SIST EN 61745:2018

SLOVENSKI STANDARD
01-januar-2018
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End-face image analysis procedure for the calibration of optical fibre geometry test sets
(IEC 61745:2017)
Ta slovenski standard je istoveten z: EN 61745:2017
ICS:
33.180.10 2SWLþQDYODNQDLQNDEOL Fibres and cables
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 61745
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2017
ICS 33.180.01
English Version
End-face image analysis procedure for the calibration of optical
fibre geometry test sets
(IEC 61745:2017)
Procédure d'analyse d'image d'extrémité pour l'étalonnage Endflächen-Bildanalyseverfahren für die Kalibrierung von
de dispositifs d'essais de géométrie des fibres optiques Prüfeinrichtungen für die Geometrie von Lichtwellenleitern
(IEC 61745:2017) (IEC 61745:2017)
This European Standard was approved by CENELEC on 2017-09-01. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 61745:2017 E
European foreword
The text of document 86/510/CDV, future edition 2 of IEC 61745, prepared by IEC/TC 86 "Fibre
optics" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
latest date by which the document has to be implemented at (dop) 2018-06-01
national level by publication of an identical national
standard or by endorsement
latest date by which the national standards conflicting with (dow) 2020-09-01
the document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 61745:2017 was approved by CENELEC as a European
Standard without any modification.

IEC 61745 ®
Edition 2.0 2017-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
End-face image analysis procedure for the calibration of optical fibre geometry

test sets
Procédure d'analyse d'image d’extrémité pour l'étalonnage de dispositifs

d'essais de géométrie des fibres optiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.01 ISBN 978-2-8322-4614-6

– 2 – IEC 61745:2017 © IEC 2017
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 General information and preparation for calibration . 11
4.1 Geometrical parameters of optical fibres . 11
4.2 Description of geometry test sets . 11
4.3 Calibration standard requirements . 12
5 Calibration . 12
5.1 General . 12
5.2 Rationale for calibration of geometry test sets . 12
5.2.1 General . 12
5.2.2 Verification of calibration state . 13
5.3 Calibration procedure . 14
5.3.1 General advice and organization. 14
5.3.2 Test requirements . 14
5.3.3 Calibration standard requirements . 14
5.3.4 Determination of calibration factors. 14
5.4 Check calibration procedure . 16
5.5 Spatial linearity . 16
5.6 Calibration of core/cladding concentricity error measurement. 17
5.7 Calibration of non-circularity measurement . 17
6 Evaluation of uncertainties . 17
6.1 General . 17
6.2 Evaluation of uncertainty in test set calibration . 18
6.2.1 General . 18
6.2.2 Uncertainty in scaling factor . 18
6.2.3 Uncertainty in offset correction factor . 19
6.3 Evaluation of uncertainty in fibre measurement . 20
6.3.1 General . 20
6.3.2 Determination of u . 21
Op,I,F
6.3.3 Determination of u' . 21
I,F
6.4 Evaluation of uncertainty in chromium mask measurement. 21
6.4.1 General . 21
6.4.2 Determination of u . 21
Op,I,C
6.4.3 Determination of u′ . 21
I,C
6.5 Summary . 22
7 Documentation . 22
7.1 Records . 22
Annex A (normative) Mathematical basis for measurement uncertainty calculations . 23
A.1 General . 23
A.2 Type A evaluation of uncertainty . 23
A.3 Type B evaluation of uncertainty . 23
A.4 Determining the combined standard uncertainty . 24
A.5 Reporting . 25

