Hi Felix,
By pluging directly the 10M ohm resistor on the PSU and with 2 banana wire plus an aligator clamp, I get the same result.
I am able to measure the expected 100 nA in a 10 Mohm resistor with 1V on my dc supply on the mA range : (I measure 0.10 mV)
For 2V, I am able to measure 0.20 mV, 0.30 mV for 3V It's pretty accurate.
But in the nA range, it's totally not the case. After a switch to nA range, I measure 0.37 mV for the same 100 nA expected to flow in the resistor.
So it cannot be à problem of noise. If I have 400 nA of noise in the circuit, why is it picked only by the nA range, and not by the mA range ?
Moreover, if I put a 1M ohm resistor in parralele to the 10M ohm, it add 1000 nA in the current ranger (with 1V on the PSU), and I correctly measure 1100 nA.
So it really seem there is a non linear offset voltage on my current ranger on the nA range.
For now I have to add some resistor in parallel to use my current ranger in the "linear part" of the nA range.
By the way, I don't know if it's a part of the problem, but, I use the display of the current ranger to show values, and I see it jumping all over the place.
For example, while measuring the 1100 nA in the 10M // 1M parallel resistor from 0 to 2000 nA while I measure nA currents. The multimeter show a smooth 1100 mV.
Thanks for your help.