ETL 1110-2-560
30 Jun 01
- d ln Rs ( t )
(16)
hs(t) =
dt
or
N
∏
- d ln 1 -
[1 - Ri ( t )]
i=1
hs(t) =
(17)
dt
The result of hs(t) becomes rather complex and the reader is referred to the reference literature.
(2) Standby redundant system. A two-component standby redundant system is shown in Figure 8.
This system contains equipment that is in primary use and also equipment standing idle ready to be used.
Upon failure of the primary equipment, the equipment standing idle is immediately put into service and
switchover is made by a manual or automatic switching device (SS).
A
SS
B
Figure 8. Standby redundant system
The system reliability function for the exponential distribution can be calculated for a two-component,
standby redundant system using the following equation:
[λARB( t)]
1 - exp[-λ + λ + λ - λ d t]
'
RS ( t ) = RA( t ) +
A SS B B i
(18)
λ +λ +λ' -λ
A SS B B
where
λ A = hazard rate of A
λSS = hazard rate of switching device
′
λB = hazard rate of the standby equipment while not in use
λ B = hazard rate of B
di = duty factor for respective failure rate
10
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