Experimental determination of the frequency response of a linear transfer function for arbitrary transient inputs of finite duration

IN MANY PRACTICAL situations when frequency-domain information about a process is required, the input is not sinusoidal and of a constant-frequency steady-state nature. For example, it may be necessary to obtain the frequency response of the changing linear plant in an adaptive control system at a specified time. A problem arises in that the plant is controlling some quantity and usually cannot be disturbed by measurement devices. Consequently, the measurement must be made using only input and output information of the linear plant, which is not usually sinusoidal in form. The problem then is one of obtaining frequency-domain information about the system from the given input.1