Cathode ray tube monitors. Projectors and monitors CRT monitors with socket mask

What is a CRT monitor?

CRT (CRT) monitor- a device that is designed to display various information (graphics, video, text, photos). The CRT (Cathode Ray Tube) monitor image is formed thanks to a special electro-ray tube, which is the main component of this device. Typically, such monitors are used to display images from computers, acting as a display.

A brief history of the appearance of CRT monitors

The progenitor of CRT monitors can be considered Ferdinand Braun, who in 1897 developed the fundamental principle of image formation using a cathode ray tube. This German scientist devoted a lot of time to research related to cathode rays.

From the very beginning, the Brown tube (CRT) was used as an oscilloscope to experiment with electrical vibrations. It was a glass tube with an electromagnet located on the outside. Although Brown did not patent his unique invention, it became a powerful impetus for the creation of CRT monitors. The first mass-produced televisions with electro-ray tubes appeared in the 1930s. Moreover, CRT monitors began to be used already in the 1940s. Subsequently, the technology was constantly improved, and the black and white picture was replaced with a high-quality color image.

CRT monitor design

If we consider the characteristics of CRT monitors, then their main link is the electro-ray tube. This is the most important element, which is also called a kinescope. There are deflection and focusing coils that direct the electron beams. It is worth noting the shadow mask and the internal magnetic screen through which the rays pass to display the picture.

Each CRT monitor has a clamp with mounting brackets for reliable protection internal structure. There is also a phosphor coating, which creates the necessary colors. Glass could not be avoided either, because it is what the user constantly sees in front of him.

Operating principle of a CRT monitor

The sealed electro-ray tube is made of glass. There is absolutely no air inside it. The neck of the tube is not only long, but also quite narrow. Its other part is called the screen, and also has a wide shape. The front of the glass tube is coated with phosphor (a mixture of rare metals). An image is created using an electron gun. It is from here that electrons begin their rapid path to the display surface, bypassing the shadow mask. Since the beam must hit the entire screen surface, it begins to deviate in terms of the plane.

Therefore, the movement of the electron beam can be vertical or horizontal. When electrons hit the phosphor layer, their energy is transformed into light. Thanks to this, we see different color shades.

This is how images are formed in CRT monitors. Moreover, the human eye is able to clearly recognize red, green and blue colors. Everything else is a combination of these colors with each other. For this reason, the latest generation of CRT monitors are equipped with three electron guns, each of which emits a specific light.

CRT monitor settings

When users purchase a new display, they often wonder how to configure a CRT monitor as correctly as possible? Of course, you can use professional calibrators. But for this you need to be a real specialist for this equipment to bring the desired effect. Or you can use the services of appropriate specialists who will come to you with a calibrator for high-quality monitor settings.

There is a much cheaper and simpler option in the form of manual image adjustment. Almost every monitor has a corresponding settings menu that can be changed.

You should set the screen resolution from the very beginning. The higher it is, the more detailed the picture will be. Here, a lot also depends on the diagonal of the display. If the monitor is 17-inch, then the optimal resolution will be 1024 by 768 pixels. If it is 19-inch, then 1280 by 960 pixels.
You don't need to try to increase the resolution too much to prevent the image from becoming extremely small.
Screen refresh rate is another important parameter of a CRT monitor. Numerous safety standards set a minimum threshold of 75 Hz. When the frame rate is lower given value, then noticeable flicker will create a strong strain on your eyes. Recommended refresh rates range from 85-100 Hz.
With flexible adjustment of contrast and brightness, you can get an almost perfect picture. It is advisable to do this, because factory setting may not seem the most successful to the user. Moreover, we all have our own ideas about a quality image. Some people will want to make the picture as juicy as possible, while others will prefer calmer shades. In terms of setting the appropriate values, you need to be guided solely by your feelings and perceptions. That is why there are no ideal contrast and brightness parameters. At the same time, I want to make the image brighter on sunny days. But in the dark, it’s better to lower the contrast level so that your eyes don’t get tired of the abundance of colors.
If desired, you can also adjust the image geometry. To do this, you need to use the built-in tools, or download third party program(for example, Nokia Monitor Test). An excellent result is achieved if the test picture fits completely into the screen. It is also possible to adjust the vertical and horizontal lines so that they are as straight as possible.

Advantages and disadvantages of CRT monitors

The main advantages of a CRT monitor:

Natural colors are transmitted as accurately as possible and without distortion.
High-quality picture from any angle.
There is no problem with dead pixels.
High response speed, which will especially appeal to fans of games and movies.
Really deep black color.
Increased contrast and image brightness.
Possibility of using commutation 3D glasses.

The main disadvantages of a CRT monitor:

Significant physical dimensions.
Problem with displaying geometric shapes and their proportions.
Large invisible area in terms of diagonal selection.
Quite harmful radiation.
Increased electricity consumption.

What is dangerous about CRT monitors is their harmful electro-ray radiation. It creates a powerful electromagnetic field that negatively affects health. It is highly not recommended to be behind such a screen, because the harmful field extends back to a distance of one and a half meters. It is also necessary to properly dispose of such monitors so that lead oxide and other harmful substances do not spoil the environment.

Where are CRT monitors used?

CRT monitors are almost always used in conjunction with system unit. Their main task is to display text and graphic information, which comes from the computer device. They are often used at home, and can also be found in offices and offices. Such displays are used in a variety of areas of life. On this moment they are actively being replaced by LCD monitors.

Comparison of CRT and LCD monitors

Unfortunately, the era of CRT monitors is gradually coming to an end. They are being replaced by more advanced and advanced liquid crystal displays, which take up much less space on our desks.

Here's the difference between CRT and LCD monitors:

Energy consumption. LCD screens consume less power than CRT monitors.

If LCD monitors have a stable and safe screen refresh rate, then monitors with electro-ray tubes allow you to select a lower or higher frame rate.

