core skills training.docx

7/28/2019 Core Skills Training.docx

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Core Skills Training

How to use a Digital Multimeter

Course Prerequisites

This course has no prerequisites, but may be used as aprerequisite forother courses.This course assumes the learner has basic knowledge ofelectricity.Due to the number of graphics in this course, you areencouraged toprint the study material to view offline.

Click on Print Doc at the top of this page to view thePDF. Youmay save the document to your computerand print it.

Course Introduction

A Digital Multimeter (DMM) is a piece of test equipmentused formeasuring voltage, current, continuity, resistanceand other electricalquantities.In this course, you will learn:

Basic safety precautions when using a multimeter,Important terms and symbols used when working withelectricity,Basic multimeter functions,Voltage measurement,Continuity measurement,Resistance measurement.

Safety Precautions

Never ground yourself when taking electrical measurements.

Do not touch exposed metal pipes, outlets, etc. which might be at groundpotential; keep yourbody isolated from ground with rubber shoes, rubbermats or any approved insulating material.

It is recommended you wear gloves, protective eyewear and flame-retardant clothing.

Never use a multimeter to measure voltage beyond its rating.Always set the function switch correctly to measure AC or DC voltage.Never measure Resistance or Continuity with the power on.Follow all Safety instructions and precautions for your brand of multimeter.

When connecting the probes to a power source, handle theinsulatedpart. NEVER touch the metal part with your bare hand.


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Safety Precautions

Failure to operate a multimeter properly can result indamage to the

meter, personal injury or death.

Terms and Symbols

When working with electricity or a multimeter, you shouldbe able torecognize the industrys standard symbols.Some of these symbols are used for safety while othersgive informationon electrical measurements.The following three pages list the most common symbolsand theirmeanings or functions.

Terms and Symbols

V~ (AC Voltage)This multimeter function measures the Voltage foralternating current(AC). Wall outlets useAC voltage.

V (DC Voltage)This multimeter function measures the Voltage fordirect current (DC).Printers andcomputers use DC Voltage for most of their components.

(Ohms) ResistanceThis multimeter function measures how easily current flows through anobject.

(Ohms) Continuity

This multimeter function verifies whether a circuit is open or closed. Anopen circuit cannotconduct electricity a closed circuit can.A (Amps)

This multimeter function measures current (flow of electricity). Thismeasurement is rarelyused in our printers.

V (Voltage/OhmsThis is jack on a multimeter. When measuring Voltage, Continuity andResistance, the Redtest probe is always connected to this jack.

The V symb ols are always p resent next to this jack, however, othersymb ols mayappear depending o n the m eter ex. VmA.

COM (Common)This is jack on a multimeter. The Black probe is always connected to thisport for takingmeasurements

Basic Multimeter Functions

On the next page is a picture of a generic multimeter wherethe functionsand connections and are labeled.


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The less commonly used areas are illustrated in graythese will not becovered in this course.Do you recognize some of the symbols from the previouspages?Use the BACK button at the top right of your computerscreen to go back in thestudy material if you want toreview the symbols.

All multimeters have the same basic functions, however, some arecapable ofperforming advanced measurements and will look slightlydifferent.Despite this, there are two basic types of multimeters:

Switched Range you have to set the appropriate range for thedesiredmeasurement.

Auto-ranging the meter automatically adjusts itself to the appropriaterange forthe desired measurement.An example of each of these is shown on the next page.The auto-ranging multimeter is the easiest to use.If you have a switched range multimeter, however, follow theseguidelines to set theappropriate range:The best range is the smal lest work ing rangein which a reading isobtained.

If you dont know the approximate voltage to read, start with the highestrange first and workyour way down to the smallest possible range.When measuring voltage, an OLon the display means the reading isOpen Loop and yourrange is too low.If you know the voltage range to read, select the appropriate range withthe function switch.

The next page shows examples.Suppose you are are reading DC Voltage in a printer. You are not surewhat thevoltage is, so you start with the highest setting first (1000V).Try each range until you get an accurate reading.For our example, the Third Setting results in the most accurate reading.

If you already knew the voltage would read 20V or less, you couldselect 20V on the

function switch and take the reading.

When you are ready to use the multimeter, connect the Red and Blackprobes (testprobes) to the meter.


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The Black probe always connects to the COM jack.The Red probe connects to the Vjack to read Voltage, Continuityand Resistance.Next, set the function switch to the measurement you want to read(and the correctrange if using a switched range meter).The following pages will explain how to take various measurementsusing themultimeter.

Voltage Measurement

How to read AC Voltage:Plug the Black test probe into the COM jack and plug the Red test probeinto the V jack.Set the function/range switch to V~ (AC Volts) set the correct range!Insert the free ends of the red and black probes in the wall outlet. With ACVoltage, it does notmatter which probe is placed in the hot and neutral slot.Power must be ON to take this reading.Real life Example: US Wall Outlet VoltageBelow we connected our Red and Black probes to the multimeter and setthe function switch toread V~ (AC Voltage).The multimeter is auto-ranging, so we didnt have to set the range.Next, we inserted the probes into the wall outlet (with the power ON) andrecorded the reading.Applications for AC Voltage measurements: (others not listed mayapply)Check the voltage at an outlet,Check the voltage through a power cord,Check certain voltages in the Printers Low Voltage Power Supply.

