File Name: difference between mttf and mtbf .zip
MTTR is a metric used by maintenance departments to measure the average time needed to determine the cause of and fix failed equipment. Anytime you see the phrase "mean time to," it means you're looking at the average time between two events. Mean time to repair MTTR is a metric used by maintenance departments to measure the average time needed to determine the cause of and fix failed equipment.
Mean Time Between Failure MTBF is one of the most widely recognised and yet least understood indicators in the maintenance and reliability world. Manufacturers quote it as a rating of their products and industry uses it as a measure of success. In this article, I will explain in simple terms what MTBS is, what it's not, when to use and when not. It is said that the great Greek philosopher Socrates argued that "the beginning of wisdom is the definition of terms. Sure, there are clear definitions for MTBF.
But, unfortunately, there is a lack of common understanding of what MTBF really means. For example, three identical pieces of equipment are put into service and run until they fail.
The first system fails after hours, the second after hours and the third after hours. The MTBF of the systems is the average of the three failure times, which is MTBF is related to failure rate. It assumes a constant random failure rate during the useful life of a piece of equipment. We need a clear set of definitions so that we understand what an MTBF number is telling us and what the limitations of that number are.
There is even a movement to abandon MTBF because of the misunderstanding and misuse of the term. We can learn more about MTBF by exploring its origin and the reasons why it came into use. It also helps to compare MTBF with other indicators to avoid confusion about terms.
This article covers all these aspects along with some clear guidance about where to use and not to use MTBF. The failure rate is the number of failures in a component or piece of equipment over a specified period. It is important to note that the measurement excludes maintenance-related outages. These outages are not deemed to be failures and therefore, do not form. A failure rate does not correlate with online time or availability for operation - it only reflects the rate of failure. In industrial applications, the failure rate represents past performance based on historical data.
But in engineering design, the failure rate can also be predicted. It is common to use a bathtub curve to illustrate failures over the entire life of a product. There is a high rate of infancy failures at the beginning of its life and a high rate of wear out failures at the end of its life.
But in between, during the product's useful life, its rate of. Manufacturers seek to reduce infancy failures by testing products and removing early failures before they get to the customer.
The disadvantage of failure rate as an indicator is that it yields a tiny result, which is difficult to interpret. The failure rate of a pump could be 0. Before World War II, the term reliability described how repeatable a test was. The more repeatable the results, the more reliable the test, whether it be in the field of mechanics, psychology or any other scientific endeavour.
However, the challenges of World War II caused new developments in the definitions and engineering associated with reliability. Electronics equipment during the war was highly problematic.
Up to half of the electronic equipment on a naval vessel could be out of service at any time - leading to a renewed focus on understanding and improving equipment reliability. Working groups developed strategies like setting quality and reliability standards for electronic equipment suppliers.
Military and commercial aviation continued to drive improvements in reliability engineering throughout the twentieth century. The most commonly used reliability prediction formula is the exponential distribution, which assumes a constant failure rate i. The flat part of the bathtub curve. Engineers report reliability as a percentage. It indicates the probability of failure for a piece of equipment in the time given.
Reliability does not predict when the equipment could fail during that time, but only the chance of that failure occurring at any point during the time given. We calculate MTBF by dividing the total running time by the number of failures during a defined period.
As such, it is the inverse of the failure rate. During normal operating conditions, the chance of failure is random. It could happen at any time on the flat part of the bathtub curve, just as easily as it could at any other time. The MTBF calculation comes out of the reliability initiatives of the military and commercial aviation industries.
It was introduced as a way to set specifications and standards for suppliers to improve the quality of components for use in mission-critical equipment like missiles, rockets and aviation electronics. Maintenance practitioners first used MTBF as a basis for setting up time-based maintenance strategies. Inspection intervals and routine maintenance tasks were set up based on MTBF. These programs aimed to identify potential failures before they occurred, but time-based systems are not the most effective strategy.
As mentioned in the definition, MTBF is calculated by dividing the total time by the number of failures. Let's look at a few examples:.
Assuming a situation where there are 1, cars that run for one year. If one car fails in that time, the MTBF would be:. In an unusual case, consider the MTBF of human life, assuming a population of , If during the course of a year, people died of random causes, the MTBF would be:. This example highlights where MTBF could be misleading as no human being expects to live for years.
In a population of ANSI pumps in water service across multiple sites, fail in a period of three years. The MTBF would be:. On their own, these numbers provide some information about reliability but not enough to fully understand the reliability performance of the equipment.
Every equipment has a life expectancy based on its components, its design, operating conditions and maintenance history. But not everyone is talking about life expectancy in the same way when they use the term. The service life, the mission life and the useful life of a piece of equipment all refer to different things. We can unpack those differences in more detail. Service life refers to the entire duration of an equipment's use. We measure it from the time of commissioning to its final failure or decommissioning.
Engineers also predict service life based on the design specifications. A service life prediction would typically be used in calculations to justify the capital expense of a new asset.
Actual service life can be compared with the design service life of a piece of equipment to determine whether it met the expectations of engineers when it was first purchased. One unique example is that of a missile. By nature, we expect a very high MTBF for a missile indicating the very low probability of failure.
But the service life of a missile is very short. It can be as little as a few minutes from the time a missile is fired to the time it explodes. Mission life is the duration used for reliability calculations and analysis.
For example, we base the failure rate calculation on the number of failures in a specific time. This time is known as the mission life. Engineers use reliability indicators to predict failures and make decisions about the future mission life of their equipment. This includes making decisions about spares holding or maintenance strategies for a mission life of the next five years.
