The technique is to place a metal triax cap over the trax jack of the instrument, force 0V and measure current.
The technique is to place a metal triax cap over the trax jack of the instrument, force 0V and measure current.
i am curious about the measurement cables. i got some PTFE 2 core shielded, i applied 1000v 2 any 2 of the conductors, and measured the leakage (0.04uA/m or 26Gohm/m). so im not sure, how does this compare to a good PTFE insulated cable suitable for "low low loss" ?
You can test this waving your hand near some unshielded wire that is connected to an instrument that has a noise floor well below 1nA.
I once tried to measure insulation resistance of a piece of ceramic substrate. I set the bias voltage to 1kV, and my meter reads as low as a couple tens of nA. Forget about moving hands or any conductive metal parts around, even only blowing air can cause displacement current of air dielectric, which considerably alters readings by up to hundreds of nA, so one word or suggestion: shield your DUT, not only electrically, but also mechanically. Don't let air to pass by it, or any thing that can carry charges.
I'll throw my cheap little Picoammeter project into the mix. You could easilly de-sensititize it if you only want to go as low as nA's :P
https://www.eevblog.com/forum/projects/picoammeter-design/msg790045/#msg790045 (https://www.eevblog.com/forum/projects/picoammeter-design/msg790045/#msg790045)
P.S: Just reading through the thread again. In terms of 'tips', there are plenty among the replies, including a number from Alex.
DIY pA meter is very cool. Someone had to build the first one!
For every beginner Ninja in this thread:
http://www.tek.com/sites/tek.com/files/media/document/resources/LowLevelHandbook_7Ed.pdf (http://www.tek.com/sites/tek.com/files/media/document/resources/LowLevelHandbook_7Ed.pdf)
Low current measurement or electron counting is like ppm chasing in voltage standard section, sometimes more difficult I must say :)
VintageNut
What is your application for K6430?
This is a K6430 measuring a 1T resistor using 0.5VDC. The measurement yields 6 significant digits.
The metal pans are at GUARD potential.
What shape is this 1 TOhm resistor?
That is kind of impressive, measuring such a resistor at less than 1V
This is a K6430 measuring a 1T resistor using 0.5VDC. The measurement yields 6 significant digits.
The metal pans are at GUARD potential.
:palm: What do you mean "6 significant digits" ?! The last digit in this case equals about 3 electrons a second . The Keithley is a nice unit, but it can manage only about 0.4fA p-p noise, or ~2500 electrons/sec .
Cheers
Alex
The aluminum pans are qty 3 for USD $1.00. Almost for free. The edges can be folded over to make the air current almost zero.Yep it is pretty smart, but I cannot remember when I saw it for first time :)
The aluminum pans are qty 3 for USD $1.00. Almost for free. The edges can be folded over to make the air current almost zero.Yep it is pretty smart, but I cannot remember when I saw it for first time :)
If it was invented by Keithley or by Agilent or someone else...
For normal measurement I prefer light-tight enclosure.
It can be interesting to see what is inside preamp box, can expect teardown of it? :scared:
BTW why you are measuring resistor with such a low voltage, these resistors should withstand 200V.
I recently acquired a KE487 and a KE8002A. There is a 10G in the enclosure. Voltage source is a Fluke 731B. The resistor appears to be about 0.25% low. The 487 spec is 0.3% of reading so a better picoammeter would be required to make this measurement. The 6517B is only slightly better at 0.2% for the 2nA range. The 6430 is 0.05% on the 1nA range. The 6430 costs more than a 3458A.
This is probably why high resistance bridges remain in production.
Looking at these numbers I now more and more appreciate the Keithley 263 calibrator I've bought recently. My 617 electrometer is specified at 0.25%+500fA at 2nA range and 1.6% +10fA on 200pA, 20pA and 2pA ranges (1 year accuracy). The 263 however is specified (as a current source) at 0.065% +100fA at 2nA range, 0.25% +30fA at 200pA range, 0.375% +10fA at 20pA range and 0.425% +10fA at 2pA range. And I've paid less for it 8) .
