Application of uncertainty of measurement to conformity assessment activities in the electrotechnical sector

IEC GUIDE 115:2021 is available as IEC GUIDE 115:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC Guide 115:2021 presents a practical approach to the application of uncertainty of measurement to conformity assessment activities in the electrotechnical sector. It is specifically conceived for use in IECEE Schemes as well as by testing laboratories engaged in testing electrical products to national safety standards. It describes the application of uncertainty of measurement principles and provides guidance on making uncertainty of measurement calculations. It also gives some examples relating to uncertainty of measurement calculations for product conformity assessment testing. IEC Guide 115 has been prepared by the IECEE Committee of Testing Laboratories (CTL) to provide guidance on the practical application of the measurement uncertainty requirements of ISO/IEC 17025 to the electrical safety testing conducted within the IECEE CB Scheme. The IECEE CB Scheme is a multilateral, international agreement, among over 40 countries and some 60 national certification bodies, for the acceptance of test reports on electrical products tested to IEC standards.The aim of the CTL is, among other tasks, to define a common understanding of the test methodology with regard to the IEC standards as well as to ensure and continually improve the repeatability and reproducibility of test results among the member laboratories. The practical approach to measurement uncertainty outlined in this document has been adopted for use in the IECEE Schemes, and is also extensively used around the world by testing laboratories engaged in testing electrical products to national safety standards.

Application de l’incertitude de mesure aux activités d’évaluation de la conformité dans le secteur électrotechnique

IEC GUIDE 115:2021 est disponible sous forme de IEC GUIDE 115:2021 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L'IEC Guide 115:2021 présente une approche pratique de l’application de l’incertitude de mesure aux activités d’évaluation de la conformité dans le secteur électrotechnique. Il est spécifiquement conçu pour être utilisé dans les méthodes du système IECEE ainsi que par les laboratoires qui réalisent les essais des produits électriques selon les normes nationales de sécurité. Il décrit l’application des principes de l’incertitude de mesure et donne des recommandations pour la réalisation des calculs de l’incertitude de mesure. Le présent Guide donne également quelques exemples de calculs de l’incertitude de mesure pour des essais d’évaluation de la conformité de certains produits. L'IEC Guide 115 a été établi par le Comité des laboratoires d’essai (CTL, Committee of Testing Laboratories) du système IEC d’essais de conformité et de certification des équipements électriques (IECEE, IEC System of Conformity Assessment Schemes for Electrotechnical Equipment and Components) afin de donner des recommandations pour l’application pratique des exigences concernant l’incertitude de mesure de l’ISO/IEC 17025 aux essais de sécurité électrique réalisés dans le cadre de la méthode des organismes de certification (OC) du système IECEE. La méthode OC du système IECEE est un accord international multilatéral conclu entre plus de 40 pays et quelque 60 organismes nationaux de certification pour l’acceptation des rapports d’essai sur les produits électriques soumis à essai selon les normes IEC. Le but du CTL est, entre autres tâches, de définir une analyse commune de la méthodologie d’essai selon les normes IEC ainsi que d’assurer et d’améliorer de manière continue la répétabilité et la reproductibilité des résultats d’essai entre les laboratoires membres. L’approche pratique de l’incertitude de mesure décrite dans le présent document a été adoptée pour être utilisée dans les méthodes du système IECEE et elle est également largement utilisée dans le monde par les laboratoires d’essai pour les essais des produits électriques selon les normes nationales de sécurité.

General Information

Status
Published
Publication Date
10-Mar-2021
Current Stage
PPUB - Publication issued
Completion Date
11-Mar-2021
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IEC GUIDE 115
Edition 2.0 2021-03
GUIDE
GUIDE
Application of uncertainty of measurement to conformity assessment activities
in the electrotechnical sector
Application de l’incertitude de mesure aux activités d’évaluation de la
conformité dans le secteur électrotechnique
IEC GUIDE 115:2021-03(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC GUIDE 115
Edition 2.0 2021-03
GUIDE
GUIDE
Application of uncertainty of measurement to conformity assessment activities
in the electrotechnical sector
Application de l’incertitude de mesure aux activités d’évaluation de la
conformité dans le secteur électrotechnique
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.020; 19.080 ISBN 978-2-8322-9480-2

Warning! Make sure that you obtained this publication from an authorized distributor.

