Comparing MTBF, MTTF, MTTR | Get Certified Get Ahead
Understand the impact of Reliability tools on Maintenance Excellence. 3 .. The relationship between Reliability and MTTF is given by the Capacity Quiz. Being successful in this area can be the difference between winning and losing in the market place. . Failure Rate & MTTF Relationship .. Practice Quiz. Metrics such as MTBF, MTTF, MTTR, and others are commonly used within risk It is similar to MTBF, but the primary difference is that “between” in the MTBF.
Each one of these important indices will be discussed below in detail.
Consider the following example, where 20 units are put on test and run at their normal operating condition for 1, hours.
If 6 of those units fail, at the following hours,the Failure Rate of the product can be calculated as such: This calculation captures the 14 units that survived the entire test time 1, hoursand the 6 units that failed at the given times. In the case above, the Mean Time Between Failure assuming that the product is repairable would be: If the units above were not repairable, then we could calculate MTTF using the following calculation: Both of these metrics measure the Central Tendency for the exponential distribution.
MTTR is calculated as the total amount of time spent in maintenance divided by the number of discrete maintenance activities performed. Maintainability is defined as a measure of a units ability to be retained in, or restored to a specific condition when maintenance action is performed by personnel having specified skill levels and using prescribed procedures and resources at each prescribed level of maintenance and repair. If a product is highly maintainable, it means that the MTTR is low, and that the product is easily retained in or restored to a specific condition.
High Maintainability also can have a huge impact on the lifetime cost associated with your product or process. As an example, if your car can go 6 months without any maintenance activities oil change, tire rotation, etcand the maintenance activities only take 6 hours, then the availability of your vehicle could be calculated as such: This means that your car is available for use The first model that we should discuss is one that is unique to reliability and is used in conjunction with the other distributions used to make reliability predictions, this is the Bathtub Curve.
Bathtub Curve The bathtub curve is a reliability tool that is used to model the reliability of a unit or system over the units entire life.
MTTR and MTBF, what are they and what are their differences?
Aptly named the bathtub curve because of its shape, the curve has 3 distinct regions that are meant to convey the general pattern of product failure rates over time.
Then the failure rate is someone constant and low from ages 4 — 35, representing the Useful life region, and then the death rate starts increasing upwards from there. The Early Failure Period of the Bathtub Curve The first region of the bathtub curve is called the Early-Failure Period which starts with a high failure rate that decreases over time. Your goal in this region of the products lifecycle is NOT to be predicting or estimating reliability.
Your goal is to work to improve reliability and reduce the number of early life failures associated with your product. More on this below. The end of life region is also known as the wear out period because of the increase in the failure rate of your product due to wear and tear. Utilizing the Normal Distribution Curve you can make reliability predictions by calculating the area under the curve at any given moment in time.What is MTBF (Mean Time between Failure), MTTF (Mean time to Failure), MTTR (Mean time to Repair) ?
What is the reliability of the motor at 7, hours? This is the probability that the motor has not failed yet.
Mean time between failures
Remember though that the Z-Score and the resulting probability represent the area to the left of the time value 7, hours. The reliability is the area to the right of the curve, which is 1 —.
Therefore there is an 8. Or, said differently, 8. We can do another example real quick. Using the standard Z-Tables, we can look up the Z-Score associated with. This equation can be re-arranged to solve for t1. The Exponential Distribution The Exponential Distribution is considered the most basic and widely used distribution model within reliability.
This distribution is used to model a system that is within its Useful Life Region or period where the system is experiencing a constant failure rate. The beauty of this region of the bathtub curve and the exponential distribution is the ease at which you can make reliability calculations.
This reliability calculation can be applicable to the entire population of product; i. We can take the Natural Log of both sides of the equation, and we get: 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. 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.
Conceptual differences, different formulas!
Adding to all failures, we have 60 minutes 1 hour. Calculating the MTBF, we would have: The opportunity to spot this index allows you to plan strategies to reduce this time. Therefore, the company knows that every 2 hours, the system will be unavailable for 15 minutes. Being aware of our limitations is the first step to eliminate them. We can get to the uptime of a system, for instance, using these 2 KPIs. Imagine the following situation: How long the system should work: