| 摘要 |
PROBLEM TO BE SOLVED: To reduce influence of noise and to improve the detection accuracy by amplifying phase difference of free oscillatory wave to hold down the occurrence of errors due to the difference in detection period related to both resonance circuits, in a metal state detecting device. SOLUTION: A driving signal is output to a first resonance circuit 2 including a first detecting coil L1 and a first capacitor C1; and after the stoppage of outputting of the drive signal, the phase difference of free oscillatory wave output in the damping state from the first resonance circuit 2 is measured, based on the free oscillatory waves counted during a predetermined period. A drive signal is output to a second resonance circuit 3, including a second detecting coil L2 and a second capacitor C2; and after the stoppage of outputting of the drive signal, a phase difference of the free oscillatory waves output in the damping state from the second resonance circuit 3 are measured, based on the free oscillatory wave count during the predetermined period. The difference in the free oscillatory waves counted between both resonance circuits 2 3 is computed. COPYRIGHT: (C)2008,JPO&INPIT
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