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Re: Measuring Capacitance (fwd)
---------- Forwarded message ----------
Date: Fri, 24 Apr 1998 14:26:59 -0700
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Measuring Capacitance (fwd)
> ---------- Forwarded message ----------
> Date: Fri, 24 Apr 1998 00:23:53 +0000
> From: "Patrick J. Gustafson" <gustafpj-at-uwec.edu>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Measuring Capacitance
>
> Hello All:
>
> What is the preferred method of physically finding the actual
> capacitance of a capacitor? Does anybody still use impedance bridges?
Yes...
> Your description of test procedure here...
>
> I have not directly measured the actual k-value of the LDPE, but I
> suspect that it does not deviate far from the 2.2 mark. If in fact the
> bridge is working properly, I believe that the real culprit of the added
> capacitance is in the oil that I used (Caltron 60/30). I received 10
> gal. from the local power company for free. They use the same oil in all
> of their high voltage pole transformers. I now of course would like the
> determine the value of this oil, but I am hesitant to use the bridge.
It is probably around 2-3, or, not much different from the PE.
> So, back to my original question, what does everyone else use to measure
> capacitance?
Method #1) Put it in a tuned circuit with a known L and measure the
resonant frequency.
Method #2) Charge it with a known constant current and measure the change
in voltage per unit time (this is what the DMM capacitance meter uses)
Method #3) Use an impedance bridge, and make sure you don't have a lot of
resistive loss throwing off the reactance measurement.
For measuring the dielectric constant of oil, the typical way is to make a
coaxial transmission line (or a parallel plate line), fill the line with
the liquid to be tested, and measure the impedance at a series of
frequencies.