The principle of operation of the CRT monitor. Modern CRT Types of CRT monitors

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

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 huge place on the table. They also consume less electricity. But which is better today, CRT or LCD? Ordinary users will answer in unison 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 that is filled with vacuum. The front part of the monitor is a phosphor. For a phosphor, complex compositions based on rare earth metals such as yttrium and erbium are used. In simple terms, 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 sends a stream of electrons through a metal mask (lattice) to the inner surface of the glass screen of the monitor, which is covered with multi-colored phosphor dots.

Conventional CRT monitors use three electron guns, while in old, still black and white monitors, only one was involved.

The human eye can only respond to three primary colors, these are red, blue and green and their combinations, and they create a huge number of colors or shades. The front 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 RGB primary colors.

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, with the help of which the incoming signal from the computer's video card is processed. Electronics optimizes the output image - it amplifies the signal and stabilizes it, which is why the picture on the monitor is stable, even if the signal is unstable.

LCD or liquid crystal monitors

Liquid crystals, on which LCD monitors are based, are characterized by a transitional state of matter between solid and liquid, while maintaining the crystal structure of molecules and providing fluidity. The matrix of such a monitor is really liquid in a sense, for example, if you lightly press your finger on a working monitor, you will see how the liquid inside is displaced. It is a liquid crystal solution. At first, liquid crystals were used in the displays of calculators, as well as digital clocks, then they switched to PDAs and computer monitors.

Today, not almost, but completely CRTs have been superseded by LCD monitors.

LCDs are two panels, they are made of very thin and clean 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 concept as "native" resolution - this is the one at which the monitor is desirable to work. It is this extension that will allow the monitor to display the picture in the best quality. If you set a different extension, the image will be either 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 to maintain quality.

Monitor contrast is determined by the ratio of brightness between white (as the brightest) and black (darkest). A good indicator is 120: 1. Monitors with a contrast ratio of 300: 1 are able to 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 that of a CRT monitor, and color saturation can also be higher. There is no distortion, as well as the eternal problem of "soap" (cloudy image) - all this is absent in "thin" monitors, which is why they are ahead of the CRT.

Here in this picture there is additional information about the difference between monitors, but it is interesting that the picture is a little muddy, blurry, this is how many CRT monitors are now showing (since new ones are not released already 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 during prolonged work at the computer.

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

Hello readers of my blog who are interested in a CRT monitor. I will try to make this article interesting to everyone, both those who have not found them, and those who have this device pleasantly associated with the first experience of mastering a personal computer.

Today, PC displays are flat and thin screens. But in some low-budget organizations, you can also find massive CRT monitors. An entire era in the development of multimedia technologies is associated with them.

The CRT monitors got their official name from the Russian abbreviation of the term "cathode ray tube". The English equivalent is the phrase Cathode Ray Tube with the corresponding abbreviation CRT.

Before PCs appeared in homes, this electrical device was represented in our everyday life by CRT TVs. They were even used at one time as displays (think). But more on that later, and now let's understand a little about the principle of operation of a CRT, which will allow us to talk about such monitors at a more serious level.

Progress of CRT monitors

The history of the development of the cathode-ray tube and its transformation into CRT monitors with a decent screen resolution is full of interesting discoveries and inventions. At first, these were instruments such as an oscilloscope, radar screens, radars. Then the development of television gave us more convenient devices for viewing.

If we talk specifically about displays of personal computers available to a wide range of users, then the title of the first monica should probably be given to the vector display station IBM 2250. It was created in 1964 for commercial use together with the System / 360 series computers.

IBM owns many developments for equipping PC monitors, including the design of the first video adapters, which became the prototype of modern powerful and standards for the image transmitted to the display.

So, in 1987, a VGA (Video Graphics Array) adapter was released, working with a resolution of 640 × 480 and an aspect ratio of 4: 3. These parameters remained basic for most monitors and televisions produced until the advent of widescreen standards. During the evolution of CRT monitors, there have been many changes in their production technology. But I want to dwell on such points separately:

What determines the shape of a pixel?

