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Ethernet/IP Stalls for 11 second every 6.5 to 7 hours

My Rockwell PLC is expecting an heartbeat echo back from my LV2018 application running on a PC. I am using the EIP toolkit (2018) to read and write tags. One loop handles just the heartbeat and reset. The heartbeat just reads a PLC tag and writes the same bool value to another tag. It has a 250 msec loop timer. My PLC will change the tag the LV reads when the two tags match. If the tags match for more than 7 seconds the PLC records a fault record.

 

My actual application does other data collection and EIP transfers to the PLC too, but to rule that out I made a separate .exe that only handles the heartbeat, records the max loop time for that loop, and records LV errors. The PLC records the fault every 6.5 to 7 hours. Normally the max loop time for the EIP read/write cycle is 252 to 255 msec. When the PLC registers the fault, that max loop time is 11 seconds. The EIP are set up for a 1000 msec timeout. No error come from either the EIP read or write.

 

Also, there are two copies of this equipment and it does it on both. I have turned off power save for the Ethernet cards and ports and checked over other settings. My latest troubleshooting was to put my test program on another PC that is the same model DELL on the line that is on the same Ethernet network. I stopped the local PCs version of the heartbeat test and started it from the third PC and the heartbeat connection is maintained. No PLC faults. Max loop time 300 ms.

 

Next test I just started was to restart only the PC on one machine and the whole system on another to see how that effects the 6.5 to 7 hr. cycle. I believe previous restarts have not effected the timing of the coms disruption.

 

I seem to have ruled out a LV coding issue with the third PC and am now looking at the LV or Windows environment it is running on. Any insights would be appreciated.

 

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Update on last test. Both machines faulted on their independent previously determined 6.5 to 7 hr. schedule. I forgot to mention in the original post that the two systems faulted at different times on their own 6.5 to 7 hr schedules. 

 

So neither shutting down the PC on one machine nor shutting down the entire system reset the timing for the faults.

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