IEC/IEEE 62582-5:2015

Nuclear power plants - Instrumentation and control important to safety - Electrical equipment condition monitoring methods - Part 5: Optical time domain reflectometry

IEC/IEEE 62582-5:2015 contains methods for monitoring the attenuation condition of optical fibres and cables in instrumentation and control systems using optical time domain reflectometer measurements in the detail necessary to produce accurate and reproducible measurements. It includes the requirements for the measurement system and conditions, and the reporting of the measurement results.

Centrales nucléaires de puissance - Instrumentation et contrôle-commande importants pour la sûreté - Méthodes de surveillance de l'état des matériels électriques - Partie 5: Technique de rétrodiffusion

L'IEC/IEEE 62582-5:2015 présente des méthodes de surveillance du phénomène d'affaiblissement affectant les câbles à fibres optiques intégrés dans les systèmes d'instrumentation et de contrôle-commande en utilisant des techniques de rétrodiffusion, de façon suffisamment détaillée pour obtenir des mesures reproductibles et précises. Elle comprend des exigences concernant les systèmes de mesure et les conditions de mesure, ainsi que les rapports des résultats de mesure.

General Information

• Status: Published
• Publication Date: 18-Jun-2015
• ICS: 27.120.20 - Nuclear power plants. Safety
• ICS: 31.200 - Integrated circuits. Microelectronics
• Technical Committee: SC 45A - Instrumentation, control and electrical power systems of nuclear facilities
• Drafting Committee: WG 10 - TC 45/SC 45A/WG 10
• Current Stage: PPUB - Publication issued
• Start Date: 19-Jun-2015
• Completion Date: 30-Jun-2015

Overview

IEC/IEEE 62582-5:2015 is an international standard dedicated to nuclear power plants focusing on the instrumentation and control important to safety. This part of the standard series specifically addresses electrical equipment condition monitoring methods using Optical Time Domain Reflectometry (OTDR). The standard provides comprehensive methods for assessing the attenuation condition of optical fibres and cables deployed within instrumentation and control systems at nuclear facilities.

The standard ensures that OTDR measurements are accurate, reproducible, and consistent, detailing the necessary requirements for measurement systems, methodologies, environmental conditions, and reporting. Developed jointly by the IEC and IEEE, this publication supports ongoing safety and reliability in nuclear power plant operations by enhancing the ability to detect and monitor the ageing and degradation of optical fibres critical to safety communications.

Key Topics

• Scope and Objectives: Establishes protocols for monitoring optical attenuation to detect fibre degradation and failures before they impact nuclear safety systems.
• OTDR Measurement Procedures:
  • Selection of appropriate measurement wavelengths.
  • Use and calibration of OTDR equipment.
  • Guidelines for the preparation and conditioning of optical cables before measurement.
  • Detailed procedures for conducting OTDR measurements minimizing errors.
• Measurement System Requirements:
  • Instrumentation specifications to ensure precise backscatter detection.
  • Environmental considerations such as temperature and humidity effects.
• Reporting Standards:
  • Formatting of measurement results.
  • Interpretation guidelines to classify faults or fibre aging.
• Factors Affecting Accuracy:
  • Effects of fibre bending, connector interfaces, and transmission power variations.
• Ageing and Degradation Considerations:
  • Influence of thermal ageing and ionizing radiation on optical fibre performance.
  • Recommended monitoring intervals and diagnostic thresholds for nuclear-grade cables.

Applications

The IEC/IEEE 62582-5:2015 standard is critical for nuclear power plants aiming to implement robust condition monitoring programs for their safety-related optical fibre systems. Practical applications include:

• Tracking attenuation changes over time to detect early signs of fibre degradation due to thermal and radiation aging environments typical in nuclear facilities.
• Supporting preventive maintenance activities by identifying faults such as fibre breaks, splices, and connector losses before system failures occur.
• Enhancing the reliability of instrumentation and control (I&C) systems that depend on optical fibre communications for sensor and control signal transmission.
• Delivering standardized methods that improve diagnostic consistency among maintenance teams and across different plants or vendors.
• Assisting in compliance with nuclear regulatory safety requirements related to maintaining the functional integrity of electrical equipment critical for safety.

By applying this standard, operators ensure that optical fibres used in safety systems meet stringent quality and performance criteria that safeguard reactor operations and personnel.

