SIST EN 61124:2012

Reliability testing - Compliance tests for constant failure rate and constant failure intensity

IEC 61124:2012 gives a number of optimized test plans, the corresponding operating characteristic curves and expected test times. In addition the algorithms for designing test plans using a spreadsheet program are also given, together with guidance on how to choose test plans. This standard specifies procedures to test whether an observed value of: failure rate, failure intensity, meantime to failure (MTTF), and mean operating time between failures (MTBF). The main changes with respect to the previous edition are as follows:  - A number of new test plans have been added based on the Russian standard GOST R 27.402 [1], and it is intended to align the new edition of MIL-HDBK-781 [2] with this edition. Algorithms for optimizing test plans using a spreadsheet program are given and a number of optimized test plans are listed. Furthermore, emphasis is laid on the fact that the test should be repeated following design changes;  - Discrepancies in test plans A, B as well as Annexes A and B that originated in IEC 60605-7 [3], now withdrawn, have been corrected so these test plans differ from those given in previous editions of IEC 61124. As requested by the National Committees, mathematical background material and spreadsheet program information has been moved to informative annexes. In addition, the symbol lists have been divided, so that some annexes have separate lists of symbols;  - Guidance on how to choose test plans has been added as well as guidance on how to use spreadsheet programs to create them. Test plans A.1 to A.9 and B.1 to B.13 have been corrected;  - Subcluses 8.1, 8.2, 8.3, Clause 9, Annex C, Clauses G.2, I.2, I.3 and Annex J are unchanged, except for updated terminology and references.

Prüfungen der Funktionsfähigkeit - Prüfpläne für konstante Ausfallrate und konstante Ausfalldichte

Essais de fiabilité - Plans d'essais de conformité d'un taux de défaillance constant et d'une intensité de défaillance constante

La CEI 61124:2012 fournit un certain nombre de plans d'essais optimisés, les courbes OC associées et les valeurs moyennes des temps d'essais.  De plus, les algorithmes pour la conception de plans d'essais à l'aide d'un tableur électronique sont également fournis avec des lignes directrices sur la manière de choisir les plans d'essais. La présente norme spécifie les méthodes utilisées pour vérifier qu'une valeur observée: d'un taux de défaillance, d'une intensité de défaillance, d'une durée moyenne de fonctionnement avant défaillance (MTTF), moyenne des temps de bon fonctionnement (MTBF). Les modifications techniques majeures par rapport à l'édition précédente sont les suivantes:  - de nouveaux plans d'essais sont ajoutés, basés sur la Norme russe GOST R 27.402 [1], et son objectif est d'être cohérent avec la nouvelle édition de MIL-HDBK-781 [2]. Elle comprend les algorithmes pour l'optimisation des plans d'essais en utilisant un tableur électronique, ainsi qu'une liste de plan d'essais. En outre l'accent est mis sur le fait qu'il convient de réitérer l'essai à la suite des modifications de conception;  - Les écarts dans les plans d'essais A, B et les Annexes A et B qui provenaient de la CEI 60605-7 [3], (retirée) ont été corrigés et ces plans sont donc différents de ceux donnés dans les précedentes éditions de la CEI 61124. Comme demandé par les Comités nationaux, les informations concernant la base mathématique et le tableur électronique ont été déplacées aux annexes informatives. De plus, les listes de symboles ont été divisées, pour obtenir des listes de symboles séparées dans certaines annexes.  - Des lignes directrices sur la manière de choisir les plans d'essais ont été ajoutées de même que sur la manière d'utiliser les tableurs électroniques pour les créer. Les plans d'essais A.1 à A.9 et B.1 à B.13 ont été corrigés;  - Les paragraphes 8.1, 8.2, 8.3, l'Article 9 et l'Annexe C, les Articles G.2, I.2, I.3 et l'Annexe J ne changent pas, sauf pour la terminologie et les références mises à jour.

