TV monitoring system, the quality of the system, must be reflected from the image on the monitor. Therefore, we can determine and monitor the quality of the TV surveillance system equipment or system construction project based on the image on the monitor, as well as the causes of poor quality and interference and failure, and seek solutions to it.
This article based on the relevant literature, and combined with their own practical work experience, introduced the display of images and their interference from the monitor, analyzed and judged the TV monitoring system or equipment failure causes, and proposed some solutions.
One, there is no image on the monitor
1. The causes and solutions for the display of no-image display caused by devices such as the monitoring host and their connections:
A short circuit or open circuit occurred in the coaxial cable connector output from the microcomputer switching host to the monitor;
The corresponding output terminal of the microcomputer switching host is damaged;
The dual-purpose television is not in the TV state, or the monitor is bad;
If a VCR is connected at the same time, the DVR needs to be powered on and set to TV accordingly.
2. Causes and Solutions for No Image Display Caused by DVR The screen protection is not cancelled or the power management is not properly set. The graphics card is not compatible. You can pass DirectDraw tests. If the tests pass, this is not the reason.
PCI interface contact is not good. You can change a PCI slot test.
The board may be damaged. You can consider changing a card test.
3, the camera causes no image display causes and their solutions First check whether the power supply is connected, if connected, then detect the power supply voltage and supply current is in line with the camera's requirements;
Whether the camera lens aperture is open (usually caused by the aperture closed), if the auto iris, video or DC drive and the camera corresponds, the lens control line is connected (including three variable lens)? If the connection is correct, check the decoder problem;
Whether the video coaxial cable and the BNC connector is in poor contact, open circuit or short circuit, and the camera itself.
4, fiber transmission mode caused by monitoring? The reason why the device does not have an image display and its solution method is to check whether the connection of the electric and optical cable, the light emitting device and the terminator is correct, and then check whether the supply voltage and current meet the requirements.
The output carrier of the optical transmitter has no video input signal. Check the video input process on the optical transmitter: Disconnect the video signal from the optical transmitter and input the video signal directly to the monitor with the video coaxial cable. If there is any image, it indicates that there is a problem with the optical transmitter.
Optical receiver problems. If there is no problem with the light transmitter, the monitor and the connection, and the screen is still black, then the light receiver is more light;
Monitor problem. If there is no problem with the light receiver and transmitter, the connection with the monitor is correct, and the screen is still black.
Second, poor image quality, snow-like
On the image of the monitor, a relatively uniform snowflake-like disturbance occurs and the image quality is poor. The main reason for this phenomenon can be analyzed from the following two aspects:
1. The cause of the snow on the monitor image caused by the optical fiber transmission method and the solution to the problem. First, the optical power meter is used to check the optical power entering the optical receiving terminal. If the optical power meets the requirements, a more optical receiving terminal is required.
Optical transmitter problems. If it is checked that the optical power entering the optical receiving terminal is lower than the calibration value, the optical power meter and an optical fiber jumper are used to check the optical output of the optical transmitting terminal. If the optical output is low, a more optical transmitting terminal is required;
Optical connector problem. If the light output of the optical transmitter is checked to meet the requirements, it is an optical connector problem, and the optical connector can be wiped cleanly or with better quality.
The transmission distance is too far, and the loss of the optical fiber is too great. An optical amplifier must be added.
2. Coaxial cables and other transmission lines cause surveillance? The reason why the image has snow on the device and its solution method The illumination intensity of the monitored point of view is too low, which makes the amplitude of the video signal smaller;
The camera's sensitivity is low or the head aperture is too small;
The monitor itself has quality problems;
The video transmission line is not good, so that the video signal declines too much, resulting in a smaller amplitude of the video signal;
The quality of video equipment such as video amplifiers in video transmission lines is not good;
Video cable plugs and sockets are soldered badly.
The solution is to use good quality video equipment and video transmission lines to ensure that the amplitude of the video signal meets the specifications of the standard.
