How does a CRT monitor work? History of the creation of CRT monitors Modern CRT monitors
Since 1902, Boris Lvovich Rosing has been working with Brown's tube. On July 25, 1907, he filed an application for the invention “Method of electrically transmitting images over distances.” The beam was scanned in the tube by magnetic fields, and the signal was modulated (change in brightness) using a capacitor, which could deflect the beam vertically, thereby changing the number of electrons passing to the screen through the diaphragm. On May 9, 1911, at a meeting of the Russian Technical Society, Rosing demonstrated the transmission of television images of simple geometric figures and their reception with reproduction on a CRT screen.
At the beginning and middle of the 20th century, Vladimir Zvorykin, Allen Dumont and others played a significant role in the development of CRTs.
Design and principle of operation
General principles
Black and white kinescope device
In a cylinder 9 a deep vacuum is created - first the air is pumped out, then all the metal parts of the kinescope are heated by an inductor to release the absorbed gases; a getter is used to gradually absorb the remaining air.
To create an electron beam 2 , a device called an electron gun is used. Cathode 8 , heated by filament 5 , emits electrons. To increase the emission of electrons, the cathode is coated with a substance that has a low work function (the largest CRT manufacturers use their own patented technologies for this). By changing the voltage on the control electrode ( modulator) 12 you can change the intensity of the electron beam and, accordingly, the brightness of the image (there are also models with cathode control). In addition to the control electrode, the gun of modern CRTs contains a focusing electrode (until 1961, domestic picture tubes used electromagnetic focusing using a focusing coil 3 with core 11 ), designed to focus a spot on the kinescope screen into a point, an accelerating electrode for additional acceleration of electrons within the gun and anode. After leaving the gun, the electrons are accelerated by the anode 14 , which is a metallized coating of the inner surface of the kinescope cone, connected to the gun electrode of the same name. In color picture tubes with an internal electrostatic screen, it is connected to the anode. In a number of picture tubes of early models, such as 43LK3B, the cone was made of metal and represented the anode itself. The voltage at the anode ranges from 7 to 30 kilovolts. In a number of small-sized oscillographic CRTs, the anode is only one of the electrodes of the electron gun and is supplied with voltages of up to several hundred volts.
The beam then passes through the deflection system 1 , which can change the direction of the beam (the figure shows a magnetic deflection system). Television CRTs use a magnetic deflection system as it provides large deflection angles. Oscillographic CRTs use an electrostatic deflection system as it provides greater performance.
The electron beam hits the screen 10 , coated with phosphor 4 . Bombarded by electrons, the phosphor glows and a rapidly moving spot of variable brightness creates an image on the screen.
The phosphor acquires a negative charge from the electrons, and secondary emission begins - the phosphor itself begins to emit electrons. As a result, the entire tube acquires a negative charge. To prevent this from happening, over the entire surface of the tube there is a layer of aquadag, a conductive mixture based on graphite, connected to a common wire ( 6 ).
The kinescope is connected through the leads 13 and high voltage socket 7 .
In black-and-white TVs, the composition of the phosphor is selected so that it glows in a neutral gray color. In video terminals, radars, etc., the phosphor is often made yellow or green to reduce eye fatigue.
Beam angle
The deflection angle of the CRT beam is the maximum angle between two possible positions of the electron beam inside the bulb at which a luminous spot is still visible on the screen. The ratio of the diagonal (diameter) of the screen to the length of the CRT depends on the angle. For oscillographic CRTs it is usually up to 40 degrees, which is due to the need to increase the sensitivity of the beam to the effects of deflection plates. For the first Soviet television picture tubes with a round screen, the deflection angle was 50 degrees, for black-and-white picture tubes of later releases it was 70 degrees, and starting in the 60s it increased to 110 degrees (one of the first such picture tubes was 43LK9B). For domestic color picture tubes it is 90 degrees.
As the beam deflection angle increases, the dimensions and weight of the kinescope decrease, however, the power consumed by the scanning units increases. Currently, the use of 70-degree picture tubes has been revived in some areas: in color VGA monitors of most diagonals. Also, an angle of 70 degrees continues to be used in small-sized black and white picture tubes (for example, 16LK1B), where length does not play such a significant role.
Ion trap
Since it is impossible to create a perfect vacuum inside the CRT, some air molecules remain inside. When colliding with electrons, they form ions, which, having a mass many times greater than the mass of electrons, practically do not deviate, gradually burning out the phosphor in the center of the screen and forming a so-called ion spot. To combat this until the mid-60s. an ion trap was used, which has a major drawback: its correct installation is a rather painstaking operation, and if installed incorrectly, there is no image. At the beginning of the 60s. A new method of protecting the phosphor was developed: aluminizing the screen, which also doubled the maximum brightness of the kinescope, and the need for an ion trap was eliminated.
Delay in supplying voltage to the anode or modulator
In a TV, the horizontal scanning of which is made using lamps, the voltage at the anode of the kinescope appears only after the output horizontal scanning lamp and the damper diode have warmed up. By this time, the kinescope heat has already warmed up.
The introduction of all-semiconductor circuitry into horizontal scanning units gave rise to the problem of accelerated wear of the kinescope cathodes due to the supply of voltage to the anode of the kinescope simultaneously with switching on. To combat this phenomenon, amateur units have been developed that provide a delay in the supply of voltage to the anode or modulator of the kinescope. It is interesting that in some of them, despite the fact that they are intended for installation in all-semiconductor televisions, a radio tube is used as a delay element. Later, industrial televisions began to be produced, in which such a delay was initially provided.
Scan
To create an image on the screen, an electron beam must constantly pass across the screen at a high frequency - at least 25 times per second. This process is called sweep. There are several ways to scan an image.
Raster scan
The electron beam passes the entire screen in rows. There are two options:
- 1-2-3-4-5-… (interlaced scanning);
- 1-3-5-7-…, then 2-4-6-8-… (interlaced).
Vector scan
The electron beam passes along the image lines.
Color picture tubes
Color kinescope device. 1 - Electron guns. 2 - Electron rays. 3 - Focusing coil. 4 - Deflection coils. 5 - Anode. 6 - A mask, thanks to which the red beam hits the red phosphor, etc. 7 - Red, green and blue phosphor grains. 8 - Mask and phosphor grains (enlarged).
A color kinescope differs from a black and white one in that it has three guns - “red”, “green” and “blue” ( 1 ). Accordingly, on the screen 7 three types of phosphor are applied in some order - red, green and blue ( 8 ).
Only the beam from the red gun hits the red phosphor, only the beam from the green gun hits the green one, etc. This is achieved by installing a metal grid between the guns and the screen, called mask (6 ). In modern picture tubes, the mask is made of invar, a type of steel with a small coefficient of thermal expansion.
