5.4 ACCELERATION SPECTRUM

In the past, the acceleration spectrum was usually defaulted to the PSD
level shown in Figure
2-3(b) commonly known as the NAVMAT profile. A technique has been
developed by NAVSEA and takes into consideration the parameters of the Printed
Wiring Board (PWB) and the parameters of the parts most susceptible to
overstress. This technique computes the maximum allowable PSD level in each of
the three axes. The methods presented in Section
5* *can be used on any part that resembles the part described. The
parameters needed to begin this technique are: the length of the long side of
the PWB or thermal plane m inches (designated as a), the length of the short
side of the PWB or thermal plane in inches (b),the thickness of the PWB or
thermal plane in inches (t), the weight of the PWB or thermal plane in pounds
(W), and the type of supports (fixed, free, or simply supported) for the PWB
or thermal plane during RVSS. With these parameters and the following
equations, the natural frequency of both the PWB and the thermal plane (if any
exists) and their maximum deflections can be calculated. If vibrating in an
axis other than perpendicular to the PWB’s surface, section 5.4.1
through 5.4.2.4
may be omitted.