Common faults of monitoring system and their solutions

( 1)

After a monitoring system enters the debugging stage, trial operation stage and delivery, there may be some faults, such as: it can't run normally, the system can't meet the design requirements, and the overall performance and quality are not ideal, that is, some "soft faults". These problems are inevitable for a monitoring project, especially for a complex large-scale monitoring project.

1. Equipment failure caused by wrong power supply. There are several possibilities for incorrect power supply: incorrect power supply line or voltage, insufficient power (or insufficient line diameter of a power supply line, excessive voltage drop, etc.). ), short circuit, open circuit and instantaneous overvoltage in the transmission line of power supply system. In particular, equipment damage caused by power supply error or instantaneous overvoltage occurs from time to time. Therefore, in the system debugging, before the power is turned on, we must seriously and strictly check and check, and we must not take it lightly.

2. Because some devices (such as the three-variable lens and the camera of the pan/tilt) are connected a lot, if they are not handled well, especially the lines connected to the devices are not handled well, there will be problems such as open circuit, short circuit, poor insulation between lines, wiring errors, etc., which will lead to equipment damage and performance degradation. In this case, we should calmly analyze the fault phenomenon and judge which lines in several lines have connection problems to produce that fault phenomenon. This will narrow down the problem. In particular, it is very common for cameras with pan/tilt to lose connection due to long-term omni-directional movement. Therefore, in this case, special attention should be paid to the connection of equipment and various lines to meet the requirements of long-term operation.

3. Quality problems of the equipment or components themselves. Theoretically, all kinds of equipment and components may have quality problems. However, from the experience, it is purely the quality problem of the product itself, which mostly occurs in decoders, electric pan/tilt, 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.

In addition, the most common problem is due to improper adjustment of equipment. For example, the adjustment of the camera's 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. In addition, 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.

4. Problems caused by incorrect connection between devices (or components) generally appear in the following aspects:

(1) impedance mismatch.

⑵ The communication interface or communication mode does not correspond. This situation often occurs between the control host and the devices with communication control relationship such as decoder or control keyboard, which means that the selected control host and decoder or control keyboard are not the products of the same manufacturer. Therefore, the host, decoder and control keyboard should all be made by the same manufacturer.

(3) The driving capacity is insufficient or exceeds the specified number of equipment connections. For example, some splitters have alarm input interfaces, and their product manuals show that they are connected with alarm probes, long-delay video recorders and other system hosts. If the alarm probe is connected in parallel to the alarm input end of the image splitter, the alarm signal of the probe will drive the alarm host and the image splitter. In this case, the problem of insufficient driving ability often occurs. The phenomenon is that although the image splitter can give an alarm, due to the weak alarm signal and unstable operation, the image picture of the camera corresponding to the alarm signal is instantly converted into a full-screen picture on the monitor but lost (unable to be maintained), so that the image on the monitor is still a multi-picture before the alarm.

One of the ways to solve the above problems is to connect the alarm probe signal with the screen splitter or video switching host through a special alarm interface box. Second, when there is no alarm interface box, we can design and process signal expansion equipment or driving equipment ourselves.

The above problems sometimes appear in the output and distribution of video signals.

(2)

1. In video transmission, the most common fault phenomenon is that a black bar or white bar appears on the monitor screen, and it slowly rises or falls.

Scroll. Therefore, when analyzing this fault phenomenon, we should distinguish two different fault causes.

A simple way to distinguish between power supply problems and ground loop problems is to connect only one camera without power supply problems to the control 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 camera and check each camera one by one. If there is, it will be handled. If not, the interference is caused by other reasons such as grounding circuit.

2. There is wood grain interference on the monitor. The appearance of this kind of interference will not slightly drown the normal image, but in severe cases, it will be impossible to watch the image (or even destroy the synchronization). There are many complicated reasons for this failure. There are roughly the following reasons:

(1) The quality of video transmission line is not good, especially the shielding performance is poor (the shielding net is not a good copper net, or it is too thin to shield). At the same time, the line resistance of this video line is too large, which leads to a large signal attenuation and aggravates the fault. In addition, the characteristic impedance of this video cable is not 75 Ω, and the parameters are not in conformity with the specifications, which is also one of the reasons for the failure. Because the above interference phenomenon is not necessarily a fault caused by poor video lines, it is necessary to accurately and carefully judge the cause of this fault. Only by excluding other possibilities can we consider it from the perspective of bad video lines. If it is really a cable quality problem, of course, the best way is to replace all these cables and replace them with cables that meet the requirements. This is the best way to solve the problem completely.

