INDRETNING I BILLEDROER TIL NEDSAETTELSE AF DEN MAGNETISKE FELTSTYRKE I BILLEDROERETS OMGIVELSER

摘要

A display tube 3 is provided with a deflection coil 1 which is surrounded by a funnel-shaped casing 4 of a magnetic material. The deflection coil causes a magnetic deflection field B for the electron beams and a magnetic leakage field BL in the vicinity of the display tube. The leakage field is composed of a di-pole field and a four-pole field. For the reduction of the strength of the magnetic field in the vicinity of the display tube 3 there is a magnetic compensation field which is opposite in direction to the leakage field. The compensation field is composed of a di-pole field which is produced by a first compensation winding 7 and a four-pole field which is produced by a second compensation winding 9. The first compensation winding 7 is principally flat and lies perpendicular to the magnetic deflection field B. The second compensation winding 9 is flat and lies perpendicular to the longitudinal axis of symmetry z of the display tube, and is provided with an upper 9a and a lower 9b part, which produce two four-pole fields DK2, DK3 in opposite directions. The centres TP1, TP2 of the compensation windings lie on the axis of symmetry z at the front edge 6 of the funnel-shaped casing 4 and on the front part of the deflection coil 1 respectively. The compensation windings 7, 9 are connected in series with the deflection coil 1. <IMAGE>