Third, the image has a wood grain
The image on the monitor is grainy. When it is light, it often does not overwhelm the normal image, but in severe cases it even destroys the synchronization and makes the image unviewable. The cause of this kind of failure phenomenon is more and more complicated. There are roughly the following reasons:
1, the quality of the video transmission line is not good The quality of the video transmission line is not good, mainly in the following aspects:
The shielding performance of the wire is poor, such as the screen is not a good quality copper wire screen, or the screen screen is too thin to be shielded. Generally, a 96-copper shielded copper cable should be used, and the core wire should be a multi-copper coaxial cable.
The line resistance of this kind of video line is too large, which causes a large attenuation of the signal. The core wire of the coaxial cable should be a copper wire with a relatively low resistivity. If the core wire resistance is too large, the signal attenuation will be too large, which will increase the interference of the mesh.
The characteristic impedance of this kind of video line is not 75Ω, and the distribution parameters are beyond specification.
It should be pointed out that the appearance of wood grain on the screen is not necessarily the fault of the video line (for example, there are still two reasons), so it is necessary to be accurate and careful when judging. Only when the other possibilities are ruled out, the remaining video cable (if no remainder is left, a segment of such cable must be intercepted in the system) is sent to the inspection department for inspection. If the test result is unqualified, it can be determined as a cable quality problem. If it has been judged that the quality of the video transmission line is not good, it is difficult to solve it by changing the line or the like since the cabling has been completed. Therefore, the use of video cables that comply with the standards and requirements before construction must be guaranteed in advance. Never consider the need to save money and purchase poor quality video cables. If it is definitely a cable quality problem, the best way is to replace all of these cables. This is the best way to completely solve the problem.
It is worth mentioning that if the interference is not very serious, you can try to adopt the way of purifying the power supply and connecting the online UPS to the entire system, sometimes to reduce or basically eliminate the interference. However, this method may not be effective because of the difference in signal conditions in the space around the system, or it is sometimes used or sometimes not used.
2. The power supply system is not "clean"
The power source referred to here is not "clean", that is, to enter the comparison? The interference signal specifically refers to an interference signal superimposed on a 50 Hz sine wave. This kind of interference signal on the power supply comes from the thyristor equipment used in the power grid. In particular, high-current, high-voltage thyristor devices have a very serious pollution to the power grid, which leads to the fact that the power supply in the same power grid is not "clean." If there are high-power thyristor frequency modulation speed control devices, thyristor rectifier devices, thyristor AC-DC converter devices, etc. in the power grid, it will cause pollution to the power supply.
The solution to this situation is relatively simple, as long as the entire system uses a clean power or power supply using an online UPS, it can basically eliminate this interference.
3. There is a strong electromagnetic interference source near the system. There is a strong electromagnetic interference source near the TV monitoring system. This type of interference will cause faults. In this case, it can be judged by investigating and understanding the environmental conditions in the vicinity of the television monitoring system. If this is the reason, the solution is to strengthen the shielding of video equipment such as video cameras and video amplifiers, as well as to perform good grounding of the video cable connections, plugs, and pipe outlets.
Fourth, the image has equal spacing vertical bars
On the screen of the monitor, there are sometimes several vertical bars with equal intervals. The frequency of such interference signals is basically an integral multiple of the line frequency. If you use an oscilloscope to view the waveform of the disturbed image, you will find that a higher-order line-frequency harmonic oscillation waveform is superimposed on the back of the horizontal synchronization head, and the vertical bar interference is caused by this.
1. The cause of this interference is due to the fault phenomenon caused by the mismatch of the characteristic impedance of the transmission line. It is caused by impedance mismatch because the characteristic impedance of the video transmission line is not 75Ω;
Through the analysis of the waveform and the quantitative measurement of the video cable, it was found that this impedance does not meet the requirements of the video cable, the distribution parameters do not meet the requirements, which is one of the reasons for the impedance mismatch.
Therefore, this interference phenomenon is caused by the fact that the characteristic impedance and distribution parameters of the video cable do not meet the requirements. If there is a serious mismatch between the "starting" or "terminal" impedance of poor coaxial cable or signal transmission of 250m or more, even an open end may cause the above interference.
