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Most of the x1000 high-voltage oscilloscope probes I find seem to have input impedance around 100M Ohm. For example the P6015A from Tektronix (100M Ohm) or the PPE6KV from LeCroy (50M Ohm) or these from North Star (100-400M Ohm). I thought that the passive attenuating probes just have a resistor in them (and a capacitor) which forms a voltage divider with the oscilloscope's internal resistance of 1M Ohm, so I'd expect a 1000M Ohm input impedance for a x1000 probe.

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They all use 50 Ohm cable for optimal BW of >50MHz thus Rin is 50MOhm to 400M with (?) 2 stage dividers. Using 1Gohm requires active FET probes rated only for 25V or so.

It would also become unsafe at hiV with creapage going to insulator resistances of 1GOhm. Leakage would cause Partial Discharges. (faults)

Why would you want 1GOhm for high voltage in a tiny probe?

Use C ratio divider for HVAC. Then use a divider with 50 Ohm termination.

2000:1 probes use 93 Ohm coax to reduce capacitance.

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  • \$\begingroup\$ "2 stage dividers" - thanks, that's what I was looking for (an explanation how it is different from an x10 probe). "Why would you want 1GOhm for high voltage in a tiny probe?" here's a probe that comes close (a 40kV probe with 900MOhm). caltestelectronics.com/ctitem/… \$\endgroup\$ – Slava P Jun 3 '17 at 19:17
  • \$\begingroup\$ that's a "phat" trojan with ribs out loud said Leisure Suit Larry in the drug store (lol) I remember testing these ribbed porcelain bushings on 50kV that were as long as my forearm rated for 200BIL (lightning) but failed below 90kV when I wanted to test at 200kV even after alcohol,wipes . This is due to creepage charge turning into a Unijunction relaxation oscillator or corona at higher levels with continuous voltage so I had to cascade two bushings in series to test the oil in a 5MVA tank. There are over 100k papers on this called Partial Discharge (PD) on Microsoft Scholar or Google Academic \$\endgroup\$ – Sunnyskyguy EE75 Jun 3 '17 at 19:40
  • \$\begingroup\$ "2000:1 probes use 93 Ohm coax to reduce capacitance." High impedance passive probes do not use standard coax - they commonly use a special cable with thin resistance wire as the center conductor since they are not terminated with their characteristic impedance. \$\endgroup\$ – Kevin White Jun 3 '17 at 19:47
  • \$\begingroup\$ @TonyStewart.EEsince'75 Could you please explain what would be the symptoms one would observe? (I understand the concept of PD, I think, but I don't understand what would be the practical implications). Also - do you think that the probe I linked in the comment will similarly fail at a significantly lower voltage than 40kV? \$\endgroup\$ – Slava P Jun 3 '17 at 19:55
  • \$\begingroup\$ PD is often heard as static discharge pulsing or hair on the back of your neck standing up for HVDC but not AC or like lightning noise on AM radio. Corona is simply external PD with a high rep . Since these are solid plastic like porcelain check if the rating is for BIL basic insulation level defined by 10us pulses like lightning induction, but it may not be rated for 40kV DC or AC unless extremely clean. BDV ratings range from 3kV/mm to 100V/mm for surface creepage fro mionic dust and humidity, so its like a dirt controlled resistance with ion charge flow due this and charge accum. then PD \$\endgroup\$ – Sunnyskyguy EE75 Jun 3 '17 at 21:44

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