SIST EN IEC 61757-8-1:2026

SLOVENSKI STANDARD
01-marec-2026
Optični senzorji - 8-1. del: Merjenje tlaka - Tlačni senzorji na podlagi
optovlakenskih Braggovih rešetk (IEC 61757-8-1:2025)
Fibre optic sensors - Part 8-1: Pressure measurement - Pressure sensors based on fibre
Bragg gratings (IEC 61757-8-1:2025)
Lichtwellenleiter-Sensoren – Teil 8-1: Druckmessung - Drucksensoren auf der Basis von
Faser-Bragg-Gittern (IEC 61757-8-1:2025)
Capteurs fibroniques - Partie 8-1: Mesure de pression - Capteurs de pression basés sur
des réseaux de bragg à fibres (IEC 61757-8-1:2025)
Ta slovenski standard je istoveten z: EN IEC 61757-8-1:2026
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 61757-8-1

NORME EUROPÉENNE
EUROPÄISCHE NORM January 2026
ICS 33.180.99
English Version
Fibre optic sensors - Part 8-1: Pressure measurement - Pressure
sensors based on fibre Bragg gratings
(IEC 61757-8-1:2025)
Capteurs fibroniques - Partie 8-1: Mesure de pression - Lichtwellenleiter-Sensoren - Teil 8-1: Druckmessung -
Capteurs de pression basés sur des réseaux de Bragg à Drucksensoren auf der Basis von Faser-Bragg-Gittern
fibres (IEC 61757-8-1:2025)
(IEC 61757-8-1:2025)
This European Standard was approved by CENELEC on 2026-01-16. 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
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61757-8-1:2026 E

European foreword
The text of document 86C/1970/CDV, future edition 1 of IEC 61757-8-1, prepared by SC 86C "Fibre
optic systems, sensing and active devices" of IEC/TC 86 "Fibre optics" was submitted to the IEC-
CENELEC parallel vote and approved by CENELEC as EN IEC 61757-8-1:2026.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-01-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-01-31
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 61757-8-1:2025 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 2-1: Tests - EN IEC 60068-2 series
Test A: Cold
IEC 61300-2 series Fibre optic interconnecting devices and EN IEC 61300-2 series
passive components - Basic test and
measurement procedures - Part 2-1: Tests
- Vibration (sinusoidal)
IEC 61754 series Fibre optic interconnecting devices and EN 61754 series
passive components - Fibre optic
connector interfaces - Part 1: General and
guidance
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
ISO/IEC Guide 98-3 - Uncertainty of measurement - Part 3: - -
Guide to the expression of uncertainty in
measurement (GUM:1995)
IEC 61757-8-1 ®
Edition 1.0 2025-12
INTERNATIONAL
STANDARD
Fibre optic sensors-
Part 8-1: Pressure measurement - Pressure sensors based on fibre Bragg
gratings
ICS 33.180.99  ISBN 978-2-8327-0900-9

IEC 61757-8-1:2025-12(en)
IEC 61757-8-1:2025 © IEC 2025
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, symbols and abbreviated terms . 6
3.1 Terms and definitions . 6
3.2 Symbols . 8
3.3 Abbreviated terms. 8
4 Structure and characteristics. 8
4.1 Fibre Bragg grating . 8
4.2 FBG pressure sensor configuration . 9
4.3 Reference wavelength . 11
4.4 Stability behaviour . 11
4.4.1 Drift and creep . 11
4.4.2 Hysteresis . 11
4.5 Indication of the measured values . 12
4.6 Zero-point related measurement . 12
4.7 Non-zero-point related measurement . 12
4.8 Production set . 12
4.9 FBG pressure sensor standard type . 12
4.10 FBG pressure sensor series. 12
5 Features and characteristics to be measured . 13
5.1 Sampling and statistical evaluation . 13
5.1.1 Sampling . 13
5.1.2 Reporting the measuring result . 13
5.1.3 Sample conditioning . 14
5.1.4 Ambient test conditions . 14
5.1.5 Required types of tests for individual characteristics . 14
5.2 Bragg wavelength λ . 14
Β
5.2.1 General. 14
5.2.2 Measurement procedure . 15
5.2.3 Evaluation . 15
5.2.4 Reporting . 15
5.3 FBG spectral width . 15
5.3.1 Measurement procedure . 15
5.3.2 Evaluation . 15
5.3.3 Reporting . 15
5.4 FBG reflectivity . 15
5.4.1 Measurement procedure . 15
5.4.2 Evaluation . 16
5.4.3 Reporting . 16
5.5 Pressure measurement . 16
5.5.1 General. 16
5.5.2 Test setup . 16
5.5.3 Measurement procedure . 18
5.5.4 Calibration and evaluation . 20
IEC 61757-8-1:2025 © IEC 2025
5.6 Pressure conversion factor . 20
5.7 Temperature and humidity ranges . 21
5.7.1 Storage and transportation, installation, and operation. . 21
5.7.2 Measurement procedure . 21
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 . 22
6.1 Construction details . 22
6.2 Configuration of the FBG pressure sensor . 22
6.3 Temperature and humidity range . 22
6.4 Connecting requirement . 23
7 Recommendations for use of FBG measuring instruments. 23
Bibliography . 24

