EN 61810-2:2017

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Osnovni elektromehanski releji - 2. del: ZanesljivostElektromechanische Elementarrelais - Teil 2: Funktionsfähigkeit (Zuverlässigkeit)Relais électromécaniques élémentaires - Partie 2: FiabilitéElectromechanical elementary relays - Part 2: Reliability29.120.70RelejiRelaysICS:Ta slovenski standard je istoveten z:EN 61810-2:2017SIST EN 61810-2:2018en01-januar-2018SIST EN 61810-2:2018SLOVENSKI
STANDARDSIST EN 61810-2:20111DGRPHãþD

EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 61810-2
October 2017 ICS 29.120.70
Supersedes
EN 61810-2:2011
English Version
Electromechanical elementary relays - Part 2: Reliability (IEC 61810-2:2017)
Relais électromécaniques élémentaires - Partie 2: Fiabilité (IEC 61810-2:2017)
Elektromechanische Elementarrelais -
Teil 2: Funktionsfähigkeit (Zuverlässigkeit) (IEC 61810-2:2017) This European Standard was approved by CENELEC on 2017-07-04. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17,
B-1000 Brussels © 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 61810-2:2017 E SIST EN 61810-2:2018

The following dates are fixed: • latest date by which the document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2018-04-06 • latest date by which the national standards conflicting with the document have to be withdrawn (dow) 2020-10-06
This document supersedes EN 61810-2:2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice The text of the International Standard IEC 61810-2:2017 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 61810-2-1 NOTE Harmonized as EN 61810-2-1. IEC 61810-3 NOTE Harmonized as EN 61810-3. IEC 62061 NOTE Harmonized as EN 62061. ISO 13849-1:2015 NOTE Harmonized as EN ISO 13849-1:2015 (not modified). SIST EN 61810-2:2018

(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
NOTE 1
Where an International Publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
NOTE 2
Up-to-date information on the latest versions of the European Standards listed in this annex is available here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 61649 2008
Weibull analysis EN 61649 2008
IEC 61810-1 2015
Electromechanical elementary relays -
Part 1: General and safety requirements EN 61810-1 2015
IEC 61810-2 Edition 3.0 2017-05 INTERNATIONAL STANDARD NORME INTERNATIONALE Electromechanical elementary relays –
Part 2: Reliability
Relais électromécaniques élémentaires –
Partie 2: Fiabilité
INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE
ICS 29.120.70
ISBN 978-2-8322-4388-6
– 2 – IEC 61810-2:2017 © IEC 2017 CONTENTS FOREWORD . 4 INTRODUCTION . 6 1 Scope . 7 2 Normative references . 7 3 Terms and definitions . 7 3.21 Terms and definitions related to tests . 10 4 General considerations . 10 5 Test conditions . 11 5.1 Sample items . 11 5.2 Environmental conditions . 12 5.3 Operating conditions . 12 5.4 Test equipment . 13 6 Failure criteria . 13 7 Output data . 13 8 Analysis of output data . 13 9 Presentation of reliability measures . 13 Annex A (normative)
Data analysis . 15 A.1 General . 15 A.2 Abbreviations . 15 A.3 Symbols and definitions . 15 A.4 Weibull distribution . 16 A.5 Procedure . 17 A.5.1 Graphical methods . 17 A.5.2 Numerical methods . 22 A.5.3 Confidence Intervals . 23 A.5.4 WeiBayes Approach . 25 Annex B (informative)
Example of data analysis . 28 B.1 Graphical methods case study (cumulative hazard plot) . 28 B.1.1 General . 28 B.1.2 Procedure of cumulative hazard plot . 28 B.1.3 Example applied to life test data . 30 B.2 Numerical methods case study (Weibull probability) . 33 B.2.1 General . 33 B.2.2 Distribution parameters . 33 B.2.3 Mean cycles to failure (MCTF) . 33 B.2.4 Value of 10ˆB . 34 B.2.5 Mean time to failure (MTTF) . 34 B.3 Confidence intervals case study . 34 B.3.1 General . 34 B.3.2 Interval estimation of β . 34 B.3.3 Interval estimation of . 35 B.3.4 Lower confidence limit for B10 . 35 B.3.5 Lower confidence limit for R . 36 B.4 WeiBayes case study . 36 Annex C (informative)
Statistical tables . 38 SIST EN 61810-2:2018

