In the explosive dangerous environment in installation and construction of industrial television system in addition to the general industrial television system of relevant national standards and norms, but also to follow the standard installation of electrical equipment in explosive environment and norms, appeared in the two contradictions in explosive dangerous environment electrical equipment installation standards.

Line design

Coaxial cable is widely used in audio and video or radio frequency transmission, the transmission impedance is generally 75_, has become the standard impedance of video. Because of the reliable physical characteristics of coaxial cable, it can provide excellent audio and video performance. The frequency, resolution and the effective transmission distance of the cable play a decisive role in the audio and video system.

Using 75-7 coaxial cable to transmit video images, the real-time, clarity, brightness, color saturation and other indicators of the image can meet the requirements. At the same time, saving investment, easy installation and maintenance system. Thus, we give the following design scheme of wiring system:

1. The video signal of all monitoring points in front end is transmitted by -7 type 75 ohm coaxial cable. All the video cables are concentrated in a slot, and concentrated to the monitoring center

2, the front-end RS485 communication signal decoding controller using all explosion-proof 2 x 1.5mm2 shielded twisted pair cable transmission, and adopt effective lightning protection measures. The RS485 communication cable adopts the bus structure, which can be connected with the video cable in a slot, and concentrated to the monitoring center.

3, all front-end explosion-proof decoding controller using AC220V power supply, power supply from the scene, using galvanized steel pipe with explosion-proof flexible pipe protection.

4, the camera DC12V power supply and lens control from the explosion-proof decoder controller, lead wire with explosion-proof flexible tube to protect.

5. The control cable of explosion-proof pan head is drawn out from the explosion-proof decoding controller, and the cable is protected by explosion proof flexible pipe.

Two. General requirements for installation

1, cable laying

According to the standard requirements and experience, the distribution line design in the inflammable and explosive environment workshop is mainly based on the bridge, the laying of the steel pipe and cable ditch is auxiliary, and all the cables should be used flame retardant cable. The route of cable laying should be far away from the pipeline of explosive source and explosive substance. For flammable and explosive gas should be investigated in the environment of explosive gas proportion, if the proportion of dangerous gas is lighter than air, the cable should be laid in the following as (along the wall or ground); and for dangerous gas is heavier than air environment, the cable should be laid in the above (as far as possible along a wall or shelf space). Under normal circumstances, within the 0.00m plane, the outdoor bridge is introduced, after entering the room near to the equipment along the wall or column to lead cable trench (after laying sealed to prevent water and termites), and then put tube along the ground to lay beside the equipment, and equipment access to the explosion-proof explosion-proof flexible tube. For the plane which is more than 0.00m, the electrical circuit is basically introduced by overhead bridge, and then the bridge is put through the pipe and laid to the explosion-proof equipment, and then the explosion-proof flexible pipe is connected to the explosion-proof equipment. Holes in the walls or floors between the different areas of the trench, bridge or steel pipe for electrical wiring shall be blocked by non combustible materials (such as 100# cement mortar). There should be no joint in the cable line, and the galvanized steel pipe should adopt galvanized water gas pipe with wall thickness not less than 2.5 mm. To set the connection pipe wire connection, the pipe diameter is less than 32mm at least with 5 buttons, the pipe diameter is more than 32mm at least with 6 buttons (the effective length of thread should not be less than 8 mm), and tighten the lock nut fixed on the screw thread part, coated with non drying oil, hemp and oil paint is prohibited around. The middle connection of the pipeline also needs to use the electrical connection line to ensure the pipeline electrical transfixion.

2, special explosion-proof tools

Usually made of steel materials, brazing picks, hammer, pliers, wrenches, spreader tools and equipment in the fierce action or missed fall when the friction and impact of spark ignition source when hidden, so the installation equipment need to use no friction and impact sparks in hazardous environments, or even not have hot surface temperature, special the explosion-proof tools made of special materials. The hardness of steel increases with the increase of carbon content, while the carbon in steel produces the source of friction sparks. The explosion-proof tools made of copper alloy, aluminum, titanium, beryllium, adding nickel and magnesium smelting in the strength and hardness of low copper in copper base alloy, strength and hardness are improved, because it does not contain carbon friction or impact will not produce sparks; strength, hardness and thermal conductivity of copper alloy than iron and steel materials well, the local friction will occur plastic deformation and avoid friction energy concentrated in the individual contact point, can be dangerous and friction heat quickly spread to the substrate and reduce the friction impact point of hot temperatures. At present, many copper based alloys such as bronze, aluminum bronze and J892 copper alloy have been successfully used in explosion-proof tools in industry. Explosion proof tools are generally divided into explosion-proof hand tools, explosion-proof pneumatic and hydraulic tools and special tools, including a variety of wrenches, pliers, hammer chisel, cutting tools, etc..

3. Installation of equipment

The explosion-proof equipment itself weight and load are generally large, in the actual installation, first of all to choose a stable, strong installation surface and enough to support equipment assembly support equipment. All electrical equipment should be in the joint cavity explosion proof equipment or explosion-proof type explosion-proof junction box inside the cavity, the connections between devices using explosion-proof flexible tube, explosion-proof sealing wire tube should use explosion-proof equipment supplied products or with on-site environmental explosion-proof grade products, according to the different risk areas for lead pipe cable should be with rubber sealing. If the device has a rotating or moving function, introducing equipment cables and flexible tube should have enough margin to avoid breaking the lead equipment rotation flexible pipe interface and cable, the bare exposed environment.

4 、 grounding

The grounding of the system should be adopted one point grounding mode. Copper wire shall be adopted for earthing bus. The grounding wire shall not form a closed circuit, and shall not be short circuited or mixed with the strong power grid zero line;

The system adopts a special grounding device, the grounding resistance should be less than 4 ohm; the integrated grounding grid, the grounding resistance should be less than 1 ohm; and both ends of the hanging overhead cable and overhead cable line in the metal pipe should be grounded; in the 1 District to District 2 to 1 area, in the application of transition 0, before entering another dangerous area must be grounded; wire not less than 6mm2; and the explosion-proof junction box equipment and access equipment before the explosion-proof flexible tube connection, respectively and ensure electrical through repeated grounding.

5, lightning protection

In dangerous environment, the equipment is mainly front-end equipment, and some are installed outdoors. For the dangerous environment, equipment lightning protection mainly refers to the lightning protection of the front-end explosion-proof equipment. For the control equipment in non hazardous areas, according to the application of television system control room lightning protection methods. In the 50057-94 chapter of GB national standard "code for design of building lightning protection", the second chapter deals with the manufacture, use or storage of explosives, gunpowder, and initiation of explosives in People's Republic of China.