kSIST FprEN IEC 61757:2025

SLOVENSKI STANDARD
oSIST prEN IEC 61757:2025
01-marec-2025
Optična zaznavala - Splošna specifikacija
Fibre optic sensors - Generic specification
LWL-Sensoren - Fachgrundspezifikation
Capteurs à fibres optiques - Spécification générique
Ta slovenski standard je istoveten z: prEN IEC 61757:2025
ICS:
33.180.99 Druga oprema za optična Other fibre optic equipment
vlakna
oSIST prEN IEC 61757:2025 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN IEC 61757:2025
oSIST prEN IEC 61757:2025
86C/1952/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 61757 ED2
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2025-01-10 2025-04-04
SUPERSEDES DOCUMENTS:
86C/1932/CD, 86C/1942A/CC
IEC SC 86C : FIBRE OPTIC SYSTEMS, SENSING AND ACTIVE DEVICES
SECRETARIAT: SECRETARY:
United States of America Mr Fred Heismann
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):
TC 17,TC 18,TC 20,TC 38,TC 45,TC 65,TC 85
ASPECTS CONCERNED:
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft
for Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some
Countries” clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is
the final stage for submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Fibre optic sensors - Generic specification

PROPOSED STABILITY DATE: 2028
NOTE FROM TC/SC OFFICERS:
download this electronic file, to make a copy and to print out the content for the sole purpose of preparing National
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1 CONTENTS
3 FOREWORD . 6
4 INTRODUCTION . 8
5 1 Scope . 9
6 2 Normative references . 9
7 3 Terms and definitions . 11
8 3.1 Fibre optic sensor principles . 11
9 3.2 Fibre optic sensor performance parameters . 17
10 3.3 Interfaces . 20
11 4 Abbreviated terms . 21
12 5 Quality assurance . 21
13 6 Test and measurement procedures . 21
14 6.1 General . 21
15 6.2 Standard conditions for testing . 22
16 6.3 Test and measurement equipment requirements . 22
17 6.4 Visual inspection . 22
18 6.5 Dimensions and weight . 23
19 6.6 Metrological properties. 23
20 6.6.1 General . 23
21 6.6.2 Metrological parameters . 23
22 6.7 Optical tests . 23
23 6.7.1 General . 23
24 6.7.2 Optical power . 23
25 6.7.3 Nominal wavelength and appropriate spectral characteristics . 23
26 6.7.4 State of polarization . 24
27 6.7.5 Fibre connector performance . 24
28 6.8 Electrical tests . 24
29 6.8.1 General . 24
30 6.8.2 Parameters and test procedures . 24
31 6.8.3 Voltage stress. 24
32 6.9 Mechanical tests . 25
33 6.9.1 General . 25
34 6.9.2 Parameters and test procedures . 25
35 6.10 Climatic and environmental tests . 25
36 6.10.1 General . 25
37 6.10.2 Parameters and test procedures . 26
38 6.11 Susceptibility to ambient light . 26
39 6.12 Resistance to solvents and contaminating fluids . 26
40 7 Classification . 27
41 7.1 General . 27
42 7.2 Measurand . 27
43 7.2.1 General . 27
44 7.2.2 Presence or absence of objects or features . 27
45 7.2.3 Position . 27
46 7.2.4 Rate of positional change . 27

