Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Regarding making your own extreme high-value resistors - any object that has insulators and leads but with nothing connected inside will have some high R that can be perhaps be measured, but won't be stable against environment effects on the outer surfaces. There's not much point to carbonizing things for home-made ones, except for curiosity. You can, however, use existing things that are fairly stable internally, have hermetic seals, and can be treated externally to reduce environment issues. I mentioned that reed relay capsule that I used as an unknown, but very high, yet not infinite R. Burned out light bulbs, vacuum tubes (especially something like a 5642 HV rectifier - fairly small, lots of glass), and xenon flashtubes are other examples of common hermetic glass/metal parts that can be used. But, the R is what it is, and can't readily be adjusted, only measured and maybe used in circuits that can accommodate the value. Also, along with the R, there will be some C that depends on the structure of whatever is used. The C can be good or bad, depending on the application. At extreme values, the surface characteristics will dominate, so the glass envelope would have to be silicone treated. Then the measured R of the device will be almost all intrinsic. So, you can measure it, but you won't know how stable it may be with temperature and voltage and time, for example, so don't expect much precision. Regarding over-voltaging electrolytic caps - you can reform caps to somewhat higher voltage, given enough time. They are formed electrolyitically to begin with, so the dielectric layer thickness is right for the rated voltage. If you gradually up the voltage, the thickness will increase and the C will go down over time. It's best to just use them only up to the design rating though, or the leakage will become unpredictable. A good way to do voltage splitting/protecting on medium-high voltage series connected electrolytic caps with low leakage, is with an appropriate high voltage "Zener" (actually an avalanche device, not truly Zener) across each one. The Zeners will prevent over-voltage of the caps in the normal direction, and reverse protection in the diode's forward region. Look for transient voltage suppressors (TVS or TVSS) devices to get into the hundreds of volts region, and of course they can be stacked for more. Unipolar ones will provide intrinsic reverse protection for the cap, while bipolar ones will not. They are usually specified fairly loosely in terms of leakage current, but it should be possible to find ones in the low nA region at applied V reasonably below the knee, at room temperature. That sounds like a lot in a High-Z context, but it's almost certainly much less than the leakage of a typical electrolytic cap. Ed ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Help needed identifying triaxial connector on HP 4339B high resistance meter - measures to 1.6 x 10^16 ohms.
On 23 March 2018 at 15:27, Jerry Hancock wrote: > what others do is just buy the available Trompeter triax connector and > file-off the host connector pins. I went through all the trouble to get > the right connectors and then looked at my Electrometer and saw someone had > already filed off the extra pins leaving one. I was a upset on many levels > as I would never file off anything on a piece of test equipment, except may > the RIGOL label. > > look for an eBay seller n2cbu. Great guy, sent me extra connectors and > cable. The biggest challenge in making your own cables is the fit between > the connector and cable. There are about a dozen types of triax connectors > for the same number of cables. > > Regards, > > Jerry > Thank you Jerry, The idea of destroying an instrument to make the socket fit a plug is one I would not do! Worst case, on a cheap and nasty bit of kit, I might consider changing the socket for triaxial BNC, but I have no desire whatsoever to do that on the 4339B, which sell for several thousands of dollars. I have already sent the meter once to Keysight for calibration, which they can obviously do if it has the right connector on it. If one started changing the connectors, then it would never get calibrated again. Depending on the age/value/rarity of the connector, I might consider other options, but not this time. On Monday I should have a partially complete Agilent 16339A component test fixture https://www.ebay.co.uk/itm/Agilent-16339A-Component-Test-Fixture/112871963210 arrive. (It cost me $400, which is more than the $350 I paid for the meter). That fixture will have the correct plug on it. HOPEFULLY there will be a manufacturer and part number on the plug. Also, I will have the ability to take a decent photo, so hopefully someone experienced has more chance of being able to positively identify the connector. I might try asking Keysight again. They told me the interlock connector was a Hirose, and knowing that I managed to work out a plug that fits. I've bought a couple of 4349Bs, which are quad channel high-resistance meters that take the same CPU as my 4339B. I'm hoping to do a bit of transplant surgery and hopefully get my 4339B to the point it can be calibrated properly - Keysight were unable to adjust it before as the CPU board apparently has a fault which is stopping the EEPROM being updated. When sent back to Keysight, it will have a 'heat transplant' of a CPU, and a new EEPROM, so all calibration data will be missing, as that's stored in the EEPROM. I'm pleased to say Keysight are not going to charge any extra to calibrate the meter with a blank EEPROM. So hopefully I will get this meter right. Dave ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
