Optimum PLC CPU use % of continuous task?

[unsaint32]

Our HMI is slow to update some PLC tags. I noticed the PLC project has only one continuous task and it is using about 80% of CPU. Is that too much? It's CLGX5K L71 with eight I/O cards. What is the optimum percentage of PLC CPU usage of a continuous task? If 80% is too much, does that mean some of the continuous task should be rewritten to be periodic tasks?

 

[jdbrandt]

Our HMI is slow to update some PLC tags. I noticed the PLC project has only one continuous task and it is using about 80% of CPU. Is that too much? It's CLGX5K L71 with eight I/O cards. What is the optimum percentage of PLC CPU usage of a continuous task? If 80% is too much, does that mean some of the continuous task should be rewritten to be periodic tasks?

Actually, the "80%" number you quote can't possibly be the CPU usage, if there is a cont. task. Because: by definition, the CPU is 100% utilized when a cont. task is present.
Now, if you change your MAIN to a Periodic Task,
THEN the Task Monitor tool will work, and show you where your hang up is.

 

[jstolaruk]

I would check the refresh rate on the HMI displays first.

 

[nhatsen]

If you're using HMI tags, you can expect a minimum delay of 1 sec + the HMI refresh time.