFORM REQUIRING THE MINIMUM OF MENTAL TRANSLATIONTO OTHER UNITS?

IS THE RELATIONSHIP OF THE REQUIRED CONTROL MOVEMENTSNATURAL TO THE EXPECTED INSTRUMENT MOVEMENT?

IS THE INFORMATION PERTINENT WITH RELATION TO THE NEED?

IS THE INSTRUMENT DISTINGUISHABLE FROM OTHERINSTRUMENTS?

WILL THE OPERATOR BE AWARE OF AN INOPERATIVE CONDITION?

IS ILLUMINATION SATISFACTORY UNDER ALL CONDITIONSOF EXPECTED OPERATION?

2-2


2.1.1.1 Scalar Indicators. Dials andscales provide qualitative as well asquantitative information. Dialsprovide greater scale length in lessspace than straight-line scales. Thestraight-line scale, however, is notas apt to confuse the observer as tothe direction of numerical increase.Moving pointers with fixed scalesare generally preferred to fixed-pointer and moving-scale design forboth dial and straight-line scales.The fixed-pointer type, however, maybe used satisfactorily for setting-inoperations such as match the pointeroperations .An open window with fixed pointeris slightly better than an entirelyexposed scale when reading accuracyalone is the criterion of choice.

2.1.1.2 Design of Numerals , Letters,and Graduations . In general, thelarger the size of letters and numeralsthe less we have to worry about background and illumination.Capital letters are recommendedfor most panel labels although upper-and lower-case letters are suggestedfor extended instructional material.All labels should be normallyoriented so that they can be readfrom left to right. Special cases ofvertical orientation are permissiblewhen the label is generally ignoredand confusion might arise if it wereadjacent to more critical labels .For panel use, the design ofletters and numerals should be withoutflourishes. Such details are confusing,especially under thresholdillumination conditions . The criticaldetails of the figures should be simplebut prominent. Diagonal portions ofthe characters should be as near 45degrees as possible and suchcharacteristic features as openingsand breaks should be readilyapparent.

15 20

SCALAR INDICATORS

N 5 M5PREFFERED POOR

PANEL LABEL DESIGN

2-3

OP 2230

4

LETTERING TECHNIQUES

The stroke width of black characters on white background should beabout one- sixth of the characterheight. Stroke width of white figureson black background should be aboutone- seventh to one- eighth of thecharacter height; the narrowerstroke is necessary since thelight figure tends to spread orirradiate.

The height-to-width ratio of thenormal character should be aboutthree to two. Although there areexceptions to this rule, a closeapproximation to this ratio isrecommended, especially forpanel and scale design.

CHARACTER HEIGHT FOR GENERAL DIALAND PANEL DESIGN

VIEWING DISTANCE CHARACTER HEIGHT() (MM)

2/3 or l.u 0.092/3 to 3 0.17

Minimum space between character!,one strata width; betwMn words, one character width.

MAJOR

INTERMEDIATEMINOR

SCALE GRADUATIONS

Scale graduations should belimited in number by the accuracyrequired. Furthermore thesmallest readable division shouldnever be finer than the probableerror in the metering apparatus .A minimum of 0.5 inch isrecommended for the distancebetween "major" graduations .These figures are for the normalreading distances, 13 to 28 inches.The minimum graduation dimension shown in the illustration is for28-inch viewing distance.

2-4


The number of graduation marksbetween numbered points shouldnot exceed nine. Optimumdimensions on a dial are shown.

For ease in reading, figuresshould be oriented according to thetype of scale or dial used.

Orient figures vertically ondials which have a fixed scale andmoving pointer .

When the scale is of finite length,there should be a scale breakbetween the end and the beginningof the scale. The break should beequal to a major scale division.

Orient figures radially on dialswhich have a fixed pointer andmoving scale. When possible,orient the index at the 12-o'clockposition.

When the figures of a dial movepast an open window, they should beoriented so that they appearvertically at the window opening.Two or more figures should appearin the window simultaneously.

Numbers should appear toincrease in a clockwise direction,left to right, or bottom to top.Avoid the use of irregular scaleswhenever possible. Some machineand slide-rule type scales areconsidered as exceptions to this rule,

When two or more similar scalesappear on the same panel, theyshould have compatible numericalprogression and scale organization.

.035- 030--OZ5-

-p- ,". -HK- II i i i MI i 1 1 1V

.07wcenterto center

SCALE MARK DIMENSIONS

S 93I I

20 aI

POO*

root

INDICATOR SCALE DESIGN

2-5

OP 2230

RECOMMENDED NUMERICAL PROGRESSION

GOOD FAIR POOR

1 I a 4 5 2 4 I 10 3 6 9 12-S 10 15 25 20 40 60 80 100 4 8 12 1610 20 10 40 50 til 4 5 7.5

* Except for bearing dials where cardinal directions ore standard orienting pointsor wher* operating doctrine specifies conditions of time scales, or turn rates.

RECOMMENDED SCALE BREAKDOWN

0 10 20*

1 . I I . 1 . I I . 1

of thii de.ign shawed lej. variability In MMdial marking,.

whm Mtting-in than did inual

40

SCALE ORIENTATION

Whenever possible, orient adial scale so that the criticalrange to be read will appear asleft to right or bottom to top, toavoid confusion as to direction ofincrease. This is especiallyimportant for check-readinginstruments. For multir evolutiondials, orient zero at the 12-o'clockposition.

POINTER AND SCALERELATIONSHIP

MOVING

40 70 80

FIXED

Pointers and scale graduationsshould be oriented so that thepointer, either moving or fixed, isclose to the index and yet does notcover the number .

- 6


When the dial diameter must betoo small for adequate pointer andgraduation design, it is possible toutilize bezel or panel space forengraving the numbers. (Thismethod should be used only whengross pointer position is all thatis needed). The pointer tip shouldbe the same width as the smallestgraduation.The pointer should be designed

so that there is a minimum distancebetween tip and graduation - 1/16inch maximum.The pointer should be mountedso that visual parallax is minimized.This can generally be achieved byplacing the pointer close to the dialscale. The pointer should bepainted the same color as numbersand graduations when possible.When reciprocal readings arenecessary, the two ends of thepointer must be identifiable.Simplicity in pointer-tip designis important for reading speedand accuracy.

PREFERRED POOR

lit! t 4DIAL AND POINTER DESIGN

CHECKLIST FOR DIAL AND SCALE DESIGN

HAS MAXIMUM SIMPLICITY COMMENSURATE WITH INFORMATIONAL REQUIREMENTS BEEN MAINTAINED?

CAN THE DIAL OR SCALE BE INTERPRETED (NO SPECIALCOMPUTATIONS OR MULTIPLIERS REQUIRED)?

HAS MAXIMUM CONTRAST BETWEEN FIGURES AND BACKGROUNDAS RELATED TO EXPECTED ILLUMINATION BEEN PROVIDED?

HAS OPTIMAL DIAL SIZE BASED ON BEST FIGURE AND GRADUATIONSIZE AND SPACING BEEN USED?

