Fine tuning generates a constant, limited oscillation of the process value. The PID parameters are optimized for the operating point from the amplitude and frequency of this oscillation. All PID parameters are recalculated on the basis of the findings. PID parameters from fine tuning usually have better master control and disturbance behavior than PID parameters from pretuning.
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
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The PID_Compact instruction is called in a cyclic interrupt OB.
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ManualEnable = FALSE
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The setpoint and the process value lie within the configured limits (see "Process value monitoring" configuration).
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The control loop has stabilized at the operating point. The operating point is reached when the process value corresponds to the setpoint.
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No disturbances are expected.
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The setpoint may not be changed during controller tuning.
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PID_Compact is in inactive mode, automatic mode or manual mode.
Process depends on initial situation
Fine tuning can be started in "inactive", "automatic" or "manual" mode. Fine tuning proceeds as follows when started in:
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Automatic mode
Start fine tuning in automatic mode if you wish to improve the existing PID parameters using controller tuning.
PID_Comact will regulate 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.
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Inactive or manual mode
If the requirements for pretuning are met, pretuning is started. The PID parameters established will be used for adjustment 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 will change to "Inactive" mode.
An attempt is made to reach the setpoint with a minimum or maximum output value if the process value for pretuning is already too near the setpoint. This can produce increased overshoot.
Procedure
Proceed as follows to carry out "fine tuning":
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Select the entry "Fine tuning" in the "Tuning mode" drop-down list.
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Click the "Start" icon.
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An online connection will be established.
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Value recording is started.
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The process of fine tuning is started.
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The "Status" field displays the current steps and any errors that may have occurred. The progress bar indicates the progress of the current step.
Note
Click the "Stop" icon in the "Tuning mode" group when the progress bar has reached 100% and it is to be assumed the controller tuning function is blocked. Check the configuration of the technology object and, if necessary, restart controller tuning.
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Result
The PID parameters will have been optimized if fine tuning has been executed without errors. PID_Compact changes to automatic mode and uses the optimized parameters. The optimized PID parameters will be retained during power OFF and a restart of the CPU.
If errors occurred during "fine tuning", PID_Compact will change to "inactive" mode.