SIST EN ISO 2360:2017

SLOVENSKI STANDARD
01-november-2017
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SIST EN ISO 2360:2004
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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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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.

Contents Page
European foreword . 3

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.

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
ISO 2360:2017(E)
© 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. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

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 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

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 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

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 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).
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

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 probe and coating (lift-off)
will affect the measurement as if it were an additional coating. Lift-off can be produced unintentionally
due to the presence of small particles between the probe and coating. The probe tip shall frequently be
checked for cleanliness.
5.8 Probe pressure
The pressure that the probe exerts on the test specimen can affect instrument reading and shall always
be the same during adjustment and measurements.
The influence of the probe pressure is more pronounced in case of soft coatings because the probe tip
can be indented into the coating. Therefore, the probe pressure should be as small as possible. Most
commercially available instruments are equipped with spring loaded probes, which ensure a constant
pressure during the placement. A suitable auxiliary device should be used in case the probe is not
spring loaded.
NOTE 1 The contact pressure and the probe tip indentation depth can be reduced by reducing the applied load
force or by using a probe with a larger diameter of the probe tip.
NOTE 2 An indentation of the probe tip into soft coatings can be reduced by placing a protective foil with
known thickness onto the coated surface. In this case, the coating thickness is the measured thickness minus
the foil thickness. This procedure is not applicable when measuring non-magnetic metallic coatings on non-
conductive base materials.
5.9 Probe tilt
Unless otherwise instructed by the manufacturer, the probe shall be applied perpendicularly to the
coating surface as tilting the probe away from the surface normal can cause measurement errors.
The risk of inadvertent tilt can be minimized by the probe design or by the use of a probe-holding jig.
NOTE Most commercially available instruments are equipped with spring loaded probes, which ensure a
perpendicular placement on the sample surface.
5.10 Temperature effects
As temperature changes affect the characteristics of the probe, it should be used under approximately
the same temperature conditions as when the instrument was calibrated.
NOTE 1 The influence of temperature variations can be reduced by a temperature compensation of the probe.
The manufacturer’s specification is taken into account.
NOTE 2 Temperature differences between the probe, electronics of the instrument, environment and sample
can cause large thickness errors. One example is the thickness measurement of hot coatings.
Most metals change their electrical conductivity with temperature. Because the measured coating
thickness is influenced by changes in the electrical conductivity of the base metal, large temperature
changes should be avoided (see 5.2).
ISO 2360:2017(E)
5.11 Intermediate coatings
The presence of an intermediate coating can affect the measurement of the coating thickness if the
electrical characteristics of that intermediate coating differ from those of the coating or base metal. If
a difference does exist, then the measurements will, in addition, be affected by an intermediate coating
thickness of less than t . If the thickness is greater than t , then the intermediate coating, if non-
min min
magnetic, can be treated as the base metal (see 5.3).
5.12 External electromagnetic fields
The measurement results can be influenced by strong electromagnetic interfering fields. In cases
showing unexpected results or a strong variation of results, which cannot be explained by other factors,
this influence should be taken into account. In this situation, a comparison measurement should be
carried out at a location without interfering fields.
6 Calibration and adjustment of the instrument
6.1 General
Prior to use, every instrument shall be calibrated or adjusted according to the instructions of the
manufacturer by means of suitable thickness reference standards and base metal. The material,
geometry, and surface properties of the base metal used for calibration or adjustment should be similar
to those for the test specimens in order to avoid deviations caused by the factors described in Clause 5.
Otherwise, these influences shall be considered in the estimation of the measurement uncertainty.
During calibration or adjustment, the instruments, standards and base metal should have the same
temperature as the test specimens to minimize temperature induced differences.
In order to avoid the influence of instrument drift, periodic control measurements with reference
standards or control samples are recommended. If required, the instrument has to be re-adjusted.
NOTE Most instruments automatically adjust themselves during a function called “calibration”, carried out
by the operator, whereas the result of the calibration is often not obvious.
6.2 Thickness reference standards
Thickness reference standards for calibration and adjustment are either coated base metals or foils,
which are placed onto uncoated base metals.
Foils and coatings shall be non-conductive and non-magnetizable. Thickness values of the reference
standards and their associated uncertainties shall be known and unambiguously documented. The
surface area for which these values are valid shall be marked. The thickness values should be traceable
to certified reference standards.
The uncertainties shall be documented with their confidence level, e.g. U (95 %), i.e. the probability, that
the “true” value is within the reported uncertainty interval around the documented thickness value, is
minimum 95 %.
Prior to use, foils and coatings are to be checked visually for damage or mechanical wear as this would
cause an incorrect adjustment and thus systematic deviation of all measurement values.
In most cases, the foil material is plastic. In contrast to the magnetic method (see ISO 2178), conductive
materials, e.g. copper alloys, cannot be used because in such foils, eddy currents can be induced. They
would affect the measurement and cause thickness errors.
NOTE When measuring non-magnetic metallic coatings on non-conductive base materials, the situation is
“inverted”.
6 © ISO 2017 – All rights reserved

