ASE 6 - Electrical Electronic...

ASE 6 - Electrical ElectronicSystems

Module 4Digital Multi-Meter

AcknowledgementsGeneral Motors, the IAGMASEP Association Board of Directors, and RaytheonProfessional Services, GM's training partner for GM's Service Technical College wish tothank all of the people who contributed to the GM ASEP/BSEP curriculum developmentproject 2002-3. This project would not have been possible without the tireless efforts ofmany people. We acknowledge:

• The IAGMASEP Association members for agreeing to tackle this large project tocreate the curriculum for the GM ASEP/BSEP schools.

• The IAGMASEP Curriculum team for leading the members to a single vision andimplementation.

• Direct contributors within Raytheon Professional Services for their support oftranslating a good idea into reality. Specifically, we thank:

– Chris Mason and Vince Williams, for their leadership, guidance, and support.– Media and Graphics department under Mary McClain and in particular, Cheryl

Squicciarini, Diana Pajewski, Lesley McCowey, Jeremy Pawelek, & NancyDeSantis.

– For his help on the Electrical curriculum volume, Subject Matter Expert, KenBeish, Jr., for his wealth of knowledge.

Finally, we wish to recognize the individual instructors and staffs of the GM ASEP/BSEPColleges for their contribution for reformatting existing General Motors training material,adding critical technical content and the sharing of their expertise in the GM product.Separate committees worked on each of the eight curriculum areas. For the work on thisvolume, we thank the members of the Electrical committee:

– Jack Davis, Community College of Baltimore County - Catonsville– Jim Halderman, Sinclair Community College– Megan Kuehm, Community College of Allegheny County– Frank Longbottom, Camden County College– Jeff Rehkopf, Florida Community College at Jacksonville– Randy Peters, Des Moines Area Community College– David Rodriguez, College of Southern Idaho– Ed Schauffler, Longview Community College– Vince Williams, Raytheon

ContentsModule 4 – Digital Multi-MeterAcknowledgements .......................................................................................... 2Objective .......................................................................................................... 4

Display ............................................................................................................................ 6Excercise ...................................................................................................................... 10Fluke 87 Components ....................................................................................................11Overload (OL) ............................................................................................................... 14Measuring Voltage ........................................................................................................ 15Measure Voltage Drop .................................................................................................. 16Measuring Resistance .................................................................................................. 17Measuring Amperage .................................................................................................... 18Exercise ........................................................................................................................ 19

© 2002 General Motors CorporationAll Rights Reserved

ASE 6 - ElectricalElectronic Systems

Module 4 - DigitalMulti-Meter

4-4

Student WorkbookObjectiveAt the end of this section, the student will be able to:• Describe how the multimeter must be set-up and the leads connected

to a circuit to measure voltage, voltage drop, current flow, andresistance

• Define voltage drop

NATF Area VIA6: Demonstrate the proper use of a DMM during diagnosis of electricalproblems.A9: Measure current flow in electrical/electronic circuits and componentsusing an ammeter; determine necessary action.A10: Check continuity and measure resistance in electrical/electroniccircuits and components using an ohmmeter; determine necessary action.




4-5

Student WorkbookThe Fluke 87 digital multi-meter (J 39200) combines the precision a digitalmeter with the speed and versatility of a high-resolution analog display.Powered by a 9-volt battery, the meter is sealed against dirt, dust, andmoisture.

Figure 4-1, Fluke 87 DMM - J 39200




4-6

Student WorkbookDisplayIn order to make it easier to work with large numbers, digital mult-metersuse the metric system. The metric system is based on the number 10,making it possible to change the unit by moving the decimal point.Each metric system unit has a prefix that is used to describe the unit ofmeasurement. The most common prefixes are the micro, milli, kilo, andmega. The meter will tell you the unit it is reading in the lower right of thedisplay.

Another way to remember this is that the decimal moves three places witheach prefix. For example to convert from milliamps to amps, the decimalwill move three places to the left.

