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HP 3457A DMM reads 0.550 Ohm over value
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Swake:
2-wire mode, 3 first ranges are over spec.


--- Code: ---Range Reading
 30 Ohm 00.44432 Ohm
300 Ohm 000.4279 Ohm
  3 kOhm 0.000443 kOhm
 30 kOhm 00.00022 kOhm
300 kOhm 000.0002 kOhm
  3 MOhm 0.000001 MOhm
 30 MOhm 00.00001 MOhm

--- End code ---
Kleinstein:
0.22 mOhm in 4 wire mode is OK. That corresponds to 0.22 µV of offset voltage, which is within the expected range for thermal EMF and errors from the calibration.
The 0.44 ohm difference with 2 wire mode can be from a relay contact and also the front / rear switch.
If really stable to switching of front / rear and 2/4 wire mode the offset for the 2 wire modes could be corrected in the calibration.
bdunham7:
OK, can you take the same 2W measurements with the wire only shorting the 2W terminals? 

It seems clear that you need to make sure that the offset is stable and doesn't change if you cycle the F/R switch or ranges.  If it is consistent, calibrate the 2W offset and it should be good.  If it is not consistent, then you get to have more fun.  The only nagging doubt I have is that with your readings, I'm not sure how it could have been miscalibrated like that.
Swake:
Similar reading with 2-Wire mode with only 2 wires shorted with a piece of clean 2.5mm² copper wire.
00.45005 Ohm. 2 last digits jumping around a bit.

Will keep it on for a couple hours, not that I expect it to change anything.

Now that you mention rear reading maybe it is important to know there is a 44492A multiplexer card inserted. Not the usual posts. There is nothing connected to that card at the moment. Have switched over from F/R and the several channels several times. Absolutely no change in resistance reading on the front in 2-wire.

Have also power cycled the DMM just in case, but this didn't change anything.

Thanks for your help, it is very much appreciated.

Swake:
Calibration done, all good, me happy


--- Code: --- Offset test 2-Wire Ohms
Range Reading
30 Ohm 00.00022 Ohm
300 Ohm 000.0002 Ohm
  3 kOhm 0.000000 kOhm
30 kOhm 00.00000 kOhm
300 kOhm 000.0000 kOhm
  3 MOhm 0.000000 MOhm
30 MOhm 00.00000 MOhm
300 MOhm 00.00000 MOhm

Offset test 4-Wire Ohms
Range Reading
30 Ohm 00.00012 Ohm

--- End code ---
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