NationMaster - Encyclopedia: Cathode ray tube

The cathode ray tube (CRT) is an evacuated glass envelope containing an electron gun (a source of electrons) and a fluorescent screen, usually with internal or external means to accelerate and deflect the electrons. When electrons strike the fluorescent screen, light is emitted. Image File history File links Cathode_ray_tube. ... Image File history File links Cathode_ray_tube. ... Image File history File links Download high resolution version (1280x1024, 875 KB) // Summary Description Illustration showing the interior of a cathode-ray tube for color televisions and monitors. ... Image File history File links Download high resolution version (1280x1024, 875 KB) // Summary Description Illustration showing the interior of a cathode-ray tube for color televisions and monitors. ... Image File history File links Metadata Size of this preview: 600 Ã— 600 pixelsFull resolution (700 Ã— 700 pixel, file size: 476 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Metadata Size of this preview: 600 Ã— 600 pixelsFull resolution (700 Ã— 700 pixel, file size: 476 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Look up Vacuum in Wiktionary, the free dictionary. ... Electron gun from a cathode ray tube An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology, and in other instruments, eg. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ...

The electron beam is deflected and modulated in a way which causes it to display an image on the screen. The image may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), echoes of aircraft detected by radar, etc. Categories: Physics stubs ... Modulate Bob Moulds fifth solo album, released in 2002 after a four-year layoff. ... Waveform quite literally means the shape and form of a signal, such as a wave moving across the surface of water, or the vibration of a plucked string. ... Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. ... Nineteen inch (48 cm) CRT computer monitor A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. ... Reflected light following path B arrives shortly after the direct flash following path A but before light following path C. B and C have the same apparent distance from the star as seen from Earth. ... Flying machine redirects here. ... For other uses, see Radar (disambiguation). ...

The single electron beam can be processed in such a way as to display moving pictures in natural colours.

The generation of an image on a CRT by deflecting an electron beam requires the use of an evacuated glass envelope which is large, deep, heavy, and relatively fragile (this has earned it the nickname "Fishbowl"). The development of imaging technologies without these disadvantages has caused CRTs to be largely displaced by flat plasma screens, liquid crystal displays, DLP, OLED displays, and other technologies. A plasma display is an emissive flat panel display where light is created by phosphors excited by a plasma discharge between two flat panels of glass. ... LCD redirects here. ... This article is about Digital Light Processing. ... A 3. ...

An exception to the typical bowl-shaped CRT would be the flat CRTs[1][2] used by Sony in their Watchman series (the FD-210 was introduced in 1982). One of the last flat-CRT models was the FD-10A (last produced in 1989 as Sony moved to LCD displays in 1990). The CRT in these units was flat with the electron gun located roughly at right angles below the display surface thus requiring sophisticated electronics to create an undistorted picture free from keystoning and the like. Sony Corporation ) is a Japanese multinational corporation and one of the worlds largest media conglomerates with revenue of $66. ... The Watchman (also Sony Watchman) is the brand name (and trademark) given by Sony to its portable pocket television devices. ... Electron gun from a cathode ray tube An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology, and in other instruments, eg. ... Keystone correction, colloquially also called keystoning, is a function that allows multimedia projectors that are not placed perpendicular to the horizontal centerline of the screen (too high or too low) to skew the output image, thereby making it rectangular. ...

General description

The earliest version of the CRT was a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen, sometimes called a Braun tube. The first version to use a hot cathode was developed by John B. Johnson (who gave his name to the term Johnson noise) and Harry Weiner Weinhart of Western Electric, and became a commercial product in 1922. Note: Principles are mostly the same for cold cathode ion sources as in particle accelerators to create electrons. ... Closeup of the image below, showing the square shaped semiconductor crystal various semiconductor diodes, below a bridge rectifier Structure of a vacuum tube diode In electronics, a diode is a two-terminal component, almost always one that has electrical properties which vary depending on the direction of flow of charge... The Crookes tube is an evacuated glass cone with 3 node elements (one anode and two cathodes). ... Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ... Karl Ferdinand Braun (June 6, 1850 - April 20, 1918) was a German physicist, born in Fulda. ... John Bertrand Johnson (1887-1970) was a Swedish-born American electrical engineer and physicist. ... Johnson-Nyquist noise, thermal noise, Johnson noise, or Nyquist noise) is the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor, which happens regardless of any applied voltage, due to the random thermal motion of the charge carriers (the electrons). ...

The cathode rays are now known to be a beam of electrons emitted from a heated cathode inside a vacuum tube and accelerated by a potential difference between this cathode and an anode. The screen is covered with a phosphorescent coating (often transition metals or rare earth elements), which emits visible light when excited by high-energy electrons. The beam is deflected either by a magnetic or an electric field to move the bright dot to the required position on the screen. A schematic diagram of a Crookes tube apparatus. ... For other uses, see Electron (disambiguation). ... Diagram of a copper cathode in a Daniells cell. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... Potential difference is a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. ... Diagram of a zinc anode in a galvanic cell. ... Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ... In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. ... de;Metalle der Seltenen Erden Categories: Stub | Chemical element groups ... Excitation is the amount of energy (energy in a general sense, not energy as defined in physics) that something or someone has. ... Categories: Physics stubs ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ... In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ...