Safety. LCD models win here, as they emit much less harmful radiation.

Image quality. CRT monitors reproduce natural colors more accurately and also boast deep shades of black.

Viewing Angles. CRT screens have better viewing angles. At the same time, some expensive LCD matrices are trying to level out the lag.

One of the most well-known problems with LCD monitors is slow response time. Here the advantage is on the side of CRT displays.

Dimensions. LCD monitors have compact physical dimensions, which cannot be said about similar devices with CRT technology. The difference is especially noticeable in terms of thickness.

Now liquid crystal displays come in a variety of diagonals, reaching up to 37 inches or more. In this regard, CRT options offer more limited solutions up to 21 inches.

Although CRT monitors can be called outdated, they can still please the user with high-quality pictures, fast response and other important advantages.

CRT monitor design

Most of the monitors used and produced today are built on cathode ray tubes (CRT). IN English language- Cathode Ray Tube (CRT), literally - cathode ray tube. Sometimes CRT is deciphered as Cathode Ray Terminal, which no longer corresponds to the tube itself, but to the device based on it. Electron beam technology was developed by 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 bulb, 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 fairly flat screen. The inner glass surface of the screen is coated with phosphor. 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 with charged particles. Note that sometimes the phosphor is called phosphorus, but this is not correct, since the phosphor used in the coating of CRTs has nothing in common with phosphorus. Moreover, phosphorus glows only as a result of interaction with atmospheric oxygen during oxidation to P2O5, and the glow does not last long (by the way, white phosphorus is a strong poison).

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

The deflection system consists of several inductance coils located at the neck of the kinescope. Using an alternating magnetic field, two coils deflect the electron beam in the horizontal plane, and the other two in the vertical plane. A change in the magnetic field occurs under the influence of an alternating current flowing through the coils and changing according to a certain law (this is, as a rule, a sawtooth change in voltage over time), while the coils give the beam the desired direction. Solid lines are the active beam stroke, the dotted line is the reverse one.

The frequency of transition to a new line is called the horizontal (or horizontal) scanning frequency. The frequency of transition from the lower right corner to the upper left is called the vertical (or vertical) frequency. The amplitude of the overvoltage pulses on the horizontal scanning coils increases with the frequency of the lines, so this node turns out to be one of the most stressed parts of the structure and one of the main sources of interference in a wide frequency range. The power consumed by the horizontal scanning units is also one of the serious factors taken into account when designing monitors. After the deflection system, the flow of electrons on the way to the front part of the tube passes through an intensity modulator and an accelerating system, operating on the principle of potential difference. As a result, electrons acquire greater energy (E=mV2/2, where E-energy, m-mass, v-velocity), part 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 phosphor dots to glow. These glowing phosphor dots form the image you see on your monitor. Typically, a color CRT monitor uses three electron guns, as opposed to the single gun used in monochrome monitors, which are rarely produced today.

It is known that human eyes react to the primary colors: red (Red), green (Green) and blue (Blue) and to their combinations that 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 primary colors with different intensities is combined to form an image with the desired color. For example, if you activate red, green and blue phosphor particles, their combination will form white.

To control a cathode ray tube, control electronics are also required, 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 determines 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 action, a special mask is used, whose structure depends on the type of picture tubes from different manufacturers, ensuring discreteness (rasterization) 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 would be more accurate to say that they are all shadow masks. In this case, tubes with a planar arrangement of electron guns are also called picture tubes with self-converging beams, since the effect of the Earth’s magnetic field on three planarly located beams is almost identical and when the position of the tube relative to the Earth’s field changes, no additional adjustments are required.

Types of CRT

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 the 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 picture tubes. The surface of picture tubes with a shadow mask is usually spherical (convex). This is done so that the electron beam in the center of the screen and at the edges has the same thickness.

The shadow mask consists of a metal plate with round holes that occupy approximately 25% of the area. The mask is placed in front of a glass tube with a phosphor layer. As a rule, most modern shadow masks are made from invar. Invar (InVar) is a magnetic alloy of iron (64%) with nickel (36%). This material has an extremely low coefficient of thermal expansion, so although the electron beams heat the mask, it does not negatively affect the color purity of the image. The holes in the metal mesh act as a sight (albeit not an accurate one), which ensures that the electron beam hits only the required phosphor elements and only in certain areas. The shadow mask creates a lattice with uniform points (also called triads), where each such point consists of three phosphor elements of the 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, you can achieve an arbitrary color of the image element formed by a triad of dots.

One of the weak points of monitors with a shadow mask is its 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 occurs. The resulting displacement of the holes of the shadow mask leads to the effect of screen variegation (shift of 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 a shadow mask are well known: firstly, it 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 luminous efficiency, and this in turn worsens the monochrome of the glow, reducing the color rendering range , and secondly, it is quite difficult to ensure an exact coincidence of three rays that do not lie in the same plane when they are deflected at large angles. 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 reproduced on the monitor. The horizontal distance between two adjacent points is equal to the point pitch multiplied by 0.866.

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

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

An aperture grille is a type of mask used by different manufacturers in their technologies to produce picture tubes 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 is the case with the shadow mask, but has a grid made of vertical lines. Instead of dots with phosphor elements of three primary colors, the aperture grille contains a series of threads consisting of phosphor elements arranged in vertical stripes of three primary colors. This system provides high image contrast and good color saturation, which together ensure high quality tube monitors based on this technology. The mask used in Sony (Mitsubishi, ViewSonic) handsets is a thin foil on which thin vertical lines are scratched. It is held on a horizontal wire (one in 15", two in 17", three or more in 21"), 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 do not like these lines, while others, on the contrary, are happy and use them as a horizontal ruler.

The minimum distance between phosphor strips of the same color is called 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 array, only the horizontal size of the dot makes sense. Since the vertical is determined by the focusing of the electron beam and the deflection system.

CRT with 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 that contain groups of three phosphor elements of three primary colors.

The slot 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 you cannot directly compare step sizes for tubes different types: The pitch of the dots (or triads) of a shadow mask tube is measured diagonally, while the pitch of the aperture array, otherwise known as the horizontal dot pitch, is measured horizontally. Therefore, with the same pitch of points, a tube with a shadow mask has a higher density of points than a tube with an aperture grid. 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 - latest technology shadow mask. In a typical shadow mask, the triads are spaced more or less equilaterally, creating triangular groups that are distributed evenly across the inner surface of the tube. Hitachi has reduced the horizontal distance between the elements of the triad, thereby creating triads that are closer in shape to an isosceles triangle. To avoid gaps between the triads, the dots themselves have been elongated, appearing more like ovals than circles.

Both types of masks - the shadow mask and the aperture grille - have their advantages and their supporters. For office applications, text editors and electronic tables, picture tubes with a shadow mask are more suitable, providing very high image clarity and sufficient contrast. For working with raster and vector graphics packages, tubes with an aperture grille are traditionally recommended, which are characterized by excellent image brightness and contrast. In addition, the working surface of these picture tubes is a cylinder segment with a large horizontal radius of curvature (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 diagonal

Monitor screen diagonal is the distance between the lower left and upper right corners of the screen, measured in inches. The size of the screen area visible to the user is usually slightly smaller, on average 1" than the size of the handset. Manufacturers may indicate two diagonal sizes in the accompanying documentation, with the visible size 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" have emerged as the standard for PCs, which approximately corresponds to 36-39 cm diagonal of the visible area. To work in Windows, it is advisable to have a monitor of at least 17" in size. For professional work with desktop publishing systems (DPS) and computer-aided design (CAD) systems, it is better to use a 20" or 21." monitor.

Screen grain size

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

Monitor resolution

The resolution of a monitor is determined by the number of image elements it can reproduce horizontally and vertically. Monitors with a screen diagonal of 19" support resolutions up to 1920*14400 and higher.

Monitor power consumption

Screen coverings

Screen coatings are necessary to give it anti-glare and antistatic properties. The anti-reflective coating allows you to observe 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 gives the surface roughness. However, the graphics on such a screen look blurry and the image quality is low. The most popular method is to apply a quartz coating that scatters incident light; This method is implemented by Hitachi and Samsung. Antistatic coating is necessary to prevent dust from sticking 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 manufacturing technology, protective filters are divided into 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 placed on the monitor.

Mesh filters

Mesh filters provide virtually no protection from electromagnetic radiation and static electricity and somewhat degrade image contrast. However, these filters do a good job of reducing glare from external lighting, 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 image contrast, almost completely absorb ultraviolet radiation and reduce the level of x-ray radiation. Polarizing film filters, such as those from Polaroid, can 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 the intensity of ultraviolet radiation and increase image contrast. Glass filters category " full protection» 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.

Advantages and disadvantages

Symbols: (+) advantage, (~) acceptable, (-) disadvantage
	LCD monitors	CRT monitors
Brightness	(+) from 170 to 250 cd/m2	(~) from 80 to 120 cd/m2
Contrast	(~) 200:1 to 400:1	(+) from 350:1 to 700:1
Viewing angle (by contrast)	(~) 110 to 170 degrees	(+) over 150 degrees
Viewing angle (by color)	(-) from 50 to 125 degrees	(~) over 120 degrees
Permission	(-) Single resolution with fixed pixel size. Optimally can only be used in this resolution; Depending on the supported expansion or compression functions, higher or lower resolutions can be used, but they are not optimal.	(+) Various resolutions are supported. With all supported resolutions, the monitor can be used optimally. The limitation is imposed only by the acceptability of the regeneration frequency.
Vertical frequency	(+) Optimal frequency 60 Hz, which is enough to avoid flickering	(~) Only at frequencies above 75 Hz there is no clearly noticeable flicker
Color registration errors	(+) no	(~) 0.0079 to 0.0118 inches (0.20 - 0.30 mm)
Focusing	(+) very good	(~) from satisfactory to very good>
Geometric/linear distortion	(+) no	(~) possible
Broken pixels	(-) up to 8	(+) no
Input signal	(+) analog or digital	(~) analog only
Scaling at different resolutions	(-) is absent or interpolation methods that do not require large overheads are used	(+) very good
Color Accuracy	(~) True Color is supported and the required color is simulated Colorful temperature	(+) True Color is supported and 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	(~) not noticeable above 85 Hz
Inertia time	(-) from 20 to 30 ms.	(+) negligible
Image formation	(+) 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 superior focus, clarity and definition. The image is more complete 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 pitch or line pitch and on the quality of the CRT
Energy consumption and emissions	(+) There are practically no dangerous electromagnetic radiations. Power consumption is approximately 70% lower than standard CRT monitors (25 to 40 W).	(-) Electromagnetic radiation is always present, but the level depends on whether the CRT meets any safety standard. Energy consumption in operating condition is 60 - 150 W.
Dimensions/weight	(+) flat design, light weight	(-) heavy design, 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

CRT monitor device

The image is created by a beam of electrons incident on the inner surface of a cathode ray tube (CRT or CRT - Cathode Ray Tube), coated with a layer of phosphor (a compound based on zinc and cadmium sulfides). The electron beam is emitted by the electron gun and is controlled by the electromagnetic field created by the monitor's deflection system.
To create a color image, three electron guns are used and three types of phosphor are applied to the surface of the CRT to create red, green and blue (RGB), which are then mixed. Mixed with equal intensity, these colors give us the color white.
A special device is placed in front of the phosphor<маска> (<решетка>), narrowing the beam and focusing it on one of the three sections of the phosphor. The monitor screen is a matrix consisting of triad sockets of a certain structure and shape, depending on the specific manufacturing technology:

three-point shadow mask (Dot-trio shadow-mask CRT)
slotted aperture grille (Aperture-grille CRT)
nest mask (Slot-mask CRT)

