Mean Overall Repairing Time


expected time to achieve the following actions:

• 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 is put back into operation d

Note 1 to entry: See Figure 5, Figure 6 and Figure 7.

Note 2 to entry: The terms “repair”, “repairable”, “repaired” used in this Technical Report, unless otherwise

specified, are related to the overall repairing time (see Figure 5).

Note 3 to entry: When a safety system operating in demand mode is faulty, the risk disappears as soon as the

protected installation is placed in a safe state (e.g. stopped). In this case (see Figure 6 and Figure 7) the MTTS

replaces the MRT (see 3.1.36) with regard to the probabilistic calculations.

Note 4 to entry: This definition is in line with IEC 61508[2] but not with IEC 60050–191.[14].







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

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