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC GUIDE 115:2021  IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Application of uncertainty of measurement principles ....................................................... 8

4.1 General ................................................................................................................... 8

4.2 Uncertainty of measurement principles ................................................................. 10

4.3 Background........................................................................................................... 10

4.4 Uncertainty of measurement principles – Application of procedures ...................... 11

4.5 Conclusion ............................................................................................................ 13

5 Guidance on making uncertainty of measurement calculations including examples

of how to perform the calculations ................................................................................. 13

5.1 General principles ................................................................................................. 13

5.2 Summary of steps when estimating uncertainty ..................................................... 14

5.3 Simple example – Estimation of measurement uncertainty for a temperature-

rise test with thermocouples .................................................................................. 17

Annex A (informative) Uncertainty of measurement calculations for product conformity

assessment testing – Examples 1 to 6 .................................................................................. 19

Bibliography .......................................................................................................................... 30

Figure 1 – Procedure 1: uncertainty of measurement calculated ........................................... 11

Figure 2 – Procedure 2: accuracy method ............................................................................. 12

Table 1 ................................................................................................................................. 12

Table 2 ................................................................................................................................. 13

Table 3 ................................................................................................................................. 14

Table 4 ................................................................................................................................. 17

Table 5 ................................................................................................................................. 18

Table 6 ................................................................................................................................. 18

Table A.1 – Input test............................................................................................................ 20

Table A.2 – Input power test ................................................................................................. 22

Table A.3 – Leakage current measurement test .................................................................... 23

Table A.4 – Distance measurement using calliper gauge ...................................................... 25

Table A.5 – Torque measurement ......................................................................................... 27

Table A.6 – Pre-conditioning for ball pressure test ................................................................ 28

---------------------- Page: 4 ----------------------
IEC GUIDE 115:2021  IEC 2021 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
APPLICATION OF UNCERTAINTY OF MEASUREMENT
TO CONFORMITY ASSESSMENT ACTIVITIES
IN THE ELECTROTECHNICAL SECTOR
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.

This second edition of IEC Guide 115 has been prepared, in accordance with

ISO/IEC Directives, Part 1, Annex A, by IECEE/CTL. This is a non-mandatory guide in

accordance with SMB Decision 136/8.
This second edition cancels and replaces the first edition published in 2007.
The main changes with respect to the previous edition are as follows:

a) editorial alignment to ISO/IEC 17025:2017 without adapting the technical content;

b) references to ISO/IEC 17025:2005 and ISO/IEC 17025:2017 in order to help for the

transition to the new edition of ISO/IEC 17025.
---------------------- Page: 5 ----------------------
– 4 – IEC GUIDE 115:2021  IEC 2021
The text of this IEC Guide is based on the following documents:
Four months' vote Report on voting
SMBNC/8/DV SMBNC/14/RV

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 Guide is English.

This publication has been drafted in accordance with the 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.

---------------------- Page: 6 ----------------------
IEC GUIDE 115:2021  IEC 2021 – 5 –
INTRODUCTION

This document has been prepared by the IECEE Committee of Testing Laboratories (CTL) to

provide guidance on the practical application of the measurement uncertainty requirements of

ISO/IEC 17025 to the electrical safety testing conducted within the IECEE CB Scheme.

The IECEE CB Scheme is a multilateral, international agreement, among over 40 countries

and some 60 national certification bodies, for the acceptance of test reports on electrical

products tested to IEC standards.

The aim of the CTL is, among other tasks, to define a common understanding of the test

methodology with regard to the IEC standards as well as to ensure and continually improve

the repeatability and reproducibility of test results among the member laboratories.

The practical approach to measurement uncertainty outlined in this document has been

adopted for use in the IECEE Schemes, and is also extensively used around the world by

testing laboratories engaged in testing electrical products to national safety standards.

