Hello,
my first post here, unfortunately reporting a problem and wondering have anyone ever seen a similar glitch.
Purchased for the Lab Keithley 6510 with 7708 40 channels scanner card, primarily for temperature measurement (both Pt100 RTD and thermocouples).
At first run I connected 12 channels Pt100 2W to test the heat exchanger, after two hours of logging measured results went blatantly weird (see picture, temperature in degC calculated from resistance).
Tested front and rear inputs with decade resistor, on continuous measurement results were Ok, but starting scanning measurement on the 7708 card readings went higher by several Ohms (!), both with Kickstarter and in the standalone mode. Tested for several days.
Borrowed new 7700 card from other department, upgraded FW to version 1.7, and for half day problem seemed solved, scanning went flawlessly.
Then after couple of hours measured resistances on the card went up and with jitter, playing with other parameters could not rectify the problem. Did not test voltage signals on the card.
At first the obvious suspect was the 7708 card, but the persistence of the problem with second card suggests problems in software.
Returned 6510/7708 under warranty to the local representative, got demo 2002 to keep working
.
Does anyone have suggestion how to pinpoint the problem, as I am dubious they will test 6510 and 7708 separately and find them valid, although I have stated that problem occurs only in scanning mode?