Which controller action is proportional to the magnitude of the current error and provides an immediate response, typically leaving a steady-state error when used alone?

Which controller action is proportional to the magnitude of the current error and provides an immediate response, typically leaving a steady-state error when used alone?

• A. Derivative Controller
• B. Integral Controller
• C. On-Off Controller
• D. Proportional Controller

Answer: (D)

Proportional control outputs a correction that is directly proportional to the current error, so as soon as there’s any deviation from the setpoint, the controller moves the process variable immediately in the direction needed, with size scaled by the gain. This gives a fast, proportional response to present error. However, because the action relies only on the present error and not its history or future trend, it typically leaves a nonzero steady-state error when used alone. Derivative action responds to how quickly the error is changing, not its current magnitude, so it affects damping rather than eliminating steady-state offset. Integral action accumulates past errors to drive the offset to zero but can slow the response and risk instability if used alone. On-off control switches between states without a continuous proportional correction, so it cannot provide the immediate proportional response described. In short, the described behavior matches a proportional controller.

Proportional control outputs a correction that is directly proportional to the current error, so as soon as there’s any deviation from the setpoint, the controller moves the process variable immediately in the direction needed, with size scaled by the gain. This gives a fast, proportional response to present error. However, because the action relies only on the present error and not its history or future trend, it typically leaves a nonzero steady-state error when used alone. Derivative action responds to how quickly the error is changing, not its current magnitude, so it affects damping rather than eliminating steady-state offset. Integral action accumulates past errors to drive the offset to zero but can slow the response and risk instability if used alone. On-off control switches between states without a continuous proportional correction, so it cannot provide the immediate proportional response described. In short, the described behavior matches a proportional controller.