在 TwinCAT 3 PLC 上读取循环时间

Question

Is there a way for a PLC program to know its own cycle time?

As a workaround, I can just add a persistent variable or a constant to tell it manually, but that's obviously error prone.

Answer 1

For TwinCAT3 this is available in PlcTaskSystemInfo (variable CycleTime ). Combine it with the FB GETCURTASKINDEX to get the data you want.

See one example (though not cycle-time, but still same FB) here at AllTwinCAT .

Answer 2

To add to Jakob's answer - you can also use GETCURTASKINDEXEX function ( Infosys ) instead of GETCURTASKINDEX FB. This way you don't have to instantiate it.

_TaskInfo[GETCURTASKINDEXEX()].CycleTime

Will return cycle time as multiples of 100ns (UDINT)

UDINT_TO_LREAL(_TaskInfo[GETCURTASKINDEXEX()].CycleTime) / 10_000_000

Will return cycle time as seconds (LREAL)

Answer 3

This is not directly an answer to your question, but can be used to determine the Cycle time.

I like to use the Time() function. It returns a value of data type TIME . It does not represent an absolute time, but can be used to calculate the time between two calls to Time() . In this way you can calculate the Cycle time.

I use it in function blocks (FB) where timing is critical. In this way the FB knows when it was lastly called instead of assuming that it is being run each scan. Even if I or another user of my FB "forgets" to call the FB each scan, the FB still delivers correct outputs.

I cannot link directly to the Beckhoff Infosys page, but you can find info on Time() using this link and navigating to "Operands" and then "Functions" on the left hand side. There is also a function called LTime() which returns a value of data type LTIME , but it seems that Beckhoff did not bother to document this function.