Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
On 24 March 2018 at 17:34, Jeremy Nichols wrote: > I made a high-value resistor using motor oil and a couple of stainless > bolts. It worked for what I was doing (testing an HP-425A > Microvolt-Ammeter) but calculated as only 8,500 Megohms. > > Jeremy > I had some discussions some time ago about using oil as a dielectric in a capacitor with someone at NPL. He said the loss of both cyclohexane and Polydimethylsiloxane (PDMS = silicon oil) is very low. He said the only way I would measure the loss of them was a resonate method, and detecting small changes in Q. My thoughts on putting them as the dielectric in a capacitor and measuring on an LCR meter would not work, nor would my transmission line. I had already satisfied myself that using a coaxial probe and VNA would not work. As he said, cyclohexane is nasty stuff, but PDMS is much more environmentally friendly. 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 03/22/2018 09:07 PM, Bob Albert via volt-nuts wrote: > I found several electrostatic voltmeters on ebay. The brand I remember is > Sensitive Research. I have an electrostatic voltmeter (photo attached) that I no longer use that I'd part with for $50. This thing is big and heavy so shipping will probably be $100. It is mechanically sensitive enough that I'll probably need to build a wooden crate and pack that inside a large box filled with with padding. A local pickup would be wonderful. I live near Knoxville, TN and would go maybe 100 miles to meet someone. We have a motorhome and that would be the start of a nice trip. There are two kinds of electrostatics. The first type is like the ones currently on sleazebay. Relatively small, phenolic block input terminals and conventional internal wiring. Very high impedance but no where near infinite. Good enough to measure, say, the screen voltage on a tube but not suitable for measurements where the input impedance must be essentially infinite. Nuclear radiation ion chambers, for example. The second one is like the one pictured. Designed to have as close to infinite input impedance. That huge input tower is not for voltage withstand - this is a 2500 volt meter - but to lengthen the creepage path to ground. I sent this unit to a calibration lab about 10 years ago. With the tower carefully cleaned and a new dessicant pack inside, they could not measure the input impedance. The only practical flaw is that there are a few pF of capacitance between the plates that must be charged. Once the meter is deflected, there is no current flow. To satisfy myself that it was truly infinite impedance, I connected a 2000 volt power supply to the unit through the resister used in the Fluke 40kV high voltage probe. It took a couple of seconds for the capacitance to charge but once deflected, the electrostatic read the same value as the voltage output of the supply to within a minor division. Anyway, this instrument is available if anyone wants it. John -- John DeArmond Tellico Plains, Occupied TN http://www.tnduction.com<-- THE source for induction heaters http://www.neon-john.com<-- email from here http://www.johndearmond.com <-- Best damned Blog on the net PGP key: wwwkeys.pgp.net: BCB68D77 ___ 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?
I made a high-value resistor using motor oil and a couple of stainless bolts. It worked for what I was doing (testing an HP-425A Microvolt-Ammeter) but calculated as only 8,500 Megohms. Jeremy On Sat, Mar 24, 2018 at 10:18 AM Mark Sims wrote: > Many years ago, there was an article (in Popular Electronics?) that > needed a very high value resistor. They built it by drawing a line > between two terminals with Higgins India Ink. No idea if the ink is still > made the way it was 50 years ago... > > > > > So how does one make ones own resistor? > ___ > 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. > -- Sent from my iPad 4. ___ 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Many years ago, there was an article (in Popular Electronics?) that needed a very high value resistor. They built it by drawing a line between two terminals with Higgins India Ink. No idea if the ink is still made the way it was 50 years ago... > So how does one make ones own resistor? ___ 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?
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] 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 impor
Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Vibrating capacitor non contact field probe in feedback loop to create a voltage follower: https://www.monroe-electronics.com/ESD/pdf/244a_m.pdf Bruce > > On 23 March 2018 at 15:12 Neville Michie wrote: > > Improvise by holding a metal disk over an electronic balance and > measuring the force of attraction. > Calibrate it with a lower known voltage. > > cheers, > Neville Michie > > > > > > On 23 Mar 2018, at 12:58, Dr. David Kirkby > > wrote: > > > > 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 the same with identical input voltages, that is fine. > > > > 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. > > > > > > ___ > 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Improvise by holding a metal disk over an electronic balance and measuring the force of attraction. Calibrate it with a lower known voltage. cheers, Neville Michie > On 23 Mar 2018, at 12:58, Dr. David Kirkby > wrote: > > 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 the same with identical input voltages, that is fine. > > 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. ___ 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?
