Measurement Computing CIO-DAS16Jr/16 - Manual (Page 11)

2.2.8 Large Common Mode Voltages
If the ground differential is large enough, the CIO-DAS800’s +/- 10V common mode range will be exceeded. In this case
the CIO-DAS16Jr/16 cannot be directly connected to the signal source. You must change your system grounding
configuration or add isolation signal conditioning. (Please look at our ISO-RACK and ISO-5B-series products to add
electrical isolation, or give our technical support group a call to discuss other options).
NOTE
Do not rely on the earth prong of a 120VAC 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 120
VAC outlets happen to be on different phases!)
2.2.9 CIO-DAS16Jr/16 and Signal Source Have Isolated Grounds
Some signal sources are already electrically isolated from the CIO-DAS16Jr/16. The diagram below shows a typical
isolated ground system. These signal sources are often battery powered, or are fairly expensive pieces of equipment
(isolation can be expensive). Isolated ground systems provide excellent performance but requires careful design and
installation to assure optimum performance. Please refer to the following sections for further details
2.3 WIRING CONFIGURATIONS
Combining all the grounding and input type possibilities provides us with the following connection configurations.
The combinations along with our recommendations on usage are summarized in Table 2-1 below.
Table 2-1. Ground Condition/Input Type Compatibility
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
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