Cyclic Load in PM861

What is the recommended limit for cyclic loading on a PM861?

What happens if this limit is exceeded? Do they stop performing some tasks (for example not write outputs)?

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Camilo Arenas   

asked 5 months ago



Hi Camilo,

What ABB recomends as limit for cyclic loading on AC800M is 50% as this value not show the firmware load. But in some projects I'm working with 75% without any issues. Normally what happens when you raise too much the load is that the controller miss the start of some tasks because it not find any window on the processing table to execute the task. In the latest versions the processor pause the execution of a less priority to start a higher priority task.



answered 5 months ago


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The cyclic load of PM861 will not exceed 70% of CPU capacity if Load Balancing - Enable Overload Compensation is checked under controller settings. If an application require more than 70% of CPU capacity, the task scheduler automatically increases the task interval times to re-establish a 70% load.

If the Load Balancing - Enable Overload Compensation is not enabled in your project tasks will be executed/effected as per Fatal Overrun settings (Reaction and Limit) in controller settings.

I suggest you to check the task analysis window to find out the summary of execution.

You can find the above and other more detailed information in 3BSE041434 (System_Guide_Technical_Data_and_Configuration) and 3BSE035980 (AC_800M_Configuration) manuals.

Hope this helps you.

Source: 3BSE041434, 3BSE035980


answered 5 months ago


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