HAS AN APPROPRIATE NUMERICAL PROGRESSION (OPTIMUMNUMBER PROGRESSION; SCALE BREAKDOWN; RELATIONSHIPBETWEEN NUMERICAL INCREASE, POINTER MOVEMENT,AND RELATED CONTROL MANIPULATION BEEN USED)?

2-7

OP 2230

2.1.1.3 Design of Counters . Indesigning or selecting a counter,strive to provide a device which iseasy to read. The style, size, andfigure-to-background contrasts ofthe numerals on the counter drummust be chosen with care. Ingeneral, the design rules fornumbers and letters given in 2.1.1.2are good. In addition, however,counter displays present severalspecific problems of their own.

The height-to-width ratio ofnumerals for counter displays shouldbe one to one, rather than three totwo as recommended for dials andscales. This factor is importantsince the curved surface of thecounter drum plus the movementof the display make it difficult torecognize the critical portions ofthe numeral, the top and bottom.

Whenever practicable, thenumbers should "snap" into placeto eliminate blurring.

Numbers should not follow eachother faster than about, two persecond if the observer is expectedto read the numbers consecutively .An upward movement of the counterdrum should indicate a numericalincrease. Although this is notcritical in reading the number out,it is quite important when a manualcontrol is used to set the numericalvalue into the device.

41(31(6

COUNTER DESIGN

Avoid large horizontal spacingbetween number drums . Largespaces between counter drums makeit especially difficult to read largenumbers .

2-8


When last digits have little value,as in large values of range or altitude,they should be replaced with stationaryzeros. Similar treatment isrecommended for preceding digitswhich are seldom used; in this case,however, the space should be blankedout completely during the time whenno numerical value is to appear .Counters should be mounted asclose to the panel surface as possibleto provide maximum viewing angleand minimum shadow effects fromambient lighting. Counters should beoriented so that they may be readfrom left to right.

2.1.1.4 Indicator and Warning Lights.Brightness factors are of utmostconcern in light displays. Lightswhich must attract immediateattention should be at least twice asbright as the immediate background.The background should be dark incontrast to the light and should be ina dull finish. When the major panelarea is light in color, it is possibleto improve the effectiveness of thelight display by painting the immediatearea a dark matte finish. Theaddition of a matte-black panelaround a signal light improves theeffectiveness of even an outdoorsignal. Control of indicator-lightbrightness should be provided whenthe range of ambient illuminationvaries . This control is especiallyimportant when dark adaptation isnecessary.

Printed information on pilot andwarning lights should be designed tofit the job at hand. Black printingon the bright background of the pilotlight allows a maximum of brightnessand is ideal for a warning signal,whereas a perforated mask betweenthe bulb and the filter emits lessglare for the dark-adapted eye.

rooe

I 2900 I 2924

425 00425

NUMERAL PLACEMENT

LIGHT TO BACKGROUND CONTRAST

SAFE

WARNING AND PILOT LIGHTIDENTIFICATION

2 - 9

OP 2230

Pilot lights need not be largeto be effective since the brightnessand color are more importantvariables . Colors for pilot orwarning lights should be chosenwith care. For general usage,colors to be used on the samepanel should be widely separatedin spectral wave length. Thecolor red should be preservedfor danger signals when possible .Avoid using similar colors, suchas red with orange or purplewith blue. Approved red, blue, andgreen are recommended for paneldisplays when erroneousinterpretation, by an observerdeficient in the ability to distinguishcolors, might be dangerous.

Lights of varying size, color,brightness, and grouping providean effective means for presentingsimple, discrete information.Critical lights should beisolated from less importantlights whenever possible. Simplicity is important in using lightdisplays . Too many lights or toomany colors tend to confuse apanel layout.

Mounting of warning lights andother visual displays within 30degrees of the normal visualaxis is recommended when theoperator must attend to othertasks . A central warning lightmay be used to direct anoperator's attention to anotherpanel. Flashing lights are usefulin getting attention when theyprovide flash rates of 3 to 10 persecond and each flash durationis of the order of at least0.05 second.

2.1.1.5 Cathode-Ray TubeDisplays . Electronic displaysare usually presented oncathode-ray tubes in rectangularor polar co-ordinate form.Display considerations that affectoperator performance arepresented as follows:

Size - When plotting orsimultaneous viewing by severaloperators is not important,there is no significant advantagebetween large or small tubes .More time is required to scanthe whole scope of an extremelylarge tube, but such a tube willallow use of a more adequategrid overlay and thus improveaccuracy. Scopes of 5- to 7-inchdiameter are quite adequatewhen plotting is not required.

Shape - The bezel or framearound a CRT display shouldconform to the generalconfiguration of the type ofpresentation - round for aPlan- Position Indicator (PPI)or rectangular for an A- scan.

2-10


Mounting Position - CRT'sshould be mounted so that thevisual axis of the operator isperpendicular to the face of thetube at its center . Recom menda-tions for various operatorpositions and tube mountingangles may be found in 2.1.3 .Normal viewing distance is14 to 18 inches.

Cursors - Electronic cursorswhich are continuously printed aresuperior to mechanical cursorsfrom the operators point of view,since parallax can be eliminatedand accuracy improved. Theaddition of a scale is essential forbearing accuracy; the addition ofa counter which presents the exactnumerical values found by thecursor manipulation improvesaccuracy still more . When bearingaccuracies of 5 degeres or moremay be tolerated, there is noreal need for the cursor sincethe operator can interpolatebearing position to that degree ofaccuracy .

Grids - Accuracy of interpolatingtarget position is improved by addinggrid markings. The more accuratethe reading requirements, themore elaborate the grid structureshould be. To minimize theconfusion caused by many finegrid lines, it is important toincrease scope size. The sizecompromise cannot be predicted,but certain design suggestionscan be made.

Range Rings - The minimumspacing between range rings on apolar display should be of the orderof 1 degree 36 minutes visual anglesubtended at the eye, or about

PPI BEARING SCALE

o 10

PPI GRID SYSTEM

2-11

OP 2230

0 0 00e a

1/2 inch at 18- inch viewingdistance. For bearing, a solidline for each 30 degrees anddotted lines for each 10 degreesare recommended for maximumaccuracy. If more than fourrange rings are necessary tocover the scale it is wise todivide the rings into subgroupsby making half of them dotted andhalf solid lines. Use of separatecolors per subgroups is alsosatisfactory. Range rings mayalso be designed to act asunnumbered bearing aids onvery large grid systems (30-inchdiameter or larger) .

0 0 O0e e|

Illumination - Brightnesscontrasts between signal andbackground and between targetand "noise" vary to such adegree that exact optimumlevels cannot be stated. Contrastratios may be improved by minimizing background brightnessand surface reflections. Byproper filtering, the trace tobackground ratio can bemaximized. A cross- polarization filter technique has provenquite adequate . The techniqueutilizes a polarized light overthe scope face. With thistechnique it is not necessary towork in completely darkenedrooms . Scope hoods arerecommended for a singleoperator when ambientillumination cannot beadequately controlled.

