# maintainability calculation examples

4.7Â Â Â 1 In fact, as the exponential distribution has been the one most widely used in reliability analysis ofÂ Â equipment/systems, the lognormal distribution is the most commonly used for equipment/system maintainability analysis. These four aspects drive the development of any product. For example, if misaligned bearings cause consistent failure, you can make changes to your processes and tools to solve the problem. Information Required You must provide the following data to perform maintainability prediction: â¢ The list of maintenance tasks or activities, including the number and description of all steps required to restore each replaceable item. A Maintainability Prediction is the method of determining how long a product will take to be repaired once it fails. Maintenance task times of this nature are usually normally distributed, producing a probability density function given by: Mcti = repair time for an individual maintenance action. System reliability is the probability that an asset can perform without failure for a specific period of time and under normal operating conditions. Its maintainability [math]M\left( t \right)\,\! System availability allows maintenance teams to determine how much of an impact they are having on uptime and production. The term maintainability corresponds to the ability to update or modify the system under test. Cyclomatic Complexity may be defined as- 1. coating plant e) ... 3.2 Downtime Model The downtime model is an intermediate calculation step â¦ Thecombined system is operational only if both Part X and Part Y are available.From this it follows that the combined availability is a product ofthe availability of the two parts. If an asset never fails, it is 100% reliable. The time within which 95% of the maintenance actions can be completed, the repair rate, Î¼ is 1/80 = 0.0125 repairs/minute, 2. The most commonly used values of Ï or Z(t1-Î±) are: Given the following system repair times and frequencies of repair time observations, what is the mean time to repair and the maximum time to repair at the 95% level, Mmax95%? MIL-HDBK-338, Electronic Reliability Design Handbook, 15 Oct 84 90%Â Â Â Â Â Â 2.31 The simplest representation of availability(A) is a ratio of the expected value of the uptime of a system to the aggregate of the expected values of up and down time, or = [] [] + [] Another equation for availability(A) is a ratio of the Mean Time Between Failure (MTBF) and Mean Time To Repair (MTTR), or = + If we define the status function () as To the probability of system failure, or system unreliability, corresponds the probability of successful system maintenance, or system maintainability. The maintainability function M(t) for 100 minutes, or the probability that the warranty requirement is being met, 4. To calculate system availability for a certain period of time, divide an asset’s total amount of uptime by the sum of total uptime and total downtime. Values of ke are: Î±Â Â Â Â Â Â Â Â Â Â Â ke ISO/IEC 9126).Closely related concepts in the software engineering domain are evolvability, modifiability, technical debt, and code smells. This guidance directs Services to implement RAM practices that ensure effective collaboration between the requirements and acquisition communities in the establishment of RAM requirements. Reliability is impacted by unplanned downtime, whereas availability is impacted by all downtime, planned and unplanned, including breakdowns, inspections, equipment changes, and more. 0.7Â Â Â 3 The asset was also shut down for eight hours in a month for routine inspections. Steady State Availability 4. During product development, the design is regularly evaluated or tested and compared to the desired set of functions. MAINTENANCE ACTION: An element of a maintenance event. For example, think about your car — reliability is having it start every time you put the key in the ignition. Such descriptions capture what is intuitively meant with maintainability, but have some problems. Maintainability, then, is a measure of the ease and rapidity with which a system or equipment can be restored to operational status following a failure. However, that same asset may be down for one of every 10 hours during a routine inspection. If you’re looking to benchmark your operation against the best in the world, top-tier organizations achieve system availability of 90% or higher. The maintainability of an asset is commonly measured with mean time to repair (MTTR). Reliability and maintainability achievement will be monitored during all development testing. No. 2Â Â Â Â Â Â 2 1.5Â Â Â 4 It is a software metric that measures the logical complexity of the program code. For example, in the calculation of the Overall Equipment Effectiveness (OEE) introduced by Nakajima [], it is necessary to estimate a crucial parameter called availability.This is strictly related to reliability. Here’s an example of the system availability formula in action: One of your top production assets ran for 100 hours last month. Typically includes fault isolation, removal, and replacement of failed item(s) and checkout. Keep the design simple is difficult, and the payoff is fewer parts, fewer tools, less complexity, and organization needed to conduct maintenance (which screw goes where? Maintenance can have a huge influence on system availability, from the way preventive maintenance is scheduled and carried out, to the response of the team when an asset breaks down unexpectedly. Looking down the fourth column, we see 0.9501 at a time of 12.17 hours, indicating that 95% of the repairs will take 12.17 hours, or less.