Mickle writes:
Solartron 7071/7081 manuals don't have official information about the Only one of the docs - Instruments Test Specification - have a 10 V noise limits: "10 V noise - The rms noise of 10 readings at 10 V is measured. It must be less than 3 uV". This is roughly equal to 12 uV p-p (with p=0.998, f=10). My old measurements (7.5-digits, short, 5-10 minutes): 0.1 V = 0.2 uV 10 V = 5 uV
Correct, not quite sure what I was thinking there. Re-reading what the OP said, looked like he was measuring the p-p reading over 10 mins. The posted values I gave were 'transfer standard' worst-case stability values at full scale, which of course isn't noise, but is a passable average over the specified transfer time limit. An averaged measurement over 10 mins should be pretty close to within those values, and of course you wouldn't make a precision measurement without averaging multiple samples. I actually have a 7081, but that shouldn't matter for the noise measurement (except possibly for a selected zener). My measured 7.5 digit p-p over 5 mins was 3uv (+2, -1). I've noticed that the average reading variation is usually in that range, but looking at a histogram of a few hundred readings, there are certainly occasional significant glitches of multiple microvolts. It's really hard to determine the source of those kinds of glitches, which is why when I'm trying to make the best measurements I can, I capture the samples and process them myself, throwing our any outliers. I also decided to check calibration, because I haven't recalibrated in over a year. I use dual Datron 4910's that I compare to each other, sending one out for Fluke calibration if they disagree by more than 2 ppm. I used to pay for hot-shipping, but Fluke said not to bother. Anyway, my 7081 has only drifted by 5ppm. I'm impressed. Question - did you find the switch to the LTC1052 to make a significant difference? That's an easy one to do, and I always have some on hand. I've considered making the LTZ1000 replacement you did, since I have a spare ref board from a 3458A, but given the stability of my meter, not sure if this is really worth the effort. Any opinion? -- Bill Ezell ---------- The day Microsoft makes something that doesn't suck will be the day they make vacuum cleaners. _______________________________________________ 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.
