Vibration amplitude is important to evaluate the severity of the phenomenon. Another key value in rotating machine analysis is the phase. The phase allows to quantify the delay between the vibration and one specific event: typically, the tach pulse. The picture below shows how this can be traditionally illustrated.
One will typically look at how phase evolve as a function of speed: graphics used for that are the Bode plot and the polar diagram. Order analysis is the typical analysis used to calculate these results.
- Bode plot: Amplitude and phase vs RPM
- Polar diagram: Vibration vector represented as amplitude and angular position