CRT with shadow mask
For this type of CRT, the mask is a metal (usually Invar) grid with round holes opposite each triad of phosphor elements. The criterion for image quality (sharpness) is the so-called grain pitch or dot pitch, which characterizes the distance in millimeters between two phosphor elements (dots) of the same color. The shorter this distance, the higher quality image the monitor can reproduce. A CRT screen with a shadow mask is usually part of a sphere with a fairly large diameter, which can be noticeable by the convexity of the screen of monitors with this type of CRT (or may not be noticeable if the radius of the sphere is very large). The disadvantages of a CRT with a shadow mask include the fact that a large number of electrons (about 70%) are retained by the mask and do not reach the phosphor elements. This can cause the mask to heat up and become thermally distorted (which can cause colors on the screen to distort). In addition, in CRTs of this type it is necessary to use a phosphor with higher light output, which leads to some deterioration in color rendition. If we talk about the advantages of CRTs with a shadow mask, then we should note the good clarity of the resulting image and their relative cheapness.

CRT with aperture grille
In such a CRT there are no pinholes in the mask (usually made of foil). Instead, thin vertical holes are made in it from the top edge of the mask to the bottom. Thus, it is a lattice of vertical lines. Due to the fact that the mask is made in this way, it is very sensitive to any kind of vibration (which, for example, can occur when lightly tapping on the monitor screen. It is additionally held in place by thin horizontal wires. In monitors with a size of 15 inches, such a wire is one in 17 and 19 two , and in large ones three or more. On all such models, shadows from these wires are noticeable, especially on a bright screen. At first they can be somewhat annoying, but over time you will get used to it. Probably this can be attributed to the main disadvantages of CRTs with an aperture grille. The screen of such CRTs is is part of a large diameter cylinder. As a result, it is completely flat vertically and slightly convex horizontally. An analogue of the dot pitch (as for a CRT with a shadow mask) here is the strip pitch - the minimum distance between two phosphor strips of the same color (measured in millimeters). The advantage of such CRTs compared to the previous one is more saturated colors and a more contrasting image, as well as a flatter screen, which quite significantly reduces the amount of glare on it. The disadvantages include slightly less clarity of the text on the screen.

CRT with slit mask
The slit mask CRT is a compromise between the two technologies already described. Here, the holes in the mask corresponding to one phosphor triad are made in the form of elongated vertical slits of short length. Adjacent vertical rows of such slits are slightly offset relative to each other. It is believed that CRTs with this type of mask have a combination of all the advantages inherent in it. In practice, the difference between the image on a CRT with a slit or aperture grating is little noticeable. CRTs with a slit mask are usually called Flatron, DynaFlat, etc.

Technical specifications
Technical characteristics of monitors in price lists and on packaging are usually expressed in one line like “Samsung 550B / 15” / 0.28 / 800x600 / 85Hz”, which is deciphered as follows:

15" is the screen diagonal size in inches (38.1 cm). In general, the larger the monitor, the more convenient it is to use. For example, with the same resolution, a 17-inch monitor reproduces the image in the same way as a 15-inch one, but the picture itself turns out to be physically larger and the details stand out more clearly. However, in reality, part of the CRT screen at the edges is hidden by the housing or lacks phosphor. Therefore, take an interest in such a parameter as the visible diagonal. For 17-inch monitors from different manufacturers, this parameter can be from 15.9" and higher.
0.28 - dot size. This is one of the main indicators of monitor quality. In fact, this parameter characterizes the size of each pixel in the image: the smaller this size, the closer the pixels are to each other and the more detailed the image appears. More expensive monitors have a dot size of 0.25 or 0.22. Keep in mind that dot sizes larger than 0.28 lose a significant amount of detail and create grain on the screen.
800 x 600 - recommended or maximum possible resolution (in the example - recommended). This means that the screen has 800 pixels per line horizontally and 600 lines vertically. With a higher resolution (1024x768) on the screen, you can display more different images, data at once, or a Web page without scrolling. This parameter also depends on the properties of the video card: some video cards do not support high resolutions.
85 Hz - maximum screen refresh rate (regeneration frequency, vertical frequency, FV). This means that each pixel on the screen changes 85 times per second. The more times the screen is crossed out every second, the more contrast and stability the image becomes. If you intend to carry out long hours in front of the monitor, your eyes will be less tired if the monitor has a higher refresh rate - at least 75 Hz. At higher resolutions, the screen refresh rate may decrease, so you need to keep these settings balanced. The refresh rate also depends on the properties of the video card: some video cards support high resolutions only at a low refresh rate. A monitor screen with a matte (anti-glare) finish can be very useful in a brightly lit office. The same problem can be solved by a special matte panel attached to the monitor.
TCO 99 is a safety standard. The standards are set by the Swedish Technical Accreditation Authority (MPR) or European standard TSO. The essence of TCO recommendations is to determine the minimum acceptable parameters of monitors, for example, supported resolutions, phosphor glow intensity, brightness reserve, power consumption, noise, etc. Compliance of the monitor with the TCO standard is confirmed by a sticker.

