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Availability
In reliability engineering, the term availability has the following meanings: * The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, ''i.e.'' a random, time. * The probability that an item will operate satisfactorily at a given point in time when used under stated conditions in an ideal support environment. Normally high availability systems might be specified as 99.98%, 99.999% or 99.9996%. The converse, unavailability, is 1 minus the availability. Representation 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 (that results in the "total amount of time" ''C'' of the observation window) : A = \frac = \frac Another equation for availability (''A'') is a ratio of the Mean Time To Failure (MTTF) and Mean Time Between Failure (MTBF), or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Availability
High availability (HA) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. There is now more dependence on these systems as a result of modernization. For example, to carry out their regular daily tasks, hospitals and data centers need their systems to be highly available. Availability refers to the ability of the user to access a service or system, whether to submit new work, update or modify existing work, or retrieve the results of previous work. If a user cannot access the system, it is considered ''unavailable from the user's perspective''. The term '' downtime'' is generally used to refer to describe periods when a system is unavailable. Resilience High availability is a property of network resilience, the ability to "provide and maintain an acceptable level of service in the face of faults and challenges to normal operation." Threats and challenges for services can range from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reliability Engineering
Reliability engineering is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. Reliability is defined as the probability that a product, system, or service will perform its intended function adequately for a specified period of time, OR will operate in a defined environment without failure. Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time. The ''reliability function'' is theoretically defined as the probability of success. In practice, it is calculated using different techniques, and its value ranges between 0 and 1, where 0 indicates no probability of success while 1 indicates definite success. This probability is estimated from detailed (physics of failure) analysis, previous data sets, or through reliability testing and reliability modeling. Availability, testability, maintainability, and maintenance ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Availability Factor
The availability factor of a power plant is the duration it achieves production of electricity divided by the duration that it was planned to produce electricity. In the field of reliability engineering, ''availability factor'' is known as operational availability, A_o. The capacity factor of a plant includes numerous other factors which determine the durations the plant is planned to produce electricity. A solar photovoltaic plant is not planned to operate in the dark of a night, hence unplanned maintenance occurring whilst the sun is set does not impact the availability factor. Periods of generation where only partial generation of planned capacity occurs may or may not be deducted from the availability factor. An example of partial generation is a power plant with four installed turbines planned to be concurrently operational, but one of those turbines subsequently requires unplanned maintenance. Where deductions are made the metric is titled ''equivalent availability factor' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of System Quality Attributes
Within systems engineering, quality attributes are realized non-functional requirements used to evaluate the performance of a system. These are sometimes named architecture characteristics, or "ilities" after the suffix many of the words share. They are usually architecturally significant requirements that require architects' attention. In software architecture, these attributed are known as "architectural characteristic" or non-functional requirements. Note that it's software architects' responsibility to match these attributes with business requirements and user requirements. Note that synchronous communication between software architectural components, entangles them and they must share the same architectural characteristics. Quality attributes Notable quality attributes include: * accessibility * accountability * accuracy * adaptability * administrability * affordability * agility * auditability * autonomy * availability * compatibility * composability * con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spurious Trip Level
Spurious trip level (STL) is defined as a discrete level for specifying the spurious trip requirements of safety functions to be allocated to safety systems. An STL of 1 means that this safety function has the highest level of spurious trips. The higher the STL level the lower the number of spurious trips caused by the safety system. There is no limit to the number of spurious trip levels. Safety functions and systems are installed to protect people, the environment and for asset protection. A safety function should only activate when a dangerous situation occurs. A safety function that activates without the presence of a dangerous situation (e.g., due to an internal failure) causes economic loss. The spurious trip level concept represents the probability that safety function causes a spurious (unscheduled) trip. The STL is a metric that is used to specify the performance level of a safety function in terms of the spurious trips it potentially causes. Typical safety systems that ben ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fault Tree Analysis
Fault tree analysis (FTA) is a type of failure analysis in which an undesired state of a system is examined. This analysis method is mainly used in safety engineering and reliability engineering to understand how systems can fail, to identify the best ways to reduce risk and to determine (or get a feeling for) event rates of a safety accident or a particular system level (functional) failure. FTA is used in the aerospace, nuclear power, chemical and process, pharmaceutical, petrochemical and other high-hazard industries; but is also used in fields as diverse as risk factor identification relating to social service system failure. FTA is also used in software engineering for debugging purposes and is closely related to cause-elimination technique used to detect bugs. In aerospace, the more general term "system failure condition" is used for the "undesired state" / top event of the fault tree. These conditions are classified by the severity of their effects. The most severe conditi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spare Part
A spare part, spare, service part, repair part, or replacement part, is an interchangeable part that is kept in an inventory and used for the repair or Refurbishment (electronics), refurbishment of defective equipment/units. Spare parts are an important feature of logistics engineering and supply chain management, often comprising dedicated spare parts management systems. Spare parts are an outgrowth of the industrial development of interchangeable parts and mass production. In an industrial environment, spare parts are described in several manner to distinguish key features of various spare parts. The following describes spare part types and their typically functionality. 1. Capital parts are spare parts which, although acknowledged to have a long life or a small chance of failure, would cause a long shutdown of equipment because it would take a long time to get a replacement for them. Capital parts are typically repaired or replaced during planned overhauls/scheduled inspect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Downtime
In computing and telecommunications, downtime (also (system) outage or (system) drought colloquially) is a period when a system is unavailable. The unavailability is the proportion of a time-span that a system is unavailable or offline. This is usually a result of the system failing to function because of an unplanned event, or because of routine maintenance (a planned event). The terms are commonly applied to networks and servers. The common reasons for unplanned outages are system failures (such as a crash) or communications failures (commonly known as network outage or network drought colloquially). For outages due to issues with general computer systems, the term computer outage (also IT outage or IT drought) can be used. The term is also commonly applied in industrial environments in relation to failures in industrial production equipment. Some facilities measure the downtime incurred during a work shift, or during a 12- or 24-hour period. Another common practice is to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RAMS
In engineering, reliability, availability, maintainability and safety (RAMS) Norwegian University of Science and Technology is used to characterize a product or system: * Reliability: Ability to perform a specific function and may be given as design reliability or operational reliability * : Ability to keep a functioning state in the given environment * : Ability to be timely and easily ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fault Reporting
Fault reporting is a maintenance concept that increases operational availability and that reduces operating cost by three mechanisms: * Reduce labor-intensive diagnostic evaluation * Eliminate diagnostic testing down-time * Provide notification to management for degraded operation That is a prerequisite for condition-based maintenance. Active redundancy can be integrated with fault reporting to reduce the down time to a few minutes per year. History Formal maintenance philosophies are required by organizations whose primary responsibility is to ensure systems are ready when expected, such as space agencies and military. Labor-intensive planned maintenance began during the rise of the Industrial Revolution and depends upon periodic diagnostic evaluation based upon calendar dates, distance, or use. The intent is to accomplish diagnostic evaluations that indicate when maintenance is required to prevent inconvenience and safety issues that will occur when critical equipment fai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
