RE: HV meter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Hi Terry:

I have a cheap eBay HV probe that I bought years ago and never used.
I've long since lost the instructions that came with it so I don't know
if it states that it may be used for AC measurement.  Basically it's a
two terminal device, with just a 990 Meg HV resistor between the
terminals.  So if one plugs it into a meter with a 10 Meg input
impedance, it works out to a 100:1 division ratio.

I tried it tonight on both DC and AC measurements.  With a 10kV DC
source, it read a stable 94.6V DC on my Fluke 27 DMM.  Multiplying by
the 100X puts it clearly close to 10kV.  I don't know how accurate the
meter on my HV supply is, but it's clearly in the ballpark.

But things were far less stable with AC measurements.  I used a 4kV NST
for the source.  When I put my 120.3VAC line voltage on the secondary
winding, I measured 2.91VAC on the primary, so that suggests that when
hooked up normally, I'd get 4973VAC from the secondary.  It does seem a
bit high for a 4kV NST...

When I hooked the normal output from the secondary to my eBay HV probe
and my DMM, I got readings between 56-263(!) VAC, depending on which NST
lead the HV probe went to and the routing of the probe wires.  With such
an unstable reading, it doesn't seem to be of much value.

I noticed in the Fluke probe you cited, it forms a 3-terminal divider.
But since it also claims a 1000 Meg input impedance and it's also made
to be used with a 10 Meg input impedance meter, I don't see how the
resistor that shunts the meter can be anything but an open circuit.
Maybe having both meter leads being part of the probe assembly results
in a stable and "appropriate" capacitance between them?

Regards, Gary Lau
MA, USA

> Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> At 05:51 AM 6/22/2006, you wrote:
> >The 40kV HV probes often seen on eBay are usually rated only for DC
> >measurements.  I've not tried them on AC, and would be concerned that
> >their very high resistance is not compensated for AC use, and may
> >deliver misleading results.  Has anyone else tried these probes on
60Hz
> >AC?
>
> They are used for AC all the time.  The usual accuracy is 5% for AC.
>
> http://hot-streamer.com/temp/80k40___iseng0900.pdf
>
> The HP 34300A is rated DC to 150Hz.
>
> Cheers,
>
>          Terry
>