Lastly, eliminate unnecessary PMs. Average Uptime Availability (or Mean Availability) 3. These are the same for the normal distribution because of its symmetry, and Creating better processes and using all the tools at your disposal are the quickest ways the maintenance team can make a big impact on availability and help the business take a step forward. are 29.16 minutes as calculated in step 1 above. 2.5    1 This means that there is a 53% chance of making a repair in 30 minutes. Some of the commonly used maintainability engineering terms are portrayed graphically in the figure below as a maintainability “function” derived as illustrated for the case where the pdf has a lognormal distribution. Values from the probability density of time-to-repair data shown on page 5-49 are duplicated by the tool along with the plot of the lognormal pdf that is shown on page 5-50, and the plot of the maintainability function, M(t), that is shown on page 5-54.  The MTTR is calculated on page 5-52 as 3.595 hours, the median time to repair is calculated on page 5-52 as 1.932 hours and the 95 % value for Mmax are shown on page 5-55 is 12.08 hours. Software engineering. The maintainability of an asset is commonly measured with mean time to repair (MTTR). Points 1, 2, and 3 are defined as follows: 1. It is a software metric that measures the logical complexity of the program code. Its purpose is to measure the probability that a piece of equipment in a failed state can be restored to normal operating conditions after undergoing maintenance. Find the following: 2. A reliable piece of equipment performs like it’s supposed to every time you use it. If an asset is failing often in spite of regular PMs, there could be other reasons for failure. If a piece of equipment isn’t available at the right times…it can mean late orders, missed shipments, broken contracts, upset customers, and lost money. System availability is a metric used to measure the percentage of time an asset can be used for production. Such descriptions capture what is intuitively meant with maintainability, but have some problems. 24.5  1. A warranty contract between the computer company and the customer calls for a penalty payment of any downtime exceeding 100 minutes. Information Required You must provide the following data to perform maintainability prediction: • The list of maintenance tasks or activities, including the number and description of all steps required to restore each replaceable item. 0.8    2 Points 1, 2, and 3 shown in the figure identify the mean, median, and maximum corrective time-to-repair, respectively. Software is not static. Downtime is any time the equipment is not available for production, including planned and unplanned downtime. 0.2    1 Cyclomatic complexity indicates several information about the program code- 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.  Since this represents the green shaded area of the pdf curve, the red shaded area is 0.90.  This occurs at 43 minutes, as shown in the pop-up in the figure below (ignore units of hours shown on plot). A shorter MTTR means higher maintainability. c) 12 hours a day. Inherent Availability 5. Night only, e.g.. Mirror surface heating. The probability density function is given by, SlnMct = standard deviation of the natural logarithm of the repair times. In maintainability analysis, the exponential distribution applies to maintenance tasks and maintenance actions whose completion times are independent of previous maintenance experience (e.g., substitution methods of failure isolation where several equally likely alternatives are available and each alternative is exercised, one at a time, until the one which caused the failure is isolated), producing a probability density function given by: The fundamental maintainability parameter is repair rate, u(t), which is the reciprocal of Mct, the mean time to repair (MTTR). All Rights Reserved, A look at the tools that empower your maintenance team, Manage maintenance from anywhere, at any time, Track, control, and optimize asset performance, Simplify the way you create, complete, and record work, Connect your CMMS and share data across any system, Collect, analyze, and act on maintenance data, Make sure you have the right parts at the right time, AI for maintenance. Get the Executive's Guide to Digital Transformation and find out how. Below are examples of tracking and measuring that can produce tangible results for both departments and facilities. In maintainability, the random variable is time-to-repair, in the same manner as time-to-failure is the random variable in reliability. The pdf of g(t) and its value at 30 minutes, 4. 3.2.1 The test method to be used to demonstrate Maintainability is often determined by the Maintainability parameter of interest. Thus, another expression for g(t) in terms of u(t), the repair rate is. 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. Reliability and maintainability are two factors that are heavily influenced by maintenance. Tasks can be done faster and done properly, human error is minimized, and equipment is more reliable. Welcome to our series of blog posts about maintenance metrics. However, that same asset may be down for one of every 10 hours during a routine inspection. Cooling Plant. 4.5    1 During product development, the design is regularly evaluated or tested and compared to the desired set of functions. Maintainability is a probability measure that a product will be maintained or restored to the specified function for a specified period of … It measures the number of linearly independent paths through the program code. 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.  (Note, the exact time for 0.9500, as calculated by the tool, is 12.08 hours.). Asset availability is impacted by several factors. Maintenance SOPs help your team keep one eye on the present and the other on the future. Join over 14,000 maintenance professionals who get monthly CMMS tips, industry news, and updates. obtained from. Thankfully, that’s all it takes to cook your turkey. Eight questions shaping the future of maintenance. 1.5    4 3. They impact availability by helping you reduce downtime. Bazovsky, Igor, Reliability Theory and Practice Comparison of Reliability and Maintainability Functions. 2       2 System reliability is the probability that an asset can perform without failure for a specific period of time and under normal operating conditions. Availability and reliability are often confused for one another, although they are very different. 