Bets practice: IO in local 1756 chassis?

[wildswing 0]

Good morning,

Does anyone know if Rockwell has an official stance on whether or not it's a best practice to have IO modules in the local 1756 processor chassis?

I recently spoke with someone who insisted that the local 1756 processor chassis should be left for communication and high speed IO modules like counter cards. All other "standard" IO should be in a remote chassis. He also said this is a recommendation from Rockwell and it's on their web site somewhere.

Can you confirm or deny this? If it's on RA's website, can you post a link please? What do you guys do? Beyond what Rockwell says, what are your standard practices?

Once again, thanks in advance. Your feedback is always very much appreciated.

[PLCMentor.com 60]

That's somewhat a loaded question.  Practically that depends on the project.  I agree that giving preference to such modules in your design is a good best practice; however, deciding which modules to put where depends on what you need for your situation.  We don't do a lot of motion control so I cant speak to that.  We do have a variety of communication modules, but that is highly dependent on the project.  I would make sure my comms modules get priority for being located in the main chassis.  I also would allow for expansion and growth of such modules in the future.  Then practicality kicks in. For example, often our main PLC is located close or in the MCC room.  That makes it highly efficient to locate the I/O modules associated with motor control in that chassis.  Often of our other I/O is spread about the process and remote cabinets are used for that.  I'm sure Rockwell doesn't really like my preference for Flex modules over point I/O, but the stupid way they arranged the wiring on those makes them an electricians nightmare (and thus mine also).  I guess to sum it up:  best practices as you mention are great, but each project must be evaluated within its own criteria to make sure the best practices are "best" for it.