Relying on the earth prong of a 120VAC for signal ground connections is not advised.. Different
ground plugs may have large and potentially even dangerous voltage differentials. Remember that the
ground pins on 120VAC outlets on different sides of the room may only be connected in the basement.
This leaves the possibility that the “ground” pins may have a significant voltage differential (especially
if the two 120 VAC outlets happen to be on different phases!)
PCI-DAS1000 and signal source already have isolated grounds
Some signal sources will already be electrically isolated from the PCI-DAS1000. The diagram below shows a typical
isolated ground system. These signal sources are often battery powered, or are fairly expensive pieces of equipment (since
isolation is not an inexpensive proposition), isolated ground systems provide excellent performance, but require some extra
effort during connections to assure optimum performance is obtained. Please refer to the following sections for further
details.
4.2 WIRING CONFIGURATIONS
Combining all the grounding and input type possibilities provides us with the following potential connection configurations.
The combinations along with our recommendations on usage are shown in the chart below.
Ground Category
Input Configuration Our view
Recommended
Differential Inputs
Already Isolated
Grounds
Acceptable
Single-ended Inputs
Already Isolated Grounds
Unacceptable without
adding Isolation
Differential Inputs
Common Mode
Voltage > +/-10V
Unacceptable without
adding Isolation
Single-Ended Inputs
Common Mode
Voltage > +/- 10V
Recommended
Differential Inputs
Common Mode
Voltage < +/-10V
Not Recommended
Single-Ended Inputs
Common Mode
Voltage < +/-10V
Acceptable
Differential Inputs
Common Ground
Recommended
Single-Ended Inputs
Common Ground
The following sections depicts recommended input wiring schemes for each of the 8 possible input configuration/grounding
combinations.
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