Control system manufacturers have adopted different technologies to implement on-demand tuning. Because these tools are designed to work in a noisy process measurement environment, the tuning results are usually better than those achieved through manual tuning techniques. To illustrate the features that may be included in on-demand tuning capability, the on-demand tuning capability of the DeltaV control system is examined in Chapter 4 of Advanced Control Foundation – Tools, Techniques, and Applications. Other tools may differ in the technique used to introduce a change in the manipulated process input and the methods used to identify the process gain and process dynamics and to provide the recommended tuning.
The auto-tuning user interface is used by a variety of people in the plant and must be designed to be easy to use. The interface will typically include a trend of the controlled parameter PV, the setpoint SP and output of the PID block. Also, other information may be automatically displayed that is needed in loop commissioning, such as the current tuning of the PID. In this example, the PID tuning process is initiated using the Test button. Once the tuning begins, the output of the PID is changed automatically from its initial value by the default step size as illustrated below.
Based on the process gain and dynamics identified through the automated test, the auto-tuning application calculates a recommended setting for the PID proportional, integral, and derivative gains. To use the tuning determined by the application, the user simply selects the Update button, and the tuning values are automatically written to the PID block. Thus, with two clicks of the mouse, a control loop can be tuned.
The workshop for Chapter 4 illustrates some of the features that may be found in an on-demand tuning product. An example heater process is used in this workshop. A YouTube video that shows the workshop solution may be viewed by accessing the book’s web site.