ISO 2360:2017(E)
The use of foils as reference standards, compared to selected coated base metals, benefits from the
possibility of placing the foils directly on each base metal. The geometry influence and other factors are
already considered within the adjustment.
However, by placing the probe on foils, elastic or plastic deformation may occur, which can affect the
measurement result. Moreover, any gap between the pole of the probe, foil and base metal has to be
avoided. Especially for concave specimens, or if the foil is wrinkled or bent, the usually low pressure of
the spring loaded guiding sleeve of the probe may not be sufficient to ensure there is no gap.
Possible elastic or even plastic deformation of a reference foil depends on the applied force of the
probe and the probe tip diameter (see 5.9). Consequently, the calibration of such reference foils should
be carried out with comparable values of the applied force and tip diameter to avoid indentation
differences during the probe calibration. In this way, respective indentation errors are already taken
into account in the foil thickness value, i.e. this value can be smaller than the unaffected geometric
thickness. The values of both the applied force and the tip diameter used at the foil calibration should
be known from the reference foil manufacturer so that possible thickness errors can be estimated.
6.3 Methods of adjustment
Adjustment of the coating thickness gauges is executed by placing the probes on uncoated and/or one
or more coated pieces of base metal with known coating thickness. Depending on the instrument types,
instructions of the manufacturer and on the functional range of the instrument under use, adjustments
can be carried out on the following items:
a) a piece of uncoated base metal;
b) a piece of uncoated base metal and a piece of coated base metal with defined coating thickness;
c) a piece of uncoated base metal and several pieces of coated base metal with defined but different
coating thickness;
d) several pieces of coated base metal with defined but different coating thickness.
According to 6.2, the term “coated base metal” includes foils placed onto uncoated base metal.
The stated adjustment methods may lead to different accuracies of the measuring results. Thus,
a method that best fits the given application and leads to the desired accuracy should be used. The
measuring uncertainty that can be achieved by the different adjustment methods depends on the
evaluation algorithm of the gauges as well as on the material, geometry and surface condition of the
standards and of the base metals to be measured. If the desired accuracy is not achieved by one method,
a different adjustment method may lead to better results. In general, the measuring uncertainty can be
reduced by increasing the number of adjustment points and the better and closer the adjustment points
cover the expected thickness interval of the coating to be measured.
NOTE 1 The process that is used to adapt the probe to the given base metal by placing the probe onto the
uncoated base metal, is often called “zeroing” or “zero point calibration”. However, even this procedure is an
“adjustment” or part of an adjustment process as defined by this document.
NOTE 2 Depending on how many pieces of coated and uncoated base metals are used to adjust the instrument,
the corresponding adjustment method is often called “single-point”, “two-point” or “multiple-point adjustment”.
The measurement uncertainty resulting from an adjustment of the instrument cannot be generalized
to all subsequent measurements. In each case, all specific and additional influencing factors need to be
considered in detail, see Clause 5 and Annex D.
NOTE 3 Some types of gauges permit resetting the instrument to an original adjustment of the manufacturer.
This adjustment is valid for the manufacturer’s uncoated or coated reference standards only. If these standards
or the same types of standards are used to check the instrument after a period of use, any deterioration of gauge
and probes, e.g. wear of the probe by abrasion of the contact pole, can be recognized by observing deviations of
the measuring results.
ISO 2360:2017(E)
7 Measurement procedure and evaluation
7.1 General