This document is of particular interest to the following IEC technical committees, which can

decide to make use of it if necessary:
TECHNICAL COMMITTEE 13: ELECTRICAL ENERGY MEASUREMENT AND CONTROL
TECHNICAL COMMITTEE 17: HIGH-VOLTAGE SWITCHGEAR AND CONTROLGEAR
TECHNICAL COMMITTEE 18: ELECTRICAL INSTALLATIONS OF SHIPS AND OF MOBILE
AND FIXED OFFSHORE UNITS
TECHNICAL COMMITTEE 20: ELECTRIC CABLES
TECHNICAL COMMITTEE 21: SECONDARY CELLS AND BATTERIES
TECHNICAL COMMITTEE 22: POWER ELECTRONIC SYSTEMS AND EQUIPMENT
TECHNICAL COMMITTEE 23: ELECTRICAL ACCESSORIES
TECHNICAL COMMITTEE 32: FUSES
TECHNICAL COMMITTEE 33: POWER CAPACITORS AND THEIR APPLICATIONS
TECHNICAL COMMITTEE 34: LIGHTING
TECHNICAL COMMITTEE 35: PRIMARY CELLS AND BATTERIES
TECHNICAL COMMITTEE 38: INSTRUMENT TRANSFORMERS
TECHNICAL COMMITTEE 40: CAPACITORS AND RESISTORS FOR ELECTRONIC
EQUIPMENT
TECHNICAL COMMITTEE 47: SEMICONDUCTOR DEVICES
TECHNICAL COMMITTEE 59: PERFORMANCE OF HOUSEHOLD AND SIMILAR
ELECTRICAL APPLIANCES
TECHNICAL COMMITTEE 61: SAFETY OF HOUSEHOLD AND SIMILAR ELECTRICAL
APPLIANCES
TECHNICAL COMMITTEE 62: ELECTRICAL EQUIPMENT IN MEDICAL PRACTICE
TECHNICAL COMMITTEE 64: ELECTRICAL INSTALLATIONS AND PROTECTION
AGAINST ELECTRIC SHOCK
TECHNICAL COMMITTEE 65: INDUSTRIAL-PROCESS MEASUREMENT, CONTROL AND
AUTOMATION
TECHNICAL COMMITTEE 66: SAFETY OF MEASURING, CONTROL AND LABORATORY
EQUIPMENT
TECHNICAL COMMITTEE 76: OPTICAL RADIATION SAFETY AND LASER EQUIPMENT
TECHNICAL COMMITTEE 77: ELECTROMAGNETIC COMPATIBILITY
---------------------- Page: 7 ----------------------
– 6 – IEC GUIDE 115:2021  IEC 2021
TECHNICAL COMMITTEE 78: LIVE WORKING
TECHNICAL COMMITTEE 80: MARITIME NAVIGATION AND RADIOCOMMUNICATION
EQUIPMENT AND SYSTEMS
TECHNICAL COMMITTEE 82: SOLAR PHOTOVOLTAIC ENERGY SYSTEMS
TECHNICAL COMMITTEE 110: ELECTRONIC DISPLAYS
---------------------- Page: 8 ----------------------
IEC GUIDE 115:2021  IEC 2021 – 7 –
APPLICATION OF UNCERTAINTY OF MEASUREMENT
TO CONFORMITY ASSESSMENT ACTIVITIES
IN THE ELECTROTECHNICAL SECTOR
1 Scope

This Guide presents a practical approach to the application of uncertainty of measurement to

conformity assessment activities in the electrotechnical sector. It is specifically conceived for

use in IECEE Schemes as well as by testing laboratories engaged in testing electrical

products to national safety standards. It describes the application of uncertainty of

measurement principles and provides guidance on making uncertainty of measurement

calculations. It also gives some examples relating to uncertainty of measurement calculations

for product conformity assessment testing.
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.