Main advantages

Low price. CRT monitor 1.5-4 times cheaper LCD display similar class.
Longer service life. MTBF CRT monitor several times higher than that of LCD display. Actual service life LCD monitor does not exceed four years, while CRT devices have to be replaced due to moral rather than physical obsolescence. The problem is further aggravated by the fact that the backlights of a number of models LCD displays cannot be replaced, and they are the ones that most often fail. Moreover, the image quality LCD displays Over time it degrades, in particular, a foreign tint appears. CRT screens do not have the problem of “dead pixels”, a small number of which is not considered defective. In addition, LCD matrices are very sensitive to static electricity, shocks and shocks. Plus, light weight and small dimensions LCD displays cause additional risks such as the likelihood of falling from the table and theft.
Fast response time, while LCD displays There is a significant inertia of the image. So if the task is to create animations for the Web or presentations, then LCD display it won't be far best choice.
High contrast. On LCD displays Only in the latest models have things started to improve, and in mass-produced models one can only dream of pure black.
No restrictions on viewing angle, while LCD displays they exist, and they are very significant.
Lack of image discreteness. The peculiarities of image formation on a CRT are such that the elements are blurred and therefore practically invisible to the naked eye. And on LCD displays the image has a distinct discreteness, especially at non-standard resolutions.
No problems associated with image scaling. On CRT monitor you can change the screen resolution within a fairly wide range, while LCD display Comfortable work is possible only with one resolution.
Good color rendition. On mass LCD displays With TN+Film and MVA/PVA matrices this is far from all right, and they are still not recommended for use with color printing and video.

Flaws

Radiation. Electromagnetic and soft x-ray radiation. Although monitors are considered one of the most secure office devices, in fact the radiation from them is through the roof. Let the monitor screen be protected. And what's behind? And the fact is that the main radiation from the monitor comes from its back. So if there are several computers in the office, it is better not to sit around all day back cover neighbor's CRT monitor, but rearrange the furniture so that it at least rests against the wall. But the screen, although protected, still emits a fair amount of radiation. I myself have sat behind so many models of monitors - from monochrome ones that came with machines produced in 1982 (on Intel 8086) - to modern ones CRT monitors highest price category. For all of them, the sensations were approximately the same - after some time (the better the monitor, the longer the time, naturally) a certain discomfort was felt. Even just being near a working monitor cannot avoid this. I also need to say about<пользе>protective screens. Yes, they seem to protect the user, but they usually just<отодвигают>electromagnetic field. It turns out that just before the screen it is reduced, and about a meter and a half later, it is seriously increased.
Flicker. Theoretically, it is believed that after 75 hertz the human eye does not see flicker. But this, believe me, is not entirely true. Eye and more high frequency The screen update gets tired of this, albeit imperceptible, flickering. Again, sometimes you go into an office and there is a computer there. It seems to be new, the monitor is normal, but when you look at it, it immediately looks bad - the refresh rate is 65 hertz. And those who have been working on it for several months do not notice anything.
A non-obvious factor is dust. The point here is this. Dust settles on the monitor screen, like everything else. The screen, even if well protected, becomes electrified and electrifies the dust that has settled on it. From the physics course we know that like charges repel. And a stream of dust begins to slowly fly towards the unsuspecting user. As a result, the eyes become irritated. Sometimes very much. Especially if a person suffers from myopia and tries to take off his glasses to take a closer look at the image.
Phosphor burnout
High power consumption

DISPLAY DEVICES

Monitors

Information display devices include primarily monitors, as well as devices aimed at solving multimedia or presentation problems: devices for forming three-dimensional (stereoscopic) images and projectors.

The monitor is the most important device display of computer information. The types of modern monitors are very diverse. Based on the principle of operation, all PC monitors can be divided into two large groups:

· based on a cathode ray tube (CRT), called a kinescope;

· flat panel, made mainly on the basis of liquid crystals.

CRT based monitors

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

The design of a CRT monitor is a glass tube with a vacuum inside. On the front side, the inside of the glass tube is coated with phosphor. 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 with charged particles. To create an image, a CRT monitor uses an electron gun that emits a stream of electrons through a metal mask or grid onto the inside surface of the monitor's glass screen, which is covered with multi-colored phosphor dots. The electrons hit the phosphor layer, after which the energy of the electrons is converted into light, i.e., the flow of electrons causes the phosphor dots to glow. These luminous phosphor dots form the image on the monitor. Typically, a color CRT monitor uses three electron guns, as opposed to the single gun used in monochrome monitors.

Along the path of the electron beam there are usually additional electrodes: a modulator that regulates the intensity of the electron beam and the associated image brightness; a focusing electrode that determines the size of the light spot; deflection system coils placed on the base of the CRT, which change the direction of the beam. Any text or graphic image on a monitor screen consists of many discrete phosphor dots called pixels and representing the minimum element of the raster image.

The raster is formed in the monitor using special signals supplied to the deflection system. Under the influence of these signals, the beam is scanned across the surface of the screen along a zigzag path from the upper left corner to the lower right, as shown in Fig. 4.1. The horizontal beam travel is carried out by a horizontal (horizontal) scanning signal, and vertically - by a vertical (vertical) scanning signal. Translation of the beam from the extreme right point of the line to the extreme left point of the next line (reverse horizontal beam travel) and from the extreme right position last line screen to the extreme left position of the first line (reverse beam travel vertically) is carried out using special reverse signals. Monitors of this type are called raster. In this case, the electron beam periodically scans the screen, forming closely spaced scan lines on it. As the beam moves along the lines, the video signal supplied to the modulator changes the brightness of the light spot and forms an image visible on the screen. The resolution of a monitor is determined by the number of image elements it can reproduce horizontally and vertically, for example, 640x480 or 1024 x 768 pixels.

Unlike a TV, where the video signal that controls the brightness of the electron beam is analog, PC monitors use both analog and digital video signals. In this regard, PC monitors are usually divided into analog And digital. The first PC information display devices were digital monitors.

IN digital monitors control is carried out by binary signals that have only two values: logical 1 and logical 0 (“yes” and “no”). The logical one level corresponds to a voltage of about 5 V, the logical zero level - no more than 0.5 V. Since the same levels “1” and “0” are used in the widespread standard series of microcircuits based on transistor-transistor logic (TTL- Transistor Transistor Logic- transistor-transistor logic), digital monitors are called TTL monitors.

