ISO/DTS 24858

Plastics — Conducting materials — Eddy current measurement on spread carbon fibre tow

This international standard specifies the apparatus, measurement procedure for evaluating the homogeneity of a material for each section in conductive material using eddy current measurements. This draft is applicable to most conductive materials and is also suitable for evaluating the homogeneity of fibrous conducting materials composed of multi-filaments.

Plastiques — Matériaux conducteurs — Mesure par courants de Foucault sur un câble en fibres de carbone étiré

General Information

• Status: Not Published
• ICS: 19.100 - Non-destructive testing
• ICS: 59.100.20 - Carbon materials
• Technical Committee: ISO/TC 61 - Plastics
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 07-May-2026
• Completion Date: 07-May-2026

Overview

ISO/DTS 24858: Plastics - Conducting materials - Eddy current measurement on spread carbon fibre tow is an international standard developed by ISO Technical Committee 61. It provides a standardized method for evaluating the homogeneity of electrically conductive materials, particularly spread carbon fibre tow, using eddy current measurement techniques. The document outlines the apparatus, procedures, and reporting requirements essential for quality assessment of conductive plastics and composite fibers in industrial and research settings.

Eddy current measurement is especially valuable as a non-destructive testing (NDT) method, supporting quality control and defect detection in advanced materials used in next-generation electronic devices and composite manufacturing.

Key Topics

• Conducting Materials: Focuses on materials with electrical conductivity, such as carbon fibre tows comprising multiple filaments.
• Homogeneity Evaluation: Defines procedures for continuous measurement of impedance across the width of spread fibre tows to assess material uniformity and detect defects.
• Eddy Current Measurement: Utilizes electromagnetic induction principles to measure discontinuities and inhomogeneities within conductive composites.
• Non-Destructive Testing: Offers a contactless technique, minimizing damage or alteration of specimens during quality assessment.
• Sample Preparation and Apparatus: Specifies requirements for sampling, sample size, fixing methods, probe selection, and environmental controls.
• Standardized Reporting: Outlines mandatory reporting elements including environmental conditions, apparatus details, test setup, and result interpretation.

Applications

The methods specified in ISO/DTS 24858 have wide-ranging applications across multiple industries:

• Composites Manufacturing: Ensures uniformity and quality in carbon fibre-reinforced plastic components, essential for automotive, aerospace, and sports equipment parts.
• Printed Electronics: Supports development and quality assurance in advanced flexible electronics using conductive fibre-based substrates.
• Textile Engineering: Facilitates systematic quality control in the production of conductive textiles and technical fabrics.
• Research & Development: Provides a reliable framework for materials scientists seeking to characterize new conductive fiber configurations or to optimize fibre processing.
• Quality Assurance and Defect Analysis: Enables rapid detection of defects such as filament breaks, non-uniform arrays, or foreign inclusions through statistical analysis of impedance standard deviation.
• Process Optimization: Assists in the continual monitoring and improvement of manufacturing processes to maintain consistent material properties.

Related Standards

For integrated testing and further specialization, ISO/DTS 24858 references or is complemented by several other international standards relevant to conducting materials and eddy current methodology:

• ISO 24584:2022 – Requirements for carbon fibre sampling and fixing procedures.
• DS/ISO 12718 – General procedures for electronic measurements in plastics.
• IEC 62899-202-3:2019 – Measurement of sheet resistance in conductive films; includes definitions and measurement principles for eddy current methods.
• Other ISO and IEC resources – Terminology and test method developments available via ISO Online Browsing Platform and IEC Electropedia.

Practical Value

Implementing ISO/DTS 24858 ensures:

• Consistent quality control across international supply chains for conductive plastics and fibre materials.
• Rapid identification of material inconsistencies or manufacturing defects before further processing.
• Enhanced traceability and reporting accuracy for compliance with industry or regulatory requirements.
• Improved product performance and durability in applications where electrical conductivity and structural integrity are critical.

By following this standard, organizations can confidently advance the reliability and applicability of conductive fibre materials in innovative product designs and high-performance applications.

