Circuit design of branded electrometers - Page 1
Forum section: electronics / general

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 29, 2020, 05:01:52 pm
content: Hi friends,I want to study the question of building a voltmeter with a high input resistance. You will help me very much in this if you name the models of industrial voltmeters that have manuals with diagrams in the public domain. You just know a lot more about Western measuring equipment than I doThe main requirement - the device must be from the transistor era, even better if it is built on operational amplifiers. This is much easier to analyze than dealing with vacuum tubes circuitry.Well, I'll tell you what I'm most interested in. The biggest problem is to provide a path for the operational amplifier's bias current to drain. I want to know how this is implemented in industrial voltmeters.Thanks.

author: tkamiya
author_rank: Super Contributor
timestamp: January 29, 2020, 05:26:46 pm
content: There is a very nice application note here. While this is not about a production model, it meets your needs almost exactly.http://www.ti.com/lit/an/snoa620/snoa620.pdf

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 29, 2020, 06:00:35 pm
content: Thanks, tkamiya!Let's look at a simple bufferThis is so primitive that it does not need comments, and if I wanted to make my voltmeter exactly like this, I would not ask for help on the forumPreviously, dear David Hess recommended me app note 242, which describes a trick to increase the equivalent input resistance:We disconnect the lower end of the leakage resistor from the ground and feed it an auxiliary potential, in-phase and proportional to the input voltage. For example, if the auxiliary voltage is half the input, the equivalent input resistance is doubled with the leakage resistor unchanged.Is there a brand voltmeter that uses this trick?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 29, 2020, 07:51:14 pm
content: Download the manual for the Keithley 610 or similar model. They use a floating scheme that's very effective and it will also measure charge.

author: MiDi
author_rank: Frequent Contributor
timestamp: January 29, 2020, 08:05:05 pm
content: Take a look at the Keithley 617 electrometer.Design is from mid 80s, couple of things are a bit outdated, but principle remains.The manual includes circuit description and schematics.Valuable information and some improvements to the Frontend are described in theK617 Thread.

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 29, 2020, 09:29:53 pm
content: Ok, thanksOh, the K617 circuit is what's causing me a headache. I've looked at it several times, trying to understandI much prefer the old HP manuals, everything is absolutely clear, clear flowcharts, detailed notes on the diagram, and so on.Yes, floating topology and bootstrapped supply are classics, I know that. There are no alternative solutions?

author: MadTux
author_rank: Frequent Contributor
timestamp: January 29, 2020, 11:15:12 pm
content: I find Keithley 617 input stage rather easy to understand, schematics are great IMO, too.Basically isolated gate FET pair as differential amplifier for input, that keeps itself at input potential by driving +/- 210V transistor amplifier.Perhaps find a broken K617 on ebay, fixing it usually helps understanding itKeithley electrometers are rather simple in principle, if you want something more hardcore, try understanding HP 3456A AC converter for example

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 29, 2020, 11:26:11 pm
content: Yes, I understand the operation of the device in General terms. But I'm trying to trace the path of the signals through various sheets on the diagram and alphanumeric links. I want to understand the nuancesI think I'll try it again

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 30, 2020, 01:24:13 pm
content: Yes, apparently, you are right, it is easier than it seems. A 250 GOM resistor is used to drain the bias current.It remains to understand what COM and Signal Ground are and why there is a 100 Ohm resistor between them. And perhaps a few more nuances.K617 input buffer manages its own power supply and guarding. But sometimes a separate buffer is used for supply and guarding management, and input signal buffering is assigned to a separate operational amplifier. What is the difference between such topologies?

author: Stray Electron
author_rank: Super Contributor
timestamp: January 30, 2020, 02:20:17 pm
content: Quote from: Kirill V. on January 29, 2020, 05:01:52 pmGo look for that subject in the archives of the Hewlett Packard Journal and the Hewlett Packard Application Notes. I can't say what they have regarding electrometers but they most likely covered them. The other good thing about the HP stuff is that there is often a FULL service manual available so you can study every inch of the schematics and get exact descriptions of the parts and usually even who supplied them to HP. The old General Radio (aka GenRad aka GR) articles are also very good but harder to find.

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 30, 2020, 03:02:46 pm
content: Okay, I'll look at these sourcesI will describe my own idea in General terms.I have a lovely large laboratory voltmeter with a very low input resistance ( starts at 100 Ohms at the 7.5 Volt range). At first I wanted to make a simple external buffer prefix, but then I wanted more, and to achieve as high an input resistance as possible with my home capabilities and zero experienceNow I have started studying the K617 circuit again, and suddenly I see that this is very similar to my idea. In General, it is very simple. But if the voltmeter input floats... the ideal voltmeter should show zero in this case. In order for this to be the case in reality, it is necessary to provide a path for the bias current, while the voltage drop on the leakage resistor should not be shown by the voltmeter. That's my problem

author: MiDi
author_rank: Frequent Contributor
timestamp: January 30, 2020, 06:23:44 pm
content: For example if there is 1fA input bias and 1Gohm input resistance, this contributes only 1uV offset voltage.So it depends on your requirements for max voltage error and min input resistance when "floating".

