How does the MPC block handle PID wind-up?



On the Blocks Configuration page - which you can reach by going to 'Edit' for any MPC block on explorer tree- you will find these items on the causes:

  • PID Wind-up Status: This should be calculated within the APC software (e.g. in Python or Basic), to provide a status to the MPC block, as follows:
    • PID Windup Status = 0. Loop not wound up or down
    • PID Windup Status =1. Loop wound up to high limit.
    • PID Windup Status =2. Loop wound down to low limit
    • This will tell the MPC block that this cause is in wind-up mode (1, or 2), or is not (0). The MPC will react accordingly.
  • PID Process Value: This should be configured to be the read-back of the process measurement. For example, for a PID Flow Loop - this would be configured to be the Flow measurement from the instrument.

The MPC will handle the CL (low constraint limit) or CH (high constraint limit) signals based on the above status being set. For example, if the windup status is 1, it will set the CH (high constraint limit) to track the process variable. This ensures the MPC block can't push the setpoint any higher than the process current operating point.

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