The difference between ordinary TV and monitor
2019-03-08 15:09:58
First, the difference between ordinary TV and monitor
The monitor is functionally simpler than the television but in terms of performance but requires higher requirements than the television, reflecting the following three points:
First, the definition of the image: As the traditional TV receives the RF signal emitted by the TV station, the bandwidth of the video image corresponding to this signal is usually less than 6M, so the definition of the TV is usually greater than 400 lines, requiring the monitor to have a high The image sharpness, so the professional monitor in the channel circuit than the traditional television should have bandwidth compensation and lifting circuit, so that the passband is wider, the image clarity is higher.
The second is the degree of color reproduction. If the definition is mainly determined by the amplitude and frequency characteristics of the video channel, the reduction is mainly caused by the chromaticity of the three primary colors red (R), green (G), and blue (B) in the monitor. The phase of the signal and the luminance signal are determined. Since the monitor usually observes static images, the requirement for the color reproduction of the monitor is higher than that of the television. Therefore, the channel for the viewing channel of the professional monitor should have the brightness, color processing, and R, G, and B processing. Accurate compensation circuit and delay circuit to ensure phase synchronization of light/color signals and R, G, B signals.
The third is the stability of the whole machine: When the monitor forms a closed-circuit monitoring system, the monitor usually needs to be used 24 hours a day, 365 days a year without interruption (while the TV usually only works for several hours per day), and some monitor applications. The environment may be harsher, which requires a higher reliability and stability of the monitor. Compared with televisions, in terms of design, the monitor's current, power consumption, temperature and resistance to electrical interference, the ability and margin of electrical shock, and average time between failures are much greater than those of televisions. At the same time, the monitor must also The use of a fully shielded metal shell ensures electromagnetic compatibility and interference performance; in the selection of components, the characteristics of the components used in the monitor, such as voltage resistance, current, temperature, and humidity, are higher than those used by the television; In the installation and debugging, especially the components and the aging process requirements of the whole machine, the requirements of the monitor are also higher. The aging of the whole television during the television manufacturing is usually about 8 hours at the normal temperature on the assembly line, and the whole machine of the monitor Aging requires aging for more than 24 hours in the aging pipeline of a high-temperature, high-humidity, sealed environment to ensure the stability of the entire machine.
What is the difference between an interlaced monitor and a progressive monitor?
Interlaced and progressive lines mainly refer to the way the monitor tubes are scanned. The image of the monitor is a two-dimensional image, and the process of its reproduction is to convert the two-dimensional input image into a one-bit pixel string, and the image is moved from the left side to the right side through the horizontal scanning process; the vertical scanning will horizontally The scanning line moves from the vertical direction at a uniform speed. Interlaced scanning refers to dividing an image into two fields for scanning. The first field (odd field) scans for odd lines such as 1, 3, 5, and the second field (even field) scans for even lines such as 2, 4, and 6; It forms a complete image (ie, a frame). So for the PAL system, scanning 50 fields per second, the field frequency is 50HZ, and the frame frequency is 25HZ; for NTSC, the field frequency is 60HZ, and the frame rate is 30HZ, although in the human visual screen reproduction It is a continuous image, but even field switching will cause the screen flicker and obvious line spacing effect on odd occasions. The progressive scan means that the scan lines are scanned one by one in a row. Interlaced monitors have the disadvantages of poor image quality, low resolution, large noise, and serious image flickering. The progressive scan monitor is used to eliminate the defects of interlaced scanning, converting analog video signals to digital signals, and using digital color decoding to achieve the repetitive use of one line or one signal by means of digital signal storage and control technology (ie, low-speed reading, High-speed readout) 50HZ progressive scan, or increase the frame rate, to achieve 60HZ, 75HZ so 85HZ progressive scan mode. Progressive scanning technology converts input signals into digital video signals through A/D conversion, and then performs digital line decoding and digital image processing circuits to perform line and field scan processing. The channel bandwidth is greatly improved (up to 10 MHz - 20 MHz) and the definition is greatly improved. The noise is greatly reduced, while the progressive display eliminates line spacing and inter-line flicker, while the increase in frame rate (eg, 60 Hz to 85 Hz) reduces or eliminates large area image flicker.
Therefore, when the line-by-line monitor came out, it was very popular among users. Of course, since the progressive monitor uses one line or one field for repeated use, the line frequency is doubled from the interlace, from 15625HZ to 31250HZ, and the 75Hz line-by-line line frequency is 46875Hz. After the line frequency is increased, the stability and reliability of the output stage will be severely tested, and the overall design and manufacturing costs will be greatly increased, so the price of the entire machine is also high.
Third, is the nominal 100Hz monitor currently on the market interlaced or progressive?
As described in Question 2, due to obvious defects in the 50HZ interlaced monitor, we can implement a 50Hz progressive scan by means of a double line, or a 100Hz interlaced scan by means of a doubled field, in addition to a double line + frequency conversion (50Hz field Frequency *1.2 or *1.5) forms 60Hz progressive or 75Hz progressive scan, but so far we have not found domestic and foreign R&D institutions and chip manufacturers to introduce double-row + double-field 100Hz progressive technology and chips, in addition, In order to realize 100Hz progressive display, the line frequency of the kinescope yoke will reach the drive frequency of 62500Hz. The current technology of this high line rate kinescope is also difficult to manufacture (except for the display tube used in the display), so it can be determined. The 100Hz nominal monitor on the market today is only a 100Hz interlace monitor.
The 100Hz interlace scanning technology was once popular in the TV market in previous years, and its representative chip solutions are Philips MK-9 frequency multiplication processing module and Toshiba's digital 100 module. However, with the United States Pixel Technology and Taiding's equalization (variable) frequency 60Hz (75Hz) progressive processing module appears. 100Hz interlaced scanning technology has gradually been eliminated. 100Hz interlace scanning technology and 50Hz interlace scanning technology also have inter-line flicker, apparent crawling, peristaltic movement, image roughness and edge sawing and so on. The 60 Hz and 75 Hz progressive scan monitors are ideally eliminated because of the use of high frame and progressive techniques. Therefore, the 100 Hz interlace technology has basically been replaced by 60 Hz or 75 Hz progressive technology.
4. Why is the monitor more susceptible to magnetization? What should I do if the monitor is magnetized?
The magnetic field surrounding the monitor tube and the magnetic material surrounding the monitor tube, such as the magnetic leakage of the metal cabinet, will cause additional deflection of the electron beam of the electron gun, affecting the color purity and the trajectory accuracy of the electron gun R, G, and B tertiary electron beams. In addition, metal parts inside the color cathode ray tube and its brackets are made of metal components such as an external explosion-proof ring. When the color monitor moves, the orientation of the geomagnetic field will be changed. Magnetizing these components between the geomagnetic field directly or indirectly affects the color of the picture tube. Purity and convergence will cause a partial color cast on the screen. Therefore, it is recommended that the monitor should be placed as far north and south as possible (vertical screen north-south direction) and away from magnetic objects to minimize the influence of the geomagnetic field. There is an automatic degaussing circuit in the monitor. The monitor can eliminate the influence of the magnetization of the external magnetic field in the internal metal parts of the CRT under normal conditions. If the monitor is magnetized (has a poor color purity), the switch can be used to degauss the magnetized metal parts; if the magnetization is severe, even if the switch is still poor in color, the external demagnetization must be used. The way.
5. What is the difference between the performance of the CRT monitor and the LED monitor? Will CRT be replaced by LCD?
Color monitors using cathode ray ray tubes (CRTs) and color monitors using liquid crystal displays (LCDs) are distinguished by the principle of image reproduction. The former uses magnetic deflection drives to implement line-field scanning (also called analog driving). Mode), while the latter uses a dot-matrix drive (also called a digital drive). Therefore, the former often uses television lines to define its sharpness, while the latter defines its resolution by the number of pixels. The clarity 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.
