Keithley 2015 Won't Save Calibration  - Page 1
Forum section: electronics / general

author: oddiohead44
author_rank: Newbie
timestamp: December 30, 2018, 09:26:45 am
content: Hi everyone! I am wondering if somebody can help me with this issue.I had to replace some components in one of my 2015 meters and I had to do a partial calibration. DCV, R and DCI. After I have finished all of those test spot on against my 34401 which I know is within spec. I choose Y to save and everything seems fine until I turn the power off and when I turn it back on it reverts back to where it was before I calibrated it.Any thoughts?

author: oddiohead44
author_rank: Newbie
timestamp: December 31, 2018, 04:04:05 am
content: Nobody?

author: TiN
author_rank: Super Contributor
timestamp: December 31, 2018, 05:36:24 am
content: Does it give any errors after any calibration step? If error generated, than meter will reject calibration and lock out of calibration mode.

author: oddiohead44
author_rank: Newbie
timestamp: December 31, 2018, 07:05:38 am
content: Hi there! I was hoping you would chime in! I have watched every video and read every article that you have produced. No it shows no errors whatsoever. If I check all of the values compared to my 34401 they are bang on! But as soon as I turn it off and back on it reverts back to the previous cal status. Problem with NVRAM U136?I did have to do some extensive repairs to the power supplies and the voltage reference circuity.

author: oddiohead44
author_rank: Newbie
timestamp: January 01, 2019, 09:59:36 pm
content: The voltages on pin 1 and 3 of the TF-245 are 14.123 and -14.123 and the schematic shows +-14. I would have imagined that the error could have been taken out during calibration. The lm399 is producing 7.06 V. The original reference has a green mark on top. I am assuming hand selected. Lowering that voltage to 6.95 volts shows almost dead on accuracy. Am I on the right track? Should I not be able to cal that difference out? Thanks for any help in this matter.

author: Andreas
author_rank: Super Contributor
timestamp: January 01, 2019, 10:34:40 pm
content: Hello,6.95 V is the nominal voltage according to data sheet.So it could be that this is also some default value.Tolerance is worst case +/-4%. So calibration should work within these limits.The original references are selected at least for a maximum ageing drift.(with the data sheet specs of the reference you cannot guarantee the 1 year tolerances of the instrument).And most probably there is also a selection for (popcorn-) noise.If you want a highly stable instrument you should go for references with a voltage near 6.875 Vsee here:https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg422367/#msg422367with best regardsAndreas

author: Macbeth
author_rank: Super Contributor
timestamp: January 01, 2019, 11:09:05 pm
content: Are you doing front panel manual calibration? (The "press Y" indicates this). Front panel requires going through complete procedures.Do the same cal procedure using RS232 or GPIB and you will be able to save calibration at any point. You still have to go through the chain but you can stop and save before you have to recal ohms and DCI, etc.

author: oddiohead44
author_rank: Newbie
timestamp: January 02, 2019, 03:09:27 am
content: Thanks guys for the replies. I am going to try it through GPIB. I figured it was something trivial like that as it actually did accept the references and worked great until I powered down.