Elevator monitoring installation is not a simple thing. The video monitoring images of many projects are disturbed to varying degrees in the elevator shaft environment, which has always been one of the most common, difficult and concerned problems. Let's discuss the solution to the problem.

(1) Power, lighting, fan, control, communication and other cables are usually arranged in the elevator shaft, and various cables will produce electromagnetic radiation; If the coaxial cable is used for transmission, the same as the antenna receiving principle, the coaxial cable will also "receive" these interferences, that is, the interference electromagnetic field will generate interference induced current on the cable, and this interference induced current will also generate interference induced voltage (electromotive force) on the longitudinal resistance of the outer conductor (braided mesh) of the cable. This interference induced voltage is just connected in series in the video signal transmission circuit In the "long ground wire", interference is formed;

(2) More importantly, these accompanying cables are parallel to the video cable and tied together at a close distance, which forms a close to "the best and most effective" Interference coupling relationship. In general engineering, the method of shielding interference through metal pipe or metal groove can be adopted, but this method is powerless in the elevator follow-up environment. Therefore, it is very difficult to resist interference in the elevator environment, so only better design and construction methods can be selected;

(3) Understanding the basic principle of interference generation is very important to improve anti-interference design and construction.

2、 There are the following forms of interference to the elevator.
(1) Horizontal stripes roll up and down.
This phenomenon shows that the stripes roll up or down continuously, and the stripes are relatively wide. It looks like interference. In fact, it 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 certainly be said to be the problem of grounding potential, which means that there is a potential difference between the ground of front-end equipment and the ground of central control room. This problem cannot be tested by multimeter. If the measured figure is zero, it does not mean that there is no potential difference. The only way is to disconnect its circuit, that is to say, disconnect one of the ground at both ends (it is best to choose the front end). If the ground at both ends does not want to be broken, it may affect the lightning protection. Then add a ground isolator to solve the problem. This equipment is a passive equipment. As long as it is connected in series at any end of the coaxial cable, it has convenient installation and good effect, and can completely eliminate this stripe phenomenon. The figure shows UTP signal isolator.

(2)  mesh interference.
The image quality of this phenomenon is very poor, basically no object can be seen, the image is sometimes absent, and the picture crashes. This phenomenon is due to the broken and short wire core and shield of the cable. Most of this happens on the joints, and some of them are not well constructed during wiring. The interference caused by welding problems or poor quality of joints also accounts for a lot in engineering.

(3) Interference of space electromagnetic wave.
This kind of interference source is relatively complex, mainly because there are strong radiation sources or high-power equipment running in the front-end equipment, cables and near the terminal. The main manifestations are image distortion, jitter and so on. Therefore, the surrounding environment should be understood before construction, and radiation sources should be avoided as far as possible. In the case of unavoidable interference in the completed project, only anti-interference equipment can be added. This method is economical, fast, and the image is guaranteed.

3、 Research on Application of twisted pair transmission elevator monitoring.
For the complex environment in the hoistway, the twisted pair transmission mode can be used according to the following three recommended schemes:

A: Routing in the middle of hoistway.
(1) . select unshielded high-quality Cat 5 cables.
(2) . open holes on the wall in the middle of the shaft for outgoing line.
(3) . the cable shall be bundled with the accompanying cable, and the cable below the middle of the hoistway shall be reserved.
(4) The transmitter shall be selected according to the distance requirements, and the transmitter shall be powered separately.

B: Outgoing line of elevator machine room.
(1) . select unshielded high-quality Cat 5 cables.
(2) The cables shall be bundled with the accompanying cables. The cables below the middle of the hoistway shall be reserved, and the cables at the upper part of the hoistway shall be fastened.
(3) The cables in the elevator machine room should not go through the strong current bridge, and should be connected to the monitoring engineering center separately from the bridge as soon as possible.
(4) The transmitter shall be selected according to the distance requirements, and the transmitter shall be powered separately.

C: Installation of elevator machine room.
(1) . use the video cable provided with the accompanying cable as the front medium, and install the transmitter in the elevator machine room.
(2) The transmitter selects passive or active transmitters according to the length of the video line.
(3) The receiver is installed in the monitoring center, and the passive or active receiver is selected according to the distance of the twisted pair.

In addition, the conveyor and elevator grounding system shall be carried out separately. We recommend grounding the remaining lines in the network cable in the monitoring center, and grounding the receiver is to ensure that the equipment is protected from overvoltage. Independent grounding devices are used for the above grounding, which is often difficult to achieve. Common grounding devices are usually used. Generally, the grounding resistance of common grounding device shall not be greater than 1 Ω. The grounding wire can be a copper core wire (PE wire) with a cross-sectional area of not less than 16 mm2. The head end can be connected with the PE wire in the building distribution room, and can be laid in the same way with the elevator power cable. The end of the grounding wire is connected with the auxiliary equipotential board in the elevator machine room.

4、 Pay attention to the following points when binding the network cable.
(1)  Select qualified and soft unshielded network cable.
(2)  first fix the traveling cable with thick tie.
(3) The net wire shall be bound with a thin tie and fixed in a thick tie.
(4) the spacing of thick ties is 30cm, and 3cm is reserved for each section of network cable.

5. Precautions for twisted pair wiring construction.
1. Twisted pair must comply with the national twisted pair product standard:

(1) The twisted pair used shall be pure copper core. The wire diameter is 0.5mm.
(2) The resistance of single core 100m is 9.38 ohms, and the resistance of 305 meters of a box line is about 28 ohms, not more than 30 ohms.
(3) The twist density shall meet the standard of class V wire.
(4)  flexibility and flame retardancy shall meet the national inspection standards.

2. For outdoor use, please use outdoor waterproof twisted pair.

3. During project wiring, it is forbidden to mix with high-voltage cables or equipment, and it cannot be placed together with frequency conversion equipment and communication signal generator.

4. Each of the four pairs of wires in the cable transmits one signal, so video can be transmitted at the same time. Audio and control signals, and prevent the transmission of high current power supply in the cable. If a pair of low-voltage power supply in the network cable is required, DC12V shall be controlled within 150m, AC24V shall be controlled within 300m, and the control signal shall be controlled within 1000.

5. Active and some passive products have built-in surge protection and need to be grounded. Outdoor applications can be grounded together with the camera. Note that the resistance of the grounding electrode must be qualified (reference value 4 Ohm).

6. The video line from the camera to the transmitter shall be as short as possible to ensure stable signal quality.