| 摘要 |
PURPOSE:To measure even a material which has large magnetic hysteresis by producing a bias magnetic field by an AC magnet and demagnetizing the object material when it moves away from a measurement position. CONSTITUTION:The AC magnet 7 is excited by an AC power source 8 to produce magnetic flux which is phi delayed in phase behind the voltage of the power source 8. A controller 9, on the other hand, generates and sends a pulse to a pulser receiver 3 when the density of the generated magnetic flux exceeds a specific value phi1+phi2 after the zero-cross point of the voltage of the power source 8. Then, a pulse current flows through an eddy current generating and detecting coil 2 to generate an eddy current on the object material 1, generating an ultrasonic wave. This ultrasonic wave propagates in the object material 1 and is reflected by its back surface to generate an eddy current on the surface, and the eddy current is detected by the coil 2. The thickness of the object material 1 is measured from the time from the pulse generation to the detection. The object material 1 after being measured is demagnetized when the coil 2 moves away, and then there is no residual magnetism left, so that even a material having large magnetic hysteresis is measured. |
