The function of the monitor is to restore the full TV signal output by the camera to an image signal. According to the cathode ray tube (CRT) used, it can be divided into high-grade CRT monitors (600 to 800 lines), high-quality CRT monitors (370 to 500 lines), image monitors (300 to 370 lines), and dual-use CRTs. Monitor (less than 300 lines).
The function of the professional monitor is basically the same as that of the TV set, but due to the special use requirements and standards of the monitor, the line structure and technical specifications are quite different. In contrast, monitors have the following characteristics:
1. The input signal of the monitor in the application television system is an unmodulated positive full TV signal (video signal). Although the TV has a video and audio input terminal (advanced dual-use machine), the most basic is to receive the RF signal.
2. The monitor must display the original appearance of the subject 100% without any additional influence, including the inadequacies of the subject. Televisions, especially color televisions, are designed to satisfy people's visual enjoyment, so the defects of the subject are modified as much as possible and processed in color, so that bright, beautiful images can be viewed.
3. The clarity of the monitor is much higher than that of the TV. In general, the resolution of a TV set is only 270 lines, while professional monitors can generally reach 400 lines (color) and 500 lines (black and white). As for broadcast monitors, it can reach 800 lines (color) and 1000 lines (black and white).
4. The monitor has more adjustment devices and external control mechanisms, mainly because the monitor circuit cannot design any compensation or balance lines.
5, the general monitor does not have high-level, frequency conversion, middle-mounted and other parts, and some do not have audio.
6. The picture tube of a general professional monitor is different from that of a television set, especially a monitor with high definition. According to China's TV standard, the bandwidth of 1MHZ corresponds to 80 TV line definition, then the 6MHZ band can pass 480 lines of image signals. However, whether the signal can be displayed on the fluorescent screen depends on whether the resolution of the picture tube can meet the requirements. Otherwise, a TV with a wide frequency band cannot be converted into a high-definition monitor.
In addition, the frequency response of the monitor's video channel is different from that of the general small-signal amplifier. The load is a picture tube, and the excitation of the picture tube is to achieve a certain brightness contrast. Therefore, the monitor's video final stage amplifier has high back pressure, wide frequency band, medium power, and capacitive load.
For surveillance systems that are not too demanding, an occupancy monitor with video and audio input terminals can be used instead of expensive professional monitors.
Monitors/TVs vary in size and should be selected based on site conditions and other device configurations. In addition to clarity, the observation of the scene is directly related to the distance of viewing. In general, the larger the size, the farther the viewing distance should be; the smaller the size, the closer the viewing distance. Less than or greater than a reasonable viewing distance will cause the image to be unclear and the eyes will be prone to fatigue. The best viewing distance for a typical 14-inch monitor is 1.0 m to 1.5 m, and 21 inches is 1.6 m to 3.0 m.
In addition, with the development of TV technology and computer technology, the performance of CRT is also constantly improving. The emergence of the current flat-panel display has become a new highlight of CRT, and the use of 100Hz digital scanning technology (Digital Scan) technology can completely weaken the tremor phenomenon of moving object images, the picture is more stable, and more beneficial to vision protection. With Progressive Scan, the horizontal scanning lines are multiplied and the vertical sharpness is greatly improved. In addition, the reduction of radiation, the environmentally-friendly and healthy TCO standard will be universally adopted, and the introduction of a 16:9, 100-line high-resolution full-digital monitor supporting the 1920×1080i display format will bring new vitality to CRT monitors. Therefore, CRT monitors will not be quickly replaced by new image display devices and will coexist with new display devices for a long time.
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