Knowing how a picture tube works, we will be able to understand the features of CRT monitors. The beam emitted by the electron gun is deflected by an induction magnet to hit precisely the special holes in the mask in front of the screen.

They form a pixel, and their shape determines the configuration of color dots and the quality parameters of the resulting image:

• Classic round holes, the centers of which are located at the vertices of a conventional equilateral triangle, form a shadow mask. A matrix with evenly spaced pixels provides maximum line reproduction quality. And ideal for office design applications.
• To increase the brightness and contrast of the screen, Sony used an aperture mask. There, instead of dots, the rectangular blocks located nearby shone. This allowed the maximum use of the screen area (monitors Sony Trinitron, Mitsubishi Diamondtron).
• It was possible to combine the advantages of these two technologies in a slotted lattice, where the holes looked like elongated rectangles rounded at the top and bottom. And the blocks of pixels were displaced relative to each other vertically. This mask has been used in NEC ChromaClear, LG Flatron, Panasonic PureFlat displays;

But not only the shape of the pixel determined the merits of the monitor. Over time, its size began to play a decisive role. It ranged from 0.28 to 0.20 mm, and the mask with smaller, denser holes allowed for high resolution images.

An important and, alas, noticeable characteristic for the consumer remained the screen refresh rate, which was expressed in the flickering of the image. The developers tried their best, and gradually, instead of sensitive 60 Hz, the dynamics of changing the displayed picture reached 75, 85 and even 100 Hz. The latter indicator already made it possible to work with maximum comfort and the eyes almost never tired.

The work on quality improvement continued. The developers did not forget about such an unpleasant phenomenon as low-frequency electromagnetic radiation. In such screens, this radiation is directed by an electron gun directly at the user. To eliminate this drawback, various technologies were used and various protective screens and protective coatings for screens were used.

The safety requirements for monitors have also become more stringent, which are reflected in constantly updated standards: MPR I, MPR II, TCO "92, TCO" 95 and TCO "99.

The monitor trusted by professionals

Work on the continuous improvement of multimedia video technology and technology has led over time to the emergence of high definition digital video. A little later, thin screens with backlighting from economical LED lamps appeared. These displays are a dream come true because they:

• lighter and more compact;
• were distinguished by their low energy consumption;
• much safer;
• did not have flicker even at lower frequencies (there is flicker of a different kind);
• had several supported connectors;

And it was clear to non-specialists that the era of CRT monitors was over. And it seemed that there would be no return to these devices. But some professionals, knowing all the features of new and old screens, were in no hurry to get rid of high quality CRT displays. Indeed, according to some technical characteristics, they clearly outperformed their LCD competitors:

• excellent viewing angle, allowed reading information from the side of the screen;
• CRT technology made it possible to display a picture with any resolution without distortion, even when using scaling;
• the concept of dead pixels is absent here;
• after-image inertia time is negligible:
• practically unlimited range of displayed shades and stunning photorealistic color reproduction;

It was the last two qualities that left CRT displays a chance to prove themselves once again. And they are still in demand among gamers and, especially, among specialists working in the field of graphic design and photo processing.

Here is such a long and interesting story from an old, good friend called a CRT monitor. And if you still have one at home or at the enterprise, you can try it again in business and evaluate its qualities in a new way.

On this I say goodbye to you, my dear readers.

Most monitors used and produced today are built on cathode ray tubes (CRT). In English - Cathode Ray Tube (CRT), literally - cathode ray tube. Sometimes CRT stands for 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 an oscilloscope.

The CRT, or CRT, is the most important element of a monitor. The kinescope consists of a sealed glass bulb with a vacuum inside (the main structural units of the kinescope are shown in Fig. 1). 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 luminophor. Rather complex compositions based on rare earth metals - yttrium, erbium, etc. are used as phosphors for non-ferrous 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 as 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 long (by the way, white phosphorus is a strong poison).

