home Audio Video How does a CRT monitor work? CRT Monitors Modern CRT Monitors

How does a CRT monitor work? CRT Monitors Modern CRT Monitors

Televisions, which have kinescopes in their design, have long been replaced by plasma and liquid crystal devices. However, there are people in whose houses you can still see these devices. Due to the long service life, they often fail, therefore, despite the development of technology, the repair of CRT TVs is still a popular service.

kinescope device

The role of the main part in the old-style television receiver is performed by a cathode ray tube (CRT), called a kinescope. The principle of its operation is based on electronic emission. The mechanism of such a tube includes:

electron guns;
focusing and deflecting coils;
anode terminal;
a shadow mask to separate color images;
phosphor layer with different glow zones.

A kinescope made of glass is coated inside with a discrete phosphor. The coverage consists of triads - a set of three points, each of which corresponds to red, blue and green.

A point included in the triad takes on a beam emanating from a particular electron gun and begins to emit light of varying intensity. To achieve the desired shade, special metal gratings of a shadow, slot or aperture type are built into the tube design.

Principle of operation

For the image to appear on the TV screen, the beam emitted by the electron gun must sequentially touch all points in the direction from left to right and from top to bottom, causing them to glow. The speed of beam propagation across the screen should reach 75 times per second, otherwise the dots will go out. If the speed drops to 25 times per second, it will cause the picture to flicker.

In order for the rays that touched the phosphor coating to be reflected from it, a system consisting of four coils is attached to the neck of the kinescope. The magnetic field created on them contributes to the reflection of rays in the right direction. Individual luminous dots are combined into a single image under the action of control signals. A specific sweep is responsible for each direction of beam movement:

lowercase provides a direct horizontal stroke;
personnel is responsible for the vertical movement.

In addition to straight trajectories, there are zigzag (from the top left to the bottom right corner of the monitor) and reverse moves. Signals with the brightness turned off are responsible for moving in the opposite direction.

The main technical characteristic of a kinescope screen is the frame rate, measured in hertz. The higher it is, the more stable the image will be. The product of the vertical frequency and the number of lines output in one frame determines the line frequency parameter in kilohertz. Depending on how the picture is formatted (progressive or interlaced), even and odd lines may appear one after the other or all at once during one frame scan period.

Another important parameter - phosphor dot size. It affects the clarity of the output image. The smaller the dots, the better. In order for the picture on the screen to be of high quality, the distance between them should be 0.26-0.28 mm.

In black and white televisions, the cathode ray tube screen is completely covered with a phosphor that emits only white light. An electronic spotlight fixed in the neck of the tube forms a thin beam that scans the screen line by line and contributes to the glow of the phosphor. The intensity of this glow is controlled by the strength of the video signal containing all the information about the image.

Possible problems

At work CRT TV various problems may occur. The reason for their occurrence lies in the breakdown of parts of the electron beam mechanism.

Failure of the power supply unit will lead to the fact that the device will not turn on. To check its performance, you must first turn off the line scan cascade, which acts as a load, then solder a household lamp into the circuit. The absence of light in the lamp indicates that the power supply is faulty.

Identification of problems in horizontal scanning is carried out using the same lamp. Its constant glow indicates a malfunction of the output transistor. Normally, the lamp should flash on and off.

With a luminous horizontal strip, you should pay attention to the scan of the frames. To restore its operation, you will need to reduce the brightness level, thereby protecting the phosphor layer. Additionally, you need to check the health of the master oscillator and the output stage. In this case, it must be taken into account that their operating voltage is in the range of 24-28 volts.

The complete absence of glow can most often be caused by problems with the power supply of the kinescope. During the diagnostic process, you will need to check the filament and the voltage level on it. If the integrity of the thread is not broken, then the output will be winding the winding. Replacement of the transformer in this case is not required.

If there are problems with the color block and the video amplifier, the sound disappears. The opposite situation, when there is no image in the presence of sound, means there is a problem in the low-frequency amplifier. If the image disappears along with the sound, then the cause should be sought in a malfunctioning radio channel that starts the video processor and tuner.

TV Repair Services

To troubleshoot the operation of a television receiver on your own, you must have the appropriate knowledge about the device and operation of the kinescope. If there is no such knowledge, it is best to contact qualified specialists. Find a repair company CRT TVs, will not be difficult.

