IEC TR 63304:2021
(Main)Methods of measurement of the magnetic properties of permanent magnet (magnetically hard) materials in an open magnetic circuit using a superconducting magnet
Methods of measurement of the magnetic properties of permanent magnet (magnetically hard) materials in an open magnetic circuit using a superconducting magnet
IEC TR 63304:2021(E) describes the general principle and technical details of the methods of measurement of the DC magnetic properties of permanent magnet materials in an open magnetic circuit using a superconducting magnet (SCM).
This method is applicable to permanent magnet materials, such as those specified in IEC 60404-8-1, the properties of which are presumed homogeneous throughout their volume.
There are two methods:
– the SCM-Vibrating Sample Magnetometer (VSM) method;
– the SCM-Extraction method.
This document also describes methods to correct the influence of the self-demagnetizing field in the test specimen on the demagnetization curve measured in an open magnetic circuit. The magnetic properties are determined from the corrected demagnetization curve.
NOTE These SCM-methods can determine the magnetic properties of permanent magnet materials with coercivity higher than 2 MA/m. The methods of measurement in a closed magnetic circuit specified in IEC 60404-5 can lead to significant measurement error due to saturation effects in the pole pieces of yoke for the magnetic materials with coercivity higher than 1,6 MA/m (see IEC 60404-5).
General Information
Standards Content (Sample)
IEC TR 63304 ®
Edition 1.0 2021-04
TECHNICAL
REPORT
Methods of measurement of the magnetic properties of permanent magnet
(magnetically hard) materials in an open magnetic circuit using a
superconducting magnet
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.
IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.
IEC publications search - webstore.iec.ch/advsearchform IEC online collection - oc.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 000 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 18 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary
(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc
If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: sales@iec.ch.
IEC TR 63304 ®
Edition 1.0 2021-04
TECHNICAL
REPORT
Methods of measurement of the magnetic properties of permanent magnet
(magnetically hard) materials in an open magnetic circuit using a
superconducting magnet
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20; 29.030 ISBN 978-2-8322-9714-8
– 2 – IEC TR 63304:2021 © IEC 2021
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 General principle . 11
4.1 Principle of the method . 11
4.2 Superconducting magnet (SCM). 12
4.3 Magnetic field strength sensor (H sensor) . 13
4.4 Magnetic dipole moment detection coil (M coil) . 13
4.5 Specimen rod and moving device . 14
4.6 Measuring devices and the data processing device . 14
5 Test specimen . 14
6 Preparation of measurement . 15
6.1 Measurement of volume of the test specimen . 15
6.2 Initial magnetization of the test specimen to saturation . 15
7 Determination of magnetic polarization . 15
7.1 Measurement of the magnetic dipole moment . 15
7.2 Determination of magnetic polarization . 16
8 Measurement of magnetic field . 17
9 Calibration of the magnetic dipole moment detection coil (M coil) . 17
10 Determination of demagnetization curve . 17
11 Demagnetizing field correction . 18
11.1 General . 18
11.2 Method A: Method using a demagnetizing factor determined by the shape of
the test specimen only . 20
11.3 Method B: Method using a demagnetizing factor determined by the shape
and the magnetic susceptibility of the test specimen . 20
11.4 Method C: Method using an inverse analysis considering the spatial
distribution of the self-demagnetizing field strength in the test specimen . 21
12 Determination of principal magnetic properties . 21
12.1 Remanent magnetic polarization J . 21
r
12.2 Maximum energy product (BH) . 22
max
12.3 Coercivity (H and H ) . 22
cJ cB
13 Reproducibility . 22
14 Test report . 22
Annex A (informative) SCM-Magnetometer method . 24
Annex B (informative) Effects of the test specimen dimensions . 26
Annex C (informative) Superconducting magnets (SCMs) . 27
Annex D (informative) Magnetic dipole moment detection coils (M coils) . 29
Annex E (informative/normative) Details of the demagnetizing field correction . 31
E.1 General . 31
E.2 Symbols . 31