Types of masks
There are two types of masks:
- the shadow mask itself, which exists in two types:
- Shadow mask for picture tubes with a delta-shaped arrangement of electron guns. Often, especially in translated literature, it is referred to as a shadow grid. Currently used in most monitor picture tubes. Television picture tubes with a mask of this type are no longer produced, however, such picture tubes can be found in televisions of previous years (59LK3Ts, 61LK3Ts, 61LK4Ts);
- Shadow mask for picture tubes with planar arrangement of electron guns. Also known as slotted grating. Currently used in the vast majority of television picture tubes (25LK2Ts, 32LK1Ts, 32LK2Ts, 51LK2Ts, 61LK5Ts, foreign models). Almost never found in monitor picture tubes, with the exception of Flatron models;
- aperture grille (Mitsubishi Diamondtron). This mask, unlike other types, consists of a large number of wires stretched vertically. The fundamental difference between a mask of this type is that it does not limit the electron beam, but focuses it. The transparency of the aperture grille is approximately 85% versus 20% for the shadow mask. Picture tubes with such a mask are used in both monitors and televisions. Attempts were made to create such picture tubes in the 70s in the USSR (for example, 47LK3Ts).
- Color picture tubes of a special type stand apart - single-beam chromoscopes, in particular, 25LK1Ts. In terms of design and principle of operation, they are strikingly different from other types of color picture tubes. Despite obvious advantages, including reduced power consumption, comparable to that of a black-and-white picture tube with a diagonal of the same size, such picture tubes are not widely used.
There is no clear leader among these masks: the shadow one provides high quality lines, the aperture one provides more saturated colors and high efficiency. Slit combines the advantages of shadow and aperture, but is prone to moire.
Types of gratings, methods of measuring pitch on them
The smaller the phosphor elements, the higher the image quality the tube can produce. An indicator of image quality is mask step.
- For a shadow grating, the mask pitch is the distance between the two nearest mask holes (accordingly, the distance between the two closest phosphor elements of the same color).
- For aperture and slot gratings, the mask pitch is defined as the horizontal distance between the mask slits (respectively, the horizontal distance between vertical phosphor strips of the same color).
In modern CRT monitors, the mask pitch is 0.25 mm. Television picture tubes, which view images from a greater distance, use steps of about 0.8 mm.
Convergence of rays
Since the radius of curvature of the screen is much greater than the distance from it to the electron-optical system up to infinity in flat picture tubes, and without the use of special measures, the point of intersection of the rays of a color picture tube is at a constant distance from the electron guns, it is necessary to ensure that this point is located exactly at surface of the shadow mask, otherwise a misalignment of the three color components of the image will occur, increasing from the center of the screen to the edges. To prevent this from happening, the electron beams must be properly biased. In picture tubes with a delta-shaped arrangement of guns, this is done by a special electromagnetic system, controlled separately by a device, which in old televisions was placed in a separate block - the mixing block - for periodic adjustments. In picture tubes with a planar arrangement of guns, adjustment is made using special magnets located on the neck of the picture tube. Over time, especially for picture tubes with a delta-shaped arrangement of electron guns, the convergence is disrupted and requires additional adjustment. Most computer repair companies offer a monitor reconvergence service.
Demagnetization
Necessary in color picture tubes to remove residual or random magnetization of the shadow mask and electrostatic screen that affects image quality. Demagnetization occurs due to the appearance in the so-called demagnetization loop - a ring-shaped flexible coil of large diameter located on the surface of the kinescope - a pulse of rapidly alternating damped magnetic field. To ensure that this current gradually decreases after turning on the TV, thermistors are used. Many monitors, in addition to thermistors, contain a relay, which, upon completion of the kinescope demagnetization process, turns off the power to this circuit so that the thermistor cools down. After this, you can use a special key, or, more often, a special command in the monitor menu, to trigger this relay and carry out repeated demagnetization at any time, without turning off and on the monitor’s power.
Trinescope
A trinescope is a design consisting of three black-and-white picture tubes, light filters and translucent mirrors (or dichroic mirrors that combine the functions of translucent mirrors and filters), used to obtain a color image.
Application
CRTs are used in raster image formation systems: various types of televisions, monitors, and video systems. Oscillographic CRTs are most often used in systems for displaying functional dependencies: oscilloscopes, wobuloscopes, also as a display device at radar stations, in special-purpose devices; in the Soviet years they were also used as visual aids in studying the design of electron beam devices in general. Character-printing CRTs are used in various special-purpose equipment.
Designation and marking
The designation of domestic CRTs consists of four elements:
- The first element: a number indicating the diagonal of the rectangular or the diameter of the round screen in centimeters;
- The second element: the purpose of the CRT, in particular, LC - television kinescope, LM - monitor kinescope, LO - oscillographic tube;
- Third element: a number indicating the model number of a given tube with a given diagonal;
- Fourth element: a letter indicating the color of the screen glow, in particular, C - color, B - white glow, I - green glow.
In special cases, a fifth element may be added to the designation, carrying additional information.
Example: 50LK2B - black and white kinescope with a screen diagonal of 50 cm, second model, 3LO1I - oscilloscope tube with a green screen diameter of 3 cm, first model.
Health effects
Electromagnetic radiation
This radiation is created not by the kinescope itself, but by the deflection system. Tubes with electrostatic deflection, in particular oscilloscopes, do not emit it.
In monitor picture tubes, to suppress this radiation, the deflection system is often covered with ferrite cups. Television picture tubes do not require such shielding, since the viewer usually sits at a much greater distance from the TV than from the monitor.
Ionizing radiation
CRTs contain two types of ionizing radiation.
The first of these is the electron beam itself, which is essentially a stream of low-energy beta particles (25 keV). This radiation does not escape outside and does not pose a danger to the user.
The second is bremsstrahlung X-ray radiation, which occurs when the screen is bombarded with electrons. To reduce the output of this radiation to completely safe levels, the glass is doped with lead (see below). However, in the event of a malfunction of the TV or monitor, leading to a significant increase in the anode voltage, the level of this radiation can increase to noticeable levels. To prevent such situations, line scanning units are equipped with protection units.
In domestic and foreign color TVs produced before the mid-1970s, additional sources of X-ray radiation may be found - stabilizing triodes connected in parallel to the kinescope, and used to stabilize the anode voltage, and therefore the size of the image. The Raduga-5 and Rubin-401-1 TVs use 6S20S triodes, and the early ULPTsT models use GP-5. Since the glass of the container of such a triode is much thinner than that of a kinescope and is not doped with lead, it is a much more intense source of X-ray radiation than the kinescope itself, so it is placed in a special steel screen. In later models of ULPTST TVs, other methods of stabilizing high voltage are used, and this source of X-ray radiation is excluded.
Flicker
Mitsubishi Diamond Pro 750SB monitor (1024x768, 100 Hz), shot at 1/1000 s shutter speed. Brightness is artificially high; shows the actual brightness of the image at different points on the screen.
