Fine Tuning V2 - Siemens SIMATIC S7-1200 Function Manual

Using PID_Compact
4.2 PID_Compact V2
4.2.2.2

Fine tuning V2

Fine tuning generates a constant, limited oscillation of the process value. The PID
parameters are tuned for the operating point from the amplitude and frequency of this
oscillation. 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. 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 PID parameters are backed up before being recalculated.
Requirement
● The PID_Compact instruction is called in a cyclic interrupt OB.
● ManualEnable = FALSE
● Reset = FALSE
● The setpoint and the process value lie within the configured limits.
● The control loop has stabilized at the operating point. The operating point is reached
when the process value corresponds to the setpoint.
● No disturbances are expected.
● PID_Compact is in one of the following operating modes: Inactive, automatic mode, or
manual mode.
Process depends on initial situation
Fine tuning can be started from the following operating modes: "Inactive", "automatic mode",
or "manual mode". Fine tuning proceeds as follows when started from:
● Automatic mode
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 or manual mode
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. Only then will fine tuning start. If pretuning is
not possible, PID_Compact responds with the configured reaction to errors.
An attempt is made to reach the setpoint with the minimum or maximum output value if
the process value for pretuning is already too near the setpoint. This can produce
increased overshoot.
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Function Manual, 03/2017, A5E35300227-AC
PID control