Reliability engineering is an engineering field, that deals with the study of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time.^[2] It is often reported in terms of a probability. Engineering is the discipline of acquiring and applying knowledge of design, analysis, and/or construction of works for practical purposes. ... Reliability concerns quality or consistency. ... For other uses, see System (disambiguation). ... Probability is the likelihood that something is the case or will happen. ...

Overview

A Reliability Block Diagram

Reliability may be defined in several ways: Download high resolution version (1253x422, 8 KB) From US DOD public domain source File links The following pages link to this file: User:Wyatts User:Wyatts/Draft article C Reliability engineering Categories: U.S. military images ... Download high resolution version (1253x422, 8 KB) From US DOD public domain source File links The following pages link to this file: User:Wyatts User:Wyatts/Draft article C Reliability engineering Categories: U.S. military images ...

• The idea that something is fit for purpose with respect to time;
• The capacity of a device or system to perform as designed;
• The resistance to failure of a device or system;
• The ability of a device or system to perform a required function under stated conditions for a specified period of time;
• The probability that a functional unit will perform its required function for a specified interval under stated conditions.

Reliability engineers rely heavily on statistics, probability theory, and reliability theory. Many engineering techniques are used in reliability engineering, such as reliability prediction, Weibull analysis, thermal management, reliability testing and accelerated life testing. Because of the large number of reliability techniques, their expense, and the varying degrees of reliability required for different situations, most projects develop a reliability program plan to specify the reliability tasks that will be performed for that specific system. This article is about the concept of time. ... In computer engineering, an execution unit is a part of a CPU that performs the operations and calculations called for by the program. ... This article is about the field of statistics. ... Probability theory is the branch of mathematics concerned with analysis of random phenomena. ... Reliability theory developed apart from the mainstream of probability and statistics, and was used originally as a tool to help nineteenth century maritime insurance and life insurance companies compute profitable rates to charge their customers. ... In probability theory and statistics, the Weibull distribution (named after Waloddi Weibull) is a continuous probability distribution with the probability density function where and is the shape parameter and is the scale parameter of the distribution. ...

The function of reliability engineering is to develop the reliability requirements for the product, establish an adequate reliability program, and perform appropriate analyses and tasks to ensure the product will meet its requirements. These tasks are managed by a reliability engineer, who usually holds an accredited engineering degree and has additional reliability-specific education and training. Reliability engineering is closely associated with maintainability engineering and logistics engineering. Many problems from other fields, such as security engineering, can also be approached using reliability engineering techniques. This article provides an overview of some of the most common reliability engineering tasks. Please see the references for a more comprehensive treatment. Accreditation is a process by which a facilitys services and operations are examined by a third-party accrediting agency to determine if applicable standards are met. ... Logistic Engineering deals with the science of Logistics. ... Security engineering is the field of engineering dealing with the security and integrity of real-world systems. ...

Many types of engineering employ reliability engineers and use the tools and methodology of reliability engineering. For example: Engineering is the discipline of acquiring and applying knowledge of design, analysis, and/or construction of works for practical purposes. ...

• System engineers design complex systems having a specified reliability
• Mechanical engineers may have to design a machine or system with a specified reliability
• Automotive engineers have reliability requirements for the automobiles (and components) which they design
• Electronics engineers must design and test their products for reliability requirements.
• In software engineering and systems engineering the reliability engineering is the subdiscipline of ensuring that a system (or a device in general) will perform its intended function(s) when operated in a specified manner for a specified length of time. Reliability engineering is performed throughout the entire life cycle of a system, including development, test, production and operation.

Systems engineering (or systems design engineering) as a field originated around the time of World War II. Large or highly complex engineering projects, such as the development of a new airliner or warship, are often decomposed into stages and managed throughout the entire life of the product or system. ... Mechanical engineering is the application of physical principles to the creation of useful devices, objects and machines. ... Electronic engineering is a professional discipline that deals with the behavior and effects of electrons (as in electron tubes and transistors) and with electronic devices, systems, or equipment. ... Software engineering (SE) is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ... Systems engineering techniques are used in complex projects: from spacecrafts to chip design, from robotics to creating large software products to building bridges, Systems engineering uses a host of tools that include modeling & simulation, requirements analysis, and scheduling to manage complexity Systems Engineering (SE) is an interdisciplinary approach and means... For other uses, see System (disambiguation). ... Engineering is the discipline of acquiring and applying knowledge of design, analysis, and/or construction of works for practical purposes. ... In business and engineering, new product development (NPD) is the term used to describe the complete process of bringing a new product or service to market. ...

Reliability theory

Main articles: reliability theory, failure rate. Reliability theory developed apart from the mainstream of probability and statistics, and was used originally as a tool to help nineteenth century maritime insurance and life insurance companies compute profitable rates to charge their customers. ... Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. ...

