SIST EN IEC 61757-6-1:2024

SLOVENSKI STANDARD
01-april-2024
Optični senzorji - 6-1. del: Merjenje premikov - Zaznavala premikov na podlagi
vlakenske Braggove uklonske mrežice (IEC 61757-6-1:2024)
Fibre optic sensors - Part 6-1: Displacement measurement - Displacement sensors
based on fibre Bragg gratings (IEC 61757-6-1:2024)
Lichtwellenleitersensoren - Teil 6-1: Wegmessung - Wegsensoren auf der Basis von
Faser Bragg-Gittern (IEC 61757-6-1:2024)
Capteurs fibroniques - Partie 6-1: Mesure de déplacement - Capteurs de déplacement
basés sur des réseaux de bragg sur fibre (IEC 61757-6-1:2024)
Ta slovenski standard je istoveten z: EN IEC 61757-6-1:2024
ICS:
33.180.99 Druga oprema za optična Other fibre optic equipment
vlakna
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61757-6-1

NORME EUROPÉENNE
EUROPÄISCHE NORM March 2024
ICS 33.180.99
English Version
Fibre optic sensors - Part 6-1: Displacement measurement -
Displacement sensors based on fibre Bragg gratings
(IEC 61757-6-1:2024)
Capteurs fibroniques - Partie 6-1: Mesure de déplacement - Lichtwellenleitersensoren - Teil 6-1: Wegmessung -
Capteurs de déplacement basés sur des réseaux de Bragg Wegsensoren auf der Basis von Faser Bragg-Gittern
sur fibre (IEC 61757-6-1:2024)
(IEC 61757-6-1:2024)
This European Standard was approved by CENELEC on 2024-02-23. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61757-6-1:2024 E

European foreword
The text of document 86C/1874/CDV, future edition 1 of IEC 61757-6-1, prepared by SC 86C "Fibre
optic systems and active devices" of IEC/TC 86 "Fibre optics" was submitted to the IEC-CENELEC
parallel vote and approved by CENELEC as EN IEC 61757-6-1:2024.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2024-11-23
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2027-02-23
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61757-6-1:2024 was approved by CENELEC as a
European Standard without any modification.
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60068-2 series Environmental testing - Part 2-X: Tests EN IEC 60068-2 series
IEC 61300-2 series Fibre optic interconnecting devices and EN IEC 61300-2 series
passive components - Basic test and
measurement procedures - Part 2-X: Tests
IEC 61754 series Fibre optic interconnecting devices and EN IEC 61754 series
passive components - Fibre optic connector
interfaces
IEC 61757 - Fibre optic sensors - Generic specification EN IEC 61757 -
IEC 61757-1-1 2020 Fibre optic sensors - Part 1-1: Strain EN IEC 61757-1-1 2020
measurement - Strain sensors based on fibre
Bragg gratings
IEC 62129-1 - Calibration of wavelength/optical frequency EN 62129-1 -
measurement instruments - Part 1: Optical
spectrum analyzers
IEC 62129-2 - Calibration of wavelength/optical frequency EN 62129-2 -
measurement instruments - Part 2: Michelson
interferometer single wavelength meters
IEC 62129-3 - Calibration of wavelength/optical frequency EN IEC 62129-3 -
measurement instruments - Part 3: Optical
frequency meters internally referenced to a
frequency comb
ISO/IEC Guide - Uncertainty of measurement - Part 3: Guide - -
98-3 to the expression of uncertainty in
measurement (GUM:1995)
The ENs referred to in this series are limited to those corresponding to the IEC standards still in force. Moreover,
some IEC standards in this series do not currently have a corresponding EN; for these standards the IEC
standard only is here intended to be referred to.
IEC 61757-6-1 ®
Edition 1.0 2024-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Fibre optic sensors –
Part 6-1: Displacement measurement – Displacement sensors based on fibre

Bragg gratings
Capteurs fibroniques –
Partie 6-1: Mesure de déplacement – Capteurs de déplacement basés sur des

réseaux de Bragg sur fibre
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.99 ISBN 978-2-8322-8134-5

– 2 – IEC 61757-6-1:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviated terms . 8
3.1 Terms and definitions . 8
3.2 Symbols . 9
3.3 Abbreviated terms . 9
4 Structure and characteristics . 9
4.1 Fibre Bragg grating (FBG) . 9
4.2 FBG displacement sensor configuration . 10
4.3 Reference wavelength . 12
4.4 Stability behaviour . 13
4.4.1 Drift and creep . 13
4.4.2 Hysteresis . 13
4.5 Indication of the measured values . 13
4.6 Zero-point related measurement . 14
4.7 Non-zero-point related measurement . 14
4.8 Production set . 14
4.9 FBG displacement sensor standard type . 14
4.10 FBG displacement sensor series . 14
5 Features and characteristics to be measured . 14
5.1 Sampling and statistical evaluation . 14
5.1.1 Sampling . 14
5.1.2 Reporting the measuring result . 15
5.1.3 Sample conditioning . 15
5.1.4 Ambient test conditions . 16
5.1.5 Required types of tests for individual characteristics . 16
5.2 Bragg wavelength λ . 16
Β
5.2.1 General . 16
5.2.2 Measurement procedure . 16
5.2.3 Evaluation . 16
5.2.4 Reporting . 17
5.3 FBG spectral width. 17
5.3.1 Measurement procedure . 17
5.3.2 Evaluation . 17
5.3.3 Reporting . 17
5.4 FBG reflectivity . 17
5.4.1 Measurement procedure . 17
5.4.2 Evaluation . 17
5.4.3 Reporting . 18
5.5 Displacement measurement . 18
5.5.1 General . 18
5.5.2 Test setup . 18
5.5.3 Measurement procedure . 19
5.5.4 Calibration and evaluation . 20

