Thursday, 2 July 2015

what is CRT monitor?describe the refresh rate or refresh CRT and persistence.

CRT Monitor


CRT stands for cathode-Ray tube. A type of monitor that uses CRT to display output on the screen is known as CRT monitor. CRT is also used in TV set. a cathode ray tube is a vacuum tube. it creates the image of the output and displays on the screen the front of the tube is the screen. the back of the screen is coated with phosphor (chemical material that lights up when electron beam falls on it). the screen is organized into a grid of tiny dots of phosphor material. these dost are called pixels (picture elements).

CRT consists of one or more electronic guns. A stream of bits defining the image of output is sent from the computer ( from the CPU) to the CRT, where the bits are converted into beam of electrons passes through focusing and deflection systems. they direct the beam towards specified points on the phosphor-coated screen. when beam of electrons hits the screen, it lights up the selected pixels and an image of output is generated on the screen. Today, most of the PCs have color monitors. CRT in color monitor contains three electron guns; on for red color , second for green and third for blue color (RGB). other colors for output are generated with the combination of three colors. computer controls the three guns. color monitors consume relatively more power.

Refresh Rate or Refresh CRT
the refresh rate is the number of times per second the electron guns scan every pixel on the screen to redraw the images on the screen. it is measured in Hertz (Hz) or in cycles per second. refresh rate is also called refresh CRT.

Persistence
the screen of the CRT monitors may be coated with different types of phosphors. the light emitted by some type of phosphor fades rapidly, while other type fades slowly. the duration of emitting light by dots of phosphor after the electron beam is removed is called persistence (the word"persist" means "continue to be").

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