Related Standards

IEC/IEEE 62582-5:2015 is part of a broader series covering electrical equipment condition monitoring methods in nuclear power plants. Other relevant standards in the series include:

• IEC/IEEE 62582-1: Covers general condition monitoring principles for electrical equipment important to safety.
• IEC/IEEE 62582-2 to 4: Address complementary condition monitoring techniques such as thermal imaging, electrical signature analysis, and vibration monitoring.
• Standards on nuclear-grade instrumentation and control system requirements that specify design, qualification, and testing of safety-related electrical equipment.
• Additional IEC and IEEE standards related to optical fibre communications, testing methodologies, and instrumentation.

Adopting IEC/IEEE 62582-5 within the context of these related standards enables nuclear facilities to implement a comprehensive and internationally harmonized condition monitoring framework that aligns with best practices in nuclear safety and electrical engineering.

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By adhering to IEC/IEEE 62582-5:2015, nuclear power plants benefit from a detailed and technically robust framework for maintaining optical fibre integrity, which is vital for safe and reliable plant operation in demanding environments. This standard enhances safety instrumentation life cycle management through precise, reliable, and reproducible OTDR condition monitoring techniques.

Standards Content (Sample)

IEC/IEEE 62582-5 ®
Edition 1.0 2015-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Instrumentation and control important to safety –
Electrical equipment condition monitoring methods –
Part 5: Optical time domain reflectometry

Centrales nucléaires de puissance – Instrumentation et contrôle-commande
importants pour la sûreté – Méthodes de surveillance de l'état des matériels
électriques –
Partie 5: Technique de rétrodiffusion

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IEC/IEEE 62582-5 ®
Edition 1.0 2015-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Instrumentation and control important to safety –

Electrical equipment condition monitoring methods –

Part 5: Optical time domain reflectometry

Centrales nucléaires de puissance – Instrumentation et contrôle-commande

importants pour la sûreté – Méthodes de surveillance de l'état des matériels

électriques –
Partie 5: Technique de rétrodiffusion

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-2704-6

– 2 – IEC/IEEE 62582-5:2015
© IEC/IEEE 2015
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope and object . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Abbreviations and acronyms . 10
5 General description . 10
6 Applicability and reproducibility . 10
7 OTDR measurements procedure . 11
7.1 General . 11
7.2 Instrumentation . 11
7.3 Measurement wavelengths . 12
7.4 Calibration . 12
7.5 Precautions for OTDR measurements . 12
7.6 Conditioning . 12
7.7 OTDR measurement . 13
7.8 Measurement errors . 15
7.9 Test report . 15
Annex A (informative) Factors affecting the measurement of attenuation in fibre optic
systems . 16
A.1 General . 16
A.2 Temperature and humidity . 16
A.3 Bending . 16
A.4 Transmission light power . 16
A.5 Connector interface . 16
Annex B (informative) Ageing and degradation of optical fibres in nuclear power plants . 17
B.1 Factors affecting ageing . 17
B.1.1 General . 17
B.1.2 Thermal ageing . 17
B.2 Ageing in ionising radiation . 18
B.2.1 General . 18
B.2.2 Increase of attenuation . 18
Annex C (informative) Guidance on selection of parameters for the measurement . 22
C.1 Selection of distance range . 22
C.2 Selection of pulse duration and definition of dead zone . 22
C.3 Selection of wavelength . 22
C.4 Selection and position of markers . 22
C.5 Selection of method for averaging . 24
C.6 Setting of the vertical and horizontal scale (v-zoom, h-zoom) . 24
C.7 Vertical and horizontal shifts . 24
C.8 Laser on/off . 25
C.9 Setting of IOR, group index . 25
C.10 Use of attenuator . 25
Bibliography . 26

© IEC/IEEE 2015
Figure 1 – Block functions of the OTDR . 12
Figure 2 – A typical OTDR waveform – Backscattered power vs distance (km) . 14
Figure 3 – Examples of faults . 14
Figure B.1 – A typical OTDR-trace . 17
Figure B.2 – RIA of different fibre types . 19
Figure B.3 – Example for RIA and its wavelength dependence of an optical fibre . 20
Figure C.1 – Markers for measuring attenuation . 23
Figure C.2 – Markers for measuring splice loss . 23
Figure C.3 – LSA and 2PA as approximation methods . 24
Figure C.4 – Fibre signature with the attenuator set at 0 dB and 5 dB, respectively . 25

