## 3 Results and Discussion
\begin{table}
\begin{tabular}{l r r l r} \hline \hline
**Ranking CI** & **\# Failures** & **Weighing** & **Ranking CI** & **\# Failures** & **Weighing** \\ \hline TMHO & 4 & 100 & Clearance factor & 3 & 23 \\ Mean & 4 & 98 & Latitud factor & 3 & 16 \\ Skewness & 4 & 70 & Waveform & 3 & 13 \\ Zero crossing & 4 & 65 & Impulse factor & 3 & 12 \\ SSC & 4 & 61 & Crest factor & 2 & 7 \\ Energy operator & 4 & 59 & Log-Log ratio & 2 & 5 \\ Kurtosis & 4 & 37 & Pulse & 1 & 3 \\ FSM & 3 & 35 & Verosneg & 1 & 2 \\ SDIF & 4 & 27 & MarginF & 1 & 1 \\ Shape factor & 4 & 25 & Wavelength & 1 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ranking CI. In the work done by [PERSON] et al. [13], the vibration signal was analysed using 6 conventional and 6 non-conventional CIs to analyse bearing failures. In [PERSON] et al. [10], feature extraction was performed starting from 30 CIs, and then a ranking of 10 CIs was performed using different filtering methods for different gear DB. In [PERSON] et al. [38], 15 CIs were used to detect bearing failures. In contrast to the above mentioned works, we propose extracting features from the vibration signal using 64 CIs in the time domain. This leads to expand the options of CIs that can be included in the feature selection process for later use in the classification models. The second objective presented was to measure the performance of the 7 selected CIs in the RF and K-NN classification models, for which, in the first instance, the \(\lambda\)-values in the classification models were determined and adjusted, being mtry = 3 for RF and k = 5 for K-NN. Subsequently, the accuracy and AUC in classifying the fault severity level were \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline
**CI** & **P10,P1** & **P2,P1** & **P3,P1** & **P4,P1** & **P5,P1** & **P6,P1** & **P7,P1** & **PS,P1** & **PS,P1** & **Selected** \\ \hline Mean & 0.0467 & 0.2361 & 0.1220 & 0.1081 & 0.1406 & 0.0883 & 0.0663 & 0.0858 & 0.0475 & ✓ \\ Kurtosis & 0.6123 & 0.4206 & 0.6007 & 0.4965 & 0.1207 & 0.1125 & 0.1914 & 0.1097 & 0.3974 & ✓ \\ Skewness & 0.1861 & 0.1702 & 0.0954 & 0.2048 & 0.3924 & 0.0068 & 0.2588 & 0.0923 & 0.0442 & ✓ \\ Energy operator & 0.0285 & 1.3385 & 0.9205 & 0.7314 & 1.2899 & 0.8833 & 0.7326 & 0.6104 & 0.5430 & ✓ \\ Zero crossing & 0.0289 & 0.1653 & 0.0218 & 0.1630 & 0.1393 & 0.1320 & 0.0774 & 0.4657 & 0.0853 & ✓ \\ Slope sign change & 0.0016 & 0.3010 & 0.0116 & 0.1294 & 0.3340 & 0.5692 & 0.2089 & 0.3196 & 0.0809 & ✓ \\ IMHO & 0.1989 & 0.2753 & 0.4340 & 0.3886 & 0.4875 & 0.3356 & 0.2727 & 0.3128 & 0.2164 & ✓ \\ Log energy entropy & 0.0069 & 0.0212 & 0.0532 & 0.0356 & 0.1946 & 0.2358 & 0.0917 & 0.1494 & 0.0118 & � \\ Norm entropy & 0.0074 & 0.0137 & 0.0577 & 0.0370 & 0.2174 & 0.2710 & 0.0337 & 0.1746 & 0.0093 & � \\ Wave form & 0.0370 & 0.0103 & 0.1494 & 0.1015 & 0.2426 & 0.2064 & 0.0313 & 0.1860 & 0.0403 & � \\ Log detector & 0.0093 & 0.0144 & 0.0666 & 0.0468 & 0.2575 & 0.2878 & 0.0763 & 0.2004 & 0.0075 & � \\ Wilson amplitude & 0.0018 & 0.0075 & 0.0526 & 0.0345 & 0.2109 & 0.3241 & 0.0926 & 0.2138 & 0.0181 & � \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Bhattacharyya distance by CIs in cracking failure.