The beam of a CRT monitor, forming an image on the screen, causes phosphor particles to glow. Before the next frame is formed, these particles have time to go out, so you can observe “screen flickering.” The higher the frame rate, the less noticeable the flickering. Low frequency leads to eye fatigue and harms health.
For most televisions based on a cathode ray tube, 25 frames change every second, which, taking into account interlaced scanning, is 50 fields (half frames) per second (Hz). In modern TV models, this frequency is artificially increased to 100 hertz. When working behind a monitor screen, flickering is felt more strongly, since the distance from the eyes to the kinescope is much smaller than when watching TV. The minimum recommended monitor refresh rate is 85 hertz. Early models of monitors do not allow working with a scanning frequency of more than 70-75 Hz. The flickering of a CRT can clearly be observed with peripheral vision.
Fuzzy image
The image on a cathode ray tube is blurry compared to other types of screens. Blurred images are believed to be one of the factors contributing to user eye fatigue.
Currently (2008), in tasks that are not demanding on color reproduction, from an ergonomic point of view, LCD monitors connected via a DVI digital connector are certainly preferable.
High voltage
A CRT uses high voltage to operate. Residual voltage of hundreds of volts, if no measures are taken, can linger on CRTs and wiring circuits for weeks. Therefore, discharge resistors are added to the circuits, which make the TV completely safe within a few minutes after turning it off.
Contrary to popular belief, the anode voltage of a CRT cannot kill a person due to the low power of the voltage converter - there will only be a noticeable blow. However, it can also be fatal if a person has heart defects. It can also cause injury, including death, indirectly when a person withdraws their hand and touches other circuits in the television and monitor that contain extremely life-threatening voltages - which are present in all models of televisions and monitors that use CRTs.
Toxic substances
Any electronics (including CRTs) contain substances that are harmful to health and the environment. Among them: lead glass, barium compounds in cathodes, phosphors.
Since the second half of the 60s, the dangerous part of the kinescope has been covered with a special metal explosion-proof bandage, made in the form of an all-metal stamped structure or wound in several layers of tape. Such a bandage eliminates the possibility of spontaneous explosion. Some models of picture tubes additionally used a protective film to cover the screen.
Despite the use of protective systems, it is not excluded that people will be injured by shrapnel when a kinescope is deliberately broken. In this regard, when destroying the latter, for safety, the extension is first broken - a technological glass tube at the end of the neck under a plastic base, through which air is pumped out during production.
Small-sized CRTs and picture tubes with a screen diameter or diagonal of up to 15 cm do not pose a danger and are not equipped with explosion-proof devices.
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 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 = 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).
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. 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.
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 shadow mask holes leads to the effect of screen variegation (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.
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. 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.
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 slit mask (Slot Mask)
The slot mask is widely used by NEC under the name CromaClear. This solution in practice is a combination of a shadow mask and an aperture grille. In this case, the phosphor elements are located in vertical elliptical cells, and the mask is made of vertical lines. In fact, the vertical stripes are divided into elliptical cells 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 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 .
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 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.
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 for displaying 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. The beam is transferred from the rightmost point of the line to the leftmost point of the next line (horizontal beam retracement) and from the rightmost position of the last line of the screen to the leftmost position of the first line (vertical beam retracement) is carried out using special reverse stroke signals. This type of monitor is 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 from a great 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 at high speed, so the screen appears to be constantly glowing. 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.
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 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.
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 and capabilities of the provided software, because not a single type of information will be displayed visually. Only through the monitor you use can you receive up to 100% of information.
Currently, cathode ray tube monitors are no longer common and widespread. This technique can only be seen in rare users. CRTs have successfully replaced LCD 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 does it become possible to truly appreciate the previous products and understand why they have lost their relevance. Is it really just the large size and excessive weight, high power consumption and potentially harmful radiation for users? 
What were old CRT monitors like?
All CRT monitors can be divided into three types.
- Cathode ray monitors with shadow mask. This option turned out to be one of the most popular and truly worthy among manufacturers. The equipment had a convex monitor.
- LT with an aperture grille, which includes several vertical lines.
- Monitors with a slit mask.
What technical characteristics of CRT monitors need to be taken into account? How to figure out how worthy a technique is for its use?
- Screen diagonal. This parameter is usually calculated from opposite corners from the top and bottom: 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.
- Monitor Screen Grain Size A. In this case, it is assumed to consider special holes located in the color separation mask of the monitor at certain distances. If this distance is smaller, you can count on improved image quality. The grain size should indicate the distance between the nearest holes. For this reason, you can focus on the following indicator: a smaller characteristic is proof of the high quality of the computer display.
- Power consumption b, measured in W.
- Type of display coating.
- Presence or absence of a protective screen. Scientific researchers have 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, or mesh. The main goal was to strive to reduce radiation levels.
Advantages of CRT monitors
Despite the features and specifics of CRT monitors, it remains possible to appreciate the advantages of the previous products offered:
- CRT models can work with switching (shutter) stereo glasses. However, even the most advanced LCD displays have not acquired such a skill. If a person wants to note how versatile and perfect a full-fledged 3D stereo video can be, it is best to give preference to a CRT model, which will be 17 inches. With this approach, you can allocate 1,500 - 4,500 rubles for the purchase, but still get the opportunity to enjoy 3D in stereo switching glasses. The most important thing is to check, based on the passport data of the released equipment, its characteristics: the resolution should be 1024x768. Frame scanning frequency – from 100 Hz. If these details are not observed, there is a risk of flickering of the stereo image.
- A CRT monitor, when installed with a modern video card, can successfully display images of various resolutions, including thin lines and slanted letters. This characteristic depends on the resolution of the phosphor. The LCD display will correctly and efficiently reproduce 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 you with dynamic (transient) characteristics, allowing you to enjoy watching dynamically changing scenes in games and films. It is assumed that it is possible to successfully and easily remove unwanted smear from image parts that change quickly. This can be explained by the following nuance: the transition response time of a CRT phosphor cannot exceed 1 - 2 ms according to the criterion of a decline in full brightness to several percent. LCD displays have a transient response of 12 - 15 ms, and 2, 6, 8 ms are purely a publicity stunt, as a result of which in dynamic scenes there may be lubrication of rapidly changing parts.
- CRT monitors that meet high criteria and are correctly color-tuned can guarantee correct color reproduction of the observed scenes. This characteristic is valued by artists and designers. LCD monitors cannot please you with ideal color reproduction.
Disadvantages of CRT monitors
- Large dimensions.
- High level of energy consumption.
- Presence of harmful electromagnetic radiation.
Perhaps LCD displays will catch up with CRTs in their technical characteristics, because modern manufacturers are trying to combine convenience and practicality, functionality in the products they offer.
