The standby engineering: classification and quantification of standby in reliability

Abstract

Due to an increasing sensitiveness on energy consumption and environmental impact, the interest on the standby concept and related issues is growing in the last years. Such trend has to be adequately supported by techniques, mechanisms and tools for the evaluation of standby phenomena, in order to provide valid methodologies to system designer. This is particularly true in reliability contexts, where often standby behaviors are approximated or not considered at all. There are a plenty works in literature dealing with standby, but some aspects of standby in reliability are partially covered and therefore can be further analyzed, also from a different perspective. Aim of the paper is to provide an in depth investigation of standby issues in reliability and availability, starting from the characterization from both an internal and an external point of view. In the former case the standby effects into a unit in isolation are considered, observed and characterized, while in the latter case the unit is considered as a component of a system, taking into account its interactions with the external environment or with the other components of the system. Thus, by applying dynamic reliability equations a formal characterization of the problem and its analytical formulation are provided. These are therefore used in the evaluation of standby redundant systems and their management.