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Camera Housing Technical Info
1. Camera Housing for General Purpose
Indoor camera housing must be able to protect surveillance cameras and lenses from the harm of dust, erosive gases, and violent damage. It is usually made of powder coated or anodizing treated aluminum, steel, bronze or plastics. If made of plastics, the material must be heat-resistant or fire proof. The camera housing must be strong with secure installation, and the window of the camera housing must be crystal clear safety glass or plastics (polycarbonate). The connecting position of the electrical lines must be easy to install or maintain.
The working temperature of the camera housing is between -5 ℃～45 ℃. The most appropriate temperature is 0 ℃～30 ℃, otherwise the quality of the pictures will be affected, or worse, the camera will be damaged. Therefore, outdoor camera housings must be suitable for all kinds of weather conditions, such as strong wind, heavy rain, snow, frost, scorching sun, etc. According to different application cases, outdoor camera housing is equipped with various supplemental appliances like sun shield, blower, heater, cleaner, etc.
First of all, outdoor camera housings should have high encapsulation property to avoid the rain getting in. Besides, the wires should be placed under the camera housing to prevent the rain flowing into the housing along the wires.
Secondly, the camera housing is usually equipped with heater and blower. The heater keeps the camera housing warm in cold weather, thus provide normal working conditions for the camera or lenses. The blower can keep the camera housing under good ventilation, thus reduce the heat in hot weather.
The control function for the supplemental appliances is usually automatic. It is automatically on or off using the temperature sensor in the camera housing.
The outdoor camera housing is usually made of aluminum, coated steel, stainless steel, or plastics. The materials must be able to stand the ultraviolet; otherwise it will have cracks, faded color, or lowered strength. Stainless steel camera housing will be used when the housing is required to be durable, highly safe, and anti-violent; Aluminum camera housing is fairly popular after proper surface treatment: powder coating, anodizing, and both. In corrosive circumstances, aluminum or steel camera housing should not be used. While in Salt acid circumstances, stainless steel or plastics camera housing should be used.
Furthermore, to enhance the safety characteristics of the camera housing and prevent the destruction from vandalism, some of the camera housings are equipped with anti-open function. Once the camera housing is opened, an alarm signal will be started.
There are many kinds of camera housings in surveillance systems. If classified in shape, there is rectangular camera housings, dome camera housings, cylindrical camera housings, sloping camera housings, etc.
(1) Rectangular camera housing:
Rectangular camera housings are the most common shape. It is cost effective, durable, with various size options available. Indoor rectangular camera housings don’t need special anti-rust treatment. Usually powder painted or anodized aluminium, steel, or high-strength plastics such as PVC, ABS, Lexan, etc.
The opening device of rectangular camera housing includes top-open style, front & back open style, slide open style, top-pole style, chain hanging style, top slide style, etc. All kinds of opening styles are used for the purpose of easy installation, fixing, and maintenance.
(2) Dome camera housing
Dome camera housings are divided into semi-dome camera housing and full-dome camera housing. For outdoor camera housings usually full-dome housings are used. While for indoor camera housings either semi-dome or full-dome is applicable, depending on different working environment. Full-dome camera housings are usually installed in bracket hanging or ceiling mounting style. Semi-dome camera housings are usually installed in ceiling mounting style or ceiling inlaid style.
There are three kinds of plastic dome housings that can provide necessary light for camera lenses: transparent, film-coated( with semi-transparent aluminum or chromium), and dark brown. When the dome housing is only used for protecting the camera and the lens instead of for hidden purpose, transparent type is often used. The light loss for such type is most minimum (as little as 10%-15%). If the camera needs to be hidden to obtain safe effect, film-coated or dark brown types shall be used. The light through the film-coated dome reduces by about 2 f-stop (equivalent to by 75% ), while for the dark brown dome the light reduces by about 1 f-stop (about 50% ).
Different from the excellent optical quality and light performance given by horizontal plastics and glass used by rectangular housings, all dome housings will bring the image some optical distortion to some extent. Dome housings of good quality will have the least optical fault. The axis of the camera must be vertical to the out-cut plane intersected with the dome housing. In this way, the optical distortion is at least even. Above all, the focal length of the lens has tiny changes, which are normally unnoticeable or unannoying. Otherwise, the image will have horizontal or vertical distortion, especially when the pan tilt is installed inside the dome. When the camera turns around, the image fault will be discovered easily. Therefore, optical distortion is an important norm for inspecting dome housings.
Similar to rectangular housings, the outdoor dome housings must meet the IP requirements for outdoor environment. Furthermore, they can be equipped with heaters and blowers to make up for the temperature difference. To prevent the raindrops from forming into water stain, some are equipped with sun-shield or similar appliances.
(3) corner camera housing
Corner camera housing is specially used for indoor corners(the intersection among two walls and the ceiling). Usually they are installed in small rooms or sitting rooms, lift, stairs, or prisons.
The camera tilts inside the corner housing towards the surveillance area under the ceiling. The observation window of the housing is vertical to the lens axis. One special corner housing is that the camera points towards the ceiling, with a reflection mirror in front of the upper side of the camera. The image can be reflected to the camera. The position of the reflection mirror can be adjusted at any angle to change the viewing scope of the camera. As the image is inverted, the camera must be inverted, too.
(4) Inlaid camera housing
The inlaid camera housing is installed on the ceiling or the wall with part of it revealed and part of it inlaid. Such housings are suitable for unnoticeable circumstances.