Most of these firms provide customers with a convenient repair method (in the workshop or at home) and free diagnostics. Experienced craftsmen quickly diagnose the problem and fix it, using high-quality parts recommended by TV manufacturers and modern equipment. All work carried out is guaranteed. All problems that arose during the period of validity warranty period, removed free of charge

CRT monitor design

Most monitors in use and produced today are built on cathode ray tubes (CRTs). AT English language- Cathode Ray Tube (CRT), literally - cathode ray tube. Sometimes CRT stands for Cathode Ray Terminal, which no longer corresponds to the handset itself, but to the device based on it. The electron beam technology was developed by the German scientist Ferdinand Braun in 1897 and was originally created as a special instrument for measuring alternating current, that is, for an oscilloscope. The cathode ray tube, or kinescope, is the most important element of the monitor. The kinescope consists of a sealed glass flask, inside of which there is a vacuum. One of the ends of the flask is narrow and long - this is the neck. The other is a wide and rather flat screen. The inner glass surface of the screen is coated with a luminophor. Quite complex compositions based on rare earth metals - yttrium, erbium, etc. are used as phosphors for color CRTs. A phosphor is a substance that emits light when bombarded by charged particles. Note that sometimes the phosphor is called phosphorus, but this is not true, since the phosphor used in the CRT coating has nothing to do with phosphorus. Moreover, phosphorus glows only as a result of interaction with atmospheric oxygen during oxidation to P2O5, and the glow does not last very long (by the way, white phosphorus is a strong poison).

To create an image in a CRT monitor, an electron gun is used, from where a stream of electrons comes from under the action of a strong electrostatic field. Through a metal mask or grate, they fall on the inner surface of the glass screen of the monitor, which is covered with multi-colored phosphor dots. The electron flow (beam) can be deflected in the vertical and horizontal planes, which ensures that it consistently hits the entire screen field. The beam is deflected by means of a deflecting system. Deflecting systems are subdivided into saddle-toroidal and saddle-shaped. The latter are preferable because they have a reduced level of radiation.

The deflecting system consists of several inductors located at the neck of the kinescope. With the help of an alternating magnetic field, two coils create a deflection of the electron beam in the horizontal plane, and the other two - in the vertical plane. A change in the magnetic field occurs under the action of an alternating current flowing through the coils and changing according to a certain law (this is usually a sawtooth change in voltage over time), while the coils give the beam the desired direction. The solid lines are the active path of the beam, the dotted line is the reverse.

The frequency of transition to a new line is called the horizontal (or horizontal) scanning frequency. The frequency of the transition from the bottom right corner to the top left corner is called the vertical (or vertical) scan frequency. The amplitude of the overvoltage pulses on the horizontal scanning coils increases with the horizontal frequency, so this node is one of the most stressed places in the structure and one of the main sources of interference in a wide frequency range. The power consumed by the horizontal scanning nodes is also one of the major factors to consider when designing monitors. After the deflecting system, the electron flow on its way to the front of the tube passes through the intensity modulator and the accelerating system, which operate on the principle of a potential difference. As a result, electrons acquire more energy (E=mV2/2, where E is energy, m is mass, v is velocity), some of which is spent on the glow of the phosphor.

The electrons hit the phosphor layer, after which the energy of the electrons is converted into light, that is, the flow of electrons causes the dots of the phosphor to glow. These glowing dots of phosphor form the image you see on your monitor. As a rule, three electron guns are used in a color CRT monitor, as opposed to a single gun used in monochrome monitors, which are now practically not produced.

It is known that human eyes react to the primary colors: red (Red), green (Green) and blue (Blue) and their combinations, which create an infinite number of colors. The phosphor layer covering the front of the cathode ray tube consists of very small elements (so small that the human eye cannot always distinguish them). These phosphor elements reproduce the primary colors, in fact there are three types of multi-colored particles whose colors correspond to the primary RGB colors(hence the name of the group of phosphor elements - triads).

The phosphor begins to glow, as mentioned above, under the influence of accelerated electrons, which are created by three electron guns. Each of the three guns corresponds to one of the primary colors and sends a beam of electrons to different phosphor particles, whose glow of the primary colors with different intensities is combined and as a result an image with the required color is formed. For example, if red, green, and blue phosphor particles are activated, their combination will form white.

To control a cathode ray tube, control electronics is also needed, the quality of which largely determines the quality of the monitor. By the way, it is the difference in the quality of control electronics created by different manufacturers that is one of the criteria that determine the difference between monitors with the same cathode ray tube.

So, each gun emits an electron beam (or stream, or beam) that affects phosphor elements of different colors (green, red or blue). It is clear that the electron beam intended for the red phosphor elements should not affect the green or blue phosphor. To achieve this effect, a special mask is used, whose structure depends on the type of kinescopes from different manufacturers, providing discreteness (raster) of the image. CRTs can be divided into two classes - three-beam with a delta-shaped arrangement of electron guns and with a planar arrangement of electron guns. These tubes use slit and shadow masks, although it is more correct to say that they are all shadow masks. At the same time, tubes with a planar arrangement of electron guns are also called kinescopes with self-convergence of beams, since the effect of the Earth's magnetic field on three planar beams is almost the same, and when changing the position of the tube relative to the Earth's field, no additional adjustments are required.