Looking at these numbers I now more and more appreciate the Keithley 263 calibrator I've bought recently. My 617 electrometer is specified at 0.25%+500fA at 2nA range and 1.6% +10fA on 200pA, 20pA and 2pA ranges (1 year accuracy). The 263 however is specified (as a current source) at 0.065% +100fA at 2nA range, 0.25% +30fA at 200pA range, 0.375% +10fA at 20pA range and 0.425% +10fA at 2pA range. And I've paid less for it 8) .
These are really impressive specs. How do you want to verify them?
Yes the 263 is very good for current.
My quandary is that measuring a 100G or 1T resistor is not going to be much better than 1% using any current source or current measurement instrument.
1% is 10,000 ppm uncertainty. Thats like a crappy handheld DMM performance.
If you think 1% is crappy, check high-dollar Guildline 9337 10POhm resistance standard, which has amazing 25% spec :D. I wonder what insulator is used there. :)
I have a KE515 bridge but have not attempted an overhaul. The output connector appears to have been hacked to install a BNC. I think that it is supposed to have a triax connector.Without derailing the thread (too much), I have a question regarding those triax connectors: those connectors and cables are astonishingly expensive (probably due to the niche market and target audience). Can't one just replace a triax connection with two BNC connections (one being signal shielded by guard, the other return (GND) shielded by, well, shield)? I realize guard might be on high potential, but the preamps driving guard are limited to quite low currents, so this should be fairly safe (for humans, not necessarily for semiconductors) as long as one is not charging up CRT-sized capacitors and after being zapped for the third time, one will be more careful anyhow. (where's the SHOCKED emoticon when one needs one?)
I have a KE515 bridge but have not attempted an overhaul. The output connector appears to have been hacked to install a BNC. I think that it is supposed to have a triax connector.Without derailing the thread (too much), I have a question regarding those triax connectors: those connectors and cables are astonishingly expensive (probably due to the niche market and target audience). Can't one just replace a triax connection with two BNC connections (one being signal shielded by guard, the other return (GND) shielded by, well, shield)? I realize guard might be on high potential, but the preamps driving guard are limited to quite low currents, so this should be fairly safe (for humans, not necessarily for semiconductors) as long as one is not charging up CRT-sized capacitors and after being zapped for the third time, one will be more careful anyhow. (where's the SHOCKED emoticon when one needs one?)
Ordinary coax has a problem with triboelectric induction during ordinary usage. The high dollar triax cable is constructed with lubricant that reduces or eliminates the effects of triboelectric induction.
Ordinary coax has a problem with triboelectric induction during ordinary usage. The high dollar triax cable is constructed with lubricant that reduces or eliminates the effects of triboelectric induction.
It is not connected to the coaxial/triaxial difference. You can get a "low noise" coaxial cable with a graphite lubricant and you can get a "standard" triaxial cable without any lubricants. Unfortunately, two triaxial cables I can get easily are of the "standard" type. So far I've used the Belden 9222 which works very well as long as you are not moving it during the measurement. I am trying to get some "low noise" triaxial cable but so far without much success!
Cheers
Alex
Ordinary coax has a problem with triboelectric induction during ordinary usage. The high dollar triax cable is constructed with lubricant that reduces or eliminates the effects of triboelectric induction.
It is not connected to the coaxial/triaxial difference. You can get a "low noise" coaxial cable with a graphite lubricant and you can get a "standard" triaxial cable without any lubricants. Unfortunately, two triaxial cables I can get easily are of the "standard" type. So far I've used the Belden 9222 which works very well as long as you are not moving it during the measurement. I am trying to get some "low noise" triaxial cable but so far without much success!
Cheers
Alex
Where did you see 7078-TRX-5 for 40$? I see only 80$ one, and it's very short..It was offer which has been accepted, the buy now prices are ridicilous:)
Nice!
