This paper introduces the selection techniques of the elevator monitoring cable model. The application of monitoring in the elevator must consider the speciality of its continuous up and down movement. It requires the way of the pipe (slot) that is different from the fixed point monitoring. The mechanical strength must be used. For higher tensile transmission cables, general engineering companies pay attention to the use of high-strength cables in the wiring. The electrical characteristics of the transmission cables have not attracted enough attention, resulting in the widespread interference of elevators.
Since the elevator room is a nearly closed narrow space, and there are many cables such as control, lighting, fan, etc. in the elevator room, it is difficult to make the wiring of the video cable. According to the actual analysis, the following principles should be followed in the selection of the cable in the elevator monitoring.
1. Meet the tensile strength: Half of the elevator cable is used for extension. The high-rise elevator can reach more than 100 meters, and the self-weight of the one-meter cable is nearly 100 kilograms, so the cable must have sufficient tensile strength. Now on the market
Self-supporting flat composite elevator monitoring special cable, which combines video coaxial cable, power cable, data cable and steel strand to form a flat ribbon cable (TSYV75-5+TVVB2X1.0+ G), so that the tension of the whole cable is taken up by the steel strand, the tensile strength is very good, and the signal cable is not broken during the operation of the elevator due to gravity.
2, good electrical parameters: in the process of the cable moving up and down with the elevator, there will be a section of the bending deformation caused by gravity, resulting in changes in electrical parameters such as cable impedance and distributed capacitance. When the cable of poor quality is deformed by force, the parameter changes greatly, which will cause impedance mismatch, increase video attenuation and generate signal reflection. This will cause the signal-to-noise ratio of the video signal to decrease and cause video interference. Therefore, it should be selected as much as possible. Shielded, thick cable video cable to prevent interference signals from "invasion." Practice has proved that SYWV coaxial cable is better than SYV, multi-layer shielding is better than single-layer shielding.
Elevator monitoring cable model selection skills
In the elevator monitoring wiring, most of the methods are bundled with other cables. However, since the AC signals in other cables will leak out through the transmission cable, the video cables are equal to an "antenna" when they are bundled in parallel with their long distances. The signal is coupled into the video signal and video interference occurs. Therefore, the parallel strap length of the video cable and other cables should be shortened as much as possible in the wiring. If necessary, the video cable can be fixed from the intermediate point of the elevator shaft and returned to the main control room from other channels (cable shaft), so as to avoid audible radiation. Coupling interference. Conditional engineering, the control line and lighting cable used in the elevator can be shielded to reduce external radiation and avoid video interference.
Elevator monitoring of inverter control
Now the elevators basically use AC frequency conversion speed regulation technology, and the frequency converter itself has strong high frequency parasitic interference. According to the measured results, the frequency bandwidth of the frequency converter is 0~10 MHz, and the interference signal amplitude is very strong. . The video baseband signal of 0~6 MHz is just in this frequency band, and the interference signal can invade the video signal from the power line and space, which affects the image monitoring effect. This is the main cause of elevator interference and the most difficult problem to solve.
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