SIST EN 61746-2:2011

Calibration of Optical Time-Domain Reflectometers (OTDR) - Part 2: OTDR for multimode fibres (IEC 61746-2:2010)

This part of IEC 61746 provides procedures for calibrating multimode optical time domain reflectometers (OTDR). It covers OTDR measurement errors and uncertainties. The test of the laser(s) source modal condition is included as an optional measurement. This standard does not cover correction of the OTDR response.

Kalibrierung optischer Rückstreumessgeräte (OTDR) - Teil 2: OTDR für Mehrmodenfasern (IEC 61746-2:2010)

Etalonnage des réflectomètres optiques dans le domaine de temps (OTDR) - Partie 2: OTDR pour les fibres multimodes (CEI 61746-2:2010)

L'IEC 61746-2:2010 fournit des procédures destinées à l'étalonnage des réflectomètres optiques dans le domaine de temps pour fibres multimodales (OTDR). Elle traite des erreurs de mesure et incertitudes de l'OTDR. L'essai des conditions modales des sources laser est une mesure facultative. La présente norme ne couvre pas la correction de la réponse de l'OTDR.
Mots clés: l'étalonnage des réflectomètres optiques dans le domaine de temps pour fibres multimodales (OTDR).

Kalibriranje optičnih reflektometrov v časovnem prostoru (OTDR) - 2. del: OTDR za večrodovna vlakna (IEC 61746-2:2010)

Ta del IEC 61746 podaja postopke kalibriranja večrodovnih optičnih časovnih reflektometrov (OTDR). Zajema napake merjenja OTDR in negotovosti. Preskus pogoja modalnega vira laserjev je vključen kot mogoče merjenje. Ta standard ne zajema popravka odziva OTDR.

General Information

• Status: Published
• Publication Date: 03-Feb-2011
• ICS: 17.180.30 - Optical measuring instruments
• ICS: 33.180.99 - Other fibre optic equipment
• Technical Committee: iTEL - Communication cables
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 25-Jan-2011
• Due Date: 01-Apr-2011
• Completion Date: 04-Feb-2011
• Ref Project: EN 61746-2:2011 - Calibration of optical time-domain reflectometers (OTDR) - Part 2: OTDR for multimode fibres

Relations

• Revised: SIST EN 61746:2005 - Calibration of optical time-domain reflectometers (OTDR)
• Effective Date: 07-Jan-2014
• Corrected By: SIST EN 61746-2:2011/AC:2014 - Calibration of optical time-domain reflectometers (OTDR) - Part 2: OTDR for multimode fibres
• Effective Date: 27-Aug-2014

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 61746-2:2011
01-marec-2011
.DOLEULUDQMHRSWLþQLKUHIOHNWRPHWURYYþDVRYQHPSURVWRUX27'5GHO27'5]D
YHþURGRYQDYODNQD,(&
Calibration of Optical Time-Domain Reflectometers (OTDR) - Part 2: OTDR for
multimode fibres (IEC 61746-2:2010)
Kalibrierung optischer Rückstreumessgeräte (OTDR) - Teil 2: OTDR für
Mehrmodenfasern (IEC 61746-2:2010)
Etalonnage des réflectomètres optiques dans le domaine de temps (OTDR) - Partie 2:
OTDR pour les fibres multimodes (CEI 61746-2:2010)
Ta slovenski standard je istoveten z: EN 61746-2:2011
ICS:
17.180.30 2SWLþQLPHULOQLLQVWUXPHQWL Optical measuring
instruments
33.180.99 'UXJDRSUHPD]DRSWLþQD Other fibre optic equipment
YODNQD
SIST EN 61746-2:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 61746-2:2011

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SIST EN 61746-2:2011

EUROPEAN STANDARD
EN 61746-2

NORME EUROPÉENNE
January 2011
EUROPÄISCHE NORM

ICS 33.180.01 Supersedes EN 61746:2005 (partially)