Figure 4-2, Measurement Prefixes

Figure 4-3, Prefix Chart




4-7

Student Workbook

Figure 4-4, Metric Prefixes




4-8

Student WorkbookMegaMega stands for one million and is abbreviated with a capital letter M. Onemega ohm equals one million ohms. To convert any value from megohmsto ohms, move the decimal point six places to the right. For example, 3.5megohms will convert to 3,500,000 ohms.

KiloKilo means one thousand and is abbreviated with a lowercase letter k. Akilohm is equal to 1,000 ohms. To convert any value from kilohm to ohms,move the decimal point three places to the right. For example, .657kilohms will covert to 657 ohms.

Base UnitsBase units are standard units without a prefix. Volts, ohms, and amperesare the primary base units used in electronics. Prefixes are added to baseunits to change the unit of measurement.

MilliMilli stands for one thousandth and is abbreviated by the lowercase letterm. A millampere is one-thousandth of one ampere. To convert any valuefrom milliamperes to amperes, move the decimal point three places to theleft. For example, 0.355 millimps will convert to .000355 amps.

MicroMicro means on millionth and is abbreviated by the symbol u. Amicroampere is equal to one millionth of an amp. To convert any valuefrom microamperes to amperes, move the decimal point six places to theleft. For example, 355 microamperes will covert to .000355 amps.




4-9

Student Workbook

Prefix chart: Start with the “FROM” column, and cross reference over tothe proper “TO” column.

TO

FROM

M (Mega) K (Kilo) BASE m (milli) U (micro)

M (Mega) 0 places 3 places to

right

6 places to

right

9 places to

right

12 places to

right

K (Kilo) 3 places to

left

0 places 3 places to

right

6 places to

right

9 places to

right

BASE 6 places to

left

3 places to

left


right

6 places to

right

m (milli) 9 places to

left

6 places to

left

3 places to

left


right

U (micro) 12 places to

left

9 places to

left

6 places to

left

3 places to

left

0 places




4-10

Student WorkbookExcercise




4-11

Student Workbook

Figure 4-5, Fluke 87 DMM Components Liquid Crystal Display

Fluke 87 ComponentsThe meter has four main areas: the liquid crystal display, push buttons,rotary dial function switch, and inputs for the meter leads.




4-12

Student WorkbookLiquid Crystal DisplayThe meter’s crystal display, or LCD, uses display segments and indicators.The display segments have a pointer that “rolls” across them indicating ameasurement change. The display also uses indicators to abbreviatevarious display modes and meter functions.

Figure 4-6, Fluke 87 DMM Liquid Crystal Display

Push ButtonsThe buttons on the meter are used to perform additional functions. Futurecourses will cover additional button functions. For this course, the onlybutton you need to understand is the range button.When the meter is first switched on and a measurement is made, itautomatically selects a range and displays the word AUTO in the upperleft. Pressing the range button puts the meter in the manual range modeand displays the current scale in the lower right. With each additionalpress of the range button, the next increment is displayed. Press and holddown the range button to return to the auto range mode.The yellow button can be used to back light the meter display.

Figure 4-7, Fluke 87 DMM Push Buttons




4-13

Student WorkbookRotary SwitchVarious meter functions are selected by turning the meter’s rotary switch.Each time the rotary switch is moved from the OFF position to a functionsetting, all display segments and indicators tun on as pat of a self-testroutine.

Meter Lead InputsDepending on the measurement you wish to make, the meter leads willhave to be placed in the correct terminal. Notice the insides of the inputterminals are color-coded red or black. The positive lead can go in any ofthe red inputs.The COM, or common terminal, is used for most measurements. Theblack lead will always remain in the COM terminal.From left to right the first input terminal is for measuring amps. This inputis fused at 10 amps.

Figure 4-8, Fluke 87 DMM Meter Lead Inputs




4-14

Student WorkbookThe next position is for measuring milli or micro amps. No more than 400milliamps can be measured when the rotary switch is in this position. Ifyou are unsure of a circuit’s amperage, you may want to start out with thered meter lead in the 10-amp input.The final input terminal is for measuring voltage, resistance, and checkingdiodes.

