IEC 60688:2021
(Main)Electrical measuring transducers for converting AC and DC electrical quantities to analogue or digital signals
Electrical measuring transducers for converting AC and DC electrical quantities to analogue or digital signals
IEC 60688:2021 applies to transducers with electrical inputs and outputs for making measurements of AC or DC electrical quantities. The output signal can be in the form of an analogue direct current, an analog direct voltage or in digital form.
This document applies to measuring transducers used for converting electrical quantities such as
– current,
– voltage,
– active power,
– reactive power,
– power factor,
– phase angle,
– frequency,
– harmonics or total harmonic distortion, and
– apparent power
to an output signal.
This document is not applicable for
– instrument transformers that complies with IEC 61869 (all parts),
– transmitters for use in industrial process application that complies with IEC 60770 (all parts), and
– performance measuring and monitoring devices (PMD) that comply with IEC 61557 12:2018.
Within the measuring range, the output signal is a function of the measurand. An auxiliary supply can be needed.
This document applies
a) if the nominal frequency of the input(s) lies between 0 Hz and 1 500 Hz,
b) to the electrical measuring transducer if it is part of a system for the measurement of a non-electrical quantity, and if it otherwise falls within the scope of this document, and
c) to transducers for use in a variety of applications such as telemetry and process control and in one of a number of defined environments.
This document is intended:
– to specify the terminology and definitions relating to transducers whose main application is in industry,
– to unify the test methods used in evaluating transducer performance, and
– to specify accuracy limits and output values for transducers.
IEC 60688:2021 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) updating normative references;
b) additional requirements for specific transducers used for LV monitoring applications;
c) creation of interface coding to ease selection by the end-user.
Transducteurs électriques de mesure convertissant les grandeurs électriques alternatives ou continues en signaux analogiques ou numériques
L'IEC 60688:2021 s'applique aux transducteurs à grandeurs d'entrées et de sorties électriques destinés à mesurer des grandeurs électriques alternatives ou continues. Le signal de sortie peut être sous la forme d’un courant continu analogique ou d’une tension continue analogique ou d’un signal numérique.
Le présent document s'applique aux transducteurs de mesure destinés à convertir des grandeurs électriques, telles que:
– le courant,
– la tension,
– la puissance active,
– la puissance réactive,
– le facteur de puissance,
– l’angle de phase,
– la fréquence,
– les harmoniques ou la distorsion harmonique totale, et
– la puissance apparente
en signal de sortie.
Le présent document ne s’applique pas:
– aux transformateurs de mesure conformes à la série IEC 61869,
– aux transmetteurs utilisés dans le processus industriel conformes à la série IEC 60770, et
– aux dispositifs de mesure et de surveillance des performances (PMD – performance measuring and monitoring device) conformes à l’IEC 61557-12:2018.
Dans l’étendue de mesure, le signal de sortie varie en fonction du mesurande. Une alimentation auxiliaire peut être nécessaire.
Le présent document s'applique:
a) si la fréquence nominale de la ou des grandeurs d'entrée est comprise entre 0 Hz et 1 500 Hz;
b) à un transducteur de mesure électrique appartenant à une chaîne de mesure d'une grandeur non électrique, et si, par ailleurs, celui-ci relève du domaine d'application du présent document, et
c) aux transducteurs destinés à une utilisation générale, par exemple à la télémesure, à la commande de processus et dans un des nombreux environnements spécifiés.
Le présent document a pour objet:
– de spécifier la terminologie et les définitions relatives aux transducteurs dont l'application principale relève du domaine de l'industrie,
– d'unifier les méthodes d'essai utilisées pour évaluer les performances des transducteurs, et
– de spécifier les limites de précision et les valeurs de sortie des transducteurs.
L'IEC 60688:2021 annule et remplace la troisième édition parue en 2012. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) mise à jour des références normatives;
b) exigences supplémentaires pour les transducteurs spécifiques utilisés pour les applications de surveillance de la BT (basse tension)
c) création d'un codage d'interface pour faciliter la sélection par l'utilisateur final.
