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Cathode Ray Tube (CRT) in Computer Graphics

Computer Graphics | Cathode Ray Tube (CRT): In this tutorial, we are going to learn about the Cathode Ray Tube (CRT), it's working and about its different components.
Submitted by Monika Sharma, on April 07, 2020

What is Cathode Ray Tube (CRT)?

CRT stands for "Cathode Ray Tube".

Cathode Ray Tube is a technology that is used widely in the traditional televisions and screens. An image is created on the screen on Cathode Ray Tube. That image is formed by firing electrons from the backside of the tube with the help of phosphorus which is located towards the screen on Cathode Ray Tube. It accelerates and deflects the electron beam onto the screen to create images. There are three electron guns in the Cathode Ray Tube: Red, Blue, and Green. Every gun streams a steady flow of electrons. Whenever a new line begins at the screen the guns will start from the left and continue right. This is a complex process that is repeated many times until the screen is fully drawn line by line.

Components of CRT

  1. Electron Gun
  2. Focusing System
  3. Deflection Yoke
  4. Phosphorus coated Screen

Let us explain each of them in detail.

1) Electron Gun

The Electron Gun of a Cathode Ray Tube consists of a cathode, a control grid all around the cathode and an anode to focus the electron beam. The main purpose of the Electron Gun is to generate a beam of focused electrons accelerated towards the screen with the coating of phosphorus. The Cathode emits electrons when we supply heat to it. The surface from where the Cathode emits the beam must be as small as possible. The rate of emitted electrons depends upon the current we apply to the cathode.

2) Focusing System

The Focusing System of the Cathode Ray Tube helps the electron not to spread. Without this focusing system, the electrons will spread in the shape of a cone because it is the tendency of the electrons. The Focusing System consists of the electric and magnetic fields. All of the Focusing System is adjacent to the electrode which is accelerating the electron beam. There are two main systems inside this focusing system: The Electrostatic system and the Magnetic system. The whole of the electrons are being controlled at the time of emission and once it is controlled the beam goes in a straight line to the phosphorus coated screen.

3) Deflection Yoke

There are two types of deflection needed in the Cathode Ray Tube: One controls the beam horizontally and the other controls the beam vertically. It is also necessary that the beam must be very very thin when it falls on the screen. The electron beam is moved in Raster Scan on the screen. We can adjust the brightness of the screen created by phosphorus by adjusting the electrode current. The Deflection Yoke consists of coils which are present in a set of two. Both the sets are perpendicular to each other and on the neck of the Cathode Ray Tube. These coils are shaped in a way to provide a linear magnetic field distribution.

Phosphorus Coated Screen

It is the screen of Cathode Ray Tube on which the electron beam falls. Its inner surface is coated by phosphorus. The reason for using phosphorus is that Phosphorus glows whenever a beam of high intensity of electrons hits on it.

Working of Cathode Ray Tube

The electron beam controls the working of Cathode Ray Tube. The electron gun generates an electron beam of high intensity when it is connected to high voltage. When the electron beam emits from the electron gun it passes through a pair of electrostatic and magnetic deflection coil which is on the neck of the electron gun. These coils are responsible for the horizontal and vertical movement of the beam. This beam falls on the screen and creates phosphorescence. This is the working of Cathode Ray Tube.

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