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Monitors

The most important output devices, where we can see immediately our graphics results, are monitors. Because their development did not lag behind that of any other information technologies, we can state that for a reasonable price we can get a quality monitor. Despite the fast development and increases in LCD monitor production volumes, the basic element in the field of monitors remains the cathode ray tube (CRT) monitor.

The majority of classical display monitors are based on the principle of the cathode screen. This screen is based on an emitting cathode and a phosphor screen. In creating a display, the emitting cathode emits a beam of rays which passes through focusing electrode systems, and then it is swept through an electromagnetic field to the monitor screen, where it emits a weakening light. For keeping a quality image, it continual renewal is necessary. This is called as monitor renewal frequency. Sweeping is the result of two pairs of electrodes, moving the electron beam in the horizontal and in the vertical directions concurrently. To form a color image, we need three cathodes, a special luminescent layer, and a screen mask. On the screen, there are regularly spread three luminescent points, representing individual components of RGB. These three points appear for the human eye as only one resulting point.

As a standard, the sweeping electrodes use a 90-degree angle of sweeping. Some of the latest models, use also a 100-degree angle, which enables a reduction in overall dimensions, but on the other hand, brings higher requirements for displaying.

In the contrast to LCD monitors where the given diagonal sets the dimension of a monitor, in classical monitors the 17-inch monitor only rarely exceeds 16 inches, and a 15-inch unit has in fact only about 13.8 up to 14.1 inches, a 17-inch one about 15.7 up to 16.2 inches, and a 14-inch model is about 13.3 inches.

For determining the renewal frequency is important the value of the horizontal frequency given in kHz (kilo Hertz), which gives the number of lines per second which can be drawn on the given monitor.

    The value of the vertical frequency means what frequency the monitor can deal with.

Example : Calculation of the frequency of the monitor with horizontal frequency 70 kHz with the resolution 1024x768.

    The number of displayed lines is 768. The beam can draw 70 000 lines, because the transition to another line takes about 7 percent (this value is approximate, and with every monitor type it depends on the producer of the relevant monitor), so the resulting frequency is:

 Resulting frequency = (70 000 * 0.93 ) / 768 = 85 Hz



Maximum renewal frequency

 For a monitor with the given horizontal frequency in the given resolution

 Note: These values are only an example of which frequencies a monitor uses in the case of a given resolution. In no case can you expect that a 14-inch monitor with 30 kHz can run in the resolution 1600x1200 with 23 Hz. Real renewal frequencies depend on the given monitor.

18.5.2 Categorization of CRT monitors by mask type

    At present, we can meet with three types of mask in CRT monitors.

1. Cathode display with dot mask.  
       Most frequently is used a display with a dot mask. In front of the screen there is a dotted invar foil where display points are separated. The quality of the resulting image is proportional to the distance of the dots in this mask. The lower the distance, the better quality the image. Currently this distance is in the range 0.25 ? 0.28 mm.
   
   
2. Cathode display with the slot grid .  
       Newer types of display use a grid with pre-stressed wires in the vertical direction. To ensure the stability of this sort of grid, there are two wires whose shades are apparently visible in the display. This type of design is used in monitors like: SONY, TRINITRON, and MITSUBHITSHI DIAMONDTRON. Their advantage is the excellent quality of colors and higher contrast and brightness
   
   
3. Cathode display with slot mask . 
       The new display combines a slot grid with a dot mask.
   
   

18.5.3 What minimum requirements a monitor should fulfill

    When buying a new monitor, you should in the first place realize that in working with it your eyes are in a game. Accordingly, if we have a good quality monitor, your eyes do not get tired so quickly and strained. Therefore don't skimp, invest in a high quality monitor. It should comply with the following requirements: in the working resolution a renewal frequency of at least 85 Hz plus some of the certificates MPR-II, TCO' 95, TCO' 99, and EPA EnergyStar. The image should be quality, stable, and not blinking, small distances between points (0.28 mm good, 0.26 mm excellent, 0.24 mm the best), moir? control, digital control, on screen menu (OSM), and horizontal frequency: with a 15-inch model of at least 70 kHz, with a 17-inch model at least 86 kHz, with a 19-inch model at least 96 kHz.

18.5.4 What is the most appropriate resolution for monitors.

    The important criterion is the real resolution that can be used in a given monitor in relation to its diagonal.

In conclusion: Do not use the monitor in a resolution other than those recommended, even if only to a limited extent, otherwise you can overfatigue your eyes.

18.5.5 Radiation and ergonomics

     VGreat attention is paid to the damaging effects of monitors on humans. In the course of working at a PC often there are headaches and deterioration of sight. These problems are due to the wrong working environment and wrong setting of the display system.

Some practical advice:

1. Place great importance on the correct layout of surrounding light sources reflecting off the monitor and diminishing the readability of the text
   
2. Use the recommended resolution for a given monitor
   
3. Renewal frequency at least 85 Hz
   

Radiation load in front of the monitor :


Radiation load in an environment :

    The most important point with ergonomics evaluation is the maximum frequency of image renewal in various resolutions. The main requirement is a uniform shining display, without blinking or flickering of the image. The second parameter is the anti-reflection feature of the surface of the display. A quality monitor must have a stable display in transits from clear into dark picture, while replaying a video and clear switching in the course of changing the resolution of the screen.

18.5.6 Terms and abbreviations

 

	CRT (Cathode Ray Tube): the cathode ray tube is used in classical monitors. The picture is formed through a continually renewed electron beam on a screen covered by a luminescent material
	Degaussing (or de-magnetizing): removal of any distortion due to magnetizing the screen.
	Color temperature: defines character of white color established on the screen of the display through the rate of basic colors ? red, green, and blue.
	Convergence (taper): controlling rays of the basic color so that they establish with line. Errors in this feature result in a worsening sharpness and color hues mainly in white lines.
	LCD (Liquid Crystal Display): (liquid crystal display): flat displays based on using changes in the optical features of so-called liquid crystals in relation to the changes of an electric field acting upon them
	Moire: nunwanted disturbing patterns of a wave character due to interference between image elements, the defined image signal, and the actual decomposition of image elements defined on the retina via the mask or the grid of the display.
	Renewal frequency of the image (often only 'refre') determines the number of complete renderings of the image per second.
	Spacing of image points is the smallest diagonal distance between image points of the same color; at present gap spacing is given also for the horizontal which are smaller and comparable to the spacing of a strip of the same color, given for a screen with an aperture grid.
	VESA (Video Electronics Standards Association), is the organization dealing with standards for video and communication between the monitor and the graphical card.
	TCO There is frequently seen a sticker on monitors stating 'TCO95' or 'TCO99'. What in fact does this logo mean? It is the certificate of an organization (Swedish Trade Unions), http://www.tco-info.com) in cooperation with the Swedish Nature Protection organization and NUTEK (National Swedish Commission for Industrial Development) who appraise the relationship of a given monitor (or other device) to the environment and health of the user. Gradually, there have been established the following standards: MPR I (1990). MPR II (1991), TCO 92 (1992), TCO 95 (1995), TCO (1998). The better the monitor complies with a standard the better quality of the monitor. Today, the minimum requirement is that monitors should comply with the standard TCO 95.