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Chapter 3 Signal Connections 15

Differential Channel Connections

The differential input configuration has two signal wires for each

channel, and the differential input responds only to voltage differenc-

es between High and Low inputs. On the PCI-1713 card, when all

channels are configured to differential input, up to 16 analog

channels are available.

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-1713 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

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-1713 card.

With this connection, the PGIA rejects a common-mode voltage V

between the signal source and the PCI-1713 ground, shown as V

Figure 3-3.

Figure 3-3: Differential input channel connection with grounded referenced

signal source

ExternalInternal

Ground-

Referenced

nal

Source

Multiplexer

PGIA

AI30

AI31

Measured

Volta

AI0

AI2

AI1

AI3

GND

I/O Connector

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Advantech PCI-1720 Manuale Utente Pagina 19