[Design Application]
Integrating COTS Components Into Open Rugged Computer Systems
PCI, VME, and CompactPCI architectures offer varying levels of suitability in military applications.
Rapidly evolving processors, memory devices, and other commercial off-the-shelf (COTS) component technologies provide rugged military computers with state-of-the-art performance. Most COTS components, however, cannot meet the stringent environmental requirements of rugged applications without special packaging or modification. In addition, rugged-computer designers seeking to take advantage of evolving commercial technology must build systems to "open" standards. This allows for an easy expansion or upgrade, and it helps to avoid obsolescence and a shorter product life.
The PCI, VME, and CompactPCI open-system architectures all accommodate COTS components with varying levels of performance and ruggedness. Therefore, the choice of a rugged-computer architecture depends upon cost, performance, and expansion requirements, as well as the quantity of systems to be produced. For example, the architecture that is selected for an inexpensive computer needed in large numbers on a digital battlefield is typically different from that of a high-value signal processing workstation that's used on a warship.
Makers of rugged computers require experience with all of the open architectures to provide the best solution for military users. Moreover, users have to understand the advantages and limitations of the standard architectures to pick the best long-term system for their applications.
Environmental requirements for military computers are more demanding than those applied to commercial equipment. Some of the specifications for rugged systems in three broad application classes—airborne, ground-based mobile, and shipboard—are presented in Table 1.
Environmental Hazards Airborne applications of rugged computers, particularly aboard propeller-driven airplanes and rotorcraft, are characterized by sustained vibration that can shake components loose or break them. Additionally, airborne systems cannot be allowed to emit sparks that may ignite fuel fumes, or to emit electromagnetic interference (EMI) that might disturb navigation or communications equipment. Furthermore, rugged computers in aircraft are commonly required to withstand altitudes up to 40,000 feet, and they must be able to survive rapid decompression.
Ground-based mobile computers are subject to vibration and shock. In vehicles or shelters that don't have heat or air conditioning, they also must contend with sustained temperature extremes. Temperatures can range from the −40°C cold that's encountered in Greenland up to the 70°C heat that's experienced in Saudi Arabia. Portable or partially exposed mobile computers must stand up to rain, sand, and dust. Plus, they are expected to operate from unregulated power with irregular waveforms, changing voltage, and frequent "brown-outs" or "drop-outs."
Shipboard applications make shock or impact resistance critical for the protection of computers aboard large vessels hit in combat or smaller frigates and patrol boats slammed by rough seas. Electronics that are used on deck or otherwise exposed to the elements cannot allow contamination by corrosive salt fog. Also, EMI must be contained to shield the tightly packed electronics of modern vessels.
Implementing COTS components in rugged applications often requires a mix of packaging and component modifications. Enclosures for hot climates, for instance, can incorporate active-cooling solutions that range from forced air in a clean environment to sealed heat pipes or heat exchangers in sandy, dusty deserts. For applications in extremely cold environments, heaters are incorporated into the de-sign to prevent hard-drive lubricants from thickening and liquid-crystal displays from freezing.
Regardless of the environment or ap-plication, the long life cycle expected from most military systems demands that rugged computers be engineered to accept COTS technology upgrades without costly redesign. While many manufacturers use commercial components, not all have integrated them into open-system architecture designs. A comparison of common architectures for rugged systems appears in Table 2.
The ATX form factor is an industry standard that's widely employed by original equipment manufacturers. It requires that ATX computer boards conform to a uniform set of physical and electrical requirements. By using common-size parameters, input/output (I/O) locations, and power connections, ATX computer boards can be readily adapted to common enclosures. Plus, they can easily accept many COTS power supplies and other third-party accessories.
Most commercial computer manufacturers have accepted the ATX standard, so there's a wide variety of PCI/ATX-compatible add-on devices. Power supplies, storage peripherals, and I/O boards, for example, are interchangeable among ATX computer manufacturers. Because of their widespread use, commercial PCI/ATX components are available at low cost.
Leveraging COTS hardware in the ATX form factor, PCI open-system architectures offer rugged-computer designers and their end users the most current technology that's readily configured for specific applications. The potential for upgrade has been a key design feature of the ATX computer board. With socket memory, PCI expansion slots, and modular central processor units, ATX computers provide users with an upgrade path long after the initial purchase.
Additionally, airborne systems cannot be allowed to emit sparks that may ignite fuel fumes, or to emit electromagnetic interference (EMI) that might disturb navigation or communications equipment. http://www.electrocomputerwarehouse.com/
Anonymous -June 18, 2008
I would like to know if the author has suggestions for a manufacturer of PCI expansion boards (similar to the MAGMA 1-slot card bus) that will coat the boards and has performed some measure of qualification testing for military environments.
Jeff -August 06, 2004
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