From: J. Forster (jfor@quik.com)
Date: Thu Apr 03 2003 - 16:54:01 PST
Joe Foley wrote:
> But, if you still want a test while the thing is in the circuit you could get
> a ZM-11 which will put a 10.79 MHz signal through the capacitor and will let
> you vary the voltage according to what the circuit and cap like.
A measurement at 10 MHz will be meaningless. The wiring is significant fractions
of a wavelength and will not yield anything meaningful. If you want to measure
the capacitance it should be done at some audio frequency, like 60, 400, or 1000
Hz. I'd still suggest disconnecting the battery and using the capacitance range
of a cheap DMM. (Check for voltage before connecting the capacitance function)
For Techies: These meters likely use a current source and time the rise of the
capacitor's voltage to a specific value. Since I=C dV/dT, if you re-arrange
this you get dT = C * dV / I . So if dV and I are constant, and scaled
correctly, the time to charge is directly proportional to the C.
-John
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