AUTOMATIC FEEDBACK CONTROL SYSTEM SYNTHESIS.

By John G. Truxal '45.New York: McGraw-Hill, 1955. 645 pp.$12.50.

A feedback control system is one which measures its own performance, compares this with the desired performance, and corrects itself. The feedback concept applies to a wide variety of physical systems and in fact to many aspects of human behavior. For example, the driver of a car acts as part of a feedback control system. He observes the position of the car on the road and makes corrections so as to keep it in the right lane. A commonplace example of an automatic feedback control system is the thermostatically controlled house heating system.

Although examples of automatic feedback controls such as the steam-engine speed governor have been used for a great many years, it was only about 25 years ago that the basic principles common to all feedback control systems were recognized and a generalized theory developed. The discovery of this basic theory resulted in rapid developments of control devices of all sorts. During World War II most of the effort was devoted to military applications such as anti-aircraft fire-control devices, automatic pilots, etc. Automatic feedback controls are now being applied widely to many industrial processes.

Professor Truxal's book is designed for use in a graduate-level course or as a reference text for industrial engineers. It assumes a knowledge of basic servomechanisms theory and a good grounding in mathematics especially complex-variable theory and Laplace transforms, although a brief review of these topics and a chapter on network synthesis are given. The relationships between time-domain and frequency-domain characteristics are treated more rigorously than in many other texts on feedback systems. Advanced topics such as statistical design, sampled-data systems, and nonlinear systems are treated. The book gathers together technical information which has previously been available only in articles in the publications of a number of technical societies.