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 30, 2020, 08:30:14 pm
content: So, in 2016, I bought AD549LHZ for my future projects. All this time it was lying in my box with nothing to do. Suddenly, today I wanted to test it and conduct some experiments. Especially for this purpose, I had prepared a Board with aluminum foil, an antistatic bracelet and a Bernstein ESD tweezers.I put together a circuit with a unipolar supply and a resistive divider to form the midpoint of the supply. The non-inverting pin is bent 90 degrees and does not touch anything around it.I also have a homemade cable Assembly made by RG-174 coaxial cable and alligator clips.You can see the 4700 pF capacitor and the clips from the alkaline battery (gives 6.1 Volt, because used) connected to the wires insulation. The leakage current charges the capacitor and the AD549 buffers the voltage. I measured the current using the integration method.Current about 1.4-1.5 pA, therefore, insulation resistance more 4 POhm.I've been want to make picoammeter with this amplifier. Suddenly, quite unexpectedly, I made it in half an hour. WOW!!!Now I can experiment with the design of the electrometer. And picoammeter. And ohmmeter too

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 30, 2020, 09:38:28 pm
content: Quote from: MiDi on January 30, 2020, 06:23:44 pmYes, of course. but the K617 has an input resistance in the TOhm range, while the circuit does not have a single resistor with this rating. The floating resistor is the secret. But I don't understand why this idea doesn't lead to strong drift and negative feedback persists even with floating input

author: MiDi
author_rank: Frequent Contributor
timestamp: January 30, 2020, 10:17:34 pm
content: The 250Gresistor is only able to deliver a couple of +-10s fA, so 1% drift in this current source converts to drift of sub-fA only.Do not understand what you mean by nfb persists - in voltage mode the frontend is just a buffer and the power supply is referenced to this.Do not expect that the voltage stays near 0V when the input is floating...

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 30, 2020, 11:04:00 pm
content: If the buffer operates within a constant supply voltage, then we can force the bias current to flow through the external resistor, rather than through the signal source, if the potential difference between the ends of the resistor corresponds to Ohm's law. This can be achieved using a potentiometer. And any drift related to the input will appear at the output of the buffer with a transfer coefficient of one. The buffer output does not affect the potential at the right end of the bias compensation resistor.And if the supply voltages now follow the buffer output, how does this technique work in this case?

author: MiDi
author_rank: Frequent Contributor
timestamp: January 31, 2020, 08:11:05 am
content: Quote from: Kirill V. on January 30, 2020, 11:04:00 pmSimply connect OP1 output to the GND of supply rails.This GND is than bootstrapped and should not be confused with Signal GND.

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 31, 2020, 11:28:45 am
content: Now it is necessary that the OP1 output controls the external output stage, and the inverting input monitors the load voltage. I showed the diagram above. When nothing is connected to the input, the op-amp cannot compensate for its own drifts because the inverting input is outside op-amp power railsI redrawn the diagramNow the leakage resistor is located between the op amp inputs and any drifts are amplified by open loop gainOr do I not understand something?

author: MiDi
author_rank: Frequent Contributor
timestamp: January 31, 2020, 12:02:17 pm
content: Quote from: Kirill V. on January 31, 2020, 11:28:45 amThere are two power supplies involved, the bootstrapped one for Frontend (+-5V referred to buffer output ~=Signal HI) and the second one for the LOAD (+-210V referred toSignal GND/LO) - the LOAD is input impedance of ADC.Edit:When nothing is connected to the input, the effective input bias-current will load the input impedance and create a voltage drop on it.Lets assume the input impedance is 1Tand the effective input bias-current is 1pA, then the output voltage will settle to 1V, for 1Pit would theoretically settle to 1000V.1000V is outside the range of Signal GND referred power supply (+-210V) and the output will clip at around this rails.

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 31, 2020, 01:17:02 pm
content: Yes, separate coil of transformer with one-half rectifier and 78/337 regulators. It's like two small batteries on my circuit, right? Potentiometers of offset voltage and bias current adjustment refers to this supply.In other words, the voltage drop on the isolation of the input circuit is perceived by the buffer as a input signal and gives to the output?By the way, what can I make a multi-gigaohm resistor from? Two lengths of insulated wires intertwined? Or a piece of FR-4?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 31, 2020, 01:54:25 pm
content: I'd also like to know how to DIY high value resistors. Making a bad one is easy, but making one that's stable with time, temperature and humidity is much harder. As a first go, try mixing some powdered pencil lead with epoxy or lacquer and painting it between two traces on a piece of PCB. The type (#) and quantity of pencil lead in the mix will determine the value.

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 31, 2020, 02:00:49 pm
content: Cool, this will be a thick-film resistor. This is how they were made in hybrid integrated circuitsI have a graphite suspension with glue

author: MiDi
author_rank: Frequent Contributor
timestamp: January 31, 2020, 04:04:32 pm
content: Quote from: Kirill V. on January 31, 2020, 01:17:02 pmCorrect.First I was a bit confused what you meant by drift related to the input, to be clear, this is not drift - it is interaction of input bias current with input impedance.This impedance consists of the resistive part and the capacitive part, the capacitive part will be charged by the bias current, so the output "drifts" - or better said settles - to the final value given by the resistive part.As you already noticed, if the output hits the high voltage rails, the NFB does not persist.This leads to a voltage difference of the op amp inputs and finally will be clamped either by protection circuit between the inputs or to the bootstrapped power supply rails.When the protection kicks in, the input impedance will drop dramatically.To protect the protection circuits from to high currents there is the need for current limiting the inputs, this is simply achieved by putting a suitable resistor at each input (most op amps are rated for 10mA absolute max).If a specific resistor with specific properties is needed, I would recommend to buy one - up to 10Gare awailable for ~1EUR with not to shabby specs.

