removing usb-6009 floating voltage

[mgbglasgow]

hello,

I have created a VI that logs 6 voltages from 6 seperate batteries, and all is well, until i disconnected one of the batteries and it stills sees approx 1.4 volts. how can i remove this offset(?)

Is it present on the connected readings?

Regards

Steven

[Dennis_Knutson]

You are probably seeing what is called 'ghosting'. There are numerous threads on this. You can do a search for this. One solution is to not leave any inputs floating.

[mgbglasgow]

i have to test batteries down to below 1.0 volts, will this ghosting be present then with a 1ma load?

Steven

[johnsold · Accepted solution]

The USB-6009 has a non-standard input circuit which is terminated into ~1.4 V through ~144000 ohms. Check the manual for a schematic.

As long as your source has an impedance much lower than 144000 ohms and can sink current (if the source voltage < 1.4V), then you should be OK.  Batteries, even nearly discharged, should not be a problem.

Lynn