IEC 61745:2017 © IEC 2017 – 3 –
Annex B (informative) Derivation of calibration factors . 26
B.1 Derivation of scaling factors . 26
B.2 Derivation of correction offset factor . 27
Annex C (informative) Examples for the determination of calibration factors . 29
C.1 Example of determination of scaling factor . 29
C.2 Example of determination of offset correction factor . 29
Annex D (informative) Calculation of uncertainties . 30
D.1 General . 30
D.1.1 Overview . 30
D.1.2 Examples of type B evaluation of uncertainty . 30
D.2 Combining sources of uncertainty . 30
D.2.1 General . 30
D.2.2 Example of combining several sources of uncertainty . 31
D.3 Student's t distribution . 31
Annex E (informative) Worked examples for the determination of uncertainties . 33
E.1 General . 33
E.2 Example of determination of scaling factor uncertainty . 33
E.3 Example of determination of correction offset uncertainty . 33
E.4 Example of determination of fibre measurement uncertainty. 34
E.5 Example of determination of chromium mask measurement uncertainty . 34
Annex F (informative) Generation of working standards . 35
F.1 Generation of working standards . 35
F.1.1 General . 35
F.1.2 Measurement conditions . 35
F.2 Procedure for generation of working standards . 35
F.2.1 In the case where the infant artefact is a fibre. 35
F.2.2 In the case where the infant artefact is a chromium-on-glass artefact . 35
Annex G (informative) Estimation of uncertainty in the measurement of core/cladding
concentricity error . 36
G.1 Method of estimating uncertainty in concentricity error measurement . 36
G.1.1 General . 36
G.1.2 Determination of u . 36
G.1.3 Determination of u . 36
OP
G.1.4 Determination of CB . 36
G.1.5 Determination of u . 38
CB
G.2 Correcting for concentricity bias . 38
Annex H (informative) Estimation of uncertainty in the measurement of non-circularity . 39
H.1 Method of estimating uncertainty in non-circularity measurement . 39
H.2 Determination of u . 39
H.3 Determination of u . 39
Op
H.4 Determination of NCB . 39
H.4.1 General . 39
H.4.2 Method A: uncalibrated artefact . 40
H.4.3 Method B: calibrated artefact . 40
H.5 Determination of u . 40
NCB
Bibliography . 41

Figure 1 – Example of a calibration chain and the accumulation of uncertainties . 13

– 4 – IEC 61745:2017 © IEC 2017
Figure B.1 – Representation of a grid calibration mask . 26
Figure B.2 – Representation of an annulus calibration mask . 27
Figure B.3 – Derivation of correction offset . 28

Table D.1 – Values of t for specified confidence level . 32
Table G.1 – Measured values for angular positions . 37

IEC 61745:2017 © IEC 2017 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
END-FACE IMAGE ANALYSIS PROCEDURE FOR THE CALIBRATION
OF OPTICAL FIBRE GEOMETRY TEST SETS

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 61745 has been prepared by IEC technical committee 86: Fibre
optics.
This second edition cancels and replaces the first edition, published in 1998, and constitutes
a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) removal of the limitation of single mode optical fibre geometry test sets to include
multimode;
b) addition of a new annex as mathematical basis.

– 6 – IEC 61745:2017 © IEC 2017
The text of this International Standard is based on the following documents:
CDV Report on voting
86/510/CDV 86/516/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://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.
IEC 61745:2017 © IEC 2017 – 7 –
INTRODUCTION
In the research and production environments, there exists a range of test methods for
characterizing the geometry of optical fibres. Furthermore, each test method may determine
one or more of the many parameters required for complete geometrical characterization.
IEC 61745 describes the calibration of test sets that perform end-face image analysis, also
known as "near-field" or "grey-scale" analysis. The principles, however, may be applied to test
sets of a different type.
– 8 – IEC 61745:2017 © IEC 2017
END-FACE IMAGE ANALYSIS PROCEDURE FOR THE CALIBRATION
OF OPTICAL FIBRE GEOMETRY TEST SETS

