SIST EN 60688:2013

SLOVENSKI STANDARD
01-marec-2013
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SIST EN 60688:1995
SIST EN 60688:1995/A1:2001
SIST EN 60688:1995/A2:2002
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Electrical measuring transducers for converting a.c. electrical quantities to analogue or
digital signals (IEC 60688:2012)
Elektrische Messumformer zur Umwandlung von elektrischen Wechselstromgrößen und
Gleichstromgrößen in analoge oder digitale Signale (IEC 60688:2012)
Transducteurs électriques de mesure convertissant les grandeurs électriques
alternatives en signaux analogiques ou numériques (CEI 60688:2012)
Ta slovenski standard je istoveten z: EN 60688:2013
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60688
NORME EUROPÉENNE
January 2013
EUROPÄISCHE NORM
ICS 17.220.20 Supersedes EN 60688:1992 + A1:1999 + A2:2001

English version
Electrical measuring transducers for converting A.C. and D.C. electrical
quantities to analogue or digital signals
(IEC 60688:2012)
Transducteurs électriques de mesure Elektrische Messumformer
convertissant les grandeurs électriques zur Umwandlung von elektrischen
alternatives ou continues en signaux Wechselstromgrößen
analogiques ou numériques und Gleichstromgrößen in analoge
(CEI 60688:2012) oder digitale Signale
(IEC 60688:2012)
This European Standard was approved by CENELEC on 2012-11-23. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the CEN-CENELEC Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,
Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

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

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2013 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60688:2013 E
Foreword
The text of document 85/421/FDIS, future edition 3 of IEC 60688, prepared by IEC/TC 85 "Measuring
equipment for electrical and electromagnetic quantities" was submitted to the IEC-CENELEC parallel
vote and approved by CENELEC as EN 60688:2013.

The following dates are fixed:
(dop) 2013-08-23
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2015-11-23
standards conflicting with the
document have to be withdrawn
This document supersedes EN 60688:1992 + A1:1999 + A2:2001.

A1:1999 + A2:2001:
- extending the scope to DC quantities;
- extending the scope to harmonics, total harmonic distortion and apparent power;
- adaptation of the requirements for digital transducers;
- updating normative references;
- updating safety requirements with the EN 61010 series;
- updating EMC requirements with EN 61326-1.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
This standard covers the Principle Elements of the Safety Objectives for Electrical Equipment
Designed for Use within Certain Voltage Limits (LVD - 2006/95/EC).
Endorsement notice
The text of the International Standard IEC 60688:2012 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 standards indicated:

IEC 60044-7 NOTE Harmonised as EN 60044-7.
IEC 60044-8 NOTE Harmonised as EN 60044-8.
IEC 60051 Series NOTE Harmonised as EN 60051 Series (not modified).
IEC 60068-2-30 NOTE Harmonised as EN 60068-2-30.
IEC 60359 NOTE Harmonised as EN 60359.
IEC 60770-1 NOTE Harmonised as EN 60770-1.
IEC 60770-2 NOTE Harmonised as EN 60770-2.
IEC 60770-3 NOTE Harmonised as EN 60770-3.

- 3 - EN 60688:2013
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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

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

IEC 60051-1 1997 Direct acting indicating analogue EN 60051-1 1998
electrical measuring instruments
and their accessories -
Part 1: Definitions and general requirements
common to all parts
IEC 60068-2-6 - Environmental testing - EN 60068-2-6 -
Part 2-6: Tests - Test Fc: Vibration
(sinusoidal)
IEC 60068-2-27 - Environmental testing - EN 60068-2-27 -
Part 2-27: Tests - Test Ea and guidance:
Shock
IEC 60255-151 - Measuring relays and protection EN 60255-151 -
equipment -
Part 151: Functional requirements
for over/under current protection

IEC 61010 Series Safety requirements for electrical EN 61010 Series
equipment for measurement, control,
and laboratory use
IEC 61010-1 - Safety requirements for electrical EN 61010-1 -
equipment for measurement, control
and laboratory use -
Part 1: General requirements
IEC 61010-2-030 - Safety requirements for electrical EN 61010-2-030 -
equipment for measurement, control
and laboratory use -
Part 2-030: Particular requirements for
testing and measuring circuits

