Hi
Can someone explain why there are so big differences between a old goldplated MC-connector an a cheap pomona clone with a wire as a shorting bridge.
In particular, I would be interested to know why the deviation from zero is not approximately the same after turning over.
Hello,
The mc short is quite fine, I also use them on my 3458A for shorting the input between measurements.
Usually, the e.m.f. is well below 200nV.
The Cu wire obviously is strongly oxidized, because its color is dark orange, instead of bright orange.
I can't recognize, which material this double jack has, but it's probably also not a low-e.m.f. alloy.
Therefore, you have built a nice thermocouple, which explains the big e.mf. of 1µV, as well the turnover effect.
Any small temperature difference, especially w/o shield, will give a huge e.m.f., which is not the case for properly designed shorts.
For zero calibration of the 3458A, a fresh, cleaned (polished) copper wire is required, which brings down the e.m.f. to around 100nV.
Frank