The CRT monitor has the advantages of low cost, high brightness, wide viewing angle and high service life, while the LCD monitor has the advantages of small size (flat plate), light weight, and no flashing and no radiation of the image, but the LCD monitor The main disadvantages are high manufacturing cost, narrow viewing angle (darkened image when viewed from the side, reversed color when viewed from the side), and short service life (usually the LCD screen brightness is reduced to less than 60% of the normal brightness after 5,000 hours of burning, but The average life span of CRT is up to 30,000 hours or more. It should be affirmed that price, perspective, and service life are the three bottlenecks that affect the popularity of LCD monitors. Of course, LCD is one of the most mature leading-edge products of flat panel display devices, and it has been increasingly concerned by manufacturers at home and abroad, and its technology is continuously improving. At present, the LCD screen of the new TFT technology using in-plane switching technology can achieve a horizontal viewing angle of 160° and a vertical viewing angle of 140°. At the same time, the price of LCD screens will increase with the gradual popularity of products and yield. The gradual increase and gradually decline; LCD's life will also be with LCD backlight and liquid crystal material technology continues to improve. Therefore, there is no doubt that after several years (perhaps 5 or 10 years later), LCD monitors may completely replace CRT monitors as the mainstream products in the monitor market.
6. When the monitor is used as the monitor terminal of the matrix control system, why does the matrix controller switch the image for a period of time that is not synchronous?
In the monitoring system, if there is a phase difference between the field sync signals in the image signals output from each front-end device (such as a camera), the monitor will display a period of non-synchronization when the matrix controller switches the image signals of each channel. The larger the phase difference, the longer the time that is not synchronized. Therefore, it is recommended that when constructing a monitoring system, front-end devices with GEN-LOOK input should be used as much as possible, and all front-end devices should use external synchronization. That is, the synchronization of each image signal is controlled by the same synchronization signal. Causes the monitor screen to show sync.
Seven, when using the monitor to observe the image, why sometimes there is image distortion, distortion, line and field asynchronous or even no input signal failure, phenomenon?
1. The monitor's industry standard specifies that the input amplitude of the 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 the BNC head of the transmission cable, the input signal amplitude is much lower than 0.7 pp; either the camera output is not regulated or some irregularity is connected. When the input signal (such as distributor, amplifier, etc.) causes the input signal amplitude to be much larger than 1.4Vp-p, it may cause image distortion, line and field synchronization, etc.
2. Due to the wide video frequency range, video signals are more susceptible to interference during transmission (including 50Hz power interference, electromagnetic interference, etc.), which affects the image quality. Severe disturbances may cause images to be distorted, deformed, raceways, and lines and fields to be out of sync. Therefore, during the installation of the monitoring system, the video line must be far away from sources of electromagnetic interference.
3. The potential difference between the front-end device, the control host device and the terminal device may also interfere with the video signal, resulting in distortion of the image signal or image appearance of a race track, if the whole system is powered on (ie, the front-end device, the master When the equipment and terminal equipment are connected to the BNC head to connect the front and rear equipment when they are powered on, it may be caused by the potential difference between the ground wire of the front and rear equipment (actually the shielding layer of the transmission cable). Fire, this severe flash fire will destroy the components at the input or the ground line in the PCB board casserole. Causes the input to open circuit and input no image fault. Therefore, the construction of monitoring system engineering should be designed and constructed in strict accordance with the specifications. The grounding bus should use copper conductors with sufficient cross-sectional area to ensure that the ground-to-ground resistance of the front and rear ends is <1Ω. The grounding line must not form a closed loop, and must not be short-circuited or mixed with the strong grid neutral line.
Eight, how to define the definition of the monitor? What instrument can detect the clarity of the monitor?
The definition of the monitor is determined by the bandwidth of the monitor video channel and the dot pitch and convergence error of the kinescope. For PAL signals, the channel bandwidth and resolution of the monitor is a 1M78 line. For the NTSC system , for 1M56 line; In addition, to ensure the corresponding monitor clarity, the monitor uses the kinescope dot pitch and convergence error must also meet the corresponding requirements, such as convergence error: monitor horizontal resolution ≤ horizontal width ( Mm)/central convergence error (mm).