Figure 1 – Examples of sensor types for measuring pressure changes . 9
Figure 2 – Bragg wavelength changes caused by an increase in pressure . 10
Figure 3 – Schematic diagram of pressure sensor using two FBGs . 10
Figure 4 – Pressure measurement test setup scheme by a dead weight tester . 17
Figure 5 – Schematic diagram of a pressure measurement test setup . 18
Figure 6 – Example of temperature dependence of the Bragg wavelengths of two FBGs . 19
Figure 7 – Example of pressure dependence of the Bragg wavelengths of FBG1 and
FBG2 . 19

Table 1 – Required types of tests for individual characteristics . 14

IEC 61757-8-1:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Fibre optic sensors -
Part 8-1: Pressure measurement -
Pressure 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 61757-7-1 has been prepared by subcommittee 86C: Fibre optic systems, sensing 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/1970/CDV 86C/1993/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 61757-8-1:2025 © IEC 2025
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.
IEC 61757-8-1:2025 © IEC 2025
INTRODUCTION
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 measurand and T the technology. The IEC 61757-8-T series deals with pressure
measurements.
IEC 61757-8-1:2025 © IEC 2025
1 Scope
This part of IEC 61757 defines the terminology, structure, and measurement methods of optical
pressure sensors for gases or liquids based on a diaphragm in combination with fibre Bragg
gratings (FBGs) as the sensing element. This document also specifies the most important
features and characteristics of these fibre optic pressure 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: Tests
IEC 61300-2 (all parts), Fibre optic interconnecting devices and passive components - Basic
test and measurement procedures - Part 2: 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
ISO/IEC GUIDE 98-3, Uncertainty of measurement - Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
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
IEC 61757-8-1:2025 © IEC 2025
3.1.1
pressure
p
amount of force applied perpendicular to the surface of an object per unit area
Note 1 to entry: Pressure is calculated as
F
p=
A
where
F is the magnitude of the normal force, expressed in newtons (N);
A is the area of the contact surface, expressed in square metres (m ).
Note 2 to entry: This definition addresses measurement methods of optical pressure sensors for gases or liquids
based on fibre Bragg gratings in combination with a diaphragm. IEC 60050-113:2011, 113-03-65 provides a broader
definition of pressure.
3.1.2
FBG pressure sensor
fibre optic sensor using one or more fibre Bragg gratings as a sensing element for pressure
measurement of gases or liquids
3.1.3
pressure conversion factor
κ
p
ratio of the relative change in wavelength to a pressure change introduced to an FBG pressure
sensor
Note 1 to entry: The pressure conversion factor κ is expressed in m /N and calculated as
p
Δλλ
( )
κ =
p
Δp
where
∆λ/λ is the relative change in wavelength;
∆p is the pressure change.
Note 2 to entry: The pressure conversion factor κ is commonly used by manufacturers to characterize the pressure
p
response of their products.
Note 3 to entry: The conversion factor κ for an FBG pressure sensor assumes a linear relation between wavelength
p
change and pressure. Considering the whole measurement system (sensor, device, and cabling), it can be separately
defined for the various 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 pressure change is considered to be linear
within a defined permissible measurement error.
Note 4 to entry: The term pressure sensitivity, expressed for example in pm/kPa, is used by some manufacturers
to characterize the pressure response of their products.
IEC 61757-8-1:2025 © IEC 2025
3.1.4
temperature compensation constant
C
constant for correcting the influence of temperature changes when the pressure is obtained
from wavelength changes
Note 1 to entry: The temperature compensation constant is usually 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 in 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
∆p pressure 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
Fibre Bragg gratings (FBGs) 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 (through
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
Β
attenuated accordingly, due to the reflectance in the FBG.
The value of the reflected Bragg wavelength λ is determined by the Bragg condition shown in
Β
Formula (1).
λ = 2n Λ
(1)
B eff
IEC 61757-8-1:2025 © IEC 2025
where
n is the effective refractive index of the FBG;
eff
Λ is the FBG period, expressed for example in nanometres (nm).
According to Formula (1), the Bragg wavelength depends on the effective refractive index and
the period of the FBG. The spectral width of the Bragg wavelength peak is determined by the
number of grating periods and the magnitude of the refractive index modulation (for more details
see IEC 61757-1-1:2020, 5.1).
4.2 FBG pressure sensor configuration
The FBG pressure sensor can be manufactured from various materials and in various forms
(using one or more FBGs as sensing elements). The FBG pressure sensor is typically used to
monitor the pressure of fluids, such as liquids or gases. Typical applications include water level
measurement in rivers, drainage status measurement for excavations, and water pressure
measurement within pressure pipes, banks and perforations.
The method used to convert a pressure change into a change of the Bragg wavelength of an
FBG depends on the manufacturer of the pressure sensor. There are a variety of methods, but
a comprehensive description of these methods is outside the scope of this document.
The principle of fibre optic pressure measurement is based on a base body that deforms under
pressure in a controlled manner. This body often has an intentionally weakened (thin) surface,
a diaphragm, as shown in Figure 1. The diaphragm should be strong and elastic enough to
withstand the external pressure. The amount of deformation of the diaphragm under pressure
is measured with an FBG (see FBG2 in Figure 1). If the diaphragm bulges under pressure, the
FBG will be strained or, if pre-strained, compressed accordingly. This change in strain in the
FBG then changes the Bragg wavelength reflected from this FBG, as shown schematically in
Figure 2. Therefore, the pressure can be determined by measuring the reflected Bragg
wavelength of the FBG.
a) Axial directional force applied to FBG b) Lateral force applied to FBG

