Cameron Baldwin

Good day,

I am using a keithley 6485 as an electrometer in combination with a DUT and a power supply. I am having a problem making measurements. When I make the connections which are as follows:

positive Power supply terminal to terminal of DUT
Other terminal of DUT to keithley BNC Input
I am using the common input at the back of the 6485 as a return path ( I Know one can also use the shielding for LO return path) to negative terminal of power supply.

The porblem i am having is after i have turned on the equipment and given sufficient warm up time, when i apply a voltage across the DUT the readings on the pico start at some high value and slowly trickle down (to what i am assuming is the correct value of current) however this trickling down can taken serveral minutes if not hours. Does anyone know what could be going wrong?

many thanks 
Cameron