RTD Module question

[ceilingwalker]

Good day all. I would like to know if anyone might know why the Control Logix RTD modules do not require a drain wire (shield) connected to it, but the SLC500 module does? I assume it's because the SLC uses a back-plane and the Control Logix does not. Thank you.

 

[Mickey]

A shield is not required for either system, they will both work without it. But is is recommended for noise reduction on any analog wiring.

 

[ceilingwalker]

Ok, thanks Mickey. Would you happen to know why my RTD Module has 6 "shield" connections on it and only 4 channels? I'm reading the book but it isn't specified.

 

[Mickey]

Would you happen to know why my RTD Module has 6 "shield" connections on it and only 4 channels?

Convenience.

What is the complete catalog number of your module?

 

[ceilingwalker]

Sorry, I left out the most important piece of info: 1746-NR4

 

[Mickey]

Sorry, I left out the most important piece of info: 1746-NR4

Until someone comes up with a better answer I will stand by my "Convenience" answer.

 

[ceilingwalker]

Ok, so I don't need to run a ground wire to the module, right? I beleive I read in the book that it gets the proper ground from the back-plane, but now I can't find where it said it.

 

[Mickey]

Ok, so I don't need to run a ground wire to the module, right? I beleive I read in the book that it gets the proper ground from the back-plane, but now I can't find where it said it.

See exert from the manual below and make sure the chassis is grounded properly

 

[rdrast]

It is convenience.
We don't bother usually with any device (PLC Module, Drive, Encoder etc) shield connection. We typically terminate the shields only at a single grounding buss running under the connection terminal strip in panels, and leave the other ends isolated by heat shrink tubing.

Life has gotten much better in the past ten years or so with regards to grounding shields, but still, a noisy ground loop can result in hours or days of searching.