The preamp outputs 0,09 always in all ranges. At least it is stable
For current is outputs -0,09. So changes the polarity.
Both the preamp and the display show the same value in all ranges, e.g. I mean 90mV in all ranges.NO! Sorry, I was wrong. For volts it shows 90mV in all ranges. But in resistance it shows this in the ranges, with rounded values:
0,09G -> 0,090G -> 0,0900G
9,00M -> 0,900M -> 0,0900M
9,00k -> 0,900k -> 0,9000k
0,90mA -> 0,9000mA
0,90uA -> 0,900uA -> 0,9000uA
0,90nA -> 0,900nA -> 0,9000nA
For picoamps the sequence is the same. Actually for current it is straightforward, it is always 0,9xxx.
It seems an offset voltage is injected somewhere in the measurement loop.