2, the solution to rely on "start resistance series" or "terminal parallel resistance." That is, "start" string 75Ω resistor, "terminal" and 75Ω resistor to avoid impedance mismatch and distribution parameters are too large;
Use high quality coaxial cable. That is, the outer shielding net is copper, not less than 96 series, and the core wire is also multi-strand copper material;
It is worth mentioning that when the video transmission distance is within 150m, using the video cable with the above impedance mismatch and distribution parameters is too large, the above interference phenomenon may not occur. Therefore, in a system where the transmission distance is widely different, analysis of this type of failure should not be confused by short-distance and no interference.
The fundamental solution to the above problem is to ensure the quality of the video cable. When necessary, the cable should be sampled and tested.
Fifth, the image has black and white bars and scroll up and down
1. Causes and judgments on the monitor A black bar or white bar appears on the monitor screen, and it may scroll up or down slowly. The reason for this phenomenon is mostly caused by the ground loop generated by the system and the introduction of 50Hz AC interference. However, this kind of failure may also occur due to poor performance of the power supply of the control unit such as a camera or matrix switcher, or partial damage, or system grounding or equipment grounding. Therefore, when analyzing such failure phenomena, the two different causes of failures must be distinguished first.
To distinguish between the problem of power supply and the problem of ground loops, it is common to connect the output signal of a video camera with no problem to the nearest control host. If the above phenomenon does not appear on the monitor, it indicates that the control host has no problem. . Next, a portable monitor can be connected nearby to the video output of the front camera, and one camera can be checked one by one to find out if there is a problem with the power supply. If so, proceed with the treatment; if not, the interference is caused by ground loops and other causes.
2. Problems caused by power supply problems or system and equipment grounding problems Video equipment, especially the camera power supply voltage is too low, or the power supply is not "clean", the ripple coefficient is relatively large, or the larger interference is strung in.
Poor system or equipment grounding;
Video equipment such as cameras or video amplifiers or video matrices have quality problems;
There are more serious electromagnetic interferences in the surrounding areas of the system, such as welding, radio transmission, and interference of large motors and large relays.
Six, the image has a large area of ​​reticulate 1, the cause of the large area of ​​the screen produced on the monitor, will lead to a serious decline in image quality, serious images are usually destroyed, that is not form images and synchronization signals. The main cause of this failure is:
This type of interference often occurs on BNC connectors, or on other types of video connectors.
The faults caused by the short circuit and open circuit of the video cable's core wire and shielding network, such as the cable laying, make the outer shield damaged, and the shielded network cable is torn off;
After the cable is laid, it will encounter corrosive liquid, gas or rodent damage, which will damage the outer shield of the cable;
The connection between the cable plug and the video equipment is not good.
2, the solution method Obviously, this type of fault is relatively easy to judge, because this kind of fault phenomenon occurs, it is often not the entire system of signals in each way have problems, but only in the bad number of those connections. As long as you carefully check these connectors one by one, you can solve this problem.
1. Causes On the monitor, the image has trails, glitches or distortions, or even out of sync. This is mainly due to the following reasons:
The video transmission line adopts inferior coax cable, or the cable shielding line is connected by only a few small network cables, or there is a disconnection in the middle;
In the video transmission line, the BNC plug is badly soldered;
The transmission distance is long, no video amplifier is added (if the device is added, the device is of poor quality), and the 75Ω impedance is seriously mismatched;
The monitor or camera itself is out of sync, or the camera power supply voltage is too low, such as 12VDC voltage is less than or equal to 10V;
The power supply is not "clean" and it breaks into the interference signal.
If high-frequency wired, wireless, or fiber-optic transmission methods are used, most of them are quality problems of high-frequency transmission equipment or optical fiber transmission equipment. For example, if a radio frequency equipment is of poor quality, the synchronization head is limited in amplitude and cut.
2. Solution If you suspect a device, you can use alternative methods. Others correct for the cause, so that the transmission line can meet the requirements.
