## 4 Conclusions  
In this study, a concept for a novel rotational angle sensor, designated as the gear wheel sensor, which utilizes a gear wheel as a material measure, is evaluated in comparison with a conventional angle sensor (the pole ring sensor) and an acceleration sensor for the purpose of damage classification. The gear wheel sensor offers distinct advantages, including its capacity for seamless integration into the gearbox without necessitating alterations to the existing rotating components; additional packaging has been a requirement for many earlier condition monitoring concepts [23]. This feature of a potentially seamless integration renders it a suitable retrofitting solution. The classification results demonstrate the gear wheel sensor's efficacy in classifying gear damage. However, under stationary operating conditions, the classification performance is inferior to those of the pole ring and acceleration sensors. Conversely, under transient operating conditions, such as speed ramps, the gear wheel sensor demonstrates an ability to achieve superior classification results. In  
Figure 8: Classification results at transient conditions with five-fold cross-validation: (**a**) gear wheel sensor, 69% accuracy; (**b**) pole ring sensor, 58% accuracy; (**c**) acceleration sensor, 41% accuracy, according to [16]. scenarios where speeds are variable, the rotational angle sensors exhibit an advantage over the acceleration sensor. This is due to the rotational angle information, which enables the consideration of gear-specific frequencies. There are methods that extract the rotational angle information with acceleration sensors, but these require significant computational effort and are not reliable across all operating conditions [24]. As previously outlined in other publications, significant tooth-specific fluctuations in the angle measurement are observed with the gear wheel sensor due to the deviations of individual teeth [15]. This reduces the accuracy of the rotational angle measurement and, consequently, affects the classification accuracy. Further investigation into the tooth-specific influence on the acquired data could lead to the identification of methodologies by which to increase measurement accuracy. These methodologies may include calibrating the gear wheel sensor or using the fluctuations to obtain an absolute rotational angle reference. Additionally, the database used for classification is limited in size, which necessitates expansion in future studies to enhance the comparability between the sensors. It is noteworthy that the artificially induced damage exhibited in this study is significantly more pronounced in comparison to the initial pitting observed on a tooth flank during actual operation. Consequently, further research translating these findings into various realistic or actual damage scenarios is necessary. Conceptualization, Y.K. ; methodology, Y.K. ; software, Y.K. ; validation, F.M.B.-D. and Y.K. ; investigation, Y.K. ; resources, F.M.B.-D.; data curation, Y.K. ; writing--original draft preparation, Y.K. and F.M.B.-D.; writing--review and editing, E.K. and F.M.B.-D.; visualization, Y.K. ; supervision, F.M.B.-D.; project administration, E.K. ; funding acquisition, E.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The original data presented in the study are openly available in the TUDatalib repository, \"Gearbox Condition Monitoring based on Angle Measurement using a Gear as Material Measure--Test data\", at [[https://tudatalib.ulb.tu-darmstadt.de/handle/tudatalib/4298](https://tudatalib.ulb.tu-darmstadt.de/handle/tudatalib/4298)]([https://tudatalib.ulb.tu-darmstadt.de/handle/tudatalib/4298](https://tudatalib.ulb.tu-darmstadt.de/handle/tudatalib/4298)). The authors declare no conflicts of interest. The following abbreviations are used in this manuscript: