AutoQuiz: What Control is Used When a Specific Blend of Two Different Materials is Required?

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

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control AutoQuiz20150710System 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 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. In this figure, 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.

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