Tune Cascade Loops from a Web Browser

The PlantTriage system monitors control system performance continuously, 24 hours a day. It automatically diagnoses and prioritizes process, control, and instrumentation problems. Integrated analysis and tuning tools improve plant results by focusing effort on the most critical issues.

Typical cascade control loops involve two instruments, two controllers, and a single control valve or variable-speed drive. Cascade controls are designed to reduce variation, by offering faster response to process upsets. The outer loop provides a setpoint to the inner loop. Unfortunately, says Gerry, “Most cascade loops in plants are poorly tuned, resulting in constant oscillations and interactions between the inner and outer cascade loop.”

The new tools allow users to tune both loops, with a single bump test, directly from a web browser interface. Oscillations are eliminated because the PlantTriage tools select tuning constants that are outside the range of interaction. The new tools are also fully integrated with PlantTriage’s “Active Model Capture Technology”, so dynamic models and controller tuning can be developed based on normally-occurring events, such as operator setpoint changes.

Mr. Gerry, a member of the Process Automation Hall of Fame, who was recently awarded the position of ISA Fellow, says “Cascade control, especially cascade tuning, is often mis-understood. These tools make it simple to tune loops the right way, which will help to stabilize plant operations, improving quality and energy efficiency.”

The new tools are included in the version 10 release of ExperTune’s PlantTriage software.