Specifications

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To avoid the ground loop noise effect caused by common-mode
voltages, you can connect the signal ground to the Low input.
Fig. 3-3 shows a differential channel connection between a
ground-reference signal source and an input channel on the
PCI-1710/1710L/1710HG/1710HGL/1716/1716L. With this
connection, the PGIA rejects a common-mode voltage V cm between
the signal source and the PCI-1710/1710L/1710HG/1710HGL/1716/
1716L ground, shown as V cm in Fig. 3-3.
Fig. 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