Final answer:
A PID controller functions correctly when it maintains a steady state and meets the desired set point value, using proportional, integral, and derivative controls to minimize errors and adjust the process variable.
Step-by-step explanation:
A PID controller is operating properly when the output of the PID circuitry has a steady state AND reaches the set point value. PID stands for Proportional-Integral-Derivative, which are the three basic coefficients employed in this control mechanism. When adjusted correctly, the PID controller minimizes the difference between a measured process variable and a desired set point by calculating and outputting a corrective action that can adjust the process accordingly.
Proportional control takes into account the present value of the error. Integral control considers the accumulation of past errors. Derivative control predicts future error based on its rate of change. Combined, these controls ensure that the system output follows the set point as closely as possible without large overshoots or steady-state errors.