Image ghosting <br> <br> seven or image ghosting
1. Causes On the monitor, the displayed image overlaps with the shadow of another image. When the image is bright, the shadow does not look serious. When the image is dark, the ghost is more obvious. The reason for this failure is:
The video transmission line uses a poor quality coaxial cable, or the outer shield of the cable is damaged badly, or the cable or system is badly grounded.
The wiring in the system is seriously unreasonable, causing crosstalk to each other. For example, if the transmission line between the transmission coaxial cable and another cable is unreasonable, serious signal and crosstalk are caused.
The isolation of the video matrix is ​​too small to meet the technical requirements;
Load impedance is not 75Ω, but does not match;
If you use high-frequency, wireless transmission, it may be the system's interference modulation and intermodulation too large.
2, the solution to the solution is that if it is a device, you can use alternative methods to determine, and other for the reasons to correct.
Eight, the image is light, the contrast is too small
1. The reason why the image of the monitor is pale and the contrast is too small is mainly due to the insufficient amplitude of the video signal. The specific reasons are:
The image contrast of the monitor is improperly adjusted or the quality of the monitor itself is a problem;
The transmission distance is too far or the attenuation of the video transmission line is too great, and the plugs and sockets of the transmission line are badly soldered.
The illuminance at the monitoring point is too low, or the camera sensitivity is low or the lens aperture is too small.
2. The solution to the problem The solution is to add the device for line amplification and compensation so that the video signal amplitude can reach the specified requirements.
Nine, the image is not clear, the edges are not clear or color is missing
1. Cause The image is not clear, the edges are not clear, and the details are lost. In severe cases, color signal loss or color saturation is too small. The specific reasons are:
The loss of the high-frequency end of the image signal is so great that the signal at frequencies above 3 MHz is essentially lost;
The transmission distance is too long, and there is no amplification compensation device in the middle, and the amplitude attenuation of the video signal is too large;
The distribution capacitance of the video transmission cable is too large, so that the high frequency component is attenuated too much;
The resolution of the camera and monitor is not high;
Video signal path bandwidth is too narrow, such as video amplifier bandwidth is too narrow, or transmission cable quality is low;
In the transmission link, there is a concentrated distribution of equivalent capacitance between the core wire and the shielded wire of the transmission line.
2, the solution can be solved for the above reasons, such as high-frequency compensation, amplification compensation.
Image tone distortion
Ten, image tone distortion
This is a fault phenomenon that easily occurs in long-distance video baseband transmission.
1. The main cause of tone distortion is caused by the large phase shift of the high-frequency band caused by the long-distance transmission line. When the transmission distance is not far, image tone distortion is not easily recognized by human eyes.
2, the solution should be added phase compensator. Its preventive measure is to use high-quality coaxial cable, and the transmission line should be short and not long.
Eleventh, the mosaic of image picture and video file playback
1, due to the host signal is not good, the network is not good, resulting in loss of some video and audio signals;
2. During the period when the client generated the mosaic video, did he have any other reasons that caused serious shortage of resources? For example, while the client is previewing the data transmitted from the host, it is performing a multi-channel playback operation that exceeds the system capability, thereby consuming the CPU resources. Therefore, once the host resource is exhausted, video data cannot be written to the hard disk normally, so mosaic may occur.
Twelve, the image has animated
1, the server host corresponding channel video settings, the frame rate is adjusted too low;
2. The bandwidth of the network communication is not enough. At this time, the video quality of the host should be appropriately lowered.
3. Since the server host sets this channel to the LAN transmission mode and is in the same LAN as the first-level client and the extended client, the extended client may not be previewed properly at this time.
Normally, when there is a problem in the system, the system recovery disk that is to be brought up is put into the floppy disk drive to restart the system. At this time, the system will automatically recover, that is, it will return to the factory settings. After the system recovery is complete, remove the floppy disk and restart the machine. When the system starts up, set it again according to your own needs.
Thirteen, the image screen has a sense of jitter
The reason is because the display refresh rate is set too low.
