The large-scale video surveillance system linked with anti-theft alarm is a system with high technical content and complex structure. After the monitoring system enters the debugging stage, trial operation stage and delivery, there may be equipment failure caused by incorrect power supply, equipment damage caused by power supply error or instantaneous overvoltage, and poor handling of equipment connection. For example, the system can't run normally, can't meet the technical indicators required by the design, and the overall performance and quality are not ideal, which is some "soft faults". These problems are inevitable for a monitoring project, especially for a complex large-scale monitoring project. Let's explain the corresponding problems and solutions. \x0d\ 1, the display is in a mess. An image and a synchronization signal cannot be formed. \x0d\ Faults caused by short circuit and open circuit between video cable core and shielding net. This kind of fault mostly occurs on bnc connectors or other types of video connectors. That is to say, when this fault phenomenon occurs, not all signals of the whole system are faulty, but only those signals with bad connectors. As long as these connectors are carefully checked one by one, they can be solved. \ x0d \ 2。 There are several possibilities for equipment failure caused by incorrect power supply. \ x0d \ The power cord or voltage is incorrect. \ x0d \ Insufficient power (or insufficient line diameter of power supply line, excessive voltage drop, etc.). ). \ x0d \ Short circuit, open circuit, instantaneous overvoltage, etc. occur in the transmission line of the power supply system. \ x0d \ especially. Before the system is debugged and powered on, it must be carefully and strictly checked and checked, and it must not be taken lightly. \x0d\3。 The camera with variable lens and the pan/tilt don't rotate/the lens doesn't move \ x0d \ There are many connections between these devices, which often lead to equipment damage and performance degradation, such as open circuit, short circuit, poor insulation between wires, wiring errors, etc. \ x0d \ It is very common that the camera with pan/tilt moves in all directions for a long time, resulting in disconnection and disconnection of the connecting cable. Therefore, in this case, it is necessary to pay special attention to the connection between the equipment and various lines and meet the requirements of long-term operation. \x0d\4。 Quality problems of equipment or components themselves. \ x0d \ Theoretically, all kinds of equipment and components may have quality problems. But in terms of experience, it is purely a problem of the product itself. Most of them occur in decoders, electric ptz, transmission parts and other equipment. It is worth pointing out that some equipment may not be unavailable as a whole, but some technical indicators can not meet the indicators given in the product manual. Therefore, it is necessary to carry out necessary sampling inspection on the selected products. If it is really a product quality problem, the best way is to replace the product, rather than dismantle and repair it yourself. \x0d\ 5。 Problems caused by improper adjustment of equipment. \x0d\ For example, the adjustment of camera back intercept is a very detailed and accurate work. If not carefully adjusted, there will be problems such as poor focus or defocus during various operations of the three variable lenses. \ x0d \ Whether the positions of some switches and adjusting knobs on the camera are correct, whether they meet the technical requirements of the system, and whether the encoder switches or other adjustable parts of the decoder are set correctly will directly affect the normal use of the equipment itself or the normal performance of the whole system. \x0d\6。 Problems caused by incorrect connection between devices (or components) generally appear in the following aspects: \x0d\ impedance mismatch. \ x0。 Communication interface or communication mode does not correspond. \ x0d \ The driving capacity is insufficient or exceeds the specified number of equipment connections. \x0d\7。 A black or white bar appears on the monitor screen, which slowly scrolls up or down. There may be two different reasons for failure. \ x0d \ The simple way to distinguish the power supply problem from the ground loop problem is to control the nearby host. If the above interference phenomenon does not appear on the display, there is no problem with the control host. Next, you can connect a portable monitor to the video output end of the nearby front-end camera and check each camera one by one. \x0d\ If yes, it will be handled. If not, the interference is caused by other reasons such as grounding circuit. \x0d\8。 There is wood grain interference on the monitor. \ x0d \ This interference. In severe cases, the image can't be watched (even the synchronization is destroyed). There are many complicated reasons for this failure. Generally, there are the following reasons: \ x0d \ The quality of video transmission line is poor, especially the shielding performance is poor (the shielding net is not a copper net with good quality, or the shielding net is too thin to shield). At the same time, the line resistance of this kind of video cable is too large, which leads to the signal attenuation and is also the cause of the fault. The characteristic impedance of this video cable is not 75 ohms, which is also one of the intentional reasons. Because the above interference phenomenon is not necessarily a fault caused by poor video, the cause of this fault should be accurately and carefully judged. Only by excluding other possibilities can we consider it from the perspective of bad video lines. If it is really a cable quality problem, the best way is of course to replace all such cables. Replacing it with a cable that meets the requirements is the best way to completely solve the problem. \ x0d \ is caused by unclean power supply system. The dirty power supply here means that the normal power supply (50-cycle sine wave) is superimposed with interference signals. Most of the interference signals on the power supply come from the devices using SCR in the power grid, especially the SCR devices with high current and high voltage. This has caused the power supply in the same power grid to be "unclean". For example, there are high-power SCR frequency modulation and speed regulation devices, SCR rectifier devices and SCR AC /DC converter devices in this power grid, which will cause pollution to the power supply. The solution to this situation is relatively simple, as long as the whole system adopts purified power supply or online ups power supply, it can basically be solved. ]\x0d\ There are strong interference sources near the system, which can be judged through investigation. If this is the case, the solution is to strengthen the shielding of the camera and ground the pipeline of the video line. \x0d\9。 