MIL-DTL-25427B
4.8.14.1 Sinusoidal vibration. The tests shall be performed at ambient temperature of
70 °F to 90 °F, along two axes, one axis parallel to the direction of flow and the other axis
perpendicular to the direction of flow. The vibration input accelerometer shall be mounted on the
fixture close to the mounting point of the coupling to the fixture. A second accelerometer shall be
mounted directly on the test item for monitoring resonant frequencies. Sinusoidal excitation shall
consist of three tests, resonance search (see 4.8.14.1.1), resonance dwell (see 4.8.14.1.2), and
cycling (see 4.8.14.1.3).
4.8.14.1.1 Resonance search. Resonant frequencies of the coupling shall be determined
along each axis by slowly sweeping through the frequency range of 15 Hertz (Hz) to 2000 Hz
logarithmically (see figure 6). The applied vibration shall be at reduced levels (0.5g) but with
sufficient amplitude to excite the test item. A resonant frequency shall be considered to be
any natural frequency with an amplification factor of 2.0 or greater of the output response relative
to the input level. The resonant frequencies shall be recorded.
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