author: serg-el
author_rank: Regular Contributor
timestamp: January 31, 2020, 04:11:16 pm
content: Кирилл, посмотри здесь.Схема похожа на то, что ты ищешь.Cyril, look here.The circuit is similar to what you are looking for.http://bbs.1ppm.cn/topic/276/%E8%87%AA%E5%88%B6%E6%8C%87%E9%9B%B6%E4%BB%AA%E7%9A%84%E6%80%9D%E8%80%83-some-thoughts-on-diy-null-meter/16

author: guenthert
author_rank: Frequent Contributor
timestamp: January 31, 2020, 05:10:54 pm
content: Quote from: Kirill V. on January 30, 2020, 08:30:14 pmOn a breadboard? That is, er, quite remarkable.

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 31, 2020, 05:16:08 pm
content: Quote from: guenthert on January 31, 2020, 05:10:54 pmThe non-inverting input hangs in the air, the signal is received via a coax cable with polyethylene insulation, the external shield is connected to the buffer output and guarding forms. Nothing remarkable, the classic construction of measuring instrumentsUpdate:I made a mistake when working with decimals, sorry. There's about 14-15 pA, not POhms, of course. But the breadboard has nothing to do with it

author: Kirill V.
author_rank: Regular Contributor
timestamp: January 31, 2020, 06:55:07 pm
content: Quote from: MiDi on January 31, 2020, 04:04:32 pmOk, thanks. In fact, the parasitic leakage resistance and the bias current compensation resistor form a voltage divider. This can be represented by an equivalent circuit. Please note that this is not bootstrapped supply:We can achieve zero output with two independent adjustments. But the bias current, offset voltage and all resistances drift with time and temperature. Here any drifts referred to the input are multiplied by the noise gain equal to one.Now equivalent circuit with BS supplyHere, a positive feedback is formed through the parasitic leakage resistance and the bias current compensation resistor. This is what confuses meUpdate:The diagram I drew exactly corresponds to the ohmmeter mode. This means that if there is the slightest mismatch in the bias current compensation, the difference current will flow through the insulation of the input circuit. This means that with significant input circuit resistances, the adjustment must be very fine and painstaking. And the difference current will still appear over time and temperature changes. Correct me if I'm wrong

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 01, 2020, 03:49:47 pm
content: Quote from: serg-el on January 31, 2020, 04:11:16 pmThank you, Sergey, I will study this. А вы нарочно пишете по-русски на международном форуме?!Friends, is there any difference between styrene and polystyrene capacitors?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 01, 2020, 03:57:21 pm
content: Quote from: Kirill V. on February 01, 2020, 03:49:47 pmNo there is no difference, just a shortened name. Just simple styrene is a liquid. It is the polymer that is used to make styrofoam, capacitors and some cheap plastics.Keep in mind they don't like higher temperature and most solvents.

author: serg-el
author_rank: Regular Contributor
timestamp: February 02, 2020, 11:02:08 am
content: PTFE wire test. Useful.https://misrv.com/teflon-wire-test/

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 02, 2020, 07:19:17 pm
content: Quote from: MiDi on January 30, 2020, 10:17:34 pmOkay, now tell me, friends, what does the carefully adjusted and long-warmed K617 with float input show on the display? As well as other electrometers that you are dealing with. Is there a significant difference with the connected cable and without it?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 02, 2020, 08:52:59 pm
content: Like with other very high input impedance meters, the expected behavior with an open input is drift of the displayed voltage. How much depends on the individual instrument. The slower the drift the better - as the drift rate is given by input current divided by input capacitance Adding a cable chances are the drift would slow down as the cable adds capacitance. If the cable is poor quality (poor isolation) the voltage may stabilize.

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 02, 2020, 09:24:18 pm
content: Thanks, Kleinstein. That's what I meant - drift. So it's inevitable.

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 08, 2020, 12:05:48 am
content: How does the K617 electrometer implement the SUPPRESSION function-at the analog or digital level?

author: MiDi
author_rank: Frequent Contributor
timestamp: February 08, 2020, 01:45:13 am
content: It is just as Nulling on DMMs, so only digital math.

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 08, 2020, 03:18:58 pm
content: Then if the digital part subtracts from the ADC result ,say, 10 Volts, and the input voltage is 200 Volts, then the display will show 190 Volts, but the analog part is already working almost at the limit, right?Nulling/suppression at the analog level has some important advantages?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 08, 2020, 03:52:27 pm
content: There is not much advantage to get nulling at the analog side. There could be a small advantage to have a crude offset adjustment at the analog side, as the offset tends to be temperature dependent and often, but not always with FET circuits the temperature effect is larger when the offset is large. So the analog "offset" trim is more like a TC trim. The digital zero also includes later effects all the way to the ADC. The big advantage there is that is can be fast and does not need a trimmer that may be drifty.The offset compensated by the digital part should be more like < 500 mV, not 10 V. A main part would be a difference in FET gate threshold.

