1. Will the CRT monitor be replaced by an LCD monitor?
A color monitor using a cathode ray tube (CRT) and a color monitor using a liquid crystal display (LCD) differ in the principle of image reproduction. The former uses a magnetic deflection drive to implement a field scan method (also called an analog drive). The latter, while the latter uses a dot matrix drive (also known as digital drive). Thus the former often uses television lines to define its sharpness, while the latter defines its resolution by the number of pixels. The sharpness of a CRT monitor is mainly determined by the channel bandwidth of the monitor and the dot pitch and convergence error of the picture tube, while the latter is determined by the number of pixels of the LCD screen used. CRT monitors have the advantages of low price, high brightness, wide viewing angle and high service life, while LCD monitors have the advantages of small size (flat shape), light weight, no flickering and no radiation of images, but LCD monitors. The main disadvantages are high cost and narrow viewing angle (the image becomes dark when viewed from the side, and the color drifts even if it is reversed). The service life is short (usually the brightness of the LCD screen drops below 60% of the normal brightness after 5000 hours of burning, but The average life of CRT can reach more than 30,000 hours. It should be affirmed that price, viewing angle and service life are the three major bottlenecks affecting the popularity of LCD monitors. Of course, LCD, as one of the most mature front-end products of flat panel display devices, has been paid more and more attention by domestic and foreign manufacturers, and its technology is constantly improving. At present, the LCD screen of the new film body (TFT) process using in-plane switching technology has a horizontal viewing angle of 160° and a vertical viewing angle of 140°. At the same time, the price of the LCD screen will gradually increase with the product. And the gradual increase in output and gradually decline; LCD's service life will also increase with the continuous improvement of LCD backlight and liquid crystal material technology. So it is undoubted that after a few years (may be 5 or 10 years later) LCD monitors are entirely possible to replace CRT monitors as the mainstream product in the monitor market.
Second, when the monitor is used as the monitor terminal of the matrix control system, why is there a period of unsynchronization when switching images in the matrix controller?
In the monitoring system, if there is a phase difference in the field sync signal in the image signal outputted by each front-end device (such as a camera), when the matrix controller switches each image signal, the monitor will be out of sync for a period of time. The larger the phase difference, the longer the time of unsynchronization. Therefore, it is recommended to use a front-end device with external synchronization (GEN-LOOK) input when constructing the monitoring system, and all front-end devices use the external synchronization mode, that is, the synchronization of each image signal is controlled by the same synchronization signal. Causes the monitor screen to display synchronization.
3. When using a monitor to observe an image, why do image distortions, distortions, unsynchronized fields, or even input signals fail?
1. The industry standard for monitors specifies that the input signal amplitude of a professional monitor is 1Vp-P±3dB (about 0.7Vp-P-1.4Vp-p) and the input impedance is 75 ohms. Therefore, if the input signal is not standardized due to cable attenuation, impedance mismatch or BNC head of the transmission cable, the input signal amplitude is much lower than 0.7pp; or because the output of the camera is not standardized or some irregularities are accessed. When the access device (such as a distributor, amplifier, etc.) causes the input signal amplitude to be much larger than 1.4Vp-p, the image distortion and the line field may be unsynchronized.
2. Due to the wide frequency range of video, video signals are more susceptible to interference during transmission (including 50Hz power supply interference, electromagnetic wave interference, etc.), thus affecting image quality. Serious interference may result in image distortion, distortion, raceway, and field synchronization. Therefore, during the installation of the monitoring system, the video line must be kept away from electromagnetic interference sources.
3. The potential difference between the front-end device, the control host device and the terminal device may also interfere with the video signal, causing distortion of the image signal or image rolling, if the entire system is powered on (ie front-end equipment, master control) When the device and the terminal device are both connected to the front and rear devices of the BNC head when they are powered on, the ground potential may be caused by the potential difference between the ground wire of the front and rear devices (actually the shielding layer of the transmission cable). Fire, this severe fire will destroy the components at the input or the ground level wire in the PCB casserole. The input is open and the input has no image failure. Therefore, the construction of the monitoring system project should be designed and constructed in strict accordance with the specifications. The grounding busbar shall be made of copper conductor with sufficient cross-sectional area to ensure that the ground-to-ground resistance of the front and rear ends is <1Ω. The grounding wire shall not form a closed loop and shall not be short-circuited or mixed with the neutral line of the strong power grid.
4. How is the definition of the monitor defined? What instrument can detect the clarity of the monitor?
The clarity of the monitor is determined by the bandwidth of the monitor video channel and the dot pitch and convergence error of the picture tube. For the PAL signal, the conversion relationship between the channel bandwidth and the resolution is 1M78 line. For the NTSC system, 1M56 line; in addition, to ensure the corresponding clarity of the monitor, the pitch and convergence error of the picture tube used by the monitor must also meet the corresponding requirements, for example, for convergence error: monitor horizontal resolution ≤ horizontal width ( Mm) / Center Convergence Error (mm) It must be pointed out that some manufacturers exaggerate the nominality of the monitor when the monitor is on the scene. In fact, the judgment of the definition of the monitor can be discriminated by the subjective evaluation of the image, and can also be discriminated by the display result of the dedicated signal-image signal generator with the multi-group image.
