study unit - multimeter operation manual

Study Unit

Multimeter OperationManual

DIGITAL MULTIMETERElectric devices and circuits can be dangerous. Safe practices

are necessary to prevent electrical shock, fires, explosions,

mechanical damage, and injuries resulting from the careless

or improper use of tools.

Perhaps the greatest hazard is electric shock. Electricity affects

the body by overriding brain impulses and contracting mus-

cles. Therefore, a current through the human body in excess

of 10 milliamperes can paralyze the victim and make it impos-

sible to let go of a “live” conductor.

Your skin can have approximately one thousand times more

resistance to the flow of electricity when dry, which would be

in the vicinity of several hundred thousand ohms. When moist

or cut, the skin’s resistance may become as low as several

hundred ohms. In this circumstance, even so-called safe volt-

ages as low as thirty or forty volts might produce a fatal shock.

Naturally, the danger of harmful or fatal shock increases

directly as the voltage increases. You should be very cautious,

even with low voltages. Never assume a circuit is dead, even

though the switch is in the OFF position.

General Safety Rules forElectricity and ElectronicsSafe practices will protect you and those around you. Study

the following rules.

1. Don’t work when you’re tired or taking medicine that

makes you drowsy.

2. Don’t work in poor light.

3. Don’t work in damp areas.

4. Use approved tools, equipment, and protective devices.

5. Don’t work if you or your clothes are wet.

6. Remove all rings, bracelets, and similar metal items.

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7. Never assume that a circuit is off. Check it with a device

or piece of equipment that you are sure is operating

properly.

8. Don’t tamper with safety devices. Never defeat an inter-

lock switch. Verify that all interlocks operate properly.

9. Keep your tools and equipment in good condition. Use

the correct tool for the job.

10. Verify that capacitors have discharged. Some capacitors

may store a lethal charge for a long time.

11. Don’t remove equipment grounds. Verify that all grounds

are intact.

12. Don’t use adapters that defeat ground connections.

13. Use only an approved fire extinguisher. Water can conduct

electric current and increase the hazards and damage. Dry

chemical extinguishers coat the fire with a nonflammable

foam that hinders reignition. Carbon dioxide (CO2) and

certain halogenated extinguishers are preferred for most

electrical fires; these leave no residue behind to damage

circuitry. (For more information on the class designations

for fires and fire extinguishers, go to www.fire-extin-

guisher101.com.) To test a fire extinguisher, refer to its

manual and review the proper procedures before beginning

the test. After a while, you’ll learn the “rules” and apply

them automatically.

14. Follow directions when using solvents and other chemicals.

They may explode, ignite, or damage electrical circuits.

15. Certain electronic components affect the safe performance

of equipment. Always use the correct replacement parts.

16. Use protective clothing and safety glasses when handling

high-vacuum devices such as television picture tubes.

17. Don’t attempt to work on complex equipment or cir-

cuits without proper training. There may be many

hidden dangers.

18. Some of the best safety information for electrical and

electronic equipment is the literature prepared by the

manufacturer. Find it, read it, and use it!

19. When possible, keep your left hand in your pocket while

working with electricity. This reduces the possibility of

your body providing an electrical path through the heart.

Any of the above rules could be expanded. As your study pro-

gresses, you’ll learn many of the details concerning proper

procedure. Learn them well because they’re the most important

information available. Remember, always practice safety; your

life depends on it.

Equipment Safety1. Never connect more than 1000 volts DC or 750 volts

RMS AC.

2. Never connect a source of voltage with the function

switch in the OHM (�) position or DIODE ( )

position.

3. Never operate the multimeter unless the battery cover

is in place and fully closed.

4. Battery and/or fuse replacement should proceed only

after the test leads have been disconnected and the

power is OFF.

5. When making current measurements, make certain the

multimeter is connected in series with the load. Never

connect the meter in parallel to measure current. To do

so can result in blowing the overload protection fuse or

damaging the device being tested.