CRT design

Figure 1. Construction of a cathode-ray tube.

To create an image in a CRT monitor, an electron gun is used, from which a stream of electrons emanates under the influence of a strong electrostatic field. Through a metal mask or lattice, 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 plane, which ensures its consistent hit on the entire field of the screen. The deflection of the beam takes place by means of a deflection system (see Fig. 2). Deflection systems are subdivided into saddle-toroidal and saddle-shaped. The latter are preferable because they have a lower radiation level.

Deflection system design

Figure 2. Design of the CRT deflection system.

The deflection system consists of several inductors located at the throat of the tube. Using an alternating magnetic field, two coils create a deflection of the electron beam in the horizontal plane, and the other two - in the vertical one.
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, as a rule, a sawtooth voltage change over time), while the coils give the beam the desired direction. The path of the electron beam on the screen is schematically shown in Fig. 3. Solid lines are the active path of the ray, the dashed line is the opposite.

Electron beam path

Figure 3. Schematic of the electron beam sweep

The frequency of the transition to a new line is called the horizontal (or horizontal) frequency. The frequency of transition from the lower right corner to the upper left corner is called the vertical (or vertical) frequency. The amplitude of overvoltage pulses on the line coils increases with the line frequency, so this node turns out to be 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 line scan units is also one of the major factors in the design of monitors.
After the deflecting system, the flow of electrons on the way to the front of the tube passes through the intensity modulator and the accelerating system, operating on the principle of potential difference. As a result, electrons acquire high energy (E \u003d mV 2/2, where E is energy, m is mass, v is velocity), some of which is spent on the glow of the phosphor.

Electrons fall on the phosphor layer, after which the energy of the electrons is converted into light, that is, the flow of electrons makes the dots of the phosphor glow. These glowing dots of the phosphor form the image you see on your monitor. Typically, a color CRT monitor uses three electron guns, as opposed 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, which create an infinite number of colors. The phosphor layer covering the front of the cathode ray tube is made up 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 - triad).

Color combinations

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 luminescence with the 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, then their combination will form a white color.

To control the cathode-ray tube, control electronics are 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 determines the difference between monitors with the same cathode ray tube.

So, each gun emits an electron beam (or stream, or beam), which affects the phosphor elements of different colors (green, red or blue). It is understood that the electron beam destined for red phosphor elements should not affect the green or blue phosphor. To achieve this, a special mask is used, whose structure depends on the type of picture tubes from different manufacturers, which ensures the 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 slot and shadow masks, although it would be more accurate to say that they are all shadows. At the same time, tubes with a planar arrangement of electron guns are also called self-aligning kinescopes, since the effect of the Earth's magnetic field on three planar beams is practically the same and when the position of the tube relative to the Earth's field changes, additional adjustments are not required.

Shadow mask

The shadow mask is the most common type of mask. It has been in use 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 around the edges has the same thickness.

Shadow mask design

Figure 5. The design of the shadow mask (enlarged).

The shadow mask consists of a metal plate with round holes that occupy about 25% of the area (see Fig. 5, 6). The mask is located in front of a glass tube with a phosphor layer. Typically, 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, therefore, although the electron beams heat up the mask, it does not negatively affect the color purity of the image. The holes in the metal mesh work like a sight (albeit not precise), which is what ensures that the electron beam hits only the required phosphor elements and only in certain areas. The shadow mask creates a lattice with homogeneous points (also called triads), where each such point 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 varying the current of each of the three electron beams, an arbitrary color of an image element formed by a triad of dots can be achieved.

Shadow mask design 2

Figure 6. Shadow mask design (general view).

