Automatic control through signal polarities

This paper describes an analogue computer study that was made of an automatic control system in which signal polarities control the amount of proportional feedback that is used. The system consists of a conventional second-order linear feedforward section, and a subsidiary feedback loop which produces the desired control action. The sensitivity of the system to changes in the damping and bandwidth of the linear feedforward section was determined using sinusoidal and transient inputs. It is shown that the system is insensitive to damping variations provided that the damping is less than about critical. It is, however, quite sensitive to variations in the bandwidth.