| 摘要 |
PURPOSE:To prevent the disorder to be generated to the horizontal amplitude when a horizontal scanning is peformed at the upper part of an effective screen, by obtaining fixed time intervals at all times between the starting time point of the horizontal scan and a time point when an electron beam scans a detecting index for horizontal amplitude. CONSTITUTION:An inner beam shield 5 in a rectangular frame shape is set to a shadow mask 3 with a proper distance secured toward an electronic gun so that the shield 5 cuts the electron beam going toward the areas excepting an effective screen 6. An index 8 for detection of horizontal amplitude is attached vertically to the shield 5 at the electronic gun side. The index 8 is formed by coating a material which generates the fluorescent light when the surface of the shield 5 receives the electron beam. Furthermore the index 8 is set vertically at the left side of the shield 5 when viewed from the front of a picture tube 1. Both the electronic beam deflected to the highest part and the electron beam deflected to the lowest part are formed in such a length respectively that can scan horizontally over the index 8. A photodetector 9 is provided to face the outer wall of the picture tube 1 and so as to receive the light from the index 8. It is possible to control the horizontal amplitude at a fixed level so as to obtain fixed time intervals at all times between the horizontal scan starting time point and a time point when the electron beam scans the index 8. |