CRT types

Depending on the location of the electron guns and the design of the color separation mask, there are four types of CRTs used in modern monitors:

CRT with shadow mask (Shadow Mask)

CRTs with a shadow mask (Shadow Mask) are most common in most monitors manufactured by LG, Samsung, Viewsonic, Hitachi, Belinea, Panasonic, Daewoo, Nokia. A shadow mask is the most common type of mask. It has been used since the invention of the first color kinescopes. The surface of kinescopes with a shadow mask is usually spherical (convex). This is done so that the electron beam in the center of the screen and along the edges has the same thickness.

The shadow mask consists of a metal plate with round holes that cover approximately 25% of the area. There is a mask in front of a glass tube with a phosphor layer. As a rule, most modern shadow masks are made from invar. Invar (InVar) - a magnetic alloy of iron (64%) with nickel (36%). This material has an extremely low coefficient of thermal expansion, so even though the electron beams heat up the mask, it does not adversely affect the color purity of the image. The holes in the metal grid work as a sight (although not accurate), it is this that ensures that the electron beam hits only the required phosphor elements and only in certain areas. The shadow mask creates a lattice with uniform dots (also called triads), where each such dot consists of three phosphor elements of primary colors - green, red and blue, which glow with different intensities under the influence of beams from electron guns. By changing the current of each of the three electron beams, it is possible to achieve an arbitrary color of an image element formed by a triad of dots.

One of the weak points of shadow mask monitors is their thermal deformation. In the figure below, how part of the rays from the electron beam gun hits the shadow mask, as a result of which heating and subsequent deformation of the shadow mask occur. The ongoing displacement of the shadow mask holes leads to the appearance of a variegated screen effect (displacement RGB colors). The material of the shadow mask has a significant impact on the quality of the monitor. The preferred mask material is Invar.

The disadvantages of the shadow mask are well known: firstly, this is a small ratio of electrons transmitted and retained by the mask (only about 20-30% passes through the mask), which requires the use of phosphors with high light output, and this, in turn, worsens the monochrome glow, reducing the color rendering range , and secondly, it is rather difficult to ensure the exact coincidence of three rays that do not lie in the same plane when they are deflected at large angles. The shadow mask is used in most modern monitors - Hitachi, Panasonic, Samsung, Daewoo, LG, Nokia, ViewSonic.

The minimum distance between phosphor elements of the same color in adjacent rows is called dot pitch and is an index of image quality. Dot pitch is usually measured in millimeters (mm). The smaller the dot pitch value, the higher the quality of the image displayed on the monitor. The horizontal distance between two adjacent points is equal to the step of the points multiplied by 0.866.

CRT with an aperture grill of vertical lines (Aperture Grill)

There is another type of tube that uses the Aperture Grille. These tubes became known as the Trinitron and were first introduced to the market by Sony in 1982. Aperture grating tubes use original technology, where there are three beam guns, three cathodes and three modulators, but there is one common focus.

An aperture grille is a type of mask used by different manufacturers in their technologies to produce kinescopes that have different names but are essentially the same, such as Sony's Trinitron technology, Mitsubishi's DiamondTron, and ViewSonic's SonicTron. This solution does not include a metal grid with holes, as in the case of the shadow mask, but has a grid of vertical lines. Instead of dots with phosphor elements of the three primary colors, the aperture grille contains a series of filaments consisting of phosphor elements arranged in vertical stripes of the three primary colors. This system provides high image contrast and good color saturation, which together provide high quality tube monitors based on this technology. Mask applied in tubes Sony(Mitsubishi, ViewSonic), is a thin foil on which thin vertical lines are scratched. It rests on a horizontal wire (one in 15", two in 17", three or more in 21") wire, the shadow of which is visible on the screen. This wire is used to dampen vibrations and is called a damper wire. It is clearly visible, especially with a light background images on the monitor.Some users fundamentally dislike these lines, while others, on the contrary, are satisfied and use them as a horizontal ruler.

The minimum distance between phosphor strips of the same color is called the strip pitch and is measured in millimeters (see Fig. 10). The smaller the stripe pitch value, the higher the image quality on the monitor. With an aperture grille, only the horizontal size of the dot makes sense. Since the vertical is determined by the focusing of the electron beam and the deflecting system.

CRT with slit mask (Slot Mask)

The slot mask is widely used by NEC under the name "CromaClear". This solution in practice is a combination of a shadow mask and an aperture grille. In this case, the phosphor elements are located in vertical elliptical cells, and the mask is made of vertical lines. In fact, the vertical stripes are divided into elliptical cells, which contain groups of three phosphor elements in three primary colors.