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Standards Content (Sample)
IEC 60688 ®
Edition 4.0 2021-09
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical measuring transducers for converting AC and DC electrical quantities
to analogue or digital signals
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
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IEC 60688 ®
Edition 4.0 2021-09
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical measuring transducers for converting AC and DC electrical quantities
to analogue or digital signals
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20 ISBN 978-2-8322-1029-1
– 2 – IEC 60688:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 9
INTRODUCTION . 11
1 Scope . 12
2 Normative references. 13
3 Terms and definitions . 13
3.1 General terms . 14
3.2 Terms describing transducers according to the measurand . 17
3.3 Terms describing transducers according to their output load . 18
3.4 Nominal values . 18
3.5 User adjustment Terms describing transducers with provisions to be
adjusted by users . 19
3.6 Influence quantities and reference conditions . 20
3.7 Errors and variations . 20
3.8 Accuracy, accuracy class, class index . 21
4 Class index, permissible limits of intrinsic error, auxiliary supply and reference
conditions General . 21
4.1 Transducer general architecture . 21
4.2 Classification of transducers (TRD) . 22
5 Requirements for TRD1 . 22
5.1 Safety requirements: clearances and creepage distances . 22
5.2 EMC requirements . 22
5.2.1 Immunity . 22
5.2.2 Emission . 23
5.3 Class index requirements . 23
5.3.1 Class index . 23
5.3.2 Class index for transducer used with sensors . 23
5.3.3 Intrinsic error . 23
5.4 Conditions for the determination of intrinsic error . 23
5.5 Auxiliary supply . 25
5.5.1 General . 25
5.5.2 DC supply . 25
5.5.3 AC supply . 25
5.6 Input values . 26
5.6.1 General . 26
5.6.2 Adjustment ranges . 26
5.6.3 Preferred nominal values . 26
5.7 Analogue output signals . 26
5.7.1 General . 26
5.7.2 Output current . 26
5.7.3 Compliance voltage . 26
5.7.4 Maximum output voltage . 26
5.7.5 Interference risk of output current . 27
5.7.6 Output voltage . 27
5.8 Output transfer function . 27
5.9 Digital output signals . 30
5.10 Ripple (for analogue outputs) . 30
5.11 Response time . 30
5.12 Variation due to over-range of the measurand . 30
5.13 Limiting value of the output signal . 30
5.14 Limiting conditions of operation . 31
5.15 Limits of the measuring range . 31
5.16 Limiting conditions for storage and transport . 31
5.17 Sealing . 31
5.18 Stability . 31
6 Tests for TRD1 . 31
6.1 General . 31
6.1.1 Determination of variations . 31
6.1.2 Environmental conditions . 32
6.1.3 Computations . 32
6.2 Variations due to auxiliary supply voltage . 32
6.2.1 Application . 32
6.2.2 Procedure . 32
6.2.3 Computation . 33
Permissible variations . 33
6.3 Variations due to auxiliary supply frequency . 33
6.3.1 Application . 33
6.3.2 Procedure . 33
6.3.3 Computation . 33
6.3.4 Permissible variations . 34
6.4 Variations due to ambient temperature . 34
6.4.1 Application . 34
6.4.2 Procedure . 34
6.4.3 Computation . 34
6.4.4 Permissible variations . 34
6.5 Variations due to the frequency of the input quantity(ies) . 35
6.5.1 Application . 35
6.5.2 Procedure . 35
6.5.3 Computation . 35
6.5.4 Permissible variations . 35
6.6 Variations due to the input voltage . 35
6.6.1 Application . 35
6.6.2 Procedure . 35
6.6.3 Computation . 36
6.6.4 Permissible variations . 36
6.7 Variations due to the input current . 36
6.7.1 Application . 36
6.7.2 Procedure . 36
6.7.3 Computation . 36
6.7.4 Permissible variations . 36
6.8 Variations due to power factor . 37
6.8.1 Application . 37
6.8.2 Procedure . 37
6.8.3 Computation . 37
6.8.4 Permissible variations . 37
6.9 Variation due to output load . 38
– 4 – IEC 60688:2021 RLV © IEC 2021
6.9.1 Application . 38
6.9.2 Procedure . 38
6.9.3 Computation . 38
6.9.4 Permissible variations . 38
6.10 Variations due to distortion of the input quantity(ies) . 38
6.10.1 Application . 38
6.10.2 Procedure . 38
6.10.3 Computation . 39
6.10.4 Permissible variations . 39
6.11 Variation due to magnetic field of external origin . 39
6.11.1 Application . 39
6.11.2 Procedure . 39
6.11.3 Computation . 39
6.11.4 Permissible variations . 40
6.12 Variation due to unbalanced currents . 40
6.12.1 Application . 40
6.12.2 Procedure . 40
6.12.3 Computation . 40
