EN 4861:2020

SLOVENSKI STANDARD
01-februar-2021
Aeronavtika - Postopek meteorološkega ocenjevanja kinematičnih polj, ki se
merijo z digitalno slikovno korelacijo
Aerospace series - Metrological assessment procedure for kinematic fields measured by
digital image correlation
Luft- und Raumfahrt - Metrologisches Messverfahren für kinematische Felder durch
digitale Bildkorrelation
Série aérospatiale - Procédure d’évaluation métrologique applicable aux mesures de
champs cinématiques par corrélation d’images numériques
Ta slovenski standard je istoveten z: EN 4861:2020
ICS:
49.020 Letala in vesoljska vozila na Aircraft and space vehicles in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 4861
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2020
EUROPÄISCHE NORM
ICS 17.180.01; 49.025.01
English Version
Aerospace series - Metrological assessment procedure for
kinematic fields measured by digital image correlation
Série aérospatiale - Procédure d'évaluation Luft- und Raumfahrt - Metrologisches Messverfahren
métrologique applicable aux mesures de champs für kinematische Felder durch digitale Bildkorrelation
cinématiques par corrélation d'images numériques
This European Standard was approved by CEN on 26 August 2019.

CEN 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 CEN
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 CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 4861:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Symbols and abbreviations . 5
5 Principle . 5
6 System for the assessment of the metrological performance . 6
7 Pre-assessment inspection . 6
8 Measurement of physical pixel size . 7
9 Metrological assessment process . 7
10 Classification of the extensometer system . 11
11 Uncertainty determination . 13
12 Metrological performance assessment intervals for extensometer systems . 13
13 Metrological performance assessment certificates . 13
Annex A (informative) Uncertainty of measurement . 15
Annex B (informative) Classification of the system for the assessment of the metrological
performance . 21
Annex C (normative) Covariance and covariance matrix . 22
Annex D (informative) Template for metrological assessment report for kinematic fields
measured by digital image correlation . 28
Annex E (informative) Alternative approach for optical model identification in the case of
monovision measurements . 35
Bibliography . 37

European foreword
This document (EN 4861:2020) has been prepared by the Aerospace and Defence Industries Association
of Europe — Standardization (ASD-STAN).
After enquiries and votes carried out in accordance with the rules of this Association, this Standard has
received the approval of the National Associations and the Official Services of the member countries of
ASD-STAN, prior to its presentation to CEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2021, and conflicting national standards shall be
withdrawn at the latest by June 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
1 Scope
This document specifies the monitoring of mechanical tests and inspections performed both at the
material (coupon) and at the structural scale by the implementation of kinematic field measurements by
digital image correlation. This document describes an in situ method for evaluating the metrological
performance of an extensometer system using image correlation for the delivery of displacement fields,
and by extrapolation, of deformation fields. It can be implemented prior to the actual start of the test
(or inspection). It will inform of the metrological performance in testing conditions.
This document allows the metrological performance of the measuring technology to be quantified.
The methodology described herein is not to be considered as a calibration step. This reference document
does not exhaustively specify the constitutive elements of a generic system of Digital Image Correlation
measurement. This reference does not address the measurement of 3D shapes via stereocorrelation
systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• ISO Online browsing platform: available at http://www.iso.org/obp
• IEC Electropedia: available at http://www.electropedia.org/
3.1
extensometer system
equipment used to measure displacement or strain fields on the surface of a tested piece
Note 1 to entry: The equipment consists of an image acquisition device and a computer system for calculating the
displacement and / or strain fields from the recorded images.
Note 2 to entry: For the purposes of this document, the term "Extensometer system" applies in particular to
kinematic field measurements by digital image correlation.
3.2
user
person in charge of the extensometer system implementation
3.3
2D measurement – monovision
extensometer system consisting of a single imager is a monovision system
Note 1 to entry: This system can provide full-field measurements in two (2) dimensions. The relevant plane is
perpendicular to the optical axis of the imaging system.

3.4
3D surface measurement – stereocorrelation
extensometer system consisting of (at least) 2 (two) imagers is a stereovision system
Note 1 to entry: Through prior calibration following the supplier’s instructions, the system provides measured
displacement fields in three (3) dimensions of the monitored surface. This practice applied to image correlation is
defined by the term stereocorrelation.
4 Symbols and abbreviations
Symbols used throughout this document are given in Table 1 together with their designation.
Table 1 — Symbols and designations
Symbol Designation Unit
l Maximum limit of measured displacement mm
max
l Minimum limit of measured displacement mm
min
l Displacement indicated by extensometer system µm
i
l Displacement given by apparatus for assessment of metrological performance µm
t
q Relative bias error of extensometer system %
rb
q Absolute bias error of extensometer system µm
b
r Resolution of extensometer system µm
5 Principle
The assessment of the metrological performance of an extensometer system involves a comparison of the
readings given by the extensometer system with known variations in length provided and prescribed by
a system for the assessment of the metrological performance.
NOTE 1 The user can define the displacement range(s) over which the metrological performance assessment is
to be performed. In this way, the performance of the extensometer system can be optimized. The user should take
special care to distinguish real displacements induced in the structure of interest motions from the experimental
displacement commonly called “rigid body motions”. Hence, it would be appropriate in this case to concentrate the
performance assessment to the centre of the operating range.
The assessment process compares the known displacement from the calibration device with the output
of the extensometer system. This output is provided in the form of data from computer files generated by
the software performing the kinematic field analysis based on the acquired images. These files should
contain the displacement fields that will be evaluated and the coordinate at which they are evaluated.
NOTE 2 For certain types of extensometer systems, the calibration and classification will also be dependent upon
the ability of the system for the assessment of the metrological performance.

6 System for the assessment of the metrological performance
6.1 Principle
The system for the assessment of the metrological performance, which allows a known displacement l to
t
be applied with respect to the object of interest, may consist of a rigid frame to which the image
acquisition device is attached. The system for the assessment of the metrological performance shall
comprise a mechanism for moving along the 3 (three) axes in space by translation, optionally from
1 (one) to 3 (three) rotations and a measuring device allowing to allow these displacements to be known
accurately. These variations in length can be measured by, for example, by an interferometer, a linear
incremental encoder or gauge blocks and a comparator, or a micrometre.
The calibration apparatus should be calibrated and should meet the performance requirements given in
Table B.1.
6.2 Traceability of metrological performance assessment
The calibration apparatus and the supporting equipment (such as micrometres, callipers, and optical
projection microscopes) shall be calibrated using standards that are traceable to the International System
of Units (SI).
The uncertainty associated with any measurement made by the supporting equipment shall not exceed
one third of the allowable error of the extensometer system being calibrated, see Table 2.
The temperature measurement instrument shall have a resolution of 0,1 °C.
7 Pre-assessment inspection
7.1 Aim
Prior to the assessment, the extensometer system shall be inspected. The quality of mechanical, optical,
electronic components and devices have been validated in terms of equipment such as the free motion of
tables, lenses, wiring and connections, hard drive space.
The extensometer system shall be assessed in the as-found condition if at all possible. The results shall
be analyzed and, if necessary, the system shall be adjusted and re-assessed. In this case, both data sets
shall be reported.
7.2 Records of the inspection
Records of the pre-assessment inspection shall be kept, identifying the “as-found” condition of the
extensometer system, when the inspection was performed and who performed it. These pre-assessment
inspection records can take the form of either a written report or a completed “pro-forma” checkli
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