English version


Calibration of optical time-domain reflectometers (OTDR) -
Part 2: OTDR for multimode fibres
(IEC 61746-2:2010)


Etalonnage des réflectomètres optiques Kalibrierung optischer
dans le domaine de temps (OTDR) - Rückstreumessgeräte (OTDR) -
Partie 2: OTDR pour les fibres multimodes Teil 2: OTDR für Mehrmodenfasern
(CEI 61746-2:2010) (IEC 61746-2:2010)




This European Standard was approved by CENELEC on 2011-01-02. 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 Central Secretariat 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 Central Secretariat 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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels


© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61746-2:2011 E

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SIST EN 61746-2:2011
EN 61746-2:2011 - 2 -
Foreword
The text of document 86/336/CDV, future edition 1 of IEC 61746-2, prepared by IEC TC 86, Fibre optics,
was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61746-2 on
2011-01-02.
This European Standard partially supersedes EN 61746:2005.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2011-10-02
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2014-01-02
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61746-2:2010 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
[2] IEC 60793-1-1 NOTE  Harmonized as EN 60793-1-1.
[3] IEC 60793-1-40 NOTE  Harmonized as EN 60793-1-40.
[4] IEC 60794-1-2 NOTE  Harmonized as EN 60794-1-2.
[5] IEC 60825-1 NOTE  Harmonized as EN 60825-1.
[6] IEC 60825-2 NOTE  Harmonized as EN 60825-2.
[7] IEC 61280-1-3 NOTE  Harmonized as EN 61280-1-3.
[8] IEC 61280-2-10 NOTE  Harmonized as EN 61280-2-10.
[9] IEC 61300-3-6 NOTE  Harmonized as EN 61300-3-6.
__________

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SIST EN 61746-2:2011
- 3 - EN 61746-2:2011
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

IEC 60793-2-10 - Optical fibres - EN 60793-2-10 -
Part 2-10: Product specifications - Sectional
specification for category A1 multimode fibres


IEC 60793-2-50 - Optical fibres - EN 60793-2-50 -
Part 2-50: Product specifications - Sectional
specification for class B single-mode fibres


IEC 61280-1-4 - Fibre optic communication subsystem test EN 61280-1-4 -
procedures -
Part 1-4: General communication subsystems
- Light source encircled flux measurement
method


IEC 61280-4-1 - Fibre optic communication subsystem test EN 61280-4-1 -
procedures -
Part 4-1: Installed cable plant - Multimode
attenuation measurement


IEC 61745 - End-face image analysis procedure for the - -
calibration of optical fibre geometry test sets


ISO/IEC 17025 - General requirements for the competence of EN ISO/IEC 17025 -
testing and calibration laboratories

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SIST EN 61746-2:2011

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SIST EN 61746-2:2011
IEC 61746-2
®
Edition 1.0 2010-06
INTERNATIONAL
STANDARD


Calibration of optical time-domain reflectometers (OTDR) –
Part 2: OTDR for multimode fibres


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 33.180.01 ISBN 978-2-88912-026-0
® Registered trademark of the International Electrotechnical Commission

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SIST EN 61746-2:2011
– 2 – 61746-2 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references.7
3 Terms, definitions and symbols .7
4 Preparation for calibration.13
4.1 Organization .13
4.2 Traceability.13
4.3 Preparation.13
4.4 Test conditions .13
4.5 Documentation .13
5 Distance calibration – General .14
5.1 General .14
5.2 Location deviation model .14
5.3 Using the calibration results.16
5.4 Measuring fibre length .17
6 Distance calibration methods .17
6.1 General .17
6.2 External source method .17
6.2.1 Short description and advantage .17
6.2.2 Equipment .17
6.2.3 Calibration of the equipment .19
6.2.4 Measurement procedure .20
6.2.5 Calculations and results .20
6.2.6 Uncertainties .21
6.3 Concatenated fibre method (using multimode fibres) .23
6.3.1 Short description and advantages .23
6.3.2 Equipment .23
6.3.3 Measurement procedures.24
6.3.4 Calculations and results .24
6.3.5 Uncertainties .25
6.4 Recirculating delay line method.26
6.4.1 Short description and advantages .26
6.4.2 Equipment .27
6.4.3 Measurement procedure .28
6.4.4 Calculations and results .28
6.4.5 Uncertainties .29
7 Vertical scale calibration – General .30
7.1 General .30
7.2 Loss difference calibration .31
7.2.1 Determination of the displayed power level F.31
7.2.2 Development of a test plan.31
7.3 Characterization of the OTDR source near field .33
7.3.1 Objectives and references .33
7.3.2 Procedure.33
8 Loss difference calibration method.34