In television sets and computer monitors the entire front area of the tube is scanned systematically in a fixed pattern called a raster. An image is produced by modulating the intensity of the electron beam with a received video signal (or another signal derived from it). In all CRT TV receivers except some very early models, the beam is deflected by magnetic deflection, a varying magnetic field generated by coils (the magnetic yoke), driven by electronic circuits, around the neck of the tube. Television set may refer to: Television, a device to display television programs Television studio, an installation in which television or video productions take place Set construction, theatrical scenery This is a disambiguation page: a list of articles associated with the same title. ... Nineteen inch (48 cm) CRT computer monitor A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. ... Raster can refer to either of the following items: Raster graphics, Bit array, the general-purpose data structure, or The scanning pattern of the electron beam to a screen of a Cathode Ray Tube. ... Composite video is the format of an analog television (picture only) signal before it is combined with a sound signal and modulated onto an RF carrier. ...

The source of the electron beam is the electron gun, which produces a stream of electrons through thermionic emission, and focuses it into a thin beam. The gun is located in the narrow, cylindrical neck at the extreme rear of a CRT and has electrical connecting pins, usually arranged in a circular configuration, extending from its end. These pins provide external connections to the cathode, to various grid elements in the gun used to focus and modulate the beam, and, in electrostatic deflection CRTs, to the deflection plates. Since the CRT is a hot-cathode device, these pins also provide connections to one or more filament heaters within the electron gun. When a CRT is operating, the heaters can often be seen glowing orange through the glass walls of the CRT neck. The need for these heaters to 'warm up' causes a delay between the time that a CRT is first turned on, and the time that a display becomes visible. In older tubes, this could take fifteen seconds or more; modern CRT displays have fast-starting circuits which produce an image within about two seconds, using either briefly increased heater current or elevated cathode voltage. Once the CRT has warmed up, the heaters stay on continuously. The electrodes are often covered with a black layer, a patented process used by all major CRT manufacturers to improve electron density. Image File history File links Summary This is a close up photo of an Thermionic Electron Gun assembly found on a colour Samsung CRT monitor. ... Image File history File links Summary This is a close up photo of an Thermionic Electron Gun assembly found on a colour Samsung CRT monitor. ... Electron gun from a cathode ray tube An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology, and in other instruments, eg. ... Closeup of the filament on a low pressure mercury gas discharge lamp showing white thermionic emission mix coating on the central portion of the coil. ... Hot cathode is also a name for a hot filament ionization gauge, a vacuum measuring device. ... A filament for an indirectly heated cathode for a CRT is coated with a so-called black layer, a layer consisting of a tungsten-aluminum suspension. ...

The electron gun accelerates not only electrons but also ions present in the imperfect vacuum (some of which result from outgassing of the internal tube components). The ions, being much heavier than electrons, are deflected much less by the magnetic or electrostatic fields used to position the electron beam. Ions striking the screen damage it; to prevent this the electron gun can be positioned slightly off the axis of the tube so that the ions strike the side of the CRT instead of the screen. Permanent magnets (the ion trap) deflect the lighter electrons so that they strike the screen. Some very old TV sets without an ion trap show browning of the center of the screen, known as ion burn. The aluminum coating used in later CRTs reduced the need for an ion trap. Look up Vacuum in Wiktionary, the free dictionary. ... Outgassing (sometimes called Offgassing, particularly when in reference to indoor air quality) is the slow release of a gas that was trapped, frozen, absorbed or adsorbed in some material. ... An ion trap is a combination of electric or magnetic fields that captures ions in a region of a vacuum system or tube. ...

When electrons strike the poorly-conductive phosphor layer on the glass CRT, it becomes electrically charged, and tends to repel electrons, reducing brightness (this effect is known as "sticking"). To prevent this the interior side of the phosphor layer can be covered with a layer of aluminum connected to the conductive layer inside the tube, which disposes of this charge. It has the additional advantages of increasing brightness by reflecting towards the viewer light emitted towards the back of the tube, and protecting the phosphor from ion bombardment. Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ...

Oscilloscope tubes

For use in an oscilloscope, the design is somewhat different. Rather than tracing out a raster, the electron beam is directly steered along an arbitrary path, while its intensity is kept constant. Usually the beam is deflected horizontally (X) by a varying potential difference between a pair of plates to its left and right, and vertically (Y) by plates above and below, although magnetic deflection is possible. The instantaneous position of the beam will depend upon the X and Y voltages. It is most useful for the horizontal voltage, repeatedly, to increase linearly with time until the beam reaches the edge of the screen, then jump back to its starting value (sawtooth waveform, generated by a timebase). This causes the display to trace out the Y voltage as a function of time. Many oscilloscopes only function in this mode. However it can be useful to display, say, the voltage versus the current in an inductive component with an oscilloscope that allows X-Y input, without using the timebase. Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. ... The sawtooth wave (or saw wave) is a kind of basic non-sinusoidal waveform. ...

