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must exist between LOW and ground to define a common reference
point for floating signal sources. To measure a floating source
connect the input channel as shown below:
If the signal source has one side connected to a local ground, the
+
Vs
-
signal source ground and the PCL-818L 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 voltages 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 PCL-818L ground directly. In some
cases you may also need a wire connection between the PCL-818L
ground and the signal source ground for better grounding. The
following two diagrams show correct and incorrect connections for a
differential input with local ground:
+
Vs
-
HIGH
Vin
LOW
A.GND
HIGH
LOW
GND
_
+
Vcm
+
+
-
-
+
+
Vin
-
-
Chapter 3 Signal connections
Vin=Vs
23
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