MIL-PRF-38715B
4.5 Methods of inspection
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4.5.1 Response. The indicator shall respond to a 50 percent LEL methane-air mixture within 5
seconds at standard temperature.
4.5.2 Scale accuracy The indicator shall be tested with 25% and 50% LEL mixtures (gases of
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para.3.4.1) in air as well as with a 15% oxygen in nitrogen mixture. The indicated concentration
shall not be less than the true concentration or exceed the true by more than 10 percent of full
scale. The oxygen detector shall be tested for compliance with 3.4.4. Finally, at the
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discretion of the government inspector, the contractor may be required to demonstrate the
satisfactory operation of any indication.
4.5.3 Alarm. The alarm shall be set at a chosen percent LEL below that used in 4.5.2 and then
tested for compliance with requirement 3.4.5 during a test for scale accuracy in 4.5.2.
4.5.4 Calibration The indicator shall be calibrated with a standard gas and tested for scale
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accuracy (4.5.2).
4.5.5 Stability On each range, the indicator shall be operated on fresh air for 15 minutes, and
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"zeroed" by means of the proper controls. On each range, the indicator shall then be operated on
a methane-air mixture of known concentration and identity for 3 consecutive periods of 5 minutes
each, while being quickly and accurately "zeroed" again on fresh air before each period of 5
minutes. The variation in reading shall not be lower than the true concentration nor exceed the
true concentration by more than 10 percent of full scale.
4.5.6 High temperature The indicator shall be mounted in its normal operating position in a
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chamber. The test shall be performed in accordance with Method 501.3, Procedure II of MIL-
STD-810, Operation. The high end temperature shall be set at 52°C. The indicator shall then be
tested for scale accuracy (4.5.2).
4.5.7 Low temperature. The indicator shall be mounted in its normal operating position in a
chamber. The test shall be performed in accordance with Method 502.3, Procedures II and III of
MIL-STD-810, Operation and Manipulation. The low end temperature shall -18°C. The indicator
shall then be tested for scale accuracy (4.5.2).
4.5.8 Temperature shock The indicator shall be mounted in its normal operating position in a
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chamber. The test shall be performed in accordance with Method 503.3, Procedure III of MIL-
STD-810, Ground Transfer. The low end temperature used shall be -18°C. The indicator shall
then be tested for scale accuracy (4.5.2).
4.5.9 Rain. The indicator shall be mounted for one hour with the dial/display in a vertical
plane and one hour with the dial/display in a horizontal plane (face upward) in a rain test chamber.
The external connections shall be made to the indicator in such a manner as to simulate installed
conditions. The test shall be performed in accordance with Method 506.3, Procedures I and II of
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