To provide an apparatus for highly accurately detecting very small defects concentratively present in an area.
The flaw detecting apparatus 3 is installed along a transfer path of a steel plate 1. The magnetic flaw detecting apparatus 3 is mainly constituted of a magnetizer 4; a magnetizing electric power source 5; a magnetizing coil 6; a magnetic sensor 8; and a signal processing device 9. A DC current is supplied for the magnetizing coil 6 from the magnetizing electric power source 5 to excite the steel plate 1 through the magnetizer 4. Leakage flux from the steel plate 1 is converted into electric signals at the magnetic sensor 8. The electric signals detected by the magnetic sensor 8 are fed to a signal processing device 9 and divided for every area of an appropriate size of, for example, 5 mm at an area diving device 10. A statistic value computing circuit 11 computes the Root Mean Square (RMS) of the signals in each area. When the RMS value exceeds a threshold value, the presence of defects is determined.
KATO HIROHARU
NAGAMUNE AKIO
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