– 4 – IEC/IEEE 62582-5:2015
© IEC/IEEE 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
ELECTRICAL EQUIPMENT CONDITION MONITORING METHODS –

Part 5: Optical time domain reflectometry

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organisation for standardisation comprising
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© IEC/IEEE 2015
International Standard IEC/IEEE 62582-5 has been prepared by subcommittee 45A:
Instrumentation, control and electrical systems of nuclear facilities, of IEC technical
committee 45: Nuclear instrumentation, in cooperation with the Nuclear Power Engineering
Committee of the IEEE Power & Energy Society , under the IEC/IEEE Dual Logo Agreement
between IEC and IEEE.
This publication is published as an IEC/IEEE Dual Logo standard.
The text of this standard is based on the following documents:
FDIS Report on voting
45A/1008A/FDIS 45A/1021/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC/IEEE 62582 series, published under the general title Nuclear
power plants – Instrumentation and control important to safety – Electrical equipment
condition monitoring methods, can be found on the IEC website.
The IEC Technical Committee and IEEE Technical Committee have decided that the contents
of this publication will remain unchanged until the maintenance result date indicated on the
IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At
this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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_____________
A list of IEEE participants can be found at the following URL:
http://standards.ieee.org/downloads/62582/62582-5-2015/62582-5-2015_wg-participants.pdf.

– 6 – IEC/IEEE 62582-5:2015
© IEC/IEEE 2015
INTRODUCTION
a) Technical background, main issues and organisation of the Standard
This IEC/IEEE standard specifically focuses on optical time domain reflectometer methods for
condition monitoring for the management of ageing of optical fibres and cables in electrical
equipment installed in nuclear power plants.
This IEC/IEEE standard is the fifth part of the IEC/IEEE 62582 series. It contains detailed
descriptions of condition monitoring based on optical time domain reflectometer
measurements on optical fibres and cables.
The IEC/IEEE 62582 series of standards is issued with a joint logo, which makes it applicable
to management of ageing of electrical equipment qualified to IEEE as well as IEC Standards.
Historically, IEEE Std 323™-2003 introduced the concept and role that condition based
qualification could be used in equipment qualification as an adjunct to qualified life. In
equipment qualification, the condition of the equipment for which acceptable performance was
demonstrated is the qualified condition. The qualified condition is the condition of equipment,
prior to the start of a design basis event, for which the equipment was demonstrated to meet
the design requirements for the specified service conditions.
Significant research has been performed on condition monitoring techniques and the use of
these techniques in equipment qualification as noted in NUREG/CR-6704, vol.2
(BNL-NUREG-52610) and JNES-SS-0903, 2009.
It is intended that this standard be used by test laboratories, operators of nuclear power
plants, systems evaluators and licensors.
b) Situation of the current standard in the structure of the IEC SC 45A standard series
IEC/IEEE 62582-5 is the third level IEC SC 45A document tackling the specific issue of
application and performance of optical time domain reflectometer measurements in
management of ageing of optical fibres and cables in electrical instrument and control
equipment in nuclear power plants.
IEC/IEEE 62582-5 is to be read in association with IEC/IEEE 62582-1, which provides
requirements for application of methods for condition monitoring of electrical equipment
important to safety of nuclear power plants.
For more details on the structure of the IEC SC 45A standard series, see item d) of this
introduction.
c) Recommendations and limitations regarding the application of this standard
It is important to note that this standard establishes no additional functional requirements for
safety systems.
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents and other bodies documents (IAEA, ISO)
The top-level document of the IEC SC 45A standard series is IEC 61513. It provides general
requirements for I&C systems and equipment that are used to perform functions important to
safety in NPPs. IEC 61513 structures the IEC SC 45A standard series.
IEC 61513 refers directly to other IEC SC 45A standards for general topics related to
categorisation of functions and classification of systems, qualification, separation of systems,

