| 摘要 |
PURPOSE:To surely evade the influence of an external magnetic field with simple constitution by supplying a current for magnetic field formation to a Helmholtz coil so as to cancel the external magnetic field in first and second directions based on the magnetic field detection result in first and second directions intersected orthogonally with each other. CONSTITUTION:In a display device using a cathode ray tube, the magnetic field detection results S1, S2 in the first and second directions (x), (y) of a magnetic sensor 2 are integrated by the respective operational amplifier circuits 10, 11 and the detection signals SD 1, SD 2 varying the signal level in accordance with the magnitude of a synthetic magnetic field and the direction are obtained. After these detection signals SD 1, SD 2 are subjected to a voltage/ current conversion by operational amplifier circuits 28, 30, the magnetic field is formed to be '0' at the synthetic magnetic field by being outputted to the Helmholtz coils 33, 34, 43, 44 forming the magnetic field so as to cross the cathode ray tube in the first and second direction. Thus even when the display device is mounted on a traffic means, for example, a vessel, etc., and is moved to several places, the display picture can be formed in the state that the external magnetic field is '0'. |
