Downloaded from https://www.everyspec.com MIL-STD-81OC B sinusoidal resonance search, resonance dwel1, and cycling tests of items weighing more than 80 pounds mounted in airplanes, and missiles, the vibra- tory accelerations shall be reduced lg for each 20-pound increment over 80 pounds. Acceleration derating shall apply only to the highest test level of the selected curve, but in no case shall the derated test level be less than 50 percent of the selected curve (see note 1 of the applicable table). When the input vibration is measured at more than one control point, the control signal shall be the average of all the accelerometers unless otherwise specified. For massive test items.
fixtures and large force exciters, it is recommended that the input control level be an aver- age of at least three or more inputs. 4.5.1.1 Resonance search. :Resonant frequencies of the equipment shall be determined by varying the frequency of applied vibration slowly through the specified range at reduced test levels but with sufficient amplitude. to excite the item. Sinusoidal resonance search may be performed using the test level and cycling time specified for sinusoidal cycling test, provided the resonance search time.is included in the required cycling test time of 4.5.1.3. 4.5.1.2 Resonance dwell.
The test item shall be vibrated along,each axis at the most severe resonant frequencies determined in 4.5.1.1. Test levels, frequency ranges, and test times shall be in accordance with the applicable conditions from the tables and figures for each equipment category. If more than four significant resonant frequencies are found for any one axis, . the four most severe resonant frequencies shall be chosen for the dwell test. If a change in the resonant frequency occurs during the test, its time of occurrence shall be recorded and immediatelythe frequency shal1 be adjusted to maintain the peak resonance condition. The final resonant frequency shal1 be recorded. 4.5.1.3 Cycling.
The test item shal1,be vibrated along each axis in accordance with the applicable test levels, frequency range, and times from the applicable tables and figures. The frequency of applied vibration. shall be swept over the specified range logarithmicallyin accordance with figure 514.2-10. The specified sweep time is that of an ascending plus a descending sweep and is twice the ascending sweep time shown on figure 514.2-10 for the specified range. 4.5.2 Random vibration test. The test item shal1 be subjected to random vibration along each of three mutually perpendicular axes according to the specified curve. Test times shall be according to the applicable schedule from the tables.
The instantaneousrandom vibration accelerationpeaks may be limited to three times the rms acceleration level. The power spec- tral density of the test control signal shall not deviate from the speci- fied requirements by more than +100,-30 percent (+3, -1.5 dB) below 500 Hz 514.2-5 METHOD 514.2