Re: HV Measurement - Back to Basics

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Hi all,

Here's the schematic of a high voltage buffer I've been using for quite some
time now. Works great. You can use either a voltmeter or O-scope.
Calibration is done with a known voltage source and a good meter. And as
mentioned elsewhere I employ the "No-Touch" method when in use.

ftp://ftp.xmission-dot-com/pub/users/p/potluck/pics/HV-buffer.jpg

Here is a pic of the actual project.

ftp://ftp.xmission-dot-com/pub/users/p/potluck/pics/HV-Buffer.jpg

Rick W.
Salt Lake

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, January 04, 2003 9:13 AM
Subject: HV Measurement - Back to Basics


 > Original poster: "Matthew Smith by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <matt-at-kbc-dot-net.au>
 >
 > Hi All
 >
 > Could some kind soul give me a hand with this little problem?
 >
 > I bought (blind) a 15kV voltmeter, which I planned to sit on the end of my
 > MOT-based power supply.  When I first saw it and discovered that the
 > terminals are about 8mm apart, I decided that this is just a meter with a
 > 15kV *scale*, not a meter than can be connected to and measure up to
 > 15kV...  Never fear, I thought, it's just the question of sizing an
 > appropriate resistor/resistor network.
 >
 > Looking at the base of the scale, I see some small symbols; the first
 > appears to be an underscore - possibly this is a moving coil (DC) meter
 > (terminals are also marked + and - which would tend to confirm this). The
 > second symbol is a star with a 2 in it - goodness knows what this
 > means.  The third symbol is an upside-down capital T with 1.5 above
 > it.  The fourth symbol appears to be a horseshoe magenet, pointed
 > downwards, with something between the poles.  The fourth symbol is a
 > standard Euro resistor symbol with a very helpful R in it.
 >
 > If anyone can shed any light on the above, I'd be interested, but the
 > imporant bits followed: 500uA 100V.  Now, I'd read that as being 500uA
FSD,
 > and a maximum voltage rating of 100V.  (A bit less than 15kV, eh?)
 >
 > I canna remember how I'm supposed to wire this up!  I'm fumbling with
 > this:  if FSD is 500uA, I would need a series resistance of:
 >
 > R = 15,000V/500uA = 30Mw (where w represents capital Omega)
 >
 > This, however, doesn't sound right because then the whole thing would be
 > dissipating:
 >
 > 15,000V x 15,000V / 30Mw = 7.5W  Wouldn't this be getting a bit warm?
 >
 > I assume that I'd have to have a potential divider somewhere around here
to
 > make sure that the meter never sees more than 100V across it (if, indeed,
 > that is it's rating.)
 >
 > ...and that's where I've come to a grinding halt.  I don't know whether I
 > started off going the wrong way or if I've just got the math wrong
 > somewhere.  Thought it was just basic Ohm's Law...
 >
 > In a word, help!
 >
 > Cheers
 >
 > M
 >
 > PS - FWIW, the meter is made by Ateliers Pekly of Paris.
 >
 > --
 > Matthew Smith            | Business: http://www.kbc-dot-net.au
 > IT Consultant            | PGP Key:  http://gpg.mss.cx
 > Kadina, South Australia  | * Tivis Project * Community Connect *
 >
 >
 >
 >
 >