The electron gun is always centered in the tube neck; the problem of ion production is either ignored or mitigated by using an aluminized screen.

The beam can be moved much more rapidly, and it is easier to make the beam deflection accurately proportional to the applied signal, by using electrostatic deflection as described above instead of magnetic deflection. Magnetic deflection is achieved by passing currents through coils external to the tube; it allows the construction of much shorter tubes for a given screen size. Circuit arrangements are required to approximately linearize the beam position as a function of signal current, and the very wide deflection angles require arrangements to keep the beam focused (dynamic focusing). Electrostatic deflection refers to a technique for modifying the path of a stream of charged particles by the use of an electric field applied transverse to the path of the particles. ... For other uses, see Linear (disambiguation). ...

In principle either type of deflection can be used for any purpose; but electrostatic deflection is best for oscilloscopes with relatively small screens and high performance requirements, while a television receiver with a large screen and electrostatic deflection would be many meters deep.

Some issues must be resolved when using electrostatic deflection. Simple deflection plates appear as a fairly large capacitive load to the deflection amplifiers, requiring large current flows to charge and discharge this capacitance rapidly. Another, more subtle, problem is that when the electrostatic charge switches, electrons which are already part of the way through the deflection plate region will only be partially deflected. This results in the trace on the screen lagging behind a rapid change in signal. Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. ... Electric current is the flow (movement) of electric charge. ...

Extremely high performance oscilloscopes avoid these problems by subdividing the vertical (and sometimes horizontal) deflection plates into a series of plates along the length of the "deflection" region of the CRT, and electrically joined by a delay line terminated in its characteristic impedance; the timing of the delay line is set to match the velocity of the electrons through the deflection region. In this way, a change of charge "flows along" the deflection plate along with the electrons that it should affect, almost negating its effect on those electrons which are already partially through the region. Consequently the beam as seen on the screen slews almost instantly from the old point to the new point. In addition, because the entire deflection system operates as a matched-impedance load, the problem of driving a large capacitive load is mitigated. The term delay line has multiple meanings: In electronics and derivative fields such as telecommunications, a delay line is rigorously defined as a single-input-channel device, in which the output channel state at a given instant, t, is the same as the input channel state at the instant t... The characteristic impedance of a uniform transmission line is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. ... Impedance matching is the practice of attempting to make the output impedance of a source equal to the input impedance of the load to which it is ultimately connected, usually in order to maximize the power transfer and minimize reflections from the load. ... If an electric circuit has a well-defined output terminal, the circuit connected to this terminal (or its input impedance) is the load. ...

It is very common for oscilloscopes to have amplifiers which rapidly chop or swap the beam, blanking the display while switching. This allows the single beam to show as two or more traces, each representing a different input signal. These are properly called multiple-trace (dual trace, quadruple trace, etc.) oscilloscopes.

Much rarer is the true dual beam oscilloscope, whose tube contains an electron gun that produces two independent electron beams. Usually, but not always, both beams are deflected horizontally by a single shared pair of plates, while each beam has its own vertical deflection plates. This allows a time-domain display to show two signals simultaneously. Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. ...

Many modern oscilloscope tubes pass the electron beam through an expansion mesh. This mesh acts like a lens for electrons and has the effect of roughly doubling the deflection of the electron beam, allowing the use of a larger faceplate for the same length of tube envelope. The expansion mesh also tends to increase the "spot size" on the screen, but this tradeoff is usually acceptable.

When displaying one-shot fast events the electron beam must deflect very quickly, with few electrons impinging on the screen, leading to a faint or invisible display. A simple improvement can be attained by fitting a hood on the screen against which the observer presses his face, excluding extraneous light, but oscilloscope CRTs designed for very fast signals give a brighter display by passing the electron beam through a micro-channel plate just before it reaches the screen. Through the phenomenon of secondary emission this plate multiplies the number of electrons reaching the phosphor screen, giving a brighter display, possibly with a slightly larger spot. A micro-channel plate is a planar device which intensifies impinging radiation or particles by multiplication of electrons in small channels under the presence of a high electric field. ... Secondary emission is a phenomenon that occurs in electron tubes where electrons impact an electrode with sufficient energy to knock additional electrons from the surface of that electrode. ...

The phosphors used in the screens of oscilloscope tubes are different from those used in the screens of other display tubes. Phosphors used for displaying moving pictures should produce an image which fades very rapidly to avoid smearing of new information by the remains of the previous picture; i.e., they should have short persistence. An oscilloscope will often display a trace which repeats unchanged, so longer persistence is not a problem; but it is a definite advantage when viewing a single-shot event, so longer-persistence phosphors are used.