© IEC/IEEE 2015
defence against common cause failure, software aspects of computer-based systems,
hardware aspects of computer-based systems, and control room design. The standards
referenced directly at this second level should be considered together with IEC 61513 as a
consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 are standards
related to specific equipment, technical methods, or specific activities. Usually these
documents, which make reference to second-level documents for general topics, can be used
on their own.
A fourth level extending the IEC SC 45A standard series, corresponds to the Technical
Reports which are not normative.
IEC 61513 has adopted a presentation format similar to the basic safety publication
IEC 61508 with an overall safety life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, it provides an interpretation of the general requirements of
IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application sector. In this
framework IEC 60880 and IEC 62138 correspond to IEC 61508-3 for the nuclear application
sector. IEC 61513 refers to ISO as well as to IAEA GS-R-3 and IAEA GS-G-3.1 and IAEA GS-
G-3.5 for topics related to quality assurance (QA).
The IEC SC 45A standards series consistently implements and details the principles and
basic safety aspects provided in the IAEA code on the safety of NPPs and in the IAEA safety
series, in particular the Requirements SSR-2/1, establishing safety requirements related to
the design of Nuclear Power Plants, and the Safety Guide NS-G-1.3 dealing with
instrumentation and control systems important to safety in Nuclear Power Plants. The
terminology and definitions used by SC 45A standards are consistent with those used by the
IAEA.
NOTE It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions (e.g.,
to address worker safety, asset protection, chemical hazards, process energy hazards) international or national
standards would be applied that are based on the requirements of a standard such as IEC 61508.

– 8 – IEC/IEEE 62582-5:2015
© IEC/IEEE 2015
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
ELECTRICAL EQUIPMENT CONDITION MONITORING METHODS –

Part 5: Optical time domain reflectometry

1 Scope and object
This part of IEC/IEEE 62582 contains methods for monitoring the attenuation condition of
optical fibres and cables in instrumentation and control systems using optical time domain
reflectometer (OTDR) measurements in the detail necessary to produce accurate and
reproducible measurements. It includes the requirements for the measurement system and
conditions, and the reporting of the measurement results.
The different parts of IEC/IEEE 62582 are measurement standards, primarily for use in the
management of ageing in initial qualification and after installation. IEC/IEEE 62582-1 includes
requirements for the application of the other parts of IEC/IEEE 62582 and some elements
which are common to all methods. Information on the role of condition monitoring in
qualification of equipment important to safety is found in IEEE Std 323. Detailed descriptions
of methods for OTDR measurement of the quality and functionality of fibre optic cables are
given in IEC 61280-4-1 for multimode attenuation and in IEC 61280-4-2 for single-mode
attenuation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61746-1, Calibration of optical time-domain reflectometers (OTDR) – Part 1: OTDR for
single mode fibres
IEC 61746-2, Calibration of optical time-domain reflectometers (OTDR) – Part 2: OTDR for
multimode fibres
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
annealing
recovery of radiation-induced attenuation of an optical fibre by temperature (thermal
annealing) and/or transmission light power (photobleaching)
Note 1 to entry: Annealing is related to fibre material and to dose rate and exposure.
3.2
attenuation annealing time
time that is necessary to decrease the attenuation to a certain fraction (e.g., ½ or 1/e) of the
attenuation immediately after the end of the irradiation

© IEC/IEEE 2015
3.3
graded index fibre
optical fibre having a graded index profile in which the refractive index varies continuously in
the core as a function of distance from the axis
[SOURCE: IEC 60050-731:1991, 731-02-11 and 731-02-15, modified]
3.4
index of refraction
the index of refraction (group index) is defined as:
IOR = c/c (1)
fibre
where
IOR is the index of refraction;
c is the velocity of light in vacuum (299 792 458 m/s);
c is the velocity of light in the fibre.
fibre
IOR determines the length of the cable over which the OTDR measurements are made.
3.5
optical attenuation
A(λ)
measure of the decreasing transmission light power in a fibre at a given wavelength. The
definition is:
A(λ) = 10 lg (P1(λ)/P2(λ))  (2)
where
A(λ) is the attenuation, in dB, at wavelength λ;
P1(λ) is the transmission light power traversing one cross-section (marker 1);
P2(λ) is the transmission light power traversing a second cross-section (marker 2).
Note 1 to entry: It depends on the nature and length and condition of the fibre and is also affected by
measurement conditions.
Note 2 to entry: The term loss is used synonymous with attenuation in this International Standard.
3.6
optical attenuation coefficient
a(λ)
attenuation per unit length, defined as:
a(λ) = A(λ)/L (3)
where L is the unit length in km.
3.7
optical time domain reflectometer
device for characterizing an optical fibre whereby an optical pulse is transmitted through the
optical fibre and the optical power of resulting light scattered and reflected back to the input is
measured as a function of time
[SOURCE: IEC 60050-731:1991, 731-07-08, modified]