Choosing a monitor is not such an easy task. A mere mortal can easily become confused by the countless different technologies: shadow mask, Trinitron, DiamondTron, Chromaclear. Every company makes it a point to proclaim their technology to be the best, but how are they actually different? Let's figure it out. Each technology listed uses a different path for electron beams to hit the screen, or, more precisely, a mask that the electron beam must overcome. There is no ideal or best technology; each has its pros and cons, both in terms of price and image quality. A kinescope can be assessed using the grain size (the distance between the daughters, dot pitch), but you need to know exactly what is hidden behind the proposed figures. For example, a monitor with 0.25 grain does not necessarily have better image clarity than a monitor with "only" 0.27. Therefore, although grain size indicates the distance between two points on the screen, different technologies measure this distance differently. Some measure diagonally, others measure horizontally.
Please note that a key factor in monitor quality is the available range of horizontal refresh rates. We can divide monitors into five classes according to horizontal scan size, each of which indicates the optimal refresh rate at the optimal resolution.
85 kHz = 1024 x 768 @ 85 Hz
95 kHz = 1280 x 1024 @ 85 Hz
107 kHz = 1600 x 1200 @ 85 Hz
115 kHz = 1600 x 1200 @ 92 Hz
125 kHz = 1856x1392 @ 85 Hz
Technologies
All CRT monitors have a common element - a cathode ray tube, which, in fact, gave the monitors their name. The tube is filled with vacuum and contains several elements. The cathode at the back emits electrons when heated. The electron gun "shoots" electrons towards the anode, so a stream of electrons moves from the back of the kinescope to the screen. In this case, a flow of electrons passes through two coils that direct the beam. One coil is responsible for vertical deflection, the other for horizontal deflection. So, as you can see, the tube has no moving parts, which guarantees durability. If the monitor is color, then it uses three electron guns, each of them responsible for its own color - red, blue or green. This technology is called additive color technology. Halftones on the screen are formed from three colors, depending on their intensity. Glow occurs when electrons hit phosphor particles from the inner surface of the tube. The particles are very close to each other, so that three particles of different colors are perceived by the eye as one pixel.
All of the above is true for all manufacturers, however, further, when considering the mask, differences are revealed.
Shadow mask
Shadow mask technology is used in regular TVs and some monitors. Each gun's beam passes through a metal sheet containing thousands of small round holes. Behind each hole there are particles of phosphor. The distance between the cathode and the center of the plate is less than the distance between the cathode and the edge of the plate. Therefore, the effect of overheating the center of the plate occurs, which leads to uneven expansion and visual interference. However, manufacturers have found a solution to this problem. The mask in such monitors is now made of invar, an alloy of nickel and steel, which is practically not subject to thermal expansion. The Invar mask improves visual quality and prevents the appearance of a dull spot in the center of the screen.
The main problem with such a system is the large area occupied by the shadow mask. The mask absorbs a large number of electrons, and, accordingly, less light is emitted by the screen. For example, the image here will be darker than on a monitor with a Trinitron tube. Some manufacturers have improved the technology and added a filter behind each phosphor particle (note here Toshiba Microfilter, Panasonic RCT and ViewSonic SuperClear). The filter works like this: it passes the beam (produced by electrons) in one direction, and at the same time, it captures outside light. At the same time, the color remains pure, and the brightness of the glow increases.
Shadow mask technology is cheaper than others, it is not very effective, but it is quite suitable for regular computer monitors. It is also good for graphics work because it produces true-to-life colors.
Trinitron
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Sony began developing Trinitron technology back in 1968, although at that time it was intended for televisions. In 1980, the technology was tested on CRT computer monitors. The principle of operation remained unchanged - instead of grouping phosphorus particles at the vertices of a triangle, they were lined up in solid vertical lines of different colors. The shadow mask was replaced by another mask, in which, instead of holes, continuous vertical stripes were made. The opaque mask elements occupy a smaller area than previous technology, resulting in brighter, clearer images.
The only problem is that the mask is essentially made up of thousands of little wires that must be tightly stretched and secured. Therefore, two horizontal damper wires are added to the Trinitron tube, stretched from one edge of the screen to the other. Damper wires prevent the mask from vibrating and stretching when heated (to some extent, of course). But as a result, on such a monitor you can easily notice these wires against a light background. Some users find this annoying, while others, on the contrary, like to draw horizontal lines along them like a ruler. Moreover, your eyes quickly get used to these delays, and you are unlikely to notice them at all. The number of delays depends on the size of the screen (or, to be more precise, on the size of the mask). On screens smaller than 17"" one wire is used, on 17"" and larger sizes there are two. So, the three advantages of Trinitron are: reduced heat dissipation, higher brightness and contrast at the same power, and, of course, a completely flat screen.
Only two companies produce tubes using Trinitron technology - Sony (FD Trinitron) and Mitsubishi (DiamondTron). ViewSonic's PerfectFlat is just a slight adaptation of the DiamondTron. The main difference between the FD Trinitron and DiamondTron is that Sony uses three electron guns for three base colors, while Mitsubishi uses just one. This technology is also associated with the term “aperture grill”, since the Trinitron brand belongs to Sony.
Crevice mask
Not so, NEC and Pansonic have developed a new method, a shadow mask/aperture grille hybrid that combines both technologies to get the benefits of both. The new method was called a slot mask, and it features both vertical slits and a rigid shadow mask (using a real metal mask, not wires). As a result, the brightness here is not as high as in Trinitron technologies, but the image is more stable. Monitors with this technology are mainly manufactured by NEC and Mitsubishi, using the brands ChromaClear or Flatron (Flat Tension Mask).Elliptical Mask - Improved Grain
The elliptical mask was developed by Hitachi, one of the most influential players in the monitor tube market, in 1987. It was called EDP (Enhanced Dot Pitch - improved grain). The technology differs from Trinitron because it focuses more on improving phosphor performance rather than changing the mask. In a tube with a shadow mask, three phosphor particles are located at the vertices of an equilateral triangle. Thus, they are evenly distributed over the entire display area. In the EDP, Hitachi reduced the distance between the horizontal particles so that the triangle became an isosceles triangle. To avoid increasing the area covered by the mask, the particles have an elliptical shape. The main advantage of EDP is the correct representation of vertical lines. On a regular monitor with a shadow mask, you can notice some zigzag in the vertical lines. EDP eliminates this effect and also improves image clarity and brightness.
Safety Standards
Accepted monitor safety standards have evolved quite rapidly. In 1990, a standard for reducing electrostatic emissions, MPR2, was introduced. In 1990, the Swedish Trade Union Association released the TCO standard, which was then further developed and released as TCO92, TCO95 and TCO99. The standard stipulates visual comfort, recycling of obsolete monitors and the use of only harmless chemical compounds. TCO99 is the latest standard and most monitors comply with it. It provides for a minimum sweep frequency of 85 Hz (100 Hz recommended), specifies the degree of reflection of external light sources and the emitted electromagnetic field. Both TCO95 and TCO99 ensure uniform contrast and brightness across the entire screen surface.
What is purity?
When applied to CRT monitors, purity refers to color. Each beam should theoretically hit a phosphor section of its own color (one of the three basic ones). Defects in color purity are caused by the wrong beam from one of the guns. In this case, the beam will not only hit a particle of the desired color, but one or two neighboring particles. As a result, the pixel color will become incorrect. Such defects are best detected by drawing one color over the entire surface of the screen. Sometimes it happens that at one or more points the red color has a slightly yellowish or pinkish tint, which means that the red beam is misdirected and hits the blue or green areas.
On a monitor with a shadow mask, a cleanliness defect often appears due to lattice deformation resulting from metal fatigue (after prolonged use). The holes in the mask become deformed or elongated, causing them to no longer direct the electron beam as effectively. A mask made from invar is less susceptible to such defects.
On a monitor with an aperture grille, clarity defects occur for two reasons - due to a strong mechanical shock that moves the mask, or due to the action of an external electromagnetic field. The latter reason is often associated with the earth's natural electromagnetic field. Fortunately, most monitors today have color purity adjustment.
White balance
White balance problems are often mistaken for color purity defects. Areas of different colors appear on the screen. However, while purity defects are caused by improperly aimed guns, white balance defects arise from differences in the brightness of the base colors. For example, if you display blue color on the entire screen, then some areas of the screen will be darker, others lighter. The defect occurs due to slight differences in the shape or quality of some phosphor particles. In fact, it is very difficult to distribute the phosphor evenly over the surface of the screen.
Moire
There are two types of moire. The first and most common one appears on monitors with a shadow mask. Due to the production technology of such monitors, peculiar waves consisting of dark and bright areas may appear on the screen. This effect is due to differences in brightness between neighboring areas. The more accurate a monitor's guns are, the more prone it is to moire. Changing the targeting accuracy solves the problem, even if it means reducing the accuracy.
An example of the moire effect
The second type is television moire. Both monitors with a shadow mask and those with an aperture grille are susceptible to it. As a result, dark and light areas appear on the screen, arranged in a checkerboard pattern. This defect is associated with poor regulation of the refresh rate of each beam, as well as with the uneven distribution of the phosphor across the screen.
Mixing
Convergence refers to the ability of three electron beams (RGB) to hit the same point on the monitor screen. Proper mixing is very important because CRT monitors work on the principle of color additivity. If all three colors have equal intensity, a white pixel appears on the screen. If there are no rays, the pixel is black. Changing the intensity of one or more rays creates different colors. Convergence defects occur when one of the beams is out of sync with the other two, and appears, for example, as colored shadows next to the lines. Incorrect convergence may be caused by a defective deflector or incorrect placement of phosphor particles on the screen. The external electromagnetic field also affects the mixing.
Update frequency
Refresh rate refers to the number of times an image is displayed per second. The refresh rate is expressed in Hertz (Hz), respectively, with a refresh rate of 75 Hz, the monitor “rewrites” the image on the screen 75 times per second. Please note that the 75 Hz figure was not chosen by chance, since 75 Hz is considered the minimum necessary to display a flicker-free image. The refresh rate depends on the horizontal scan rate and the number of horizontal lines shown (and therefore the resolution used). The horizontal frequency shows the number of times the electron beam travels along a horizontal line, from its beginning to the beginning of the next, per second. The horizontal frequency is expressed in kilohertz (kHz). A 120 kHz horizontal scan monitor draws 120,000 lines per second. The number of horizontal lines depends on the resolution, for example, at a resolution of 1600x1200, 1200 horizontal lines are displayed. To calculate the total travel time of a ray across the surface of the screen, you must take into account the time that the ray travels when returning from the end point of the screen to the start point. It equals approximately 5% of screen rendering time. Therefore, below we will use a coefficient of 0.95.
So, to calculate the refresh rate, you can use the following formula:
Vf = horizontal frequency / number of horizontal lines x 0.95
For example, a monitor with a horizontal scan rate of 115 kHz at 1024x768 can operate at a maximum refresh rate of 142 Hz (115000/768 x 0.95).
Testing
| Test system | |
| CPU | Intel Celeron 800 MHz |
| Memory | 256 MB PC100 |
| HDD | Western Digital 40 GB |
| CD Rom | Teac CD540E and Pioneer A105S |
| Video card | ATI Radeon 7500 |
| Software | |
| DirectX | 8.0a |
| OS | Windows XP Professional |
In testing we used the following programs.
NTest for check:
- monitor calibration;
- geometric distortions;
- presence of moire;
- correctness of information;
- picture stability;
- picture clarity;
- color purity;
- brightness and contrast.
Other tests:
- viewing images and color tables (gradations of red, green, blue and gray) to determine the quality of color display, as well as their range;
- additional settings for displaying the maximum number of shades;
- DVD video playback ("Brotherhood of the Wolf" and "Saving Private Ryan") and game testing (Quake III Arena and Aquanox) to test quality in a gaming environment;
- testing and research of monitor menu modes (OSD).
NTest was used in several resolutions (1024x768, 1280x1024, 1600x1200) at 85 Hz to test how monitors react to changes in resolution. And also to make sure that there is no electronic optimization of the monitor for certain resolutions.
ViewSonic P95f
Although the ViewSonic brand is a big success in North America, it is not as well known in Europe. The P95f is the latest 19" flat screen model from the professional range. The monitor uses PerfectFlat tube with a grit of 0.25 to 0.27. The technology is borrowed from the Mitsubishi DiamondTron, so two horizontal wires are visible against a light background. The screen has a coating called ARAG that reduces the reflection of external light sources. Keep in mind that the diagonal of the useful part of the screen on the P95f, like a regular 19" monitor, is 18". 19"" is the diagonal of the tube without the housing. The monitor has a classic design and three small parrots in the upper left corner. The P95f has two types of connectors - 5 BNC and a standard 15-pin. The horizontal scanning frequency is 117 kHz, which inspires respect. The maximum bandwidth is also quite high - 300 MHz. The maximum monitor resolution is 1920x1440 at 77 Hz. In practice, we managed to set 2048x1536 at 75 Hz, a pretty good result.
In most of the tested resolutions, there were no complaints about the geometry. The positioning of the visible part was almost perfect, and we made only minor adjustments when switching modes. The monitor menu is quite easy to navigate. To do this, there are four keys on the monitor. The menu contains many options, you can make almost any setting. The menu has a full range of geometry options, and correction of color purity in areas of the screen is available. The moire effects were extremely minor, so they can be ignored. By the way, only monitors with a shadow mask suffer from classic moire. Monitors with a slit mask are susceptible to video moire. According to the documentation, the convergence in the center was 0.25 mm and 0.35 mm at the edges. Mixing defects were virtually unnoticeable in tests, and with some tweaking we were able to keep them to a minimum. We didn't notice any issues with image clarity. Even at 1920x1440 resolution we were able to read the smallest text. Differences in image clarity between the center and edges of the screen are extremely small. Brightness and contrast are excellent, and we enjoyed the picture both when watching DVDs and playing games. The color gamut of the monitor is quite good, although it does not reach the level of the Vision Master Pro 454.