CRT CONTRAST RATIOS

sotncE olAMKEN!ILLUMINATION

REDUCTION OF BACKGROUNDBRIGHTNESS BY USE OF CROSS-POLARIZED FILTERS

2-12


2.1.1.6 Combined Indicators . Thecombination of different types ofvisual displays within oneinstrument or of severalinstruments into an array orgroup should be governed by thefollowing principles:

Combine only those forms ofinformation which bear a commonrelationship.

Keep the common factor ofinterpretation (fixed and movingparts, scale values, etc.) the same.

Do not confuse the operator withunnecessary information.

Combining on one dial morethan one item of information savesthe operator time which would betaken in locating parts of atotal picture.

Scale range may be increasedby combining pointers and counters.The total range may be increasedby extension (pointer plus counter)or the range may be given with moreprecision (pointer plus sub- dialand pointer) .

Note that this type of scaleexpansion is to be used only whensome qualitative informationrelative to rate or normaloperating range is needed. Thecounter is best when onlyquantitative information is needed.

Do not use multiple-pointerdisplays with more than two pointers .

With two pointers on the samedial face proper orientation willmake check reading easier, however,avoid unrelated informationcombinations such as azimuth andgrid current.

SYMBOLICIN FORMAT,ON

PICTORIALINFORMATION

CADAS 22.211FT

POOR

COMBINED DISPLAY ONA SINGLE DIAL

2-13

OP 2230

When the number of sources ofinformation becomes too great andare apt to complicate oneinstrument, it is wise to combineseveral simple instruments intoan array. Such arrays ofinstruments will allow the rapidcheck-reading of a large numberof instruments in a minimum oftime if the pointer positions forthe normal operating conditionsare arranged at the 9- or12-o'clock position. The slightdeviation of any one of theinstrument pointers from thissymmetrical pattern of pointersis easily and quickly locatedduring even a cursory scan.

CHECKLIST FOR SINGLE OR MULTIPLEINSTRUMENTS COMBINED ON ONE DISPLAY

HAS THE BEST SCALE AND DIAL FACE DESIGN BEEN USED?

ARE ALL THE SCALE VALUES AND THEIR RESPECTIVEGRADUATION CONSISTENT IN THE DIRECTION OF INCREASEOR DECREASE?

HAS THE SAME NUMERICAL SCALE PROGRESSION PRINCIPLEBEEN USED ON ALL SCALES OF THE COMBINED DISPLAY ?HAS THE SAME PICTORIAL RELATIONSHIP BEEN USED FORALL INSTRUMENTS ON THE SAME PANEL?HAS THE NORMAL VISUAL AXIS OF THE OPERATOR BEENCONSIDERED SO THAT PARALLAX WILL NOT BE A PROBLEM?

ARE ALL PARTS OF THE INSTRUMENT OR INSTRUMENTSILLUMINATED EQUALLY WELL AND ARE DIMMERS PROVIDEDFOR COMBINED DISPLAYS WHERE DARK ADAPTATIONREQUIREMENTS CALL FOR SELECTIVELY LOWERING THEILLUMINATION OF SPECIFIC PORTIONS OF A DISPLAY ?

2-14


2.1.2 ControlsIn the design or selection ofcontrol devices it is important toconsider two basic factors: (1) thecompatibility between the movementand location of the control deviceand of the elements to be controlled;and (2) the physiological andanatomical efficiency with whichthe operator can utilize thecontrol and display.

IMC to

FOR POINTERMOVEMENTUP

2.1.2.1 Compatibility. There arecertain accepted relationshipsbetween control and display thatshould be provided so thatmovement errors will be at aminimum.

Whenever possible, controlmovements and location should beparallel to the axis of the displaymotion they affect. Variouscontrol motions for a givendisplay are illustrated.

Controls should be oriented tofit normal habit-pattern reflexes .An operator will normally movehis control so as to centerdeviations or reduce errorspresented by the visual display.

2.1.2.2 Physiological Efficiency(Location of Controls) . To reducefatigue controls which must beused most often should be placedsomewhere between elbow andshoulder height. Locationsforward and slightly belowshoulder height are found mosteasily when "blind" reachingis required.

o

oDIRECTIONAL COMPATIBILITY

CONTROL PLACEMENT

2-15

OP 2230

Mounting eigher side of center issuperior to mounting in the centerof the operator's position.

Cranks which require extremetorque should be mounted so thatthe turning axis is parallel tothe frontal plane of the body.

Crank-type controls which areto be turned rapidly should bemounted so that the turning axislies within a range from perpendicular to about 60 degreesoff the frontal plane of the body .

Controls which must beoperated from a fixed operator'sposition, such as that of anaircraft pilot secured by meansof shoulder harness, should bewithin an arc of 28 inchesmeasured from the individualsshoulder position.

OPTIMUM CRANK HANDLE SHAPt

2.1.2.3 Size of Controls.Control dimensions should takeinto consideration the normalhand-grasp limitations.

Adjustment knobs forinstrument-type equipmentsshould, when possible, belimited in diameter to 2 inchesor less for most convenienthand grasp.

Handles for cranks shouldbe about 1-1/2 inches in length by1/2 inch in diameter for operationsrequiring fast wrist and fingermovements, 3-3/4 inches in lengthby 1 inch in diameter for operationsrequiring arm movement of heavyloads .

For high-speed cranking, thediameter can vary from 3 to 9inches, with 4-1/2 inchesrecommended for general use.

2 - 16


Wheel and crank diametersdepend upon the mounting positionand torque to be expected as wellas the speed of turning required.

The table below shows theoptimum diameters for severalmounting conditions and torqueconditions .

OPTIMUM CONTROL DIAMETERS *

2

*

POSITION(d.a.)

* fffHandwhe.l (W). Diom.Ur in Inch'i,Crank (C). lodius In Indws

SIZE

ATfOHM8 IU OF

0 in. Ibx ; i- 40 in. Ib 90 in. Ib

24 0 W 34 10 16

36 0 W 3-8 10-16 16

I w 34 10 10

0 c 114-414 414-7'A 414-714

39 90 w 3-10 10-16 16

90 c 214-414 414-714 414-714

40 45 w 34 6-16 10-16

-45 c 214-714 414-714 414-714

42 45 w 34 10 10-16

45 c 214-414 214-414 414

48 0 w 34 8-16 10-16

0 c 214414 414 414-714

* These data were based on setting the control device in only onerevolution. The author infers that for less than 90-degree turn,handwheels would be more effective than cranks .

** Angle in degrees from horizontal*** Code: W - Handwheel, C - Crank

2-17

OP 2230

J

2.1.2.4 Force Limitations, Thehuman operator should not beexpected to perform at maximumcapacity for any great length oftime, so it is wise to leave asafety factor in force required.

A maximum force of 8 to 16ounces is recommended forsmall toggle switches.

A maximum torque of 2 inch-pounds is suggested for rotatingknobs .

