1、 EIA STANDARD Weibull Analysis EIA 61649 (IEC 61649:2008 Ed.2.0, IDT) May 2017 EIA 61649 ANSI/EIA 61649-2017 Approved: May 11, 2017 NOTICE EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers,
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5、l (IDT) with the International Standard IEC Publication 61649:2008: Weibull Analysis. This document is the EIA Standard EIA 61649 Edition 2.0: Weibull Analysis. The text, figures and tables of IEC 61649:2008 are used in this Standard with the consent of the IEC and the American National Standards In
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15、se of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that
16、 some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 61649 has been prepared by IEC technical committee 56: Dependability. This second edition cancels and replace
17、s the first edition, published in 1997, and constitutes a technical revision. The main changes with respect to the previous edition are as follows: the title has been shortened and simplified to read “Weibull analysis”; provision of methods for both analytical and graphical solutions have been added
18、. The text of this standard is based on the following documents: FDIS Report on voting 56/1269/FDIS 56/1281/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the
19、 ISO/IEC Directives, Part 2. EIA 61649 Page 2 The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under “http:/webstore.iec.ch“ in the data related to the specific publication. At this date, the publica
20、tion will be reconfirmed, withdrawn, replaced by a revised edition, or amended. EIA 61649 Page 3 INTRODUCTION The Weibull distribution is used to model data regardless of whether the failure rate is increasing, decreasing or constant. The Weibull distribution is flexible and adaptable to a wide rang
21、e of data. The time to failure, cycles to failure, mileage to failure, mechanical stress or similar continuous parameters need to be recorded for all items. A life distribution can be modelled even if not all the items have failed. Guidance is given on how to perform an analysis using a spreadsheet
22、program. Guidance is also given on how to analyse different failure modes separately and identify a possible weak population. Using the three-parameter Weibull distribution can give information on time to first failure or minimum endurance in the sample. EIA 61649 Page 4 WEIBULL ANALYSIS 1 Scope Thi
23、s International Standard provides methods for analysing data from a Weibull distribution using continuous parameters such as time to failure, cycles to failure, mechanical stress, etc. This standard is applicable whenever data on strength parameters, e.g. times to failure, cycles, stress, etc. are a
24、vailable for a random sample of items operating under test conditions or in-service, for the purpose of estimating measures of reliability performance of the population from which these items were drawn. This standard is applicable when the data being analysed are independently, identically distribu
25、ted. This should either be tested or assumed to be true (see IEC 60300-3-5). In this standard, numerical methods and graphical methods are described to plot data, to make a goodness-of-fit test, to estimate the parameters of the two- or three-parameter Weibull distribution and to plot confidence lim
26、its. Guidance is given on how to interpret the plot in terms of risk as a function of time, failure modes and possible weak population and time to first failure or minimum endurance. 2 Normative references The following referenced documents are indispensable for the application of this document. For
27、 dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-191:1990, International Electrotechnical Vocabulary Part 191: Dependability and quality of service IEC 60300-3-5:2001, Dependability
28、management Part 3-5: Application guide Reliability test conditions and statistical test principles IEC 61810-2, Electromechanical elementary relays Part 2: Reliability ISO 2854:1976, Statistical interpretation of data Techniques of estimations and tests relating to means and variances ISO 3534-1:200
29、6, Statistics Vocabulary and symbols Part 1: General statistical terms and terms in probability 3 Terms, definitions, abbreviations and symbols For the purposes of this document, the definitions, abbreviations and symbols given in IEC 60050-191 and ISO 3534-1 apply, together with the following. 3.1
30、Terms and definitions 3.1.1 censoring terminating a test after either a given duration or a given number of failures NOTE A test terminated when there are still unfailed items may be called a “censored test“, and test time data from such tests may be referred to as “censored data”. EIA 61649 Page 5
31、3.1.2 suspended item item upon which testing has been curtailed without relevant failure NOTE 1 The item may not have failed, or it may have failed in a mode other than that under investigation. NOTE 2 An “early suspension” is one that was suspended before the first failure. A “late suspension” is s
32、uspended after the last failure. 3.1.3 life test test conducted to estimate or verify the durability of a product NOTE The end of the useful life will often be defined as the time when a certain percentage of the items have failed for non-repairable items and as the time when the failure intensity h