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47 7.2.5 Flow . 28
48 7.2.6 Temperature . 28
49 7.2.7 Force per directional vector . 28
50 7.2.8 Force per area . 28
51 7.2.9 Strain . 28
52 7.2.10 Electromagnetic quantities . 28
53 7.2.11 Ionizing and nuclear radiation . 28
54 7.2.12 Other physical properties of materials . 28
55 7.2.13 Composition and specific chemical quantities . 28
56 7.2.14 Particulates . 28
57 7.3 Transduction principle . 29
58 7.3.1 General . 29
59 7.3.2 Active generation of light . 29
60 7.3.3 Atom-field interaction . 29
61 7.3.4 Coherence modulation . 29
62 7.3.5 Intensity modulation . 29
63 7.3.6 Optical spectrum modulation . 29
64 7.3.7 Phase modulation . 29
65 7.3.8 Polarization modulation . 29
66 7.4 Spatial distribution . 29
67 7.5 Interface level . 30
68 8 Marking, labelling, packaging and instruction manual . 30
69 8.1 Marking of component . 30
70 8.2 Marking of sealed package and instruction manual . 30
71 9 IEC type designation . 30
72 10 Safety aspects . 30
73 10.1 General . 30
74 10.2 Personal safety . 31
75 10.3 Safety in explosive environment . 31
76 11 Ordering information . 31
77 12 Drawings . 31
78 Annex A (informative) Examples of fibre optic sensors . 32
79 A.1 General . 32
80 A.2 Presence or absence of objects or features . 32
81 A.2.1 Level . 32
82 A.2.2 Proximity . 32
83 A.2.3 Photo interruption . 32
84 A.3 Position . 32
85 A.3.1 End position . 32
86 A.3.2 Linear position . 32
87 A.3.3 Angular position . 33
88 A.3.4 Proximity . 33
89 A.3.5 Zone (area) . 33
90 A.3.6 Dimensional . 33
91 A.4 Rate of positional change. 33
92 A.4.1 Linear speed or velocity . 33
93 A.4.2 Rotational speed or velocity . 33
94 A.4.3 Gyroscope . 33

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95 A.4.4 Linear acceleration . 34
96 A.4.5 Rotational acceleration . 34
97 A.5 Flow . 34
98 A.6 Temperature . 34
99 A.7 Force per directional vector . 34
100 A.7.1 Seismic. 34
101 A.7.2 Vibration . 35
102 A.7.3 Torque . 35
103 A.7.4 Weight and mass . 35
104 A.8 Force per area . 35
105 A.8.1 Acoustic . 35
106 A.8.2 Pressure . 35
107 A.9 Strain . 35
108 A.10 Electromagnetic quantities . 37
109 A.10.1 Magnetic field . 37
110 A.10.2 Electrical current . 37
111 A.10.3 Electric field . 37
112 A.10.4 Voltage . 37
113 A.10.5 Electromagnetic radiation . 37
114 A.11 Ionizing and nuclear radiation . 38
115 A.12 Other physical properties of materials . 38
116 A.12.1 Material refractive index . 38
117 A.12.2 Density . 38
118 A.12.3 Viscosity . 38
119 A.12.4 Damage . 38
120 A.13 Composition and specific chemical quantities . 38
121 A.14 Particulates . 39
122 A.14.1 Count . 39
123 A.14.2 Atomic . 39
124 A.14.3 Turbidity . 39
125 A.15 Spatial distribution . 39
126 A.15.1 Single point . 39
127 A.15.2 Multiple point . 39
128 A.15.3 Integrating . 39
129 A.15.4 Distributed . 39
130 Bibliography . 40
132 Figure 1 – Fibre optic sensor in transmittance configuration with a passive fibre
133 sensing element and separate fibre leads for optical input and output . 12
134 Figure 2 – Fibre optic sensor in reflectance configuration with a passive sensing
135 element and separate fibre leads for optical input and output . 12
136 Figure 3 – Fibre optic sensor with an optical radiation-generating sensing element and
137 separate fibre lead for optical output . 13
138 Figure 4 – Fibre optic sensor with an optical radiation-generating sensing fibre and
139 separate fibre lead for optical output . 13
140 Figure 5 – Fibre optic sensor in backscattering configuration with a passive fibre
141 sensing element and one fibre lead for optical input and output . 14
142 Figure 6 – Distributed fibre optic sensor in loop configuration . 14
143 Figure 7 – Multiple point fibre optic sensor in backscattering configuration . 15

