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INTRODUCTION
Basicinstructions(-A.90.A.05)
67,67XL
HOWTOMEASUREVOLTAGESINTHEELECTRONICSSYSTEM
Whenaskedtomeasureavoltage,thevoltagebeingmeasuredisalwaysatonepointwithrespectto(relative
to)thevoltageatanotherpoint.
Example:T omeasurethevoltageatpointAwithrespecttopointB,placeonemeterprobe(typicallyredincolor,
andconnectedtothemeterconnectorlabeled“V“).Placetheothermeterprobe(typicallyblackincolor,and
connectedtothemeterconnectorlabeled“COM“).
Iftheunitsofvoltagearespeciedas“voltsdc”,besureyourmeterissetto“dc”.Iftheunitsofvoltagearespecied
as“voltsac”,besureyourmeterissetto“ac”.
NorthAmericanautomotiveelectricalsystemsoftenusethechassis(metalframe)oftheautomobileasthereturn
path(oftenreferredtoasground)forelectricalcurrent.Theelectronicssystemdoesnotusethechassisforareturn
path,andnovoltagemeasurementsshouldbemadewithrespecttothechassis.Allcomponentsintheelectronics
systemshouldbeconsideredtobeelectricallyisolatedfromthechassis,althoughatthetractortheelectronics
systemreturnisconnectedtothebatterynegativeterminalwhichisinturnconnectedtothetractorchassis.
ELECTRICALISOLATION
Twopointsareelectricallyisolatedwhentheresistancebetweenthemis“innite”(verylarge,greaterthan
10,000,000ohms).Toverifytwopointsareelectricallyisolated.
1.Setyourmetertomeasureresistance(usuallylabeledwiththeohmsymbol).
2.Holdthetwoprobesapartfromeachotherintheair.Themetermustindicateinniteresistance(usually
indicatedbytheinnitysymbolorondigitalmultimeters,“++++”or“0L”foroverload).
3.Holdthetwoprobestogether.Themetermustindicateaverylowresistance,lessthan1.0ohms.The
resistancemeasuredwillvarydependingonwhatscalethemeterissetto.
4.Placeoneprobeononepointandtheotherprobeontheotherpoint.Itdoesnotmatterwhichprobeis
placedonwhichpointwhenmeasuringresistance.Themetermustindicateinniteresistanceasitdidin2
aboveforthetwopointstobeelectricallyisolated.
ELECTRICALCONTINUITY
Twopointshaveelectricalcontinuitywhentheresistancebetweenthemisverysmall,lessthan0.1ohms.T o
verifytwopointshaveelectricalcontinuity
1.Setyourmetertomeasureresistance(usuallylabeledwiththeohmsymbo).
2.Sinceweareexpectingtomeasurearesistanceof0ohms,setthescaletothelowestavailable.
3.Holdthetwoprobesapartfromeachotherintheair.Themetermustindicateinniteresistance(usually
indicatedbytheinnitysymbolorondigitalmultimeters,“++++”or“0L”foroverload).
4.Holdthetwoprobestogether.Themetermustindicateaverylowresistance,lessthan1.0ohms.Recordor
memorizethisresistance.Thisistheproberesistance.
5.Placeoneprobeononepointandtheotherprobeontheotherpoint.Itdoesnotmatterwhichprobeis
placedonwhichpointwhenmeasuringresistance.Subtracttheproberesistancemeasuredin4above
fromthemeterreading.Ifthemeterreadingminustheproberesistanceislessthan0.1ohms,thetwo
pointshaveelectricalcontinuity.
RESISTANCE
Tomeasuretheresistancebetweentwopoints.
1.Setyourmetertomeasureresistance(usuallylabeledwiththeohmsymbol).
2.Holdthetwoprobesapartfromeachotherintheair.Themetermustindicateinniteresistance(usually
indicatedbytheinnitysymbolorondigitalmultimeters,“++++”or“0L”foroverload).
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