Mean Time Between failure / Economical informatics

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MTBF (English mean time between failures) is the middle length of time between two losses. MTBF serves as measure for the reliability of devices or plant note: Error is not equivalent in technical systems to loss. An equipment component develops an error, the error leads to the disturbance and these can in a loss end.

Colloquially the term is used synonymously for the MTTF (English mean time ton of failures), however MTTF refers to a system, which is exchanged after a loss. The MTBF does not close the MTTR (English mean time ton repair) with in this refers only on the time in that the system again repaired, thus functionally, is.

The MTBF flows also into the computation of the availability (English Availability), which indicates, how large the probability is that a system offers the specified service:

A = \ frac {MTBF} {MTBF + MTTR}

The more highly the MTBF value, the more reliably should be the equipment. Equipment with a MTBF of 100 hours will thus exhibit probably rather a defect as otherwise homogeneous equipment with a MTBF of 1.000 hours.

A non removable disk has a typical MTBF of approx. 500,000 hours, which would correspond with naive conversion 57.07 years continuous operation. However the MTBF refers to the number of summed error free operation hours of a large quantity of drive assemblies (already alone, because no manufacturer before the sales of the new development could test these for many years). In particular the rising probability of failure is not received in the course of the time by manifestations of wear with such a computer forecast.

In connection with individual equipment the naive conversion of the MTBF does not apply also if the drive assembly is exchanged regularly after its service Life. The statement "is built into the computer a non removable disk with 500.000 hours of MTBF and these every five years exchanged, one 58 years long no overrun will always experience" the user will little please, whose non removable disk precipitates two weeks after start-up.

The value is calculated by an artificial aging process, in which the equipment radiation, humidity, vibrations, heat and the like is suspended. That that for example a computer mouse on a run volume is operated 24 hours continuously, in order to look, is called concrete how many kilometers these without errors put back can. The tests are not standardized, therefore all indicated values are comparable usually only within the product rows of a manufacturer.

Another possibility of the determination of the MTBF is the computation. In addition exact knowledge of the structure of the equipment and the used elements is necessary. For many elements so-called probabilities of failure exist in tables (often also as FIT ONE, failure in Time, designates). The MTBF results then from the reciprocal value (entire) of the FIT ONE of the building group/unit. The entire FIT ONE is the sum of the single FITs.

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