Useful life refers to the flat part of the bathtub failure curve. It leaves out the time associated with infancy failures at the beginning as well as the time associated with wear out failures at the end of a product's life. Useful life is, therefore, the operational life of any piece of equipment. In design terms, it reflects the maximum life expectancy of any equipment during normal operations.
The useful life does not take into account operating conditions or maintenance history - it assumes a constant and random failure rate. In other words, the MTTF calculation is as follows:. Engineers determine MTTF by observing a large number of identical components and their combined service time. In this way, it gives some indication of the probability of failure. It is an important indicator for complex systems where some parts cannot be replaced but could impact on the MTBF of the system as a whole.
A fan belt in a motor is a typical example. Otherwise, the whole equipment may fail when the fan belt fails. This correlation provides a key for improving an engineering design. Nevertheless, one must always bear in mind that MTTF and MTBF are probability related and do not guarantee the life of a piece of equipment up to that duration.
It is calculated by adding together the total time for repairs and then dividing by the number of failures during that period. This acronym could also describe the Mean Time To Recovery, which is slightly different. When using recovery as the basis, the time added must include the notification time of maintenance tasks. In other words, besides the repair time, there is additional time to diagnose the fault and plan the repair. Using recovery as the basis for the calculation gives a higher result than using repair time alone.
MTTR does not give enough information on its own to improve maintenance performance. Reasons for the duration must be investigated to determine whether the time to repair can be reduced.
Strategies to reduce repair times may include spares holding strategies or developing in-house skills instead of relying on outside contractors. Lengthy repairs have the potential to cause a loss in production.
Only by tracking these critical KPIs can an enterprise maximize uptime and keep disruptions to a minimum. Tracking the reliability of assets is one challenge that engineering and maintenance managers face daily. While failure metrics can be very useful in this context, to use them effectively, you need to know what meaning hides behind their acronyms, how to distinguish between them, how to calculate them, and what does that tell you about your assets. Introduction to Failure Metrics Even the most efficient maintenance teams experience equipment failures. But first, what does equipment failure look like?
Despite its importance in the performance of the processes, most managers do not make full use of these key performance indicators KPIs in their control activities. Find out in the next few lines the differences between these two metrics and how they can be used to improve the efficiency of the processes in your company. These lapses of time can be calculated by using a formula. That is, it is the time spent during the intervention in a given process. Remember that we are dealing with systems, facilities, equipment or processes that can be repaired. Differentiating these concepts is essential for businesses of all sectors, especially those working with high-availability environments where failures can result in large losses with sales forgone or with loss of confidence in the delivery of services.
Mean time between failures MTBF is the average time between system breakdowns. MTBF is a crucial maintenance metric to measure performance, safety, and equipment design, especially for critical or complex assets, like generators or airplanes. It is also used to determine the reliability of an asset. To calculate MTBF, divide the total number of operational hours in a period by the number of failures that occurred in that period. MTBF is usually measured in hours. For example, an asset may have been operational for 1, hours in a year.
Mean Time Between Failure MTBF is one of the most widely recognised and yet least understood indicators in the maintenance and reliability world. Manufacturers quote it as a rating of their products and industry uses it as a measure of success. In this article, I will explain in simple terms what MTBS is, what it's not, when to use and when not. It is said that the great Greek philosopher Socrates argued that "the beginning of wisdom is the definition of terms.
Usually people think of it as the average time that something works until it fails and needs to be repaired again. As reliable production processes are crucial in a Lean Manufacturing environment, MTBF is vital for all lean initiatives. In other words, the mean time between failures is the time from one failure to another.
Mean time to failure MTTF is a maintenance metric that measures the average amount of time a non-repairable asset operates before it fails. Because MTTF is relevant only for assets and equipment that cannot or should not be repaired, MTTF can also be thought of as the average lifespan of an asset. To calculate MTTF, divide the total number of hours of operation by the total number of assets in use. There are identical rollers, which operated a total of 60, hours in the last year.
Mean time between failures MTBF is the predicted elapsed time between inherent failures of a mechanical or electronic system, during normal system operation.
Сьюзан знала, что такое могло произойти только по одной причине - если бы в Следопыте завелся вирус. Вирусы были самой большой неприятностью, с которой сталкивались в своей работе программисты. Поскольку компьютеры должны были выполнять операции в абсолютно точном порядке, самая мелкая ошибка могла иметь колоссальные последствия. Простая синтаксическая ошибка - если бы, например, программист по ошибке ввел вместо точки запятую - могла обрушить всю систему. Происхождение термина вирус всегда казалось Сьюзан весьма забавным. Этот термин возник еще во времена первого в мире компьютера Марк-1 - агрегата размером с комнату, построенного в 1944 году в лаборатории Гарвардского университета.
Энсея Танкадо отдали в приемную семью. Каждую ночь юный Танкадо смотрел на свои скрюченные пальцы, вцепившиеся в куклу Дарума note 1и клялся, что отомстит - отомстит стране, которая лишила его матери, а отца заставила бросить его на произвол судьбы. Не знал он только одного - что в его планы вмешается судьба. В феврале того года, когда Энсею исполнилось двенадцать, его приемным родителям позвонили из токийской фирмы, производящей компьютеры, и предложили их сыну-калеке принять участие в испытаниях новой клавиатуры, которую фирма сконструировала для детей с физическими недостатками. Родители согласились.
MTTF is a statistical value and is meant to be the mean over a long period of time and a large number of units. Technically, MTBF should be used only in reference to a repairable item, while MTTF should be used for non-repairable items. However, MTBF is commonly used for both repairable and non-repairable items.