SIST EN IEC 61124:2023
(Main)Reliability testing - Compliance tests for constant failure rate and constant failure intensity (IEC 61124:2023)
Reliability testing - Compliance tests for constant failure rate and constant failure intensity (IEC 61124:2023)
This International Standard gives a number of optimized test plans, the corresponding border lines and characteristics. 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 operating 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 assumed to be constant.
Four types of test plans are described as follows:
- truncated sequential probability ratio test (SPRT);
- fixed time/failure terminated test (FTFT);
- fixed calendar time terminated test without replacement;
- combined test.
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.
Prüfungen der Funktionsfähigkeit - Prüfpläne für konstante Ausfallrate und konstante Ausfalldichte (IEC 61124:2023)
Essais de fiabilité - Plan d'essais de conformité d'un taux de défaillance constant et d'une intensité de défaillance constante (IEC 61124:2023)
L'IEC 61124:2023 spécifie un certain nombre de plans d’essai optimisés, ainsi que les limites et caractéristiques correspondantes. De plus, les algorithmes pour concevoir des plans d’essai à l’aide d’une feuille de calcul sont également fournis, avec des recommandations relatives au choix de ces plans.
Le présent document spécifie les procédures utilisées pour vérifier qu’une valeur observée:
- d’un taux de défaillance;
- d’une intensité de défaillance;
- d’un temps moyen de fonctionnement avant défaillance (MTTF);
- d’un temps moyen de fonctionnement entre défaillances (MTBF).
est conforme à une exigence donnée.
Il est présumé, sauf spécification contraire, que pendant le temps d’essai cumulé, les temps de fonctionnement avant défaillance ou les temps de fonctionnement entre défaillances sont indépendants et suivent une distribution identique et exponentielle. Cette hypothèse implique que le taux de défaillance ou l’intensité de défaillance est présumé constant.
Preskušanje zanesljivosti - Ustreznostni preskusi za konstantno pogostost odpovedi in konstantno intenzivnost odpovedi (IEC 61124:2023)
Ta mednarodni standard navaja optimizirane preskusne načrte, ustrezne meje in lastnosti. Poleg tega navaja algoritme za projektiranje preskusnih načrtov s programom s preglednicami in smernice za izbiro preskusnih načrtov.
Ta standard določa splošne postopke preskusa, ali je ugotovljena vrednost
– pogostosti odpovedi,
– intenzivnosti odpovedi,
– povprečnega časa delovanja do odpovedi (MTTF),
– povprečnega časa delovanja med odpovedmi (MTBF),
skladna z navedeno zahtevo.
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:
– skrajšan sekvenčni preskus razmerja verjetnosti (SPRT);
– časovno/z odpovedjo zaključeni preskus (FTFT);
– koledarsko zaključeni preskus brez zamenjave;
– kombinirani preskus.
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.
Ta standard ne opisuje preskusnih pogojev. Te informacije so navedene v standardu IEC 60605-2 in standardu IEC 60300-3-5.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2023
Preskušanje zanesljivosti - Ustreznostni preskusi za konstantno pogostost
odpovedi in konstantno intenzivnost odpovedi (IEC 61124:2023)
Reliability testing - Compliance tests for constant failure rate and constant failure
intensity (IEC 61124:2023)
Prüfungen der Funktionsfähigkeit - Prüfpläne für konstante Ausfallrate und konstante
Ausfalldichte (IEC 61124:2023)
Essais de fiabilité - Plan d'essais de conformité d'un taux de défaillance constant et
d'une intensité de défaillance constante (IEC 61124:2023)
Ta slovenski standard je istoveten z: EN IEC 61124:2023
ICS:
03.120.01 Kakovost na splošno Quality in general
19.020 Preskuševalni pogoji in Test conditions and
postopki na splošno procedures in general
21.020 Značilnosti in načrtovanje Characteristics and design of
strojev, aparatov, opreme machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN IEC 61124
NORME EUROPÉENNE
EUROPÄISCHE NORM April 2023
ICS 03.120.30; 19.020; 21.020 Supersedes EN 61124:2012
English Version
Reliability testing - Compliance tests for constant failure rate and
constant failure intensity
(IEC 61124:2023)
Essais de fiabilité - Plans d'essai de conformité pour un Prüfungen der Funktionsfähigkeit - Prüfpläne für konstante
taux de défaillance constant et une intensité de défaillance Ausfallrate und konstante Ausfalldichte
constante (IEC 61124:2023)
(IEC 61124:2023)
This European Standard was approved by CENELEC on 2023-03-31. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61124:2023 E
European foreword
The text of document 56/1980/FDIS, future edition 4 of IEC 61124, prepared by IEC/TC 56
"Dependability" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2023-12-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2026-03-31
document have to be withdrawn
This document supersedes EN 61124:2012 and all of its amendments and corrigenda (if any).
