UNIVERSITY OF EASTERN AFRICA, BARATON.

SCHOOL OF SCIENCE AND TECHNOLOGY.

SUB- DEPARTMENT OF TECHNOLOGY.

ASSIGNMENT: COLOR TV PICTURE TUBE WITH LABELED PARTS

ASSIGNMENT PRESENTED IN PARTIAL FULLFILMENT OF THE COURSE: CMMT 381 TELEVISION CIRCUIT I.

PRESENTER: KIBARO ISAIAH.

ID. NUMBER: 05S0004.

INSTRUCTOR: PROF. JESSE ROLE

DATE AND PLACE: 14TH FEBRUARY 2008, BARATON UNIVERSITY.

INTRODUCTION.

In a color-television tube, three electron guns (one each for red, green, and blue) fire electrons toward the phosphor-coated screen. The electrons are directed to a specific spot (pixel) on the screen by magnetic fields, induced by the deflection coils. To prevent “spillage” to adjacent pixels, a grille or shadow mask is used. When the electrons strike the phosphor screen, the pixel glows. Every pixel is scanned about 30 times per second.

HISTORY. Crooke’s tube (OLD)

Sir William Crooke’s constructed this forerunner of the modern television picture tube in the 1870s to investigate the properties of cathode rays. When the tube is evacuated and a high voltage applied, one end of the tube glows, caused by cathode rays (now known to be electrons) striking the glass. The modern television picture tube, also known as a CRT (Cathode Ray Tube) is a direct descendant of the Crooke’s tube. The major differences are that a CRT uses a heated cathode to increase the number of electrons, while the Crooke’s tube does not, and the CRT has extra electrodes to focus and deflect the beam as it travels toward the screen. FIGURE 1

Color TV picture tube (MODERN).

A color television picture tube contains three electron guns, one corresponding to each of the three primary colors of light—red, green, and blue. Electromagnets direct the beams of electrons emerging from these guns to continuously scan the screen. As the electrons strike red, green, and blue phosphor dots on the screen, they make the dots glow. A screen with holes in it, called a shadow mask, ensures that each electron beam only strikes phosphor dots of its corresponding color. The glow of all the dots together forms the television picture. FIGURE 2a and FIGURE 2b

Trinitron Cathode Ray Tube.

Many televisions still use cathode ray tubes (CRTs) for receivers. Until the Sony Corporation patented the simplified Trinitron system in the late 1960s, RCA’s original and more complex color tube dominated the market. Today, flat-screen TVs, based on a different technology, are becoming increasingly popular. Electron gun electrode structure that produces and may control, focus, and deflect a beam of electrons, as in a television picture tube, here the beam produces a visual pattern on the tube's screen. The source of the electron beam is the cathode, a flat metal support covered with oxides of barium. Cathode-ray tube Vacuum tube that produces images when its phosphorescent surface is struck by electron beams.

figures

FIGURE 3

FIGURE 2b

FIGURE 2a

REFERENCE:
Encyclopedia Britannica.
Britannica Concise Encyclopedia.
www.digchip.com