6.12.4 Permissible variations . 40
6.13 Variation due to interaction between measuring elements . 40
6.13.1 Application . 40
6.13.2 Procedure . 41
6.13.3 Computation . 41
6.13.4 Permissible variations . 41
6.14 Variation due to self-heating . 41
6.14.1 Application . 41
6.14.2 Method . 41
6.14.3 Computation . 41
6.14.4 Permissible variations . 41
6.15 Variation due to continuous operation . 42
6.15.1 Application . 42
6.15.2 Procedure . 42
6.15.3 Computation . 42
6.15.4 Permissible variation . 42
6.16 Variation due to common mode interference . 42
6.16.1 Application . 42
6.16.2 Procedure . 42
6.16.3 Computation . 42
6.16.4 Permissible variations . 42
6.17 Variation due to series mode interference . 43
6.17.1 Application . 43
6.17.2 Procedure . 43
6.17.3 Computation . 43
6.17.4 Permissible variations . 43
6.18 Permissible excessive inputs . 43
6.18.1 General . 43
6.18.2 Continuous excessive inputs . 43
6.18.3 Excessive inputs of short duration . 44
6.19 Voltage test, insulation tests and other safety requirements . 44
6.20 Impulse voltage tests . 44
6.21 High frequency disturbance test . 44
6.22 Test for temperature rise . 44
6.23 Other tests . 45
7 Marking and information for TRD1 . 45
7.1 Marking on the case . 45
7.2 Markings relating to the reference conditions and nominal ranges of use for
transducers . 46
7.3 Identification of connections and terminals . 46
7.4 Information to be given in a separate document . 46
Annex A (normative) Requirements for TRD2 . 50
A.0 General . 50
A.1 Scope . 50
A.2 Normative references . 50
A.3 Terms and definitions . 50
A.4 Environmental conditions . 50
A.4.1 General . 50
A.4.2 Normal environmental conditions . 50
A.4.3 Special environmental conditions . 50
A.5 Ratings for TRD2 . 50
A.5.1 General . 50
A.5.2 Input ratings . 51
A.5.3 Output ratings . 52
A.5.4 General ratings . 53
A.6 Requirements for design of TRD2 . 54
A.6.1 General . 54
A.6.2 Safety requirements . 54
A.6.3 EMC requirements . 57
A.6.4 Climatic requirements . 59
A.6.5 Mechanical requirements . 59
A.6.6 Interface requirements . 60
A.6.7 Accuracy requirements . 60
A.6.8 Marking requirements . 64
A.6.9 Documentation requirements . 65
A.7 Tests for TRD2 . 66
A.7.1 Type tests . 66
A.7.2 Routine tests. 75
Annex B (normative) Interface coding . 77
B.1 General . 77
B.2 Characteristics of interface connection . 77
B.3 Coding of rated output values for transducers . 77
B.4 Coding of auxiliary power supply for transducers . 79
B.5 Coding of transfer function curves for transducers . 80
B.6 Interface full coding for output of transducers . 80
B.6.1 General . 80
B.6.2 Examples of interface codes and most common interface codes . 81
Annex C (informative) Anti-aliasing requirements . 83
Annex D (informative) Requirements for the measurement of harmonics and low
frequencies . 85
– 6 – IEC 60688:2021 RLV © IEC 2021
D.1 General . 85
D.2 Measuring accuracy classes with harmonics . 85
D.3 Accuracy class extensions of transducers for high bandwidth applications . 86
Annex E (normative) Markings terminals of TRD2 . 87
E.1 Marking of terminals for TRD2 monitoring AC current . 87
E.2 Marking of terminals for TRD2 monitoring voltage . 87
Annex F (informative) Guidance related to cables, busbars and bare conductors within
an installation . 89
F.1 Insulation of cables . 89
F.2 Temperature of cables and busbars . 89
F.2.1 Cables . 89
F.2.2 Busbars . 89
Annex G (informative) Guidance related to overvoltage categories and measurement
categories . 90
G.1 Concept of overvoltage category . 90
G.2 Approach of IEC 60664-1 for primary circuits of TRD2 . 90
G.2.1 General . 90
G.2.2 Examples with IEC 60664-1:2020, for primary measuring circuits, OVC
III, PD 2, altitude under 2 000 m, inhomogeneous field . 90
G.3 Approach of IEC 61010 for primary circuits of TRD2 . 91
G.3.1 General . 91
G.3.2 Example with IEC 61010-2-030:2017, for primary measuring circuits,
OVC III, PD 2, altitude under 2 000 m, inhomogeneous field . 91
G.4 Approach for secondary circuits of TRD2 . 92
Bibliography . 93
Figure 1 – Transducer (TRD) architecture . 22
Figure 2 – Transfer function curve A . 27
Figure 3 – Transfer function curve B . 28
Figure 4 – Transfer function curve C . 28
Figure 5 – Transfer function curve D . 29
Figure 6 – Transfer function curve E . 29
Figure A.1 – Relationship between ambient air temperature and relative humidity . 54
Figure A.2 – Accuracy limits of a TRD2-IDC . 62
