Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July .1983 MSTHOD 507.2 HUMIDITY SECTION 11 11-1” AUAEUUS 11-1.1 a. The required apparatus consists of a chamber or cabinet, and auxiliary instrumentation capable of maintaining and continuously monitoring the required conditions of temperature, and relative humidity throughoutan envelope of air surrounding the test item(a). (See General Requirements, 4.4.1.) b. Unless otherwise speoified, the test volume of the chamber or cabinet and the accessories contained therein shall be constructed and arranged in such a manner as to prevent condensate from dripping on the test item(s).
The test volume shall be vented to the atmosphere to prevent the buildup of total pressure and preve~t centamination from entering. Relative humidity shall be determined by employing either solid-state sensors whose calibration is not “affectedby water condensation or by an equivalent method, such aa fast-reacting wet-bulb/dry-bulb sensors or dewpoint indicator. Sensors that are sensitive to condensation, such as the lithium chloride type, are not recommended for tests with high relative humidity levels. A data collection system separate from the chamber controllers shall be employed to measure teet volume conditions. A recording device shall be mandatory for the data collection system.
If charts are used, the charta shall be readable to within ~0.6oc. If the wet-wick control method is approved for use, the wet bulb and tank shall be cleaned and a new wick installed before each test and at least every..30 days. Water used in wet-wick systems shall be,of the same quality as that used to produce the humidity. Water bottle, wick, sensor, and othqr components making up relative humidity measuring systems shall ba visually examined at leaat once every 24 hours during the test.
The velocity of air flowing across the wet-bulb sensor shall be not less than 4.5 meters per second (900 feet per minute), and the wet wick shall be on the suction side of the fan to eliminate the effect of fan heat. The flow of air anywhere within the envelope of air surrounding the test item shall be maintained between O.5 and 2 meters per aacond (98.to 394 ft/min). c. Relative humidity within the envelope of air surrounding the test item shall be created by steam or water injection. Water used in either method shall be distilled, demineralized, or deionized and have a resistance of not less than 500,000 ohms.
Its quality shall be determined at periodic intervals (not to exceed 15 days) to asaure its acceptance. If water injection ia used to humidify the envelope of air, the water shall be temperature conditioned before its injection to prevent upset of ths test conditions.and shall not be injected directly into tbe test section. Condensation developed within the chamber test volume during the test, shall be drained from the test velume and discarded. 19 July 1983 507.2-13 MRTHOD 507.2 ,