Designing for reliability

A mathematical model is presented which will enable the designer of electronic equipment to compute its survival probability. Thus, he can make the engineering decision on whether or not the equipment meets its reliability specification. Although only electronic circuits are discussed here, the model is equally applicable to mechanical and electrical systems. In the model the performance parameters (gain, power output, bandwidth, etc.) are expressed as a function of the individual components of the circuit. The statistical distributions of the component characteristics (dependent on both operating time and environment) are then used in conjunction with the circuit equations to yield a simplified expression for the circuit survival probability. This simplification involves an approximation method using the multivariate Gram-Charlier expansion. These methods are applicable even if the component characteristics are correlated and are described by any probability density function. The fact that individual performance parameters may be correlated is taken into account automatically.