Figure A.3 – Measurement of the step response time. 70
Figure A.4 – Temperature cycle accuracy test . 72
Figure C.1 – Digital data acquisition system example . 83
Figure C.2 – Frequency response mask for metering accuracy class 1 (f = 60 Hz,
r
f = 4 800 Hz) . 84
s
Table 1 – Functional classification of transducers with minimal required functions . 22
Table 2 – Relationship between the limits of intrinsic error, expressed as a percentage
of the fiducial value, and the class index . 23
Table 3 – Pre-conditioning . 24
Table 4 – Reference conditions of the influence quantities and tolerances or testing
purposes . 24
Table 5 – Reference conditions relative to the measurand . 25
Table 6 – Usage groups . 32
Table 7 – Permissible variations due to AC auxiliary supply . 33
Table 8 – Permissible variations due to DC auxiliary supply . 33
Table 9 – Permissible variations due to auxiliary supply frequency . 34
Table 10 – Permissible variations due to ambient temperature . 34
Table 11 – Permissible variations due to the frequency of input quantity . 35
Table 12 – Permissible variations due to the input voltage . 36
Table 13 – Permissible variations due to the input current . 37
Table 14 – Permissible variations due to power factor . 37
Table 15 – Permissible variations due to output load . 38
Table 16 – Permissible variations due to distortion of input quantities . 39
Table 17 – Permissible variations due to magnetic field of external origin . 40
Table 18 – Permissible variations due to unbalance currents . 40
Table 19 – Permissible variations due to interactions between measuring elements . 41
Table 20 – Permissible variations due to self-heating . 42
Table 21 – Permissible variations due to continuous operation . 43
Table 22 – Permissible variations due to series mode interference . 43
Table 23 – Examples of marking relating to the reference conditions and nominal range
of use for temperature. 46
Table 24 – Symbols for marking transducers . 47
Table A.1 – Rated burden for TRD2 with an AC or DC voltage output, or a frequency
output . 52
Table A.2 – Rated burden for TRD2 with an AC or DC current output . 53
Table A.3 – Rated temperatures for TRD2 . 53
Table A.4 – Rated humidity classes . 54
Table A.5 – Definition of ports . 58
Table A.6 – Performance criteria for EMC immunity tests . 59
Table A.7 – RJ45 connector pinout . 60
Table A.8 – Limits for error and phase error for TRD2-IAC . 61
Table A.9 – Limits of ratio error for TRD2-IDC . 62
Table A.10 – Limits of ratio error for TRD2-UAC . 63
Table A.11 – Limits of ratio error for TRD2-UDC . 63
Table A.12 – Burden values for basic accuracy tests . 68
Table B.1 – Coding of interface connection. 77
Table B.2 – Rated AC RMS voltage output . 78
Table B.3 – Rated DC voltage output . 78
Table B.4 – Rated range of DC voltage output . 78
Table B.5 – Rated AC RMS current output less than 1A . 78
Table B.6 – Rated range of DC current output . 79
Table B.7 – Rated frequency output . 79
Table B.8 – Rated pulse density output . 79
Table B.9 – Coding of power supply for transducers supplied from measuring
instrument via the connector . 80
Table B.10 – Coding of external power supply for transducers . 80
– 8 – IEC 60688:2021 RLV © IEC 2021
Table B.11 – Coding of transfer function curves for transducers . 80
Table B.12 – Interface full coding for output of transducers . 81
Table B.13 – Examples of interface codes and most common interface codes . 81
Table C.1 – Anti-aliasing filter . 83
Table D.1 – Limits of error for harmonics – Accuracy classes . 85
Table D.2 – Limits of error for harmonics – Accuracy class extensions WB1 and WB2 . 86
Table E.1 – Marking of terminals for TRD2 monitoring current . 87
Table E.2 – Marking of terminals for TRD2 monitoring voltage . 88
Table G.1 – Clearances according to IEC 60664-1:2020 . 90
Table G.2 – Creepage distances according to IEC 60664-1:2020 . 91
Table G.3 – Clearances according to IEC 61010-2-030:2017 . 92
Table G.4 – Creepage distances according to IEC 61010-2-030:2017 . 92
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL MEASURING TRANSDUCERS FOR CONVERTING AC AND DC
ELECTRICAL QUANTITIES TO ANALOGUE OR DIGITAL SIGNALS
FOREWORD
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This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60688:2012. A vertical bar appears in the margin wherever a change has
been made. Additions are in green text, deletions are in strikethrough red text.