An oscilloscope trace can be any color without loss of information, so a phosphor with maximum effective luminosity is usually used. The eye is most sensitive to green: for visual and general-purpose use the P31 phosphor gives a visually bright trace, and also photographs well and is reasonably resistant to burning by the electron beam. For displays meant to be photographed rather than viewed, the blue trace of P11 phosphor gives higher photographic brightness; for extremely slow displays, very-long-persistence phosphors such as P7, which produce a blue trace followed by a longer-lasting amber or yellow afterimage, are used. The luminosity function is a standard function established by the Commission Internationale de lÉclairage to account for the variable sensitivity of the human eye to radiation at different wavelengths. ... Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ... Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ... Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ...

The phosphor screen of most oscilloscope tubes contains a permanently-marked internal graticule, dividing the screen using Cartesian coordinates. This internal graticule allows for the easy measurement of signals with no worries about parallax error. Less expensive oscilloscope tubes may instead have an external graticule of glass or acrylic plastic. Most graticules can be side-illuminated for use in a darkened room. This article is about longitude and latitude; see also UTM coordinate system Map of Earth showing lines of latitude (horizontally) and longitude (vertically); large version (pdf) The geographic (earth-mapping) coordinate system expresses every horizontal position on Earth by two of the three coordinates of a spherical coordinate system which... Cartesian means relating to the French mathematician and philosopher Descartes, who, among other things, worked to merge algebra and Euclidean geometry. ... For other uses, see Parallax (disambiguation). ... Polymethyl methacrylate (PMMA) or poly (methyl 2-methylpropenoate) is the synthetic polymer of methyl methacrylate. ...

Oscilloscope tubes almost never contain integrated implosion protection (see below). External implosion protection must always be provided, either in the form of an external graticule or, for tubes with an internal graticule, a plain sheet of glass or plastic. The implosion protection shield is often colored to match the light emitted by the phosphor screen; this improves the contrast as seen by the user. In an explosion (top), force radiates away from a source. ...

Computer displays

Graphical displays for early computers used vector monitors, a type of CRT similar to the oscilloscope but typically using magnetic, rather than electrostatic, deflection. Here, the beam traces straight lines between arbitrary points, repeatedly refreshing the display as quickly as possible. Vector monitors were also used by some late-1970s to mid-1980s arcade games such as Asteroids. Vector displays for computers did not noticeably suffer from the display artifacts of Aliasing and pixelization, but were limited in that they could display only a shape's outline (advanced vector systems could provide a limited amount of shading), and only a limited amount of crudely-drawn text (the number of shapes and/or textual characters drawn was severely limited, because the speed of refresh was roughly inversely proportional to how many vectors needed to be drawn). Some vector monitors are capable of displaying multiple colors, using either a typical tri-color CRT, or two phosphor layers (so-called "penetration color"). In these dual-layer tubes, by controlling the strength of the electron beam, electrons could be made to reach (and illuminate) either or both phosphor layers, typically producing a choice of green, orange, or red. Image File history File linksMetadata Download high-resolution version (580x1012, 170 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cathode ray tube Shadow mask Portal:Australia/Anniversaries/March Portal:Australia/Anniversaries/March/March 1 Metadata This file... Image File history File linksMetadata Download high-resolution version (580x1012, 170 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cathode ray tube Shadow mask Portal:Australia/Anniversaries/March Portal:Australia/Anniversaries/March/March 1 Metadata This file... Image File history File linksMetadata Download high-resolution version (818x1200, 267 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cathode ray tube Aperture grille Metadata This file contains additional information, probably added from the digital camera or... Image File history File linksMetadata Download high-resolution version (818x1200, 267 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cathode ray tube Aperture grille Metadata This file contains additional information, probably added from the digital camera or... Graphical displays for early computers used vector monitors, a type of CRT similar to the oscilloscope but typically using magnetic, rather than electrostatic, deflection. ... Asteroids is a popular vector-based video arcade game released in 1979 by Atari. ... Properly sampled image of brick wall. ... Pixelization is a video- and image-editing technique where an image, or part of it, is blurred by displaying part or all of it at a lower resolution. ...

Other graphical displays used 'storage tubes', including Direct View Bistable Storage Tubes (DVBSTs). These CRTs inherently stored the image, and did not require periodic refreshing. Mostly obsolete, a storage tube is a special monochromatic CRT whose screen has a kind of memory (hence the name): when a portion of the screen is illuminated by the CRTs electron gun, it stays lit until a screen erase command is given. ... DVBST was an acronym used by Tektronix to describe their line of Direct-View Bistable Storage Tubes. These were cathode ray tubes (CRTs) that stored information written to them using an analog technique inherent in the CRT and based upon the secondary emission of electrons from the phosphor screen itself. ...