2. Camera housings for special purposes
Sometimes, cameras are installed in highly adverse circumstances. So camera housings need not only be airtight, and resistant to chill, heat, wind, sand, rain, snow but also anti-violence, anti-corrosion, and even anti-explosion if necessary. In this case, some special camera housings are applied.
(1) High safety camera housing
High safety housing is also called armor housing. Such housings are suitable for prisons or other environment liable to damages. It is made of #10 welded steel with thickness of 0.134 inch. The window materials are 0.5-inch-thick polycarbonate after anti-wear treatment. The housing can stand the beat from hammer, stone, or bullet without cracking or penetrating. The housing is sealed with a big mechanical lock and shall not be dismantled.
(2) Special camera housing for elevator purpose
This kind of housings are used specially for elevators which are hardened. They are made of stainless welded steel and are anti-theft. The connecting lines are behind the housing, so is normally inaccessible. The window is made of anti-wear polycarbonate. The best pointing direction is 45 degrees from both side walls, and 45 degrees tilted downwards from the ceiling. When the horizontal viewing angle is above 90 degrees (wide angle), one can see everywhere inside the lift without any blind angles.
(3) Dust proof camera housing
Dust proof camera housings are similar to general purpose camera housings. The difference is that such housing is entirely cut off from the outside. It is applied in dusty and sandy environment, even erosive environment for stainless steel materials. Window materials are tempering glass, which can provide the best safety, anti-corrosion, and anti-wear requirements. To avoid the temperature inside the housing being too high, it is usually equipped with sunshields and fans. It can also maintain the inner temperature through filtered compressed air source from outside.
(4) Anti-riot Camera Housing
Anti-riot camera housing has the same working theory as anti-riot pan tilt. It also must meet the safety regulations of anti explosion and anti powder explosion for electrical appliances. All materials used is the same as that by pan tilt. Usually they are thick-walled pure aluminium structure or stainless steel structure. Anti riot camera housings are generally 6’’, 8’’, or 10’’ in diameter. The connectors are sealed with anti explosion materials.
(5) High Pressure Camera Housing
High pressure camera housing is used in situation with poisonous gas. By filling the housing with pressurized inert gas, it can meet the requirements by National Firefighting Association. This kind of housings is made of thick-walled aluminium which has gone through anti corrosion treatment. The window is made of tempering polished glass as thick as 1/2 inch. The filling pressure is 15 pound/ square meter of low pressure nitrogen. Nitrogen is complete inert gas, thus it can prevent the explosion caused by electrical spark or electrical disorder that happens inside the housing. There is a O-shape air-tight ring between the housing body and the cover. All electrical lines shall be connected through air tight sealing ring.
(6) High Temperature Camera Housing
High temperature camera housings refers to those used in temperature above 40 degrees, which can still protect the camera and the lens to work normally without natural convection, or radiation exchange. For extreme high temperature, housings should take special cooling measures. Common cooling systems include wind cooling system, water cooling system, semi-conductor cooling system, and whirlpool cooling, Freon cooling, ammonia cooling, etc.
Wind cooling system applies air flowing theory. It sends coolant(purified air) into the housing in the way of forced blowing to carry out the heat. There are direct cooling and indirect cooling for forced cooling system.
When the temperature is above 80 degrees (such as inside heating stove, iron stove), it is impossible to control the temperature by forced blow cooling. The forced water cooling system should be used. The thermal conductivity and specific heat of water is bigger than air. So compared with air cooling, water cooling greatly decreased the heat resistance in the heat exchange process, thus improved the heat exchange efficiency. The water sandwich cover inside the housing can effectively isolate the camera and the lens with outside environment.
According to different usages, materials can be aluminium or stainless steel. There is a fan inside the housing to keep the air circulating.
There are two basic types for water cooling system. One is water cooling anti dust type, whose structure is simple without alarm equipment or air filter system. It uses fixed zoom or varifocal zoom. The other type is oven type, which can be used above temperature of 1600 degrees. Its structure is more complex with alarm system, air filter system, maintenance gate and high temperature auto exit system.
High temperature auto exit system is a system that when the camera cooling function has problems, the electric controlled retreat device will automatically retreat the camera from the burning chamber to prevent the camera and the lens from being damaged. Generally speaking, the retreat system is on under the following conditions: (1) when the cooling water above the sensor head is over the preset value(≤ 40 ℃; (2)when there is compress air disorder or the pressure drops to the preset value（≤ 0.4Mpa ）；⑶ when the air purification pipe on the sensor head has fault or pressure drops to preset value（≤ 0.02MPa ）; (4) when water current volume is smaller than the preset value（≤ 6.8 liter /minute）; (5) when air or water surveillance system is cut off; (6) when main power voltage fails; (7) when control system or control center gives ‘exit’ order.
Semi-conductor cooling system is also called thermoelectricity cooling, which is based on the effect by several different semi-conductors. When two different conductors form one even charge and the direct current is connected, the corresponding connector of the even charge will have heat absorb and heat release phenomenon. Such effect is weak in metal while obvious in semi-conductors. Semi-conductor cooling has no mechanic turning parts, so it has the advantage of no noise, no vibration, long life, simple structure, easy installation, high reliability, etc. It does not need any coolant. The cooling extent can be adjusted by electric currents. Its disadvantages are high consumption, big working current and direct current must be used. (end)
2008-11-28 16:12 |
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