– 10 – IEC/IEEE 62582-5:2015
© IEC/IEEE 2015
3.8
step index fibre
fibre having a uniform IOR within the core
Note 1 to entry: The step is the shift between the core and the cladding, which has a lower IOR.
4 Abbreviations and acronyms
Al Aluminum
A/D Analog/digital
F Fluorine
FUT Fibre under test
Ge Germanium
GI Graded index
IOR Index of refraction (Group index)
LSA Least square approximation
OH Hydroxide ion
OTDR Optical time domain reflectometer
P Phosphorus
RIA Radiation induced attenuation
Si Silicon
SI Step index
SNR Signal to noise ratio
UV Ultra-violet
2PA Two point approximation
5 General description
Optical time domain reflectometry is a measurement technique for characterising an optical
fibre whereby an optical pulse is transmitted through the optical fibre and the transmission
light power of the resulting light scattered and reflected back to the input is measured as a
function of time. The result is reported as the attenuation coefficient (in dB/km).
OTDR measurements are useful in estimating the attenuation coefficient for fibres with
uniform attenuation and for identifying and localizing defects and localized losses. The
method gives results that are accurate, reproducible and related to practical use.
Details about attenuation uniformity of optical fibres can be found in IEC TR 62033.
6 Applicability and reproducibility
This International Standard is limited to the use of an OTDR as an instrument for monitoring
the attenuation of optical fibres and optical cables as part of management of ageing. The
method is not suitable for monitoring the condition of fibre with respect to mechanical integrity.
In general optical fibres are sensitive to ageing, e.g., due to exposure to ionising radiation,
which manifests itself mainly through the increase of the optical attenuation, see also
Annexes A and B. The attenuation (in dB/km) is used as an indicator of ageing for both optical
and hybrid (electrical-optical) cables, with in-situ access, whilst these cables are being
operated in nuclear environments.

© IEC/IEEE 2015
OTDR measurements allow analysis of the condition of the entire fibre, particularly of
longitudinal subsections of the fibre, or even identification of discrete points such as splices. It
also permits calculation of the fibre length, although this is outside the scope of this
international standard.
Optical cables in safety related applications in nuclear power plants may be shorter than in
general applications. Measurement of short optical cables (< 500 m) requires OTDR
instruments with high resolution.
The OTDR measurement is affected by the propagation speed and the backscattering
behaviour of the fibre. Best accuracy is obtained by measuring the attenuation from both ends
of the fibre and averaging the two backscatter traces. Therefore, measurements shall
normally be repeated from both ends. This is especially useful in case of unexpected
discontinuities. However, the improvement to the accuracy from measurements on both ends
is limited and measurements from one end are acceptable in cases where two ends are not
accessible.
7 OTDR measurements procedure
7.1 General
For condition monitoring one supervisory channel over all cable segments shall be accessible
for OTDR measurements. This could be one spare fibre in each cable segment, one
multiplexer channel or the use of an OTDR wavelength not disturbing the data transmission in
a fibre (or vice versa) using splitters.
7.2 Instrumentation
An OTDR may contain a number of parts, or modules, which provide the required functions.
These include a waveform generator (laser diode), a detector, a signal processing function
and a display. The instrument will also provide facilities to allow connection to the fibre cable
under test, such as a directional coupler and a fibre connector. The configuration of the OTDR
is shown in Figure 1.
The contact between the instrument fibre (adaptor cord) and the FUT shall be of a type
assuring repeatability and be clean and free from debris. A mechanical splice is usually used
as the contact.
The OTDR shall have a sufficient dynamic range to allow measurement over the FUT.
The instrument may contain facilities for changing the wavelength of the test pulses. In
addition, the OTDR may allow operation in either single-mode or multimode configuration.
A typical design of an OTDR consists of two main parts. These include the main frame, with a
microprocessor and a waveform display; and a plug-in unit that houses the laser diode, the
detector, a directional coupler and the fibre connector. Different plug-in units with separate
wavelengths can be used together with the same main frame. The plug-in units can be
adapted to either single-mode or multimode applications.
The configuration of the OTDR is shown in Figure 1.
A sequence of pulses of light is sent from a laser diode, and is transmitted via an optical
directional coupler and an optical connector into the fibre. The back scattered light, due to
Rayleigh scattering, is reflected back to the OTDR via the connector and is led through the
directional coupler to the detector. The detector converts the light to an electrical analogue
signal, which is amplified and sent to an A/D converter. A microprocessor treats the digital
signal and generates a presentation on the waveform display. The adaptor cord is typically

