Frequency response of rotating servo components

The frequency response approach to the design of automatic controls is the dominant one today. This approach in a strict sense may be said to have started with a paper in 1932 by Dr. H. Nyquist, a physicist at the Bell Telephone Laboratories. In this paper Dr. Nyquist was concerned with the stability of feedback amplifiers. This work can be said to have made possible the transcontinental telephone as well as modern radio and television. Dr. Hendrick Bode, mathematician at the Bell Laboratory, extended the results of Dr. Nyquist and obtained some simple design criteria that enabled even technicians without much mathematical training, to determine whether or not a system is stable. In the study of physical devices one is generally concerned with inputs and outputs to the devices. As the inputs are varied the outputs are affected. This study is often reduced to that of the relation between one input and one output. In a broad sense the frequency response approach to the design of a physical device, may be said to be that in which use is made of the response of the output of the device to sinusoidal oscillation of the input. The needed information about the system is visualized easier from the frequency response curves, than from the differential equations. In writing down the differential equations for a physical system the dominant factors need to be considered. Except for errors in measurement, the experimental frequency response curves for a physical device truly represent this device. The system frequency response is much affected by the behaviour of its components with variation of the frequency. The frequency response of each component should be on hand before the overall frequency response has to be predicted theoretically. Experimental frequency response will give more accurate results, because a simple analytical approach does not involve the nonlinear effects of the components characteristics --Introduction, pages 1-2