Circuit design of branded electrometers

[Kirill V.]

I see that the power supply consists of two transformers that are connected in series. I have heard that this method is used in highly sensitive devices. I would like to hear from you some useful comments about this and links to documents where it is explained in detail.

[Kleinstein]

The idea with 2 transformers in series is to reduce the capacitive coupling. In addition this allows to double check the isolation of both halves.  The link between the two transformers can be with a low number of turns and this can simplify the shape of the windings. This can give repeatable and predictable capacitive common mode signal. Two small transformers can also be easier to mount on a PCB than a special one with larger distance to the core.

AFAIK there is even a patent on the use of 2 or 3 transformers with a single turn link. Somewhat odd, as the same is long know common practice with pulse transformers for signal isolation.

[Kirill V.]

Thanks!
A very interesting technique, perhaps, I will take note. By the way, what is it called in English literature? I think this technique should have an original name

[antintedo]

I see that the power supply consists of two transformers that are connected in series. I have heard that this method is used in highly sensitive devices. I would like to hear from you some useful comments about this and links to documents where it is explained in detail.

Keithley 617? It has one transformer with shielded windings and one common mode choke. If you are still interested, here is what is being used in 10mA CERN standard and 7001 voltage reference:
https://patents.google.com/patent/EP0864165B1/
https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902910/#msg902910

[MiDi]

The second transformer sits on EM-Board and powers the bottom ADC-Section (hidden) over ribbon cable too.

I have another question about K617. Why do some verification procedures require a jumper between the COM terminal and the chassis?

Good question, in principle it should not matter when source is floating.
Maybe it is just for safety against hazardous CM voltages on floating part.

[Kirill V.]

It is interesting to note that all Soviet electrometers, whose circuits are available on the Internet, did not have a power source with two transformers. Perhaps the exception is the most sensitive and perfect V7-45 with a vibrating capacitor, which was created closer to the collapse of the USSR. Electrical diagrams of this device are not available on the Internet.
A bit of lyrics
Keithley was able to create the most advanced electrometer of its time , model 640. The vibrating capacitor was made entirely of glass, the electrodes made of tantalum, which was deposited on the glass in a vacuum. The tantalum was then treated with ozone to create a surface film. The carrier excitation frequency is 1 MHz, but the generation occurs in flashes with a repetition frequency of 6 kHz, this makes it easier to filter the useful signal from the excitation frequency.
Siemens produced a double vibrating capacitor, the inner cavity of which was filled with hydrogen.
And now I look at the latest devices and see printed circuit boards. And printed circuit boards. And again printed circuit boards... Even Teflon stand-offs are a thing of the past. Manual soldering is excluded and there is nothing unique technologies, but the devices have not become cheaper and more accessible

[Kirill V.]

I have another question about K617. Why do some verification procedures require a jumper between the COM terminal and the chassis?

Good question, in principle it should not matter when source is floating.
Maybe it is just for safety against hazardous CM voltages on floating part.

I think you're wrong. This depends on the range at which the verification is performed . Moreover, on the most sensitive ranges, this jumper is needed, while on the coarser ranges it is not.
The external cable shield is connected to the voltage source chassis or to the K617 chassis. This is similar to various versions of electromagnetic shielding. Someone pay attention to the verification section in the service manual, does my assumption make sense?

[MegaVolt]

Perhaps the exception is the most sensitive and perfect V7-45 with a vibrating capacitor, which was created closer to the collapse of the USSR. Electrical diagrams of this device are not available on the Internet.

Here is a document with a description that was found on Russian forums.
https://yadi.sk/d/c3s0VnoaC7MKS

The device is on sale and not very expensive. About $ 1000 considering that it is capable of measuring up to 10^-17A (10aA)

[Kirill V.]

The technical description consists of two books. The first book contains verbal descriptions of the principle of operation, operating conditions, verification methods. The second book contains detailed circuit diagrams, lists of parts. You found the first book I've already seen .
In the USSR, the more old V7-29 electrometer with a sensitivity of 10 aA was also created. For verification of such devices, calibrators were created that can reproduce a current of 10 aA. All this was done without color TFT screens and microprocessors (as example V7-29 - around 13 kg of steel). The connections between the electrometer and the calibrator have been designed to eliminate any spurious currents that any insulation can generate. This makes them stand out from the Keithley that are so popular here, which require a lot of extra cables with connectors to connect various beautiful boxes.

The device is on sale and not very expensive. About $ 1000 considering that it is capable of measuring up to 10^-17A (10aA)

In principle, I agree with you so much that I am ready to provide a Bank card number so that anyone can transfer me $ 1000 and I can buy it for myself

[MegaVolt]

The device is on sale and not very expensive. About $ 1000 considering that it is capable of measuring up to 10^-17A (10aA)

In principle, I agree with you so much that I am ready to provide a Bank card number so that anyone can transfer me $ 1000 and I can buy it for myself

Ha ha )) It’s cheap with respect to electrometers of other companies with the same parameters.

[bsw_m]

For verification of such devices, calibrators were created that can reproduce a current of 10 aA.

That's name is EK1-6
Some little facts: V7-29, V7-45, EK1-6 developed in MNIPI, Minsk.
Some interesting facts: insulators in V7-45 and EK1-6 made from sapphire for minimize leakage.

[Kirill V.]

No, not just to minimize leaks. Artificial sapphire generates the least spurious current from all solid insulators. This dielectric has no analogues for creating extremely sensitive electrometric equipment.

