MIL-DTL-21393B
TABLE VIII. Reliability test sampling plan.
Lot Size
Quantity to be Tested
2 to
25
2
26 to 200
3
201 to 500
4
Over 500
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4.7.1.2 Test routine. With the test circuit apparatus assembled and connected as shown on figure 2,
the test shall consist of thermal cycling, with periodic operation as shown on figure 7. The profile of the
actual test figure may be altered to account for variations in test chamber facilities and limitations of test
equipment. Description of thermal and operational profiles shall be defined in a test plan and procedure,
to be approved by the government inspector.
4.7.1.3 Test duration. The duration of the reliability test shall be 500 hours.
4.7.1.4 Performance check. At the start of test and at approximately 100 hour intervals during and at
the conclusion of the test, a limited performance check shall be conducted on each unit, immediately after
(temporary) removal from the thermal chamber. These performance checks shall be performed during
various thermal chamber temperature conditions (see figure 7). The performance check shall consist of
the following:
Sensitivity and frequency response:
No more than ± 3 dB variation, at any frequency, from
4.7.1.5 Repair or replacement of failed microphones. Failed units under test may be replaced with
new units or repaired and returned to test, with concurrence of the procuring activity and government
inspector. All failures occurring during testing shall be documented and investigated to determine root
cause.
5. PACKAGING
5.1 Packaging. For acquisition purposes, the packaging requirements shall be as specified in the
contract or order (see 6.2). When actual packaging of materiel is to be performed by DoD or in-house
contractor personnel, these personnel need to contact the responsible packaging activity to ascertain
packaging requirements. Packaging requirements are maintained by the Inventory Control Point's
packaging activities within the Military Service or Defense Agency, or within the military service's system
commands. Packaging data retrieval is available from the managing Military Department's or Defense
Agency's automated packaging files, CD-ROM products, or by contacting the responsible packaging
activity.
6. NOTES
(This section contains information of a general or explanatory nature that may be helpful, but is not
mandatory.)
6.1 Intended use. It is intended that these microphones convert normal speech input to electrical
signals suitable for connection to speech amplifiers and or modulators of radio or audio equipment. The
M21393/1-01 microphone is intended for use in high noise and radio frequency interference environments
on or about military aircraft. The M21393/2-01 microphone is intended for use in low noise and radio
frequency interference environments, on or about military submarines.
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