Bearing monitoring in variable speed regime using normalized indicators

In this paper, the diagnostic of rolling element bearings in variable regime is addressed. In the nonstationary regime, permanent changes of operating system parameters (load and speed) prevent fault diagnostic with classical tools (RMS value and spectral indicator). To overcome this problem, two new indicators are proposed: RMS value and spectral indicator normalized by the active power. To do that, the vibration signal was acquired simultaneously with the current and voltage signals, and then these signals were divided into segments. For each segment, the RMS value (respectively the spectral indicator) and the power active were calculated, then the RMS was divided by the active power. An analytical model of vibration signal was given and a simulation model signal was used to investigate the proposed indicators. For the experimental validation, a test rig was performed to extract signals (vibration, current and voltage signals) at different degradation states of bearings in a variable speed regime. The thrust bearings (SKF 51207) were used with different states of degradation: free fault and faults created with different sizes. Several operating parameters were considered: variable speed (50–950 rpm) and different loads. The experimental tests showed a linear relationship between the classical RMS value and the active power. The results showed a correlation between the proposed indicators and the bearings state in variable regime. Thus, the proposed indicators are very simple and may be implemented in real time for large industrial applications.