Re: funky voltage readings

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

Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

Meter input impedance is a possibility. I had to break out the Agilent 34401
meter Service Guide, and it says AC input impedance is 1Mohm in parallel
with 100pF. That sounds rather low, and there is no mention of this in the
normal spec sheet or User's Guide. I'm not sure of the probe schematic and
how much it depends on 10Mohm meter impedance.

As for AC ranges I was using, the meter clicked it's little relays to
autorange. I belive they just change the "second stage" amplifier settings.
I'll try again with the range forced to a certain scale and try again.

Odd.

KEN


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, June 14, 2003 12:18 PM
Subject: Re: funky voltage readings


 > 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
 >
 >
 >