Some displays for early computers (those that needed to display more text than was practical using vectors, or that required high speed for photographic output) used Charactron CRTs. These incorporate a perforated metal character mask (stencil), which shapes a wide electron beam to form a character on the screen. The system selects a character on the mask using one set of deflection circuits, and selects the position to draw the character at using a second set. The beam is activated briefly to draw the character at that position. Graphics could be drawn by selecting the position on the mask corresponding to the code for a space (in practise, they were simply not drawn), which had a small round hole in the center; this effectively disabled the character mask, and the system reverted to regular vector behaviour. A Charactron was a specific type of cathode ray tube that contained a form of read-only memory. ... Visual diagram of a basic stencil. ...

Many of the early computer displays used "slow", or long-persistence, phosphors to reduce flicker for the operator. While it reduces eyestrain for relatively static displays, the drawback of long-persistence phosphor is that when the display is changed, it produces a visible afterimage that can take up to several seconds to fade. This makes it inappropriate for animation, or for real-time dynamic information displays.

Color tubes use three different phosphors which emit red, green, and blue light respectively. They are packed together in strips (as in aperture grille designs) or clusters called "triads" (as in shadow mask CRTs). Color CRTs have three electron guns, one for each primary color, arranged either in a straight line or in a triangular configuration (the guns are usually constructed as a single unit). Each gun's beam reaches the dots of exactly one color; a grille or mask absorbs those electrons that would otherwise hit the wrong phosphor. Since each beam starts at a slightly different location within the tube, and all three beams are perturbed in essentially the same way, a particular deflection charge will cause the beams to hit a slightly different location on the screen (called a 'subpixel'). Color CRTs with the guns arranged in a triangular configuration are known as delta-gun CRTs, because the triangular formation resembles the shape of the Greek letter delta. Aperture grille in close-up An aperture grille (tension mask) is one of two major technologies used to manufacture cathode ray tube (CRT) televisions and computer displays; the other is shadow mask. ... For other meanings see Triad (disambiguation). ... The shadow mask is one of two major technologies used to manufacture cathode ray tube (CRT) televisions and computer displays that produce color images (the other is aperture grille). ...

Dot pitch defines the "native resolution" of the display. On delta-gun CRTs, as the scanned resolution approaches the dot pitch resolution, moiré (a kind of soft-edged banding) appears, due to interference patterns between the mask structure and the grid-like pattern of pixels drawn. Aperture grille monitors do not suffer from vertical moiré, however, because the phosphor strips have no vertical detail. Dot pitch (sometimes called line pitch or phosphor pitch) is a specification for a computer display that describes the distance between phosphor dots (sub-pixels) or LCD cells of the same color on the inside of a display screen. ... A moirÃ© pattern is an interference pattern created for example when two grids are overlaid at an angle, or when they have slightly different mesh sizes. ...

The glass envelope

The outer glass allows the light generated by the phosphor out of the monitor, but (for color tubes) it must block dangerous X-rays generated by high energy electrons impacting the inside of the CRT face. For this reason, the glass is leaded. Color tubes require significantly higher anode voltages than monochrome tubes (as high as 32,000 volts in large tubes), partly to compensate for the blockage of some electrons by the aperture mask or grille; the amount of X-rays produced increases with voltage. Because of leaded glass, other shielding, and protective circuits designed to prevent the anode voltage from rising too high in case of malfunction, the X-ray emission of modern CRTs is well within approved safety limits. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

CRTs have a pronounced triode characteristic, which results in significant gamma (a nonlinear relationship between beam current and light intensity). In early televisions, screen gamma was an advantage because it acted to compress the screen contrast. However in systems where linear response is required (such as when desktop publishing), gamma correction is applied. The gamma characteristic exists today in all digital video systems. Simplified diagram of a triode. ... Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in logâ€“log space (blue). ... Left side of the image has low contrast, the right has higher contrast. ... Adobe InDesign CS2, one of many popular desktop publishing applications. ... Digital video is a type of video recording system that works by using a digital, rather than analog, of the video signal. ...

CRT displays accumulate a static electrical charge on the screen, unless preventive measures are taken. This charge does not pose a safety hazard, but can lead to significant degradation of image quality through attraction of dust particles to the surface of the screen. Unless the display is regularly cleaned with a dry cloth or special cleaning tissue (using ordinary household cleaners may damage anti-glare protective layer on the screen), after a few months the brightness and clarity of the image drops significantly. Static electricity is a class of phenomena involving the net charge present on an object; typically referring to charged object with voltages of sufficient magnitude to produce visible attraction, repulsion, and sparks. ... Look up dust in Wiktionary, the free dictionary. ...

