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Understanding Automotive Electronics 5E Episode 12

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Tham khảo tài liệu 'understanding automotive electronics 5e episode 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | AUTOMOTIVE INSTRUMENTATION 9 circuits a relatively simple overview of the functional operation of the CRT as a display device is straightforward and should serve to illustrate some potential automotive applications. Figure 9.20 is a sketch of a typical CRT. It is an evacuated glass tube that has a nominally flat surface that is coated with a phosphorescent material. This surface is the surface or face on which the displayed messages appear. At the rear is a somewhat complex structure called an electron gun. This device generates a stream of electrons that is accelerated toward the screen and brought to convergence at a spot on the screen. A system of coils in the form of electromagnets causes this convergence of electrons or beam and is referred to as the magnetic focusing system. The focused stream of electrons is called the beam. The electron beam generates a spot of light at the point on the screen. The intensity of the light is proportional to the electron beam current. This current is controlled by the voltage T which is called the video signal on an electrode that is located near the electron gun. Figure 9.20 CRT and Associated Circuitry UNDERSTANDING AUTOMOTIVE ELECTRONICS 319 9 AUTOMOTIVE INSTRUMENTATION In the majority of applications including TV the electron beam is scanned in a pattern known as a raster by means of specially located electromagnets see Figure 9.20 . The magnetic fields created by the scanning coils deflect the beam horizontally and vertically. The amount of deflection is proportional to the current flowing through the respective coils. The raster pattern traced by the beam is illustrated on the face of the CRT in Figure 9.21. The scanning motion is done in synchronism with the source of information being displayed. At the end of each horizontal scan line a synchronizing pulse called horizontal sync causes the beam to deflect rapidly to the left and then to begin scanning at a constant rate to the right. A similar synchronizing pulse is .