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 08, 2020, 05:35:39 pm
content: Why often do not use the offset adj. pins of the operational amplifier? The question is not related to the suppression function

author: MiDi
author_rank: Frequent Contributor
timestamp: February 08, 2020, 05:53:42 pm
content: If adj. Pins are used, most of these op amps suffer from elevated noise and drift introduced from adj. circuit.Nowadays in most situations just choose an op amp that meets offset voltage requirements.For volume production it is simply a cost factor to manually adj. something.It is much cheaper to do a full digital and automated factory calibration.

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 08, 2020, 06:59:04 pm
content: But the external offset adjustment circuit also has its own noise and drift. What are the advantages?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 08, 2020, 07:32:50 pm
content: Most modern OPs often don't have the Offset trim pins anymore. They are rarely used as the factory adjustment / precision got better - 100 µV offset specs are no longer that special. In addition the offset pins can add noise, pic up hum and effect the frequency response.There is still some use to analog offset trim in OPs. Especially with BJT based OPs the offset trim also gets a low temperature drift So something like the old 741 can get low drift (e.g. 0.5 µV/K range) if the offset is trimmed to zero.There are a few, rare examples where the offset pins can be used for alternative uses not originally intended (e.g. as a FB to get a kind of instrumentation amp, or to add a correction signal from another circuit).

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 08, 2020, 08:26:04 pm
content: Let's discuss the compensation of the bias current. The K617 implements temperature-dependent correction using two thermistors, right? I propose for this purpose an IC temperature sensor with a known dependence of the output voltage. It is possible to enter a scale factor with the desired sign using the op-amp.What do you say?

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 09, 2020, 02:38:32 pm
content: I would also like to learn about the noise aspects when using bias compensation similar to K617

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 18, 2020, 07:36:34 pm
content: Two thermistors in the bias current compensation circuit - I'm interested in the type and specifications

author: MiDi
author_rank: Frequent Contributor
timestamp: February 19, 2020, 11:59:00 am
content: Quote from: Kirill V. on February 09, 2020, 02:38:32 pmThere are mainly two noise sources from bias compensation, thermal current noise from impedance (essentially the 250Gresistor) and voltage noise from supply that transforms to current noise through the resistor.You want to keep the current noise contribution of bias compensation low.Maybe it is not that important for electrometer application as there is large contribution to current noise from charged particles picked up by the input.Quote from: Kirill V. on February 18, 2020, 07:36:34 pmI guess there is nothing special on these 100k thermistors, they are for (partially) compensation of change of bias current of input JFET over temperature.The glass encapsulation helps to reduce long term drift and effect of humidity and maybe pressure.

author: Kirill V.
author_rank: Regular Contributor
timestamp: February 19, 2020, 01:21:26 pm
content: Thanks MiDi. Yes, it looks quite clear and logical. I just compare my view of this with the opinion of professionals.QuoteCurrent noise flowing through the high internal resistance of the signal source can cause noise voltage, but parasitic capacitances that create a low-pass filter come into play. This is a nice bonus from parasitic parameters:)I want to develop a temperature-dependent system similar to these two thermistors but using a temperature sensor. While I am at the stage of brainstorming. It is quite enough if it will work in a narrow temperature range near the room (like the K617, which has a working temperature range of only 18-28 degrees).

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 19, 2020, 05:02:25 pm
content: Sorry for a slightly offtopic question, but I got a broken Keithley 617 recently and before I start to repair it: Does anyone know if they used cadmium solder inside? I also got a triax cable for the 617 (quite new, from 2007) with a sheet of paper with declares, that the cables and wires contains Cd.

author: MiDi
author_rank: Frequent Contributor
timestamp: February 19, 2020, 09:37:29 pm
content: Quote from: Kirill V. on February 19, 2020, 01:21:26 pmI have to regret, I am not a pro, just hobbyist.As stated earlier, the K617 is a mid 80s design, today one would use appropriate jfet op amp, which were not awailable back in the days - e.g. LMC662, LMC6001 and if you want to get serious: ADA4530-1.You should ask yourself what your requirements are and if it is necessary to develop a temperature compensation or just use a better op amp.Do not forget that appropriate high value resistors are expensive and cost more than even the pricey ADA4530-1, so if you can omit bias compensation completely, this will save you cost.Quote from: e61_phil on February 19, 2020, 05:02:25 pmPhilipp,I would be afraid if there is Cd-solder used, I hope that it is only common solderCd-solder would not make any sense, because there is no need for low T-EMF - and with respect to the design and layout: it makes even lesser sense.Maybe your question is better suited in theK617-Thread.Which cable are you talking about?

author: David Hess
author_rank: Super Contributor
timestamp: February 20, 2020, 07:17:28 pm
content: There is another way to make a high voltage electrometer input stage *without* bootstrapping. A varactor diode input stage is limited only by the breakdown of the isolation transformers:https://www.electronicdesign.com/technologies/analog/article/21801819/whats-all-this-varactorinput-amplifier-stuff-anywayAC coupling also reduces flicker noise.

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 13, 2020, 11:31:08 am
content: I have not viewed this topic for a long time and it turned out that you wrote a lot of interesting things, thank you!Yes, I know about these old methods. I will tell you in confidence that the USSR has written excellent books on this issue at a very high quality scientific level. It describes a large number of original solutions. I think that even experienced engineers on this forum do not know the things that are available to me in these booksVaractors, ceramic converters, vibrating capacitors, air capacitors with amber insulators, methods for measuring the triboelectric effect, electrometer-grade vacuum tubes , and so on... Small-current radioactive sources , ionization chambers for generating small currents...I have another question about K617. Why do some verification procedures require a jumper between the COM terminal and the chassis?