It must be pointed out that some manufacturers exaggerate the definition of monitor clarity when the monitor appears. In fact, the evaluation of the monitor definition can be judged by the subjective evaluation of the image on the one hand, and it can also be determined by the display result of a dedicated instrument, an image signal generator with multiple groups of images.
9. Why do some of the same color cameras display color on different color monitors, and some can only display black and white images?
Cameras and monitors as the front and back of the monitoring system, the principle is just the opposite, the former is through the CCD (or other sensor) to convert the imaging of the subject into electrical signals, and processed into a video signal through the video processing circuit; The monitor is used for decomposing the red (R), green (G), blue (B) and luminance (Y) signals from the decoding circuit of the video signal through the video channel, and the R, G is formed by the electron gun driving the picture tube to release the circuit. , B Three beams of electron beam to the screen. The input video signal also simultaneously separates the line and field synchronization signals through the synchronous separation circuit, and generates line and field scanning signals through the line and field deflection coils, so as to prompt the electron beams of the camera screen to fall to the corresponding positions 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 camera produces a color subcarrier frequency shift, 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 that the reproduced image cannot be displayed in color and becomes a black and white image with a moire 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, the monitor may not be able to Present color image. Of course, the monitor's color synchronization range can also be adjusted to be wider (eg, ±500 Hz), but the color subcarrier signal's width and quality factor are equal to each other. 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 composite video signal input from the monitor is seriously degraded or severely distorted, it may cause the reproduced image to be achromatic. This is because the industry standard of the color monitor stipulates that professional-grade monitor input signal amplitude is less than 0.7. Vpp, or high-frequency attenuation due to the use of a non-75Ω standard coaxial cable, causing the color subcarrier signal amplitude to be less than 0.21Vpp, may also cause the reproduced image to be achromatic, in which case it must be added at the time of wire laying. Video amplifier or use 75Ω standard coaxial cable.
The monitor is functionally simpler than the television but in terms of performance but requires higher requirements than the television, reflecting the following three points:
First, the definition of the image: As the traditional TV receives the RF signal emitted by the TV station, the bandwidth of the video image corresponding to this signal is usually less than 6M, so the definition of the TV is usually greater than 400 lines, requiring the monitor to have a high The image sharpness, so the professional monitor in the channel circuit than the traditional television should have bandwidth compensation and lifting circuit, so that the passband is wider, the image clarity is higher.
The second is the degree of color reproduction. If the definition is mainly determined by the amplitude and frequency characteristics of the video channel, the reduction is mainly caused by the chromaticity of the three primary colors red (R), green (G), and blue (B) in the monitor. The phase of the signal and the luminance signal are determined. Since the monitor usually observes static images, the requirement for the color reproduction of the monitor is higher than that of the television. Therefore, the channel for the viewing channel of the professional monitor should have the brightness, color processing, and R, G, and B processing. Accurate compensation circuit and delay circuit to ensure phase synchronization of light/color signals and R, G, B signals.
The third is the stability of the whole machine: When the monitor forms a closed-circuit monitoring system, the monitor usually needs to be used 24 hours a day, 365 days a year without interruption (while the TV usually only works for several hours per day), and some monitor applications. The environment may be harsher, which requires a higher reliability and stability of the monitor. Compared with televisions, in terms of design, the monitor's current, power consumption, temperature and resistance to electrical interference, the ability and margin of electrical shock, and average time between failures are much greater than those of televisions. At the same time, the monitor must also The use of a fully shielded metal shell ensures electromagnetic compatibility and interference performance; in the selection of components, the characteristics of the components used in the monitor, such as voltage resistance, current, temperature, and humidity, are higher than those used by the television; In the installation and debugging, especially the components and the aging process requirements of the whole machine, the requirements of the monitor are also higher. The aging of the whole television during the television manufacturing is usually about 8 hours at the normal temperature on the assembly line, and the whole machine of the monitor Aging requires aging for more than 24 hours in the aging pipeline of a high-temperature, high-humidity, sealed environment to ensure the stability of the entire machine.
