PLC going offline at similar intervals

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      I have compact logix that we have known has connection issues for some time but we never looked into it much. We have recently gotten a way to track when the PLC goes offline and store the time stamp in a database. Since doing this we have noticed that the PLC is going offline at very specific intervals. I have attached a document showing the time stamps from recently. But it is either every 10, 20, or 30 minute intervals in between the PLC losing connection. And when i say every ten minutes i mean almost to the millisecond. Some examples from today were 9:41:47.476, 10:21:47.460, 11:01:47.476…And this lasts throughout the day and night.

      Does anyone have any ideas as to what could be causing such a repeating issue like this?

      thank you

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        I had a similar issue on a Control Logix PLC a few years back.  In my case it was talking to a Wonderware system.  Long story short I had to install a firmware upgrade to the Ethernet module and had to install a DAS server patch in order to clear this problem up.

        I recommend looking at the firmware that you are using on the Compact Logix and then the revision of whatever it is that you are interfacing to and digging in to see if there are any issues with the particular combination.  You may need to upgrade both the firmware of the PLC and the comm link software of whatever you are interfacing to.


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          OK thank you I will check that out.

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            I have personally experienced this issue ..
            What Compact Logix PLC and revision?  Do you have an Analog Input Module such as an IT6 ?

            Do you have a power up routine ?
            Do you have a separate fault handling routine?
            Yes it matters .. certain things happen in the processor when these routines are present..  especially wacky powerup routines – they are not as simple as hey it runs at power up.. when a routine is present regardless if it really runs or not the processor does some things differently that it would not , unfortunately I don’t remember the specific details.

            You might have a fault that is clearing by itself when it goes offline (or code in a fault routine doing this ??)  – you don’t mention if you have any minor or major faults occurring …

            One of the things that would be nice to capture is what system is operating at the time of this situation. So depending on how many inputs / outputs you have, you might add a routine that allows you to see what inputs and outputs are triggered just prior and at the time the processor goes offline. Store and rotate in an array of 100 bits or so with a time stamp.

            We really need more information in order to provide the best help.
            I suspect a bad power supply or a sensor / output being shorted at a particular time. I can’t be certain because compact logix goes offline is extremely limited information.
            Provide some detail : Fault Routine Yes/ No .
            If yes does it clear major faults ? Cycle to  offline at that point ?
            Fault Codes Majors or Minors Yes / No
            Is a power up routine present – and Clearing Majors and the processor comes up in offline mode ?

            If yes does it clear major faults ? Come up offline at that point
            There is a lot that can be happening here  ..

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