DIY CRO Protection HV Probe

On a sunny day (Tue, 25 Mar 2014 17:53:57 +1100) it happened snipped-for-privacy@protec.com wrote in :

Look how ididit here:

If you blow up you 10,000,00,000 cents scope I havenotdunnit.

On a sunny day (Tue, 25 Mar 2014 07:56:04 GMT) it happened Jan Panteltje wrote in :

BTW do NOT use you existing probe directly, this goes between HV and probe, and use a low value to ground:

scope probe ------------R1 - R2 - R3 - ... - Rn ---> object under test 10x | [ ] 10k | ///

If you are still paranoid add a zener over the 10k, or for AC 2 zeners in series reversed, or better some NEON bulb, or whatever..

If you are really working with high power HV that can do real lethal currents get a real HV probe, If you die from it ihavenotdunnit.

All this assumes you have some xperience with electrons. If no task somebody who has... Oh that was what you were doing, hell should add more disclaimers. Whataworld

Maybe better go sunbathing, oh no, the radiation may kill too. Go to sleep?

On Tue, 25 Mar 2014 17:53:57 +1100, snipped-for-privacy@protec.com wrote as underneath :

Try for info

If you just want wave *form*, and can do without amplitude, just hold a normal 10x probe somewhere in the vicinity. It'll AC-couple in just fine. Or put a single turn sense winding on the transformer.

Making a wideband probe is tricky. If you use a chain of resistors, the capacitances from each resistor to free space (and to each other, and to whatever kind of shielding you have nearby) screws with compensation in a complicated manner. You can get a step response that's more-or-less correct, but has odd risey-dippy behavior in the 1-100kHz range. It's only give or take a dB or so, but it really sucks for a probe.

You can attempt to dominate parasitic capacitances with a bulk capacitance (for this kind of ratio, really just having a high voltage wire near the divider node -- a gimmick capacitor), but you can quickly run into unfavorable ratios: say, needing 10nF to ground to compensate it -- and no way to adjust it, because you can't just buy 10nF trimmer caps...cheaply, anyway.

The pros do it by keeping things small -- under oil if possible, like the sealed Tek (6026??!?) probe, which uses a small resistor and a guard ring / shield / capacitance hat to help with compensation.

I've done it before for lower voltages (~2kV) by stacking chip resistors and capacitors, say 200V each. That's about as much as you'd want to risk with them. Still needs a big compensation cap, and you can't vary AC gain because of it. You'd want a better approach for 10kV.

Tim