| 摘要 |
PURPOSE:To make a correction detection signal accurate by automatically correcting quantity of correction even when a magnetic field due to magnetization changes hourly, by correcting the quantity of correction on the basis of two sets of detection signal pairs from an earth magnetism detection means by a quantity-of-correction correcting means. CONSTITUTION:Coordinates corresponding to detection signal pairs obtained after a magnetic field due to magnetization changes from HV1 to HV2 are set to (x1, y1), (x2, y2) and the coordinates of the foot of a perpendicular dropped to the vertical bisector (l) of the segment connecting said coordinates points are set to xP, yP. The coordinates point of the foot of said perpendicular becomes equal or near to the coordinates point corresponding to the magnetic field HV2 due to magnetization after change rather than the coordinates (x0, y0), that is (xV1, xV2) corresponding to quantity of correction before the change of the magnetic field HV1 due to magnetization. Therefore, after the change of the magnetic field due to magnetization, the coordinates components xP, yP of the foot of the perpendicular are respectively set to quantities of correction x0, y0 and, when said means is repeatedly performed on and after, the quantities of correction x0, y0 can be allowed to approach the coordinates components xV2, yV2 corresponding to the magnetic field HV2 due to magnetization, that is, the quantity of correction necessary for negating the effect of the magnetic field HV2 due to magnetization as near as possible.
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