Hi guys

i have analog sinyal that controlled by PID control, i have read manual that OB30 (cyclic interrupt) used for PID control for the cycle of PID, but instead the PID block have cycle too, so what the different? can i still use PID control in FC than the FC callin in OB1, or must put the FC in OB30 for PID control

thank you

Hi fernando,

which software (TIA, Step7 lite?) and devices are you using?

Hi Fernando

as the PID includes infinitesimal calculation it is mandatory know the time lapse from a feedback value sampling and the following, and the lapse must be constant, for this reason you have to use OB3x to host PID blocks as they are called on fixed period interrupt, finally using OB3x you have a constant sampling frequency.

fernando13

Hi guys

i have analog sinyal that controlled by PID control, i have read manual that OB30 (cyclic interrupt) used for PID control for the cycle of PID, but instead the PID block have cycle too, so what the different? can i still use PID control in FC than the FC callin in OB1, or must put the FC in OB30 for PID control

thank you

 You can call PID in OB1 without any problems, just call it with counter which is incremented in one of the OB30s. Counter counts elapsed time from previous call. 

Hello fernandoi,

you must call the PID at a cyclic interrupt.

If you call the PID at the OB1 then you haven't a correct calculation at your PID-controller.

Important for a correct function is a exactly time between the calls of the PID.
Please look at the manual of the PID.
There you can find that you must call the PID at a cyclic interrupt.

regard
CaOd