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AutoQuiz: What Happens When a Reset Action Is Added to an Industrial Controller Tuned for a Fast Control Loop?

AutoQuiz is edited by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

A controller is being tuned for a fast control loop. It has proportional action and the gain has been adjusted for a value by the technician.

As reset action is added to the loop, which of the following will need to take place?  

The technician will need to:

a) add derivative
b) increase the gain
c) decrease the gain
d) increase the dead time
e) none of the above

The correct answer is C, decrease the gain. Both gain and reset (integral action) act upon the error in the same direction, per the simplified proportional, integral, derivative (PID) control algorithm:

Output 
=  Gain Term + Integral Term
=  Kc (E)  +   Kc · E(t) / Ti

If integral action is added, it is often necessary to reduce Kc, the gain, in order to keep the resulting tuning from being too aggressive.

Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition

About the Editor
Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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Joel Don
Joel Don
Joel Don is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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