The post AutoQuiz: What Is the Best Tuning Method for a Catalyst Feed Flow Controller? first appeared on the ISA Interchange blog site.
Today’s automation industry quiz question comes from the ISA Certified Automation Professional certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional’s skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.
a) open-loop, shortcut tuning method
b) general purpose, closed-loop tuning method
c) Lambda tuning method
d) modified Ziegler-Nichols tuning method
e) none of the above
Answer A, Open-loop shortcut method, and Answer C, Lambda tuning, are, by definition, open-loop tuning methods. Open-loop tuning methods are suitable only for self-regulating processes.
Answer D, modified Ziegler-Nichols tuning, can be done either open-loop or closed-loop. However, with this method, the gain is adjusted upward until the control output oscillates, which may cause a runaway reaction. This tuning method is not acceptable for this type of process.
The correct answer is B, General purpose, closed-loop tuning method. The key to this problem is to identify that only a closed-loop tuning method can be used with an exothermic reaction where the reactor can “run away” (increasing speed of reaction as the reaction progresses, catalyzed by its own heat of reaction). The tuning, and hence position, of the catalyst flow actuator, is directly related to the ability to maintain reaction stability. Only answer B gives a closed-loop tuning method which maintains the loop in automatic during the tuning process, suitable for this type of reaction.
Reference: Gregory K. McMillan, Good Tuning: A Pocket Guide.
Source: ISA News