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C.1 Table of gamma function . 38 C.2 Fractiles of the normal distribution . 38 Annex D (informative)
Success run – Test without failures . 40 D.1 General . 40 D.2 Confidence level and minimum reliability . 40 D.3 Example. 41 Bibliography . 42
Figure A.1 – An example of Weibull probability paper . 18 Figure A.2 – An example of cumulative hazard plotting paper . 20 Figure A.3 – Plotting of data points and
drawing of a straight line . 20 Figure A.4 – Estimation of distribution parameters . 21 Figure B.1 – Estimation of distribution parameters . 30 Figure B.2 – Cumulative hazard plots . 32 Figure B.3 – Type test versus WeiBayes analysed periodic test . 37
Table A.1 – Confidence levels for WeiBayes without failures . 26 Table B.1 – Worksheet for cumulative hazard analysis . 28 Table B.2 – Example worksheet . 31 Table B.3 – First twenty failures in this example . 33 Table C.1 – Values of the gamma function . 38 Table C.2 – Fractiles of the normal distribution . 39 Table D.1 – Number of samples and life cycles . 41
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ELECTROMECHANICAL ELEMENTARY RELAYS –
Part 2: Reliability
FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use 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 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 61810-2 has been prepared by IEC technical committee 94: All-or-nothing electrical relays. This third edition cancels and replaces the second edition published in 2011. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) not only graphical but also numerical methods are added; b) reduction of number of samples in specified cases; c) new subclauses of confidence intervals are added; d) the WeiBayes approach is added to facilitate compliance tests (routine test) with lower effort; SIST EN 61810-2:2018

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e) annexes have been restructured into an Annex A for data analysis (normative) and Annex B (informative) where various examples of the data analysis are given; f) the former Annex C has been incorporated into the modified Annex B; g) a new Annex C replaces the old Annex D. The text of this International Standard is based on the following documents: FDIS Report on voting 94/415/FDIS 94/418/RVD
Full information on the voting for the approval of this International Standard can be found in the report on voting indicated in the above table. This document has been drafted in accordance with the ISO/IEC Directives, Part 2. This International Standard is to be used in conjunction with IEC 61649:2008. A list of all parts in the IEC 61810 series, published under the general title Electromechanical elementary relays, can be found on the IEC website. The committee has decided that the contents of this document will remain unchanged until the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to the specific document. At this date, the document will be
• reconfirmed, • withdrawn, • replaced by a revised edition, or • amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
– 6 – IEC 61810-2:2017 © IEC 2017 INTRODUCTION Within the IEC 61810 series of basic standards covering elementary electromechanical relays, IEC 61810-2 is intended to give requirements and tests permitting the assessment of relay reliability. All information concerning endurance tests for type testing have been included in IEC 61810-1. NOTE According to IEC 61810-1, a specified value for the electrical endurance under specific conditions (e.g. contact load) is verified by testing 1 or 3 relays. None is allowed to fail. Within this document, a prediction of the reliability of a relay is performed using statistical evaluation of the measured cycles to failure of a larger number of relays (generally 10 or more relays). This document is the base for IEC 61810-2-1 to determine reliability values for relays where enhanced requirements for the verification of reliability (B10 and B10D) apply. The technical committee responsible for dependability has developed IEC 61649 dealing with Weibull-distributed test data. It contains both numerical and graphical methods for the evaluation of Weibull-distributed data as well as WeiBayes estimation. On the basis of this basic reliability standard, this document was developed. It comprises test conditions and an evaluation method to obtain characteristic reliability values for electromechanical elementary relays. The life of relays as non-repairable items is primarily determined by the number of operations. For this reason, the reliability is expressed in terms of mean cycles to failure (MCTF). Commonly, equipment reliability is calculated from mean time to failure (MTTF) figures. With the knowledge of the frequency of operation (cycling rate) of the relay within a piece of equipment, it is possible to calculate an effective MTTF value for the relay in that application. Such calculated MTTF values for relays can be used to calculate respective reliability, probability of failure, and availability (e.g. MTBF (mean time between failures)) values for equipment into which these relays are incorporated. Generally, it is not appropriate to state that a specific MCTF value is “high” or “low”. The MCTF figures are used to make comparative evaluations between relays with different styles of design or construction, and as an indication of product reliability under specific conditions. SIST EN 61810-2:2018

