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Common faults and exclusions of monitoring systems
1. Incorrect equipment caused by power failure. The following are possible due to incorrect power supply.
a. The power supply line or power supply voltage is incorrect.
b. The power is not enough (or the wire diameter of a certain power supply line is not enough, the pressure drop is too large, etc.).
c. For the system's transmission lines, there are short circuit, open circuit, and instant overvoltage.
d. In particular, due to power supply errors or instantaneous overvoltages, equipment damage may occur from time to time. Therefore, before the system is commissioned, before power is supplied, it must be carefully and strictly checked and checked. It must not be taken lightly.
2, the failure of the PTZ. A pan/tilt will not operate quickly or at all after it is used. It is a common fault of the PTZ. The appearance of this situation, apart from the factors of product quality, is generally caused by the following reasons:
a. The pan/tilt head that only allows the camera to be mounted is lifted when used. In this case, the hoisting method leads to an increase in the operational load of the pan/tilt. Therefore, the use of the hoisting method will soon lead to damage to the drive mechanism of the pan/tilt, or even burn the motor.
b. 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).
c. The outdoor pan/tilt is faulty or even damaged due to bad ambient temperature, too low, waterproof, and antifreeze measures.
3, the quality of equipment or components itself.
In theory, quality problems may occur on various equipment and components. However, from an experience point of view, the pure quality of the product itself occurs in decoders, electric gimbals, and transmission components. It is worth pointing out that the quality of some devices may not appear to be unusable due to their overall quality. However, some technical indicators do not meet the specifications given in the product specifications. Therefore, the necessary sample testing must be performed on the selected product. If it is indeed a product quality problem, the best way is to replace the product and not to dismantle and repair it.
4, due to improper adjustment of the equipment.
a. For example, the adjustment of the intercept after the camera is very detailed and precise. If the adjustment is not carefully performed, problems such as poor focus or defocusing during various operations of the three variable lenses will occur.
b. Whether the positions of some switches and adjustment knobs on the camera are correct, whether they meet the technical requirements of the system, the correctness of the encoder coding switch or other adjustable part settings will directly affect the normal use of the device itself or affect the normal performance of the entire system. .
5. Problems arising from incorrect connection between equipment (or parts) and equipment (or parts) will generally occur in the following areas:
Impedance mismatch.
• The communication interface or communication method does not correspond.
• Drive capacity is insufficient or exceeds the prescribed number of device connections.
6. A black bar or white bar appears on the screen of the monitor, and it may scroll up or down slowly. There are two possible causes of failure.
To distinguish between the problem of power supply and the problem of the ground loop, a simple method is to connect only a camera output signal with no problem to the nearest power supply on the control host. If the above interference does not occur on the monitor , then there is no problem with the control host. Next, a portable monitor can be connected nearby to the video output of the front camera and each camera can be checked one by one. If yes, proceed with the processing. If not, the interference is caused by other reasons such as the ground loop.
7. Wood grain interference on the monitor.
The occurrence of such interference does not submerge the normal image when it is light, and the image cannot be viewed (or even destroy synchronization) when it is severe. The cause of this kind of failure phenomenon is more and more complicated. There are roughly the following reasons:
a. The quality of the video transmission line is not good, especially the shielding performance is poor (the shielding network is not a copper network with good quality, or the shielding network is too thin to be used for shielding). At the same time, the line resistance of this type of video line is too large, which causes a large attenuation of the signal, which is also aggravating the problem. In addition, the characteristic impedance of this type of video line is not 75 ohms, which is also one of the causes of intentionality when the main parameter is out of specification. Since the above-mentioned interference phenomenon is not necessarily a failure caused by a poor video, the reason for this failure should be accurate and careful when judging. Only from the point of view of the video line can be considered when other possibilities are excluded. If it is really a cable quality problem, the best way is of course to replace all of these cables and replace them with cables that meet the requirements. This is the best way to completely solve the problem.
