Siemens SIMATIC S7-1200 Function Manual page 363

State / Re- Description
tain.Mode
2 Fine tuning
Fine tuning generates a constant, limited oscillation of the process value. The PID parameters are tuned
based on the amplitude and frequency of this oscillation. The differences between the process response
during pretuning and fine tuning are analyzed. All PID parameters are recalculated from the results. PID
parameters from fine tuning usually have better master control and disturbance characteristics than PID
parameters from pretuning.
PID_3Step automatically attempts to generate an oscillation greater than the noise of the process value.
Fine tuning is only minimally influenced by the stability of the process value.
The PID parameters are backed up before fine tuning. They can be reactivated with Config.LoadBackUp.
The setpoint is frozen in the CurrentSetpoint tag.
Requirements for fine tuning:
The motor transition time has been configured or measured.
•
The setpoint and the process value lie within the configured limits.
•
ManualEnable = FALSE
•
Automatic (State = 3), inactive (State = 0) or manual (State = 4) mode
•
Fine tuning proceeds as follows when started from:
Automatic mode (State = 3)
•
Start fine tuning from automatic mode if you wish to improve the existing PID parameters through tuning.
PID_3Step 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) or manual mode (State = 4)
•
Pretuning is always started first. The determined PID parameters will be used for control until the control
loop has stabilized and the requirements for fine tuning have been met.
If PIDSelfTune.TIR.RunIn = TRUE, pretuning is skipped and an attempt is made to reach the setpoint
with the minimum or maximum output value. This can produce increased overshoot. Fine tuning then
starts automatically.
The controller switches to automatic mode following successful fine tuning. If fine tuning was not successful,
the controller switches to "Inactive" mode.
The fine tuning phase is indicated with the TIR.State tag.
3 Automatic mode
In automatic mode, PID_3Step controls the controlled system in accordance with the parameters specified.
The controller switches to automatic mode if one the following requirements is fulfilled:
Pretuning successfully completed
•
Fine tuning successfully completed
•
Changing the Retain.Mode tag to the value 3.
•
When the CPU is switched on or switches from Stop to RUN mode, PID_3Step starts in the most recently
active operating mode. To leave PID_3Step in "Inactive" mode, set RunModeByStartup = FALSE.
The ActivateRecoverMode tag is taken into consideration in automatic mode.
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.2 PID_3Step
363