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Physics, Techniques and Procedures

Television monitor

a special purpose television receiver that accepts a direct video signal (instead of modulated electromagnetic waves). These are common in X-ray fluoroscopy units and diagnostic workstations for digital images. For use in X-ray departments, the demands on TV monitors are much more rigorous than on TV monitors used in closed-circuit applications in other fields. This applies to both high and low contrast resolution properties and image brightness.

The television monitor consists of a picture tube and brightness and contrast controls. The picture tube is quite similar to a television camera tube, being composed of a vacuum tube, cathode and control grid (see electron gun), anode, focusing coils and deflecting coils (Fig.1). Instead of scanning a target as in the television camera, the electron beam of the picture tube scans a fluorescent screen. The coils regulate the movement of the electron beam in exact synchrony with the scanning beam in the television camera. The control grid receives the video signal and regulates the intensity of the electron beam, thus regulating the brightness produced on the screen. The anode carries a high positive voltage (10 000 V) and accelerates the electrons to high velocities. The complete light image is generated by scanning the entire screen surface line by line. See also video and television scan mode.

MN

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Fig.1

Schematic drawing of the picture tube.
Television monitor, Fig.1