To solve the elevator interference, we should mainly start from the following points.
This cable combines the video coaxial cable, power line, data line and steel strand to make a flat ribbon cable.
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Centralized DC power supply mode shall be preferred for camera power supply, followed by car lighting power, and power power power shall not be used.
It is more effective to vertically route the video cable close to the well wall in the elevator shaft, and thread this part of the cable through metal pipe or metal groove to shield the impact of interference on this part of the cable.
3、 Simple elevator wiring skills in elevator monitoring wiring, the method of binding with other cables is mostly adopted.
If the interference is eliminated, it is proved to be power interference, and if it cannot be eliminated, it is proved to be intrusion interference in the transmission cable.
In this case, considering that only half of the cable moves with the line, and the other half is only fixed extension connection without movement, we call this part “fixed cable”; This provides a possibility that half of the traveling cable can only be bundled with other traveling cables; The other half of the fixed cable can be routed separately away from the accompanying cable.
The high-rise elevator can reach more than 100 meters at most.
In the past, without understanding the principle, most outgoing lines went out with other accompanying cables from the top or bottom of the cable well.
So what are the skills of elevator monitoring wiring? 1、 The ideal position for the video cable to go out of the elevator shaft should be in the middle of the shaft, because at this time, the length of the accompanying video cable in the shaft is only a little more than half of the well depth, which is the shortest and the interference introduced naturally is the smallest; However, this outgoing line requirement in the project can only be achieved according to the situation, which is not necessarily allowed in the actual project.
Therefore, the shielded video cable with thick wire diameter should be selected as far as possible to prevent the “invasion” of interference signal.
When binding, the video cable shall be far away from the cable with large current and high frequency and close to the cable with small current and low frequency; Here, even if there is a choice of 1 cm, we may have to strive for it, because the influence of interference is at least inversely proportional to the square of the distance.
However, since the AC signals in other cables will leak outward through the transmission cable, when the video line is tied in parallel with it for a long distance, they are equivalent to a pair of “antennas”, so the interference signal will be coupled into the video signal, resulting in video 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 interference signals from “invading” interference from the video cable shielding layer.
As the elevator room is a close and narrow space, and there are many cables such as control, lighting and fan in the elevator room, it is more difficult to route video cables.
The video cable from the elevator shaft exit to the control center shall go through metal pipe or metal groove to shield the impact of environmental interference on this part of the cable, and pay attention to the electrical connection between this part of the shield and the shield in the elevator shaft.
It is best to use centralized power supply in the machine room to avoid power interference.
Now there is a special self-supporting flat composite elevator monitoring cable in the market.
2、 Cable selection for elevator monitoring In the application of monitoring in elevators, the particularity of its continuous up and down movement must be considered.
When the cable with poor quality is stressed and deformed, the parameter changes greatly, which will cause impedance mismatch, increased video attenuation and signal reflection, which will lead to the decline of video signal-to-noise ratio and video interference.
If it is impossible to judge where the interference signal is introduced into the system, first judge whether it is power interference, find a battery and directly supply power to the camera.
§ 3) Use clean power supply to prevent power interference.
Good electrical parameters: when the cable moves up and down with the elevator, a section in the middle will be bent and deformed by gravity, resulting in changes in electrical parameters such as impedance and distributed capacitance of the cable.
In this way, the tension of the whole cable is borne by the steel strand, and the tensile strength is very good.
If possible, the video cable can be fixed from the middle point of elevator shaft and led back to the main control room from other channels (cable shaft), so as to avoid AC acoustic radiation coupling interference.
The self weight of the 100 meter cable is nearly 100 kg, so the cable must have sufficient tensile strength.
It will not break the signal cable due to gravity during elevator operation.
For conditional projects, the control line and lighting cable used by the elevator can be shielded to reduce external radiation and avoid video interference.
The interference from the power supply into the video signal is also the most difficult interference problem to solve.
Meet the tensile strength: half of the elevator cables are used for extension.
It is required that the wiring is different from the way of pipe (groove) monitoring at fixed points, and the transmission cable with high mechanical strength and tensile pull must be used.
The “ground” of video signals such as the metal shell of the camera, the shell of the NC head and the outer conductor of the coaxial cable shall be insulated from the elevator car and guide rail, which shall be paid special attention when installing the camera.
4、 Avoidance and solution of elevator interference The main interference sources of elevator video are: the traction motor of elevator, AC type is more serious than DC type; The interference of elevator in the process of start-up, acceleration and integral (other) deceleration leveling is greater than that in the straight-line uniform speed operation; The high-frequency interference radiated by the elevator using frequency converter is greater than that of thyristor and line / phase voltage variable speed; The elevator radiation interference of process specification is small.
Practice has proved that SYWV coaxial cable is better than SYV, and multi-layer shielding is better than single-layer shielding.
Generally, engineers pay attention to the link of using high-strength cable in wiring, but the electrical characteristics of transmission cable have not attracted enough attention, As a result, elevator interference is widespread.
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§ 1.
With the popularity of security monitoring, the elevator has also been equipped with a camera system, but for the complex environment such as elevator, the video monitoring images of many projects are disturbed in varying degrees in the elevator shaft environment.
§ 2.
Therefore, in the wiring, the parallel binding length of video cable and other cables shall be shortened as far as possible.
Cables for power supply, control and other monitoring shall be shielded as far as possible to prevent the leakage of interference signals.
When binding the video cable of traveling part with other traveling cables, the designer shall fully understand the structure and distribution of other traveling cables.
According to the actual analysis, the following principles should be followed in the selection of cables in elevator monitoring.
§ 2) Reasonable wiring: the reasonable wiring section can effectively avoid the “coupling” of interference signals through cables, minimize the parallel binding distance with other cables, and keep the video cable away from the interference source, so as to “avoid” interference.
