HV Measurement - The Divider Problem (fwd)

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---------- Forwarded message ----------
Date: Wed, 22 Sep 2004 12:05:39 +0930
From: Matthew Smith <matt@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: HV Measurement - The Divider Problem

Hi All

I recently built a voltage divider, using a string of 10 x 33M, 0.5W HV resistors.

It's not quite a divide-by-ten due to inconsistencies in the resistance values 
(all off same tape).  This isn't a worry - I have measured the resistances and 
know the exact factor to apply.

I hooked this up to a small HV supply I'd been working on, and put my Wavetek 
DMM across the 1/10th resistor.  The voltage read far below what I was 
expecting.  I checked again at the 1/2 point and still got a reading much lower 
than expected.

Assuming that the supply wasn't delivering what I thought it should, I put the 
DMM straight across it.  Bang.  No more DMM.

So, the voltage WAS what I had calculated, it's just that the divider was 
reading very low.

I have had a similar experience before (and another fried DMM), but thought that 
I was dealing with a fault divider - this is why I checked and double-checked my 
resistances.

Would anyone care to point out what I'm missing here?  I really can't afford to 
buy quality DMMs on a consumable basis ;-)

Cheers

M

-- 
Matthew Smith
Kadina Business Consultancy
South Australia