See Part One for test facility, test conditions, and test control information.
4.1 Test Facility
In addition to the requirements specified in Part One, recommend using two chambers for Procedures II and III in order to simulate the sudden temperature changes often associated with movement between outside ambient and indoor conditions. Either a single chamber or combination of chambers is acceptable, as long as the test procedure requirements are satisfied.
MIL-STD-810H METHOD 524.1
4.2 Controls
- a. Temperature. Unless otherwise specified in the test plan, if any action other than test item operation (such as opening the chamber door) results in a significant change of the test item temperature (more than 2 °C (3.6 °F)), re-stabilize the test item at the required temperature before continuing. If the operational check is not completed within 15 minutes, reestablish the test item temperature conditions before continuing.
- b. Rate of temperature change. Unless otherwise specified, control the rate of temperature change to not exceed 3 °C (5.4 °F) per minute to prevent thermal shock.
- c. Temperature measurement. Install temperature sensor instrumentation on or in the test item to measure temperature stabilization data (see Part One, paragraph 5.4).
- d. Temperature recording. Continuously record the chamber and test item temperature, if required.
4.3 Test Interruptions
4.3.1 Interruption Due To Chamber Malfunction
Test interruptions can result from two or more situations, one being from failure or malfunction of test chambers or associated test laboratory equipment. The second type of test interruption results from failure or malfunction of the test item itself during operational checks.
- a. General. See Part One, paragraph 5.11 of this Standard.
- b. Specific to this Method. Interruption of a freeze-thaw test is unlikely to generate any adverse effects. Normally, continue the test from the point of interruption once the test conditions have been re-established.
4.3.2 Interruption Due To Test Item Operation Failure
Failure of the test item(s) to function as required during mandatory or optional performance checks during testing presents a situation with several possible options.
- a. The preferable option is to replace the test item with a “new” one and restart from Step 1.
- b. A second option is to replace / repair the failed or non-functioning component or assembly with one that functions as intended, and restart the entire test from Step 1.
4.4 Test Execution
4.4.1 Preparation for Test
4.4.1.1 Preliminary Steps
Before starting the test, review pretest information in the test plan to determine test details (e.g., procedures, test item configuration/orientation, cycles, durations, parameter levels for storage/operation, etc.). (See Part One, paragraph 5.9, and paragraph 3.1, above.)
4.4.1.2 Pretest Standard Ambient Checkout
- Step 1 Remove unrepresentative coatings/deposits and contaminants such as oils, grease and dirt that could affect the adhesion of ice to the specimen surface.
- Step 2 Ensure any fluids contained in the test item are compatible with the temperatures used in the test.
- Step 3 Install temperature sensors in, on, or around the test item (as described in the test plan) to measure temperature stabilization and surface temperatures.
- Step 4 Place the test item in the test chamber at standard ambient conditions and in the required configuration.
- Step 5 Conduct a visual examination of the test item with special attention to stress areas, such as corners of molded cases, and document the results.
- Step 6 Conduct an operational checkout (Part One, paragraph 5.8.2) as described in the plan and record the results.
MIL-STD-810H
METHOD 524.1
Step 7 If the test item operates satisfactorily; proceed to paragraph 4.4.2, 4.4.3, or 4.4.4 as appropriate. If not, resolve the problems and repeat Step 6 above.
4.4.2 Procedure I – Diurnal Cycling Effects
Step 1 Spray the test item sufficient to fill any horizontal pockets to simulate water collected during a rain storm.
Step 2 Reduce the temperature inside the chamber to -10 °C (14 °F) or as otherwise specified for the initial conditions at a rate not exceeding 3 °C (5 °F) per minute. Maintain the condition for a minimum of one hour after the test item temperature has stabilized.
Step 3 Increase the chamber temperature to 4 °C (39 °F) over a period of three hours. When the chamber air temperature reaches 0 °C (32 °F), introduce moisture using water vapor, steam, vapor generator or other means to raise and maintain the humidity at or close to saturation.
Step 4 When the test item surface temperature reaches 0 °C (32 °F), ensure frost has formed on the test item surfaces.
Step 5 Continue raising the test chamber towards a test item surface temperature of 4 °C (39 °F) (water at maximum density) until the frost just melts, then reduce the temperature to -10 °C (14 °F) over a period of three hours. Maintain the conditions for a minimum of one hour following test item temperature stabilization.
Step 6 Repeat Steps 3 through 5 for a total of twenty cycles unless otherwise specified.
Step 7 Maintain the chamber and test item at the low temperature conditions until a visual examination and/or operational checks have been completed. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2. Otherwise go to Step 8.
Step 8 Return the test item to standard ambient conditions. Perform a complete visual and operational check, and document the results. See paragraph 5 for analysis of results.
4.4.3 Procedure II – Fogging
Step 1 Adjust the chamber temperature to 10 °C (18 °F) below the freezing point or as otherwise specified for the initial conditions at a rate not exceeding 3 °C (5 °F) per minute. Maintain the condition until the test item temperature has stabilized plus one hour.
Step 2 Transfer the test item to another chamber (previously adjusted to the upper specified temperature) as quickly as possible such that condensation or fogging occurs. The use of insulated transport containers is recommended. Maintain this second chamber at the specified upper temperature (usually room ambient) with a relative humidity of 95 ± 5 percent.
Step 3 Start operation and any performance tests of the test item 60 ± 15 seconds after completion of the transfer, and document results. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 4 Return the test item to the low temperature chamber and repeat Steps 1-3 as required to complete the number of cycles identified in paragraph 2.3.4.
Step 5 Return the test item to standard ambient conditions. Perform a complete visual and operational check, and document the results. See paragraph 5 for analysis of results.
4.4.4 Procedure III – Rapid Temperature Change
Step 1 Adjust the chamber temperature to the specified upper temperature (usually standard ambient) at a rate of approximately 3 °C (5 °F) per minute, and a relative humidity of 95 ± 5 percent. Maintain these conditions until the test item temperature has stabilized plus one hour.
- Step 2 Transfer the test item as quickly as possible and in not more than 5 minutes to another chamber stabilized at -10 °C (14 °F). Stabilize the test item temperature and hold for one additional hour.
- Step 3 Unless otherwise specified, perform an operational check. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
MIL-STD-810H
METHOD 524.1
- Step 4 Transfer the test item as quickly as possible and in not more than 5 minutes to another chamber stabilized at the specified upper temperature (usually standard ambient) and a relative humidity of percent. Note the presence of any free water, and repeat Step 2 through 4 for a total of three cycles unless otherwise specified.
Step 5 Return the test item to standard ambient conditions. Perform an operational check and physical inspection, and document results. If the test item fails to operate as intended, see paragraph 5 for analysis of results, and follow the guidance in paragraph 4.3.2 for test item failure.