Mean time to failure applies to parts that are discarded when they fail, such as chips, lamps, bearings and fuses. It equals the area under the reliability curve; for a Weibull distribution it is the characteristic life eta times the gamma function of (1 plus 1 over beta). MTTF hides the shape of the failure distribution, so two parts with equal MTTF can have very different early failure rates.
Lamp MTTF is quoted at 2,000 hours, but beta is 4, so only about 4 percent fail before 1,000.
Also heard as
- mean time to failure
- mean life
Related terms
MTBF
Mean time between failures: average operating time between successive failures of a repairable system.
Weibull distribution
Flexible life distribution with a shape and a scale parameter, the standard model for fitting time-to-failure data.
Shape parameter
Weibull beta: the slope of a Weibull plot, which shows whether failures are early-life, random or wear-out.
FIT
Failures in time: one failure per billion device-hours, the standard unit for semiconductor failure rates.