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Track 2 Session 9
8:00 to 9:00 a.m. Friday June
22, 2007
Trapped by MTBF - A Study of Alternative
Reliability Metrics
MTBF is probably the most
common metric used to describe the reliability of a product, but it
is perhaps the least understood and most misleading metric as well.
What do we really mean by MTBF and how much information does it
really give us? We find that it is very difficult to write
reliability plans with only MTBF as the metric. It is difficult to
allocate down to subassemblies, and it is difficult to measure where
we are against our goals.
When we use MTBF, we make generalized assumptions such as
constant failure rate, and these assumptions are not only rarely
true, but also cause us to miss meaningful information relative to
the design attributes of our product, especially in what happens in
the early life portion and in the wearout portion of our product
life. For us to perform a robust Design for Reliability process, we
must include all areas of our product life, not just the steady
state portion of our product life.
In this presentation, we shall study a number of other more
descriptive and useful metrics, including Reliability, DOA, AFR,
Life, and others, to help describe product reliability in a richer
context.
Key Words: MTBF, MTTF,
Non-repairable, AFR, DOA, Exponential, Weibull
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