| 摘要 |
PURPOSE:To avoid the effect of the separating distance between a detecting part and an object to be detected on detecting accuracy and to make it possible to perform detection even in water and oil, by providing detecting coils, an oscillator, differential voltage detectors, and phase detecting circuits, and detecting the edge of a metal body by the output of an adding circuit and/or a subtracting circuit. CONSTITUTION:When a metal plate A is located at a position separated from a probe 1, the voltages at non-grounding-side terminals of detecting coils 21, 22, and 23 are equal. Therefore, the output signals of differential amplifiers 5a and 5b are zero, and an added signal PS and a difference signal MS are both zero. Then, the metal plate A is moved from the side of the detecting coil 23 to the side of the detecting coil 21. In this case, when the edge of the metal plate A faces the detecting coil 23, the eddy current generated in the metal plate A by the high frequency current flowing the detecting coil 23 is larger than that caused by the detecting coil 22. Therefore, the impedance of the detecting coil 23 is lower than the impedance coil 22. As a result, the terminal voltage of a winding 23b of the detecting coil 23 becomes lower than the terminal voltage of a winding 22b of the detecting coil 22. A voltage signal corresponding to the difference is obtained as the output of the differential amplifier 5b. |
