Special Feature
is also improved as the air is channeled from bottom to top of the board by the faceplate on one side and the backplane on the other. Many military applications use CompactPCIe modules and chassis as is, but for those applications that demand more ruggedness, additional features can be added to improve shock and vibration resistance, extend the operating temperature, reduce EMI radiation and provide independent system monitoring and alarming. The system shown in Figure 4 is based on the chassis within a chassis concept, where a normal CompactPCIe chassis is shock mounted within a larger rugged enclosure. This provides exceptional shock, vibration and EMI suppression, and is often the technique used to allow off-the-shelf boards to be used and still meet MIL-SPEC-810B requirements. Improved Shock and Vibration Resistance: Shock and vibration resistance is key to keeping a system running in many environments. One technique for extending the shock and vibration characteristics of CompactPCIe systems is to use steel cable rope isolators to suspend the CompactPCIe card cage within a larger enclosure. The rope isolator size and locations can be chosen such that even under the most extreme shock, the inner chassis never touches the outer chassis. These isolators dramatically attenuate the high-frequency component of the shock, allowing the electronics to survive shocks that would otherwise have ripped the electronics to pieces. Extended Temperature Range: Temperature range is often dictated by startup situations where a vehicle has been sitting idle without its normal heating and cooling systems operating. In these cases the start-up temperatures can be much colder or warmer than the normal board-level products are specified to. Fortunately many manufactures provide extended temperature versions of their board-level products. Providing additional chassis airflow can also extend the top end of these products. The type of insulation used in the wiring is also key to extended temperature operation. Teflon
Figure 4
This chassis inside a chassis design extends the environmental robustness of CompactPCIe systems.
Figure 5
In harsh environments it is often essential to have an independent controller monitoring the internal chassis operation. Shown here is an independent system monitoring and alarming board.
August 2007 COTS Journal [ 29 ]