IEC 60404-15:2012
(Main)Magnetic materials - Part 15: Methods for the determination of the relative magnetic permeability of feebly magnetic materials
Magnetic materials - Part 15: Methods for the determination of the relative magnetic permeability of feebly magnetic materials
IEC 60404-15:2012 specifies a solenoid method, a magnetic moment method, a magnetic balance method and a permeability meter method for the determination of the relative magnetic permeability of feebly magnetic materials (including austenitic stainless steel). The magnetic balance and permeability meter methods are both comparison methods calibrated using reference materials to determine the value of the relative magnetic permeability of the test specimen.
Matériaux magnétiques - Partie 15: Méthodes de détermination de la perméabilité magnétique relative des matériaux faiblement magnétiques
La CEI 60404-15:2012 spécifie une méthode utilisant un solénoïde, une méthode utilisant le moment magnétique, une méthode utilisant une balance magnétique et une méthode utilisant un appareil de mesure de la perméabilité pour déterminer la perméabilité magnétique relative des matériaux faiblement magnétiques (y compris l'acier inoxydable austénitique). La méthode utilisant une balance magnétique et la méthode utilisant un appareil de mesure de la perméabilité sont toutes les deux des méthodes de comparaison étalonnées utilisant des matériaux de référence en vue de déterminer la valeur de la perméabilité magnétique relative de l'éprouvette.
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IEC 60404-15 ®
Edition 1.0 2012-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Magnetic materials –
Part 15: Methods for the determination of the relative magnetic permeability of
feebly magnetic materials
Matériaux magnétiques –
Partie 15: Méthodes de détermination de la perméabilité magnétique relative des
matériaux faiblement magnétiques
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IEC 60404-15 ®
Edition 1.0 2012-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Magnetic materials –
Part 15: Methods for the determination of the relative magnetic permeability of
feebly magnetic materials
Matériaux magnétiques –
Partie 15: Méthodes de détermination de la perméabilité magnétique relative des
matériaux faiblement magnétiques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.220.01; 29.030 ISBN 978-2-83220-343-9
– 2 – 60404-15 IEC:2012
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Solenoid and magnetic moment method . 7
4.1 General . 7
4.2 Principle . 7
4.3 Apparatus . 8
4.4 Test specimen for the solenoid method . 10
4.5 Procedure . 11
4.6 Calculation . 12
4.7 Uncertainty . 13
5 Magnetic balance method . 13
5.1 Principle . 13
5.2 Disc inserts and reference materials . 14
5.3 Test specimen . 14
5.4 Procedure . 15
5.5 Evaluation of the relative magnetic permeability . 15
5.6 Uncertainty . 15
6 Permeability meter method . 15
6.1 Principle . 15
6.2 Reference specimens and materials . 16
6.3 Test specimen . 17
6.4 Procedure . 17
6.5 Uncertainty . 17
7 Test report . 17
Annex A (informative) Correction for self-demagnetization . 18
Bibliography . 20
Figure 1 – Circuit diagram for the solenoid method . 8
Figure 2 – Coil system for the determination of the magnetic dipole moment . 9
Figure 3 – Magnetic balance: side view . 14
Figure 4 – Schematic of the permeability meter arrangement and magnetic field
distribution without and with test specimen . 16
Table 1 – Relative magnetic permeability ranges for the methods described . 6
Table 2 – Cylindrical sample with a 1:1 aspect ratio . 10
Table 3 – Circular cross section rod with an aspect ratio of 10:1 . 10
60404-15 IEC:2012 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MAGNETIC MATERIALS –
Part 15: Methods for the determination of the relative
magnetic permeability of feebly magnetic materials
FOREWORD
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60404-15 has been prepared by IEC technical committee 68:
Magnetic alloys and steels.
