How it works
MTBF is the average operating time between two failures of a repairable asset, and MTTR is the average duration of a repair from detection to restart. Together they give the inherent availability.
Formula
MTBF = (T − Tdown) / failures MTTR = Tdown / failures A = MTBF / (MTBF + MTTR) R(t) = e^(−t / MTBF)
The reliability figure assumes a constant failure rate (exponential distribution), which is a good approximation for the useful-life phase of equipment. Count only unplanned failures, not planned maintenance.
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