TABLE OF CONTENTS A spectrum analyzer is an electronic device that is capable of taking the time waveform of a given signal and converting it into its frequency components. There is an unfortunate irony concerning spectrum analyzers: although they are designed and built by the most sophisticated electronic engineers and computer specialists, their greatest economic value lies in the assistance they give to mechanical engineers and maintenance personnel to keep machinery running. Thus, for years, the machinery man has asked questions in g's, inches per second, and mils and the spectrum analyzer manufacturer has steadfastly insisted on answering in volts, amperes, and bytes.
In this chapter, the operation of a spectrum analyzer will be described in terms familiar to machinery specialists. By knowing how the analyzer works, it is possible to do a more comprehensive job of machinery diagnostics and monitoring.
Ever since Baron J. B. Fourier, the French mathematician, showed that it is possible to represent any time waveform (the plot of a signal whose amplitude varies with time) by a series of sines and cosines of particular frequencies and amplitudes, engineers have sought ways to simplify their work by looking for the frequency content of signals. In the machinery world, the goal is to relate the various frequencies seen in a spectra (plot of amplitude versus frequency) to the various physical phenomena occurring in a machine.
For many years, analog filters were used to look at the sound and vibration of a piece of machinery...