1 Scope
This document describes the calibration of test sets that perform end-face image analysis,
also known as "near-field" or "grey-scale" analysis. The principles, however, can be applied to
test sets of a different type.
The procedures outlined are performed by calibration laboratories and by the manufacturers
or users of geometry test sets, for the purpose of calibrating geometry test sets and for
evaluating the uncertainties in measurements made on calibrated test sets. The calibration of
fibre coating or cable measurement test sets is not covered by this document.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purpose of this International Standard, the following definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
accredited calibration laboratory
calibration laboratory authorized by an appropriate national organization to issue calibration
certificates that demonstrates traceability to national standards
3.2
artefact
object that is measured on or used to calibrate a geometry test set
EXAMPLE An optical fibre and a chromium-on-glass pattern are examples of artefacts.
3.3
calibration
set of operations that establish, under specified conditions, the relationship between the
values of quantities indicated by a measuring instrument and the corresponding values
realized by standards
Note 1 to entry: The results of a calibration permit either the assignment of measurand values to the indications
or the determination of corrections with respect to the indications.
Note 2 to entry: A calibration may also determine other metrological properties such as the effects of influence
quantities.
Note 3 to entry: The result of a calibration may be recorded in a document, called a "calibration certificate" or a
"calibration report".
IEC 61745:2017 © IEC 2017 – 9 –
3.4
calibration chain
chain of transfers from a national standard to the geometry test set through intermediate or
working standards
Note 1 to entry: See U = k × u.
3.5
calibration checking
establishing that a geometry test set that has been previously calibrated but has reached its
calibration due date remains within specified uncertainty limits
Note 1 to entry: If the geometry test set has drifted outside these limits, then re-calibration is required. Otherwise,
the re-checking period can be extended for a stated period.
Note 2 to entry: The test set may be checked using a working standard.
3.6
calibration standard
artefact that is calibrated against a reference standard and is used to calibrate test sets
Note 1 to entry: The artefact may be a fibre or a chromium-on-glass pattern.
Note 2 to entry: Proper use of a calibration standard ensures traceability.
Note 3 to entry: The term includes the reference standard, the transfer standard and the working standard(s), in
descending order of metrological uncertainty.
3.7
combined standard uncertainty
combination of a number of individual standard uncertainties
Note 1 to entry: The term "accuracy" should be avoided in this context.
Note 2 to entry: In calibration reports and technical data sheets, the combined standard uncertainty in the
geometry test set measurement is reported as an overall expanded uncertainty with the applicable confidence
level, for example 95,5% or 99,7 %.
3.8
confidence level
estimation of the probability that the true value of a measured parameter lies within a given
range (expanded uncertainty)
3.9
correction offset
number that is added to or subtracted from the measurement result of a test set to correct for
a known physical effect
3.10
coverage factor
k
factor used to calculate the expanded uncertainty, U, from the standard uncertainty, u
3.11
expanded uncertainty
U
range of values within which the measurement parameter, at the stated confidence level, can
be expected to lie
Note 1 to entry: It is equal to the coverage factor, k, times the combined standard uncertainty u
U= k× u (1)
– 10 – IEC 61745:2017 © IEC 2017
Note 2 to entry: When the distribution of uncertainties is assumed to be normal and a large number of
measurements are made, then confidence levels of 68,3 %, 95,5 % and 99,7 % correspond to k values of 1, 2 and
3 respectively.
3.12
geometry test set
instrument used to measure the geometrical parameters of an optical fibre
Note 1 to entry: The parameters measured will depend on the type of geometry test set.
3.13
infant fibre
fibre whose geometry is to be measured on a calibrated geometry test set
3.14
instrument state
description of the measurement conditions of the geometry test set during calibration and
measurement
Note 1 to entry: The measurements conditions are for instance form-fits used, data filtering schemes employed
and other important information concerning the test set such as warm-up time and date of calibration.
3.15
national standard
standard recognized by a national decision to serve, in a country, as the basis for assigning
values to other standards of the quantity concerned
[SOURCE: ISO/IEC Guide 99:2007, 5.3, modified – The first preferred term "national
measurement standard" has been deleted, and the definition has been rephrased.]
3.16
national standards laboratory
laboratory which maintains the national standard
3.17
operating range
range of conditions under which the geometry test set is designed to perform within the stated
expanded uncertainty
Note 1 to entry: Such conditions include the diameter of the fibre being measured and environmental conditions,
such as temperature.
3.18
reference standard
artefact measured at a calibration laboratory, with the measurement traceable to national
standards
3.19
scaling factor
ratio of the known standard values for a calibration standard to the values indicated by the
geometry test set when no correction offsets are applied
3.20
standard uncertainty
u
uncertainty of a measurement result expressed as a standard deviation
Note 1 to entry: For further information, see Annex A and ISO/IEC Guide 98-3.