The text of this standard is based on the following documents:
FDIS Report on voting
68/442/FDIS 68/443/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
– 4 – 60404-15 IEC:2012
A list of all the parts in the IEC 60404 series, under the general title Magnetic materials, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
60404-15 IEC:2012 – 5 –
INTRODUCTION
The determination of the relative magnetic permeability of feebly magnetic materials is often
required to assess their effect on the ambient magnetic field. Typical feebly magnetic
materials are austenitic stainless steels and "non-magnetic" brass.
The relative magnetic permeability of some of these materials can vary significantly with the
applied magnetic field strength. In the majority of cases, these materials find application in the
ambient earth's magnetic field. This field in Europe is 35 A/m to 40 A/m, in the far East, it is
25 A/m to 35 A/m and in North America, it is 25 A/m to 35 A/m. However, at present, methods
of measurement are not available to determine the relative magnetic permeability of feebly
magnetic materials at such a low value of magnetic field strength.
Studies of the properties of feebly magnetic materials have been carried out, primarily with a
view to the production of improved reference materials. These studies have shown [1] that it
is possible to produce reference materials which have a substantially constant relative
magnetic permeability over the range from the earth's magnetic field to at least a magnetic
field strength of 100 kA/m.
Since conventional metallic materials can also be used as reference materials their relative
magnetic permeability can be determined using the reference method. It is important that the
magnetic field strength used during the determination of the relative magnetic permeability is
stated for all materials but in particular for conventional materials since the changes with
applied magnetic field can be large. This behaviour also needs to be considered when using
reference materials made from conventional materials to calibrate comparator methods. This
is because these methods use magnetic fields that vary through the volume of the material
being tested and this makes it difficult to know the relative magnetic permeability to use for
the calibration.
Where the effect of a feebly magnetic material on the ambient earth's magnetic field is critical,
the direct measurement of this effect using a sensitive magnetometer should be considered.
___________
Figures in square brackets refer to the bibliography.
– 6 – 60404-15 IEC:2012
MAGNETIC MATERIALS –
Part 15: Methods for the determination of the relative
magnetic permeability of feebly magnetic materials
1 Scope
This part of IEC 60404 specifies a solenoid method, a magnetic moment method, a magnetic
balance method and a permeability meter method for the determination of the relative
magnetic permeability of feebly magnetic materials (including austenitic stainless steel). The
magnetic balance and permeability meter methods are both comparison methods calibrated
using reference materials to determine the value of the relative magnetic permeability of the
test specimen. The relative magnetic permeability range for each of these methods is shown
in Table 1. The methods given are for applied magnetic field strengths of between 5 kA/m and
100 kA/m.
Table 1 – Relative magnetic permeability ranges for the methods described
Measurement method Relative magnetic permeability range
Solenoid 1,003 to 2
Magnetic moment 1,003 to 1,2
Magnetic balance 1,003 to 5
Permeability meter 1,003 to 2
NOTE 1 The relative magnetic permeability range given for the magnetic balance method covers the inserts
provided with a typical instrument. These can only be assessed at values for which calibrated reference materials
exist.
NOTE 2 For a relative magnetic permeability larger than 2, a reference material cannot be calibrated using this
written standard. A note of this is given in the test report explaining that the values measured using the magnetic
balance are for indication only.
The solenoid method is the reference method. The magnetic moment method described is
used mainly for the measurement of the relative magnetic permeability of mass standards.
Two comparator methods used by industry are described. These can be calibrated using
reference materials for which the relative magnetic permeability has been determined using
the reference method. When suitable, the magnetic moment method can also be used. The
dimensions of the reference material need to be given careful consideration when determining
the uncertainty in the calibration value due to self-demagnetization effects. See Annex A for
more information on correcting for self-demagnetization.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
60404-15 IEC:2012 – 7 –
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-221,
IEC 60050-121 as well as the following apply.
