Editing Mean time between failures (section)

{{Short description|Predicted elapsed time between inherent failures of a system during operation}}
'''Mean time between failures''' ('''MTBF''') is the predicted elapsed time between inherent [[failure]]s of a mechanical or electronic system during normal system operation. MTBF can be calculated as the [[arithmetic mean]] (average) time between failures of a system. The term is used for repairable systems while '''mean time to failure''' ('''MTTF''') denotes the expected time to failure for a non-repairable system.<ref name="lienig">{{Cite book|author=J. Lienig, H. Bruemmer|title=Fundamentals of Electronic Systems Design|pages=45–73|chapter=Reliability Analysis|publisher=Springer International Publishing|date=2017|isbn=978-3-319-55839-4|doi=10.1007/978-3-319-55840-0_4}}</ref>

The definition of MTBF depends on the definition of what is considered a failure. For complex, [[repairable]] systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair. Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures under this definition.<ref>Colombo, A.G., and Sáiz de Bustamante, Amalio: ''Systems reliability assessment &ndash; Proceedings of the Ispra Course held at the Escuela Tecnica Superior de Ingenieros Navales, Madrid, Spain, September 19&ndash;23, 1988 in collaboration with Universidad Politecnica de Madrid'', 1988</ref>  In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure.<ref>{{Cite web|title = Defining Failure: What Is MTTR, MTTF, and MTBF?|url = http://blog.fosketts.net/2011/07/06/defining-failure-mttr-mttf-mtbf/|website = Stephen Foskett, Pack Rat|date = 6 July 2011|access-date = 2016-01-18}}</ref> The higher the MTBF, the longer a system is likely to work before failing.