The high voltage (EHT) used for accelerating the electrons is provided by a transformer. For CRTs used in televisions, this is usually a flyback transformer that steps up the line (horizontal) deflection supply to as much as 32,000 volts for a color tube (Monochrome tubes and specialty CRTs may operate at much lower voltages). The output of the transformer is rectified and the pulsating output voltage is smoothed by a capacitor formed by the tube itself (the accelerating anode being one plate, the glass being the dielectric, and the grounded (earthed) Aquadag coating on the outside of the tube being the other plate). Before all-glass tubes, the structure between the screen and the electron gun was made from a heavy metal cone which served as the accelerating anode. Smoothing of the EHT was then done with a high voltage capacitor, external to the tube itself. In the earliest televisions, before the invention of the flyback transformer design, a linear high-voltage supply was used; because these supplies were capable of delivering much more current at their high voltage than flyback high voltage systems, in the case of an accident they proved extremely deadly. The flyback circuit design addressed this; in the case of a fault, the flyback system delivers relatively little current, making a person's chance of surviving a direct shock from the high voltage anode (the suction cup on the back) lead more hopeful (though by no means guaranteed). A flyback transformer or line output transformer (LOPT) is a type of transformer used to generate the high voltage needed for driving a cathode ray tube or picture tube. It converts the input voltage, usually mains voltage in the range 120 to 240 volts, to an output voltage in the... Aquadag is a trade name for a graphite based coating commonly found in Cathode ray tubes. ...

The future of CRT technology

CRT screens have much deeper cabinets compared to LCD screens for a given area, however, they can display higher resolutions on a smaller screen. Also, LCDs have worse color rendition due to the fluorescent lights used as backlights, even though they can be brighter overall. The result is that CRTs are useful for displaying photos with a high pixels per unit area and correct color balance, and for having large desktop area concentrated into a small screen. Having 1600 × 1200 resolution in 18 inch 4:3 rather than 20–24 inch on most LCDs also allows less eye movement to view different parts of the screen. In addition to offering high-resolutions in a smaller screen area, they offer the resolutions more cheaply for a given resolution. However, the end of most high-end CRT production in the mid 2000s (including high-end Sony, NEC, and Mitsubishi product lines) means an erosion of the CRT's capability. A compact fluorescent lamp A fluorescent lamp is a type of electric lamp that excites argon and mercury vapor to create luminescence. ... Backlights are lights that are attached to LCD displays so that they can be seen at night. ...

In general, rear-projection displays and LCDs require less power per display area, but plasma displays consume as much as or more than CRTs.^[1] However, CRTs still find adherents in computer gaming^[2]^[3] because of higher resolution per initial cost and small response time. CRTs are also still popular in the printing and broadcasting industries as well as in the professional video, photography, and graphics fields due to their greater color fidelity and contrast, better resolution when displaying moving images, and better view from angles, although improvements in LCD technology increasingly alleviate these concerns. The demand for CRT screens is falling rapidly,^[4] and producers are responding to this trend. For example, in 2005 Sony announced that they would stop the production of CRT computer displays. Similarly, German manufacturer Loewe ceased production of CRT TVs in December 2005. It has been common to replace CRT-based televisions and monitors in as little as 5–6 years, although they generally are capable of satisfactory performance for a much longer time. An example of a plasma display Composition of plasma display panel A plasma display panel (PDP) is a type of flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm). ... ... LOEWE is a german TV manufacturer founded 1923 in Berlin. ...

This trend is less progressed in television CRT displays. Due to the high cost of large LCD panels and plasma displays, a market niche for CRTs still exists as a cheaper alternative to these technologies. In addition some videophiles prefer CRT televisions because the pixels are not fixed. This allows perceived better image quality, because CRT displays do not have fixed native resolutions. Non-native resolutions on Plasma, DLP, LCD and OLED technology cause blurring of the image. For example: The perceived image quality of a progressive-scan DVD player on a CRT television is much better than on a 1080P Plasma Television. This is because the 1080i CRT can display 480P natively due to its ability to change the size of the pixels on the display. Fixed Pixel technology (used in PDP, LCD, DLP and OLED technology) requires the display to use many more pixels to display the lower resolution, thus causing "blurring" of the image. The effect is similar to the digital zoom feature on a digital camera; the display blows up the pixels and fills in the dots, thus fixed pixel displays interpolate the lower resolution signal to a higher resolution. Techniques such as anti-aliasing and video scaling minimize this issue, but the image quality is still considered better on a CRT despite these techniques. Not having fixed pixels allows image quality to be superior for lower resolution sources, such as DVD players and older generation game consoles. 1080P/i fixed pixel displays have an even larger issue with lower resolution sources due to the difference in the native resolution and input resolution from the device hooked up to the television. Since (as of September 2007), most television programming is still only available in SDTV, users who watch regular (non HDTV) programming will benefit greatly in terms of image quality by using a CRT HDTV rather than a fixed pixel display. An example of a plasma display Composition of plasma display panel A plasma display panel (PDP) is a type of flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm). ...

