difference between MTBF,MTTR,MTTF and FIT

This page on MTBF vs MTTR vs MTTF vs FIT describes difference between MTBF, MTTR, MTTF and FIT reliability terminologies.

MTBF- Mean Time Between Failure

MTBF is the most popular reliability term of the product manufactured by any company. It provides measure of amount of failures per million hours of the product. This is very important in critical applications such as telephone networks, data communication network where due to failure entire system will be down and services to the consumers will be hampered. Usually price centric end users never consider MTBF before purchasing any product. MTBF is used for both repairable and non-repairable items.

MTBF = 1/(FR1+FR2+FR3+••••• +FRn)
Where FR is the failure of the each component of the system
To calculate the Overall MTBF, failure rate of all the individual components used to make the system is taken into calculation. Operating and storage temperature need to be considered for calculation.

Example: There are total 10 devices being tested for about 600 hours. During the test 3 failures have occured. Let us calculate MTBF of this batch of products.
MTBF=10 x 600 hours/3 failures
MTBF= 2000 hours/failure

MTTR- Mean Time To Repair

MTTR is the time required to repair a failed hardware product/module. Usually this is the time needed to replace the new product with the failed one to the end user/customer from the manufacturing company. Usually it takes time to replace and hence to reduce the time of replacement manufacturer keeps enough backup of the product delivered.

MTTF- Mean Time To Failure

MTTF is a measure of reliability for non repairable products/systems. Mean time expected until the 1st failure is referred as MTTF.

FIT- Failure In Time

This is also reliability term used in place of MTBF.FIT measures number of expected failures per 1 billion hours of operation of the product/device. The term is used both by component manufacturers as well as semiconductor industry.

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