The past of PID controllers

The history of pneumatic PID controllers covering the invention of the flapper-nozzle amplifier, the addition of negative feed back to the amplifier and the incorporation of rest (integral) and pre-act (derivative) actions is described. The transition of the controller from a special purpose unit to a robust, reliable, widely used unit; the change to electronic implementation and then the development of the digital controller is examined. It is concluded that a systems approach to control was important in the development of PID controllers as was a close relationship between instrument companies, plant designers and plant operators. Copyright (C) 2000 IFAC.