Importance

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Abstract

A magnetic compensation system for a CRT display that includes a magnetic shield and a compensation coil for generating a bucking field is disclosed. The magnetic shield houses the CRT and shunts the transverse component of an external magnetic field. An annular metal face plate is attached to the shield at its open end and extends inward from the edges of the shield in a plane substantially parallel to the display. The compensation coil is disposed on the face plate's outer surface, and provides a bucking magnetic field to oppose the axial component of the external magnetic field in response to a drive signal. A pair of magnetic field sensors for sensing the difference between the external and bucking fields are spaced inward from the coil and opposite each other. The sensors are positioned substantially perpendicular to the plane of the face plate at its inner edge. A circuit senses the average of the outputs of the sensors, and adjusts the drive signal to the coil to reduce the magnitude of the average sensed field. The system also includes a magnetic field sensor outside the shield for sensing the transverse component of the external field. When either the transverse or axial components traverse predetermined triggering levels, the circuit produces a degaussing trigger signal.

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First Claim