Downloaded from https://www.everyspec.com MIL-STD-81OC 3.4 Determination of test levels (secondarystructure). This paragraph shall apply to those equipment arrays located on or in secondary structure and whose aggregate of equipments and structure are of a size, weight and complexity to preclude the testing of the entire configuration as a single entity. In such cases the equipment may be removed from the secondary structure for individual vibration tests. Note that the equipment shall be excited in the isolated or hard mounted mode-in compliance with the actual mounting configuration in or on the secondary structure.
.411other equipments not identified with secondary structure shal1 be associated with primary structure and treated in accordance with 3.3. Special transfer functions have been provided in order that the pri- mary test spectium Gs and Gr may be operated o: to reflect a response spectrum which becomes the secondary, or input, test spectrum for the appropriate equipment. The operation and the resultant response spectrum Y~ and Yr for the sine and the random case, respectively,is shown as follows:
Gs \H(f)12 = y~ (13) Gr lH(f)\2 = Yr (14) ) Since Gs and Gr have be;n expressed in decibel fOrm (see equations 6 and 7) and lH(f)[2 is also expressed in this form (see figures 519.2-18 and 519.2-19) then Ys and Yr may be found by algebraically adding the spectral values of the primary structure to the appropriate transfer func- tion as follows: dBy = dB~ + dB s H (15) dBy = dBr + dB.H r (16) dBy = sine test spectrum for equipments associated s with secondary structure. dEj = random test spectrum for equipments associated r with secondary structure dBs = sine test spectrum for equipments associated with primary structure (re. Gs ~ax) 519.2-9 METHOD 519.2