Figure 1 – Examples of sensor types for measuring pressure changes
Figure 1 a) shows a structure in which the central part of the diaphragm moves to the left as
the external pressure increases on the right side of the diaphragm, so that the tensile strength
acting on FBG2 weakens and its grating period decreases. As a result, the wavelength reflected
from FBG2 decreases, according to Formula (1). In Figure 1 a), FBG2 is attached to the
diaphragm in a pre-stretched state, so it should be assembled with care. In Figure 1 b), on the
other hand, the grating period of FBG2 increases with increasing external pressure, so that the
wavelength reflected from FBG2 increases with external pressure. In this case, adhesion of
FBG2 to the diaphragm is important, because the diaphragm can repeatedly expand and
contract as the external pressure varies.
IEC 61757-8-1:2025 © IEC 2025
a) with axial directional force applied to FBG b) with lateral force applied to FBG

Figure 2 – Bragg wavelength changes caused by an increase in pressure
A broadband light source and an optical spectrometer can be used to measure the change in
the Bragg wavelength of an FBG. The light source and the spectrometer are typically connected
to the pressure sensing FBG via an optical circulator, as shown schematically in Figure 3.
In Figure 1 a) and Figure 1 b), an additional FBG (denoted FBG1) is inserted near the pressure
sensing FBG (denoted FBG2) to allow for compensation of the temperature dependence of
FBG2 (as described in 5.5.3). The additional FBG1 measures only temperature changes,
whereas FBG2 measures pressure and temperature changes. FBG1 and FBG2 can be
connected in series, as shown in the schematic diagrams of Figure 3, or alternatively in parallel.

a) with axial directional force applied to FBG

b) with lateral force applied to FBG

Figure 3 – Schematic diagram of pressure sensor using two FBGs
IEC 61757-8-1:2025 © IEC 2025
4.3 Reference wavelength
The Bragg wavelength measured with a given FBG can depend on the evaluation method and,
more importantly, on the specific installation of the FBG. In the context of this document, the
wavelength measured after installation of the FBG in the pressure sensor is denoted as the
reference wavelength λ .
The reference wavelength is not necessarily the same as the Bragg
...