In a closed-loop process control system featuring negative feedback, what is the function of the error detector within the controller?

Correct Answer: Option C — The error detector computes the difference between the measured value of the controlled variable and the desired value (set point).

The error detector is the primary component in a controller that performs the mathematical subtraction of the measured process variable from the desired set point. This resulting error signal is then processed by the controller to determine the necessary corrective action for the final control element.