OPERATING TEMPERATIRE AND HUMIDITY – environmental test – comparison of standards

John Roberts

October 16, 2007

Combined temperature and humidity test, equipment in operation

The references are:

o [VVSG0708] – the August 31, 2007 draft of the new VVSG

o [VVSG05] – the 2005 version of the VVSG

o [M810D] – MIL-STD-810D, dated July 19, 1983, “MILITARY STANDARD ENVIRONMENTAL TEST METHODS AND ENGINEERING GUIDELINES”, the reference used in both the 2005 VVSG and the July 6 2007 draft VVSG

o [M810F] – MIL-STD-810F, dated January 1, 2000, “DEPARTMENT OF DEFENSE TEST METHOD STANDARD FOR ENVIRONMENTAL ENGINEERING CONSIDERATIONS AND LABORATORY TESTS”, the current version of the military environmental testing standard

Test parameter: temperature – humidity cycle

o [VVSG0708]: No cycle specified – range of conditions bounded by four points: (1) 5 °C (41 °F) and 5% RH, (2) 5 °C (41 °F) and 85% RH, (3) 40 °C (104 °F) and 85%, and (4) 40 °C (104 °F) and 5% RH.

o [VVSG05]: reference to [M810D] Table 507.2-I “High-humidity diurnal categories”, Column “Natural / Hot-Humid (Cycle 1)

o [M810D]: Humidity test: Table 507.2-I “High-humidity diurnal categories”, Column “Natural / Hot-Humid (Cycle 1)

o [M810F]: No longer includes natural temperature/humidity cycles, instead specifying a severe test with temperatures cycling as high as 60 °C, and relative humidity continuously at 95%. The philosophy of testing (2.4, p 507.4-3, and 1.3, p 507.4-1) is to produce a highly stressful situation that may uncover potential problem areas. “Alternative Tests” (2.5, p 507.4-3) provides tailoring guidance for the use of natural or induced cycles when the use of such is indicated, and lists AR 70-38 and NATO STANAG 2895 as references. In AR 70-38 (which can be found at http://www.army.mil/usapa/epubs/pdf/r70_38.pdf ), Army Regulation 70-38, “RESEARCH, DEVELOPMENT, TEST AND EVALUATION OF MATERIEL FOR EXTREME CLIMATIC CONDITIONS, September 15, 1979”, Table 2-3, “Hot Climatic Design Type: Hot-Humid Daily Cycle of Temperature, Solar Radiation, and Humidity”, columns for Operational Conditions, the 24-hour temperature – humidity cycle is identical to the [VVSG05] Table 507.2-I, Natural / Hot-Humid (Cycle 1) that is the reference for the storage humidity test in [VVSG05], with the exception that the time listed in the [VVSG05] table as “0000” is listed as “2400” in the AR 70-38 table.

o Comment: The Natural Hot/Humid cycle is not suitable to test for conformance to [VVSG0708] performance requirements, because it is out of range of the [VVSG0708] requirements, and because it does not provide for testing of different humidity levels at a given temperature. Tailoring of the temperature-humidity cycle (for both [M810D] and [M810F]) is necessary.

o A 24-hour temperature-humidity cycle is not needed for conformance to the [VVSG0708] operating performance requirements so it is not necessary to require a specific timeline for the test procedure. The critical requirements for timing of the temperature-humidity cycle are (1) avoidance of thermal shock, (2) avoidance of condensation, and (3) stabilization of the test chamber and equipment at the desired test conditions.

Test parameter: Number of temperature-humidity cycles, operational test timing

o [VVSG0708]: specified only by reference to [M810D]

o [VVSG05]: 10 cycles total, operational test after 5th cycle and 10th cycle (storage humidity)

o [M810D]:

o humidity test: at least 10 cycles total, operational test after 5th cycle and 10th cycle (I-3.2b (1)(b) (pp 507.2-8 to 507.2-9), also II-3.1 (pp 507.2-15 to 507.2-16))

o operating high temperature test: at least 3 cycles (I-3.2c(2), p 501.2-11)

o [M810F]:

o humidity test: same as [M810D] at least 10 cycles total, operational test after 5th cycle and 10th cycle ([M810F] Change 3, 4.5.2 (p 507.4-6))

o operating high temperature test: at least 3 cycles for cyclic test, alternative is single cycle, test at peak response (see pp 501.4-10 to -11)

o Comment: [M810D] (and [M810F]) has no distinct “operating humidity” test, and voting devices already have a 10-cycle storage humidity test. Recommend 3 temperature-humidity cycles for the operating temperature-humidity test for [VVSG0708].

Test parameter: Pretest – controlled ambient conditions for 24 hours prior to test

o [VVSG0708]: specified only by reference to [M810D]

o [VVSG05]: no

o [M810D]: yes (II-2.2 (p 507.2-15))

o [M810F]: yes (23 ± 2 °C, 50% ± 5% R.H.) ([M810F] Change 3, 4.5.2 Step 1 (p 507.4-6)

o Comment: 24 hours at ambient conditions assures that all test items will start with the same conditions – recommend that 24 hour pretest be included. (Not necessarily require use of environment chamber for pretest – sitting in the test lab for 24 hours may be sufficient.)