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 standard are linked to
the delays defined in the IEC 60050–191 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