In the United Kingdom, the largest retailer of domestic electronic equipment, DSG (Dixons) reported that CRT models made up 80–90% of the volume of televisions sold at Christmas 2004 and 15–20% a year later, and that they were expected to be less than 5% at the end of 2006. Dixons have announced that they will cease selling CRT televisions in 2007.^[5] The United Kingdom based company DSG international plc (aka DSGi), formerly Dixons Stores Group plc, is one of the largest consumer electronics retailers in Europe. ...

Magnets

Magnets should never be put next to a color CRT, as they may cause magnetization of the shadow mask, and in severe cases can permanently distort it mechanically, which will cause incorrect colors to appear in the magnetized area. This is called a "purity" problem, because it affects the purity of one of the primary colors, with the residual magnetism causing the undesired deflection of electrons from one gun to the wrong color's phosphor patch. This can be expensive to have corrected, although it may correct itself over a few days or weeks. Most modern television sets and nearly all newer computer monitors have a built-in degaussing coil, which upon power-up creates a brief, alternating magnetic field which decays in strength over the course of a few seconds (typically, the decay is implemented with a specialized resistor in the circuit which increases resistance with its increasing temperature as a result of the current passing through it). The coil's interaction with the shadow mask, screen band and chassis components is the reason for the characteristic 'hum' associated with turning on many CRT-equipped displays. This degaussing field is strong enough to remove most cases of shadow mask magnetization. For other uses, see Magnet (disambiguation). ... Degaussing, named after the German scientist Carl Friedrich Gauss, is the process of removing permanent magnetism (magnetic hysteresis) from an object. ...

It is possible to purchase or build an external degaussing coil, which can aid in demagnetizing older sets, or in cases where the built-in coil is ineffective. Image File history File links Download high-resolution version (2444x1591, 71 KB) Spectra of individual color phosphors of a typical CRT video monitor. ... Image File history File links Download high-resolution version (2444x1591, 71 KB) Spectra of individual color phosphors of a typical CRT video monitor. ...

A transformer, which produces a large alternating magnetic field (one can typically be found in soldering guns, though not soldering irons), may also be used to degauss a monitor, by holding it up to the center of the monitor, activating it, and slowly moving the gun in ever wider concentric circles past the edge of the monitor until the shimmering colors can no longer be seen (if a soldering gun is being used, ensure that the hot tip is facing away from the glass). To see the shimmering colors clearly, you may need to display a white or light-colored screen. This process may need to be repeated several times to fully remove severe magnetization. A soldering gun is in affect a transformer. ... Using a soldering iron. ...

In extreme cases, very strong magnets such as the now popular neodymium iron boron, or NIB magnets, can actually deform (and likely, permanently bend) the shadow mask. This will create an area of impure color rendition on the screen and if the shadow mask has been bent, such damage usually can't be repaired. Subjecting an old black and white television or monochrome (green or amber screen) computer monitor to magnets is generally harmless; this can be used as an effective demonstration tool for seeing the immediate and dramatic effect of a magnetic field on moving charged particles. General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Standard atomic weight 144. ... For other uses, see Iron (disambiguation). ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Standard atomic weight 10. ... Neodymium magnet on a bracket from a hard drive A neodymium magnet or NIB magnet (also, but less specifically, called a rare-earth magnet) is a powerful magnet made of a combination of neodymium, iron, and boron â€” Nd2Fe14B. They have replaced marginally weaker and significantly more heat-resistant samarium-cobalt...

Health concerns

Electromagnetic

It is believed the electromagnetic fields emitted by CRT monitors constitute a health hazard to the functioning of living cells. Exposure to these fields diminishes considerably at distances of 85 cm or farther according to the inverse square law, which describes the propagation of all electromagnetic radiation.^{[citation needed]} In physics, an inverse-square law is any physical law stating that some quantity is inversely proportional to the square of the distance from a point. ...

Electromagnetic radiation can be classified into ionizing radiation and non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking chemical bonds. ... Bioelectromagnetics is the study of how electromagnetic fields interact with and influence biological processes. ...

Ionizing radiation

CRTs can emit a small amount of X-ray radiation as a result of the electron beam's bombardment of the shadow mask/aperture grille and phosphors. The amount of radiation escaping the front of the monitor is widely considered harmful. The Food and Drug Administration regulations in 21 C.F.R. 1020.10 are used to strictly limit, for instance, television receivers to 0.5 milliroentgens per hour (mR/h) (0.13 µC/(kg·h) or 36 pA/kg) at a distance of 5 cm from any external surface; since 2007, most CRTs have emissions that fall well below this limit.^[6] In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... â€œFDAâ€ redirects here. ... The Code of Federal Regulations (CFR) is the codification of the general and permanent rules and regulations (sometimes called administrative law) published in the Federal Register by the executive departments and agencies of the Federal Government of the United States. ... The rÃ¶ntgen or roentgen (symbol R) is a unit of exposure to ionizing radiation (X or gamma rays), and is named after the German physicist Wilhelm RÃ¶ntgen. ...