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 the same with identical input voltages, that is fine. 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 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 the same with identical input voltages, that is fine. 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 01:37, Jerry Hancock wrote: > The part I struggle with is “make one” as T ohm meters are ridiculously > sensitive to things like fingerprints, for example. I had a hard time just > putting cables together that had the particular… I was going to say > insulation, but it was more than that, basically everything is important > and specific when you are dealing with T ohm meters. Setting aside the > stupid tri-bnc connector on most of them. > Yes, I can see these are tricky. I wish my high-resistance meter had a triaxial BNC. It has a triaxial cable, but screw on. I can't find out what the connector is. > > How about just using a voltage divider with a standard electrometer? I’m > sure you thought of that though. I like playing around with my Keithley > 616 as you can show the kids how electrostatics work. > I can't see how to use a voltage divider with the electrometer. If you know how, please let me know. I don't have an electrometer, but will buy one. Someone in the UK has one he is going to dig out the garage, so I will probably buy that. > > Regards, > > Jerry > 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?
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 Sent from my SMRTphone Original message From: "Dr. David Kirkby" Date: 3/22/18 7:33 PM (GMT-06:00) To: Discussion of precise voltage measurement Subject: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms? I want to measure a high voltage, but put minimal load on the circuit. Looking at the Keithley electrometers, the input resistance is at least 200 T ohms, but they tend to have a maximum of 200 V FSD. A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which itself is easy to measure. But one can't buy 200 T ohm resistors. I looked at RS in the UK, and the highest value resistor I could find is 1 T ohm, and they are £163 each (around $200). Maybe fabricating ones own resistor is possible, but I suspect there's a better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV range, and there's no way that can be measured with an ammeter, which would require an ammeter with a full scale deflection of 1 fA, which is much smaller than the 2 pA FSD on its most sensitive range. Any thoughts? Dr David Kirkby Ph.D C.Eng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom. Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 01621-680100 / +44 1621-680100 ___ 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
On 23 March 2018 at 01:07, Bob Albert via volt-nuts wrote: > I found several electrostatic voltmeters on ebay. The brand I remember > is Sensitive Research. > Bob > So something like this? https://www.ebay.com/itm/Singer-ESD-7-Sensitive-Research-Electrostatic-Voltmeter-1500-Volt-Range/122976453378 1500 V would probably do. I must admit, I don't understand how these work. Do you need to have a power supply to balance the voltage? I can't see how taking almost no current can physically make a meter needle move, as that needs energy. I see some are contact, and some non-contact. It is 01:45 here, so I am just about to go asleep, but will read any replies later today. I would be interested in making a more modern version, but really don't know how. 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?