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INTRODUCTION 1Functional Description 1Specifications 2Battery Installation 3Fuse Replacement 3

REVIEW OF ELECTRICAL FUNDAMENTALS 4Electrical Theory 4Ohm’s Law 5Power 6

MULTIMETER OPERATION 9Controls and Terminals 9Resistance Measurements 10Resistance Measurement Procedure 10DC Voltage Measurement 11DC Voltage Measurement Procedure 12AC Voltage Measurement 13AC Voltage Measurement Procedure 14DC Current Measurement 15DC Current Measurement Procedure 16Diode Measurement 17Diode Measurement Procedure 17Transistor hFE 18Transistor hFE Procedure 18Multimeter Repair 19

PRACTICAL APPLICATIONS 21Appliance Tests 21Motor Tests 22Automotive Electrical Systems 22

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INTRODUCTION

Functional DescriptionA multimeter is the most useful single instrument for testing

electric circuits. This one instrument enables you to make

many different tests. For example, you can use the multi-

meter to measure AC (alternating current) and DC (direct

current) voltages, to measure direct currents, to measure

resistance, to determine transistor hFE, and to test diodes.

Whenever you’re not sure about a test procedure, always refer

to the manual and review the proper procedures before begin-

ning the test. After a while, you’ll learn the procedures and

apply them automatically.

The multimeter is a versatile, multiple-range AC/DC volt-

meter, DC ammeter, ohmmeter, transistor hFE tester, and

diode checker with the following features:

• Single, 20-position, easy-to-use rotary switch for

FUNCTION and RANGE selection

• 0.5-inch high-contrast LCD

Multimeter Operation Manual

Remember to regularly check “My Courses” on your student homepage.

Your instructor may post additional resources that you can access to

enhance your learning experience.

Multimeter Operation Manual2

• Automatic overrange indication displays “1” during

overrange

• Automatic polarity indication on DC ranges

• All ranges fully protected

• Diode testing with 1.5 mA max current

• Transistor hFE Test

SpecificationsThe multimeter specifications are as follows:

DC Voltage Ranges:

0–200 mV, 0–2 V (2,000 mV), 0–20 V, 0–200 V, and 0–1000 V

Input Impedance: 1 M� on all ranges

Overload Protection: 500 VDC/350 VAC 200 mV range

1100 VDC/800 VAC all other ranges

AC Voltage Ranges:

0–200 V, and 0–750 V

Input Impedance: 450 k� on all ranges

Frequency Range: 45–450 Hz

Overload Protection: 750 V RMS

DC Current Ranges:

0–200 �A, 0–2 mA (2,000 �A), 0–20 mA, 0–200 mA, 0–10 A

Overload Protection: 2 A/250 V fuse

Resistance Range:

0–2 M� (2,000 k�)

Overload Protection: 350 V DC/AC RMS on all ranges

Open Circuit Voltage: 2.8 Vmax

Diode Test:

Forward DC Current: 1.4 mA

Reversed DC Voltage: approximately 3.0 V

Transistor hFE Test:

Base Current: approximately 10 �A

VCE: approximately 2.8 V

Periodically, the battery should be replaced. A low battery

can cause the meter to give incorrect readings.

Multimeter Operation Manual 3

Battery InstallationBattery installation should be performed only after the test

leads have been disconnected and the POWER IS OFF. Open

the back cover and install the battery provided. Replace the

back cover.

Fuse ReplacementFuse replacement should be attempted only after the test leads

have been disconnected and the POWER IS OFF. Open the back

cover and replace with a 2-amp fuse identical in physical size

to the original. Replace the back cover.

CAUTION: Occasionally, you’ll need to replace a blown fuse. When

replacing the battery or fuse, use only the recommended type, size,

and voltage/amperage.

WARNING: To avoid shock, do not operate the multimeter unless

the covers are secure.


REVIEW OF ELECTRICAL FUNDAMENTALS

Electrical TheoryTo use the multimeter effectively, you need a basic under-

standing of electrical formulas and of electricity itself (Figure 1).

Electric current consists of charged particles flowing through a

conductor either in one direction (direct current) or alternately,

first in one direction and then in the other (alternating current).

These charged particles are known as electrons. The amount

of current is proportional to the number of these particles

passing any one point in the conductor each second.

The amount of current passing through a conductor is

expressed in amperes, or amps. A milliampere (mA) is

one-thousandth of an ampere, and a microampere (�A)

is one-millionth of an ampere. Resistance is comparable to

friction and determines the current that flows in a conductor

with a given applied force. The resistor can be a long wire,

an electric light, a motor winding, the heating element of a

FIGURE 1—Basic ElectricalFormulas ELECTRICAL TERMS

DC direct current

AC alternating current

A ampere (amp)

� ohm

m milli = 1/1000

� micro = 1/1,000,000

K Kilo = 1000

M Meg = 1,000,000

Hz Hertz (cycles per

second)

OHM’S LAW

E = I � R

I = E/R

R = E/I


toaster or broiler, and so on. The amount of resistance is

expressed as ohms (�). A kilohm (k� or K) is one thousand

ohms, and a megohm (M� or meg) is one million ohms.

