Optimized Derating to Support Reliable System Design

To meet the evolving needs of advanced airborne and high reliability systems with ever-increasing levels of complexity requires both classical and innovative reliability practices, as elements of a coordinated model-based, system engineering environment. One commonly used approach to improving reliability is derating, which is the practice of deliberately operating components at applied stress levels (i.e., voltage, current, temperature, power, etc.) that are less than the component ratings specify. Derating levels may be specified in a contractual framework or chosen based on industry standards and best-known practices. In the past, derating specification was based on rules of thumb or prior practices. This may have led to over-stressing of the designed product or even over-designing the product to assure system availability or safety. The amount of derating necessary to achieve a desired level of reliability must be known to optimize cost, weight, and power of a system design. A new ANSI standard for derating, VITA 51.4 [7], is being developed to fill this need. The standard provides guidelines for deriving an optimal level of derating. This paper provides an overview of standard industry derating methods, application environments, selection criteria, and examples of how to select optimal derating levels to support reliable system design.