Hi all To the best of my memory Keithley never made vibrating reed electrometers, the only one that I am aware of is the Varian Cary 401 which did use Sapphire insulators. I was the European product line specialist for Varian Cary in the late 1960/1970 era and was involved with the 401.
George G6HIG ________________________________________ From: volt-nuts <[email protected]> on behalf of [email protected] <[email protected]> Sent: 03 March 2018 17:00 To: [email protected] Subject: volt-nuts Digest, Vol 103, Issue 3 Send volt-nuts mailing list submissions to [email protected] To subscribe or unsubscribe via the World Wide Web, visit https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.febo.com%2Fcgi-bin%2Fmailman%2Flistinfo%2Fvolt-nuts&data=02%7C01%7C%7Cb5818846d36e4ecd914908d581283c52%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636556932161076932&sdata=cp01qd%2FkRw4yYSLYOqJ8RwUF8oOxtdqLVOmDal7gBhs%3D&reserved=0 or, via email, send a message with subject or body 'help' to [email protected] You can reach the person managing the list at [email protected] When replying, please edit your Subject line so it is more specific than "Re: Contents of volt-nuts digest..." Today's Topics: 1. Re: Precision high resistance measurements / calibration of HP 4339B high-resistance meter. (ed breya) 2. Re: Precision high resistance measurements / calibration of HP 4339B high-resistance meter. (Mitch Van Ochten) ---------------------------------------------------------------------- Message: 1 Date: Fri, 2 Mar 2018 09:22:32 -0800 From: ed breya <[email protected]> To: [email protected] Subject: Re: [volt-nuts] Precision high resistance measurements / calibration of HP 4339B high-resistance meter. Message-ID: <[email protected]> Content-Type: text/plain; charset=utf-8; format=flowed Oops - I think I didn't send this message properly yesterday - here goes again. Ed Yes, David, unless you go to very extreme measures, you won't see real R values that have any practical meaning beyond E12 ohms or so. Most practical insulation Rs may be around E12-E14 tops, unless you go to sapphire. Up in that region, the R may be all within a material, or include surface components like a film of dirt or moisture, or a fingerprint. E11 resistors can be made to fairly high precision, and maybe E12 nowadays. In the old days, higher values were made by stacking E11s - like ten in series to get E12 with decent precision. The glass packaging also limits how high it can go, due to leakage within and on the surface. I once used a glass reed relay capsule as an ultra-high resistance in a circuit. There was no precision or stability at all, but it made a nice high resistor (probably E14-ish dry) even though there was no element in there, and the circuit didn't care, as long as it was very high, but not infinite. The specs on this HP unit are likely just the most extreme capability taking maximum voltage over minimum current resolution, but any measurements would tend to be very noisy and unstable anyway. Also, testing at the extreme 1 kV makes the numbers seem more impressive, but the voltage coefficient of resistance will pretty much be unpredictable. If this is a digital meter, then the other spec trick that tends to obscure the real performance limit is that the ultimate resolution and noise is that last digit - or even last two or three - that may may be pretty jumpy, unless very long averaging time is used. There may be newer, fancier electrometers nowadays, but Keithley used to be the standard for these in the old days, before several digits of DVM resolution complicated the specs. They had a vibrating capacitor electrometer with all-sapphire input structure back in the 1970s/80s I think, that was the epitome of electrometers. I forget the model number, but vaguely recall that it could reach the aA region full scale - not that last digit of resolution thing. It's long obsolete, and I don't think they ever made anything actually better - only added DVM digits to less capable, conventional semiconductor amplifier techniques. If you can find info on it, it's an interesting read. I found a pdf of the manual years ago, but have no idea where it is now, or what info may still be around. Ed ------------------------------ Message: 2 Date: Fri, 2 Mar 2018 20:41:10 -0500 From: "Mitch Van Ochten" <[email protected]> To: "'Discussion