Siemens SIMATIC S7-1200 Function Manual page 294

Instructions
9.1 PID_Compact
Meaning of values
State / Description of the operating mode
sRet.i_Mode
0 Inactive
The controller is switched off.
The controller was in "inactive" mode before pretuning was performed.
The PID controller will change to "inactive" mode when running if an error occurs or if the "Deactivate con-
troller" icon is clicked in the commissioning window.
1 Pretuning
The pretuning determines the process response to a jump of the output value and searches for the point of
inflection. The optimized PID parameters are calculated as a function of the maximum rate of rise and dead
time of the controlled system.
Pretuning requirements:
The controller is in inactive mode or manual mode
•
ManualEnable = FALSE
•
The process value must not be too close to the setpoint.
•
|Setpoint - Input| > 0.3 * |sPid_Cmpt.r_Pv_Hlm - sPid_Cmpt.r_Pv_Llm| and
|Setpoint - Input| > 0.5 * |Setpoint|
The setpoint may not be changed during pretuning.
•
The higher the stability of the process value, the easier it is to calculate the PID parameters and increase
precision of the result. Noise on the process value can be tolerated as long as the rate of rise of the process
value is significantly higher compared to the noise.
PID parameters are backed up before they are recalculated and can be reactivated with
sPid_Cmpt.b_LoadBackUp.
There is a change to automatic mode following successful pretuning and to "inactive" mode following un-
successful pretuning.
The phase of pretuning is indicated with Tag i_Event_SUT V1 (Page 300).
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Function Manual, 03/2017, A5E35300227-AC
PID control