NI USB-5132/5133 AC/DC/GND Coupling
The NI 5132/5133 has software selectable AC, DC, and GND coupling. Select AC coupling if the input signal has a DC component that you want to reject, provided you are not concerned about low-frequency flatness. A DC input adjustment is available if you do not want to enable AC coupling.
Ground coupling internally connects the input to the local ground.