IEC 61745:2017 © IEC 2017 – 11 –
3.21
traceability
ability to demonstrate, for a measurement result or a geometry test set, a calibration chain
originating from a national standard
Note 1 to entry: Geometry test sets calibrated by the procedures in this document are traceable. Direct
traceability of the measurement results either to a national standards laboratory or to an accredited calibration
laboratory need to be demonstrated. Such traceability includes the calibration schedules of all artefacts in the
calibration chain and detailed calculations of all (cumulative) transfer uncertainties in the calibration chain.
Note 2 to entry: The use of a working standard alone to compare or monitor geometry test set calibration cannot
establish or re-establish traceability, but can only extend the duration of the traceability certification if no change is
found.
3.22
transfer standard
standard that is calibrated against a reference standard and is used for calibrating geometry
test sets
3.23
transfer uncertainty
estimate characterizing the uncertainty of a measurement caused by uncertainties in the
transfer process, at the given confidence level (such as changes in environmental conditions)
Note 1 to entry: These uncertainties may arise from the calibration standards used as well as from the geometry
test set.
3.24
working standard
standard that is used on a routine basis to calibrate or check measuring instruments
4 General information and preparation for calibration
4.1 Geometrical parameters of optical fibres
It is necessary to characterize the geometrical properties of optical fibres in order to ensure
satisfactory mechanical and optical performance. The geometrical parameters measured by
the types of test sets consist of the following:
a) cladding (reference surface) diameter;
b) cladding non-circularity;
c) core/cladding concentricity error.
4.2 Description of geometry test sets
End face image, or grey-scale, test sets usually comprise an optical microscope, an
illumina-tion source, an electronic image recording device, such as a camera, and a means of
storing image data for processing by digital computer. A second illumination source is usually
employed to launch light into the other end of the fibre. This enables the position of the fibre
core also to be measured. A typical measurement sequence is as follows: a cleaved fibre end
is positioned in the measurement port of the instrument and an image of the fibre end is
formed on the camera. The image of the fibre is focused, usually under automatic computer
control, digitized, and then transferred to a computer, which determines the geometrical
parameters of the fibre.
The quality of the fibre end is critical in this method, and the presence of cleave damage,
such as chips or edge roughness, can seriously affect the measurement. It is thus usual to
employ data-filtering methods to reduce the sensitivity of the measured result to the presence
of cleave damage.
– 12 – IEC 61745:2017 © IEC 2017
4.3 Calibration standard requirements
The calibration procedure detailed in this document requires the use of traceable calibration
artefacts. These artefacts consist of a calibrated fibre end and a chromium-on-glass mask.
Their nominal dimensions are discussed in 5.3.3 and 5.5.
5 Calibration
5.1 General
The calibration procedure comprises the following two operations.
a) The magnification, or scaling factor, of the imaging system is calibrated. This is a similar
process to conventional calibration methods for optical microscopes, except that, in this
case, a two-dimensional calibration is required.
b) A correction offset is determined. This offset is required to correct for systematic effects
such as diffraction at the fibre edge, differences between the way the calibration artefact
is calibrated and the method of measurement in the test set, and distortion of the image of
the fibre edge by camera sampling.
Worked examples for the determination of calibration factors are given in Annex B.
The calibration will be valid when applied to measurements in the following way:
– the scaling factors are applied multiplicatively to the raw data from the camera, before
applying form-fits and computing the cladding diameter of the fibre under test;
– the correction offset is applied additively to the computed cladding diameter of the fibre
under test.
NOTE 1 The choice of an edge-setting criterion defining the position of the cladding edge is important, and
calibration applies only to measurements using the same criterion as that used at the time of calibration.
NOTE 2 In certain circumstances, it has been found sufficient to calibrate only the scaling factor using a fibre or
chromium-on-glass standard. This approach, however, can lead to increased uncertainties when measuring fibres
that are of significantly different diameter from the calibration standard used.
5.2 Rationale for calibration of geometry test sets
5.2.1 General
The measurement of cladding diameter is common to most types of geometry test sets, so
calibration of this parameter is very important in comparing test sets of different types. This
document, however, details only the calibration of test sets that perform end-face image
analysis.
Basically, calibration is achieved by exposing the test set to independent geometrical
calibration standards. It is these standards that form the calibration chain and, therefore,
contribute to the transfer uncertainty.
The procedure is detailed in 5.3. The complete calibration chain is illustrated in Figure 1.

