Protecting Cameras: Domes, Housings and Enclosures
The goal of this installment, the fourth in our six-part digital CCTV series, is to inform security dealers on the advancements and features added to environmental enclosures required by advancing digital camera equipment. For the most part, enclosures are divided into two groups. The first is a standalone version with optional accessories such as heaters, blowers and defoggers. The second grouping consists of dome enclosures, which can either be configured with a fixed camera and lens or be outfitted with a complete pan/tilt/zoom assembly.
Variety of Standalone Enclosures Offer Flexibility
In discussions of digital CCTV technology it is unlikely that the conversation will turn to environmental camera housings or enclosures. However, these standalone devices, whether they are made in the shape of spheres or elongated cylinders, are still a major consideration in every system design.
Configuring such a system requires integrators to select an individual enclosure to meet the needs of the chosen camera and lens types rather than having to settle for preselected camera and lens combinations found in integrated dome packages. This freedom of choice offers the system designer the ability to customize systems in order to meet different surveillance applications.
Environmental enclosures come in all shapes, sizes and ratings. A brief discussion of housing ratings will help when we discuss advanced housing technology. As categorized by the National Electrical Manufacturers Association (NEMA), each enclosure must meet certain environmental requirements (see chart above). Every rating defines the housing protection standard for contact and foreign bodies, water protection and impact.
NEMA 1: Intended for indoor use primarily to provide a degree of protection against (hand) contact with the enclosed equipment. Sometimes known as a “finger-tight” enclosure. This is the least costly enclosure, but is suitable only for clean, dry environments.
NEMA 3: Intended for outdoor use primarily to provide a degree of protection against windblown dust, rain, and sleet; undamaged by ice that forms on the enclosure.
NEMA 4: Intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water; and hose-directed water; undamaged by ice that forms on the enclosure.
NEMA 6: Intended for use indoors or outdoors where occasional temporary submersion is encountered.These ratings will remain the same regardless of the size or shape of the individual enclosure.
Advanced Enclosures Solve Environment Problems
In the past, all outdoor housings were equipped with optional heater and/or blower assemblies that many manufacturers still offer today. The thought was that the blowers were incorporated to keep the housing cool during warm temperatures and heaters were incorporated to keep the enclosure warm during cold temperatures. However, the rules are changing, especially with advancing digital camera technology.
Growth in digital processed charged coupler device (CCD) cameras has resulted in some recent changes in blower and heater applications. It is a proven fact that, in most cases, the addition of just a sunshield results in the same cooling effect as a blower assembly vented to the outside environment.
With increased testing of improved housing materials and reduced wattage cameras, many manufacturers are now eliminating blower assemblies in their new camera housing designs. This does not mean that applications will never require a blower assembly. In fact, with new camera circuitry and smaller camera sizes, blower assemblies have taken on a new role. They are providing air circulation that prevents fogging or frosting of the housing’s faceplate.
This role still requires blower or fan assemblies, but they are not vented to the outside of the enclosure. This reduces maintenance requirements by more than 50 percent by preventing dirt and bugs from entering the housing, a predicament that once plagued every service technician. In addition to reducing maintenance due to the elimination of the outside vent, this change also ensures that the housing integrity still meets the initial selected NEMA rating of the enclosure.
Many housing applications fall into this standard area, but for extreme environments, new camera enclosures are now available with built-in solid-state air conditioning units. These enclosures offer a cooling capacity of 100 BTUs per minute, which can provide the necessary cooling for extreme camera applications.
Recent changes to cooling parameters have also reached the housing’s heating requirements as well. During the early days of CCTV, heater assemblies were used to keep the lens motors from becoming inoperable during cold temperatures due to oils used by the motor assemblies. However, as the camera CCD sensor formats decreased in size, so did the overall size of motorized lens assemblies. This resulted in smaller motor and lens designs with less dependence on adverse temperatures.
Calculate Power Required for Camera, Enclosure
In the past, available power was not a big concern because most heaters and blowers, as well as cameras, required 115VAC to operate. For today’s applications, the camera, heater and blower assemblies use 24VAC for their input power.
These thermostatically controlled blower and heater assemblies only require power when they are activated. However, because these assemblies – especially the heater – require a large amount of current to operate, sufficient power must be available. To determine the amount of power required by equipment, certain information must be known.
The factors are: operating voltage, total current draw, and whether or not the system operates within a +/- 10-percent tolerance.
Power Requirements Are Cause for Concern
New digital camera assemblies, due to their smaller size and internal electronics, require only a small amount of operating power. However, most heater and blower assemblies require much more power for proper operation. If the camera, blower and heater are to be powered by the same 24VAC supply, ensure that the power supply can handle the current load.
If improperly sized wire is installed or insufficient power is available, the camera equipment will not work properly. Dealers’ demands for improvements in more efficient low-voltage operating system have resulted in the development of a newer type of heater, called positive temperature coefficient (PTC). This model of low-voltage heater assembly requires less than 1A to operate compared to the 2A to 3A of current needed by the older strip heaters. This current reduction allows for smaller wire size and lower installation costs.
Dome Enclosures Can Offer Advantages
Dome housings comprise the second grouping of environmental enclosures. Whether incorporating fixed cameras or integral camera and lens assemblies with high-speed pan and tilt, domes offer a unique choice for the CCTV industry. This area has improved with the introduction of compact DSP cameras and new lens designs. The once oversized and cumbersome dome enclosure has been replaced with spaceage designs and materials.
Dome housings have the same selection criteria as conventional housing types with some additional advantages.
Today’s domes not only incorporate the pan and tilt units, as well as single camera/lens assemblies molded within a dome, but with the reduction of camera size, new dome assemblies can house up to four individual cameras. This design eliminates any loss in coverage due the rotation of the pan and tilt unit.
Modern-day dome assemblies also offer complete packages, including microprocessor receivers/drivers that allow the pan-and-tilt camera assembly direct connection to a matrix or coaxial control system. The interfacing of microprocesso
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