Field demonstration of a robust humidity sensor system for condition monitoring of lubricating grease in axlebox bearings of rail wheelsets

Purpose This study aims to investigate if sensors used for condition monitoring of lubricated systems can provide high-level robustness against environmental factors, such as temperature, humidity, vibrational load and mechanical shock, thereby ensuring long-term reliable operation. After successful laboratory tests of the Humidity Sensor in Axle Bearings (HSAB) system using accelerated aging for robustness evaluation, a field demonstration was performed to assess its functionality for monitoring water in grease-lubricated axlebox bearings of rail wheelsets. For that purpose, a humidity sensor was integrated inside the bearing cover to measure the relative humidity of the air surrounding the grease. Despite harsh environmental conditions, the HSAB system provided reliable output signals under varying environmental conditions. Design/methodology/approach In this study, the field evaluation of a unique approach for the detection of water in lubricated wagon components is presented. The key element of this system is a robust humidity sensor located in the immediate atmosphere of the investigated grease-lubricated rail component. Findings The HSAB system proved to have satisfactory robustness for both the sensor system and the developed algorithm to calculate the grease–water content for the intended application in axle bearings. Furthermore, the grease–water content of the investigated lubrication grease showed a good correlation with the prevailing weather conditions. Originality/value The proposed method can significantly enhance the reliability and reduce the maintenance costs and downtime of railway wagons. The presented approach paves the way for an online monitoring tool to predict the water content of grease-lubricated rail parts.