3.24  (vibratory) acceleration level. Ten times the logarithm to the base ten of the ratio of a time-mean-square vibratory acceleration to the square of a specified reference value for acceleration. Unit, decibel (dB); symbol, La.

Annotation 1          Clause A.2 of ANSI/ASA S1.8-1989 (R 2011) notes that a reference value for acceleration of 10 µm/s2 was used in ANSI S1.8-1969, in contrast with 1 µm/s2 given in ISO 1683-2008. It is particularly important to state the reference value for acceleration when describing acceleration levels.

Annotation 2          The numerical value of a given acceleration level is 20 dB less if based on 10 µm/s2 for the reference value than if based on 1 µm/s2. The reference value for acceleration of 10 µm/s2 is within 2% of one millionth of the international standard acceleration for free fall, gn = 9.806650 m/s2.

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