The solution is: enter the "Display Properties", click "Settings", select "Advanced", and then select "Monitor", adjust the new frequency to 75Hz, determine the exit can solve this problem.
This article based on the relevant literature, and combined with their own practical work experience, introduced the display of images and their interference from the monitor, analyzed and judged the TV monitoring system or equipment failure causes, and proposed some solutions.
One, there is no image on the monitor
1. The causes and solutions for the display of no-image display caused by devices such as the monitoring host and their connections:
A short circuit or open circuit occurred in the coaxial cable connector output from the microcomputer switching host to the monitor;
The corresponding output terminal of the microcomputer switching host is damaged;
The dual-purpose television is not in the TV state, or the monitor is bad;
If a VCR is connected at the same time, the DVR needs to be powered on and set to TV accordingly.
2. Causes and Solutions for No Image Display Caused by DVR The screen protection is not cancelled or the power management is not properly set. The graphics card is not compatible. You can pass DirectDraw tests. If the tests pass, this is not the reason.
PCI interface contact is not good. You can change a PCI slot test.
The board may be damaged. You can consider changing a card test.
3, the camera causes no image display causes and their solutions First check whether the power supply is connected, if connected, then detect the power supply voltage and supply current is in line with the camera's requirements;
Whether the camera lens aperture is open (usually caused by the aperture closed), if the auto iris, video or DC drive and the camera corresponds, the lens control line is connected (including three variable lens)? If the connection is correct, check the decoder problem;
Whether the video coaxial cable and the BNC connector is in poor contact, open circuit or short circuit, and the camera itself.
4, fiber transmission mode caused by monitoring? The reason why the device does not have an image display and its solution method is to check whether the connection of the electric and optical cable, the light emitting device and the terminator is correct, and then check whether the supply voltage and current meet the requirements.
The output carrier of the optical transmitter has no video input signal. Check the video input process on the optical transmitter: Disconnect the video signal from the optical transmitter and input the video signal directly to the monitor with the video coaxial cable. If there is any image, it indicates that there is a problem with the optical transmitter.
Optical receiver problems. If there is no problem with the light transmitter, the monitor and the connection, and the screen is still black, then the light receiver is more light;
Monitor problem. If there is no problem with the light receiver and transmitter, the connection with the monitor is correct, and the screen is still black.
Second, poor image quality, snow-like
On the image of the monitor, a relatively uniform snowflake-like disturbance occurs and the image quality is poor. The main reason for this phenomenon can be analyzed from the following two aspects:
1. The cause of the snow on the monitor image caused by the optical fiber transmission method and the solution to the problem. First, the optical power meter is used to check the optical power entering the optical receiving terminal. If the optical power meets the requirements, a more optical receiving terminal is required.
Optical transmitter problems. If it is checked that the optical power entering the optical receiving terminal is lower than the calibration value, the optical power meter and an optical fiber jumper are used to check the optical output of the optical transmitting terminal. If the optical output is low, a more optical transmitting terminal is required;
Optical connector problem. If the light output of the optical transmitter is checked to meet the requirements, it is an optical connector problem, and the optical connector can be wiped cleanly or with better quality.
The transmission distance is too far, and the loss of the optical fiber is too great. An optical amplifier must be added.
2. Coaxial cables and other transmission lines cause surveillance? The reason why the image has snow on the device and its solution method The illumination intensity of the monitored point of view is too low, which makes the amplitude of the video signal smaller;
The camera's sensitivity is low or the head aperture is too small;
The monitor itself has quality problems;
The video transmission line is not good, so that the video signal declines too much, resulting in a smaller amplitude of the video signal;
The quality of video equipment such as video amplifiers in video transmission lines is not good;
Video cable plugs and sockets are soldered badly.
The solution is to use good quality video equipment and video transmission lines to ensure that the amplitude of the video signal meets the specifications of the standard.
