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Video Cameras
(Chapter 2   Video Surveillance, Continued)

Camera housings

One of the first considerations in selecting a camera housing is the environment. Is the camera to be installed outdoors or indoors? For indoor housings, the overall conditions where the camera is to be installed must be considered. Is the camera to be installed in a classroom, pool area, gymnasium, hallway, lobby area, or inside a school bus? A camera housing design can either help or hinder the installation and maintenance of a camera. In the outdoors, a watertight housing is desired; in some areas a heater may be required. Good ventilation is required in warmer climates. Domed enclosures are a special version of housings that can be used to conceal the position of the camera(s) via the use of viewing windows and various liners. The dome housing may also offer a more attractive look that can be designed to blend into its environment.

When installing housings in areas that drop below 30F, the housing should have a heater. This is not so much to keep the camera warm as it is to protect the lens and to keep the viewplate free from condensation. Many auto-iris and zoom lenses can begin to experience mechanical problems at temperatures close to and below freezing. For this reason, the housing heater should be located toward the front of the housing, preferably in a U-shape or circle around the lens area. This will keep the lens warm and the front faceplate clear. The camera itself will provide ample heat (under most conditions) to keep it operational. Check the specifications listing for the camera's operating temperatures. In extremely cold environments, it may be necessary to purchase a housing that is also insulated. Extremely cold environments would be any location where temperatures drop to less than -30F.

A sunshield may be required in some locations. A sunshield can provide artificial shade and serve as a glare screen. A sunshield can lower the internal temperature of a housing by 10-15F and can reduce the effects of sunrise/sunset glare. Dome housings, because of their overall design, do not usually have a sunshield option.

In warmer climates, housing ventilation may be required. Many housings or domes have an optional fan attachment and air vents. Filters over the vents will need to be cleaned or replaced on a regular basis, thus adding to maintenance requirements. Sealed housings with fans for heat dissipation or condensation control can be used, but are usually more expensive.

Humidity can do the most damage to cameras and other electronic equipment. If the camera is to be installed in an obviously high-humidity area, a pressurized environmental housing may be required. These are purged and pressurized with dry nitrogen. The sealed pressurized housing ensures that changing outside pressures will not force any dirt, humidity, and/or oxygen into the tube. Cabling for these units is installed through the back via a specialized plug.

Corrosion caused by salt can be a major problem in areas of the country with high humidity that are near an ocean (such as Florida). In pool areas, chlorine is a problem. These different types of corrosives can reduce the life expectancy of a camera or lens dramatically. Therefore, if an environment is considered corrosive, only those housings or domes that are considered environmentally sealed should be used.

Exhibit 2.12A camera's vulnerability to vandalism must be taken into consideration (exhibit 2.12). A housing or dome that can accommodate a lock may be required. To prevent tampering, the housing should be made of steel, although fairly tough plastic housings are available. Such tamper-proof housings or domes are often made of 10-gauge (or higher) steel.

Some situations call for bullet-resistant housings. These units are usually constructed of 12-gauge stainless steel. The front glass will be constructed of a 1/4-inch or thicker Lexan-type material. Two squares of 1/4 -inch plate glass sandwiched around a 1/4-inch square of Lexan can probably prevent scratching of the surface due to washing, wind, and dust.

When choosing a proper housing or dome, it is important to consider the actual dimensions of the unit. Refer to the camera and lens specification sheets to determine the size of the housing. Leave enough room for cable connectors. The objective is to keep the unit small but allow room for everything to fit and to be accessible. Ideally, the selected housing will allow the camera to be focused and the parameters adjusted while the camera is mounted inside the housing. This depends on the design of the housing. Some housings have a hinged cover, opening from the top, that allows for easy focusing and adjustment. If mounted inside near the ceiling, this type of housing may not be feasible. Some housings allow the cover to slide off the base for easy adjustment of the camera parameters.

The prices of camera housings vary considerably. When going out on bid, be certain that your requirements document includes the features you will need.

 



Research Report:   The Appropriate and Effective Use of Security Technologies in U.S. Schools