Wireless temperature and vibration sensor for real-time bearing condition monitoring

This article presents a unique sensor capable of simultaneously measuring the bearing cage temperature and vibration signature using inductive coupling. The temperature sensing is based on thermal-induced shift in resonant frequency of an inductive coil and a temperature-sensitive capacitor mounted on a bearing cage. This shift is detected remotely by placing an interrogator coil in close proximity to the sensor coil and the bearing cage. Bearing cage vibrations, result in change in the coupling factor between the sensor and interrogator coils along the bearing´s axial direction. This leads to amplitude modulation of excitation frequency by a signal proportional to bearing cage vibration. In this article the authors present bearing cage temperature measurements from 20°C to 90°C for Timken MMC9112K at 1280 rpm to 3250 rpm. The corresponding vibration frequencies at each speed are measured and compared with theoretical values calculated using standard bearing frequency equations. A good agreement between measurement and theory is observed for various vibration components such as ball spin, fundamental train and ball pass-outer race frequencies with average variation of 2.8%.