Open and Closed-Loop Feedback Systems:
Tuning the Controller

To make a process system respond as desired, a tuning (or “tweaking”) process is necessary. This consists of adjusting the gain, reset, and rate (proportional, integral, and derivative). Usually a process engineer will provide specifications to indicate the type of response the system should have. Once the gain, reset, and rate are adjusted, the controller will automatically change the output to ensure the system responds correctly when the PV is above or below the SP.

Several methods may be used to determine what the original tuning variables for a new controller should be. The Ziegler-Nichols method includes setting the controller in manual mode, changing the output in percentage steps, and observing and recording the rate of change in the PV. A second method involves setting the controller in auto mode and causing the system to oscillate around the SP, and a third way is to use the auto-tuning function of the controller where the controller automatically performs the test described in the first method.

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