Vibration Sensor for Wireless Condition Monitoring

Abstract

ABSTRACT A microelectromechanical system (MEMS) accelerometer has been manufactured for wireless vibration measurements on AC motors for condition monitoring. The vibration sensor element has been encapsulated with glass using wafer scale adhesive bonding with Benzycyclobutene (BCB). Cavities in the glass allow the moving mass on the silicon sensor to vibrate freely. The wafer scale packaging greatly simplifies the subsequent packaging which includes mounting on a ceramics substrate. The ceramic board with the sensor element is densely packed inside a sensor node together with other components. The battery driven sensor node solution is optimized with regard to small scale and low power consumption to reduce price and extend life time. The sensor element has a linear response up to 30 g with a sensitivity of 0.3 mV/Vg and a resonance frequency of 7.7 kHz. Measurements were performed on a bare, unpackaged die and after glass encapsulation. The only recognizable effect of the glass encapsulation on the frequency response is a moderate damping.