[Echo88]

Cant comment on the interesting vibrating electrometer due to language barrier.
But id like to point out the "Ultrastable Low-noise Current Amplifier (ULCA)", which is an interesting device in itself and which could maybe be replicated.
https://arxiv.org/ftp/arxiv/papers/1808/1808.08881.pdf

The many references at the bottom of the document lead to more pdfs of the ULCA and different other methods of fA/pA-calibration like voltageramp-capacitor-calibrators and electron pumps.

[MegaVolt]

That's name is EK1-6

An interesting device. But there are no documents for him.
The only thing that could be found is the mention of the relay with an amber insulator. http://www.155la3.ru/rv4.htm

[bsw_m]

Input commutator from V7-49 (edited due error in instrument model name)
And may be amplifier U5-11

[Kirill V.]

It's very cool, it's associated with science and it's something that can't be repeated at home.
It is interesting to note that this device has a lot more secrets than it seems. The angle at which the switch contacts meet is selected to avoid bouncing. Contacts have a gold coating or are made of gold completely. Numerous metal screens are designed not so much to protect against electromagnetic interference, but to reduce the capacitance between the contacts. The case is made of stainless steel for a reason - only stainless steel has minimal contamination with radioactive impurities. Radioactive particles fly out of the housing material and ionize the air around the sensitive circuits. In Soviet electrometric equipment, this was taken into account.

[bsw_m]

After EK1-6 (very old), MNIPI developed new one calibrator for high resistance an low currents: NK4-1

[strannik2039]

Hello dear forumites. I apologize in advance for Google translation.
Since it was about old Soviet devices, I will share some photos. This is a capacitor from a differentiator ЕК1-6
The small current calibrator itself consists of a linearly variable voltage generator and a set of differentiators with capacitors of different small capacity.

[bsw_m]

Hello dear forumites.

Glad to see You Vladimir in this topic! Thanks for your photo integrating capacitor from differentiator of EK1-6

[Kirill V.]

How is the capacity of this capacitor adjusted?

[strannik2039]

It 's a constant capacity capacitor. The plates are positioned with a clearance of 0.3 millimeters between them.

The structural diagram is ЕК1-6 attached.

[Vgkid]

Thanks for all of these posts, and keep posting more.
I remember reading about using saphire insulators in a nbs document from the 1940's I believe.
Looks like fused quartz has replaced it.

[strannik2039]

Hello. We continue to discuss electrometric voltmeters. I think you 've read books like:
1.ТЕХНИКА  ЭЛЕКТРОМЕТРИИ   Илюкович А.М.    1976г. ( ELECTROMETRICS TECHNIQUE Ilukovich A.M. 1977. )
2. ПРИБОРЫ ДЛЯ ИЗМЕРЕНИЯ МАЛЫХ НАПРЯЖЕНИЙ И ТОКОВ   Алексантров В.С.,  Прянишников В.А.  1971г.  ( DEVICES FOR MEASUREMENT OF LOW VOLTAGES AND CURRENTS Aleksantrov V.S., Spinnishnikov V.A. 1971. )
3. ЭЛЕКТРОННЫЕ ГАЛЬВАНОМЕТРЫ ПОСТОЯННОГО ТОКА Алексантров В.С.,  Прянишников В.А.  1974г.  (ELECTRONIC DC GALVANOMETERS Aleksantrov V.S., Spinnishnikov V.A. 1977.)
4.  ИЗМЕРЕНИЯ В ВЫСОКООМНЫХ ЦЕПЯХ  ( 2 издание )Грибанов Ю.И.  1967г.  (MEASUREMENTS IN HIGH-OHM CIRCUITS (2 edition) by Kruanov Yu. )
Even though the books are old, they are still relevant. Next, I think with a triaxial cable and the same connector, you know each other. To create a voltmeter with them first of all it is necessary to decide. Further on devices. Of those done in the USSR and done in Belarus:
A2-4  10A - 14A
B7-29  10E-17A
B7-30  10E - 15A
В7Э-42  10E - 15A
B7-45  10E - 17A
B7-49  10E - 15A
B7-57/1  10E - 15A
B7-57/2  10E - 17A
All MNIPI devices. There 's a description on the internet for some.
As for KEITHLEY, this is of course 617 and 642. The description is on the Internet. On these voltmeters you can read and learn a lot.
I also recommend to read the articles of Dvornikov Oleg Mikhail. Next, look at these editions

https://dspace.ut.ee/discover?scope=%2F&query=электрометрия&submit=

There 's a lot of interesting stuff in them. Especially author Anso.

[MegaVolt]

The small current calibrator itself consists of a linearly variable voltage generator and a set of differentiators with capacitors of different small capacity.

How to keep the current stable when the load changes.
And how do you manage to keep the current constant? After all, sooner or later, the linear voltage will not be able to grow further?

[MegaVolt]

2. ПРИБОРЫ ДЛЯ ИЗМЕРЕНИЯ МАЛЫХ НАПРЯЖЕНИЙ И ТОКОВ   Александров В.С.,  Прянишников В.А.  1971г.  ( DEVICES FOR MEASUREMENT OF LOW VOLTAGES AND CURRENTS Aleksantrov V.S., Spinnishnikov V.A. 1971. )
3. ЭЛЕКТРОННЫЕ ГАЛЬВАНОМЕТРЫ ПОСТОЯННОГО ТОКА Александров В.С.,  Прянишников В.А.  1974г.  (ELECTRONIC DC GALVANOMETERS Aleksantrov V.S., Spinnishnikov V.A. 1977.)

These books could not be found electronically. Maybe you have one?