From: "Terrell W. Fritz"
Date: Sat, 01 Jun 2002 12:37:48 -0600
Subject: Re: [TSSP] Re: Top V Probe Design
Hi Bart,
At 06:53 PM 5/31/2002 +0000, you wrote:
>
>The Pearson CT and cable was waiting for me when I got home from work.
>Everything
>in perfect condition. Thanks for sending and also for thinking about the
cable.
>I'll be able to get going on some base current measurements this weekend.
>Any tips
>beyond the apnotes at Pearson?
>
Not really. You just put the wire through it and scope away. You may want to
put insulation between the CT and the Pearson incase you worry about arc over
but that is just a paranoid safety thought for a ground lead current. If I run
like 20kV on the wire, I add a bunch of insulation and ground the CT's case.
For the Top-V Probe, here is the latest design:
http://hot-streamer.com/temp/HVProbe-2.gif
I ordered up the plastic stuff today. Still need double shield coax and oil...
I figure the probe will be about a 15pF load but that can be reduced by making
the rod shorter. The rod to pickup capacitance is about 12.5 pF and the pickup
to inner shield is roughly 750 pF. So the coax and other capacitor will have
to be about 500pF for a 1000:1 ratio. Then the TEK5100 HV probe can go from
there.
The secondary is #24 wire 11 inches in diameter and 13 inches long so 46.3 tpi
gives 602 turns and 61.1mH.
The 1 inch diameter rod has a breakdown at about 40kV in air but I figure oil
is 10X better so the diameter should be OK to 400kV. I'll get a 1 inch round
ball for the end. Darn! Forgot to order that!... Should be easy to find.
The 0.002 inch copper foil pickup and shields are wrapped around the
polycarbonate tube and overlapped on the ends with poly insulation sheeting
preventing shorted turns and separating the layers. Pretty simple really...
If anyone has double shielded coax I could use some ;-)
My favorite farm and ranch store went out of business but I'll search around
for cow lub...
So this is the design I am going with...
Cheers,
Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.