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 14, 2020, 05:43:11 pm
content: 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 14, 2020, 06:13:26 pm
content: 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.

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 15, 2020, 12:05:08 am
content: 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

author: antintedo
author_rank: Contributor
timestamp: March 15, 2020, 01:45:01 am
content: Quote from: Kirill V. on March 14, 2020, 05:43:11 pmKeithley 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

author: MiDi
author_rank: Frequent Contributor
timestamp: March 15, 2020, 06:51:09 am
content: The second transformer sits on EM-Board and powers the bottom ADC-Section (hidden) over ribbon cable too.Quote from: Kirill V. on March 13, 2020, 11:31:08 amGood question, in principle it should not matter when source is floating.Maybe it is just for safety against hazardous CM voltages on floating part.

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 15, 2020, 10:28:14 am
content: 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 lyricsKeithley 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

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 22, 2020, 07:41:37 pm
content: Quote from: MiDi on March 15, 2020, 06:51:09 amI 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?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 23, 2020, 11:51:05 am
content: Quote from: Kirill V. on March 15, 2020, 10:28:14 amHere is a document with a description that was found on Russian forums.https://yadi.sk/d/c3s0VnoaC7MKSThe device is on sale and not very expensive. About $ 1000 considering that it is capable of measuring up to 10^-17A (10aA)

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 23, 2020, 01:07:48 pm
content: 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.Quote from: MegaVolt on March 23, 2020, 11:51:05 amIn 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

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 23, 2020, 01:22:57 pm
content: Quote from: Kirill V. on March 23, 2020, 01:07:48 pmHa ha)) It’s cheap with respect to electrometers of other companies with the same parameters.

author: bsw_m
author_rank: Frequent Contributor
timestamp: March 24, 2020, 07:51:51 pm
content: Quote from: Kirill V. on March 23, 2020, 01:07:48 pmThat's name is EK1-6Some 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.

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 25, 2020, 12:14:09 am
content: 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.

author: Echo88
author_rank: Frequent Contributor
timestamp: March 25, 2020, 05:28:21 am
content: 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.pdfThe 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.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 25, 2020, 08:15:17 am
content: Quote from: bsw_m on March 24, 2020, 07:51:51 pmAn 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

author: bsw_m
author_rank: Frequent Contributor
timestamp: March 25, 2020, 10:08:05 am
content: Input commutator from V7-49 (edited due error in instrument model name)And may be amplifier U5-11

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 25, 2020, 01:50:06 pm
content: 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.

author: bsw_m
author_rank: Frequent Contributor
timestamp: March 25, 2020, 02:49:11 pm
content: After EK1-6 (very old), MNIPI developed new one calibrator for high resistance an low currents: NK4-1

author: strannik2039
author_rank: Contributor
timestamp: March 25, 2020, 04:54:34 pm
content: 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 ЕК1-6The small current calibrator itself consists of a linearly variable voltage generator and a set of differentiators with capacitors of different small capacity.

author: bsw_m
author_rank: Frequent Contributor
timestamp: March 25, 2020, 04:58:49 pm
content: Quote from: strannik2039 on March 25, 2020, 04:54:34 pmGlad to see You Vladimir in this topic! Thanks for your photo integrating capacitor from differentiator of EK1-6

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 25, 2020, 07:04:52 pm
content: How is the capacity of this capacitor adjusted?

author: strannik2039
author_rank: Contributor
timestamp: March 25, 2020, 07:18:25 pm
content: 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.

author: Vgkid
author_rank: Super Contributor
timestamp: March 25, 2020, 08:36:13 pm
content: 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.

author: strannik2039
author_rank: Contributor
timestamp: March 27, 2020, 04:24:20 am
content: 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 - 14AB7-29 10E-17AB7-30 10E - 15AВ7Э-42 10E - 15AB7-45 10E - 17AB7-49 10E - 15AB7-57/1 10E - 15AB7-57/2 10E - 17AAll 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 editionshttps://dspace.ut.ee/discover?scope=%2F&query=электрометрия&submit=There 's a lot of interesting stuff in them. Especially author Anso.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 27, 2020, 07:39:31 am
content: Quote from: strannik2039 on March 25, 2020, 04:54:34 pmHow 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?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 27, 2020, 08:19:15 am
content: Quote from: strannik2039 on March 27, 2020, 04:24:20 amThese books could not be found electronically. Maybe you have one?

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 27, 2020, 09:23:42 am
content: Quote from: MegaVolt on March 27, 2020, 07:39:31 amThe current does not depend on the load because the capacitor resistance for DC is very large, this resistance becomes the internal resistance of the source. This source is very close to idealThis source works periodicallyI have book DEVICES FOR MEASUREMENT OF LOW VOLTAGES AND CURRENTS electronically

author: strannik2039
author_rank: Contributor
timestamp: March 27, 2020, 10:27:57 am
content: Calibrators are ЕК1-6 and НК4-1 old. Especially ЕК1-6 (1979). From them the DC source is formed in two ways. Up to 0 .1- 1nA is a source of constant voltage U and a set of resistances R. Further according to formula I = U/R. Low limits are provided by linear voltage generator and differentiators. Current is equal in this chain to I=C ∙∆U / ∆t it simply from the theory. The device generates different output voltage and time intervals, at the end of which output voltage is disconnected and differentiators are discharged. If during this time the device could not be removed, everything is repeated with intervals for discharge. It 's in general about the principle of work.

