100G -1000G Resistors

[jwet]

Looking for very high value resistors- 1 TOhm ideally with a 5kV rating, <=1/4w fine, <=250 ppm/C and decent voltage coefficient.  I can stack a couple but the capacitance quickly gets out of hand.  I plan to air wire this stuff on Teflon standoffs but don't want to resort to anything more exotic.  The application is high impedance voltage measurement around 2kV nominal- consulting job.

Stackpole, Murata, and Ohmite make the kinds of parts I want but they appear to be unobtanium or are $100/unit.  Victoreen, Cleveland used to make parts like this but they got bought by Fluke and I can't find them anymore- maybe internal use only.  New Old Stock in decent shape would be fine if they can provide 100'+s.  One time build of a few hundred units is most likely.  I've looked on Ebay and see some very old NOS Russian/Bulgarian beauties from early cold war, probably 70 years old.  Qtys are low but am asking suppliers, will buy some to test with.  The Bulgarian units are sealed in glass, tolerances are loose (5-10%), no specs other than ohms and quantities are limited (so far).  Does anyone have any experience with these- photo below.  They're about $5 in singles which is in the ball park.  I used to get these from Victoreen for about $1. 

Any other suppliers, leads or ideas would be appreciated.

[Benta]

Did you try Vishay (didn't check myself)?

[TimFox]

The Bulgarian unit shown is very similar to the older Victoreen deposited-carbon, sealed-in-glass units that were used in systems such as Keithley electrometers.
I'm not sure they were rated for 5 kV.
A modern source for 5 kV units is Ohmcraft  https://ohmcraft.com/wp-content/uploads/2022/02/HVR-datasheet.pdf  but I don't know their pricing or minimum order.

[jwet]

Thanks- funny you should mention Keithley- another Danaher, Tektronix, Fluke, Victoreen, Fortive?  head spinning acquisition circle.  As a Maxim FAE, I used to love going to Cleveland for Victoreen, Keithley and AB/Rockwell - I did several studies of industrial electronic companies and Cleveland was ground zero- great products and engineers.

Did Keithley make those resistors in house?  Victoreen had them made by Dale/Vishay I think but also sold them as components to get their volumes up to where Vishay cared.

[wraper]

The Bulgarian units are sealed in glass, tolerances are loose (5-10%), no specs other than ohms and quantities are limited (so far).  Does anyone have any experience with these- photo below.

This is not Bulgarian but Soviet and has datasheet.
https://www.quartz1.com/price/PIC/480Q0717900.pdf
http://www.155la3.ru/datafiles/kvm_kim_klm_tu_1977.pdf
You can google translate it and ask if something is not clear, I speak Russian. КВМ are vacuum composite resistors. +1000/-2000ppm/^oC TC, -60/+85^oC, 100V max. Rated to drift not more than 30% during 10k hours of operation and not more than 25% during 12 years of storage.

[TimFox]

I thought those resistors were made by Victoreen, but used in Keithley equipment (from the same city).
An interesting 1965 article in Rev Sci Instrum mentions Victoreen electrometer resistors on page 4  https://escholarship.org/content/qt3v68c7vw/qt3v68c7vw_noSplash_eac5c3bdc7d1f17286456241063f249c.pdf
However, that circuit has maybe 10 V across the Victoreen range resistors (max 24 V supply).
In grad school (1970s), we had a good supply of high-voltage resistors made from a helix of carbon on ceramic pillars (not precision, but good voltage ratings), from Resistance Products Co, now part of Vishay/Dale.
Unfortunately, that series seems to go up to only 500 megohm.   https://www.vishay.com/docs/31039/bt.pdf
None of these carbon resistors will have a good tempco or voltage co-efficient of resistance.
Even the Caddock resistors have a noticeable co-efficient at these voltages.

[Someone]

vacuum composite resistors. +1000/-2000ppm/^oC TC

Its a nasty problem, air is a G ohm resistor, but vacuum kills the thermal performance. Porcelain/glazed resistors + dry purged enclosure would be a start. Honest suppliers note the TCR and VCR ratings fall apart at higher voltages:
http://www.token.com.tw/resistor-hv/index.html

[pcm81]

vacuum composite resistors. +1000/-2000ppm/^oC TC

Its a nasty problem, air is a G ohm resistor, but vacuum kills the thermal performance. Porcelain/glazed resistors + dry purged enclosure would be a start. Honest suppliers note the TCR and VCR ratings fall apart at higher voltages:
http://www.token.com.tw/resistor-hv/index.html

Funny you mentioned that. At work we have to do certain bonding/ground tests in an environmentally controlled room, because high humidity air, here in Florida, can make a 10GOHM test fail.

[Someone]

vacuum composite resistors. +1000/-2000ppm/^oC TC

Its a nasty problem, air is a G ohm resistor, but vacuum kills the thermal performance. Porcelain/glazed resistors + dry purged enclosure would be a start. Honest suppliers note the TCR and VCR ratings fall apart at higher voltages:
http://www.token.com.tw/resistor-hv/index.html

Funny you mentioned that. At work we have to do certain bonding/ground tests in an environmentally controlled room, because high humidity air, here in Florida, can make a 10GOHM test fail.

Some systems a dry nitrogen purge isn't adequate! then you're off into the weird and wonderful.

