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What's reading for multimeter set to read dc voltage and bandwidth of 10khz

  1. Mar 12, 2007 #1
    Happened to come across this qn:

    Noise from receiver is measured by rms voltmeter with bandwidth 100khz, and voltmeter reads 2mV. what will be the reading for multimeter set to read dc voltage and bandwidth of 10khz?

    My ans is 10/100 x 2 = 0.2mV. cos smaller bandwidth reduced by a factor of 10.

    Can anyone comment whether my answer is correct? tks
     
  2. jcsd
  3. Mar 12, 2007 #2

    AlephZero

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    Read the question carefully - in particular, the abbreviations "rms" and "dc".
     
  4. Mar 12, 2007 #3
    so u mean the voltage reading shdnt change? since rms value and dc value are the same.
     
  5. Mar 12, 2007 #4

    AlephZero

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    RMS and DC are not the same if you are measuring an voltage that varies with time.

    A DC meter measure the average (mean) value of an AC signal, which is zero for a symmetrical wave form like a sine wave or a square wave.

    Connect a DC voltmeter to a low voltage AC signal generator sometime, and see what reading you get - zero.

    The "noise" in the question is basically an AC signal so its average value measured on a DC meter will be 0.

    Check out what "root mean square" means, and how it is different from "mean" or "average".
     
  6. Mar 13, 2007 #5
    Oh now i get it. Thanks for the explanation! ;)
     
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