| 摘要 |
PURPOSE:To simultaneously perform a great variety of flaw detections, by measuring the moving distance of an inspection coil caused by the disturbance of an eddy current. CONSTITUTION:An electromagnet 5 is provided so as to permit the passage of a slab 1 and, when a current is flowed to said electromagnet 5 from a DC power source 11 through a change-over switch 13, a static magnetic field is formed in the surface layer part of the slab 1 in the lateral direction. When a pulse current is flowed to an exciting coil 2 from a pulse current generation circuit 12 through the switch 13, an eddy current is generated in the surface layer part of the slab 1. When a flaw is present at the surface part of the slab 1 opposed to the coil 3 at the time of the generation of the eddy current or the formation of the static magnetic field, an inspection coil 3 is vibrated in a vertical direction by the difference between electromagnetic forces varied before and behind the flaw. A distance sensor 4 measures the gap distance L between the sensor 4 and the coil 3 and the measuring result is inputted to a signal processing apparatus 17. The apparatus 17 discriminates the supply of a current to either one of the coil 2 and the electromagnet 5 on the basis of the timing pulse from a switch control circuit 14 and compares the measuring result by the sensor 4 with a threshold value to operate alarms 18a, 18b. |
