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2010 4 wire resistance measurements

Posted: September 18th, 2012, 2:46 pm
by ejohnson
I have a 2010 DMM. When I make 4 wire resistance measurements, the reading drifts down over at least 30 minutes.

For example after initial contact I get a reading of 0.001XXXX, after 30 minutes 0.0002XXX. Is this normal?

The unit had been powered up for 2 hours. It has also been calibrated recently.

Thank you

Re: 2010 4 wire resistance measurements

Posted: September 19th, 2012, 6:24 am
by Mark W
This sounds like a thermal EMF issue, which is caused by dissimilar metal junctions (DUT - Test leads). To verify, you could heat or cool the individual junctions and see if your measurement drift changes direction. What you have in effect is a thermocouple. This can be minimized by using high quality cables(copper) to make your connections and shielding to minimize temperature changes at the DUT. The REL function can be used right before taking your measurement to null out offset voltages.