Downloaded from https://www.everyspec.com MIL-STD-81OC 10 March 1975 METHOD 507.1 HUMIDITY 1. PURPOSE. The humidity test is conducted to determine the resistance of equi=o the effects of exposure to warm, highly humid atmosphere such as is encountered in tropical areas. This is an exaggerated environmental test, accomplished by the continuous exposure of the equipment to high rela- tive humidity at cycling elevated temperatures. These conditions impose a vapor pressure on the equipment under test which constitutes the major force behind the moisture migration and penetration. 1.1 General effects. Corrosion is one of the principal effects of humidity.
Hydroscopic materials are sensitive to moisture and may deteriorate rapidly under humid conditions. Absorption of moisture by many materials results in swelIing, which destroys their functional utility and causes loss of physical strength and changes in other important mechanical properties. Insulating materials which absorb moisture may suffer degradation of their electrical and thermal properties. Cycling temperature and humidity may cause condensa- tion of moisture inside of the equipment which could cause the equipment to malfunction due to electrical shorts or cause binding due to corrosion or fouling of lubricants between moving parts. 2. APPARATUS.
Humidity-temperaturechamber and associated equipment. 2.1 Chamber. The chamber and accessories shal1 be constructed and arranged in such a manner as to avoid condensate dripping on the test item. The chamber shall be trap-vented to the atmosphere to prevent the buildup of total pressure. Relative humidity shall be determined from the dry bulb-wet bulb thermometer comparison method or an equivalent method approved by the procuring activity. When readout charts are used, they shal1 be capable of being read with a resolu- tion within O.6° C (l”F). Wlen the wet bulb control method is used, the wet bulb and tank shall be cleaned and a new wick installed at least every 30 days.
The air velocity flowing across the wet bulb shall be not less than 900 feet per minute. Provisions shall be made for controlling the flow of air throughout the internal chamber test space where the velocity of air shall not exceed 150 feet per minute. Steam or distilled, demineralized,or deionized water having a pH value between 6.0 and 7.2 at 23° C (73”F) shall be used to obtain the specified humidity. No rust or corrosive contaminants shal1 be imposed on the test item by the test facility. 507.1-1 MST1-IODS07.1 10 March 1975