On one specific project for the US Navy, Chassis Plans knew the design was to be tested to MIL-S-901D, Grade A (now defined in MIL-DTL-901E). By understanding the environmental design parameters and knowing the design concerns of integrated COTS hardware, our designers set out to create an enclosure to pass this very intensive test procedure. Simply put, throughout a very high shock event, the computer was required to continue to operate and the enclosure is required to keep its structural integrity without having any pieces or parts come loose from the system that may injure personal within that area.

Utilizing designs that had been previously tested as well as field deployed gave us a great starting point. From there our engineers determined which, if any, components would require additional reinforcements such as heavy heat sinks, components that required further stabilization, and a review of cable routing to ensure there were clean cabling paths to prevent cable tension and chaffing as well as to ensure proper air flow. Additionally, internal shock isolators were added at strategic locations to protect sensitive equipment.

Lastly, a review of the front and rear panels of the system were reviewed to ensure that no system parts or components have the potential to break loose during a high shock event. The enclosure utilizes a milled aluminum front panel for strength and system integrity. Power and reset switches are installed behind a sealed front door to prevent the system from accidently shut down.

This design also uses locking hardware throughout the enclosure and captive hardware to ensure fasteners not fall free from the system and become lost.

On the rear panel, an extension bracket was added to the back of the enclosure to help support the cable assemblies that would be attached to the rear I/O of the unit. This allowed for external cable assemblies to be secured to the rear of the enclosure, while providing clean cabling service loops, removal of any stress on the rear I/O connectors, and to ensure no cabling will come loose during high shock and vibration events.

Customers may require additional I/O to communicate with their software, sometimes this could be an off-the-shelf I/O board, or other times an add-in board developed by the customer. Chassis Plans prefers to install these cards during the assembly process at our factory (whenever possible), to ensure installed ruggedization, proper cabling/power routing and that the board receives the required cooling it needs. Not only is this a further enhancement to the system itself, but it is one less thing a customer needs to worry about during their manufacturing process.

Below we list three of the most common Operational temperature ranges and how we address each:

LEVEL 1 - Standard Temperature Range

Most Chassis Plans customers require a 0°C to 50°C operating temperature range. At this level any Chassis Plans configuration will operate indefinitely with no impact on the lifespan of the product.

LEVEL - 2 Enhanced Temperature Range

The second operational temperature range is a requirement for -20° to 60°C.

While a stock configuration can operate at extended temperatures for a short period of time, if greater operational time is required modifications may be necessary.

We start with the review of each system component. The manufacturer's product thermal characteristics data are reviewed, the component itself is examined, and potential upgrades such as larger heat sinks, etc. are identified and implemented. We review how the components are installed within the enclosure and possible ways to route additional cooling to "hot spots" via cooling fan relocation or additional air ducting. Lastly, cooling fans can be upgraded to increase air flow and modifications can be made to the thermal management system to increase fan speed rotation. In this scenario, a standard rugged chassis is tuned to the specific requirements of a system with higher demands.

To address low temperature operation, initializing warm-up heaters may be added to the system. For cold start operations, the power would be applied to the internal heating elements and fans allowing warm air to preheat the system before start-up takes place.

LEVEL 3 - Extended Temperature Range

The third operational temperature range is -40 to 85C. As mentioned above, a computer system can operate at these levels for a very short duration (hours). If the system is required to be stored and or operational during extended periods of time, then a very different component strategy is needed, moving away from commercial grade components.

Chassis Plans can specify components certified to operate at the -40 to 85C storage and operating temperatures. As an example, the power supply for these units is solid state design. Likewise, the system hard drives are solid state and are industrial grade. The computers system board differs from a comparable commercial unit by upgrading board level components like crystal oscillators, relays, capacitors, resistors, diodes, and magnetics to better endure the extreme temperature requirements. There are a handful of low power Intel CPU's, screened for -40 to 85C storage and operating temperatures available. The selection of a proper CPU is a combination of customer performance requirements as well as environmental considerations.

Chassis Plans quickly evaluated the environmental and system performance requirements and began work on designing a ruggedized computer system that could meet all requirements under a very short timeline. A ruggedized 5U (HPC) computer enclosure was designed that utilized many of our common design criteria, such as tight-fitting seams and joints, solid front panel with integrated air filter and a light "over pressure" to keep air pushing out of all openings. The biggest challenge to the design was managing the heat generated by the system all the while maintaining proper air-filtration.

Beyond what has been described, modifications can be made to further enhance a rugged computer's EMI/RFI shielding.

As an example, Chassis Plans developed a ruggedized system for a telemetry company that was mounting the unit into an aircraft. This system required shielding above and beyond our standard shielding options. The rear panel of the computer is traditionally the weak spot for EMI/RFI emissions due to the I/O connectors and add in board slot locations as well as unshielded external cabling.

To remedy this problem for this application, our engineering team developed a "dog house" rear enclosure. The traditional I/O connectors are enclosed within a sealed metal enclosure and the I/O connections are re-routed to MIL-CIRCULAR shielded connectors. The air exhaust for the enclosure was additionally filtered as well. External cable assemblies were manufactured from shielded materials and terminated into MIL-CIRCULAR shielded connectors. The provided system was then tested to and passed MIL-STD-461 and select DO-160 EMI testing.

In conclusion, there are many ways to protect COTS hardware in harsh military and industrial environments. The challenge is a balance between providing required computer system performance along with the deployed environmental characteristics as well as keeping the platform cost effective.

Also, as shown in the examples, it becomes a true partnership between Chassis Plans and its customers to rapidly develop the best solution for each customer and project. For additional information or to speak with a dedicated Chassis Plans Program Manager please contact us at (858) 571-4330 for more information.