Ball bearings in rotating machines generate a specific spectral signature related to their kinematics. The spectral lines correspond to the elements of the bearing such as: the inner ring, the outer ring, the balls and the ball cage. These frequencies are proportional to the shaft speed (variable) and the bearing dimensions (fixed).
In the event of a bearing failure, usually a spalling of the balls or a cracking of the bearing strips, shocks are generated which are modulated by the shaft speed (inner ring frequency).
Demodulation and kinematic markers are used to diagnose the defective part. The demodulation is used to bring the vibration frequencies from the shaft speed to the DC current. The kinematic markers show the relative frequencies of the bearing elements from the manufacturers’ libraries. This allows the source of the failure to be diagnosed graphically.