Standards Content (Sample)

FINAL DRAFT
Technical
Specification
ISO/TC 61
Plastics — Conducting materials
Secretariat: SAC
— Eddy current measurement on
Voting begins on:
spread carbon fibre tow
2026-05-07
Voting terminates on:
2026-07-02
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
Technical
Specification
ISO/TC 61
Plastics — Conducting materials
Secretariat: SAC
— Eddy current measurement on
Voting begins on:
spread carbon fibre tow
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Background — Impedance . 1
5 Specimen . 2
5.1 Sampling .2
5.2 Size .3
6 Apparatus . 3
7 Test conditions . 4
8 Procedure . 4
9 Report of the results . 5
9.1 General .5
9.2 Test environment .5
9.3 Test apparatus.5
9.4 Test conditions .5
9.5 Test results .5
Annex A (informative) Eddy current measurement data for impedance analysis based on the
presence of defects . 6
Bibliography .16

iii
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
As technologies for the commercialization of textile materials have advanced, the development of various
functional materials based on fibres has increased. Conductive fibres are flexible and highly elastic
materials with significant potential for application in next-generation electronic devices, and carbon fibres
are also one of the conductive materials that exhibit electrical conductivity. The homogeneity of a conductive
material is an important factor in determining the performance of the final product, and from a quality
control perspective, it is necessary to have a method to analyse the distribution status of the raw material
before it is processed. In the case of carbon fibres, a conductive material in the form of fibres, it is important
to manage the arrangement of the fibres because the degree to which the filament strands are arranged can
cause performance degradation in localized areas. Optical image analysis is a common method for checking
the homogeneity of filaments in carbon fibres and can be used to analyse the arrangement of filaments on the
surface, but it has limitations in analysing the presence and density of filaments arranged in the thickness
direction. A method for continuously measuring the homogeneity of carbon fibres with large surface areas is
eddy current measurement, which utilizes electrical conductivity properties. An eddy current measurement
is used to detect discontinuities in materials that conduct electricity. This method is a reliable measurement
that can identify materials with low electrical conductivity, such as spread carbon fibre tow, making it
applicable to a wide range of industries. This document specifies a standard method for evaluating the
homogeneity of a spread carbon fibre tow, a conductive fibre, using eddy current measurement.
Annex A gives the eddy current measurement data for impedance analysis based on the presence of defects.

v
FINAL DRAFT Technical Specification ISO/DTS 24858:2026(en)
Plastics — Conducting materials — Eddy current
measurement on spread carbon fibre tow
1 Scope
This test method defines test terms and specifies a standard method for evaluating the homogeneity
of electrically conductive spread carbon fibre tow using eddy current measurement. The impedance in
the width direction of the fibre is measured continuously, and the standard deviation of the measured
impedance determines the homogeneity of the conductive material in fibre form.
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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
spread carbon fibre tow
large bundle of continuous carbon fibre spread thinly and widely in the width direction
3.2
eddy current
electrical currents induced within conductors by a time-varying magnetic field in the conductor
[SOURCE: IEC 62899-202-3:2019, 3.2]
3.3
impedance
value represented by the combined effect of a circuit's resistance, inductance, and capacitance, which
interferes when a voltage is applied to the circuit
3.4
homogeneity
degree of a state of being of a similar kind or of having a uniform structure or composition throughout
4 Background — Impedance
Eddy current instruments work on the principle that an electrically conductive sample is placed in an
electromagnetic field generated by a probe system, which causes an eddy current to flow. Impedance
is the total opposition a circuit presents to the flow of alternating current and is calculated as shown in
Formulae (1) and (2), including resistance, inductive reactance, and capacitive reactance. For eddy current
testing, capacitive reactance is usually not present, so impedance is calculated with Formula (3). As shown

in Figure 1, the impedance value is calculated by the amount of resistance (horizontal line), the amount of
[5]
inductive reactance (vertical line), and the amount of impedance (diagonal line) .
ZRXX (1)
Lc
ZR XX (2)