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ELECTROMECHANICAL ELEMENTARY RELAYS –
Part 2: Reliability
1 Scope This part of IEC 61810 covers test conditions and provisions for the evaluation of endurance tests using appropriate statistical methods to obtain reliability characteristics for relays. This document applies to electromechanical elementary relays considered as non-repaired items (i.e. items which are not repaired after failure). The lifetime of a relay is usually expressed in number of cycles (CTF). Therefore, whenever the terms “time” or “duration” are used in IEC 61649, they carry the meaning “cycles”. However, with a given frequency of operation, the number of cycles can be transformed into respective times (e.g. times to failure (TTF)). The failure criteria and the resulting characteristics of elementary relays describing their reliability in normal use are specified in this document. A relay failure occurs when the specified failure criteria are met. As the failure rate for elementary relays cannot be considered as constant, particularly due to wear-out mechanisms, the cycles to failure of tested items typically show a Weibull distribution. This document provides numerical and graphical methods to calculate approximate values for the two-parameter Weibull distribution, as well as lower confidence limits and a method for confirmation of reliability values with the WeiBayes method. This document does not cover procedures for electromechanical elementary relays where enhanced requirements for the verification of reliability apply. NOTE 1 Such reliability test procedures are specified in IEC 61810-2-1. In particular, when electromechanical elementary relays are intended to be incorporated in safety-related control systems of machinery in accordance with IEC 62061 and ISO 13849-1, IEC 61810-2-1 defines procedures for the manufacturer to provide B10D values. NOTE 2 Electromechanical elementary relays with forcibly guided (mechanically linked) contacts according to IEC 61810-3 offer the possibility of a high diagnostic coverage according to 4.5.3 of ISO 13849-1:2015. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 61649:2008, Weibull analysis IEC 61810-1:2015, Electromechanical elementary relays – Part 1: General and safety requirements 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. SIST EN 61810-2:2018

– 8 – IEC 61810-2:2017 © IEC 2017 ISO and IEC maintain terminological databases for use in standardization at the following addresses: • IEC Electropedia: available at http://www.electropedia.org/ • ISO Online browsing platform: available at http://www.iso.org/obp 3.1
item any component that can be individually considered Note 1 to entry: For the purpose of this document, items are electromechanical elementary relays. 3.2
non-repaired item item which is not repaired after a failure 3.3
sample one or more sampling items intended to provide information on the population [SOURCE: IEC 60050-151:2001, 151-16-19, modified – The words "or on the material" have been deleted from the definition.] 3.4
sample item one of the individual items in a population of similar items and taken from one place and at one time [SOURCE: IEC 60050-151:2001, 151-16-18, modified – The words "or a portion of material forming a cohesive entity" have been deleted from the definition.] 3.5
cycle operation and subsequent release/reset [SOURCE: IEC 60050-444:2002, 444-02-11] 3.6
frequency of operation number of cycles per unit of time [SOURCE: IEC 60050-444:2002, 444-02-12] 3.7
reliability ability of an item to perform a required function under given conditions for a given number of cycles or time interval Note 1 to entry: It is generally assumed that the item is in a state to perform this required function at the beginning of the time interval. Note 2 to entry: The term “reliability” is also used as a measure of reliability performance (see IEC 60050-312:2001, 312-07-06). [SOURCE: IEC 60050-395:2014, 395-07-131, modified – The words "number of cycles or" have been added to the definition, and the second note has been replaced by a new note.] SIST EN 61810-2:2018

