MTTF Calculations
MTTF (mean time to failure) is calculated using either an analytical method or simulation. When using the analytical method, MTTF is calculated by integrating the reliability function over 0 and infinity:
Where:
R(t) = The system reliability at time t
Numerical methods are used to compute the above integral. It should be noted that if Account for repair in reliability is cleared, the effects of repairs are not considered when calculating MTTF. In this case, reliability is calculated without considering the effects of repairs, and it is used to calculate MTTF. If Account for repair in reliability is selected, then reliability and MTTF calculations consider the effects of repairs.
The simulation procedure for calculating MTTF is similar to the simulation procedure used for reliability calculations. Instead of counting failure and success status flags at each simulation run, the time to system failure is added to the total system failure time. MTTF is then calculated by dividing the total system failure time by the number of simulations. Differences between failure rate and MTTF are described in Failure Rate Versus MTTF.