Lc
ZRX (3)
L
where
Z is the complex impedance (ohm);
Z is the magnitude of the impedance (ohm);
R is the resistance (ohm);
X is the inductive reactance (ohm);
L
X is the capacitive reactance (ohm).
C
Key
R resistance
XX- reactance
LC
Z impedance
Z impedance amplitude
ϕ phase angle
Figure 1 — Principle of impedance
5 Specimen
5.1 Sampling
Samples for fibre homogeneity measurements are preferably not impregnated with resin. Randomly take
a sample without twists from a roll or bobbin of product and fix it onto a fibreglass veil using polyvinyl
acetate(PVA) glue. Ensure that the width and density do not change during sample fixation. The purpose of

fixing the sample with PVA glue to the fibreglass veil is to minimize the floating of the sample. Alternatively,
the sample can be fixed by vacuum suction from the bottom of the sample. See ISO 24584.
5.2 Size
The size of the sample should be at least five times larger than the measured diameter of the probe in the
width direction, and a sample longer than 100 mm should be prepared in the length direction.
6 Apparatus
Eddy current testing instruments consists of an oscillator that generates alternating current electricity, a
probe with a coil connected to a direct current power supply, and a voltmeter that can measure the voltage
across the coil.
6.1 Probe
It is recommended to select a probe with an appropriate standard penetration depth based on the thickness
and characteristics of the sample. The standard penetration depth varies with electrical conductivity,
magnetic permeability, and frequency, and the standard penetration depth for eddy current inspection is
calculated by the Equation (4).
  (4)
··f ·
where
δ is the standard penetration depth (millimetre);
π is the ratio of the circumference of a circle to its diameter;
f is the frequency (Hz);
µ is the magnetic permeability (H/m);
σ is the electrical conductivity (micro ohm-centimetre).
6.2 Sample stage
The sample should be placed on top of a sample stage made of a glass plate or insulating material such as
acrylic, PVC, etc. to minimize induced currents due to interference from other objects. The sample stage
should be separated by at least 100 mm depending on the material of the table, especially if it is an electrically
conductive material such as metal. Alternatively, a separate grounding method can be devised to prevent
measurement errors caused by static electricity.

Key
1 probe
2 induction coil
3 sample, conductive materials
4 sample stage, insulating material
5 table
Figure 2 — Apparatus of eddy-current measurement
6.3 Gap
Impedance can be affected by the distance between the sample and the probe. The probe and sample shall
not be in direct contact and the gap shall be kept at a constant distance of not more than 1 mm.
7 Test conditions
The ambient temperature affects impedance of the sample when measuring eddy currents. Therefore, time
should be allowed for the instruments and sample to stabilize to the test temperature before testing, and
it is desirable that the conditions remain as constant as possible during the measurement to increase the
reliability of the measurement.
— Temperature : (23 ± 2) °C
— Humidity : (50 ± 10) %
8 Procedure
1) Place the sample closely attached to the sample stage.
NOTE Mark the position of the sample to be measured with the probe.
2) The probe shall be positioned on the surface of the sample facing vertically, and measured impedance
using eddy current probe.
3) Take at least three measurements per sample under the same conditions to analyse the impedance
standard deviation.
9 Report of the results
9.1 General
The report shall include the following items.
9.2 Test environment
a) Temperature range
b) Humidity
9.3 Test apparatus
a) Type of probe (frequency, diameter, etc.)
b) Material of the sample stage
9.4 Test conditions
a) Gap
b) Number of measurements
9.5 Test results
Homogeneity (No units); Since the homogeneity is expressed as a coefficient of variation value calculated as
a ratio of the mean and standard deviation of the impedance value, there is no unit.
The homogeneity of spread carbon fibre tow can be calculated as the mean and standard deviat
...

ISO/TC 61/ WG 5
Secretariat: SAC
Date: 2026-01-3104-23
Plastics — Conducting materials — Eddy current measurement
on spread carbon fibre tow
DTS stage
Warning for WDs and CDs
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to
change without notice and may not be referred to as an International Standard.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.

A model document of an International Standard (the Model International Standard) is available at:

ISO #####-#:####(X)
2 © ISO #### – All rights reserved

All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.orgwww.iso.org
Published in Switzerland
iii
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Background — Impedance . 2
5 Specimen . 3
5.1 Sampling . 3
5.2 Size . 4
6 Apparatus . 4
7 Test conditions . 6
8 Procedure . 6
9 Report of the results . 6
9.1 General. 6
9.2 Test environment . 6
9.3 Test apparatus . 6
9.4 Test conditions . 6
9.5 Test results . 7
Annex A (informative) Eddy current measurement data for impedance analysis based on the
presence of defects . 8
Bibliography . 25

