SIST EN ISO 2360:2017

Non-conductive coatings on non-magnetic electrically conductive base metals - Measurement of coating thickness - Amplitude-sensitive eddy-current method (ISO 2360:2017)

This document specifies a method for non-destructive measurements of the thickness of non-conductive
coatings on non-magnetic electrically conductive base metals, using amplitude-sensitive eddy-current
instruments.
In this document, the term “coating” is used for materials such as, for example, paints and varnishes,
electroplated coatings, enamel coatings, plastic coatings, claddings and powder coatings. This method
is particularly applicable to measurements of the thickness of most oxide coatings produced by
anodizing, but is not applicable to all conversion coatings, some of which are too thin to be measured by
this method (see Clause 6).
This method can also be used to measure non-magnetic metallic coatings on non-conductive base
materials. However, the phase-sensitive eddy-current method specified in ISO 21968 is particularly
usable to this application and can provide thickness results with a higher accuracy (see Annex A).
This method is not applicable to measure non-magnetic metallic coatings on conductive base metals.
The phase-sensitive eddy-current method specified in ISO 21968 is particularly useful for this
application. However, in the special case of very thin coatings with a very small conductivity, the
amplitude-sensitive eddy-current method can also be used for this application (see Annex A).
Although the method can be used for measurements of the thickness of coatings on magnetic base
metals, its use for this application is not recommended. In such cases, the magnetic method specified
in ISO 2178 can be used. Only in case of very thick coatings above approximately 1 mm, the amplitudesensitive
eddy-current method can also be used for this application (see Annex A).

Nichtleitende Überzüge auf nichtmagnetischen metallischen Grundwerkstoffen - Messen der Schichtdicke - Wirbelstromverfahren (ISO 2360:2017)

Dieses Dokument legt ein Verfahren für zerstörungsfreie Schichtdickenmessungen nichtleitender Beschichtungen auf nichtmagnetischen, elektrisch leitenden Grundmetallen mittels amplitudensensitiver Wirbelstrommessgeräte fest.
In diesem Dokument wird der Begriff „Beschichtung" verwendet für z. B. Lacke und Anstrichstoffe, galvanische Überzüge, Email, Kunststoffschichten, Umhüllungen und Pulverlacke. Dieses Verfahren ist insbesondere anwendbar für die Schichtdickenmessungen der meisten Oxidschichten, die durch Anodisieren hergestellt werden, aber nicht anwendbar bei allen Konversionsschichten, von denen einige zu dünn sind, um durch dieses Verfahren gemessen zu werden (siehe Abschnitt 6).
Dieses Verfahren kann auch bei Messung nichtmagnetischer metallischer Beschichtungen auf nichtleitenden Grundmaterialien genutzt werden. Allerdings ist das phasensensitive Wirbelstromverfahren nach ISO 21968 für diese Anwendung besonders geeignet und kann Ergebnisse mit einer höheren Genauigkeit liefern (siehe Anhang A).
Dieses Verfahren ist bei Messung nichtmagnetischer metallischer Beschichtungen auf leitenden Grundmetallen nicht anwendbar. Das phasensensitive Wirbelstromverfahren wie in ISO 21968 festgelegt ist für diese Anwendung besonders geeignet. Allerdings kann in dem speziellen Fall von sehr dünnen Beschichtungen mit einer sehr niedrigen Leitfähigkeit auch das amplitudensensitive Wirbelstromverfahren für diese Anwendung eingesetzt werden (siehe Anhang A).
Obwohl das Verfahren für Schichtdickenmessungen auf magnetischen Grundmetallen eingesetzt werden kann, wird dessen Einsatz für diese Anwendung nicht empfohlen. In solchen Fällen kann das nach ISO 2178 festgelegte magnetische Verfahren eingesetzt werden. Lediglich im Fall von sehr dicken Beschichtungen über ungefähr 1 mm kann das amplitudensensitive Wirbelstromverfahren auch für diese Anwendung eingesetzt werden (siehe Anhang A).

