How to calculate the MTBF ?

Mean Time Between Failures = (Total up time) / (number of breakdowns)

Good maintenance KPI selection gives us an overview of the situation in our plant—the past is clear and so is the future. The range of KPIs and PIs to use to monitor and focus maintenance on what is important to do include checking:

1. the delivery and quality of maintenance work,
2. the reduction in risk to the operating equipment, and
3. the effectiveness of the money and resources expended to achieve those results.

MTBF stands for Mean Time Between Failures

MTBF is the average time elapsed from one failure to the next

MTBF = (Total up time) / (number of breakdowns)

Mean Time Between Failures

How to calculate actual Mean Time Between Failures

Actual or historic Mean Time Between Failures is calculated using observations in the real world.  (There is a separate discipline for equipment designers, based on the components and anticipated workload).

Calculating actual Mean Time Between Failures requires a set of observations; each observation is:

• Uptime_moment: the moment at which a machine began operating (initially or after a repair)
• Downtime_moment: the moment at which a machine failed after operating since the previous uptime-moment

So each Time Between Failure (TBF) is the difference between one Uptime_moment observation and the subsequent Downtime_moment.

Three quantities are required:

• n = Number of observations.
• ui = This is the ith Uptime_moment
• di = This is the ith Downtime_moment following the ith Uptime_moment

So Mean Time Between Failures = Sum (di – ui)/ n  , for all i =1 through n observations.  More simply, it is the total working time divided by the number of failures.

Mean time between failures (MTBF) is the arithmetic mean (average) time between failures of a system.

The MTBF is typically part of a model that assumes the failed system is immediately repaired (zero elapsed time), as a part of a renewal process. This is in contrast to the mean time to failure (MTTF), which measures average time between failure with the modeling assumption that the failed system is not repaired.

MTBF (mean time between failures) is a measure of how reliable a hardware product or component is. For most components, the measure is typically in thousands or even tens of thousands of hours between failures. For example, a hard disk drive may have amean time between failures of300,000 hours.

If these three failures are random samples from a population and the failure times of this population follow a distribution with a probability density function (pdf) of , then the population MTTF can be mathematically calculated by:

Experts have answered the Q.  

Mean time between failures (MTBF) is the mean (average) time between failures of a system, the reciprocal of the failure rate in the special case when the failure rate is constant. Calculations of MTBF assume that a system is 'renewed', i.e. fixed, after each failure, and then returned to service immediately after failure. A related term, mean distance between failures, with a similar and more intuitive sense, is widely used in transport industries such as railways and trucking. The average time between failing and being returned to service is termed mean down time (MDT).

Agree with Ridha SAIDANI                            .

Mean Time Between Failures MTBF = (Total up time) / (number of breakdowns)

Mean Time   means, statistically, the average time.