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May
13

Easy to Apply Tuning Rules

Older control systems may not include tools that allow the PID tuning to be automatically established. In such cases, the following procedure outlined in Chapter 12 of Control Loop Foundation – Batch and Continuous Processes may be quickly applied to determine the tuning of a self-regulating process for PI control.

In Chapter 4 of Advanced Control Foundation – Tools, Techniques and Applications we address on-demand tuning. More detail is provided in the Technical Basis section on tuning rules that are commonly utilized in the process industry. One of these latest techniques is the SIMC method for PID controller tuning. This technique was developed by Professor Sigurd Skogestad, Norwegian University of Science and Technology, using direct synthesis and then applying heuristic evaluation of how to modify the formulas to improve response on disturbance rejection. One of his objectives was to develop simple and easy-to-memorize rules. The resulting formulas for a self-regulating process and PI control are shown below:

The rule integrating process and PI controller are equally simple and easy to apply:

If you want to learn more about Skogestad’s work on controller tuning then I would encourage you to read a paper he presented on SMIC tuning in one of the plenary sessions at the IFAC PID’12 conference. I had a chance to sit in on his presentation and to talk with him at the conference. The rules he developed can be easily applied with good results on a broad range of applications.