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144 Figure 8 – Single point fibre optic sensor in backscattering configuration . 16
146 Table 1 – Electrical test parameters and procedures . 24
147 Table 2 – Mechanical test parameters and procedures. 25
148 Table 3 – Climatic and environmental test parameters and procedures . 26
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150 INTERNATIONAL ELECTROTECHNICAL COMMISSION
151 ____________
153 FIBRE OPTIC SENSORS –
154 GENERIC SPECIFICATION
156 FOREWORD
157 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
158 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
159 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
160 in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
161 Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
162 preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
163 may participate in this preparatory work. International, governmental and non-governmental organizations liaising
164 with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
165 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
166 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
167 consensus of opinion on the relevant subjects since each technical committee has representation from all
168 interested IEC National Committees.
169 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
170 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
171 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
172 misinterpretation by any end user.
173 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
174 transparently to the maximum extent possible in their national and regional publications. Any divergence between
175 any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
176 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
177 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
178 services carried out by independent certification bodies.
179 6) All users should ensure that they have the latest edition of this publication.
180 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
181 members of its technical committees and IEC National Committees for any personal injury, property damage or
182 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
183 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
184 Publications.
185 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
186 indispensable for the correct application of this publication.
187 9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
188 patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
189 respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
190 may be required to implement this document. However, implementers are cautioned that this may not represent
191 the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
192 shall not be held responsible for identifying any or all such patent rights.
193 IEC 61757 has been prepared by subcommittee 86C: Fibre optic systems and active devices,
194 of IEC technical committee 86: Fibre optics. It is an International Standard.
195 This second edition cancels and replaces the first edition published in 2018. This edition
196 constitutes a technical revision.
197 This edition includes the following significant technical changes with respect to the previous
198 edition:
199 a) updates of and additions to the terms and definitions;
200 b) updates of the normative references and bibliography;
201 c) extensive revisions of Annex A.

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202 The text of this International Standard is based on the following documents:
Draft Report on voting
86C/XX/FDIS 86C/XX/RVD
204 Full information on the voting for its approval can be found in the report on voting indicated in
205 the above table.
206 The language used for the development of this International Standard is English.
207 This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
208 accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
209 at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
210 described in greater detail at www.iec.ch/publications.
211 A list of all parts in the IEC 61757 series, published under the general title Fibre optic sensors,
212 can be found on the IEC website.
213 The committee has decided that the contents of this document will remain unchanged until the
214 stability date indicated on the IEC website under webstore.iec.ch in the data related to the
215 specific document. At this date, the document will be
216 • reconfirmed,
217 • withdrawn,
218 • replaced by a revised edition, or
219 • amended.
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220 INTRODUCTION
221 A fibre optic sensor comprises an optical or optically powered sensing element in which incident
222 light is modified by the measurand in such a way that the output light of the sensing element
223 carries quantifiable information on the measurand. The sensing element can be the fibre itself
224 or an optically powered element inserted along the optical path. In a fibre optic sensor, one or
225 more parameters of the guided optical waves are directly or indirectly modified by the
226 measurand somewhere in the optical sensing element, in contrast to a fibre optic data link where
227 the optical information signal is merely transmitted from the transmitter to the receiver.
228 This document provides generic specifications on optical fibres, components, and sub-
229 assemblies that pertain specifically to fibre optic sensing applications. It is intended to be used
230 as a common working and discussion tool by the vendors of components and subassemblies
231 that are integrated in fibre optic sensors, as well as by designers, manufacturers, and users of
232 fibre optic sensors, independent of specific applications or installations. The individual parts of
233 the IEC 61757 series are numbered as IEC 61757-M-T, where M denotes the measurand and T
234 the technology of the fibre optic sensor.
235 To better illustrate this classification scheme, Annex A gives examples of various fibre optic
236 sensors. The examples are provided for illustration only and are not intended to be limitative,
237 nor do they constitute a recommendation or endorsement of a particular transduction principle.
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240 FIBRE OPTIC SENSORS –
241 GENERIC SPECIFICATION
245 1 Scope
246 This document defines, classifies, and provides a framework of generic tests or measurement
247 methods for characterizing and specifying fibre optic sensors, including their specific
248 components and subassemblies. The requirements of this document apply to all related fibre
249 optic sensor standards that are part of the IEC 61757 series. Other parts of the IEC 61757
250 series contain requirements that are specific to sensors that measure particular quantities, and
251 to a particular style or variant of such a fibre optic sensor.
252 2 Normative references
253 The following documents are referred to in the text in such a way that some or all of their content
254 constitutes requirements of this document. For dated references, only the edition cited applies.
255 For undated references, the latest edition of the referenced document (including any
256 amendments) applies.
257 IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
258 IEC 60068-1, Environmental testing – Part 1: General and guidance
259 IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
260 IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Test B: Dry heat
261 IEC 60068-2-5, Environmental testing - Part 2-5: Tests - Test S: Simulated solar radiation at
262 ground level and guidance for solar radiation testing and weathering
263 IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
264 IEC 60068-2-10, Environmental testing – Part 2-10: Tests – Test J and guidance: Mould
265 growth
266 IEC 60068-2-11, Environmental testing - Part 2-11: Tests - Test Ka: Salt mist
267 IEC 60068-2-13, Environmental testing - Part 2-13: Tests - Test M: Low air pressure
268 IEC 60068-2-14, Environmental testing – Part 2-14: Tests – Test N: Change of temperature
269 IEC 60068-2-27, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
270 IEC 60068-2-30, Environmental testing – Part 2-30: Tests – Test Db: Damp heat, cyclic (12 h +
271 12 h cycle)
272 IEC 60068-2-42, Environmental testing – Part 2-42: Tests – Test Kc: Sulphur dioxide test for
273 contacts and connections
274 IEC 60068-2-43, Environmental testing – Part 2-43: Tests – Test Kd: Hydrogen sulphide test
275 for contacts and connections

