*4.5. Analysis of center spring wear fault signal based on FK*

In order to demonstrate the effectiveness and advantages of the proposed method, the signal is also analyzed by FK, and the colormap presentation is displayed in Figure 9.

**Figure 9.** Spectrums of the simulated signal based on FK.

The maximum value of kurtosis based on FK is 2.6, corresponding to a sub-signal at level 1.6; the sub-signal has a center frequency of 170.6667 Hz and a bandwidth of 341.3333 Hz. The sub-signal is used as a data source for further investigation, and its spectrums are shown Figure 10.

**Figure 10.** Spectrums of the simulated signal data source sub-signal based on FK.

Based on above, we know that standard Autogram has the strongest extraction ability among the three methods. Compared with standard Autogram, while FK can extract 30 Hz and its harmonics, the amplitude values are too small.

It can be concluded from above that the standard Autogram based on no threshold processing has the strongest extraction ability. It can extract simulated fault feature information, and it performs best among all methods of Autogram and FK.