I will expect the burden voltage even lower.
Interesting. Can you also measure current on 3458A's GOHM range? I wonder how stable that is.
Also does guard switch to LO or to open (with connection to electrometers earth?) changes DCV current?
Can I ask how are you guys cleaning the wires / connectors / components after handling / soldering etc to avoid surface conduction?
IPA?
What sort of cloth / tissue / q tip??
Thanks Robert
That data looks like it came from a nice SMU - I would like one but can't justify the extreme $, in what is for me, a pastime.
@Alex Nikitin
thanks for nice charts.
Could You please type units (V,mV) on the horizontal axes of last plots?
How many measuring points are on these plots?
All were taken for reverse bias ?
Jim Williams advocated the use of diode connected JFETs for low leakage. Every tried those?
I've posted measurements for one JFET (BF861) earlier in this thread, taken in a somewhat different setup (K263 as a source and K617 as a meter). JFETs are much better than common signal diodes like 1N4148, however very few would come close to the performance of even the worst BAV199 devices and none will survive 100V reverse voltage or have leakages similar to the best of BAV199. I plan to measure some more JFETs and BJTs soon (the Keithley 617 has some selected BJTs as input protection diodes by the way) and will post results here.
Cheers
Alex
Bob Pease wrote an article about the problems they had testing input bias current at the femtoamp level. The standard method was to configure the operational amplifier as an integrator but the physically large low leakage air capacitor had enough capture area that incoming cosmic rays were a significant problem. Their solution was write the test software to distinguish cosmic ray events but now I wonder if a vacuum capacitor would have been better or at least feasible.
A calibration box for a hi-pot tester?We will see how usable it is :D :-DMM
http://www.sefelec.com/en/calibration-kit-MG-91 (http://www.sefelec.com/en/calibration-kit-MG-91)
There has been slow evolution of my ADA4530-1 low current to voltage converter. It has selectable 1k, 10k, 100k, 1M, 10M, 100M, 1G, 10G, 100G and 1T feedback resistors. See its attached picture.
I'm trying to find the minimum current which I can measure with the 1T feedback resistor. I knew that 1.5 pA was easy by using a 1.55 volt battery which was connected to an external 1T resistor. I added a 1/10 voltage divider inside of my shielded test box to feed 155 mV to that resistor. The second attachment shows the 165 fA current produced by that combination (1T 10% resistor is actually close to 0.955). As is typical with these converters, a positive current is converted to a negative voltage. 1 volt = 1 pA = 1,000 fA.
My test box has a switch to change to a 1/100 voltage divider. The third attachment shows the approximately 16 fA current produced by that.
Time to build a greater voltage divider.
1. No guard
2. The banana jacks appear to garden variety. These usually have significant leakage compared to pA current
On the ADA4530-1 data sheets Analog Devices warns of possible nonlinearity when using high voltage resistors at low voltages (a poor voltage coefficient).
R1 | R2 | |
100V | 1.026 | 1.026 |
200V | 1.027 | 1.023 |
500V | 1.001 | 1.016 |
I'm trying to find the minimum current which I can measure with the 1T feedback resistor...
Time to build a greater voltage divider.
This has been an interesting project. |
Let's see if people pay attention what I write. Anyone know where these beauties are from? 8)
(https://xdevs.com/doc/Keithley/6221/photo/kei_lorng_1.jpg) (https://xdevs.com/doc/Keithley/6221/photo/kei_lorng.jpg)
I checked one of the MEDER reed relays (Digikey) for current leakage (PN HI05-1A66) with the K617 Electrometer. The DUT is suspended in air inside a metal box. Test conditions 23 deg C, 35% RH.
With 31V across the contacts I had 12 fa flowing. That worked out to about 2,600 Tohms. With 100V it was 42 fa. The coil to contact leakage was 4.6 fa with a 31v Bias. It looks like a very good high isolation relay.
Could you say some words about the calibration in the lab? How did they cal these resistors?
