![]() The need for these heaters to 'warm up' causes a delay between the time that a CRT is first turned on, and the time that a display becomes visible. When a CRT is operating, the heaters can often be seen glowing orange through the glass walls of the CRT neck. Since the CRT is a hot-cathode device, these pins also provide connections to one or more filament heaters within the electron gun. These pins provide external connections to the cathode, to various grid elements in the gun used to focus and modulate the beam, and, in electrostatic deflection CRTs, to the deflection plates. The gun is located in the narrow, cylindrical neck at the extreme rear of a CRT and has electrical connecting pins, usually arranged in a circular configuration, extending from its end. The source of the electron beam is the electron gun, which produces a stream of electrons through thermionic emission, and focuses it into a thin beam. In all CRT TV receivers except some very early models, the beam is deflected by magnetic deflection, a varying magnetic field generated by coils (the magnetic yoke), driven by electronic circuits, around the neck of the tube. An image is produced by modulating the intensity of the electron beam with a received video signal (or another signal derived from it). In television sets and computer monitors the entire front area of the tube is scanned systematically in a fixed pattern called a raster. The beam is deflected either by a magnetic or an electric field to move the bright dot to the required position on the screen. The screen is covered with a phosphorescent coating (often transition metals or rare earth elements), which emits visible light when excited by high-energy electrons. The cathode rays are now known to be a beam of electrons emitted from a heated cathode inside a vacuum tube and accelerated by a potential difference between this cathode and an anode. 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 version 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 invented by the German physicist Ferdinand Braun in 1897 and is also known as the 'Braun tube'. The CRT in these units was flat with the electron gun located roughly at right angles below the display surface thus requiring sophisticated electronics to create an undistorted picture free from effects such as keystoning. ![]() ![]() One of the last flat-CRT models was the FD-10A. Display technologies without these disadvantages, such as flat plasma screens, liquid crystal displays, DLP, OLED displays have replaced CRTs in many applications and are becoming increasingly common as costs decline.Īn exception to the typical bowl-shaped CRT would be the flat CRTs used by Sony in their Watchman series (the FD-210 was introduced in 1982). The CRT uses an evacuated glass envelope which is large, deep, heavy, and relatively fragile. ![]() ![]() The single electron beam can be processed in such a way as to display moving pictures in natural colors. The image may represent electrical waveforms ( oscilloscope), pictures (television, computer monitor), radar targets and others. The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent screen. Magnified view of an aperture grille color CRT. ![]()
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