Third, the image has a wood grain
The image on the monitor is grainy. When it is light, it often does not overwhelm the normal image, but in severe cases it even destroys the synchronization and makes the image unviewable. The cause of this kind of failure phenomenon is more and more complicated. There are roughly the following reasons:
1, the quality of the video transmission line is not good The quality of the video transmission line is not good, mainly in the following aspects:
The shielding performance of the wire is poor, such as the screen is not a good quality copper wire screen, or the screen screen is too thin to be shielded. Generally, a 96-copper shielded copper cable should be used, and the core wire should be a multi-copper coaxial cable.
The line resistance of this kind of video line is too large, which causes a large attenuation of the signal. The core wire of the coaxial cable should be a copper wire with a relatively low resistivity. If the core wire resistance is too large, the signal attenuation will be too large, which will increase the interference of the mesh.
The characteristic impedance of this kind of video line is not 75Ω, and the distribution parameters are beyond specification.
It should be pointed out that the appearance of wood grain on the screen is not necessarily the fault of the video line (for example, there are still two reasons), so it is necessary to be accurate and careful when judging. Only when the other possibilities are ruled out, the remaining video cable (if no remainder is left, a segment of such cable must be intercepted in the system) is sent to the inspection department for inspection. If the test result is unqualified, it can be determined as a cable quality problem. If it has been judged that the quality of the video transmission line is not good, it is difficult to solve it by changing the line or the like since the cabling has been completed. Therefore, the use of video cables that comply with the standards and requirements before construction must be guaranteed in advance. Never consider the need to save money and purchase poor quality video cables. If it is definitely a cable quality problem, the best way is to replace all of these cables. This is the best way to completely solve the problem.
It is worth mentioning that if the interference is not very serious, you can try to adopt the way of purifying the power supply and connecting the online UPS to the entire system, sometimes to reduce or basically eliminate the interference. However, this method may not be effective because of the difference in signal conditions in the space around the system, or it is sometimes used or sometimes not used.
2. The power supply system is not "clean"
The power source referred to here is not "clean", that is, to enter the comparison? The interference signal specifically refers to an interference signal superimposed on a 50 Hz sine wave. This kind of interference signal on the power supply comes from the thyristor equipment used in the power grid. In particular, high-current, high-voltage thyristor devices have a very serious pollution to the power grid, which leads to the fact that the power supply in the same power grid is not "clean." If there are high-power thyristor frequency modulation speed control devices, thyristor rectifier devices, thyristor AC-DC converter devices, etc. in the power grid, it will cause pollution to the power supply.
The solution to this situation is relatively simple, as long as the entire system uses a clean power or power supply using an online UPS, it can basically eliminate this interference.
3. There is a strong electromagnetic interference source near the system. There is a strong electromagnetic interference source near the TV monitoring system. This type of interference will cause faults. In this case, it can be judged by investigating and understanding the environmental conditions in the vicinity of the television monitoring system. If this is the reason, the solution is to strengthen the shielding of video equipment such as video cameras and video amplifiers, as well as to perform good grounding of the video cable connections, plugs, and pipe outlets.
Fourth, the image has equal spacing vertical bars
On the screen of the monitor, there are sometimes several vertical bars with equal intervals. The frequency of such interference signals is basically an integral multiple of the line frequency. If you use an oscilloscope to view the waveform of the disturbed image, you will find that a higher-order line-frequency harmonic oscillation waveform is superimposed on the back of the horizontal synchronization head, and the vertical bar interference is caused by this.
1. The cause of this interference is due to the fault phenomenon caused by the mismatch of the characteristic impedance of the transmission line. It is caused by impedance mismatch because the characteristic impedance of the video transmission line is not 75Ω;
Through the analysis of the waveform and the quantitative measurement of the video cable, it was found that this impedance does not meet the requirements of the video cable, the distribution parameters do not meet the requirements, which is one of the reasons for the impedance mismatch.
Therefore, this interference phenomenon is caused by the fact that the characteristic impedance and distribution parameters of the video cable do not meet the requirements. If there is a serious mismatch between the "starting" or "terminal" impedance of poor coaxial cable or signal transmission of 250m or more, even an open end may cause the above interference.