Revêtements non conducteurs sur matériaux de base non magnétiques conducteurs de l'électricité - Mesurage de l'épaisseur de revêtement - Méthode par courants de Foucault sensible aux variations d'amplitude (ISO 2360:2017)

ISO 2360:2017 spécifie une méthode de mesure non destructive de l'épaisseur des revêtements non conducteurs sur des métaux de base non magnétiques, conducteurs de l'électricité, au moyen d'instruments utilisant les courants de Foucault et sensibles aux variations d'amplitude.
Dans l'ISO 2360:2017, le terme «revêtement» est utilisé pour désigner des produits tels que, par exemple, les peintures et vernis, les revêtements électrolytiques, les revêtements en émaux, les revêtements plastiques, les placages et les revêtements en poudre. Cette méthode est applicable notamment au mesurage de l'épaisseur de la plupart des revêtements d'oxydes produits par anodisation, mais elle ne s'applique pas à toutes les couches de conversion, certaines d'entre elles étant trop minces pour être mesurées par cette méthode (voir Article 6).
Cette méthode peut également être utilisée pour mesurer des revêtements métalliques non magnétiques sur des métaux de base non conducteurs. Toutefois la méthode par courants de Foucault sensible aux variations de phase spécifiée dans l'ISO 21968 est adaptée en particulier à cette application et peut fournir des résultats de mesure d'épaisseur avec une plus grande exactitude (voir Annexe A).
Cette méthode ne peut pas être appliquée pour mesurer des revêtements métalliques non magnétiques sur des métaux de base conducteurs. La méthode par courants de Foucault sensible aux variations de phase spécifiée dans l'ISO 21968 est particulièrement utile pour cette application. Cependant, dans le cas particulier des revêtements très minces avec une très faible conductivité, la méthode par courants de Foucault sensible aux variations d'amplitude peut être également utilisée pour cette application (voir Annexe A).
Bien que la méthode puisse être utilisée pour les mesurages de l'épaisseur des revêtements sur des métaux de base magnétiques, son utilisation pour cette application n'est pas recommandée. Dans ce cas, la méthode magnétique spécifiée dans l'ISO 2178 peut être utilisée. Uniquement dans le cas de revêtements très épais (épaisseur supérieure à environ 1 mm), la méthode par courants de Foucault sensible aux variations d'amplitude peut être également utilisée pour cette application (voir Annexe A).

Neprevodne prevleke na nemagnetnih električno prevodnih osnovnih kovinah - Merjenje debeline prevleke - Metoda vrtinčnih tokov, občutljiva za spremembe amplitude (ISO 2360:2017)

Ta dokument določa metodo za neporušitvene meritve debeline neprevodnih prevlek na nemagnetnih električno prevodnih osnovnih kovinah z metodo vrtinčnih tokov, občutljivo za spremembe amplitude.
V tem dokumentu se izraz »prevleka« uporablja za materiale, kot so barve in laki, elektrolitske prevleke, emajlirane prevleke, plastične prevleke, obloge in praškaste prevleke. Ta metoda
je še posebej primerna za merjenje debeline večine oksidnih prevlek, ki so proizvedene z eloksacijo, vendar se ne uporablja za vse reakcijske prevleke, od katerih so nekatere preveč tanke, da bi jih lahko izmerili s to metodo (glej točko 6).
To metodo je mogoče uporabiti tudi za merjenje nemagnetnih kovinskih prevlek na neprevodnih osnovnih materialih. Kljub temu je metoda vrtinčnih tokov, občutljiva za spremembe amplitude, ki je določena v standardu ISO 21968, še zlasti uporabna za ta namen in zagotavlja natančnejše rezultate merjenja debeline (glej dodatek A).
Ta metoda se ne uporablja za merjenje nemagnetnih kovinskih prevlek na prevodnih osnovnih materialih. Metoda vrtinčnih tokov, občutljiva za spremembe amplitude, ki je določena v standardu ISO 21968, je še zlasti uporabna za ta namen. Vendar pa je v posebnih primerih, ko so prevleke zelo tanke in zelo slabo prevodne, metodo vrtinčnih tokov, občutljivo za spremembe amplitude, mogoče uporabiti za ta namen (glej dodatek A).
Čeprav se metoda lahko uporablja za merjenje debeline prevlek magnetnih osnovnih kovin, uporaba metode za ta namen ni priporočljiva. V takih primerih je mogoče uporabiti magnetno metodo, določeno v standardu ISO 2178. Samo v primeru zelo debelih prevlek z debelino več kot približno 1 mm se lahko za ta namen uporabi tudi metoda vrtinčnih tokov, občutljiva za spremembe amplitude (glej dodatek A).

General Information

• Status: Published
• Public Enquiry End Date: 01-Jul-2016
• Publication Date: 15-Oct-2017
• ICS: 25.220.20 - Surface treatment
• Technical Committee: IPKZ - Protection of metals against corrosion
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 05-Oct-2017
• Due Date: 10-Dec-2017
• Completion Date: 16-Oct-2017
• Ref Project: EN ISO 2360:2017 - Non-conductive coatings on non-magnetic electrically conductive base metals - Measurement of coating thickness - Amplitude-sensitive eddy-current method (ISO 2360:2017)

Relations

• Replaces: SIST EN ISO 2360:2004 - Non-conductive coatings on non-magnetic electrically conductive basis materials - Measurement of coating thickness - Amplitude-sensitive eddy current method (ISO 2360:2003)
• Effective Date: 01-Nov-2017
• Replaces: SIST EN ISO 2360:2004 - Non-conductive coatings on non-magnetic electrically conductive basis materials - Measurement of coating thickness - Amplitude-sensitive eddy current method (ISO 2360:2003)
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 2360:2017
01-november-2017
1DGRPHãþD
SIST EN ISO 2360:2004
1HSUHYRGQHSUHYOHNHQDQHPDJQHWQLKHOHNWULþQRSUHYRGQLKRVQRYQLKNRYLQDK
0HUMHQMHGHEHOLQHSUHYOHNH0HWRGDYUWLQþQLKWRNRYREþXWOMLYD]DVSUHPHPEH
DPSOLWXGH,62
Non-conductive coatings on non-magnetic electrically conductive base metals -
Measurement of coating thickness - Amplitude-sensitive eddy-current method (ISO
2360:2017)
Nichtleitende Überzüge auf nichtmagnetischen metallischen Grundwerkstoffen - Messen
der Schichtdicke - Wirbelstromverfahren (ISO 2360:2017)
Revêtements non conducteurs sur matériaux de base non magnétiques conducteurs de
l'électricité - Mesurage de l'épaisseur de revêtement - Méthode par courants de Foucault
sensible aux variations d'amplitude (ISO 2360:2017)
Ta slovenski standard je istoveten z: EN ISO 2360:2017
ICS:
25.220.20 Površinska obdelava Surface treatment
SIST EN ISO 2360:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 2360:2017

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SIST EN ISO 2360:2017


EN ISO 2360
EUROPEAN STANDARD

NORME EUROPÉENNE

August 2017
EUROPÄISCHE NORM
ICS 25.220.20 Supersedes EN ISO 2360:2003
English Version

Non-conductive coatings on non-magnetic electrically
conductive base metals - Measurement of coating
thickness - Amplitude-sensitive eddy-current method (ISO
2360:2017)
Revêtements non conducteurs sur matériaux de base Nichtleitende Überzüge auf nichtmagnetischen
non magnétiques conducteurs de l'électricité - metallischen Grundwerkstoffen - Messen der
Mesurage de l'épaisseur de revêtement - Méthode par Schichtdicke - Wirbelstromverfahren (ISO 2360:2017)
courants de Foucault sensible aux variations
d'amplitude (ISO 2360:2017)
This European Standard was approved by CEN on 8 July 2017.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 2360:2017 E
worldwide for CEN national Members.