Reliability theory is the foundation of reliability engineering. For engineering purposes, reliability is defined as:

the probability that a device will perform its intended function during a specified period of time under stated conditions.

Mathematically, this may be expressed as, Probability is the likelihood that something is the case or will happen. ...

,

where is the failure probability density function and t is the length of the period (which is assumed to start from time zero).

Reliability engineering is concerned with four key elements of this definition: In mathematics, a probability density function (pdf) is a function that represents a probability distribution in terms of integrals. ...

• First, reliability is a probability. This means that failure is regarded as a random phenomenon: it is a recurring event, and we do not express any information on individual failures, the causes of failures, or relationships between failures, except that the likelihood for failures to occur varies over time according to the given probability function. Reliability engineering is concerned with meeting the specified probability of success, at a specified statistical confidence level.
• Second, reliability is predicated on "intended function:" Generally, this is taken to mean operation without failure. However, even if no individual part of the system fails, but the system as a whole does not do what was intended, then it is still charged against the system reliability. The system requirements specification is the criterion against which reliability is measured.
• Third, reliability applies to a specified period of time. In practical terms, this means that a system has a specified chance that it will operate without failure before time . Reliability engineering ensures that components and materials will meet the requirements during the specified time. Units other than time may sometimes be used. The automotive industry might specify reliability in terms of miles, the military might specify reliability of a gun for a certain number of rounds fired. A piece of mechanical equipment may have a reliability rating value in terms of cycles of use.
• Fourth, reliability is restricted to operation under stated conditions. This constraint is necessary because it is impossible to design a system for unlimited conditions. A Mars Rover will have different specified conditions than the family car. The operating environment must be addressed during design and testing.

Random redirects here. ... In this diagram, the bars represent observation means and the red lines represent the confidence intervals surrounding them. ... Fail and Phail redirect here. ... A Mars Rover is an unmanned land vehicle for exploration of the planet Mars. ...

Reliability program plan

Many tasks, methods, and tools can be used to achieve reliability. Every system requires a different level of reliability. A commercial airliner must operate under a wide range of conditions. The consequences of failure are grave, but there is a correspondingly higher budget. A pencil sharpener may be more reliable than an airliner, but has a much different set of operational conditions, insignificant consequences of failure, and a much lower budget. An Airbus A340 airliner operated by Air Jamaica An airliner is a large fixed-wing aircraft with the primary function of transporting paying passengers. ...

A reliability program plan is used to document exactly what tasks, methods, tools, analyses, and tests are required for a particular system. For complex systems, the reliability program plan is a separate document. For simple systems, it may be combined with the systems engineering management plan. The reliability program plan is essential for a successful reliability program and is developed early during system development. It specifies not only what the reliability engineer does, but also the tasks performed by others. The reliability program plan is approved by top program management. For the similarly-named Surrealist journal, see Documents (journal). ... Systems engineering techniques are used in complex projects: from spacecrafts to chip design, from robotics to creating large software products to building bridges, Systems engineering uses a host of tools that include modeling & simulation, requirements analysis, and scheduling to manage complexity Systems Engineering (SE) is an interdisciplinary approach and means...

Reliability requirements

For any system, one of the first tasks of reliability engineering is to adequately specify the reliability requirements. Reliability requirements address the system itself, test and assessment requirements, and associated tasks and documentation. Reliability requirements are included in the appropriate system/subsystem requirements specifications, test plans, and contract statements.

System reliability parameters

Requirements are specified using reliability parameters. The most common reliability parameter is the mean-time-between-failure (MTBF), which can also be specified as the failure rate or the number of failures during a given period. These parameters are very useful for systems that are operated on a regular basis, such as most vehicles, machinery, and electronic equipment. Reliability increases as the MTBF increases. The MTBF is usually specified in hours, but can also be used with any unit of duration such as miles or cycles. The factual accuracy of this article is disputed. ... Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. ... Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. ... The Trikke is a Human Powered Vehicle (HPV) Automobiles are among the most commonly used engine powered vehicles. ... This article is about the engineering discipline. ...

In other cases, reliability is specified as the probability of mission success. For example, reliability of a scheduled aircraft flight can be specified as a dimensionless probability or a percentage.

A special case of mission success is the single-shot device or system. These are devices or systems that remain relatively dormant and only operate once. Examples include automobile airbags, thermal batteries and missiles. Single-shot reliability is specified as a probability of success, or is subsumed into a related parameter. Single-shot missile reliability may be incorporated into a requirement for the probability of hit. An airbag is a flexible membrane or envelope, inflatable to contain air or some other gas. ... A battery is of one or more electrochemical cells, which store chemical energy and make it available in an electrical form. ... A missile (British English: miss-isle; U.S. English: missl) is, in general, a projectile—that is, something thrown or otherwise propelled. ...