IEC 61745:2017 © IEC 2017 – 13 –
National
Uncertainty
standard
Uncertainty
Transfer of reference
uncertainty
standard
Reference
Uncertainty
standard
of transfer
standard
Transfer
Uncertainty
uncertainty
Transfer
of working
standard
standard
Uncertainty
Transfer
of test set
uncertainty
Working
standard
Combined
Transfer
uncertainty
uncertainty
of test set
Geometry
test set
Operational
uncertainty
Operating
conditions
IEC
Figure 1 – Example of a calibration chain and the accumulation of uncertainties
Calibration of the core/cladding concentricity error and non-circularity measurement is not
described, as there are no suitable standard reference materials available at the time of
writing. However, procedures enabling estimation of the uncertainties obtained in the
measurement of these parameters are given in Annex G and Annex H respectively.
5.2.2 Verification of calibration state
For routine verification, such as may frequently be carried out on geometry test sets in use, it
is sufficient to check (but not to reset) the state of calibration of the geometry test sets using a
working standard. The working standard may be a fibre or a chrome-on-glass mask.
A procedure for generation of a working standard is given in Annex F.
The distinction between checking the state of calibration and the calibration itself shall be
clearly made. While it is sufficient to establish stability of the geometry test set using the
working standard, this is not a substitute for full calibration.
The use of a working standard allows continued traceability to national standards to be
claimed, if it can be satisfactorily established that the existing instrument state, correction
factors, and so on, are sufficient to provide geometry results within a specified uncertainty
and without alteration. This simply means that the geometry test set has remained stable
since the last calibration.
Continued traceability can be claimed on a calibrated test set provided that the measured
values for the working standard agree with its calibrated values within the uncertainties.
Calibration is essential in the commissioning of geometry test sets, whereas a working
standard is used for routine calibration checking.
The procedure for calibration checking is described in 5.4.

– 14 – IEC 61745:2017 © IEC 2017
5.3 Calibration procedure
5.3.1 General advice and organization
Ensure that the environmental conditions are commensurate with the working environment as
specified by the manufacturer. Employ good metrological practices at all times.
Ensure that all calibration standards used in the calibration are calibrated according to a
documented programme with traceability to national standards laboratories or to accredited
standards laboratories. If possible, maintain more than one standard on each hierarchical
level of the calibration chain, so that the performance of standards can be verified by
comparisons on the same level.
Develop a documented measurement procedure for each type of calibration performed, giving
step-by-step operating instructions and equipment to be used. Use pro-forma result sheets,
uncertainty budgets and calibration certificates (see Clause 7).
Operate a quality system appropriate to the range of measurements. Ensure that there is
independent scrutiny of measurement results, intermediate calculations and calibration
certificates are prepared.
5.3.2 Test requirements
a) Perform all tests at a temperature and relative humidity that are within the manufacturer’s
specification for the test set.
b) Allow sufficient time for the geometry test set and test equipment to reach thermal
equilibrium with the environment in accordance with the manufacturer's recommendations
for the test set and the calibration standards used, before commencing the calibration
procedure.
c) Set up the geometry test set to the appropriate settings for calibration procedures, as
recommended by the manufacturer.
d) Ensure, where possible, that all accessible optical surfaces and calibration standards are
clean before measurement.
5.3.3 Calibration standard requirements
The use of calibration standards which are traceable to national standards laboratories is
mandatory. The calibration procedure requires the use of the following.
a) A calibrated measurement scale. This is a chromium-on-glass mask with a pattern,
typically, of dots, lines, circles or annuli.
b) A fibre end with calibrated cladding diameter. The fibre should be of similar material to
and within 5,0 µm of the nominal cladding diameter of the fibres to be measured by the
test set and have a non-circularity of less than 0,5 %.
The calibrated fibre end shall not be re-cleaved. This is due to variations of diameter along
the length of the fibre.
If the fibre end becomes damaged or cannot be cleaned sufficiently, it should not be used for
.
the purpose of calibration
For calibration checking (see 5.4), the standard may be either a fibre or a chromium-on-glass
pattern with traceable geometry values.
5.3.4 Determination of calibration factors
5.3.4.1 General
A derivation of the calibration factors used is given in Annex B.