To force these electrons through the wire, there must be an

electromotive force (EMF). This EMF is called voltage (DC or

AC) and is measured in volts. Sources of this voltage can be

the battery in an automobile, a dry-cell battery, or the alter-

nators supplying voltage to the home. Because power is

dissipated when current flows through a resistance, a voltage

source is generally considered a power source.

An electric circuit consists of an electromotive force (voltage)

to drive electrons (current in units of amperes) through a

resistance (ohms). The voltage supply always has two termi-

nals, one supplying the electrons (the positive anode) and the

other receiving them (the negative cathode). If a resistor or

wire connects these two terminals, a current flows through

the resistor or wire.

Ohm’s LawThe volt, ohm, and ampere are related to each other in a

simple formula known as Ohm’s law:

Voltage = current � resistance,

or

E = I � R

As indicated in Figure 2, Ohm’s law can be stated in various

ways, depending upon which two of the three factors are

known and which factor is to be found.

(1) Voltage = current � resistance

(2) Current = voltage � resistance

(3) Resistance = voltage � current

For example, if a current of 5 amps flows through a resistance

of 40 ohms, the voltage across that resistor, according to for-

mula 1, is

Volts = amps � ohms

= 5 amps � 40 ohms = 200 volts


If a voltage of 200 volts across a 40-ohm resistor is measured,

the amperes passing through the resistor are determined by

formula 2. Thus,

Amps = volts � ohms, or

= 200 volts � 40 ohms = 5 amps

If it’s found that when applying 200 volts, 5 amps pass through

an unknown resistor, the value of the resistor can be calcu-

lated from formula 3. Thus,

Ohms = volts � amps

= 200 volts � 5 amps = 40 ohms

PowerWhen consumers buy electricity, they buy power.

The unit of power is the watt. A simple formula for relating

watts to voltage and current is

Power = voltage � current, or

Watts = volts � amps

FIGURE 2—Ohm’s LawWheel


Thus, if there are 5 amps going through a resistor, due to a

voltage of 200 volts, the power is

Watts = volts � amps

= 200 volts � 5 amps

= 1000 watts

If the volts and ohms are known, use formula 2 of the pre-

ceding section to find the amperes, and then substitute the

current value in the preceding equation to find the watts. If

the current and resistance are known, use formula 1 of the

preceding article to find the volts, and then substitute the

volts value in the equation to find the watts.

It should finally be noted that 1000 watts = 1 kw.

These measurements, plus an understanding of the nature

of electricity, are essential to anyone working with electricity.

The user of the multimeter should have some knowledge of

the operation and mechanics of the particular circuits and/or

the device being tested.

Note that when you’re performing calculations with Ohm’s

law, the variable E stands for voltage in volts, the variable I

stands for current in amperes, and the variable R stands for

resistance in ohms. If the problem you need to solve contains

other units (such as millivolts, microamperes, or megohms)

you’ll need to convert those values to volts, amperes, and

ohms before you use them in the Ohm’s law formula. The

conversion table on the following page can help you make such

conversions.


CONVERSION TABLE

To express the given quantity of voltage in different units,

use the following conversion relations.

To Convert To Multiply First

Column by

volts millivolts 1000

millivolts volts 0.001

volts microvolts 1,000,000

microvolts volts 0.000001

volts kilovolts 0.001

kilovolts volts 1000

volts megavolts 0.000001

megavolts volts 1,000,000

For conversion from one current unit to the other, use the following relations.


Column by

amperes milliamperes 1000

milliamperes amperes 0.001

amperes microamperes 1,000,000

microamperes amperes 0.000001

For conversion of resistance units, use the following relations.


Column by

ohms kilohms 0.001

kilohms ohms 1000

ohms megohms 0.000001

megohms ohms 1,000,000

ohms microhms 1,000,000

microhms ohms 0.000001


MULTIMETER OPERATION

Controls and Terminals

–

FIGURE 3—Multimeter Front Panel


Resistance Measurements

Resistance Measurement ProcedureResistances up to 2 M� can be measured with the digital

multimeter (Figure 3). The multimeter can also be used for

measuring the continuity of practically every electrical device

made. The procedure is as follows:

1. Remove all sources of power from the device or resistor

being tested.

2. Insert the black test lead plug into the COM jack and the

red test lead plug into V/� jack.

