Downloaded from https://www.everyspec.com MIL-STD-81OC 2.2.2 Accelerometer,piezoelectric;.’When a piezoelectiic accelerometer is employed as the shock sensor, the funhapenthl resonant frequency of the accelerometer shall be greater thsn 14;000 Hz (resonantfrequencies of 30,,000 Hz or higher are recommended). For suitable low.frequency response the accelerometer and load (cathode follower, smplifier, or other load) sIiall have the following characteristics: RC>O.2 Where R = load resistance (ohms), C = accelerometer capacitan,ce,pltis shunt capacitance of cable and load (farads] I 2.2.3 Accelerometer, strain gage.
A strain gage accelerornet&may be used, provided.the undamped natural frequency is equal to or greater than 1,500 Hz with dimping approximately 0.64 .tb0.70 of critical.’ 2.2.4 Accelerometer calibration. The accelerometer shall be dynamically I calibrated to the specified accuracy. ., 2.2.5 A~. The monitoring accelerometer shall be rigidly attached to the test item support fixture at or near the attach- ment point(s) of the test item. 3. PROCEDURES 3.1 Shock pulse. The-shock pulses for procedures I, III, and IV shall be as shown on figure 516.2-1 or 516.2-2 (whicheveris specified).
All points of the acceleration waveform obtained shall lie within the area enclosed by the tolerance limit lines. It is recommended that the saw tooth shock pulse be used, since its broad frequency spectrum tends to excite all resonant frequencies. 3.2 Mounting of test item. The test item shall be rigidly attached to the shock machine table for procedures I, III, and IV, in accordance with General Requirements, 3.2. Wherever possible, the test load shall be distributed uniformly on the test platform in order to minimize the effects of unbalanced loads. I 3.3 Procedure I, basic design test.
This procedure shall be used for shock testing of equipment assemblies(mechanical, electrical, hydraulic, electronic, etc.) of medium size, including items.whichmount on vibration isolators and equipment racks. Three shocks in each direction shall be applied alOng three mutually perpendicular,axes of the test item (total of 18 shocks). If the test item is normally mounted on vibration isolators, o MSTHOD 516.2 516.2-2