Development of the PID controller - IEEE Control Systems Magazine

n 1939, the Taylor Instrument CompaI nies introduced a completely redesigned version of its “Fulscope” pneumatic controller: this new instrument provided, in addition to proportional and reset control actions, an action which the Taylor Instrument Companies called “pre-act.” In the same year the Foxboro Instrument Company added “Hyper-reset’’ to the proportional and reset control actions provided by their “Stabilog” pneumatic controller. Pre-act and Hyper-reset actions each provided a control action proportional to the derivative of the error signal. Reset (also referred to as “floating”) provides a control action proportional to the integral of the error signal and hence both controllers offered PID control. Of the two instruments, only the Fulscope provided for full field adjustment of the controller parameters; the Stabilog had to be set to one of four fixed settings of the derivative-plus-integral term in the factory, the proportional band (gain) of the controller could be adjusted in the field. Field adjustment did, however, pose a problem since there was no established method of choosing the appropriate settings for each of the three terms of the controller. Recognizing this as a weakness, the Taylor Instrument Companies