With the development and progress of science and technology, some special industries also have special requirements for monitoring, chemical, petroleum, coal and other occupational operating environments have the existence of risk explosive gases or dust, so the installation of explosion-proof cameras is very necessary, to ensure the safety environment of industrial production, is the primary meaning of the existence of explosion-proof surveillance cameras.
Now the factory pays more and more attention to production safety, and the requirements for operating power are getting higher and higher, the factory should improve production safety, improve production power, rational use of human resources, explosion-proof cameras have played a great role, today I will briefly introduce the relevant knowledge of explosion-proof monitoring equipment.
01. What is an explosion-proof camera?
Explosion-proof camera belongs to explosion-proof monitoring products, is the explosion-proof industry and the monitoring industry cross product, because in the high-risk flammability, explosive scene can not use conventional camera products, need to have explosion-proof function and have the relevant certificate issued by the national authority to be called explosion-proof camera.
02. The working principle of explosion-proof camera
The working principle of the explosion-proof camera is to inhibit the generation and occurrence of the four elements of the explosion, so that the electrical products can still work normally in a high-risk environment, and the four elements of the explosion are:
1. There are flammable gases, dusts and mixtures on site and constitute a certain concentration;
2. There is sufficient oxygen on site to react with combustibles;
3. There is enough temperature on site to cause the mixture to burn with oxygen;
4. The space on site is narrow enough to make the heat after combustion accumulate a certain concentration or even blast in a short time.
03. How to choose explosion-proof surveillance cameras
THE PRINCIPLE OF SELECTING THE LENS OF THE EXPLOSION-PROOF CAMERA IS LIKE THAT OF A GENERAL CAMERA, AND THERE ARE 4-25MM LENSES TO CHOOSE FROM. The first thing is to select the appropriate lens according to the interval and scale to be monitored on the spot. FOR EXAMPLE, IF THE OBJECT TO BE MONITORED IS ABOUT 30 METERS AWAY FROM THE DEVICE POINT, THEN A 12MM OR 16MM LENS SHOULD BE SELECTED. IF YOU WANT TO SEE CLEARLY, THEN CHOOSE A 16MM LENS, AND IF YOU ARE VAGUE, CHOOSE A 12MM LENS. In practice, the lens has a theoretical value of length, and the number of lens millimeters multiplied by 2 is equal to the interval of the object being measured. The disadvantage of the lens is that the width does not look far, and the distance does not look wide. The smaller the number of millimeters of the lens, the larger the scale, and the shorter the interval between the lenses.
04. Waterproof and moisture-proof work of explosion-proof monitoring equipment
In the application of explosion-proof video surveillance system, explosion-proof cameras are distributed in various front-end environments, of which outdoor occupies a large proportion. Due to the interference of various weather factors, outdoor cameras often have functions such as infrared night vision, waterproof, anti-fog, rain and snow, etc. In the event of a heavy rain, it is particularly important for the monitoring equipment to take precautions in advance.
Explosion-proof camera temperature changes greatly when working, easy to appear water mist, especially in the rainy season, the formation of fog and frost is due to the saturation of temperature and humidity in the air, water vapor condenses into frost and fog due to the strength and weakness of the low temperature environment. The camera works in an environment with high humidity and dust, and the window glass of the protective cover is prone to dirt, which causes the light entering the camera to be blocked, resulting in blurred lenses and unable to shoot objects clearly, which directly affects the video capture effect. Wipers can be added to the shield to clean the glass by controlling the wipers. to fix fog and dirt on the camera.
At this stage, there are some explosion-proof surveillance cameras on the mainland market that have certain technical problems in sealing, such as the design of the shell, in the joints and screw interfaces and other places, which are prone to water leakage.
How to make the sealing better? You can add a waterproof rubber sleeve and add a water pad at the interface, and the effect is ideal; Playing waterproof glue at the mouth of the wiring screw can enhance the waterproofness; The infrared waterproof camera adopts an aluminum alloy shell to improve the accuracy of the interface, and the use of high-quality silicone material is used to stain it, and the effect is also ideal.
05. The necessity of lightning protection of monitoring equipment
Heavy rain is often accompanied by lightning, modern security system equipment is basically electronic products, lightning overvoltage, electrostatic discharge, electromagnetic radiation and other hazards are very sensitive, very easy to be damaged. Video surveillance systems are often prone to "injury" during thunderstorms. According to data from a safety monitoring center in Beijing, more than 80% of lightning disasters in recent years are caused damage to internal equipment, including electrical appliances, video surveillance systems, and probes.
Generally speaking, most of the front-end cameras of explosion-proof video surveillance systems are installed outdoors, in a relatively open area, and the risk of lightning strikes is relatively large, and it is very sensitive to electromagnetic interference such as lightning overvoltage, power system transient overvoltage, electrostatic discharge, etc., which makes the video surveillance system equipment very vulnerable to lightning overvoltage damage, resulting in the paralysis of the entire CCTV video surveillance system. However, some residential community video surveillance probes, intercom systems and other facilities do not have lightning protection design at all, and induction lightning is easy to take advantage of the void and destroy the system.