3. Select the � range and connect the test leads across the

resistor under measurement as shown in Figure 4.

FIGURE 4—Resistance Measurement Setup


Note:

1. If the resistance value being measured exceeds

the maximum value of the selected range, an over-

range indication of “1” will be displayed. Select a

higher range.

2. When the resistor or device is open, the “1” will be

displayed regardless of the range selected.

3. After resistance measurements are made, ALWAYS

turn the function/range switch to the OFF posi-

tion. This will help prevent the meter from being

damaged and increase the life of the battery.

DC Voltage Measurement

CAUTION: NEVER apply voltage or current to the test leads when

the function/range switch is in � position. A good habit is to always

check the function/range switch position before making measurements.

FIGURE 5—DC Voltage Measurement Setup


DC Voltage Measurement Procedure1. Insert the black test lead plug into the COM jack and the

red test lead plug into the V/� jack.

2. Select a higher DCV range than you anticipate measuring.

For example, to measure 700 DCV, select the 1000 DCV

range. If the magnitude of voltage isn’t known, select the

highest range (1000 V).

Note: If you tried to measure 700 DCV on the 200 DCV

range, an out-of-range indication of “1” would be displayed.

Conversely, you wouldn’t measure 1.5 DCV on the 1000

DCV range because accuracy would suffer.

3. Connect the test leads across the source or device being

measured as shown in Figure 5. The voltage value will

appear on the digital display along with the voltage

polarity.

4. Reduce the range until a usable reading is obtained.

5. Disconnect the test leads.

6. Turn switch to the OFF position.

Note:

1. Do not apply more than 1000 V to the input.

2. Use extreme caution to avoid contact with “live”

circuits when measuring voltage.


AC Voltage Measurement

FIGURE 6—AC Voltage Measurement Setup


AC Voltage Measurement Procedure1. Insert the black test lead plug into the COM jack and the

red test lead plug into to the V/� jack.

2. Select a higher ACV range than you anticipate measuring.

For example, to measure 120 ACV, select the 200 ACV

range. If the magnitude of voltage isn’t known, select

the highest range (750 V).

Note: If you tried to measure 240 ACV on the 200 ACV

range, an out-of-range indication of “1” would be dis-

played. If you select too small a range (such as trying

to measure 1.5 ACV on the 750 ACV range), accuracy

would suffer.

3. Connect the test leads across the source or device being

measured as shown in Figure 6. The voltage value will

appear on the digital display.

4. Reduce the range until a satisfactory reading is obtained.

5. Disconnect the test leads.

6. Turn the switch to OFF.

Note:

1. Do not apply more than 750 ACV.

2. Use extreme caution to avoid contact with “live”

circuits when measuring voltage.


DC Current Measurement

FIGURE 7—DC Current Measurement Setup


DC Current Measurement Procedure1. Insert the red test lead plug into the A/� jack and the

black test lead plug into the COM jack for a maximum

measurement of current up to 200 mA. For a maximum

of 10 A, insert the red test lead plug into the 10 ADC jack.

2. Turn OFF the power to the device being measured.

3. One of the functions of the multimeter is that of an amme-

ter that measures current. To safely measure current, an

ammeter must be placed in series with the branch circuit

through which the current is to be measured. To do this,

open the branch at some convenient point and connect

one test lead to each side of the break, as shown in

Figure 7.

4. Select a higher DCA range than you anticipate measuring.

If the magnitude of current isn’t known, select the highest

range (200 mA) and reduce the setting until a satisfactory

reading is obtained. If you expect the current to exceed

200 mA, begin measurements using the 10 A range.

When the 10 A range is necessary, insert the red test

lead plug into the 10 ADC jack and turn the switch to

the 10 A position.

5. Read the current value and polarity on the display.

6. De-energize the circuit, disconnect the test leads, and

restore the circuit to its pretest condition.

7. Turn the switch to the OFF position.

CAUTION: Always place an ammeter in series with the circuit. Never

place it across or in parallel with the circuit. Doing so will present a

short circuit to the source and can damage the multimeter.


Diode Measurement

Diode Measurement Procedure1. Insert the red test lead plug into the V/� input jack and

the black test lead plug into the COM input jack.

2. Select the diode test range position ( ) and connect

the test leads across the diode under test as shown in

Figure 8.

FIGURE 8—Diode Measurement Setup


3. Read the forward voltage drop on the display in millivolts.

Reverse the test leads, and “1” should indicate an out-of-

range. These results indicate a good diode.

