Built-in-test design for cost-effective fault-isolation

The author presents a methodology for evaluating alternate system structures consisting of lowest replaceable units (LRUs) that correspond to different levels of partitioning and fault isolation introduced through the incorporation of built-in-test (BIT) into the system design. The attendant operations and support cost for each partitioning is established as a function of the cost drivers associated with the maintenance and support environment. A program-specific maintenance and support cost model is developed to evaluate alternate BIT-influenced system structures and their associated fault isolation strategies using a set of linked spreadsheets as the core of the methodology. The initial setting up of the linked spreadsheets requires paying attention to detail, but once the linking is established the what if´s are easy to execute since a change in an input/design parameter is effected through the adjustment of a single spreadsheet value and propagated throughout the set of spreadsheets using the linking structure. A measure of cost-effective fault isolation is constructed for the candidate systems using the cost elements of BIT engineering development cost and system maintenance and support cost