iv
iv
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, WG5, Electrical, Magnetic & Opto-
electrical Properties of Plastics and Composites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
As technologies for the commercialization of textile materials have advanced, the development of various
functional materials based on fibres has increased. Conductive fibres are flexible and highly elastic materials
with significant potential for application in next-generation electronic devices, and carbon fibres are also one
of the conductive materials that exhibit electrical conductivity. The homogeneity of a conductive material is
an important factor in determining the performance of the final product, and from a quality control
perspective, it is necessary to have a method to analyzeanalyse the distribution status of the raw material
before it is processed. In the case of carbon fibres, a conductive material in the form of fibres, it is important
to manage the arrangement of the fibres because the degree to which the filament strands are arranged can
cause performance degradation in localized areas. Optical image analysis is a common method for checking
the homogeneity of filaments in carbon fibres and can be used to analyzeanalyse the arrangement of filaments
on the surface, but it has limitations in analyzinganalysing the presence and density of filaments arranged in
the thickness direction. A method for continuously measuring the homogeneity of carbon fibres with large
surface areas is eddy current measurement, which utilizes electrical conductivity properties. An eddy current
measurement is used to detect discontinuities in materials that conduct electricity. This method is a reliable
measurement that can identify materials with low electrical conductivity, such as spread carbon fibre tow,
making it applicable to a wide range of industries. This document specifies a standard method for evaluating
the homogeneity of a spread carbon fibre tow, a conductive fibre, using eddy current measurement.
Annex A gives the eddy current measurement data for impedance analysis based on the presence of defects.
vi
Plastics — Conducting materials — Eddy current measurement on
spread carbon fibre tow
1 Scope
This test method defines test terms and specifies a standard method for evaluating the homogeneity of
electrically conductive spread carbon fibre tow using eddy current measurement. The impedance in the width
direction of the fibre is measured continuously, and the standard deviation of the measured impedance
determines the homogeneity of the conductive material in fibre form.
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.
DS/ISO 12718,
IEC 62899-202-3:2019, Printed electronics — Part 202-3: Materials-Conductive ink — Measurement of sheet
resistance of conductive films — Contactless method
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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
3.1 Spreadspread carbon fibre tow
A large bundle of continuous carbon fibre spread thinly and widely in the width direction
3.2
3.2 Eddyeddy current
electrical currents induced within conductors by a time-varying magnetic field in the conductor
[SOURCE: IEC 62899-202-3:2019, 3.2]
3.3
3.3 Impedance
The impedance
value represented by the combined effect of a circuit's resistance, inductance, and capacitance, which
interferes when a voltage is applied to the circuit.
3.4
3.4 Homogeneity
the homogeneity
degree of a state of being of a similar kind or of having a uniform structure or composition throughout
ISO #####-#:####(X/DTS 24858:(en)
4 Background — Impedance
Eddy current instruments work on the principle that an electrically conductive sample is placed in an
electromagnetic field generated by a probe system, which causes an eddy current to flow. Impedance is the
total opposition a circuit presents to the flow of alternating current and is calculated as shown in
Formulae (1)Equation (1) and (2)(2),, including resistance, inductive reactance, and capacitive reactance. For
eddy current testing, capacitive reactance is usually not present, so impedance is calculated with
Formula (3)Equation (3). As shown in Figure 1Figure 1,, the impedance value is calculated by the amount of
resistance (horizontal line), the amount of inductive reactance (vertical line), and the amount of impedance
(diagonal line) ) [4].
¯
𝑍𝑍̅𝑍𝑍 =𝑅𝑅 +𝑋𝑋 −𝑋𝑋 (1)
𝐿𝐿 𝑐𝑐
2 2
𝑍𝑍 = 𝑅𝑅 + (𝑋𝑋 −𝑋𝑋 )              (2)
� �
� 𝐿𝐿 𝑐𝑐
𝑍𝑍 = �𝑅𝑅 +𝑋𝑋                 (3)
� �
𝐿𝐿
Where
2 2
¯
𝑍𝑍̅  |𝑍𝑍| =  𝑅𝑅 + (𝑋𝑋 −𝑋𝑋 ) (2)
� 𝐿𝐿 𝑐𝑐
2 2
¯
|𝑍𝑍| =  𝑅𝑅 +𝑋𝑋 (3)
�
𝐿𝐿
where
¯
𝑍𝑍 is the complex impedance (ohm));
¯
𝑍𝑍 |𝑍𝑍| is the magnitude of the impedance (ohm));
� �
R is the resistance (ohm));
𝑋𝑋 is the inductive reactance (ohm));
𝐿𝐿
𝑋𝑋 is the capacitive reactance (ohm)).
𝐶𝐶
© ISO #### 2026 – All rights reserved
Key
R resistance
𝑋𝑋 −𝑋𝑋 reactance
𝐿𝐿 𝐶𝐶
¯
𝑍𝑍 impedance
¯
|𝑍𝑍| impedance amplitude
𝜑𝜑 phase angle
Figure 1— Principle of impedance
5 Specimen
5.1 5.1 Sampling
Samples for fibre homogeneity measurements are preferably not impregnated with resin. Randomly take a
sample without twists from a roll or bobbin of product and fix it onto a fibreglass veil using polyvinyl
acetate(PVA) glue. Care must be taken to ensureEnsure that the width and density do not change during
sample fixation. The purpose of fixing the sample with PVA glue to the fibreglass veil is to minimize the floating
of the sample. Alternatively, the sample can be fixed by vacuum suction from the bottom of the sample. See
ISO 24584.
[SOURCE: ISO 24584:2022]
ISO #####-#:####(X/DTS 24858:(en)