The first TTL monitors were monochrome, later color ones appeared. In monochrome digital monitors, the dots on the screen can only be light or dark, varying in brightness. A monochrome monitor's cathode ray tube has only one electron gun; It is smaller than color CRTs, making monochrome monitors smaller and lighter than others. In addition, a monochrome monitor operates with a lower anode voltage than a color monitor (15 kV versus 21 - 25 kV), so its power consumption is significantly lower (30 W instead of 80 - 90 W for color monitors).

In a kinescope color digital monitor contains three electron guns: for red (Red), green (Green) and blue (Blue) colors with separate control, which is why it is called an RGB monitor.

Digital RGB monitors also support monochrome operation with up to 16 shades of gray.

Analog monitors, just like digital ones, they come in color and monochrome, while a color monitor can operate in monochrome mode.

The main reason for switching to analog video is the limited color palette of a digital monitor. The analog video signal, which regulates the intensity of the electron beam, can take any value in the range from 0 to 0.7 V. Since there are an infinite number of these values, the palette of the analog monitor is unlimited. However, the video adapter can only provide a finite number of gradations of the video signal level, which ultimately limits the palette of the entire video system as a whole.

For understanding the principle of forming a raster for color monitors the mechanism of color vision should be introduced. Light is electromagnetic vibrations in a certain range of wavelengths. The human eye is capable of distinguishing colors corresponding to different regions of the visible radiation spectrum, which occupies only a small part of the total spectrum of electromagnetic oscillations in the wavelength range from 0.4 to 0.75 microns.

The total radiation of wavelengths of the entire visible range is perceived by the eye as white light. The human eye has three types of receptors responsible for the perception of color and differing in their sensitivity to electromagnetic vibrations of different wavelengths. Some of them react to violet-blue, others to green, and others to orange-red. If light does not reach the receptors, the human eye perceives black color. If all receptors are illuminated equally, a person sees gray or white. When an object is illuminated, some of the light is reflected from it, and some is absorbed. Color density is determined by the amount of light absorbed by an object in a given spectral range. The denser the color layer, the less light is reflected and, as a result, the darker the color shade (tone).

The physiological features of color vision were studied by M. V. Lomonosov. The theory of color vision he developed was based on the experimentally established fact that all colors can be obtained by adding three light streams with high saturation, for example, red, green and blue, called basic or primary.

Typically, light radiation excites all receptors in the human eye at the same time. The human visual apparatus analyzes light, determining the relative content of various radiations in it, and then they are synthesized into a single color in the brain.

Thanks to the remarkable property of the eye - the three-component nature of color perception - a person can distinguish any of the color shades: there is enough information only about the quantitative ratio of the intensities of the three primary colors, so there is no need for direct transmission of all colors. Thus, thanks to the physiological characteristics of color vision, the amount of information about color is significantly reduced and many technological solutions related to the registration and processing of color images are simplified.

Another important property of color vision is spatial color averaging, which means that if there are closely spaced colored details in a color image, then long distance the colors of individual parts are indistinguishable. All closely spaced colored parts will appear to be painted the same color. Thanks to this property of vision, the color of one image element is formed in the monitor’s cathode ray tube from three colors of adjacent phosphor grains.

The indicated properties of color vision were used in developing the operating principle of a CRT color monitor. The cathode ray tube of a color monitor contains three electron guns with independent control circuits, and a phosphor of three primary colors is applied to the inner surface of the screen: red, blue and green.

Rice. 4.2. Scheme of color formation on the monitor screen

In Fig. Figure 4.2 shows a diagram of the formation of colors on the monitor screen. The electron beam from each gun excites the phosphor dots, and they begin to glow. The dots glow differently and form a mosaic image with each element being extremely small in size. The glow intensity of each point depends on the control signal of the electron gun. In the human eye, the dots with the three primary colors intersect and overlap each other. By changing the ratio of the intensities of the points of the three primary colors, the desired shade is obtained on the monitor screen. In order for each gun to direct the flow of electrons only to phosphor spots of the corresponding color, each color kinescope has a special color separation mask.

Depending on the location of the electron guns and the design of the color separation mask (Fig. 4.3), there are four types of CRTs used in modern monitors:

· CRT with shadow mask (Shadow Mask)(see Fig. 4.3, A) most common in most monitors manufactured by LG, Samsung, Viewsonic, Hitachi, Belinea, Panasonic, Daewoo, Nokia;

· Enhanced Shadow Mask CRT (EDP)- Enhanced Dot Pitch)(see Fig. 4.3, 6);

· CRT with slit mask (Slot Mask)(see Fig. 4.3, V), in which the phosphor elements are located in vertical cells, and the mask is made of vertical lines. The vertical stripes are divided into cells containing groups of three phosphor elements of three primary colors. This type of mask is used by NEC and Panasonic;

· CRT with an aperture grid of vertical lines (Aperture Grill) (see Fig. 4.3, d). Instead of dots with phosphor elements of three primary colors, the aperture grille contains a series of threads consisting of phosphor elements arranged in the form of vertical stripes of three primary colors. Sony and Mitsubishi tubes are produced using this technology.

Structurally, the shadow mask is a metal plate made of a special material, invar, with a system of holes corresponding to the phosphor points applied to the inner surface of the kinescope. Temperature stabilization of the shape of the shadow mask when bombarded by an electron beam is ensured by the small value of the linear expansion coefficient of Invar. The aperture grille is formed by a system of slits that perform the same function as the holes in the shadow mask.

Both types of tubes (shadow mask and aperture grille) have their own advantages and applications. Tubes with a shadow mask produce a more accurate and detailed image because the light passes through the holes in the mask with sharp edges. Therefore, monitors with such CRTs are recommended for intensive and long-term work with texts and small graphic elements. Tubes with an aperture grille have a more openwork mask, they obscure the screen less and allow you to get a brighter, contrasting image in rich colors. Monitors with these tubes are well suited for desktop publishing and other applications that require color images.

