Question about a reading on a multimeter

Discussion in 'General Electronics Chat' started by MrZeus, May 14, 2009.

  1. MrZeus

    Thread Starter New Member

    Mar 8, 2009
    3
    0
    Hi guys, I'm not too sure if this is the right place to ask about this so I apologize if it's not in the right place.

    Anyway, I just got out a multimeter that I forgot I had and noticed that when on the VDC setting, even when the connectors aren't touching anything, it reads something like 0.5 mV. I'm just curious if this is actually just some ambient voltage in the air or something. I just had a physics course on this kind of thing but I'm still unsure on this. If someone could help me out, that'd be great, thanks!
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    It can be due to radio waves, noise inside the multimeter's circuit, inaccuracies of the multimeter's components etc.
     
  3. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    If it is a digital meter. I think the term they use is "phantom readings"

    If you put the probes to a solid voltage source you should get a steady reading at least in the range of voltage being measured.
     
  4. Mike2545

    Active Member

    Mar 26, 2009
    116
    3
    If its an analog meter there is a zeroing knob to fix that.
     
  5. DonQ

    Active Member

    May 6, 2009
    320
    11
    Try it with the probes touching each other firmly. Better yet, get a shorting plug, a small block with two banana plugs at the right spacing. Even with the long leads shorted together, they are a big antenna. A shorting block gets rid of that.

    As far as trusting any readings of 0.5 mV... Try measuring the same thing with two separate meters sometime and you may start to just ignore fractional millivolts.
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Bet you did this indoors.
    Bet you also did this within a few feet of mains wiring.

    Try it again near a flourescent light.
     
  7. flat5

    Active Member

    Nov 13, 2008
    403
    17
    If it is an analog meter, before you turn the zeroing screw breath on the plastic or glass to remove static charge. Sometimes this will drop the needle to zero.
     
  8. MACROcontroller

    New Member

    May 15, 2009
    1
    0
    Check the model accuracy on the manual from manufacturer. Depending on how old it is, the manufacturer dont guarantee .1mV. Also check if they can be relacalibrated which may reduce the noise.
     
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    MrZeus,

    You have to understand one thing:

    Electronics are not perfected but you modify/adjust the parameters to achieve the best results for each application.
     
Loading...