MIL-DTL-21393B
4.6.3.5.2 Radiated susceptibility. The procedures of RS103, Radiated Susceptibility, Electric Field,
and 2 MHz to 40 GHz shall be applied to the microphone under test (see MIL-STD-461).
4.6.3.5.3 Conducted susceptibility. The procedures of CS114, Conducted Susceptibility, Bulk Cable
Injection, 10 kHz to 200 MHz (see CS114 calibration limit for all applications, Curve #3) shall be applied
to the microphone under test (see MIL-STD-461).
4.6.3.5.4 Conducted susceptibility. The procedures of CS115, Conducted susceptibility, bulk cable
injection, impulse excitation shall be applied to the microphone under test (see MIL-STD-461).
4.6.3.6 Distortion (see 3.6.8). The distortion measurements shall be made for conformance with 3.6.8,
by employing a distortion analyzer of the wave analyzer or total distortion type (see figure 2). The
frequency range of the analyzer shall be at least 100 to 10,000 Hz with high selectivity and an input
voltage range from 0.001 to 10 volts. The measurement of distortion under service conditions may be
made immediately after subjecting the microphone to the temperature extremes.
4.6.3.7 Vibration (see 3.6.9). The microphone under test shall be subjected to the appropriate
vibration test in accordance with MIL-STD-810, method 514, procedure I, Transportation: Category 7 (Jet
Aircraft), Operational Service: Category 12 (Fixed Wing Jet Aircraft). The microphone shall be connected
in a test circuit providing for an amplifier current of 10 milliamperes. The test shall be conducted for a
period of one hour. The current shall be turned on for 2 minutes and off for 2 minutes alternately for the
duration of the test period.
4.6.3.8 Impact test (see 3.6.10). The microphone unit shall be subjected to 20 random drops, from a
6-foot height to a covered concrete floor. The covering shall consist of 1/8 or 3/16 inch thick asphalt tile
thoroughly cemented to the concrete floor using a minimum thickness of cement.
4.6.3.9 Altitude.
4.6.3.9.1 Pressure cycling (see 3.6.11.1). The microphone unit shall be subjected to 5 varying
pressure cycles. Each pressure cycle shall consist of 30 minutes at 3.4 inches of mercury (approximately
50,000 feet) and 30 minutes at 30 inches of mercury (approximately sea level). The pressure transition
shall be approximately 5,000 feet per minute. The response characteristic for each microphone unit
under test shall then be measured and compared to the initial response characteristic for that
microphone.
4.6.3.9.2 Pressure equalization (see 3.6.11.2). The microphone unit shall be placed in an altitude
chamber and the pressure inside the chamber reduced to that corresponding to an altitude of 15,000 feet
(approximately 16.7 inches of mercury). The response of the microphone unit at a frequency of 1,000 Hz
shall be measured at that altitude. The response of the microphone unit shall also be measured at a
frequency of 1,000 Hz, while the microphone is subjected to a pressure increase corresponding to a
descent from an altitude of 15,000 feet (16.7 inches of mercury) to sea level (30.0 inches of mercury) at a
rate of 5,000 feet per minute.
4.6.3.10 Humidity (see 3.6.13). The microphone shall be subjected to the humidity test, in accordance
with method 507 of MIL-STD-810.
a. The number of 48-hour cycles for this test is 5 (five).
b. The temperature/humidity levels shall be 60°C and 95 percent respectively.
c. Measurements after test: Within 1 hour after the test, the frequency response at ground level
shall be measured; the microphone may then be examined for evidence of damage.
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