If a system has a proof test period of 1 year (T1 = 8760 hrs) and a MRT of 3 weeks (504 hrs) then the MTTR = 4884 hours
Based on
MTTR = (MTR/2)+MRT
Really I wish to validate the above formula is correct as I have it ustilised but cannot find the original source again in either 61508 or 61511, probably just being blind but work a check.
IEC 61508 Pt 4
3.6.21
mean time to restoration
MTTR
expected time to achieve restoration
NOTE MTTR encompasses:
. 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 put back into operation (d)
The start time for (b) is the end of (a); the start time for (c) is the end of (b); the start time for (d) is the end of (c).
3.6.22
mean repair time
MRT
expected overall repair time
NOTE MRT encompasses the times (b), (c) and (d) of the times for MTTR (see 3.6.21).
Many Thanks in advance
Geof I]]>