How Are the Various Components of a CompactRIO Grounded?

Issue Details

I have a CompactRIO with multiple modules installed. How are the modules grounded in relation to the chassis and controller? How does the chassis ground relate to the power supply input and module grounds?

Solution

C-Series modules in a CompactRIO chassis have various types of channel and bank isolations, which are detailed in the module's specifications document. The COM (common) lines are all tied together and ground within the module. They are isolated and floating to the chassis and controller. The specifications for the isolation between the chassis and module are listed in the C-series module's specifications guide as channel-to-earth ground isolation.

For older models, the controller shares a ground with the chassis. This ground is, in turn, connected to the chassis ground screw located on the side of the chassis. The C (common) input on the power supply connector for the CompactRIO controller is also tied to the chassis ground. Therefore, there is one common ground for the chassis and controller, while each module retains its isolated ground. However for newer models (cRIO-904x and cRIO-905x) the C input of the power supply is isolated from the chassis ground.

This configuration allows the user to create many grounding arrangements. If you want the modules tied to the same ground within the chassis and controller, connect a wire between the COM input on the module and the chassis ground screw. Or, if you do not want them share a ground, you can connect the module's COM input to any ground you wish.

If additional power supply isolation is desired for your application you can also connect a DC to DC power supply to the power supply connector of the CompactRIO controller to isolate it from the rest of the power network.

Additional Information

Please read through your specific hardware's User Manual and Specification sheet to see additional information on its grounding and isolation.