The elevator is a complex wiring environment in the wiring project. Many video surveillance images in the elevator shaft environment are subject to different degrees of interference, and in the closed-circuit monitoring system project, the elevator monitoring video interference problem has always been the most common and most difficult to solve. One of the most concerned issues is that there are many causes of video jamming in elevator monitoring. The following is a detailed introduction of the cause of the video jamming in elevator monitoring and its solutions, which are available for reference.
First, the principle of elevator monitoring interference
1. Power, lighting, fans, control, communications, etc. in elevator shafts, all kinds of cables will produce electromagnetic radiation. Like the antenna reception principle, the coaxial cable will also “receive†these interferences, that is, the interference electromagnetic field will produce interference induced currents on the cable, and the interference induced current will also generate interference induced voltages on the longitudinal resistance of the cable outer conductor (woven mesh). (Electromotive force), and the interference induced voltage is just connected in series in the "long ground" of the video signal transmission circuit, forming interference.
2. The accompanying cables are all in parallel with the video cable and are bundled together in close quarters. This results in a near “best and most effective†interference coupling relationship. In general engineering, the method of shielding and interfering with metal pipes or metal channels can be used. However, this method cannot do anything in the elevator follow-up environment. Therefore, the anti-jamming in the elevator environment is very difficult, and only good design and construction methods can be selected. It is important to understand the basic principles of interference and improve anti-jamming design and construction.
Second, the elevator monitoring and the causes of interference and solutions
1, horizontal stripes scroll up and down
If the image appears to be constantly rolling up and down, and the stripes are wider, it is generally not the interference of the external electromagnetic waves. The image disturbance in elevators is about 80% or more. This type of interference is generally a problem of ground potential, which means there is a potential difference between the ground of the front-end device and the central control room. This problem cannot be tested by the multimeter.
Solution: Turn off the circuit, which means that the ground at both ends is disconnected (preferably the front end). If both ends do not want to break, fear of affecting lightning protection. That is to say, an isolating device is used to solve this problem. This device is a passive device. If it is connected in series at any end of the coaxial cable, the installation is convenient and the effect is good. This phenomenon of streaking can be completely eliminated.
2. Mesh interference
When the image quality is very poor, basically no objects can be seen. At times, even when the screen freezes, the images are net-like interference. In general, the network interference is caused by the disconnection and shortness of the wire core and the shield. Most of them appear on the joints, and some of them are also not properly constructed during wiring. The interference caused by welding problems or the poor quality of the joint parts also accounts for a lot in the project.
3, the interference of space electromagnetic waves
The general performance is image distortion, jitter, etc., mainly in the front-end equipment, cables, there is a strong radiation source near the terminal or high-power equipment in operation. Too strong radiation sources can seriously affect signal transmission. If there are unavoidable radiation sources on site, anti-jamming devices can be added.
Solving the situation in which the monitoring image of the elevator is disturbed by the environment can enable the security personnel in the monitoring room to clearly observe the situation in the car. In the event of an accident such as a power outage, a failure, or a security accident in the elevator, the security personnel can promptly discover and go to the rescue.
If you can not determine where the interference signal is introduced into the system, first determine whether it is power interference, find a battery, directly to the camera power supply, if the interference is excluded, it is proved to be power interference, can not be ruled out is to prove that the transmission cable intrusion interference.
Third, how to avoid the elevator interference
1. Select the video cable with small attenuation coefficient, good shielding performance and high tensile strength, which can improve its anti-interference ability, reduce video attenuation, and prevent the interference signal from “invasion†interference from the video cable shield.
2. Reasonable cabling: Reasonable cabling can effectively avoid the "coupling" of the interference signal through the cable, minimize parallel strapping distances with other cables, and keep the video cable away from the interference source so as to "avoid" interference.
3, the use of a clean power supply to prevent power interference, the best use of centralized power supply room to avoid power interference, interference from the power into the video signal is also the most difficult to solve the interference problem.
4, choose the appropriate wireless bridge, it is recommended to choose the best elevator wireless bridge, such as Feng Runda elevator bridge S350, S400, etc., not only can better fit the elevator environment, but also can reduce the interference caused by itself, to the maximum The guarantee of clear and smooth monitor picture.
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