Cathode ray tube

The cathode ray tube or CRT, invented by Karl Ferdinand Braun, is the display device used in most computer displays, video monitors, televisions and oscilloscopes. The CRT developed from Philo Farnsworth's work was used in all television sets until the late 20th century and the advent of plasma screens, LCDs, DLP, OLED displays, and other technologies.

High vacuum safety

Because CRTs "contain" a high vacuum and represent a large surface area, the constant compressive force of normal atmospheric pressure means that CRTs also represent a large store of mechanical energy; they can implode very forcefully if the outer glass envelope is damaged. Most modern CRTs used in televisions and computer displays include a bonded, multi-layer faceplate that prevents implosion if the faceplate is damaged, but the bell of the CRT (back portions of the glass envelope) offers no such protection. Certain specialized CRTs (such as those used in oscilloscopes) do not even offer a bonded faceplate; these CRTs require an external plastic faceplate or other cover to render them implosion safe while in use. Before the use of bonded faceplates one of the hazards would be that a broken neck or envelope would cause the neck and electron gun to be propelled by atmosperic pressure at such a velocity that it would erupt through the face of the tube.

Related Topics:
Vacuum - Atmospheric pressure - Oscilloscope

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When handling or disposing of a CRT, you must take steps to avoid creating an implosion hazard for you or your trash removal service. The most simple and safe method to make the tube safe is to identify the small sealed glass nib at the far back of the tube (this may be obscured by the electrical connector) and then (while wearing safety glasses and gloves) filing a small nick across this and then to break it off using a pair of pliers. A sucking sound will be heard as the air enters the tube, releasing the vacuum. One must be very cautious not to break the neck of the tube when it is evacuated since there is no plastic coating preventing shattering of the glass. High vacuum and high voltage can be dangerous.

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