CONTROL OF CONTROL.

In the last ten years, a considerable amount of work has been put into developing control theories for nonlinear and multivariable systems. However, few of the systems being installed rely on this theory. It is also not uncommon to find many of the automatic-control loops switched out and the plant run on manual control. The paper examines the development of control systems used in the power-supply industry and considers the role of theoretial simulations which are carried out and the design requirements for high availability. It is concluded that it is often difficult to design a control system to control the plant within specified limits under all possible plant operating conditions, but that, in any case, more attention should be directed to simplifying the construction of the control loops and to easing the accuracy requirements to achieve long mean times between failures.