Re: Unknown type of HV capacitor

["John Sanderson" <john.sanderson-at-eng.monash.edu.au> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Thanks for the test suggestion, Jim.  When I get the chance to carry 
out this procedure, I'll post the results.  (May take a while, 
though, because some travel is involved.)
Regarding the resonant frequency test, would it perhaps be better to 
drive the "suspect cct" through a small capacitor (say 1nF) than a 
resistor?  

John S.

> 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.
> 
> 
> >
> ><< 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.