Hello,
I finally analysed the Ohm function.
The 500k and 5M ranges are especially unstable, sometimes giving an unreadable display.
But sometimes, also the 50 Ohm range is unstable on the last two digits, but may stabilize after some 'warmup'.
The 50M range sampling rate is a bit slower, and therefore delivers more stable readings, which makes sense for these high values.
Anyhow, it seems that in this range, there also exist some disturbance, which cause a virtually static shift of the reading (gain error).
I have digitized the probing current of the 121GW by means of my 34465A.
All currents from 470µA down to 20nA, were absolutely stable apart from some amplifier noise.
When I digitized the voltage across the D.U.T. resistor, I encountered a huge 50Hz signal, 100mVpp @ 700mV DC, which might be picked up by the mains environment (Germany = 50Hz). The 121GW seemed to be extremely sensitive to that 50Hz pickup, although its A/D should suppress the mains frequencies of either 50Hz, or 60Hz.
I have the suspicion, that the sampling rate especially in Ohms mode is not selected correctly, for 60Hz only, so that this would be stable in U.S. or other countries with 60Hz mains frequency, but unstable here in Europe.
Do other owners here in EU see that same effect?
How can I check inside the guts of the 121GW, which mains frequencies are suppressed?
Frank