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3.8
reliability test experiment carried out in order to measure, quantify or classify a reliability measure or property of an item [SOURCE: IEC 60300-3-5:2001, 3.1.27, modified – The notes have been deleted.] 3.9
life test test with the purpose of estimating, verifying or comparing the lifetime of the class of items being tested [SOURCE: IEC 60300-3-5:2001, 3.1.17, modified – The note has been deleted.] 3.10
cycles to failure CTF total number of cycles of an item, from the instant it is first put in an operating state until failure 3.11
mean cycles to failure MCTF expectation of the number of cycles to failure 3.12
time to failure TTF total time duration of operating time of an item, from the instant it is first put in an operating state until failure 3.13
mean time to failure MTTF expectation of the time to failure [SOURCE: IEC 60050-192:2015, 192-05-11, modified – The word "operating" has been deleted from the term and the definition, and the notes have been deleted.] 3.14
useful life number of cycles or time duration until a certain percentage of items have failed Note 1 to entry: In this document, this percentage is defined as 10 %. 3.15
failure termination of the ability of an item to perform a required function as defined in the failure criteria [SOURCE: IEC 60050-603:1986, 603-05-06, modified – The words "as defined in the failure criteria" have been added to the definition.] 3.16
malfunction event when an item does not perform an expected function SIST EN 61810-2:2018

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contact failure occurrence of break and/or make malfunctions of a contact under test, exceeding a specified number 3.18
failure criteria specified conditions to judge if a fault or malfunction is a failure 3.19
contact load category classification of relay contacts dependent on wear-out mechanisms Note 1 to entry: Various contact load categories are defined in IEC 61810-1. 3.20
fault deviation of the existing condition from the expected condition 3.21 Terms and definitions related to tests 3.21.1
type test conformity test made on sample relays representative of the production to get basic performance data or to verify that these relays comply with the specified requirements 3.21.2
routine test conformity test made on sample without any modifications and specification changes during or after mass production with specified repetition 4 General considerations The provisions of this document are based on the relevant publications on dependability. In particular, the following documents have been taken into account: IEC 60050-191, IEC 60300-3-5 and IEC 61649. The aim of reliability testing as given in this document is to obtain objective and reproducible data on reliability performance of relays representative of standard production quality. The tests described and the related statistical tools to gain characteristic reliability values can be used for the estimation of such characteristic reliability values, as well as for the verification of stated characteristic values. NOTE 1 Examples for the application of characteristic reliability values are: • establishment of characteristic reliability values for a new relay type; • comparison of relays with similar characteristics, but produced by different manufacturers; • evaluation of the influence, on a relay, of different materials or different manufacturing processes; • comparison of a new relay with a relay which has already worked for a specific period of time; • calculation of the reliability of an equipment or system incorporating one or more relays. According to Clauses 8 and 9 of IEC 60300-3-5:2001, for non-repaired items showing a non-constant failure rate, the Weibull model is the most appropriate statistical tool for evaluation of reliability measures. This analysis procedure is described in IEC 61649. Relays within the scope of this document are considered as non-repaired items. They generally do not exhibit a constant failure rate but a failure rate increasing with number of SIST EN 61810-2:2018

