How to protect Home Security Cameras from pollutants

Indoor Housings

Indoor housings must protect the Home Security Cameras and lens from pollutants such as dust and other particulate matter, a corrosive atmosphere, and tampering or vandalism. Indoor housings are constructed of painted or anodized aluminum, painted steel, stainless steel, and several types of plastic. The material for plastic housings must be flameproof or flame-retardant, as designated by local codes and UL recommendations. The housings must have sufficient strength to protect the lens and camera, and be sturdily mounted onto a fixed wall or ceiling mount, or recessed in a wall or ceiling. The lens should view through a clear window made of safety glass or plastic. Recommended plastic window material is either high impact acrylic or polycarbonate with a mar-resistant finish. The electrical input/output access locations should be designed and positioned for easy maintenance. For easy access and servicing of internal parts, the top half of the housing should be hinged or be able to slide open, or be removable. In some designs, the entire camera/lens assembly is removable for servicing.

The common rectangular housing is available in many sizes and is the least expensive. For vandalism protection, many housings are available with key locks or tamperproof hardware that allows the cover to be removed only with a special tool. In very high risk areas, welded stainlesssteel housings with thick polycarbonate windows (3/8 or 1/2 inch) and high-security locks are used. Some housings are designed to provide concealment and improved aesthetics by recessing them into the wall or ceiling. The five housing types that account for most security installations are: 

(1) rectangular

(2) dome

(3) wedge

(4) triangular

(5) wall- and ceiling-recessed and surface-mounted.

Indoor Types

1. Rectangular

The most popular type of housing is the standard rectangular design since it can be fabricated at low cost, is sturdy, and is available from many manufacturers in many sizes and attractive styles. Under normal circumstances, indoor housings do not require any special corrosion-resistant finishes. The housings are made from painted or anodized aluminum, painted steel, or high-impact plastic, such as polyvinyl chloride (PVC), acritile buterated styrene (ABS), or polycarbonate (General Electric Lexan, etc.). In high crime areas and jails, stainless steel housings are used. Accessibility to the camera/lens assembly for installation and servicing is important. Video surveillance cameras are always mounted near or at ceiling height, on a pedestal, or at some elevated location requiring service personnel to be on ladders or power lifts. The housing design must permit easy access and serviceability under these conditions. Manufacturers provide one of several means to gain access to the housing: 

(1) removable top cover

(2) hinged top cover

(3) top cover or camera/lens on slide

(4) removable front and/or rear cover

(5) hinged bottom cover (dome)

(6) top cover on slide.

2. Dome

A second category of indoor housing is of a round or hemispherical, clear or tinted dome in which a camera, lens, and an optional pan/tilt mechanism are housed. Chapter 14 described dome cameras in detail. The ceilingmounted hemispherical dome and the below-the-ceiling and wall-mounted domes on brackets look totally different from the rectangular housing, and often blend in better with architectural decor. Since they look like a lighting fixture, they are less obtrusive than rectangular housings. Since the hemispherical dome is circularly symmetrical, it can be in a fixed position and the Home Security Camera pointed in any direction to view the scene. A pan/tilt unit used in a dome can rotate and tilt the camera and lens while still remaining inside the confines of the dome. This is in contrast to cameras inside rectangular and other housings: if the camera moves, the entire housing assembly has to move as a unit. If the dome is tinted so that the person down at floor level viewing the dome cannot see the camera and lens, it is possible to point the camera in any direction without the observer seeing it move. This capability can act as an additional security deterrent because the observer does not know when he or she is under surveillance. 

There are three different types of plastic dome materials through which the lens views the scene: 

(1) clear

(2) semitransparent aluminum- or chrome-coated

(3) tinted or smoked plastic. 

When the dome housing is used for protection only and its pointing direction need not be concealed, the clear plastic dome is the best choice, since it produces only a small 10 or 15% light loss. If the camera’s pointing direction is to be concealed for additional security a coated or tinted dome is required. The aluminized dome is the earliest version of the coated dome and attenuates the light passing through it by approximately two f-stops (equivalent to approximately a 75% light reduction or loss). While this type of dome is still in use, the preferred dome material is a smoked plastic or tinted plastic that attenuates the light approximately one f-stop, or 50%. In contrast to rectangular housings using flat plastic or glass windows with excellent optical quality and transmission, some dome systems add slight optical distortion to the video picture. In high-quality domes the image distortion is almost negligible, but in some systems the distortion or loss in resolution is noticeable. 