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.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61124:2023 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 standard indicated:
IEC 62506 NOTE Approved as EN 62506
IEC 61014 NOTE Approved as EN 61014
IEC 61710 NOTE Approved as EN 61710
IEC 61649 NOTE Approved as EN 61649
Annex ZA
(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.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-192 - International electrotechnical vocabulary - Part - -
192: Dependability
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 2019 Reliability testing - Compliance test plans for EN IEC 61123 2020
success ratio
IEC 61124 ®
Edition 4.0 2023-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Reliability testing – Compliance tests for constant failure rate and constant
failure intensity
Essais de fiabilité – Plans d’essai de conformité pour un taux de défaillance
constant et une intensité de défaillance constante
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 03.120.30; 19.020; 21.020 ISBN 978-2-8322-6453-9
– 2 – IEC 61124:2023 © IEC 2023
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, abbreviated terms and symbols . 11
3.1 Terms and definitions . 11
3.2 Abbreviated terms and symbols . 11
3.2.1 Abbreviated terms . 11
3.2.2 Symbols . 11
4 General requirements and area of application . 13
4.1 Requirements and characteristics . 13
4.2 Applicability to replaced and repaired items . 13
4.3 Types of test plans . 14
4.3.1 General . 14
4.3.2 Advantages and disadvantages of the different test plan types . 14
5 General test procedure . 16
5.1 Test conditions . 16
5.2 General characteristics of the test plans . 17
5.3 Data to be recorded . 17
*
5.4 Calculation of accumulated test time, T . 17
5.5 Number of failures . 18
6 Truncated sequential probability ratio test (SPRT) plans . 18
6.1 General . 18
6.2 Common test procedure . 19
6.3 Decision criteria . 19
6.4 Operating characteristic (OC) curve . 20
6.5 Expected accumulated test time to decision (ETT) . 21
6.6 Overview of test plans . 22
7 Fixed time/failure terminated test plans – Fixed duration (to acceptance) test
plans . 25
7.1 General . 25
7.2 Common test procedure . 26
7.3 Decision criteria . 26
7.4 Test plans . 26
8 Design of alternative time/failure terminated test plans (FTFT) . 27
8.1 General . 27
8.2 Design procedures . 27
8.3 Common FTFT procedure . 28
8.4 Decision criteria . 28
9 Calendar time/failure terminated test plans (FTFT) for non-replaced items . 28
9.1 General . 28
9.2 Common test procedure . 29
9.3 Decision criteria . 29
9.4 Use of IEC 61123:2019, Table 5 for fixed calendar time tests . 29
9.4.1 General . 29
9.4.2 Procedure when the test time is given . 30
IEC 61124:2023 © IEC 2023 – 3 –
9.4.3 Procedure when the number of items is given . 30
10 Combined test plans . 30
10.1 General . 30
10.2 Common test procedure . 30
10.3 Decision criteria . 31
10.4 Test plans . 31
11 Performing the test and presenting the results . 32
Annex A (normative) Tables for border lines of SPRT plans (types A and C) . 33
A.1 Symbols . 33
A.2 Border lines . 33
A.3 Example of the SPRT plan from Clause 6 . 37
Annex B (normative) Tables and graphs for combined test plans (type D) . 39
B.1 General . 39
B.2 Test plans D.3 and C.3 (α = β = 10 %, D = 1,7 ) . 41
Annex C (informative) Extension of the set of SPRTs type A . 44
C.1 Symbols . 44
