VIBRATION ANALYSIS:LOGARITHMS AND DECIBELS

LOGARITHMS AND DECIBELS

A logarithmic scale is often used for vibration velocity and acceleration values due to the very wide range of vibration levels encountered with industrial machinery. Since the measurements of both sound and vibration vary from very low to very high levels, the decibel (dB) is often used. The definition of decibel is

For sound, the standard reference is a pressure of 0.0002 f.Lbar. By definition, doubling the amplitude is equal to an increase of 6 dB.

Two machines each generate 100 dB when operating alone; if they operate in phase, they generate a maximum total noise of 106 dB (not 200 dB).