TCO 99

Let's consider the main requirements to screen monitors reflected in the standard ТСО 99.

Screen monitors

All requirements presented to electron-beam (CRT) screen monitors, are divided into 6 main categories. In first two the properties describing visual ergonomics of the device - clearness of the image and its stability are joined. The clearness of the image is estimated according to 8 parameters:

1. Linearity - at output to the screen of a matrix of the image the units, which generate it columns and strings, should be drawn up on direct and not breaking lines; otherwise image loses clearness. The maximum deviation from a straight line should not make more than 1 % on half of active screen (on width or on height).

2. Orthogonality - geometrically correct build-up of perpendicular lines. Violations of a perpendicularity horizontal and vertical lines gives an appearance of the typical phenomenon of "cushion". The mean deviation on height and width should not be no more than 0, 02, and on a diagonal - 0,03.

3. Level of luminosity - quantity of projected light. The luminosity can be determined both for one point of a oscillator of light, and for any part of an illuminated surface. For an estimation of luminosity of the screen as a whole, and also separate symbol the second technique takes. The sense of this requirement consists in support of sufficient luminosity of the screen (taking into account the dispelled lighting), at which the user should not strain eyes to understand, that on the screen is reflected. A required value of the parameter - not less than 100 Cd on a square meter, and advisable - 125.

4. Uniformity of lighting - support of an identical level of luminosity of the screen on a hole active region. This parameter is calculated as the ratio of maximum luminosity in a viewed zone to minimum. For realization of an estimation of illumination uniformity all working square of the screen monitor takes as an active region. The strong discontinuity can give an error perception of the information, which is outputed on the screen. The standard assigns to this parameter do not quit for frameworks of a relation 1,5:1 and even narrower range is recommended - 1,25:1.

5. The screen contrast - sufficient contrast between the separate screen symbol and its environment. It is clear, that it is extremely difficult to read the symbol, which is not differed from a background on luminosity. This parameter is calculated with the formulas of contrast modulation; the valid value should not be less than 0,5, and recommended - 0,7.

6. Level of reflection - conditional coefficient between actual luminosity of a frame and standard luminosity for white color. A degree of reflection from a glass of the screen monitor calculated in gloss here is taken into account. The closer illumination to rated and the less light is mirrored by glass, the more convenient is to read from the screen monitor. TCO-99 sets a maximum level of reflection peer to 30 unites, and illumination of a frame - not less than 20 % from luminosity of the screen (the range 20-75 %) is recommended).

7. Variation of temperature of color - saturation of white light is frequently measured through so-called temperature of color. So, for example, light radiated usual filament lamp, has very low temperature, while white clouds on a bright summer palate - very high. Color temperature is measured in degrees on a Kelvin scale. Depending on conditions of illumination of a workstation, ТСО-99 installs some values - 9300, 7500, 6500, 5000 ^oК.

8. The uniformity of color - visual characteristic describing, how homogeneously looks the display at its %100 -s' flood filling with a white color. At distortion of the color characteristics the screen monitor cannot be used. The standard admits relative offset on scales RGB no more than on 0,01, and recommends - 0,005.

The indexes of stability of the image describe, how the screen monitor manages to save the static image constant. The requirements to speed of the vertical scanning and working permission are introduced in this section:

• 14 ", 15 ": 800x600
• 17 ": 1024x768
• 19 ", 21 ": 1280x1024

Thus the speed of the scanning should not be less than 85 kGz, and it is recommended - 100 kGz.

The following section of ТСО-99 is directly interlinked with questions of safety of the user, because it concerns those effects, which the screen monitor renders on an environment, and factors of an environment effecting on stability of the screen monitor work.

So:

1. The influence of external magnetic fields - in the cathode-ray tube a ray is inspected through magnetic fields, the availability near to the working screen monitor of a source of radiomagnetic radiation can give an interference and in the issue a disbalance of the image. The screen monitor should have a sufficient degree of protection, for such problems did not arise in conditions of its application at office or house.

2. The radioactive radiation – the most dangerous for the user negative effect of work behind the electron-beam screen monitor is a danger to be subjected to radioactive radiation. The closer radiation level of the screen monitor to a natural background, the more safely it for the user. The valid radiation level according to ТСО-99 should not to exceed 5000 nGy at one hour.

3. The electrostatic potential - originate from an difference of potentials between the cathode CRT and environment on a surface of the screen. The availability of a potential in limits 0,5 В. is admitted

4. The variable electric fields arise between objects, which have different electrical potentials. In our case it is the screen monitor, and, for example, user. The negative consequences of work in such field can have an effect variously.

5. A variable magnetic field – the same it is fair for electric fields.

6. The power conservation mode - one of sore points for western users, where an electricity costs much more. The standard provides two levels of power conservation work, with consumption no more than 15 and 5 W.

The fifth group of the characteristics describes electrical safety of the screen monitor. Basically same approaches which are fair for other office technics are applied here; the standard IEC 60 950 lays in their basis.

And, at last, the requirements presented to convenience of the screen monitor tunings are also entered to the composition of the standard.