Problems with AC 800M PLC, the PLC Fault when I change the time of the tasks, please help

Currently the normal PLC task is configured to:
interval time: 250 ms
execution time: 180 ms
offset: 0
this combination gives me a 65% load cycle, but I want to reduce it is to fault, I put:
interval time: 500 ms
execution time: 180 ms
offset: 0
the PLC fault lasts 3 hrs operating, it fails if the load cycle is less?

Only I have two assignments, normal and slow, the last declaron:
time interval: 1000 ms
execution time: 1 ms
offset: 320 ms

thank you

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Gsaucedo Rank: 1952

Asked 3 years ago

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Answers

If your PLC runs for 3 hours after you extended the cycle time from 250 ms to 500ms then it is not likely that the cycle time is causing you a problem. Please post the crash dump of the PLC.

If the PLC really is crashing because the program execution time exceeds the available task interval time then this must be because some additional code is causing the program execution time to become much longer or because you have another program running on a task that interrupts your Normal task for longer than 500ms. This would also happen with a cycle time of 250ms.

To monitor and diagnose CPU loading issues, you should trend the "cyclic load" of the PLC and verify that this never exceeds 70%. Also log the "Total Load" and available memory.

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Rob Lyon

Rank: 2

Answered 3 years ago

Attached here with log file

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Gsaucedo Rank: 1952

Answered 3 years ago

log.txt

Source:

The crash dump does not give an obvious cause for why your PLC faults ( or rather no reason that I can easily read in the crash dump). You need to raise an urgent supportline case with ABB.

Increasing the task scan interval should not cause a crash like this and there is no indication that the task execution time has exceeded the available interval.

However, here are some Scientific Wild Ass Guesses about what might be wrong ....

The operating system tasks that are running when the PLC crashes are CI854, CI867, IAC_MMS and IP.

- Are you doing anything "unusual" related to these tasks? - for example a lot of IAC communications, user defined devices on the CI854, a lot of Modbus communications ?

- Are you getting any other errors while the PLC is running ? - for example missed IAC communication errors, missing Modbus messages, Modbus message bursts, problems with user defined devices on the Profibus ?

- Are you monitoring and trending the CPU memory ?

- Is this a redundant CPU ? Can you safely terminate redundancy (remove the RCU link and replace with an RCU terminator) and operate as a single CPU ? Is this any more reliable ?

As I said, these are simply guesses as to what might be wrong and I could be way off base. You need to get help from ABB supportline.

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Rob Lyon

Rank: 2

Answered 3 years ago

Thank you for your prompt response.

I give a little more information:

If I have redundant PLC
I have enabled communication Modbus TCP / IP with several teams, some still am not seeing because they are turned off.
I have enabled Profibus communication to read an intelligent CCM brand ABB, some nodes are not enabled
The communication via MMS is taking from 3 I just PLCs.
The charge cycle in the PLC that is failing me is 65%, so I decided to move the task. Currently I have only two tasks engaged in, to lower the load cycle increase the time intervals of 250 ms to 750 ms but I present the fault, the execution time of the task that I have set to Normal, is 180 ms and the slow is 1 ms.

Greetings

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Gsaucedo Rank: 1952

Answered 3 years ago

Is this the same system you asked about in this question .... http://www402.abbext.com/CI867-Card-I...?

Did you successfully solve your Modbus TCP communication problems ?

I am not an ABB development engineer so I cannot interpret the PLC crash dump for you. But reading the dump shows that an operating system task related to MBTCP was active at the time of the failure.

Have you logged a supportline case with ABB ?

I understand that you increased the application task intervals to reduce CPU load and this caused the problem to appear in the PLC. But this does not seem to be the root cause of your problem.

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Rob Lyon

Rank: 2

Answered 3 years ago

Is this the same system you asked about in this question .... Yes http://www402.abbext.com/CI867-Card-I-I-placing-Modbus-TC...?

Did you successfully solve your Modbus TCP communication problems ? - YES

I am not an ABB development engineer so I cannot interpret the PLC crash dump for you. But reading the dump shows that an operating system task related to MBTCP was active at the time of the failure.

Have you logged a supportline case with ABB ?

- NO, can you help me?

thank you

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