HV HF AC voltmeter?

ErnieM

Joined Apr 24, 2011
8,083
I am looking at a project where a pair of supplies drive a fluorescent display backlight. Two for bright, one for dim. To troubleshoot return units we typically remove both supplies (soldered in bricks) to test each one in turn.

Our customer is asking us to "just stick a voltmeter there" to check the output and not risk his expensive display. However, these things are outputting a 38KHz wave at some 2,000 volts.

Does anyone know of a meter or probe adaptor that can do this? I only checked Fluke but their meters only work up to some 600 v, still trying to find at what frequency. They do have a HV probe good to 40KV but only at 60 Hz.

Do meters that do both high voltage and high frequency exist?

AnalogKid

Joined Aug 1, 2013
8,814
Is this a go/no-go test, or do you want to measure the actual voltage? For basic testing, you should be able to wave an inductor nearby and see the switching waveform on a scope.

ak

#12

Joined Nov 30, 2010
18,216
a HV probe good to 40KV but only at 60 Hz.
I thought those probes were just lots of megs and lots of voltage protection (for you). I doubt the frequency limitations (as advertised?).

nsaspook

Joined Aug 27, 2009
7,890
The Tek P6015A will do the trick if you can find one cheap used.

Lestraveled

Joined May 19, 2014
1,946
The Tek P6015A will do the trick if you can find one cheap used.
Agreed, the Tektronix P6015a is the scope probe to use. They are still being made by Tek for about $2000 each (new). Used <$1000

Lestraveled

Joined May 19, 2014
1,946
If you want to go cheap, build your own. (I have.) It is just a voltage divider with some compensation. Want some help??

The Electrician

Joined Oct 9, 2007
2,814
Have you actually used either of these probes? Looking at the pictures, I have a hard time believing that they are safe at the voltages claimed.
What do you want them to look like? The Tek P5100A is rated 2.5 kV and looks like this: http://www.ebay.com/itm/Tektronix-P...740612?hash=item3a991a4c04:g:R8YAAOSwEppUNywU

The Tek P6015A is rated 20 kV (overkill for the TS) and looks like this: http://www.ebay.com/itm/Tektronix-P...103432?hash=item41a621be08:g:6BgAAOSwP~tW4Jqj and costs like it should.

I haven't used either of the two I linked in post #4, but I have used one similar to the second one. Mine is a 100x, 2 kV rated probe like the second one linked. I paid about \$70 for it a few years ago.

Lestraveled

Joined May 19, 2014
1,946
It is not a good idea to use a probe at the edge of its voltage rating. Look at the voltage waveform you are measuring. A 2KV square wave is not compatible with a probe that has a 2KV peak rating. May I suggest that you would want some head room.

Please notice something. There is a gap between the 2KV max probes and the next higher voltage probes. The higher voltage probes jump from 2KV to 20KV. They look different than the lower voltage probes. This is because it takes a different structure to safely handle the higher voltages.