E.3 Method using a demagnetizing factor determined by the shape and magnetic
susceptibility of the test specimen (Method B). 32
E.4 Method using an inverse analysis considering the spatial distribution of the
self-demagnetizing field strength in the test specimen (Method C) . 34
Annex F (informative) Result of the international round robin test of magnetic
properties of permanent magnets using the SCM-VSM and SCM-Extraction methods . 39
F.1 General . 39
F.2 Protocol of the RRT . 39
F.3 Result of the RRT . 40
F.4 Reproducibility of the measurements . 43
Bibliography . 45
Figure 1 – Demagnetization curve J(H) . 10
Figure 2 – Schematic diagrams of the test apparatus . 11
Figure 3 – Schematic diagrams of the first order gradiometer coil . 13
Figure 4 – Relationship between magnetic polarization and self-demagnetizing field . 18
Figure 5 – Schematic diagram of the demagnetizing field correction . 19
Figure 6 – Conceptual diagram of the procedure of Method C . 21
Figure A.1 – Schematic diagram of the test apparatus for the SCM-Magnetometer
method . 24
Figure A.2 – Schematic diagrams of the test apparatus for the method in a closed
magnetic circuit in accordance with IEC 60404-5 . 25
Figure B.1 – Effects of test specimen dimensions on magnetic properties [B , H , H
r cJ cB
and (BH) ] for Nd-Fe-B sintered magnets with different coercivities . 26
max
Figure C.1 – Typical cross-sectional structure of the ceramic SCM . 28
Figure D.1 – Schematic diagram of the second order gradiometer coil for the SCM-
VSM method . 29
Figure D.2 – Schematic diagram of the dependence of induced voltage on the position
of the test specimen in the SCM-Extraction method . 30
Figure E.1 – Axes of a cuboid magnet . 32
Figure E.2 – Conceptual diagram of the procedure of Method C. 35
Figure E.3 – Flowchart of the procedure of Method C . 36
Figure E.4 – Comparison of the demagnetization curves corrected using demagnetizing
field correction Methods A, B and C . 38
Figure F.1 – Comparison of J measured by the laboratories . 40
r
Figure F.2 – Comparison of H measured by the laboratories . 41
cJ
Figure F.3 – Comparison of (BH) measured by the laboratories . 41
max
Figure F.4 – Comparison of hysteresis loops measured by the laboratories . 43
Figure F.5 – Relative standard deviation of J , H and (BH) . 44
r cJ max
Table 1 – Features of the demagnetizing field correction methods in comparison with
Method B . 20
Table 2 – Reproducibility of the magnetic properties . 22
– 4 – IEC TR 63304:2021 © IEC 2021
Table C.1 – Performance of SCMs . 27
Table F.1 – Nominal values of coercivity . 39
Table F.2 – Participating laboratories and their employed measuring methods . 40
Table F.3 – Comparison of magnetic properties measured by the laboratories . 42
Table F.4 – Comparison of the reproducibility . 44
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHODS OF MEASUREMENT OF THE MAGNETIC PROPERTIES OF
PERMANENT MAGNET (MAGNETICALLY HARD) MATERIALS IN AN OPEN
MAGNETIC CIRCUIT USING A SUPERCONDUCTING MAGNET
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC TR 63304 has been prepared by IEC technical committee 68: Magnetic alloys and steels.
It is a Technical Report.
The text of this Technical Report is based on the following documents:
DTR Report on voting
68/675/DTR 68/680/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
– 6 – IEC TR 63304:2021 © IEC 2021
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
Permanent magnet materials with high coercivity e.g. Nd-Fe-B magnets, have been used in
industry and its usage increases rapidly to meet demands to improve energy saving and to
increase efficiency of electromagnetic applications, e.g. traction motors for Electric Vehicle (EV)
and Hybrid Electric Vehicle (HEV).
However, there is no standard method which can determine all the magnetic properties of the
permanent magnet materials with coercivity H higher than 2 MA/m. The method specified in
cJ
IEC 60404-5, which is a method of measurement in a closed magnetic circuit, can lead to
significant measurement errors for measurement of H ≥ 1,6 MA/m due to magnetic saturation
cJ
in parts of the pole faces of the yoke (see IEC 60404-5).
In order to solve the problem, several methods of measurement in an open magnetic circuit
using a superconducting magnet (SCM) without a yoke have been developed. The methods
using a SCM have been considered to be candidates for solution to accurate measurement of
high performance permanent magnets.