Under this condition, there is at least symmetry of distortion, that is, the primary effect is that of a weak lens producing a small change in the focal length of the total lensing system and is usually not noticeable. If the camera/lens pointing axis is not perpendicular to the dome surface and looks at an oblique angle through the dome housing material, noticeable distortion will occur; for example, images may appear elongated vertically or horizontally. If the dome and camera are in a fixed position with respect to one another, the distortion is generally less noticeable than if the lens is scanning or tilting while the dome remains still.

3. Wedge Housing

One version of the wedge housing is designed to replace an existing standard 2 feet × 2 feet drop ceiling tile and another version is designed for surface mounting.There are no additional accessories required. The design allows for manual pan adjustments of 360 and minor tilt adjustments. After final pointing the center camera/lens section is restricted from rotating by tightening thumbscrews. The camera’s wedge shape aims the camera about 15 down from the horizontal. The front of  the protrusion has a viewing window of clear acrylic with no distortion and virtually no light transmission loss. Another version is a small surface-mounted wedgeshaped housing that can be attached to any ceiling. These are available in either a surface- or recessed-mounting configuration.

4. Corner Mount

For example a high-security housing of welded stainless steel with a polycarbonate window. The tamperproof corner mount camera housing has a camera bracket assembly permitting the camera to be tilted vertically ±10 for minor adjustments of the vertical pointing angle. The lens viewing window permits viewing a 95 horizontal FOV and 75 vertical FOV. The optimum pointing direction for the lens and camera is 45 with respect to both adjacent walls and 45 down from the ceiling horizontal plane. For an elevator cab application this housing with a wide-angle, 95 horizontal FOV can view entire elevator cab with no hidden areas and provide 100% video coverage of the cab area. The high-security housing has a hinged, lockable cover for easy, controlled access to all internal parts, and a tough mar-resistant polycarbonate (Lexan) window. All mounting, video, and electrical power access holes are located on the rear and top surfaces and inaccessible to the public. The installation meets codes that require unbroken firewalls. Three different housing sizes of this design accommodate most CCD solid-state cameras and wide-angle manual- or automaticiris lenses or variable focus (vari-focal) lenses. Since the housing is exposed to the public, it is securely locked and manufactured using tamperproof materials, such as steel or stainless steel, and a polycarbonate (Lexan) window.

The plastic housing has a lockable front cover and all mounting and electrical access holes are out of sight, and not accessible to the public. The housing has an adjustable bracket for tilting the camera vertically. There are many manufacturers supplying these types of corner mount housings in materials ranging from stainless steel, steel, and plastic. Finishes include brushed stainless steel and painted aluminum, steel, and plastic.

5. Ceiling- or Wall-Recessed or Surface Mount

Recessed or partially concealed housings are often mounted in ceilings and walls. The round, semicircular, and tapered housings shown offer design flexibility since the camera and lens can be pointed in any horizontal direction while the square or rectangular ceiling tile remains in place. These housings are used where a low-profile (but not covert) type of surveillance camera is required.  These cameras are well suited for looking down hallways, at cash registers, etc. In ceiling installations, most of the housing, camera, and lens are mounted above the ceiling level. The only portion below ceiling level is a small part of the housing and the window through which the camera lens views. The cameras and lenses are accessible from below ceiling level by unlocking a cover that swings down, or by gaining access from the rear of the housing above the ceiling from an adjacent ceiling tile. It is important that all ceiling tile mount housings be securely attached to a structural member of the building above the ceiling with a chain or cable so that if the hanging ceiling support fails, the housing and contents do not fall to the floor or possibly injure personnel below.

With the increased use of video surveillance in public locations, be they government, industrial, or private, more attention is being given to the decorative and aesthetic features of the housing. These housings often have finishes of brass, gold, or chrome, with satin or polished finishes. They are also available with custom paint colors and textures, and custom-colored plastics. Several manufacturers offer special shapes and custom configurations for matching specific architectural designs.

More information at http://www.jimilab.com/tutorial/ .