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Changing Values on Multimeter

  1. Mar 9, 2012 #1
    When using a multimeter, how come the values for the current and voltage fluctuate?
     
  2. jcsd
  3. Mar 9, 2012 #2

    Bobbywhy

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    1. The multimeter is defective, or
    2. The current and the voltage really are fluctuating.

    I suggest you check your multimeter by reading the voltage and current of a battery-operated device. The voltage and current should not fluctuate.
     
  4. Mar 10, 2012 #3

    Redbelly98

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    or
    3. The batteries in the multimeter need replacing.
    What are you measuring? What is the value of the voltage or current you are reading, and by how much is it fluctuating? That information might help us narrow down the cause.
     
  5. Mar 10, 2012 #4
    I got a voltage of about 6.692V. The digit after the 2 was fluctuating between 2 and 4. For the current, I got 1.236 mA with a similar fluctuation right after the 6. My assignment was to verify Kirchoff's current and voltage laws. Only a few of the calculations actually equal zero. The majority are off by a few milivolts or microamps. I am trying to account for the non-zero values in my discussion.
     
  6. Mar 10, 2012 #5

    Redbelly98

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    Those appear to be real -- and very small -- fluctuations. Your readings are stable to 4 significant figures, it doesn't get much better than that! :smile: (At least in a student lab setting.)

    As for the cause, it could have been the voltage source, or it could be the meter itself. In hindsight, it might have been good to measure the power supply voltage directly (with the circuit connected to it), and see what level of fluctuations were there.

    At any rate, you can use the fluctuations to estimate the uncertainty in the measurements, and add a digit for the meter possible being off. As long as the loop voltage ±uncertainty contains zero, you are fine.
     
  7. Mar 10, 2012 #6
    Welcome to the real world where measurements do fluctuate (I think the multimeter is working well).
    The last digit of any multimeter should be regarded with suspicion.
    I strongly suggest reading the user's manual as regards uncertainties.
     
  8. Mar 10, 2012 #7

    cmb

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    Just PM me if you want to swap your multimeter for one of my 3 digit meters - your problem will then disappear! :approve:
     
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