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|  MIL-S-85419 (AS)
motion of the fixture is not induced due to any unsymmetrical
weight or stiffness distribution of the equipment, Measurements
of vibratory accelerations or displacements shall be made at the
mounting base of the valve. All frequency measurements shall be
accurate within 5 percent. All displacement or acceleration
measurements shall be accurate within 10 percent. The motion
of the vibrator table shall be simple harmonic motion with not
more than 20 percent distortion.
4.5.6.2.2 Resonance Survey. The equipment shall be vibrated
with essentially simple harmonic motion in each of three mutually
perpendicular directions to explore for resonant frequencies.
Frequency scans between 5 and 1000 Hz shall be made very slowly
and carefully. The frequency range shall be broken into small
convenient intervals and each interval scanned at a 0.01 inch
double amplitude or 2g, whichever is less. The fixture motion
shall be observed closely during the frequency scans to detect
the frequencies of minimum fixture motion which defines the
frequencies at which major components of the unit are in
resonance, These frequencies are quite sharply tuned and do not
necessarily coincide with the frequencies at which maximum
component amplitudes or noises occur when scanning at constant
applied force amplitude. When the resonant components are small,
the reduction of fixture motion at resonance may not be
discernible, in which case the resonant frequencies may be
determined from observations of maximum component amplitudes or
noises, phase shift between fixture motion, and motion of a
resonant part. In all cases, the resonant frequencies shall be
verified, if possible, by checking for minimum fixture motion.
The test report must contain complete descriptions of all
resonances, including the resonant frequencies, parts in
resonance, and modes of vibration.
4.5.6.2.3 Resonance Endurance Tests. After completion of the
resonance survey, a resonance endurance test shall be conducted
at all resonant frequencies, with applied force adjusted as
necessary to obtain the applicable fixture displacements or
accelerations specified in Figure 10. The vibrator and power
supply must produce the prescribed fixture motions of all
Endurance tests shall not be conducted at any
frequencies.
frequency at which the fixture amplitude abruptly increases when
scanning at a constant applied force amplitude or at which the
transmissibility (output/input) is less than two. Resonance
endurance tests shall be conducted for a period of 30 minutes at
the four most severe resonant points on each axis.
4.5.6.2.4 Cycling Endurance Test. The starter/APU shall be
subjected to the following cycling tests at room temperatures in
addition to the resonance survey and resonance endurance tests.
The starter/APU shall be mounted as specified in 4.5.6.2.1 and
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