What does the task analysis tool in CBM takes into account to raise a warning
I'm using a test system, with PM865+SM811 without the actual I/O modules connected.
When I download the applications to the controller the task analysis tool in CBM raises a warning informing that the calculated cyclic load is x% which is above the recommended figures.
However, the standard SystemDiagnostics function block running in the controller informs a cyclic load considerably lower than the one calculated by the task analysis tool.
- Is that due to the lack of the I/O modules, since ModuleBus has a significant processing load?
- If so, what does the in calculation from the tool takes into account?
- Should the actual load to be checked in the field when using the real system match with the calculated one?
- Is this calculation valid for High Integrity controllers?
I have a need for a reliable figure but still cannot check that in the real system.
Voted best answer
Firstly, Cyclic load has nothing to do with module bus load. Module bus will impact the network load which inturn impacts total system load. Cyclic load is ONLY dependent on the task time.
I think the reason for the behavior you were mentioning could be due to the update rate of system diagnostic function block. Can you try the same by changing the "Cyclic update" field in system diagnostics function block to a lower value, say 1s ? ( by default this value is 5minutes)
Generally, the value of cyclic load in function block and task analysis tool will always be the same no matter which controller type we use. You can also cross check cyclic load by double clicking on any task in cbm when the controller is in online mode.
NOTE: Dont forget to revert the changes in cyclic update rate of system diagnostics function block if not required.