A load of 2 to 5 pounds issuggested for smooth operationof small, high-speed cranks.

Hand levers of the gearshifttype should not require morethan 30 pounds of appliedforce .

2.1.2.5 Coding. Coding techniquessuch as location, shape, size andcolor are useful in the layoutof control panels from thestandpoint of reducing operatorerror in the selection of thecorrect control.

Location or position codingprovides spacing or positioningof controls in groups far enoughapart to establish a positionhabit pattern. An operator soonestablishes a code for himself;the more definite spacings wegive him, the sooner heestablishes accurate habitpatterns .

2-18


Shape coding is useful to augmentlocation coding under black-outconditions. It is more useful withlever-type controls such as toggleswitches, rotary detented switches,and joysticks, because the shape.will not interfere with themanipulation of this type ofcontrol. Shape coding is notgenerally recommended, however,for electronic types of controlknobs since manipulation is oftenhampered and recognition isdifficult when the knob is inverted.Some shape variability may behad from selected commercial designs,

Size coding provides tactual cuesof size which may be used to identifygross categories of control functionsand enhance location habits acquiredinitially through position coding.

Color coding establishesrelationships from one equipmentto another. Since all colors arenot equally distinguishable andare variously affected by lowerlight levels , it is important toselect colors that are recognizableunder the expected illuminationconditions .

2.1.2.6 Selection and Use ofStandard Devices. Select toggleswitches which provide a visualcue as to the switch position;30 degrees either side of thecenter position is satisfactory.Mount toggle switches so thatthe ON position is always forward,up, or to the right as the operatorlooks at the switch.

Use small knobs (approximately1 inch in length) for non-criticaladjustments such as volume,focus, and dimmers. Uselarger knobs (approximately 2inches in diameter) for morecritical adjustments such astuning or frequency selection.

o o

oot

USE ROUND KNOBS FORCONTINUOUS TURN

BAR KNOB FORSTEPWISE TURN

2-19

OP 2230

Use bar or pointer- shapedcontrols exclusively for switchingfunctions which have mechanicaldetents to aid positioning. Sizeis not important as long as thereis sufficient gripping surface.

When using two controls on aconcentric shaft arrangement, usethe larger for vernier adjustmentso that the scale spread will bemaximized.

Knobs which are less than 3/4inch in depth should be knurledrather than serrated to provideadequate gripping surface. Forknobs with a depth greater than3/4 inch, serrations are adequatebut should be chosen with care.Serrations should be chosenwhich give the best grippingcharacteristics, that is, pointcontacts rather than round ones,and evenly spaced serration ratherthan uneven or widely spaced ones.

Select skirt designs which allowan engraved index to be seen inspite of the fingers. Specialskirts should be fabricated foredge-lighted panels used underblackout conditions. A transparent pointer which allows lightto come through should be usedwith a back-lighted panel.

Push buttons should notrequire extreme pressure foractuation (maximum, 31 pounds).The contact should be definite,that is, the finger should feel a"click." There should besufficient finger contact area sothat the pressure is not irritating.The push button or buttons shouldbe mounted, possibly by recessing,as shown, so that they cannot beaccidentally tripped. Properillumination should be providedwhen there is a possibility ofpressing the wrong button.

2-20


2.1.3 Console Design and PanelLayout

The layout and design of instrument panels with suitablepackaging into a well human-engineered unit are, at best,a compromise. It is importantto approach each design in sucha manner that the best compromises are made. As in the designof any piece of hardware, it is ofutmost improtance to have answersto certain technical aspects of

the problem in hand beforestarting to work on the actuallayout. The engineer mustknow the answers to thefollowing questions if he wishesto incorporate good human-engineering principles intohis finished panel or console.Armed with answers tothese questions, the engineer isready to acquaint himself withthe human- engineering rulesfor panels and consoles.

CHECKLIST FOR CONSOLE DESIGNAND PANEL LAYOUT

WHAT LIMITATIONS ARE FDCED BY SPECIFICATION OR BYULTIMATE SPACE FACTORS IN THE INSTALLATION AREA?

WHAT VISUAL DISPLAYS ARE NECESSARY? WHAT SIZEMUST THEY BE? WHICH OF THESE MUST BE ACCESSIBLETO THE OPERATOR DURING OPERATION AND WHICHACCESSIBLE ONLY TO THE MAINTENANCE MAN?

WHAT CONTROLS ARE NECESSARY ? WHAT SIZE? WHICHMUST BE ACCESSIBLE TO THE OPERATOR; TO THEMAINTENANCE MAN?

WHAT AUDITORY DISPLAYS AND WHAT MEANS OFCOMMUNICATION BETWEEN OPERATORS ARE NECESSARY?

WHAT OPERATING CONDITIONS ARE EXPECTED - ILLUMINATION,NOISE ENVIRONMENT, TEMPERATURE, VIBRATION, PITCHAND ROLL?

WHAT OPERATOR CONDITIONS ARE EXPECTED - ONE ORMORE OPERATORS, CONTINUOUS OR INTERMITTENTOPERATION, OPERATOR'S POSITION, STATIC OR DYNAMIC?

WHAT MAINTENANCE FACILITIES ARE REQUIRED DURINGOR BETWEEN OPERATIONS ?

2-21

OP 2230

At this point it is suggestedthat a mock-up be constructed.The mock-up need not be elaboratebut it should be accurately scaled.A miniature mock-up is recommendedbecause it is easier to handle andmay be all that is required to solvethe problem, thus saving theexpense and time consumed in theconstruction of a full-scalemock-up. The sheet followingprovides a 1/8 scale layout foruse with mock-ups. The scalemodel may be made frommaterials such as cardboard,solid wood pieces , or erector-type building blocks . Thismodel will be found to be quitehelpful even when used inconnection with engineeringdrawings. It is suggested thatthese manikins be reproducedin I/' 8- inch thick clear plasticand that the joints be flush- riveted.Stiff cardboard may be used inlieu of plastic .

2-22

UNASSEMBLED 1/8 INCH 1 INCH

2 - 23


o o o

The illustrations show recommendations for angular mountingof visual displays such as plan-position indicators (PPI) .

Dimensions are approximate.They do, however, representusable standards for 90 percentof the male population.

2-25

OP 2230

The size of an instrument paneldepends primarily upon the normalarm reach of the human operator.In general, convenient arm reachis about 28 inches from therespective shoulder pivot point.This rule cannot be hard and fastfor the obvious reason that in mostsituations the operator has freedomto bend his body and thus extendthe useful reaching distance. Aword of caution, however, is thathe cannot be expected to bendtwo directions at once, so do nottake advantage of his flexibilityunless it is clearly necessary.Further, he will tire quickly ifhis arm is in the extended positionfor a prolonged time period asshown. Controls in this positionshould be either switches orcontrols requiring infrequentadjustment.

win ALLOW THE OPERATORTO REACH THE CORNERS

Convenience limits for placement of controls on horizontal60-degree, and 30-degree consolepanels are shown in the illustrationson the preceeding page. A visualdisplay may limit the flexibilityof the operator's position or special

apparatus may restrict hisflexibility for reasons of safety,Convenience limits may beestablished to restrictnecessary arm reach when theoperator is restricted to amore or less static position.