– 10 – IEC 60688:2021 RLV © IEC 2021
IEC 60688 has been prepared by IEC technical committee 85: Measuring equipment for
electrical and electromagnetic quantities. 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) updating normative references;
b) additional requirements for specific transducers used for LV monitoring applications;
c) creation of interface coding to ease selection by the end-user.
The text of this International Standard is based on the following documents:
CDV Report on voting
85/748/CDV 85/781/RVC
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
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In this document, the following print types are used:
– requirements and definitions: in roman type;
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– compliance: in italic type.
The committee has decided that the contents of this document will remain unchanged until the
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INTRODUCTION
New transducers can now be equipped with microprocessors that utilise digital data processing,
communication methods and auxiliary sensors. This makes them more complex than
conventional analogue transducers and gives them considerable added value.
The class index system of classification used in this document is based upon IEC 60051 (all
parts). Under this system, the permitted variations of the output signal due to varying influence
quantities – ambient temperature, voltage, frequency, etc. – are implicit in the classification.
For those unfamiliar with the class index system, a word of warning is necessary. If, for example,
a transducer is classified as class 1, it does not mean that the error under practical conditions
of use will be within ±1 % of the actual value of the output or ±1 % of the full output value. It
means that the error should not exceed ±1 % of the fiducial value under clos
...
IEC 60688 ®
Edition 4.0 2021-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electrical measuring transducers for converting AC and DC electrical quantities
to analogue or digital signals
Transducteurs électriques de mesure convertissant les grandeurs électriques
alternatives ou continues en signaux analogiques ou numériques
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About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.
IEC publications search - webstore.iec.ch/advsearchform IEC online collection - oc.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always have
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and withdrawn publications.
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Stay up to date on all new IEC publications. Just Published
containing more than 22 000 terminological entries in English
details all new publications released. Available online and once
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IEC 60688 ®
Edition 4.0 2021-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electrical measuring transducers for converting AC and DC electrical quantities
to analogue or digital signals
Transducteurs électriques de mesure convertissant les grandeurs électriques
alternatives ou continues en signaux analogiques ou numériques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20 ISBN 978-2-8322-1009-1
– 2 – IEC 60688:2021 © IEC 2021
CONTENTS
FOREWORD . 9
INTRODUCTION . 11
1 Scope . 12
2 Normative references. 13
3 Terms and definitions . 13
3.1 General terms . 13
3.2 Terms describing transducers according to the measurand . 15
3.3 Terms describing transducers according to their output load . 17
3.4 Nominal values . 17
3.5 Terms describing transducers with provisions to be adjusted by users . 18
3.6 Influence quantities and reference conditions . 18
3.7 Errors and variations . 19
3.8 Accuracy, accuracy class, class index . 19
4 General . 19
4.1 Transducer general architecture . 19
4.2 Classification of transducers (TRD) . 20
5 Requirements for TRD1 . 20
5.1 Safety requirements: clearances and creepage distances . 20
5.2 EMC requirements . 20
5.2.1 Immunity . 20