IEC 61326 Series Electrical equipment for measurement, EN 61326 Series
control and laboratory use -
EMC requirements
IEC 61326-1 - Electrical equipment for measurement, EN 61326-1 -
control and laboratory use -
EMC requirements -
Part 1: General requirements
IEC 61557-12 - Electrical safety in low voltage distribution EN 61557-12 -
systems up to 1 000 V a.c. and 1 500 V d.c. -
Equipment for testing, measuring or
monitoring of protective measures -
Part 12: Performance measuring and
monitoring devices (PMD)
IEC 60417-DB Graphical symbols for use on equipment - -

IEC 60688 ®
Edition 3.0 2012-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical measuring transducers for converting A.C. and D.C. 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
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 17.220.20 ISBN 978-2-83220-435-1

– 2 – 60688 © IEC:2012
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 8
3.1 General terms . 8
3.2 Description of transducers according to the measurand . 11
3.3 Description of transducers according to their output load . 12
3.4 Nominal values . 12
3.5 User adjustment . 13
3.6 Influence quantities and reference conditions . 14
3.7 Errors and variations . 14
3.8 Accuracy, accuracy class, class index . 14
4 Class index, permissible limits of intrinsic error, auxiliary supply and reference
conditions . 15
4.1 Transducer general architecture . 15
4.2 Class index . 15
4.3 Class index for transducer used with sensors . 16
4.4 Intrinsic error . 16
4.5 Conditions for the determination of intrinsic error . 16
4.6 Auxiliary supply . 18
4.7 Safety requirements: Clearances and creepage distances . 19
5 Requirements . 19
5.1 Input values . 19
5.2 Analogue output signals . 19
5.3 Output transfer function . 20
5.4 Digital output signals . 23
5.5 Ripple (for analogue outputs) . 23
5.6 Response time . 23
5.7 Variation due to over-range of the measurand . 23
5.8 Limiting value of the output signal . 23
5.9 Limiting conditions of operation . 23
5.10 Limits of the measuring range . 24
5.11 Limiting conditions for storage and transport . 24
5.12 Sealing . 24
5.13 Stability . 24
Tests . 24
6.1 General . 24
6.2 Variations due to auxiliary supply voltage . 25
6.3 Variations due to auxiliary supply frequency . 26
6.4 Variations due to ambient temperature . 27
6.5 Variations due to the frequency of the input quantity(ies) . 27
6.6 Variations due to the input voltage . 28
6.7 Variations due to the input current . 29
6.8 Variations due to power factor . 29
6.9 Variation due to output load . 30

60688 © IEC:2012 – 3 –
6.10 Variations due to distortion of the input quantity(ies) . 30
6.11 Variation due to magnetic field of external origin . 31
6.12 Variation due to unbalanced currents . 32
6.13 Variation due to interaction between measuring elements . 32
6.14 Variation due to self-heating . 33
6.15 Variation due to continuous operation. 33
6.16 Variation due to common mode interference . 34
6.17 Variation due to series mode interference . 34
6.18 Voltage test, insulation tests and other safety requirements . 35
6.19 Impulse voltage tests . 35
6.20 High frequency disturbance test . 36
6.21 Test for temperature rise . 36
6.22 Other tests . 36
7 Marking and information . 36
7.1 Marking on the case . 36
7.2 Markings relating to the reference conditions and nominal ranges of use for
transducers . 37
7.3 Identification of connections and terminals . 38
7.4 Information to be given in a separate document . 38
Bibliography . 40

Figure 1 – Transducer architecture . 15
Figure 2 – Transfer function curves . 22

Table 1 – Relationship between the limits of intrinsic error, expressed as a percentage
of the fiducial value, and the class index . 16
Table 2 – Pre-conditioning . 16
Table 3 – Reference conditions of the influence quantities and tolerances or testing
purposes . 17
Table 4 – Reference conditions relative to the measurand . 18
Table 5 – Usage groups . 25
Table 6 – Examples of marking relating to the reference conditions and nominal range
of use for temperature . 37
Table 7 – Symbols for marking transducers . 38

