What is the function of the 'D' in a PID controller?

In a PID controller, the 'D' stands for the derivative term, which plays a crucial role in predicting future system behaviors based on the rate of change of the process variable. This predictive control action is achieved by assessing how quickly the process variable is changing at the moment.

By incorporating this derivative action, the controller can respond not only to the present error but also to the anticipated future trend of that error. This ability to react before the error has a chance to reach a critical level can greatly improve the stability and responsiveness of the control system.

This predictive nature allows the PID controller to mitigate overshoot, improve settling time, and enhance overall system performance, particularly in dynamic environments where changes can occur rapidly. In essence, the derivative action helps in smoothing out the control response and achieving better control over the process being managed.