Eizo Flexscan T765
The Eizo brand is not so well known in the world of multimedia, but professionals are familiar with it. The T765 is the newest 19" model with a DiamondTron tube. The monitor's grain varies from 0.24mm in the center to 0.25mm at the edges. The diagonal of the usable part of the screen is only 17.8" versus 18" for competitors. Eizo has reduced the diagonal to reduce distortion and produce a smoother picture. The screen has a Super ErgoCoat coating, which reduces reflections from external sources and improves image clarity. When it comes to design, don't expect Eizo to use any fancy materials or colors. The T765 has a cream color, and from the front the monitor looks somewhat rough and conservative. The monitor is equipped with two types of connectors: 5 BNC and standard 15-pin. The T765 also has a built-in USB hub with 4 ports, one of which is located under the screen and extends. The horizontal frequency is 110 kHz, the bandwidth is 280 MHz. Eizo recommends a resolution of 1280x1024 at 107Hz, but of course it's not the maximum. You can set higher refresh rates, which are just as attractive here as on the ViewSonic P95f (for example, you can set it to 75 Hz in all supported resolutions).
As far as geometry is concerned, the T765 is fine. At high resolutions (starting from 1280x1024) the monitor works great. When switching resolutions, there is no trapezoid or other distortion. We only adjusted the screen positioning. The monitor menu is quite easy to use; the control panel is located on the bottom. The panel allows you to specify four directions, the center is used for confirmation. The menu has many options for any kind of settings, including mixing and moire. One of the advantages of the monitor is that it can be controlled without menus using the included Screen Manager Pro utility. To do this, you just need to install the program and connect the monitor via USB. This solution is much more convenient and ergonomic than using a panel.
The T765 has several Fine Modes that allow you to specify contrast, brightness and color temperature: Movie, Text, Graphics and Browser modes. Switching between them is done with one keystroke. The monitor is also compatible with Windows Movie Mode, which allows you to optimally configure video playback. Video moire is barely noticeable and can be easily removed with the appropriate settings. The same goes for the mixing, which is impeccable. The T765 uses digital convergence correction, which divides the screen into 256 squares. This solution allows you to very accurately adjust the mixing. As for the color gamut, the T765 showed some of the best results in testing, although there were some shortcomings here too. We'd happily crown the T765 a winner considering its price and overall quality. However, as our color chart examination showed, contrast and saturation are good, but not excellent. Even with additional color adjustments, you'll notice that the yellows, for example, aren't as deep or clear as on the Iiyama Vision Master Pro 454 or the ViewSonic P95f. On the other hand, the T765 has several nice touches mentioned above and overall good quality.
Iiyama Vision Master Pro 454
Iiyama is known for the good price/quality ratio of its products, although quality is sometimes lacking in this formula. The company's latest model is the Vision Master Pro 454, also known as HM903DT. The monitor features DiamondTron's High Brightness tube, which makes it stand out from the rest. As the name suggests, High Brightness increases the brightness of the screen. The diagonal of the useful part of the screen is 18"", the grain is 0.25 in the center and 0.27 at the edges. As you can see from the photo, the Vision Master Pro 454 is quite elegant; special attention should be paid to the stand. It is on it that the controls, a pair of 1 W speakers and a 4-port USB hub are placed. The design seems a little blurry, but it is very ergonomic. The monitor is equipped with two 15-pin connectors, allowing you to connect two computers. To switch between them, use the button on the front. The horizontal frequency is 115 kHz, the bandwidth is 300 MHz. The manufacturer allocates a maximum resolution of 1920x1440 at 77 Hz. In practice, most modes (from 800x600 to 1920x1440) are predefined and work optimally at 85 Hz.
From a geometry point of view, the Vision Master Pro 454 is doing well. The quality is not up to the Eizo T765, but it is still acceptable. In predefined resolutions, vertical and horizontal lines are fine up to 1600x1200. Next, you need to make additional settings to get a good rectangular image across the entire screen. The menu here is the same as in other Iiyama models, with the exception of support for additional modes, which, like in the Eizo T765, can be quickly switched. The range of settings options is impressive, especially considering the ability to adjust color purity in the corners. The moire effect is more noticeable here than on the T765, but it can be easily managed. The black-and-white tables did not cause any comments, but it should be noted that, given equal contrast and brightness, the Vision Master Pro 454 does not produce as good blacks as the ViewSonic or Eizo. Brightness and contrast are nearly excellent for both video and gaming, but midtones aren't ideal. To sum it up, Iiyama's latest model is clearly a success, delivering excellent picture quality and ideal for gaming. The contrast and brightness of the monitor will add additional comfort during use.
NEC Multisync FP955
The FP955 is a new and improved model of the FE950Plus. It also features a 19" DiamondTron NF tube, but the horizontal frequency is 110 kHz. Good promotion since the FE950Plus was only 96 kHz. Like other monitors, the diagonal of the usable screen area is 18". The screen uses an OptiClear coating to reduce reflections from external light sources and improve clarity. The design of the monitor is classic, although when turned on the green Multisync sign on the front lights up. Looks funny. Another unique feature of the FP955 is its connectors. It uses not only the usual 15-pin RGB connector, but also DVI (Digital Visual Interface). The purpose of DVI is to perform digital-to-analog conversion inside the monitor rather than on the graphics card, which should reduce distortion. Of course, in such a situation the quality should improve, but this does not apply to the FP955, since it receives the signal via DVI-A - the analog pins of the connector. You can read more about DVI in the article (). So, in any case, the digital-to-analog conversion of the FP955 is performed on the video card. Moreover, the kit comes with a 15-pin-DVI cable, not DVI-DVI, so we are critical of the presence of a DVI connector - it is not needed here. Since adding a DVI input is cheaper than adding another 15-pin port or a BNC port, NEC was clearly motivated by marketing and money rather than anything else. According to our tests, the DVI-A input on the FP955, compared to the 15-pin port, does not degrade the throughput, which is 290 MHz. NEC specifies a maximum resolution of 1920x1440 at 73Hz. This is indeed the case, as we reached a refresh rate of 73.94 Hz, and not a hundredth of Hz more.
The FP955's screen is known as 'unipitch' - with the same grain. That is, unlike Vision Master Pro 454, for example, the grain size here is the same both in the center and at the edges, and is 0.24 mm. This is achieved by adding an electronic deflector to the tube. In terms of geometry, NEC's latest model performs well all the way up to 1600x1200. At higher resolutions, you will have to work hard with the settings to get an acceptable picture. The monitor's menus are easy to use and are navigated using a directional pad and two keys on the front. The menu has all the necessary options, including reducing moire and changing the purity of color in the corners. Color tests showed decent color reproduction, with well-defined midtones and excellent blacks. Brightness and contrast were also not satisfactory, although we liked them less than on the Iiyama Vision Master Pro 454. So, the FP955 is one of the best monitors in the test. While its options and resolution didn't blow us away, and its refresh rate wasn't superb, the monitor's picture quality was excellent and met all of our test criteria. It's a shame that the price of the monitor is too high compared to other worthy models.