of precise voltage measurement'" <[email protected]> Subject: Re: [volt-nuts] Precision high resistance measurements / calibration of HP 4339B high-resistance meter. Message-ID: <[email protected]> Content-Type: text/plain; charset="UTF-8" Here are specs from an older General Radio Bridge for observation. GR 1644-A specifications: Resistance Range: 1 kΩ to 1000 TΩ (10^3 to 10^15 Ω) in ten ranges. Accuracy: 10^3 Ω to 10^10 Ω, ±1 %. After self-calibration: 10^10 to 10^12 Ω, ±1%*; 10^13 Ω, ±2%; 10^14 Ω, ±10%; 10^15 Ω, ± one scale division. ΔR% Dial: ±5% range; accurate to ±0.2% or, for small changes, to ±0.1%. Test Voltage: Voltage accuracy is ±3% ±0.5 V. Fixed Voltages** 10 20 50 100 200 500 1000 v Best regards, mitch -----Original Message----- From: volt-nuts [mailto:[email protected]] On Behalf Of ed breya Sent: Friday, March 02, 2018 12:23 PM To: [email protected] Subject: Re: [volt-nuts] Precision high resistance measurements / calibration of HP 4339B high-resistance meter. Oops - I think I didn't send this message properly yesterday - here goes again. Ed Yes, David, unless you go to very extreme measures, you won't see real R values that have any practical meaning beyond E12 ohms or so. Most practical insulation Rs may be around E12-E14 tops, unless you go to sapphire. Up in that region, the R may be all within a material, or include surface components like a film of dirt or moisture, or a fingerprint. E11 resistors can be made to fairly high precision, and maybe E12 nowadays. In the old days, higher values were made by stacking E11s - like ten in series to get E12 with decent precision. The glass packaging also limits how high it can go, due to leakage within and on the surface. I once used a glass reed relay capsule as an ultra-high resistance in a circuit. There was no precision or stability at all, but it made a nice high resistor (probably E14-ish dry) even though there was no element in there, and the circuit didn't care, as long as it was very high, but not infinite. The specs on this HP unit are likely just the most extreme capability taking maximum voltage over minimum current resolution, but any measurements would tend to be very noisy and unstable anyway. Also, testing at the extreme 1 kV makes the numbers seem more impressive, but the voltage coefficient of resistance will pretty much be unpredictable. If this is a digital meter, then the other spec trick that tends to obscure the real performance limit is that the ultimate resolution and noise is that last digit - or even last two or three - that may may be pretty jumpy, unless very long averaging time is used. There may be newer, fancier electrometers nowadays, but Keithley used to be the standard for these in the old days, before several digits of DVM resolution complicated the specs. They had a vibrating capacitor electrometer with all-sapphire input structure back in the 1970s/80s I think, that was the epitome of electrometers. I forget the model number, but vaguely recall that it could reach the aA region full scale - not that last digit of resolution thing. It's long obsolete, and I don't think they ever made anything actually better - only added DVM digits to less capable, conventional semiconductor amplifier techniques. If you can find info on it, it's an interesting read. I found a pdf of the manual years ago, but have no idea where it is now, or what info may still be around. Ed _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.febo.com%2Fcgi-bin%2Fmailman%2Flistinfo%2Fvolt-nuts&data=02%7C01%7C%7Cb5818846d36e4ecd914908d581283c52%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636556932161076932&sdata=cp01qd%2FkRw4yYSLYOqJ8RwUF8oOxtdqLVOmDal7gBhs%3D&reserved=0 and follow the instructions there. ------------------------------ Subject: Digest Footer _______________________________________________ volt-nuts mailing list [email protected] https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.febo.com%2Fcgi-bin%2Fmailman%2Flistinfo%2Fvolt-nuts&data=02%7C01%7C%7Cb5818846d36e4ecd914908d581283c52%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636556932161076932&sdata=cp01qd%2FkRw4yYSLYOqJ8RwUF8oOxtdqLVOmDal7gBhs%3D&reserved=0 ------------------------------ End of volt-nuts Digest, Vol 103, Issue 3 ***************************************** _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
