Video surveillance has a wide range of applications and many fault phenomena. How to take corresponding measures to solve the problems according to different fault conditions is of great significance to improve the quality of the monitoring system and ensure the stable operation of the system. Let’s talk about the common fault points and troubleshooting experience of video monitoring system.
1. Short circuit
Because the connection between the monitoring system and its equipment involves many lines, if it is not handled well, especially the lines connected with the main equipment are improperly or wrongly connected, there will be open circuit, short circuit, poor insulation between lines, wrong wiring and other problems that will lead to the decline or even damage of equipment performance. In this case, calm analysis and troubleshooting shall be carried out according to the fault phenomenon to judge what kind of fault phenomenon may occur when there is a problem in the connection of which lines. In addition, it shall be noted that the connection between each system equipment and various lines shall meet the requirements for long-term operation of the monitoring system.
The characteristic impedance mismatch of the transmission cable may cause several 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 video cable do not meet the requirements. For such interference, try to match the impedance of each equipment in the system. Especially when purchasing video cables, ensure the cable quality, and sample the cables if necessary.
3. Parameters such as communication interface or communication protocol are not set properly
This situation often occurs between the control host and devices with communication control relationship such as decoder or control keyboard. In other words, the selected control host, decoder or control keyboard are caused by the failure to set communication protocol and other parameters during project installation. Therefore, pay attention to the setting of communication protocol and other parameters during installation of host, decoder and control keyboard.
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 50Hz power frequency interference. This interference is mostly caused by the potential difference loop formed by the improper grounding of the front-end and control center equipment into the system, or the degradation of the power performance of the equipment itself.
*The image has snowflake noise, which is mainly caused by signal attenuation on the transmission line and coupling high-frequency interference.
*The video image has ghosting, or the image is white, the characters shake, or there are several vertical bars with equal spacing on the monitor screen. This is because the characteristic impedance between video transmission lines or devices is not 75 Ω, resulting in impedance mismatch.
*Twill interference, runout interference, power interference. This interference will not drown the normal image when it is slight, but distort the image when it is serious. There are many and complex reasons, such as poor quality of video transmission line, especially poor shielding performance, clutter in the power supply of power supply system, or strong interference sources near the system.
*Large area moire interference, also known as single frequency interference. This phenomenon is mainly caused by short circuit and open circuit between the core wire of video cable and shielding network, or poor contact of BNC connector.
5. Equipment failures caused by power supply problems mainly include the following possibilities:
*Incorrect power supply line or voltage;
*Insufficient power (or the wire diameter of a certain power supply line is sufficient, the step-down is too large, etc.);
*The transmission line of the power supply system has short circuit, open circuit, instantaneous overvoltage, etc.
It should be noted that equipment damage may occur due to power supply error or instantaneous overvoltage. Therefore, before power supply, we must carefully and strictly check and check, and we must not take it lightly.
6. Fault caused by short circuit and open circuit between the core wire of video cable and shielding network
The manifestation of this fault is the deep and chaotic large-area moire interference on the monitor, so that all the images are damaged and the image and synchronization signal cannot be formed. This often occurs on BNC connectors or other types of video connectors. That is, when this kind of fault occurs, it often does not occur in the whole signal line, but only in the number of bad connectors. It can be solved as long as these connectors are carefully checked one by one.
7. Space radiated interference introduced by transmission line
This interference phenomenon is mostly due to strong and high-frequency spatial radiation sources near the transmission system, the front end of the system or the central control room. The first solution to this situation is to have a comprehensive understanding of the surrounding environment when building the system, and then try to avoid or stay away from the radiation source; Secondly, when the radiation source cannot be avoided, the front-end and central equipment shall be shielded, and the pipeline of the transmission line shall be made of steel pipe and well grounded.
8. PTZ fault
The common faults of PTZ are that it doesn’t work well or can’t rotate at all soon after use. In addition to product quality reasons, this situation is generally caused by the following reasons:
*Only the PTZ with the camera installed is allowed, and the lifting method is adopted during use. The lifting method increases the operation load of the PTZ, so the transmission mechanism of the PTZ will be damaged and even the motor will be burned out soon.
*The total weight of the camera and its protective cover exceeds the load of the PTZ. Especially for the PTZ used outdoors, the weight of the protective cover is often too large, and the PTZ often fails to rotate (especially in the vertical direction).
*The outdoor PTZ is faulty or even damaged due to too high or too low ambient temperature or poor performance such as waterproof and antifreeze.
*When the distance is too long, the operation keyboard cannot remotely control the camera (including lens) and PTZ through the decoder. This is mainly because the control signal attenuation is too large and the control signal received by the decoder is too weak when the distance is too long. At this time, a relay box should be installed at a certain distance to amplify the control signal.
9. The matrix host is not clean for image switching.
This kind of fault is generally shown on the screen after selective cutting, such as superimposed with other screen interference or line synchronization signal interference of other images. It is caused by the poor quality of matrix switch, which can not meet the requirements of isolation between images. If the RF transmission system is adopted, it may also be caused by excessive crosstalk modulation and mutual modulation of the system.
10. The image contrast of the monitor is too small and the image is light.
If this phenomenon is not the problem of controlling the host and monitor itself, or the transmission distance is too far, resulting in too much attenuation of the video transmission line. In this case, a device for line amplification and compensation shall be added.
11. The image definition is not high and the details are lost
When this situation is serious, the phenomenon of color signal loss or too small color saturation may occur, which is caused by the excessive loss of high-frequency end of image signal, that is, the loss of frequency signal above 3MHz. In this case, the attenuation of high-frequency signal is too large due to the long transmission distance, and there is no amplification and compensation device in the middle; Or the distributed capacitance of video transmission cable is too large; Or due to the centralized distribution of equivalent capacitance between the core wire and shielding wire of the transmission line in the transmission link.
12. Tone distortion.
This is an easy fault phenomenon in the long-distance video baseband transmission mode. It is also mainly caused by the excessive attenuation of the high frequency band of the signal caused by the long transmission line. In this case, a compensator should be added.
A large-scale video monitoring system, which is linked with anti-theft alarm, is a system with high technical content and complex composition. Although various failures may occur, as long as the quality of equipment and equipment is controlled and the construction is carried out in strict accordance with standards and specifications, there will generally be no major problems. Once there is a problem, as long as we do calm analysis and thinking, we can solve the problem quickly.