Jamie t wrote:
Mike Cook wrote:

the input impedance on throw away (and even good bench) meters can be
really really low on some ranges, like AC.

I use a Leader FET input? meter for stuff like this. These replaced VTVMs
but retain the essentially zero load on the test circuit.

One use is for takings readings with the 40kV Fluke probe. You'll get
dangerously low readings with pretty much any digital meter on AC ranges.


Would you explain please? Is the FET input impedance so much higher that it
loads less than even a high-quality DMM?

Thanks.


My Fluke 289 will measure correctly with the 40k probe doing
AC or DC. So won't a couple of older flukes I have.

Those particular probes (I think Pomona had some too) require a fixed
input impedance on your meter, or the divider math falls apart. It seems
Fluke has no problem with this, although I've not yet tested the probe
with my latest Fluke meter. THere really isn't warning about this on those
probes, although it says so in the manual, but who has those laying
around?

for microwave ovens, when they were worth fixing, a yoke tested was easier
and more certain for HV measurements.

THe only problem with AC and a HV-probe is you need to keep
the frequency down, otherwise, the small amount of cap present
on the input of the meter is going to attenuate it some.

I have no way to test outside of 60Hz, but I am curious about how far they
drift off.

It's very possible cheap meters on AC mode may not behave correctly
with a HV-PROBE and show great losses in readings.

I also have a scope meter that works very well with the HV-probe.
I just need to remember to scale the input properly.