| 摘要 |
PROBLEM TO BE SOLVED: To optimize a resonance frequency corresponding to detection conditions even when a plurality of detection coils are arranged. SOLUTION: A drive signal is output to one of a plurality of resonance circuits 2A to 2D, and 3A to 3D whose driving order is determined, and free oscillatory wave counting processing for counting free oscillatory waves outputted from the resonance circuits 2A to 2D, and 3A to 3D after the drive signal output is stopped is carried out. Next one of the resonance circuits 2A to 2D, and 3A to 3D is driven in a relay manner based on the time when the count of free oscillatory waves in the free oscillatory wave counting processing reaches a predetermined number to repeat the free oscillatory wave counting processing, and the time required for a predetermined number of times of the free oscillatory wave counting processing is measured and then output in a predetermined signal form. COPYRIGHT: (C)2008,JPO&INPIT
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