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cycles, being tested until wear-out mechanisms become predominant. The cycles to failure of a random sample of tested items typically show the Weibull distribution. NOTE 2 In cases where no wear-out mechanisms prevail, random failures with constant failure rate can be assumed. Then the shape parameter
of the Weibull distribution equals 1, and the reliability function becomes the well-known exponential law. The first step in the analysis of the recorded cycles to failure (CTF) of the tested relays is the determination of the two distribution parameters of the Weibull distribution. In a second step, the mean cycles to failure (MCTF) is calculated as a point estimate. In a third step, the useful life is determined as the lower confidence limit of the number of cycles by which 10 % of the relay population will have failed (B10) (see 10.5 and 10.6 of IEC 61649:2008). With a given frequency of operation, these reliability measures expressed in number of cycles (MCTF) can be transformed into respective times (MTTF); see Annex B for an example. The statistical procedures require some appropriate computing facility. Software for evaluation of Weibull-distributed data is commercially available on the market. Such software may be used for the purpose of this document provided it shows equivalent results when the data given in Annex B are used. Since the number of cycles to failure highly depends on the specific set of test conditions (particularly the electrical loading of the relay contacts), values for MCTF and useful life derived from test data apply only to this set of test conditions, which have to be stated by the manufacturer together with the reliability measures. Upon explicit specification of the manufacturer, the test may be performed with even less than 10 relays, provided the uncertainty of the estimated Weibull parameters is acceptable to him. In such a case, the minimum number of tested relays shall be specified; this number then replaces the minimum number of 10 relays wherever prescribed in this document. This reduction of relay specimens is acceptable in both numerical and graphical methods. Here, the number of failures or specimens may be determined, being concerned with confidence interval, which can be calculated by A.5.3. On the other hand, the reduction due to WeiBayes approach shown in A.5.4 is also acceptable if the shape parameter, , is assumed from historical data from prior experiments, or from engineering knowledge of the physics of the failure. However, the WeiBayes approach applies only for routine test. 5 Test conditions 5.1 Sample items For useful life estimation, a minimum of 10 failures need to be recorded to perform the analysis described in this document, 10 or more items (relays) should be submitted to the test. However, at least 2/3 of the tested relays shall fail physically. This allows the test to be carried out with 10 relays only, even when the test is stopped before all relays have physically failed (with a minimum of 7 physical failures recorded). When the test is stopped at a specific number of cycles, all relays that have not yet failed shall be considered as suspended or censored at that number of cycles. Upon explicit specification of the manufacturer, less than 10 items can be tested to determine the basic Weibull parameters (B10 and ), but the minimum number of samples to be tested is 5. The requirement to truncate a test still remain with 2/3 of the number of samples. The results with less than 10 samples shall be published in conjunction with the confidence level and number of samples. The evaluation method in this specific case shall be the numeric method. SIST EN 61810-2:2018

– 12 – IEC 61810-2:2017 © IEC 2017 For a WeiBayes test, the number of samples and failures shall be selected according to the desired confidence level. The items shall be selected at random from the same production lot and shall be of identical type and construction. No action is allowed on the sample items from the time of sampling until the test starts. Where any particular burn-in procedure or reliability stress screening is employed by the manufacturer prior to sampling, this shall apply to all production. The manufacturer shall describe and declare such procedures, together with the test results. Unless otherwise specified by the manufacturer, all contacts of each relay under test shall be loaded as stated and monitored continuously during the test. The test starts with all items and is stopped at a certain number of cycles. At that instant, a certain number of items have failed. The number of cycles to failure of each of the failed items is recorded. Items failed during the test are not replaced once they fail. 5.2 Environmental conditions The testing environment shall be the same for all items. – The items shall be mounted in the manner intended for normal service; in particular, relays for mounting onto printed circuit boards are tested in the horizontal position, unless otherwise specified. – The ambient temperature shall be as specified by the manufacturer. – All other influence quantities shall comply with the values and tolerance ranges given in Table 1 of IEC 61810-1:2015, unless otherwise specified. 5.3 Operating conditions The set of operating conditions – rated coil voltage(s), – coil suppression (if any), – frequency of operation, – duty factor, – contact load(s), shall be as specified by the manufacturer. Recommended values should be chosen from those given in Clause 5 of IEC 61810-1:2015. The test is performed on each contact load and each contact material as specified by the manufacturer. All specified devices (for example, protective or suppression circuits), if any, which are part of the relay or stated by the manufacturer as necessary for particular contact loads, should be operated during the test. The contacts shall be continuously monitored to detect malfunctions to open and malfunctions to close, as well as unintended bridging (simultaneous closure of make and break side of a changeover contact). SIST EN 61810-2:2018

