Solution
A variety of phenomena, such as the instrumentation amplifier input bias currents, can cause the voltage level of a floating source to go out of the valid measurable range of the DAQ board. To anchor this voltage level to some reference, bias resistors (10k-100kOhm) should be used to provide a DC path from the instrumentation amplifier inputs to its ground.
- For DC-coupled signals only 1 resistor is necessary and should be placed across the (-) terminal of the signal input and the measurement system ground (AIGND).
- For AC-coupled signals, in addition to the (-) bias resistor mentioned above, another resistor should be placed across the (+) terminal of the signal input and AIGND.