External magnetic field compensator for a CRT
AssigneeHazeltine Corporation
InventorsArthur L. Romeo, Robert T. Bonelli, Harvey E. Fishman
Life of this patent
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Abstract
Light sensors with red filters are located at four corners of a CRT out of view of the operator. A red raster is generated in the corners of the CRT, the pattern of the raster corresponding to the area covered by the sensors. A pair of coils is located about the face of the CRT in a Helmholtz configuration and are driven by a current generator in response to the sensor output to maximize sensor output, thereby generating a compensating magnetic field which cancels external axial fields affecting the CRT.
Claims21
Apparatus for compensating for an external magnetic field affecting a cathode ray tube (CRT) display, said apparatus comprising:
- (a) means for generating a reference display of a given color in a predetermined area on the face of said CRT;
- (b) means for sensing an optical characteristic of the reference display and generating an output signal representative thereof;
- (c) means for generating a compensating magnetic field about said CRT;
- and
- (d) means for controlling the strength of said compensating magnetic field in response to said output signal.
Apparatus for compensating for an external magnetic field affecting a cathode ray tube (CRT) display, said apparatus comprising:
- (a) first means for generating a reference display of a given color in a predetermined area on the face of said CRT, said first means including a first counter for counting lines during a field displayed on said CRT and a pulse generator for applying a pulse to an electron gun of said CRT in response to said first counter;
- (b) second means for sensing an optical characteristic of the reference display and generating an output signal representative thereof, said second means including at least one photosensor located associated with said predetermined area on the face of said CRT;
- (c) third means for generating a compensating magnetic field about said CRT, said third means including a pair of coils in a Hemholtz configuration located about the face of said CRT;
- and
- (d) fourth means for controlling the strength of said compensating magnetic field in response to said output signal, said fourth means including a current generator feeding said coils, a peak detector coupled to said photosensor, first and second sample and hold circuits alternately coupled to said peak detector, and a comparator comparing the output of said first and second sample and hold circuits, said current generator being coupled to an output of said comparator for providing a current whose magnitude corresponds to the output of said comparator.
Dependencies are inferred from the claim text.