Written by Kevin Tavolaro
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CRT stands for "Cathode Ray Tube," referring to the main visual display component of most televisions and computer screens, as well as other types of video monitors, and oscilloscopes. The device was invented by Karl Ferdinand Braun, as a tool for capturing high-speed electrons, and transforming them into concentrated, illuminated visual icons. When installed in conjunction with a specifically designed grid, the CRT distributes and renders these transformed electrons into a pattern, resulting in the graphics and images displayed on a video source.

The high-speed electrons captured by the tubes are known as cathode rays. The cathode ray tube focuses these electrons into a highly concentrated beam, which a magnetic field then intercepts and redirects at the anode (the viewing field of the screen or monitor). The redirected cathode ray scans the anode, which is surrounded by phosphor or other luminescent materials, resulting in a visual reaction. The concentrated electrons, reflected off the luminescent surface begin to emit light. This process is engineered at various levels of complexity, depending on the graphical requirements of the monitor or screen.

CRT Scanning

For a color display, extra acceleration must be applied to the electrons, providing for the numerous hues and contrasts in a color image. This is done by applying extra voltage to the anode. The most basic CRTs employ only three electrode beams. The more complex the CRT, the greater the number of electrodes. These beams are then aligned with the aid of a fixed control grid.

A patterned grid organizes the beams and rays into varying degrees of intensity, resulting in the hues and images displayed on a screen. A raster, which is a pattern affixed to the surface of each tube, scans the rays, and modulates the intensity of each. This creates the countless tiny pixels that compose the image. The intensity is already dictated by the video signal as it transmits the electrons. In a monochrome display, however, such as an oscilloscope, the intensity of the beam remains constant, and the signal scans the surface, selecting which ones to illuminate.

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