Use the Proportional Integral Derivative instruction

Adding a feedback loop for the manipulated value prevents excessive overshooting by providing a minimum and maximum value for the MV.

At the beginning of the temperature control process, the difference between the process value (PV) and the setpoint value (SP) is large, as shown in the following graph. In this example of a temperature feedback loop, the PV starts at 0 degrees Celsius and moves towards the SP value of 40 degrees Celsius. Notice also that the fluctuation between the high and low manipulated value (MV) decreases and stabilizes with time. The behavior of the MV depends on the values used in each of the P, I, and D parameters.

The following function block diagram includes a feedback loop for the manipulated value that prevents excessive overshooting by providing a minimum and maximum value for the MV.

Use AutoTune parameter of the IPIDController function block to implement auto-tuning in the control program.

The following is a summary of requirements and recommendations for implementing successful auto-tuning:

Autotuning must cause the output of the control loop to oscillate, which means the IPIDController must be called frequently enough to adequately sample the oscillation.
The IPIDController instruction block must be executed at a relatively constant time interval.
Configure the scan time of the program to be than half of the oscillation period.
Consider using a Structured Text Interrupt (STI) instruction block to control the IPIDController instruction block.

Add UDFBs outside the main program to perform specialized functions, such as converting units or transferring values.

This UDFB transfers the Autotune gain value to My_GainTransfer. So it can be used by the controller.

This UDFB converts a manipulated value (MV) to a digital output (DO). So it can be used to control a digital input n(DI).

This UDFB converts a manipulated value (MV) to an analog output (AO). So it can be used to control an analog input (AI).