On 23 March 2018 at 18:49, ed breya wrote: > I'm guessing the application relates back to your leaf electrometer > project discussed earlier - trying to assess how the bias charge on the > capacitor holds up from leakage and use of the instrument. Yes it is. If this is the case, then it's for a one-time use for design of the item, > so shouldn't be too fancy or expensive. > I believe the original goal was to have the cap get charged up and then not > need any electric support for the leaf electrometer, appearing totally > passive, for some amount of operating time. If built-in monitoring of the > cap voltage is now desired, that's a different story. > Built in monitor is not required, but if I could design something that has a performance to allow that, I would be interested to see exactly when the voltage drops (or rises). > > If the measurement is just for design, to roughly see the cap > charge-holding time situation, then I'd recommend using methods that Chris > described, comparing to a variable HV supply at various times and settings > - all manual iterations, but doable. You can always say, recharge the cap, > then guess what the voltage may be after so much time, then set the test > supply and compare - over and over and over. > Part of my reason was to know if its possible to connect two electrolytic caps in series to increase the working voltage, without any parallel bleeder resistance. In one test, I tried charging a 600 V cap up to 1000 V, using the power supply in my 4339B high resistance meter, which is limited to 1 mA. The voltage would not rise above about 700 V, suggesting to me that perhaps the leakage might increase as the voltage rises, so maybe bleeder resistors are not required, apart for safety reasons. Safety could be addressed other ways. > > If continuous, long-term, fairly accurate monitoring is desired, then > you'd have to go with some sort of non-contact electrostatic voltmeter or > such, as others have mentioned. > > Relating back to recent discussions, it's pretty clear that you're not > going to find an actual specified resistor in the hundred T-ohm region. You > can certainly make your own from T-ohms to infinite, but you won't be able > to know the "exact" value. The commercial instruments that have say "200 > T-ohms" input R don't actually have that resistor value inside - it's an > "effective" or "equivalent" derived value that depends on a real resistance > of maybe E11-E12, multiplied by system gain. > So how does one make ones own resistor? I was thinking of perhaps nails in wood, where the moisture content would control the resistance. I suspect that idea would fail because DC would polarise the water molecules. But it did cross my mind as a possible way. The highest value commercial resistor I have found at a sensible price is 10 T ohms for £41 from Mouser, but that is on a 2 month lead time. I do have the Agilent 4339B high resistance meter, so can measure high value resistors. The basic uncertainty of that meter is 0.6%. Measuring 10 T ohm, I calculate the uncertainty would be 4.5%, so more than adequate as a starting point. Later a DVM could calibrate a setup. For the case of a 47 uF cap charged up, if I used a commercial 10 T ohm resistor, then the time constant is 15 years. So a 10 T ohm input R would be fine. For a 2.2 nF cap, which is one of which I have a 15 kV model, 10 T ohms would give a time constant of 6 hours, which would mean the load is not be negligible. > > Some electrometers like the old Keithleys have a voltage mode where the > high-Z input amplifier is bootstrapped up as a voltage follower, but have > less range than you want. It's conceivable that you could build the same > thing, but with a HV amplifier follower that can reach the desired level. > This would not be trivial. > Most/all the Keithleys do 200 V, which is outside the range of most semiconductors directly. > Again, if the purpose is just to measure the droop in bias voltage of the > charged cap over certain time intervals, there may be another option. Since > this is a dv/dt rather than DC measurement, you could possibly set up an > electrometer to view the change of the bias voltage via current through > another capacitor, and conceivably even rig it up to directly measure the > total change in cap voltage over a given time. > > My main issue was to measure the voltage across two series connected capacitors, to find out how equally it split. > Let's say the charge storage cap is 1 uF, and you put a much smaller, less > leaky, test cap plus some protective series R from the HV node to the input > of the electrometer, and also clamp the input with a low leakage diode > circuit. The test cap could be say 100 or 1000 times smaller than the main > cap, so its effect will be small. This could be in the 10 nF or less range, > where it should be fairly easy to find 3 kV or so rated metalized film > plastic capacitors with suitably low leakage. Any constant DC leakage
Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
I'm guessing the application relates back to your leaf electrometer project discussed earlier - trying to assess how the bias charge on the capacitor holds up from leakage and use of the instrument. If this is the case, then it's for a one-time use for design of the item, so shouldn't be too fancy or expensive. I believe the original goal was to have the cap get charged up and then not need any electric support for the leaf electrometer, appearing totally passive, for some amount of operating time. If built-in monitoring of the cap voltage is now desired, that's a different story. If the measurement is just for design, to roughly see the cap charge-holding time situation, then I'd recommend using methods that Chris described, comparing to a variable HV supply at various times and settings - all manual iterations, but doable. You can always say, recharge the cap, then guess what the voltage may be after so much time, then set the test supply and compare - over and over and over. If continuous, long-term, fairly accurate monitoring is desired, then you'd have to go with some sort of non-contact electrostatic voltmeter or such, as others have mentioned. Relating back to recent discussions, it's pretty clear that you're not going to find an actual specified resistor in the hundred T-ohm region. You can certainly make your own from T-ohms to infinite, but you won't be able to know the "exact" value. The commercial instruments that have say "200 T-ohms" input R don't actually have that resistor value inside - it's an "effective" or "equivalent" derived value that depends on a real resistance of maybe E11-E12, multiplied by system gain. Some electrometers like the old Keithleys have a voltage mode where the high-Z input amplifier is bootstrapped up as a voltage follower, but have less range than you want. It's conceivable that you could build the same thing, but with a HV amplifier follower that can reach the desired level. This would not be trivial. Again, if the purpose is just to measure the droop in bias voltage of the charged cap over certain time intervals, there may be another option. Since this is a dv/dt rather than DC measurement, you could possibly set up an electrometer to view the change of the bias voltage via current through another capacitor, and conceivably even rig it up to directly measure the total change in cap voltage over a given time. Let's say the charge storage cap is 1 uF, and you put a much smaller, less leaky, test cap plus some protective series R from the HV node to the input of the electrometer, and also clamp the input with a low leakage diode circuit. The test cap could be say 100 or 1000 times smaller than the main cap, so its effect will be small. This could be in the 10 nF or less range, where it should be fairly easy to find 3 kV or so rated metalized film plastic capacitors with suitably low leakage. Any constant DC leakage from the cap could be zeroed out or accounted for, at least for short-term measurements. The electrometer could then read the test cap current directly proportional to dv/dt, or integrate it back up to delta V in the charge mode. There are limits to the reasonable measuring ranges, of course. For example, 1 nF would provide 1 nA at 1V/sec - a fairly easy measurement. But 1V/1000 seconds could be tricky - only 1 pA to work with. Ed On 3/22/2018 7:12 PM, kc9ieq via volt-nuts wrote: I guess I don't see what the issue is. No, impedance is not infinate when not nulled, but this is why V supply #2 Is adjustable by whatever convenient means. Rough adjust, connect, adjust for null, measure. Rinse and repeat. If it were my project, I'd just run up an HV transformer on a variac, with a rectifier, cap, and probably some series R thrown at it to limit current through the meter. Curious to know what the application is, if this will not work. Good luck with whatever solution you choose. Regards, Chris Sent from my SMRTphone Original message From: "Dr. David Kirkby" Date: 3/22/18 8:58 PM (GMT-06:00) To: kc9ieq , Discussion of precise voltage measurement Subject: Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms? On 23 March 2018 at 01:49, kc9ieq via volt-nuts wrote: How about using (or building) an additional 2kV power supply and a sensitive meter movement like a differential voltmeter, adjusting for/measuring the null? Impedance at null will be theoretically infinate, current will be theoretically zero, and you can measure/monitor the voltage of your second supply directly with the probe/meter of your choice. Regards,Chris No, that will not work for me, as while the impedance at null is infinite, it is not when not nulled, and that will mess up the measurements. Absolute accuracy is not important. +/- 10% or even 20% would be okay. I want to measure a couple of voltages and compare them. As long as the meter reads
Re: [volt-nuts] Help needed identifying triaxial connector on HP 4339B high resistance meter - measures to 1.6 x 10^16 ohms.