The slit mask is used, in addition to monitors from NEC (where the cells are elliptical), in Panasonic monitors with a PureFlat tube (formerly called PanaFlat). Note that it is not possible to directly compare the pitch size for tubes different types: The pitch of the dots (or triads) of the shadow mask tube is measured diagonally, while the pitch of the aperture grille, otherwise known as the horizontal dot pitch, is measured horizontally. Therefore, for the same dot pitch, a tube with a shadow mask has a higher dot density than a tube with an aperture grating. For example, a stripe pitch of 0.25 mm is approximately equivalent to a dot pitch of 0.27 mm. Also in 1997, Hitachi - the largest CRT designer and manufacturer - developed the EDP - latest technology shadow mask. In a typical shadow mask, the triads are placed more or less equilaterally, creating triangular groups that are evenly distributed across the inner surface of the tube. Hitachi reduced the horizontal distance between the triad elements, thereby creating triads that are closer in shape to an isosceles triangle. To avoid gaps between the triads, the dots themselves have been lengthened, and are more ovals than circles.

Both types of masks - the shadow mask and the aperture grille - have their own advantages and their supporters. For office applications, text editors and spreadsheets, shadow mask kinescopes are more suitable, providing very high definition and sufficient image contrast. To work with raster and vector graphics Aperture-grille tubes have traditionally been recommended for superior image brightness and contrast. In addition, the working surface of these kinescopes is a segment of a cylinder with a large horizontal curvature radius (unlike CRTs with a shadow mask, which have a spherical screen surface), which significantly (up to 50%) reduces the intensity of glare on the screen.

Main characteristics of CRT monitors

Monitor screen size

Monitor screen diagonal - the distance between the lower left and right top corner screen, measured in inches. The size of the screen area visible to the user is usually somewhat smaller, on average 1 ", than the size of the handset. Manufacturers may indicate two diagonal sizes in the accompanying documentation, while the visible size is usually indicated in brackets or marked "Viewable size", but sometimes only one is indicated size - the size of the diagonal of the tube. Monitors with a diagonal of 15" stand out as a standard for PCs, which approximately corresponds to 36-39 cm of the diagonal of the visible area. For Windows it is desirable to have a monitor of at least 17".

Screen grain size

The screen grain size determines the distance between the closest holes in the type of separation mask being used. The distance between the mask holes is measured in millimeters. The smaller the distance between the holes in the shadow mask, and the more holes there are, the better the image quality. All monitors with grain greater than 0.28mm are classified as coarse and cost less. The best monitors have a grain of 0.24mm, reaching 0.2mm on the most expensive models.

Monitor resolution

The resolution of a monitor is determined by the number of image elements it can display both horizontally and vertically. 19" monitors support resolutions up to 1920*14400 and above.

Monitor Power Consumption

Screen covers

Screen coatings are needed to give it anti-glare and anti-static properties. The anti-reflective coating allows you to watch only the image generated by the computer on the monitor screen, and not tire your eyes by observing reflected objects. There are several ways to obtain an anti-reflective (non-reflective) surface. The cheapest of them is etching. It makes the surface rough. However, the graphics on such a screen look blurry, the image quality is poor. The most popular method of applying a quartz coating that scatters incident light; this method has been implemented by Hitachi and Samsung. An anti-static coating is necessary to prevent dust from adhering to the screen due to the accumulation of static electricity.

Protective screen (filter)

A protective screen (filter) should be an indispensable attribute of a CRT monitor, since medical studies have shown that radiation containing rays in a wide range (X-ray, infrared and radio radiation), as well as electrostatic fields accompanying the operation of the monitor, can have a very negative effect on human health .

According to the manufacturing technology, protective filters are: mesh, film and glass. Filters can be attached to the front wall of the monitor, hung on the top edge, inserted into a special groove around the screen, or put on the monitor.

Screen filters

Grid filters provide little or no protection against electromagnetic radiation and static electricity, and slightly degrade image contrast. However, these filters are good at reducing glare from ambient light, which is important when working with a computer for a long time.

Film filters

Film filters also do not protect against static electricity, but significantly increase the image contrast, almost completely absorb ultraviolet radiation and reduce the level of X-ray radiation. Polarizing film filters, such as Polaroid, are able to rotate the plane of polarization of reflected light and suppress glare.

Glass filters

Glass filters are produced in several modifications. Simple glass filters remove static charge, attenuate low-frequency electromagnetic fields, reduce ultraviolet radiation and increase image contrast. Glass filters of the “full protection” category have the greatest combination of protective properties: they practically do not produce glare, increase the image contrast by one and a half to two times, eliminate the electrostatic field and ultraviolet radiation, and significantly reduce low-frequency magnetic (less than 1000 Hz) and X-ray radiation. These filters are made of special glass.

