Fibre optic sensors - Part 3-2: Acoustic sensing and vibration measurement - Distributed sensing

IEC 61757-3-2:2022 specifies the terminology, characteristic performance parameters, related test and calculation methods, as well as specific test equipment for interrogation units used in distributed fibre optic acoustic sensing and vibration measurement systems. This document refers to the Rayleigh backscatter and phase detection method by phase-sensitive coherent optical time-domain reflectometry (ϕ-OTDR) only. Quasi-static and low frequency operation modes are not covered by this document. Generic specifications for fibre optic sensors are defined in IEC 61757.

Capteurs fibroniques – Partie 3-2: Détection acoustique et mesure des vibrations - Détections réparties

IEC 61757-3-2:2022 spécifie la terminologie, les paramètres de performance caractéristiques, les méthodes d’essai et de calcul associées, ainsi que le matériel d’essai spécifique pour les unités d’interrogation utilisées dans les systèmes fibroniques répartis de mesure de vibrations et de détection acoustique. Le présent document se réfère uniquement à la méthode de rétrodiffusion de Rayleigh et de détection de phase par réflectométrie optique cohérente dans le domaine temporel sensible à la phase (ϕ-OTDR). Les modes de fonctionnement quasi statiques et à basses fréquences ne sont pas traités dans le présent document. Les spécifications génériques applicables aux capteurs fibroniques sont définies dans l’IEC 61757.

General Information

Status
Published
Publication Date
28-Mar-2022
Current Stage
PPUB - Publication issued
Completion Date
29-Mar-2022
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IEC 61757-3-2
Edition 1.0 2022-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic sensors –
Part 3-2: Acoustic sensing and vibration measurement – Distributed sensing
Capteurs fibroniques –
Partie 3-2: Détection acoustique et mesure des vibrations – Détections réparties
IEC 61757-3-2:2022-03(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61757-3-2
Edition 1.0 2022-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic sensors –
Part 3-2: Acoustic sensing and vibration measurement – Distributed sensing
Capteurs fibroniques –
Partie 3-2: Détection acoustique et mesure des vibrations – Détections réparties
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.99 ISBN 978-2-8322-1093-1

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® Registered trademark of the International Electrotechnical Commission
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---------------------- Page: 3 ----------------------
– 2 – IEC 61757-3-2:2022 © IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms, definitions, abbreviated terms and symbols .......................................................... 8

3.1 Terms and definitions .............................................................................................. 8

3.2 Abbreviated terms ................................................................................................. 11

3.3 Symbols ................................................................................................................ 12

4 Performance parameters of a distributed acoustic sensing system ................................ 13

5 Test apparatuses for performance parameter determination .......................................... 13

5.1 Simulated fibre sensor (SFS) ................................................................................ 13

5.2 Fibre stretcher ...................................................................................................... 14

5.3 Signal generation and amplification instrumentation .............................................. 15

5.4 Optical attenuator ................................................................................................. 15

5.5 Isolation chamber ................................................................................................. 15

6 Test procedures of performance parameters .................................................................. 16

6.1 General ................................................................................................................. 16

6.2 Dynamic range ...................................................................................................... 16

6.2.1 General ......................................................................................................... 16

6.2.2 Set-up ........................................................................................................... 16

6.2.3 Stimulus ........................................................................................................ 16

6.2.4 Data collection and processing ...................................................................... 17

6.2.5 Data reporting................................................................................................ 19

6.3 Frequency response ............................................................................................. 19

6.3.1 General ......................................................................................................... 19

6.3.2 Set-up ........................................................................................................... 19

6.3.3 Stimulus ........................................................................................................ 20

6.3.4 Data collection and processing ...................................................................... 20

6.3.5 Data reporting................................................................................................ 21

6.4 Fidelity .................................................................................................................. 23

6.4.1 General ......................................................................................................... 23

6.4.2 Set-up ........................................................................................................... 23

6.4.3 Stimulus ........................................................................................................ 23

6.4.4 Data collection and processing ...................................................................... 24

6.4.5 Data reporting................................................................................................ 24

6.5 Self-noise ............................................................................................................. 24

6.5.1 General ......................................................................................................... 24

6.5.2 Set-up ........................................................................................................... 24

6.5.3 Stimulus ........................................................................................................ 25

6.5.4 Data collection and processing ...................................................................... 25

6.5.5 Data reporting................................................................................................ 28

6.6 Spatial resolution .................................................................................................. 28

6.6.1 General ......................................................................................................... 28

6.6.2 Set-up ........................................................................................................... 29

6.6.3 Stimulus ........................................................................................................ 29

6.6.4 Data collection and processing ...................................................................... 29

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IEC 61757-3-2:2022 © IEC 2022 – 3 –

