From: "Terrell W. Fritz"
Date: Wed, 29 May 2002 12:47:43 -0600
Subject: [TSSP] Re: Top V Probe Design
Hi All,
Here is a little design I just thought up.
http://hot-streamer.com/temp/HVProbe-1.gif
(334kB) Sorry it's kind of large...
It is just the Jennings/Ross engineering style probe put inside a Tesla coil.
The cylinders would have to be split to prevent a shorted turn effect (A Ross
oil immersion HV probe could almost be used directly except they are not
split).
Basically it is a 9 inch dia by 14 inch tall tank of oil. The ground shield is
a thin metal can that protects the next pickup cylinder from external effects.
A thin rod from the top is inserted inside. The rod and the pick up cylinder
have a low value of capacitance and the pickup to ground and have a much higher
capacitance forming a voltage divider. The signal could be led out the bottom
where a high voltage probe could pick the few hundred volt signal (if it were
1000:1). A Victoreen spark gap could be added there for further protection.
One may want to used double shielded coax to bring the bottom signal out
further to get away from the primary coil. Note that the internal can edges
have corona rings.
The secondary of the Tesla coil could be simply wrapped around the outer tank
(plastic).
This should have very high bandwidth and a very strong signal that would resist
interference. It is also how the "real" ones are made so I figure I would take
the hint ;-) The real ones are expensive since they are very accurate, but if
one is willing to calibrate it with math rather than precision hardware, it is
easy.
One may want to shorten the windings so that the affect of the internal can is
uniform along the secondary to make modeling easier. Just a uniform
capacitance to ground along the coil.
I just though this up so I have no real idea about the dimensions or anything
like that. Just a concept drawing with no calculation behind it...
Any thoughts are more than welcome.
Bart - I got the 2100 current monitor sent so It should be there late this week
by priority mail.
Mark R. - Let me know if you have any questions about the pinger stuff. If you
have the HV supply the pinger part is just a cap, spark gap, and resistors.
You can even borrow mine if you want. I don't have any plans for it in the
immediate future. Pictures at:
http://hot-streamer.com/temp/Paul/4-06/
I think Dr. Resonance once tried to measure TC voltage by putting a very big
X-Ray tube on a coil and measured the x-rays. I guess he did it in a dirt
pit. Not sure if anything was learned. I don't know if you could get much
bandwidth out of something like that but maybe better stuff now days.
Definitely an "X-ray guy" project there!
High voltage probes that uses CuSO4 are simply a coiled tube with distilled
water in them and enough CuSO4 to get a certain resistance value. They then
coil them up until the inductance and capacitance is just right so high
frequency signals can pass undistorted. You would probably need to put it in a
shielded can since external fields would affect it greatly. God only knows
what one would have do to try to get the tuning right. Maybe just "copy" one
;-) Might have a patent out there for more info.
There are normal resistor/capacitor divider stacks used in HV labs but they
tend not to like heavy external fields. I think Marco's lab has these so maybe
he could tell more. I don't think these probes are good at high frequency but
not sure there. External probes are usually connected by a long wire to the
generator so that adds to the complexity of precision measurement and modeling.
These scopes are supposed to be real nice and only $150 (1/2 the price of a
good probe)!
http://www.calcentron.com/Pages/Velleman/Velleman_HPS5_PersonalScope.htm
But I don't think they store to a computer or anything :-( But good for
measurements that "might" destroy the scope. Be careful of some of the "cheap"
cards and scope things. They are usually designed by "digital guys" rather the
"scope guys".
Cheers,
Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.