a signal applied to a controlled object from a setting device or automatic controller and affecting the controlled variable of the object.
In some automatic control systems, control signals are altered to make the controlled variable correspond to the desired value (as in servomechanisms, stabilization systems, and programmed control) or achieve some optimum or extreme value (as in optimal control systems and self-aligning systems). In other automatic control systems, the control signal depends on the control law and is determined by the characteristics of the controlled object and the nature of commands and disturbances acting on the automatic control system.
Control signals may be applied in single-capacity or multiple-capacity systems. In the latter, each control signal may influence one or several controlled variables, which makes controlling the object more difficult. Thus, one of the most important problems to be solved in the design of automatic control systems is the lessening or elimination of the effect of the control signal on all but the desired controlled variable.