| 摘要 |
PURPOSE:To clearly discriminate a signal level even when the difference in the signal level is small, by applying square operation to the signal detected by a magnetic detector, rectified by a synchronous rectifying circuit and differentiated and amplified by a differential amplifier before outputting said signal. CONSTITUTION:A magnetic detector 1 for magnetically detecting a magnetic metal body when said metal body arrives at the vicinity, an oscillator 2 exciting the exciting coil of the detector 1, a frequency doubling circuit 4 converting the signal of frequency (f) of the oscillator 2 to two times to output the same, a synchronous rectifier 3 for synchronously rectifying the output of the detector 1 by the signal of frequency 2f and a differential amplifier 5 for obtaining the change portion of detection output synchronously rectified are mounted. Then, the output of the amplifier 5 is inputted to a multiplier-divider 10. The multiplier-divider 10 has a function of x.y/z and the output of the amplifier 5 is inputted to the input terminals (x), (y) thereof and the signal of the square of said output is obtained as output to be applied to a comparator 9. Further, a sensitivity controller 11 is connected to the z-terminal of the multiplier-divider 10 and the voltage thereof is adjusted to change a dividing ratio and sensitivity is controlled.
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