IEC 61757-6-1:2024 © IEC 2024 – 3 –
5.6 Displacement conversion factor . 21
5.7 Temperature and humidity ranges . 21
5.7.1 General . 21
5.7.2 Measurement procedure . 22
5.7.3 Evaluation . 22
5.7.4 Reporting . 22
5.8 Durability . 22
5.8.1 General . 22
5.8.2 Measurement procedure . 22
5.8.3 Reporting . 22
6 Features and characteristics to be reported . 23
6.1 Construction details . 23
6.2 Configuration of the FBG displacement sensor. 23
6.3 Temperature and humidity range . 23
6.4 Connecting requirement . 23
7 Recommendations for use of FBG measuring instruments . 23

Figure 1 – Examples of sensor types for measuring displacement changes . 10
Figure 2 – Bragg wavelength change caused by displacement in a spring-type sensor . 11
Figure 3 – Bragg wavelength changes caused by displacement in a metal-plate-type
sensor . 11
Figure 4 – Schematic diagrams of displacement sensors using two FBGs . 12
Figure 5 – Schematic diagram of a displacement measurement test setup . 18
Figure 6 – Example of temperature dependence of the Bragg wavelengths of two FBGs . 19
Figure 7 – Example of displacement dependence of the Bragg wavelengths of FBG1

and FBG2 . 20

Table 1 – Required types of tests for individual characteristics . 16

– 4 – IEC 61757-6-1:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC SENSORS –
Part 6-1: Displacement measurement –
Displacement sensors based on fibre Bragg gratings

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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61757-6-1 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
86C/1874/CDV 86C/1891/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.

IEC 61757-6-1:2024 © IEC 2024 – 5 –
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61757 series, published under the general title Fibre optic sensors,
can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
– 6 – IEC 61757-6-1:2024 © IEC 2024
INTRODUCTION
This document is part of the IEC 61757 series, which is dedicated to fibre optic sensors. Generic
specifications for fibre optic sensors are defined in IEC 61757.
The individual parts of the IEC 61757 series are numbered as IEC 61757-M-T, where M denotes
the measure and T the technology. The IEC 61757-6-T series is concerned with displacement
measurements.
IEC 61757-6-1:2024 © IEC 2024 – 7 –
FIBRE OPTIC SENSORS –
Part 6-1: Displacement measurement –
Displacement sensors based on fibre Bragg gratings

1 Scope
This part of IEC 61757 defines the terminology, structure, and measurement methods of optical
displacement sensors based on fibre Bragg gratings (FBGs) as the sensing element. This
document also specifies the most important features and characteristics of these fibre optic
displacement sensors and defines procedures for measuring these features and characteristics.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60068-2 (all parts), Environmental testing – Part 2-X: Tests
IEC 61300-2 (all parts), Fibre optic interconnecting devices and passive components – Basic
test and measurement procedures – Part 2-X: Tests
IEC 61754 (all parts), Fibre optic interconnecting devices and passive components – Fibre optic
connector interfaces
IEC 61757, Fibre optic sensors – Generic specification
IEC 61757-1-1:2020, Fibre optic sensors – Part 1-1: Strain measurement – Strain sensors
based on fibre Bragg gratings
IEC 62129-1, Calibration of wavelength/optical frequency measurement instruments – Part 1:
Optical spectrum analyzers
IEC 62129-2, Calibration of wavelength/optical frequency measurement instruments – Part 2:
Michelson interferometer single wavelength meters
IEC 62129-3, Calibration of wavelength/optical frequency measurement instruments – Part 3:
Optical frequency meters internally referenced to a frequency comb
ISO/IEC GUIDE 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)

– 8 – IEC 61757-6-1:2024 © IEC 2024
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61757, IEC 61757-1-1
and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
displacement
D
distance change between two given points
Note 1 to entry: A displacement is designated as an absolute displacement if only one of the two given points
changes its position.
Note 2 to entry: A displacement is designated as a relative displacement if both of the two given points change their
position.
3.1.2
FBG displacement sensor
fibre optic sensor that uses one or more fibre Bragg gratings as a sensing element for
displacement measurements
3.1.3
displacement conversion factor
κ
D
ratio of the relative change in wavelength ∆λ / λ to a displacement change ∆D introduced to an
FBG displacement sensor
Note 1 to entry: The displacement conversion factor κ is calculated as
D
 