2, the solution to rely on "start resistance series" or "terminal parallel resistance." That is, "start" string 75Ω resistor, "terminal" and 75Ω resistor to avoid impedance mismatch and distribution parameters are too large;
Use high quality coaxial cable. That is, the outer shielding net is copper, not less than 96 series, and the core wire is also multi-strand copper material;
It is worth mentioning that when the video transmission distance is within 150m, using the video cable with the above impedance mismatch and distribution parameters is too large, the above interference phenomenon may not occur. Therefore, in a system where the transmission distance is widely different, analysis of this type of failure should not be confused by short-distance and no interference.
The fundamental solution to the above problem is to ensure the quality of the video cable. When necessary, the cable should be sampled and tested.
Fifth, the image has black and white bars and scroll up and down
1. Causes and judgments on the monitor A black bar or white bar appears on the monitor screen, and it may scroll up or down slowly. The reason for this phenomenon is mostly caused by the ground loop generated by the system and the introduction of 50Hz AC interference. However, this kind of failure may also occur due to poor performance of the power supply of the control unit such as a camera or matrix switcher, or partial damage, or system grounding or equipment grounding. Therefore, when analyzing such failure phenomena, the two different causes of failures must be distinguished first.
To distinguish between the problem of power supply and the problem of ground loops, it is common to connect the output signal of a video camera with no problem to the nearest control host. If the above phenomenon does not appear on the monitor, it indicates that the control host has no problem. . Next, a portable monitor can be connected nearby to the video output of the front camera, and one camera can be checked one by one to find out if there is a problem with the power supply. If so, proceed with the treatment; if not, the interference is caused by ground loops and other causes.
2. Problems caused by power supply problems or system and equipment grounding problems Video equipment, especially the camera power supply voltage is too low, or the power supply is not "clean", the ripple coefficient is relatively large, or the larger interference is strung in.
Poor system or equipment grounding;
Video equipment such as cameras or video amplifiers or video matrices have quality problems;
There are more serious electromagnetic interferences in the surrounding areas of the system, such as welding, radio transmission, and interference of large motors and large relays.
Six, the image has a large area of ​​reticulate 1, the cause of the large area of ​​the screen produced on the monitor, will lead to a serious decline in image quality, serious images are usually destroyed, that is not form images and synchronization signals. The main cause of this failure is:
This type of interference often occurs on BNC connectors, or on other types of video connectors.
The faults caused by the short circuit and open circuit of the video cable's core wire and shielding network, such as the cable laying, make the outer shield damaged, and the shielded network cable is torn off;
After the cable is laid, it will encounter corrosive liquid, gas or rodent damage, which will damage the outer shield of the cable;
The connection between the cable plug and the video equipment is not good.
2, the solution method Obviously, this type of fault is relatively easy to judge, because this kind of fault phenomenon occurs, it is often not the entire system of signals in each way have problems, but only in the bad number of those connections. As long as you carefully check these connectors one by one, you can solve this problem.
1. Causes On the monitor, the image has trails, glitches or distortions, or even out of sync. This is mainly due to the following reasons:
The video transmission line adopts inferior coax cable, or the cable shielding line is connected by only a few small network cables, or there is a disconnection in the middle;
In the video transmission line, the BNC plug is badly soldered;
The transmission distance is long, no video amplifier is added (if the device is added, the device is of poor quality), and the 75Ω impedance is seriously mismatched;
The monitor or camera itself is out of sync, or the camera power supply voltage is too low, such as 12VDC voltage is less than or equal to 10V;
The power supply is not "clean" and it breaks into the interference signal.
If high-frequency wired, wireless, or fiber-optic transmission methods are used, most of them are quality problems of high-frequency transmission equipment or optical fiber transmission equipment. For example, if a radio frequency equipment is of poor quality, the synchronization head is limited in amplitude and cut.
2. Solution If you suspect a device, you can use alternative methods. Others correct for the cause, so that the transmission line can meet the requirements.