5. Why do the same color camera display color on different color monitors, and some can only display black and white images?
The camera and monitor are used as the front and rear devices of the monitoring system. The principle is just the opposite. The former converts the image of the subject into an electrical signal through a CCD (or other sensor device) and processes it into a video signal through the video processing circuit; The monitor is used to decompose the video signal through the decoding circuit of the video channel to red (R), green (G), blue (B) and luminance (Y) signals, and drive the electrons of the picture tube through the release circuit to form R, G and B three electron beams are taken to the screen. The input video signal also separates the line and field sync signals through the synchronous separation circuit, and generates line and field scan signals through the line and field deflection coils, so that the electron beams that are directed to the screen fall to the corresponding positions one by one, and finally reproduce a frame. Stable image. For PAL color video signals, the chrominance signal is usually modulated on a color subcarrier with a center frequency of 4.43 MHz, if the color subcarrier frequency generated by the camera is shifted, or the 4.43 MHz load wave oscillation of the monitor decoding circuit If the center frequency of the device is shifted, it is possible to make the reproduced image unable to display color and become a black and white image with a moiré signal. The color subcarrier synchronization range specified by the color monitor industry standard is 4.43MHz±300Hz. Therefore, if the color subcarrier frequency offset of the composite video signal output by the camera exceeds ±300Hz, it may not be heavy on the monitor. Now color image. Of course, the color synchronization range of the monitor can also be adjusted wider (such as ±500Hz), but the width and quality factor of the color subcarrier signal are gram, and if the synchronization range is intentionally enlarged, the color noise will increase accordingly. That is, the quality of the color signal will also decrease accordingly.
On the other hand: if the amplitude of the composite video signal input by the monitor is severely degraded or severely distorted, it may also cause the image to be achromatic. This is because the industry standard for color monitors requires professional-grade monitor input signal amplitudes below 0.7. Vpp, or high-frequency attenuation due to the use of a non-75Ω standard coaxial cable, resulting in a color subcarrier signal amplitude of less than 0.21Vpp, may also result in a reproduction of the image without a color, then it must be added when the line is applied The video amplifier is either a 75Ω standard coaxial cable.
A color monitor using a cathode ray tube (CRT) and a color monitor using a liquid crystal display (LCD) differ in the principle of image reproduction. The former uses a magnetic deflection drive to implement a field scan method (also called an analog drive). The latter, while the latter uses a dot matrix drive (also known as digital drive). Thus the former often uses television lines to define its sharpness, while the latter defines its resolution by the number of pixels. The sharpness of a CRT monitor is mainly determined by the channel bandwidth of the monitor and the dot pitch and convergence error of the picture tube, while the latter is determined by the number of pixels of the LCD screen used. CRT monitors have the advantages of low price, high brightness, wide viewing angle and high service life, while LCD monitors have the advantages of small size (flat shape), light weight, no flickering and no radiation of images, but LCD monitors. The main disadvantages are high cost and narrow viewing angle (the image becomes dark when viewed from the side, and the color drifts even if it is reversed). The service life is short (usually the brightness of the LCD screen drops below 60% of the normal brightness after 5000 hours of burning, but The average life of CRT can reach more than 30,000 hours. It should be affirmed that price, viewing angle and service life are the three major bottlenecks affecting the popularity of LCD monitors. Of course, LCD, as one of the most mature front-end products of flat panel display devices, has been paid more and more attention by domestic and foreign manufacturers, and its technology is constantly improving. At present, the LCD screen of the new film body (TFT) process using in-plane switching technology has a horizontal viewing angle of 160° and a vertical viewing angle of 140°. At the same time, the price of the LCD screen will gradually increase with the product. And the gradual increase in output and gradually decline; LCD's service life will also increase with the continuous improvement of LCD backlight and liquid crystal material technology. So it is undoubted that after a few years (may be 5 or 10 years later) LCD monitors are entirely possible to replace CRT monitors as the mainstream product in the monitor market.
Second, when the monitor is used as the monitor terminal of the matrix control system, why is there a period of unsynchronization when switching images in the matrix controller?
In the monitoring system, if there is a phase difference in the field sync signal in the image signal outputted by each front-end device (such as a camera), when the matrix controller switches each image signal, the monitor will be out of sync for a period of time. The larger the phase difference, the longer the time of unsynchronization. Therefore, it is recommended to use a front-end device with external synchronization (GEN-LOOK) input when constructing the monitoring system, and all front-end devices use the external synchronization mode, that is, the synchronization of each image signal is controlled by the same synchronization signal. Causes the monitor screen to display synchronization.
