MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)cause permanent damage to the system or equipmentunder consideration.“When electromagnetic fields become very large, permanentdamage can occur to operating equipment. Forexample, if the electrical field becomes sufficiently high,electronic breakdown can occur, destroying the equipment.On the other hand, at some intermediate values offield strength, overheating can occur in which the RF fieldinduces currents that contribute to the heat load alreadypresent as a consequence of operation of the equipment.This overheating can lead to failure of components andmalfunction of the system.“In addition to the effects of electromagnetic radiationon equipment, another consideration involves the effectsof the electromagnetic environment on man and theextent that this must be considered in the design of electronicmateriel. Basically, the effects produced by electromagneticfields on man are classified into thermal andnonthermal. Some portions of a man’s physiology areparticularly susceptible to certain frequencies of electromagneticenergy. One of the prime areas of environmentalconcern involves the effect of microwaves on humanbeings. ”10-3.2.2 Summary of Environmental EffectsThe environmental conditions under which unshelteredequipment should be designed are given in Table10-10. A summary of the major environmental effects isgiven in Table 10-11 (Ref. 6), and the failure modes ofelectronic components due to some of these environmentalfactors are presented in Table 10-12 (Ref. 22).TABLE 10-10. ENVIRONMENTAL REQUIREMENTS FOR UNSHELTERED EQUIPMENTTemperatureEnvironmentStandard AreaOperatingNonoperatingCold Weather AreaOperatingOperatingNonoperatingDesert and Tropical AreasOperatingNonoperatingHumidityOperatingNonoperatingSolar RadiationWindBarometer PressureOperatingNonoperating-29 to 52°C (-20 to-54 to 54° C (-65 toEnvironmental Limits25°F)30°F)-40°C (-40°F) if operator is unsheltered-54°C (-65°F) if operator is sheltered-62°C (-80°F) for 3 days and achieve rated capacity after 30min preheating and warm-up52°C (125°F)71°C (160°F) for 4 h per day indefinitelyUp to 100% at 38°C (100°F) including condensationUp to 100% including condensationEndure a solar intensity of 4X10 6 J/m 2 (360 Btu/ft 2 for aperiod of 4 h at 52°C (125°F)Withstand wind pressures up to 1435 Pa (30 lb/ft 2 ) ofprojected surface, either empty or under loadFrom 101 to 57 kPa (30 to 16.8 in. of mercury)4572 m (0-15,000 ft)From 101 to 19 kPa (30 to 5.54 in. of mercury)12,190 m (0-40,000 ft)10-18