author: strannik2039
author_rank: Contributor
timestamp: March 28, 2020, 09:21:51 am
content: Hello. As promised, the book of Alexandrov, Spynishnikov "Electronic DC galvanometers." In addition, part of the description is ЕК1-6 during current reproduction.https://drive.google.com/drive/folders/1vome9_QqLaweis-r045eWefezxteb9ju?usp=sharing

author: Kirill V.
author_rank: Regular Contributor
timestamp: March 28, 2020, 01:30:08 pm
content: I also want to show a sample of engineering art - this is the input unit of the V7-30 electrometerhttps://radikal.ru/lfp/s15.radikal.ru/i189/1104/d6/a0c2f7456d8e.jpg/htmThe input stage is made on two MOSFETs. Soviet industry did not produce pairs of such transistors and single transistors were selected in pairs manually. These are gold-plated cases in the photo, and you can also see two bipolar transistors in black cases that protect the input from overvoltage.More photo of this electrometerhttp://kxk.ru/dustyattic/v20_700390_16.php

author: strannik2039
author_rank: Contributor
timestamp: March 28, 2020, 05:25:45 pm
content: Hello. Old lamp light.I like these indicators.According to the MNIPI album, this voltmeter was released in 1978. But the design of MNIPI (Minsk Research Instrumentation Institute) cannot be repeated because of their input switches. This product was done by the institute itself. If you look towards KEITHLEY 617 for example, we see the herkon switches that can be bought now. And so, on the principle of work, the instruments are little different. Voltage drop across resistor due to low current flow and feedback.As for pairs of transistors, there were also such.In В7Э-42 for example stood hybrid assembly НТ002.On Google disk I showed the diagram of the input device of the electrometer В7Э-42

author: strannik2039
author_rank: Contributor
timestamp: March 29, 2020, 08:14:59 am
content: Hello. As a continuation of the theme of В7-45, I created a folder in which I showed a pair of photos of the remote 1Е-15А dynamic capacitor unit and the measurement limit, and patents for dynamic capacitor and input device (Шуклин and ВХОДНОЕ УСТРОЙСТВО).https://drive.google.com/open?id=1-YYb--vVrcen3OqlZ5mA3dBsl4o4uw_bOf course, it is not possible to repeat this at home. But here at the limit of measurement I would like to stop. Today, manufacturers are seeking to switch to so-called "long scales." It 's beautiful, I don 't argue. But if you look deeper, how true is that? Let 's present a web device with 0.000000Е-12А readings. Looks beautifully. But, the difference between 1E-12A and 1E-18A is 1000000. And the measurement error at a given limit 1Е-12А say 0.1% is 0.001 of the limit. So we 're better than 0.001Е-12А. But everything else seems to be in doubt.Now let 's look at the 1Е-15А range and the error of 0.1%. Now we have 0.001Е-15А. Here 's a truer statement. Of course it 's just math. But all this is to the fact that when developing the instrument, it is necessary to decide on the circuitry of the electrometric amplifier.

author: strannik2039
author_rank: Contributor
timestamp: March 29, 2020, 03:44:44 pm
content: I mentioned the University of Tartu and the surname Anso for a reason above. In principle, there are many articles in the publications of the university. But there is work in which he summarized everything and defended his thesis.The work is called:"DEVELOPMENT OF BASIC DESIGN OF SMALL CURRENT METERS WITH HIGH SPEED RESPONSE ON THE BASIS OF HIGH-OHM MEASURING RESISTORS" (РАЗРАБОТКА ОСНОВ КОНСТРУИРОВАНИЯ ИЗМЕРИТЕЛЕЙ МАЛЫХ ТОКОВ С ПОВЫШЕННЫМ БЫСТРОДЕЙСТВИЕМ НА БАЗЕ ВЫСОКООМНЫХ ИЗМЕРИТЕЛЬНЫХ РЕЗИСТОРОВ)https://drive.google.com/open?id=1_lvb3UCbdrooXv3b7DbDMHjtKGJyHnHOTo be honest, there were doubts whether this work should be posted on the forum. But I hope she 's useful to anyone.

author: strannik2039
author_rank: Contributor
timestamp: March 31, 2020, 04:23:40 am
content: Hello. Something came silence on this branch of the forum.Did I so scare the forum with my photos of old Soviet equipment?Yes, I repeat such a house not to do, but it is not necessary to do it. You can look at the Pomona website and find the connectors, and the cable.https://www.pomonaelectronics.com/products/connectors/rf

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 01, 2020, 12:56:11 pm
content: The silence came because forum participants know nothing but Keithley instruments and a single source of information - low level measurements handbook.And personally I am engaged in reading Soviet books and designing my future electrometric buffer for a DMM based on the AD549I suggest that we continue to frighten local residents with Soviet devices. They already know our bears, but electrometers are unlikelyI would very much like to discuss why manufacturers use printed circuit boards to conduct input circuits. What own current can be generated by the Board material and what is the influence of environmental factors. But I know it's impossible, because those who know won't say anything

author: MegaVolt
author_rank: Frequent Contributor
timestamp: April 02, 2020, 09:26:01 am
content: Quote from: Kirill V. on April 01, 2020, 12:56:11 pmI think many will be grateful for the new well-structured information on how to make electrometers correctly.