That is a beast, can handle fA like nothing wow, minor teardown at least coming? ::) ::)
Oh I was asking TiN, that shiny new equipment calls for a teardownThat is a beast, can handle fA like nothing wow, minor teardown at least coming? ::) ::)
We're you asking me or TiN? :palm:
Question to the Electrometer-ninjas about the K617:
As far as i understand guarding is only usable when measuring voltage sources with high source resistance and when measuring high resistance DUTs with the electrometer-internal-current-source up to 200GR.
With the internal voltage source the K617 is capable of determining the resistance/leakage current of higher resistance DUTs like a reed contact, but without guarding it takes a great amount of measurement settling time.I don't quite follow. Why can't guarding be used here and in which way would you want another instrument to be 'better'?
Is there a way to get faster settling time with additional equipment like an external current source or would i need a better Electrometer?
Attached is the measurement of a reed contact MDSR-10, where the long settling time is visible. Cable used: 1.5m Keithley-7078-TRX
the ATTO Amp resolution of the meter.
Testing insulation of spark plugs/gaps via resistance makes absolutely no sense and is just a waste of time. It should be done like a dielectric strength test (IEC 60243) with a high voltage source (meaning a source of at least 10kV) until discharge occursMost of the things in life do not make any sense, metrology included tbh. I was not interested at all of how the townsend avalance forms on sparkplug, or how the dielectric strength of the material might statistically behave.
Vtile:I might (but do not know where as of there is no "measurement and technologies" section other than metrology), but there were reason I did use this particular thread to begin with Measuring nanoamps and below like a Ninja is not the most scientific subject window if I'm not terribly mistaken.
Best to open a new thread for testing insulation properties of spark plugs.
This discussion does not really fit in this metrology section.
Oh, normally I would just use GPIB directly from the 617, however right now the GPIB interface on my 617 doesn't work :( , so I use one of my two Keithley 2015, connected to the 2V analogue output on the 617, and read over GPIB, the data is then imported into Excel.When I got my 617, the GPIB connector was bust. On my 181 (same vintage) however both output drivers needed to be replaced (and fortunately nothing else).
Cheers
Alex
My tests on mosfet solid state relays indicated that a lower LED drive current reduces the mosfet output EMF.
When the led current is just above the threshold to switch on the mosfet output it should produce the lowest EMF.
In my case the measured EMF was <100nV afair at about 1 or 2mA LED drive current.
Is that a thermocouple effect from self heating of the optocoupler by the LED?I think, yes.
Looks like sweep error into range +10V...-10V(20V span) with programmable speed 1mV/s is less 100nV/s
On top - P597 100pF air capacitance standard and Micron-GLIN.
The capacitors at the transformer are a bit unconventional, but they are a good idea, filtering some of the mains and in addition providing some of the magnetization current from the secondary side too.Thanks for sharing - I enjoyed to follow your post. I even tried to read the Russian text without translator.
The usual way are capacitors (usually smaller ones) in parallel to all diodes at the rectifier. With the capacitors at the supply the shown caps are mostly equivalent.
With a low voltage they don't have to be X2 type, but it does not hurt if they are.
I thought the capacitors are supposed to be the same value in a Sallen-Key section?
My preferred idea for today: op-amp SHE(self heating effect) and load problems of OPA 4140 which is used as R2R matrix power driver. Op-amp error may expand DAC errors.An easy litmus test would be an additional load resistor...
My dear friend, please don't worry about load of precision circuits... a few days ago i try use my new precision resistors as led current driver, they works fine!
(https://ampnuts.com/wp-content/uploads/2022/02/DSC_0356-scaled.jpg)
:-DD :-DD :-DD
The mkp4 seems to be “bad”. DA sb around 0.0002How are you measuring DA? My understanding is this is not a trivial thing to measure and not available on your typical LCR meter?
My 10 all measure similarly. Also my Russian K71-7 is lower ( but larger ) as you demonstrate.