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SIST EN ISO 2360:2017
EN ISO 2360:2017 (E)
Contents Page
European foreword . 3

2

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SIST EN ISO 2360:2017
EN ISO 2360:2017 (E)
European foreword
This document (EN ISO 2360:2017) has been prepared by Technical Committee ISO/TC 107 “Metallic
and other inorganic coatings” in collaboration with Technical Committee CEN/TC 262 “Metallic and
other inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys”
the secretariat of which is held by BSI.
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 February 2018, and conflicting national standards
shall be withdrawn at the latest by February 2018.
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.
This document supersedes EN ISO 2360:2003.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 2360:2017 has been approved by CEN as EN ISO 2360:2017 without any modification.

3

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SIST EN ISO 2360:2017

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SIST EN ISO 2360:2017
INTERNATIONAL ISO
STANDARD 2360
Fourth edition
2017-07
Non-conductive coatings on non-
magnetic electrically conductive base
metals — Measurement of coating
thickness — Amplitude-sensitive
eddy-current method
Revêtements non conducteurs sur matériaux de base non
magnétiques conducteurs de l’électricité — Mesurage de l’épaisseur
de revêtement — Méthode par courants de Foucault sensible aux
variations d’amplitude
Reference number
ISO 2360:2017(E)
©
ISO 2017

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle of measurement . 2
5 Factors affecting measurement uncertainty . 3
5.1 Basic influence of the coating thickness . 3
5.2 Electrical properties of the base metal . 3
5.3 Geometry: Base metal thickness . 4
5.4 Geometry: Edge effects . 4
5.5 Geometry: Surface curvature . 4
5.6 Surface roughness . 4
5.7 Cleanliness: Lift-off effect . 5
5.8 Probe pressure . 5
5.9 Probe tilt . 5
5.10 Temperature effects . 5
5.11 Intermediate coatings . 6
5.12 External electromagnetic fields . 6
6 Calibration and adjustment of the instrument . 6
6.1 General . 6
6.2 Thickness reference standards . 6
6.3 Methods of adjustment . 7
7 Measurement procedure and evaluation . 8
7.1 General . 8
7.2 Number of measurements and evaluation . 8
8 Uncertainty of the results . 8
8.1 General remarks . 8
8.2 Uncertainty of the calibration of the instrument . 9
8.3 Stochastic errors .10
8.4 Uncertainties caused by factors summarized in Clause 5 .10
8.5 Combined uncertainty, expanded uncertainty and final result .11
9 Precision .11
9.1 General .11
9.2 Repeatability (r) .11
9.3 Reproducibility limit (R) .12
10 Test report .12
Annex A (informative) Eddy-current generation in a metallic conductor .14
Annex B (informative) Basics of the determination of the uncertainty of a measurement of
the used measurement method corresponding to ISO/IEC Guide 98-3 .18
Annex C (informative) Basic performance requirements for coating thickness gauges which
are based on the amplitude-sensitive eddy-current method described in this document .20
Annex D (informative) Examples for the experimental estimation of factors affecting the
measurement accuracy .22
Annex E (informative) Table of the student factor .27
Annex F (informative) Example of uncertainty estimation (see Clause 8) .28
Annex G (informative) Details on precision .30
Bibliography .34
© ISO 2017 – All rights reserved iii

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.
This fourth edition cancels and replaces the third edition (ISO 2360:2003), which has been technically
revised.
iv © ISO 2017 – All rights reserved

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SIST EN ISO 2360:2017
INTERNATIONAL STANDARD ISO 2360:2017(E)
Non-conductive coatings on non-magnetic electrically
conductive base metals — Measurement of coating
thickness — Amplitude-sensitive eddy-current method
1 Scope
This document specifies a method for non-destructive measurements of the thickness of non-conductive
coatings on non-magnetic electrically conductive base metals, using amplitude-sensitive eddy-current
instruments.
In this document, the term “coating” is used for materials such as, for example, paints and varnishes,
electroplated coatings, enamel coatings, plastic coatings, claddings and powder coatings. This method
is particularly applicable to measurements of the thickness of most oxide coatings produced by
anodizing, but is not applicable to all conversion coatings, some of which are too thin to be measured by
this method (see Clause 6).
This method can also be used to measure non-magnetic metallic coatings on non-conductive base
materials. However, the phase-sensitive eddy-current method specified in ISO 21968 is particularly
usable to this application and can provide thickness results with a higher accuracy (see Annex A).
This method is not applicable to measure non-magnetic metallic coatings on conductive base metals.
The phase-sensitive eddy-current method specified in ISO 21968 is particularly useful for this
application. However, in the special case of very thin coatings with a very small conductivity, the
amplitude-sensitive eddy-current method can also be used for this application (see Annex A).
Although the method can be used for measurements of the thickness of coatings on magnetic base
metals, its use for this application is not recommended. In such cases, the magnetic method specified
in ISO 2178 can be used. Only in case of very thick coatings above approximately 1 mm, the amplitude-
sensitive eddy-current method can also be used for this application (see Annex A).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 2064, Metallic and other inorganic coatings — Definitions and conventions concerning the measurement
of thickness
ISO 4618, Paints and varnishes — Terms and definitions
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2064 and ISO 4618 and the
following 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
© ISO 2017 – All rights reserved 1

