Measurement Computing CIO-DAS160x/1x - Manual (Page 17)

NOTE
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
120VAC outlets happen to be on different phases.)
CIO-DAS1600 and signal source already have isolated grounds
Some signal sources will already be electrically isolated from the CIO-DAS1600. 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.
5.2 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
Table 5-1 below.
Table 5-1. Input vs. Grounding Recommendations
Ground Category Input Configuration Our Recommendation
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 eight possible input
configuration/grounding combinations.
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