What is the difference between an interlaced monitor and a progressive monitor?
Interlaced and progressive lines mainly refer to the way the monitor tubes are scanned. The image of the monitor is a two-dimensional image, and the process of its reproduction is to convert the two-dimensional input image into a one-bit pixel string, and the image is moved from the left side to the right side through the horizontal scanning process; the vertical scanning will horizontally The scanning line moves from the vertical direction at a uniform speed. Interlaced scanning refers to dividing an image into two fields for scanning. The first field (odd field) scans for odd lines such as 1, 3, 5, and the second field (even field) scans for even lines such as 2, 4, and 6; It forms a complete image (ie, a frame). So for the PAL system, scanning 50 fields per second, the field frequency is 50HZ, and the frame frequency is 25HZ; for NTSC, the field frequency is 60HZ, and the frame rate is 30HZ, although in the human visual screen reproduction It is a continuous image, but even field switching will cause the screen flicker and obvious line spacing effect on odd occasions. The progressive scan means that the scan lines are scanned one by one in a row. Interlaced monitors have the disadvantages of poor image quality, low resolution, large noise, and serious image flickering. The progressive scan monitor is used to eliminate the defects of interlaced scanning, converting analog video signals to digital signals, and using digital color decoding to achieve the repetitive use of one line or one signal by means of digital signal storage and control technology (ie, low-speed reading, High-speed readout) 50HZ progressive scan, or increase the frame rate, to achieve 60HZ, 75HZ so 85HZ progressive scan mode. Progressive scanning technology converts input signals into digital video signals through A/D conversion, and then performs digital line decoding and digital image processing circuits to perform line and field scan processing. The channel bandwidth is greatly improved (up to 10 MHz - 20 MHz) and the definition is greatly improved. The noise is greatly reduced, while the progressive display eliminates line spacing and inter-line flicker, while the increase in frame rate (eg, 60 Hz to 85 Hz) reduces or eliminates large area image flicker.
Therefore, when the line-by-line monitor came out, it was very popular among users. Of course, since the progressive monitor uses one line or one field for repeated use, the line frequency is doubled from the interlace, from 15625HZ to 31250HZ, and the 75Hz line-by-line line frequency is 46875Hz. After the line frequency is increased, the stability and reliability of the output stage will be severely tested, and the overall design and manufacturing costs will be greatly increased, so the price of the entire machine is also high.
Third, is the nominal 100Hz monitor currently on the market interlaced or progressive?
As described in Question 2, due to obvious defects in the 50HZ interlaced monitor, we can implement a 50Hz progressive scan by means of a double line, or a 100Hz interlaced scan by means of a doubled field, in addition to a double line + frequency conversion (50Hz field Frequency *1.2 or *1.5) forms 60Hz progressive or 75Hz progressive scan, but so far we have not found domestic and foreign R&D institutions and chip manufacturers to introduce double-row + double-field 100Hz progressive technology and chips, in addition, In order to realize 100Hz progressive display, the line frequency of the kinescope yoke will reach the drive frequency of 62500Hz. The current technology of this high line rate kinescope is also difficult to manufacture (except for the display tube used in the display), so it can be determined. The 100Hz nominal monitor on the market today is only a 100Hz interlace monitor.
The 100Hz interlace scanning technology was once popular in the TV market in previous years, and its representative chip solutions are Philips MK-9 frequency multiplication processing module and Toshiba's digital 100 module. However, with the United States Pixel Technology and Taiding's equalization (variable) frequency 60Hz (75Hz) progressive processing module appears. 100Hz interlaced scanning technology has gradually been eliminated. 100Hz interlace scanning technology and 50Hz interlace scanning technology also have inter-line flicker, apparent crawling, peristaltic movement, image roughness and edge sawing and so on. The 60 Hz and 75 Hz progressive scan monitors are ideally eliminated because of the use of high frame and progressive techniques. Therefore, the 100 Hz interlace technology has basically been replaced by 60 Hz or 75 Hz progressive technology.
