Fine tuning as of V2 (S7-1200, S7-1500) - PID

Using PID_Compact (S7-1200, S7-1500)
ft:publication_title
Using PID_Compact (S7-1200, S7-1500)
Product
PID
Version
V20
Publication date
11/2024
Language
en-US
Fine tuning as of 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 inactive mode, 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 responses in the event of an error.

    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.

Procedure

To perform fine tuning, follow these steps:

  1. Select the entry "Fine tuning" in the "Tuning mode" drop-down list.

  2. Click the "Start" icon.

    • An online connection will be established.

    • Value recording is started.

    • The process of fine tuning is started.

    • 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 that tuning is blocked. Check the configuration of the technology object and, if necessary, restart controller tuning.

Result

If fine tuning was performed without errors, the PID parameters have been tuned. PID_Compact switches to automatic mode and uses the tuned parameters. The tuned PID parameters will be retained during power OFF and a restart of the CPU.

If errors occurred during "fine tuning", PID_Compact responds with the configured response to errors.