Re: funky voltage readings

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Ken,

I have done that test many many times with similar probes (mine is the B&K 
version) without problem.  It sounds like you have done all the tricks like 
check it against the 120 VAC line and tried two different NSTs.  I can't 
think of anything that would cause this.  But, It really "should" work just 
fine...

Those "same" probes are also sold by Fluke, B&K, Tektronix...  They are 
well proven and free from funkyness for tests like this.

I assume the meter is in the "same" range for the 120VAC and 7.5kVAC 
tests.  Some meters have different impedances for different ranges.  But I 
think those probes have a base resistor so it should not matter other than 
skewing the reading slightly.  Any modern digital meter should work 
fine.  They just don't want you to try a 10k ohm panel meter or something 
with really low resistance like that.

You make want to check the continuity on the ground connection of the probe 
back to the ground plug for the meter.  I would be extra careful with the 
probe too until you know what's going on.  A defective HV probe is pretty 
dangerous if that is what it is.

Cheers,

         Terry

At 10:45 PM 6/13/2003 -0500, you wrote:
>I was playing around with a HV prove and meter and noticed I get odd
>readings. I'm using an Agilent 34136 AC/DC probe which is just 1Gohm 1000:1
>divider for meters with a 10Mohm impedance (which I'm using.)
>
>DC voltages read ok for DC as far as I can tell so far.
>
>For AC, digital meter and scope measures the same voltages, which are 3.4kV
>for the 7.5kV winding of a 15kV neon sign transformer, which seems wrong.
>High voltage probe goes to one HV lead on the transformer, and ground lead
>of the probe goes to the ground on the transformer. I get the same with two
>different transformers.
>
>The waveform is almost a clean sine wave according to scope, so I'm not sure
>where this number is coming from. I'd expect 7500 volts /1000 for 7.5 volts
>on the meter, but I read 3.4
>
>120 volts from an outlet give the expected readings with the HV probe in AC
>mode.
>
>Maybe soembody can explain this, or share what they get with a close setup.
>The probe is rated for 60Hz AC use, and should be good to 2%.
>
>KEN