Question 3 1AE01 - First Assistant Engineer

The Correct Answer is C **Why Option C is Correct:** The derivative mode (D control) in a closed-loop process control system (such as PID control) generates an output signal that is based on the speed, or rate, at which the error signal is currently changing. Mathematically, the derivative term calculates the derivative of the error with respect to time ($K_d \cdot \frac{de}{dt}$). If the error is rapidly increasing or decreasing, the derivative action provides a large, immediate corrective effort to oppose this change. This feature is primarily used for **anticipation**—it predicts future error by observing the current trend, allowing the controller to react strongly before the error grows too large, thus improving stability and reducing overshoot. **Why Other Options Are Incorrect:** * **A) It is a control mode that produces a control action that is proportional to the error.** This describes the **Proportional (P) mode** of control. The proportional term produces an output proportional to the *current magnitude* of the error ($K_p \cdot e$). * **B) It is a control mode that produces a control action that is proportional to the accumulation of error over time.** This describes the **Integral (I) mode** of control. The integral term accumulates the error over time ($\frac{1}{T_i} \int e \, dt$) to eliminate steady-state offset (or "droop") that the proportional mode cannot correct. * **D) It is a control mode that produces a control action that is proportional to the gain.** Gain is a tuning parameter ($K_p$, $K_i$, $K_d$) used in conjunction with the error signal (or its integral/derivative) to calculate the control action. The control action is proportional to the *product* of the gain and the relevant error term (error, accumulated error, or rate of change of error), not merely proportional to the gain itself.