Thursday 7 August 2014

Simplifying modern control system tuning! #PAuto #ISAuto

The International Society of Automation (ISA) tells us that the newly released third edition of its Tuning of Industrial Control Systems book simplifies modern control system tuning by eliminating mathematical complexity and addressing the real-world needs of control system technicians.

The authors, Dr Armando B. Corripio,  and Michael Newell, drew upon their project management experiences at major oil refineries to move away from the more academic approach of the two previous editions, and more simply explain how to improve control performance.

For example, the authors concentrate on just two rules for tuning—one that works best for common loops and the other for dead-time dominated loops.
Dr. Corripio, Professor Emeritus in chemical engineering at Louisiana State University (LSU), says that a more simplified explanation of tuning makes it easier to master today’s fundamental control techniques.
“By being less academic in approach, and removing a lot of the mathematical terminology, we’re able to improve understanding of how modern control systems work and help technicians better apply what they’re learning in the workplace,” he points out.

For instance, the third edition:
  • Eliminates references to first- and second-order models since these terms are highly mathematical and reduce appreciation for the usefulness of the models.
  • Removes the distinction between series and parallel proportional-integral-derivative controllers (PIDs) since most modern installations use the series version and there is little difference between the tuning of the two versions.
  • Relies on a single set of tuning strategies: the quarter-decay-ratio (QDR) formulas slightly modified by the Internal Model Control (IMC) rules for certain process characteristics.
Corripio says the project management experience the authors gained at oil refineries gave them valuable insights and exposure to real-world issues and dynamics.
“I became better able to address a non-academic audience,” he relates. “When I co-wrote the first two editions, I was a professor and made much more of an academic mindset and perspective.”
Also unique to the third edition are:
  • A chapter on auto-tuning software, a feature of most modern control systems that the authors contend greatly simplifies the acquisition of process data for effective tuning.  During their work at oil refineries, the authors utilized auto-tuning as a reference to guide selection of final tuning parameter for the controllers, and found it less disruptive than relying on manual processes.
  • A thorough explanation of the control strategies of cascade, feedforward and decoupling—all of which are demonstrated with simulation examples.
All of the example responses were generated using simulation software to illustrate the tuning and show the differences of:

  • Tuning controllable versus dead-time dominated loops
  • Averaging versus tight level control
  • Cascade control versus simple feedback control of a jacketed chemical reactor
  • Feedforward control versus simple feedback control
  • Decoupler control versus simple feedback control of a blender

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