Randall
There is a mil-spec measurement for dielectric absorption (DA): a specific sequence of applying a certain voltage, disconnection, waiting, and re-measuring voltage. It is good as a "figure of merit" to compare different capacitors with each other, but I don't understand how to use that standardized value to predict the effect in a practical circuit, with different voltages and times, since it is a non-linear effect (analogous to ferromagnetism).With film capacitors the dielectric absorbtion is usually still linear. So more voltage gives more recovered valtage. The DA itself may be nonlinear mainly with electrolytic and class 2 /3 ceramic.
"D" = 1/Q is closer to being a linear effect, but depends on frequency. For non-linear dielectrics, such as Z5U ceramic and electrolytic capacitors, it also varies with voltage.
Essentially all the newer MS- ADCs in the modern DMMs (e.g. from K2000 or 34401/3458 on) use ceramic (likely C0G) capacitors. The ones I use are about 1/5 the DA of PP caps and AFAIK were some 10 cents each. So nothing expensive, one just needs to know which ones are good and which ones are not (about the same as PP and should still be good enough for the HP/KS meters). The HP3458 has a PTFE cap for the S&H stage, but not sure of they really need it there - the coax form may have additional effects and could be more than just a capacitance.
I don't know how good the higher capacitance G0Gs are - they may still be an alternative with 100 nF available in relatively small size (e.g. 1206 and small THT).
Bob pease once published a compensation circuit for DA. Unfortunately I wasn't able to find it anymore - maby someone recalls that RAP stuff anyhow....
But we are in to digital era, wasn't it? >:DYeah, digital capacitors without DA - what is the DigiKey order-No? ;)
QuoteBut we are in to digital era, wasn't it? >:DYeah, digital capacitors without DA - what is the DigiKey order-No? ;)
Vgkid, device will be completed in next month... If world not be destroyed in this period...
I'm planned use 0.01pF to 10pF capacitors with air or nitrogen dielectric, to generate current. They must be extremely low DA.
About 100pF and 1000pF i'm not sure... maybe its be K71-7 or K72P-6 or some else...
Yes I'm understand, but 10-20m to "near-zero fA" may increased to hours with "near-zero aA".
Anyway... when my smugglers buy some sanctioned toys for me, i try get a couple MLO caps for testing.
chances are the observed settling is more something other than the the capacitor, e.g. the PCB, case of the LMC662.
Were there ever leakage measurements done on MEMS switches (ADGM1004 for example), just to get a rough estimate in reality compared to the usually conservative leakage spec?
Are there any other MEMS switches that are capable of DC-range with interesting specs compared to normal analog switches?
https://www.analog.com/media/en/technical-documentation/data-sheets/adgm1004.pdf (https://www.analog.com/media/en/technical-documentation/data-sheets/adgm1004.pdf)
I noticed that the Russian word for voltage has been translated into 'tension'. I've seen the same in other documents (google-)translated from Chinese. I found that amusing, as the German word for both tension and voltage is 'Spannung'.Yes. The translation into Russian of these two words sounds the same.
In Romanian, too, it's tension. Usual (and academic, too) is to say, for example for AC voltage, "tensiune alternativă", as opposed to "voltaj alternativ". "Voltaj alternativ" just sounds wrong, though the word "voltaj" is listed in our dictionary as a neologism, imported from the French "voltage".
"Electric tension" seems to be fair game, though? It is unambiguous and seems to be actually used, if you google it!
I'm still searching different types of large capacitor in range 10pF-5000pFWhat about sovietn green (primarily green) and big K71-7 capacitors? As far as I know their insulator is also polystyrol.
first try to make realtime CPLD software
Soldering complete... ready to program...Wow! It looks like a highly precision metrology equipment! Nice design! I'm looking forward to first run!
Hmmm...measure the current accuracy?It's complicate.... as any SI units (http://en.wikipedia.org/wiki/International_System_of_Units) which converts from others.
