MIL-DTL-68G
Measurement procedure. Measurements shall be made in accordance with ANSI S1.13 and as
4.6.8.1.2
specified herein. The microphone positions shall be one meter from the smallest imaginary parallelepiped that
will just enclose the fan. In addition to the horizontal array, a vertical array of microphone positions shall be used,
with measurement points located directly above the center of the parallelepiped and at two of the horizontal array
positions. Ambient noise shall be at least 10 dB below the sound level of the fan and corrections for ambient are
not permitted.
4.6.8.2 Conformance inspection. Observation (no instruments required) shall be made of the fans to
determine that the fans operate without objectionable airborne noise at rated speeds.
4.6.9 Operation for 100 hours. Operation for 100 hours at rated voltage shall be conducted to ascertain
satisfactory operation of the following:
(a)
Bearings.
(b)
Input.
(c)
Speed.
4.6.10
Life test.
4.6.10.1
The fans shall be run continuously for 5,000 hours at rated voltage and frequency. Upon completion
of the life test, input, output, speed and airborne noise shall be measured to determine conformance with 3.10.
4.6.10.2
Dielectric. Upon the expiration of the 5,000 hour run, the fans shall be subjected to an
a.c. potential of 1000 volts for 1 minute applied between the current carrying parts and the frame.
4.6.10.3
Wear. Upon the completion of the dielectric test, the fans shall be dismantled and
examined for wear and defects to determine whether wear is excessive (see 3.18).
4.6.11
Shock. The fans shall be subjected to class HI shock in accordance with MIL-S-901.
The features of test shall be as follows:
(a)
Type Type A.
(b)
Class Class I.
(c)
Grade Grade B.
(d)
Weight designation Light.
(e)
Principal functions Circulating air.
(f)
Cause for rejection Any breakage or damage which would permits the fan or a part thereof to
become airborne and cause injury to personnel.
(g)
Mounting the fan shall be mounted as shown on fixture 4A of MIL-S-901.
(h)
Exceptions to MIL-S-901 None.
Note Starting or stopping of the fan due to the switch changing position during shock shall not cause
for rejection.
4.6.12
Vibration. Vibration tests shall be conducted in accordance with type I vibration of MIL-STD-167-1.
4.6.13
Permeability (class 2 fans only). The permeability of nonmagnetic material shall be determined by
the use of permeability indicators conforming to ASTM A342/A342M.
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