Cathode Ray Tube
The Cathode Ray Tube, which has internal or external means to accelerate and deflect electron beams, is a vacuum tube containing an electron gun and a fluorescent screen. The electron beams that are deflected are used to create images in the form of light emitted from the fluorescent screen. The CRT works by using an evacuated glass envelope which is large, deep, heavy, and relatively fragile.
Ferdinand Braun is credited with the first CRT in 1897. It can also be known as the Braun tube. Boris Rosing was the first to use CRT to display shapes on the screen marking him as the first to use it as a television. The cathode ray tube consists of a vacuum tube with one or more electron guns, possibly internal electrostatice deflection plates, and a phosphor target. The raster within computer monitors and TV’s scan the front area of the tube repetitively and systematically in a fixed pattern. There are three electron beams, one for each primary color with a video signal as a reference. The beams are sent by magnetic deflection, which is a varying magnetic field created by coils and driven by electronic circuits around the neck of the tube.
Electrostatic deflection is used in oscilloscope CRT’s, unlike magnetic deflection that is used commonly in television and other large CRTs. The beam is deflected horizontally by applying an electric field between a pair of plates to its left and right, and vertically by applying an electric field to plates above and below.
The three different colors are pack together in stripes or clusters called “triads”. The three electron guns for each color are aligned in a straight line or in a triangular configuration. The CRT uses a shadow mask tube, a metal plate with tiny holes, placed so that the electron beam only illuminates the correct phosphors on the face of the tube.