2-26


Arm reach from static sittingand standing positions are shown,when the operator is at a normalviewing distance (18 to 28 inches)

from the control panel. Theseare not maximum reaches, butdo take into consideration somenormal bending of the operator's body

2-27

OP 2230

PPI ScopePPI Controls

FocusIntensityRange CursorVideo gain

B

Speaker

Audio controlOutput meterFreq. selector

Communications Receiver

Tuning dialRF gain controlAudio gain controlSelectivity control

D

Intercom. Cont .

Phone jacksStation selectorVolume control

Navigation Instr ,

CompassCourse indicator

0OOOooo

GOOO0O

Once a rough idea of the formand size factors of the panel orconsole have been decided upon,it is then necessary to organizethe components that are to beplaced on the panels . The components will undoubtedly vie foroptimum positions and compromiseswill have to be made. A suggestedmethod for arriving at the bestcompromise and organizations,first, itemize all components byrelated groups .

Next prepare cardboard"cutouts" of each separate item.These "cutouts" should be drawnto scale and should represent theinterior dimension of such itemsas dial face or control knob, andthe interior dimension of thephysical structure of the controlmechanism that will limit theproximity of adjacent items .These cutouts can now be placedin the proposed panel area andmoved about until you have arrivedat the best organization and fit.It is much more economical tofind out that you do not haveroom in this manner than tobuild a finished package thatmust be modified later . Thefollowing group procedures shouldbe used as a guide in organizingpanel components .

2.1.3.1 Grouping Procedures ForPanel Layout (Check-ReadingDials). For a single group offive or fewer check-reading dialsin a horizontal row, normaloperating position of the pointersshould be located at the9-o'clock position; for thevertical groups, orient thepointers to the 12-o'clockposition.

2-28


For groups of six or more, userows or columns rather thanextending a single row; long rowsor columns impose undesirablescanning movements upon theoperator.

For several groups on the samepanel, use a consistent pointerposition regardless of the aboverecommendations .

Linear gauges or meters shouldfollow the same general rules asspecified for dials .

The positions of specific dialswhich are grouped together shouldbe determined by the sequence inwhich they are to be read, thatis, the operator should be ableto read in order of sequence fromleft to right or from the top of thepanel to the bottom.

Controls should be placed:

Close to the display which theyaffect, when possible.

Below or to the left for left-handoperation; below or to the rightfor right-hand operation.

Sequentially with respect to theexpected order of operation.

At the optimum position formanipulation of the control whichis to be used most frequently.

So that there is an equitabledistribution of work load betweenright and left hands; right handoperation should be reserved foroperations requiring the finestadjustment .

o ooo

o o

STEP 1

POWER

STEP 2 STEP 3

0SELECT TRACK

o - 3 t- . o2-29

OP 2230

o OControl-display organizationshould be such that visual displaysoccupy central areas and controlsoccupy peripheral areas so thathand movements do not obstructthe view of visual indicators.

Area or group identificationis quite important in complexlayouts. It may be accomplishedsatisfactorily in several waysas follows:

O o 444Adequate spacing of displayor control groups; horizontalseparations are preferred tovertical separations.

Marked outlines aroundeach group.

0 o o o oo o 0 0Area color patterning.

Symmetry.

Differential place of mounting.

REMOTE COURSE INDICATORS

/

Label consistently either aboveor below for a specific category,that is, group title above, asshown; individual labels belowor centered. Lable in terms ofwhat is measured (rpm), notby the name of the instrument(tachometer). Company tradenames should not appear on theface of a dial .

Space saving may be accomplished by overlapping partiallyhidden dials .

2-30


2.1.4 Lighting ApplicationsCertain human-operator tasksinvolve the need for maintainingthe eye at an optimum dark- adaptationlevel and yet allowing for adequatevisibility of instrument markings ona panel or console. Unfortunately,the optimum level of dark adaptationis not possible with even theminimum amount of instrumentillumination, but is possible toreach a satisfactory compromisewith a minimum amount of "redlight" of the proper wavelengths .

Other special tasks requirereduced ambient illumination foroptimum visibility, but therequired level of dark adaptationis not so stringent. The sonar orradar operator, for instance, needsa rather low level of ambientillumination in order to operatehis scope satisfactorily, whileother operators in the same areamay need to write or move about andmust have sufficient light toaccomplish their own tasks .This condition we have chosen tocall "dimout" since actual blackout isnot necessary even for the scopeoperators .

DIRECT

INDIRECT

DIFFUSED

GENERAL ILLUMINATION

For blackout conditions(night lookouts, ship's bridge) useillumination at wavelengths above600 millicrons . Incandescent lightpassing through filters conformingto Federal Standard No. 3,Identification Red, meets thisr equir ement . BACKLIGHTING

2-31

OP 2230

RED- LIGHTING LEVELS FOR DARK ADAPTATION

AREA LIGHTLEVEL(fool candl.)

Control Roomi Illumination on working oreoiIllumination on block and white dial., Agures,noliM plotel

Brightness of in>lrumenlfacei (white portion)Brightn.si of indicator lights (not to e


Individual ring lighting may beprovided satisfactorily by housingtwo miniature lamps under a hingedshield which protects the operatorfrom direct glare.

A stand-out fixture providesmaximum compactness for individualinstrument illumination .

The following precaution shouldbe exercised. Floodlighting castsshadows. Keep instrument facesflush with the panel; orient sourcesso that shadows do not interferewith other instruments ; diffuse thelight with appropriate filtermaterials .

2.1. 4. 2 Transillumination. Trans-illumination is an indirect type ofillumination utilizing edge andbacklighting techniques on clear,fluorescent, or sandwich-typeplastic materials .

Clear plastics such as Plexiglasor Lucite possess excellent light-transmitting characteristics whichcan be used to advantage ininstrument lighting problems .

FILTER

Figures may be engraved on thereverse side of clear plastic andedgelighted for dials, pointers,and nameplates. Maximum contrastfor reading may be achieved bybacking up the display with a backpanel. Illumination may be in anydesired color by dyeing the edgesof the plastic .

ENGRAVINGSON REVERSESIDE

BLACK BACKING PLATE'LAMP

2-33

OP 2230

BUCK

Excellent blackout displays maybe made with a sandwiched fabrication of clear plastic plus a whitelayer of translucent paint or vinyltopped with an opaque black paintor vinyl. Illuminated with redlight, this type of display, whenengraved properly, will servefor daytime use (the figure willappear white on a black background) as well as for nightimeuse (the figures will appear redon a black background) . Similarresults may be accomplishedwith a silk-screen process .

FRONT OF DIAL

REFLECTOR

Light piping may be accomplishedby bending clear Lucite . Suchdevices may serve to pipe lightto hard-to-reach pilot indicatorsor may be used to illuminate alubber line or index in front ofa moving-scale dial. In thelatter use, a single lightilluminates the translucent dialas well as the inscribed index.

