## 2 Dataset Description and Processing
### Variable Speed and Load  
The variable-speed and -load experiment aimed to study the behavior of bearings with damage of different types and sizes under different operating conditions of rotational speed and load. The test was mainly carried out on the bearing in position B1 (see Figure 1a-c), which was designed to be easily removed from its support to allow for the artificial crafting of different types of defects, mounting, and the monitoring (i.e., taking photos) of bearings with damage of different types and sizes during testing. The test involved running the bearings at different speeds and under different loads to collect data on bearing behavior and performance using vibration sensors. Table 1 discusses different experimental conditions in this case. Table 1 demonstrates that there are 17 operational conditions in this scenario; however, only 13 are available in the public dataset files. Unfortunately, there is no direct and explicit explanation of this matter in the dataset's original introductory publication [7]. However, according to paragraph 2 on page 265 in [7], the differences between the 17 conditions in Table 1 and the 13 conditions publicly available in the dataset may be attributed to the fact that only a restricted number of samples for each condition were used in the study. The remaining samples might have been removed for a variety of reasons, including data quality concerns or a desire to reduce the computational cost of the study. It is assumed that the load voltage was actually measured during the experiment. Its different values are provided in Appendix A, Table A1 in [7].  
As a result, a list of several operating modes was investigated, including one healthy mode (0A) and six unhealthy/fault ones (1A-6A). Using a Rockwell tool, the localized faults on the rolling components resulted in a conical indentation on the inner ring or on a single roller. The damaged elements are reported in Table 2. The size of the resultant circular region is indicated by its approximate measured diameter (i.e., 150 mm, 250 mm, 450 mm). The entire process took around 30 min, and the greatest rotating speeds were not achieved under heavier load conditions due to the restricted power of the inverter.  
Figure 2 is a further example showing the indentation of bearing 4A. This indentation is considered to be very useful, as monitoring its evolution makes it possible to understand fault characteristics (e.g., severity and location), assess their impact on bearing performance, guide design improvements, and evaluate corrective maintenance actions.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Load (N)** & \multicolumn{5}{c}{**Speed (Hz)**} \\ \hline
0 & 100 & 200 & 300 & 400 & 500 \\
1000 & 100 & 200 & 300 & 400 & 500 \\
1400 & 100 & 200 & 300 & 400 & – \\
1800 & 100 & 200 & 300 & – & – \\ \hline \hline \end{tabular}
\end{table}
Table 1: Different operating conditions of the tested bearings in the variable-speed and -load experiment [7].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Defect** & **Size (mm)** \\ \hline
0A & No defect & - \\
1A & Diameter of an indentation on & 450 \\  & the inner ring & \\
2A & Diameter of an indentation on & 250 \\  & the inner ring & \\
3A & Diameter of an indentation on & 150 \\
4A & Diameter of an indentation on & 450 \\  & a roller & 250 \\
6A & Diameter of an indentation on & 150 \\  & a roller & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Different types of crafted defects of tested bearings [7].