For such systems the probability of failure on demand PFD is the reliability measure. This PFD is derived from failure rate and mission time for non-repairable systems. For repairable systems, it is obtained from failure rate and MTTR and test interval. This measure may not be unique for a given system as this measure depends on the kind of demand. In addition to system level requirements, reliability requirements may be specified for critical subsystems. In all cases, reliability parameters are specified with appropriate statistical confidence intervals. PFD may stand for: Alaska Permanent Fund Dividend Democratic Federal Party, Equatorial Guinea Pelvic floor disorders Personal flotation device or life vest— see Boating for more information. ... Measure can mean: To perform a measurement. ... In this diagram, the bars represent observation means and the red lines represent the confidence intervals surrounding them. ...

Reliability modelling

Reliability modelling is the process of predicting or understanding the reliability of a component or system. Two separate fields of investigation are common: The physics of failure approach uses an understanding of the failure mechanisms involved, such as crack propagation or chemical corrosion; The parts stress modelling approach is an empirical method for prediction based on counting the number and type of components of the system, and the stress they undergo during operation. Reliability concerns quality or consistency. ... This does not cite any references or sources. ... For the hazard, see corrosive. ... Parts stress modelling is a method in engineering and especially electronics to find an expected value for the rate of failure of the mechanical and electronic components of a system. ...

For systems with a clearly defined failure time (which is sometimes not given for systems with a drifting parameter), the empirical distribution function of these failure times can be determined. This is done in general in an accelerated experiment with increased stress. These experiments can be divided into two main categories: In statistics, an empirical distribution function is a cumulative probability distribution function that concentrates probability 1/n at each of the n numbers in a sample. ...

Early failure rate studies determine the distribution with a decreasing failure rate over the first part of the bathtub curve. Here in general only moderate stress is necessary. The stress is applied for a limited period of time in what is called a censored test. Therefore, only the part of the distribution with early failures can be determined.

In so-called zero defect experiments, only limited information about the failure distribution is acquired. Here the stress, stress time, or the sample size is so low that not a single failure occurs. Due to the insufficient sample size, only an upper limit of the early failure rate can be determined. At any rate, it looks good for the customer if there are no failures.

In a study of the intrinsic failure distribution, which is often a material property, higher stresses are necessary to get failure in a reasonable period of time. Several degrees of stress have to be applied to determine an acceleration model. The empirical failure distribution is often parametrised with a Weibull or a log-normal model.

It is a general praxis to model the early failure rate with an exponential distribution. This less complex model for the failure distribution has only one parameter: the constant failure rate. In such cases, the Chi-square distribution can be used to find the goodness of fit for the estimated failure rate. Compared to a model with a decreasing failure rate, this is quite pessimistic. Combined with a zero-defect experiment this becomes even more pessimistic. The effort is greatly reduced in this case: one does not have to determine a second model parameter (e.g. the shape parameter of a Weibull distribution, or its confidence interval (e.g by an MLE / Maximum likelihood approach) - and the sample size is much smaller. Look up praxis in Wiktionary, the free dictionary. ... This article is about the mathematics of the chi-square distribution. ... Goodness of fit means how well a statistical model fits a set of observations. ... In probability theory and statistics, the Weibull distribution (named after Waloddi Weibull) is a continuous probability distribution with the probability density function where and is the shape parameter and is the scale parameter of the distribution. ... Maximum likelihood estimation (MLE) is a popular statistical method used to make inferences about parameters of the underlying probability distribution from a given data set. ...

Reliability test requirements

Because reliability is a probability, even highly reliable systems have some chance of failure. However, testing reliability requirements is problematic for several reasons. A single test is insufficient to generate enough statistical data. Multiple tests or long-duration tests are usually very expensive. Some tests are simply impractical. Reliability engineering is used to design a realistic and affordable test program that provides enough evidence that the system meets its requirement. Statistical confidence levels are used to address some of these concerns. A certain parameter is expressed along with a corresponding confidence level: for example, an MTBF of 1000 hours at 90% confidence level. From this specification, the reliability engineer can design a test with explicit criteria for the number of hours and number of failures until the requirement is met or failed. In this diagram, the bars represent observation means and the red lines represent the confidence intervals surrounding them. ...

The combination of reliability parameter value and confidence level greatly affects the development cost and the risk to both the customer and producer. Care is needed to select the best combination of requirements. Reliability testing may be performed at various levels, such as component, subsystem, and system. Also, many factors must be addressed during testing, such as extreme temperature and humidity, shock, vibration, and heat. Reliability engineering determines an effective test strategy so that all parts are exercised in relevant environments. For systems that must last many years, reliability engineering may be used to design an accelerated life test. For the Macintosh operating system, which was called System up to version 7. ... For other uses, see System (disambiguation). ...