b, due to the power supply system is not "clean" and caused. The power source referred to here is not "clean" and means that an interference signal is superimposed on a normal power source (a 50-cycle sine wave). This type of interference signal on the power supply mostly comes from devices that use thyristors in the power grid. In particular, high-current, high-voltage thyristor equipment has a very serious pollution to the power grid, which leads to the fact that the power supply in the same power grid is not “cleanâ€. For example, in this power grid, there are high-power thyristor frequency modulation speed control devices, thyristor rectifier devices, thyristor AC-DC converter devices, and so on, all of which will cause pollution to the power supply. The solution to this situation is relatively simple, as long as the entire system is powered by a clean power supply or an online UPS.
c. There is a strong source of interference near the system. This can be judged through investigation and understanding. If this is the reason, the solution is to strengthen the shielding of the camera, as well as to ground the pipeline of the video cable.
8, the monitor produces a deeper and chaotic large-area moire interference, as well as all image destruction, the formation of images and synchronization signals.
The fault caused by the short circuit and open circuit of the core wire of the video cable and the shield network. This type of fault is most often seen on BNC connectors or other types of video connectors. That is, when this kind of fault phenomenon occurs, it is not always the signal of the entire system that causes problems, but only appears in the number of poorly-connected paths. As long as you carefully check these joints one by one, you can solve.
9. A number of vertical bars of equal spacing are generated on the screen of the monitor, which is an integral multiple of the frequency of the interference signal.
The fault phenomenon due to the mismatch of the characteristic impedance of the transmission line: This is due to the impedance mismatch caused by the characteristic impedance of the video transmission line not being 75 ohms. It can also be said that this interference phenomenon is caused by the fact that the characteristic impedance and distribution parameters of the video cable do not meet the requirements.
The solution to this problem is usually solved by means of "connected resistors at the beginning" or "connected resistors at the terminals". In addition, it is worth noting that when the video transmission distance is short (usually within 150 meters), using the above video cable with impedance mismatch and excessive distribution parameters does not necessarily cause the above-mentioned interference phenomenon. The fundamental method to solve the above problems is to ensure the quality when purchasing video cables. When necessary, the cable should be sampled and tested.
10. There are several fine streaks on the monitor screen.
This interference phenomenon is mostly caused by strong, high-frequency spatial radiation sources near the transmission system, the system front-end, or the central control room.
Solution: When the system is set up, it should be aware of its surroundings and try to avoid or stay away from the radiation source:
Another approach is to strengthen the shielding of the front-end and central equipment when the radiation source cannot be avoided, and use steel pipes for the transmission lines and pipelines and ground them well.
11. When the distance is too far, the operating keyboard cannot remotely control the camera (including the lens) and the pan-tilt through the matrix.
This is mainly because when the distance is too far, the attenuation of the control signal is too large and the control signal received by the matrix is ​​too weak. At this time, a relay box should be installed at a certain distance to amplify the shaping control signal.
12, image clarity is not high, the details of the loss, serious color signal loss or color saturation is too small.
This is due to the fact that the loss of the high-frequency end of the image signal is too large, resulting in the basic loss of signals above 3 MHz. In this case, either the transmission distance is too long and there is no amplification compensation device in the middle; or the distribution capacitance of the video transmission cable is too large; or the equivalent capacitance is concentrated in the transmission link between the core wire and the shielded wire. Caused.
8, tone distortion.
This is a fault phenomenon that easily occurs in long-distance video baseband transmission. The main reason is caused by the large phase shift of the high frequency band caused by the transmission line. In this case, a phase compensator should be added.
The construction of a high-quality video surveillance system is a high-tech, complex system. Although various kinds of failure phenomena may occur, as long as the quality of selected equipment and equipment is properly shut down and construction is strictly conducted in accordance with standards and specifications, generally no major problems will arise. Even if it appears, as long as you calmly analyze and think, and don't blindly dismantle, you will solve the problem faster.
Common faults and exclusions of monitoring systems
There are so many devices used in a video surveillance system that there will always be such a problem in the final debugging stage or later maintenance stage. If you cannot understand the root cause of the problem, it is difficult to completely solve it, and this will cause customers to The dissatisfaction affects the company's reputation. Here are some common problems and solutions.