In process control, what does a proportional-integral-derivative (PID) controller achieve?

A proportional-integral-derivative (PID) controller in process control achieves precise and stable control of a process variable by continuously calculating an error value as the difference between a desired setpoint and a measured process variable, and then applying a corrective action based on proportional, integral, and derivative terms. A PID controller is a feedback control loop mechanism widely used in industrial control systems. The proportional term provides a corrective action that is proportional to the current error. The integral term eliminates steady-state error by accumulating the error over time and applying a corrective action proportional to the accumulated error. The derivative term anticipates future error by calculating the rate of change of the error and applying a corrective action that dampens oscillations and improves stability. By tuning the gains (Kp, Ki, Kd) for each of these terms, the PID controller can be optimized to achieve the desired control performance, such as fast response time, minimal overshoot, and zero steady-state error. For example, in a temperature control system, the PID controller adjusts the flow of steam to a heat exchanger to maintain the desired temperature of a process fluid, continuously responding to changes in the process and disturbances to maintain the setpoint.