Cellular Wireless Outdoor System Enclosure Selection
Crime moves around, and criminals have become smarter and more aware of permanent outdoor video surveillance cameras. It is more difficult for law enforcement to covertly monitor and visually record suspects from distant and safer locations. With budget constraints placed on these departments, manned surveillance is often cost prohibitive, and there is not enough manpower for all of the surveillance operations desired. As a result, it is becoming increasingly popular in the public safety sector to connect a digital, IP-camera to a cellular modem, put it in an outdoor housing, and continuously stream live video at as high a data rate as possible to a distant monitoring and recording station.
However, as many law enforcement agencies are learning --- bandwidth on public wireless networks is limited. Not only are agencies limited in the number of cameras they can place in a neighborhood, but also they are also limited in the amount of video they can transfer per day or month. Cellular Internet Service Providers have Fair Usage Bandwidth Policies in their service agreements to help ensure that a few customers do not use excessive bandwidth at the expense of quality of service for most customers. Users of IP cameras can consume their entire monthly bandwidth in a few days a month, or a few hours a day. Users of excessive bandwidth can have their service restricted or terminated, and this is occurring more often as cellular data networks become faster, since the use of outdoor digital video surveillance using IP-cameras is increasing.
To help law enforcement view criminal activity, record better video evidence than can be sent live over cellular networks, increase the number of cameras they can operate in a neighborhood, and stay within bandwidth usage limits, Boundless Security Systems, Inc., developed the Nail-and-GoT. Not just a camera and a cellular modem in an outdoor enclosure, the Nail-and-GoT is the first comprehensive, ULTRA low bandwidth, cellular wireless pole camera SYSTEM for temporary outdoor digital video surveillance.
The Nail-and-GoT is an easy to use, turnkey solution. It can be installed quickly on a utility pole or the side of a building. The system has two built-in cameras - a PTZ camera for close-ups and an ultra wide angle camera for a more global view, Boundless' ultra low bandwidth, Multi-Stream Video Server for many functions including continuous digital video recording, live video, and motion searching, Boundless' power and thermal management systems, and an optional industrial grade, AirLink Sierra Wireless Raven-X cellular IP-data modem. Boundless' Control Panel live and recorded viewing, and motion searching client software runs on a PC and accesses one or more Nail-and-Go's via the Internet. Boundless' optional Battery Box Set, with high capacity batteries supplied by the user, and Stahlin enclosures, can power the Nail-and-GoT for brief operations so no wired connections of any kind are required.
Explosion in Demand for Outdoor Wireless Digital Video Surveillance Forces Changes in Type of Enclosures Used
Traditionally, outdoor video surveillance systems have been installed permanently, usually on lamp poles or telephone utility poles, with a wired video connection to a nearby central monitoring station. Some very expensive systems have used dedicated, very high speed, private, wireless networks. Boundless faced the challenge of how to make it easy and practical for outdoor digital video surveillance systems to use readily available, public wireless communications networks, be moved every few days, and to be as benign in appearance as possible so they don't scream, "Cameras Here !"
The vast majority of enclosure cabinets used today for outdoor applications are made of painted carbon steel. In the US, over 90% of enclosures are made from steel, stainless steel, or other non-ferrous material. The remaining 10% are made from non-metallic materials such as thermoset composites and thermoplastic materials.
When we approached enclosure manufacturers with our project we had four important factors that had to be accommodated: Corrosion Resistance, Extreme Temperature Fluctuations, Thermal Management, and Tensile Strength. So we set out to verify if steel or non-metallic materials would meet our needs. The great associates at Stahlin Non-Metallic Enclosures ended up providing us with evidence we needed---composite was the way to go.
High Resistance to Weather and Corrosion
Boundless wanted a sealed, outdoor, weatherproof system that could stand up to prolonged dampness, corrosive atmospheres, and salt-water air. Boundless chose stainless steel and aluminum hardware for exposure to the air, and Stahlin's fiberglass housings.
Boundless houses its system in white Stahlin enclosures for use in warmer climates, and gray enclosures for use in colder climates, to help control the amount of solar radiation absorbed. Pigment is embedded throughout the walls of the fiberglass enclosures for stable, scratch-resistant operation. We use thick aluminum angles to protect the mounting flanges.
Composite fiberglass materials are well suited for use in coastal areas such as marinas and other municipal infrastructure. Because they are not susceptible to attack like stainless steel by uniform halogens such as chlorine, bromine, or fluorine composite fiberglass products will provide many years of reliable performance in environments such as this. In addition, due to their inert chemical makeup, composite fiberglass materials will also withstand a wide range of aggressive acidic compounds or caustic alkali solutions. Also, because Stahlin products are made from a patented base material known as SolarGuard that is designed to provide improved resistance to ultraviolet wavelengths when used in outdoor environments, the enclosure is able to withstand exposure to both UV and aggressive chemical attacks.
