| 摘要 |
PROBLEM TO BE SOLVED: To drive an ultrasonic oscillator with signals consonant with a resonance frequency of the ultrasonic oscillator regardless of dispersion of individuals and make driving signals follow alteration of the resonance frequency of the ultrasonic oscillator due to a change of surroundings such as an ambient environment temperature. SOLUTION: At the time of starting, while oscillation frequency of VCO 3 is continuously changed, detected outputs of a rectifier circuit 6 are loaded to monitor an impedance of an ultrasonic oscillator 1. When resonance frequency of the ultrasonic oscillator 1 is detected from the detected outputs of the rectifier circuit 6, the control voltage at that time is set in the VCO 3. Accordingly, the oscillation frequency of the VCO 3 is made consonant with the resonance frequency of the ultrasonic oscillator 1. Thereafter, the phase difference generated by the ultrasonic oscillator 1 is detected and the oscillation frequency of the VCO 3 is changed according to the phase difference to make the oscillation frequency of the VCO 3 follow the alteration of the resonance frequency of the ultrasonic oscillator 1. COPYRIGHT: (C)2008,JPO&INPIT
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