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"negative" resistivity

Discussion in 'Electronic Basics' started by Ben, Feb 25, 2004.

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  1. Ben

    Ben Guest


    I'm measuring the AC resistivity of a number of parts (capacitors,
    actually). Obviously the apparent resistivity decreases with
    increasing frequency; however, in certain cases with a certain type of
    component I get low resistivity at the high frequency end and
    _negative_ resistivity at the low frequency end. I know that this is
    bull; however, I don't know why my meters (an agilent 4263B and an
    analyser made by somebody else, if that matters)are reading negative.
    What does this negative number actually mean ?

    thanks for your opinions
  2. Fred Bartoli

    Fred Bartoli Guest

    Your cap is becoming inductive. Or better said, the series inductance of
    your cap has its impedance becoming greater than the one of your cap :

    j L w > 1/(j C w) when w rises.

    BTW one don't speak of AC resistivity but impedance (ac generalization for
    resistance) and its reciprocal is admittance.

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