There are many reasons why lightning protection is not widespread in practical applications.
On the one hand, many Party A has insufficient understanding of lightning protection in the system, and is not aware of the importance of lightning protection design to the entire system, which is limited by the project cost; On the other hand, some engineering contractors do not pay much attention to the lightning protection of the system, because if this aspect of the requirements is considered, the project quotation will be increased, which will affect the price advantage in the bidding; As a result, the security and effectiveness of the system will be extremely hidden.
06. Construction plan of explosion-proof monitoring equipment
1. Laying of explosion-proof camera cables
According to the requirements of the specification and the actual construction experience, the design of the distribution line in the workshop in the flammable and explosive environment is generally based on the bridge, supplemented by the laying of steel pipes and cable trenches, and all cables used should use flame-retardant cables.
Cables should be routed as far away as possible from explosive sources and pipelines for the transport of explosive substances. For explosive gas atmosphere, the specific gravity of flammable and explosive gas should be investigated, if the specific gravity of dangerous gas is lighter than air, the cable should be laid below (along the wall or buried); In environments where hazardous gases are lighter than air, cables should be laid on top of them as much as possible (along walls or overhead).
Under normal circumstances, in the ±0.01m plane, it is first introduced by the outdoor bridge, and after entering the room, it is led down to the cable trench along the wall or column near the equipment (sealed after laying to prevent water ingress and termite infestation), and then the pipe is laid along the ground to the side of the equipment, and then the explosion-proof flexible pipe is connected to the explosion-proof camera. The explosion-proof monitoring system composed of explosion-proof PTZ and explosion-proof decoder. For the plane above ±0.00m, the electrical circuits are basically introduced by the bridge overhead, and then laid overhead by the bridge through the pipe to the explosion-proof equipment, and then connected to the explosion-proof monitoring system with explosion-proof flexible pipes. The cavities in the walls or floors between the different areas through which the trenches, bridges or steel pipes of the electrical lines are laid should be tightly plugged with non-combustible materials (such as 100# cement mortar or fireproof mastic). There should be no joints in the cable line, and the galvanized steel pipe for low-pressure fluid transportation should be used for threading steel pipes.
The pipe connection needs to be connected by thread, and the pipe diameter below 32mm needs to be socketed with at least 5 buckles, and the pipe diameter above 32mm needs to be socketed with at least 6 buckles. Explosion-proof lines need to be equipped with galvanized steel pipes, and galvanized pipes are required to connect steel pipes with steel pipes. An explosion-proof junction box needs to be installed at every 5 galvanized pipes. When the end of the galvanized pipe is connected with the explosion-proof box, explosion-proof PTZ and explosion-proof camera, it needs to be connected with explosion-proof flex pipe. Generally speaking, 2 to 3 cables of less than one square can be threaded into the 4-point galvanized pipe. However, in the actual construction process, when the end of the galvanized pipe is connected with the explosion-proof box, explosion-proof PTZ and explosion-proof camera, due to the limitation of the pipe diameter of the equipment at the connection position, only one line can be threaded into every 4-minute flexible pipe. Therefore, in the scheme design and on-site construction, galvanized steel pipes with a diameter of more than 6 points should be used for laying as far as possible. (For only fixed-point explosion-proof cameras, it can be considered to use 4 points from the economic cost). And the corresponding end wiring equipment should also be equipped with the corresponding pipe diameter equipment standards.
2. Installation of explosion-proof cameras
The weight and load of the explosion-proof camera monitoring system are generally large, and the first thing to choose is a stable, solid installation surface and enough to carry the equipment assembly in the actual installation. All electrical connections of the equipment should be in the explosion-proof equipment cavity or explosion-proof explosion-proof junction box cavity, the connection between the equipment should use explosion-proof flexible pipes, explosion-proof sealed lead pipes should use explosion-proof monitoring equipment to provide products randomly or select products that meet the explosion-proof level of the on-site environment, according to the different hazardous areas, the lead pipe should be sealed with cement after penetrating the cable. If the equipment has the function of turning or moving, the cable and flexible pipe that enter the equipment should leave sufficient margin to avoid the equipment from turning and pulling off the flexible pipe interface and cable, so that the bare wire is exposed to the dangerous environment. The explosion-proof junction box should be installed as far as possible from the position of the explosion-proof PTZ and the explosion-proof camera. Due to the large number of cables between the explosion-proof PTZ and the camera. The use of explosion-proof flexure pipe connection during installation can reduce the difficulty of construction, facilitate debugging and maintenance and find the cause of failure.
