3/4 ATR 3-Phase 400 Watt 8-Slot VME/VPX or CompactPCI


ML-750 Series Convection-Cooled  Air Transport Rack Electronic Equipment Enclosure

ML-750 Series Convection-Cooled  Air Transport Rack Electronic Equipment Enclosure

  • This specification defines the performance, design, development, and test requirements of an electronic equipment enclosure intended for use in various United States Air Force and Navy aircraft (i.e. C-130, F-15).

  • The following documents of the exact issue shown form part of this specification to the extent specified herein. In the event of conflict between the documents referenced and the contents of this specification, the contents of this document shall be questioned. Where a paragraph of a referenced document is cited, the citation shall be considered to include all subparagraphs, unless otherwise noted.


    Document Number Description Revision
    MIL-E-5400T Electronic Equipment, Airborne, General Specification 08 Aug   1990
    MIL-C-5541D Chemical Conversion Coatings on Aluminum and Aluminum Alloys 28 Feb. 1989
    MIL-STD-454M Standard General Requirements for Electronic Equipment 15 Dec. 1989
    MIL-STD-461C Electromagnetic Emissions and Susceptibility Requirements for the Control of Electromagnetic Interference 04 Aug. 1986
    MIL-STD-704D Electric Power, Aircraft, Character
    MIL-STD-810E Notice 1 Environmental Test Methods 09 Feb. 1990
    ATR/ARINC 404A STANDARDS Air Transport Cases, Equipment 15 Mar. 1974
  • The Electronic Equipment Enclosure is a custom-sized 3/4 ATR chassis containing the following items:

    • 3/4 ATR 3-Phase 400 Watt 8-Slot VME/VPX or CompactPCI
    • Up To 8 VME/VPX or cPCI compliant Circuit Card Assemblies (CCA)
    • VME 64 compliant backplane
    • I/O connector panel
    • Interface assembly
    • Auxiliary CCA(S)
    • Disk drive
    • Disk drive housing
    • Power supply
    • AC line/EMI filters
    • Power and signal wiring
    • AC fan(s)
    • Handle and access covers

    The Electronic Equipment Enclosure shall be designed to be mounted on a standard ARINC 404A type vibration/shock tray.

    The supplier is responsible for the design, fabrication, assembly and test of the enclosure containing the following items:

    • Power supply
    • DC line/EMI filtering
    • 6U card cage and VME/VPX or cPCI compliant backplane
    • AC fan(s), air, and EMI filter
    • Front panel power connector, switch circuit breaker, LED, and ground stud
    • Power, ground, and fan wiring
    • I/O connector panel

    In addition, the supplier shall design the enclosure to mechanically interface, and electrically operate with the following items supplied by the customer.

    • 6U VME/VPX or cPCI CCA(s)
    • Disc drive and disc drive housing
  • The size of the Electronic Equipment Enclosure shall be 7.50 inches W x 8.195 inches H x 19.56 inches L (3/4 ATR Long with modified height). The front panel will contain a doghouse for the disk drive while the rear panel may contain a doghouse for the mounting of the fan(s), air, and EMI filters.

  • The weight of the Electronic Equipment Enclosure shall be 42 pounds maximum, fully loaded.

  • The center of gravity of the fully loaded Electronic Equipment Enclosure shall be within two inches of the dimensional center along each axis.

  • The Electronic Equipment Enclosure shall comply with standard ATR/ARINC 404A mounting interface specifications for a 3/4 ATR, long. The rear panel doghouse, if used, shall not interfere with the mounting specifications.

  • Content for Item 2
  • Materials, processes, and parts shall be selected that will enable the hardware to meet the performance, quality, reliability, and maintainability requirements specified herein. Best commercial practices shall be used.

  • The hardware shall be packaged in plug-in subassembly form. The disk drive shall be accessible from the front of the enclosure and the 6U VME cards shall be accessible from the top of the enclosure. The backplane, interface assembly, power supply, filtering, and auxiliary CCA(s) shall be accessible by the removal of access covers. The fan(s), air filter, and EMI filter shall be removable from the rear of the enclosure. The fan(s) wiring shall contain a pluggable connector.

