Video Monitoring 12 Failure Analysis
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1. Because the connection between the monitoring system equipment involves many lines, if the processing is not good, especially if the line connected to the main equipment is improperly connected or connected incorrectly, there will be disconnection, short circuit, poor insulation between the lines, miswiring, etc. Causes the performance of the device to be degraded or even damaged. In this case, cool analysis and troubleshooting should be performed according to the fault phenomenon to determine what kind of fault phenomenon may occur when there is a problem with the line connection. In addition, it should be noted that the connections between the various system devices and the various lines should meet the requirements for long-term operation of the monitoring system.
2. The mismatch of the characteristic impedance of the transmission cable may cause some vertical bars with equal spacing on the monitor screen, and the frequency of the interference signal is basically an integral multiple of the line frequency. This interference phenomenon is caused by the fact that the characteristic impedance and distribution parameters of the video cable do not meet the requirements. For such interference, the impedance of each device in the system should be matched as much as possible. Especially when the video cable is purchased, the cable quality must be ensured. If necessary, the cable should be sampled and tested.
3, the communication interface or communication protocol and other parameters are not set well, this situation often occurs between the control host and decoder or control keyboard and other devices with communication control relationship. In other words, the selected control host and decoder or control keyboard, etc., are not set during the installation of the communication protocol and other parameters, so the host, decoder, control keyboard, etc. should pay attention to the communication protocol and other parameters during installation Settings.
4. Common faults of video interference.
* A black bar or white bar appears on the monitor screen and scrolls up or down, which is the so-called 50 Hz power frequency interference. This type of interference is caused by the potential difference loop between the front end and the control center, which causes potential difference loops to enter the system. It is also possible that the power supply performance of the device itself is reduced.
* The image has snowflake noise. This kind of interference is mainly caused by signal attenuation on the transmission line and coupling of high-frequency interference.
* The video image has ghosting, or the image is whitish, the character is jittery, or there are several vertical bars with the same spacing on the screen of the monitor. This is because the characteristic impedance between the video transmission line or the device is not 75Ω, resulting in impedance mismatch.
* Twill interference, jitter, power interference. When this interference is slight, it does not overwhelm the normal image, but when it is severe, the image is distorted and cannot be viewed. The reason for this is more and more complicated. For example, the quality of the video transmission line is not good, especially the shielding performance is poor, or the power supply of the power supply system has clutter, and there may be a strong interference source near the system.
* Large area moire interference, also known as single-frequency interference. This phenomenon is mainly caused by the short circuit caused by the short-circuit of the video cable's core wire and the shield, or the failure caused by the open circuit, or due to the bad contact of the BNC connector.
5, equipment failure caused by power problems, there are the following possibilities:
* Incorrect supply line or supply voltage;
* The power is not enough (or the line of a certain power supply line is enough, the pressure drop is too large, etc.);
* Short circuit, open circuit, instantaneous overvoltage, etc. in the transmission line of the power supply system.
It should be noted that the device may be damaged due to a power supply error or an instantaneous overvoltage. Therefore, before the supply of electricity, it must be carefully and strictly checked and checked. It must not be taken lightly.
6, due to the video cable's core and shielding network short circuit, open circuit caused by the failure. This kind of failure manifests itself in a deep and chaotic large-area moire on the monitor, so that the image is completely destroyed and images and synchronization signals cannot be formed. This happens mostly on BNC connectors or other types of video connectors. That is, when such a fault occurs, it is not always a problem in the entire signal line, but merely in the number of unfavorable connections. As long as these joints are carefully checked one by one, it can be solved.
7. Space radiation interference introduced by the transmission line. The reason for this interference phenomenon is that there are strong and high-frequency space radiation sources near the transmission system, the system front-end, or the central control room. The first solution to this situation is to build a system, to achieve a comprehensive understanding of the surrounding environment, and then try to avoid or stay away from radiation sources; Second, when the radiation source can not be avoided, the front-end and center equipment to strengthen the shielding, The pipeline of the transmission line adopts steel pipe and is well grounded.
8. The pan/tilt's faulty pan/tilt common faults are often not used in operation soon or cannot be turned at all. In addition to product quality reasons, this situation is generally caused by the following reasons:
* The pan/tilt head that only allows the camera to be mounted is lifted during use. The hoisting method leads to an increase in the operating load of the pan/tilt. Therefore, the use of the hoisting method will soon cause damage to the drive mechanism of the pan/tilt, or even burn the motor.
* The total weight of the camera and its protective cover exceeds the weight of the PTZ. Especially for PTZs that are used outdoors, the weight of the protective cover is often too large, and there is often the problem that the PTZ will not move (especially the vertical direction).
* The outdoor pan/tilt is malfunctioning or even damaged due to poor ambient temperature, too low or waterproof, antifreeze and other poor performance.
* When the distance is too far, the keyboard (including the lens) and the pan/tilt cannot be controlled by the decoder through the operation keyboard. This is mainly because when the distance is too far, the attenuation of the control signal is too great and the control signal received by the decoder is too weak. At this time, a relay box should be installed at a certain distance to amplify the control signal.
9, the matrix host does not clean the image switch. This kind of failure is generally manifested in the screen after the cut, such as superimposed with other screen disturbances, or other lines of image synchronization signal interference. This is caused by the poor quality of the matrix switch and the lack of isolation between the images. If a radio frequency transmission system is used, it may also be caused by the system's cross-talk modulation and excessive modulation.
10, the monitor image contrast is too small, the image is light. If this phenomenon is not the problem of controlling the host computer and the monitor itself, it means that the transmission distance is too far and the video transmission line is attenuated too much. In this case, the line amplification and compensation device should be added.
11, the image clarity is not high, the details of the missing part, serious color signal may be missing or color saturation is too small and other phenomena, which is the high-frequency end of the image signal loss is too large, that is more than 3MHz frequency signal caused by the loss. In this case, the high frequency signal attenuation is too great due to the long transmission distance, and there is no amplification compensation device in the middle; or the distribution capacitance of the video transmission cable is too large; or because the transmission line core and shield line appear in the transmission link. Focused distributed equivalent capacitance.
12, color distortion. This is a fault phenomenon that easily occurs in long-distance video baseband transmission. It is also mainly caused by the transmission line being too long, causing excessive attenuation in the high frequency band of the signal. In this case, a compensator should be added.
A large-scale television monitoring system that operates in conjunction with burglar alarms is a high-tech and complex system. Although various failure phenomena may occur, as long as good quality is applied to the selection of equipment and equipment, and construction is strictly conducted in accordance with standards and specifications, there are generally no major problems. Whenever there is a problem, as long as you are calm and analytical, you can solve the problem faster.