Downloaded from https://www.everyspec.com MIL-STD-1311D 3.4 Frequency sweep. Logarithmic vibration frequency sweeps are recommended. Linear sweeps may be used if the sweep rates are adjusted for equal time per octave, while maintaining the desired overall rate. The units used for expressing sweep rates shall be minutes per decade. The recommended sweep rate is 2.3 minutes per decade (for example, 10 to 2,000 Hz in 5.3 minutes.) 4. Test procedures for sinusoidal vibration. 4.1 Survey. The frequency at the specified vibration level shall be cycled at a logarithmic rate from the lowest to the highest frequency specified on the TSS.
The instantaneous sweep rate shall be such that one decade is swept in 2.3 minutes. If necessary, the sweep may briefly be slowed, stopped, or reversed for the proper location and identification of resonances. Record all resonances and relative magnitude. 4.2 Single sweep. With the specified vibration level applied, the vibration frequency shall be swept once from the lowest to the highest frequency. The instantaneous sweep rate shall be such that one decade is swept in 2.3 minutes. The TUT shall operate as specified on the TSS throughout the test. 4.3 Cycling. With the specified vibration level applied, cycle the vibration frequency twice from the lowest to the highest frequency and back.
The instantaneous sweep rate shall be such that one decade is swept in 2.3 minutes. Before and after cycling in each axis, the TUT shall be subjected to procedure 4.1. The TUT shall operate as specified on the TSS throughout the test. 4.4 Endurance at resonance. This test shall be preceded and followed in each axis by procedure 4.1. With the vibration level applied, the TUT shall be vibrated for the time specified on the TSS at each vibration frequency at which evidence of resonance was observed during the initial survey. During the resonance period, the vibration frequency shall be adjusted as often as necessary to maintain the maximum amplitude or output.
If more than four resonances were observed, the four judged most likely to cause failure shall be chosen. If no resonance was observed, endurance at resonance shall be omitted. The TUT shall operate as specified on the TSS throughout the test. Note: This test may be destructive. If this is considered a destructive test, the TSS shall so indicate. 5, Summary of information required on TSS. For each test procedure selected, specify the following information on the TSS: a. Test limits and conditions (see 2.3). b. Axes of application (see 2.4). c. Frequency range (see 3.2). d. Vibration level (see 3.3 and note below). e. Time at each resonance (see 4.4). f.
When endurance at resonance is considered constructive (see 4.4). g. Exceptions of modifications, if any. NOTE: Vibrate at a constant displacement as specified in the 3.3 table, up to the listed crossover frequency and then go to constant acceleration at the specified table 3.3 acceleration value. METHOD 1032A 1032-2 19 April 1968