# Can you measure Impedance with an Ohm Meter..

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

1. ### Denny BGuest

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. ### Jean-Michel FriedtGuest

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

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.  Continue to site