Counter illumination is possiblewith clear-plastic edgelightingtechniques . The plastic paneledges should be roughened todiffuse the light.

Translucent plastics in variouscolors may be used for backlighting purposes. Figures shouldbe engraved on the front surfacesand filled with an opaque paint,preferably black, for best results.Even illumination requires thatthe lamp be placed very close to thesurface of the plastic for best results;a reflector behind the lamp helps.The brightness drops off rapidlywithin a very short distance fromthe light source. This type ofmaterial is not recommendedfor large displays but rather forindividual nameplates with aminimum number of figures.

2-34


Laminated sandwich-type plasticscombine translucent with opaquecharacteristics and are treatedsomewhat the same as the clearsandwich. The major differenceis that backlighting rather thanedgelighting is necessary. Thesame problems of evenillumination are found here aswere mentioned in the foregoingparagraph. These displays aremore satisfactory for smallnameplates than for large areadisplays . Engravings appearwhite in daylight and red atnight .

CLACKOPAQUE

WHITETRANSLUCENT

COLOREDTRANSLUCENT

\

SPECIAL TECHNIQUES FOR ILLUMINATIONOF PANEL CONTROLS

CUT-OUT SKIRT WITHTRANSILLUMINATED RftNEL

ENGRAVING(Either bock or (dp-lighting)

TRANSILLUMINATEDPANEL AND KNOB

(Either bock or edge-lighting)

TRANSLUCENT LIGHT RING\

2-35

OP 2230

GENERAL RECOMMENDATIONS FOR INSTRUMENTAND CONSOLE LIGHTING

CONDITION OF USERECOMMENDEDSYSTEM

BRIGHTNESSOF MARKINGS(foot Lamberts)

BRIGHTNESSADJUSTMENT

Instrument lighting,dark adaptationcritical

Red flood, indirect, orboth, with operatorchoice

0.02 to 0.1 Continuousthrough range

Instrument lighting,dark adaptation notcritical

Red or low color temperature white; flood,indirectt or both, withoperator choice


Instrument lighting,no dark adaptationrequired

White flood 1 to 20 May be fixed

Control consolelighting, darkadaptation required

Red edgelighting, additional optional red orwhite flood desirable,with operator choice


Control consolelighting, dark adaptation not required

White flood 1 to 20 May be fixed

Possible exposureto bright flashes

White flood 10 ta 20 Fixed

Chart reading, darkadaptation required

Flood, operatori! chokeof red or white

0.1 to 1.0 onwhite portionsof chart

Continuousthrough range

Chart reading, darkadaptation notrequired

White flood 3 or above May >1efixed

Acknowledgement

The foregoing material on Operational Features was obtained fromHuman Engineering Guide by Wesley Woodson, University ofCalifornia Press .

2-36


2.2 MAINTENANCE FEATURESGood design can greatly reduce

the time and skill required formaintenance. Provision must bemade for testing, adjusting, andrepairing of equipment, in keepingwith its size and complexity.

2.2.1 Testing

2.2.1.1 Test Points. The selectionof test points must be carefullymade based upon circuit functionsand conditions . A criticalexamination of the equipmentblock diagram and schematic isnecessary. Major test pointsshould be provided with suitableterminals, readily accessible.A turrett terminal, properlydesigned is satisfactory.Terminals on tube sockets andother inaccessible points arenot satisfactory. Where criticalcircuits, or high voltages areinvolved a simple isolatingarrangement may be used.

HIGHVOLTAGE

HIGHRESISTANCE

TEST POINT

ISOLATION OF TEST POINTS

A terminal board containing keytest points and located above-chassisis desirable. No disassemblyshould be required to use testpoints. A multipoint selectorswitch is practical in someapplications .

2. 2.1. 2 Failure Indicators . Fusesshould be supplied with neonindicators to indicate failure.In complex equipment wherefunctions are sectionalized, allsections, where applicable,should be provided withadditional fuses.Panel meters are an excellentmeans of indicating failure. Asufficient but minimum numberto monitor all critical functionsshould be provided. In someapplications, meter scalesmay be colored to indicate thenormal operating range. Whereequipment is to be automaticallyprotected, high and low limitalarm contacts on the meterare useful. "Push-to-read"buttons or rotary multiplecontact switches enable severalpoints to be monitored with asingle meter .Monitoring dscilloscopesand similar apparatus may beused where waveform, inaddition to magnitude, mustbe critically monitored.Suitable switching arrangementcan extend the usefulness ofa single oscilloscope. In manycases, where a cathode-raytube is provided for operation,switching arrangements canbe made to adapt the tube formaintenance purposes.

2.2.1.3 Built-In Testers .Built-in test facilities are moredesirable than portable testequipment in achieving rapidservicing. These facilitiesshould provide for over- allperformance checks and circuitisolation. For example, in aradar apparatus, means shouldbe provided to continuouslymonitor the power into theantenna; a built-in noise generatorcoupled to the receiver imput wouldquickly check its performance.

2-37

OP 2230

2.2.1.4 Test Equipment. Thereare many standard test equipmentsavailable for maintenancepurposes. The design of systemsshould be such that special testequipment is not required. Thiscan sometimes be accomplishedduring circuit development bymaking proper provisions toadapt the circuit to be measuredto the test equipment characteristics. Use of built-in adaptersis a simple solution.

2.2.2 Assembly Slides

2.2.2.1 Types. Where equipmentis complex and of unitizedconstruction, chassis slides,runners, and tilting mechanismsare usually required.

ROLLER SLIDE

FLEXIBLECABLE

TERMINALS

Continuous operation of suchequipment under severe environmental conditions requires thatrapid servicing be possible. Withdrawal must be toward the front ofthe equipment, and provisions shouldbe incorporated to prevent damageto any rear-connected cabling.Position locking of the chassisin operating position is required.A stop must be provided to limitthe extent of withdrawal. Additionalprovisions for positioning duringmaintenance, such as devices fortilting and turning must be madeaccident proof.

SLIDE

AN APPROVED ARRANGEMENT

Some expedients which can beused in conjunction with thesearrangements are counterbalancing springs, adequate detents,and over-center locking linkages.

2-38


Complete release and removalof the chassis must require anothermanual releasing operation.

2.2.2.2 Permanent Links . Whereinterconnecting cables arepermanently wired at one end toa terminal board, adequatepreparation and location of thecable must be considered.Cables should be suitablysheathed with flexible plasticsleeving and anchored to thechassis. Storage space and anobstruction-free path preventchafing when the chassis ismoved. The cable must be longenough to permit disconnectionwith the chassis withdrawn.Strain on individual wires mustbe avoided by proper lacing, andstrain-relieving clips orclamping devices.

2.2.2.3 Auxiliary Links . Wherethe chassis is of the "plug-in"type, similar to a module, anauxiliary "link-connecting"cable with mating plugs maybe supplied for maintenancepurposes. This method allowsrapid removal of equipmentfor testing .