what others do is just buy the available Trompeter triax connector and file-off the host connector pins. I went through all the trouble to get the right connectors and then looked at my Electrometer and saw someone had already filed off the extra pins leaving one. I was a upset on many levels as I would never file off anything on a piece of test equipment, except may the RIGOL label. look for an eBay seller n2cbu. Great guy, sent me extra connectors and cable. The biggest challenge in making your own cables is the fit between the connector and cable. There are about a dozen types of triax connectors for the same number of cables. Regards, Jerry Jerry Hancock je...@hanler.com (415) 215-3779 > On Mar 23, 2018, at 6:40 AM, Stephen Locke wrote: > > It looks to me like a MIL-C-49142 style connector, however I'm not sure > what the rated voltage of that style connector is. > > Either way, Trompeter sells their 370 series that are essentially threaded > BNC-size triax connectors that conform to the 49142 spec. I believe > Trompeter is now absorbed into Cinch. Maybe something like the PL375. > Digikey has some in stock that accept various cables. The datasheet > drawings + calipers may be enough for you to confirm a match, or at least > this might be a starting point for you. > > http://www.jrhelec.com/assets/images/manufacturers/cinch/catalogs/catalog.pdf > https://www.digikey.com/products/en/connectors-interconnects/coaxial-connectors-rf/437?k=pl375 > > > > > On Sat, 17 Feb 2018 at 12:32 Florian Teply wrote: > >> Hi David, >> >> Am Sat, 17 Feb 2018 15:32:15 + >> schrieb "Dr. David Kirkby" : >> >>> In order to use the meter, I would obviously need to be able to make >>> connections to it. >>> >>> Is there anyone here that knows what the triaxial (tri-axial?) >>> connector in the attached pictures ? One picture is of the female on >>> the 4339B and the other the male plug on a fixture that I don't have. >>> >>> The picture of the meter is not the one I have, since the meter is at >>> Keysight. But it has a better picture of the triaxial connector than >>> the meter I have. >>> >>> Does anyone have a bit of trixial cable with one of these connectors >>> on? >>> >> Unfortunately, I don't know this kind of connector either. >> I can confirm however - which probably does help a bit still - that it >> is neither the three-lug BNC triax HP/Agilent/Keysight uses on all >> measurement equipment capable of going down to picoamp levels I have >> ever seen, nor the two-lug BNC triax that Keithley uses for the same >> purpose. To me it seems to be a threaded connector, and dimension-wise >> should be pretty close to BNC, so TNC-style triax it might indeed be. >> >> But be prepared that these are a bit pricey, the last time I bought the >> standard three-lug BNC-style triax connectors they were about 80 Euros >> a piece. >> >> HTH, >> Florian >> ___ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> > ___ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Help needed identifying triaxial connector on HP 4339B high resistance meter - measures to 1.6 x 10^16 ohms.
It looks to me like a MIL-C-49142 style connector, however I'm not sure what the rated voltage of that style connector is. Either way, Trompeter sells their 370 series that are essentially threaded BNC-size triax connectors that conform to the 49142 spec. I believe Trompeter is now absorbed into Cinch. Maybe something like the PL375. Digikey has some in stock that accept various cables. The datasheet drawings + calipers may be enough for you to confirm a match, or at least this might be a starting point for you. http://www.jrhelec.com/assets/images/manufacturers/cinch/catalogs/catalog.pdf https://www.digikey.com/products/en/connectors-interconnects/coaxial-connectors-rf/437?k=pl375 On Sat, 17 Feb 2018 at 12:32 Florian Teply wrote: > Hi David, > > Am Sat, 17 Feb 2018 15:32:15 + > schrieb "Dr. David Kirkby" : > > > In order to use the meter, I would obviously need to be able to make > > connections to it. > > > > Is there anyone here that knows what the triaxial (tri-axial?) > > connector in the attached pictures ? One picture is of the female on > > the 4339B and the other the male plug on a fixture that I don't have. > > > > The picture of the meter is not the one I have, since the meter is at > > Keysight. But it has a better picture of the triaxial connector than > > the meter I have. > > > > Does anyone have a bit of trixial cable with one of these connectors > > on? > > > Unfortunately, I don't know this kind of connector either. > I can confirm however - which probably does help a bit still - that it > is neither the three-lug BNC triax HP/Agilent/Keysight uses on all > measurement equipment capable of going down to picoamp levels I have > ever seen, nor the two-lug BNC triax that Keithley uses for the same > purpose. To me it seems to be a threaded connector, and dimension-wise > should be pretty close to BNC, so TNC-style triax it might indeed be. > > But be prepared that these are a bit pricey, the last time I bought the > standard three-lug BNC-style triax connectors they were about 80 Euros > a piece. > > HTH, > Florian > ___ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