C.2 Extension of the set of type A tests (through interpolation by α and β ) . 44
Annex D (informative) Approximation of operating characteristic for type A SPRTs by
Wald's formula . 47
D.1 Symbols . 47
D.2 Approximations of OC in this document . 47
D.3 Approximation of OC for type A SPRT by Wald's formula . 47
D.4 Construction of the approximated OC curve using a spreadsheet . 49
Annex E (informative) Mathematical references and examples for fixed time/failure
terminated test (FTFT) plans . 51
E.1 Symbols . 51
E.2 Mathematical references . 51
E.2.1 General . 51
E.2.2 Mathematical references . 51
E.2.3 Design procedure {a} . 54
E.2.4 Design procedure {b} . 55
E.2.5 Design procedure {c} . 55
E.2.6 Design procedure {d} . 56
E.3 Examples of FTFT design using test plans B . 56
E.3.1 Example 1 . 56
E.3.2 Example 2 . 57
E.4 Test OC approximation using formula for FTFT . 58
Annex F (informative) Examples of FTFT design using a spreadsheet program . 59
F.1 General . 59
F.2 Finding the test border lines using optimization on the example of the design
procedure {b} . 61
F.3 ETT and OC curves . 63
F.4 Example of FTFT design by procedure {a} . 65
F.5 Example of FTFT design by procedure {c} . 67
F.6 Example of FTFT design by procedure {d} . 69
F.7 Example of a test with replacement of failed items . 72
F.8 Evaluation of an approximate OC for non-FTFT plans using a spreadsheet . 73
Annex G (informative) Examples and mathematical references for the calendar time
terminated test plans . 78
– 4 – IEC 61124:2023 © IEC 2023
G.1 Examples . 78
G.1.1 Example 1 . 78
G.1.2 Example 2 . 78
G.2 Mathematical background . 79
Annex H (informative) Derivation and mathematical reference for the optimized test
plans of GOST R 27 402 [12] . 80
H.1 Symbols . 80
H.2 Test plan types and terminology . 81
H.3 Introductory remarks . 81
H.4 Procedure used for developing the optimized test plans . 82
Bibliography . 89
* *
Figure 1 – Relative ETT (T /m ) and MaxTT (T /m ) of various tests with
e 0 t 0
the same risks . 16
Figure 2 – SPRT diagram and test example . 20
Figure 3 – OC curve, P . 21
a
Figure 4 – SPRT – Curve of expected accumulated test time to decision (ETT) . 22
Figure 5 – Example of a decision graph for combined test plan (type D) and for SPRT
type C . 31
Figure A.1 – Decision graph of SPRT plan . 34
Figure B.1 – Expected accumulated test time to acceptance decision, T *(+) for D.3
e
and C.3 test plans . 43
Figure B.2 – Operating characteristic P for D.3 and C.3 test plans . 43
a
Figure D.1 – Approximation of OC for type A SPRT using Wald's formula . 48
Figure E.1 – Example 1 – Expected accumulated test time to decision (ETT) of tests
B.2 and A.25 . 57
Figure E.2 – Example 1 – Operating characteristic of tests B.2 and A.25 . 58
Figure F.1 – Using Solver to find T */m – Accumulated test truncation time in terms
t 0
of m . 63
Figure F.2 – ETT plotted from the spreadsheet calculations . 64
Figure F.3 – OC curve plotted from the spreadsheet calculations . 64
Figure F.4 – Using Solver to find T */m and c in Step {a1} . 66
t 0
Figure F.5 – Using Solver to find T */m in Step {a2} . 67
t 0
*
Figure F.6 – Using Solver to find T /m in Step {c2} . 69
t 0
Figure F.7 – Using Solver to find D and c in Step {d1} . 71
*
Figure F.8 – Using Solver to find D and T in Step {d2} . 72
t
*
Figure F.9 – Using Solver to find c and T /m from Clause F.8 . 75
t 0
Figure F.10 – OC approximated by formula for FTFT (example from Clause F.8) . 77