– 12 – IEC/IEEE 62582-5:2015
© IEC/IEEE 2015
1 km to 2 km long and may act as an attenuator. It is usually connected to the FUT with a
mechanical splice. In this way dirt is avoided in the OTDR-connector.
Adaptor cord
FUT
B
Laser diode Directional coupler A
Detector
A light pulse is sent from the laser diode
through the directional coupler via connector A
Amplifier
into an adaptor cord and then via connector B
into the FUT. A small backscattered signal is
detected as indicated. An attenuator is used to
protect the detector from overloading
(see Annex C, Clause C.10).
A/D Converter
Microprocessor
Waveform display
IEC
Figure 1 – Block functions of the OTDR
7.3 Measurement wavelengths
For single-mode fibres, it is recommended that the attenuation at wavelength 1 310 nm,
1 550 nm and 1 625 nm is reported. For multimode fibres it is recommended that the
attenuation at wavelength 850 nm and 1 300 nm is reported. If wavelengths other than these
are used in the field application, the attenuation at those wavelengths shall be reported in
addition.
7.4 Calibration
The OTDR equipment shall be calibrated, including the internal clock (for timing accuracy)
and the laser emitter (for pulse energy and pulse duration). The calibration shall be performed
in accordance with IEC 61746-1 for single-mode fibres, IEC 61746-2 for multimode fibres.
7.5 Precautions for OTDR measurements
Consecutive and comparative OTDR measurements shall be performed using the same
parameters, particularly for the pulse energy and duration. Also the wavelength of operation
for the condition monitoring equipment shall be selected within the range of wavelengths
being transported by the FUT and under operation. Special attention shall be given to the
maximum transmitted light power. To avoid photobleaching, the power shall be limited to
≤ 1 µW. The values of the parameters used shall be recorded and reported. Guidance for the
selection of measurement parameters is given in Annex C.
Ageing and additional attenuation can make it necessary to increase pulse durations and
averaging time, as well as change marker positions, see Annex C.
7.6 Conditioning
For laboratory measurements after artificial thermal ageing, the specimen shall be conditioned
at a laboratory temperature of (25 ± 5) ºC and a relative humidity of 45 % to 75 % for at least
3 h prior to measurement.
© IEC/IEEE 2015
For laboratory measurements after artificial exposure to ionising radiation, the OTDR
measurements shall be made as soon as possible after the exposure. The laboratory
temperature shall be (25 ± 5) ºC and the relative humidity shall be 45 % to 75 %. The
temperature at which the measurements are made and the time between the finishing of the
exposure and the start of the measurements shall be reported.
NOTE Due to annealing, the effect on the attenuation from ageing in ionising radiation will revert after finishing
the exposure. The rate of reversion depends on the surrounding temperature – the higher the temperature, the
higher the rate of reversion. See Annex B.
For field measurements, the temperature of the surrounding atmosphere shall be recorded.
7.7 OTDR measurement
Prior to the start of the condition monitoring program, all the parameters of the OTDR shall be
determined and fixed, in order to optimise the measurements, both in terms of accuracy and
acquisition time. The following parameters shall be selected, stored for consecutive
measurements, and reported:
• measurement points (marker 1 and marker 2 in Figure 2);
• wavelength of test;
• pulse duration;
• distance range (the instrument selects power level when the distance range has been set);
• type of connection between the adaptor cord and the FUT;
• number of pulses for averaging;
• backscattering coefficient;
• IOR (group index).
Guidance on selection of parameters is given in Annex C.
A pulse duration shall be selected that is long enough to obtain an OTDR trace which
visualises the entire FUT, and short enough to optimise the resolution. Repeated
measurements may be needed, using longer/shorter pulse durations in order to optimise the
resolution.
A typical OTDR trace presenting the received backscattered power versus the distance along
the FUT is presented in Figure 2 together with set values and calculated results. Figure 3
gives two examples of possible faults in the cable, identified by the OTDR.

