Modeling it both ways: hybrid diagnostic modeling and its application to hierarchical system designs

Hybrid diagnostic modeling (HDM) is an extension of diagnostic dependency modeling that allows the inter-relationships between a system or device´s tests, functions and failure modes to be captured in a single representation (earlier dependency modeling approaches could represent the relationships between tests and either functions or failure modes). With hybrid diagnostic modeling, the same model can be used for early evaluations of a design´s diagnostic capability, creation of hierarchical FMECAs, prediction of diagnostic performance, and generation of actual runtime diagnostics. This paper examines issues associated with the application of HDM to hierarchical systems, including: the types of diagnostic inference used to interpret the relationships between functions and failure modes, the correlation of functional and failure-based reliability data, and diagnostic assessment using hybrid diagnostic models.