The method using a conventional SCM made of metallic superconducting coil has not been
used widely for industrial applications due to costs for using expensive liquid helium, limited
speed of variation of magnetic field strength, and the difficulty to deal with test specimens of
industrial size.
However, nowadays these problems have been solved thanks to the development of a ceramic
SCM made of ceramic high temperature superconducting coil. This method has enabled the
higher speed of variation of magnetic field strength without using precious resource of liquid
helium (see Annex C). Furthermore, test apparatus using the ceramic SCM which can treat test
specimens of industrial size have been commercialized globally for industrial use.
However, results of measurement in an open magnetic circuit are different from those of
measurement in accordance with IEC 60404-5, particularly in terms of the squareness of
demagnetization curves. This is caused by the influence of the self-demagnetizing field in the
test specimen, which is opposed to magnetization. This is particular to the measurement in an
open magnetic circuit. Therefore, a correction of the influence of self-demagnetizing field
(demagnetizing field correction) on the demagnetization curve measured in an open magnetic
circuit is indispensable.
This document describes three methods of measurement in an open magnetic circuit using a
superconducting magnet (SCM), as follows:
a) SCM-Vibrating Sample Magnetometer (VSM) method;
b) SCM-Extraction method;
c) SCM-Magnetometer method.
In these methods, a test specimen is placed in a detection coil placed in a uniform magnetic
field generated by a SCM. For methods a) and b), the magnetic dipole moment of the test
specimen is detected by voltage induced in the detection coil due to a vibration and an
extraction of the test specimen, respectively. For the method c), a variation of magnetic
polarization of a stationary test specimen is detected by voltage induced in the detection coil
due to a variation of the magnetic field strength applied to the test specimen.
The reproducibility of measurements of the methods a) and b) has been confirmed by an
international round robin test (RRT) that was comparable with that of IEC 60404-5 (see
Annex F). However, the reproducibility of the method c) has not been confirmed by a RRT yet.
Therefore, the method c) is described separately in Annex A.
– 8 – IEC TR 63304:2021 © IEC 2021
There is another method of the measurement in an open magnetic circuit, i.e. the pulsed field
magnetometer (PFM), which is described in IEC TR 62331 [1] . The PFM is different from the
methods described in this document. The PFM measures a steep AC magnetic response of a
test specimen in a pulsed current magnetic field. Consequently, additional correction is
indispensable due to the influence of eddy currents in the test specimen and the magnetic
viscosity of the magnetic materials.
A demagnetization curve should be measured by decreasing the magnetic field strength with a
sufficiently slow speed during the reversal of the polarization to avoid significant magnetic
viscosity and eddy current effects in accordance with IEC 60404-5. In the case of adopting a
conventional metallic SCM made of metallic superconducting coil, the speed of variation of the
magnetic field is too slow so that it takes an hour to obtain a demagnetization curve because
of a limit of variation rate of the magnetic field to maintain the coil in a superconducting state.
The problem has been solved by adopting a newly developed ceramic SCM made of ceramic
high temperature superconducting coil so that a demagnetization curve can be measured within
several minutes (see Annex C).
A new method of the demagnetizing field correction has been developed (see Annex E). It is a
finite element method (FEM) considering the spatial distribution of self-demagnetizing field
strength in the test specimen. The squareness of the corrected demagnetization curve is
comparable with that measured in accordance with IEC 60404-5.
___________
Numbers in square brackets refer to the Bibliography.
METHODS OF MEASUREMENT OF THE MAGNETIC PROPERTIES OF
PERMANENT MAGNET (MAGNETICALLY HARD) MATERIALS IN AN OPEN
MAGNETIC CIRCUIT USING A SUPERCONDUCTING MAGNET
1 Scope
This Technical Report describes the general principle and technical details of the methods of
measurement of the DC magnetic properties of permanent magnet materials in an open
magnetic circuit using a superconducting magnet (SCM).
This method is applicable to permanent magnet materials, such as those specified in
IEC 60404-8-1, the properties of which are presumed homogeneous throughout their volume.
There are two methods:
– the SCM-Vibrating Sample Magnetometer (VSM) method;
– the SCM-Extraction method.