Figure H.1 – Test plan types and terminology . 81
Figure H.2 – Principle of test plans . 83
Figure H.3 – Partitioning of the test plan graph . 83
Figure H.4 – Interior nodes and border nodes . 83
Figure H.5 – Paths to the accept line . 84
IEC 61124:2023 © IEC 2023 – 5 –
Figure H.6 – Paths to the reject line . 84
Figure H.7 – Probabilities of paths transfer between nodes . 85
Figure H.8 – Recurrent element – Two cases . 88
Table 1 – Advantages and disadvantages for the different test plan types . 15
Table 2 – OC curve . 20
Table 3 – Relative ETT versus m/m . 21
Table 4 – Overview of type A SPRT plans . 23
Table 5 – Overview of type C SPRT plans . 25
Table 6 – Type B FTFT plans . 27
Table 7 – Overview of type D combined plans . 32
Table A.1 – Constants for border line formulae and their coordinates for type A SPRT
plans. 35
Table A.2 – Constants for border line formulae and their coordinates for type C SPRT
plans. 36
Table A.3 – Example for SPRT using test plan A.41 (with example data) . 38
Table B.1 – Combined test plans in Annex B. 39
Table B.2 – Type D test plans – Accept and reject lines . 40
Table B.3 – Expected accumulated test time to acceptance decision, T *(+), for D and
e
C test plans . 41
Table B.4 – Accept and reject lines for D.3 and C.3 test plans . 42
Table C.1 – Example for interpolation by α and β . 46
Table D.1 – Spreadsheet set-up for construction of the OC curve by Wald . 50
Table D.2 – Formulae embedded in the spreadsheet . 50
Table E.1 – List of the typical FTFT design procedures . 54
Table F.1 – Set-up of the spreadsheet with embedded formulae . 60
Table F.2 – Formulae embedded in the spreadsheet . 61
Table F.3 – Fragment from Table 6 . 62
Table F.4 – Set-up 1 of the spreadsheet for example by procedure {a} . 65
Table F.5 – Set-up 2 of the spreadsheet for example by procedure {a} . 66
Table F.6 – Set-up 3 (final solution) for example by procedure {a} . 67
Table F.7 – Set-up 2 for example by procedure {c} . 68
Table F.8 – Set-up 3 (final solution) for example by procedure {c} . 69
Table F.9 – Set-up 1 of the spreadsheet for example by procedure {d} . 70
Table F.10 – Set-up 2 of the spreadsheet for example by procedure {d}. 71
Table F.11 – Set-up 3 (final solution) for example by procedure {d} . 72
Table F.12 – Set-up of the spreadsheet with embedded formulae from Clause F.8 . 74
Table F.13 – Set-up 1 of the spreadsheet from Clause F.8. 75
Table F.14 – Set-up 2 of the spreadsheet for example from Clause F.8 . 76
– 6 – IEC 61124:2023 © IEC 2023
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, 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
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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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
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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.
IEC 61124 has been prepared by IEC technical committee 56: Dependability. It is an
International Standard.
This fourth edition cancels and replaces the third edition published in 2012. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) The truncated sequential probability ratio test (SPRT) [1], [2], [3] has been significantly
developed in recent years [4], [5], [6]. In this edition, type A test plans (optimally truncated
SPRT) have been significantly changed, as follows:
___________
Numbers in square brackets refer to the Bibliography.
