
INTRODUCTION
Basicinstructions
HOWTOMEASUREVOLTAGESINTHEELECTRONICSSYSTEM
Whenaskedtomeasureavoltage,thevoltagebeingmeasuredisalwaysatonepointwithrespectto(relativeto)the
voltageatanotherpoint.
Example:T omeasurethevoltageatpointAwithrespecttopointB,placeonemeterprobe(typicallyredincolor,and
connectedtothemeterconnectorlabeled“V“).Placetheothermeterprobe(typicallyblackincolor,andconnected
tothemeterconnectorlabeled“COM“).
Iftheunitsofvoltagearespeciedas“voltsdc”,besureyourmeterissetto“dc”.Iftheunitsofvoltagearespecied
as“voltsac”,besureyourmeterissetto“ac”.
NorthAmericanautomotiveelectricalsystemsoftenusethechassis(metalframe)oftheautomobileasthereturnpath
(oftenreferredtoasground)forelectricalcurrent.Theelectronicssystemdoesnotusethechassisforareturnpath,
andnovoltagemeasurementsshouldbemadewithrespecttothechassis.Allcomponentsintheelectronicssystem
shouldbeconsideredtobeelectricallyisolatedfromthechassis,althoughatthetractortheelectronicssystemreturn
isconnectedtothebatterynegativeterminalwhichisinturnconnectedtothetractorchassis.
NOTE:OnVRaircartswithabatteryandahydraulicmotordrivenalternator,theaircartbatterynegativeterminalis
electricallyisolatedfromtheaircartchassis.
ELECTRICALISOLATION
Twopointsareelectricallyisolatedwhentheresistancebetweenthemis“innite”(verylarge,greaterthan
10,000,000ohms).Toverifytwopointsareelectricallyisolated.
1.Setyourmetertomeasureresistance(usuallylabeledwiththeohmsymbol).
2.Holdthetwoprobesapartfromeachotherintheair.Themetermustindicateinniteresistance(usuallyindicated
bytheinnitysymbolorondigitalmultimeters,“++++”or“0L”foroverload).
3.Holdthetwoprobestogether.Themetermustindicateaverylowresistance,lessthan1.0ohms.Theresistance
measuredwillvarydependingonwhatscalethemeterissetto.
4.Placeoneprobeononepointandtheotherprobeontheotherpoint.Itdoesnotmatterwhichprobeisplacedon
whichpointwhenmeasuringresistance.Themetermustindicateinniteresistanceasitdidin2aboveforthetwo
pointstobeelectricallyisolated.
ELECTRICALCONTINUITY
Twopointshaveelectricalcontinuitywhentheresistancebetweenthemisverysmall,lessthan0.1ohms.To
verifytwopointshaveelectricalcontinuity
1.Setyourmetertomeasureresistance(usuallylabeledwiththeohmsymbol).
2.Sinceweareexpectingtomeasurearesistanceof0ohms,setthescaletothelowestavailable.
3.Holdthetwoprobesapartfromeachotherintheair.Themetermustindicateinniteresistance(usuallyindicated
bytheinnitysymbolorondigitalmultimeters,“++++”or“0L”foroverload).
4.Holdthetwoprobestogether.Themetermustindicateaverylowresistance,lessthan1.0ohms.Recordor
memorizethisresistance.Thisistheproberesistance.
5.Placeoneprobeononepointandtheotherprobeontheotherpoint.Itdoesnotmatterwhichprobeisplaced
onwhichpointwhenmeasuringresistance.Subtracttheproberesistancemeasuredin4abovefromthemeter
reading.Ifthemeterreadingminustheproberesistanceislessthan0.1ohms,thetwopointshaveelectrical
continuity.
RESISTANCE
Tomeasuretheresistancebetweentwopoints.
1.Setyourmetertomeasureresistance(usuallylabeledwiththeohmsymbol).
2.Holdthetwoprobesapartfromeachotherintheair.Themetermustindicateinniteresistance(usuallyindicated
bytheinnitysymbolorondigitalmultimeters,“++++”or“0L”foroverload).
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