Advantech PCI-1718 Manual de usuario descargar pdf (Pagina 39)

31 Chapter 3

If the signal source has one side connected to a local ground, the signal

source ground and the PCI-1718HDU/HGU ground 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 volt-

ages forms a common-mode voltage.

To avoid the ground loop noise effect caused by common-mode voltages,

connect the signal ground to the LOW input. Do not connect the LOW

input to the PCI-1718HDU/HGU ground directly. In some cases you may

also need a wire connection between the PCI-1718HDU/HGU ground

and the signal source ground for better grounding. The following two dia-

grams show correct and incorrect connections for a differential input with

local ground:

Correct Connection

Incorrect Connection

HIGH

LOW

Vin

Vcm GND

Vin=Vs

Vcm

HIGH

LOW

GND

Vin

-Vin=Vs+Vcm

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Advantech PCI-1718 Manual de usuario Pagina 39