Requirements for reliability tasks

Reliability engineering must also address requirements for various reliability tasks and documentation during system development, test, production, and operation. These requirements are generally specified in the contract statement of work and depend on how much leeway the customer wishes to provide to the contractor. Reliability tasks include various analyses, planning, and failure reporting. Task selection depends on the criticality of the system as well as cost. A critical system may require a formal failure reporting and review process throughout development, whereas a non-critical system may rely on final test reports. The most common reliability program tasks are documented in reliability program standards, such as MIL-STD-785 and IEEE 1332.

Design for reliability

Main article: Reliable system design Reliable system design is the design of systems with high levels of reliability and availability. ...

Design For Reliability (DFR), is an emerging discipline that refers to the process of designing reliability into products. This process encompasses several tools and practices and describes the order of their deployment that an organization needs to have in place in order to drive reliability into their products. Typically, the first step in the DFR process is to set the system’s reliability requirements. Reliability must be "designed in" to the system. During system design, the top-level reliability requirements are then allocated to subsystems by design engineers and reliability engineers working together. All Saints Chapel in the Cathedral Basilica of St. ...

Reliability design begins with the development of a model. Reliability models use block diagrams and fault trees to provide a graphical means of evaluating the relationships between different parts of the system. These models incorporate predictions based on parts-count failure rates taken from historical data. While the predictions are often not accurate in an absolute sense, they are valuable to assess relative differences in design alternatives. A mathematical model is an abstract model that uses mathematical language to describe the behaviour of a system. ...

A Fault Tree Diagram

One of the most important design techniques is redundancy. This means that if one part of the system fails, there is an alternate success path, such as a backup system. An automobile brake light might use two light bulbs. If one bulb fails, the brake light still operates using the other bulb. Redundancy significantly increases system reliability, and is often the only viable means of doing so. However, redundancy is difficult and expensive, and is therefore limited to critical parts of the system. Another design technique, physics of failure, relies on understanding the physical processes of stress, strength and failure at a very detailed level. Then the material or component can be re-designed to reduce the probability of failure. Another common design technique is component derating: Selecting components whose tolerance significantly exceeds the expected stress, as using a heavier gauge wire that exceeds the normal specification for the expected electrical current. Fault tree diagram. ... Fault tree diagram. ... In engineering, the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe, is called redundancy. ... All dimmers rely on heat conduction and convection to keep the electronic components cool. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...

Many tasks, techniques and analyses are specific to particular industries and applications. Commonly these include:

• Built-in test (BIT)
• Failure mode and effects analysis (FMEA)
• Reliability simulation modeling
• Thermal analysis
• Reliability Block Diagram analysis
• Fault tree analysis
• Sneak circuit analysis
• Accelerated Testing
• Reliability Growth analysis
• Weibull analysis
• Electromagnetic analysis
• Statistical interference

Results are presented during the system design reviews and logistics reviews. Reliability is just one requirement among many system requirements. Engineering trade studies are used to determine the optimum balance between reliability and other requirements and constraints. Failure Mode and Effects Analysis (FMEA) is a risk assessment technique for systematically identifying potential failures in a system or a process. ... Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. ... Safety engineering is used to assure that a life-critical system behaves as needed even when pieces fail. ... When two probability distributions overlap, statistical interference exists. ... In mathematics, the term optimization, or mathematical programming, refers to the study of problems in which one seeks to minimize or maximize a real function by systematically choosing the values of real or integer variables from within an allowed set. ...

Reliability testing

A Reliability Sequential Test Plan

The purpose of reliability testing is to discover potential problems with the design as early as possible and, ultimately, provide confidence that the system meets its reliability requirements. Example of a reliability sequential test plan. ... Example of a reliability sequential test plan. ...

Reliability testing may be performed at several levels. Complex systems may be tested at component, circuit board, unit, assembly, subsystem and system levels. (The test level nomenclature varies among applications.) For example, performing environmental stress screening tests at lower levels, such as piece parts or small assemblies, catches problems before they cause failures at higher levels. Testing proceeds during each level of integration through full-up system testing, developmental testing, and operational testing, thereby reducing program risk. System reliability is calculated at each test level. Reliability growth techniques and failure reporting, analysis and corrective active systems (FRACAS) are often employed to improve reliability as testing progresses. The drawbacks to such extensive testing are time and expense. Customers may choose to accept more risk by eliminating some or all lower levels of testing. For the Parker Brothers board game, see Risk (game) For other uses, see Risk (disambiguation). ...

It is not always feasible to test all system requirements. Some systems are prohibitively expensive to test; some failure modes may take years to observe; some complex interactions result in a huge number of possible test cases; and some tests require the use of limited test ranges or other resources. In such cases, different approaches to testing can be used, such as accelerated life testing, design of experiments, and simulations. Failure mode The Manner by whick a failure is observed; it generally describes the way the failure occurs and its impact on equipment operation. ... The first statistician to consider a methodology for the design of experiments was Sir Ronald A. Fisher. ... This article is about the general term. ...

