kelvin probes

Discussion in 'General Electronics Chat' started by kdbmos, Sep 1, 2011.

  1. kdbmos

    Thread Starter New Member

    Sep 1, 2011
    I am looking to buy a miliohm meter with kelvin probes. My question is can I splice the probe leads to make one set 10 ft. long the other set of leads to 30 ft. long. Will this mess with the calibration of the miliohm meter.
  2. colinb

    Active Member

    Jun 15, 2011
    The lead length should be essentially irrelevant with four-terminal sensing. The current electrodes will experience an increased voltage drop as length increases, but the voltage electrodes have essentially zero current, so no voltage drops across the voltage leads, no matter how long.

    Of course there must be a practical limit. Perhaps EMI could introduce error when leads are very long, but if the meter has a decently long integration time, and if leads are shielded or twisted pairs, then this should be mitigated. At some point, as lead length increases significantly and resistance increases, the very miniscule current that flows in the voltage leads might result in measurable voltage drop, resulting in detectable error.
  3. someonesdad

    Senior Member

    Jul 7, 2009
    You can also use a current source with your DMM to measure low resistances.