Transistor hFE

Transistor hFE ProcedureTransistors are semiconductor devices used primarily as

switches and amplifiers. Typically they have at least three

terminals. A small voltage flows through the middle terminal

to control the current flow (like a valve) through the outer

terminals. In an NPN transistor, the electricity flows when the

center terminal is positive. In a PNP transistor, the electricity

flows when the center terminal is negative.

FIGURE 9—Setup to Test Transistor hFE


1. Select the hFE position.

2. Determine whether the transistor is NPN or PNP and

locate the emitter, base, and collector leads of the

transistor.

3. Insert the transistor leads into the proper holes in the

socket on the front panel of the multimeter as shown in

Figure 9.

4. The display will read the approximate hFE value, or

transistor gain.

5. Remove transistor.

6. Turn switch to the OFF position.

Multimeter RepairThe multimeter won’t operate properly if open connections

exist at either the test leads or the test lead plugs. If after

checking these connections the multimeter continues to mal-

function, follow these troubleshooting procedures:

1. Read the digital display with the power switch ON. If the

battery is weak, “LO BAT” will appear in the upper left

corner of the display. If nothing appears in the display,

the 9-volt battery may be dead.

2. Turn the power OFF.

3. Remove the test leads.

4. Open the battery compartment.

5. Check the battery connections.

6. Check the battery for power using a battery tester, or

another device that uses 9-volt batteries.

7. If the battery has power, check the 2-amp fuse. (See the

“Resistance Measurements” section on page 10).

If performing the above steps enables you to discover the

problem, resolve it, and replace the covers.

WARNING: Do not tamper with or attempt to make any repairs to

the multimeter other than replacing the battery and/or fuse.


If the multimeter continues to malfunction, e-mail your

instructor immediately. Be prepared to provide symptoms to

help diagnose the problem. Your instructor will recommend

corrective measures.

Do not return the multimeter to the school. We don’t have

repair facilities, and returning it to us will cause unneces-

sary and time-consuming delays. If the malfunction must

be repaired by the manufacturer, you’ll be instructed to

ship it to the manufacturer’s repair center.

Note: If the multimeter must be returned to the manufacturer,

include your name, student number, return address, and a

list of symptoms that might help to diagnose the malfunction.


PRACTICAL APPLICATIONS

Appliance TestsToasters, broilers, electric irons, electric blankets, and electric

heating pads all work on the same principle. Electricity flows

through a wire or resistor and causes the heating element to

heat up. This wire is made in several forms. When it’s put on

a flat plate, it becomes the familiar home electric iron. When

it’s flattened out on a larger area, it can become a heating

pad or an electric blanket.

A toaster also has just such a heating element. When checking

a toaster for continuity, make certain that the line cord is

disconnected from the AC outlet. Select the ohm (�) range

of the multimeter. Connect the tester directly across the heat-

ing element. If the heating element is good, its relatively low

resistance will be indicated on the meter. Next check the con-

nection to the line cord for indications of continuity or lack of

continuity. The final check is the line cord itself. If the line cord

is good, the heating-element resistance will be indicated on the

multimeter when the tester leads are measuring the resistance

across the line cord and the toaster switch is depressed to the

operative position. If the line cord is defective, the multimeter

indicates either overrange “1” or zero resistance and the line

cord should be replaced. Similar tests can be made on elec-

tric irons.

Heating pads have several temperature ranges. The lowest

temperature range indicates the highest resistance. All other

checks are identical with the checks described for the toaster.

The electric blanket is identical to the heating pad as far as

test procedures are concerned. Broilers, too, work on the

same principle. The heating elements, the switch, and the

connecting wire should be checked.

After completing any required repairs, make a final resistance

check on the line cord of the appliance. If the approximate

calculated resistance is measured (computed from the formu-

las for power and Ohm’s law), the appliance should function

properly.


Motor TestsMotors should show continuity (an unbroken circuit) when

checked on the ohm (�) scale. First check the winding and

then the cord for resistance or continuity.

Automotive Electrical SystemsElectrical equipment in a car can be checked with the selector

switch in the ohm (�) position. First the equipment is discon-

nected. Continuity measurements are then made, using the

ohm (�) scale of the multimeter. These tests can be made on

the switches, lights, starter, alternator, relays, horns, fuses,

cigarette lighter, heater fan, radio, and so on.

study unit - multimeter operation manual

Documents

dont work

dont use adapters

dont attempt

dont tamper

safety devices

complex equipment

equipment grounds

safe performanceof equipment