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SIST EN 61746-2:2011
61746-2 © IEC:2010(E) – 3 –
8.1 General .34
8.2 Long fibre method.34
8.2.1 Short description.34
8.2.2 Equipment .34
8.2.3 Measurement procedure .36
8.2.4 Calculation and results.36
Annex A (normative) Multimode recirculating delay line for distance calibration.37
Annex B (normative) Mathematical basis .41
Bibliography .44

Figure 1 – Definition of attenuation dead zone .8
Figure 2 – Representation of the location deviation ΔL(L).15
Figure 3 – Equipment for calibration of the distance scale – External source method .18
Figure 4 – Set-up for calibrating the system insertion delay.19
Figure 5 – Concatenated fibres used for calibration of the distance scale.23
Figure 6 – Distance calibration with a recirculating delay line .27
Figure 7 – OTDR trace produced by recirculating delay line .28
Figure 8 – Determining the reference level and the displayed power level .31
Figure 9 – Region A, the recommended region for loss measurement samples .32
Figure 10 – Possible placement of sample points within region A .33
Figure 11 – Linearity measurement with a long fibre .35
Figure 12 – Placing the beginning of section D outside the attenuation dead zone .35
1
Figure A.1 – Recirculating delay line.37
Figure A.2 – Measurement set-up for loop transit time T .38
b
Figure A.3 – Calibration set-up for lead-in transit time T .39
a

Table 1 – Additional distance uncertainty.16
Table 2 – Attenuation coefficients defining region A.32

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SIST EN 61746-2:2011
– 4 – 61746-2 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

CALIBRATION OF OPTICAL TIME-DOMAIN
REFLECTOMETERS (OTDR) –

Part 2: OTDR for multimode fibres


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) 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.
International Standard IEC 61746-2 has been prepared by IEC technical committee 86: Fibre
optics.
The text of this standard is based on the following documents:
CDV Report on voting
86/336/CDV 86/359/RVC

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.

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SIST EN 61746-2:2011
61746-2 © IEC:2010(E) – 5 –
A list of all parts of IEC 61746 series, under the general title Calibration of optical time-domain
reflectometers (OTDR), can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until the
stability 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.
A bilingual version of this publication may be issued at a later date.

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SIST EN 61746-2:2011
– 6 – 61746-2 © IEC:2010(E)
INTRODUCTION
In order for an optical time-domain reflectometer (OTDR) to qualify as a candidate for complete
calibration using this standard, it must be equipped with the following minimum feature set:
a) the ability to measure type A1a or A1b IEC 60793-2-10 fibres;
b) a programmable index of refraction, or equivalent parameter;
c) the ability to present a display of a trace representation, with a logarithmic power scale and
a linear distance scale;
d) two markers/cursors, which display the loss and distance between any two points on a trace
display;
e) the ability to measure absolute distance (location) from the OTDR's zero-distance reference;
f) the ability to measure the displayed power level relative to a reference level (for example, the
clipping level).
Calibration methods described in this standard may look similar to those provided in Part 1 of
this series. However, there are differences: mix of different fibre types, use of mode conditioner
or different arrangement of the fibres. This leads to different calibration processes as well as
different uncertainties analysis.

