Keithley 197 DMM - issue with uV DC/AC - diyAudio
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Old 22nd February 2013, 01:55 PM   #1
Telstar is offline Telstar  Italy
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Join Date: Dec 2007
Location: Italy
Default Keithley 197 DMM - issue with uV DC/AC

Hi guys,

I have this bench DMM, bought 2 years ago. Since last week the highest sensitivity ranges readings are out of whack with values that start from 0.2V and go to 1V with or without probes attached. If i set the range immediately greater (200m), everything is fine. Therefore I cannot do measurements smaller than 0.1 mV, which is OK for DC offsets, but not for measuring the ripple of a PSU.
This is ******* me off very much.

I checked the manual, which says only to zero (with probes shorted I read all 0 or almost that, so it is NOT a DC offset issue), and be careful of EMC. I dont believe I have halv volt of DC floating in the air... but If i get closer or farther from the multimeter (or the probes, if attached) the voltage fluctuates a good .3-.4V (!)

The DMM is mains-powered, and I don't have the battery-pack installed (but I plan to get one if i find reasonably cheap).

I googled but didnt find any help. So thanks in advance to anyone giving me some clue.
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Old 25th February 2013, 12:14 PM   #2
Telstar is offline Telstar  Italy
diyAudio Member
 
Join Date: Dec 2007
Location: Italy
found the issue (it was the probes!)
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"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
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