Question:
Why does a servo PLC with operating system 6.3 recognise a task overrun although the project with was running perfectly with operating system V6.0 to V6.2?
Answer:
To ensure a high operating safety in a multitasking system three monitoring mechanisms are mandatory.
1. Exceeding the monitoring time (watchdog)
2. Displacing a low-priority task by a high-priority task (task is no longer called)
3. Equidistance of time between calls of the same task is no longer achieved.
The operating systems ≤ 6.2 (dSMC control board) no longer ensured that e.g. a 3 ms task was called again after 3 ms (deterministics) which may endanger safe operation under high task loads. This necessary deterministics was not monitored safely in operating systems ≤ 6.2. This error was eliminated as from operating system 6.3. This may cause a correct release of a task overrun in single projects with several tasks.
The following measures can result in a better use of the computing time:
1. Sequential processes instead of parallel processes
2. Avoiding parallel processes (evaluation of master frequency with simultaneous homing)
3. Increasing task run times in low-priority tasks.
