TSSP: List Archives

From: "RMC"
Date: Sun, 15 Oct 2000 23:20:51 +0100
Subject: Re: [TSSP] Surprising secondary voltage profiles

Greetings all.

Wasn't there an article from a Dr Gary Johnson in USA on making a capacitive
voltage divider, which lived on the toroid and passed it's divided-ratio
information down a length of fibre-optic cable? This approach seemed not to
disturb any of the field geometry.

we spoke on the Pupman list about it ages ago: the idea that was suggested
at the time was to build the electronics inside the toroid, thus placing it
in a zero field gradient; at which point an FM radiio link could maybe do
the job.

the reference that I have on my book shelf is

"  Prcoeedings of the 1992 International Tesla Symposium", and the article
was page 93, "Tesla Coil Instrumentation". The name of the author is indeed
Gary johnson, from Kansas State University, Dept of Elec. Eng.

The article is quite good (in contrast to the other articles in that book)
but Johnson reckoned that you should see VSWRs of "100 or more" whereas all
my previous work has seen values of half that figure from memory.

Richard Craven, Malvern, England


----- Original Message -----
From: "Malcolm Watts" 
To: 
Sent: Sunday, October 15, 2000 9:13 PM
Subject: Re: [TSSP] Surprising secondary voltage profiles


> Hi all,
>          I'd be a bit wary of any measurements which rely on
> placing a probe close to the coil, no matter how small the
> probe is. I remind all of the "gimmick" capacitor beloved of
> super-regenerative radio set builders. Distance is the key
> here. I just wanted to put in a cautionary note here. I
> realise it is a nightmare to probe a low capacitance structure
> without upsetting it. A possible way forward would be to probe
> a set of equipotential rings of some significantly greater
> diameter than the secondary. If the capacitance to ground of
> the non-probed rings was adjusted to compensate for the ring
> being probed..............
>
>   gnd----||-------o      o   o       o
>                          o   o
>   gnd----||-------o      o   o       o
>                          o   o
> scope-------------o      o   o       o
>                          o   o
>   gnd----||-------o      o   o       o
>                          o   o
>
> Some shunt R for each compensating cap to match that of the
> probe would also be required I would think. This of course
> assumes that each C is equal to the scope and might need to be
> adjusted to allow for the normal difference in proximity to
> ground of the various portions of the secondary. The major
> point about this is how to avoid distorting the electric
> fields.
>
> Regards,
> Malcolm
>


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.