عملية تركيز الشعاع (Focus) ١-a .. كتاب التلفزيون الملون والعادي

8-11 Focusing the beam:

Since the beam begins to repel each time it moves away from the launcher and leads to its dispersion and lack of effect. Therefore, the beam is focused in a manner similar to focusing the light beam with optical lenses, and in two stages. The first stage is carried out by the first anode with positive polarity, then the second stage is carried out by the second high-voltage anode. Thus, the beam collides with the points of the phosphorescent screen in a very small point (Fig. (11)-27) and (11-28), and the control of the second elevator with the highest voltage is appropriate for focusing the beam. The efforts of the networks 3-4-5 are proportional to the method of making these networks - and their locations inside the screen tube.

In the black and white screen, network No. 4 has a voltage equal to 20% of the elevator voltage, i.e. from (2000) to 3000 volts, and it has a special circuit to adjust its voltage and thus adjust the centering and accuracy of the beam to produce a good image.

By improving the design of the screen, and adjusting the distances between the networks (3-5), it was possible to reduce the voltage of the centralizer to about (150-300 volts). After that, it was also possible to dispense with the voltage of the centralizer in network 4 and even ground it, so that its voltage would be zero. . Thus, the circuit is simplified, but the image is not completely accurate and of the required quality. The focus electrode is fed from the high-voltage stage with a rectifier voltage, and it can be controlled by a special variable resistance of a large value in mega-ohms.

Center beam rings:

They are placed in the monochrome TV behind the deflection coils, and they are in the form of two rings around the neck of the screen (Fig. (11) - (29). Its job is to set the beam in the middle of the screen. It is set by rotating the two rings on the axis of the screen. These rings are not used in the colored device because the centering is done automatically.

9-11 Traps of ions (electrolytes):

​​​​​​The ion beam is formed with the electron beam. It is one of the gas particles that must have a part of it, even if it is very small, in the screen - and some of the ions have a positive charge and the other negative - so the negative ones move towards the elevator of the screen. While the positive is attracted to the network and the cathode. And since these ions are ions whose mass is about 1800 times greater than the electron, it is therefore difficult for them to deviate with the beam, so they collide with the center of the screen and lead to its damage by what is called (ionic combustion). This phenomenon differs from the continuation of the white light in the center of the screen after the device is turned off as a result of the presence of high voltage for a short period. To prevent ions from reaching the screen and damaging them, a magnet is placed on the neck of the screen to catch these ions and prevent them from reaching the center of the screen. For this purpose, the method of placing the electronic ejector is used at an angle inclined to the axis of the screen by 10, so that these ions collide with the neck of the valve (Fig. 11-30). corrects
The ray path is directed towards the center of the screen. The phosphorescent layer of the screen is covered with a thin layer of aluminum metal that protects it from being affected by ions, in addition to the benefit of the aluminization process in restricting light reflection to improve the brightness and contrast of the screen. In the color screen, there is no need for an ion trap because the aluminum layer is sufficient to prevent the ions from affecting the screen.

11-10 Static and kinetic convergence or convergence in the color screen:

A - Static Convergence:

The static convergence or convergence process means that the beam falls in a medium where there is no current in the screen deflection coils
Then it passes through the hole or aperture of the mask to reach the three phosphorescent particles, and it hits every ray of the color assigned to it. The beams are adjusted using a continuous DC voltage or by using the magnetization of a fixed magnet located inside the screen accompanied by a grid / 4 / for each launcher. Figure (11) - (33) and Figure (11 - 34). The external unit of conformity, consisting of three coils, is installed to meet the internal magnets and is affected by their magnetic fields that adjust each beam and direct it to its correct place. The matching process of the three rays may not be done except by using another tuning process: that is the tuning of the blue ray that must be corrected from its place B2 to within the matching circle B3 as in Figure (11-32) and it is called the side magnet of the blue. As for 1 1 1, it is the direction of the three rays before performing the static matching process.

B - Dynamic Convergence:

​​​​​​The movement of the three rays to wipe the entire screen leads to the loss of the static convergence achieved by the convergence of the rays in the center of the screen. And correcting the direction of these rays in all the screen is called kinetic matching. When the beam deviates from the center, it travels a longer distance because the surface of the screen does not have a completely circular curvature