Every instrument shall be operated according to the manufacturer’s instructions especially considering
the factors affecting measurement accuracy discussed in Clause 5.
Before using the instrument and after changes affecting the measurement accuracy (see Clause 5), the
adjustment of the instrument shall be checked.
To ensure that the instrument measures correctly, it shall be calibrated with valid standards at the
place of inspection each time:
a) the instrument is put into operation,
b) material and geometry of the test specimens are changed, or
c) other conditions of the inspection have changed (e.g. temperature) whose effects are not known.
As not all changes of measurement conditions and their influences on the measurement accuracy can
be immediately recognized (e.g. drift, wear of the probe), the instrument should be calibrated at regular
time intervals while in use.
7.2 Number of measurements and evaluation
The coating thickness should be determined as the arithmetic mean of several single values, which
are measured in a defined area of the coating surface. In addition to the mean, the standard deviation
should be reported (see Annex B). The random part of the measurement uncertainty can be reduced by
increasing the number of measurements. If not otherwise specified or agreed upon, it is recommended
to measure at least five single values (depending on the application).
NOTE 1 From the standard deviation, a variation coefficient V can be calculated. V corresponds to the relative
standard deviation (e.g. in percent) and enables a direct comparison of the standard deviation for different
thicknesses.
NOTE 2 The total scatter of the measurement is composed of the scatter of the instrument itself and the
scatter caused by the test specimen. The standard deviation of the operator and probe in the measured thickness
range is determined by repeated measurements at the same location, if necessary with the help of an auxiliary
device for placing the probe.
When measuring on rough coating surfaces or on test specimens with known large thickness gradients
(e.g. due to their size and/or their shape), the reason for deviations between the single measurements
should be determined by a series of measurements.
8 Uncertainty of the results
8.1 General remarks
A complete evaluation of the uncertainty of the measured thickness shall be carried out in accordance
with ISO/IEC Guide 98-3. Details of the background of the expression of the uncertainty are summarized
in Annex B and a typical example of this calculation is described in Annex F.
Uncertainty of the thickness measuring result is a combination of uncertainties from a number of
different sources. Important sources that should be considered include the following:
a) uncertainty of the calibration of the instrument;
b) stochastic influences affecting the measurement;
c) uncertainties caused by factors summarized in Clause 5;
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ISO 2360:2017(E)
d) further influences, drifts, digitalization effects and other effects.
All uncertainty components shall be estimated and summarized to the combined standard uncertainty
as described in ISO/IEC Guide 98-3, see Annex B.
A possible procedure for the estimation of the uncertainty is given in the following simplified approach
(see 8.2 to 8.5).
The single uncertainty components of the listed sources are dependent on the respective measurements,
the properties of the samples measured, the instrument, the environmental condition, etc. and can
show large differences for different applications. Therefore, the single uncertainty components shall
be estimated for each measurement in all detail. The quality of the uncertainty is determined by
the quality of the estimation of all uncertainty components. Missing components result in incorrect
uncertainty estimations and consequently in incorrect thickness results.
In particular, the factors listed in Clause 5 can result in large uncertainty values and should be
minimized by an adjustment if possible.
NOTE In addition to the need to express the uncertainty in the result, the analysis of possible uncertainty
components provides detailed information in order to improve the measurement.
8.2 Uncertainty of the calibr
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