An example of Scheduled Maintenance System (SMS)

SMS equipped with:
- a primary unit A
- a backup unit B
- a switching logic: when A fails, the control of operation is immediately passed to B

Cyclic execution of two types of mission:
- mission 1 has  a single phase of duration t11
- mission 2 has two phases of duration t21 and t22

Fault hypothesis:
- As failure rate:
   - l1a during the missions of type 1
   - l2a during the missions of type 2
- Bs failure rate: lb
- the switching logic is fault-free
- the system is up as long as either A or B are up

Scheduled maintenance actions:
- a complete and exhaustive maintenance check is performed after 100 missions.
- the primary unit A is replaced at the end of each mission, if failed. After the replacement, A takes again the role of primary unit.
- backup unit B is subject to a partial check at the end of each a pairs of missions. Faults of B are detected with probability c.

Dependability measures of interest:
- reliability R of the SMS between major checks
- the Cost function:

   Cost(c, a) = F * (1-R) + j(c) * Î50/aÎ

 F  is the cost paid for a system failure,
 j(c) is the cost to perform the partial check as a function of c

Model of the system in DEEM: Phase Net (PhN) and System Net (SN):

Obtained results:

This file was generated Tue Jul  4 12:09:32 2000


Time 1.500000e+03
lb [0.0001,0.01,*10]
p 9.500000e-01
a {1,2,5}

PREDICATE: mark(Afail)+mark(Bfail)<2

lb/a 1.000000e+00 2.000000e+00 5.000000e+00
1.000000e-04 9.941818e-01 9.907599e-01 9.813445e-01
1.000000e-03 9.440268e-01 9.132017e-01 8.353453e-01
1.000000e-02 6.015980e-01 4.783397e-01 3.020994e-01


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