Deterministic Signals
Deterministic signals are a special class of stationary signals, and they have a relatively constant frequency and level content over a long time period. Deterministic signals are generated by rotating machines, musical instruments, and electronic function generators. They are further divisible into periodic and quasi-periodic signals. Periodic signals have waveforms whose pattern repeats at equal increments of time, whereas quasi-periodic signals have waveforms whose repetition rate varies over time, but still appears to the eye to be periodic. Sometimes, rotating machines will produce quasi-periodic signals, especially belt-driven equipment.
Deterministic signals are probably the most important in vibration analysis and their spectra resemble the following:
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Most quasi-periodic signals are actually a combination of several harmonic series.
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Periodic signals always produce spectra with discrete frequency components that are a harmonic series. The term "harmonic" comes from music, where harmonics are multiples of the fundamental frequency. |
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