The principle is based on the use of an electronic screen called a cathode ray tube. Everything about cathode ray tube (CRT)?
Contents
Introduction
The cathode-ray tube is a vacuum tube consisting of an electron gun and a fluorescent screen, with internal and external means to accelerate and deflect the electron beam. It is used to create images in the form of light emitted from the fluorescent screen. CRT monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam. It scans twice each time, first filling in the odd “hole” than the even ones. Each scan is about 1/60 of seconds.
Features of CRT?
Features of a CRT can be split into 3 main sections:
- Electron gun
- Deflection system
- Fluorescent screen
Electron gun
the role of this section is to produce electrons at a high.
- This is done through a process called thermionic emission.
- Black and white monitor has only one electron gun and color monitor have 3 (RGB)
- The assembly of the cathode, control grid anode is called electron gum.
Deflection system
Two pairs of deflecting plates allow the beam of electrons over both horizontal and vertical axes.
- An electric field between the first pair of plates deflects the electrons horizontally, and an electric field between the second pair deflects them vertically. The electrons travel in a straight line from the hole in the accelerating anode to the center of the screen when no deflecting fields are present.
Fluorescent screen
The role of this part is to display where the electrons are hitting the CRT.
- It is a screen coated with a Phosphorus material that emits light when struck by electrons.
- In a CRT monitor tube, the cathode is a heated filament.
- Electrons are negative and the screen is a positive charge so the screen glows.
Steps of CRT?
Step1: The heated filament which heats a cathode(-) and emits electrons(-).
Step2: Control grid controls the density of the electron beam to focus the electron beam on the screen.
Step3: Then these electrons are then attracted through two large potential positive anodes (+).
Ø Focusing anode(1200 V) and accelerating anode(2000V): these are used for producing a narrow and sharply focused a beam of electrons.
Ø The anode has a hole in the Centre through which a beam of electrons flows.
Step4: The x(vertical) and y(horizontal) plates can apply an external field to deflects this beam.
Ø For controlling the path(horizontal and vertical path) of the beam.
Step5: The beam then hits a fluorescent screen coated with tiny dots of phosphor materials and is detected as light.
Ø Each dot consists of a red blue and green phosphor.
Shadow mask?
- The shadow mask is one of the technologies used to manufacture CRT televisions and compute displays that produce color images.
- A shadow mask is a metal plate punched with tiny holes that separate the colored phosphors in the layer behind the front glass of the screen.
- The screen is patterned with dots of colored phosphor positioned so that each can only be hit by one of the beams coming from the three electron guns.
- For instance, the blue phosphor dots are hit by the beam from the “blue gun” after passing through a particular hole in the mask.
| Advantages | Disadvantages |
|---|---|
| The CRT can easily increase the monitor’s brightness by reflecting the light. | Operate at very voltage which can overheat system. |
| Lower cost | High power consumption |
| Best color quality | Higher heat generation. |
