correct Answer ( C )

A PID (proportional-integral-derivative) controller is a feedback control mechanism widely used in industrial control systems . Its primary function is to regulate a process variable (like temperature, pressure or speed) by continuously comparing the desired setpoint to the actual measurement value . The controller calculates an error signal (the difference between setpoint and measurement) and adjusts a manipulated variable (e.g., valve position and motor speed) to minimize the error . The combined action of these three terms