33、as increased to a specified level for repairable items. 3.1.4 non-repairable item item that cannot, under given conditions, after a failure, be returned to a state in which it can perform as required NOTE The given conditions may be technical, economic, ecological and/or others. 3.1.5 operating time
34、 time interval for which the item is in an operating state NOTE ”Operating time” is generic, and should be expressed in units appropriate to the item concerned, e.g. calendar time, operating cycles, distance run, etc. and the units should always be clearly stated. 3.1.6 relevant failure failure that
35、 should be included in interpreting test or operational results or in calculating the value of a reliability performance measure NOTE The criteria for inclusion should be stated. 3.1.7 reliability test experiment carried out in order to measure, quantify or classify a reliability measure or property
36、 of an item NOTE 1 Reliability testing is different from environmental testing where the aim is to prove that the items under test can survive extreme conditions of storage, transportation and use. NOTE 2 Reliability tests may include environmental testing. 3.1.8 repairable item item that can, under
37、 given conditions, after a failure, be returned to a state in which it can perform as required NOTE The given conditions may be technical, economic, ecological and/or others. 3.1.9 time to failure operating time accumulated from the first use, or from restoration, until failure NOTE In applications
38、where the time in storage or on standby is significantly greater than “operating time”, the time to failure may be based on the time in the specified service. EIA 61649 Page 6 3.1.10 time between failures time duration between consecutive failures NOTE 1 The time between failures includes the up tim
39、e and the down time. NOTE 2 In applications where the time in storage or on standby is significantly greater than operating time, the time to failure may be based on the time in the specified service. 3.1.11 B life L percentiles age at which a given percentage of items have failed NOTE “B10“ life is
40、 the age at which 10 % of items (e.g. bearings) have failed. Sometimes it is denoted by the L (life) value. B lives may be read directly from the Weibull plot or determined more accurately from the Weibull equation. The age at which 50 % of the items fail, the B50life, is the median time to failure.
41、 3.2 Abbreviations ASIC application specific integrated circuit BGA ball grid array CDF cumulative distribution function PDF probability density function MLE maximum likelihood estimation MRR median rank regression MTTF mean time to failure 3.3 Symbols t time variable Weibull characteristic life or
42、scale parameter Weibull shape parameter t0 starting point or origin of the distribution, failure free time r2coefficient of determination f(t) probability density function F(t) cumulative distribution function h(t) hazard function (t) instantaneous failure rate H(t) cumulative hazard function F1numb
43、er of failures with failure mode 1 F2number of failures with failure mode 2 F3number of failures with failure mode 3 EIA 61649 Page 7 4 Application of the techniques Table 1 shows the circumstances in which particular aspects of this standard are applicable. It shows the three main methods for estim
44、ating parameters from the Weibull distribution, namely graphical, computational and WeiBayes, and indicates the type of data requirements for each of these three methods. Table 1 Guidance for using IEC 61649 Method/ Kinds of data Graphical methods Computational methods WeiBayes Interval censored NC
45、Multiple censored NC Singly censored Zero failures NC NC Small sample (20) NC Large sample NC Curved data NC NC Complete data NOTE NC means not covered in this standard. 5 The Weibull distribution 5.1 The two-parameter Weibull distribution The two-parameter Weibull distribution is by far the most wi
46、dely used distribution for life data analysis. The Weibull probability density function (PDF) is shown in Equation (1): 1f()ttte (1) where t is the time, expressed as a variable; is the characteristic life or scale parameter; is the shape parameter. The Weibull cumulative distribution function (CDF)
47、 has an explicit equation as shown in Equation (2): -(t/ )F( ) 1 - et (2)The two parameters are , the characteristic life, and , the shape parameter. The shape parameter indicates the rate of change of the instantaneous failure rate with time. Examples include: infant mortality, random or wear-out.
48、It determines which member of the Weibull family of distributions is most appropriate. Different members have widely different shaped PDFs (see Figure 1). The Weibull distribution fits a broad range of life data compared with other distributions. The variable t is generic and can have various measur
49、es such as time, distance, number of cycles or mechanical stress applications. EIA 61649 Page 8 Datum in time = 3,44 = 1 = 0,5 3,5 0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 f(t) 3,0 2,5 2,0 1,5 1,0 0,5 0 IEC 1321/08 Figure 1 The PDF shapes of the Weibull family for = 1,0 From Figure 1, the PDF shape for = 3,44 (indicated) looks like the normal distribution: it is a fair approximation, except for the tails of the distribution. The instantaneous failure rate (t) (or h(t), the hazard function) of