ISO/IEC 17025, General requirements for the competence of testing and calibration

laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

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
coverage factor

number that, when multiplied by the combined standard uncertainty, produces an interval

(the expanded uncertainty) about the measurement result that can be expected to encompass

a large, specified fraction (e.g. 95 %) of the distribution of values that could be reasonably

attributed to the measurand
3.2
combined standard uncertainty
result of the combination of standard uncertainty components
3.3
error of measurement
result of a measurement minus a true value of the measurand

Note 1 to entry: The error of measurement is not precisely quantifiable because the true value lies somewhere

unknown within the range of measurement uncertainty.
---------------------- Page: 9 ----------------------
– 8 – IEC GUIDE 115:2021  IEC 2021
3.4
expanded uncertainty

value obtained by multiplying the combined standard uncertainty by a coverage factor

3.5
level of confidence

probability that the value of the measurand lies within the quoted range of uncertainty

3.6
measurand

quantity subjected to measurement, evaluated in the state assumed by the measured system

during the measurement itself
[SOURCE: IEC 60359:2001, 3.1.1, modified – The NOTES have been deleted.]
3.7
quantity X
source of uncertainty
3.8
standard deviation
positive square root of the variance
3.9
standard uncertainty
estimated standard deviation
3.10
uncertainty of measurement

parameter, associated with the result of a measurement, that characterizes the dispersion of

the values that could reasonably be attributed to the measurand
[SOURCE: IEC 60359:2001, 3.1.4, modified – The NOTES have been deleted.]
3.11
Type A evaluation method

method of evaluation of uncertainty of measurement by the statistical analysis of a series of

observations
3.12
Type B evaluation method

method of evaluation of uncertainty of measurement by means other than the statistical

analysis of a series of observations
4 Application of uncertainty of measurement principles
4.1 General

4.1.1 Qualification and acceptance of Certification Body Testing Laboratories (CBTLs), e.g.

in the IECEE, are performed according to ISO/IEC 17025.
---------------------- Page: 10 ----------------------
IEC GUIDE 115:2021  IEC 2021 – 9 –
ISO/IEC 17025:2005, 5.4.6.2

"Testing laboratories shall have and apply procedures for estimating uncertainty of measure-

ment. In certain cases, the nature of the test method may preclude rigourous, metrologically

and statistically valid, calculation of uncertainty of measurement. In these cases the

laboratory shall at least attempt to identify all the components of uncertainty and make a

reasonable estimation, and shall ensure that the form of reporting of the result does not give a

wrong impression of the uncertainty. Reasonable estimation shall be based on knowledge of

the performance of the method and on the measurement scope and shall make use of, for

example, previous experience and validation data.

NOTE 1 The degree of rigour needed in an estimation of uncertainty of measurement depends on factors such as:

– the requirements of the test method;
– the requirements of the client;

– the existence of narrow limits on which decisions on conformance to a specification are based.

NOTE 2 In those cases where a well-recognized test method specifies limits to the values of the major sources of

uncertainty of measurement and specifies the form of presentation of calculated results, the laboratory is

considered to have satisfied this clause by following the test method and reporting instructions (see 5.10)."

ISO/IEC 17025:2017, 7.6
"7.6 Evaluation of measurement uncertainty

7.6.1 Laboratories shall identify the contributions to measurement uncertainty. When

evaluating measurement uncertainty, all contributions that are of significance, including those

arising from sampling, shall be taken into account using appropriate methods of analysis.

7.6.2 A laboratory performing calibrations, including of its own equipment, shall evaluate the

measurement uncertainty for all calibrations.

7.6.3 A laboratory performing testing shall evaluate measurement uncertainty. Where the

test method precludes rigorous evaluation of measurement uncertainty, an estimation shall be

made based on an understanding of the theoretical principles or practical experience of the

performance of the method.

NOTE 1 In those cases where a well-recognized test method specifies limits to the values of the major sources of

measurement uncertainty and specifies the form of presentation of the calculated results, the laboratory is

considered to have satisfied 7.6.3 by following the test method and reporting instructions.