Pros and cons

Conventions: (+) dignity, (~) acceptable, (-) disadvantage
	LCD monitors	CRT monitors
Brightness	(+) from 170 to 250 cd/m2	(~) 80 to 120 cd/m2
Contrast	(~) 200:1 to 400:1	(+) 350:1 to 700:1
Viewing angle (by contrast)	(~) 110 to 170 degrees	(+) over 150 degrees
Viewing angle (by color)	(-) 50 to 125 degrees	(~) over 120 degrees
Permission	(-) Single resolution with fixed pixel size. Optimally can only be used in this resolution; higher or lower resolutions may be used depending on the supported expansion or compression functions, but these are not optimal.	(+) Various resolutions are supported. At all supported resolutions, the monitor can be used optimally. The limitation is imposed only by the acceptability of the refresh rate.
Vertical frequency	(+) Optimum frequency 60 Hz, which is sufficient for no flicker	(~) Only at frequencies above 75 Hz there is no clearly noticeable flicker
Color matching errors	(+) no	(~) 0.0079 to 0.0118 inch (0.20 - 0.30 mm)
Focusing	(+) very good	(~) fair to very good>
Geometric/linear distortion	(+) no	(~) possible
Pixels that don't work	(-) up to 8	(+) no
Input signal	(+) analog or digital	(~) analog only
Scaling at different resolutions	(-) absent or interpolation methods are used that do not require large overheads	(+) very good
Color display accuracy	(~) True Color is supported and the required color temperature is simulated	(+) True Color is supported and at the same time there are a lot of color calibration devices on the market, which is a definite plus
Gamma correction (color adjustment to the characteristics of human vision)	(~) satisfactory	(+) photorealistic
Uniformity	(~) often the image is brighter at the edges	(~) often the image is brighter in the center
Color Purity/Color Quality	(~) good	(+) high
flicker	(+) no	(~) imperceptibly above 85 Hz
Inertia time	(-) 20 to 30 ms.	(+) disparagingly small
Imaging	(+) The image is formed by pixels, the number of which depends only on the specific resolution of the LCD panel. The pixel pitch depends only on the size of the pixels themselves, but not on the distance between them. Each pixel is individually shaped for superb focus, clarity and clarity. The image is more coherent and smooth	(~) Pixels are formed by a group of dots (triads) or stripes. The pitch of a point or line depends on the distance between points or lines of the same color. As a result, the sharpness and clarity of the image is highly dependent on the size of the dot or line pitch and on the quality of the CRT.
Power consumption and emissions	(+) Virtually no hazardous electromagnetic radiation. Power consumption is about 70% lower than standard CRT monitors (25W to 40W).	(-) Electromagnetic emissions are always present, however their level depends on whether the CRT complies with any safety standard. Energy consumption in working condition at the level of 60 - 150 watts.
Dimensions/weight	(+) flat design, light weight	(-) heavy construction, takes up a lot of space
Monitor interface	(+) Digital interface, however, most LCD monitors have a built-in analog interface for connecting to the most common analog outputs of video adapters	(-) Analog interface

Let's talk about monitors - LCD and CRT, about which is better. Previously, when there were still black and white convex monitors, working at a computer was always unsafe for the eyes. But now the time has changed and the progress of monitors is visible to the naked eye.

Comparison of LCD and CRT

Today, monitors have already changed a lot, they have become completely different - LCD monitors have replaced CRTs, they are not large compared to CRTs and no longer take up a lot of space on the table. They also use less electricity. But which is better today, CRT or LCD? Regular Users they will answer in chorus that LCD, but is it really so?

The monitor, as there is a lot in this word, often we look at it more time than at relatives or children, therefore, unfortunately, the choice of a monitor must be approached very seriously and responsibly.

CRT or cathode ray tube

A CRT monitor is a glass tube filled with vacuum. The front part of the monitor is a phosphor. For the phosphor, complex compositions based on rare earth metals, such as yttrium, erbium, are used. If a in simple terms, then a phosphor is a substance that forms light when charged particles are applied to it. In order for a CRT monitor to display an image, an electron gun is used, it passes a stream of electrons through a metal mask (grid) onto the inner surface of the monitor's glass screen, which is covered with multi-colored phosphor dots.

If we take for example a new CRT-type monitor, then of course it will show very well (if necessary, the image can be corrected). The CRT monitor has one strong point that only expensive LCDs have - it's color reproduction. Like it or not, but CRT is much better than LCD. Only IPS matrices in LCD monitors can match the color reproduction of a CRT.

Conventional CRT monitors use three electron guns, while the old black-and-white monitors used only one.

The human eye can only respond to three primary colors, these are red, blue and green, and their combinations, they create great amount colors or shades. The front part of the monitor is a phosphor, or rather its layer, and it consists of dots - so small that they are almost impossible to see. They literally reproduce the primary colors of RGB.

RGB (Red, Green, Blue) is an additive color model that describes a color synthesis method for color reproduction.

