Equivalent Failure Rate Calculations
The equivalent failure rate (EFR) is also known as the exponential approximation method. The EFR provides a simple approximation method for verification of results based on standards set forth in The Rome Laboratory Reliability Engineer's Toolkit Reliability Toolkit The EFR takes into account the calculated reliability at time t and uses the reliability equation for an exponential distribution to solve for λ.
The EFR is generated by substituting the reliability of the entire block diagram determined at the end time into the exponential failure distribution and solving for the value of λ. The equation is:
R(t) = exp(−λ equivalent * t)
Where R(t) is the reliability of the system at time t (End Time)
For clarity, the exponential failure distribution for this case can be restated as:
R Diagram (End Time) = exp(−EFR * End Time)
As an example, the reliability of a complex block diagram is determined to be 0.001 at an end time of 1000 hours. In this case:
EFR = −ln(R Diagram (End Time)) / End Time
= −ln(0.001) / 1000 = 6907.8 failures per million hours