– 4 – 60688 © IEC:2012
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL MEASURING TRANSDUCERS
FOR CONVERTING A.C. AND D.C. ELECTRICAL
QUANTITIES TO ANALOGUE OR DIGITAL SIGNALS

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.
International Standard 60688 has been prepared by IEC Technical Committee 85: Measuring
equipment for electrical and electromagnetic quantities.
This third edition cancels and replaces the second edition published in 1992 and its
Amendment 1 (1997) and Amendment 2 (2001). It constitutes a technical revision
This edition includes the following significant technical changes with respect to the previous
edition:
– extending the scope to DC quantities;
– extending the scope to harmonics, total harmonic distortion and apparent power;
– adaptation of the requirements for digital transducers;
– updating normative references;
– updating safety requirements with the IEC 61010 series;
– updating EMC requirements with IEC 61326-1.

60688 © IEC:2012 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
85/421/FDIS 85/436/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
In this standard, the following print types are used:
– requirements and definitions: in roman type;
– NOTES: in smaller roman type;
– compliance: in italic type.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60688 © IEC:2012
INTRODUCTION
New transducers can now be equipped with micro-processors that utilize 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 standard is based upon the IEC 60051
series: Direct acting indicating analogue electrical measuring instruments and their
accessories. Under this system, the permitted variations of the output signal due to varying
influence quantities – ambient temperature, voltage, frequency, etc., – are implicit in the clas-
sification.
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 closely
specified conditions. If the influence quantities are varied between the limits specified by the
nominal ranges of use, a variation of amount comparable with the value of the class index
may be incurred for each influence quantity.
The permissible error of a transducer under working conditions is the sum of the permissible
intrinsic error and of the permissible variations due to each of the influence quantities.
However, the actual error is likely to be much smaller because not all of the influence
quantities are likely to be simultaneously at their most unfavourable values and some of the
variations may cancel one another. It is important that these facts be taken into consideration
when specifying transducers for a particular purpose.
Furthermore, some of the terms used in this standard are different from those used in
IEC 60051 due to the fundamental differences between indicating instruments and measuring
transducers.
All statements of performance are related to the output which is governed by two basic terms:
– "the nominal value", which may have a positive or a negative sign or both;
– "the span", which is the range of values of the output signal from maximum positive to
maximum negative, if appropriate.

60688 © IEC:2012 – 7 –
ELECTRICAL MEASURING TRANSDUCERS
FOR CONVERTING A.C. AND D.C. ELECTRICAL
QUANTITIES TO ANALOGUE OR DIGITAL SIGNALS

1 Scope
This International Standard applies to transducers with electrical inputs and outputs for
making measurements of a.c. or d.c. electrical quantities. The output signal may be in the
form of an analogue direct current, an analogue direct voltage or in digital form. In this case,
that part of the transducer utilized for communication purposes will need to be compatible with
the external system.
This standard applies to measuring transducers used for converting electrical quantities such
as the following:
– current,
– voltage,
– active power,
– reactive power,
– power factor,
– phase angle,
– frequency,
– harmonics or total harmonic distortion,
– apparent power
to an output signal.
This standard is not applicable for:
– instrument transformers that comply with IEC 60044 series;
– transmitters for use in industrial process applications that comply with the IEC 60770
series;
– performance measuring and monitoring devices (PMD) that comply with IEC 61557-12.
Within the measuring range, the output signal is a function of the measurand. An auxiliary
supply may be needed.
This standard applies:
a) if the nominal frequency of the input(s) lies between 0 Hz and 1 500 Hz;
b) if a measuring transducer is part of a system for the measurement of a non-electrical
quantity, this standard may be applied to the electrical measuring transducer, if it
otherwise falls within the scope of this standard;
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 International Standard 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;

