Wang and Mcfadden (1983) utilized the wavelet transform to
represent all possible types of transients in vibration signals generated
by faults in a gearbox. Petrille, Paya, Esat, and Badi (1995) proposed
the neural network to diagnose a simple gear system after
the data have been pre-processed by the wavelet transform. Boulahbal
and Ismail (1997) used the wavelet transform to analyze
the vibration signal from the gear system with pitting on the gear.
The raw vibration signal in any mode from a single point on a machine
is not a good indicator of the health or condition of a machine.
Vibration is a vectorial parameter with three dimensions
and requires to be measured at several carefully selected points.