Pretuning 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
Pretuning as of V2

The pretuning determines the process response to a jump change of the output value and searches for the point of inflection. The PID parameters are calculated from the maximum rate of rise and dead time of the controlled system. You obtain the best PID parameters when you perform pretuning and fine tuning.

The more stable the process value is, the easier it is to calculate the PID parameters and the more precise the result will be. Noise on the process value can be tolerated as long as the rate of rise of the process value is significantly higher compared to the noise. This is most likely the case in operating modes "Inactive" and "manual mode". 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

  • PID_Compact is in one of the following modes: "Inactive", "Manual mode", or "Automatic mode".

  • The setpoint and the process value lie within the configured limits (see "Process value monitoring" configuration).

  • The difference between setpoint and process value is greater than 30% of the difference between process value high limit and process value low limit.

  • The distance between the setpoint and the process value is > 50% of the setpoint.

Procedure

To perform pretuning, follow these steps:

  1. Double-click the "PID_Compact > Commissioning" entry in the project tree.

  2. Select the entry "Pretuning" in the "Tuning mode" drop-down list.

  3. Click the "Start" icon.

    • An online connection will be established.

    • Value recording is started.

    • Pretuning 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 when the progress bar has reached 100% and it can be assumed the controller tuning function is blocked. Check the configuration of the technology object and, if necessary, restart controller tuning.

Result

If pretuning was performed without an error message, 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 pretuning is not possible, PID_Compact responds with the configured reaction to errors.