Elevator video monitoring system transmission and cable layout

As the main tool for high-rise passengers/cargoes, elevators will become more and more widely used in the future. It is the most common public place. Therefore, it is necessary to install surveillance cameras in elevators. In the past, elevator monitoring was to mix video cables in accompanying cables. The output from the elevator room was connected to the monitoring center. The system architecture was simple. However, the elevator shaft is a relatively complicated environment. The video surveillance images of many projects are disturbed to varying degrees in the lift shaft environment. This has always been one of the most common, difficult and most concerned problems. Here we discuss the solution to this problem.

First, we first analyze the principle of elevator interference:

1. Cables for power, lighting, fans, control, communication, etc. are usually arranged in elevator shafts. Electromagnetic radiation is generated by various cables. If coaxial cables are used, the same principle as antenna reception, coaxial cables will also “accept” these. Interference, that is, interference electromagnetic field in the cable interference induced current, the interference induced current will also produce a disturbance induced voltage (electromotive force) in the longitudinal resistance of the cable outer conductor (woven mesh), this interference induced voltage just in series with the video signal transmission circuit In the "long ground", interference is formed;

2. More importantly, these accompanying cables are all in parallel with the video cable and bundled together at close range. This forms a close to "best and most effective" interference coupling. In general engineering, the method of shielding and interfering with metal pipes or metal channels can be used. However, in the elevator follow-up environment, this method cannot do anything. Therefore, the anti-jamming in the elevator environment is very difficult and only good design and construction methods can be selected.

3. Understand the basic principle of interference, and it is very important to perfect anti-jamming design and construction.

Second, there are the following types of interference for elevators:

1, horizontal stripes rolling up and down;

This phenomenon is manifested by the continuous rolling up or down of the stripes, and the widening of the stripes. It seems that interference is not caused by external electromagnetic waves. If you put aside the stripes, the image is clear. This phenomenon basically accounts for more than 80% of the image interference. This phenomenon can be said to be the problem of the ground potential. It means that 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. If the measured number is zero, it does not mean that there is no potential difference. The only way is to disconnect its loop, that is to say disconnect the ground at both ends (preferably select 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. The picture shows the UTP signal isolator.

2. Mesh interference;

This kind of phenomenon has very poor image quality. Basically, it can't see any objects. There are sometimes no images, and there are still picture freezes. This phenomenon is due to the fact that the core and shield of the cable are broken and short. Most of these cases occur on joints, and individual ones have not been constructed during wiring. The interference caused by welding problems or poor quality of joint parts also accounts for a large part of the project.

3, the space electromagnetic wave interference This interference source is more complex, mainly in the front-end equipment, cable, terminal near the strong radiation source or high-power equipment in operation. Mainly for the image distortion, jitter and so on. Therefore, you should understand the surrounding environment before construction and try to avoid the radiation source. In the case of a project that has already been completed and interference is unavoidable, only anti-jamming equipment shall be added. This method is more economical, faster, and the image is guaranteed.

Third, twisted pair transmission elevator monitoring application research

For the complicated environment within the well, the use of twisted pair transmission can be carried out according to the following three recommended schemes:

A) Route the middle of the hoistway 1. Select unshielded high-quality Super Category 5 cables.

2. Open the hole on the wall of the middle of the hoistway.

3. Cables shall be bundled with the accompanying cable. The cable bundles below the middle of the hoistway shall be reserved. 4. The transmitter shall be selected according to the distance requirements. The transmitter shall take power independently.