  • The chassis shall be constructed of .090 inch minimum, 6061-T4 aluminum alloy, dip brazed or solid seam welded. The rear of the chassis shall provide mounting holes to accept a cooling air duct. The size of the duct and details of the mounting interface will be supplied during the design phase.

  • Covers shall be constructed of .090 inch minimum, 5052, or 6061-T4, aluminum alloy. EMI gaskets shall be used on all cover seams.

  • The front panel assembly will be designed to mount to the front of the chassis, and be constructed of .090 inch minimum, 5052, or 6061-T4, aluminum alloy. The disk drive, disk drive housing, handle, I/O connectors, and wiring will be part of the front panel assembly. Connectors will be attached to the front panel wiring harness to provide a pluggable interface for the estimated 250 signal lines which interface with the enclosure. The style and quantity are optional.

  • The enclosure and hardware shall be treated to provide resistance against corrosion. Aluminum shall be gold irridite chemical film coated per MIL-C-5541, Class 3 Conductive. Steel, and other parts, shall be suitably treated. The exterior surface shall be primed using MIL-P-23377F, Type 1, Class 2 or equivalent, and painted using MIL-C-83286B, Type 1, Lusterless Gray #36231, or equivalent.

  • Military, or best commercial grade and style connectors shall be used. Connectors shall be keyed, whenever possible, to prevent incorrect mating.

  • The backplane shall be an 8-Slot 6U x 160 mm VME/VPX or cPCI-compliant, monolithic, multilayer backplane with integral terminations for all VME signal lines. It shall contain standard 96-pin connectors on .8 inch pitch. The connectors shall contain 1-level wire wrap tails on all P2 pins, and the P1 and P8 pins to which jumper wires can be attached by the customer. The card cage shall use standard VME card guides but the material shall be metal, not plastic. Provisions for accepting standard VME CCA mounting screws shall be provided.

    This assembly is screwed to the CCA(s) and extends beyond the VME panel .357 inch. See attached figure. The card cage must be appropriately positioned in the chassis to make room for this assembly.

  • The design, construction, and assembly of printed wiring boards shall be in accordance with standard IPC specifications, or equivalent.

  • It is critical that the enclosure wiring be designed to accept changes easily during test and deployment. No printed wiring, other than the VME backplane, shall be used. Pluggable connections shall be used to the maximum extent possible. Commercial grade, UL-approved, stranded wiring, or equivalent, shall be used. Strain relief shall be provided wherever practicable. PVC insulation shall not be used.

  • Input voltage shall be per MIL-STD-704A, CAT B Equipment, 115 VAC, 360 to 440 HZ, 3-phase, except that performance during low line transients is not required.

    The VME card cage, auxiliary CCA(s), and disk drive require 380 watts DC Power (+2.5 V at 60 A, +12 V at 3.7 A, -12 V at 2.7 A). Overload fault conditions on the +5, +12, and -12 VDC shall not cause the fan to stop operating. The DC regulation shall be +5%/-2.5%. Hold-up time at maximum output load shall be 20×10-3 seconds minimum.

    The VME compliant power supply shall be capable of operating from full load to 20% of full load. Efficiency shall be 75% minimum. Overload protection and fuse/circuit breaker protection shall be provided.

  • MIL-STD-461A, Part 2, as modified for 1553 and tested in accordance with MIL-STD-462, CE03, CE04, CE07, CS01, CS02, CS06, CS11, RE01, RS02, RS03 and RS06 (Chatter Relay).

  • The thermal design of the Electronic Equipment Enclosure shall be based on direct impingement, forced-air cooling. The air shall enter the rear of the enclosure and exit the front. The enclosure shall contain air and EMI filters on the rear of the chassis. In the case of fan failure, reduced cooling air flow, or abnormally hot cooling air, a power cut-off switch shall be used to protect the electronics in the enclosure.

    For operation up to 10,000 feet, the cooling air shall be provided by internally mounted fan(s). For operation up to 50,000 feet, cooling air will be supplied by an external source. When using externally supplied cooling air the fan(s), air filter, and EMI filter will be removed from the enclosure and a cooling air duct will be attached to the rear of the enclosure.