One of the weak points of shadow mask monitors is its thermal deformation. In fig. 7 shows how some of the beams from the electron beam gun hit the shadow mask, as a result of which heating and subsequent deformation of the shadow mask occurs. The resulting displacement of the shadow mask holes leads to the appearance of the screen speckle effect (RGB color shift). The material of the shadow mask has a significant impact on the quality of the monitor. The preferred mask material is Invar.

Deflection system design 2

Figure 7. Design of the deflection system.

The disadvantages of a shadow mask are well known: firstly, this is a small ratio of electrons transmitted and trapped 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 luminescence, reducing the color rendering range , and secondly, it is rather difficult to ensure the exact coincidence of three rays not lying 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.

Shadow mask step

Figure 8. Step of the shadow mask.

The minimum distance between phosphor elements of the same color in adjacent lines is called the dot pitch and is an index of image quality (see Fig. 8). The dot pitch is usually measured in millimeters (mm). The smaller the dot pitch, the better the image displayed on the monitor. The horizontal distance between two adjacent points is equal to the step of points multiplied by 0.866.

Aperture grille

There is another type of tubing that uses the Aperture Grille (aperture grille). These tubes became known as Trinitron and were first introduced to the market by Sony in 1982. In tubes with aperture grating, an original technology is used, where there are three beam guns, three cathodes and three modulators, but with one common focusing (see Fig. 9).

Aperture grille design

Figure 9. Design of the aperture grille.

An aperture grille is a type of mask used by different manufacturers in their technologies to produce CRTs 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 (see Fig. 10). Instead of dots with phosphor elements of three primary colors, the aperture grille contains a series of filaments consisting of phosphor elements arranged in vertical stripes of 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 tubes (Mitsubishi, ViewSonic) is a thin foil on which thin vertical lines are scratched. It is held 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 damp vibrations and is called damper wire. It is clearly visible, especially with a light background Some users do not like these lines in principle, while others, on the contrary, are happy and use them as a horizontal ruler.

Aperture grille pitch

Before the advent of LCD technology, personal computers were equipped with CRT monitors. They are distinguished by their large dimensions and large mass.

IMPORTANT. CRT monitors are not energy efficient. In particular, the consumption of electricity by such displays is comparable to that of powerful incandescent lamps.

The resulting image quality is characterized by high definition. Therefore, this type of monitor is in demand for the graphic design of raster images.

The CRT monitor is equipped with a glass vacuum tube. The inner part of this element facing the user is coated from the inside with a special compound - Luminofor. This special coating emits light when bombarded with electrons. The composition of this layer in non-ferrous CRT devices includes complex elements based on rare earth metals. The brightness and luminescence period created by the phosphor depends on the percentage and properties of the components used.

Principle of operation

The formation of a picture on such a display occurs with the help of an electron beam gun. It emits a stream of electrons that pass through a specialized metal mask and are directed to the inside of the glass surface of the display.

The flow of charged electroparticles on the way to the front surface of the screen is converted in an intensity modulator, which accelerates the system. Functioning is based on the principle of potential difference. By passing through the modulator, charged particles receive a lot of energy, which is spent on illuminating the pixels. Electrons enter the luminofor, then the electron energy contributes to the glow of certain areas of the screen. Pixel activation provides image formation.

REFERENCE. Conventional color CRT monitors use the RGB color gamut.

The housing contains three electronic emitters. They generate one of 3 basic shades, and transmit a beam of electroparticles to specific areas of the phosphor layer. The glow intensity of each tone from the palette is different. This parameter is varied in such a way that by increasing the power of each of the three beams to the limit value, white light is formed. By combining all three base tones at the minimum level, a pixel of gray or black is obtained. A mask is a design element that provides precise illumination of the required area of \u200b\u200bthe screen by an electron beam. The design features of the mask are determined by the type of picture tube and the brand. The quality of this element affects the clarity of the picture (bitmap).

A personal computer monitor is a truly important component for every type of computer.

