ADLINK PXI-2006 - Manual (Page 36)

26 Signal Connections
Differential Connection for Floating Signal Sources
Figure 3-3 shows how to connect a floating signal source to
DAQ/PXI-20XX in differential input mode. For floating signal
sources, you need to add a resistor at each channel to provide
a bias return path. The resistor value should be about 100
times the equivalent source impedance. If the source imped-
ance is less than 100ohms, you can simply connect the nega-
tive side of the signal to AGND as well as the negative input of
the Instru-mentation Amplifier, without any resistors at all. In
differential input mode, less noise couples into the signal con-
nections than in single-ended mode.
Figure 3-3: Floating source and differential input