Re: Reliable Moderate HV testing

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

Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>" <scepp-at-mts-dot-net>


> Hi All,
>
> I am having trouble measuring the output of my flyback system. The
measurements
> vary widely. I am using a 100:1 HV probe marked " X100 For 10mohm inputs
model
> 1MA-100-10" and a Metex M-4650CR DMM, rated to 200kHz. When I hold the
probe, I
> get much lower readings when measuring AC off the flyback. I understand
that I
> am capacitively coupled to the probe and grounding it, but which reading
is
> "real" me hanging on to it or not? Which represents the "working" voltage
of
> the system?
>
The reason your getting incorrect readings is that your meter is probably 1
Mohm input impedance on AC range, and your HV probe is calibrated for 10
Mohms - probably DC range only.  Also the input capacitance of the meter
plays into effect, especially at high frequencies.   To measure AC HV with
your meter, you need a lower resistance HV probe so that you get a good
division ratio and so that the input capacitance doesn't interfer as much.
Also the fields given off from a flyback will probably screw up you readings
too, When I ran mine it did, it also shut down my PC computer many times.

Hope this explains a few things,
Shaun Epp

> Also, while hanging on to the probe, if I put the flyback output through a
full
> wave bridge, I get much less than 1/2 of what I read on the AC side.
>
> Further, when reading the AC output of the system, if I disconnect the
ground
> lead, sparks will jump a good distance from the lead to the ground. This
makes
> me nervous. I tried using my mains ground, which should be isolated from
the RF
> ground of the system, and the same thing happens. What if I put a HV probe
on
> the ground side? Is my DMM at serious risk?
>
> So what can I do to get at least consistent if not accurate readings?
>
> Thanks all,
>
> Jonathan Peakall
>