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What - Reliability Block Diagrams (RBD)
are used for modeling the exact propagation of a failure. These models are
similar to fault trees except they map exactly to the physical architecture of
a design. Whereas Fault Trees look more for combinations of events that lead to
a problem, an RBD models how each failure mode affects other (usually
phyiscally connected) components.
Why - RBDs provide the reliability engineer
with a highly detailed view of a subsystem so that a design can be improved in
terms of redundancy, safety, etc. This makes them useful for supporting a wide
range of reliability engineering tasks.
When - RBDs can be developed and support
throughout the entire design process, however, they take a fair amount of work
to keep up to date as the design matures. This is due to the fact that early
RBDs tend to represent functional loss, while later RBDs tend to represent
failure mode propagation. The transition between the two occurs throughout the
development process. While this effort is acceptable and even expected for the
reliability engineer, it represents an unacceptable overhead as a diagnostic
approach. For this reason, Functional Models
and Hybrid models were created
Related Links -
Fault Trees
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