IEC 61745:2017 © IEC 2017 – 15 –
5.3.4.2 Scaling factor
To calibrate the scaling factor, use a chromium-on-glass mask. This may comprise an array of
dots or lines, or an annular structure. The principle of calibration is to measure the distance
between graduations.
NOTE The uniformity of the scaling factor over the field of view of the imaging system (known as "spatial
linearity") will affect the uncertainty that can be transferred to measurements on fibres and also to measurements
of core/cladding concentricity error. A method for estimating spatial linearity is described in 5.5.
The scaling factors for the x and y axes of the camera are given by:
Dx
c
S = (2)
x
Dx
m
Dy
c
S = (3)
y
Dy
m
where
Dx is the measured spacing of graduations along the x-axis;

m
Dy is the measured spacing of graduations along the y-axis;

m
Dx is the calibrated spacing of graduations along the x-axis;

c
Dy is the calibrated spacing of graduations along the y-axis.
c
The procedure to measure the distance between graduations will depend on the type of
chrome mask used, as follows.
a) Regular array of dots or lines
Form an image of the array in a manner consistent with normal operation of the test set.
Measure the distances between graduations in two orthogonal directions, these being
parallel to the scan axes of the camera. The distance over which calibration is effected
should be within 5 µm of the nominal diameter of the fibres to be measured by the test set.
It is desirable to align the axes of the array to be parallel to the scan axes of the camera.
However, if they are not so aligned, compensation for the angular misalignment needs to
be applied.
b) Annulus
Form an image of the annulus in a manner consistent with normal operation of the test set.
Apply elliptical form fits to the inner and outer edges of the annulus. Determine the
measured diameters Dx and Dy along the x and y axes as follows:
m m
Dx + Dx
inner outer
Dx = (4)
m
Dy + Dy
inner outer
and Dy = (5)
m
where
Dx is the measured diameter of the inner annulus along the x-axis;

inner
Dy is the measured diameter of the inner annulus along the y-axis;

inner
Dx is the measured diameter of the outer annulus along the x-axis;
outer
Dy is the measured diameter of the outer annulus along the y-axis.

outer
– 16 – IEC 61745:2017 © IEC 2017
The diameter of the annulus should be within 5 µm of the nominal diameter of the fibres to be
measured by the test set. If, for convenience of use, it is assumed that Dx equals Dy , any
m m
non-circularity in the annulus will affect the determination of the uncertainty in subsequent
fibre non-circularity measurements (see 5.7).
Calculate the uncertainty in the determination of the scaling factors using Clause 6.
5.3.4.3 Correction offset
To calibrate the correction offset, a calibrated fibre is required. Form an image of the fibre end
in a manner consistent with normal operation of the test set and apply a form-fitting algorithm
to the fibre edge. Determine the correction offset O as follows:
O= D − D' × S (6)
P,F P,F
where
D is the calibrated diameter of the fibre;

P,F
D′ is the measured diameter of the fibre (scaling factor not applied);

P,F
P stands for "parent";
F stands for "fibre".
And S, the mean scaling factor, is:
S + S
x y
S=
Thus D′ × S is equal to the measured diameter of the fibre, in micrometres.
P,F
Calculate the uncertainty in the determination of the correction offset using Clause 6.
5.4 Check calibration procedure
This procedure is used for checking the calibration of a geometry test set. The procedure is
not used for determining calibration factors but may be used to check for test set stability
since the last calibration was performed.
As long as the geometry test set has already been calibrated and measurement of a working
standard does not reveal a geometry uncertainty greater than the permitted total uncertainty,
the claim of traceability may be extended.
a) Ensure that the test requirements given in 5.3.2 have been met.
b) Present the working standard to the geometry test set under consideration.
c) In the case where the working standard is
– a fibre: measure the mean cladding diameter;
– a chromium-on-glass mask: measure the distance between graduations.
Compare the measured values with the reference values and record any differences. It is
necessary to repeat the measurement several times to statistically reduce uncertainty in the
mean measured value.
5.5 Spatial linearity
The uncertainty in the measurement of fibres the diameter of which differs by more than 5 µm
from that of the fibre used for calibration may be estimated in one of two ways.

IEC 61745:2017 © IEC 2017 – 17 –
a) Measure a chromium-on-glass artefact at different positions within the field of view.
b) Measure the spacing between graduations of an array of lines or dots over the whole field
of view.
In either case, the linear dimension of the artefact or the interval shall be less than
one-quarter of the diameter
...