Trouble with 4-wire measurement

Discussion in 'General Electronics Chat' started by fhernandezx3fh, Jun 10, 2008.

  1. fhernandezx3fh

    Thread Starter New Member

    Jun 10, 2008
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    All,

    Hi everyone, I just joined the forum but I've been visiting this site for a while now. It helped solidify some of the concepts learned in school. There is something that I am not able to grasp when talking about 4-wire resistance measurements. With 2-wire measurements, the DMM acts as a constant current source then measures the voltage drop, thus calculating the resistance. With 4-wire measurement why isn't the resistance of the sense lines an issue.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. Wendy

    Moderator

    Mar 24, 2008
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    The two methods are fundimentally identical, but the 4 wire measures the voltage from the current regulator at the resistor, thus eliminating a potential error source, the resistance of the leads themselves. If you have 6 digits or more of accuracy it matters quite a bit. Industry does actually have such meters, and uses them in a routine basis.
     
  4. John Luciani

    Active Member

    Apr 3, 2007
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    Because the current is zero (or close to it) through the sense lines.
    0 * Rsense = 0V drop

    (* jcl *)
     
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