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 02, 2020, 10:33:45 am
content: Yes, this is probably the only place where such devices are discussed and where there are unique photos.After the collapse of the USSR, a huge number of unique devices were destroyed for scrap. Nevertheless, some concerned people have made their contribution to preserving knowledge about this equipment - detailed photos and documentation. And we are talking about very ancient equipmentI don't see anyone here offering to look at ancient devices or talk about their circuitry. Where are the photos of Cary Instruments electrometers? Old Takeda Ricken? English, GDR, FRG devices? Yokogawa? Or at least links?Why didn't anyone mention vacuum tubes in floating grid mode? These old tubes had a bias current less than that of modern op-amps. Attoampere range currents were measured back in the 60s, but no one mentioned these techniquesWhere are the books on Electrometry in English? Where are the links to the IEEE articles?Only guys from Belarus offered information and unique photos

author: strannik2039
author_rank: Contributor
timestamp: April 02, 2020, 04:57:42 pm
content: Hello forumites. Thank you Kirill V. for the kind words.I apologize for absence. The tooth decided to show its character.He had to explain who was in charge.By the way, dentistry is one of the directions of electrometrics. But that 's the way it is.Now let 's get back to the boards. To be honest, there 's no great choice. If we take the same KEITHLEY 617 for example, we see Teflon racks in important places.https://www.google.com/search?rlz=1C1ASUM_enBY845BY845&q=KEITHLEY617&tbm=isch&source=univ&sa=X&ved=2ahUKEwja-evl6sjoAhVoiYsKHeFzCkUQsAR6BAgJEAEIf you look at 6517,https://xdevs.com/fix/k6517a_u2/'s where we see the protectors on the board to prevent leaks.And if you look at the board В7-49https://drive.google.com/open?id=1Xy1Bgb5u_dvljgYzZz7XzpQNcl9yN7VY, we will not see varnish in the area of the input device of the electrometer at all. This is done to reduce leakage currents across the varnish coating. And since the switch is of its own design, neither props nor Teflon racks are required.

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 02, 2020, 05:37:35 pm
content: Wow, you never cease to amaze with your richesWhy does B2987A not have Teflon?https://xdevs.com/doc/HP_Agilent_Keysight/B2987A/img/bem_eopen.jpgAnd if it's really so cool, why haven't they done it before? That's what worries me

author: razvan784
author_rank: Regular Contributor
timestamp: April 02, 2020, 08:46:24 pm
content: Quote from: Kirill V. on April 02, 2020, 05:37:35 pmLook carefully at the board. It's not the usual FR-4 material. It looks more like something used for microwave PCBs. It might even be teflon-basedAlso, leakage is drastically reduced by driven guard rings.This being said, the B2987A is not really a metrology-grade instrument and is not marketed as such. It's marketed as a "Femto/Picoammeter", it is quite clearly specified with a 3fA uncertainty on its lowest range, and therefore you shouldn't expect it to be comparable to a metrology-grade device that measures attoampsThe construction is good enough for 3 fA it seems.

author: strannik2039
author_rank: Contributor
timestamp: April 04, 2020, 03:17:12 pm
content: Hello. This electrometer is positioned as a 10Е-17А current meter (0.01 fA minimum measurement resolution). It is difficult for me to judge such a statement without having an instrument.But I can quote lines from the В7-45 description. If the input resistance of the electrometric unit is not less than 10Е+16 Ohm and the input capacity is not more than 30pF the equivalent input resistance of the voltmeter is more 10Е+19 Ohm, and the input capacity is not more than 0. 6pF taking into account the negative feedback. All these values are provided by sapphire insulators. And this electrometer measures the currents from the 10Е-17А.I think that if the designers B2987A put teflon insulators and make props in the board in responsible places and applied electrometric Reed relay, such an electrometer would have more credibility.

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 10, 2020, 02:14:09 pm
content: Keithley book says that the effective noise bandwidth of an analog panel meter is 1 Hz. Why?

author: Grandchuck
author_rank: Super Contributor
timestamp: April 10, 2020, 02:36:25 pm
content: For higher frequencies the meter damping and inertia hold the pointer still.

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 10, 2020, 02:52:20 pm
content: Qualitatively, yes, but quantitatively? Do all analog panel meters give 1 Hz bandwidth? Where did they get this number?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 10, 2020, 03:39:46 pm
content: Quote from: Kirill V. on April 10, 2020, 02:52:20 pmThe speed of the analog meter depends on the design and size. Larger meter movements are usually slower.Depending on the movement one may have to add extra damping to avoid longer ringing. This can also slow down the movement.1Hz bandwidth is kind of convenient for a reading the movement, so it needs some 5 seconds to be fully settled.

