Advantech USB-4702, Руководство пользователя

Страница: 20 / 26

USB-4702 User Manual 14
Figure 3.2: Single-Ended Input Channel Connection
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-4702, when all channels are configured to differential
input, up to 4 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-4702. With this connection, the
PGIA rejects a common-mode voltage V
cm
between the signal source and
USB-4702 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 =0,2,4,6)