Effectively Battle Rugged Environments: Composites Have Higher Strength to Weight Ratio
When designing our system we knew many of these remote units were going to be moved from location to location every couple of days so were concerned about the structural integrity of composites. We quickly learned while tensile strength may be higher in steels, that steel's flexural strength, or its ability to resist denting is actually quite lower. Steels are ductile in nature and can be stretched and drawn and will retain their shape after a load has been applied. Most composite or thermoplastic materials will have a lower tensile strength but yield a higher flexural strength or toughness. This is further simplified in the terms of strength and toughness. As a general rule of thumb, the higher the strength the lower the toughness or its ability to resist denting. A good composite tensile strength characteristic is in the range of 10k-18k psi. Flexural strength for non-metallic materials ranges from 1500-2000 psi and Modulus of Elasticity is 1750 kpsi.
Denting in a cabinet may seem insignificant and in most applications where the cabinet is fully secured in a separate room would not cause much concern. However in those environments where the cabinet is exposed to the elements like ours, and can be moved every couple of days, this can be of high importance. Denting can cause two major concerns in carbon steel products. One is a breach of the protective coating. When this happens, the substrate can corrode causing unsightly stains or in some cases a breach of the enclosure proper exposing the components inside to the elements and potential for system failure. The other factor is that the dent, or deformation, can cause the cabinet door and its gasket to lose contact with the cabinet side. This can expose the components to the elements and potential for failure something that we did not want our customers to experience. The Stahlin enclosures we are using have passed field testing for failure against denting.
Additionally, the strength to weight ratio, calculated as the tensile strength (kpsi) to weight (specific gravity) of three common materials used in industrial cabinets, is much higher in composites than carbon steel and even stainless steel. Typically you will see a 50% to 100% improvement in the strength to weight ratio of composites over common steels.
Handle Extreme Temperatures: Composites-- Low Thermal Co-Efficient of Linear Expansion.
Boundless' Nail-and-GoT system could be hung from a telephone pole in the Northeast during winter when temperatures could be -10 or placed somewhere in the city during the summer heat with temperatures at 90-100. This temperature range forced us to consider if composite materials could survive. We now are aware that composites have been capable of withstanding the most extreme temperatures without the loss of structural integrity due to its low thermal co-efficient of linear expansion. In addition, because they are a thermoset type non-metallic material, they do not change shape under excessive heat loads often seen in exposed outdoor environments. Such exposure to a combination of ultraviolet rays and temperature can cause warping and degradation in thermoplastic materials. In simpler terms, they do not change shape or chemistry under extreme temperatures. The Stahlin composite enclosures' we are using are rated -40 (-40) to 250 (121).
Thermal Management
Electronic equipment operates best and lasts the longest if its operating temperature is limited. Outdoor applications must stand the rigors of heat and cold, as well as dry and wet. Camera domes that are exposed to the elements must be heated to melt ice and snow, and avoid condensation and fogging.
Boundless wanted a material for its outdoor enclosures that helped maintain heat in the cold, but helped dissipate heat when hot. Boundless designed a sealed, thermal management system and novel heat exchanger that uses low power to operate, and that takes advantage of Stahlin's thermal properties to maintain as narrow an operating temperature range inside the enclosure as possible.
Because composites are insulators, both thermally and electrically, they provide excellent thermal insulating properties in extreme cold and help resist additional heat loads in the summer from ultraviolet exposure. While heat transfer of steel is higher than with composites, this is the opposite of what is needed when using trying to keep equipment within the enclosure warm in the winter. Additionally, in the summer months of high solar loading, the transfer of UV energy converted to heat energy to the interior can happen more quickly in steels compared to composites, similar to what happens to a car parked in the summer sun.
Conclusion: Temporary Outdoor Digital Video Surveillance Using Cellular Networks is More Difficult than it Looks
Crime moves around, and law enforcement needs an economical way to monitor many suspects outdoors in ever-changing locations. With the cost of manned surveillance vans prohibitive, and too few personnel available, it is becoming increasingly popular to use a digital IP-camera connected to a cellular modem so suspects can be monitored remotely via the Internet. Unfortunately, this method does not solve the problem because the quality of live video that cellular networks can carry is limited, the number of cameras that can be used in a neighborhood is limited, and the amount of video that can be moved over time over the network is limited by cellular carriers' Fair Usage Bandwidth policies.
Boundless Security Systems, Inc., developed the comprehensive Nail-and-GoT outdoor digital video surveillance system to solve these many problems. It uniquely solves the communications aspects of using cellular and other public wireless networks, and solves the video monitoring and evidence problems encountered by law enforcement. It can be used in both permanent and temporary applications. It enables law enforcement to carry out more, and more comprehensive, surveillance operations, at less risk to law enforcement personnel, and at less cost. And, it uses the proper enclosure to protect the system when it is moved often from place to place. We are satisfied that Stahlin's composite enclosures will meet the needs of our very demanding clients.