How about using a high voltage probe that used to be commonly used to measure anode voltages of TV picture tubes. There were probes that had a KV meter built into the probe and there are ones that were used with VOM'S. Joe K3WRY In a message dated 3/22/2018 8:59:08 PM Eastern Standard Time, bruce.griffi...@xtra.co.nz writes: Electrostatic voltmeter? Either the classical version or the modern electronic variant perhaps? Bruce > > On 23 March 2018 at 13:33 "Dr. David Kirkby" > wrote: > > I want to measure a high voltage, but put minimal load on the circuit. > Looking at the Keithley electrometers, the input resistance is at least 200 > T ohms, but they tend to have a maximum of 200 V FSD. > > A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which > itself is easy to measure. But one can't buy 200 T ohm resistors. I looked > at RS in the UK, and the highest value resistor I could find is 1 T ohm, > and they are £163 each (around $200). > > Maybe fabricating ones own resistor is possible, but I suspect there's a > better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV > range, and there's no way that can be measured with an ammeter, which would > require an ammeter with a full scale deflection of 1 fA, which is much > smaller than the 2 pA FSD on its most sensitive range. > > Any thoughts? > > Dr David Kirkby Ph.D C.Eng MIET > Kirkby Microwave Ltd > Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, > Essex, CM3 6DT, United Kingdom. > Registered in England and Wales as company number 08914892 > http://www.kirkbymicrowave.co.uk/ > Tel 01621-680100 / +44 1621-680100 > > ___ > 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
The part I struggle with is “make one” as T ohm meters are ridiculously sensitive to things like fingerprints, for example. I had a hard time just putting cables together that had the particular… I was going to say insulation, but it was more than that, basically everything is important and specific when you are dealing with T ohm meters. Setting aside the stupid tri-bnc connector on most of them. How about just using a voltage divider with a standard electrometer? I’m sure you thought of that though. I like playing around with my Keithley 616 as you can show the kids how electrostatics work. Regards, Jerry > On Mar 22, 2018, at 6:00 PM, Bob Albert via volt-nuts > wrote: > > What about an electrostatic voltmeter? Those have been around for decades > and draw zero static current. You didn't indicate how accurate your > measurement needs to be. I am trying to recall the maker of the unit, I think > ESI but not sure. > They were somewhat popular in the 1950s as I recall and there should be some > around, gathering dust and mold, in storage places. They were large, which > is a benefit because they had a long scale with good resolution. > Bob >On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby > wrote: > > I want to measure a high voltage, but put minimal load on the circuit. > Looking at the Keithley electrometers, the input resistance is at least 200 > T ohms, but they tend to have a maximum of 200 V FSD. > > A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which > itself is easy to measure. But one can't buy 200 T ohm resistors. I looked > at RS in the UK, and the highest value resistor I could find is 1 T ohm, > and they are £163 each (around $200). > > Maybe fabricating ones own resistor is possible, but I suspect there's a > better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV > range, and there's no way that can be measured with an ammeter, which would > require an ammeter with a full scale deflection of 1 fA, which is much > smaller than the 2 pA FSD on its most sensitive range. > > Any thoughts? > > Dr David Kirkby Ph.D C.Eng MIET > Kirkby Microwave Ltd > Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, > Essex, CM3 6DT, United Kingdom. > Registered in England and Wales as company number 08914892 > http://www.kirkbymicrowave.co.uk/ > Tel 01621-680100 / +44 1621-680100 > ___ > 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
I found several electrostatic voltmeters on ebay. The brand I remember is Sensitive Research. Bob On Thursday, March 22, 2018, 6:00:39 PM PDT, Bob Albert via volt-nuts wrote: What about an electrostatic voltmeter? Those have been around for decades and draw zero static current. You didn't indicate how accurate your measurement needs to be. I am trying to recall the maker of the unit, I think ESI but not sure. They were somewhat popular in the 1950s as I recall and there should be some around, gathering dust and mold, in storage places. They were large, which is a benefit because they had a long scale with good resolution. Bob On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby wrote: I want to measure a high voltage, but put minimal load on the circuit. Looking at the Keithley electrometers, the input resistance is at least 200 T ohms, but they tend to have a maximum of 200 V FSD. A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which itself is easy to measure. But one can't buy 200 T ohm resistors. I looked at RS in the UK, and the highest value resistor I could find is 1 T ohm, and they are £163 each (around $200). Maybe fabricating ones own resistor is possible, but I suspect there's a better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV range, and there's no way that can be measured with an ammeter, which would require an ammeter with a full scale deflection of 1 fA, which is much smaller than the 2 pA FSD on its most sensitive range. Any thoughts? Dr David Kirkby Ph.D C.Eng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom. Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 01621-680100 / +44 1621-680100 ___ 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