IEC 61124:2023 © IEC 2023 – 7 –
– the tests are significantly truncated (the maximal test time is low) without substantially
increasing the expected accumulated test time to decision (ETT);
– the true producer's and consumer's risks (α′, β′) are given and are very close to the
nominal values;
– the range of the test parameters is wide (risks and discrimination ratio);
– the test plans include various risk ratios (not restricted to equal risks only);
– the values of the ETT are accurate and given in the relevant region (for practical use);
– guidelines for extension of the tests set (using accurate interpolation) are included.
b) Other ready-to-use test plans (types B, C, D) are not changed, only the form of presentation
of the data on their border lines and the characteristics has been changed. This form is
made unified for all types of test plans, which helps the comparison of different plans and,
accordingly, to facilitate the selection of the most appropriate.
c) FTFT design procedures, to extend the set of test plans B, are significantly changed and
make the design accurate and simple. The implementation of this design is given on a
spreadsheet program. A unified approach to the calculation of the operational
characteristics of all types of test plans is introduced.
The text of this International Standard is based on the following documents:
Draft Report on voting
56/1980/FDIS 56/1985/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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 document 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.
– 8 – IEC 61124:2023 © IEC 2023
INTRODUCTION
A compliance test is an essential part of the reliability assurance system [7], [8], [9]. Reliability
is affected by many random factors, so its prediction is not accurate. The direct way to check if
the item meets its reliability specifications is to perform a compliance test.
The tests described in this document can be applied to items that have a failure rate or failure
intensity (denoted by λ) which can be considered as a constant. The procedures are based on
the assumption that trials of the test are statistically independent. If it is necessary to test the
constant failure rate and constant failure intensity assumption, the procedures given in
IEC 60605-6 should be used.
The test serves to verify the compliance with a specified λ , that is, to verify that λ ≤ λ .
0 0
The probability of making the correct decision in the test depends on the test duration and on
the sample size (number of failures). The tests usually require a large sample size and,
accordingly, a large consumption of time and funds. The consumptions are especially high for
reliability testing. For this reason, sampling plans of the tests should be carefully planned in
order to reduce the consumption.
This document is dedicated to sampling plans for the tests.
The tests are characterized by the operating characteristic (OC) and test duration until the test
stops with the accept/reject decision on the compliance.
OC is the probability of accepting an item as meeting the requirements. In this document, the
OC is represented by the coordinates of its two points (see ISO 3534-2 [10]):
– (λ , 1 – α) are the coordinates of the producer's risk point (PRP);
– (λ , β) are the coordinates of the consumer's risk point (CRP);
where α and β are producer's and consumer's risks, and λ > λ .
1 0
The test duration (test time) is a random value and in this document is usually characterized by
its expected (ETT) and maximum (MaxTT) values.
This document contains the following types of tests:
– optimally truncated sequential probability ratio test (SPRT, type A);
– maximally truncated SPRT (type C);
– fixed time/failure terminated test (FTFT, type B);
– FTFT – calendar time terminated test without replacement;
– combined test plan (type D).
The tests can be used for testing equipment (repaired or non-repaired) as well as for
components (replaced or not replaced when failing).
All the plans in this document are sequential, that is, every time an event occurs during the test,
a decision is made to continue or stop the test. An event occurs in two cases: when a failure
occurs, or when the acceptance boundary is crossed, which means that there is compliance
hree types:
with the requirements. The decision can be one of t
• accept the compliance and stop the test;
• reject the compliance and stop the test;
• continue the test, because there is not enough information to stop it.
IEC 61124:2023 © IEC 2023 – 9 –
The difference between the types of tests is in the shape of border lines.
