Siemens SIMATIC S7-1200 Function Manual page 266

Instructions
9.1 PID_Compact
State / Mode Description of operating mode
2 Fine tuning
Fine tuning generates a constant, limited oscillation of the process value. The PID parameters are recalcu-
lated based on the amplitude and frequency of this oscillation. PID parameters from fine tuning usually have
better master control and disturbance characteristics than PID parameters from pretuning. You obtain the
best PID parameters when you perform pretuning and fine tuning.
PID_Compact 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 setpoint is frozen in the CurrentSetpoint tag. Tuning is canceled when:
Setpoint > CurrentSetpoint + CancelTuningLevel
•
or
Setpoint < CurrentSetpoint - CancelTuningLevel
•
Before the PID parameters are recalculated, they are backed up and can be reactivated with LoadBackUp.
Requirements for fine tuning:
No disturbances are expected.
•
The setpoint and the process value lie within the configured limits.
•
ManualEnable = FALSE
•
Reset = 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_Compact 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)
•
If the requirements for pretuning are met, pretuning is started. 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 the process value for pretuning is already too near the setpoint or PIDSelfTune.TIR.RunIn = TRUE, an
attempt is made to reach the setpoint with the minimum or maximum output value. This can produce in-
creased overshoot.
Only then will fine tuning start.
The controller switches to automatic mode following successful fine tuning. If fine tuning is unsuccessful,
the switchover of the operating mode is dependent on ActivateRecoverMode.
The "Fine tuning" phase is indicated with PIDSelfTune.TIR.State.
3 Automatic mode
In automatic mode, PID_Compact corrects the controlled system in accordance with the parameters speci-
fied.
The controller switches to automatic mode if one the following requirements is fulfilled:
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.
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Function Manual, 03/2017, A5E35300227-AC
PID control