HomeFeatures Filtered Conduction Empowers Mil-Spec Desert Systems
Filtered Conduction Empowers Mil-Spec Desert Systems
May 01 2007
Page 2 of 3
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Exterior Mechanical Design
The first challenge is providing a rugged outside housing for the payload. In this solution, we chose to go with an ATR-style (see Figure 1) form factor because it is a common platform that has had a proven record for many years. The other advantage to this style of form factor is that it will easily mount into many existing applications, and there are a number of readily available shock-isolated trays on the market that can help meet the rugged vibration environments. It is also important to find that optimal balance between the weight and ruggedness required. A designer could go with a brazing approach, but this typically adds unacceptable cost and lead time to the program. The more economical approach would be to go with a welded/bolted-together construction method. This still provides significant strength, but also reduces the weight, cost, and lead time. It is also very important to include a rugged military finish or paint on the outside surfaces to further protect the enclosure from the harsh environments. The paint for this solution was chosen for its UV reflective properties to reduce the heat load generated by external solar radiation. In addition to the structural integrity and resistance to the environments, serviceability plays a big factor in the final design. The air intake filters on this unit are important to get the air into the chassis, but just as important is the ability to remove these filters and service them in the field, eliminating costly depot maintenance time.
Internal Structure The second challenge is the requirement that the internal air be isolated from the external environment. The COTS air-cooled cards are not robust against accumulation of airborne sand and dust, and must be protected against this environmental threat. In addition, many board sets can generate substantial EMI, which must not only be contained within the unit, but must also be prevented from interfering with sensitive components in the electronics package (see Figure 2). Directly beneath the card cage is a small volume approximately 1.5" high, which can be used for additional payload. This space is EMI-isolated by aluminum walls and a conductive plane on the backplane. Airflow into this space is provided by ventilation holes in the backplane on the pressurized side of the recirculation fan.
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