Frequency Analysis of Random Stationary Vibrations

The most powerful method of representing random stationary vibrations is based upon the power density spectrum or the mean square density spectrum. Among the many procedures devised to obtain this spectrum is an analog method described here which is particularly suitable for processes lasting some minutes or tens of minutes with frequencies ranging from less than one cycle per second to some thousands of cycles per second. First, the principle on which the procedure is based is described; then the block diagram is discussed with some information about the band filter, the squarer, and the integrating unit. The control logic unit is then described in detail; this unit permits complete automation of the chain. Lastly, some information about the performance of a chain practically built up is given and the degree of repeatability is discussed.