Analysis of 12 common faults of video surveillance system

Video surveillance has a wide range of applications and encounters many fault phenomena. How to take corresponding measures to solve problems in different fault situations is of great significance for improving the quality of the monitoring system and ensuring the stable operation of the system. Let's talk about some common fault points and troubleshooting experiences of video surveillance system based on some personal engineering experience.

1.Short circuit

Because the connection between the monitoring system and its equipment involves many lines, if it is not handled properly, especially the line connected to the main equipment is improperly connected or incorrectly connected, there will be disconnection, short circuit, poor insulation between the lines, incorrect wiring, etc. Performance degradation or even damage. In this case, you should calmly analyze and troubleshoot according to the fault phenomenon to determine what kind of fault phenomenon may occur when there are problems with the connection of the lines. In addition, it should be noted that the connection of various system equipment and various lines should meet the requirements of long-term operation of the monitoring system.

2. Interference

Mismatch of the characteristic impedance of the transmission cable may cause a number of vertical bars with equal spacing on the monitor screen, and the frequency of the interference signal is basically an integer multiple of the horizontal frequency. This interference phenomenon is caused by the combination of the characteristic impedance and distribution parameters of the video cable. For such interference, the impedance of each device in the system should be matched as much as possible. Especially when purchasing video cables, the quality of the cables should be ensured, and the cables should be sampled when necessary.

3.The parameters such as communication interface or communication protocol are not set.

This situation often occurs between the control host and a device that has a communication control relationship, such as a decoder or a control keyboard. In other words, the selected control host and decoder or control keyboard are caused by the communication protocol and other parameters not being set during the project installation. Therefore, the host, decoder, and control keyboard should pay attention to the communication protocol and other parameters during installation. Settings.

4.Common faults of video interference

* A black or white bar appears on the monitor screen and scrolls up or down, which is the so-called 50HZ power frequency interference. This kind of interference is mostly caused by the improper grounding of the two devices at the front end and the control center, which forms a potential difference loop into the system, and it may also be caused by the power supply performance of the device itself.

* The image has snowflake noise. This type of interference is mainly caused by signal attenuation on the transmission line and coupling with high frequency interference.

* The video image has ghosting, or the image is whitish, the characters are flickering, or there are several vertical bars with equal spacing on the monitor screen. This is because the characteristic impedance between the video transmission line or the device is not 75Ω, resulting in impedance mismatch.

* Twill interference, beat interference, power supply interference. This kind of interference will not drown the normal image when it is slight, but it will distort the image when it is severe. The causes are many and complicated, such as the poor quality of the video transmission line, especially the poor shielding performance, or the power supply system has clutter, or it may be due to a strong interference source near the system.

* Large-area moire interference, also called single-frequency interference. This phenomenon is mainly caused by a short circuit or a break of the core of the video cable and the shielding network, or by a bad contact of the BNC connector.

5. The equipment failure caused by the power problem mainly has the following possibilities:

* The power supply line or voltage is incorrect;

* Insufficient power (or the diameter of a certain power supply line is sufficient, the voltage is too large, etc.);

* The transmission line of the power supply system has a short circuit, an open circuit, an instantaneous overvoltage, etc.

It should be noted that the equipment may be damaged due to incorrect power supply or transient overvoltage. Therefore, check and check carefully before power supply, and must not be taken lightly.

6.Fault caused by short circuit or open circuit of video cable's core wire and shielding network

This failure manifests itself in the form of deep and chaotic large-area moire interference on the monitor, so that all the images are destroyed, and images and synchronization signals cannot be formed. This situation often occurs on BNC connectors or other types of video connectors. That is to say, when this kind of failure occurs, it is often not the problem of the entire signal line, but only the bad number of those connectors. As long as you carefully check these connectors one by one, you can solve it.

7. Space radiation interference introduced by transmission lines

This interference phenomenon occurs mostly because there is a strong and high-frequency spatial radiation source near the transmission system, the front end of the system, or near the central control room. The solution to this situation is to fully understand 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, strengthen the shielding of the front-end and center equipment, and The pipeline of the transmission line is made of steel pipe and well grounded.

8.Pan head failure

The common faults of the gimbal are that they do not work well or cannot be turned at all soon after use. In addition to product quality reasons, this situation is generally caused by the following reasons:

* Only the gimbal with the camera installed is allowed. It is hoisted during use. The hoisting method leads to an increase in the operation load of the gimbal, so the transmission mechanism of the gimbal will be damaged or the motor will be burned soon after use.

* The total weight of the camera and its protective cover exceeds the weight of the gimbal. Especially for outdoor PTZ, the weight of the protective cover is often too large, and the PTZ cannot rotate (especially in the vertical direction).

* Outdoor PTZ malfunctions or even damages due to excessively high or low ambient temperature or poor performance such as waterproofing and antifreeze.

* When the distance is too far, the operation keyboard cannot remotely control the camera (including the lens) and the gimbal through the decoder. This is mainly because when the distance is too long, the control signal attenuation is too large, 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, matrix host is not clean image switching

This kind of failure is generally manifested in the selected picture, such as superimposed by other picture interference, or by other image line synchronization signal interference. It is caused by the poor quality of the matrix switch, which cannot meet the requirements of the isolation between the images. If a radio frequency transmission system is used, it may also be caused by excessive crosstalk modulation and mutual modulation of the system.

10. The monitor's image contrast is too small and the image is faint

If this phenomenon is not a problem of the control host and the monitor itself, or the transmission distance is too long, the video transmission line is attenuated too much. In this case, a device for line amplification and compensation should be added.

11, the image clarity is not high, the details are lost

When this situation is serious, the phenomenon of color signal loss or color saturation is too small, which is caused by the loss of the high frequency end of the image signal, that is, the loss of the frequency signal above 3MHz. In this case, the high-frequency signal attenuation is too large because the transmission distance is too long, and there is no amplification compensation device in the middle; or because the distributed capacitance of the video transmission cable is too large; or because the transmission line is between the core and shielded lines Centralized distributed equivalent capacitance.

12.Tone distortion

This is a malfunction that easily occurs under the long-distance video baseband transmission mode. It is also mainly caused by the transmission line being too long, which causes the signal high frequency band attenuation to be too large. In this case, a compensator should be added.

A large-scale video surveillance system that operates in conjunction with burglar alarms is a high-tech, complex system. Although various failure phenomena may occur, as long as the quality of equipment and equipment is selected, and construction is strictly in accordance with standards and specifications, generally no major problems will occur. Once a problem occurs, as long as you calmly analyze and think, you can solve the problem faster.