PID Tuning and Features Simplified to Meet Process Objectives
Free Seminar Overview (Jan 16)
The three major types of process responses are self-regulating, integrating, and runaway. Self-regulating processes behave quite differently depending upon whether they are deadtime dominant or not. The tuning objectives can be minimum peak error and integrated error for load disturbances, minimum rise time and overshoot for setpoint changes, maximum coordination of loops, minimum interaction between loops, and optimization of process metrics, such as process efficiency and capacity. Tuning rules have not addressed all types of responses and meeting objectives is often left to a consultant.
A unification and simplification of major tuning rules has been discovered. Major PID tuning rules for maximum disturbance rejection and minimum rise time have been found to have the same simple expression for controller gain that is inversely proportional to deadtime. Additionally many tuning methods have the same expression for reset time that is proportional to deadtime when the process is treated as a "near integrator" and the reset time is coordinated with this controller gain. It will also be shown deadtime is the most important parameter for loop performance. The minimum peak error and integrated error are proportional to deadtime and deadtime squared, respectively. Fortunately, deadtime is the easiest and fastest dynamic parameter to measure online. The other term needed, the change in the process variable over the loop deadtime, can be straightforward to compute online.
However, PID tuning for maximum disturbance rejection and minimum rise time has not been generally used because of oscillations for changes in dynamics and the failure to meet other process objectives.
The use of a simple online identification of deadtime and the use of a secondary loop such as flow to isolate nonlinearities can prevent oscillatory responses associated with aggressive PID action. The simple addition of a setpoint filter can eliminate overshoot. The use of setpoint directional velocity limits in conjunction with external-reset feedback can eliminate interactions, coordinate the response of loops, provide a gradual approach to optimums, and ensure a fast getaway from operational problems preventing safety instrumentation system (SIS) trips or environmental releases. The use of a simple enhancement developed for wireless sensors in coordination with external-reset feedback can eliminate oscillations for analyzer loops with large cycle times. The addition of a threshold sensitivity setting can stop limit cycles from backlash and stiction.
This free educational session for process automation professionals will be one of several presentations in the day's agenda that covers Leading Trends in Industrial Processing.
•· When: Wednesday, January 16 at 12:30 p.m. EST
•· What: Simplify PID Tuning to Meet Process Objectives
•· Speaker: Gregory K McMillan - ISA Life Achievement Award Recipient
Where: Online - www.globalspec.com/events
•· Contacts: Molly Kray, GlobalSpec senior marketing manager, e-Events, firstname.lastname@example.org or 518-880-0200 x5471
About the Industrial Processing Online Event
GlobalSpec's free online event, Industrial Processing, will explore the latest developments across key industrial processing technology areas including: fluid/gas handling equipment; thermal processing; solids handling; plus filtration, separation, and recycling. Participants will be able to network with their peers and suppliers, participate in key educational sessions, and gain the knowledge needed to help your company remain competitive in today's marketplace.