G. This Headset-Microphone Kit is designed to fit both the regular and large size Combat Vehicle Crewman\'s Helmet. The electrical characteristics of the kit are compatible with Tactical Radio Systems, such as the VRC-12.

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MIL-DTL-55535A

4.13 Service conditions tests.

4.13.1 Temperature test (see 3.8.1). The equipment shall be subjected to the temperature shock,

method 503 of MIL-STD-810. The test shall begin at + 77� F. The test in 4.9 shall be performed at

+ 150� F and � 40� F. Following these tests and after thermal equilibrium is attained at + 77� F, the

equipment shall meet the requirements of 3.6.1 and 3.7.1, with degradation not to exceed 3 dB.

4.13.2 Moisture resistance (see 3.8.2).

4.13.2.1 Test conditions.

a. Do not remove equipment from the humidity chamber for measurements.

b. Start measurements not more than 5 minutes after power is applied to the equipment. Complete

measurements as rapidly as possible. Do not leave power on after measurements have been

completed.

4.13.2.2 Test procedure. The equipment shall be tested as follows:

a. Dry at + 130� � 5� F for 24 hours.

b. Condition at + 77� � 5� F and 40 to 50 percent relative humidity for 24 hours.

c. Perform the test of 4.9.

d. Subject to continuous cycling for five 48-hour cycles. Temperature, relative humidity, and period

of time for each portion of the cycle shall conform to method 507 of MIL-STD-810. Perform the

test of 4.9 at the times specified on the standard.

e. After cycling has been completed, condition the equipment for 24 hours at + 77� � 5� F at 40 to 60

percent relative humidity.

4.13.3 Altitude test (see 3.8.3).

4.13.3.1 Operating. The microphone and earphone units shall be placed in an altitude chamber. The

response of the microphone and earphone units at sea (ground) level (30 inches of mercury) shall be

obtained at 300, 600, 1,000, 2,000, and 3,500 Hz. Pressure inside the chamber shall then be reduced to

that corresponding to an altitude of 15,000 feet (16.7 inches of mercury). The response of the

microphone and earphone units shall be taken again at the same frequencies as mentioned above. The

degradation in response of either unit shall be not more than 5 dB from the requirements of 3.6.1 and

4.13.3.2 Non-operating. The microphone and earphone shall be subjected to 5 varying pressure

cycles. Each pressure cycle shall consist of 30 minutes at 50,000 feet (3.4 inches of mercury) above sea

level. The pressure transition shall be approximately 5,000 feet per minute. The response characteristics

of the earphone and microphone shall be measured, and shall not exhibit degradation in performance in

excess of 5 dB from the requirements of 3.6.1 and 3.7.1 after being subject to five pressure cycles.

4.13.4 Immersion (see 3.8.4). The equipment shall be immersed to a depth of 3 feet of fresh water at

room temperature for 2 hours. After completion of the 2 hour period of immersion, evidence of water in

the switch cavity shall be cause for rejection. Shake any excess water from the earphone and

microphone. The microphone and earphone shall then meet the requirements of 3.6.1 and 3.7.1,

respectively.