CTX PR960F
CTX's PR960F is based on the FD Trinitron tube. The screen uses ARAG coating to reduce extraneous reflection. The flat screen has the same grain size of 0.24 mm over the entire screen area. The appearance is reminiscent of professional models. As for the electronic filling, the bandwidth is 232 MHz, the horizontal frequency is 110 kHz. CTX specifies a maximum resolution of 1800x1440 at 72Hz. In practice, it is a little more, since we were able to set 1920x1440 at 74 Hz, which is not bad. PR960F has not only a 15-pin VGA connector, but also a BNC input (RGBHV). The monitor is also equipped with a two-port USB hub. In addition to everything, the PR960F broke the weight record in our testing - 31 kg, almost two pounds.
You should expect only high-quality geometry from such a monitor. At standard resolutions from 800x600 to 1600x1200, we didn't notice any distortion. The monitor menu is standard; it contains the necessary settings for geometry, positioning and size. The menu also includes options for moire correction and mixing. It's a shame that here you can't correct the color purity by zone and the correctness of the image on the screen; such options can be useful for getting a good image. The overall quality can be considered very good. The PR960F produces good pictures and the screen is quite accurate in its display. You will be able to read even the smallest print. There is no classic moire here, the brightness matches most Trinitron monitors. Colors are well rendered, although they don't reach the same level as the ViewSonic P95f.
NEC Multisync FE950Plus
The NEC FE950+ is based on the DiamondTron NF tube and is slightly lower in performance than the FP955. The 18" screen has OptiClear anti-glare coating. The grain varies from 0.25 mm in the center to 0.27 mm at the edges. The stated horizontal scan frequency is 96 kHz, the maximum resolution is 1792x1344 at 68 Hz. As tests have shown, the maximum acceptable resolution is 1600x1200 at 77 Hz. This resolution is best suited for working with a 19" monitor. Similar to other aperture grille monitors, you'll easily notice the two horizontal wires that support the mask. As for the differences from other models, in the FE950+ they are minimal, since the monitor is not equipped with either a USB hub or speakers. There is only one 15-pin input here.
The FE950+ boasts a 1280x1024 geometry. At 1600x1200, on the other hand, things aren't quite as good, and you'll have to make a number of adjustments to get a somewhat normal image around the edges. The menu is rich and easy to use. It's well made and has all the options found in the best monitors. Note the full range of settings for geometry, color and color purity by zone, moire, vertical and horizontal convergence. The monitor's picture is excellent, as is its stability at 1280x1024. We liked the colors and the brightness too. Halftones are clearly visible, and the overall picture quality can be considered above average. So, FE950+ is a good choice considering the picture quality and low price. But this model is distressed by low refresh rates and unstable behavior at high resolutions.
Sony A420 and G420
As the Sony brand suggests, the A420 is based on an FD Trinitron tube. The monitor stands out for its attractive design. Instead of the usual beige or gray shades, the monitor is painted in metallic gray. The stand, as you can see, is very stylish; instead of the usual base, the monitor rests on small round legs. In fact, the A420 looks like a regular TV and would fit right into a bedroom or living room. So people will buy such a monitor more because of its appearance and design, and not because of its technical characteristics. The A420 has a beautiful FD Trinitron flat screen, grain varies from 0.24 to 0.25. The diagonal of the usable surface of the screen is 18"; the screen uses anti-reflective and antistatic Hi-Con (High Contrast) coating. The monitor is equipped with a 4-port USB hub. The A420 is certified to TCO92 only. It is unlikely that this is due to a discrepancy; rather, they simply did not test the monitor under TCO95 and TCO99. The horizontal scan frequency is 96 kHz. Sony lists a maximum resolution of 1600x1200 at 78Hz. It seems to us that it is much more convenient to work in 1280x1024 at 91 Hz. For those who need something better, but design is not critical, the G420, which we also tested, is more suitable. The quality of the monitor is exactly the same, but the maximum refresh rate in various resolutions is higher (1600x1200 at 87 Hz), which is better suited for working with graphics. The G420 is TCO99 certified and also features a 15-pin connector. In addition, the G420 has an additional ASC setting for automatic scaling and centering. It does work, but the image still doesn't take up all the usable real estate on the screen, so you still have to do some extra adjustments. In addition, the G420 is more expensive than the A420.
The geometry of the A420 is not much different from the NEC FE950+. It works well up to 1280x1024, after which the quality drops exponentially. The menu is beautifully designed, clear and easy to use. It has most of the necessary settings, such as geometry, positioning and temperature, but there are no options for controlling mixing and color purity. It's a shame, but this monitor stands out for nothing more than good standard quality and good picture quality. We liked the picture, the contours are quite clear and the colors are quite decent. We noticed virtually no moire; the brightness and contrast settings are present and were set optimally. Another advantage of the A420 is the subjective improvement in video and picture quality due to the dark background.
ADI Microscan G910
ADI monitors haven't always been good quality monitors, but the G910 with FD Trinitron tube will silence the critics. The monitor has a flat screen, the same 0.24 mm grain along the entire length of the screen. Additional features include a built-in microphone and USB hub. ADI monitors with Trinitron tubes come with Color Wizard, a program that allows you to make all sorts of adjustments, including creating color profiles. The bandwidth is 229.5 MHz, the horizontal frequency is 110 kHz, which theoretically gives 87 Hz at 1600x1200, which is quite good. In practice, the monitor reached 88 Hz at this resolution, and 73 Hz at 1920x1440.
The geometry is not bad, up to 1600x1200. Although you will have to make a few adjustments to get an acceptable result. After 1600x1200 there is a lot of keystone distortion, so you are unlikely to use higher resolutions. The G910's menu is decent, although it lacks zone-by-zone color purity correction and is not as easy to navigate due to the use of only three keys. On the other hand, the menu has many options, among which we can note the adjustment of horizontal and vertical moire. In any case, moire is not noticeable, and the colors are the same over the entire surface. We always expect a good picture from Trinitron, and the color display here is more than correct. Brightness and contrast aren't bad either, although they're not quite up to par with the ViewSonic P95f.
Hitachi CM721F
Hitachi's CM721F uses EDP (Enhanced Dot Pitch) technology, or also called elliptical mask. It is similar to the shadow mask, although it has a few differences, the most noticeable being the better horizontal grain size. On the CM721F, the grain is 0.20mm, which is really very small, but this value is typical for EDP monitors. The CM721F has no connectors, only one built-in 15-pin RGB cable. So if one of the contacts breaks, you will have to send the entire monitor for repair. The bandwidth is 205 MHz, the horizontal frequency is 95 kHz, which theoretically gives 75 Hz at 1600x1200. Practice fully confirms the theory. 75 Hz is the minimum required to work at this resolution, so we can't recommend the CM721F for working at higher resolutions. For example, at 1920x1440 you'll get a miserable 63 Hz.