NOTE 2 For a particular method where the measurement uncertainty of the results has been established and

verified, there is no need to evaluate measurement uncertainty for each result if the laboratory can demonstrate

that the identified critical influencing factors are under control."
4.1.2 ISO/IEC 17025:2005, 5.10.3.1 c) states:

"c) where applicable, a statement on the estimated uncertainty of measurement; information

on uncertainty is needed in test reports, when it is relevant to the validity or application of

the test results, when a customer’s instruction so requires, or when the uncertainty affects

compliance to a specification limit;".
ISO/IEC17025:2017, 7.8.3.1 c) states:

"c) where applicable, the measurement uncertainty presented in the same unit as that of the

measurand or in a term relative to the measurand (e.g. percent) when:
– it is relevant to the validity or application of the test results;
– a customer's instruction so requires, or
---------------------- Page: 11 ----------------------
– 10 – IEC GUIDE 115:2021  IEC 2021
– the measurement uncertainty affects conformity to a specification limit;".

4.1.3 ISO/IEC 17025 was written as a general use document, for all industries. Uncertainty

of measurement principles are applied to laboratory testing and presentation of test results to

provide a degree of assurance that decisions made about conformance of the products tested

according to the relevant requirements are valid. Procedures and techniques for uncertainty of

measurement calculations are well established. This document is written to provide more

specific guidance on the application of uncertainty of measurement principles to reporting of

testing results under the CB Scheme.

4.1.4 Clause 4 of this document focuses on the application of uncertainty of measurement

principles under the CB Scheme, while Clause 5 provides guidance on making uncertainty of

measurement calculations and includes examples.
4.2 Uncertainty of measurement principles

A challenge to applying uncertainty of measurement principles to conformity assessment

activities is managing the cost, time and practical aspects of determining the relationships

between various sources of uncertainty. Some relationships are either unknown or would take

considerable effort, time and cost to establish. There are a number of proven techniques

available to address this challenge. These techniques include eliminating from consideration

those sources of variability which have little influence on the outcome and minimizing

significant sources of variability by controlling them.
4.3 Background

4.3.1 Test methods used under the IECEE CB Scheme are in essence consensus standards.

Criteria used to determine conformance with requirements are most often based on a

consensus of judgment of what the limits of the test result should be. Exceeding the limit by a

small amount does not result in an imminent hazard. Test methods used can have a precision

statement expressing the maximum permissible uncertainty expected to be achieved when the

method is used. Historically, test laboratories have used state-of-the-art equipment and not

considered uncertainty of measurement when comparing results to limits. Safety standards

have been developed in this environment and the limits in the standards reflect this practice.

4.3.2 Test parameters that influence the results of tests can be numerous. Nominal

variations in some test parameters have little effect on the uncertainty of the measurement

result. Variations in other parameters can have an effect. However, the degree of influence

can be minimized by limiting the variability of the parameter when performing the test.

4.3.3 A frequent way of accounting for the effects of test parameters on test results is to

define the acceptable limits of variability of test parameters. When this is done, any variability

in measurement results obtained due to changes in the controlled parameters is not

considered significant if the parameters are controlled within the limits. Examples of the

application of this technique require:

a) input power source to be maintained: voltage ±2 %, frequency ±0,5 %, total harmonic

distortion maximum 3 %;
b) ambient temperature: 23 °C ± 2 °C;
c) relative humidity: 93 % ± 2 % (RH);
d) personnel: documented technical competency requirements for the test;
e) procedures: documented laboratory procedures;
f) equipment accuracy: instrumentation with accuracy according to CTL OD-5014.

NOTE The acceptable limits in items a) through c) are given as examples and do not necessarily represent actual

limits established.
---------------------- Page: 12 ----------------------
IEC GUIDE 115:2021  IEC 2021 – 11 –

4.3.4 The end result of controlling sources of variability within prescribed limits is that the

measurement result can be used as the best estimate of the measurand. In effect, the

uncertainty of measurement about the measured result is negligible with regard to the final

pass/fail decision.
4.4 Uncertainty of measurement principles – Application of procedures

4.4.1 When a test results in measurement of a variable, there is uncertainty associated with

the test result obtained.

4.4.2 Procedure 1, see Figure 1, is used when calculation of uncertainty of measurement is

required by ISO/IEC 17025:2017, 7.6.3 and 7.8.3.1 c). Calculate the uncertainty for

measurement (see Clause 5) and compare the measured result with the uncertainty band to a

defined acceptable limit. The measurement complies with the requirement if the probability of

its being
...

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