This document also describes methods to correct the influence of the self-demagnetizing field
in the test specimen on the demagnetization curve measured in an open magnetic circuit. The
magnetic properties are determined from the corrected demagnetization curve.
NOTE These SCM-methods can determine the magnetic properties of permanent magnet materials with coercivity
higher than 2 MA/m. The methods of measurement in a closed magnetic circuit specified in IEC 60404-5 can lead to
significant measurement error due to saturation effects in the pole pieces of yoke for the magnetic materials with
coercivity higher than 1,6 MA/m (see IEC 60404-5).
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.
IEC 60404-5, Magnetic materials – Part 5: Permanent magnet (magnetically hard) materials –
Methods of measurement of magnetic properties
IEC 60404-8-1, Magnetic materials – Part 8-1: Specifications for individual materials –
Magnetically hard materials
IEC 60050-121, International Electrotechnical Vocabulary – Part 121: Electromagnetism
IEC 60050-151, International Electrotechnical Vocabulary – Part 151: Electrical and magnetic
devices
IEC 60050-221, International Electrotechnical Vocabulary – Chapter 221: Magnetic materials
and components
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-121,
IEC 60050-151, IEC 60050-221 and the following apply.
– 10 – IEC TR 63304:2021 © IEC 2021
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
demagnetization curve
part of a hysteresis loop in which the magnetic polarization goes from the remanent magnetic
polarization to zero when the applied magnetic field strength varies monotonically, as illustrated
in Figure 1
Key
J saturation magnetic polarization, in T
s
J remanent magnetic polarization, in T
r
H coercivity relating to the magnetic polarization, in A/m
cJ
Figure 1 – Demagnetization curve J(H)
Note 1 to entry: A demagnetization curve can be measured from near magnetic saturation.
[SOURCE: IEC 60050-121:1998, 121-12-72, modified – magnetic flux density is replaced by
magnetic polarization and Note 1 to entry and Figure 1 have been added]
3.2
magnetic dipole moment
m
vector quantity given by the volume integral of the magnetic polarization
[SOURCE: IEC 60050-221:1990, 221-01-07, modified – the symbol j is changed to m which is
used industrially and the note has been removed]
3.3
M coil
detection coil for magnetic dipole moment
3.4
J coil
detection coil for magnetic polarization
4 General principle
4.1 Principle of the method
Figure 2 illustrates schematic diagrams of typical test apparatuses. The test apparatus consists
of a superconducting magnet (SCM), a moving device, a specimen rod, a magnetic field sensor
(hereafter H sensor), a magnetic dipole moment detection coil (hereafter M coil), measuring
devices and a data processing device (PC). The measurement is carried out in an open
magnetic circuit to enable the determination of magnetic properties of permanent magnet
materials with coercivity higher than 2 MA/m.
The axis of the DC magnetic field generated by the SCM is vertical and coaxial with the M coil
and the specimen rod. The moving test specimen is placed in a zone where the magnetic field
strength is uniform with a tolerance of ±1 % at the centre of the SCM. The H sensor is placed
in a zone where the influence of the magnetic dipole moment of the test specimen can be
ignored.
A test specimen is firmly attached on the specimen rod so that the direction of magnetization is
parallel to the axis of the specimen rod, and then placed in the test apparatus as shown in
Figure 2.
a) The SCM-VSM method b) The typical SCM-Extraction method
Figure 2 – Schematic diagrams of the test apparatus
The test specimen is initially magnetized to saturation (see 6.2), and then a DC magnetic field
is applied to the test specimen in the direction opposite to that used for the initial magnetization.
The magnetic field strength is measured by the H sensor (see 4.3).
– 12 – IEC TR 63304:2021 © IEC 2021
The magnetic dipole moment of the test specimen is detected by the voltage induced in the M
coil due to the movement of the test specimen (see 4.4). The magnetic polarization of the test
specimen is calculated from the magnetic dipole moment and the volume of the test specimen
(see 7.2). For calibration aspects, see Clause 9.
There are two methods different in modes of the movement of the test specimen:
a) the SCM-VSM method: the test specimen is vibrated with a small amplitude in the M coil;
b) the SCM-Extraction method: the test specimen is extracted through the M coil.
