Siemens SIMATIC S7-1200 Function Manual page 436

Instructions
9.3 PID_Temp
State / Mode Description of operating mode
2 Requirements for fine tuning cooling:
Heat.EnableTuning = FALSE
•
Cool.EnableTuning = TRUE
•
The cooling output is activated (Config.ActivateCooling = TRUE).
•
The PID parameter switching is activated (Config.AdvancedCooling = TRUE)
•
The cooling output must be active at the operating point at which tuning is to take place (PidOutputSum
•
< 0.0 (see tuning offset)).
The course of fine tuning is determined by the mode from which it is started:
Automatic mode (State = 3) with PIDSelfTune.TIR.RunIn = FALSE (default)
•
Start fine tuning from automatic mode if you wish to improve the existing PID parameters through tuning.
PID_Temp controls the system using the existing PID parameters until the control loop has stabilized
and the requirements for fine tuning have been met. Only then will fine tuning start.
Inactive (State = 0), manual mode (State = 4), or automatic mode (State = 3) with PIDSelf-
•
Tune.TIR.RunIn = TRUE
Attempts are made to reach the setpoint with the minimum or maximum output value:
– with minimum or maximum output value heating for fine tuning heating
– With minimum or maximum output value cooling for fine tuning cooling.
This can produce increased overshoot. Fine tuning starts when the setpoint is reached.
If the setpoint cannot be reached, PID_Temp does not automatically abort tuning.
The setpoint is frozen in the CurrentSetpoint tag. Tuning is canceled when:
Setpoint > CurrentSetpoint + CancelTuningLevel
•
or
Setpoint < CurrentSetpoint - CancelTuningLevel
•
The method for calculation of the PID parameters can be specified separately for heating and cooling with
PIDSelfTune.TIR.TuneRuleHeat and PIDSelfTune.TIR.TuneRuleCool.
Before the PID parameters are recalculated, they are backed up in the CtrlParamsBackUp structure and
can be reactivated with LoadBackUp.
The controller changes to automatic mode after successful fine tuning.
After unsuccessful fine tuning, the switch to the mode is determined by ActivateRecoverMode.
The "Fine tuning" phase is indicated with PIDSelfTune.TIR.State.
3 Automatic mode
In automatic mode, PID_Temp corrects the controlled system in accordance with the parameters specified.
The controller switches to automatic mode if one the following requirements is met:
Pretuning successfully completed
•
Fine tuning successfully completed
•
Changing of the Mode in-out parameter to the value 3 and a rising edge at ModeActivate.
•
The switchover from automatic mode to manual mode is only bumpless if carried out in the commissioning
editor.
The ActivateRecoverMode tag is taken into consideration in automatic mode.
436
Function Manual, 03/2017, A5E35300227-AC
PID control