2.2.3 Replacing Subassemblies .All essential subassembliesshould be mounted, whenpracticable, so that they maybe removed as a unit. Thisapplies to mechanical as wellas to electrical and electronicunits. Riveting, welding, andother permanent methods offastening must be avoided."Pile-ups" of assemblies thatnecessitate a chain of removalsshould be avoided. The needfor special tools should beminimized, but, if necessary,such tools must be suppliedwith the equipment.Free access to parts in largeequipment requires adequatedoors, covers, and openings .

Replacement of any part shouldbe possible from the front ofthe equipment .

DIFFICULT TO DISASSEMBLE

SCREW

SPLIT COLLET

SCHEMATIC ASSEMBLY AT "A"TO FACILITATE DISASSEMBLY2.2.4 Replacing Parts

2.2.4.1 Accessibility. Anyfeature that leads to betteraccessibility should be a primeconsideration of design.

BRACE

PARTS ACCESSIBLE

2-39

OP 2230

Ease of replacement and maintenance should take precedence overmanufacturing simplifaction. Thetype of enclosure required to meetthe environmental conditionsimposed should be constantly keptin mind when designing foraccessibility.All component mounting areasshould be utilized uniformly toprevent the crowding that mayresult from the inefficient useof space .

APPROVED MOUNTING

\ M

This provides increased accessibilityto fastenings and leads . Ampleclearance must be provided forinstallation and the securing ofscrews and nuts.Component fasteners should not

be located under cabling andapparatus. Permanently securedbolts and fasteners should beused wherever possible.Finger room for starting nuts

and screws must be provided.Nuts must not be located close toa barrier such that a spinner orsocket wrench cannot be used toproperly engage them.Clearance holes for screwsmust be large enough and locatedsuitably to allow for variationsin component mounting holes .Small screws, nuts, washers,pins, clamps, springs, andsimilar hardware are difficult tohandle. For facility in assembly,the largest practical size ofscrews, nuts, washers, andclamps should be employed.Inaccessible fasteners shouldbe avoided.

2.2.4.2 Removal Method. Asingle chassis panel and cabinetcombination usually requires captivescrews or quick-locking fastenersas the panel attachment element.

INACCESSIBLE FASTENERS QUICK LOCKING FASTENER

2-40


Where the chassis is providedwith a bottom plate, quick-lockingfasteners permit rapid access. Itis desirable to supply sturdymechanical devices on the chassissuch that the unit may be placedin any position for servicing withoutdamage to components .Sectionalized constructionoffers considerable advantages inease of maintenance. Minorrepairs can be made with theequipment in position or singleunits can be removed andcarried to the service bench forrepairs. For easy maintenance,the depth of equipment is usuallylimited. Cables, terminals,receptacles, and similar connections should be easily accessible.Large and heavy parts must

be located so that their replacementis possible. Heavy powertransformers or rotatingequipment should be locatedin the lower sections.Accessibility of cabinet-rackenclosures and consoles madeof sheet metal is usually somewhatreduced because size of the accessopening is limited in area by thebracing requirements. The rearsurface of many equipments,particularly where depth isconsiderable, is located againstwalls. The use of slides anddrawers is especially importantin this type of equipment.Where waterproofing andsplashproofing are required,access plates are held againstgasket seals by means ofcaptive screws or theequivalent. Removable doorswith suitable clamp- lockhandles, offset hinges , gaskets,and similar attachments arerequired to provide readyaccess for minor servicing.

Hinged doors should beprovided with position retainersto prevent accidental closingwhen equipment is installedaboard ship or in a movingvehicle.

2.2.4.3 Tools. Equipmentshould be designed to minimizethe need for special maintenancetools . Tools not ordinarilycommercially available shouldbe considered "special."It is good practice to forward

a list of special tools to theagency concerned for approval.Those items deemed necessarymay be mounted in the equipment or located in a separatecontainer .

2.2.4.4 Wiring and Slack .Cabling technique in thevicinity of terminals shouldbe planned carefully for easeof parts replacement. Enoughslack should be providedfor each lead to permit atleast one replacement. Cableends well "fanned out" arerequired to prevent errorsin connections and permitrapid installation.

2-41

Chapter 3

ASSEMBLY DESIGN

3.0 GENERALThe following material is intendedfor use by the designer whenformulating a general plan and layoutfor an assembly and should aid insolving specific problems relating toassembly design. A plan and layoutinvolve the arrangement of all theparts and a preliminary conceptionof the structural form which willinclude a consideration of all factors .The final design is usually acompromise in which these factorsare satisfactorily adjusted to meetperformance requirements.

The table of contents of thispublication is helpful as a checklistfor the design of an assembly.Before attempting a layout, a reviewof all subjects would be of assistance,As the layout and general planprogress, and as problems arise,reference to specific subjects canbe made through the index.

A tabulation of all the requirementsstated in the equipment specificationis helpful. In addition, a study ofall other referenced specificationsshould be made. Often thesespecifications yield enoughinformation to establish a planfor an assembly design.

3.1 HEAT TRANSFERThe reliable performance ofelectronic equipment is greatlyinfluenced by operating andambient temperatures . Militaryequipment is subjected to temperature conditions which vary widely,Individual equipment specificationsmay call out one of severaloperating and nonoperatingtemperature ranges . Hightemperature operating limitsvary from 50C to 65C . Lowtemperature operating limitsvary from 0 to -55C .Nonoperating limits are usually-62Cto85C. Nonoperatinglimits are significant in thatequipment shall not be damagednor shall the operationalperformance be degraded whenrestored to operating temperatures .

Each-h 75C source of heatshould be carefully examined inorder to eliminate excesses.For example, high efficiencyrectifiers and inductors shouldbe utilized and power suppliesshould not be overdesigned oroverloaded. Heat- sensitiveparts should be separated fromheat-generating elements.

Insulation life is materiallyaffected by temperature . Chemicalreaction rate, plasticizermigration, and softeningincrease in direct proportionto the temperature, resultingin a degradation of materialsand decreased operatinglife .

3 - 1

OP 2230

Heat removal may be dividedinto three phases: removal of heatfrom the source, transfer of heatalong a thermal bus to a sink, and

dissipation at the ultimate sink.The heat transferred in each phaseis a combination of conduction,radiation, and convection.

TOTAL _ CASE CASEHEAT

~CONVECTION RADIATION

CONVECTION

TOTAL _ CASE CASE COMPONENTHEAT

"CONVECTION

TRADIATION CONVECTION

3-2CONVECTION

AIR INTAKE AT AMBIENT

ASSEMBLY DESIGN

As illustrated, all three types ofheat transfer may occur at the sametime, and it is recommended that eachtype be considered in any particularcase .A discussion of each of thefundamental types of heat transfer isgiven as follows .

Heat Transfer by Radiation. -Radiation is a surface phenomenom ,Surfaces emit and absorb radiantenergy in various degrees, dependingon the nature of the surface.