3.1
self-demagnetization
generation of a magnetic field within a magnetized body that opposes the magnetization
3.2
demagnetize
to bring a magnetic material to a magnetically neutral state
3.3
feebly magnetic material
material that is essentially non-magnetic in character
4 Solenoid and magnetic moment method
4.1 General
The methods that are described in Clause 4 are reference methods for determining the
relative magnetic permeability of test specimens of feebly magnetic materials with a length to
diameter ratio of at least 10:1. When the relative magnetic permeability is less than 1,2, it is
possible to use a moment detection coil and a test specimen with a length to diameter ratio of
1:1. Both methods use similar equipment and involve similar calculations to determine the
relative magnetic permeability. The descriptions of both methods are therefore presented
together here with significant differences explained in the text.
4.2 Principle
The relative magnetic permeability of a feebly magnetic test specimen is determined from the
magnetic polarization J and the corresponding magnetic field strength H measured using the
circuit shown in Figure 1, using
J
= 1+
μ
r
H
μ
(1)
where
μ is the relative magnetic permeability of the test specimen (ratio);
r
-7
μ is the magnetic constant (4π × 10 ) (in H/m);
J is the magnetic polarization (in T);
H is the magnetic field strength (as calculated from the magnetizing current and the
magnetic field strength to current ratio (known as the coil constant) for the solenoid)
(in A/m).
– 8 – 60404-15 IEC:2012
N
N
Test specimen
R S
A
F
E
IEC 1691/12
Key
A current measuring device or ammeter
E d.c. supply
F flux integrator
N solenoid
N search coil or magnetic moment detection coil
R variable resistor (controlling magnetizing current)
S switch
Figure 1 – Circuit diagram for the solenoid method
NOTE In Figure 1, the search coil N is replaced by a moment detection coil for the magnetic moment method.
4.3 Apparatus
4.3.1 Solenoid. The solenoid shall have a length to diameter ratio of not less than 10:1 or, in
the case of lower length, it shall contain coaxial supplementary coils at the ends or it shall
consist of a split pair coil system (Garrett [2]). The last two coil systems shall yield at least the
same degree of field homogeneity in the centre as is obtained with the long solenoid. The
coils shall be wound on non-magnetic, non-conducting formers. The winding shall have a
sufficient number of turns of wire to be capable of carrying a current that will produce a
magnetic field strength of 100 kA/m. The magnetic field to current ratio of the solenoid (known
as the coil constant) shall be determined with an uncertainty of ± 0,5 % or better, either by an
independent calibration or alternatively by measuring the magnetic field strength by means of
a calibrated Hall effect probe and by measuring the corresponding magnetizing current (using
the method described in 4.3.5).
NOTE 1 More than one solenoid (or split pair coil system) may be required to cover the complete range of
magnetic field strength.
NOTE 2 The optimal diameter of the solenoid depends upon the diameter of test specimens to be measured and
the sensitivity of the measurement. For measurements on bars up to 30 mm in diameter having a relative magnetic
permeability of 1,005, the internal diameter of the solenoid would be approximately 80 mm to accommodate the
requisite search coil.
60404-15 IEC:2012 – 9 –
4.3.2 Search coil. The search coil shall be wound on a non-magnetic, non-conducting former.
Typically, for test specimens up to 30 mm in diameter, the internal diameter of the aperture in
the search coil is 32 mm to allow test specimens to be freely inserted and withdrawn. The
length of the winding shall be 40 mm; end cheeks of between 75 mm and 80 mm diameter
shall be fitted to the former. The winding can be, for example, 10 000 turns of 0,2 mm
diameter insulated wire with interleaving as necessary.
NOTE The winding may be tapped at intervals to facilitate the adjustment of the sensitivity of the measuring
system when determining the relative magnetic permeability of test specimens in the higher part of the permeability
range.
4.3.3 For much shorter solid right cylinders with a length to diameter ratio of 1:1, a moment
detection coil with a homogeneous sensitivity over the volume of the test specimen shall be
used for measuring the magnetic dipole moment of the cylinder (see Figure 2). The magnetic
polarization is calculated from
j
J= (2)
V
where
j is the magnetic dipole moment (in Wbm);
V is the volume of the test specimen (in m ).
The moment detection coil can be a solenoid with additional homogenizing windings close to
the ends of the coil.
