| 摘要 |
PURPOSE: To mitigate external magnetic field interference by providing an electromagnetic field sensor and a backing field coil driving circuit on the inner surface of a CRT magnetic shield; and a backing field coil which generates a backing electromagnetic field around CRT. CONSTITUTION: An external magnetic field 37 is added to a backing coil field(BCF) 39 generated by the backing field coil(BFC) 41. The sensor 11 provided inside the field 30 of a CRT jacket decides whether or not uncancelled field exists by the addition of BCF 39 and the external magnetic field 37. A clear sensor output 29 is transmitted to an amplifier 43 for nomalizing the output of the sensor 11 in a proper driving signal to be transmitted to BFC 41. The amplifier 43 is provided with an adjusting material for correcting a device by which an optional circuit error and the offset error of the sensor made into a null at the time of no external magnetic field 37. Thus, the generation of BF in response to a low level sensor output, which is caused only by the characteristic function of the nullifying device is avoided. |
