How does CRT-Television work ?

History of CRT

The development of electronic television systems was based on the development of the cathode ray tube (CRT).
A cathode ray tube or picture tube was found in all electronic television sets until the invention of the LCD or LED screens.
The first cathode ray tube scanning device was invented by the German scientist Karl Ferdin and Braun in 1897.
Braun introduced a CRT with a fluorescent screen, known as the cathode ray oscilloscope.
The screen would emit a visible light when struck by a beam of electrons.


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What is CRT?

The cathode-ray tube (CRT) is the oldest version of the television.
It is a specialized vacuum tube in which images are produced when an electron beam strikes a phosphorescent surface.
Most desktop computer displays make use of CRTs.
The CRT in a computer display is similar to the "picture tube" in a television receiver.

Working of CRT

A glass cathode-ray tube which contains a vacuum has three electron guns at its narrow end, each containing an anode and cathode assembly.
The cathodes here emit electrons; the anodes draw the electrons away from the cathodes, focusing and accelerating them into electron beams.
The deflection yoke, around the tube base, manipulates the three beams via electromagnetic force, working with the CRT's circuit to sweep them across the screen in precise, horizontal lines, where a beam hits the screen, it causes a red, green, or blue (RGB) phosphor dot to glow; the screen's inner surface is coated with these coloured phosphors.
In shadow-mask models, the RGB phosphors on the inside of the screen are arranged as a staggered pattern of dots.
In a shadow-mask CRT, when the monitor receives commands from television’s graphics adapter, the electron guns fire their three beams, in concert, through tiny holes in the shadow mask, a metal screen just behind the phosphor-coated display glass.
Their channeled beams illuminate a trio of phosphor dots (a triad) lining the inside of the glass.
A pixel-the smallest image element we can see-comprises one or more triads; how many depends on the resolution we specify.
The lower the resolution, the more triads that are assigned to each pixel.
The electron guns blaze across the screen, row by row, illuminating phosphors in their wake. Varying the beams' intensity strengthens or weakens the glow from a given phosphor dot; by careful manipulation of every one, the triads and pixels, seen by the eye as single units, create the illusion of different-colour dots.
Phosphors don't glow for long, though. Once the guns have scanned the whole screen, they repeat the process-typically, 60 to 80 times a second. (This number is what is known as the refresh rate.)