Early-Warning Wireless Telemeter for Harsh-Environment Bearings

We demonstrate an early-warning wireless and high-temperature telemeter that continuously monitors the temperature of a roller bearing during operation. The telemeter detects imminent temperature-induced failure of the bearing four minutes before conventional thermocouple sensors respond to conditional changes, leaving ample time for appropriate actions to avoid complete failure. The telemeter includes a commercially available temperature-sensitive capacitor that operates up to 220deg C. In addition, the telemeter's natural frequency changes with capacitance, which in turn is dependant on temperature. Information transmission between the bearing and a monitoring station is accomplished with a matched interrogator driven by a sinusoidal signal at 2.27 MHz. The telemeter's natural frequency shifts by about 0.65 kHz/degC, which is measured as a change in voltage on the interrogator inductor.