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High voltage probe and high voltage resistors
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xzswq21:

--- Quote from: Gyro on August 01, 2021, 10:10:53 am ---Here's a 10kV peak R-C attenuator I built for my Gay MTA Memory (peak capture) Voltmeter.

https://www.eevblog.com/forum/testgear/high-voltage-x10-attenuator-for-my-gay-mta-memory-voltmeter/
I was more interested in the overall frequency response of the probe and meter combination, so I had to check the roll-off with a signal generator. It made it to 5MHz though.


--- End quote ---

You have used SL temperature coefficient capacitors, Do you recommend me SL capacitors? Even 1MHz passband flatness is good
Gyro:

--- Quote from: xzswq21 on August 01, 2021, 11:29:46 am ---You have used SL temperature coefficient capacitors, Do you recommend me SL capacitors? Even 1MHz passband flatness is good

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It's not so much a recommendation, as what is available. Ideally you would use C0G or NP0, but these are not commonly available, that I could find, in 6kV rating (possibly overkill but I wanted a good safety margin with 3 capacitors in series on 10kV - the MTA original probe stated 15kV pk).

Murata information indicates that SL is a class 1 dielectric and 5% tolerance, even though probably not as good as [Edit: higher Dissipation Factor than],  NP0 and C0G (also class 1). So seemed good enough for the purpose - certainly much better than the Yxx and Zxx dielectrics found in other high voltage ceramics.

Here's a link to the Murata High voltage capacitor and dielectric data... https://www.murata.com/-/media/webrenewal/support/library/catalog/products/capacitor/ceramiccapacitor/c85e.ashx?la=en-us&cvid=20210203042629000000

EDIT: and detailed spec sheet...  https://search.murata.co.jp/Ceramy/image/img/A01X/G101/ENG/DEC_E.pdf
Gyro:
The TE Connectivity HB series thick film resistors are also a good choice. They're low inductance and have good voltage coefficient, I don't know what overall resistance you are aiming for in your divider (and split across how many resistors) but they achieve around 1ppm/V up to 10Meg, and 2ppm/V up to 100Meg. Not cheap, but not ridiculously expensive either.

https://uk.farnell.com/w/search/prl/results?st=hb%20resistor
joeqsmith:
I designed and constructed a few different high voltage probes.   Normally I use wire or copper foil to form the compensation network.    This video goes over the design of my 40kV 20MHz wideband probe.  I broke the ceramic insulator a few years back and ended up changing the design a bit to improve the performance.   


TimFox:

--- Quote from: xzswq21 on August 01, 2021, 05:29:52 am ---
--- Quote from: TimFox on July 31, 2021, 10:01:31 pm ---I would never use X, Y (such as Y5P), or Z dielectric ceramic capacitors in a measurement system, since they lose capacitance drastically with applied voltage.  For ceramic, you need NP0 or C0G (basically synonymous).  However, there are special capacitors for high voltage, such as reconstituted mica or high-voltage polypropylene film.

You didn't give a country flag:  to where would the freight charge get that high from Texas?

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Before I come here, I had googled about high voltage capacitors, for low voltage filters I always use C0G capacitors but for high voltage capacitor I couldn't find anything in Digikey or Mouser except Y5P, N4700, Z5T, . I found several large size and unusual and very expensive capacitors. Can I use 1kV C0G capacitors in series? In theory there is a problem, for example, the voltage drops by 1kV per capacitor but there is 20kV and 19kV on the first capacitor!

20kV -||- 19kV  -||- 18kV -||- 17kV  -||- 16kV  -||- ....

I think I can't use 1kV capacitors

I wanted to buy from Digikey.com, the shipping cost for other components is 30$ but for the Ohmite resistors is 150$. It's better for me to find the the components from other distributors.

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Of the three dielectrics you mentioned, "N4700" has a high temperature co-efficient (-4700 ppm/K), but its voltage dependence should be reasonable.  See others' comments about DC distribution across series capacitors:  you must use resistors to equalize the DC voltages.
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