RSLogix5000 scans

drewster said:

We're having momentary comm losses to a remote IO rack. We have a comm_fail tag that we use in the logic to jump over the rungs that read the remote IO and perform other logic functions. Sometimes, the comm loss happens during the scan of the remote IO before our comm_fail tag becomes true.

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I've seen Remote IO inputs reset like that on a few different ControlLogix systems that turned out to be caused by a failing Ethernet switch. We never got any faults reported, nor saw the condition last for quite so long. Basically just 1 or 2 sweeps with all RIO inputs at zero, then back to normal.

Yes that would be a good band-aid! Thanks for your input. Hopefully I can find the root cause soon.

Just a thought
the remote I/O communications is handled by the scanner module
the I/O scan is independent of the ladder scans
if the I/O is Ethernet then the Ethernet module handled all the communications
the same fir is Device net then the Device Net scanner module handles all communication
the timing of the I/O read write is setup in the I/O configuration
the processor I/O handler reads the data from the scanner module as it needs
if you are having I/O communication loss I would look at the communications module
or if the problem is isolated to just one I/O module then that module should be replaced.

Bit_Bucket_07 said:

I've seen Remote IO inputs reset like that on a few different ControlLogix systems that turned out to be caused by a failing Ethernet switch. We never got any faults reported, nor saw the condition last for quite so long. Basically just 1 or 2 sweeps with all RIO inputs at zero, then back to normal.

Click to expand...

Thank you. I looked for errors on the ports of our Ethernet switch but don't see any.

Maybe we'll put a new one in and see if that fixes it.