How does PID control work in automation?

Question

I've been searching for a clear explanation of PID (Proportional-Integral-Derivative) control in different forums but haven't found a satisfactory answer. I understand that PID is widely used in automation for process control, but I want to know how it works.

How do the proportional, integral, and derivative terms contribute to maintaining system stability and accuracy? Also, in what types of automation applications is PID control most commonly used?

I would appreciate a clear explanation with examples.

Tech Geek · Answer

PID (Proportional-Integral-Derivative) control is a fundamental feedback mechanism used in automation to maintain the stability and accuracy of a system. It continuously calculates an error value as the difference between a desired setpoint and a measured process variable, then applies corrections based on three terms: proportional, integral, and derivative.

The proportional term (P) reacts to the current error. It produces an output that is directly proportional to the magnitude of the error. The larger the error, the stronger the corrective response. However, relying on proportional control alone often leaves a steady-state error, where the system stabilizes near the setpoint but not exactly at it.

The integral term (I) addresses this by considering the accumulation of past errors. It integrates the error over time and adds a correction based on the sum of those errors. This helps eliminate the steady-state error and brings the output closer to the exact setpoint. However, too much integral action can cause the system to become unstable and oscillate.

The derivative term (D) predicts future error by looking at the rate of change of the error. It provides a damping effect by slowing the response as the system approaches the setpoint, reducing overshoot and helping stabilize the system.

A common example of PID control is in temperature regulation, such as in an oven. If the oven is set to maintain 200°C, the PID controller compares the actual temperature with the setpoint. If the temperature is too low (error), the proportional term increases the heater output. If the temperature has been low for a while, the integral term adds more power. As the temperature rises quickly, the derivative term kicks in to prevent overshooting beyond 200°C.

PID controllers are widely used in industrial automation for applications like motor speed control, robotic arm positioning, pressure control in chemical processes, and flight control systems in drones. Their ability to provide precise and stable control makes them essential in systems where accuracy and reliability are critical.