Question

Which of the following statements are CORRECT for a controller?

• A. P and Q only
• B. P and R only
• C. P and S only
• D. Q and S only

Hint:

A proportional-integral controller (PI) is designed to eliminate the steady-state error, while a proportional controller alone cannot do so.

Answer 1

The Correct Option is C

Let's break down the statements and assess their correctness: - P: In a proportional controller, a control action is proportional to the error.
- This statement is correct. A proportional controller adjusts the control output in direct proportion to the error value.
- Q: In an integral controller, a control action is proportional to the derivative of the error.
- This statement is incorrect. In an integral controller, the control action is proportional to the integral of the error, not the derivative.
- R: There is no “offset” in the response of the closed-loop first-order process with a proportional controller.
- This statement is incorrect. A proportional controller typically exhibits a steady-state error (offset) in response to a constant disturbance or setpoint change.
- S: There is no “offset” in the response of the closed-loop first-order process with a proportional-integral controller.
- This statement is correct. A proportional-integral (PI) controller eliminates the steady-state error (offset) in the closed-loop system by continuously integrating the error.
Thus, the correct answer is (C) P and S only.