– 8 – 60688 © IEC:2012
– to specify accuracy limits and output values for transducers.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60051-1:1997, Direct acting indicating analogue electrical measuring instruments and
their accessories – Part 1: Definitions and general requirements common to all parts
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
IEC 60255-151, Measuring relays and protection equipment – Part 151: Functional
requirements for over/under current protection
IEC 61010 (all parts), Safety requirements for electrical equipment for measurement, control
and laboratory use
IEC 61010-1, Safety requirements for electrical equipment for measurement, control and
laboratory use – Part 1: General requirements
IEC 61010-2-030, Safety requirements for electrical equipment for measurement, control, and
laboratory use – Part 30 Special requirements for testing and measuring circuits
IEC 61326 (all parts), Electrical equipment for measurement, control and laboratory use –
EMC requirements
IEC 61326-1, Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 1: General requirements
IEC 61557-12, Electrical safety in low voltage distribution systems up to 1 000 V a.c. and
1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures –
Part 12: Performance measuring and monitoring devices (PMD)
IEC 60417, Graphical symbols for use on equipment
NOTE Please refer to the Bibliography for the list of informative references.
3 Terms and definitions
For the purpose of this document the following terms and definitions apply:
3.1 General terms
3.1.1
electrical measuring transducer
transducer
device for converting an a.c or d.c. measurand to a direct current, a direct voltage or a digital
signal for measurement purposes

