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A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen.^[2] The images may represent electrical waveforms on an oscilloscope, a frame of video on an analog television set (TV), digital raster graphics on a computer monitor, or other phenomena like radar targets. A CRT in a TV is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.

In CRT TVs and computer monitors, the entire front area of the tube is scanned repeatedly and systematically in a fixed pattern called a raster. In color devices, an image is produced by controlling the intensity of each of three electron beams, one for each additive primary color (red, green, and blue) with a video signal as a reference.^[3] In modern CRT monitors and TVs the beams are bent by magnetic deflection, using a deflection yoke. Electrostatic deflection is commonly used in oscilloscopes.^[3]

The tube is a glass envelope which is heavy, fragile, and long from front screen face to rear end. Its interior must be close to a vacuum to prevent the emitted electrons from colliding with air molecules and scattering before they hit the tube's face. Thus, the interior is evacuated to less than a millionth of atmospheric pressure.^[4] As such, handling a CRT carries the risk of violent implosion that can hurl glass at great velocity. The face is typically made of thick lead glass or special barium-strontium glass to be shatter-resistant and to block most X-ray emissions. This tube makes up most of the weight of CRT TVs and computer monitors.^[5][6]

Since the mid–late 2000's, CRTs have been superseded by flat-panel display technologies such as LCD, plasma display, and OLED displays which are cheaper to manufacture and run, as well as significantly lighter and thinner. Flat-panel displays can also be made in very large sizes whereas 40–45 inches (100–110 cm)^[7] was about the largest size of a CRT.^[8]

A CRT works by electrically heating a tungsten coil^[9] which in turn heats a cathode in the rear of the CRT, causing it to emit electrons which are modulated and focused by electrodes. The electrons are steered by deflection coils or plates, and an anode accelerates them towards the phosphor-coated screen, which generates light when hit by the electrons.^[10][11][12]

History

Discoveries

Cathode rays were discovered by Julius Plücker and Johann Wilhelm Hittorf.^[13] Hittorf observed that some unknown rays were emitted from the cathode (negative electrode) which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines. In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, and William Crookes showed they could be deflected by magnetic fields. In 1897, J. J. Thomson succeeded in measuring the mass-to-charge ratio of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first "subatomic particles", which had already been named electrons by Irish physicist George Johnstone Stoney in 1891. The earliest version of the CRT was known as the "Braun tube", invented by the German physicist Ferdinand Braun in 1897.^[14] It was a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen. Braun was the first to conceive the use of a CRT as a display device.^[15] The Braun tube became the foundation of 20th century TV.^[16]

In 1908, Alan Archibald Campbell-Swinton, fellow of the Royal Society (UK), published a letter in the scientific journal Nature, in which he described how "distant electric vision" could be achieved by using a cathode-ray tube (or "Braun" tube) as both a transmitting and receiving device.^[17] He expanded on his vision in a speech given in London in 1911 and reported in The Times^[18] and the Journal of the Röntgen Society.^[19][20]

The first cathode-ray tube to use a hot cathode was developed by John Bertrand Johnson (who gave his name to the term Johnson noise) and Harry Weiner Weinhart of Western Electric, and became a commercial product in 1922.^[21] The introduction of hot cathodes allowed for lower acceleration anode voltages and higher electron beam currents, since the anode now only accelerated the electrons emitted by the hot cathode, and no longer had to have a very high voltage to induce electron emission from the cold cathode.^[22]

Development

In 1926, Kenjiro Takayanagi demonstrated a CRT TV receiver with a mechanical video camera that received images with a 40-line resolution.^[23] By 1927, he improved the resolution to 100 lines, which was unrivaled until 1931.^[24] By 1928, he was the first to transmit human faces in half-tones on a CRT display.^[25]

In 1927, Philo Farnsworth created a TV prototype.^{[26][27][28][29][30]}

The CRT was named in 1929 by inventor Vladimir K. Zworykin.^[25]: 84 He was subsequently hired by RCA, which was granted a trademark for the term "Kinescope", RCA's term for a CRT, in 1932; it voluntarily released the term to the public domain in 1950.^[31]

In the 1930s, Allen B. DuMont made the first CRTs to last 1,000 hours of use, which was one of the factors that led to the widespread adoption of TV.^[32]

The first commercially made electronic TV sets with cathode-ray tubes were manufactured by Telefunken in Germany in 1934.^[33][34]

In 1947, the cathode-ray tube amusement device, the earliest known interactive electronic game as well as the first to incorporate a cathode-ray tube screen, was created.^[35]

