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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%. 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 amont 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 To Repair (MTTR), or : A = \frac = \frac If we define the status function X(t) as : X ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Availability
High availability (HA) is a characteristic of a system which aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. Modernization has resulted in an increased reliance on these systems. For example, hospitals and data centers require high availability of their systems to perform routine daily activities. Availability refers to the ability of the user community to obtain a service or good, access the system, whether to submit new work, update or alter existing work, or collect the results of previous work. If a user cannot access the system, it is – from the user's point of view – ''unavailable''. Generally, the term ''downtime'' is used to refer to periods when a system is unavailable. Principles There are three principles of systems design in reliability engineering which can help achieve high availability. # Elimination of single points of failure. This means adding or building redundancy into the system so th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Generating Availability Data System
The Generating Availability Data System (GADS) is a database produced by the North American Electric Reliability Corporation (NERC). It includes annual summary reports comprising the statistics for power stations in the United States and Canada. GADS is the main source of power station outage data in North America. This reporting system, initiated by the electric utility industry in 1982, expands and extends the data collection procedures begun by the industry in 1963. NERC GADS is recognized today as a valuable source of reliability, availability, and maintainability (RAM) information.North American Electric Reliability Corporation's (NERC) Generating Availability Data System (GADS) Data Reporting Instructions (DRI). This information, collected for both total unit and major equipment groups, is used by analysts industry-wide in numerous applications. GADS maintains complete operating histories on more than 5,800 generating units representing 71% of the installed generating capaci ... [...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 describes the ability of a system or component to function under stated conditions for a specified period of time. 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 at time t, which is denoted R(t). This probability is estimated from detailed (physics of failure) analysis, previous data sets or through reliability testing and reliability modelling. Availability, testability, maintainability and maintenance are often defined as a part of "reliability engineering" in reliability programs. Reliability often plays the key role in the cost-effectiveness of systems. Reliability engineering deals with the prediction, prevention and mana ... [...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 describes the ability of a system or component to function under stated conditions for a specified period of time. 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 at time t, which is denoted R(t). This probability is estimated from detailed (physics of failure) analysis, previous data sets or through reliability testing and reliability modelling. Availability, testability, maintainability and maintenance are often defined as a part of "reliability engineering" in reliability programs. Reliability often plays the key role in the cost-effectiveness of systems. Reliability engineering deals with the prediction, prevention and mana ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RAMS
In engineering, RAMS (reliability, availability, maintainability and safety) Norwegian University of Science and Technology is used to characterize a product or system: * – as ability to perform a specific function and may be given as design reliability or operational reliability. * , – as ability to keep a functioning state in the given environment. * |
Mean Time Between Failures
Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system. The term is used for repairable systems while mean time to failure (MTTF) denotes the expected time to failure for a non-repairable system. The definition of MTBF depends on the definition of what is considered a failure. For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair. Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures under this definition. In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure. The higher the MTBF, the longer a system ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mean Time Between Failures
Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system. The term is used for repairable systems while mean time to failure (MTTF) denotes the expected time to failure for a non-repairable system. The definition of MTBF depends on the definition of what is considered a failure. For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair. Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures under this definition. In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure. The higher the MTBF, the longer a system ... [...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 through three mechanisms. * Reduce labor-intensive diagnostic evaluation * Eliminate diagnostic testing down-time * Provide notification to management for degraded operation This is a prerequisite for Condition-based maintenance. Active redundancy can be integrated with fault reporting to reduce down time to a few minutes per year. * Passive redundancy * Active redundancy 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. This 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 th ... [...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 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 inspections. As description im ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mean Time To Repair
Mean time to repair (MTTR) is a basic measure of the maintainability of repairable items. It represents the average time required to repair a failed component or device. Expressed mathematically, it is the total corrective maintenance time for failures divided by the total number of corrective maintenance actions for failures during a given period of time. It generally does not include lead time for parts not readily available or other Administrative or Logistic Downtime (ALDT). In fault-tolerant design, MTTR is usually considered to also include the time the fault is latent (the time from when the failure occurs until it is detected). If a latent fault goes undetected until an independent failure occurs, the system may not be able to recover. MTTR is often part of a maintenance contract, where a system whose MTTR is 24 hours is generally more valuable than for one of 7 days if mean time between failures is equal, because its Operational Availability is higher. However, in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reliability Block Diagram
A reliability block diagram (RBD) is a diagrammatic method for showing how component reliability contributes to the success or failure of a redundant. RBD is also known as a dependence diagram (DD). An RBD is drawn as a series of blocks connected in parallel or series configuration. Parallel blocks indicate redundant subsystems or components that contribute to a lower failure rate. Each block represents a component of the system with a failure rate. RBDs will indicate the type of redundancy in the parallel path. For example, a group of parallel blocks could require two out of three components to succeed for the system to succeed. By contrast, any failure along a series path causes the entire series path to fail. An RBD may be drawn using switches in place of blocks, where a closed switch represents a working component and an open switch represents a failed component. If a path may be found through the network of switches from beginning to end, the system still works. An RB ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subsystem
A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purpose and expressed in its functioning. Systems are the subjects of study of systems theory and other systems sciences. Systems have several common properties and characteristics, including structure, function(s), behavior and interconnectivity. Etymology The term ''system'' comes from the Latin word ''systēma'', in turn from Greek ''systēma'': "whole concept made of several parts or members, system", literary "composition"."σύστημα" Henry George Liddell, Robert Scott, '' |