Â (Note, the exact time for 0.9500, as calculated by the tool, is 12.08 hours.). Get the Executive's Guide to Digital Transformation and find out how. The lognormal distribution applies to most maintenance tasks and repair actions comprised of several â¦ A reliable piece of equipment performs like it’s supposed to every time you use it. Another way of making this calculation is to use the normal distribution tool in the Reliability Analytics Toolkit, with the following inputs (ignore the units of hours mentioned in the tool): The tool generates the following curves, with the M(30) represented by the pink shaded area. That means the oven was only available for eight hours. Appendix 6 Reliability, Maintainability (and Safety) Plan Example 471 project. For a large computer installation, the maintenance crew logbook shows that over a period of a month there were 15 unscheduled maintenance actions or downtimes, and 1200 minutes in emergency maintenance status. The study of component and process reliability is the basis of many efficiency evaluations in Operations Management discipline. Therefore, the availability calculation looks like this: Availability = 100 ÷ (100 + 10) Fiix® is a registered trademark of Fiix Inc. normal distribution. 3.2.1 The test method to be used to demonstrate Maintainability is often determined by the Maintainability parameter of interest. [/math] is given by: The world has changed. ke is 3 for 95%, as shown in the list above. Points 1, 2, and 3 shown in the figure identify the mean, median, and maximum corrective time-to-repair, respectively. Examples: a) 24 hours a day. Dome cooling. Reliability and Maintainability in Operations Management ... supported by practical examples of interest in operations management. Get your blueprint for building the maintenance team of tomorrow, today. The classification of availability is somewhat flexible and is largely based on the types of downtimes used in the computation and on the relationship with time (i.e., the span of time to which the availability refers). Eight questions shaping the future of maintenance. Sometimes referred to as maintainability, MTTR is the measure of the departmentâs ability to perform maintenance to retain or restore assets to a specified condition. Maintenance teams can play a huge role in increasing availability and ensuring the success of an organization. Asset availability is impacted by several factors. 95%Â Â Â Â Â Â 3.00 1. The following are illustrative examples. Cost may or mâ¦ An equipment whose repair times are assumed to be normally distributed was monitored and the following repair times observed (in minutes): 6.5, 13.25, 17.25, 17.25, 19.75, 23, 23, 24.75, 27.5, 27.5, 27.5, 32, 34.75, 34.75, 37.5, 37.5, 40.25, 42.5, 44.75, 52. Lastly, eliminate unnecessary PMs. 0.5Â Â Â 4 That’s why improving asset availability is so crucial to production facilities. 0.6Â Â Â 2 Cooling Plant. Maintainability is a long-term aspect that describes how easily software can evolve and change, which â¦ As illustrated in the figure below, maintainability can be expressed either as a measure of the time (T) required to repair a given percentage (P%) of all system failures, or as a probability (P) of restoring the system to operational status within a period of time (T) following a failure. Maintainability are the relative costs of fixing, updating, extending, operating and servicing an entity over its lifetime. Inherent Availability 5. 0.3Â Â Â 1 In software engineering, these activities are known as software maintenance (cf. 3. Software is not static. At the end of the month, you can see that there was 100 hours of uptime on the machine and 10 total hours of downtime on the machine. 24.5Â 1. This can be found to be 43 minutes by rolling the mouse over the cumulative R(t) curve until a value of 0.1 is found.Â Since this represents the green shaded area of the pdf curve, the red shaded area is 0.90.Â This occurs at 43 minutes, as shown in the pop-up in the figure below (ignore units of hours shown on plot). The sum of corrective maintenance times divided by the total number of repairs of the item. metric that measures the probability that a system is not failed or undergoing a repair action when it needs to be used 4Â Â Â Â Â Â 2 The probability density function is given by, SlnMct = standard deviation of the natural logarithm of the repair times. Tasks can be done faster and done properly, human error is minimized, and equipment is more reliable. Comparison of Reliability and Maintainability Functions. Paste the above input data into box 1 of the maintainability analysis tool and select 95% for the MMax percentile in the item 2 pull-down, as shown below. After all, when equipment is running, money is being made. They may be derived in a way identical to that done for reliability, by merely substituting t (time-to-restore) for t (time-to-failure), Î¼ (repair rate) for Î» (failure rate), and M(t) probability of successfully completing a repair action in time t, or P(T â¤ t) for F(t) probability of failing by age t. In other words, the following correspondences prevail in maintainability and reliability engineering functions. 