The desired level of statistical confidence also plays an important role in reliability testing. Statistical confidence is increased by increasing either the test time or the number of items tested. Reliability test plans are designed to achieve the specified reliability at the specified confidence level with the minimum number of test units and test time. Different test plans result in different levels of risk to the producer and consumer. The desired reliability, statistical confidence, and risk levels for each side influence the ultimate test plan. Good test requirements ensure that the customer and developer agree in advance on how reliability requirements will be tested. In this diagram, the bars represent observation means and the red lines represent the confidence intervals surrounding them. ...

A key aspect of reliability testing is to define "failure". Although this may seem obvious, there are many situations where it is not clear whether a failure is really the fault of the system. Variations in test conditions, operator differences, weather, and unexpected situations create differences between the customer and the system developer. One strategy to address this issue is to use a scoring conference process. A scoring conference includes representatives from the customer, the developer, the test organization, the reliability organization, and sometimes independent observers. The scoring conference process is defined in the statement of work. Each test case is considered by the group and "scored" as a success or failure. This scoring is the official result used by the reliability engineer. Fail and Phail redirect here. ... For the geological process, see Weathering or Erosion. ...

As part of the requirements phase, the reliability engineer develops a test strategy with the customer. The test strategy makes trade-offs between the needs of the reliability organization, which wants as much data as possible, and constraints such as cost, schedule, and available resources. Test plans and procedures are developed for each reliability test, and results are documented in official reports.

Accelerated testing

The purpose of accelerated life testing in to induce field failure in the laboratory at a much faster rate by providing a harsher, but nonetheless representative, environment. In such a test the product is expected to fail in the lab just a it would have failed in the field - but in much less time. The main objective of an accelerated test is either of the following:

• To discover failure modes
• To predict the normal field life from the high stress lab life

Accelerated testing need planning and as following

• Define objective and scope of the test
• Collect required information about the product
• Identify the stress(es)
• Determine level of stress(es)
• Conduct the Accelerated test and analysis the accelerated data.

Common way to determine a life stress relationship are

• Arrhenius Model
• Eyring Model
• Inverse Power Law Model
• Temperature-Humidity Model
• Temperature Non-thermail Model

Software reliability

Software reliability is a special aspect of reliability engineering. System reliability, by definition, includes all parts of the system, including hardware, software, operators and procedures. Traditionally, reliability engineering focuses on critical hardware parts of the system. Since the widespread use of digital integrated circuit technology, software has become an increasingly critical part of most electronics and, hence, nearly all present day systems. There are significant differences, however, in how software and hardware behave. Most hardware unreliability is the result of a component or material failure that results in the system not performing its intended function. Repairing or replacing the hardware component restores the system to its original unfailed state. However, software does not fail in the same sense that hardware fails. Instead, software unreliability is the result of unanticipated results of software operations. Even relatively small software programs can have astronomically large combinations of inputs and states that are infeasible to exhaustively test. Restoring software to its original state only works until the same combination of inputs and states results in the same unintended result. Software reliability engineering must take this into account. For other uses, see Hardware (disambiguation). ... Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... This article is about the engineering discipline. ... Look up material in Wiktionary, the free dictionary. ... In combinatorial mathematics, a combination of members of a set is a subset. ...

Despite this difference in the source of failure between software and hardware — software doesn’t wear out — some in the software reliability engineering community believe statistical models used in hardware reliability are nevertheless useful as a measure of software reliability, describing what we experience with software: the longer you run software, the higher the probability you’ll eventually use it in an untested manner and find a latent defect that results in a failure (Shooman 1987), (Musa 2005), (Denney 2005).

As with hardware, software reliability depends on good requirements, design and implementation. Software reliability engineering relies heavily on a disciplined software engineering process to anticipate and design against unintended consequences. There is more overlap between software quality engineering and software reliability engineering than between hardware quality and reliability. A good software development plan is a key aspect of the software reliability program. The software development plan describes the design and coding standards, peer reviews, unit tests, configuration management, software metrics and software models to be used during software development. Software engineering (SE) is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ... This article or section does not cite any references or sources. ... In engineering and manufacturing, quality control or quality engineering is a set of measures taken to ensure that defective products or services are not produced, and that the design meets performance requirements. ... In computer programming, a unit test is a procedure used to validate that a particular module of source code is working properly. ... In information technology and telecommunications, the term configuration management or configuration control has the following meanings: The management of features and assurances through control of changes made to hardware is hot so is, software, firmware, documentation, test, test fixtures and test documentation of an automated information system, throughout the development... Wikipedia does not yet have an article with this exact name. ...

A common reliability metric is the number of software faults, usually expressed as faults per thousand lines of code. This metric, along with software execution time, is key to most software reliability models and estimates. The theory is that the software reliability increases as the number of faults (or fault density) goes down. Establishing a direct connection between fault density and mean-time-between-failure is difficult, however, because of the way software faults are distributed in the code, their severity, and the probability of the combination of inputs necessary to encounter the fault. Nevertheless, fault density serves as a useful indicator for the reliability engineer. Other software metrics, such as complexity, are also used.

