MIL-PRF-49446B(CR)
4.5.14 Microphonics. Microphonics shall be measured while the Detector is vibrated in
accordance with paragraph 4.5.14.1. The Detector-Dewar shall be cooled to 60-80oK with full
operating bias applied. Mounting to the cooler shall be made by tightening the mounting screws
to a torque of 3.50 inch pounds minimum. Vibration excitation shall be measured by an
accelerometer mounted on the mounting plate of the Detector-Dewar. The white noise reference
level may be determined by averaging the noise in each channel from 12,000 to 20,000 Hz with
vibration applied. Noise spectra shall be measured using a bandwidth between 50 Hz and 365
Hz. Failure of any channel to meet the requirements of 3.5.14 shall constitute a defect as defined
in paragraph 3.5.1.
4.5.14.1 Microphonics Vibration. The Detector-Dewar shall be coupled to a mechanical
cryogenic refrigerator that produces random vibrational excitation of the Detector-Dewar in three
mutually perpendicular axis. The frequency distribution of the vibrations shall be in a range from
0 to 20,000 Hz. The RMS sum of the three axis vibration shall be at least of 1.0g RMS. Each
axis shall produce a minimum vibrational excitation of 0.4 g RMS. In the frequency range of
2,000 to 20,000 Hz, the RMS sum shall be at least 0.8 g RMS. The mechanical cryogenic
refrigerator may be mated to the Dewar with a bellows.
4.5.15 Apparent thermal mass. (Cooldown). An HD-1132/UA cryogenic cooler shall
be mated to a standard test mass (Figure 3). The capacity of the HD-1132/UA shall be such
that the 1.25 gram (250 joules) test mass is cooled from ambient (296oK) temperature to 80oK
±1.5o K in not less than 5, nor greater than 6, minutes. This measurement shall be made using
a highly polished metal Dewar without any radiation shielding. This test Dewar and test mass
shall consist of the following: A high vacuum of less than 10 microtorr, and a 1.25 gram
aluminum test mass. The time to cool the thermal mass shall be recorded. The voltage output
of the temperature sensor diodes in the Detector-Dewar under test shall be measured at 77o ±
1oK and at ambient temperature. The voltage output at 80oK shall then be interplated. The
cooler shall then be coupled to the Detector using thermal grease and bellows. Operating bias
power shall be applied and the time for the temperature of the diode to reach 80oK shall be
recorded. Failure of the diode to cool within the requirements of 3.5.15 shall constitute failure
of this test.
4.6 Environmental tests. Environmental testing methods contained in 6.2.d are
acceptable methods for determining compliance with Section 3.6 et el. The contractor may elect
to use alternative methods and testing procedures. In such cases, the contractor shall be required
to show where his own tests and measurements for verifying the environmental conditions are
equivalent to the methods cited herein. When the contractor desires to deviate from these cited
methods, he shall be prepared to show equivalency via a test plan which has been approved by
the Government contracting office. Also, environmental tests shall be accomplished using
known testing apparatus such as an environmental test chamber, vibration test table, pendulum
shock device, or similar test equipment for which the technical capabilities to properly simulate
extreme climatic or transportation conditions are scientifically documented. The methods for
testing to verify compliance with all stated performance characteristics selected by the
contractor shall be equivalent to the recommended procedures found herein.
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