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Video surveillance system common faults
In a monitoring system, the occurrence of problems mostly occurs during the installation, commissioning and commissioning phases. Some of the more common faults are provided to the reader for reference.
5.4.1 Power Failure The power supply is incorrect. There are several possibilities:
(1) the power supply voltage is too high to burn out the equipment;
(2) the power supply voltage is too low or the line diameter of a certain power supply line is insufficient, and the step-down is too large, causing the equipment to work abnormally;
(3) The power supply line has a short circuit, open circuit, instantaneous overvoltage, etc., especially when the equipment is damaged due to power supply error or transient overvoltage;
(4) The equipment is faulty due to poor ventilation.
5.4.2 Faults Caused by Line Connections
The line is not handled well, resulting in disconnection, short circuit, poor insulation between wires, miswired, etc., resulting in equipment damage, performance degradation or system malfunction. Some devices, such as cameras with three variable lenses and pan/tilt, have a lot of connections. If the processing is not good, the above problems often occur. In particular, the quality of some connectors is not good, and the connection process is not good.
It is a common cause of problems. In this case, it should be analyzed calmly according to the fault phenomenon to determine which lines are on several lines.
If there is a problem with the connection, the fault phenomenon will occur. This will narrow the problem. For example, the image signal of a camera with a three-variable lens is normal, but the lens cannot be controlled, so it is no longer necessary to check the video output.
Line, and just check the lens control line. In addition, the connector, especially the BNC type connector, has a very high requirements on the soldering process and the connection process of the video cable.
If the processing is not correct, even if there is no problem during the debugging and trial operation, there is a problem after the operation.
It is particularly worth noting that the camera with the pan/tilt is a common cause because of the all-round movement and the long time, which causes the connection to fall off. Therefore, it is necessary to pay special attention to the connection of various lines of such equipment should meet the requirements of long-term operation.
5.4.3 Failure caused by improper adjustment or configuration of the equipment
In addition to the quality problems of the products mentioned above, the most common problems are caused by improper adjustment of the equipment.
A. Impedance mismatch. If the video is connected to a monitor with high impedance, the image will be bright, and the characters will be jittery or sometimes there will be no characters.
B. The communication interface or communication method is wrong. This situation often occurs between the control host and the device with communication control relationship such as decoder or control keyboard.
This is mostly because the selected control host and decoder or control keyboard are not one. The manufacturer's products are caused by different communication methods or transmission control codes used by different manufacturers.
Therefore, the same manufacturer's products should be selected for the host, decoder, control keyboard, etc.
C. The drive capability is insufficient or exceeds the specified number of device connections. For example, the number of keyboards corresponding to the matrix control host is specified. If the number exceeds the specified number, the system will work abnormally. If the power of the PTZ is greater than the output power of the decoder PTZ, the PTZ will not be driven.
D. The adjustment of the rear intercept of the camera is a very precise and precise work. If you do not adjust it carefully, there will be problems of poor focus or defocusing when the three variable lenses are operating. In addition, the position of some switches and adjustment knobs on the camera is correct and meets the technical requirements of the system.
The correct setting of the device code switch such as decoder, keyboard, alarm interface box will directly affect the normal use of the system. 5.4.4 In the video transmission, the most common fault phenomenon is the 50-week power frequency interference phenomenon.
A black bar or white bar appears on the monitor screen and slowly scrolls up or down. The reason is that power supply interference or multi-point grounding of the video transmission line creates a ground loop and introduces 50 weeks of power frequency interference.
To solve the analysis, it is necessary to distinguish between the problem of the power supply or the problem of the ground loop. An easy way is to connect only one power supply to the control host, and if there is no problem, the camera output signal is not present on the monitor.
The interference phenomenon indicates that the control host has no problem. Next, a portable monitor can be used to connect to the video output end of the front camera, and one camera can be checked one by one to find out whether there is any interference due to power supply problems. Camera.
If so, proceed with the processing. If not, the interference is caused by other reasons such as the ground loop.
If the interference is caused by power interference, a power filter can be added to the power input of the device. If the video line is grounded at multiple points, check the grounding point except the monitoring room to eliminate the grounding phenomenon. 5.4.5 There is a wood-like interference phenomenon on the monitor. When it is slight, the normal image will not be overwhelmed. In severe cases, the image cannot be viewed or even destroyed.
1. The shielding performance of the video transmission line is poor (the shielding network is not a good quality copper wire mesh, or the shielding mesh is too thin to play a shielding role).
2. The line resistance of the video line is too large, resulting in a large attenuation of the signal.
3. The characteristic impedance of the video line is not 75Ω, and the distribution parameters are out of specification. Solve the analysis and select a video cable that meets the standards and requirements.