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 10, 2020, 04:30:33 pm
content: Does this mean that the analog meter provides unsurpassed noise filtering? Only the low frequency part of the flicker noise can affect the reading?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 10, 2020, 05:09:16 pm
content: The analog meters have no especially good noise filtering. It just does not make much sense to make them much faster, as the eye is not good in reading it so fast and there can be mechanical overshoot. The eye / brain can do some extra noise filtering that can be pretty good and easier than with digital output.One can also implement filtering in digital meters and this can even be done better, though it may need some time to get used to it.A digital filter can be FIR type and thus settles faster compared to the BW, especially if it is about settling to high accuracy (e.g. 0.1 % or better).An electrometer tends to be slow / noisy anyway when it comes to the lowest ranges. For this reason digital instruments often also have some extra filtering. The final settling of DA related background may take quite long anyway - more like connect, have a coffee and than read the result. That new graphical LCD interface can make absolute sense for a electrometer - unless directly read to a computer.

author: Kirill V.
author_rank: Regular Contributor
timestamp: April 11, 2020, 02:03:48 pm
content: Keithley book says that the noise bandwidth of an amplifier is equal to pi/2 of its true bandwidth. Why?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 11, 2020, 03:30:25 pm
content: The ratio if noise bandwidth to -3dB bandwidth depends on the filter type. By definition they are equal for an ideal brick-wall filter. The ratios for the the simple filter types (e.g. 1 st. order, 2nd order) can be calculated with "simple" math / integration. Real world filters may not follow the basic simple types and can be sightly off the ideal number. Unless one wants to measure noise, one usually does not care about the exact noise BW, though it can still help to have a low noise BW for a given response time.

author: David Hess
author_rank: Super Contributor
timestamp: April 13, 2020, 09:45:37 am
content: Quote from: Kirill V. on April 11, 2020, 02:03:48 pmNoise leaks in above the filter cutoff frequency so the noise bandwidth of a single pole roll-off filter is 1.6 times the -3 dB bandwidth.

author: Kirill V.
author_rank: Regular Contributor
timestamp: May 24, 2020, 08:20:07 pm
content: So, the idea of the output stage. I purposely abandoned the Keithley circuitry because there will be no external feedback circuits and no need for large load currents. The load will be a multimeter with an input resistance of 10 MOhm.Here there is a short-circuit protection of the load and if the output stage must sink current, the protection is obtained unintentionally, since the current generator on VT2 and VT4 can not give a greater current. If the output stage must be a current source, then VT3 is switched on and the short-circuit current is limited.Can anyone criticize this?

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 24, 2020, 10:14:15 pm
content: Quote from: Kirill V. on April 01, 2020, 12:56:11 pmSure, blame the bears for everything.

author: Kirill V.
author_rank: Regular Contributor
timestamp: May 24, 2020, 11:42:16 pm
content: Ha-ha! But still let's discuss my primitive circuitI completely forgot to clarify that the op amp has a bootstrapped supply related to the out node.And also I want to apply the microcurrent mode of operation of transistors say 50 mkA collector current. This is very attractive because transistors will emit very little heat. Interesting criticism

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 25, 2020, 12:51:06 am
content: Quote from: Kirill V. on May 24, 2020, 11:42:16 pmI just started to read through your thread when I found your comment to strannik2039, which I could not resist to answer. But I'm not yet very knowledgeable in electrometers. Somewhere I have a circuit diagram from a High-Impedance voltmeter from Siemens, but I think it is rather the normal 'Transistorvoltmeter' stuff. As I have analysed and cross-indexed most of the semiconductor appnotes I could ever reach, I can surely make a topical search and excerpt, in case I find something.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 25, 2020, 06:32:16 am
content: With a weak bootstrapped supply there could be a problem with the load to the OP, when the transistor stage goes into current limiting. It depends on the details, but usually a bootstrapped OP should only drive a small load.The circuit gets more readable with dots to mark connections if needed.The input to the current mirror could start from a lower voltage - but that is a minor detail.

author: Kirill V.
author_rank: Regular Contributor
timestamp: May 25, 2020, 07:21:25 pm
content: Quote from: Neomys Sapiens on May 25, 2020, 12:51:06 amI'd like to take a look at thisQuote from: Kleinstein on May 25, 2020, 06:32:16 amOK, thanks! Apparently you are referring to bootstrapped supply from zeners that are biased by current generators - as is often done, right? But I'm leaning towards independent sources like in K617. I do not think that in this case there will be problems with the current limiting circuit.But what I'm concerned about is that the output stage of the op amp will be taking an increased current which will cause additional heat to be released inside the amp. In principle, this problem can be solved at least by adding a buffer amplifier. But there should be more elegant solutions, in my opinion.I also don't like the fact that the output of the op amp has a constant offset of at least 600 mV, which increases when the load current is limited. This offset is translated to the input reduced by Aol times. It's not critical I'm just a bit of a perfectionistThis is a Splan and I don't know how to make it draw dots in nodes, sorryI highlight branches with color

author: coppercone2
author_rank: Super Contributor
timestamp: May 25, 2020, 09:14:20 pm
content: Quote from: Neomys Sapiens on May 24, 2020, 10:14:15 pmWhat is this device in the snow?I just get women in bikinis googling iskra site

author: Kirill V.
author_rank: Regular Contributor
timestamp: May 25, 2020, 09:39:30 pm
content: Quote from: coppercone2 on May 25, 2020, 09:14:20 pmIt seems to be a unique high-voltage laboratory in Leningrad (now Saint Petersburg). It was used in the design of high-voltage power lines. These are transformers that can produce more than a million volts.It's funny, but I've learned to dot the nodes

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 26, 2020, 03:05:13 am
content: Quote from: coppercone2 on May 25, 2020, 09:14:20 pmNot exactly. And sorry - it should have been 'Istra', not 'Iskra'.Look here:https://www.atlasobscura.com/places/abandoned-marx-generator