GLIN(ГЛИН - Генератор Линейно Изменяющегося Напряжения also called ultra-low speed ramp-generator) is responsible for part "dU/dt" into formula "I=C*dU/dt". Other important things is accuracy of "C".... capacitance accuracy on the infra-low frequency it is a cutting edge of newest metrology science... many powerfull metrology laboratories investigate that. You can see publications of the TÜBİTAK UME, Physikalisch-Technische Bundesanstalt, VTT MIKES Finland, and others metrology centers.
Accuracy of extremely high currents (like as 1nA and more) i can compare between "I=C*dU/dt" and "I=U/R" methods trough resistance standards and Keysight B2985A electrometer, as shown earlier.
Unfortunately, common "old school Soviet electrometers" can't do high precision comparison of currents which generated through different methods. But they can be very sensitive on ultra-low current ranges like as several attoamperes, it helps when need to do a component testing, material's selection and etc. (V7-45 ADEV noise floor is around 10-19A which is 100 zepto-ampere)
Sorry no.
1nA it is around 6 241 509 074 electrons per second. It is a extremely big value for true Ninja... equal to population of the planet earth, each second....
True electrometers can be sensitive to 6...7 electrons per second(1aA), it is low. >:D
Micron-GLIN v.2 PCB repository: https://github.com/shodanx/Micron-GLIN-v.2 (https://github.com/shodanx/Micron-GLIN-v.2)Hi!
Micron-GLIN v.2 schematic book: https://ampnuts.com/wp-content/uploads/2022/06/Micron-GLIN-v.2-schematic-book.pdf (https://ampnuts.com/wp-content/uploads/2022/06/Micron-GLIN-v.2-schematic-book.pdf)
Amp-porn movie: testing user interface and main functions of new GLIN with 1nF capacitor.Seems like your effort paid out and this one works even better than the last one, good job! Would you share a picture of how the capacitor was hooked up?
https://ampnuts.com/micron-glin-v2-porn/
I use this (https://www.eevblog.com/forum/metrology/measuring-nanoamps-and-below-like-a-ninja/msg4190218/#msg4190218) simple tool. One jack is BNC for connect to GLIN, other is Molex 3-lug triax, connected via 1.5m cable to electrometer (Keysight 16494A-001 cable).Wow, and for ground return current, just screws / washers biting through aluminium oxide layer are enough? :scared:
Thank you, that answers my question.just screws / washers biting through aluminium oxide layer are enough? :scared:You means resistance of Aluminum oxide layer?
Wall end of aluminum box parts is vanished from paint to provide good connections between outer shield of a triax and shield of GLIN cable.
Aluminum oxide layer is may provide problems, but magic is - you can put some KOhm resistor between signal ground of a GLIN and ground of a electrometer without any problem. You may add any offset between grounds... Electrometer can contains any input bias.... Ramp through capacitor is eliminate any offset to negligible.
Otherwise - if you generate current with HiMeg resistors, electrometer input bias is important error source.
I just had a look around ebay and found some reasonably priced triaxial cables.These are twinax, not triax, despite the auction title. Would stay far away!
While I do not know the exact quality of these cables I thought that it might find some interest here.
( https://www.ebay.com/itm/255603797766 (https://www.ebay.com/itm/255603797766) )
My completely illegal's, sanctioned refs will be delivered soon... So... it's time to start thinking about new Low-Noise, Mirror-free reference concept...
Earlier version use R+R mirror for making -7V reference for DAC, but i want try new mirror-free concept to do not amplified noise and instability. :popcorn:
(https://ampnuts.com/wp-content/uploads/2022/09/KEZ_concept_5.png)
The somewhat jagged pattern of the noise in the time domain could be due to DNL errors of the DAC. It looks like there is repetitive part with some 14 seconds period, that can be seen as some 16 steps. For comparison it may help to know at which time the DAC values are changed.
I don't see much effect of interference or an indication of a firmware problem. It is more a lack if low pass filtering and a limitation of the DAC.