In a simple ratio system, the independent variable is:

In a simple ratio system, the independent variable is:

• A. Both measured and controlled.
• B. Controlled but not measured.
• C. Measured but not controlled.
• D. Neither measured nor controlled.

Answer: (C)

In a simple ratio system, you maintain a fixed relationship between two signals by using one as the basis to drive the other. The quantity you observe and measure is not being set by the controller; it serves as the input that determines what the controller does. The controller acts on the other variable, adjusting it to keep the ratio constant. Because the measured signal is used to drive the control action and is not itself being controlled in this loop, it functions as the independent variable. The variable that the controller adjusts is the dependent (controlled) variable, since its value changes in response to the measured input to maintain the desired ratio.

In a simple ratio system, you maintain a fixed relationship between two signals by using one as the basis to drive the other. The quantity you observe and measure is not being set by the controller; it serves as the input that determines what the controller does. The controller acts on the other variable, adjusting it to keep the ratio constant. Because the measured signal is used to drive the control action and is not itself being controlled in this loop, it functions as the independent variable. The variable that the controller adjusts is the dependent (controlled) variable, since its value changes in response to the measured input to maintain the desired ratio.