Early color television receivers (many of which are now highly collectible, see CT-100) were especially vulnerable due to primitive high-voltage regulation systems. X-ray production is generally negligible in black-and-white sets (due to low acceleration voltage and beam current), and in virtually every color display since the late 1960s, when systems were added to shut down the horizontal deflection system (and therefore high voltage supply) should regulation of the acceleration voltage fail. Introduced in March 1954, the RCA CT-100 was the first consumer color television set in the USA. With 36 vacuum tubes, the CTC-2 chassis within the CT-100 (Merrill, to the marketing department) was (in its day) arguably the most complicated device sold to the general public. ...

All television receivers and CRT displays equipped with a vacuum tube based high-voltage rectifier or high-voltage regulator tube also generate X-rays in these stages. These stages are universally housed in a metal enclosure called the "high-voltage cage" made from lead to substantially reduce (and effectively eliminate) exposure. As examples, a 1B3 and a 6BK4 vacuum tube would be installed inside this metal enclosure. For both X-ray and electrical safety reasons, the set should never be operated with the cover of the high voltage cage opened. This article is about the metal. ...

Toxicity

CRTs may contain toxic phosphors within the glass envelope. The glass envelopes of modern CRTs may be made from heavily leaded glass, which represent an environmental hazard. Indirectly heated vacuum tubes (including CRTs) use barium compounds and other reactive materials in the construction of the cathode and getter assemblies; normally this material will be converted into oxides upon exposure to the air, but care should be taken to avoid contact with the inside of all broken tubes. Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ... The term leaded glass either refers to: glass containing lead oxide, which increases its density and enhances its refraction and dispersion of light. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... For other uses, see Barium (disambiguation). ... Diagram of a copper cathode in a Daniells cell. ... To prevent any remaining gases from remaining in a free state in a vacuum tube, modern tubes are constructed with getters, which are usually small, circular troughs filled with metals that oxidize quickly, with barium being the most common. ...

In some jurisdictions, discarded CRTs are regarded as toxic waste. In October 2001, the United States Environmental Protection Agency created rules stating that CRTs must be brought to special recycling places. In November 2002, the EPA began fining companies that disposed of CRTs through landfills or incineration. Regulatory agencies, local and statewide, monitor the disposal of CRTs and other computer equipment. EPA redirects here. ... The international recycling symbol. ...

In Europe, disposal of CRT televisions and monitors are covered by the WEEE Directive. WEEE Man The Waste Electrical and Electronic Equipment Directive (WEEE Directive) is the European Community directive 2002/96/EC on waste electrical and electronic equipment which, together with the RoHS Directive 2002/95/EC, became European Law in February 2003, setting collection, recycling and recovery targets for all types of...

Flicker

The constant refreshing of a CRT can cause headaches in migraine sufferers and seizures in epileptics, if they are photosensitive. Screen filters are available to reduce these effects. A high refresh rate (above 75 Hz) also helps to negate these effects. A headache (cephalalgia in medical terminology) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ... This article is about epileptic seizures. ... This article is about the neurological disorder as it affects humans. ... Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns. ... A monitor filter is an accessory to the computer display to filter out the glare and radiation emitted form a CRT dispaly. ...

High voltage

CRTs operate at very high voltages, which can persist long after the device containing the CRT has been switched off and/or unplugged, sometimes for years. Residual charges of hundreds of volts can also remain in large capacitors in the power supply circuits of the device containing the CRT; these charges may persist. Modern circuits contain bleeder resistors, to ensure that the high-voltage supply is discharged to safe levels within a couple of minutes at most. These discharge devices can fail even on a modern unit and leave these high voltage charges present. The final anode connector on the bulb of the tube carries this high voltage. A bleeder resistor is a resistor placed in parallel of a high-voltage supply for the purposes of discharging the energy stored in the power sources filter capacitors or other components that store electrical energy. ...

Implosion

A high vacuum exists within all CRT monitors. If the outer glass envelope is damaged, a dangerous implosion may occur. Due to the power of the implosion, glass may actually explode outwards. This shrapnel can travel at dangerous and potentially fatal velocities. While modern CRT used in televisions and computer displays have epoxy-bonded face-plates or other measures to prevent shattering of the envelope, CRTs removed from equipment must be handled carefully to avoid personal injury. In an explosion (top), force radiates away from a source. ...

Contents

General description

Oscilloscope tubes

Computer displays

The glass envelope

The future of CRT technology

Magnets

Health concerns

Electromagnetic

Ionizing radiation

Toxicity

Flicker

High voltage

Implosion

See also

References

Selected patents

External links

Contents

General description GA_googleFillSlot("encyclopedia_square");

Oscilloscope tubes

Computer displays

The glass envelope

The future of CRT technology

Magnets

Health concerns

Electromagnetic

Ionizing radiation

Toxicity

Flicker

High voltage

Implosion

See also

References

Selected patents

External links

General description