If buying new equipment is OK, then maybe look at http://www.trekinc.com/ Contacting Voltmeter 1 x 10^15 ohm up to 2 kV, or Non-Contacting models. Best Regards, Laurence Motteram Calibration & Service Manager Scientific Devices Australia Ph: +61 (0)3 9569 1366 M: +61 (0)425 765 019 www.scientific-devices.com.au lmotte...@scientific-devices.com.au -Original Message- From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Dr. David Kirkby Sent: Friday, 23 March 2018 11:33 AM To: Discussion of precise voltage measurement Subject: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms? I want to measure a high voltage, but put minimal load on the circuit. Looking at the Keithley electrometers, the input resistance is at least 200 T ohms, but they tend to have a maximum of 200 V FSD. A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which itself is easy to measure. But one can't buy 200 T ohm resistors. I looked at RS in the UK, and the highest value resistor I could find is 1 T ohm, and they are £163 each (around $200). Maybe fabricating ones own resistor is possible, but I suspect there's a better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV range, and there's no way that can be measured with an ammeter, which would require an ammeter with a full scale deflection of 1 fA, which is much smaller than the 2 pA FSD on its most sensitive range. Any thoughts? Dr David Kirkby Ph.D C.Eng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom. Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 01621-680100 / +44 1621-680100 ___ 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
What about an electrostatic voltmeter? Those have been around for decades and draw zero static current. You didn't indicate how accurate your measurement needs to be. I am trying to recall the maker of the unit, I think ESI but not sure. They were somewhat popular in the 1950s as I recall and there should be some around, gathering dust and mold, in storage places. They were large, which is a benefit because they had a long scale with good resolution. Bob On Thursday, March 22, 2018, 5:33:28 PM PDT, Dr. David Kirkby wrote: I want to measure a high voltage, but put minimal load on the circuit. Looking at the Keithley electrometers, the input resistance is at least 200 T ohms, but they tend to have a maximum of 200 V FSD. A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which itself is easy to measure. But one can't buy 200 T ohm resistors. I looked at RS in the UK, and the highest value resistor I could find is 1 T ohm, and they are £163 each (around $200). Maybe fabricating ones own resistor is possible, but I suspect there's a better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV range, and there's no way that can be measured with an ammeter, which would require an ammeter with a full scale deflection of 1 fA, which is much smaller than the 2 pA FSD on its most sensitive range. Any thoughts? Dr David Kirkby Ph.D C.Eng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom. Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 01621-680100 / +44 1621-680100 ___ 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Electrostatic voltmeter? Either the classical version or the modern electronic variant perhaps? Bruce > > On 23 March 2018 at 13:33 "Dr. David Kirkby" > wrote: > > I want to measure a high voltage, but put minimal load on the circuit. > Looking at the Keithley electrometers, the input resistance is at least > 200 > T ohms, but they tend to have a maximum of 200 V FSD. > > A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which > itself is easy to measure. But one can't buy 200 T ohm resistors. I looked > at RS in the UK, and the highest value resistor I could find is 1 T ohm, > and they are £163 each (around $200). > > Maybe fabricating ones own resistor is possible, but I suspect there's a > better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV > range, and there's no way that can be measured with an ammeter, which > would > require an ammeter with a full scale deflection of 1 fA, which is much > smaller than the 2 pA FSD on its most sensitive range. > > Any thoughts? > > Dr David Kirkby Ph.D C.Eng MIET > Kirkby Microwave Ltd > Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, > Essex, CM3 6DT, United Kingdom. > Registered in England and Wales as company number 08914892 > http://www.kirkbymicrowave.co.uk/ > Tel 01621-680100 / +44 1621-680100 > > ___ > 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] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
I want to measure a high voltage, but put minimal load on the circuit. Looking at the Keithley electrometers, the input resistance is at least 200 T ohms, but they tend to have a maximum of 200 V FSD. A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which itself is easy to measure. But one can't buy 200 T ohm resistors. I looked at RS in the UK, and the highest value resistor I could find is 1 T ohm, and they are £163 each (around $200). Maybe fabricating ones own resistor is possible, but I suspect there's a better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV range, and there's no way that can be measured with an ammeter, which would require an ammeter with a full scale deflection of 1 fA, which is much smaller than the 2 pA FSD on its most sensitive range. Any thoughts? Dr David Kirkby Ph.D C.Eng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom. Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 01621-680100 / +44 1621-680100 ___ 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.