I would like to use the analog output of a USB-6356 to bias a signal comming into an analor input

[BlingBling]

In theory if I wire the signal to the A+ and A- terminals, then wire the analog output to the A- and Agnd terminal, I should be able to subtract the bias voltage from the signal voltage to eliminate the background voltage. This, however, is not working. Does anyone have any recomendations?

[Henrik_Volkers]

Superposition is the key 😉

To see the influence of one voltage source, you have to shortcut (not in real!) the other source.

So you will find that whatever voltage you output, the differential input will only see your sensor source.

If you wire the sensor and the output in series you will able to bias the sensor output.

However, if you tell us the problem (or the task), maybe there is a better solution, like using a capacitor to decouple DC bias (measure in AC mode)

I am just afraid that you would like to source the sensor (what is normally done with a current source, or with a voltage source AND a matching resistor)