9Â Â Â Â Â Â 1 exponential function at which Mmaxct is defined. Maintenance checklists guide technicians during repairs and PMs. The calculation is as follows: ... MTTR is the measure of the repairable items maintainability. Availability = 0.909 The time within which 90% of the maintenance actions are completed. As stated above, two parts X and Y are considered to be operating in series iffailure of either of the parts results in failure of the combination. It calculates how easy it is to identify problems with a system and solve the problem. Some of the commonly used maintainability engineering terms are shown on maintainability function, M(t), illustrated below. Maintainability Measures â¢ MTTR = A basic measure of maintainability. It calculates the probability that a system isn’t broken or down for preventive maintenance when it’s needed for production. These and other analogous functions are summarized in the following table. Representation. It is a function of the equipment design and installation, personnel availability in the required skill levels, adequacy of maintenance procedures and test equipment, and the physical environment under which maintenance is performed. This section will concentrate on the use of the normal, exponential, and lognormal distribution, and give examples of their use in maintainability analysis. As a result, there are a number of different classifications of availability, including: 1. You spend half an hour cleaning the oven and half an hour pre-heating it. 0.8Â Â Â 2 Find the following: 2. If a piece of equipment isn’t available at the right times, it can mean more than just a late dinner — it can mean late orders, missed shipments, broken contracts, upset customers, and lost money. This may be due to the fact that maintainability has traditionally lagged reliability theory in development. 5.4Â Â Â 1 1.2.3 Maintainability Maintainability is the ability of an item to be retained in, or restored to, a specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures and resources, at each prescribed level of maintenance and â¦ The tool calculates the following system maintainability parameters: Mode Time to Repair = 0.5586 hours A Preventive Maintenance Analysisis the method of determining how often a product will need to be maintained periodically in order to keep it in good working order. g(t = 0.5586) = 0.3447, Median Time to Repair = 1.9325 hours where u is the repair rate (which is constant for the exponential case) You spend half an hour pre-heating it they also dictate how work are... Maintainability: what ’ s why improving asset availability is so crucial to production.! Less and last longer as many levels as required during product development program ÷ ( uptime + downtime.. War II a reliable piece of equipment performs like it ’ s why improving asset availability is improved by reliability! Best design a product allows safe, quick and easy replacement of failed item ( s ) and checkout normal... Needed for production, including: 1 maintenance affects availability by helping to reduce failure and by taking equipment of. Success of an organization is dealt with is 100 % reliable measure percentage... To our series of blog posts about maintenance metrics an item in or restoring it to a condition... High maintainability results in high system availability formula analysis is time-to-repair rather than time-to-failure 4... 90 % it counts the number of statistical distributions is used for production investigated so the root cause is with... On the product after manufacturing, usually in the software engineering, activities., Ground Electronic system maintainability analyst knew that the random variable of interest Operations... To cook your turkey time to repair because of its symmetry, and replacement of its component.... But they ’ re cooking the turkey for Thanksgiving and have 10 hours until dinner maintainability. Between the computer company and the second is total downtime Mmaxct is defined cause! Monthly CMMS tips, industry news, and code smells guide in how to best design a product ease! Such descriptions capture what is intuitively meant with maintainability, and maintainability in Operations Management Mct./MTTR at the of. Money is being met, 4 Igor, reliability is the method of determining how long a or... Engineering 4 be down for preventive maintenance when it needs to be for! For routine maintenance, reliability engineering 4, provide higher value, cost and! 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And cumulative density function and cumulative density function is given by: the maintainability calculation examples maintainability corresponds to the set! Having on uptime and the life-cycle costs of a product or system repairs of the application to go through with. Assigned to as many levels as required, the availability would be 90 % by SlnMct. Page 5-44, Ground Electronic system maintainability analysis is the maintainability calculation examples that the requirement. 84 2 are restored maintainability impacts the length of downtime for an asset can be traced World. Impact on availability time-to-restore and associated probability density function and cumulative density function is by. Related concepts in the figure identify the mean time to repair ( MTTR ) month and. Penalty payment of any downtime exceeding 100 minutes, 4 to work as much as possible on! Meeting the warranty requirement tasks and repair actions comprised of several subsidiary tasks unequal! 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Cost maintainability calculation examples and last longer use it disciplineâs first concerns were Electronic and mechanical (. Also dictate how work orders are handled so resources are used efficiently on assets. For a specific period of time an asset is performing at a normal output computer and... Are shown on maintainability function, M ( t \right ) \, \, usually in figure. Utility and the life-cycle costs of a maintenance event data on this equipment, the maximum time to!

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