5.2 5.2 Size
The size of the sample should be at least five times larger than the measured diameter of the probe in the
width direction, and a sample longer than 100 mm should be prepared in the length direction.
6 Apparatus
Eddy current testing instruments consists of an oscillator that generates alternating current electricity, a
probe with a coil connected to a direct current power supply, and a voltmeter that can measure the voltage
across the coil.
6.1 6.1 Probe
It is recommended to select a probe with an appropriate standard penetration depth based on the thickness
and characteristics of the sample. The standard penetration depth varies with electrical conductivity, magnetic
permeability, and frequency, and the standard penetration depth for eddy current inspection is calculated by
the Equation (4)Equation (4).
1 1
𝛿𝛿 =           (4)
𝜋𝜋∙𝑓𝑓∙𝜇𝜇∙𝜎𝜎 𝜋𝜋·𝑓𝑓·𝜇𝜇·𝜎𝜎
� �
Where
δ where
𝛿𝛿 is the standard penetration depth (millimeter)millimetre);
π  𝜋𝜋 is the ratio of the circumference of a circle to its diameter;
f  𝑓𝑓 is the frequency (Hz));
μ 𝜇𝜇 is the magnetic permeability (H/m));
σ  𝜎𝜎 is the electrical conductivity (micro ohm-centimeter)centimetre).

6.2 6.2 Sample stage
The sample should be placed on top of a sample stage made of a glass plate or insulating material such as
acrylic, PVC, etc. to minimize induced currents due to interference from other objects. The sample stage should
be separated by at least 100 mm depending on the material of the table, especially if it is an electrically
conductive material such as metal. Alternatively, a separate grounding method can be devised to prevent
measurement errors caused by static electricity.

© ISO #### 2026 – All rights reserved
Key
1 probe
2 induction coil
3 sample, conductive materials
4 sample stage, insulating material
5 table
Figure 2— Apparatus of eddy-current measurement
Key
1 Probe
2 Induction Coil
3 Sample, conductive materials
4 Sample stage, insulating material
5 Table
6.3 6.3 Gap
Impedance can be affected by the distance between the sample and the probe. The probe and sample shall not
be in direct contact and the gap shall be kept at a constant distance of not more than 1 mm.
ISO #####-#:####(X/DTS 24858:(en)
7 Test conditions
The ambient temperature affects impedance of the sample when measuring eddy currents. Therefore, time
should be allowed for the instruments and sample to stabilize to the test temperature before testing, and it is
desirable that the conditions remain as constant as possible during the measurement to increase the reliability
of the measurement.
— - Temperature : (23± ± 2) ℃ °C
— - Humidity : (50± ± 10) %
8 Procedure
1) 1) Place the sample closely attached to the sample stage.
NOTE : Mark the position of the sample to be measured with the probe.
2) 2) The probe shall be positioned on the surface of the sample facing vertically, and measured impedance
using eddy current probe.
3) 3) Take at least three measurements per sample under the same conditions to analyzeanalyse the
impedance standard deviation.
9 Report of the results
9.1 General
The report shall include the following items.