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The contacts are connected to the load(s) in accordance with Table 12 of IEC 61810-1:2015 as specified and indicated by the manufacturer. 5.4 Test equipment The test circuit described in Annex C of IEC 61810-1:2015 shall be used, unless otherwise specified by the manufacturer and explicitly indicated in the test report. 6 Failure criteria Whenever any contact of a relay under test fails to open or fails to close or exhibits unintended bridging, this shall be considered as a malfunction. Three severity levels are specified: – severity A: the first detected malfunction is defined as a failure; – severity B: the sixth detected malfunction or two consecutive malfunctions are defined as a failure; – severity C: as specified by the manufacturer. The severity level used for the test shall be as prescribed by the manufacturer and stated in the test report. Faults occurring during test like insulation fault, dielectric test fault, thermal deformation of enclosure, burning and others, shall be judged as failure. 7 Output data The data to be analysed consists of cycles to failure (CTF) for each of the items put on test. These CTF values have to be known exactly. However, it is not necessary to gather the CTF values for all items under test, under the conditions described under 5.1. 8 Analysis of output data The evaluation of the CTF values obtained during the test shall be carried out in accordance with the procedures given in Annex A. 9 Presentation of reliability measures The basic reliability measures applicable to relays as described in this document and obtained from the data analysis shall be provided. However, since the values obtained for these reliability measures using the procedures of Annex A depend to a great extent on the basic design characteristics of the relay, on the test conditions of Clause 5 and on the failure criteria of Clause 6, the following information shall also be provided together with the test results: – relay type for which the results are valid: a) contact material; b) deviations from standard types (if any); c) type of termination. – set of operating conditions (see 5.3): a) rated coil voltage(s); SIST EN 61810-2:2018

– 14 – IEC 61810-2:2017 © IEC 2017 b) coil suppression (if any); c) frequency of operation; d) duty factor; e) contact load(s); f) ambient conditions. – test schematic selected (see Clause C.3 of IEC 61810-1:2015, or test circuit details, if different from the circuit described in Clause C.1 of IEC 61810-1:2015); – severity level (see Clause 6). In addition, basic data of the test and the related analysis (see Annex A) shall be given in the test report: – analysis method; – number of items (n) on test; – number of failed items (r) registered during the test; – time (given in number of cycles) when the test was stopped (T); – confidence level, if less than 90 %. The test results are applicable to the samples specifically tested and variants, as stipulated by the manufacturer, provided that the relevant design characteristics remain the same. NOTE Acceptable examples are coil variants with the same ampere-turns. Unacceptable examples are variants with AC in place of DC coils, or different contact dynamics. When test results for various operating conditions (for example, contact loads) are available, they may be compiled as a family of curves or in suitable tables. However, it shall be ensured that a sufficient number of points are determined when plotting such curves.
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Annex A (normative)
Data analysis A.1 General This annex has been derived from the reliability standard IEC 61649:2008 with certain modifications necessary to adopt the procedures to elementary relays. The distribution considered in the reliability standard is of the Weibull type, which has been empirically recognized to correspond to an appropriate data analysis for elementary relays. The graphical method as well as the numerical method are covered in IEC 61649. In addition, not only the Weibull probability analysis but also the Weibull hazard analysis is taken up in the graphical method. Here, Weibull hazard and Weibull probability analyses are applied to complete and incomplete data, respectively. The latter is especially useful for the reliability analysis of relays because many data sets obtained from life tests are incomplete (censored tests). NOTE 1 Incomplete data are the data sets obtained from the test after either a certain number of failures or a certain number of cycles, when there are still items functioning, whereas complete data are the data sets without censoring. This annex deals with the Weibull probability plot and the Weibull hazard plot for the graphical method based upon median rank regression (MRR) principles, and the maximum likelihood estimation (MLE) for the numerical method in accordance with the provisions of IEC 61649. When more in-depth information is required, IEC 61649 is to be consulted. The concept “time” is to be understood as “cycles” in the case of relays. However, with a given frequency of operation, the values indicated in numbers of cycles can be transformed into respective times. NOTE 2 Whereas the variable “time” (symbol: t) is used within IEC 61649, this document is based on the variable “cycles” (symbol: c). For the sake of consistency, the following symbols and equations are reproduced in accordance with IEC 61649. A.2 Abbreviations CDF cumulative distribution function MRR median rank regression MLE maximum likelihood estimation MCTF mean cycles to failure PDF probability density function A.3 Symbols and definitions The following symbols are used in this Annex A, and in both Annex B and Annex C. Auxiliary constants and functions are defined in the text. f(c) probability density function F(c) cumulative distribution function (failure probability) h(c) hazard function (or instantaneous failure rate) SIST EN 61810-2:2018

