Intermittent communication loss with rack/PLC

2 posts in this topic

Good afternoon fellow members,

I once again ask for your help to know if any of you have struggled with similar issues. For the past year and a half, Every 1-2 months we seem to be losing communication with one of our PLC's/racks. We have in the rack a 1756-EN2T card (revision 3.006) that will flash as if it is communicating and status OK (green LED), yet we will be unable to ping it and our operator interfaces go into error. We could also not open the web browser page of the EN2T card, nor connect to the PLC/rack through RSLogix5000. As this happened over the weekend, the local electrician was called and he tried cycling power to the rack and there was no change after it came back on (not sure how long he left power off to the rack though). 

The problem seemed to be fixed after we told him to pull the EN2T card out of its slot and then re-insert it.

We verified the CIP cinnections for this card and it is around 98 to 101 CIP connections out of a max of 248, so not too high. the card's CPU usage is 24-29%, so no indication of problems there. 

EN2T Card is set to auto-negociate, just like all the other cards we use at all of our plants. 

Has anyone ever experienced a similar problem?

Thank you in advance for all your help and knowledge-sharing!

Edited by bboytaktix

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With intermittent communication issues, put on your detective hat and dig into the System-side (how is the network built, what devices live on the network) and the Bonding-side (what are the ground bonding methods).  

Your EN2T communication module could be getting hammered with network transactions that it suffers an early death.   Have you installed WireShark and observed your network to see what traffic is going on?

You could also have poor bonding practices combined with intermittent ground noise that could be leading to premature failure of the EN2T communication module.  An analog scope is a great, old-school tool for finding possible grounding issues (or a Dranetz/similar power analyser).

Yes, I have had new machine designs that function great until they are put on a customer's floor, and then the problems arise with system communication.


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