The FTFT is characterized by decision rules for accepting or rejecting compliance when the
MaxTT has been reached, or the acceptable number of failures has been exceeded. This test
has the smallest MaxTT among all tests with specified PRP and CRP. If, for a tested item λ ≤ λ ,
then ETT is close to MaxTT; otherwise, if λ > λ , then ETT decreases. In fact, the only advantage
of the FTFT over the SPRT is the simplicity of designing new test plans. A detailed procedure
for the design is provided in this document.
The optimally truncated SPRT (type A) has a MaxTT of 1,1 to 1,2 times greater than the FTFT
with the same PRP and CRP. However, the ETT of the SPRT is significantly smaller than that
of the corresponding FTFT, and for λ ≤ λ it can be 1,4 to 1,8 times smaller. This is a great
advantage of the SPRT. This document contains an extensive set of ready-to-use type A plans.
The set also allows the design of additional tests by simple interpolation according to the
procedure provided in this document.
The maximally truncated SPRT (type C) has a MaxTT, like the FTFT; however, its ETT is less
than that of the FTFT, but greater than that of the type A SPRT.
In the combined test plan (type D), test items with early failures will not be rejected in the initial
stages of the test.
Some of the ready-to-use tests listed in this document have a very large maximal acceptable
number of failures, which is why they are likely to be rarely used. However, the data allows the
user of this document to assess the economic benefit of the OC test requirements and, in
general, to assess the advisability of performing the test.
Accumulated test time can be reduced by accelerated testing (see IEC 62506 [11]).
An example of objects covered by this document can be electronic equipment and its
components, which usually have a failure rate or failure intensity that can be considered
constant.
Clause 4 presents the requirements and area of application of the tests and recommendations
for their selection. Clause 5 explains the general elements of the test procedure. Clause 6
explains the characteristics of the ready-to-use SPRT and the parameters of the border lines
(their values are given in Annex A). Extension of the set of SPRT tests are given in Annex C.
Clause 7 is devoted to the ready-to-use FTFT. Clause 8 presents the design of FTFT plans that
are not covered in the tables of this document. Mathematical references and procedures of the
design of FTFT plans are given in Annex E and in Annex F. Clause 9 is devoted to the calendar
FTFT for non-replaced items (examples and mathematical references of their design are given
in Annex G). Clause 10 is devoted to the combined test plans (parameters of their border lines
are given in Annex B). Clause 11 explains how to perform the test and presentation of results.
Annex D presents the approximation of OC by Wald's formula. Annex H is devoted to the
mathematical reference for the test plans of GOST R 27.402 [12].
– 10 – IEC 61124:2023 © IEC 2023
RELIABILITY TESTING –
COMPLIANCE TESTS FOR CONSTANT FAILURE RATE
AND CONSTANT FAILURE INTENSITY
1 Scope
This document gives a number of optimized test plans, the corresponding border lines and
characteristics. 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 document specifies procedures to test whether an observed value of
– failure rate,
– failure intensity,
– mean operating 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 assumed to be
constant.
Four types of test plans are described as follows:
– truncated sequential probability ratio test (SPRT);
– fixed time/failure terminated test (FTFT);
– fixed calendar time terminated test without replacement;
– combined test.
This document 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 document 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 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 60050-192, International Electrotechnical Vocabulary (IEV) – Part 192: Dependability,
available at http://www.electropedia.org
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 61124:2023 © IEC 2023 – 11 –
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 61123:2019, Reliability testing – Compliance test plans for success ratio
3 Terms, definitions, abbreviated terms and symbols
3.1 Terms and definitions
For the purposes of this document the terms and definitions given in IEC 60050-192 apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
The terms "failure rate" and "failure intensity" are used as meaning constant failure rate and
constant failure intensity.
3.2 Abbreviated terms and symbols
3.2.1 Abbreviated terms
ADT accept decision time – time that the test was terminated with accept decision
CDF cumulative distribution function
CRP consumer's risk point
ETT expected accumulated test time
...
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