NOTE There is another method to determine the magnetic polarization of the test specimen, i.e. the SCM-
Magnetometer method. In this method, variation of the magnetic polarization of the stationary test specimen due to
variation of the magnetic field strength applied to the stationary test specimen is detected by the voltage induced in
the detection coil (J coil) (see Annex A).
The measurements are carried out at an ambient temperature of (23 ± 5) °C. For permanent
magnet materials which are known to have significant temperature coefficients α(J ) and α(H ),
r cJ
the temperature of the test specimen should be in a range between 19 °C and 27 °C and
controlled within a tolerance of ±1 °C during the measurements in accordance with IEC 60404-5.
The temperature of the test specimen should be measured by a non-magnetic temperature
sensor.
The demagnetization curve measured in an open magnetic circuit is influenced strongly by the
self-demagnetizing field in the test specimen which opposes magnetization.
In order to determine the intrinsic demagnetization curve of the permanent magnet material, a
correction of the influence of the self-demagnetizing field (hereafter demagnetizing field
correction) should be applied to the measured demagnetization curve (see Clause 11).
Magnetic properties of the permanent magnet material are determined from the corrected
demagnetization curve.
These two methods have the following features:
1) The most important feature is that it is possible to determine all the magnetic properties of
permanent magnet materials with coercivity higher than 2 MA/m in contrast to the method
of measurement in a closed magnetic circuit in accordance with IEC 60404-5.
2) The reproducibility of measurement by the methods is comparable with that of IEC 60404-5.
It was confirmed by the international round robin test (see Annex F).
3) The influence of eddy currents in the test specimen is negligible.
4) By adopting the ceramic SCM made of ceramic high temperature superconducting coil,
demagnetization curve can be measured within several minutes without using expensive
liquid helium and its incidental facilities (see Annex C). Also test apparatus using the
ceramic SCM which can deal test specimens of industrial size has been commercialized for
industrial use. So, it is convenient for industrial use globally.
5) There is no drift in the signal of the magnetic dipole moment, owing to the use of a phase
sensing device (lock-in amplifier) in the SCM-VSM.
4.2 Superconducting magnet (SCM)
A variable DC source supplies a DC current to the superconducting coil, with sufficiently low
voltage noise (see Figure 2). The current source should be a bipolar type which can switch
positive-negative polarity continuously.
The SCM is recommended to have a capacity to generate a magnetic field strength more than
4,8 MA/m (6 T in magnetic flux density) in order to measure the magnetic properties of
permanent magnet materials with coercivity higher than 2 MA/m, e.g. Nd-Fe-B sintered magnets.
It is recommended to adopt the ceramic SCM made of ceramic high temperature
superconducting coil rather than a conventional metallic SCM made of metallic superconducting
coil, in order to reduce the time required to measure a demagnetization curve within several
minutes. It is particularly convenient for industrial use (see Annex C).
The zone of uniform magnetic field strength generated at the centre of the SCM should be
sufficiently large to include the space of the moving test specimen.
4.3 Magnetic field strength sensor (H sensor)
An H sensor such as a Hall probe is used to measure the magnetic field strength together with
a suitable H detection device (see Figure 2). The H sensor should be calibrated by an
appropriate method such as Nuclear Magnetic Resonance (NMR).
In the case of a calibrated SCM, the magnetic field strength may be measured from the
magnetizing current supplied to the SCM. Care should be taken if there is a small hysteresis
between the magnetizing current and the magnetic field strength of the SCM.
The total measuring error of the magnetic field strength should be smaller than ±1 %.
4.4 Magnetic dipole moment detection coil (M coil)
The magnetic dipole moment of the test specimen is measured by the voltage induced in the M
coil placed near the test specimen (see Figure 2). The M coil is wound coaxially with the axis
of magnetic field and placed symmetrically with respect to the centre of the magnetic field.
Electrical leads of the M coil should be tightly twisted to avoid errors caused by voltages induced
in loops of the leads.
The voltage induced in the M coil should be calibrated using a standard specimen of nickel
sphere and the influence of the shape and dimensions of the test specimen on the voltage
should be verified (see Clause 9).
The total measuring error of the magnetic dipole moment should be smaller than ±1 %.
