Re: High Voltage Probe Instability

["Tesla list" <tesla@xxxxxxxxxx>]

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
>
>
>
>