TABLE OF CONTENTS The principle of feedback is one of the most intuitive concepts in process control. An action is taken, more than likely to correct a less-than-satisfactory situation. Then, the results of the action are evaluated. If the situation is not corrected, then further action may be warranted.
After inspecting our young son or daughter's report card, we give the instructions, "You had better improve your grades, else no more TV for you." At the next reporting period, we evaluate the results of our instruction; stronger action may be indicated. As we are driving our vehicle, if we detect that we are drifting out of the center of the lane, we make a slight adjustment of the steering wheel, then observe the effect. If we do not return to the center of our lane, then we make a further adjustment.
These examples, and others that could be provided ad infinitum, all involve actions that are carried out without conscious knowledge of the principle of feedback control. The corrective action, and the necessity for evaluating the effect for possibly additional corrective action, is intuitively obvious. Yet automatic feedback control, implemented with self-acting mechanisms, has only been widely utilized for a little more than 250 years. It first began when windmills and especially the early steam engines created the need for a speed-governing mechanism, which was implemented with the invention of the flyball governor (Ref. [4-1]).
The study of feedback control as a science is younger than actual attempts at...
