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.

What kind of control is often used when a specific blend of two different materials is required?

A) ratio
B) cascade
C) feedforward
D) feedback
E) none of the above

Click Here to Reveal the Answer

A ratio controller maintains a predetermined ratio between two or more variables or maintains the magnitude of a controlled variable at a fixed ratio to another variable.

The hydrocarbon line receives the air’s flow rate. Then the FF − flow ratio (flow fraction) − tells the FC (flow controller) how much hydrocarbon to pass into the mix.

So if the predetermined ratio is 10 parts air to one part hydrocarbon, the FF takes the input from above and tells the FC below to allow one-tenth that amount of hydrocarbon to pass.

The correct answer is A.

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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