| 摘要 |
A magnet is provided to a vibrating plate within a detection pipe unit and an electromagnet is placed opposite to the magnet with a slight gap therebetween. A drive circuit applies, to a coil at every predetermined measurement cycle, an alternating current at a frequency which is swept over a predetermined range centered at a resonance frequency of the vibrating plate. When the alternating current is applied, a phase comparison circuit detects a change in phase that is caused according to whether or not an object contacts the vibrating plate. A microcomputer determines presence/absence of the object based on the detected change in phase, measures the temperature based on the detected change in phase in a former half cycle of the predetermined measurement cycle and changes the swept frequency based on the result of measurement of the temperature in a latter half cycle of the predetermined cycle.
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