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

3.1
adjustment of a measuring system
set of operations carried out on a measuring system so that it provides prescribed indications
corresponding to given values of a quantity to be measured
Note 1 to entry: Adjustment of a measuring system can include zero adjustment, offset adjustment, and span
adjustment (sometimes called gain adjustment).
Note 2 to entry: Adjustment of a measuring system should not be confused with calibration, which is a
prerequisite for adjustment.
Note 3 to entry: After an adjustment of a measuring system, the measuring system must usually be recalibrated.
Note 4 to entry: Colloquially, the term “calibration” is frequently, but falsely, used instead of the term “adjustment”.
In the same way, the terms “verification” and “checking” are often used instead of the correct term “calibration”.
[SOURCE: ISO/IEC Guide 99:2007, 3.11 (also known as “VIM”)]
3.2
calibration
operation that, under specified conditions, in a first step, establishes a relation between the quantity
values with measurement uncertainties provided by measurement standards and corresponding
indications with associated measurement uncertainties and, in a second step, uses this information to
establish a relation for obtaining a measurement result from an indication
Note 1 to entry: A calibration may be expressed by a statement, calibration function, calibration diagram,
calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of
the indication with associated measurement uncertainty.
Note 2 to entry: Calibration should not be confused with adjustment of a measuring system, often mistakenly
called “self-calibration”, nor with verification of calibration.
Note 3 to entry: Often, the first step alone in the above definition is perceived as being calibration.
[SOURCE: ISO/IEC Guide 99:2007, 2.39 (also known as “VIM”)]
4 Principle of measurement
Eddy-current instruments work on the principle that a high frequency electromagnetic field generated
by the probe system of the instrument will produce eddy-currents in the base metal beneath the
coating on which the probe is placed (see Figure 1). These induced currents cause a change of the
electromagnetic field surrounding the probe coil and therefore result in a change of the amplitude
of the probe coil impedance. The induced eddy-current density is a function of the distance between
the generating coil and the base metal surface. Consequently, this impedance change can be used as
a measure of the thickness of the coating on the conductor by means of a calibration with reference
standards (see also Annex A).
In order to measure a change of the coil impedance amplitude, the test coil is usually part of an oscillator
circuit with a resonant frequency determined by the coil inductance and resistance. A change of the coil
impedance amplitude results in a shift of the resonant frequency. Consequently, the measured resonant
frequency is a measure of the coating thickness. The values are either pre-processed by digital means
or are directly displayed on a usefully scaled gauge.
The probe and measuring system/display may be integrated into a single instrument.
NOTE 1 Annex C describes the basic performance requirements of the equipment.
NOTE 2 Factors affecting measurement accuracy are discussed in Clause 5.
2 © ISO 2017 – All rights reserved