4. Why is the monitor more susceptible to magnetization? What should I do if the monitor is magnetized?
The magnetic field surrounding the monitor tube and the magnetic material surrounding the monitor tube, such as the magnetic leakage of the metal cabinet, will cause additional deflection of the electron beam of the electron gun, affecting the color purity and the trajectory accuracy of the electron gun R, G, and B tertiary electron beams. In addition, metal parts inside the color cathode ray tube and its brackets are made of metal components such as an external explosion-proof ring. When the color monitor moves, the orientation of the geomagnetic field will be changed. Magnetizing these components between the geomagnetic field directly or indirectly affects the color of the picture tube. Purity and convergence will cause a partial color cast on the screen. Therefore, it is recommended that the monitor should be placed as far north and south as possible (vertical screen north-south direction) and away from magnetic objects to minimize the influence of the geomagnetic field. There is an automatic degaussing circuit in the monitor. The monitor can eliminate the influence of the magnetization of the external magnetic field in the internal metal parts of the CRT under normal conditions. If the monitor is magnetized (has a poor color purity), the switch can be used to degauss the magnetized metal parts; if the magnetization is severe, even if the switch is still poor in color, the external demagnetization must be used. The way.
5. What is the difference between the performance of the CRT monitor and the LED monitor? Will CRT be replaced by LCD?
Color monitors using cathode ray ray tubes (CRTs) and color monitors using liquid crystal displays (LCDs) are distinguished by the principle of image reproduction. The former uses magnetic deflection drives to implement line-field scanning (also called analog driving). Mode), while the latter uses a dot-matrix drive (also called a digital drive). Therefore, the former often uses television lines to define its sharpness, while the latter defines its resolution by the number of pixels. The clarity 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.
The CRT monitor has the advantages of low cost, high brightness, wide viewing angle and high service life, while the LCD monitor has the advantages of small size (flat plate), light weight, and no flashing and no radiation of the image, but the LCD monitor The main disadvantages are high manufacturing cost, narrow viewing angle (darkened image when viewed from the side, reversed color when viewed from the side), and short service life (usually the LCD screen brightness is reduced to less than 60% of the normal brightness after 5,000 hours of burning, but The average life span of CRT is up to 30,000 hours or more. It should be affirmed that price, perspective, and service life are the three bottlenecks that affect the popularity of LCD monitors. Of course, LCD is one of the most mature leading-edge products of flat panel display devices, and it has been increasingly concerned by manufacturers at home and abroad, and its technology is continuously improving. At present, the LCD screen of the new TFT technology using in-plane switching technology can achieve a horizontal viewing angle of 160° and a vertical viewing angle of 140°. At the same time, the price of LCD screens will increase with the gradual popularity of products and yield. The gradual increase and gradually decline; LCD's life will also be with LCD backlight and liquid crystal material technology continues to improve. Therefore, there is no doubt that after several years (perhaps 5 or 10 years later), LCD monitors may completely replace CRT monitors as the mainstream products in the monitor market.
6. When the monitor is used as the monitor terminal of the matrix control system, why does the matrix controller switch the image for a period of time that is not synchronous?
In the monitoring system, if there is a phase difference between the field sync signals in the image signals output from each front-end device (such as a camera), the monitor will display a period of non-synchronization when the matrix controller switches the image signals of each channel. The larger the phase difference, the longer the time that is not synchronized. Therefore, it is recommended that when constructing a monitoring system, front-end devices with GEN-LOOK input should be used as much as possible, and all front-end devices should use external synchronization. That is, the synchronization of each image signal is controlled by the same synchronization signal. Causes the monitor screen to show sync.
Seven, when using the monitor to observe the image, why sometimes there is image distortion, distortion, line and field asynchronous or even no input signal failure, phenomenon?
1. The monitor's industry standard specifies that the input amplitude of the 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 the BNC head of the transmission cable, the input signal amplitude is much lower than 0.7 pp; either the camera output is not regulated or some irregularity is connected. When the input signal (such as distributor, amplifier, etc.) causes the input signal amplitude to be much larger than 1.4Vp-p, it may cause image distortion, line and field synchronization, etc.