60688 © IEC:2012 – 9 –
3.1.2
analogue transducer
device for converting an a.c or d.c. measurand to a direct current, direct voltage for
measurement purposes
3.1.3
digital transducer
device for converting an a.c or d.c. measurand to a digital signal for measurement purposes
3.1.4
auxiliary supply
a.c. or d.c. electrical supply, other than the measurand, which is necessary for the correct
operation of the transducer
3.1.5
auxiliary circuit
circuit which is usually energized by the auxiliary supply.
Note 1 to entry: The auxiliary circuit is sometimes energized by one of the input quantities.
3.1.6
transducer with offset zero
transducer that gives a predetermined output signal other than zero when the measurand is
zero
3.1.7
transducer with suppressed zero
transducer for which zero output signal corresponds to a measurand greater than zero
3.1.8
total distortion factor
ratio of the r.m.s. value of the total distortion content to the the r.m.s. value of an alternating
quantity
Note 1 to entry: The total distortion factor depends on the choice of the fundamental component. If it is not clear
from the context which one is used, an indication should be given.
3.1.9
output load
for analogue signals, the total resistance of the circuits and apparatus connected externally
across the output terminals of the transducer
3.1.10
ripple content of an analogue output signal
with steady-state input conditions, the ratio of the peak-to-peak value of the fluctuating
component of an analogue output signal, expressed in percentage, to the fiducial value
3.1.11
output signal
an analogue or digital representation of the measurand
3.1.12
output power
power at the transducer output terminals
3.1.13
output current
output voltage
for analogue signals, the current (voltage) produced by the transducer which is an analogue
function of the measurand
– 10 – 60688 © IEC:2012
3.1.14
reversible output current
reversible output voltage
for analogue signals, the output current (voltage) that reverses polarity in response to a
change of sign or direction of the measurand
3.1.15
measuring element of a transducer
unit or module of a transducer that converts the measurand, or part of the measurand, into a
corresponding signal
3.1.16
single element transducer
transducer having one measuring element
3.1.17
multi-element transducer
transducer having two or more measuring elements, the signals from the individual elements
being combined to produce an output signal corresponding to the measurand
3.1.18
combined transducer
transducer having two or more measuring circuits for one or more functions
3.1.19
response time
time from the instant of application of a specified change of the measurand until the output
signal reaches and remains at its final steady value or within a specified interval centred on
this value
3.1.20
compliance voltage
accuracy limiting output voltage
for variable output load transducers having a current output, the value of the voltage
appearing across the output terminals up to which the transducer complies with the
requirements of this standard
3.1.21
output series mode interference voltage
unwanted alternating voltage appearing in series between the output terminals and the load
3.1.22
output common mode interference voltage
unwanted alternating voltage that exists between each of the output terminals and a reference
point
3.1.23
storage conditions
conditions, defined by means of the ranges of the influence quantities, such as temperature or
any other special condition, within which the transducer may be stored (non-operating)
without damage
60688 © IEC:2012 – 11 –
3.1.24
stability
ability of a transducer to keep its performance characteristics unchanged during a specified
time, all influence quantities remaining within their specified ranges
3.1.22.1
short-term stability
stability over a period of 24 h
3.1.22.2
long-term stability
stability over a period of one year
3.1.23
usage group
group of transducers capable of operating under a specified set of environmental conditions
3.2 Description of transducers according to the measurand
3.2.1
voltage transducer
transducer used for the measurement of a.c. or d.c. voltage
3.2.2
current transducer
transducer used for the measurement of a.c. or d.c. current
3.2.3
apparent power transducer
transducer that is used for the measurement of the apparent power
3.2.4
active power transducer
transducer used for the measurement of active electrical power
3.2.5
reactive power transducer
transducer used for the measurement of reactive electrical power
3.2.6
frequency transducer
transducer used for the measurement of the frequency of an a.c. electrical quantity
3.2.7
phase angle transducer
transducer for the measurement of the phase angle between two a.c. electrical quantities
having the same frequency
3.2.8
power factor transducer
transducer used for the measurement of the power factor of an a.c. circuit
3.2.9
harmonics transducer
transducer that is used for the measurement of the harmonics or the total harmonic distortion
of an a.c. circuit
– 12 – 60688 © IEC:2012
3.3 Description of transducers according to their output load
3.3.1
fixed output load transducer
transducer that complies with this standard only when the output load is at its nominal value,
within specified limits
3.3.2
variable output load transducer
transducer that complies with this standard when the output load has any value within a given
range
3.4 Nominal values
3.4.1
nominal value
value, or one of the values, indicating the intended use of a transducer
Note 1 to entry: The lower and upper nominal values of the measurand are those which correspond to the lower
and upper nominal values of the output signal.
3.4.2
output span
span
algebraic difference between the upper and lower nominal values of the output signal
3.4.3
fiducial value
value to which reference is made in order to specify the accuracy of a transducer
Note 1 to entry: The fiducial value is the span, except for transducers having a reversible and symmetrical output
signal when the fiducial value may be half the span if specified by the manufacturer.
3.4.4
circuit insulation voltage
highest circuit voltage to earth of a transducer that determines its voltage test
3.4.5
nominal power factor
factor by which it is necessary to multiply the product of the nominal voltage and nominal
current to obtain the nominal power
nominal power
Nominal power factor =
nominal voltage × nominal current
Note 1 to entry: When the current and voltage are sinusoidal quantities, the nominal power factor is cos ϕ where ϕ
is the phase difference between the current and the voltage. For reactive power transducers, the nominal power
factor is sin ϕ.
3.4.6
maximum permissible values of input current and voltage
values of current and voltage assigned by the manufacturer as those which the transducer will
withstand indefinitely without damage
3.4.7
limiting value of the output current signal
limiting value of the output voltage signal
upper limit of output (current or voltage) signal which cannot, by design, be exceeded under
any conditions
60688 © IEC:2012 – 13 –
3.4.8
measuring range
range defined by two values of the measurand within which the performance complies with the
requirements of this standard
(SOURCE: IEC 60051-1:1997, 2.4.3, modified – the wording of the definition has been
changed.)
3.4.9
nominal value of the measured voltage
nominal value of the voltage of the external circuit (e.g. the secondary winding of a voltage
transformer) to which the voltage input circuit of the transducer is to be connected
3.4.10
nominal value of the measured current
nominal value of the current in the external circuit (e.g. the secondary winding of a current
transformer) to which the current input circuit of the transducer is to be connected
3.4.11
nominal value of the measurand
for active power and reactive power transducers, the value of the measured quantity corres-
ponding to the nominal values of the measured voltage and current, and the power factor
3.5 User adjustment
Transducers can be supplied with provision to be adjusted by the user. (It should be noted
that power sources and measuring equipment having adequate stability and accuracy are
required). The following definitions apply to these transducers
3.5.1
calibration value
value of a quantity to which the nominal value is changed by user adjustment for a specific
application
3.5.2
calibration value of the measured voltage
value of the voltage applied to the voltage input circuit of the transducer
3.5.3
calibration value of the measured current
value of the current applied to the current input circuit of the transducer
3.5.4
calibration value of the measurand
value of the measurand resulting from user adjustment
3.5.5
calibration value of the output signal
value of the output signal of the transducer corresponding to the calibration value of the
measurand after adjustment
3.5.6
adjustment range
possible range of adjustment values of the measured current or voltage
3.5.7
conversion coefficient
relationship of the value of the measurand to the corresponding value of the output signal

