Staubli HV Probe, 100:1 - Page 1
Forum section: electronics / testgear

author: TaylorD93
author_rank: Regular Contributor
timestamp: March 28, 2021, 05:23:51 pm
content: Hello everyone,I am fault finding a few HAMEG Scopes i have been collecting/fettling (currently 8 in different degrees of repair), one common issue i am finding however is the power supplies seem to be a bit on the "weak" side. Most of the scopes are 203-5 and 203-6 models which have -1.9KVDC supply for the CRT, but in fault conditions can rise up to -2.7KVDC.I have a Tenma 40kV Probe 1000:1 Probe, which with a 10Mohm Input Z DMM can perform some basic measurements, but the DMM response time is not good enough to see the flickering/pulsating display i am getting on the CRT intensity.Therefore I want to get a HV Scope probe so that I can actually monitor the HV and see whats going on with it.I have therefore bought a Staubli IsoProbe II from CPC (im UK based) which is a 100:1 probe. They have since removed it from their sight, but it stated it was 3.5kVDC Rated.Great i thought!However it transpires that the manual says "Never use this probe to carry out measurements on sources whose potential to earth exceeds 1000V" but also says max Rating "3540V, O", with "O" being equivalent to "CAT I"With their definition of CAT I being "Other Circuits that are not directly connected to the mains"Im struggling to decide if the probe is fit for purpose or not.At the end of the day I do not have an isolation transformer, any scope measurements will be referenced to Earth via the Test Oscilloscope and the -1.9KVDC in the DUT is referenced to Chassis anyway which is then referenced back to the same Earth connection in my property so any test voltage will exceed 1000V wrt Earth because of the nature of how the oscilloscope is connected. so really it comes down to1) Does anyone agree that this probe is not fit for purpose?2) Does anyone recommend a suitable priced (sub £100) probe for measuring upto 3kVDC? Would be happier with a 5kV Rating to give a bit more headroom admittedly.Thanks in Advance,Taylor

author: threephase
author_rank: Regular Contributor
timestamp: March 29, 2021, 04:25:06 pm
content: It sounds like your setup is exceeding the common mode voltage of the probe you purchased, which puts you at risk of electric shock. There are ways that people have utilised in the past to make these kind of measurements with the equipment you have and keep themselves 'safe'. That is up to the individual.The probe you are using looks to be a relatively basic passive voltage divider and is really designed for measuring floating high voltages that are not referenced to earth at any point.To do your measurement, an active differential probe would be recommended these days, but I am not aware of a sub £100 unit that would suit you.

author: bdunham7
author_rank: Super Contributor
timestamp: March 29, 2021, 05:18:58 pm
content: Is it this one?https://www.staubli.com/en-us/connectors/test-and-measurement/test-and-measurement/high-frequency-measurement/touch-protected-passive-probes/set-isoprobe-ii-1001/If so, it is appropriate for your use and is pretty much the same thing as the common P2301C probe you see on eBay. Probably the same OEM. I can't comment on why people put things in manuals, but AFAIK the 'CAT' ratings are part of the Low Voltage Directive, and only apply up to 1kV, so I've no idea what a CAT 1 3540V rating means. The P2301C is commonly advertised as 5kVp, and that would correspond to a sine wave of 3540Vrms, so maybe someone just thought that's how it should be stated. As for the statement "1000V to earth", again, no idea. Perhaps referring to the ground side when used with a floating scope?In any case, this is exactly what I use for this exact purpose--CRT oscilloscopes. I'd recommend you use it strictly hands-off (connect, power up, measure, power down, move connection, etc), just to be safe. And always use DC coupling on your scope. I also wouldn't push the voltage limits or the frequency derating curve. Mine handles 4kVp-p@ 20kHz on the Tek 22xx scopes, but more than that would make me nervous.