MIL-PRF-85726B(AS)
3.2.3 Recycled, recovered, or environmentally safe materials. Recycled, recovered, or
environmentally safe materials shall be used, provided that the material meets the performance
requirements specified herein.
3.3 Interface and dimensional requirements.
3.3.1 Size.
3.3.1.1 Enclosure. The external dimensions of the enclosure, excluding cooling interfaces,
shall enclose Modular Concept Units (MCUs) of varying sizes. The enclosure shall be available
in the following MCU sizes: 2, 4, 6, 8, 10, and 12. The sizes are provided in table 1 and are
shown on figure 1.
3.3.1.2 Enclosure accessibility. Access panels, attachment mechanisms, and gaskets shall
be designed to permit access to interior parts, terminals, and wiring for adjustments, required
circuit checking, and for parts replacement in reparable assemblies. For routine servicing and
maintenance, unsoldering of wires, wire harnesses, parts, and subassemblies shall not be required
to gain access to terminals, soldered connections, and mounting screws. Sizes of openings,
maximum reach requirements, and allowable sizes and weights of replaceable assemblies shall
conform to MIL-STD-1472.
3.3.1.3 Protrusions. All front panel protrusions such as hold-downs, carrying handles,
controls, displays, and connectors shall be as shown on figure 1 when the enclosure and its
components are in the latched and actuated position. On the rear panel, connector-mounting
screwheads shall lie within the limits shown on figure 1. Other protrusions are permitted on the
rear panel, provided they are within the diagonally lined envelope shown on figure 1 and that
they do not interfere with the interfacing of the enclosure with the rack.
3.3.2 Modularity. The enclosures are part of a modular packaging approach that provides
electrical, mechanical, and thermal interfaces for the SEMs. This technique provides for the
joining of 2, 4, and 6 MCU-sized enclosures to form 4, 6, 8, 10, and 12 MCU sizes with a
minimum of additional components. Each enclosure tier shall accept not less than 13 modules at
a 0.60-inch (15.24 mm) pitch. The enclosure shall be capable of interfacing with SEM Format B
Span 2, the SEM Format C, and the SEM Format E as described in MIL-STD-1389. Table II
provides combinations of enclosure sizes, module sizes, and backplane module interconnection
methods in which enclosures shall be configurable. The maximum enclosure mass value
provided (see table II) is the maximum weight of an avionics system that can be packaged using
an enclosure.
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