Mean time to failure

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MTTF is the abbreviation for the mean time to failure ( English mean time to failure ) and is also called average life called. A special form is the mean time to dangerous failure, designated MTTF D.

The definition of MTTF IEC 60050 (191) reads: The expected value of the time to failure (Engl. The expectation of the time to failure ). The MTTF is particularly important as a result of the European standard EN ISO 13849-1, as it is to be used within the conformity tests to assess machine safety.

The MTTF is a statistical parameter / key figure that is determined through tests or empirical values. It does not indicate a guaranteed service life or a guaranteed failure-free time. MTTF is calculated from the reliability function R ( t ). It applies in particular to non-repairable units. In the case of repairable units, it can only be used under the assumption that the unit under consideration is as good as new after the repair. Usually, the term mean time between failures (MTBF for short) is used for repairable units . H. the mean operating time between failures.

In both the mathematical determination and the application of MTTF values ​​for reliability prognosis, it must be assumed that the units under consideration ( assemblies , devices or systems ) are used during their service life and under specified operating conditions, i.e. that there is a constant failure rate (middle range of " Bathtub curve " ). For this period, the MTTF of one unit corresponds to the reciprocal of its failure rate, with the failure rate being stated in years.

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Individual evidence

  1. ↑ IFA Report 2/2017 - Functional Safety of Machine Controls (Appendix D)
  2. ↑ EN ISO 13849-1: 2008 (D) , page 5ff
  3. ↑ Alessandro Birolini: Appendix A1 - Definitions . In: Ders .: Reliability of devices and systems . 4th edition Springer Verlag, Berlin 1997, ISBN 3-540-60997-0 .
  4. ^ J. Lienig, H. Brümmer: Reliability of electronic devices . In:  Electronic device technology . Springer Vieweg, 2014, ISBN 978-3-642-40961-5 , pp. 55-58.