CATHODE RAY TUBE (CRT)

The primary output device in a graphical system is the video monitor. The main element of a video monitor is the Cathode Ray Tube(CRT))The cathode-ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen and is used to display images. It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images. The images may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets, or other phenomena.

The operation of CRT is very simple −


• The electron gun emits a beam of electrons cathode rays.
• The electron beam passes through focusing and deflection systems that direct it towards specified positions on the phosphor-coated screen.
• When the beam hits the screen, the phosphor emits a small spot of light at each position contacted by the electron beam.
• It redraws the picture by directing the electron beam back over the same screen points quickly.

  It consists of a glass envelope made from a neck and cone. All air has been extracted so that it contains a vacuum. At the narrow end are pins which make connection with an internal ELECTRON GUN. Voltages are applied to this gun to produce a beam of electrons. This electron beam is projected towards the inside face of the screen.
The face is coated with a PHOSPHOR which PHOSPHORESCES (glows) when hit by the beam. This produces a spot of light on the centre of the face of the CRT. By varying the beam current, spot BRIGHTNESS can be controlled. Controlling the diameter of the beam controls FOCUS. Phosphors come in a range of colours.
On its way from the gun to the screen the beam passes between  2 sets of plates. They are called the X and Y plates (as in graphs). By applying voltages to these plates the beam can be deflected. This causes the spot to move from the centre of the screen to another position on the screen. The X plates plates deflect the spot horizontally, the Y plates vertically. Thus the spot can be deflected to any position on the screen. External deflection coils are often used instead of the internal deflection plates.

CRT (CATHODE RAY TUBE)

CRT stands for Cathode Ray Tubes and is the very old style display which uses the florescent blue tube in itself and it projects the electrons to the screen at a time. These projections are responsible for creating the images on the screen. These monitors are pretty heavy and have been configured for some various sizes. In CRT there is vacuum glass tube under which Electron gun shoots beam of electrons toward the back of monitor screen

• It is coated with chemical dots called phosphors glow when electrons strike them
• Beam of electrons scans the monitor from left to right, and top to bottom in a raster pattern to create the image.
• Trio of dot phosphors is grouped in triangle for each hardware picture element
• Electron beam returns regular to each phosphor to sustain the glow.
• More dots better quality
• Dot pitch
  • Measurement between the same spot in two vertically adjacent dot trios
  • Expressed in millimeters or dots per inch
  • Dot pitch tells “sharpness”
  • Software-pixel placement is limited to hardware’s transistor placement
  • Resolution
    • Number of pixels used to draw the screen.
    • Higher resolutions = more information in the same screen area.
    • indicate rows and columns of pixels on screen