Question

control systems maintain a relationship between two variables to monitor and regulate a third variable

• A. Feedback
• B. Feed forward
• C. Ratio
• D. Cascade

Hint:

Ratio control is common in the food industry (mixing ingredients for a recipe) and the automotive industry (keeping air and fuel in the perfect 14.7:1 ratio).

Answer 1

The Correct Option is C

1. Working Mechanism: In a typical ratio control setup, one flow (the "Wild Flow" or "Master Flow") is measured but not controlled. The second flow (the "Controlled Flow") is regulated so that it maintains a specific ratio ($R = F_2 / F_1$) with the first flow.

2. The "Third Variable": While the controller is physically managing the relationship (ratio) between the two flow variables, its ultimate purpose is often to regulate a "third variable" that results from this mixture, such as:

• The

Concentration of a chemical mixture.

• The

Air-Fuel Ratio in a combustion chamber to ensure efficient burning.

• The

Stoichiometry of a reaction.

3. Why not the others?: Feedback and Cascade loops focus on maintaining a single variable at a setpoint, regardless of other flows. Ratio control is unique in that the "setpoint" for one variable is derived directly from the measurement of another.