## 5 Experiment and Discussion
### Light Load LDA Application Methods  
The definition of the light load condition is required for efficient analysis at light loads. Generally, light loads are defined as light loads, but it is difficult to define exact numerical situations. However, in this paper, the light load condition is defined based on the difference of BCS change. The result of analyzing the BCS difference between each class in the steady state and the ITSC state is shown in Figure 16.  
In other words, a range between 1790 rpm and 1750 rpm can be defined as a light load, beyond which loads can be defined as heavy load and full load. On the other hand, under light load conditions, the BCS is very smooth and shows no significant difference. In general, for heavy LDA application, it is time-consuming to calculate LDA for the entire load and then LDA for each class. However, the BCS analysis shows that there is no significant change at light load. We believe that this can be effectively applied to all light loads with only one condition of light loads without having to calculate each class. For example, even if the LDA eigenvector for 1790 rpm is applied to calculate LDA for 1760 rpm, an accurate diagnosis is possible and thus it is not necessary to perform a class analysis for 1760 rpm. In order to prove this, the interaction graph of false acceptance rate (FAR) and false rejection rate (FRR), which are used as the identification tool of bio-recognition, is shown. To demonstrate the efficient method at light load, eigenvector w = [-0.704105, 0.710096] for 1790 rpm can be obtained. \(-\)15.022\({}^{\circ}\) of rotation direction by LDA is obtained as optimal direction information. Table 3 shows the LDA direction information for each speed. Figure 17 is a FAR-FRR graph that compares the normal class and the ITSC class that were measured at 1790 rpm. Figure 16: Between-class scatter (BCS) in the steady-state and the ITSC state according to speed change. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Speed (rpm)** & **1790** & **1780** & **1770** & **1760** & **1750** & **1740** & **1730** & **1720** & **1710** & **1700** & **1690** \\ \hline Angle (Degree) & \(-\)15.02 & \(-\)18.40 & \(-\)16.88 & \(-\)15.45 & \(-\)14.51 & 7.421 & 6.341 & 5.765 & 8.652 & 13.66 & 13.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: LDA direction information for each speed. In Figure 17, the black line is the result of analyzing FAR-FRR without changing the angle, the red line is the result of applying an angle of \(-15.022^{\circ}\), and the green line is the result of applying an angle of \(-45.243^{\circ}\), which is the angle from 1790 rpm to 1690 rpm, to the class for 1790 rpm. This shows that when the LDA was calculated from the entire data to be applied to a specific class (green), the performance was lower than when each class was analyzed (red). The FAR-FRR interaction graph is shown in Figure 18.  
In Figure 18, the black line indicates the result without an angle conversion, the red line indicates the result when only the LDA of 1790 rpm class was applied, and the green line indicates the result when the LDA of 1790-1690 rpm was applied to the angle at 1790 rpm. As shown in Figure 18, it is better to apply to one class than to the class in the whole data, and the performance is slightly better compared to the case without the angle conversion. Figure 17: False acceptance rate (FAR)–false rejection rate (FRR) graph at 1790 rpm. Figure 18: FAR–FRR interaction graph at 1790 rpm. Figure 19a shows the result of applying the LDA degree value obtained at 1790 rpm to the class of 1780 rpm, and Figure 19j shows the result of applying the class to 1690 rpm. Here, the black line is the result of applying LDA degree by each class (e.g., in Figure 19a, black line is FAR-FRR interaction graph by LDA degree of 1780 rpm), the red line is the result of applying LDA degree of 1790 rpm, and the green line is the result of applying the LDA degree value of 1790-1690 rpm to the class of the corresponding speed.