Unit Conversions

Acceleration and Displacement can also be expressed on dB scales. The AdB scale is the most used one, and its zero reference is set 1 micro G, commonly abbreviated G.

It turns out that AdB = VdB at 159.2 Hz. VdB levels, AdB levels, and DdB levels are related by the following formulas:

Any vibration parameter -- displacement, velocity, or acceleration can be displayed on a dB scale. The reference quantities for 0 dB on these scales were chosen such that the dB levels of all three quantities are the same at a frequency of 159.2 Hz, which is equal to 1000 radians per second.

Acceleration and Velocity in linear units are calculated from dB levels as follows:

It is convenient to remember the following rule of thumb:
At 100 Hz, 1G = 120 AdB = 124 VdB = 2.8 mils p-p.

Note that the time domain wave form is always represented in linear amplitude units - it is not possible to use a log scale in the wave form plot because some of the values are negative, and the logarithm of a negative number is not defined.

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