Preskušanje zanesljivosti - Ustreznostni preskusi za konstantno pogostost odpovedi in konstantno intenzivnost odpovedi

Ta mednarodni standard navaja optimizirane preskusne načrte, ustrezne značilne krivulje delovanja in pričakovana trajanja preskusov. Poleg tega navaja algoritme za projektiranje preskusnih načrtov s programom s preglednicami in smernice za izbiro preskusnih načrtov. Ta standard določa postopke za preskušanje, ali je meritev – pogostosti odpovedi, – intenzivnosti odpovedi, – povprečnega trajanja odpovedi (MTTF), – povprečnega trajanja delovanja med odpovedmi (MTBF) v skladu z danimi zahtevami. Če ni navedeno drugače, se predpostavlja, da so trajanja odpovedi ali povprečna trajanja delovanja med odpovedmi med skupnim trajanjem preskusov ločena in enakomerno eksponentno razporejena. Ta predpostavka pomeni, da je pogostost odpovedi ali intenzivnost odpovedi konstantna. Opisane so štiri vrste preskusnih načrtov: – prekinjeni(okrnjeni?) sekvenčni preskusi; – časovno/z odpovedjo zaključeni preskusi; – preskusi, zaključeni brez nadomestil z določenim koledarskim časom; – kombinirani preskusni načrti. Ta standard ne zajema smernic za načrtovanje, izvajanje in analizo preskusa ter poročanje o njem. Te informacije so navedene v standardu IEC 60300-3-5.

General Information

• Status: Published
• Publication Date: 23-Sep-2012
• ICS: 19.020 - Test conditions and procedures in general
• ICS: 21.020 - Characteristics and design of machines, apparatus, equipment
• Technical Committee: I11 - Imaginarni 11
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 28-Aug-2012
• Due Date: 02-Nov-2012
• Completion Date: 24-Sep-2012
• Ref Project: EN 61124:2012 - Reliability testing - Compliance tests for constant failure rate and constant failure intensity

Relations

• Replaces: SIST EN 61124:2007 - Reliability testing - Compliance tests for constant failure rate and constant failure intensity
• Effective Date: 06-May-2014
• Replaced By: SIST EN IEC 61124:2023 - Reliability testing - Compliance tests for constant failure rate and constant failure intensity (IEC 61124:2023)
• Effective Date: 01-Jun-2023
• Revised: SIST EN 61124:2007 - Reliability testing - Compliance tests for constant failure rate and constant failure intensity
• Effective Date: 09-Apr-2010

Overview

SIST EN 61124:2012 (identical to IEC 61124:2012) is a European/International standard for reliability testing that defines compliance tests for a constant failure rate and constant failure intensity. The standard provides optimized test plans, operating characteristic (OC) curves, expected test times, and algorithms - including spreadsheet-based methods - to design and choose appropriate test plans. It also clarifies when tests should be repeated after design changes.

Keywords: reliability testing, compliance tests, constant failure rate, constant failure intensity, IEC 61124, SIST EN 61124:2012, MTTF, MTBF, test plans.

Key Topics and Requirements

• Scope and purpose: Procedures to test whether observed values of failure rate, failure intensity, mean time to failure (MTTF) and mean operating time between failures (MTBF) meet specified criteria.
• Types of test plans: Sequential plans, fixed time/failure-terminated (fixed-duration) plans, alternative time/failure-terminated plans, calendar time/failure-terminated plans for non-replaced items, and combined plans.
• Test design and selection:
  • Lists of optimized test plans (including additions based on GOST R 27.402).
  • Operating characteristic curves and expected accumulated test times to decision for each plan.
  • Algorithms and spreadsheet guidance in informative annexes for designing and optimizing test plans.
• Data recording and calculations: Guidance on accumulated test time, number of failures, decision criteria and presentation of results.
• Updates from previous edition: Corrections to earlier test plans, expanded guidance on choosing plans, and emphasis on repeating tests after design changes.

Practical Applications

• Verifying that a product or component meets contractual or regulatory reliability targets expressed as failure rate/intensity, MTTF, or MTBF.
• Designing acceptance or compliance tests in production, qualification, or field trials.
• Optimizing test duration and sample sizes using spreadsheet-based algorithms to balance test cost and statistical power.
• Supporting reliability demonstrations for industries with strict dependability requirements: electronics, automotive, aerospace, defense, medical devices, and industrial equipment.

Who Should Use This Standard

• Reliability engineers and test laboratories designing or running reliability compliance tests.
• Quality assurance and product development teams validating MTTF/MTBF claims.
• Certification bodies and procurement authorities requiring statistically defensible reliability evidence.
• Military/aerospace and regulated-industry stakeholders aligning tests with standards like GOST R 27.402 and MIL-HDBK-781.

Related Standards

• IEC 60605 series (equipment reliability testing)
• IEC 61123 (reliability test plans for success ratio)
• IEC 60300-3-5 (dependability management, reliability test conditions)
• GOST R 27.402 and MIL-HDBK-781 (referenced for test-plan alignment)

SIST EN 61124:2012 is a practical, statistically grounded reference for anyone who must demonstrate or verify a constant failure rate/intensity using optimized, repeatable test plans and clear decision criteria.

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2012
Preskušanje zanesljivosti - Ustreznostni preskusi za konstantno pogostost
odpovedi in konstantno intenzivnost odpovedi
Reliability testing - Compliance tests for constant failure rate and constant failure
intensity
Prüfungen der Funktionsfähigkeit - Prüfpläne für konstante Ausfallrate und konstante
Ausfalldichte
Essais de fiabilité - Plans d'essais de conformité d'un taux de défaillance constant et
d'une intensité de défaillance constante
Ta slovenski standard je istoveten z: EN 61124:2012
ICS:
19.020 Preskuševalni pogoji in Test conditions and
postopki na splošno procedures in general
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61124
NORME EUROPÉENNE
August 2012
EUROPÄISCHE NORM
ICS 03.120.30; 19.020; 21.020 Supersedes EN 61124:2006

English version
Reliability testing -
Compliance tests for constant failure rate
and constant failure intensity
(IEC 61124:2012)
Essais de fiabilité -  Prüfungen der Funktionsfähigkeit -
Plan d'essais de conformité d'un taux Prüfpläne für konstante Ausfallrate
de défaillance constant et d'une intensité und konstante Ausfalldichte
de défaillance constante (IEC 61124:2012)
(CEI 61124:2012)
This European Standard was approved by CENELEC on 2012-06-27. 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, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2012 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61124:2012 E
Foreword
The text of document 56/1461/FDIS, future edition 3 of IEC 61124, prepared by IEC/TC 56
"Dependablility" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
(dop) 2013-03-27
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2015-06-27
• latest date by which the national
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61124:2006.

- a number of new test plans have been added based on the Russian standard GOST R 27.402, and
it is intended to align the new edition of MIL-HDBK-781 with this edition. Algorithms for optimizing
test plans using a spreadsheet program are given and a number of optimized test plans are listed.
Furthermore, emphasis is laid on the fact that the test should be repeated following design
changes;
- discrepancies in test plans A, B as well as Annexes A and B that originated in IEC 60605-7, now
withdrawn, have been corrected so these test plans differ from those given in previous edition of
EN 61124. As requested by the National committees, mathematical background material and
spreadsheet program information has been moved to informative annexes. In addition, the symbol
lists have been divided, so that some annexes have separate lists of symbols;
- guidance on how to choose test plans has been added as well as guidance on how to use
spreadsheet programs to create them. Test plans A.1 to A.9 and B.1 to B.13 have been corrected;
- Subclauses 8.1, 8.2, 8.3, Clause 9, Annex C, Clauses G.2, I.2, I.3 and Annex J are unchanged,
except for updated terminology and references;
- corrections to the second edition proposed by National Committees have been implemented.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 61124:2012 was approved by CENELEC as a European
Standard without any modification.

