Where Are Acceleration Amplitudes Useful ?

Consider a high speed centrifugal compressor. This machine, through its normal operation, generates some incredibly high vibration frequencies - well over 1,000,000 cpm (16.67kHz) in certain cases depending on the specifics of the machine components. These vibrations are generated by the gear teeth meshing together and referred to as gear mesh frequency.

Let's briefly look at the following example: Consider a machine that generates a gear mesh frequency of 1,080,000 cpm (18kHz).  Let's assume that there is some vibration (movement) occurring at the gear meshing frequency due to the interaction of the gear teeth.  Let's further assume that the amount of physical movement - the distance back and forth, so to speak - is 3 millionths of an inch (0.003 mils, or 0.076 um). Everyone can visualize the tiny, tiny amount of movement generated.  However, to cause the structure (rotor) to move back and forth even such an incredibly tiny amount 18,000 times per second  requires a force equal to 50x the force of gravity. That's right, 50 g's.  The failure will occur due to that force being applied repeatedly.

Let's look at some examples relating the different amplitude units to the likely failure mode.