1、 IEC 61746-2 Edition 1.0 2010-06 INTERNATIONAL STANDARD Calibration of optical time-domain reflectometers (OTDR) Part 2: OTDR for multimode fibres IEC 61746-2:2010(E) THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2010 IEC, Geneva, Switzerland All rights reserved. Unless otherwise specified, no p
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8、stserv If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service Centre FAQ or contact us: Email: csciec.ch Tel.: +41 22 919 02 11 Fax: +41 22 919 03 00 IEC 61746-2 Edition 1.0 2010-06 INTERNATIONAL STANDARD Calibration of optical time-dom
9、ain reflectometers (OTDR) Part 2: OTDR for multimode fibres INTERNATIONAL ELECTROTECHNICAL COMMISSION X ICS 33.180.01 PRICE CODE ISBN 978-2-88912-026-0 Registered trademark of the International Electrotechnical Commission 2 61746-2 IEC:2010(E) CONTENTS FOREWORD.4 INTRODUCTION.6 1 Scope.7 2 Normative
10、 references7 3 Terms, definitions and symbols.7 4 Preparation for calibration.13 4.1 Organization13 4.2 Traceability13 4.3 Preparation13 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
11、 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
12、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 method26 6.4.1 Short description and advantages 26 6.4.2 Equip
13、ment .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 F31 7.2.2 Development of a test plan.31 7.3 Characterization
14、 of the OTDR source near field .33 7.3.1 Objectives and references .33 7.3.2 Procedure33 8 Loss difference calibration method34 61746-2 IEC:2010(E) 3 8.1 General .34 8.2 Long fibre method34 8.2.1 Short description34 8.2.2 Equipment .34 8.2.3 Measurement procedure 36 8.2.4 Calculation and results.36
15、Annex A (normative) Multimode recirculating delay line for distance calibration.37 Annex B (normative) Mathematical basis 41 Bibliography44 Figure 1 Definition of attenuation dead zone .8 Figure 2 Representation of the location deviation L(L).15 Figure 3 Equipment for calibration of the distance sca
16、le External source method .18 Figure 4 Set-up for calibrating the system insertion delay19 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
17、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 sectio
18、n D 1outside the attenuation dead zone 35 Figure A.1 Recirculating delay line37 Figure A.2 Measurement set-up for loop transit time T b .38 Figure A.3 Calibration set-up for lead-in transit time T a .39 Table 1 Additional distance uncertainty.16 Table 2 Attenuation coefficients defining region A.32
19、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 electro
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27、n 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, pr
28、operty 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 i
29、n 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 a
30、ny 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 c
31、an 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. 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
32、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,
33、withdrawn, replaced by a revised edition, or amended. A bilingual version of this publication may be issued at a later date. 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
34、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;
35、 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 OTDRs zero-distance reference; f) the ability to measure the displayed power level relative to a reference level (for example, the c
36、lipping 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 w
37、ell as different uncertainties analysis. 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
38、 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
39、 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 fib
40、res 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
41、 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
42、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 in (watts) is the power entering one end
43、 of a segment of fibre and P out (watts) is the power leaving the other end, then the attenuation of the segment is 8 61746-2 IEC:2010(E) out in 10log 10 = P P A dB (1) IEV 731-01-48, modified 3.2 attenuation coefficient attenuation ( 3.1) of a fibre per unit length IEV 731-03-42, modified 3.3 atten
44、uation 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 F NOTE The attenuation dead zone (see Figure 1 below) will depend on the following event parameters: ref
45、lectance, loss, displayed power level and location. It may also depend on any fibre optic component in front of the event. Displayed power F (dB) Location (km) Attenuation dead zone Initial dead zone F IEC 1424/10 Figure 1 Definition of attenuation dead zone 3.4 calibration set of operations which e
46、stablish, 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 avgpower-weighted mean wa
47、velength of a light source in vacuum IEC 61280-1-3, definition 2.1.4 61746-2 IEC:2010(E) 9 3.6 displayed power level F level displayed on the OTDRs 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 displ
48、ays 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 L samplemaximum distance ( 3.7) error attributable to the distance between successive sample points NOTE 1 Usually exp
49、ressed 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 S Ldifference between the average displayed distance ( 3.7) and the correspondent reference distance ( 3.27) D refdivided by the reference distance ( 3.27) NOTE 1 Usually expressed in m/m. NOTE 2 S Lis given by the following formula 1