- 3 - EN 61124:2012
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60050-191 - International Electrotechnical Vocabulary - -
(IEV) -
Chapter 191: Dependability and quality
of service
IEC 60300-3-5 2001 Dependability management - - -
Part 3-5: Application guide - Reliability test
conditions and statistical test principles

IEC 60605-2 - Equipment reliability testing - - -
Part 2: Design of test cycles
IEC 60605-4 2001 Equipment reliability testing - - -
Part 4: Statistical procedures for exponential
distribution - Point estimates, confidence
intervals, prediction intervals and tolerance
intervals
IEC 60605-6 - Equipment reliability testing - - -
Part 6: Tests for the validity and estimation
of the constant failure rate and constant
failure intensity
IEC 61123 1991 Reliability testing - Compliance test plans for - -
success ratio
IEC 61124 ®
Edition 3.0 2012-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Reliability testing – Compliance tests for constant failure rate and constant

failure intensity
Essais de fiabilité – Plan d’essais de conformité d’un taux de défaillance

constant et d’une intensité de défaillance constante

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XF
ICS 03.120.30; 19.020; 21.020 ISBN 978-2-88912-061-1

– 2 – 61124 © IEC:2012
CONTENTS
FOREWORD . 8
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, abbreviations and symbols . 11
3.1 Terms and definitions . 11
3.2 Abbreviations and symbols . 11
3.2.1 Abbreviations . 11
3.2.2 Symbols . 11
4 General requirements and area of application . 13
4.1 Requirements . 13
4.2 Applicability to replaced and repaired items . 13
4.3 Types of test plans . 13
4.3.1 General . 13
4.3.2 Advantages and disadvantages of the different test plan types . 14
5 General test procedure . 14
5.1 Test conditions . 14
5.2 General characteristics of the test plans . 15
5.3 Data to be recorded . 15
*
5.4 Calculation of accumulated test time, T . 15
5.5 Number of failures . 16
6 Sequential test plans . 17
6.1 General . 17
6.2 Common test procedure . 17
6.3 Decision criteria . 17
6.4 Overview of test plans . 17
7 Fixed time/failure terminated test plans – Fixed duration test plans . 18
7.1 General . 18
7.2 Common test procedure . 18
7.3 Decision criteria . 19
7.4 Test plans . 19
8 Design of alternative time/failure terminated test plans . 20
8.1 General . 20
8.2 Design procedures . 20
8.3 Common test procedure . 20
8.4 Decision criteria . 21
9 Calendar time/failure terminated test plans for non-replaced items . 21
9.1 General . 21
9.2 Common test procedure . 21
9.3 Decision criteria . 21
9.4 Use of Table 2 of IEC 61123:1991 for fixed calendar time tests . 22
9.4.1 General . 22
9.4.2 Procedure when the test time is given . 22
9.4.3 Procedure when the number of items is given . 22
10 Combined test plans . 23

61124 © IEC:2012 – 3 –
10.1 General . 23
10.2 Common test procedure . 23
10.3 Decision criteria . 23
10.4 Test plans . 24
11 Performing the test . 24
12 Presentation of results . 24
Annex A (normative) Tables and graphs for sequential test plans . 25
Annex B (normative) Graphs for fixed time/failure terminated test plans . 44
Annex C (normative) Graphs for alternative time/failure terminated test plans . 53
Annex D (normative) Tables and graphs for combined test plans and additional
sequential test plans . 60
Annex E (informative) Examples and mathematical references for sequential test
plans . 78
Annex F (informative) Design of sequential test plans using a common spreadsheet
program . 86
Annex G (informative) Examples and mathematical references for fixed time/failure
terminated test plans – Fixed duration test plans . 97
Annex H (informative) Design of fixed duration time/failure terminated test plans using
a spreadsheet program . 99
Annex I (informative) Examples and mathematical references for the design of
alternative time/failure terminated test plans . 105
Annex J (informative) Examples and mathematical references for the calendar time
terminated test plans . 112
Annex K (informative) Derivation and mathematical reference for the optimized test
plans of GOST R 27 402 . 114
Bibliography . 122