The minimum distance between phosphor elements of the same color in shadow masks is called Dot Pitch(dot pitch) and is an index of image quality. Dot pitch is usually measured in millimeters. The smaller the dot pitch value, the higher the quality of the image reproduced on the monitor. The average distance between phosphor dots is called grain. For different monitor models, this parameter has a value from 0.2 to 0.28 mm. In an aperture-grid CRT, the average distance between the fringes is called Strip Pitch(stripe pitch) and is measured in millimeters. The smaller the stripe pitch, the higher the image quality on the monitor. The pitch size of different types of tubes cannot be compared: the pitch of the dots (or triads) of a tube with a shadow mask is measured diagonally, while the pitch of the aperture array, otherwise known as the horizontal pitch of the dots, is measured horizontally. Therefore, with the same pitch of points, a tube with a shadow mask has a higher density of points than a tube with an aperture grid. For example: 0.25 mm dot pitch is approximately equivalent to 0.27 mm strip pitch.

In addition to the cathode ray tube, the monitor contains control electronics that process the signal coming directly from the PC video card. These electronics must optimize signal amplification and control the operation of the electron guns.

The image displayed on the monitor screen looks stable, although in fact it is not. The image on the screen is reproduced as a result of a process during which the glow of the phosphor elements is initiated by an electron beam passing sequentially along the lines. This process occurs with high speed, so the screen appears to be lit all the time. The image is stored in the retina for about 1/20 s. This means that if the electron beam moves across the screen slowly, the eye will perceive it as a single moving bright point, but when the beam begins to move at high speed, tracing a line on the screen 20 times per second, the eye will see a uniform line on the screen. If you ensure that the beam sequentially scans the screen along horizontal lines from top to bottom in a time of less than 1/25 s, the eye will perceive a uniformly illuminated screen with a slight flicker. The movement of the beam itself occurs so quickly that the eye is unable to notice it. It is believed that flicker becomes almost unnoticeable at a frame repetition rate (passes of the beam through all image elements) of approximately 75 times per second.

The illuminated pixels on the screen must remain illuminated for as long as it takes for the electron beam to scan the entire screen and return again to activate that pixel when drawing the next frame. Consequently, the minimum persistence time must be no less than the period of changing image frames, i.e. 20 ms.

CRT monitors have the following Main characteristics.

Monitor screen diagonal- the distance between the bottom left and top right corner of the screen, measured in inches. The size of the screen area visible to the user is usually slightly smaller, on average 1" than the size of the handset. Manufacturers may indicate two diagonal sizes in the accompanying documentation, with the visible size 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" have emerged as the standard for PCs, which approximately corresponds to 36 - 39 cm diagonal of the visible area. To work in Windows, it is advisable to have a monitor of at least 17" in size. For professional work with desktop publishing systems (DPS) and computer-aided design (CAD) systems, it is better to use a 20" or 21" monitor.

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

Resolution A monitor is determined by the number of image elements it can reproduce horizontally and vertically. Monitors with a screen diagonal of 19" support resolutions up to 1920 x 14400 and higher.

Type of cathode ray tube should be taken into account when choosing a monitor. The most preferred types of picture tubes are Black Trinitron, Black Matrix or Black Planar. These types of monitors have a special phosphor coating.

Monitor power consumption indicated in its technical specifications. For 14" monitors, power consumption should not exceed 60 W.

Screen coverings necessary to give it anti-reflective and antistatic properties. The anti-reflective coating allows you to observe 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 gives the surface roughness. However, the graphics on such a screen look blurry and the image quality is low. The most popular method is to apply a quartz coating that scatters incident light; This method is implemented by Hitachi and Samsung. Antistatic coating is necessary to prevent dust from sticking to the screen due to the accumulation of static electricity.

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.

Mesh filters They practically do not protect against electromagnetic radiation and static electricity and somewhat worsen the image contrast. However, these filters do a good job of reducing glare from external lighting, which is important when working with a computer for a long time.

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

Glass filters are produced in several modifications. Simple glass filters remove static charge, attenuate low-frequency electromagnetic fields, reduce the intensity of ultraviolet radiation and increase image contrast. Glass filters in the “full protection” category have the greatest combination of protective properties: they produce virtually no glare, increase image contrast by one and a half to two times, eliminate electrostatic fields and ultraviolet radiation, and significantly reduce low-frequency magnetic (less than 1000 Hz) and X-ray radiation. These filters are made of special glass.

Monitor safety for human is regulated by TCO standards: TCO 92, TCO 95, TCO 99, proposed by the Swedish Trade Union Confederation. TCO 92, released in 1992, determines the parameters of electromagnetic radiation, provides a certain guarantee of fire safety, ensures electrical safety and determines energy saving parameters. In 1995, the standard was significantly expanded (TSO 95), including requirements for the ergonomics of monitors. In TCO 99, the requirements for monitors were further tightened. In particular, the requirements for radiation, ergonomics, energy saving, and fire safety have become stricter. There are also environmental requirements that limit the presence of various hazardous substances and elements, such as heavy metals, in the monitor parts.

Monitor life largely depends on the temperature of its heating during operation. If your monitor gets very hot, you can expect its lifespan to be short. The monitor, the case of which has a large number of ventilation holes, is correspondingly well cooled. Good cooling prevents its rapid failure.

3.5. COMPUTER VIDEO SYSTEM

CRT MONITOR

CRT based monitors– the most common and oldest 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 alternating current, i.e. for an oscilloscope.

CRT monitor design

Most of the monitors used and produced today are built on cathode ray tubes (CRT). In English - Cathode Ray Tube (CRT), literally - cathode ray tube. Sometimes CRT is deciphered as Cathode Ray Terminal, which no longer corresponds to the tube 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 instrument for measuring alternating current, that is, for oscilloscope. Electron beam The tube, or kinescope, is the most important element of the monitor. The kinescope consists of a sealed glass bulb, 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 fairly flat screen. The inner glass surface of the screen is coated 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 with charged particles. Note that sometimes the phosphor is called phosphorus, but this is not correct, since the phosphor used in the coating of CRTs has nothing in common 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 long (by the way, white phosphorus is a strong poison).

