MIL-HDBK-1908B
The TWA value can be calculated from the following alternate expression when the sound level takes on a sequence of N constant levels, Li, each lasting for a time period of Ci hours:
Q
N
Ci where: D= Ti
TWA = 85 + log102 log10(D)
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and: Ti =i=1Limiting exposure time at each A-weighted sound pressure level =
Li = ith A-weighted sound pressure level.
2(Li-85)/Q
The exchange rate must be specified when referring to TWA. Note: TWA is identical to Leq8 with an exchange rate of 3 dB as utilized by U.S. and international sound and noise standards.
Electroluminescent device (EL) gen. A device that produces light through electrical excitation of a phosphor.
Enter uci. An explicit user action that effects computer processing of user entries. For example, after typing a series of numbers, a user might press an ENTER key that will add them to a data base, subject to data validation.
Entry uci. See "Data entry" or "Control entry."
Environment gen. The aggregate of all the conditions and influences including physical location and operating characteristics of surrounding equipment and occupants, including temperature, humidity, and contaminants or surrounding air; operational procedures, acceleration, shock, vibration, and radiation.
Equipment gen. General term designating any item or group of items.
Equipment, powered ground (PGE) acq. An assembly of mechanical components including an internal combustion engine or motor, gas turbine, or steam turbine engine mounted as a single unit on an integral base or chassis. Equipment may pump gases, liquids, or solids; or produce compressed, cooled, refrigerated or heater air; or generate electricity and oxygen. Examples of this equipment: portable cleaners, filters, hydraulic test stands, pumps and welders, air compressors, air conditioners. Term applies primarily to aeronautical systems.
Equipment failure gen. Cessation of the ability to meet the minimum performance requirements of the equipment specifications. Further, equipment failure should imply that the minimum specified performance cannot be restored through permissible readjustment of operator controls.
Equipment grades snv. Categories of equipment undergoing measurements of airborne sound measurements of shipboard equipment to classify usage-driven acceptance criteria. Equipment grades are defined below:
Grade A3. Equipment to be installed in spaces where direct speech communication must be understood with minimal error and without repetition over a distance of 2 meters (6-1/2 ft) or less.
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