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. It counts the number of decisions in the given program code. Maximum Time to Repair, Mmax ct , the maximum time required to complete a specified percentage of all maintenance actions. They also dictate how work orders are handled so resources are used efficiently on critical assets. b) 12 hours a day. 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), μ (repair rate) for λ (failure rate), and M(t) probability of successfully completing a repair action in time t, or P(T ≤ t) for F(t) probability of failing by age t. In other words, the following correspondences prevail in maintainability and reliability engineering functions. Some of the commonly used maintainability engineering terms are shown on maintainability function, M(t), illustrated below. Collectively, they affect both the utility and the life-cycle costs of a product or system. 22     1 and the average repair time for N observations is: The standard deviation of the distribution of repair times, based on N observations is. Minimize spare parts inventory is just one benefit. ke is 3 for 95%, as shown in the list above. If failure rates are low, revisit the frequency of PMs on that asset. Availability = 100 ÷ 110 For example, think about your car — reliability is having it start every time you put the key in the ignition. For example, let’s say you’re cooking the turkey for Thanksgiving and have 10 hours until dinner. It calculates the probability that a system isn’t broken or down for preventive maintenance when it’s needed for production. 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. 7       1 A lack of maintainability will be evident as high product maintenance … 2.7    1 This attribute is the flexibility with which the application can be modified, for fixing issues, or to add new functionality with a degree of ease. This is similar to system reliability analysis except that the random variable of interest in maintainability analysis is time-to-repair rather than time-to-failure. ISO/IEC 9126).Closely related concepts in the software engineering domain are evolvability, modifiability, technical debt, and code smells. where u is the repair rate (which is constant for the exponential case) Next, look at historical failure codes to determine if you can avoid breakdowns by introducing a new PM. Achieved Availability 6. There is a 71.4 % chance of meeting the warranty requirement. The combination of high reliability and high maintainability results in high system availability. Start by looking at failure rates to optimize PM intervals. This post outlines everything you need to know about system availability: What it is, how to calculate it, and why it’s important to your maintenance operation. It calculates how easy it is to identify problems with a system and solve the problem. 0.6    2 In maintainability, the normal distribution applies to relatively straightforward maintenance tasks and repair actions (e.g., simple removal and replacement tasks) which consistently require a fixed amount of time to complete. 95%       3.00 It means maintenance resources are being used efficiently, production levels are as high as possible, and your company’s margins can be healthier than ever. The lognormal distribution applies to most maintenance tasks and repair actions comprised of several subsidiary tasks of unequal frequency and time duration. metric that measures the probability that a system is not failed or undergoing a repair action when it needs to be used The M(t) curve is a cumulative density function that provides an estimate of the probability of completing an arbitrary system repair action in a given amount of time. As a result, there are a number of different classifications of availability, including: 1. 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. Its maintainability [math]M\left( t \right)\,\! Reliability, maintainability, and availability (RAM) are three system attributes that are of great interest to systems engineers, logisticians, and users. 1. The above example data comes directly from MIL-HDBK-338, page 5-44, Ground Electronic System Maintainability Analysis, Example 1. Maintainability are the relative costs of fixing, updating, extending, operating and servicing an entity over its lifetime. The maintainability of an asset is commonly measured with mean time to repair (MTTR). Cost may or m… A smaller number of statistical distributions is used for maintainability analysis than for reliability analysis. MIL-HDBK-338, Electronic Reliability Design Handbook, 15 Oct 84 The most commonly used values of φ or Z(t1-α) 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%? Levelling up with improved system availability. Preventive maintenance affects availability by helping to reduce failure and by taking equipment out of production for routine maintenance. These and other analogous functions are summarized in the following table. 4. The time within which 90% of the maintenance actions are completed. A Maintainability Prediction is the method of determining how long a product will take to be repaired once it fails. System availability allows maintenance teams to determine how much of an impact they are having on uptime and production. That’s why improving asset availability is so crucial to production facilities. MAINTENANCE: All actions necessary for retaining an item in or restoring it to a specified condition. The following are illustrative examples. Mean Time to Repair, Mct, the mean time required to complete a maintenance action, i.e., total maintenance downtime divided by total maintenance actions for a given period of time, given as: λi = failure rate for the ith repairable element of the item for which maintainability is to be determined, adjusted for duty cycle, catastrophic failures, tolerance and interaction failures, etc., which will result in deterioration of item performance to the point that a maintenance action will be initiated, Mcti = average corrective time required to repair the ith repairable element in the event of its failure, 2. The discipline’s first concerns were electronic and mechanical components (Ebeling, 2010). Availability is improved by increasing reliability and reducing maintenance time. You spend half an hour cleaning the oven and half an hour pre-heating it. 3. After all, when equipment is running, money is being made.