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 -----Original Message----- From: volt-nuts [mailto:[email protected]] On Behalf Of Dr. David Kirkby Sent: 02 May 2018 00:47 To: [email protected]; Discussion of precise voltage measurement; [email protected] Subject: [volt-nuts] Two 4338B high resistance meters fail on the same range - Keysight can't adjust EEPROM of either. I"m pulling my hair out over an identical problem on two instruments. I am hoping someone might think of a possible cause I have not thought of. Sorry the post is a bit long, but this is not any easy problem to describe. I have an Agilent 4339B high resistance meter. This instrument essentially consists of a variable power supply (0.1 V to 1000 V) and a very sensitive ammeter. It works out resistance using Ohms Law. It can display resistance, current, surface resistively and volume resistively. The service manual states there are no adjustable components in this - all calibration is performed using software that updates an EEPROM. The EEPROM is on the CPU board. This was sent to Keysight in the UK for a firmware upgrade and calibration. They updated the firmware (stored in a ROM), but the 4339B failed calibration. * All the output voltages from the internal PSU were within specification. * The 10nA current range was slightly out of specification. It was reading about 0.8℅ high, but the specification is about +/- 0.6%, so it was only slightly out of specification. (All other ranges were within specification, but some were not far from the limits. One range might have been 0.5% off) I think the full scale of the current ranges are 10 pA to 100 uA, so 10 nA is not at either extreme. * All resistance measurements were within specification. (Keysight test up to 1e11 ohms, but it can read up to 1.6e16 ohms. I guess they simply can't get accurate resistors above 1e11 ohms). Calibration at Keysight includes any firmware upgrades if you request updates. It also includes the cost of any adjustments needed - unlike most calibration labs. Keysight said the EEPROM could not be adjusted to bring the 10 nA range within specification, so it needed a new CPU board. I never received a formal quote for repair, but I was told about £2000 (GBP), which seemed a lot considering the CPU board is about $600 (USD) from Keysight. These meters sell for around $3000, but other instruments available for far less use the same CPU. I was intending repairing my 4339B by swapping CPU boards from a cheaper instrument, and using a new EEPROM, just in case it was the EEPROM faulty, as that goes in a socket on the CPU board. However, I managed to find another 4339B at a good price, so that was purchased and plans to repair the first instrument were put on hold. I asked for a quote for calibration based on it having a blank EEPROM. I thought this would be advantageous, as Keysight could put each range "spot on". I expected the cost to be a bit higher but it was not. Much to my surprise, the instrument worked and seemed reasonably accurate even with the blank EEPROM. I sent this second 4338B to Keysight for calibration. A couple of days later i received an email from Keysight telling me the second instrument has a fault. The fault is on the 10 nA range (as the first instrument) and the EEPROM can't be adjusted (like the first instrument). This time it is reading about 0.7% low, which is not much out considering the specification is about +/- 0.6%. So I now have two 4339Bs, both being within specification on all ranges except 10 nA, and neither being adjustable! So naturally I queried why both instruments appear to have the same fault. I then received an email from someone st Keysight who had noticed I said the EEPROM was blank. He asked where did I get the EEPROM from. LUCKILY I had bought the EEPROM directly from Keysight, despite I could have got s very similar one from Mouser for a tenth of the price or a supposedly identical one for even less from China on eBay. I am hoping to speak to someone at Keysight tomorrow,, but does anyone have any ideas what could cause two instruments to be slightly out of specification on the same range, but neither instrument will allow them to update the EEPROM? Note one instrument reads high and the other low. I can understand that perhaps the resistors used in the current to voltage converter on the 10 nA range might be a bit less stable than used on other ranges, but I can't understand why Keysight can't bring the meters in spec just by updating the EEPROM. 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. _______________________________________________ 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.