Figure A.1 – Accept and reject lines for test plan A.1 . 25
Figure A.2 – Test plan A.1 – Operating characteristic curve . 26
Figure A.3 – Test plan A.1 – Expected accumulated test time to decision . 27
Figure A.4 – Accept and reject lines for test plan A.2 . 27
Figure A.5 – Test plan A.2 – Operating characteristic curve . 28
Figure A.6 – Test plan A.2 – Expected accumulated test time to decision . 29
Figure A.7 – Accept and reject lines for test plan A.3 . 29
Figure A.8 – Test plan A.3 – Operating characteristic curve . 30
Figure A.9 – Test plan A.3 – Expected accumulated test time to decision . 31
Figure A.10 – Accept and reject lines for test plan A.4 . 31
Figure A.11 – Test plan A.4 – Operating characteristic curve . 32
Figure A.12 – Test plan A.4 – Expected accumulated test time to decision . 33
Figure A.13 – Accept and reject lines for test plan A.5 . 33
Figure A.14 – Test plan A.5 – Operating characteristic curve . 34
Figure A.15 – Test plan A.5 – Expected accumulated test time to decision . 35
Figure A.16 – Accept and reject lines for test plan A.6 . 35
Figure A.17 – Test plan A.6 − Operating characteristic curve . 36
Figure A.18 – Test plan A.6 – Expected accumulated test time to decision . 37
Figure A.19 – Accept and reject lines for test plan A.7 . 37