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© IEC/IEEE 2015
End reflection (4 %)
P
P
Noise
L L
1 2
Distance from start of FUT (km)
Calculated results
Set and selected values:
Attenuation between the markers P – P = 0,18 dB
Distance range    = 18 km
1 2
Horizontal scale   = 250 m/div Distance between the markers L – L = 0,9 km
2 1
Vertical scale     = 0,1 dB/div Attenuation coefficient (P – P )/( L – L ) = 0,20 dB/km
1 2 2 1
Wavelength = 1 550 nm
Pulse duration = 1 µs
Attenuator = 5,0 dB
IOR = 1,500 0
Transmission loss measurement is selected (loss)
LSA is selected as approx. method
L is selected at 0,050 km
L is selected at 0,950 km
2 IEC
Key
L is the position of marker 1
L is the position of marker 2
P is the power (in dB) at the position of marker 1
P is the power (in dB) at the position of marker 2
Figure 2 – A typical OTDR waveform – Backscattered power vs distance (km)
IEC IEC
a) Attenuation step b) Fibre break
Figure 3 – Examples of faults
The measurements shall determine the average attenuation (in dB/km) over the length of the
fibre measured and the local attenuation over discontinuities (splices, faults, etc.). Information
on averaging and factors affecting SNR is given in Annex C, Clause C.5.
In the event of a degraded SNR under radiation, the fibre section monitored shall be reduced
accordingly, in order to obtain an attenuation coefficient through linear regression with a
standard deviation better than 0,9. The fibre section used for the estimation of the attenuation
coefficient shall contain a minimum of 50 measurement points.
Optical power P (dB)
© IEC/IEEE 2015
7.8 Measurement errors
For measurement errors, reference is made to IEC 61280-4-2 (single mode) and
IEC 61280-4-1 (multimode).
7.9 Test report
Data used for the condition monitoring of fibre optic cables and components shall be
organised in an auditable file or report. The measurement report shall as a minimum include
the following information:
a) Number, identification and description of the specimen, including material composition.
b) Pre-history (unaged, artificially aged, naturally aged).
c) Locality of the measurement (laboratory, on-site).
d) For laboratory measurement of thermally artificially aged specimen: time allowed for
attaining temperature equilibrium with laboratory before performing the measurements
(time interval between removing the specimen from the heat chamber until start of
measurement).
e) For laboratory measurement of specimen aged in ionising radiation: time between finishing
of radiation exposure and start of measurements.
f) The ambient temperature at which the measurements are made.
g) Measurement instrumentation, most recent calibration date and reference to the
calibration certificate.
h) Measurement conditions, including transmission light power, pulse duration, wavelength of
operation, measurement points, distance range, number of pulses for averaging, back
scattering coefficient, and IOR.
i) Connection of the specimen for measurements (dummy spool, power splitter, switch).
j) Splice losses in case of several cables spliced together.
k) Analysis of any test anomalies.
l) Attenuation coefficient in dB/km for each wavelength. The mean value over the whole
length of the fibre measured shall be given, together with the values over discontinuities
(faults, splices, etc.). It is recommended to enclose a digital trace showing the attenuation
versus distance. The cause of the discontinuities should be identified and reported.
m) Any other information of importance in interpretation of the measurement results in
relation to the purposes of the measurements.

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Annex A
(informative)
Factors affecting the measurement of
attenuation in fibre optic systems

A.1 General
There are many factors that influence the measurement of signal attenuation in a fibre optic
system. Some of these are as follows:
a) temperature;
b) humidity;
c) bending;
d) transmission light power;
e) connector interface.
A.2 Temperature and humidity
Temperature has an inverse relationship with signal attenuation, so the lower the temperature,
the more the signal attenuation. This inverse temperature relationship will have to be taken
into account when analysing the information from condition monitoring. This change in the
signal attenuation of the cable can be in a manner that is not monotonic.
Humidity can cause additional fibre attenuation. This will need to be accounted for in testing.
Change in humidity levels on subsequent tests can change the fibre attenuation in a manner
that is not monotonic.
A.3 Bending
Bending of the cable can affect the fibre attenuation. If the cable bend radius is changed, this
can change the attenuation in the cable, such that misinterpretation of the result is possible.
In these circumstances, a new baseline may be necessary.
A.4 Transmission light power
The signal used to test the fibre optic cable or a light source may cause photobleaching,
which can decrease the attenuation in the fibre (see B.2.2.6). This is taken into account by
using a power level that is the same as that used in service, but not above 1 µW.
A.5 Connector interface
Additional attenuation can be developed at the connector interface and this would need to be
taken into account when defining the starting point for calc
...