Siemens SIMATIC S7-1200 Function Manual page 85

PID algorithm sampling time
The controlled system needs a certain amount of time to respond to changes in the output
value. It is therefore not advisable to calculate the output value in every cycle. The sampling
time of the PID algorithm represents the time between two calculations of the output value. It
is calculated during tuning and rounded to a multiple of the cycle time. All other functions of
PID_Compact are executed at every call.
If you use Output_PWM, the accuracy of the output signal is determined by the ratio of the
PID algorithm sampling time to the cycle time of the OB. The PID algorithm sampling time
corresponds to the time period of the pulse width modulation. The cycle time should be at
least 10 times the PID algorithm sampling time.
Rule for tuning
Select whether PI or PID parameters are to be calculated in the "Controller structure" drop-
down list.
● PID
Calculates PID parameters during pretuning and fine tuning.
● PI
Calculates PI parameters during pretuning and fine tuning.
● User-defined
The drop-down list displays "User-defined" if you have configured different controller
structures for pretuning and fine tuning via a user program.
PID control
Function Manual, 03/2017, A5E35300227-AC
Using PID_Compact
4.2 PID_Compact V2
85