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

Key
1 ferrite core of the probe 5 induced eddy-current
2 high frequency electromagnetic field I exciting current
~
3 non-conductive coating t coating thickness
4 base metal U = f(t) measurement signal
Figure 1 — Amplitude-sensitive eddy-current method
5 Factors affecting measurement uncertainty
5.1 Basic influence of the coating thickness
The sensitivity of a probe, i.e. the measurement effect, decreases with increasing thickness within the
measurement range of the probe. In the lower measurement range, this measurement uncertainty (in
absolute terms) is constant, independent of the coating thickness. The absolute value of this uncertainty
depends on the properties of the probe system and the sample materials, e.g. the homogeneity of the
base metal conductivity, the base metal roughness and the sample surface roughness. In the upper
measurement range, the uncertainty becomes approximately a constant fraction of the coating
thickness.
5.2 Electrical properties of the base metal
The conductivity of the base metal determines the induced eddy-current density for a given probe
system and frequency. Consequently, the base metal conductivity causes the measurement effect for
this method. The relationship between coating thickness and the measured value depends strongly
on the conductivity of the base metal. Consequently, calibration procedures and measurements
shall be made on the same material. Different materials with different conductivities as well as local
fluctuations of the conductivity or variations between different samples can cause (more or less) errors
in the thickness reading.
NOTE There are instruments and probes available that are capable of automatically compensating the base
metal conductivity influence thus avoiding the resulting thickness error.
© ISO 2017 – All rights reserved 3

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

5.3 Geometry: Base metal thickness
Generation of eddy currents by the coil’s magnetic field in the depth of the base metal is obstructed
if the base metal thickness is too small. This influence can only be neglected above a certain critical
minimum base metal thickness.
Therefore, the thickness of the base metal should always be higher than this critical minimum base
metal thickness. An adjustment of the instrument can compensate for errors caused by thin base metal.
However, any variation in thickness of the base metal can cause increased uncertainty and errors.
The critical minimum base metal thickness depends on both the probe system (frequency, geometry)
and the conductivity of the base metal. Its value should be determined experimentally, unless otherwise
specified by the manufacturer.
NOTE A simple experiment to estimate the critical minimum base metal thickness is described in D.3.
However, in the absence of any other information, the required minimum base metal thickness, t ,
min
can be estimated from Formula (1).
t =⋅3 δ (1)
min 0
where
δ is the standard penetration depth of the base metal (see A.1).
0
5.4 Geometry: Edge effects
The induction of eddy currents is obstructed by geometric limitations of the base metal (e.g. edges,
drills and others). Therefore, measurements made too near to an edge or corner may not be valid unless
the instrument has been specifically adjusted for such measurements. The necessary distance in order
to avoid an impact of the edge effect depends on the probe system (field distribution).
NOTE 1 A simple experiment to estimate the edge effect is described in D.2.
NOTE 2 When compared with the phase-sensitive method of ISO 21968, the amplitude-sensitive eddy-current
instruments can be substantially more affected by edge effects.
5.5 Geometry: Surface curvature
The propagation of the magnetic field and consequently the induction of eddy currents are affected
by the surface curvature of the base metal. This influence becomes more pronounced with decreasing
radius of the curvature and decreasing coating thickness. In order to minimize this influence, an
adjustment should be performed on a base metal with the same geometry.
The influence of surface curvature depends considerably on the probe geometry and can be reduced
by reducing the sensitive area of the probe. Probes with very small sensitive areas are often called
microprobes.
NOTE 1 There are instruments and probes available that are capable of automatically compensating the base
metal surface curvature influence thus avoiding the resulting thickness error.
NOTE 2 A simple experiment to estimate the effect of surface curvature is described in D.4.
5.6 Surface roughness
Measurements are influenced by the surface topography of the base metal and the coating. Rough
surfaces can cause both systematic and random errors. Random errors can be reduced by making
multiple measurements, each measurement being made at a different location, and then calculating the
average value of that series of measurements.
4 © ISO 2017 – All rights reserved

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SIST EN ISO 2360:2017
ISO 2360:2017(E)

In order to reduce the influence of roughness, a calibration should be carried out with an uncoated base
metal with a roughness equivalent to the coated sample base metal.
If necessary, the definition of the average coating thickness that is used should be stated between the
supplier and client.
NOTE When compared with the phase-sensitive method of ISO 21968, the amplitude-sensitive eddy-current
measurement can be more affected by base metal roughness.
5.7 Cleanliness: Lift-off effect
If the probe is not placed directly onto the coating, the gap between the prob
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