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Chapter 3
– 25 – PCI-1712/1712L User’s Manual
Advantech Co., Ltd.
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same voltage. The difference between the ground voltages forms a
common-mode 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 ground-
reference signal source and an input channel on the PCI-1712/1712L.
With this connection, the PGIA rejects a common-mode voltage V
cm
between the signal source and the PCI-1712/1712L ground, shown as
V
cm
in Figure 3-3.
Figure 3-3: Differential input channel connection - ground reference
signal source
If a floating signal source is connected to the differential input
channel, the signal source might exceed the common-mode signal
range of the PGIA, and the PGIA will be saturated with erroneous
voltage-readings. You must therefore reference the signal source
against the AIGND.
Figure 3-4 shows a differential channel connection between a floating
signal source and an input channel on the PCI-1712/1712L. In this
figure, each side of the floating signal source is connected through a
resistor to the AIGND. This connection can reject the common-mode
voltage between the signal source and the PCI-1712/1712L ground.