Advantech PCI-1713U, Руководство пользователя

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15 Chapter 3
Differential Channel Connections
The differential input configuration has two signal wires for each chan-
nel, and the differential input responds only to voltage differences
between High and Low inputs. On the PCI-1713U card, when all chan-
nels are configured to differential input, up to 16 analog channels are
available.
Figure 3.3: Differential Input Ch. - Grounded
If one side of the signal source is connected to a local ground, the signal
source is ground-referenced. The ground of the signal source and the
ground of the PCI-1713U will not be at exactly the same voltage, as they
are connected through the ground return of the equipment and building
wiring. 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-referenced signal
source and an input channel on the PCI-1713U card. With this connec-
tion, the PGIA rejects a common-mode voltage V
cm
between the signal
source and the PCI-1713U ground, shown as V
cm
in Figure 3-3.
External Internal
Ground-
Referenced
Signal
Source
Multiplexer
Multiplexer
PGIA
AI30
AI31
Measured
Voltage
_
+
AI0
AI2
AI1
AI3
GND
I/O Connector