Temperature Humidity Vibration and Altitude

MIL STD 810 G – Test Method 520.3 – Temperature Humidity Vibration and Altitude

 

SCOPE

 

Purpose
The purpose of this test is to help determine the combined effects of temperature, humidity, vibration, and altitude on airborne electronic and electro-mechanical materiel with regard to safety, integrity, and performance during ground and flight operations. Some portions of this test may apply to ground vehicles, as well. In such cases, references to altitude considerations do not apply.
Application
NOTE: This method not intended to be used in lieu of Methods 500, 501, 502, 507, and 514 unless properly tailored and authorized in the requirements documents.
  1. Use this method to evaluate materiel likely to be deployed in altitude areas (above ground level) where temperature, humidity, and vibration may combine to induce failures.
  2. Use this method for engineering development, for support of operational testing, for qualification, and for other similar purposes. This method is primarily intended for actively powered materiel operated at altitude, i.e., aircraft, missiles, etc.
  3. Use this method to provide an option for use of vibration in combination with the climatic elements, or for use of the climatic tests in combination with each other. This is often noted throughout the text. Generally, the combined environment test simulates those synergistic environmental effects that occur for the majority of the deployment life.
Limitations
  1. Limit use of this method to evaluating the combined effects of two or more of the following: altitude, temperature, humidity, and vibration.
  2. Some procedures permit testing for the effects of one forcing function at a time and stressing materiel items beyond realistic limits. Doing so may reduce or eliminate synergistic or antagonistic effects of combined stresses, or may induce failures that would not occur under realistic conditions.
  3. This method does not normally apply to unpowered materiel transported as cargo in an aircraft.
  4. The tailored test cycle should not include short duration vibration events or those that occur infrequently in the test cycle. These events include firing of on-board guns, extreme aircraft motion, and shock due to hard landings. Test for these events separately using the appropriate test method.

 

TEST PROCESS

 