In addition to the cathode ray tube, there is also electronics that processes the incoming signal from the computer's video card. Electronics is engaged in optimizing the displayed image - it amplifies the signal and stabilizes, which is why the picture on the monitor is stable, even if the signal is unstable.

The disadvantage of CRT monitors is that they are harmful to the eyes, and also take a lot of light. And at the same time, over time, they become cloudy, today it is almost impossible to find a CRT monitor that shows like an LCD, and if it is also more than 17 inches, then its “soapiness” will be immediately noticeable.

LCD or LCD monitors

Liquid crystals, on which LCD monitors are based, are characterized by a transition state of matter between solid and liquid, while maintaining the crystalline structure of the molecules and ensuring fluidity. The matrix of such a monitor is indeed liquid in a sense, for example, if you lightly press your finger on a working monitor, you will see how the liquid that is inside shifts. This is a liquid crystal solution. At first, liquid crystals were used in calculator displays, as well as digital clock, then switched to PDAs and computer monitors.

Today, not almost, but completely, CRTs have been replaced by LCD monitors.

LCD is two panels, they are made of very thin and pure glass (substrate), between these panels there is a thin layer of liquid crystals (called pixels), they are involved in the construction of the image. Unlike CRT monitors, LCDs have such a thing as "native" resolution - this is the one on which the monitor is desirable to work. It is this extension that will allow the monitor to display the picture with the highest quality. If you set a different extension, the image will either be stretched (the sharpness deteriorates, there are slight distortions), or vice versa - the extension will be changed, but part of the screen will be filled with black in order to maintain quality.

The contrast of monitors is determined by the ratio of brightness between white (as the brightest) and black (the darkest) color. A good indicator is 120:1. Monitors with a contrast ratio of 300:1 can give an accurate image of halftones.

Comparison of LCD and CRT

LCD monitors are good because they are completely flat, the picture is sharper than a CRT monitor, and the color saturation can also be higher. There are no distortions, as well as the eternal problem of "soap" (cloudy image) - all this is absent from "thin" monitors, which is why they are ahead of the CRT.

Here in this picture Additional Information about the difference between monitors, but it's interesting that the picture is a little muddy, blurry, that's exactly how many CRT monitors now show (since they don't release new ones anymore and they are old):

Therefore, we can conclude that an LCD monitor is better, and CRTs are not just a thing of the past, but if possible, then buy an expensive monitor, they are less harmful to the eyes when working at a computer for a long time.

Here's a note for you. Many 15-inch LCD monitors consume about 20-40 watts in operation (less than 5 watts in standby mode), you can compare this with a 17-inch CRT monitor, which consumes 90 to 120 watts in operation (in standby mode - 15 watts). Can you imagine? I’ll also calculate for you - if the monitor works for about eight hours a day and so the whole working week, then a 17-inch CRT will consume 300 kW per year, this is taking into account the standby mode of an hour or two, while 15 inches LCD - 60 kW (17 inches, I don’t think it will be much more). These are trifles for you, but if there are a hundred, two hundred, three hundred computers in the company, then there is a reason to think about a new type of monitor.

But there is also strengths in CRT monitors, as a rule, they are interesting for the most part to designers - color reproduction. If you work on an LCD for a while and then look at a CRT, you will notice the difference between color reproduction and image volume.

3.5. COMPUTER VIDEO SYSTEM

CRT MONITOR

CRT-based monitors- the most common and old devices for displaying graphic information. The technology used in this type of monitor was developed many years ago and was originally created as a special tool for measuring AC current, i.e. for an oscilloscope.

CRT monitor design

Most monitors in use and produced today are built on cathode ray tubes (CRTs). In English - Cathode Ray Tube (CRT), literally - cathode ray tube. Sometimes CRT stands for Cathode Ray Terminal, which no longer corresponds to the handset itself, but to the device based on it. Electron beam technology was developed by the German scientist Ferdinand Braun in 1897 and was originally created as a special tool for measuring alternating current, that is, for oscilloscope. the tube, or kinescope, is the most important element of the monitor. The kinescope consists of a sealed glass flask, inside of which there is a vacuum. One of the ends of the flask is narrow and long - this is the neck. The other is a wide and rather flat screen. The inner glass surface of the screen is covered with a phosphor (luminophor). Quite complex compositions based on rare earth metals - yttrium, erbium, etc. are used as phosphors for color CRTs. A phosphor is a substance that emits light when bombarded by charged particles. Note that sometimes the phosphor is called phosphorus, but this is not true, since the phosphor used in the CRT coating has nothing to do with phosphorus. Moreover, phosphorus glows only as a result of interaction with atmospheric oxygen during oxidation to P 2 O 5, and the glow does not last very long (by the way, white phosphorus is a strong poison).