Testing is even more important for software than hardware. Even the best software development process results in some software faults that are nearly undetectable until tested. As with hardware, software is tested at several levels, starting with individual units, through integration and full-up system testing. Unlike hardware, it is inadvisable to skip levels of software testing. During all phases of testing, software faults are discovered, corrected, and re-tested. Reliability estimates are updated based on the fault density and other metrics. At system level, mean-time-between-failure data is collected and used to estimate reliability. Unlike hardware, performing the exact same test on the exact same software configuration does not provide increased statistical confidence. Instead, software reliability uses different metrics such as test coverage.

Eventually, the software is integrated with the hardware in the top-level system, and software reliability is subsumed by system reliability. The Software Engineering Institute's Capability Maturity Model is a common means of assessing the overall software development process for reliability and quality purposes. The Capability Maturity Model (CMM), also known as the Software CMM (SW-CMM), was first described by Watts Humphrey in his book Managing the Software Process [1]. The CMM is a process model based on software best-practices effective in large-scale, multi-person projects. ...

Reliability operational assessment

After a system is produced, reliability engineering during the system operation phase monitors, assesses, and corrects deficiencies. Data collection and analysis are the primary tools used. When possible, system failures and corrective actions are reported to the reliability engineering organization. The data is constantly analyzed using statistical techniques, such as Weibull analysis and linear regression, to ensure the system reliability meets the specification. Reliability data and estimates are also key inputs for system logistics. Data collection is highly dependent on the nature of the system. Most large organizations have quality control groups that collect failure data on vehicles, equipment, and machinery. Consumer product failures are often tracked by the number of returns. For systems in dormant storage or on standby, it is necessary to establish a formal surveillance program to inspect and test random samples. Any changes to the system, such as field upgrades or recall repairs, require additional reliability testing to ensure the reliability of the modification. In probability theory and statistics, the Weibull distribution (named after Waloddi Weibull) is a continuous probability distribution with the probability density function where and is the shape parameter and is the scale parameter of the distribution. ... In statistics, linear regression is a regression method that models the relationship between a dependent variable Y, independent variables Xi, i = 1, ..., p, and a random term ε. The model can be written as Example of linear regression with one dependent and one independent variable. ... Look up Logistics in Wiktionary, the free dictionary. ... For the Jurassic 5 album, see Quality Control (album) In engineering and manufacturing, quality control and quality engineering are involved in developing systems to ensure products or services are designed and produced to meet or exceed customer requirements. ...

Reliability organizations

Systems of any significant complexity are developed by organizations of people, such as a commercial company or a government agency. The reliability engineering organization must be consistent with the company's organizational structure. For small, non-critical systems, reliability engineering may be informal. As complexity grows, the need arises for a formal reliability function. Because reliability is important to the customer, the customer may even specify certain aspects of the reliability organization. Alternative meaning: Organisation (band). ... The term company may refer to a separate legal entity, as in English law, or may simply refer to a business, as is the common use in the United States. ... // Pre-bureaucratic (entrepreneurial) structures lack standardization of tasks. ...

There are several common types of reliability organizations. The project manager or chief engineer may employ one or more reliability engineers directly. In larger organizations, there is usually a product assurance or specialty engineering organization, which may include reliability, maintainability, quality, safety, human factors, logistics, etc. In such case, the reliability engineer reports to the product assurance manager or specialty engineering manager. A project manager is the person who has the overall responsibility for the successful planning and execution of any project. ... Look up engineer in Wiktionary, the free dictionary. ... In telecommunication, the term maintainability has the following meanings: A characteristic of design and installation, expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time, when the maintenance is performed in accordance with prescribed procedures and resources. ... For the Talib Kweli album Quality (album) Quality can refer to a. ... For other uses, see Safety (disambiguation). ... Human factors is an umbrella term for several areas of research that include human performance, technology, design, and human-computer interaction. ... Look up Logistics in Wiktionary, the free dictionary. ...

In some cases, a company may wish to establish an independent reliability organization. This is desirable to ensure that the system reliability, which is often expensive and time consuming, is not unduly slighted due to budget and schedule pressures. In such cases, the reliability engineer works for the project on a day-to-day basis, but is actually employed and paid by a separate organization within the company.

Because reliability engineering is critical to early system design, it has become common for reliability engineers, however the organization is structured, to work as part of an integrated product team.

Certification

The American Society for Quality has a program to become a Certified Reliability Engineer, CRE. Certification is based on education, experience, and a certification test: periodic recertification is required. The body of knowledge for the test includes: reliability management, design evaluation, product safety, statistical tools, design and development, modeling, reliability testing, collecting and using data, etc. American Society for Quality (ASQ), formerly known as American Society for Quality Control (ASQC), is a non-profit professional society comprised of almost 100,000 members who work in various aspects of the quality field (e. ...