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SIST EN 61746-2:2011
61746-2 © IEC:2010(E) – 7 –
CALIBRATION OF OPTICAL TIME-DOMAIN
REFLECTOMETERS (OTDR) –

Part 2: OTDR for multimode fibres



1 Scope
This part of IEC 61746 provides procedures for calibrating multimode optical time domain
reflectometers (OTDR). It covers OTDR measurement errors and uncertainties. The test of the
laser(s) source modal condition is included as an optional measurement.
This standard does not cover correction of the OTDR response.
2 Normative references
The following referenced documents are indispensable for the application 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 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
IEC 61280-1-4, Fibre optic communication subsystem test procedures – Part 1-4: General
communication subsystems – Light source encircled flux measurement method
IEC 61280-4-1, Fibre optic communication subsystem test procedures – Part 4-1: Installed
cable plant – Multimode attenuation measurement
IEC 61745, End-face image analysis procedure for the calibration of optical fibre geometry test
sets
ISO/IEC 17025, General requirements for the competence of testing and calibration
laboratories
3 Terms, definitions and symbols
For the purposes of this document, the following terms, definitions and symbols apply.
NOTE For more precise definitions, the references to IEC 60050-731 should be consulted.
3.1
attenuation
A
loss
optical power decrease in decibels (dB)
NOTE If P (watts) is the power entering one end of a segment of fibre and P (watts) is the power leaving the
in out
other end, then the attenuation of the segment is

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SIST EN 61746-2:2011
– 8 – 61746-2 © IEC:2010(E)
⎛ ⎞
P
in
⎜ ⎟
 A = 10log dB (1)
10
⎜ ⎟
P
⎝ out⎠
[IEV 731-01-48, modified]
3.2
attenuation coefficient
α
attenuation ( 3.1) of a fibre per unit length
[IEV 731-03-42, modified]
3.3
attenuation dead zone
for a reflective or attenuating event, the region after the event where the displayed trace
deviates from the undisturbed backscatter trace by more than a given vertical distance ΔF
NOTE The attenuation dead zone (see Figure 1 below) will depend on the following event parameters: reflectance,
loss, displayed power level and location. It may also depend on any fibre optic component in front of the event.

Initial dead zone
ΔF
Attenuation
dead zone
Location  (km)
IEC  1424/10

Figure 1 – Definition of attenuation dead zone
3.4
calibration
set of operations which establish, under specified conditions, the relationship between the
values indicated by the measuring instrument and the corresponding known values of that
quantity
NOTE See ISO Guide International vocabulary of basic and general terms in metrology.
3.5
centroidal wavelength
λ
avg
power-weighted mean wavelength of a light source in vacuum
[IEC 61280-1-3, definition 2.1.4]

Displayed power F  (dB)

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SIST EN 61746-2:2011
61746-2 © IEC:2010(E) – 9 –
3.6
displayed power level
F
level displayed on the OTDR's power scale
NOTE 1 Unless otherwise specified, F is defined in relation to the clipping level (see Figure 8).
NOTE 2 Usually, the OTDR power scale displays five times the logarithm of the received power, plus a constant
offset.
3.7
distance
D
spacing between two features
NOTE Usually expressed in metres.
3.8
distance sampling error
ΔL
sample
maximum distance ( 3.7) error attributable to the distance between successive sample points
NOTE 1 Usually expressed in metres.
NOTE 2 The distance sampling error is repetitive in nature; therefore, one way of quantifying this error is by its
amplitude.
3.9
distance scale deviation
ΔS
L
difference between the average displayed distance ( 3.7) < D > and the correspondent
otdr
reference distance ( 3.27) D divided by the reference distance ( 3.27)
ref
NOTE 1 Usually expressed in m/m.
NOTE 2 ΔS is given by the following formula
L
< D >− D < D >
otdr ref otdr
  ΔS = = − 1 (2)
L
D D
ref ref
where < D > is the displayed distance on a fibre averaged over at least one sample spacing.
otdr
3.10
distance scale factor
S
L
average displayed distance ( 3.7) divided by the correspondent reference distance ( 3.27)
NOTE 1 S is given by the following formula
L
< D >
otdr
S = (3)
L
D
ref
where < D > is the displayed distance between two features on a fibre (actual or simulated) averaged over at
otdr
least one sample spacing.
3.11
distance scale uncertainty
u
ΔSL
uncertainty of the distance scale deviation ( 3.9)
NOTE 1 Usually expressed in m/m.