5.2.2 Emission . 21
5.3 Class index requirements . 21
5.3.1 Class index . 21
5.3.2 Class index for transducer used with sensors . 21
5.3.3 Intrinsic error . 21
5.4 Conditions for the determination of intrinsic error . 21
5.5 Auxiliary supply . 23
5.5.1 General . 23
5.5.2 DC supply . 23
5.5.3 AC supply . 23
5.6 Input values . 24
5.6.1 General . 24
5.6.2 Adjustment ranges . 24
5.6.3 Preferred nominal values . 24
5.7 Analogue output signals . 24
5.7.1 General . 24
5.7.2 Output current . 24
5.7.3 Compliance voltage . 24
5.7.4 Maximum output voltage . 24
5.7.5 Interference risk of output current . 24
5.7.6 Output voltage . 25
5.8 Output transfer function . 25
5.9 Digital output signals . 27
5.10 Ripple (for analogue outputs) . 27
5.11 Response time . 28
5.12 Variation due to over-range of the measurand . 28
5.13 Limiting value of the output signal . 28
5.14 Limiting conditions of operation . 28
5.15 Limits of the measuring range . 28
5.16 Limiting conditions for storage and transport . 28
5.17 Sealing . 29
5.18 Stability . 29
6 Tests for TRD1 . 29
6.1 General . 29
6.1.1 Determination of variations . 29
6.1.2 Environmental conditions . 29
6.1.3 Computations . 30
6.2 Variations due to auxiliary supply voltage . 30
6.2.1 Application . 30
6.2.2 Procedure . 30
6.2.3 Computation . 30
6.2.4 Permissible variations . 31
6.3 Variations due to auxiliary supply frequency . 31
6.3.1 Application . 31
6.3.2 Procedure . 31
6.3.3 Computation . 31
6.3.4 Permissible variations . 31
6.4 Variations due to ambient temperature . 32
6.4.1 Application . 32
6.4.2 Procedure . 32
6.4.3 Computation . 32
6.4.4 Permissible variations . 32
6.5 Variations due to the frequency of the input quantity(ies) . 32
6.5.1 Application . 32
6.5.2 Procedure . 33
6.5.3 Computation . 33
6.5.4 Permissible variations . 33
6.6 Variations due to the input voltage . 33
6.6.1 Application . 33
6.6.2 Procedure . 33
6.6.3 Computation . 33
6.6.4 Permissible variations . 34
6.7 Variations due to the input current . 34
6.7.1 Application . 34
6.7.2 Procedure . 34
6.7.3 Computation . 34
6.7.4 Permissible variations . 34
6.8 Variations due to power factor . 35
6.8.1 Application . 35
6.8.2 Procedure . 35
6.8.3 Computation . 35
6.8.4 Permissible variations . 35
6.9 Variation due to output load . 35
6.9.1 Application . 35
6.9.2 Procedure . 35
– 4 – IEC 60688:2021 © IEC 2021
6.9.3 Computation . 36
6.9.4 Permissible variations . 36
6.10 Variations due to distortion of the input quantity(ies) . 36
6.10.1 Application . 36
6.10.2 Procedure . 36
6.10.3 Computation . 36
6.10.4 Permissible variations . 37
6.11 Variation due to magnetic field of external origin . 37
6.11.1 Application . 37
6.11.2 Procedure . 37
6.11.3 Computation . 37
6.11.4 Permissible variations . 37
6.12 Variation due to unbalanced currents . 38
6.12.1 Application . 38
6.12.2 Procedure . 38
6.12.3 Computation . 38
6.12.4 Permissible variations . 38
6.13 Variation due to interaction between measuring elements . 38
6.13.1 Application . 38
6.13.2 Procedure . 38
6.13.3 Computation . 39
6.13.4 Permissible variations . 39
6.14 Variation due to self-heating . 39
6.14.1 Application . 39
6.14.2 Method . 39
6.14.3 Computation . 39
6.14.4 Permissible variations . 39
6.15 Variation due to continuous operation . 39
6.15.1 Application . 39
6.15.2 Procedure . 40
6.15.3 Computation . 40
6.15.4 Permissible variation . 40
6.16 Variation due to common mode interference . 40
6.16.1 Application . 40
6.16.2 Procedure . 40
6.16.3 Computation . 40
6.16.4 Permissible variations . 40
6.17 Variation due to series mode interference . 40
6.17.1 Application . 40
6.17.2 Procedure . 40
6.17.3 Computation . 41
6.17.4 Permissible variations . 41
6.18 Permissible excessive inputs . 41
6.18.1 Continuous excessive inputs . 41
6.18.2 Excessive inputs of short duration . 41
6.19 Voltage test, insulation tests and other safety requirements . 41
6.20 Impulse voltage tests . 42
6.21 High frequency disturbance test . 42
6.22 Test for temperature rise . 42
6.23 Other tests . 42
7 Marking and information for TRD1 . 42
