Mean Time Between Failure MTBF

The mean time between failures MTBF is used as a measure of system reflabiUty, whereas the mean time to repair MTTR is taken as a measure for maintainabihty. Eor example, a system with an MTBF of 1200 h and a MTTR of 25 h would have an availabihty of 0.98. Furthermore, if only an MTBF of 800 h could be achieved, the same availabihty would be realized if the maintainabihty could be improved to the point where the MTTR was 16 h. Such trade-offs are illustrated in Figure 3, where each curve is at a constant availabihty. 

The GIDEP Reliability-maintainability Data Bank (RMDB) has failure rates, failure modes, replacement rates, mean time between failure (MTBF) and mean time to repair (MTTR) on components, equipment, subsystems and systems. The RMDB includes field experience data, laboratory accelerated life test data, reliability and maintainability demonstration test results. The... 

Mean Time Between Failures (MTBFs) based on 1,116 failures... 

The failure rates and times-to-restore developed used a variety of data sources and data construction methodologies and are presented in Section 2. The principal methodology used is a kind of failure mode analysis for each component several principle modes of failure are analyed by characteristics including frequency of occurence, repair time, start-up time, and shut-down time. From these an average failure rate is developed and expressed as failures per million hours and mean time between failure(MTBF). 

A side benefit of predictive maintenance is the automatic ability to monitor the mean-time-between-failures, MTBF. This data provides the means to determine the most cost-effective time to replace machinery rather than continue to absorb high maintenance costs. The MTBF of plant equipment is reduced each time a major repair or rebuild occurs. Predictive maintenance will automatically display the reduction of MTBF over the life of the machine. When the MTBF reaches the point that continued operation and maintenance costs exceed replacement cost, the machine should be replaced. 

Experience shows that some machines have more frequent failures than do others. Obviously, different failure modes have different frequencies of occurrence. This is usually described as mean-time-between-failure (MTBF) and expresses the probability of machinery failure and breakdown events as a function of time. This is of particular interest to the maintenance failure analyst and troubleshooter who have to grapple with the realization that some machinery failure modes appear slowly and predictably whilst others occur randomly and unpredictably. In most cases, both types of failures have been encountered. 

In an earlier section, we acquainted ourselves with commonly used reliability terms mean time between repairs (MTBR), mean time between failures (MTBF), etc. We saw that these terms have similar meanings but often include minor deviations. To avoid confusion, mean time to failure (MTTF) will be used in the following discussion. It can be expressed in terms of any time periods, i,e, days, months, years, etc. ... 

The time interval between two failures of the component is called the mean time between failures (MTBF) and is given by the first moment of the failure density function ... 

Firewater Reliability - A mathematical model of the ability of the firewater system to provide firewater upon demand as required by the design of the system without a component failure, e.g., a Mean Time Between Failure (MTBF) analysis. 

Reliability is a function the system failure rate or its reciprocal, mean time between failures (MTBF). The system failure rate in non-redundant systems is numerically equal to the sum of component failure rates. 

In the area of fuel cells, reliability and availability have much improved. Recent U.S. military experience with phosphoric acid fuel cells found that the mean time between failure (MTBF) was almost 1,800 h and the availability was 67%. This is comparable with the MTBF service intervals for diesel generators. These fuel cells also favorably compare with the service interval needed for a typical gas turbine generation set. Still, much more development is required to obtain a commercially viable product. Today, the typical fuel cell system still requires servicing every 3-4 days to replace its scrubber packs. 

We assume that the failure distribution is exponential, thus, only one parameter is needed to describe the reliability of equipment the mean time between failures (MTBF). Other distributions can be used but they require at least two parameters. 

Low Cost and High Reliability - All components of the spectrometer are fabricated using standard low-cost, thin film, all Nb fabrication process. The final product is packaged in an ultra-reliable cryocooler with a Mean-Time-Between-Failures (MTBF) exceeding 99 years. Superconductor circuits are extremely radiation-hard, which make them attractive for space applications. 

Sometimes the term mean time between failures (MTBF) when the product can be repaired or renewed is also used to denote E T. The problem with using only the MTTF as an indicator of... 

Mean time between failure (MTBF), 1928, 1950-1951 Mean value, testing ... 

Many components must work in harmony for an application to successfully run on a large parallel computer, and this requires an exceptional level of reliability for all components. Although a personal computer that failed only once every five years would probably be very satisfactory, a 10,000 node computer built from nodes with that same individual failure rate would fail, on average, about every 4.4 hours. This figure is known as the mean time between failures (MTBF) for the computer and is the reciprocal of the rate of failure. Let us look at a collection of N types of components with n, components of each type, and let each component type have a mean time between failures of MTBF,. For this system, the overall mean time between failures will be the reciprocal of the sum of the rates of failure for the individual components... 

Useful life period. After the weaker units die off in the infant-mortality period, the failure rate becomes nearly constant and the assemblies have entered the normal or useful life period. This period is characterized as a relatively constant failure rate and is also referred to as the system life of a product. Mean time between failures is calculated in this section of the curve. Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a system during operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system. Failure rates calculated from MIL-HDBK-217 and Telcordia-332 apply only to this period. 

The result of using the MIL-HDBK-217 standard for reliability prediction produces calculated Failure Rate and Mean Time Between Failures (MTBF) numbers for the individual components, equipment and the overall system. The final calculated prediction results are based on the roll-up, or summation, of all the individual component failure rates. 

Future versions of this application will also consider dynamic risk factors such as user error, mean-time-between failure (MTBF), device failure within 30 days of a preventive maintenance or repair, and the number of years beyond the American Hospital Association s recommended useful life. 

Reliability Reliability of equipment is the proportion of time that the equipment is functioning. For a given period of time, reliability is estimated by taking the ration of period uptime to the total period length. Suppose be the observation time period and be the number of failures observed during the mean time between failures (MTBF) and the average downtime per failure (AVDT) are, respectively, given by... 

Availability, in general, is defined as the ability of the plant/equipment to perform its required function over a stated period of time. Maintainability is the probability that a failed item can be restored to operation effectiveness within a given period of time when repair action is performed as per the specified procedure (Smith, 2011). Software is available for performing RAM studies. For smaller projects, spreadsheets can be used. Reliability and process safety are interlinked, and so combined RAM and safety (RAMS) studies can be performed with the RAMS software (Sikos and Klemes, 2010). It considers many factors affecting the plant performance such as equipment performance, redundancy, demand requirements and logistics. RAM analysis is based on statistical failure data such as mean time between failures (MTBF), mean time to repair (MTTR), mean time to failure (MTTF) and mean down time (MDT). Wherever possible, failure data available within the company should be used for RAM/RAMS study. If not, typical failure data available in the literature/software can be used. 

Mean Time Between Failures (MTBF)—MTBF is defined as the average time period of a failure/repair cycle. It includes time to failure, any time required to detect the failure, and actual repair time. This implies that a component has failed and then has been successfully repaired. For a simple repairable component. 

In (Gang 2008) two different methods - the direct simulation (DS) and the conditional expectation estimation (CEE) - are presented for the purpose of estimating the unreliability, transient unavailability, steady unavailability, mean time to failure (MTTF), mean time between failure (MTBF) and their parameter sensitivities of consecutive-k-out-of- F repairable systems with (k — 1) - step Markov dependence. 

The computation of mean time between failures (MTBF) for whole system will be accomphshed by the help of well known equation (10) ... 

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