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3.6 Influence quantities and reference conditions
3.6.1
influence quantity
quantity (other than the measurand) that may affect the performance of a transducer
3.6.2
reference conditions
specified conditions under which the transducer complies with the requirements concerning
intrinsic errors
Note 1 to entry: These conditions may be defined by either a reference value or a reference range.
3.6.2.1
reference value
specified single value of an influence quantity at which the transducer complies with the
requirements concerning intrinsic errors
3.6.2.2
reference range
specified range of values of an influence quantity within which the transducer complies with
the requirements concerning intrinsic errors
3.6.3
nominal range of use
specified range of values over which it is intended that an influence quantity can assume
without the output signal of the transducer changing by amounts in excess of those specified
3.7 Errors and variations
3.7.1
error
actual value of the output signal minus the intended value of the output signal, expressed
algebraically
3.7.2
error expressed as a percentage of the fiducial value
one hundred times the ratio of the error and the fiducial value
3.7.3
intrinsic error
error determined when the transducer is under reference conditions
3.7.4
variation due to an influence quantity
difference between the two values of the output signal for the same value of the measurand
when an influence quantity assumes successively two different specified values
3.7.5
variation due to an influence quantity expressed as a percentage of the fiducial value
one hundred times the ratio of the variation due to an influence quantity and the fiducial value
3.8 Accuracy, accuracy class, class index
3.8.1
accuracy
value defined by the limits of intrinsic error and by the limits of variations

60688 © IEC:2012 – 15 –
3.8.2
accuracy class
class of transducers for which the accuracy of all can be designated by the same number if they
comply with all the requirements of this standard
3.8.3
class index
number which designates the accuracy class
Note 1 to entry: The class index is applicable to the intrinsic error as well as to the variations.
Note 2 to entry: Throughout this standard, the phrase "x % of the class index" denotes "x % of the limits of error
relating to the class index".
4 Class index, permissible limits of intrinsic error, auxiliary supply and
reference conditions
4.1 Transducer general architecture
Organization of the measurement chain: the electrical quantity to be measured may be either
directly accessible, as is generally the case in low-voltage systems, or accessible via
measurement sensors such as voltage sensors (VS) or current sensors (CS).
Figure 1 below shows the common organization of a transducer.
Communication protocol
Transducers
Communication
management
Electrical
Measurement Acquisition Processing Evaluation

input signal
sensors unit unit unit
Analogue
Digital I/O
output
management
management
Analogue
Digital I/O
output
IEC  2017/12
Figure 1 – Transducer architecture
4.2 Class index
The class index for a transducer shall be chosen from those given in Table 1.
This class index definition only applies for the analogue output of the transducers.

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Table 1 – Relationship between the limits of intrinsic error,
expressed as a percentage of the fiducial value, and the class index
Class index
0,2 0,5 1 2 2,5 3 5 10 20
Limits of error
±0,2 % ±0,5 % ±1 % ±2 % ±2,5 % ±3 % ±5 % ±10 % ±20 %
NOTE Class indices of 0,3 and 1,5, although non-preferred, may be used.

4.3 Class index for transducer used with sensors
If the transducers are used with sensors the manufacturer shall specify the accuracy class of
the whole system transducer & sensor.
In some cases when a transducer does not include the sensors, their associated uncertainties
are not considered. When a transducer includes the sensors, their associated uncertainties
are considered.
4.4 Intrinsic error
When the transducer is under reference conditions, the error at any point between the upper
and lower nominal values of the output signal shall not exceed the limits of the intrinsic error
given in Table 1 expressed as a percentage of the fiducial value.
Values state
...