Re: Unknown type of HV capacitor

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

drive the "suspect circuit" through a reasonably large resistor (so the
generator's low output impedance doesn't perturb the circuit).  Hook the
scope probe across the cap.  When you look at the square wave, you'll see a
damped sinusoid on each of the edges.  The frequency of the sinusoid gives
you the resonant frequency  (approximately f = 1/(2*pi*sqrt(LC), but this
doesn't allow for the R, which, if the Q is low will "pull" the frequency a
bit) and the decrement ratio lets you calculate the Q and hence the R (since
you know the C, and the fRes, you can calculate Xc... Q is Xc/R)

This is good for a quick and dirty evaluation, but not so hot for precision
measurements, where some sort of LCR bridge would be a better bet.


-----Original Message-----
From: Tesla list <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Tuesday, August 29, 2000 10:59 AM
Subject: Re: Unknown type of HV capacitor


>Original poster: MShock8073-at-aol-dot-com
>
>In a message dated 8/29/00 10:39:11 AM Eastern Daylight Time,
>tesla-at-pupman-dot-com writes:
>
><< If you can somehow measure the L and R... A square wave generator of a
few
> kHz (say a TTL pulse generator or a 555), a series resistor and an
> oscilloscope will tell you... Measure the ringing frequency and the
> decrement ratio...  If the L is down in the nanohenries, and fRes is in
the
> hundreds of kHz, you might be in luck. >>
>
>
>Would you please elaborate on this procedure for us uneducated 'scope
owners.
>
>Thank you,
>Marc S.
>
>
>
>