From: "Terrell W. Fritz"
Date: Sun, 30 Jun 2002 13:21:39 -0600
Subject: Re: [TSSP] Re: Top V Probe Design
Hi Paul,
>
>Thanks for the close look at that Jennings. I see there is
>no outer shield electrode, so the thing is only accurate when
>remote from everything except the electrode being measured, so
>wouldn't do too well inside a coil!
>
It does have a shield. You can barely see the inner pickup tube in the photo
at:
http://hot-streamer.com/temp/Jennings-JP-325/P6290004a.jpg
Here is a diagram showing the rod, pickup tube and shield tube structure.
http://hot-streamer.com/temp/Jennings-JP-325/Diagram.jpg
The big outer tube you see is the grounded shield with the pickup tube hidden
inside it. It should be very well shielded against external fields. The
bottom can and all have very good multi-finger contacts to give a solid shield
up into the high MHz region.
I just remembered a patent of Joe Jennings that told of ionization problems on
things like this if you put a conductor against the glass. This problem would
affect my design. I will have to think on this. Probably a coating of
polyurethane would take care of it.
Cheers,
Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.