Test specimen
Moment detection coil
Compensation coil
Magnetizing solenoid
IEC 1692/12
Figure 2 – Coil system for the determination
of the magnetic dipole moment
The measurement of the magnetic moment of short cylinders with a length to diameter ratio of
1:1 shall be restricted to materials having a relative permeability smaller than μ = 1,2. If this
r
condition is not met, the magnetic field strength inside the test specimen and the polarization
become inhomogeneous and this will produce significant errors in the measured relative
magnetic permeability.
In the region μ = 1,003 to 1,2, a linear correction for the effect of the self-demagnetizing field
r
is appropriate. See Annex A for more information.
NOTE Typically, weight pieces of the classes E , E and F according to OIML R111-1 (2004) [3] fall into this
1 2 1
range.
For this correction, equation (A.2) of Annex A is to be used together with the value of the
magnetometric self-demagnetization factor N as obtained from reference [6].
m
For example, for a cylindrical sample with a 1:1 aspect ratio, values of the relative correction
to the applied magnetic field for different relative magnetic permeabilities due to self-
demagnetization are given in Table 2.
– 10 – 60404-15 IEC:2012
Table 2 – Cylindrical sample with a 1:1 aspect ratio
µ N ∆H/H
r m
1,000 1 0,311 6 0,003 %
1,007 0,311 4 0,22 %
1,2 0,309 3 6,2 %
ΔH/H is the relative correction of the magnetic field strength and N is the magnetometric
m
self-demagnetization factor.
This is discussed in more detail in Annex A.
4.3.4 Flux integrator. The flux integrator shall be an electronic charge integrator or similar
device, calibrated with an uncertainty of ± 0,5 % or better.
4.3.5 Current measuring device. The current measuring device shall consist of a calibrated
resistor connected in series with the magnetizing circuit and a calibrated digital voltmeter.
The magnetizing current shall be determined from the measurement of the voltage developed
across the resistor. The combined uncertainties of the resistor and voltmeter shall be such
that the magnetizing current can be determined with an uncertainty of ± 0,2 % or better.
Alternatively, an ammeter calibrated with an equivalent uncertainty can be used.
4.3.6 Micrometer. The micrometer for measuring the transverse dimensions of the test
specimen for the solenoid method shall be calibrated. For the magnetic moment method, the
volume is required and appropriate dimensional measurements shall be made.
4.4 Test specimen for the solenoid method
The test specimen shall consist of a round or rectangular bar, or a number of strips or wires
having a total cross-sectional area of at least 100 mm . The maximum cross-sectional area
shall be determined by the diameter of the central aperture of the search coil. Allowance shall
be made for the easy insertion and withdrawal of the test specimen without disturbing the
position of the search coil.
To avoid significant errors introduced by self-demagnetization, the length to equivalent
diameter ratio of the test specimen shall be not less than 10:1. When corrections for self-
demagnetization are required see Annex A.
For example, values are given in Table 3 for a rod of circular cross section with an aspect
ratio of 10:1, a diameter of 30 mm and a search coil with an effective average diameter of
52,2 mm. The relative corrections to the applied magnetic field strength and the magnetic
polarization for different relative magnetic permeabilities due to self-demagnetization are
shown.
Table 3 – Circular cross section rod with an aspect ratio of 10:1
µ N ∆H/H ∆J/J
r f
1,000 1 0,004 927 0,000 % 1,49 %
1,007 0,004 931 0,003 % 1,49 %
1,2 0,005 054 0,101 % 1,53 %
2 0,005 541 0,554 % 1,68 %
60404-15 IEC:2012 – 11 –
ΔH/H is the relative correction of the magnetic field strength, N is the fluxmetric self-
f
demagnetization factor and ΔJ/J is the relative correction of the magnetic polarization.
This is discussed in more detail in Annex A.
