Basic knowledge of camera shield
- Time of issue:2021-11-23 08:56
Basic knowledge of camera shield
- Time of issue:2021-11-23 08:56
The protective cover is used to protect the reliability of the camera and the lens and prolong its service life. In addition, the protective cover can also prevent man-made damage to the camera and lens as much as possible. Similar to PTZ equipment, protective covers are generally divided into general protective covers and special-purpose protective covers, and can be divided into indoor protective covers and outdoor protective covers. 1. Universal protective cover
(1) According to the installation environment, it can be divided into indoor protective cover and outdoor protective cover. 1. Indoor protective cover The indoor protective cover must be able to protect the camera and lens from dust, impurities and corrosive gas pollution. It must be able to cooperate with the installation site to achieve the purpose of anti-vandalism. The indoor protective cover is generally made of painted or oxidized aluminum, painted steel or plastic. If plastic is used, it should be fire-resistant or flame-retardant. The protective cover must have sufficient strength, the installation interface must be firm, and the window should be clear and transparent safety glass or plastic (polycarbonate). The design position of the electrical connection port should be convenient for installation and maintenance. 2. Outdoor protective cover The operating temperature of the camera is -5℃～45℃, and the most suitable temperature is 0℃～30℃, otherwise it will affect the image quality and even damage the camera. Therefore, the outdoor protective cover must adapt to various climatic conditions, such as wind, rain, snow, frost, low temperature, sun exposure, sand and dust. The outdoor protective cover will be equipped with sunshade, internal/external fan, heater/defroster, wiper, washer and other auxiliary equipment depending on the place of use. First of all, the outdoor protective cover must be highly sealed to prevent rainwater from entering. At the same time, the cable inlet should be opened under the protective cover to prevent rainwater from flowing into the protective cover along the cable. A windshield wiper should also be installed in front of the protective cover to clean up the accumulated rainwater and dirt in time, so that the camera can take clear images through the glass. The defroster in front of the hood or on the glass will melt when frost or snow accumulates on the window. Secondly, a heater should be installed in the protective cover to heat up in a low temperature environment to increase the internal temperature of the protective cover to ensure the normal operation of the camera/lens; the internal or external fan can make the air circulate in the protective cover and reduce the internal temperature of the protective cover. Temperature: The auxiliary equipment control function of the outdoor protective cover has two kinds of automatic control and manual control, such as heater/defroster, fan are automatically started or closed by the temperature sensor inside the protective cover, and like wiper, cleaning Actions such as the controller are realized by the control personnel through the operation of the control equipment. Outdoor protective covers are generally made of aluminum, coated steel, stainless steel, or plastic that can be used in outdoor environments. The manufacturing material must be able to withstand ultraviolet radiation, otherwise the aging phenomenon such as cracks, fading, and strength reduction will soon appear. Stainless steel protective covers should be used in environments that require durable protective covers, high safety, and resistance to man-made damage; appropriately treated aluminum protective covers are also a kind of protective covers with excellent performance. There are three treatment methods: polyurethane paint, anodizing , Anodizing and painting. Aluminum or steel mutual aid should not be chosen in an environment with corrosive gas; a protective cover made of stainless steel or special plastic should be used in a salt spray environment. In addition, in order to increase the safety performance of the protective cover and prevent man-made damage, many protective covers are also equipped with a tamper switch, once the protective cover is opened, an alarm signal will be issued.
(2) According to the shape, it can generally be divided into gun-type protective cover, ball-type protective cover and slope-type protective cover. 1. Gun-type protective cover The gun-type protective cover is the most common protective cover for monitoring systems, with low cost, sturdiness and durability, various sizes and beautiful styles. Indoor gun-type protective cover does not require special anti-rust treatment. Generally, painted or anodized aluminum, steel or high-impact plastics such as polyvinyl chloride (PVC), engineering plastics (ABS) or polycarbonate are used Ester and other materials. The opening structure of the gun-type protective cover includes the top cover detachable type, the front and rear cover detachable type, the slide way draw-out type, the top cover strut type, the top cover sliding type, etc. Various structural methods are based on easy installation, maintenance and maintenance Purpose. 2. Spherical protective cover There are two types of spherical protective cover, hemispherical and global, general outdoor applications mostly use global spherical protective cover, indoor applications will choose hemispherical or global protective cover according to the site environment. Global-type protective covers generally use bracket suspension or ceiling-mounted installation, and the most common hemispherical protective covers are ceiling-mounted and ceiling-embedded installation. There are three types of plastic domes that can provide scene light for the lens inside the dome: transparent, coated (translucent aluminum or chrome plated), and brown. When the dome is only used to protect the camera and lens without concealing the surveillance direction of the camera, a transparent dome is often used. The transparent dome has minimal light loss (10% to 15%). If you want to hide the surveillance direction of the camera to obtain additional security effects, you need to choose a coating or brown dome cover. The light attenuates about two f-stops (approximately 75% attenuation) after passing through the coating dome. The brown dome is relatively effective, and the light attenuation is only about 1 f-stop, about 50%. Different from the excellent optical quality and light transmission performance of the flat plastic or glass used in the gun-type protective cover window, all domes will bring a certain degree of optical distortion to the image, and the high-quality spherical protective cover has very little optical distortion. The axis of the camera must be perpendicular to the tangent plane of the intersection point of the dome, so that the distortion is at least uniform. The main effect is the slight change in the focal length of the lens. This change is generally not easy to detect or not annoying, otherwise the image There will be horizontal or vertical stretching, especially when the pan/tilt is installed in the dome and the camera rotates frequently, the distortion of the image is easy to be found. Therefore, optical distortion is an important indicator for testing the dome cover. The outdoor dome cover is also similar to the gun-type protective cover. In addition to the sealing protection level to meet the outdoor environment, it is equipped with fans, heaters and other devices to compensate for changes in outdoor ambient temperature. Since the dome cover cannot be equipped with wipers like a gun-type protective cover, it is generally equipped with rainproof eaves or other similar devices to prevent excessive rain from dripping through the lower dome cover and form water stains, and it also has a certain amount of sun protection. Effect. 3. Slope type protective cover The slope type protective cover adopts ceiling embedded installation, the rear part of the protective cover is hidden in the ceiling, and only the front window part is exposed outside, which is more convenient for concealment. Because the pitch angle cannot be adjusted, the use environment is limited. Suitable for use in corridors and corridors.
Second, special-purpose protective cover Sometimes, the camera must be installed in a highly harsh environment, not only has the characteristics of high sealing, high cold resistance, extreme heat resistance, wind and sand resistance, rain and snow resistance, like general outdoor protective covers, but also Anti-smashing, anti-impact, anti-corrosion, and even need to be used in explosive environments, so special protective covers with high safety must be used.
(1) High-security protective cover. This protective cover is generally called armored protective cover. This protective cover is suitable for installation in prisons or other places that are easily damaged. It is made of 0.134 inch thick No. 10 welding. Made of steel, the window material is 1/2 inch thick polycarbonate with anti-wear treatment. The protective cover can withstand the impact of hammers, stones or certain bullets without being pierced or cracked. The case is closed with a large mechanical lock and should not be disassembled.
(2) High dust protection cover High dust protection cover is similar to general protection cover, the difference is that this kind of protection cover is completely isolated from the outside world and can be used in sandy and dusty environments. Can be used in corrosive environments. The window material is tempered glass, which provides maximum safety, corrosion resistance and abrasion resistance. In order to avoid excessively high temperature in the hood, sunshades and fans are often provided, and the temperature in the hood can also be maintained through a filtered external compressed air source.
(3) Explosion-proof protective cover The explosion-proof protective cover has the same explosion-proof requirements as the explosion-proof pan/tilt, and must also comply with the safety regulations for explosion-proof and dust-proof electrical equipment. The material used is the same as the pan/tilt, usually a thick-walled all-aluminum structure or a stainless steel structure. The diameter of the explosion-proof protective cover is generally 6”, 8”, 10”, etc., and the lead-in excuses are equipped with explosion-proof seals.
(4) High-temperature protective cover The high-temperature protective cover refers to the protective cover that protects the camera and lens when the camera is used in an environment greater than 40°C and cannot reach the normal operating temperature by natural convection and radiation heat exchange. For high temperature environments, the protective cover should take special cooling measures. Common cooling systems include air cooling systems, water cooling systems, as well as vortex cooling, Freon, and ammonia cooling. The air-cooling system still uses the principle of air flow cooling, and uses forced ventilation to send the coolant (purified air) into the protective cover or the protective cover compartment, so as to take out the heat in the protective cover to achieve the purpose of cooling. The forced ventilation cooling system has two types: direct cooling and indirect cooling. When the ambient temperature is greater than 80°C (such as heating furnaces, steelmaking furnaces, etc.) when the temperature rise cannot be controlled by forced air cooling, a forced water cooling system can be used. The thermal conductivity and specific heat of water are larger than that of air, so compared with air cooling, the thermal resistance of related heat exchange links is greatly reduced, and the heat exchange efficiency is improved. The protective cover contains a built-in water jacket, which can effectively isolate the camera and lens from the external environment. Depending on the application, the material can be aluminum or stainless steel. A fan is installed inside the protective cover to reciprocate the air in the cover to improve the heat transfer efficiency. There are two basic types of forced water-cooling systems. One is water-cooled and dust-proof. Its structure is relatively simple. It does not have an alarm device and an air filter system. The lens can use a fixed focus or zoom lens and can be used in an environment of 80°C. The other is a high temperature type in the furnace, which can be used in an environment with a temperature of up to 1600°C. Its structure is more complicated. The entire system has an alarm, an air filter system, a maintenance shutter and a high temperature automatic exit system.