IEC 61124:2023

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

IEC 61124:2023-02(en-fr)

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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



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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 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

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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

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– 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
0
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

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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
0
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

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– 6 – IEC 61124:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

RELIABILITY TESTING –
COMPLIANCE TESTS FOR CONSTANT FAILURE RATE
AND CONSTANT FAILURE INTENSITY

FOREWORD
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