Sci-Tech

๐Ÿ”Ž Reliability – definition and explanation

introduction

A system is reliable if the probability of fulfilling its mission over a certain period of time corresponds to the specified in the specifications.

Reliability and quality

The Technical Union of Electricity (electricity is a physical phenomenon due to the different electrical charges of matter manifested by an energy. Electricity also refers to the branch of physics that studies electrical phenomena …) (UTE) on recommendation ( Industries do not function properly without standards that guarantee interoperability, bodies that have been issued for recommendations which, if followed, become norms or standards. A …) of the Electrotechnical Commission (Etymologically, electrical engineering means the study of technical applications of electricity In reality, electrical engineering groups disciplines that deal with …). Internationally she proposed the definition (A definition is a discourse that says what a what or what a noun means. Hence the separation between real definitions and nominal definitions.) Reliability (A system is reliable if the probability of reading its Mission over a certain period of time corresponds to that given in the specifications.) Is the ability of a device to perform a required function under certain conditions for a certain period of time (time is one of human beings to understand changes in the world.) Data (In In information technology (IT), data is an elementary description of a thing, a business transaction, an event, etc.).

Reliability is the probability (The probability (from the Latin probabilitas) is an evaluation of the probable nature of an event. In mathematics, the study of probabilities is …) not to have an error in the moment (the moment) denotes the smallest component of the Time. The point in time is not a time interval. It cannot therefore be regarded as a duration.) T.
Between 0 and 1 (or 0 and 100%), R is given for reliability (= reliability in English).

Reliability (function of time) should not be confused with control (The word control can have several meanings. It can be used as a synonym for testing, verification and control.) Of quality (static function).

For example, we test integrated circuits when they leave the line (the word string can have several meanings ๐Ÿ™‚ of production, and we see that 3% of them do not work or are wrong: we can say that the “quality” โ€of this one Chain (their production efficiency) are 97% (3% defects).

Once these circuits are put into a system, we can see that their Mean-Time To Failure (MTTF) is 100,000 hours (the hour is a unit of measure). Their failure rate (number of failures per unit of time) is therefore. This is noted and expressed in h – 1.

If it is further noted that these errors are unpredictable and occur in a completely random way, the reliability of these circuits is given as a function of time (in information technology, a date is an elementary description, often encoded). a thing, a transaction, a …) through the function:

(Expression only valid if the failure rate is constant).

We can see whatever MTTF:
– For t = 0 the reliability is always 1
– For the tendency towards infinity (the word “infinite” (-e, -s; from the Latin finitus “limited”) is an adjective that is used to qualify …), the reliability tends towards 0.

Note: The decrease in the reliability value over time should not be confused with the phenomenon of wear.

Regardless of the duration of good functioning already achieved (The whole, understood as a set of that which exists, is often interpreted as the world or the universe.) Immediately the probability of a circuit failure between time t and The time ( t + dt) remains constant and corresponds to dt / MTTF (essential property of the exponential distribution).

Forecast reliability

The predictive reliability makes it possible to estimate the a priori reliability of a component, a device or a system. To do this, we model through mathematical probability models (mathematics is a field of abstract knowledge that is built up using logical considerations of concepts such as numbers, numbers, structures and transformations …) and of aging (the term aging describes one or more functional modifications, which gradually reduce the suitability of an object, information …) Physics (physics (from the Greek ฯ†ฯ…ฯƒฮนฯ‚, nature) is etymologically the “natural science” in general …) the behavior of each elementary component. These models were created through feedback from operational experience and through the execution of tests designed to enable the reliability behavior to be modeled. In the case of electronics, there are several collections of predictive models for elementary components such as resistors, capacitors, integrated circuits, etc. The most commonly used electronic repositories for predicting reliability are:

The MIL-HDBK-217F: Standard (A standard from the Latin norm (“Set Square, Rule”) denotes a state that is usually widespread or average and is considered a rule. This …) American military, which is used for The estimate is the reliability of the equipment. The RDF2000: Reliability Compendium is based on feedback on France Telecom’s experience (In France, see http://www.arcep.fr/index.php?id=interactivenumeros on the ARCEP website (http: //) www.arcep.fr ).). Today this collection was converted into a standard called UTE C 80-810. FIDES: Predictive Reliability Guide, based on the above collections, based on feedback from a consortium of French manufacturers. Today this collection was converted into a standard called UTE C 80-811.

The various parameters that affect the reliability of a component are called factors and are represented by the Greek letter pi. for example one will quote the quality factor: ฮ q.

For non-electronic components there are also manuals in which certain elementary components (screws, valves, seals, etc.) can be assessed. We differentiate, for example:

The OREDA Compendium (Offshore Reliability Data): A reliability compendium based on feedback from companies operating offshore platforms. The data mainly refer to electromechanical industrial equipment related to oil production: compressors, heat exchangers, generators, various valves, boilers, pumps, evaporators, etc. The EIREDA collection (European Industry Reliability Database): reliability collection based on the experience of European companies , mainly in the chemical sector (chemistry is a natural science divided into different disciplines such as physics and biology, with which it shares research areas …), in relation to electromechanical devices that consume energy (energy in common sense means everything which makes it possible to carry out work, produce heat, light, generate movement.) Electric: fans, evaporators, heat exchangers, pumps, compressors. The NPRD-95 Compendium (Non Electronic Parts Reliability Data): A reliability compendium created from feedback on the experience of large American organizations such as NASA (National Aeronautics and Space Administration). space โ€) better known under the abbreviation NASA, is the agency …) and the US Navy. The data refer to mechanical and electromechanical components that are mainly used in military equipment.

The results of the calculations obtained on the basis of these compendia make it possible to estimate the failure rate of electronic systems or other basic data that are essential for SDF analyzes (fault trees, FMEA, etc.).

In France, under the leadership of Jean-Claude Ligeron, reliability has increased, particularly in the field of mechanical reliability (in common parlance, mechanics is the domain of machines, engines, vehicles, components (gears), pulleys, belts, crankshafts, shafts. ..).

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