Guide for Possible Sources of Vibration Based on Frequency and Amplitude

Practical Solutions to Machinery and Maintenance Vibration Problems

Beats		Beat frequencies, which are usually equal to the difference between two nearly equal frequencies, can cause very low frequency vibrations. Often the frequencies are so low that they are below the ability of some pickups and instruments. The source frequencies will show periodic, rhythmically-timed increases and decreases in amplitude. May be helpful to use time waveform analysis or synchronous-time-averaging. A symptom that looks like a beat but originates from only one source is gearmesh vibration, resulting from a gear that either has been machined eccentrically or "running eccentrically" due to the orbit of its centerline, due to unbalance or misalignment.

Cavitation		Cavitation produces much higher than usual amplitudes at almost all frequencies throughout the whole spectrum. Although it is usually the result of imploding condensing steam bubbles, visualize the type of frequencies that are created by very rapidly boiling water. Usually amplitudes are relatively small, but crackling noise is high.

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