Maybe one bad resistor? I've read that tin whiskering can occur even on relatively recent equipment, slower than lead free but still a problem. I'd do a visual inspection just to see, shouldn't be an issue. -A ________________________________________ From: volt-nuts <volt-nuts-boun...@febo.com> on behalf of Dr. David Kirkby <drkir...@kirkbymicrowave.co.uk> Sent: 02 March 2018 03:16:24 To: Discussion of precise voltage measurement Subject: [volt-nuts] Precision high resistance measurements / calibration of HP 4339B high-resistance meter.
I pickup up an HP/Agilent (front says HP, rear says Agilent) 4339B high-resistance meter from eBay. The 4339B has an internal supply up to 1000 V, an ammeter to measure current, and obviously computes resistance from Ohms Law. It is supposed to work up to 16 Peta ohms (1.6x10^16 ohms), which would pass a current of 62.5 fA with 1000 V. It was sold as non-working, with no output. Even attempting to get some output was challenging as it had an obscure 6-pin interlock connector, and there's no information in the manual about this. It also has a trixaxial input connector with a screw thread. I asked Keysight for some information about the connectors. I still don't know what the triaxial connector is, but I have the interlock sussed - a HiroseHR10A-7P-6P(73) plug fits, and there's some information about the wiring of this in the manual for the 11617C low-noise test leads. Keysight offered to do a free technical evaluation, so I thought I'd take them up on it, rather than waste too much time trying myself to get it working. It was sent to Keysight and they sent me a report showing there is output voltage, despite it being sold as having no output, and the output is all in spec. Unfortunately, it was out of spec on one of the current ranges. It is reading 0.082 nA low with a test current of 10 nA, but the specification is +/- 0.063 nA. So it is only a little bit out, but it is still out of spec. Test currents of 100 pA, 1 nA, 10 nA, 100 nA, 1 uA, 10 uA and 100 uA were used, so the 10 nA is neither at the low nor high end of the range of the meter. When I received an email copy of the free technical report, I assumed the 4339B had not been subjected to a full calibration as it was only tested with resistors up to 10^11 ohms, but it is supposed to read resistance up to 1.6 x 10^16 ohm, so the highest value resistor used during the technical evualation is 5 orders of magnitude lower than the what the meter can read. Also the meter was only tested at 100 V when reading resistors, whereas I would have thought it more sensible to test at a higher voltage, given it can output 1 kV. I decided to pay Keysight for a full calibration, so I got a cal certificate, which shows the out of spec reading. http://www.kirkbymicrowave.co.uk/tmp/1-9690444179-1-combined-file.pdf I was rather hoping the cal certificate would have some extra readings, but I actually received no more technical information than Keysight had given me for nothing, although they did update the firmware as I requested. I have two questions. 1) Is 10^11 ohms a practical limit on making resistors that can be used for calibration purposes? I don't know what the Keysight uncertainty on their calibration standards are, so maybe 10^11 ohms is all its practical to make. 2) Does anyone know if the meter can be adjusted on individual ranges? I find it a bit hard to believe that given the ammeter was tested with currents covering 6 orders of magnitude (100 pA to 100 uA), that there's no adjustment on individual ranges. I doubt that it is possible to design a circuit to cover that range, without switching in some different resistors at some point. But I'm told it can't be adjusted, and needs a new board. I'm wondering if anyone knows anything about this meter, just in case Keysight are wrong. I know they should not be, but it is not a current instrument, so it's just possible the engineer did not know it could be adjusted. 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 -- email@example.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- firstname.lastname@example.org To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.