Overload (OL)

While making some measurements you may see OL, or overload. Thefollowing conditions can lead to an overload display:

• In auto range, a resistance reading showing an open circuit• In manual range, a resistance showing an open circuit or incorrect

scale selected• In manual range, a voltage reading that exceeds the range selected• When doing a diode check

Figure 4-9, Fluke 87 DMM Overload




4-15

Student WorkbookMeasuring Voltage

Figure 4-10, Measuring Available Voltage

To check for available voltage:Apply power to the circuit.Place the meter leads with the black lead in the COM input and the redlead in the Volt/Ohm input.Place the rotary switch in the DC voltage position to measure DC volts, orAC voltage position to measure AC volts.Place the black meter lead on ground-side of the component and the redmeter lead on the “feed” side of the component.Checking for available voltage indicates the voltage that is available tocomponents; it indicates continuity or the voltage drop before thecomponent.Measure voltage can also be used as a quick way to locate resistance in acircuit. The measurement shown is voltage drop. Anything that hasresistance will use up voltage and, therefore, have a voltage drop.Wires and switches do drop a very small amount of voltage. So, anythingother than an extremely small voltage drop across a wire or switchindicates a problem. Lights, motors, and other load devices drop a lot ofvoltage since they are performing work.




4-16

Student Workbook

Figure 4-11, Measuring Voltage Drop

Measure Voltage DropTo check voltage drop:Apply power to the circuitPlace the meter leads with the black lead in the COM input and the redlead in the Volt/Ohm input.Place the rotary switch in the DC voltage position.Place the leads across a component or part of the circuit.This measurement indicates the voltage that the component uses up.The higher the voltage reading, the higher the resistance compared toother parts of the circuit.

The Fluke meter is a high impedance meter. This means the meter willnot significantly increase the current flow in the circuit being measured.Voltage measurements should be made with the circuit working. Thismakes the meter ideal for use in circuits controlled by solid state deviceslike computers or microprocessors.




4-17

Student WorkbookMeasuring Resistance

Figure 4-12, Measuring Resistance

To measure resistance:Make sure power in the circuit is OFF. This is necessary since the metermeasures resistance by applying a small voltage to the circuit.Place the meter leads in the COM and Volt/Ohm inputs.Place the rotary switch in the Ohm position.Place the meter leads across the component you want to check.It is important that your fingers are not touching the tips of the probessince body resistance can affect the test. Keep in mind that the meterprovides a small amount of voltage to a circuit when checking resistance,so be careful when checking the resistance of certain electricalcomponents, such as solid slate or electronic circuits. This applied voltagemay damage these circuits.

Important: Remember that resistance readings can be a good indicationof how components are functioning when the circuit is turned off. Thecomponent may act differently with current passing through it.For example, the resistance of a bulb is much lower when no power issupplied to the bulb. Using a meter to read the resistance will only testthe continuity of the filament and not the working resistance of the bulb.




4-18

Student Workbook

To measure amperage:Place the meters leads with the red lead in the AMP input and the blacklead in the COM input.Place the rotary switch in the milliamp/amperage position.Then create an open in the circuit, preferably at the fuse or connector.Place the meters leads to complete the circuit, so current will flow throughthe meter.

Apply power to the circuit to measure amperage.

Figure 4-13, Measuring Amperage

Caution: Never place the meter leads across a

component when measuring amperage.

Caution: If the current flow exceeds therating of the meter fuse, the fuse will blowsince current flows through the meter (the

meter is like a jumper wire).

Measuring Amperage

When measuring current flow, the Fluke meter is designed with lowresistance to not affect the current flow in the circuit. When measuringcurrent in a circuit, always start with the red lead of the DVOM in the Ampinput (10A fused) of the meter. Only move the red lead into the mA/uAinput after you have determined the current is below the mA/uA inputmaximum current rating (400mA).

The meter has a "buffer" which allows it to momentarily measure currentflows higher than 10A. This buffer is designed to handle the "surge"current when a circuit is first turned on.




4-19

Student WorkbookExerciseRead each question carefully and answer by filling in the blanks.

1. The meters leads must be placed across a component with the power_____________ to measure resistance.

2. The meters leads must be placed across a component with the poweron to measure on to measure __________________

3. When the multimeter is set up so that it is part of the circuit, you aremeasuring _________________

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