Reliability engineering education

Reliability engineers typically have an engineering degree, which can be in any field of engineering, from an accredited university or college program. Many engineering programs offer reliability courses, and some universities have entire reliability engineering programs. A reliability engineer may be registered as a Professional Engineer by the state, but this is not required by most employers. There are many professional conferences and industry training programs available for reliability engineers. Several professional organizations exist for reliability engineers, including the IEEE Reliability Society, the American Society for Quality (ASQ), and the Society of Reliability Engineers (SRE). Accreditation is a process by which a facilitys services and operations are examined by a third-party accrediting agency to determine if applicable standards are met. ... For the community in Florida, see University, Florida. ... For other uses, see College (disambiguation). ... Professional Engineer is the term for registered or licensed engineers in some countries, including the United States, and Canada who are permitted to offer their professional services directly to the public. ...

References

Not to be confused with the Institution of Electrical Engineers (IEE). ...

Texts

• Blanchard, Benjamin S. (1992), Logistics Engineering and Management (Fourth Ed.), Prentice-Hall, Inc., Englewood Cliffs, New Jersey.
• Ebeling, Charles E., (1997), An Introduction to Reliability and Maintainability Engineering, McGraw-Hill Companies, Inc., Boston.
• Denney, Richard (2005) Succeeding with Use Cases: Working Smart to Deliver Quality. Addison-Wesley Professional Publishing. ISBN . Discusses the use of software reliability engineering in use case driven software development.
• Kapur, K.C., and Lamberson, L.R., (1977), Reliability in Engineering Design, John Wiley & Sons, New York.
• Kececioglu, Dimitri, (1991) "Reliability Engineering Handbook", Prentice-Hall, Englewood Cliffs, New Jersey
• Leemis, Lawrence, (1995) Reliability: Probabilistic Models and Statistical Methods, 1995, Prentice-Hall. ISBN: 0-13-720517-1
• MacDiarmid, Preston; Morris, Seymour; et al., (1995), Reliability Toolkit: Commercial Practices Edition, Reliability Analysis Center and Rome Laboratory, Rome, New York.
• Musa, John (2005) Software Reliability Engineering: More Reliable Software Faster and Cheaper, 2nd. Edition, AuthorHouse. ISBN
• Neufelder, Ann Marie, (1993), Ensuring Software Reliability, Marcel Dekker, Inc., New York.
• O'Connor, Patrick D. T. (2002), Practical Reliability Engineering (Fourth Ed.), John Wiley & Sons, New York.
• Shooman, Martin, (1987), Software Engineering: Design, Reliability, and Management, McGraw-Hill, New York.
• Tobias, Trindade, (1995), Applied Reliability, Chapman & Hall/CRC, ISBN: 0-442-00469-9
• Springer Series in Reliability Engineering
• Nelson, Wayne B., (2004), Accelerated Testing - Statistical Models, Test Plans, and Data Analysis, John Wiley & Sons, New York, ISBN 0-471-69736-2

A use case is a technique used in software and systems engineering to capture the functional requirements of a system. ...

US standards

• MIL-STD-785, Reliability Program for Systems and Equipment Development and Production, U.S. Department of Defense.
• MIL-HDBK-217, Reliability Prediction of Electronic Equipment, U.S. Department of Defense.
• MIL-STD-2173, Reliability Centered Maintenance Requirements, U.S. Department of Defense.
• MIL-HDBK-338B, Electronic Reliability Design Handbook, U.S. Department of Defense.
• MIL-STD-1629A, PROCEDURES FOR PERFORMING A FAILURE MODE, EFFECTS AND CRlTlCALlTY ANALYSIS
• MIL-HDBK-781A, Reliability Test Methods, Plans, and Environments for Engineering Development, Qualification, and Production, U.S. Department of Defense.
• IEEE 1332, IEEE Standard Reliability Program for the Development and Production of Electronic Systems and Equipment, Institute of Electrical and Electronics Engineers.
• Federal Standard 1037C in support of MIL-STD-188

Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ... MIL-STD-188 is a series of U.S. military standards relating to telecommunications. ...

UK standards

In the UK, there are more up to date standards maintained under the sponsorship of UK MOD as Defence Standards.