Qualification test cycle
Step 1. Ramp to Cold/Dry – With the test item non-operating, ramp the chamber temperature from room ambient conditions down to the most extreme low operating temperature at a rate of no more than 5°C/minute (9°F/minute).
Step 2. Cold/Dry Soak – Allow the test item to soak at this temperature until it has reached thermal stabilization or for 4 hours (whichever is greater). If vibration is to be performed during this step, derive it from a low altitude, high Mach flight condition (combined temperature/vibration may be performed separately). Ground vehicles would use severe road/field vibration levels (see Method 514.6).
Step 3. Cold/Dry Warm-Up – Operate the test item at its minimum operating voltage. If supplemental cooling is supplied during this step, tailor cooling parameters for minimum heat removal (e.g., minimum temperature and minimum flow for air cooling at or above the minimum operating temperature). Maintain this condition for the minimum specified warm-up period.
Step 4. Cold/Dry Performance Check – Perform an operational check immediately following Step 3 to verify the test item operates as required. If the test item fails to operate as intended, see paragraph 5 for failure analysis and follow the guidance in paragraph 4.3.2 for test item failure.
Step 5. Ramp to Cold/Dry Altitude – With the test item operating, ramp the chamber from the site pressure to the maximum cruise altitude (use the formulas in Table 520.3-IV to derive pressure from altitude). Perform the pressure ramp at the maximum facility rate, not to exceed the predicted platform rate. Not applicable to ground vehicles.
Step 6. Cold/Dry Altitude – Maintain the maximum cruise altitude for 30 minutes. If vibration is to be performed during this step, derive it from a high altitude, high Mach flight condition. This is not applicable to ground vehicles.
Step 7. Ramp to Warm/Moist – Ramp the chamber conditions from Step 6 and uncontrolled humidity to 32°C (90°F) and site pressure and 95 percent relative humidity (RH). Perform this temperature/ humidity/ altitude ramp at the maximum facility rate, not to exceed the predicted platform rate. This step simulates a quick descent from a high altitude and allows an altitude chamber to simulate a high altitude descent to a hot/humid day landing site. This is not applicable to ground vehicles.
Step 8. Warm/Moist Dwell – Maintain 32°C (90°F), site pressure and 95 percent relative humidity for 30 minutes. If vibration is to be performed during this step, derive it from a low altitude, high Mach flight condition. Ground vehicles use an aggregate vibration schedule based on various road conditions.
Step 9. Ramp to Hot/Dry – Ramp the chamber temperature to the maximum operating temperature and the chamber humidity to less than 30 percent RH. Operate the test item at its maximum operating voltage. At the same time, supply supplemental cooling at the worst case thermal conditions (e.g., maximum temperature and minimum flow for air-cooling). Perform this temperature/humidity ramp at the maximum facility rate, not to exceed the predicted platform rate.
Step 10. Hot/Dry Soak – Allow the test item to soak at the maximum operating temperature until it has reached thermal stabilization or 2 hours (whichever is greater). If vibration is to be performed during this step, derive the vibration levels from the maximum of take-off/ascent or low altitude/high Mach (if appropriate). Ground vehicles use aggregate off-road vibration levels.
Step 11. Hot/Dry Performance Check – Operate the test item and record data for comparison with pretest data. If the test item fails to operate as intended, see paragraph 5 for failure analysis and follow the guidance in paragraph 4.3.2 for test item failure.
Step 12. Ramp to Hot/Dry Altitude – Ramp the chamber from site pressure to the maximum cruise altitude (use the formulas in Table 520.3-IV to derive pressure from altitude). Perform this pressure ramp at the maximum facility rate, not to exceed the predicted platform rate. This is not applicable to ground vehicles.
Step 13. Hot/Dry Altitude – With the test item operating, maintain the maximum operating temperature and maximum cruise altitude until the test item has reached thermal stabilization or 4 hours (whichever is greater). If vibration is to be performed during this step, derive it from a high (or ultra-high if applicable) altitude, high Mach flight condition. Not applicable to ground vehicles.
Step 14. Hot/Dry Altitude Performance Check – Perform an operational check to verify that the test item operates as required. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 15. Ramp to Room Ambient – Ramp the chamber from the maximum operating temperature and maximum cruise altitude to room ambient temperature, site pressure and uncontrolled humidity. Perform this temperature/pressure ramp at the maximum facility rate, not to exceed the predicted platform rate. Return the test item to a non-operating condition and discontinue the supplemental cooling at the conclusion of the ramp.
Step 16. Repeat the cycle (Steps 1-15) as necessary to meet the test plan duration requirementsor 10 cycles, whichever is greater.
Step 17. Perform an operational check to verify that the test item operates as required, and see paragraph 5 for analysis of results
Test development schedule
Used for each Procedure.
  • Step 1. Identify the platform missions and test materiel location.
  • Step 2. Identify the mission profiles.
  • Step 3. Select the top 80 percent of potential mission profile. (Table 520.3-III) (Procedure III only.)
  • Step 4. Select most severe potential mission profile. (Exception: short term and transient events, e.g., gunfire, crash shock, etc.) (Procedures I and III).
  • Step 5. Identify the vibration levels by mission profile.
  • Step 6. “Normalize” the high vibration use profile. Use severe mission profile vibration level (used for Method 514.6, Procedures I and III). (See paragraph 2.3.4)
  • Step 7. Create a Mach/altitude table and determine the mission profile thermal/altitude environments for hot/dry, warm/moist, and cold/dry conditions (see paragraph 2.3.2).
  • Step 8. Determine the cooling environment for the test item (see paragraph 2.3.5).
  • Step 9. Write a thermal, altitude, humidity, vibration profile for the most severe expected environments for hot/dry, warm/moist, and cold/dry conditions (see paragraph 2.3.3). (Temperature/vibration may be performed separately.)
  • Step 10. Determine the most severe operating conditions for the materiel and incorporate them into the combined environments profile (see paragraphs 2.3.4 thru 2.3.8).
  • Step 11. Determine most severe cooling environments for the materiel and incorporate them into the combined environments profile (see paragraphs 2.3.5.1 and 2.3.5.2).
  • Step 12. Develop a test plan with separate and/or combined environments (see paragraph 2.2.2).
  • Step 13. Perform the test.

 

NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.

 

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