RESONANCE FREQUENCY SENSING METHOD, RESONANCE FREQUENCY SELECTING METHOD, AND RESONANCE FREQUENCY SENSOR

摘要

A resonance frequency sensor (20) comprises sound source means (21), signal combining switch means (26, 27) and measuring means (25). The signal combining switch means (26, 27) switch between a first status of outputting a measurement signal and a second status of outputting a synthetic signal generated by combining the measurement signal and the output signal from a microphone (14). The sensor (20) determines the resonance frequency on the basis of comparison between a first amplitude frequency characteristic measured in the first output status and a second amplitude frequency characteristic measured by the second output status.