– 4 – 61124 © IEC:2012
Figure A.20 – Test plan A.7 – Operating characteristic curve . 38
Figure A.21 – Test plan A.7 – Expected accumulated test time to decision . 39
Figure A.22 – Accept and reject lines for test plan A.8 . 40
Figure A.23 – Test plan A.8 – Operating characteristic curve . 41
Figure A.24 – Test plan A.8 – Expected accumulated test time to decision . 41
Figure A.25 – Accept and reject lines for test plan A.9 . 42
Figure A.26 – Test plan A.9 – Operating characteristic curve . 43
Figure A.27 – Test plan A.9 – Expected accumulated test time to decision . 43
Figure B.1 – Operating characteristic curves for test plans B.1, B.2, B.3 and B.4 . 44
Figure B.2 – Test plan B.1 – Expected test time to decision . 45
Figure B.3 – Test plan B.2 – Expected test time to decision . 45
Figure B.4 – Test plan B.3 – Expected test time to decision . 46
Figure B.5 – Test plan B.4 – Expected test time to decision . 46
Figure B.6 – Operating characteristic curves for test plans B.5, B.6, B.7 and B.8 . 47
Figure B.7 – Test plan B.5 – Expected test time to decision . 47
Figure B.8 – Test plan B.6 – Expected test time to decision . 48
Figure B.9 – Test plan B.7 – Expected test time to decision . 48
Figure B.10 – Test plan B.8 – Expected test time to decision . 49
Figure B.11 – Operating characteristic curves for test plans B.9, B.10 and B.11 . 49
Figure B.12 – Test plan B.9 – Expected test time to decision . 50
Figure B.13 – Test plan B.10 – Expected test time to decision . 50
Figure B.14 – Test plan B.11– Expected test time to decision . 51
Figure B.15 – Operating characteristic curves for test plans B.12 and B.13. 51
Figure B.16 – Test plan B.12 – Expected test time to decision . 52
Figure B.17 – Test plan B.13 – Expected test time to decision . 52
Figure C.1 – Discrimination ratio, D, and the acceptable number of failures, c = 0 to 8,
as a function of the expected number of failures, µ , for recommended values, 2,5 %,
5 %, 10 %, 20 %, and 30 % of α = β. 56
Figure C.2 – Operation characteristic curves for c = 0 to 8; probability of acceptance
P as a function of the (unknown) true expected number of failures, µ . 57
a 0
Figure C.3 – Discrimination ratio, D, as a function of the expected number of failures,
µ , for recommended values, 2,5 %, 5 %, 10 %, 15 %, 20 % and 30 % of α = β . 58
Figure C.4 – Acceptable number of failures, c, minus expected number of failures, µ
(Δµ = c – µ ) as a function of the expected number of failures µ for recommended
0 0 0
values 2,5 %, 5 %, 10 %, 20 %, and 30 % of α = β . 59
Figure D.1 – Accept and reject lines . 61
∗
Figure D.2 – Expected test time to decision T . 62
e
∗
Figure D.3 – Expected test time to decision of acceptance T (+) . 62
e
Figure D.4 – Operating characteristic P . 62
a
Figure D.5 – Accept and reject lines . 63
∗
T
Figure D.6 – Expected test time to decision . 64
e
∗
Figure D.7 – Expected test time to decision of acceptance T (+) . 64
e
Figure D.8 – Operating characteristic P . 64
a
61124 © IEC:2012 – 5 –
Figure D.9 – Accept and reject lines . 65
∗
Figure D.10 – Expected test time to decision T . 66
e
∗
Figure D.11 – Expected test time to decision of acceptance T (+) . 66
e
Figure D.12 – Operating characteristic P . 67
a
Figure D.13 – Accept and reject lines . 68
∗
Figure D.14 – Expected test time to decision T . 69
e
∗
Figure D.15 – Expected test time to decision of acceptance T (+) . 69
e
Figure D.16 – Operating characteristic P . 69
a
Figure D.17 – Accept and reject lines . 70
∗
Figure D.18 – Expected test time to decision T . 71
e
∗
T (+)
Figure D.19 – Expected test time to decision of acceptance . 71
e
Figure D.20 – Operating characteristic P . 71
a
Figure D.21 – Accept and reject lines . 72
∗
Figure D.22 – Expected test time to decision T . 73
e
∗
Figure D.23 – Expected test time to decision of acceptance T (+) . 73
e
Figure D.24 – Operating characteristic P . 73
a
Figure D.25 – Accept and reject lines . 74
∗
Figure D.26 – Expected test time to decision . 74
T
e
∗
Figure D.27 – Expected test time to decision of acceptance . 74
T (+)
e
Figure D.28 – Operating characteristic P . 75
a
Figure D.29 – Accept and reject lines . 75
*
Figure D.30 – Expected test time to decision T . 76
e
∗
Figure D.31 – Expected test time to decision of acceptance T (+) . 76
e
Figure D.32 – Operating characteristic P . 76
a
Figure E.1 – Example of a sequential test using test plan A.3 – α = β = 10 %, D = 3,
T *
= 1,11×10 h; r versus . 80
m
mo
Figure F.1 – SPRT spreadsheet graphing example . 92
Figure F.2 – OC curve for probability of acceptance, P . 95
a
Figure F.3 – Expected test time for making a decision . 95
Figure H.1 – OC curve plotted from the spreadsheet calculations . 104
Figure K.1 – Test plan types and terminology . 115
Figure K.2 – Principle of test plans . 117
Figure K.3 – Partitioning of the test plan graph . 117
Figure K.4 – Interior nodes and border nodes . 118
Figure K.5 – Paths to the accept line . 118
Figure K.6 – Paths to the reject line . 118
Figure K.7 – Probabilities of paths transfer between nodes . 119

