Fundamental principles of automatic regulators and servo mechanisms

The elementary theory of closed-loop systems is considered; such systems are known as servo mechanisms, automatic regulators, or process controllers. Though the actual forms and applications are widely different, some common principles can be established; in particular the tendency towards self-oscillation or ¿hunting¿ is likely to be encountered in any type of closed-loop automatic controller. The reasons for this form of instability are examined in the paper, and an elementary approach to the stabilizing problem is given. Electrical systems are dealt with mainly, but the approach in the case of analogous dynamical systems is briefly indicated. The theoretical treatment given is necessarily elementary, and is thus confined to linear systems. Transient response obtained by operational methods is considered; also harmonic response, which lends itself to graphical methods of studying system performance.