The M coil used in this document is the first order gradiometer coil which is composed of an
upper coil and a lower coil connected electrically in opposite polarity as shown in Figure 3. The
second order gradiometer coil combined with a SQUID (superconducting quantum interference
device) circuit can also be used for the M coil (see Annex D).
NOTE Figure D.2 illustrates the dependence of the induced voltage on the position of the test specimen in the SCM-
Extraction method.
a) The SCM-VSM method b) The typical SCM-Extraction method
Figure 3 – Schematic diagrams of the first order gradiometer coil
– 14 – IEC TR 63304:2021 © IEC 2021
4.5 Specimen rod and moving device
The test specimen should be attached firmly at the bottom end of the specimen rod to avoid
unexpected movement of the test specimen in the magnetic field. Then the specimen rod is
inserted vertically in the SCM and connected to the moving device at the top end as shown in
Figure 2.
The specimen rod should be non-magnetic and should have high rigidity to keep the test
specimen on the axis of the magnetic field without trembling.
The moving device can be a linear motor, a voice coil or other system which can move or vibrate
the specimen rod linearly along the axis of the magnetic field.
Moving modes of the test specimen are as follows.
a) the SCM-VSM method
The test specimen is vibrated at a fixed frequency and amplitude sufficiently smaller than
the length of the M coil. The frequency is normally 20 Hz to 200 Hz and the amplitude is
typically from 0,5 mm to 2 mm [see Figure 3 a)].
b) the SCM-Extraction method
The test specimen is extracted along the axis of the magnetic field. The start point of the
moving specimen is below the lower M coil or above the upper M coil [see Figure 3 b)].
4.6 Measuring devices and the data processing device
The voltage induced in the calibrated M coil due to the movement of the test specimen is
proportional to the magnetic dipole moment of the test specimen. The signal of the M coil is fed
to a preamplifier. In the case of the second order gradiometer coil, a SQUID circuit is employed
to integrate the signal (see Figure 2).
In the SCM-VSM method, the amplified signal is fed to a phase sensing device such as a lock-
in amplifier to output the amplitude of the signal synchronized to the vibration frequency of the
test specimen. The output signal is fed to the data processing device.
In the SCM-Extraction method, the amplified signal is directly fed to the data processing device.
The output signal of the magnetic field detecting device, which is proportional to the magnetic
field strength, is fed to the data processing device.
The data processing device is usually composed of a digitizer and a digital signal calculator for
the determination of the magnetic properties. The digitizer converts the input signals into digital
data simultaneously with analogue-to-digital converters (ADC). The ADC should have at least
a 16-bit resolution.
The digital signal calculator is usually a personal computer (PC) and calculates the magnetic
properties from the digitized signals of the magnetic dipole moment and the magnetic field
strength.
5 Test specimen
The shape of the test specimen is cylinder or cuboid.
The ratio of the length L to the dimension D i.e. L/D is 1,00 within ±0,05, where D is the edge
length of the cuboid test specimen or the diameter of the cylinder test specimen. In the case of
cuboid with L/D = 1,00, care should be taken that the direction of magnetization is marked
properly during the test specimen preparation. The direction of magnetization is parallel to the
length L of the specimen.
NOTE A small difference between L and D of a cuboid test specimen is convenient to easily identify the magnetizing
direction of the test specimen.
The dimension of the test specimen, i.e. L and D, is equal to or larger than 3 mm but sufficiently
smaller than that of the M coil (see Annex B).
The test specimen should be cut carefully to the predetermined dimension from a large block
of the permanent magnet material. Care should be taken to avoid damage on its surface which
can deteriorate the magnetic properties.
Test specimens with a dimension less than 3 mm can be used, provided that the damaged
surface layer is negligible or a special treatment is applied on the damaged surface layer to
recover the intrinsic magnetic properties.
The test specimen should be marked with an arrow to indicate the direction of magnetization in
order to make it easy to attach the test specimen to the specimen rod.
6 Preparation of measurement
6.1 Measurement of volume of the test specimen
The volume V of the test specimen should be calculated from the mass and the density of the
test specimen. The mass of the test specimen can be determined accurately by means of an
electronic balance. The density of the test specimen can be determined accurately with a large
block of the permanent magnet material.
