Period and Amplitude

The relationship between period and amplitude provides another characteristic. When the waveform is plotted three measurements can be made: the "amount of change", the "rate of change" and the "rate of the rate of change".

We defined peak-to-peak amplitude as the amount of change. In vibration the term for the amount of change is DISPLACEMENT. The term for the rate of change is VELOCITY. The term for the rate of the rate of change is ACCELERATION. As seen above these units have a direct relationship, yet vary slightly in the phase.

Displacement is expressed in the unit "mils" (one mil equals 0.001 inch) or in "mm" (millimeters). Velocity is expressed in the unit "in/sec" (inch per second) or in "mm/s: (millimeter per second). Acceleration is expressed with the unit "g" (1 g equals 32.2 feet per second per second or 9.8 meters per second per second). The gravity of the Earth induces approximately 1 g of force on every object on the surface. Keep this in mind when performing "inversion testing of accelerometers".

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Last updated: November 24, 2002