Image ghosting <br> <br> seven or image ghosting
1. Causes On the monitor, the displayed image overlaps with the shadow of another image. When the image is bright, the shadow does not look serious. When the image is dark, the ghost is more obvious. The reason for this failure is:
The video transmission line uses a poor quality coaxial cable, or the outer shield of the cable is damaged badly, or the cable or system is badly grounded.
The wiring in the system is seriously unreasonable, causing crosstalk to each other. For example, if the transmission line between the transmission coaxial cable and another cable is unreasonable, serious signal and crosstalk are caused.
The isolation of the video matrix is ​​too small to meet the technical requirements;
Load impedance is not 75Ω, but does not match;
If you use high-frequency, wireless transmission, it may be the system's interference modulation and intermodulation too large.
2, the solution to the solution is that if it is a device, you can use alternative methods to determine, and other for the reasons to correct.
Eight, the image is light, the contrast is too small
1. The reason why the image of the monitor is pale and the contrast is too small is mainly due to the insufficient amplitude of the video signal. The specific reasons are:
The image contrast of the monitor is improperly adjusted or the quality of the monitor itself is a problem;
The transmission distance is too far or the attenuation of the video transmission line is too great, and the plugs and sockets of the transmission line are badly soldered.
The illuminance at the monitoring point is too low, or the camera sensitivity is low or the lens aperture is too small.
2. The solution to the problem The solution is to add the device for line amplification and compensation so that the video signal amplitude can reach the specified requirements.
Nine, the image is not clear, the edges are not clear or color is missing
1. Cause The image is not clear, the edges are not clear, and the details are lost. In severe cases, color signal loss or color saturation is too small. The specific reasons are:
The loss of the high-frequency end of the image signal is so great that the signal at frequencies above 3 MHz is essentially lost;
The transmission distance is too long, and there is no amplification compensation device in the middle, and the amplitude attenuation of the video signal is too large;
The distribution capacitance of the video transmission cable is too large, so that the high frequency component is attenuated too much;
The resolution of the camera and monitor is not high;
Video signal path bandwidth is too narrow, such as video amplifier bandwidth is too narrow, or transmission cable quality is low;
In the transmission link, there is a concentrated distribution of equivalent capacitance between the core wire and the shielded wire of the transmission line.
2, the solution can be solved for the above reasons, such as high-frequency compensation, amplification compensation.
Image tone distortion
Ten, image tone distortion
This is a fault phenomenon that easily occurs in long-distance video baseband transmission.
1. The main cause of tone distortion is caused by the large phase shift of the high-frequency band caused by the long-distance transmission line. When the transmission distance is not far, image tone distortion is not easily recognized by human eyes.
2, the solution should be added phase compensator. Its preventive measure is to use high-quality coaxial cable, and the transmission line should be short and not long.
Eleventh, the mosaic of image picture and video file playback
1, due to the host signal is not good, the network is not good, resulting in loss of some video and audio signals;
2. During the period when the client generated the mosaic video, did he have any other reasons that caused serious shortage of resources? For example, while the client is previewing the data transmitted from the host, it is performing a multi-channel playback operation that exceeds the system capability, thereby consuming the CPU resources. Therefore, once the host resource is exhausted, video data cannot be written to the hard disk normally, so mosaic may occur.
Twelve, the image has animated
1, the server host corresponding channel video settings, the frame rate is adjusted too low;
2. The bandwidth of the network communication is not enough. At this time, the video quality of the host should be appropriately lowered.
3. Since the server host sets this channel to the LAN transmission mode and is in the same LAN as the first-level client and the extended client, the extended client may not be previewed properly at this time.
Normally, when there is a problem in the system, the system recovery disk that is to be brought up is put into the floppy disk drive to restart the system. At this time, the system will automatically recover, that is, it will return to the factory settings. After the system recovery is complete, remove the floppy disk and restart the machine. When the system starts up, set it again according to your own needs.
Thirteen, the image screen has a sense of jitter
The reason is because the display refresh rate is set too low.
The solution is: enter the "Display Properties", click "Settings", select "Advanced", and then select "Monitor", adjust the new frequency to 75Hz, determine the exit can solve this problem.
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