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276 IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady state
277 IEC 60079-28, Explosive atmospheres – Part 28: Protection of equipment and transmission
278 systems using optical radiation
279 IEC 60529, Degrees of protection provided by enclosures (IP Code)
280 IEC 60793-1-20, Optical fibres – Part 1-20: Measurement methods and test procedures – Fibre
281 geometry
282 IEC 60793-1-21, Optical fibres – Part 1-21: Measurement methods and test procedures –
283 Coating geometry
284 IEC 60793-1-31, Optical fibres – Part 1-31: Measurement methods and test procedures –
285 Tensile strength
286 IEC 60793-1-32, Optical fibres – Part 1-32: Measurement methods and test procedures –
287 Coating strippability
288 IEC 60793-1-47, Optical fibres – Part 1-47: Measurement methods and test procedures –
289 Macrobending loss
290 IEC 60793-1-54, Optical fibres – Part 1-54: Measurement methods and test procedures –
291 Gamma irradiation
292 IEC 60794-1-21, Optical fibre cables – Part 1-21: Generic specification – Basic optical cable
293 test procedures – Mechanical tests methods
294 IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
295 IEC 61000-4-2, Electromagnetic compatibility (EMC) – Part 4-2: Testing and measurement
296 techniques – Electrostatic discharge immunity test
297 IEC 61000-4-3, Electromagnetic compatibility (EMC) – Part 4-3: Testing and measurement
298 techniques – Radiated, radio-frequency, electromagnetic field immunity test
299 IEC 61000-4-4, Electromagnetic compatibility (EMC) – Part 4-4: Testing and measurement
300 techniques – Electrical fast transient/burst immunity test
301 IEC 61000-4-5, Electromagnetic compatibility (EMC) – Part 4-5: Testing and measurement
302 techniques – Surge immunity test
303 IEC 61300 (all parts), Fibre optic interconnecting devices and passive components – Basic test
304 and measurement procedures
305 IEC 61300-2-1, Fibre optic interconnecting devices and passive components – Basic test and
306 measurement procedures – Part 2-1: Tests – Vibration (sinusoidal)
307 IEC 61300-2-9, Fibre optic interconnecting devices and passive components – Basic test and
308 measurement procedures – Part 2-9: Tests – Shock
309 IEC 61300-2-18, Fibre optic interconnecting devices and passive components – Basic test and
310 measurement procedures – Part 2-18: Tests – Dry heat
311 IEC 61300-2-22, Fibre optic interconnecting devices and passive components – Basic test and
312 measurement procedures – Part 2-22: Tests – Change of temperature