4.5 Procedure
4.5.1 The cross-sectional area of the test specimen shall be established from a number of
measurements of each dimension. For a test specimen for the solenoid method, the diameter
or transverse dimensions shall be measured by means of a calibrated micrometer (see 4.3.6)
at approximately 10 mm intervals along the central 40 mm of length. The mean cross-
sectional area, expressed in square metres, shall be calculated from the mean dimensions,
with an uncertainty of ± 0,5 %. The difference between the greatest and least cross-sectional
areas shall not exceed ± 0,5 % of the mean area.
For a test specimen for the magnetic moment method, the determination of the volume is
required and sufficient dimensional measurements shall be made so that this can be
determined with an uncertainty of ± 0,71 % (this is the square root of the sum of the squares
of 0,5 % for the cross section and 0,5 % for the length).
4.5.2 The calibration of the flux integrator shall be established with an uncertainty of ± 0,5 %
or better. In order to do this, the secondary winding of a calibrated mutual inductor is
connected in series with the search coil and flux integrator and the current flowing in the
primary winding of the mutual inductor is changed to give the change in magnetic flux
required. From the integrator reading, equation (3) is used to determine the calibration
constant of the integrator.
kΦ = M∆I
IR
(3)
where
k is the calibration constant of the flux integrator;
Φ is the flux integrator reading (in Wb);
IR
M is the mutual inductance for the calibration (in H);
∆I is the change in primary current in the mutual inductor (in A).
NOTE It is important that the total winding resistance at the input of the integrator is the same for calibration and
measurements on the test specimen. To avoid the possibility of coupling of the search coil or moment coil to the
mutual inductor, a non-inductive resistance equivalent to the secondary of the mutual inductor can be placed in
series with the search coil or the moment coil.
4.5.3 The test specimen shall be demagnetized immediately prior to the measurement from a
magnetic field strength of not less than 20 kA/m by the slow reversal of a gradually reducing
direct current or a gradually reducing alternating current (for the frequency, see next
paragraph), provided the magnetic field produced by the latter can completely penetrate the
test specimen. Test specimens which have been subjected to a higher magnetic field strength
shall be demagnetized from a suitably high magnetic field before measurement. The
effectiveness of the demagnetization shall be checked by inserting the test specimen into the
search coil or moment detection coil and, with no current flowing, withdrawing the test
specimen and observing the reading on the flux integrator. There shall be either a zero
reading or an insignificantly small reading on the flux integrator.
In order that the magnetic field may completely penetrate the test specimen, the frequency of
reversal shall not exceed 0,5 Hz for a cross-section of 10 mm × 10 mm and 0,1 Hz for a
cross-section of 20 mm × 20 mm. Some materials may also display magnetic viscosity effects
so that even slower reversals are required to ensure complete demagnetization. In cases of
doubt, the effect of slower and more rapid reversals shall be compared.
– 12 – 60404-15 IEC:2012
The magnetizing current to produce the required magnetic field strength shall be calculated
from the magnetic field strength to current ratio previously determined for the solenoid (see
4.3.1).
At low values of magnetic field strength, the earth's magnetic field may be significant. It is
recommended that the axis of the solenoid is aligned in a horizontal plane in a direction
normal to the horizontal component of the earth's magnetic field.
The magnetic polarization shall be measured by inserting the demagnetized test specimen
into the search coil or moment detection coil, adjust the magnetizing current to the required
value taking care not to overshoot, zero the flux integrator, withdraw the test specimen and
record the integrator reading. Care shall be taken to withdraw the test specimen from the
search coil or moment detection coil to a position where it no longer has an influence on the
search coil or moment detection coil, as indicated by the integrator reading.
For the solenoid method, the complete measurement procedure shall be repeated with the
other end of the test specimen inserted into the search coil. Either the two integrator readings
shall be averaged or used separately, depending on the customer's requirement.
The procedure is repeated as necessary to determine the given measurement repeatability.
NOTE Small fluctuations of the magnetizing current or of the ambient magnetic field can induce large instabilities
in the measured flux. To avoid this, a compensation coil can be used.