– 16 – IEC 61810-2:2017 © IEC 2017 H(c) cumulative hazard function R(c) reliability function of the Weibull distribution (survival probability) B10 expected time at which 10 % of the population have failed
(10 % fractile of the lifetime) c cycle – variable mˆ mean cycles to failure (MCTF)
Weibull shape parameter (indicating the rate of change of the instantaneous failure rate with time)
Weibull scale parameter or characteristic life (at which 63,2 % of the items have failed) 1 standard deviation A.4 Weibull distribution The fundamental Weibull formulae are defined as follows. NOTE For more information, reference is made to IEC 61649. The probability density function (PDF) of the Weibull distribution is:
βηββηβ−−=ceccf1)( (A.1) The cumulative distribution function (CDF), or the expected fraction failing at cycle c:
()()βη/1cecF−−= (A.2) The reliability function R(c), or the expected fraction surviving at cycle c:
βη)/()(1)(cecFcR−=−= (A.3) The hazard function (or instantaneous failure rate) h(c) is:
ββηβ1−=ch(c) (A.4) The cumulative hazard function H(c) is:
()βη=ccH (A.5) SIST EN 61810-2:2018

IEC 61810-2:2017 © IEC 2017 – 17 –
A.5 Procedure A.5.1 Graphical methods A.5.1.1 Overview Graphical analysis is performed by plotting the data on a suitably designed Weibull probability paper, fitting a straight line through the data, and estimating the distribution parameters (the shape parameter, and the characteristic life or scale parameter). Then the reliability characteristics (i.e. MCTF, B10 value, and standard deviation) are calculated. Graphical methods benefit from relatively straightforward processes and availability for data with a mixture of failure modes. The fundamentals of the analysis and an outline of the processes applied to Weibull probability and Weibull hazard plots are given in A.5.1. A.5.1.2 Weibull probability plot A.5.1.2.1 Ranking and plotting positions To make the Weibull plot, rank the data from the lowest to the highest number of cycles to failure (ci). This ranking will set up the plotting positions for the cycle (c), the axis and the ordinate, cumulative distribution function (F(c)), in percentage values. F(c) is calculated by median rank regression (MRR). An approximate value may be obtained using Benard’s approximation (see 7.2.1 of IEC 61649:2008):
F(ci) = (i − 0,3) / (n + 0,4)
% (A.6) where n is the number of tested items; i is the ranked position of the data item. For suspended or censored data, the values may need to be adjusted. See 7.2.3 of IEC 61649:2008 for details. Data points of (ci,F(ci)) are plotted on the Weibull probability plotting paper. For details, see 7.2.1 and 7.2.2 of IEC 61649:2008. A.5.1.2.2 Weibull probability plotting paper The design of Weibull probability paper is shown below. The Equation (A.3) can be rewritten to the following equation:
βη)/()(11cecF=− (A.7) Taking normal logarithms of both sides of the Equation (A.7) twice gives an equation of a straight line as shown below:
ηββlnln)(11lnln−=−ccF (A.8) SIST EN 61810-2:2018

– 18 – IEC 61
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