Measurement Computing CIO-DAS6402/12 - Manual (Page 14)

NOTE
Do not rely on the earth prong of a 120VAC receptacle for signal ground connections. 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-DAS6402 and signal source already have isolated grounds
Some signal sources will already be electrically isolated from the CIO-DAS6402. 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 Table 4-1 below.
Table 4-1. Input vs. Grounding Recommendations
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 eight possible input configuration/grounding
combinations.
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