On 2 May 2018 at 10:37, David C. Partridge <[email protected]> wrote:
> My bet is that they've lost the "secret sauce" for updating the EEPROM :( > So it's measuring as best it can with no calibration adjustments stored. > > Dave > Dave, Your comment got me to check something, which reveals something VERY interesting, and is perhaps the source of the problem! I owe you a beer! I initially assumed the calibration procedure required some software to check the performance of the 4339B, and if out of specificaton update the EEPROM. But upon reading the user and service manuals, I find that's NOT the case. The user manual describes how to check the performance, which requires no software. The service manual describes how to adjust the instrument if the performance is not right. The adjustment which needs software. Furthermore, it seems to me the procedure used by Keysight to verify the performance maybe wrong, although I am not going as far to say it is, as maybe they are doing something that's not obvious from the calibration certificate. Looking in the user manual, it would appear one is supposed to verify the performance on the 10 nA range by setting the output voltage of the 4339B to 1 V, measure the voltage on a 3458A, set a resistance box to 10^8 ohms and calculate the current, which should not be assumed to be 10 nA unless the 3458A indicated 1.00000000 V, I have not checked the specification of the 4339B when generating 1 V, but when set to 0 V, it should output 0 +/- 0.1 V and when set to 10 V it should output 10 +/- 0.12 V. So at low voltages, this is not an accurate voltage source. At higher voltages it is a lot more accurate. This reflects my experience when using it to measure close tolerance resistors - measuring them at low voltages gives poor results, but at higher voltage, the resistances are measured more accurately. I am wondering if Keysight are assuming the 10 nA is generated when the output voltage is set to 1.0 V. If out of specification, the EEPROM should be updated with software. I'm assuming that software is written to compute current based on what voltage the 3458A measures, rather than what voltage the 4339B is set to output. To answer Illya's questions, the EEPROM is a Xicor X28C64P-20. I can't find any reputable supplier with those - plenty on eBay, but I am always concerned about counterfeits on there. Someone suggested a Mouser P/N. AT28C64B-15PU would probably do, but I decided to buy the EEPROM directly from Keysight (P/N 1818-4808). I'm glad I did, as it is removed any doubt about the suitability of the EEPROM. I'm sure if I had bought the EEPROM from Mouser or eBay, Keysight would have suspected an incompatibility of the EEPROM. This has certainty got me thinking about what might be happening, although the fact Keysight have said they can't update the EEPROM, suggests they have the software to do it. Dave _______________________________________________ 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.
