Unless otherwise specified in the individual test methods, adhere to the test condition tolerances shown below for the following parameters. Any tolerance shown as ± X following a specified value is intended to mean the specified value is what is intended but, because of instrumentation or measurement inaccuracies, a slight deviation is acceptable but not outside of the tolerance. The accuracy and calibration requirements for instrumentation and test equipment used for control or monitoring are typically specified in the referenced test methods. Where such requirements are not specified in the referenced test methods, the accuracy shall be equal to at least 1/3 of the tolerance of the variable being measured.
Recommended default tolerances for common test parameters are provided below. Where there is conflict between these recommended values and any requirements stated in the referenced test methods, the requirements of the referenced methods take precedence.
MIL-STD-810H
All instrumentation and test equipment shall be calibrated periodically to laboratory standards whose calibration is traceable to national laboratory standards. The test facility shall maintain the calibration records.
- a. Test section air temperature. Surround the test item totally by an envelope of air (except at necessary support points), considering boundary effects. Keep the air temperature uniform in the immediate vicinity of the item. To ensure the test item is bathed in the required air temperature, place verification sensors at representative points around the entire item and as close to the test item as possible, but not so the airstream temperature is affected by the test item temperature. Keep these temperatures within ± 2°C (3.6°F) of the required test temperature. Ensure the air temperature gradient across the item does not exceed 1°C (2°F) per meter or a maximum of 2.2°C (4°F) total (test item non-operating). Wider temperature tolerances are acceptable in situations such as:
- (1) For large items with a volume greater than 5m³ (6.5 yd³), the temperature tolerance can be ± 3°C (± 5°F). Justify any larger tolerance and obtain approval for its use from the procuring activity.
- (2) For required temperatures greater than 100°C (212°F), the temperature tolerance can be ± 5°C (± 9°F). Specify the actual tolerance achieved.
- b. Pressure. ±5 percent of the value or ±200 Pa (0.029 psi), whichever is greater.
- c. Humidity. Keep relative humidity at the chamber control sensor to ±5 percent RH of the specified value.
- d. Vibration amplitude. See the tolerances specified in the test methods.
- e. Vibration frequency. See the tolerances specified in the test methods.
- f. Acceleration. See the tolerances specified in the test methods.
- g. Time. Control time (e.g., test durations and data gathering intervals) for climatic testing is within ±5 minutes for a total test duration greater than 8 hours, and within ±1 percent of the specified value for durations or intervals of 8 hours or less, unless the nature of the test requires greater accuracy.
- h. Air velocity. Maintain within ±10 percent of specified value.
- i. Water purity. See paragraph 5.16.
- j. Input Power. When input power is of major concern, use tolerances listed in the applicable power source standards (i.e., voltage, frequency, crest factor, ripple, phase displacement, distortion) referenced in Part One, paragraph 5.1.
5.2.2
Test Fluid Temperature.
Unless otherwise required by the customer, the test items are stabilized at standard ambient conditions. Where appropriate, use the temperature of the test fluid equal to its temperature during its most extreme operating condition. Design assessment may prove that other temperatures provide a more severe environment, e.g., longer exposure at lower temperatures because of slower evaporation.