Vibration Theory & Terminology: Amplitude
Amplitude is the maximum value of a periodically varying quantity. See Fig 1 . Used in vibration diagnostics, we are referring it to the magnitude of the disturbance. A severe disturbance would have a high amplitude; a minor disturbance would have a low amplitude.
Amplitude is measured by the amount of actual movement, or the displacement. For example, consider the vibration caused by an out-of-balance wheel at 50 MPH as opposed to 25 MPH. As the speed increases, the amplitude increases.