Δλ
 
 
λ
 
κ =
D
ΔD
Note 2 to entry: The displacement conversion factor κ is used by manufacturers to characterize the displacement
D
response of their products.
Note 3 to entry: The conversion factor κ for an FBG displacement sensor assumes a linear relation between
D
wavelength change and displacement. Considering the whole measurement system (sensor, device, and cabling), it
can be separately defined for the components of the measurement system. It is only valid for defined conditions. In
the case of a non-linear characteristic, the relation between wavelength change and displacement is considered to
be linear within a defined permissible measurement error.
Note 4 to entry: The term displacement sensitivity, expressed for example in pm/mm, is used by some
manufacturers to characterize the displacement response of their products.

IEC 61757-6-1:2024 © IEC 2024 – 9 –
3.1.4
temperature compensation constant
C
constant for correcting the influence of temperature changes when the displacement is obtained
from wavelength changes
Note 1 to entry: The temperature compensation constant should be provided by the manufacturer.
Note 2 to entry: The term temperature sensitivity, expressed for example in (pm/°C), is used by some manufacturers
to characterize the influence of temperature changes of their products.
3.2 Symbols
For the purposes of this document, the following symbols apply:
R reflectivity of the FBG
FBG
n effective refractive index of the FBG
eff
∆D displacement change
∆T temperature change
Λ FBG period
λ Bragg wavelength
B
λ reference wavelength
3.3 Abbreviated terms
FBG fibre Bragg grating
FWHM full width at half maximum
SNR signal-to-noise ratio
UV ultraviolet
4 Structure and characteristics
4.1 Fibre Bragg grating (FBG)
Fibre Bragg gratings are phase diffraction gratings inscribed into optical waveguides. They are
frequently produced using ultraviolet (UV) light (e.g. from an excimer laser at 248 nm). The fibre
is exposed to an interference pattern of this UV radiation. UV photosensitive processes then
produce changes in the refractive index of the fibre core, which is susceptible to this UV light.
The interference pattern is imaged onto the fibre core to permanently change the refractive
index of the fibre core, so that the refractive index varies periodically along the fibre. Incident
and transported light is reflected by these periodic refractive index changes along the fibre. At
a certain wavelength, the reflected light is additively superimposed (constructive interference);
this spectral part of the incident light is reflected back to the input port of the fibre. In the
transmitted light, this wavelength (denoted Bragg wavelength λ ) is attenuated accordingly, due
Β
to the FBG reflectivity.
The value of the reflected Bragg wavelength λ is determined by the Bragg condition shown in
Β
Formula (1).
λ = 2n Λ
B eff
(1)
– 10 – IEC 61757-6-1:2024 © IEC 2024
According to Formula (1), the Bragg wavelength λ of the FBG depends on the effective
Β
refractive index n of the FBG and on the FBG period Λ. The spectral width of the Bragg
eff
wavelength peak is determined by the number of grating periods and the magnitude of the
refractive index modulation (see IEC 61757-1-1:2020, 5.1).
4.2 FBG displacement sensor configuration
The FBG displacement sensor can be fabricated from various materials and in various forms
(using one or more FBGs as sensing elements). The FBG displacement sensor is typically used
to monitor the displacement occurring between two points of different objects, or between two
parts of the same object. One example is monitoring of displacement changes at expansion
joints that are installed in bridges to prevent damage to the structure; these joints contract and
expand due to temperature changes. Another example of detecting displacement changes is
monitoring of crack size changes in structures where cracks have occurred.
The method used to convert a displacement change into a change of the Bragg wavelength of
an FBG depends on the manufacturer of the displacement sensor. There are a variety of
methods, but a comprehensive description of these methods is outside the scope of this
document.
As an example, the FBG displacement sensor can be configured so that the movement of a
stylus (which is the displacement sensing part) by means of a mechanical transducer causes a
corresponding strain change in the FBG, as shown in Figure 1 for a spring-type sensor and for
a metal-plate-type sensor. This strain change in the FBG then changes the reflected Bragg
wavelength of the FBG, as shown in Figure 2 and Figure 3. Hence, the displacement can be
determined by measuring the reflected Bragg wavelength of the FBG.

a) Spring type b) Metal plate type

Figure 1 – Examples of sensor types for measuring displacement changes
In the spring-type sensor shown in Figure 1 a), a displacement change causes a pulley to rotate,
which changes the length of a tensile spring that is attached to an FBG. The resulting change
in the tensile force applied to the FBG causes a strain change in the FBG, which in turn changes
the reflective wavelength of the FBG, as illustrated in Figure 2 a) and Figure 2 b). When
installing the FBG displacement sensor shown in Figure 2 a), the stopper is often placed near
the centre of the expected displacement changes, so that positive as well as negative
displacement changes can be detected. If displacement changes are expected to occur in only
...