(2) Due to the power supply problem of the power supply system? Quot clean ". The power supply here is not "clean", which means that the normal power supply (50-cycle sine wave) is superimposed with interference signals. The interference signal on the power supply mainly comes from the equipment using SCR in the power grid. Especially the SCR equipment with high current and high voltage, the pollution to the power grid is very serious, resulting in the power supply of the same power grid is not "clean". For example, there are high-power SCR frequency modulation and speed regulation devices, SCR rectifier devices, SCR AC /DC conversion devices and so on. In this power grid, it will pollute 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.

(3) There are strong interference sources near the system. This can be judged by investigation. If this is the case, the solution is to strengthen the shielding of the camera and ground the pipeline of the video line.

3. The fault caused by short circuit or open circuit between the core wire of the video cable and the shielding net. The performance of this fault is that there is deep and chaotic moire interference in a large area on the display, which destroys all the images and does not form images and synchronization signals. This often happens on BNC interfaces or other types of video interfaces. That is to say, when this kind of fault phenomenon occurs, it is often not that all signals of the whole system have problems, but only those signals with bad joints. As long as these joints are carefully examined one by one, they can be solved.

4. Fault phenomenon caused by mismatch of transmission line characteristic impedance. The performance of this phenomenon is to produce several vertical bars with equal spacing on the monitor screen, and the frequency of the interference signal is basically an integer multiple of the line frequency. This is due to the characteristic resistance of the video transmission line.

Reactance is not caused by impedance mismatch caused by 75 Ω. 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. 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 when the video transmission distance is very short (generally within150m), the above interference phenomenon may not necessarily occur when using the video cable with unmatched impedance and too large distribution parameters. The fundamental way to solve the above problems is to ensure the quality when purchasing video cables. When necessary, the cable shall be sampled and tested.

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1. Failure of Yuntai.

It is a common fault of tripod head that it doesn't work well or doesn't turn at all after being used for a long time. Apart from the factors of product quality, this situation is generally caused by the following reasons:

(1) Only cameras are allowed to be installed in Yuntai, and the lifting mode is adopted when using. In this case, the hoisting mode will increase the operating load of the pan/tilt, so it will soon lead to the damage of the pan/tilt rotating mechanism and even burn out the motor.

(2) The total weight of the camera and its protective cover exceeds the bearing capacity of the tripod head. Especially for outdoor use, the weight of the protective cover is often too large, which often leads to the problem that the platform cannot turn (especially in the vertical direction).

(3) The outdoor Yuntai platform is out of order or even damaged due to the high or low ambient temperature and inadequate waterproof and antifreeze measures.

2. When the distance is too far, the keyboard cannot remotely control the camera (including the lens) and the pan/tilt through the decoder.

This is mainly because the control signal is too attenuated when the distance is too far, and 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.

3. The image contrast of the monitor is too small and the image is very weak.

This phenomenon is either the problem of the control host and the display itself, or the transmission distance is too long or the video transmission line is too attenuated. In this case, line amplification and compensation devices should be added.

4. The image definition is not high, and the details are lost. In severe cases, the color signal is lost or the color saturation is too small.

This is because the high frequency loss of image signals is too great, and the signals with frequencies above 3MHz are basically lost. In this case, the transmission distance is too long, and there is no amplification compensation device in the middle; Or the distributed capacitance of the video transmission cable is too large; Or the concentrated distribution of equivalent capacitance between the core wire and the shielding wire of the transmission line in the transmission link.

5. Tone distortion.

This is a common fault phenomenon in long-distance video baseband transmission mode. The main reason is that the high frequency phase shift of the signal caused by the transmission line is too large. In this case, a phase compensator should be added.

6.* The keyboard is out of order.

This phenomenon can basically be identified as * keyboard "crash" when there is no problem in checking the connection. There are generally methods to solve the "crash" in keyboard operation instructions, such as "whole machine reset", which can be solved by this method. If it cannot be solved, the keyboard itself may be damaged.

7. The switch from host to image is not clean.

The performance of this fault phenomenon is that the interference of other pictures or the interference of line synchronization signals of other images is superimposed on the selected picture. This is due to the poor quality of the host or matrix switch, which can not meet the requirements of isolation between mirrors.

If RF transmission system is used, it may also be caused by excessive cross modulation and mutual modulation of the system.

The large TV monitoring system associated with burglar alarm is a high-tech complex system. 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, you can solve the problem soon.