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100G -1000G Resistors

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TimFox:
Back in graduate school, we needed to apply about 10 kV to a test object and measure the (small) current through it.
We floated a battery-powered Keithley electrometer in a purpose-built acrylic enclosure, with acrylic rods to rotate the control knobs.
The case of the electrometer was connected to the power supply, so that any leakage or corona from the rectangular case did not flow through the electrometer's ammeter circuit.
To protect the input of the electrometer (a vacuum-tube input unit, with reasonable input voltage rating), we added an appropriate diode network across the input.

exe:

--- Quote from: jwet on May 13, 2023, 09:19:54 pm ---some very old NOS Russian/Bulgarian beauties from early cold war, probably 70 years old.

--- End quote ---

Oh, those can have very bad tempco. Hope it doesn't matter for your circuit. Afaik, somebody evaluated them for a (pico-)ammeter application, but I can't find the thread. Also worth cleaning and drying it properly, any surface contamination ruins precision.

Someone:

--- Quote from: bdunham7 on May 16, 2023, 02:46:22 pm ---
--- Quote from: jwet on May 16, 2023, 12:26:51 pm ---not require a transit case.
--- End quote ---
Now they're getting silly.
--- End quote ---
It ends up with the "product" they order being a branded pelican case factory fitted with the actual product inside. Several employers have done exactly this.

jwet:
Tim Fox- That's pretty cool.  My first job was at General Atomics in San Diego in 1982.  As a new grad, I was supposed to work in three groups for 6 months each- they called it the Tech Grad Rotation program.  They were an aging company with a lot of Manhattan project type guys in the hierarhcy.  They were trying to get some young blood and were hiring a few dozen grads a years from good engineering schools.  General Atomic is still around and thriving- they did the  Predator drone- (good story).   My first rotation was in an instrumentation group that did radiation monitoring equipment for Nuclear Power Plants- our system was installed in most Westinghouse PWR's around the world- over 100 sites with 100's of monitors per system, all networked together in 1982- super state of the art-  software, digital, analog, physics and instrumentation problems.  I loved it and couldn't believe I was getting paid to go play there everyday.  I was in the Detector Physics group, working on analog front ends for all different kinds of radiation detectors- GM Tubes, Ion Chamber, Fission Chambers, PMT/Scintillator, CdTe-Solid State- the gamut.  I had some great old time mentors that had seen it all.  There were also a lot of commercial Nuclear Power guys mostly brought up through the Navy.   My next rotation was supposed to be to their Fusion Research Reactor called Doublet 3- a big Tokhamak that was hot shit for its time.  About a month before I was to transfer, I took a big tour and saw these guys operating instruments behind 1/2" lexan blast shields with3 foot lucite rods to turn scope knobs, etc like you're talking about.  I decided to stay put in my group and go out of the Tech Grad deal.  I've done a lot of ion detector and PMT work up to about 2 KV and have been on projects with 200 KV X-Ray power supplies.  That stuff gets weird.  I settled down to precision data acquisition and mixed signal stuff and after Nuclear dried up went to work for Maxim for about 25 years in their standard products group defining products like Analog Swtiches, Op-Amps, etc.  A lot of fun.  Retired a while back taking little consulting projects that come along.

ZhuraYuk:
Tried to get similar 1T resistors to replace them in some old electromters. There are few options for cheap in stock:

https://mou.sr/4a3v7Sg   Mouser 1T Ohm 500ppm 5%

https://www.aliexpress.com/item/1005006645803409.html There is a lot of new Chinese high ohm resistors, all seems to be made of same material 200ppm.

https://twjohmresistor.aliexpress.com/store/912607391 This shop has large choice of Giga Ohm resistors to upgrade yuor old electrometers.

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