PURPOSE: To enhance the magnetic shielding performance conveniently, while preventing the generation of magnetic noise due to vibration, by feeding a DC current to a coil disposed on the outside of a magnetic shield room thereby generating a magnetic field reversely to the external DC magnetic field.
CONSTITUTION: Pairs of coils 4A, 4A, 5A, 5A and 6A, 6A are disposed in parallel while spacing apart from each other thus forming coil pairs in three directions of X, Y and Z. DC field in a magnetic shield room 2A is then measured by means of a magnetic sensor 22A and a magnetic measuring unit 12A. When the coils are fed with a current in same direction, a uniform field is formed in the axial direction of the coil in the center of two opposing coils. When the quantity of current is selected appropriately for each coil, a reverse field for offsetting the external DC field intruding into the magnetic shield room 2A can be generated and thereby the DC field can be reduced in the magnetic shield room 2A or at the outer periphery.
HARAKAWA KENICHI
KAZAMI KUNIO
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