To create an image, a CRT monitor uses an electron gun, from which a stream of electrons is emitted under the influence of a strong electrostatic field. Through a metal mask or grille they fall onto the inner surface of the glass monitor screen, which is covered with multi-colored phosphor dots. The flow of electrons (beam) can be deflected in the vertical and horizontal planes, which ensures that it consistently reaches the entire field of the screen. The beam is deflected by means of a deflection system. Deflection systems are divided into saddle toroidal and saddle-shaped. 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 transition from the lower right corner to the upper left is called the vertical (or vertical) frequency. The amplitude of the overvoltage pulses on the horizontal scanning coils increases with the frequency of the lines, so this node turns out to be one of the most stressed parts of the structure and one of the main sources of interference in a wide frequency range. The power consumed by the horizontal scanning units is also one of the serious factors taken into account when designing monitors. After the deflection system, the flow of electrons on the way to the front part of the tube passes through an intensity modulator and an accelerating system, operating on the principle of potential difference. As a result, electrons acquire greater energy (E = mV 2 /2, where E is energy, m is mass, v is velocity), part 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 phosphor dots to glow. These glowing phosphor dots form the image you see on your monitor. Typically, a color CRT monitor uses three electron guns, in contrast to one 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 that 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 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).

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 action, a special mask is used, whose structure depends on the type of picture tubes from different manufacturers, ensuring discreteness (rasterization) 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 would be more accurate to say that they are all shadow masks. At the same time, tubes with a planar arrangement of electron guns are also called picture tubes with self-converging beams, since the effect of the Earth’s magnetic field on three planarly arranged beams is almost the same and when the position of the tube changes relative to the Earth’s field, no additional adjustments are required.

Types of CRT

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 shadow mask are the 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 picture tubes. The surface of picture tubes with a shadow mask is usually spherical (convex). This is done so that the electron beam in the center of the screen and at the edges has the same thickness.

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

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

An aperture grille is a type of mask used by different manufacturers in their technologies to produce picture tubes 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 is the case with the shadow mask, but has a grid of vertical lines. Instead of dots with phosphor elements of three primary colors, the aperture grille contains a series of threads consisting of phosphor elements arranged in vertical stripes of three primary colors. This system provides high image contrast and good color saturation, which together ensure high quality tube monitors based on this technology. The mask used in Sony tubes (Mitsubishi, ViewSonic) is a thin foil on which thin vertical lines are scratched. It is held on a horizontal wire (one in 15", two in 17", three or more in 21"), 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 do not like these lines, while others, on the contrary, are happy and use them as a horizontal ruler.

CRT with slit mask (Slot Mask)

The slot 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 the pitch size of different types of tubes cannot be directly compared: the dot (or triad) pitch of a shadow mask tube is measured diagonally, while the aperture array pitch, otherwise known as the horizontal dot pitch, is measured horizontally. Therefore, with the same pitch of points, a tube with a shadow mask has a higher density of points than a tube with an aperture grid. 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 spaced more or less equilaterally, creating triangular groups that are distributed evenly across the inner surface of the tube. Hitachi has reduced the horizontal distance between the elements of the triad, thereby creating triads that are closer in shape to an isosceles triangle. To avoid gaps between the triads, the dots themselves have been elongated, appearing more like ovals than circles.

Both types of masks - the shadow mask and the aperture grille - have their advantages and their supporters. For office applications, word processors and spreadsheets, picture tubes with a shadow mask are more suitable, providing very high image clarity and sufficient contrast. For working with raster and vector graphics packages, tubes with an aperture grille are traditionally recommended, which are characterized by excellent image brightness and contrast. In addition, the working surface of these picture tubes is a cylinder segment with a large horizontal radius of curvature (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 diagonal– the distance between the lower left and upper right corners of the screen, measured in inches. The size of the screen area visible to the user is usually slightly smaller, on average 1" than the size of the handset. Manufacturers may indicate two diagonal sizes in the accompanying documentation, with the visible size 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" have emerged as the standard for PCs, which approximately corresponds to 36-39 cm diagonal of the visible area. To work in Windows, it is advisable to have a monitor of at least 17" in size. For professional work with desktop publishing systems (DPS) and computer-aided design (CAD) systems, it is better to use a 20" or 21." monitor.

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

Monitor resolution determined by the number of image elements that it is capable of reproducing horizontally and vertically. Monitors with a screen diagonal of 19" support resolutions up to 1920 * 14400 and higher.

Monitor power consumption

Screen coverings

Screen coatings are necessary to give it anti-glare and antistatic properties. The anti-reflective coating allows you to observe 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 gives the surface roughness. However, the graphics on such a screen look blurry and the image quality is low. The most popular method is to apply a quartz coating that scatters incident light; this method is implemented by Hitachi and Samsung. Antistatic coating is necessary to prevent dust from sticking to the screen due to the accumulation of static electricity.

Protective screen (filter)

A protective screen (filter) must 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 .

Mesh filters They practically do not protect against electromagnetic radiation and static electricity and somewhat worsen the image contrast. However, these filters do a good job of reducing glare from external lighting, which is important when working with a computer for a long time.

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

Glass filters are produced in several modifications. Simple glass filters remove static charge, attenuate low-frequency electromagnetic fields, reduce the intensity of ultraviolet radiation and increase image contrast. Glass filters in the “full protection” category have the greatest combination of protective properties: they produce virtually no glare, increase image contrast by one and a half to two times, eliminate electrostatic fields and ultraviolet radiation, and significantly reduce low-frequency magnetic (less than 1000 Hz) and X-ray radiation. These filters are made of special glass.

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