– 6 – 61124 © IEC:2012
Figure K.8 – The recurrent element – Two cases . 121

Table 1 – Advantages and disadvantages for the different test plan types . 14
Table 2 – Overview of the sequential test plans given in Annex A and D . 18
Table 3 – Fixed time/failure terminated test plans . 19
Table 4 – Combined test plans in Annex D . 24
Table A.1 – Accept and reject lines for test plan A.1 . 26
Table A.2 – Accept and reject lines for test plan A.2 . 28
Table A.3 – Accept and reject lines for test plan A.3 . 30
Table A.4 – Accept and reject lines for test plan A.4 . 32
Table A.5 – Accept and reject lines for test plan A.5 . 34
Table A.6 – Accept and reject lines for test plan A.6 . 36
Table A.7 – Accept and reject lines for test plan A.7 . 38
Table A.8 – Accept and reject lines for test plan A.8 . 40
Table A.9 – Accept and reject lines for test plan A.9 . 42
Table D.1 – Sequential test plans in this annex . 60
Table D.2 – Combined test plans in this annex . 60
Table D.3 – Accept and reject lines . 61
Table D.4 – Expected test time to decision and operating characteristic P . 62
a
Table D.5 – Accept and reject lines . 63
Table D.6 – Expected test time to decision and operating characteristic P . 65
a
Table D.7 – Accept and reject lines . 66
Table D.8 – Expected test time to decision and operating characteristic P . 67
a
Table D.9 – Accept and reject lines . 68
Table D.10 – Expected test time to decision and operating characteristic P . 69
a
Table D.11 – Accept and reject lines . 70
Table D.12 – Expected test time to decision and operating characteristic P . 71
a
Table D.13 – Accept and reject lines . 72
Table D.14 – Expected test time to decision and operating characteristic P . 73
a
Table D.15 – Accept and reject lines . 74
Table D.16 – Expected test time to decision and operating characteristic P . 75
a
Table D.17 – Accept and reject lines . 76
Table D.18 – Expected test time to decision and operating characteristic P . 77
a
Table E.1 – Example for a sequential test using test plan A.3 (with example data) . 80
Table E.2 – Constants for border line formulae and their coordinates for sequential test
plans A.1 to A.9 . 85
Table F.1 – Beginning of the spreadsheet prepared to obtain a sequential test graph . 87
Table F.2 – Continuation of parameters calculation for the lines necessary for the
SPRT graph . 88
Table F.3 – Calculations of accept and reject line for the SPRT graph . 88
Table F.4 – Determination of the test termination time . 89
Table F.5 – Formulae for accept and reject line along with the test termination . 91
Table F.6 – Spreadsheet set-up for construction of the OC curves for the SPRT . 94

61124 © IEC:2012 – 7 –
Table H.1 – Set-up of the spreadsheet with embedded formulae – Example . 100
Table H.2 – Formulae embedded into the spreadsheet shown in Table H.1 . 101
Table H.3 – OC curve for the time/failure terminated fixed duration test . 103
Table I.1 – Cumulative normal distribution for fixed u values . 111
γ
Table I.2 – Inverse cumulative normal distribution for fixed 1–γ values . 111

– 8 – 61124 © IEC:2012
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RELIABILITY TESTING –
COMPLIANCE TESTS FOR CONSTANT FAILURE RATE
AND CONSTANT FAILURE INTENSITY

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,
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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 61124 has been prepared by IEC technical committee 56:
Dependability.
This third edition of IEC 61124 cancels and replaces the second edition, published in 2006,
and constitutes a technical revision.
The main changes with respect to the previous edition are as follows:
– A number of new test plans have been added based on the Russian standard GOST R
27.402 [1] , and it is intended to align the new edition of MIL-HDBK-781 [2] with this
edition. Algorithms for optimizing test plans using a spreadsheet program are given and a
number of optimized test plans are listed. Furthermore, emphasis is laid on the fact that
the test should be repeated following design changes.
———————
Figures in square brackets refer to the bibliography.

61124 © IEC:2012 – 9 –
– Discrepancies in test plans A, B as well as Annexes A and B that originated in IEC 60605-
7 [3], now withdrawn, have been corrected so these test plans differ from those given in
previous editions of IEC 61124. As requested by the National Committees, mathematical
background material and spreadsheet program information has been moved to informative
annexes. In addition, the symbol lists have been divided, so that some annexes have
separate lists of symbols.
– Guidance on how to choose test plans has been added as well as guidance on how to use
spreadsheet programs to create them. Test plans A.1 to A.9 and B.1 to B.13 have been
corrected.
– Subclauses 8.1, 8.2, 8.3, Clause 9, Annex C, Clauses G.2, I.2, I.3 and Annex J are
unchanged, except for updated terminology and references.
– Corrections to the second edition proposed by National Committees have been
implemented.
The text of this standard is based on the following documents:
FDIS Report on voting
56/1461/FDIS 56/1468/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 ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication 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.
– 10 – 61124 © IEC:2012
RELIABILITY TESTING –
COMPLIANCE TESTS FOR CONSTANT FAILURE RATE
AND CONSTANT FAILURE INTENSITY

