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Can you measure Impedance with an Ohm Meter..

Discussion in 'General Electronics' started by Denny B, Jul 17, 2003.

  1. Denny B

    Denny B Guest

    Is it possible to measure Impedance with an ohm meter.
    For example can you measure the Impedance of a 4 ohm
    car speaker with an ohm meter?

    When I tell people they cannot measure Impedance with an
    ohm meter, you need an impedance meter and the impedance
    must be measured with the speaker in operation, with a signal generator
    supplying a fixed frequency, this always leads to disagreements
    with the person who demands an ohm meter to measure what he calls
    Impedance, when I tell him an ohm meter can only measure the resistance
    of the coil there is always disagreement.

    I tell them Impedance is AC resistance and what they measure
    with an ohm meter is DC resistance. Disagreement here again.

    Will somebody take me up on this and clarify the situation.

    Thanks in advance
    Denny B
     
  2. A quick search on google tells me that typical voice coils
    have an inductance in the 100 uH range.
    Your impedance is sqrt(Zdc^2+Zac^2) with Zdc what you measure
    with the ohmmeter (resistance) and Zac the contribution of the
    inductance of the coil.

    Assuming a working frequency of f~500 HZ, then the impedance
    of the inductor is 2*L*\pi*f=1 ohm (assuming an inductance L
    of 320 uH) so the AC contribution is not negligible compared to
    the DC resistance in the calculation of the total impedance.

    Jean-Michel
     
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