shadow mask

Definition: Type of colour monitor technology. * A plate perforated with extremely high-precision, fine holes which is placed between the electron gun (i.e. the focusing and accelerating electrodes) and the tricolour phosphor screen of red, green and blue in a television monitor tube. * The holes select correctly aligned beams to allow them to reach the correct member of the triad of coloured phosphor while blocking incorrectly aligned electrons. * Sophisticated aspherical optics and electronics enable totally flat screens to be made, even as large as 22". You don't need to know this, but ... As the plate is flooded with electrons, many of which do not pass through the holes but land on it, so it gets hot. But it must not expand or the precision alignment will be lost. A special metal alloy, called Invar, of extremely low coefficient of thermal expansion must be used. This problem does not affect aperture grille types to the same extent.

Related Terms: aperture grille

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