6.6.5 Data reporting................................................................................................ 30

6.7 Crosstalk .............................................................................................................. 32

6.7.1 General ......................................................................................................... 32

6.7.2 Set-up ........................................................................................................... 32

6.7.3 Stimulus ........................................................................................................ 32

6.7.4 Data collection and processing ...................................................................... 32

6.7.5 Data reporting................................................................................................ 33

6.8 Loss budget .......................................................................................................... 33

6.8.1 General ......................................................................................................... 33

6.8.2 Set-up ........................................................................................................... 34

6.8.3 Stimulus ........................................................................................................ 34

6.8.4 Data collection and processing ...................................................................... 34

6.8.5 Data reporting................................................................................................ 34

6.9 Sensor reflection robustness ................................................................................. 35

6.9.1 General ......................................................................................................... 35

6.9.2 Set-up ........................................................................................................... 35

6.9.3 Stimulus ........................................................................................................ 37

6.9.4 Data collection, processing, and reporting ..................................................... 38

Annex A (informative) Conversion of optical phase measurement to strain ........................... 39

Annex B (normative) Requirements for low uncertainty measurement .................................. 42

B.1 Single tone stimulus testing .................................................................................. 42

B.2 Frequency response testing .................................................................................. 43

Annex C (informative) FFT window functions ....................................................................... 45

C.1 Flat top window used for frequency domain measurements of spectral peaks ....... 45

C.2 Window functions used for frequency domain noise measurements ...................... 46

Bibliography .......................................................................................................................... 49

Figure 1 – Distributed acoustic sensing system ....................................................................... 9

Figure 2 – Signal parameters relating to time series and their spatial point identification ...... 12

Figure 3 – Simulated fibre sensor ......................................................................................... 14

Figure 4 – Configuration for SFS showing the locations TP , TP , and TP .......................... 14

1 2 3

Figure 5 – Test set-up for dynamic range test ....................................................................... 16

Figure 6 – Example of a strain stimulus signal and recovered phase of IU response

with a limit at 17 s ................................................................................................................. 18

Figure 7 – Example of a zoom view of strain stimulus signal and recovered phase of IU

response showing a phase jump at 16,98 s ........................................................................... 19

Figure 8 – Test set-up for frequency response test ............................................................... 20

Figure 9 – Magnitude response showing the 40 stimulus signals all with magnitude .............. 21

Figure 10 – Interrogator response to test stimulus, scaled in strain units, shown in the

frequency domain ................................................................................................................. 22

Figure 11 – Interrogator normalized frequency response ....................................................... 23

Figure 12 – Test set-up for fidelity test .................................................................................. 23

Figure 13 – Test set-up for self-noise .................................................................................... 25

Figure 14 – 2D data field representing the time varying acoustic field as a function of

distance ................................................................................................................................ 26

Figure 15 – System noise floor data processing schematic ................................................... 27

Figure 16 – Example plot of self-noise data .......................................................................... 28

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– 4 – IEC 61757-3-2:2022 © IEC 2022

Figure 17 – Test set-up for spatial resolution test.................................................................. 29

Figure 18 – Spatial sample points to be used for spatial resolution evaluation ...................... 30

Figure 19 – Graphical plotting approach used to determine spatial resolution ....................... 31

Figure 20 – Test set-up for crosstalk measurement ............................................................... 32

Figure 21 – Highlighted points to be sampled for crosstalk test ............................................. 33

Figure 22 – Example plot for crosstalk test results ................................................................ 33

Figure 23 – Test set-up for loss budget test .......................................................................... 34

Figure 24 – Test configurations for sensor reflection robustness ........................................... 36

Figure 25 – Fabrication examples for creating partial reflections ........................................... 37

Figure B.1 – Fibre stretcher spatial sample points ................................................................. 42

Figure B.2 – Frequency domain plot of single tone stimulus .................................................. 43

Figure B.3 – Frequency response plot of single tone stimulus ............................................... 44

Figure C.1 – Flat-top window and its Fourier transform characteristics [4] ............................. 45

Figure C.2 – Blackman-Harris window and its Fourier transform characteristics [5] ............... 46

Figure C.3 – Hamming window and its Fourier transform characteristics [6] .......................... 47

Table A.1 – Optical phase and strain relationships ................................................................ 41

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IEC 61757-3-2:2022 © IEC 2022 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC SENSORS –
Part 3-2: Acoustic sensing and vibration measurement –
Distributed sensing
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

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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

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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.

IEC 61757-3-2 has been prepared by subcommittee SC 86C: Fibre optic systems and active

devices, of IEC technical committee TC 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/1700/CDV 86C/1719/RVD

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.
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– 6 – IEC 61757-3-2:2022 © IEC 2022

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/standardsdev/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,
• replaced by a revised edition, or
• amended.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates

that it contains colours which are considered to be useful for the correct understanding

of its contents. Users should therefore print this document using a colour printer.

