Re: HV Measurement - The Divider Problem (fwd)

[<sroys@xxxxxxxxxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 22 Sep 2004 23:00:15 -0500
From: Shaun Epp <scepp@xxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: HV Measurement - The Divider Problem (fwd)

Another thing to keep in mind when your measuring really high voltages is 
leakage through the air.  Having the sides of the resistors close to 
eachother or the leads going to the HV source being close to the body of the 
resistors can cause false/ low readings.  What I've done in the past with 
500 Mohm resistors was to attach them the a plastic rod and string them 
together in a line along the plastic rod.  That way you eliminate leakage 
through the air.  Also keep the HV wires away from the rod and resistors and 
mount the rod vertical in the air.  I accuratly measured 100 Kv dc this way.

Shaun Epp


----- Original Message ----- 
From: "High Voltage list" <hvlist@xxxxxxxxxx>
To: "hvlist" <hvlist@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, September 22, 2004 8:39 AM
Subject: HV Measurement - The Divider Problem (fwd)


> Original poster: <sroys@xxxxxxxxxxxxxxxxx>
>
>
>
> ---------- 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
>
>
>