1\ Downloaded from https://www.everyspec.com MIL-STD-81OD, 19 Julyl1983 \, \ (1) Storage test: The test temperatures for storage test exposures should include cyclic conditions that are derived from the natural diurnal cycles. The cycles provided in tables 501.2-I and 501.2-II and information in I-3.2a(3) are the extreme meteorological and induced diurnal cycles for major w6rld areas. The temperature extremes given are based on a frequenty of 1% of the’hours during the most severe month in the most severe part of the area encompassed by the climatic region of interest. The map in General Require- ments, figure 4, shows the boundaries of the areas of concern.
The chamber air temperature and humidity conditions can be derived or calculated from the analysis of the storage situation (1-3.1.3.1) and the cycles provided in tables 501.2-I and 501.2-II and in paragraph I-3.2a(3). The values given in the tables represent the conditions of air within the storage place or adjacent tc the test item. Derivation of the actual test temperatures must consider the thermal path to the test iteui,type of heat transfer, mass of the test item in relation tc the mass of the Surrounding air, and other empirical and thermal properties of the test item. ... . (2) Operational test:
The chamber air temperature for the operational test can be derived f“roman analysis similar to that performed for the storage teat. Conaideration of all of the probable exposure situations must be based on the operational purpose of the test item. Again, the major contributing factor to be considered ia.the effect of solar heat~ng on the exposed materiel and the expected response of the test item to the conditions. The heating mechanism or thermal path affecting the test item as a whole or ita critical component(s) must be determined.
If the thermal path is a form of convective heat.transfer free of the effects of solar radiation, then the ambient conditions of tables 501.2-I and 501.2-II and of paragraph I-3.2a(3) could be used to derive the chamber air temperature and humidity test conditions/cycles. Operational testing should occur with the test item experiencing the maximum response to the established exposure. This exposure can be accomplished by operating the test iteemduring the temperature cycling period. Such op&at ion would also provide information on the operational ability of the test item experiencing a limited internal thermal gradient.
Equipment for which the operational testing cannot be accommodated with cycling conditions’shall be exposed to constant temperature. The temperature level used for this exposure would be the extreme value measured or obtained from field measurements or obtained from the response of the test itemwhen exposed to the temperature cycles derived from tables 501.2-I and 501.2-II and from paragraph I-3.2a(3). When the test item or its critical components are configured ao that their temperature cannot be monitored, the estimate of the value must be based upon thermal path, mass, and other properties of the teat item. Figure 501.2-1 may be used aa a guide. 0 c. Duration of exoosure.
Determine the test duration. The duration of high-temperature exposure may be as significant as the temperature itself. Because procedures I and II expcse the test items to cyclic temperatures, the number of cycles is critical. (Cycles are 24-hour periods unless otherwise specified.) . (1) Storage. The number of cycles required is that which will satisfy the design requirements. Since little is known about how to time- compress this test, the number of cycles for the storage test is set et a minimum of of extreme aeven to coincide with the 1% frequency of occurrence of the hours temperatures during the most severe month in an average year at the 19 July 1983 501.2-9 MSTHOD 501.2