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Cathode Ray Tube (CRT) Tutorial

Cathode Ray Tube (CRT) Diagram

The Cathode Ray Tube (CRT) is used in oscilloscopes, radar, monitors and television receivers. It consists of a glass envelope made from a neck and cone. All air has been extracted so that it contains a vacuum. At the narrow end are pins which make connection with an internal ELECTRON GUN. Voltages are applied to this gun to produce a beam of electrons. This electron beam is projected towards the inside face of the screen.

The face is coated with a PHOSPHOR which PHOSPHORESCES (glows) when hit by the beam. This produces a spot of light on the centre of the face of the CRT. By varying the beam current, spot BRIGHTNESS can be controlled. Controlling the diameter of the beam controls FOCUS. Phosphors come in a range of colours.

On its way from the gun to the screen the beam passes between  2 sets of plates. They are called the X and Y plates (as in graphs). By applying voltages to these plates the beam can be deflected. This causes the spot to move from the centre of the screen to another position on the screen. The X plates plates deflect the spot horizontally, the Y plates vertically. Thus the spot can be deflected to any position on the screen. External deflection coils are often used instead of the internal deflection plates.

Note that dropping a CRT causes it to IMPLODE which is as dangerous as an explosion.

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