Measurement Strategies for the Monitoring of the Electric Behavior of Journal Bearings

The condition monitoring of machine elements and, more precisely, journal bearings, is beneficial to prevent unnecessary wear and identify critical operating conditions. One method for that is the monitoring of the electric behavior of the bearing by monitoring its capacitance. While the general electric behavior of journal bearings is known, assessments of suitable measurement setups and data analysis methods are usually neglected. This contribution identifies potential measurement setups and analysis methods used in the literature for monitoring rolling-element bearings or journal bearings. These setups and analysis methods are then discussed theoretically and based on measurements of the electric behavior of journal bearings. The findings show that voltage divider setups with AC signals are the most promising solution to monitor the journal bearing electrically. Linear regression algorithms can be used to obtain the amplitude and phase of the measured voltage signal. These values are then used to calculate the impedance and capacitance of the bearing. Lastly, this contribution investigates how existing PCT (percent contact time) analyses need to be altered to improve the precision and robustness of the analysis and allow for the physical interpretation of the measurement results. These findings may be used in the future to predict wear and identify critical operating conditions in journal bearings, such as mixed lubrication.