To create an image in a CRT monitor, an electron gun is used, from where a stream of electrons comes from under the action of a strong electrostatic field. Through a metal mask or grate, they fall on the inner surface of the glass screen of the monitor, which is covered with multi-colored phosphor dots. The electron flow (beam) can be deflected in the vertical and horizontal planes, which ensures that it consistently hits the entire screen field. The beam is deflected by means of a deflecting system. Rejection systems are divided into saddle-toroidal and saddle. The latter are preferable because they have a reduced level of radiation.

The frequency of transition to a new line is called the horizontal (or horizontal) scanning frequency. The frequency of the transition from the bottom right corner to the top left corner is called the vertical (or vertical) scan frequency. The amplitude of the overvoltage pulses on the horizontal scanning coils increases with the horizontal frequency, so this node is one of the most stressed places in the structure and one of the main sources of interference in a wide frequency range. The power consumed by the horizontal scanning nodes is also one of the major factors to consider when designing monitors. After the deflecting system, the electron flow on its way to the front of the tube passes through the intensity modulator and the accelerating system, which operate on the principle of a potential difference. As a result, the electrons acquire more energy (E=mV 2 /2, where E-energy, m-mass, v-velocity), some of which is spent on the glow of the phosphor.

The electrons hit the phosphor layer, after which the energy of the electrons is converted into light, that is, the flow of electrons causes the dots of the phosphor to glow. These glowing dots of phosphor form the image you see on your monitor. As a rule, a color CRT monitor uses three electron guns, as opposed to a single gun used in monochrome monitors, which are now practically not produced.

It is known that human eyes react to the primary colors: red (Red), green (Green) and blue (Blue) and their combinations, which create an infinite number of colors. The phosphor layer covering the front of the cathode ray tube consists of very small elements (so small that the human eye cannot always distinguish them). These phosphor elements reproduce the primary colors, in fact there are three types of multi-colored particles whose colors correspond to the RGB primary colors (hence the name of the group of phosphor elements - triads).

So, each gun emits an electron beam (or stream, or beam) that affects phosphor elements of different colors (green, red or blue). It is clear that the electron beam intended for the red phosphor elements should not affect the green or blue phosphor. To achieve this effect, a special mask is used, whose structure depends on the type of kinescopes from different manufacturers, providing discreteness ( raster) of the image. CRTs can be divided into two classes - three-beam with a delta-shaped arrangement of electron guns and with a planar arrangement of electron guns. These tubes use slit and shadow masks, although it is more correct to say that they are all shadow masks. At the same time, tubes with a planar arrangement of electron guns are also called kinescopes with self-convergence of beams, since the effect of the Earth's magnetic field on three planar beams is almost the same, and when changing the position of the tube relative to the Earth's field, no additional adjustments are required.

CRT types

Depending on the location of the electron guns and the design of the color separation mask, there are four types of CRTs used in modern monitors:

CRT with shadow mask (Shadow Mask)

Shadow mask CRTs are most common in most monitors manufactured by LG, Samsung, Viewsonic, Hitachi, Belinea, Panasonic, Daewoo, Nokia. Shadow mask is the most common type of mask. It has been used since the invention of the first color kinescopes. The surface of kinescopes with a shadow mask is usually spherical (convex). This is done so that the electron beam in the center of the screen and along the edges has the same thickness.

The shadow mask consists of a metal plate with round holes that cover approximately 25% of the area. There is a mask in front of a glass tube with a phosphor layer. As a rule, most modern shadow masks are made from invar. Invar (Invar) - a magnetic alloy of iron (64%) with nickel (36%). This material has an extremely low coefficient of thermal expansion, so even though the electron beams heat up the mask, it does not adversely affect the color purity of the image. The holes in the metal grid work like a sight (albeit not an accurate one), it is this that ensures that the electron beam hits only the required phosphor elements and only in certain areas. The shadow mask creates a lattice with uniform dots (also called triads), where each such dot consists of three phosphor elements of primary colors - green, red and blue, which glow with different intensities under the influence of beams from electron guns. By changing the current of each of the three electron beams, it is possible to achieve an arbitrary color of an image element formed by a triad of dots.

One of the weak points of shadow mask monitors is their thermal deformation. In the figure below, how part of the rays from the electron beam gun hits the shadow mask, as a result of which heating and subsequent deformation of the shadow mask occur. The resulting displacement of the shadow mask holes leads to the appearance of a variegated screen effect (shifting RGB colors). The material of the shadow mask has a significant impact on the quality of the monitor. The preferred mask material is Invar.

The minimum distance between phosphor elements of the same color in adjacent rows is called the dot pitch (dot pitch) and is an index of image quality. Dot pitch is usually measured in millimeters (mm). The smaller the dot pitch value, the higher the quality of the image displayed on the monitor. The horizontal distance between two adjacent points is equal to the step of the points multiplied by 0.866.

