1.8 Results and Discussion

Tables 1.2 to 1.5 and Fig. 1.4 to 1.13 show the following:

• In the spectrum of bearing 'A' (new), certain defect frequencies such as RW, ORDFL, RRS, IRWL appear (Table 1.2), but these defects have significantly low energy levels compared with the energy levels exhibited by the same defects of bearing 'B' (new) (Table 1.4).

• Predominant defect frequencies appear in the coupled mode of operation under different speeds of operation.

• Energy levels of defect frequencies, in general, increase as the speed of operation increases to the maximum operating speed. For example, the energy level of 44.0 at 1000 rpm corresponding to the ORDFL ₁ defect (Table 1.2) increases from 80.9 at 1800 rpm to 296.5 at 2250 rpm from the magnetic base pick-up mounted on the bearing outer race for bearing 'A' (new). Similarly for bearing 'A' (defective) energy levels corresponding to the IRWL ₁ (II) defect increases to 1246 at 2250 rpm from 74 at 1000 rpm (Table 1.3). A similar trend holds good for bearing 'B' (new).

• The change of centre frequency in HFRT analysis does not appreciably alter the nature of the frequency distribution in the spectrum.

• A raw spectrum without demodulation does not reveal the intrinsic condition of a bearing (Fig. 1.11 to 1.13).

• Stud base and magnetic base pick-ups mounted on the bearing outer race show more or less identical behaviour so far as frequency distribution is concerned. A magnetic base pick-up directly mounted on the bearing outer race...