3. When using a monitor to observe an image, why do image distortions, distortions, unsynchronized fields, or even input signals fail?
1. The industry standard for monitors specifies that the input signal amplitude of a professional monitor is 1Vp-P±3dB (about 0.7Vp-P-1.4Vp-p) and the input impedance is 75 ohms. Therefore, if the input signal is not standardized due to cable attenuation, impedance mismatch or BNC head of the transmission cable, the input signal amplitude is much lower than 0.7pp; or because the output of the camera is not standardized or some irregularities are accessed. When the access device (such as a distributor, amplifier, etc.) causes the input signal amplitude to be much larger than 1.4Vp-p, the image distortion and the line field may be unsynchronized.
2. Due to the wide frequency range of video, video signals are more susceptible to interference during transmission (including 50Hz power supply interference, electromagnetic wave interference, etc.), thus affecting image quality. Serious interference may result in image distortion, distortion, raceway, and field synchronization. Therefore, during the installation of the monitoring system, the video line must be kept away from electromagnetic interference sources.
3. The potential difference between the front-end device, the control host device and the terminal device may also interfere with the video signal, causing distortion of the image signal or image rolling, if the entire system is powered on (ie front-end equipment, master control) When the device and the terminal device are both connected to the front and rear devices of the BNC head when they are powered on, the ground potential may be caused by the potential difference between the ground wire of the front and rear devices (actually the shielding layer of the transmission cable). Fire, this severe fire will destroy the components at the input or the ground level wire in the PCB casserole. The input is open and the input has no image failure. Therefore, the construction of the monitoring system project should be designed and constructed in strict accordance with the specifications. The grounding busbar shall be made of copper conductor with sufficient cross-sectional area to ensure that the ground-to-ground resistance of the front and rear ends is <1Ω. The grounding wire shall not form a closed loop and shall not be short-circuited or mixed with the neutral line of the strong power grid.
4. How is the definition of the monitor defined? What instrument can detect the clarity of the monitor?
The clarity of the monitor is determined by the bandwidth of the monitor video channel and the dot pitch and convergence error of the picture tube. For the PAL signal, the conversion relationship between the channel bandwidth and the resolution is 1M78 line. For the NTSC system, 1M56 line; in addition, to ensure the corresponding clarity of the monitor, the pitch and convergence error of the picture tube used by the monitor must also meet the corresponding requirements, for example, for convergence error: monitor horizontal resolution ≤ horizontal width ( Mm) / Center Convergence Error (mm) It must be pointed out that some manufacturers exaggerate the nominality of the monitor when the monitor is on the scene. In fact, the judgment of the definition of the monitor can be discriminated by the subjective evaluation of the image, and can also be discriminated by the display result of the dedicated signal-image signal generator with the multi-group image.
5. Why do the same color camera display color on different color monitors, and some can only display black and white images?
The camera and monitor are used as the front and rear devices of the monitoring system. The principle is just the opposite. The former converts the image of the subject into an electrical signal through a CCD (or other sensor device) and processes it into a video signal through the video processing circuit; The monitor is used to decompose the video signal through the decoding circuit of the video channel to red (R), green (G), blue (B) and luminance (Y) signals, and drive the electrons of the picture tube through the release circuit to form R, G and B three electron beams are taken to the screen. The input video signal also separates the line and field sync signals through the synchronous separation circuit, and generates line and field scan signals through the line and field deflection coils, so that the electron beams that are directed to the screen fall to the corresponding positions one by one, and finally reproduce a frame. Stable image. For PAL color video signals, the chrominance signal is usually modulated on a color subcarrier with a center frequency of 4.43 MHz, if the color subcarrier frequency generated by the camera is shifted, or the 4.43 MHz load wave oscillation of the monitor decoding circuit If the center frequency of the device is shifted, it is possible to make the reproduced image unable to display color and become a black and white image with a moiré signal. The color subcarrier synchronization range specified by the color monitor industry standard is 4.43MHz±300Hz. Therefore, if the color subcarrier frequency offset of the composite video signal output by the camera exceeds ±300Hz, it may not be heavy on the monitor. Now color image. Of course, the color synchronization range of the monitor can also be adjusted wider (such as ±500Hz), but the width and quality factor of the color subcarrier signal are gram, and if the synchronization range is intentionally enlarged, the color noise will increase accordingly. That is, the quality of the color signal will also decrease accordingly.
On the other hand: if the amplitude of the composite video signal input by the monitor is severely degraded or severely distorted, it may also cause the image to be achromatic. This is because the industry standard for color monitors requires professional-grade monitor input signal amplitudes below 0.7. Vpp, or high-frequency attenuation due to the use of a non-75Ω standard coaxial cable, resulting in a color subcarrier signal amplitude of less than 0.21Vpp, may also result in a reproduction of the image without a color, then it must be added when the line is applied The video amplifier is either a 75Ω standard coaxial cable.
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