To provide a demagnetizing system for detecting the change in the local permanent magnetism of a hollow structure and maintaining a magnetic field appearing in the outside minimum at all these.
A detection signal of a magnetic detector 5 for individual coil control is divided into an induction component and a permanent component, for the noise and other correction part 14. The change amount of the permanent component is calculated and compared with a target value 9 through a subtracter 10. Power supply to each demagnetizing coil 7 is so controlled that the permanent component becomes equal to the target value 9. A detection signal of a magnetic detector 6 for block coil control is divided into an induction component and a permanent component for the noise and other correction part 22. The change amount of the permanent component is calculated and compared with a target value through a subtracter 16. Then a current command correction signal for block coil control is obtained and added to a signal from a block control system 19 by an adder 21, thereby controlling the current to be conducted to a block coil 8.
MURAKAMI HAYATA
TANAKA TOSHIO
