Study Unit - Multimeter Operation Manual
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Transcript of 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.
Multimeter Operation Manual4
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
Multimeter Operation Manual 5
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
Multimeter Operation Manual6
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
Multimeter Operation Manual 7
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.
Multimeter Operation Manual8
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.
To Convert To Multiply First
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.
To Convert To Multiply First
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 Manual 9
MULTIMETER OPERATION
Controls and Terminals
–
FIGURE 3—Multimeter Front Panel
Multimeter Operation Manual10
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
Multimeter Operation Manual 11
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
Multimeter Operation Manual12
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.
Multimeter Operation Manual 13
AC Voltage Measurement
FIGURE 6—AC Voltage Measurement Setup
Multimeter Operation Manual14
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.
Multimeter Operation Manual 15
DC Current Measurement
FIGURE 7—DC Current Measurement Setup
Multimeter Operation Manual16
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.
Multimeter Operation Manual 17
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
Multimeter Operation Manual18
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
Multimeter Operation Manual 19
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.
Multimeter Operation Manual20
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.
Multimeter Operation Manual 21
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.
Multimeter Operation Manual22
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.