User Manual

17 Chapter 3
3.3.2 Differential Input Connections
The differential input channels operate with two signal wires for each
channel, and the voltage difference between both signal wires is mea-
sured. On USB-4711A, when all channels are configured to differential
input, up to 8 analog channels are available.
If one side of the signal source is connected to a local ground, the signal
source is ground-referenced. Therefore, the ground of the signal source
and the ground of the card will not be exactly of the same voltage. The
difference between the ground voltages forms a commonmode voltage
(V
cm ).
To avoid the ground loop noise effect caused by common-mode voltages,
you can connect the signal ground to the Low input. Figure 3-3 shows a
differential channel connection between a grounded-reference signal
source and an input channel on USB-4711A. With this connection, the
PGIA rejects a common-mode voltage V
cm between the signal source and
USB-4711A ground, shown as V
cm in Figure 3-3.
Note: In differential input mode, the input channel n should be used with
channel n+1.
(n=0,2,4…14)
Figure 3.3: Differential Input Channel Connection