Re: High Voltage Probe Instability

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sparktron01@xxxxxxxxxxx 

Steve, David

Error term on my OHVM oil immersed divider network with increasing voltage 
followed a square law relationship.   Absolute error terms (below 25kV rms) 
was < 0.4%.  At 50kV rms (70kV BIL pk), error term was ~ 1.2%.  Dielectric 
polarization of oil was my take on root cause of error term, more plausible 
with error term square law relationship with applied voltage observed...

Regards

Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA


> Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>
>
> David,
>
> I had a similar problem with a high voltage divider.  Very mysterous.  I
> finally decided the cause was corona that was ionizing the air around the
> string of resistors and in effect adding some parallel resistance, thus
> making the reading creep up.  I put the string of resistors in some vinyl
> tubing and that cured the problem, at least for me.  You could try taking
> the cover off your probe so that air circulates around the divider
> components and see if that reduces the problem.  If so, then suspect some
> sort of ionization is happening.  Perhaps your probe is supposed to be
> insulated with oil, and the oil is no longer there??
> --Steve
> ----- Original Message -----
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Monday, February 07, 2005 8:29 AM
> Subject: High Voltage Probe Instability
>
>
>  > Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
>  >
>  > Hi all,
>  >
>  >
>  > I have a question that I was hoping that some of you would have
>  > some insight on. I have been trying to measure the output voltage
>  > of my x-ray transformers with 1000:1 HV probe that I have. I mea-
>  > sure the input voltage while carefully controlling it with a variac
>  > and, at the same time, measure the output of one of the HV term-
>  > inals to ground and thereby obtain a ratio for the output/input
>  > voltage so I can have a pretty close approximaton of the output
>  > of the transformer. Sounds simple enough but the problem that I
>  > am having is that the high output voltage measured through the
>  > HV probe keeps slowly but steadily climbing while the input re-
>  > mains relatively constant. For instance, with an 80 volt input,
>  > the HV output initially reads around 28,400 volts but after around
>  > 10 minutes of constant measurement, the HV output has crept
>  > up past 30,000 volts, at least according to my HV probe/DVM
>  > combo. Of course, all measurements are taking with no load
>  > on the transformer. Is my measurement equipment defective or
>  > is this a normal phenomena? Should I wait for the output mea-
>  > surement to reach as high as it will go and go with that as an
>  > accurate measure or should I take the first initial measurement
>  > as the true measure of the voltage? Could the resistor of the
>  > 1000:1 probe be heating up and causing the instabiltiy of the
>  > reading? Any comments are welcome.
>  >
>  > David Rieben
>  >
>  >
>  >
>  >
>
>