Without a monitor, there is no opportunity to fully evaluate the characteristics, as well as the functions, capabilities of the provided software, because no type of information will be displayed visually. Up to 100% of the information can be received only through the monitor used.

Currently, cathode ray tube monitors are no longer common and widespread. This technique can only be seen in rare users. CRTs have successfully replaced liquid crystal monitors.

Despite this situation, there is a need to understand all the important advantages and nuances of the manufactured equipment, because only in this case there is an opportunity to appreciate the old products and understand why they have lost their relevance. Is it really the only reason for the large size and excessive weight, high power consumption and potentially harmful radiation for users?

What were the old CRT monitors?

All CRT monitors can be divided into three types.

1. Cathode ray monitors with shadow mask. This option turned out to be one of the most popular and truly worthy among manufacturers. The technique had a convex monitor.
2. LT with an aperture grille, which includes several vertical lines.
3. Monitors with a slit mask.

What technical characteristics of CRT monitors should be taken into account? How to figure out how worthy the technique is for its application?

1. Screen diagonal... This parameter is considered to be from opposite corners from the upper and lower parts: lower right corner - upper left. The value must be measured in inches. In most cases, the models had a diagonal of 15 and 17 inches.
2. Monitor screen grain sizeand. In this case, it is supposed to consider special holes located in the color separation mask of the monitor at certain distances. If this distance turns out to be less, you can expect an improvement in image quality. The grain size should indicate the distance between the nearest holes. For this reason, you can focus on the following indicator: a lower characteristic is proof of the high quality of a computer display.
3. Power consumptionb, measured in W.
4. Display coverage type.
5. The presence or absence of a protective screen... Scientific researchers managed to prove that the generated radiation is harmful to human health. For this reason, CRT monitors began to be offered with special protection, which can be glass, film, mesh. The main challenge was to strive to reduce radiation levels.

Benefits of CRT monitors

Despite the features and specifics of CRT monitors, there is still an opportunity to appreciate the advantages of the offered previous products:

• CRT models can work with switching (shutter) stereo glasses. However, even the most advanced LCD displays have not acquired this skill. If a person wants to note how multifaceted and perfect a full-fledged 3D stereo video can be, it is best to give preference to a CRT model, which will be 17-inch. With this approach, you can allocate 1,500 - 4,500 rubles for the purchase, but get the opportunity to enjoy 3D in switching stereo glasses. The most important thing is to check, focusing on the passport data of the released equipment, its characteristics: the resolution should be 1024x768. Frame rate - from 100 Hz. If these data are not followed, there is a risk of flickering in the stereo image.
• A CRT monitor, when installed with a modern video card, can successfully display images of various resolutions, including thin lines and oblique letters. This characteristic depends on the resolution of the phosphor. The LCD display will correctly and efficiently reproduce the text only if the resolution is set equal to the number of rows and columns of the LCD monitor itself, standard resolution, because other versions will be interpolated by the electronics of the equipment used.
• High-quality CRT monitors can delight with dynamic (transient) characteristics, allowing you to enjoy watching dynamically changing scenes in games and movies. It assumes the ability to successfully and easily remove unwanted smear from image details that are changing rapidly. This can be explained by the following nuance: the transient response time of the CRT phosphor cannot exceed 1 - 2 ms by the criterion of the full brightness decay to several percent. LCD displays have a transient response of 12-15 ms, with 2, 6, 8 ms being a purely advertising gimmick, as a result of which fast-changing parts can be lubricated in dynamic scenes.
• CRT monitors meeting high criteria and correctly color-matched can guarantee correct color reproduction of the observed scenes. This characteristic is appreciated by artists and designers. LCD monitors cannot please with perfect color reproduction.

Disadvantages of CRT monitors

• Large dimensions.
• High energy consumption.
• Presence of harmful electromagnetic radiation.

Perhaps LCD displays in their technical characteristics will catch up with CRTs, because modern manufacturers are trying to combine convenience and practicality, functionality in the products they offer.