ETL 1110-2-560
30 Jun 01
R(t)
1.0
0
t
Figure 2. Reliability function for exponential distribution
h(t)
λ
0
t
Figure 3. Hazard function for exponential distribution
(b) The average or mean of the exponential life distribution is the Mean Time to Failure (MTTF). It
is the average length of life of all units in the population. It has significance in that the reciprocal of the
hazard rate is equal to the MTTF:
1
MTTF =
(7)
λ
(4) Weibull distribution. The Weibull distribution is a generalization of the exponential distribution.
This distribution covers a variety of shapes, and its flexibility is useful for representing all three regions of
the bathtub curve. The Weibull distribution is appropriate for a system or complex component made up
of several parts. The Weibull reliability function is
5
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