Bearing cage telemeter for the detection of shaft imbalance in rotating systems

We demonstrate for the first time a low-cost battery-free wireless telemeter integrated on a dynamically balanced ball bearing operating in a test setup that mimics the operating conditions of a two-compressor turbocharger. In this method we continuously monitor the bearing cage temperature and demonstrate the ability to detect rotor imbalance during operation even at low speeds below 5,550 RPM. The telemeter is based on a simple commercially-available temperature-sensitive capacitor coupled with an inductor that is mounted on the bearing cage and is able to operate at temperatures up to 150°C. Cage temperature is sensed wirelessly through a matched interrogator tuned to the natural frequency of the cage sensor at 13.1 MHz. A 5°C temperature differential is detected at 4,700 RPM between a balanced rotor and one with an applied 2.32 × 10^-3 kg-m imbalance.