The rate of heat transfer isexpressed as follows:

Hr = x 3 . 7 10-11

where Hr is the heat radiated inwatts per square inch, is theabsorption coefficient of thereceiving surface; To the absolutetemperature of the emittingsurface in degrees Kelvin; andTa the absolute temperature ofthe absorbing surface in degreesKelvin .

Average values of radiation(and absorption) coefficientsare presented in the tablebelow .

Material

Black bodyLampblackAsbestos boardSteel, oxidizedCopper, oxidized

Lead, oxidizedCast iron, oxidizedCast iron, brightBrass, oxidizedBrass, polished

Nickel, oxidizedZinc, oxidizedSilver , polishedAluminum, polishedAluminum, oxidized

*Average Values ofRadiation (and Absorption) Coefficients

Radiant-Energy Coefficient

1,00.950.930.790.72

0.630.620.220.600.10

0.420.110.030.040.11

*Data obtained from Standard Handbook for ElectricalEngineers, Eight Edition, McGraw-Hill Company .

As illustrated, radiation coefficientsvary from 1.0 for a black body to 0.03for a polished silver. Surface finish isquite significant. Low emissivity issynonymous with high reflectivityThe rate of heat transfer byradiation, Hr in watts/inch can

also be determined graphicallyfrom the curves which follow.All curves have been plotted for equal one . If the value of is less than one, multiply theradiated heat obtained from thecurves by

3-3

30 40 50 60 7080 100 200 300 400 500 700

Radiating Body Temperature TR CRadiated Heal (hr),Watts /in2

3-5

OP 2230

Heat Transfer by Conduction. -Heat transfer by conduction cantake place in all three states ofmatter, i.e., solids, liquids, andgases . The amount of heat thatflows through any body byconduction depends upon the timeof flow, the area through whichit flows, the temperaturegradient, and the type of material.The rate of heat transfer byconduction is expressed by thefollowing relation:

Hc = k At

where Hc is the rate of heattransfer by conduction in watts/square inch; k is the thermalconductivity in watts/(in2-sec .-C/in) when HC is measured inwatts /square inch; A the area ofthe cross section of the path ofheat measured at right angles tothe direction of flow of heat insquare inches; t the time theflow continues in seconds; andAT/L. the temperature gradient.The symbol AT is the differencein temperature in degreesCentigrade between two parallelsurfaces a distance L, in inches,apart .

There is a noticeable differencein the thermal conductivities of

various materials. Gases havelow conductivities . Liquids alsoare generally poor conductors .The conductivities of solids varyover a wide range, from thevery low values for asbestosfiber or brick to the relativelyhigh values for most metals.

An illustration of therange of thermal conductivityof various metals is presentedin the plot of TemperatureDrop vs. Heat Transfer byConduction.

The rate of heat transfer byconduction can also be obtainedgraphically from these curves.All curves are plotted forAl in2, t=l sec, Ll in. Forother values of A and t,multiply Hc obtained fromthe curve by the desired value.For other values of L, divideHc obtained from the curve bythe new value of L.To determine the rate of heattransfer by conduction of amaterial not illustrated by thesecurves, multiply the ratio ofthermal conductivity of thedesired material to the thermalconductivity of any materialillustrated by the amount ofheat transfer by conduction.

Example: Find the rate of heat transfer of silverfor a temperature differential of 150C.

k for silver - 10.3 watts/(in2-sec . - C/in)k for copper 9.75 watt s/(in2- sec . - oC/in)

Ratio of k"Ag = 10.3kCu

1.054

From the plot:Hc for copper for AT = 150C is 1030 watts /in2Hc for silver for AT = 15QOC is 1030 x 1.054 or1085 watts /in2

3 - 6

oooo

o

si1331Smh.

*-wcooXCM

I

110

MIV \8ro 00

8PJ

OID

Oo oID

Temperalure Drop AT in C 3-7

ASSEMBLY DESIGN

Heat Transfer by Convection. -Natural convection is the transferof heat to or from a surface bythe movement of a fluid whenthis movement is caused solely

by a difference in fluid densityHeat transfer by naturalconvection in free air isexpressed by the followingequations:

Hcv =11.70 (AT) 1.25 x 10-4 from a vertical surface*

HCU = 15.80 (AT) 1.25 x 10~4 from a horizontal surface facing upward*

Hcd = 8.20 (AT) 1.25 x 10~4 from a horizontal surface facing downward*

In all cases Hc is in watts /squareinch and AT is the temperaturedifferential in degrees Centigrade.The first equation listed aboveapplies to a vertical plane more

than 12 inches in height. Forheight less than 12 inchesmultiply the coefficients bythe appropriate constant listedbelow:

Height in Inches*

8

6

4

Constant

1.35

1.53

1.76

2.70

*Obtained from Standard Handbook for ElectricalEngineers , Eighth Edition, McGraw-Hill Book "Co .

Heat transfer by natural convection is presented graphically in thefollowing curves. As illustrated bythese curves, the rate of heat transferby natural convection from ahorizontal surface facing upward isabout 35 percent greater, and therate from a horizontal surface facingdownward is about 30 percent lessthan from a vertical surface.

The amount of heat transferby convection can be increasedby inducing a draft over thesurface. This is known as heattransfer by forced convection.

In summary , the total heattransfer of a body is the sum ofconduction, radiation, andconvection in watts /square inch,

3-9

IO

8

6

4

3

2

I.O

.8

A3

,2

.1

08oe

.04

O3

O2

.01

.008

.006

.004

.003

.002

001

IT

25 50 75 100 125 150 175 200 225 250 275 300Temperature Differential AT C

Rate Of Heat Transfer By Convection In Free Air(Hv)3 -n

OP 2230

3.1.1 PartsFor parts using Class A insulation(magnet wire insulation rated at105C) the maximum temperatureshould not appreciably exceed 105C .At 130C, service life expectancy isreduced from 10 years to as littleas 6 months . High quality solidimpregnation, oil sealing, and ClassB insulation permit highertemperature operation. Class Hinsulation provides long life at200C. All classes are describedin the specifications for insulation.Oriented grain or tape woundcore materials are desirable toreduce core losses. Enclosed,potted transformers provide alarger heat-dissipating surfacearea and improved thermalconductivity between the windingsand case .When such cases are bolted to

a good thermal sink, substantialamounts of heat can be dissipated.Inductors should, if possible,

be located near a cabinet corner orother metallic thermal sink.Composition resistors operating

at full rating are materially affectedat 105C ambient. Their resistancevalues may change appreciably.A 2-watt size resistor maypermanently increase in resistanceby 40%; a 1-watt size, 7%; and a1/2-watt size, 5%. If environmentaltemperatures are high, resistorsshould be derated in accordancewith tables established in theapplicable specifications. Aminimum derating of 50% is normal.Composition resistors used inbridge-balancing networks, feedback loops , and similar circuitsmust be located in comparativelycool areas .Wire-wound, deposited-carbon,boro-carbon, palladium, and otherresistors are designed for high

temperature applications . Sincemost heat lost by resist

workmanship and design practices for electronic equipment.compressed

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