From: "Terrell W. Fritz"
Date: Wed, 20 Jun 2001 16:53:36 -0600
Subject: Re: [TSSP] Some Considerations
Hi All, After looking around and through some great info Bert sent me, I am leaning toward the design Jennings and Tektronix use for high voltage probes. A shielded coaxial capacitive divider. There would have to be a wire leading from the top terminal to this divider (maybe 3 to 5 feet) which would look basically like a ~5pF capacitor load. I hope to get more drawn up (busy days) soon and give this a try. I am thinking of using oil since a vacuum or freon/silicone is rather difficult for me. It would also need a fairly good scope protection circuit, which will hurt frequency response, but it would still be very good. It can also be tested with conventional equipment for accuracy and voltage standoff. The capacitor in parallel with resistors things look like they would be very susceptible to surrounding fields and their adjustment and calibration seems like a black art... I am sure it can be done on the 1000th try... So I'll look into this. This top voltage measurement issue has been around for a long time and a solution needs to be found. We also have some high voltage dividers at work (both commercial and made in-house) but they were for mostly DC work and they are in very poor condition. Nothing I would want to plug my scope and coil into... Having had a bunch of 5 kW RF stuff explode "too close" to me today (I was unscrewing the HN connect and I "thought" it was off :-)))) Glad that wasn't "my" stuff I blew up :-))), I am kind worried about what could go wrong. ;-)) Must go try and get G-10/GPO-3/Teflon soot out of white shirt now.... BTW: GPO-3 is far far better than G-10 for RF fires :-)) The Teflon was good till it got too hot... Cheers, Terry At 08:36 AM 6/19/2001 +1200, you wrote: >Hi Marc, > >> i've been pondering an idea for voltage measurments without disturbing >> the field. how does a poly tube filled with salt water or a conducting >> fluid and graphite plugs in the ends sound? >> being non-matalic it should keep disturbances to a minimum alowing >> remote voltage reading? >> any opinions on this. >> marc > >It's still a conductor though. Should there be any difference in this >respect between saltwater and a string of carbon? As I see it, the >major objection to any probe that has to reference the top of the >coil to ground is that it occupies physical space and modifies the >permittivity and/or permeability of the medium it lives in. I think I >will perform a cursory examination of the effects of a probe running >through the centre of a resonator of a reasonably large diameter. It >is not for nothing that an authoritative technique appears not to >exist. > >Regards, >Malcolm > > >
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.