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SIST EN 61746-2:2011
– 10 – 61746-2 © IEC:2010(E)
NOTE 2 u is given by the following formula
ΔSL
⎛ < D > ⎞ ⎛ < D >⎞
otdr otdr
⎜ ⎟ ⎜ ⎟
u = u −1 = u (4)
ΔSL ⎜ ⎟ ⎜ ⎟
D D
⎝ ref ⎠ ⎝ ref ⎠
NOTE 3 In the above formula, u() is understood as the standard uncertainty of ().
3.12
dynamic range at 98 % (one-way)
amount of fibre attenuation ( 3.1) that causes the backscatter signal to equal the noise level at
98 % ( 3.24)
NOTE It can be represented by the difference between the extrapolated point of the backscattered trace (taken at
the intercept with the power axis) and the noise level expressed in decibels, using a standard category A fibre (see
IEC 60793-2-10).
3.13
encircled flux
EF
fraction of cumulative near field power to total output power as a function of radial distance
from the centre of the core
3.14
group index
N
factor by which the speed of light in vacuum has to be divided to yield the propagation velocity
of light pulses in the fibre
3.15
location
L
spacing between the front panel of the OTDR and a feature in a fibre
NOTE Usually expressed in metres
3.16
location deviation
ΔL
displayed location ( 3.15) of a feature L minus the reference location ( 3.28) L
otdr ref
NOTE 1 Usually expressed in metres.
NOTE 2 This deviation is a function of the location.
3.17
location offset
ΔL
0
constant term of the location deviation ( 3.16) m odel
NOTE 1 Usually expressed in metres.
NOTE 2 This is approximately equivalent to the location of the OTDR front panel connector on the instrument's
distance scale.
NOTE 3 For a perfect OTDR, the location offset is zero.
3.18
location offset uncertainty
u
ΔL0
uncertainty of the location offset ( 3.17)

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SIST EN 61746-2:2011
61746-2 © IEC:2010(E) – 11 –
3.19
location readout uncertainty
u
Lreadout
uncertainty of the location ( 3.15) measurement samples caused by both the distance sampling
error ( 3.8) and the uncertainty type A of the measurement samples
3.20
loss deviation
ΔA

difference between the displayed loss of a fibre component A and the reference loss ( 3.29)
otdr
A , in dB
ref
NOTE 1 ΔA is given by the following formula

 ΔA = A − A (5)
otdr ref
NOTE 2 The loss deviation usually depends on the displayed power level, F.
3.21
loss uncertainty
u
ΔA
uncertainty of the loss deviation ( 3.20), in dB
3.22
loss scale deviation
ΔS
A
difference between the displayed loss of a fibre component A and the reference loss ( 3.29)
otdr
A , divided by the reference loss ( 3.29), in dB/dB
ref
NOTE 1 ΔS is given by the following formula

A
A − A
otdr ref
 ΔS = (6)
A
A
ref
NOTE 2 Refer to 7.1 for more details.
3.23
mode conditioner
a fibre set that converts any power distribution submitted at its input to an output power
distribution that fully comply with encircled flux limits
NOTE For the purposes of this standard, the encircled flux limits are defined by the IEC 61280-4-1.
3.24
noise level at 98 %
upper limit of a range which contains at least 98 % of all noise data points
3.25
non-linearity
NL
loss
difference between the maximum and minimum values of the loss deviation ( 3.20) ΔA for a
given range of power levels, in dB
NOTE 1 This is the non-linearity of a logarithmic power scale.
NOTE 2 Non-linearity is one contribution to loss deviation; it usually depends on the displayed power level and the
location.

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SIST EN 61746-2:2011
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3.26
received power level
...