The weight of the specimen can change the direction of the search coil axis used in the
solenoid method by a small amount during the withdrawal of the specimen, which leads to an
additional induced voltage in the search coil. Therefore the search coil should be fixed very
rigidly or mechanically decoupled from the movement of the specimen.
Electrostatic charging of the search coil or moment coil during the withdrawal of the specimen
can disturb the flux measurements and should be prevented. A copper shielding might be
effective to avoid signal contributions from electrostatic charges.
4.6 Calculation
For the solenoid method, the magnetic polarization shall be calculated using equation (4):
Φ
IR
J= (4)
NA
s
where
Φ is the flux integrator reading corrected in accordance with the integrator calibration (in
IR
Wb);
A is the cross sectional area of the test specimen (in m );
s
N is the number of turns of the search coil.
For the magnetic moment method, the magnetic dipole moment shall be calculated using
equation (5):
−1
H
j=Φ ⋅
(5)
IR
I
where
Φ is the flux integrator reading corrected in accordance with the integrator calibration (in
IR
Wb);
60404-15 IEC:2012 – 13 –
H/I is the coil constant (magnetic field strength to current ratio) of the moment coil system
(in (A/m)/A).
The magnetic polarization, J, shall then be calculated using equation (2).
If necessary, see Annex A for the calculation of corrections for self-demagnetization. In that
case, the relative magnetic permeability of the test specimen shall be calculated from the
following equation:
J
μ = 1+
r
μ H
(6)
where
μ is the relative magnetic permeability of the test specimen (ratio);
r
-7
μ is the magnetic constant (4π × 10 ) (in H/m);
J is the magnetic polarization (in T);
H is the magnetic field strength (in A/m) (as calculated from the magnetizing current and
the coil constant of the solenoid).
4.7 Uncertainty
The estimation of the uncertainties in the measurements associated with the solenoid and
magnetic moment methods shall be divided into three elements: the uncertainty in the
measurement of the magnetic polarization (J), the uncertainty in the measurement of the
magnetic field strength (H) and, from these, the determination of the uncertainty of the relative
magnetic permeability minus 1 (μ – 1). From this, the absolute uncertainty in the relative
r
magnetic permeability (μ) shall be determined. If corrections have been applied for
r
demagnetisation, a contribution for this shall be included in the uncertainty budget.
The individual contributions to these uncertainties shall be determined and then combined in
accordance with the guidelines set out in the ISO/IEC Guide to the expression of uncertainty
in measurement (ISO/IEC GUIDE 98-3: 2008).
5 Magnetic balance method
5.1 Principle
This is a comparator method that provides industry with a convenient way of determining the
relative magnetic permeability of a material that is “less than” or “greater than” that of disc
inserts.
The magnetic balance is designed for the determination of the relative magnetic permeability
of small test specimens and components, which are unsuitable for measurement by the
reference method. In addition, it is useful for in situ and on site measurements on materials
and complete assemblies.
The relative magnetic permeability is determined by comparing the attraction of a magnet to a
series of disc inserts and the specimen under test using commercially available instruments
such as that shown in Figure 3. See 5.2 for information about disc inserts and materials.
The magnet is either attracted to a disc insert screwed into the top of the instrument above
the magnet, or to the test specimen placed beneath the magnet, depending on which material
has the higher effective relative magnetic permeability. Some types of insert have a
ferromagnetic grub screw fitted in the cap. This screw is adjusted by the manufacturer to
– 14 – 60404-15 IEC:2012
produce specific values of effective relative magnetic permeability at the point where the
magnet contacts a metal disc of very low magnetic permeability.
NOTE 1 For the limitations regarding the dependence of relative magnetic permeability with magnetic field
strength, see the Introduction to this standard.
Reference
specimen
Case Counterweight Pivot
Magnet
Horizontal support Test specimen
IEC 1693/12
Figure 3 – Magnetic balance: side view
NOTE 2 Other forms of this instrument exist. One such instrument has a phosphor bronze hair spring attached to
the central pivot and to an index-type knob having a scale with arbitrary divisions. In this case, the force required
to detach the magnet from a reference material, as indicated by the scale reading, is compared with that for the
specimen under test. Another type of instrument employs a strain gauge to measure this force. The remainder of
this section considers the use of disc inserts only. For other types of instruments, these disc inserts can be
replaced by calibrated reference materials.