1 Scope
This International Standard gives a number of optimized test plans, the corresponding
operating characteristic curves and expected test times. In addition the algorithms for
designing test plans using a spreadsheet program are also given, together with guidance on
how to choose test plans.
This standard specifies procedures to test whether an observed value of
– failure rate,
– failure intensity,
– mean time to failure (MTTF),
– mean operating time between failures (MTBF),
conforms to a given requirement.
It is assumed, except where otherwise stated, that during the accumulated test time, the times
to failure or the operating times between failures are independent and identically
exponentially distributed. This assumption implies that the failure rate or failure intensity is
constant.
Four types of test plans are described as follows:
– truncated sequential tests;
– time/failure terminated tests;
– fixed calendar time terminated tests without replacement;
– combined test plans.
This standard does not cover guidance on how to plan, perform, analyse and report a test.
This information can be found in IEC 60300-3-5.
This standard does not describe test conditions. This information can be found in IEC 60605-2
and in IEC 60300-3-5.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-191, International Electrotechnical Vocabulary (IEV) – Chapter 191: Dependability
and quality of service
IEC 60300-3-5:2001, Dependability management – Part 3-5: Application guide – Reliability
test conditions and statistical test principles

61124 © IEC:2012 – 11 –
IEC 60605-2, Equipment reliability testing – Part 2: Design of test cycles
IEC 60605-4:2001, Equipment reliability testing – Part 4: Statistical procedures for
exponential distribution – Point estimates, confidence intervals, prediction intervals and
tolerance intervals
IEC 60605-6, Equipment reliability testing – Part-6: Tests for the validity and estimation of the
constant failure rate and constant failure intensity
IEC 61123:1991, Reliability testing – Compliance test plans for success ratio
3 Terms, definitions, abbreviations and symbols
3.1 Terms and definitions
For the purposes of this document the terms and definitions given in IEC 60050-191 apply.
The terms "failure rate" and "failure intensity" are used as meaning constant failure rate and
constant failure intensity.
3.2 Abbreviations and symbols
3.2.1 Abbreviations
MTBF mean operating time between failures
MTTF mean time to failure
OC operating characteristic
SPRT sequential probability ratio test (in some literature called probability ratio sequential
test (PRST)).
3.2.2 Symbols
The generic symbol λ is used in the following for failure rate and failure intensity.
The symbol m is used to denote both the following reliability measures:
– mean operating time between failures, MTBF;
– mean time to failure, MTTF.
When used, the relationship between the above quantities, under the given assumptions, is:
λ =
m
Sequential test plans (see Clause 6) and fixed time/failure terminated test plans (see
Clause 7) are based on m as a reliability measure, thus in these cases:
m =
λ
c acceptable number of failures during the test
discrimination ratio; D = m m   or  D = λ λ
D
0 1 1 0
k summation variable for failures

– 12 – 61124 © IEC:2012
MTBF mean operating time between failures
MTTF mean time to failure
m true MTBF or MTTF
m specified MTTF or MTBF m = 1 λ (design goal)
0 0 0
m lower limit for MTTF or MTBF m = 1 λ
1 1 1
n number of test items at the beginning of the test
P
probability of acceptance
a
p
acceptable failure ratio
q acceptable success ratio, q = 1 – p
0 0 0
R(t) reliability at time t
observed number of failures during the test
r
r
test truncation failure number for sequential tests (SPRT)
*
T accumulated test time
*
accumulated test time stated as accept criterion
T
a
T * minimum test time for r = 0 stated as accept criterion
a, min
*
T expected accumulated test time to decision
e
∗
T (+) expected accumulated test time to acceptance
e
*
T accumulated test time stated as reject criterion
r
*
T accum
...