Dear Forum Users,

We have redundant CPU 401-5H. I have a question about scan cycle time.
I observed it for a long time and the cycle time of the CPU is generally between 5- 15 ms. But sometimes the cycle time is 50 ms or more. What could be the reason for this?

 I want to add some more reasons for extra cycle time in a CPU:

1- Too much interrupts in one cycle could increase the cycle time , as an example several channels failure due to a problem in field side may need more time handle.

2- Some parts of user program would be extensive load on CPU , but  inactive for normal operation. They can be called on a condition , and you may experience a spike in cycle time.

3- TEST functions may increase the cycle time of CPU extensively.

4- If the spikes to 50 ms happen frequently , monitor current cycle for the violation and generate an alarm. This will give you some clues regarding what may trigger the spike from your hardware or plant condition.

Kind regards,

hdhosseini