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313 IEC 61300-2-34, Fibre optic interconnecting devices and passive components – Basic test and
314 measurement procedures – Part 2-34: Tests – Resistance to solvents and contaminating fluids
315 of interconnecting components and closures
316 IEC 61300-2-46, Fibre optic interconnecting devices and passive components – Basic test and
317 measurement procedures – Part 2-46: Tests – Damp heat, cyclic
318 IEC 61300-3-35, Fibre optic interconnecting devices and passive components – Basic test and
319 measurement procedures – Part 3-35: Examinations and measurements – Visual inspection of
320 fibre optic connectors and fibre-stub transceivers
321 IEC 61753 (all parts), Fibre optic interconnecting devices and passive components –
322 Performance standard
323 IEC TR 61931, Fibre optic – Terminology
324 IEC TR 62222, Fire performance of communication cables installed in buildings
325 IEC TR 62283, Optical fibres – Guidance for nuclear radiation tests
326 IEC TR 62627-01, Fibre optic interconnecting devices and passive components – Part 01: Fibre
327 optic connector cleaning methods
328 ISO/IEC Guide 99, International vocabulary of metrology – Basic and general concepts and
329 associated terms (VIM)
330 3 Terms and definitions
331 For the purpose of this document, the terms and definitions given in IEC TR 61931,
332 ISO/IEC Guide 99 (VIM), and the following apply.
333 ISO and IEC maintain terminological databases for use in standardization at the following
334 addresses:
335 • IEC Electropedia: available at http://www.electropedia.org/
336 • ISO Online browsing platform: available at http://www.iso.org/obp
337 3.1 Fibre optic sensor principles
338 3.1.1
339 fibre optic sensor
340 part of a measuring instrument, or measuring chain, which is directly affected by the measurand,
341 and which generates a change in the optical characteristics of an optical fibre related to the
342 value of the measurand
343 Note 1 to entry: The optical fibre itself can act as the sensing element, or the fibre optic sensor can include an
344 optical or optically powered sensing element and one or more of the following (see Figure 1, Figure 2, Figure 3,
345 Figure 4 and Figure 5).
346 – optical fibre lead;
347 – optical fibre termination;
348 – optical signal conditioning.
349 [SOURCE: IEV 311-05-01, modified – “signal” has been replaced by “change in the optical
350 characteristics of an optical fibre” and Note 1 to entry has been added.]

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352 Key
353 1 Light source
354 2 Optical fibre lead
355 3 Optical or optically powered fibre sensing element
356 4 Measurand or phenomenon to be detected
357 5 Optical fibre lead
358 6 Optical receiver
359 Figure 1 – Fibre optic sensor in transmittance configuration with a passive fibre
360 sensing element and separate fibre leads for optical input and output
362 Key
363 1 Light source
364 2 Optical fibre lead
365 3 Optical or optically powered sensing element
366 4 Measurand or phenomenon to be detected
367 5 Optical fibre lead
368 6 Optical receiver
369 Figure 2 – Fibre optic sensor in reflectance configuration with a passive sensing
370 element and separate fibre leads for optical input and output
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373 Key
374 1 Measurand or phenomenon to be detected (e.g. high-energy electromagnetic radiation)
375 2 Optical radiation-generating sensing element (e.g. scintillator crystal)
376 3 Optical fibre lead
377 4 Optical receiver
378 Figure 3 – Fibre optic sensor with an optical radiation-generating sensing element and
379 separate fibre lead for optical output
381 Key
382 1 Fibre termination
383 2 Measurand or phenomenon to be detected (e.g. high-energy electromagnetic radiation)
384 3 Optical radiation-generating sensing fibre (e.g. scintillating fibre)
385 4 Optical fibre lead
386 5 Optical receiver
387 Figure 4 – Fibre optic sensor with an optical radiation-generating sensing fibre and
388 separate fibre lead for optical output
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391 Key
392 1 Light source and optical receiver (e.g. optical time domain reflectometer (OTDR))
393 2 Optical fibre lead
394 3 Measurand or phenomenon to be detected
395 4 Optical or optically powered sensing element
396 5 Fibre termination
397 Figure 5 – Fibre optic sensor in backscattering configuration with a passive fibre
398 sensing element and one fibre lead for optical input and output
399 3.1.2
400 distributed fibre optic sensor
401 fibre optic sensor which provides a spatially resolved measurement of a measurand over an
402 extended region by means of a continuous sensing element (see Figure 6)
404 Key
405 1 Interrogation unit (see 3.1.8)
406 2 Front panel output connector
407 3 Optical fibre lead
408 4 Measurand or phenomenon to be spatially resolved detected
409 5 Continuous optical fibre sensing element
410 6 Optical fibre lead
411 7 Front panel input connector
412 Note to Figure 6: Distributed fibre optic sensor single-ended configuration is also possible (see Figure 5).
413 Figure 6 – Distributed fibre optic sensor in loop configuration