7.1 Marking on the case . 42
7.2 Markings relating to the reference conditions and nominal ranges of use for
transducers . 43
7.3 Identification of connections and terminals . 44
7.4 Information to be given in a separate document . 44
Annex A (normative) Requirements for TRD2 . 46
A.0 General . 46
A.1 Scope . 46
A.2 Normative references . 46
A.3 Terms and definitions . 46
A.4 Environmental conditions . 46
A.4.1 General . 46
A.4.2 Normal environmental conditions . 46
A.4.3 Special environmental conditions . 46
A.5 Ratings for TRD2 . 46
A.5.1 General . 46
A.5.2 Input ratings . 47
A.5.3 Output ratings . 48
A.5.4 General ratings . 49
A.6 Requirements for design of TRD2 . 50
A.6.1 General . 50
A.6.2 Safety requirements . 50
A.6.3 EMC requirements . 53
A.6.4 Climatic requirements . 55
A.6.5 Mechanical requirements . 55
A.6.6 Interface requirements . 56
A.6.7 Accuracy requirements . 56
A.6.8 Marking requirements . 60
A.6.9 Documentation requirements . 61
A.7 Tests for TRD2 . 62
A.7.1 Type tests . 62
A.7.2 Routine tests. 71
Annex B (normative) Interface coding . 73
B.1 General . 73
B.2 Characteristics of interface connection . 73
B.3 Coding of rated output values for transducers . 73
B.4 Coding of auxiliary power supply for transducers . 75
B.5 Coding of transfer function curves for transducers . 76
B.6 Interface full coding for output of transducers . 76
B.6.1 General . 76
B.6.2 Examples of interface codes and most common interface codes . 77
Annex C (Informative) Anti-aliasing requirements . 79
Annex D (informative) Requirements for the measurement of harmonics and low
frequencies . 81
D.1 General . 81
D.2 Measuring accuracy classes with harmonics . 81
D.3 Accuracy class extensions of transducers for high bandwidth applications . 82
– 6 – IEC 60688:2021 © IEC 2021
Annex E (normative) Markings terminals of TRD2 . 83
E.1 Marking of terminals for TRD2 monitoring AC current . 83
E.2 Marking of terminals for TRD2 monitoring voltage . 83
Annex F (informative) Guidance related to cables, busbars and bare conductors within
an installation . 85
F.1 Insulation of cables . 85
F.2 Temperature of cables and busbars . 85
F.2.1 Cables . 85
F.2.2 Busbars . 85
Annex G (informative) Guidance related to overvoltage categories and measurement
categories . 86
G.1 Concept of overvoltage category . 86
G.2 Approach of IEC 60664-1 for primary circuits of TRD2 . 86
G.2.1 General . 86
G.2.2 Examples with IEC 60664-1:2020, for primary measuring circuits, OVC
III, PD 2, altitude under 2 000 m, inhomogeneous field . 86
G.3 Approach of IEC 61010 for primary circuits of TRD2 . 87
G.3.1 General . 87
G.3.2 Example with IEC 61010-2-030:2017, for primary measuring circuits,
OVC III, PD 2, altitude under 2 000 m, inhomogeneous field . 87
G.4 Approach for secondary circuits of TRD2 . 88
Bibliography . 89
Figure 1 – Transducer (TRD) architecture . 20
Figure 2 – Transfer function curve A . 25
Figure 3 – Transfer function curve B . 25
Figure 4 – Transfer function curve C . 26
Figure 5 – Transfer function curve D . 26
Figure 6 – Transfer function curve E . 27
Figure A.1 – Relationship between ambient air temperature and relative humidity . 50
Figure A.2 – Accuracy limits of a TRD2-IDC . 58
Figure A.3 – Measurement of the step response time. 66
Figure A.4 – Temperature cycle accuracy test . 68
Figure C.1 – Digital data acquisition system example . 79
Figure C.2 – Frequency response mask for metering accuracy class 1 (f = 60 Hz,
r
f = 4 800 Hz) . 80
s
Table 1 – Functional classification of transducers with minimal required functions . 20
Table 2 – Relationship between the limits of intrinsic error, expressed as a percentage
of the fiducial value, and the class index . 21
Table 3 – Pre-conditioning . 22
Table 4 – Reference conditions of the influence quantities and tolerances or testing
purposes . 22
Table 5 – Reference conditions relative to the measurand . 23
Table 6 – Usage groups . 30
Table 7 – Permissible variations due to AC auxiliary supply . 31
Table 8 – Permissible variations due to DC auxiliary supply . 31