[HighVoltage]

I have been using these in the past:

100GOhm KVM Russian military vacuum glass resistor NOS
https://www.ebay.com/itm/265524132036

[magic]

This is not Bulgarian but Soviet and has datasheet.
https://www.quartz1.com/price/PIC/480Q0717900.pdf
http://www.155la3.ru/datafiles/kvm_kim_klm_tu_1977.pdf
You can google translate it and ask if something is not clear, I speak Russian. КВМ are vacuum composite resistors. +1000/-2000ppm/^oC TC, -60/+85^oC, 100V max. Rated to drift not more than 30% during 10k hours of operation and not more than 25% during 12 years of storage.

This is correct, including the voltage rating, and I seem to recall that people tested them and found them to fail instantly at less than 1kV.

I have a few of those resistors and their tolerance after all those years is quite sloppy, particularly the 100GΩ ones. Most were 90~95GΩ and the worst ~70G, all measured by applying 100V in series with a 10MΩ DMM and doing the obvious math.

[magic]

I can stack a couple but the capacitance quickly gets out of hand.

I don't understand this remark. Connecting capacitors in series decreases end-to-end capacitance, and resistors have low capacitance to begin with.

In fact, I think a physically long string of 1GΩ resistors would have much less capacitance than one small 100GΩ resistor.

[jwet]

Tim Fox- I could be wrong about who made Victoreen R's- I was told this somewhere along the line.  Victoreen had a lot little specialty shops in that big place near Shaker Heights.  There was a little shop for making those view through electrometer based dosimeter pens, quite an operation- saw it around 1986.

[jwet]

Magic- My capacitance concern is node capacitance to "ground", not across the R's- even on a teflon standoff, its difficult not to pickup a pF of stray.  1000G x 1 pF makes for s 1 sec RC product, even at lower resistances like 10G,  its easy to get into motor boating- low frequency oscillation in anything with feedback.  Guarding can help but it all gets kind of ugly at these voltage and currents.

[jwet]

pcm81- I think something like you're talking about is what my customer wants to do but he wants to do the test in the field.  He doesn't want to issue his field tech a fancy Keithley electrometer and the cheaper megger like gadgets available won't go down low enough in leakage.  End equipment is Ion mobility spectrometers- the detectors used at airports for explosives.

I'm going to rethink my approach.  When you get yourself designed into a box like this, its best to back out and try something else.  I originally wanted to do it with an integrator but they didn't like the slow reading speeds it would give them (1/sec).

Thanks all.

[magic]

Not sure what sort of circuit this resistor goes into, but Johnson noise and stray capacitance may make significantly faster speeds infeasible anyway, so the customer may simply need to adjust his expectations.

[TimFox]

Not sure what sort of circuit this resistor goes into, but Johnson noise and stray capacitance may make significantly faster speeds infeasible anyway, so the customer may simply need to adjust his expectations.

The article I linked above goes into great detail about optimizing the speed of a sensitive electrometer circuit with these resistors.

[TimFox]

Tim Fox- I could be wrong about who made Victoreen R's- I was told this somewhere along the line.  Victoreen had a lot little specialty shops in that big place near Shaker Heights.  There was a little shop for making those view through electrometer based dosimeter pens, quite an operation- saw it around 1986.

I looked at the BOM (1977 manual) for my Keithley 261 Picoampere source (precision voltage source driving selectable high-value resistors), designed to calibrate electrometers.
The "deposited carbon" resistors have manufacturer's code 80164 (Keithley), but that may be since Keithley measured them individually for calibration.

[jwet]

Tim Fox- I just started digging into that 1965 Article- thanks very much!  You're kind of on your own with a lot of this esoteric stuff.  Keithley made a low level measurements handbook that is very good too and I have it but its more about appplications (selling instruments) than design.

[jwet]

Magic- I agree, I think they're hoping for >5 per second for pot tweaking or other adjusting.  At these currents, you're getting down to statistical currents sort of like shot noise.  I'm in the proposal and discussion phase now- I haven't got a contract yet.  I have to be fairly polite still...  I might pass- I have a week to decide.

[jonpaul]

OP: The combination you spec is impractical.

The tradeoffs of voltage coeff, R, precision at over 1 G Ogm are unobtainable.

We used Victoreen and Caddock in 1980s, on 12 kV Avaionics HV.

The 1000M were +/- 20%

Rated to 20 kV.

I would revise your   approach to avoid the unreachable requirement.

Jon

Jon

[magic]

By the way, I still don't know what you want to use this resistor for, but if it's just low level current measurement like in the article linked by Tim Fox then I don't see why you would need a 5kV rated part.

At first I thought you want it for a high impedance voltage divider or something like that.

[PartialDischarge]

2kV is not that high, so you could use a follower opamp connected to the input and floating (bootstrapped) at the input voltage. Bandwidth is going to be high, but also is going to be the cost as you need a DCDC converter that gives 2KV although low current

[strawberry]

2kV / 1Tohm = 2nA

[jwet]

Magic- I explained as much as I could above.  The box will measure voltages up 2500V with very light loading and  measure very low currents (10e-14A) for their field techs that service Airport Ion Spectrometers- explosives detectors.  Lab gear exists that can do all this but it has a lot of features that they don't need and costs about 4k and is not easy to source.  They are doing a make/buy analysis to see if they can get something custom designed at 150 pieces for less than the cost of buying 150 $4K instruments, about 1/2 million and not really up to the task of knocking around in a tech's van.  Their current solution is to FED-X a Keithley and an elecltrostatic voltemeter out to the field which is a pain too. This ultra low current, high voltage stuff is a funny niche that I did a while ago.  I'm doing a 40 hour trade study right now to give them their options and they'll go decide.  I'm only on the hook to deliver a study and this one of several avenues.  I'm also looking at other consultants (better than myself) that specialize in this field.  We'll see.

Thanks all.