2. Due to the wide video frequency range, video signals are more susceptible to interference during transmission (including 50Hz power interference, electromagnetic interference, etc.), which affects the image quality. Severe disturbances may cause images to be distorted, deformed, raceways, and lines and fields to be out of sync. Therefore, during the installation of the monitoring system, the video line must be far away from sources of electromagnetic interference.
3. The potential difference between the front-end device, the control host device and the terminal device may also interfere with the video signal, resulting in distortion of the image signal or image appearance of a race track, if the whole system is powered on (ie, the front-end device, the master When the equipment and terminal equipment are connected to the BNC head to connect the front and rear equipment when they are powered on, it may be caused by the potential difference between the ground wire of the front and rear equipment (actually the shielding layer of the transmission cable). Fire, this severe flash fire will destroy the components at the input or the ground line in the PCB board casserole. Causes the input to open circuit and input no image fault. Therefore, the construction of monitoring system engineering should be designed and constructed in strict accordance with the specifications. The grounding bus should use copper conductors with sufficient cross-sectional area to ensure that the ground-to-ground resistance of the front and rear ends is <1Ω. The grounding line must not form a closed loop, and must not be short-circuited or mixed with the strong grid neutral line.
Eight, how to define the definition of the monitor? What instrument can detect the clarity of the monitor?
The definition of the monitor is determined by the bandwidth of the monitor video channel and the dot pitch and convergence error of the kinescope. For PAL signals, the channel bandwidth and resolution of the monitor is a 1M78 line. For the NTSC system , for 1M56 line; In addition, to ensure the corresponding monitor clarity, the monitor uses the kinescope dot pitch and convergence error must also meet the corresponding requirements, such as convergence error: monitor horizontal resolution ≤ horizontal width ( Mm)/central convergence error (mm).
It must be pointed out that some manufacturers exaggerate the definition of monitor clarity when the monitor appears. In fact, the evaluation of the monitor definition can be judged by the subjective evaluation of the image on the one hand, and it can also be determined by the display result of a dedicated instrument, an image signal generator with multiple groups of images.
9. Why do some of the same color cameras display color on different color monitors, and some can only display black and white images?
Cameras and monitors as the front and back of the monitoring system, the principle is just the opposite, the former is through the CCD (or other sensor) to convert the imaging of the subject into electrical signals, and processed into a video signal through the video processing circuit; The monitor is used for decomposing the red (R), green (G), blue (B) and luminance (Y) signals from the decoding circuit of the video signal through the video channel, and the R, G is formed by the electron gun driving the picture tube to release the circuit. , B Three beams of electron beam to the screen. The input video signal also simultaneously separates the line and field synchronization signals through the synchronous separation circuit, and generates line and field scanning signals through the line and field deflection coils, so as to prompt the electron beams of the camera screen to fall to the corresponding positions 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 camera produces a color subcarrier frequency shift, 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 that the reproduced image cannot be displayed in color and becomes a black and white image with a moire 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, the monitor may not be able to Present color image. Of course, the monitor's color synchronization range can also be adjusted to be wider (eg, ±500 Hz), but the color subcarrier signal's width and quality factor are equal to each other. 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 composite video signal input from the monitor is seriously degraded or severely distorted, it may cause the reproduced image to be achromatic. This is because the industry standard of the color monitor stipulates that professional-grade monitor input signal amplitude is less than 0.7. Vpp, or high-frequency attenuation due to the use of a non-75Ω standard coaxial cable, causing the color subcarrier signal amplitude to be less than 0.21Vpp, may also cause the reproduced image to be achromatic, in which case it must be added at the time of wire laying. Video amplifier or use 75Ω standard coaxial cable.
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5.We guarantee customers high quality products with competitive price and excellent service
6.Timely delivery
Square Shower Set,Square Shower Kit,Square Shower Head Set,Square Shower Column Set
KaiPing HuiPu Shower Metalwork Industrial CO,LTD , http://www.hp-shower.com