Historical information about the Cathode Ray Tube including real instruments. A few TVs in use today rely on a device known as the cathode ray tube, or CRT, to display their images. LCDs and plasma displays are other common. A cathode ray tube (CRT) is a specialized vacuum tube in which images are produced when an electron beam strikes a phosphorescent surface.


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The anode is positive, so it attracts the electrons pouring off the cathode. In a TV's cathode ray tube, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode.

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Cathode ray tube | University of Oxford Department of Physics

Please try again later. For a TV, many camcorders and digital stills cameras cathode ray tube have an S-video, component or composite connection; older camcorders may have these directly, but newer camcorders or digital cameras may have a bespoke cable which plugs into a mini-USB or similar jack on the camera and feeds out to multiple types of connector for insertion into the TV.

Put the strong magnet near to the Cathode ray tube screen. The image will warp, and sweeping trails of colour will appear.

Sometimes, often after repeated cycling, the TV will fail to degauss. Further adjustment of dynamic convergence and purity typically cannot be done passively, but cathode ray tube active compensation circuits. Dynamic color convergence and purity are one of the main reasons why until late in their history, CRTs were long-necked deep and had biaxially curved faces; these geometric cathode ray tube characteristics are necessary for intrinsic passive dynamic color convergence and purity.


Only cathode ray tube around the s did sophisticated active dynamic convergence compensation circuits become available that made short-necked and flat-faced CRTs workable.

These active compensation circuits use the deflection yoke to finely adjust beam deflection according to the beam target location.

The same techniques and major circuit components also make possible the cathode ray tube of display image rotation, skew, and other complex raster geometry parameters through electronics under user control. Degaussing[ edit ] A degaussing in progress. If the shadow mask or aperture grille becomes magnetized, its magnetic field alters the paths cathode ray tube the electron beams.

This causes errors of "color purity" as the electrons no longer follow only their intended paths, and some will hit some phosphors of colors other than the one intended.

For example, some electrons from the cathode ray tube beam may hit blue or green phosphors, imposing a magenta or yellow tint to parts of the image that are supposed to be pure red. This effect is cathode ray tube to a specific area of the screen if the magnetization is localized.


Therefore, it is important that the shadow mask or aperture grille not be magnetized. Most color CRT displays, i. Upon power-up of the CRT display, the cathode ray tube circuit produces a brief, alternating current through the degaussing coil which smoothly decays in strength fades out to zero over a period of a few seconds, producing a decaying alternating magnetic field from the coil.

This degaussing field is strong enough to remove shadow mask magnetization in most cases. However, an excessively strong magnetic field, whether alternating or constant, may mechanically deform bend the cathode ray tube mask, causing a permanent color distortion on the display which looks very similar to a magnetization effect.

Cathode-ray tube - Wikipedia

The degaussing circuit is often built of a thermo-electric not electronic device containing a small ceramic heating element and a positive thermal coefficient PTC resistorconnected directly to the switched AC power line with the resistor in series with the degaussing coil.

When the power is switched on, the heating element heats the PTC resistor, increasing its resistance to a point where degaussing current is minimal, but cathode ray tube actually zero. In older Cathode ray tube displays, this low-level current which produces no significant degaussing field is sustained along with the action of the heating element as long as the display remains switched on.

The electrons hit the front of the tube, where a phosphor screen is. The electrons make the phosphor light up. The electrons can be aimed by creating a magnetic field.