Mean Time to Restoration


expected time to achieve the following actions: (see Figure 5, Figure 6 and Figure 7):

• the time to detect the failure a; and,

• the time spent before starting the repair b; and,

• the effective time to repair c; and,

• the time before the component is made available to be put back into operation d


Note 1 to entry: Figure 5 illustrates how the times a, b, c and d defined in the IEC 61508[2] standard are linked to

the delays defined in the IEC 60050–191[14] standard. Time b starts at the end of a; time c starts at the end of b;

time d starts at the end of c.

Note 2 to entry: Figure 5, Figure 6 and Figure 7 can be used to understand the differences between the definitions

of MTTRes, MRT and MART used in this Technical Report.

Note 3 to entry: The MTTRes is linked to the MRT and the MFDT by the following formula: MTTRes = MFDT + MRT.









Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards



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