why does voltmeter show voltage ?

Discussion in 'General Electronics Chat' started by ol'trusty, Nov 3, 2009.

  1. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    I am looking for an explanation on why does a voltmeter show voltage when on dc volt mode and I connect a capacitor ? Also when I touch both ends it shows between 100-300 millivolts (or put it on my tongue for example).

    Can someone please explain this..

    Thanks
    Trusty
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    Most modrn meters have an input impedance of 10 MEG ohms which means even a very small amount of noise picked up on the test leads will generate a voltage which it will display.
     
  3. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    How is my tongue noise ?
     
  4. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Because of the high input resistance as mentioned above,your getting phantom readings so no matter what you touch on your body with the probes a phantom reading will show a steady display the moment the probes are touched.
     
  5. davebee

    Well-Known Member

    Oct 22, 2008
    539
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    The metal probes and your tongue may be forming a battery and chemically creating an actual voltage.
     
  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    touch some scope leads with your hands and see how much noise you are eminating.
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The human body is a pretty good antenna for various RF signals.
     
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Isn't the "noise" basically what a EKG or EEG measuring?

    Cary
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    No. An EKG measures a signal actually coming from your heart. The meter is measuring electrical junk on your skin picked up from the air.
     
  10. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    A good experiment to prove this noise is to get an oscilloscope and touch the center conductor of the probe (don't touch ground!). You will get a oscillation on the scope which will be quite distorted, likely in the mV range.

    Austin
     
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