The volume V can also be calculated from the dimensions of the test specimen measured by
means of a calibrated micrometre with four significant figures.
The volume V of the test specimen should be determined within a tolerance of ±1 %.
6.2 Initial magnetization of the test specimen to saturation
Before measurement, the test specimen is magnetized to saturation in a DC magnetic field
strength H .
mag
If it is not possible to magnetize the test specimen to saturation in the test apparatus, the test
specimen should be magnetized to saturation outside the test apparatus in a superconducting
coil or a pulse magnetizer in accordance with IEC 60404-5.
Recommended values for the DC magnetic field strength H for various permanent magnet
mag
materials can be found in IEC TR 62517 [2].
7 Determination of magnetic polarization
7.1 Measurement of the magnetic dipole moment
In the SCM-VSM method, the test specimen is vibrated at a fixed frequency and amplitude, and
then the output voltage of the phase sensing device is measured (see 4.6).
The magnetic dipole moment m is calculated from Formula (1):
– 16 – IEC TR 63304:2021 © IEC 2021
C U
VV
m= (1)
af⋅
where
m is the magnetic dipole moment, in Wb·m;
U is the output voltage of the phase sensing device, in V;
v
C is a constant, in m ;
v
a is the amplitude of the vibration, in m;
f is the frequency of the vibration, in Hz.
In the SCM-Extraction method, the test specimen is extracted through the M coil. The output
voltage of the pre-amplifier or the SQUID circuit is measured (see 4.6).
The magnetic dipole moment is calculated from Formula (2):
t
m= CdU(tt) (2)
∫
t
where
m is the magnetic dipole moment, in Wb·m;
U(t) is the output voltage of the pre-amplifier or the SQUID circuit, in V;
t is the time when the test specimen goes through the lower part of the M coil and U(t ) = 0,
1 1
in s;
t is the time when the test specimen goes through the upper part of the M coil and U(t ) = 0,
2 2
in s;
C is a constant, in m.
The constants C and C should be determined by a calibration of the M coil (see Clause 9).
v 1
7.2 Determination of magnetic polarization
The magnetic polarization J is calculated from the magnetic dipole moment m and the volume
of the test specimen V according to Formula (3).
m
J= (3)
V
where
J is the magnetic polarization, in T;
m is the magnetic dipole moment, in Wb∙m;
V is the volume of the test specimen, in m .
8 Measurement of magnetic field
The magnetic field strength H corresponding to the magnetic polarization is measured by the
calibrated H sensor, e.g. a Hall probe, and the H detection device (see Figure 2).
The temperature dependence of the measuring instrument is to be taken into account.
9 Calibration of the magnetic dipole moment detection coil (M coil)
The calibration of the M coil should be carried out by measuring a standard specimen of nickel
sphere for which the magnetic dipole moment m at an ambient temperature of (23 ± 5) °C and
an applied magnetic field strength of 398 kA/m (5 kOe) is certificated by a national or accredited
calibration laboratory with the temperature coefficient [3]. The standard specimen should be
made of 99,9 % or higher purity nickel and stress-relief annealed without oxidation. The space
occupied by the standard specimen including its movement during the measurement should be
sufficiently smaller than the uniform field region of the SCM coil. Then, the magnetic field
generated by the standard specimen is a perfect dipole field and identical to the field generated
by an ideal dipole in the centre of the spherical standard specimen.
NOTE A saturation magnetic moment is not suitable for calibration in this document.
The constant C of Formula (1) or C of Formula (2) is determined so that the measured
v 1
magnetic dipole moment at magnetic field strength of 398 kA/m (5 kOe) matches with the
certificated value of magnetic dipole moment of the nickel sphere. The difference between the
ambient temperatures at the calibration and that specified in the certification should be
compensated by using the temperature coefficient specified in the certification.
The shape and dimension dependence of the measured magnetic dipole moment of the test
specimen should be verified and compensated. The verification should be carried out by
comparison of measurements using a nickel sphere with the same dimension as the standard
specimen and a nickel cube or cylinder with the same shape and dimensions as the test
specimen. The nickel sphere and the nickel cube or cylinder should be made of the same
material of 99,9 % or higher
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...