DoMore Terminator and Click I/O timeout

[Kristjan]

We have a system with several Terminator DoMore CPUs, each of them controlling multiple Click PLCs (used as plain I/O - minimal code) over Modbus TCP. The Click PLCs have a normal scan time of 2-3 ms, but recently we have increasingly been observing the Click's watchdog timers timing out and putting the CPU to STOP mode (watchdog is set to 200 ms). When connecting with the Clicks, I see actual scan times of 300-600 ms.

What can cause scan times for the Clicks increasing so much? Can networking affect scan times?

[Bolt]

The Click line is not a Host product, I would try posting on the Automation Direct Customer Forum. https://community.automationdirect.com/s/topic/0TO3u000000l14aGAA/click

[rlp122]

Typically when I have seen this sort of behavior, it is caused by poor power or grounding.  Unsuppressed coils on the power supply being the usual suspect.  Could also be VFD wiring too close causing cross talk, plastic welders and powder coating equipment are another two common suspects.  Lastly it could be lousy power supplies.  I have found one power supply that just hates PLCs in general.  I never did write down the part number however.  The last time I had issues with a PLC it was new LED lighting that was playing havoc with it.

I'd be willing to bet that there is something that is hitting the memory or CPU on the processors fairly hard. 

[Kristjan]

Thank you for the replies.

This system has actually been running smooth for years but it seems like recent changes in the network topology has introduced some challenges. So I don't think this is a case of bad power supplies or wiring cross talk.

I realize that Click is not a Host product but I thought I'd try here first  since I have DoMore CPU's in the mix and this forum has a lot of great experts that may have had this issue. I have now posted on the AD forum.

[rlp122]

Network shouldn't have anything to do with scan time.   The only possibility there is that somehow you are writing to some memory areas that you really shouldn't be able to touch and it's corrupting the PLC master table.  I don't think that is possible on Click, however.