The relevant Standards include:

DEF STAN 00-40 Reliability and Maintainability (R&M)

• PART 1: Issue 5: Management Responsibilities and Requirements for Programmes and Plans
• PART 4: (ARMP-4)Issue 2: Guidance for Writing NATO R&M Requirements Documents
• PART 6: Issue 1: IN-SERVICE R & M
• PART 7 (ARMP-7) Issue 1: NATO R&M Terminology Applicable to ARMP’s

DEF STAN 00-41 : Issue 3: RELIABILITY AND MAINTAINABILITY MOD GUIDE TO PRACTICES AND PROCEDURES

DEF STAN 00-42 RELIABILITY AND MAINTAINABILITY ASSURANCE GUIDES

• PART 1: Issue 1: ONE-SHOT DEVICES/SYSTEMS
• PART 2: Issue 1: SOFTWARE
• PART 3: Issue 2: R&M CASE
• PART 4: Issue 1: Testability
• PART 5: Issue 1: IN-SERVICE RELIABILITY DEMONSTRATIONS

DEF STAN 00-43 RELIABILITY AND MAINTAINABILITY ASSURANCE ACTIVITY

• PART 2: Issue 1: IN-SERVICE MAINTAINABILITY DEMONSTRATIONS

DEF STAN 00-44 RELIABILITY AND MAINTAINABILITY DATA COLLECTION AND CLASSIFICATION

• PART 1: Issue 2: MAINTENANCE DATA & DEFECT REPORTING IN THE ROYAL NAVY, THE ARMY AND THE ROYAL AIR FORCE
• PART 2: Issue 1: DATA CLASSIFICATION AND INCIDENT SENTENCING - GENERAL
• PART 3: Issue 1: INCIDENT SENTENCING - SEA
• PART 4: Issue 1: INCIDENT SENTENCING - LAND

DEF STAN 00-45 Issue 1: RELIABILITY CENTERED MAINTENANCE

DEF STAN 00-49 Issue 1: RELIABILITY AND MAINTAINABILITY MOD GUIDE TO TERMINOLOGY DEFINITIONS

These can be obtained from DSTAN

There are also many commercial standards, produced by many organistions including the SAE, MSG, ARP, and IEE.

See also

Engineering Portal

• Logistic engineering
• Systems engineering
• Safety engineering
• Quality engineering
• Security engineering
• Software engineering
• Reliability
• Reliability theory
• Reliability theory of aging and longevity
• Redundancy (total quality management)
• Statistics
• Performance engineering
• Professional engineer
• Failure rate
• Human reliability
• Burn in
• Product qualification
• Reliable system design
• Reliability modelling

Image File history File links Portal. ... Logistic Engineering deals with the science of Logistics. ... Systems engineering techniques are used in complex projects: from spacecrafts to chip design, from robotics to creating large software products to building bridges, Systems engineering uses a host of tools that include modeling & simulation, requirements analysis, and scheduling to manage complexity Systems Engineering (SE) is an interdisciplinary approach and means... Safety engineering is an applied science strongly related to systems engineering and the subset System Safety Engineering. ... In engineering and manufacturing, quality control or quality engineering is a set of measures taken to ensure that defective products or services are not produced, and that the design meets performance requirements. ... Security engineering is the field of engineering dealing with the security and integrity of real-world systems. ... Software engineering (SE) is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ... Reliability concerns quality or consistency. ... Reliability theory developed apart from the mainstream of probability and statistics, and was used originally as a tool to help nineteenth century maritime insurance and life insurance companies compute profitable rates to charge their customers. ... Reliability Theory of Aging and Longevity is a scientific approach aimed to gain theoretical insights into mechanisms of biological aging and species survival patterns by applying a general theory of systems failure, known as reliability theory. ... In total quality management, TQM, redundancy in quality or redundant quality means quality which exceeds the required quality level. ... This article is about the field of statistics. ... Performance engineering is the set of roles, skills, activities, practices, tools, and deliverables applied at every phase of the Systems Development Lifecycle which ensures that a solution will be designed and implemented to meet the non-functional requirements defined for the solution. ... Professional Engineer is the term for registered or licensed engineers in some countries, including the United States, and Canada who are permitted to offer their professional services directly to the public. ... Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. ... Human reliability is related to the field of human factors engineering, and refers to the reliability of humans in fields such as manufacturing, transportation, the military, or medicine. ... Burn in is that process by which components of a system are exercised prior to being placed in service (and often, prior to the system being completely assembled from those components). ... Product certification or product qualification is the process of certifying that a certain product has passed a set of quality tests. ... Reliable system design is the design of systems with high levels of reliability and availability. ... In engineering, reliability modelling is the process of predicting or understanding the reliability of a component or system. ...

External links

• American Society for Quality
• Carnegie Mellon Software Engineering Institute
• IEEE Reliability Society
• NASA Hardware and Software Reliability report
• NIST/SEMATECH, "Engineering Statistics Handbook", [1]
• Reliability Information Analysis Center
• Safety and Reliability Society
• Society of Reliability Engineers
• University of Maryland Reliability Engineering Program
• Models and methods regarding reliability analysis
• UK Defence Standardization Organisation's Home on the Web
• Center for Risk and Reliability at University of Maryland, College Park
• On-line Reliability Engineering Resources for the Reliability Professional
• Reliability Basics (various analysis overviews)
• Online Reliability calculator
• Reliability Engineer's Toolbox - Automated tools and electronic information for reliability engineering activities.