Micromachined Capacitive Vibration Sensor with High Passband Flatness for Condition Based Monitoring

A micromachined capacitive vibration sensor is proposed in this work for machine tool condition monitoring. The sensing element design, readout circuit, system module design, and experimental results are also investigated. A systematic FIR compensation filter for the proposed vibration monitoring system enhances the flatness of the passband frequency so that the output amplitude of the sensor keeps near a constant under different excitation frequencies. The passband flatness of the compensated MEMS vibration sensor is about 7.5% with the 5kHz bandwidth and the noise density is about $31\mu g/\sqrt {Hz} $. Finally, the vibration sensor is characterized and verified by the metal milling process for the performance and the feasibility for machine condition-based monitoring.