| 摘要 |
PURPOSE:To reduce effect of liftoff due to chattering, vibration or the like of an object to be detected, by connecting exciting coils and detection coils in series. CONSTITUTION:A plurality of detection ends 1-4 are arranged about a rotor 11 and each made up of the even number of detection coils 1A and 1B and one exciting coil 1E, which is connected in series between the detection ends and the detection coils in one of the detection ends are connected in series. An object to be detected 20 moves straight while the detection ends 1-4 are turning thereabout. The sine wave voltage from an oscillator 31 at a control section is supplied to the exciting coil through an amplifier 32. The impedance of the entire exciting coil is kept almost constant as the effect of a gap with the object being detected is canceled and is detected with the detection coil on the top surface of a defect. The voltage change is equalized due to the series connection of the detection coils while the liftoff signal due to the chattering of the object being detected is canceled and thus, is limited to a large extent.
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