## 3 Results and Discussion  
### Failure Case 1 Results  
In Figure 5a, the ANN's predicted enveloped FFT CI-values from failure case 1 can be seen together with the comparison with the true values and the normalized difference between them, before data filtration with respect to rotational speed variance.  
At the top graph, the ANN's predicted CI-values are seen in red and closely followed the true values, in blue, until the defect appeared except for three distinct peaks. These three predicted values coincided with the three mentioned measurements in Section 2.3 which were taken during a high rotational speed and large variance. The ANN learned that such a high rotational speed should coincide with a high CI-value but failed to take into account the flattening effect of the spectrum when the variance in rotational speed was high. Thereby, the calculated difference, using Equation (3) and seen in normalized form by Equation (4) in the bottom graph of Figure 5a, also highlighted these peaks. When the defect appeared at measurement 510, this calculated normalized difference permanently increased to roughly 20 on the normalized scale, indicating the defect being present in the measurement. Studying the CI-values by themselves, seen in the top graph of Figure 2a, only showed a relative increase of 8. Additionally, the incorporation of the ANN could indicate the defect earlier than purely using the enveloped FFT CI-values from Figure 2a by themselves.  
After the rotational speed variance data filtration, the normalized difference between the ANN's predicted and true CI-values can be seen in Figure 4(b). Here, the three peaks before the defect appears were eliminated and the trend curve indicated normal operation of the bearing until the defect appeared at measurement 510. Additionally, the relative increase as the defect appears now increased to roughly 30 compared to 20 from before the data filtration. Thereby, the incorporation of the ANN increased the sensitivity of the monitoring by a factor of 3.75.  
In Figure 6, the comparative results to Figure 5 using the enveloped WPT CI-values can be seen.  
Figure 5: Gearbox output shaft bearing failure case 1, enveloped FFT CI-values. Comparison of ANN’s predicted CI-values in red and true CI-values in blue at the top graph in (**a**) and normalized difference between them at the bottom graph without rotational speed variance data filtration. Normalized difference between predicted and true CI-values with rotational speed variance data filtration in (**b**).  
Here, the rotational speed variance was unable to produce the large differences between the ANN's predicted CI-values and the true values, seen in Figure 5(a). Thereby, the operation of the bearing was read as normal until the defect appears and was indicated by the normalized difference between the ANN's predicted and true CI-values. In the time period when the defect appeared, however, measurements 533 and 536 where the rotational speed and variance were high resulted in a drop of the CI-values and negated the increased normalized difference. Thereby, these would be read as normal behaviour on the normalized scale while in fact, the defect was present. However, the filtration of these measurements eliminated this drop in Figure 5(b). Additionally, the relative increase of the normalized difference by the data filtration reached a level of 50, which could be compared to the relative increase of the CI-values seen in the bottom graph of Figure 2(a) of 16. Thereby, the sensitivity of the monitoring increased by a factor of 3.125 by the ANN implementation.  
Figure 6: Gearbox output shaft bearing failure case 1, enveloped WPT CI-values. Comparison of ANN’s predicted CI-values in red and true CI-values in blue at the top graph in (**a**) and normalized difference between them at the bottom graph without rotational speed variance data filtration. Normalized difference between predicted and true CI-values with rotational speed variance data filtration in (**b**).