[volt-nuts] Using a DVM to adjust a 752a divider

[acbern at gmx.de]

Resend as it did not go to the group (please also see my question at the end of my mail):


mitch,

you bring up a good point. I did not know the document, thanks for sharing. it inspired me to do some measurements, thats why it took a while to respond. the results were quite surprising to me.

i did test the 752a with the following gear:
-keithely 182-m (this is a 182 nanovoltmeter that has an internal 9v battery in its input stage, i compared it with a standard 182 some time ago and it did have about half its peak to peak noise. have not found any data on it on the web btw.)
-34420a nanovoltmeter
-keithley 2182 nanovoltmeter
-3458a
-keithley 155 (in battery operated mode)

my results in a nutshell:
besides the 40k source test as mentioned in the app-note, i also tested them with the 752a in cal mode and the input voltage of the source (5440a) set to 0 (so besides some small emf-vltages, the result should be 0 after temp stabilization). 

only the 2182 had 1+uv input measurement when doing the 40k-test, meaning all others, since they passed the test, should be usable. but it also turned out that the reading when connected to the 752a with uin = 0v, was not acceptable for others. this may also have had to do with some ground loop issues, although quick checks did not reveal any obvious issues (and there was no issue with loops with those meters that passed).

so at the end of the day, the only usable devices in my test were the 3458a and the 155. 


what I found as well, unfortunatelly, was that my 752a had an issue in the 1:100 range. I had not used it for half a year or so, and when i tried to calibrate it, everything was fine at 1:10, but I could not zero at 1:100. consistent redings with both 3458a and 155. drift relatively unstable and in the -500uv range, so pretty high deviation. also, after I had then set the internal tune setting resistors to zero (so I cannot go below), there still remains an offset of a few hundred uv. 

anybody had similar experience with the 752a? 


thanks
adrian