CRT with an aperture grill of vertical lines (Aperture Grill)

There is another type of tube that uses an aperture grille. These tubes became known as the Trinitron and were first introduced to the market by Sony in 1982. The tubes with aperture grille use original technology, where there is three ray guns, three cathodes and three modulators, but there is one common focusing.

Aperture grille is a type of mask used by different manufacturers in their technology to produce kinescopes that go by different names but are essentially the same, such as Sony's Trinitron technology, Mitsubishi's DiamondTron, and ViewSonic's SonicTron. This solution does not include a metal grid with holes, as in the case of the shadow mask, but a grid of vertical lines. Instead of dots with phosphor elements of the three primary colors, the aperture grille contains a series of filaments consisting of phosphor elements arranged in vertical stripes of the three primary colors. This system provides high image contrast and good color saturation, which together provide high quality tube monitors based on this technology. The mask used in Sony (Mitsubishi, ViewSonic) tubes is a thin foil on which thin vertical lines are scratched. It rests on a horizontal (one in 15", two in 17", three or more in 21") wire, the shadow of which is visible on the screen. This wire is used to dampen vibrations and is called damper wire. It is clearly visible, especially with a light background images on the monitor.Some users fundamentally dislike these lines, while others, on the contrary, are satisfied and use them as a horizontal ruler.

The minimum distance between phosphor strips of the same color is called strip pitch ( strip pitch) and is measured in millimeters (see Fig. 10). The smaller the stripe pitch value, the higher the image quality on the monitor. With an aperture grille, only the horizontal size of the dot makes sense. Since the vertical is determined by the focusing of the electron beam and the deflecting system.

CRT with slot mask (Slot Mask )

Slit mask ( slot mask) is widely used by NEC under the name "CromaClear". This solution in practice is a combination of a shadow mask and an aperture grille. In this case, the phosphor elements are located in vertical elliptical cells, and the mask is made of vertical lines. In fact, the vertical stripes are divided into elliptical cells, which contain groups of three phosphor elements in three primary colors.

The slit mask is used, in addition to monitors from NEC (where the cells are elliptical), in Panasonic monitors with a PureFlat tube (formerly called PanaFlat). Note that it is not possible to directly compare the pitch size for tubes of different types: the pitch of the dots (or triads) of a shadow mask tube is measured diagonally, while the pitch of the aperture grille, otherwise known as the horizontal dot pitch, is measured horizontally. Therefore, for the same dot pitch, a tube with a shadow mask has a higher dot density than a tube with an aperture grating. For example, a stripe pitch of 0.25 mm is approximately equivalent to a dot pitch of 0.27 mm. Also in 1997, Hitachi, the largest designer and manufacturer of CRTs, developed EDP, the latest shadow mask technology. In a typical shadow mask, the triads are placed more or less equilaterally, creating triangular groups that are evenly distributed across the inner surface of the tube. Hitachi reduced the horizontal distance between the triad elements, thereby creating triads that are closer in shape to an isosceles triangle. To avoid gaps between the triads, the dots themselves have been elongated, and are more ovals than circles.

Both types of masks - the shadow mask and the aperture grille - have their own advantages and their supporters. For office applications, text editors and spreadsheets, shadow mask tubes are more suitable, providing very high definition and sufficient image contrast. For raster and vector graphics packages traditionally recommended tubes with aperture grating, which are characterized by excellent image brightness and contrast. In addition, the working surface of these kinescopes is a segment of a cylinder with a large horizontal curvature radius (unlike CRTs with a shadow mask, which have a spherical screen surface), which significantly (up to 50%) reduces the intensity of glare on the screen.

Main characteristics of CRT monitors

Monitor screen size is the distance between the lower left and upper right corner of the screen, measured in inches. The size of the screen area visible to the user is usually somewhat smaller, on average 1 ", than the tube size. Manufacturers may indicate two diagonal sizes in the accompanying documentation, while the visible size is usually indicated in brackets or marked " Viewable size", but sometimes only one is indicated size - the size of the diagonal of the tube. Monitors with a diagonal of 15" stand out as a standard for PCs, which approximately corresponds to 36-39 cm of the diagonal of the visible area. For Windows it is desirable to have a monitor of at least 17".

Screen grain size defines the distance between the nearest holes in the color separation mask type used. The distance between the mask holes is measured in millimeters. The smaller the distance between the holes in the shadow mask, and the more holes there are, the better the image quality. All monitors with grain greater than 0.28mm are classified as coarse and cost less. The best monitors have a grain of 0.24mm, reaching 0.2mm on the most expensive models.

Monitor resolution is determined by the number of image elements that it is able to reproduce horizontally and vertically. 19" monitors support resolutions up to 1920*14400 and above.