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Dmm reading


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Reading a Digital Multimeter (DMM)

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Dmm reading

  1. 1. DMM ReadingNorthampton Community College Jack Schreiber
  2. 2. 1 – 3 ½ Digit display2 – Back light3 – Rotary switch4 – Hold button5 – 10A jack6 – Common jack“black probe”(negative)7 – VΩmA jack “red”probe (positive)
  3. 3. Symbols used on digital meters
  4. 4. Meter SafetyNever change the rangesetting with the meterconnected to a livecircuit.Always select a higherrange than you expect tomeasure, if you areunsure select the highestrange.The most accuratereadings are taken withthe range set to thelowest possible setting forthe value under test.
  5. 5. Meter SafetyNever hold the meter inyour hand when taking areading under power.For current readingsabove 200mA its best touse a clamp-on meter.Always wear you personalsafety protectiveequipment.For low voltage thatmeans safety glass arethe minimum
  6. 6. When the “H” is lit on thedisplay the hold functionis selectedThe “–” in the displayshows a negative voltageor current is applied thered probe – switchpolarity to take thereadingThe battery symboldenotes the battery needsto be replaced
  7. 7. Never measure morethan 240V on the 600Vrange due to the fuseprotection of the meterIt’s best to connect theblack probe to theneutral side whenmeasuring AC but it’snot requiredThe 200V range willdisplay up to 199.9VmaxReading shown is 238 VAC on the 600V ACrange
  8. 8. Measure current up to 0.2Astarting with the 200mArangeAbove 0.2A a clamp-onammeter is recommendedas the 10A range is notfusedAlways remove the probefrom the mA jackimmediately after taking thereadingAlways switch the meter offafter taking a currentreading on any rangeThe reading shown is199.9mA DC on the 200mArange
  9. 9. Ohm’s range - always makesure the power is off to thecircuit under testAlways make sure the itemis isolated when measuringohm’sFor accurate resistancereadings short the probesfirst then subtract thisamount from you finalreadingAlways use the lowestpossible range for the mostaccurate readingReading shown is 96.5ohms on the 200 ohm scale.
  10. 10. DC voltage – useproper polarity if the “-”sign shows switch theprobesAgain the lower therange the moreaccurate the readingExample use the 20 Vrange to read a 9 Vbattery not the 200 VrangeReading shown is8.73V on the 20V DCrange
  11. 11. Example of a typicalcamp-on ammeterProper use requiresclamping around onlyone current carryingconductor at a timeNot designed for highvoltage (over 600V)applications
  12. 12. Looping the conductor willincrease the reading by100% for each loop.Looping allows for readinglow values. Just rememberto divide the reading by thenumber of loops.Example: 10 loops with areading of 12 A is actually1.2 A