3. Explosion-proof camera grounding
The grounding of the system should be grounded at one point. The grounding bus should be made of copper wire. The grounding wire shall not form a closed loop, and shall not be short-circuited or mixed with the zero line of the power grid with strong electricity; When the system adopts a special grounding device, its grounding resistance shall not be greater than 4Ω; When the integrated grounding grid is used, the grounding resistance shall not be greater than 1Ω; In the optical cable transmission system, the shell of the optical transceiver of each monitoring point should be grounded, and it should be connected to the ground with the sub-monitoring points. The reinforcing core of the optical cable and the sheath of the overhead optical cable should be grounded; Both ends of the overhead cable hanging wire and the metal pipe in the overhead cable route should be grounded; Grounding must be done before entering another danger zone; The ground wire should not be less than 6mm2; The equipment is connected with an explosion-proof flexible pipe between the explosion-proof junction box before the access equipment, and the grounding is repeated respectively to ensure electrical penetration.
4. Lightning protection of explosion-proof cameras
In hazardous environments, the equipment is mainly front-end equipment, and some are installed outdoors. For equipment lightning protection in hazardous environments, it mainly refers to the lightning protection of front-end explosion-proof equipment. For the control equipment in the non-hazardous area, it shall be carried out in accordance with the lightning protection method of the control room of the application television system.
Chapter 2 of the National Standard of the People's Republic of China "Code for Lightning Protection Design of Buildings" GB50057-94 has a reference to "any building that manufactures, uses or stores a large number of explosive substances such as explosives, gunpowder, initiating charges, pyrotechnics, etc., which causes an explosion due to an electric spark, which will cause great damage and personal injury or death; Buildings with Zone 0 or Zone 1 explosion hazard atmospheres; Buildings with Zone 1 explosion hazard atmospheres that explode due to electrical sparks that can cause great damage and casualties. and other situations are listed as the first category of lightning protection buildings.
The installation of outdoor monitoring points should be in accordance with national standards to install anti-direct lightning equipment (flash receiver). At the same time, it is necessary to pay attention to the protection of induction mines. The equipment, pipes, frames, cable metal sheaths, steel roof trusses, steel windows and other large metal objects in the building, as well as the metal objects such as discharge pipes and air ducts protruding from the roof, should be connected to the grounding device of lightning protection. Every 18-24m around the metal roof, the down conductor should be grounded. For on-site poured or reinforced concrete roofs composed of prefabricated components, the steel bars should be tied or welded into a closed loop, and should be grounded with down conductors every 18-24m.
When the net distance of pipes, frames and cable metal sheaths and other long metal objects laid in parallel is less than 100mm, metal wire bridging should be used, and the spacing of the bridging points should not be greater than 30m; When the clear distance between the crosses is less than 100mm, the intersection should also be crossed. When the transition resistance of the elbow, valve, flange and other connections of long metal objects is greater than 0.03Ω, the connection should be crossed by metal wire. For flanges with no less than 5 bolts, they can not be crossed in a non-corrosive environment.
The grounding device of lightning protection induction should be shared with the grounding device of electrical equipment, and its power frequency grounding resistance should not be greater than 10Ω. There should be no less than two connections between the grounding trunk in the house and the lightning protection induction grounding device. The front-end equipment also needs to install an overvoltage protector at the main distribution box where the power supply is introduced, and the video signal is the output, and the interface of the control communication signal must be protected by an appropriate lightning protector.
5. Special explosion-proof tools
Tools and equipment such as drills, pickaxes, hammers, pliers, wrenches, spreaders, etc., which are usually made of steel materials, are the hidden ignition sources when they are rubbed and hit when they are violently operated or dropped by mistake, so the installation of equipment in hazardous environments requires the use of special explosion-proof tools made of special materials that do not cause friction and impact sparks, or even do not produce red-hot and high-temperature surfaces.
The hardness of steel increases with the increase of carbon content, and the carbon in steel material is the source of frictional sparks. The explosion-proof tool adopts copper alloy, and beryllium, aluminum, titanium, nickel, magnesium, etc. are added to the pure copper with low strength and hardness to smelt into a copper-based alloy, which improves the strength and hardness, and will not produce sparks due to the absence of carbon friction or impact; The strength, hardness and thermal conductivity of copper alloy are better than that of steel materials, and the local friction points will be plastically deformed to avoid the concentration of friction energy on individual contact points, and the heat generated by friction can be quickly dispersed to the matrix to reduce the risk of red-hot high temperature at the friction impact point.
At present, a variety of copper-based alloys such as reamed bronze, aluminum bronze, and J892 copper alloy have been successfully applied in explosion-proof tools in the industry. Explosion-proof tools are generally divided into explosion-proof hand tools, explosion-proof pneumatic and hydraulic tools and special tools, including various wrenches, pliers, hammer chisels, knives, etc.
6. Schematic diagram of explosion-proof product outlet