MIL-PRF-49175C(CR)
4.5.5 Leak rate. The cooler shall be placed in a bell jar or suitable
fixture connected to a helium mass spectrometer. The bell jar or fixture shall
be evacuated to establish an inside-out test mode. Operating test shall not be
performed during leak rate test. The leakage rate shall be measured at +23°C,
±5°C ambient. Failure to meet requirements of 3.5.5 shall constitute failure of
this test.
4.5.6 Vibration output. The cooler shall be turned on for 15 minutes to
allow it to reach equilibrium temperature. The cooler shall be vertically
suspended such that the fundamental frequency of the cooler is much higher than
the natural frequency of the suspension system. The static deflection of this
arrangement shall be in excess of 6 inches and critical frequency (fcr) of 1.3 Hz
approximately. The acceleration along each axis shall be obtained by attaching
an accelerometer to the center of the piston and motor faces and to the unit
centered on the coldfinger axis. Moments around each axis shall be obtained by
attaching two accelerometers (to the motor, piston face or coldfinger face) and
coherently subtracting the two signals. This difference divided by the
separation distance between the accelerometers yields the angular acceleration.
Moment of inertia shall be obtained from the period of a bifilar pendulum
containing the cooler. Peak forces are derived from the expression F=MA where F
is the peak force, M is the cooler mass, and A is the measured acceleration at a
given frequency. Peak torque is derived from the expression T = I℘, where T is
the peak torque, I is the moment of inertia about the principal axis, and ℘ is
the measured angular acceleration for the applicable axis at a given frequency.
Failure to meet requirements of 3.5.6 shall constitute failure of this test.
4.5.7 Restart. The cooler shall be operating at 80 K or less in a 23°C ±
5°C ambient. The power switch shall be turned off and the cooler motor shall be
at rest. The power switch shall be turned on and the cooler must start within 5
seconds. This test shall be repeated a total of twenty times. The cooler shall
also be tested at -54°C and -71°C using the above procedure during the high and
low tests of 4.6. The restart test shall be performed after the cooldown and
cooling capacity tests. Failure to meet the requirement of 3.5.7 shall
constitute failure of this test.
4.6 Environmental tests. Unless otherwise specified, the environmental
tests shall be performed in accordance with MIL-STD-810. The operating tests
required before and after environmental tests shall be those specified in table
II. During 4.6.2 and 4.6.3, operating test 4.5.1, 4.5.2, 4.5.3 and 4.5.7 shall
be performed and must be successfully completed. Operating tests are not
required during 4.6.1, 4.6.4 and 4.6.5 except that the unit under test shall
have power applied during 4.6.4 and 4.6.5.
4.6.1 Temperature shock. The cooler shall be tested in accordance with
MIL-STD-810, method 503, except that the temperature of step 2 shall be -54°C
and the temperature of step 1 and step 4 shall be +95°C. Failure to meet the
requirements of paragraph 3.6.1 shall constitute failure of this test.
4.6.2 High Temperature. The cooler shall be tested in accordance with
MIL-STD-810, Method 501, Procedure I (see figure 6) except that the temperature
of step 2 shall be +95°C. The temperature of step 4 and step 5 shall be +71°C.
Failure to meet requirements of 3.6.2 shall constitute failure of this test.
9
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business