From 1949 to the early 1960s, there was a shift from circular CRTs to rectangular CRTs, although the first rectangular CRTs were made in 1938 by Telefunken.^{[36][22][37][38][39][40]} While circular CRTs were the norm, European TV sets often blocked portions of the screen to make it appear somewhat rectangular while American sets often left the entire front of the CRT exposed or only blocked the upper and lower portions of the CRT.^[41][42]

In 1954, RCA produced some of the first color CRTs, the 15GP22 CRTs used in the CT-100,^[43] the first color TV set to be mass produced.^[44] The first rectangular color CRTs were also made in 1954.^[45][46] However, the first rectangular color CRTs to be offered to the public were made in 1963. One of the challenges that had to be solved to produce the rectangular color CRT was convergence at the corners of the CRT.^[39][38] In 1965, brighter rare earth phosphors began replacing dimmer and cadmium-containing red and green phosphors. Eventually blue phosphors were replaced as well.^{[47][48][49][50][51][52]}

The size of CRTs increased over time, from 20 inches in 1938,^[53] to 21 inches in 1955,^[54][55] 25 inches by 1974, 30 inches by 1980, 35 inches by 1985,^[56] and 43 inches by 1989.^[57] However, experimental 31 inch CRTs were made as far back as 1938.^[58]

In 1960, the Aiken tube was invented. It was a CRT in a flat-panel display format with a single electron gun.^[59][60] Deflection was electrostatic and magnetic, but due to patent problems, it was never put into production. It was also envisioned as a head-up display in aircraft.^[61] By the time patent issues were solved, RCA had already invested heavily in conventional CRTs.^[62]

1968 marked the release of Sony Trinitron brand with the model KV-1310, which was based on Aperture Grille technology. It was acclaimed to have improved the output brightness. The Trinitron screen was identical with its upright cylindrical shape due to its unique triple cathode single gun construction.

In 1987, flat-screen CRTs were developed by Zenith for computer monitors, reducing reflections and helping increase image contrast and brightness.^[63][64] Such CRTs were expensive, which limited their use to computer monitors.^[65] Attempts were made to produce flat-screen CRTs using inexpensive and widely available float glass.^[66]

In 1990, the first CRTs with HD resolution were released to the market by Sony.^[67]

In the mid-1990s, some 160 million CRTs were made per year.^[68]

In the mid-2000s, Canon and Sony presented the surface-conduction electron-emitter display and field-emission displays, respectively. They both were flat-panel displays that had one (SED) or several (FED) electron emitters per subpixel in place of electron guns. The electron emitters were placed on a sheet of glass and the electrons were accelerated to a nearby sheet of glass with phosphors using an anode voltage. The electrons were not focused, making each subpixel essentially a flood beam CRT. They were never put into mass production as LCD technology was significantly cheaper, eliminating the market for such displays.^[69]

The last large-scale manufacturer of (in this case, recycled)^[70] CRTs, Videocon, ceased in 2015.^[71][72] CRT TVs stopped being made around the same time.^[73]

In 2012, Samsung SDI and several other major companies were fined by the European Commission for price fixing of TV cathode-ray tubes.^[74] The same occurred in 2015 in the US and in Canada in 2018.^[75][76]

Worldwide sales of CRT computer monitors peaked in 2000, at 90 million units, while those of CRT TVs peaked in 2005 at 130 million units.^[77]

Decline

Beginning in the late 90s to the early 2000s, CRTs began to be replaced with LCDs, starting first with computer monitors smaller than 15 inches in size,^[78] largely because of their lower bulk.^[79] Among the first manufacturers to stop CRT production was Hitachi in 2001,^[80][81] followed by Sony in Japan in 2004,^[82] Flat-panel displays dropped in price and started significantly displacing cathode-ray tubes in the 2000s. LCD monitor sales began exceeding those of CRTs in 2003–2004^[83][84][85] and LCD TV sales started exceeding those of CRTs in some markets in 2005.^[86] Samsung SDI stopped CRT production in 2012.^[87]

Despite being a mainstay of display technology for decades, CRT-based computer monitors and TVs are now obsolete. Demand for CRT screens dropped in the late 2000s.^[88] Despite efforts from Samsung and LG to make CRTs competitive with their LCD and plasma counterparts, offering slimmer and cheaper models to compete with similarly sized and more expensive LCDs,^{[89][90][91][92][93]} CRTs eventually became obsolete and were relegated to developing markets and vintage enthusiasts once LCDs fell in price, with their lower bulk, weight and ability to be wall mounted coming as pluses.

