MAGNETIC CHARACTERISTICS OF MAGNETIC SHIELD IN A CATHODE RAY TUBE AND THEIR EFFECTS ON LANDING DRIFTS CAUSED BY TERRESTRIAL MAGNETIC FIELD

Within the tube of the cathode ray tube (CRT), a magnetic shield is formed. This shield is made of soft magnetic materials and includes the inner magnetic shield (IMS), frame, and aperture grill as a color selection mechanism. By means of this shield, the mislanding drift by the terrestrial magnetic field is controlled and each magnetic material in the magnetic shield, in general, eliminates magnetization by ac attenuation magnetic field at the time of kick-off. This ac demagnetization process is considered to be an anhysteretic magnetization process; and, to analyze its characteristic, the magnetization process is simulated. To verify the results, a method is conceived for measurement of the anhysteretic magnetization. The anhysteretic magnetization of various shielding materials is measured. (In practice, the magnetic flux density was measured.) It is shown that the measured results agree well with the prediction. It is shown also that the effective permeability of the magnetic shielding materials after ac demagnetization unknown to date can be expressed quantitatively as an anhysteretic permeability. Further, the relationship between the anhysteretic permeability of the IMS and the terrestrial magnetic field is studied by simulation and experiments. Finally, it is shown that the anhysteretic permeability is a fundamental magnetic parameter of the drift of the terrestrial magnetic field.