Line-replaceable unit: Difference between revisions

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== Specifications ==

LRUs are designed to specifications to assure that they can be interchanged, especially if they are from different manufacturers. Usually a class of LRUs will have coordinated environmental specifications (i.e. temperature, condensation, etc.). However, each particular LRU will also have detailed specifications describing its function, tray size, tray connectors, attachment points, weight ranges, etc. It is common for LRU trays to have standardized connections for rapid mounting, cooling air, power and grounding. The mounting hardware is often manually-removable, standard screw-detent quick-release fittings. Front-mounted electrical connectors are often jacks for ring-locked [[XLR connector|cannon plug]]s that can be removed and replaced (R&R) without tools. Specifications also define the supporting [[tool]]s necessary to remove and replace the unit. Many require no tools, or a standard-sized [[screwdriver#Blade types|Frearson screwdriver]]. Frearson is specified for some vehicles, and many marine systems because Frearson screws are not designed to not cam-out, and the same screwdriver can be used on many sizes of screws. Most LRUs also have handles, and specific requirements for their bulk and weight. LRUs typically need to be "transportable" and fit through a door or hatchway. There are also requirements for [[fire|flammability]], unwanted radio emissions, resistance to damage from [[fungus]], [[static electricity]], [[heat]], [[pressure]], [[humidity]], [[condensation]] drips, [[oscillation|vibration]], [[radiation]] and other environmental measurements.

LRUs may be designed to [[ARINC]] 700-series standards. The form factor of LRUs comply to ARINC Standards, [[ARINC 404]] and [[ARINC 600]]. LRUs are also defined by manufacturers like [[Airbus]] and [[Boeing]] and by various military organizations. In the military, electronic LRUs are typically designed to interface according to data bus standards such as [[MIL-STD-1553]].<ref>"The B-52H Integrated Weapon Interface Unit (IWIU) program is a newly developed Line Replaceable Unit (LRU) which will replace the current 1980s developed LRU’s which are becoming unsupportable. The LRU’s currently installed in the Stub Pylon/Heavy Stores Adapter Beam (SP/HSAB) provide the command and control link between the B-52H Offensive Avionics System and all “smart” MIL-STD 1760 current and future weapons carried on the B-52H." [http://www.defenselink.mil/contracts/contract.aspx?contractid=3521 United States Department of Defense Contracts, No. 615-07, May 21, 2007]</ref> On the [[International Space Station]], LRUs are referred to as [[Orbit Replaceable Unit]]s.