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414 3.1.3
415 extrinsic fibre optic sensor
416 fibre optic sensor in which the characteristics of the light are affected externally to the optical
417 fibre(s) by the measurand
418 3.1.4
419 integrating fibre optic sensor
420 fibre optic sensor which provides a measurement result of a measurand over an extended region
421 by means of a continuous sensing element of a defined length
422 Note 1 to entry: The measurand is not spatially resolved but is integrated or summed over the length of the sensing
423 element.
424 3.1.5
425 intrinsic fibre optic sensor
426 fibre optic sensor whose sensing element consists of one or more optical fibre(s) in which one
427 or more characteristics like intensity, phase, polarization, spectrum, wavelength or transit time
428 of light depend on the measurand
429 Note 1 to entry: There are fibre optic sensors where the sensing principle is based on a change in coating
430 characteristics only (e.g. chemical or humidity sensors) or on an interaction between core and cladding (e.g., bending
431 sensor). They can be defined as indirect intrinsic fibre optic sensors. Direct intrinsic fibre optic sensors are based
432 on a direct change of the fibre core characteristics (e.g. Brillouin, Raman or Rayleigh scattering based sensors).
433 3.1.6
434 multiple point fibre optic sensor
435 fibre optic sensor consisting of a number of single point sensors which enables a spatially
436 resolved measurement of a measurand over an extended region at discrete locations (see
437 Figure 7).
439 Key
440 1 Signal processor
441 2 Pulse generator
442 3 Laser diode
443 4 Optical splitter
444 5 Optical attenuator (optional)
445 6 Optical fibre lead
446 7 Measurand or phenomenon to be detected
447 8 Multiple optical or optically powered single point sensing elements
448 9 Fibre termination
449 10 Optical attenuator (optional)
450 11 Photo diode
451 12 Amplifier and converter
452 13 Control and display
453 14 Optical time domain reflectometer (OTDR)
454 Note to Figure 7:  Multiple point fibre optic sensors in transmission configuration are also possible.
455 Figure 7 – Multiple point fibre optic sensor in backscattering configuration

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456 3.1.7
457 single point fibre optic sensor
458 fibre optic sensor consisting of one discrete sensing element which generates a signal related
459 to the value of the measurand (see Figure 8)
461 Key
462 1 Signal processor
463 2 Pulse generator
464 3 Laser diode
465 4 Optical splitter
466 5 Optical attenuator (optional)
467 6 Optical fibre lead
468 7 Measurand or phenomenon to be detected
469 8 Optical or optically powered single point sensing element
470 9 Fibre termination
471 10 Optical attenuator (optional)
472 11 Photo diode
473 12 Amplifier and converter
474 13 Control and display
475 14 Optical time domain reflectometer (OTDR)
476 Figure 8 – Single point fibre optic sensor in backscattering configuration
477 3.1.8
478 interrogation unit
479 IU
480 opto-electronic instrument intended to be used to make measurements in conjunction with a
481 fibre optic sensor
482 Note 1 to entry: The interrogation unit comprises at least a light source that supplies optical energy to the sensor
483 (see 3.1.9) and an optical receiver that receives the light affected by the measurand in the fibre sensor (see 3.1.13).
484 It often also incorporates additional elements for optical or electrical signal processing (e.g. arrayed-waveguide
485 gratings or high-speed data acquisition units), or both, and for data archiving. Some of these functions can be
486 implemented in a separate unit that is connected to the IU. The IU, either by itself or in combination with other
487 connected units, provides signal processing functions (standardized or customized) and possibly data archiving
488 (usually standardized). It also provides a user interface to control and "set" the measuring parameters, select
489 processing options, and define and implement the data collection options (triggered, timed, or other).
490 Note 2 to entry: The term “interrogation unit” is commonly used in conjunction with sensors using fibre Bragg
491 gratings and with distributed sensors for acoustic or temperature measurements.
492 3.1.9
493 light source
494 device which supplies the optical energy required to allow the interaction between the sensing
495 element and the measurand
496 Note 1 to entry: It contains, as a minimum, a luminous source and it can contain signal conditioning. When the
497 optical energy is generated by the phenomenon sensed, a light source is not required.

oSIST prEN IEC 61757:2025
IEC CDV 61757 ED2 © IEC 2024 17 86C/1952/CDV

498 3.1.10
499 optical or optically powered sensing element
500 device which accepts information in the form of a physical quantity and converts it to information
501 in the form of an optical quantity, according to a definite law
502 3.1.11
503 optical fibre
504 filament-shaped waveguide made of dielect
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