3458A calibration forensics - Page 1
Forum section: electronics / general

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 05, 2021, 08:17:14 pm
content: I finally got an 3458A (Agilent branded) and was puzzled that CALNUM? returns 1. The meter was shipped in 2007 according to the Keysight website. The calibration string reads 20091105080621~37.4~MY45042... It also has a calibration sticker from 2012. I can see maybe the calibration lab didn't make any adjustments if it was within specs, but am not sure why the calibration string date, if original, doesn't match the shipping date. The other weird thing is that it gives SYSTEM ERROR 114- Non Volatile RAM checksum on turn on, but no other errors. The self-test and ACAL seem to work fine.

author: IanJ
author_rank: Unknown
timestamp: January 05, 2021, 08:24:28 pm
content: Quote from: maxwell3e10 on January 05, 2021, 08:17:14 pmHave you looked at the error list for other errors i.e. BLUE key ERROR key?SRAM issues:-http://literature.cdn.keysight.com/litweb/pdf/3458A-20.pdfIan.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 05, 2021, 08:47:00 pm
content: Yes, that seems to be the only error it gives and only on turn-on. Calibration seems to be OK as far as I tested it.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 05, 2021, 09:58:09 pm
content: A normal calibration only checks the readings and does not include adjustments. The cal counter usually only counts the adjustment cycles. It may happen that more than 1 is added if an adjustment is done in steps (e.g. resistance and voltage).There is battery buffered RAM for the calibration date, but also a separate one for less critical user settings. The bad checksum may effect only the non critical user data. One may have to reset the memory to clear the error. The error may be from glitch, like turning off at the wrong time. Most of the time the user data are non critical - so no worries about a drained battery here.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 05, 2021, 10:28:01 pm
content: I guess its possible that someone has performed a calibration in 2009 and updated the calibration string without making any adjustments. What is the typical threshold for making adjustments, 90 day specs?How can one reset user memory to clear the error?

author: MiDi
author_rank: Frequent Contributor
timestamp: January 05, 2021, 11:44:42 pm
content: If battery for user ram is dead than the ram would read random bits everytime it is powered on.It does not affect the reliability, so you have to live with the error on powerup or do a service for all nvsrams.A backup of the calram is recommended - there are tools to read it over gpib.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 05, 2021, 11:54:48 pm
content: Yes, that seems to be the problem, as I can't store and recall states with RSTATE command.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 06, 2021, 04:42:51 pm
content: Yea, it seems my problem is exactly the same as in this videoIs there a reason why the user memory battery runs out before the calibration memory, or its just a matter of luck?As far as memory backup, there is no easy way to put all the calibration constants back, is that right?But one can back-calibrate using any stable voltage source, stable resistor and a stable AC source for SCAL commands.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 06, 2021, 06:07:21 pm
content: Continuing with calibration forensics, the temperatures at the time of calibration read: cal?58: 35.5, cal?59: 38.3, cal?60: 38.6It doesn't seem that who ever has done this calibration (Agilent?) really waited for the temperatures to stabilize.

author: MiDi
author_rank: Frequent Contributor
timestamp: January 07, 2021, 09:56:38 pm
content: Quote from: maxwell3e10 on January 06, 2021, 04:42:51 pmDo not know the reason, but my HP3458A showed same behavior - user ram dead and calram healthy after nearly 30 years.If this is standard, than it is nice to get this warning before calram diesFor old DIL nvsram no worries as battery is inside package and before swapping just burn calram backup on new one.For newer revision with snaphat batteries it would be much more pain.Not sure if there is software somewhere to rewrite calram over gpib.If you have access to traceable & calibrated 10V & 10kstandard, no worries, not sure if special ac cal is mandatory.

author: martinr33
author_rank: Frequent Contributor
timestamp: January 07, 2021, 11:39:16 pm
content: There's an excellent article on non-volatile memories - with application to the 3458A - here:http://worldphaco.com/uploads/TEKTRONIX_2465b_OSCILLOSCOPE_CALIBRATION___REPOWERING_THE_DS1225.pdfThe high points for me are:- unsolder the ground pin last to maximize the chances of the memory being retained- when the battery is low, the RAM may still be good but you cannot read it. If you hack into the package and bring up the battery voltage, you can possibly recover the data.However, the whole thing is worth a read.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 08, 2021, 01:26:42 am
content: Thanks for an interesting reference. Luckily the meter has snaphat removable battery, which can be replaced without losing memory if the meter remains powered on. In case something goes wrong I believe one can restore old calibration constants (at least for voltage and resistance) by doing calibration backwards with any stable source. Calculate the ratio of default to saved calibration constant, measure any voltage near 10 V and adjust its value appropriately when entering as a calibration. Repeat as necessary until calibration constant is close enough to old saved value.

author: martinr33
author_rank: Frequent Contributor
timestamp: January 09, 2021, 12:32:53 am
content: That sounds pretty tricky - so the stability and noise of the 10V source don't matter as long as you can get the calibration constant close enough. Of course, if the 10V is too noisy, your chances of getting the number right in a reasonable number of tries drop qite a lot...Also, it looks like the SRAMs are now 28-pin, so maybe an MRAM will work.(although some of us are approaching the point where the batteries might last longer than we will)I guess we really need to figure out how to write that memory directly.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 14, 2021, 08:00:22 pm
content: When replacing the batteries I can see that Agilent just used two M40Z111MH NVRAM supervisor controllers which don't have any memory themselves but presumably back-up two or all three of the CY62188BLL 132kB SRAMs for calibration and user memory. They also use 120 mAh batteries. According to datasheet CY62188BLL has typical current of 1.5 uA, which gives 9 years for one SRAM chip back-up, assuming the meter stays mostly off. But this is probably a sensitive function of temperature. The battery closest to the edge of the board (user memory) was totally discharged, while the other battery was at 3V. The batteries had 2006 datecode.It doesn't seem to be a very efficient solution, backing up much more memory than necessary. Perhaps they don't mind so much if meters come back for re-calibration.

author: aronake
author_rank: Frequent Contributor
timestamp: October 28, 2024, 03:50:52 pm
content: Quote from: maxwell3e10 on January 05, 2021, 08:17:14 pmDid you eventually manage to fix the SYSTEM ERROR 114- Non Volatile RAM checksum error? Did you get to change the snaphat batteries and did that make a difference? Recalibrate?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: October 29, 2024, 05:25:43 am
content: Yes, I got two M4Z32-BR00SH1 batteries from Digikey and replaced them when the meter was powered on. Calibration was not lost and the error went away. Also for this generation 3458A one can get a free replacement chip from Keysight by asking nicely (as I learned somewhere on eevblog) and get full 100k memory.