The last known manufacturer of (in this case, recycled) CRTs ceased in 2015. įlat panel displays dropped in price and started significantly displacing cathode ray tubes in the 2000s, with LCD screens exceeding CRTs in 2008. The first commercially made electronic television sets with cathode ray tubes were manufactured by Telefunken in Germany in 1934. RCA was granted a trademark for the term (for its cathode ray tube) in 1932 it voluntarily released the term to the public domain in 1950. Zworykin, who was influenced by Takayanagi's earlier work. It was named in 1929 by inventor Vladimir K. By 1935, he had invented an early all-electronic CRT television. By 1928, he was the first to transmit human faces in half-tones on a CRT display. By 1927, he improved the resolution to 100 lines, which was unrivaled until 1931. In 1925, Kenjiro Takayanagi demonstrated a CRT television that received images with a 40-line resolution. Johnson (who gave his name to the term Johnson noise) and Harry Weiner Weinhart of Western Electric, and became a commercial product in 1922. The first cathode ray tube to use a hot cathode was developed by John B. It was a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen. The earliest version of the CRT was known as the "Braun tube", invented by the German physicist Ferdinand Braun in 1897. Thomson succeeded in measuring the mass of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first "subatomic particles", which were later named electrons. In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, and William Crookes showed they could be deflected by magnetic fields. He 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. Ĭathode rays were discovered by Johann Wilhelm Hittorf in 1869 in primitive Crookes tubes. Flat panel displays can also be made in very large sizes whereas 38 to 40 in (97 to 102 cm) was about the largest size of a CRT television, flat panels are available in 60 in (150 cm) and larger sizes.īraun's original cold-cathode CRT, 1897. Since the late 2000s, CRTs have been largely superseded by newer "flat panel" display technologies such as LCD, plasma display, and especially OLED displays, which in the case of LCD and OLED displays have lower manufacturing costs and power consumption, as well as significantly less weight and bulk. As a matter of safety, the face is typically made of thick lead glass so as to be highly shatter-resistant and to block most X-ray emissions, particularly if the CRT is used in a consumer product. The fact that it is evacuated makes handling an intact CRT potentially dangerous due to the risk of breaking the tube and causing a violent implosion that can hurl shards of glass at great velocity.
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The interior of a CRT is evacuated to approximately 0.01 pascals (9.9×10−8 atm) to 133 nanopascals (1.31×10−12 atm), evacuation being necessary to facilitate the free flight of electrons from the gun(s) to the tube's face. A CRT is constructed from a glass envelope which is large, deep (i.e., long from front screen face to rear end), fairly heavy, and relatively fragile. In all modern CRT monitors and televisions, the beams are bent by magnetic deflection, a varying magnetic field generated by coils and driven by electronic circuits around the neck of the tube, although electrostatic deflection is commonly used in oscilloscopes, a type of electronic test instrument.
An image is produced by controlling the intensity of each of the three electron beams, one for each additive primary color (red, green, and blue) with a video signal as a reference. In television sets and computer monitors, the entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster. CRTs have also been used as memory devices, in which case the visible light emitted from the fluorescent material (if any) is not intended to have significant meaning to a visual observer (though the visible pattern on the tube face may cryptically represent the stored data). The images may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets, or other phenomena. It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images.
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.
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