Table 9 – Permissible variations due to auxiliary supply frequency . 32
Table 10 – Permissible variations due to ambient temperature . 32
Table 11 – Permissible variations due to the frequency of input quantity . 33
Table 12 – Permissible variations due to the input voltage . 34
Table 13 – Permissible variations due to the input current . 34
Table 14 – Permissible variations due to power factor . 35
Table 15 – Permissible variations due to output load . 36
Table 16 – Permissible variations due to distortion of input quantities . 37
Table 17 – Permissible variations due to magnetic field of external origin . 37
Table 18 – Permissible variations due to unbalance currents . 38
Table 19 – Permissible variations due to interactions between measuring elements . 39
Table 20 – Permissible variations due to self-heating . 39
Table 21 – Permissible variations due to continuous operation . 40
Table 22 – Permissible variations due to series mode interference . 41
Table 23 – Examples of marking relating to the reference conditions and nominal range
of use for temperature. 43
Table 24 – Symbols for marking transducers . 45
Table A.1 – Rated burden for TRD2 with an AC or DC voltage output, or a frequency
output . 48
Table A.2 – Rated burden for TRD2 with an AC or DC current output . 49
Table A.3 – Rated temperatures for TRD2 . 49
Table A.4 – Rated humidity classes . 50
Table A.5 – Definition of ports . 54
Table A.6 – Performance criteria for EMC immunity tests . 55
Table A.7 – RJ45 connector pinout . 56
Table A.8 – Limits for error and phase error for TRD2-IAC . 57
Table A.9 – Limits of ratio error for TRD2-IDC . 58
Table A.10 – Limits of ratio error for TRD2-UAC . 59
Table A.11 – Limits of ratio error for TRD2-UDC . 59
Table A.12 – Burden values for basic accuracy tests . 64
Table B.1 – Coding of interface connection. 73
Table B.2 – Rated AC RMS voltage output . 74
Table B.3 – Rated DC voltage output . 74
Table B.4 – Rated range of DC voltage output . 74
Table B.5 – Rated AC RMS current output less than 1A . 74
Table B.6 – Rated range of DC current output . 75
Table B.7 – Rated frequency output . 75
Table B.8 – Rated pulse density output . 75
Table B.9 – Coding of power supply for transducers supplied from measuring
instrument via the connector . 76
Table B.10 – Coding of external power supply for transducers . 76
Table B.11 – Coding of transfer function curves for transducers . 76
Table B.12 – Interface full coding for output of transducers . 77
Table B.13 – Examples of interface codes and most common interface codes . 77
– 8 – IEC 60688:2021 © IEC 2021
Table C.1 – Anti-aliasing filter . 79
Table D.1 – Limits of error for harmonics – Accuracy classes . 81
Table D.2 – Limits of error for harmonics – Accuracy class extensions WB1 and WB2 . 82
Table E.1 – Marking of terminals for TRD2 monitoring current . 83
Table E.2 – Marking of terminals for TRD2 monitoring voltage . 84
Table G.1 – Clearances according to IEC 60664-1:2020 . 86
Table G.2 – Creepage distances according to IEC 60664-1:2020 . 87
Table G.3 – Clearances according to IEC 61010-2-030:2017 . 88
Table G.4 – Creepage distances according to IEC 61010-2-030:2017 . 88
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL MEASURING TRANSDUCERS FOR CONVERTING AC AND DC
ELECTRICAL QUANTITIES TO ANALOGUE OR DIGITAL SIGNALS
FOREWORD
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IEC 60688 has been prepared by IEC technical committee 85: Measuring equipment for
electrical and electromagnetic quantities. 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) updating normative references;
b) additional requirements for specific transducers used for LV monitoring applications;
c) creation of interface coding to ease selection by the end-user.
– 10 – IEC 60688:2021 © IEC 2021
The text of this International Standard is based on the following documents:
CDV Report on voting
85/748/CDV 85/781/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
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