National Instruments NI 9234 - Manual (Page 10)

NI 9234 Operating Instructions and Specifications 10 ni.com
NI 9234 Circuitry
The NI 9234 analog input channels are referenced to chassis
ground through a 50
Ω resistor. To minimize ground noise, make
sure the chassis ground is connected to earth ground. Each channel
is protected from overvoltages. The input signal on each channel is
buffered, conditioned, and then sampled by a 24-bit Delta-Sigma
ADC. You can configure each channel in software for AC or DC
coupling. For channels set to AC coupling, you can turn the IEPE
excitation current on or off. Refer to the software help for
information about configuring channels on the NI 9234.