Some industries still use CRTs because it is either too much effort, downtime, and/or cost to replace them, or there is no substitute available; a notable example is the airline industry. Planes such as the Boeing 747-400 and the Airbus A320 used CRT instruments in their glass cockpits instead of mechanical instruments.^[94] Airlines such as Lufthansa still use CRT technology, which also uses floppy disks for navigation updates.^[95] They are also used in some military equipment for similar reasons.

As of 2022^[update], at least one company manufactures new CRTs for these markets.^[96]

A popular consumer usage of CRTs is for retrogaming. Some games are impossible to play without CRT display hardware, and some games play better. Light guns only work on CRTs because they depend on the progressive timing properties of CRTs.

Constructions

Body

The body of a CRT is usually made up of three parts: A screen/faceplate/panel, a cone/funnel, and a neck.^{[97][98][99][100][101]} The joined screen, funnel and neck are known as the bulb or envelope.^[38]

The neck is made from a glass tube^[102] while the funnel and screen are made by pouring and then pressing glass into a mold.^{[103][104][105][106][107]} The glass, known as CRT glass^[108][109] or TV glass,^[110] needs special properties to shield against x-rays while providing adequate light transmission in the screen or being very electrically insulating in the funnel and neck. The formulation that gives the glass its properties is also known as the melt. The glass is of very high quality, being almost contaminant and defect free. Most of the costs associated with glass production come from the energy used to melt the raw materials into glass. Glass furnaces for CRT glass production have several taps to allow molds to be replaced without stopping the furnace, to allow production of CRTs of several sizes. Only the glass used on the screen needs to have precise optical properties.

The optical properties of the glass used on the screen affects color reproduction and purity in Color CRTs. Transmittance, or how transparent the glass is, may be adjusted to be more transparent to certain colors (wavelengths) of light. Transmittance is measured at the center of the screen with a 546 nm wavelength light, and a 10.16mm thick screen. Transmittance goes down with increasing thickness. Standard transmittances for Color CRT screens are 86%, 73%, 57%, 46%, 42% and 30%. Lower transmittances are used to improve image contrast but they put more stress on the electron gun, requiring more power on the electron gun for a higher electron beam power to light the phosphors more brightly to compensate for the reduced transmittance.^[65][111] The transmittance must be uniform across the screen to ensure color purity. The radius (curvature) of screens has increased (grown less curved) over time, from 30 to 68 inches, ultimately evolving into completely flat screens, reducing reflections. The thickness of both curved^[112] and flat screens gradually increases from the center outwards, and with it, transmittance is gradually reduced. This means that flat-screen CRTs may not be completely flat on the inside.^[112][113]

The glass used in CRTs arrives from the glass factory to the CRT factory as either separate screens and funnels with fused necks, for Color CRTs, or as bulbs made up of a fused screen, funnel and neck. There were several glass formulations for different types of CRTs, that were classified using codes specific to each glass manufacturer. The compositions of the melts were also specific to each manufacturer.^[114] Those optimized for high color purity and contrast were doped with Neodymium, while those for monochrome CRTs were tinted to differing levels, depending on the formulation used and had transmittances of 42% or 30%.^[115] Purity is ensuring that the correct colors are activated (for example, ensuring that red is displayed uniformly across the screen) while convergence ensures that images are not distorted. Convergence may be modified using a cross hatch pattern.^{[116][117][118]}

CRT glass used to be made by dedicated companies^[119] such as AGC Inc.,^{[120][121][122]} O-I Glass,^[123] Samsung Corning Precision Materials,^[124] Corning Inc.,^[125][126] and Nippon Electric Glass;^[127] others such as Videocon, Sony for the US market and Thomson made their own glass.^{[128][129][130][131][132]}

The funnel and the neck are made of leaded potash-soda glass or lead silicate glass^[6] formulation to shield against x-rays generated by high voltage electrons as they decelerate after striking a target, such as the phosphor screen or shadow mask of a color CRT. The velocity of the electrons depends on the anode voltage of the CRT; the higher the voltage, the higher the speed.^[133] The amount of x-rays emitted by a CRT can also lowered by reducing the brightness of the image.^{[134][135][136][100]} Leaded glass is used because it is inexpensive,^[137] while also shielding heavily against x-rays, although some funnels may also contain barium.^{[138][139][140][115]} The screen is usually instead made out of a special lead-free silicate^[6] glass formulation with barium and strontium to shield against x-rays, as it doesn't brown unlike glass containing lead.^[137][141] Another glass formulation uses 2–3% of lead on the screen.^[100] Alternatively zirconium can also be used on the screen in combination with barium, instead of lead.^[142]

Zdroj:https://en.wikipedia.org?pojem=Cathode-ray_tube
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