The geometry of the CM721F did not raise any complaints. At 1024x768 and 1280x1024 everything was fine and no noticeable distortion appeared on the screen. At higher resolutions you will have to adjust the geometry. The menu is quite ordinary, four keys are used for navigation. Options include correction of geometry, colors, brightness, contrast, vertical and horizontal moire. There is no color purity. In terms of picture quality, the CM721F is similar to the LG915FTPlus. The monitors combine the positive qualities of both a shadow mask and an aperture grille. So the monitor looks completely flat and even the smallest font is easy to read. Sometimes some moire appears, which can be easily removed with the appropriate settings. The colors are right, the mixing is great, so we didn't adjust it at all.
Samsung SyncMaster D957DF
Samsung SyncMaster 957DF is the only monitor in testing that is not equipped with a completely flat screen. It uses Dynaflat tubing, which does not use DiamondTron or Trinitron technology. Dynaflat is clearly better than a regular shadow mask because it produces less distortion. Moreover, SyncMaster 959DF uses Highlight Zone technology, also used by Philips, which can adjust the brightness depending on the area of the screen. The adjustment is made by pressing the corresponding key on the front of the display to brighten or darken an area, although you can also increase the brightness across the entire screen, similar to the Mitsubishi Super Bright handsets. The diagonal of the useful part of the display is 18"", with the same grain of 0.24 mm over the entire screen area. This model does not please us with its wealth of connectors. 15-pin RGB built-in cable only. Horizontal frequency - 96 kHz, bandwidth - 250 MHz. The manufacturer specifies a maximum resolution of 1920x1400 at 64 Hz, which is by no means high. Instead, it is recommended to use 1280x1024 at 85Hz, or 1600x1200, but only at 75Hz.
We didn't find any problems with the SyncMaster 957DF's geometry. Some tweaking was required to eliminate keystone noise at 1280x1024. Verticals and horizontals did not cause any reproaches in the preset resolutions. At other resolutions, you'll have to make adjustments to achieve a square image across the entire screen, which, as we've already mentioned, isn't as flat as the Trinitron (for example). So the boundaries are always a little curved. The menu is controlled by four direction keys and two selection keys - 'Exit' and 'Menu'. There are a large number of options available in the menu for precise removal of moire and color temperatures. Despite the Highlight Zone feature, the brightness on the SyncMaster 959DF is not up to par with the leading monitors in our testing - the Iiyama Vision Master Pro 454 and ViewSonic P95f. If you apply this function to the entire screen, the image loses its clarity and stability, which does not help at all. So this monitor is a typical average one and does not contain any special shortcomings. In addition, this monitor is the cheapest in testing.
LG 915FT Plus
The LG 915FTPlus is the only monitor in testing to use Flatron technology, a cross between Trinitron and shadow mask, an attempt to take the advantages of both technologies and avoid their disadvantages. So there are no horizontal wires familiar to Trinitron or DiamonTron, and at the same time, the curved boundaries characteristic of a shadow mask are also absent here. The grain is the same throughout the entire length of the screen and is 0.24 mm. Thanks to Tension Flat Mask technology, the image brightness is also slightly reduced. The horizontal scan frequency is 110 kHz, the pass-through frequency is 235 MHz. The manufacturer specifies a maximum resolution of 1880x1440 at 70 Hz, which is acceptable, but no more. In practice, in more usual resolutions, the monitor gives 74 Hz at 1920x1400 and 89 Hz at 1600x1200, which is much better. The 915FTPlus has the following connectors: 15-pin, five BNC and a 4-port USB hub.
When it comes to geometry, the LG 915FTPlus falls short of the best monitors in testing. Both 1280x1024 and 1600x1200 had keystone distortion on the screen, which is very difficult to correct no matter how much time you spend on it. It's a shame, because the rest of the monitor's parameters are good. The menu is easy to use and well balanced. It contains all kinds of settings, including color purity by zone. We liked the picture, the moire disappeared after proper adjustments, the colors are warm and accurate. I would like to note the quality of black color, which turned out to be better here than other monitors in testing. So, the 915FTPlus is a pretty attractive solution, and would be a good fit for Trinitron-averse users. The monitor costs a little less than its rivals, but the geometric defects are upsetting.
Conclusion
| Manufacturer | Model | Diagonal of effective screen surface | Technology | Price |
| Viewsonic | P95f | 18.1" | Perfect Flat | $499 |
| Eizo | Flexscan T765 | 17.8" | FD Trinitron/Ergoflat | $700 |
| Iiyama | HM903DT | 18.1" | DiamondTron HB | $530 |
| ADI | Microscan G910 | 18.1" | FD Trinitron | $500 |
| CTX | PR960F | 18.1" | FD Trinitron | $460 |
| Nec | Fe950Plus | 18.1" | DiamondTron | $400 |
| LG | 915FTPlus | 18.1" | Flatron | $450 |
| Samsung | SyncMaster D957DF | 18" | DynaFlat | $340 |
| Sony | G420 | 18.1" | FD Trinitron | $500 |
| Hitachi | CM721F | 18.1" | EDP | $470 |
| Sony | A420 | 18.1" | FD Trinitron | $420 |
| Nec | FP955 | 18.1" | DiamondTron | $500 |
As our testing has shown, CRT monitor technology does not stand still. Today you can buy beautiful 19" flat screen models for around $400. Users will love that today FD Trinitron and DiamondTron technologies are significantly less expensive than before, and the good old product lines continue to exist. Testing has shown that most monitors have good pictures and can be used quite comfortably at at least 1280x1024, with a refresh rate of at least 75 Hz for some models, and 85 Hz or more for others. All of the above monitors live up to their title.
But we still liked three monitors more. The Iiayama Vision Master Pro 454 was a pleasant surprise, with excellent picture quality and stability. Previously, we believed that this manufacturer maintains a good price/quality ratio, but often at the expense of quality. The Vision Master Pro 454 combines a relatively reasonable price and good adaptation of the Diamondtron High Brightness tube. Next to it is the ViewSonic P95f, which offers the same excellent picture quality and stability for about the same price. The third winner is the Eizo T675, which has very few complaints and stands out for its ergonomics, although the high price is still somewhat confusing.
Next we will mention the other monitors in testing. All of them, in general, are good and stand out with some of their own characteristics. The Sony A420, for example, by design, will easily fit into the place of a TV in a living room. The FP955 performed well, although it is somewhat more expensive than other mid-rangers. The Samsung SyncMaster 957DF is a cost-saving champion as it has the lowest price in testing. It provides adequate quality and is a good choice for budget-conscious users.