Several vertical bars with equal spacing will be generated on the monitor screen, which will interfere with the integral multiple of the signal frequency. \x0d\ Fault phenomenon caused by mismatch of characteristic impedance of transmission line: This is caused by impedance mismatch because the characteristic impedance of video transmission line is not 75 ohms. It can also be said that this interference phenomenon is caused by the fact that the characteristic impedance and distribution parameters of video cable do not meet the requirements. \ x0d \ The solution generally depends on the method of "series resistance at the beginning" or "parallel resistance at the end". In addition, it is worth noting that in the case of short video transmission distance (generally within 150m), the above interference phenomenon may not necessarily occur when using the video cable with mismatched impedance and too large distribution parameters. The fundamental way to solve the above problems is to ensure the quality when buying video cables. If necessary, the cable shall be sampled and tested. \x0d\ 10, several thin stripes will appear on the monitor screen. \ x0d This interference phenomenon is mostly caused by the strong high-frequency space radiation source near the transmission system, the front end of the system or the central control room. \ x0d \ One way to solve this situation is to know the surrounding environment when the system is established and try to avoid or stay away from the radiation source: \ x0d \ Another way is to strengthen the shielding of the front-end and central equipment when it is impossible to avoid the radiation source. Steel pipes are used for transmission lines and pipelines, with good grounding. \x0d\ 1 1。 Failure of the pan/tilt \x0d\ A The pan/tilt doesn't work well or can't rotate at all soon after use, which is a common failure of the pan/tilt. Apart from the factors of product quality, this situation is generally caused by the following reasons: \x0d\( 1. When in use, the hoisting method is adopted. In this case, the hoisting mode will increase the working load of the tripod head, so the rotating mechanism of the tripod head will damage or even burn the motor soon after use. \x0d\(2) The total weight of the camera and its protective cover exceeds the bearing capacity of the tripod head. Especially when the tripod head is used outdoors, the protective cover is too heavy, which often leads to the problem that the tripod head cannot rotate (especially in the vertical direction). \x0d\ (3) The outdoor pan/tilt is out of order or even damaged due to too high or too low ambient temperature and poor waterproof and antifreeze measures. \x0d\ 12。 When the distance is too far, the keyboard cannot remotely control the camera (including the lens) and the pan/tilt through the decoder. \ x0d \ This is mainly because the control signal is too attenuated when the distance is too far. The control signal received by the decoder is too weak. At this time, it is necessary to install a relay box at a certain distance to amplify the shaping control signal. \x0d\ 13。 The image contrast of the monitor is too small and the image is very weak. \ x0d \ This phenomenon is either caused by the control host and the display itself, or the transmission distance is too long or the video transmission line is too attenuated. \ x0d \ In this case, X0d\ 14, the image definition is not high, the details are lost, the color signal is lost or the saturation is too small, which is serious. \ x0d \ This is caused by excessive loss at the high-frequency end of the image signal, and signals with frequencies above 3mhz are basically lost. \ x0d \ This situation may be caused by long transmission distance and no amplification compensation device in the middle; Or the distributed capacitance of the video transmission cable is too large; Or the concentrated distributed equivalent capacitance between the core wire and the shielding wire of the transmission line in the transmission link. \x0d\ 15, tone distortion. \x0d\ This is a common fault phenomenon in long-distance video baseband transmission mode. The main reason is that the high-frequency signal is too large. In this case, a phase compensator should be added. \ x0d \65438+ If there is no problem with the connection, this phenomenon can basically be determined to be caused by the "crash" of the operating keyboard. In the operating instructions of the keyboard, there are generally methods to solve the "crash", such as "resetting the whole machine", which can be solved by this method. If it cannot be solved, the keyboard itself may be damaged. \x0d\ 17。 The host switching image is not clean. The interference of other pictures or the interference of line synchronization signals of other images are superimposed. This is caused by the poor quality of the host or matrix switch, which can not meet the requirements of mirror isolation. \x0d\ If RF transmission system is used, it may also be caused by excessive system intermodulation. \x0d\ 18, the digital hard disk video recorder can't be started, and there may be the following situations. \ x0d \ The host power switch is faulty. \ x0d \ The host power supply is damaged. \ x0d \ The boot area of the main system hard disk is damaged, or the hard disk itself is faulty. \ x0d \ The operating system is corrupted. \ x0d \ The above reasons should be carefully analyzed and eliminated one by one. Embedded hard disk video host is a monitoring software problem. The main reasons are as follows: \ x0d \ A file of the system software is damaged, and the system or monitoring software is reinstalled for the pc hard disk host; The embedded host needs to upgrade the software. \x0d\ The hard disk in the host has bad disk tracks and needs to be repaired or replaced. \ x0d \ The power supply in the host is insufficient, so the high-power power supply needs to be replaced. \ x0d \ Too many host hard disks generate too much heat, leading to fatal machine. \ x0d \ The host computer's graphics card was overheated, which led to the crash, so the graphics card was replaced. Large-scale TV monitoring system is a complex system with high technical content. Although there may be various failures, as long as the quality of the selected equipment and equipment is well controlled and the construction is carried out in strict accordance with standards and specifications, there will generally be no major problems. Even if there is, as long as you calmly analyze and think, and don't blindly disassemble, the problem will be better solved. \x0d\ 20。 The equipment failure \x0d\ caused by incorrect power supply selection is manifested in the following aspects: incorrect voltage of power supply line or power supply system, insufficient power (or insufficient line diameter of a power supply line, too high copper resistance, too large line voltage drop, etc. ), short circuit, open circuit and instantaneous overvoltage of the transmission line of the power supply system, which leads to the failure of the front-end monitoring equipment and terminal display system. For example, the pan/tilt can't rotate normally, and the monitoring image is unclear, especially when the equipment is burned due to power supply error or instantaneous overvoltage. Therefore, during the system debugging, do not rush to power on. Before electrifying, it must be carefully checked and checked according to the design scheme or drawings to prevent blind operation.