HV Measurement - Back to Basics

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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
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