Before reading printerDC Voltage,you must gather the followinginformation fromtheservice manual, training material or otherdocuments:The vol tage measurement you should expect ,Any change in the vol tage that you s hould obs erve (depending onhow /what is beingtested),

The connector name/number to test on the ci rcu i t board,

The specif ic conn ector PIN num ber(s) to measure. Typically, you are measuring DC Voltage across two specific PINs ona cable while itis connected to a circuit board.To find the correct PINs to test, look on the circuit board above andbelow where theconnector is located.You should see a 1 or asmall triangle () pointing to a specific PIN. This willindicate PIN 1.Once you know the location of PIN 1, count over to the PIN numbersspecified in thedocumentation to perform the test.When measuring DC voltage, i t does matterwhich probe is plugged inthe Positiveand Negative.

Red always plugged into positive.

Black always plugged into negative.If the probes are positioned backwards, the polarity of the reading willbe the oppositeof what it should be.With most voltage measurements on our printers, however, you willconnectthe Red probe to one PIN with voltage and connect the Blackprobe to Ground.How to read DC Voltage:Plug the Black test probe into the COM jack and plug the Red test probeinto the V jack.Set the function/range switch to V (DC Volts) set the correct range!Insert the free ends of the Red and Black probes in the correct cable PINsto be measured.


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Power must be ON to take this reading.Real life Example: Lexmark C750 Bin Full SensorTo check the voltage of the Bin Full Sensor in the printer, we need thefollowing information fromthe service manual:The voltage measurement expected:+5V dcAny ch ange in the voltage we shou ld observe (depending o n how /what isbeing tested):nonementioned

The connector name/number to test on the circui t board:J11 on the EngineBoardThe specif ic conn ector PIN num ber(s) to m easure:PIN 1 +5V dc and PIN 3ground

Applications for DC Voltage measurements: (others not listed mayapply)Check the voltage on circuit board connectors,Check the change in voltage from sensors.Below, we connected our Red and Black probes to the multimeter and setthe function switch toread V (DC Voltage).The multimeter is auto-ranging, so we didnt have to set the range.Next, we located PIN 1 (+5V dc) and PIN 3 (ground) on the Engine Board.We inserted the probes into the cable at PIN 1 (+5V dc Red probe) andPIN 3 (ground Blackprobe) and recorded the measurement with thepower ON

Continuity MeasurementBefore checking Continuity,be aware of the following:For your safety, power must be OFF when checking for Continuity.The multimeter sends a small amount of voltage through the test probesduring the measurement,so be careful what they touch.For the test, the cable can either be removed from the printer or unpluggedat both ends. This willreduce the chance of feedback from the othercircuits. If at all possible, it is recommended toremove the cable.A reading of OL indicates an open circuit.A reading ofzero or any numerical value indicates that the circuit isclosed.A closed circuit can conduct electricity. An open circuit cannot.How to read Continuity:

Plug the Black test probe into the COM jack and the Red test probe intothe V jack.Set the function/range switch to (Ohms).Connect one probe (Red or Black) to one wire and the other probe to the oppos i te end ofthe same wire.Check the measurement to see if it reads OL or a numerical value.

Real life Example: Printer Cable checkBelow, we connected our Red and Black probes to the multimeter and setthe function switch toread (Ohms).The multimeter is auto-ranging, so we didnt have to set the range.We removed the cable from the printer and inserted one probe into eachend of the cable makingsure we had the probes touching the same wire.We repeated this until we checked all of the wires for continuity. Thereading indicates that thiswire has a closed circuit.

Applications for Continuity measurements: (others not listed mayapply)Check printer cables for breaks in the wires,Check for continuity between printer options,Check fuses.

Resistance Measurement


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Before checking Resistance,be aware of the following:For your safety, power must be OFF when checking for Resistance.The multimeter sends a small amount of voltage through the test probesduring the measurement,so be careful what they touch.A reading of OL indicates infinite resistance.A reading ofzero or any numerical value indicates the resistance value inOhms.

How to read Resistance:Plug the Black test probe into the COM jack and the Red test probe intothe V jack.Set the function/range switch to (Ohms).Touch the probes to different sections of the object to be tested.If a numerical reading displays, this is the resistance in Ohms.If the LCD displays "OL", the resistance is beyond the selected range. Trya larger range (if usinga switched range meter). If you continue to get anOL reading, the resistance is infinite and currentcannot flow.Real life Example: C750 BOR Motor Cable shortBelow, we connected our Red and Black probes to the multimeter and setthe function switch toread (Ohms).The multimeter is auto-ranging, so we didnt have to set the range.We powered the printerOFF and unplugged the BOR cable from theEngine Board and insertedone probe into the cable opening and the otherto the printer chassis.The reading should be about 100kOhms on each wire. Applications for Resistance measurements: (others not listed mayapply)Check for high/low resistance in cables,Check for high/low resistance on surfaces.

This concludes the module onHow to use a Digital Multimeter

You may review the study material again or continue to thetestquestions in the next phase of this course.

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