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IEC 61757-3-2:2022 © IEC 2022 – 7 –
INTRODUCTION

This document is based on SEAFOM Measuring Sensor Performance Document – 02 (SEAFOM

MSP-02) [1] . Within the framework of a type C liaison, SEAFOM proposed this document as a

new work item, which was approved by the participating members of IEC SC 86C.

NOTE Except for Figure 1, Figure C.1, Figure C.2, and Figure C.3, all figures in this document were adopted from

SEAFOM MSP-02 either in original or in modified form with permission from SEAFOM.

The IEC 61757 series is published with the following logic: the sub-parts are numbered as

IEC 61757-M-T, where M denotes the measure and T, the technology.
___________
Numbers in square brackets refer to the Bibliography.
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– 8 – IEC 61757-3-2:2022 © IEC 2022
FIBRE OPTIC SENSORS –
Part 3-2: Acoustic sensing and vibration measurement –
Distributed sensing
1 Scope

This part of IEC 61757 specifies the terminology, characteristic performance parameters,

related test and calculation methods, as well as specific test equipment for interrogation units

used in distributed fibre optic acoustic sensing and vibration measurement systems. This

document refers to the Rayleigh backscatter and phase detection method by phase-sensitive

coherent optical time-domain reflectometry (ϕ-OTDR) only. Quasi-static and low frequency

operation modes are not covered by this document.
Generic specifications for fibre optic sensors are defined in IEC 61757.
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 61757:2018, Fibre optic sensors – Generic specification

IEC 61757-2-2:2016, Fibre optic sensors – Part 2-2: Temperature measurement – Distributed

sensing
3 Terms, definitions, abbreviated terms and symbols
3.1 Terms and definitions

For the purposes of this document, terms and definitions given in IEC 61757, IEC 61757-2-

2:2016 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• ISO Online browsing platform: available at https://www.iso.org/obp
• IEC Electropedia: available at http://www.electropedia.org/
3.1.1
distributed fibre optic sensor

fibre optic sensor that provides a spatially resolved measurement of a measurand over an

extended region by means of a continuous sensing element
[SOURCE: IEC 61757:2018, 3.5]
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IEC 61757-3-2:2022 © IEC 2022 – 9 –
3.1.2
distributed fibre optic acoustic sensing system
DAS

measurement set-up consisting of a distributed fibre optic sensor connected to an interrogation

unit including processor, data archive, and user interface, which can locally detect acoustic or

vibration induced disturbances (phase change of the backscattering centres) in the fibre

Note 1 to entry: The alternative term fibre optic distributed vibration sensing (DVS) is also used in the industry.

Note 2 to entry: See Figure 1 for a principal DAS set-up. Pulses from a coherent source are sent into the sensor

fibre through an optical circulator, which also taps the coherent Rayleigh backscattering signal to a detector for

subsequent digitization and fast real-time acquisition.

Note 3 to entry: Typically, a DAS detects acoustic or vibration induced disturbances at frequencies below 2 kHz.

Figure 1 – Distributed acoustic sensing system
3.1.3
distance measurement range

maximum distance (specified in length units) from the interrogation unit output connector along

the simulated fibre sensor within which the DAS measures an acoustic signal with specified

measurement performance under defined conditions
[SOURCE: IEC 61757-2-2:2016, 3.2, modified – adapted to acoustic sensing.]
3.1.4
fibre stretcher

device where an external stimulus causes a linearly proportional amount of fibre strain uniformly

across the fibre length attached

Note 1 to entry: Normally the fibre stretcher consists of a piezoelectric cylinder with an electrical stimulus.

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– 10 – IEC 61757-3-2:2022 © IEC 2022
3.1.5
interrogation unit

opto-electronic instrument that is connected to the distributed fibre optic sensor and measures

and records dynamic strain along the fibre

Note 1 to entry: The processor, data archive, and user interface could be combined within the IU or could be a

separate unit connected to the IU. The IU provides processing functions (standardized or customized), data archiving

(usually standardized), and provides an interface to control and "set" the interrogation unit, select processing options,

and define and implement the data collection options (triggered, timed, or other).

3.1.6
location

optical distance (expressed in length units) from the interrogation unit output connector to a

desired sample point in the simulated fibre sensor
[SOURCE: IEC 61757-2-2:2016, 3.7, modified – adapted to simulated fibre sensor.]
3.1.7
measurement time
time between independent acoustic signal measurements when making successive
measurements along the simulated fibre sensor

Note 1 to entry: Equivalently, it is the time interval between successive trace timestamps under these conditions

(see Figure 2).
Note 2 to entry: The interrogation rate (specified in Hz) is equiva
...

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