9.19.2 9.1 Test environment
a) a) Temperature range
b) b) Humidity
9.29.3 9.2 Test apparatus
a) a) Type of probe (frequency, diameter, etc.)
b) b) Material of the sample stage

9.39.4 9.3 Test conditions
a) a) Gap
b) b) Number of measurements
© ISO #### 2026 – All rights reserved
9.49.5 9.4 Test results
Homogeneity (No units) ;); Since the homogeneity is expressed as a coefficient of variation value calculated as
a ratio of the mean and standard deviation of the impedance value, there is no unit.
The homogeneity of spread carbon fibre tow can be calculated as the mean and standard deviation of the
impedance values in the width direction (row direction) measured continuously.
ISO #####-#:####(X/DTS 24858:(en)
Annex A
(informative)
Eddy current measurement data for impedance analysis based on the presence
of defects
A.1 1. Test sample
— · Materials : T700-12K Spread carbon fibre tow
A.2 2. Test conditions
— · Probe: Differential probe (radius 1.0mm,0 mm, frequency 27MHz) 27 MHz)
— · Sample stage: Glass plate
— · Overlap of the probe's measured diameter: 0 %
— · Gap between sample and probe: less than 1.,0 mm
[SOURCE:See ISO 24584:2022].
© ISO #### 2026 – All rights reserved
Key
nd
A 2 measurement direction
st
B 1 measurement direction
Figure A.1 ­— Measurement positions
A.3 3. Test results
Table A.1Table A.1 shows the impedance standard deviation data for a specific row of each sample using eddy
current measurements. A row is measured with 10 points, and for the edge data, we calculated the impedance
standard deviation with 8 points of measurements, excluding the edge data, according to the width of the
sample can cause a fibre absence phenomenon. For the data measured for the insulating materials, glass plate
and fibreglass veil, the impedance standard deviation ranged from 10 to 20, indicating the homogeneity of the
materials. The homogeneous carbon fibre samples with no defects attached to the fibreglass veil did not show
significant differences from the insulation material, with impedance standard deviations ranging from 25 to
40, except where some fibres cracked. However, with defects, the value of impedance standard deviation
varied significantly depending on the type of defect. In the case of fibre breaks, the impedance standard
deviation was measured to be between 70 and 130, depending on the size of the broken area, for cases such
as fuzz or the influx of other fibres, the impedance standard deviation was measured to be between 180 and
300. For non-uniform arrays without fibre breakage, impedance standard deviations of 50 to 70 were
measured, depending on the density of the section. This measurement method establishes impedance
standard deviation criteria for various defects that could occur during the production process of spread
carbon fibre tows, allowing the type of defect to be determined by eddy current measurements only.
Table A.1 -— Result of the measured impedance deviation for each row in the sample from the eddy
current measurement
Type
Standard
Sampl of Presence
Sample appearance deviation of
e No. sampl of defects
Impedance
e
10th row 15.,0
1 Only -
25th row 11.,1
ISO #####-#:####(X/DTS 24858:(en)
Type
Standard
Sampl of Presence
Sample appearance deviation of
e No. sampl of defects
Impedance
e
Glass
plate
40th row 15.,1
10th row 17.,7
Glass
25th row 18.,9
plate
2 -
+ Glass
fibre
40th row 14.,5
veil
Glass 10th row 26.,3
plate
25th row 30.,6
+
Glass
3 X
fibre
veil
40th row 25.,4
+
Carbon
fibre
13th row 289.,1
Merged Cells
O
Split Cells
30th row 47.,2
(Fuzz,
Influx of
other
40th row 181.,0
fibres)
Glass
Merged Cells
plate
+ Glass
fibre
11th row 86.,1
veil
O
+
(Fibre
Carbon
breakage)
fibre
Split Cells
25th row 77.,2
34th row 112.,2
18th row 126.,7
Merged Cells
6 O
Split Cells
30th row 66.,5
© ISO #### 2026 – All rights reserved
Type
Standard
Sampl of Presence
Sample appearance deviation of
e No. sampl of defects
Impedance
e
(Fibre
breakage)
40th row 76.,7
10th row 38.,3
Merged Cells
Split Cells
25th row 52.,6
O
(Fibre
splitting)
35th row 63.,7
Figure A.2
Figure A.2 is a graph showing the impedance at each point and its deviation from the mean value of the
impedance measured in one row. The impedance deviation graph allows you to determine the location of
defects in the samp
...