    Cooling air flow rate of 0.75 pound/minute minimum with a velocity of 300 feet/minute minimum. The total air flow rate required for all the VME CCA(s) is 5.25 pound/minute minimum. The temperature of the cooling air entering the VME card cage shall not exceed 50°C when the enclosure is exposed to the environmental conditions described herein.

  • The fully loaded Electronic Equipment Enclosure shall satisfy all performance requirements when exposed to the following environments.

  • Ambient air operating range is -20°C to +50°C. Non-operating range is -40°C to +75°C.

  • Operating range is sea level to 10,000 feet when cooled by internally mounted fans, and sea level to 50,000 feet when provided with cooling air at a rate of 5.25 pounds/minute minimum.

  • Random vibration input to the vibration/shock tray for 15 minutes in each axis is:

    • 10-60 Hz 0.01 g2/Hz
    • 60-80 Hz 0.30 g2/Hz
    • 80-120 Hz 0.01 g2/Hz
    • 120-140 Hz 0.08 g2/Hz
    • 140-190 Hz 0.01 g2/Hz
    • 190-220 Hz 0.04 g2/Hz
    • 220-260 Hz 0.01 g2/Hz
    • 260-300 Hz 0.02 g2/Hz
    • 300-2000 Hz 0.01 g2/Hz

    The vibration/shock tray and enclosure shall limit the random vibration input to the electronics and disk drive in each axis to:

    • 15-50 Hz 0.15 g2/Hz
    • 50-75 Hz Sloping down to 0.1 g2/Hz at 75 Hz
    • 75-100 Hz Sloping down to 0.01 g2/Hz at 100 Hz
    • 100-500 Hz 0.01 g2/Hz
    • 500-2000 Hz -6 dB/OCT
  • 6G, all three axes, each direction.

  • The input to the vibration/shock tray in all three axes, each direction, is a 30G, half sine wave, 11 msec shock pulse. The vibration/shock tray and enclosure shall limit the shock level input to the electronics and disk drive to 15G.

  • The humidity of the ambient air can be as high as 100% relative humidity with condensation. The electronic hardware shall be suitably protected to ensure operation under these conditions. The corners of the chassis shall contain weep holes.

  • Materials used shall not support fungus growth.

  • The enclosure containing a power supply, AC line/EMI filtering, VME 64 backplane, fan(s), and power/ground wiring shall not cause an explosion when operating in a flammable atmosphere as defined in MIL-STD-810, Method 511.1, Procedure I.

  • The enclosure containing a power supply, AC line/EMI filtering, VME 64 backplane, fan(s), and power/ground wiring shall not sustain damage when exposed to explosive decompression as defined in MIL-STD-810, Method 500.2, Procedure III.

  • The enclosure containing a power supply, AC line/EMI filtering , VME 64 backplane, fan(s), and power/ground wiring shall be designed to have a minimum MTBF of 40,000 hours.

  • The following guidelines shall be used to the maximum extent possible during the design process:

    Access to subassemblies shall be achieved by the removal of covers. Structural members shall not prevent access to subassemblies for removal or replacement. Each subassembly shall be capable of being removed or replaced without having to remove another subassembly. For routine servicing and maintenance the unsoldering of wires, parts, or subassemblies shall not be required. The design shall prevent subassemblies from being inserted into the wrong location.

  • Hardware used shall not contain toxic materials or constitute a radiation hazard. PVC shall not be used in the construction of the LRU.

  • Workmanship shall be to best commercial practice.

  • The supplier shall have documentation to ensure that units manufactured are built and tested consistently. Drawings shall be best commercial practice. Changes to the hardware shall be documented. As a minimum, the following drawings shall be supplied: top assembly & parts list, detail parts, and wire list.

  • The supplier shall notify customer prior to the implementation of any change to the hardware that may affect performance, quality, reliability, maintainability, or interchangeability.

  • The supplier shall supply a copy of the following items:

    • Assembly drawing package
    • Drawing change documentation
    • Test procedures and test results in vendor format
  • The supplier shall package all hardware so as to ensure protection against corrosion, oxidation, deterioration, and physical damage during shipment. All connectors shall be protected with environmental/ESD caps.