5.2 Disc inserts and reference materials
5.2.1 A series of disc inserts (supplied with the balance) covering the range of relative
magnetic permeability from 1,005 to 5 can be used (see 5.1).
The relative magnetic permeability of the disc inserts is assessed by using a number of
calibrated reference materials. Disc inserts that have a nominal relative magnetic permeability
larger than 2 cannot be assessed.
For a relative magnetic permeability larger than 2, a reference material cannot be calibrated
using this standard. A note of this should be given in the test report explaining that the values
measured using the magnetic balance are for indication only.
Reference materials in the form of a rod made up of a number of short cylinders of similar
materials should be calibrated by the solenoid method or magnetic moment method. Individual
cylinders should then be used to check the approximate relative magnetic permeability of the
disc insert.
NOTE The reference materials or disc inserts may be sent to national measurement laboratories that offer this
calibration capability.
5.3 Test specimen
The dimensions of the test specimen shall be either:
60404-15 IEC:2012 – 15 –
a) 25 mm × 25 mm (or 25 mm diameter) and 25 mm thick; or
b) less than this subject to agreement between the respective parties.
One face shall be finished smooth, flat and clean from machine tool contamination. Since the
relative magnetic permeability of most materials and alloys is sensitive to heat treatment and
mechanical working, material immediately adjacent to cut edges shall not be used. Care shall
be taken to avoid the effects of heating and work hardening during machining.
Where necessary, finishing shall be carried out by light grinding with sufficient coolant.
NOTE For test specimens of dimensions less than 25 mm, an error in the measured permeability value could be
introduced [4]. The magnitude of this error will be dependent upon the dimensions and permeability of the material.
The best results are achieved when the test and reference materials are of similar dimensions.
5.4 Procedure
5.4.1 The test specimen and the reference material shall be demagnetized in accordance
with 4.5.3.
Where the size or location of the test specimen does not allow demagnetization to be carried
out, this shall be stated on the test report.
5.4.2 The magnetic balance shall be placed on a horizontal surface with the disc insert of
highest value of relative magnetic permeability in place. The test specimen shall be offered up
to the underside of the magnet. If the magnet is attracted to the test specimen then the
relative magnetic permeability of the material is greater than can be determined by the
instrument. If the magnet is attracted to the disc insert then sequentially replace the disc
insert with those of progressively lower relative magnetic permeability until the magnet is
attracted to the test specimen.
The procedure shall be repeated several times over the surface of the test specimen to check
the consistency and uniformity of the value. Measurements shall not be taken close to edges
or in small re-entrant areas.
5.5 Evaluation of the relative magnetic permeability
The relative magnetic permeability of the test specimen shall be taken as being in the range
between the last two disc inserts, that is between the one in place when the magnet is
attracted to the test specimen and the one of lowest permeability to which the magnet is
attracted.
NOTE The disc inserts can be compared to reference materials calibrated at national measurement institutes that
offer this capability.
5.6 Uncertainty
The uncertainty in the calibration of the disc inserts or reference materials used shall be
stated (see 4.7 for the uncertainty of the solenoid method).
NOTE Due to the fact that the instrument can only determine the range in which the relative magnetic
permeability lies, it is not possible to assign an uncertainty value to the measurement.
6 Permeability meter method
6.1 Principle
This is a comparator method that provides industry with a convenient method of determining
the relative magnetic permeability of a material.
– 16 – 60404-15 IEC:2012
The permeability meter method, schematically shown in Figure 4, is suitable for determining
the relative permeability of feebly magnetic materials between μ = 1,0 and 2,0.
r
The change in magnetic flux density produced in the air at one pole of a permanent magnet is
measured, using commercially available permeability meters, when a low magnetic
permeability test specimen is placed in contact with that pole. The changes in magnetic flux
density are small and are measured with a fluxgate magnetometer(s) in a gradiometer
arrangement built into a probe which also houses the permanent magnet, see Figure 4.
