How can faults be diagnosed by vibration measurement?

There are aspect to vibration measurement in condition monitoring. The first is overall vibration measurement, which can be compared to a standard for land based industrial machinery, to inform the stsyem that an exception exists. This parameter is of limited value in marine applications because the low frequency background vibration (from diesel engines and propeller blades for example) significantly affects the vibration level.

The relevant part of vibration analysis for marine applications are the frequency of vibration and the amplitude of vibration at those frequencies. The frequency of vibration indicates the possible fault diagnosis. e.g. the rotational frequency generally indicates the quality of the rotor balance. If the trend of this parameter over a period of time increases to the point where it exceeds a preset value a pre-alarm is initiated. 

The short explanation is that the vibration amplitude can indicate that a problem may exist. The vibration frequency, meanwhile, indicates the diagnosis of the problem

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