When the instrument is calibrated against standards with known permeability values as
determined by the manufacturer of the instrument against their calibrated standards or
national standards, the measured values of
...
IEC 60404-15 ®
Edition 1.1 2016-12
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Magnetic materials –
Part 15: Methods for the determination of the relative magnetic permeability of
feebly magnetic materials
Matériaux magnétiques –
Partie 15: Méthodes de détermination de la perméabilité magnétique relative des
matériaux faiblement magnétiques
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IEC 60404-15 ®
Edition 1.1 2016-12
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Magnetic materials –
Part 15: Methods for the determination of the relative magnetic permeability of
feebly magnetic materials
Matériaux magnétiques –
Partie 15: Méthodes de détermination de la perméabilité magnétique relative des
matériaux faiblement magnétiques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.01; 29.030 ISBN 978-2-8322-3688-8
IEC 60404-15 ®
Edition 1.1 2016-12
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Magnetic materials –
Part 15: Methods for the determination of the relative magnetic permeability of
feebly magnetic materials
Matériaux magnétiques –
Partie 15: Méthodes de détermination de la perméabilité magnétique relative des
matériaux faiblement magnétiques
– 2 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Solenoid and magnetic moment method . 7
4.1 General . 7
4.2 Principle . 7
4.3 Apparatus . 9
4.4 Test specimen for the solenoid method . 12
4.5 Procedure . 13
4.6 Calculation . 15
4.7 Uncertainty . 16
5 Magnetic balance method . 16
5.1 Principle . 16
5.2 Disc inserts and reference materials . 17
5.3 Test specimen . 17
5.4 Procedure . 18
5.5 Evaluation of the relative magnetic permeability . 18
5.6 Uncertainty . 18
6 Permeability meter method . 18
6.1 Principle . 18
6.2 Reference specimens and materials . 19
6.3 Test specimen . 20
6.4 Procedure . 20
6.5 Uncertainty . 20
7 Test report . 20
Annex A (informative) Correction for self-demagnetization . 21
Bibliography . 23
Figure 1 – Circuit diagram for the solenoid method with withdrawal of test specimen . 8
Figure 2 – Coil system for the determination of the magnetic dipole moment . 11
Figure 3 – Magnetic balance: side view . 17
Figure 4 – Schematic of the permeability meter arrangement and magnetic field
distribution without and with test specimen . 19
Figure 5 – Circuit diagram for the solenoid method with reversing of magnetizing
current . 9
Table 1 – Relative magnetic permeability ranges for the methods described . 6
Table 2 – Cylindrical sample with a 1:1 aspect ratio . 11
Table 3 – Circular cross section rod with an aspect ratio of 10:1 . 12
IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MAGNETIC MATERIALS –
Part 15: Methods for the determination of the relative
magnetic permeability of feebly magnetic materials
FOREWORD
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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.
This consolidated version of the official IEC Standard and its amendment has been prepared
for user convenience.
IEC 60404-15 edition 1.1 contains the first edition (2012-09) [documents 68/442/FDIS and 68/443/
RVD] and its amendment 1 (2016-12) [documents 68/531/CDV and 68/544/RVC].
In this Redline version, a vertical line in the margin shows where the technical content is
modified by amendment 1. Additions are in green text, deletions are in strikethrough red text. A
separate Final version with all changes accepted is available in this publication.
– 4 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
International Standard IEC 60404-15 has been prepared by IEC technical committee 68:
Magnetic alloys and steels.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60404 series, under the general title Magnetic materials, can
be found on the IEC website.
The committee has decided that the contents of the base publication and its amendment will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
IEC 2016
INTRODUCTION
The determination of the relative magnetic permeability of feebly magnetic materials is often
required to assess their effect on the ambient magnetic field. Typical feebly magnetic
materials are austenitic stainless steels and "non-magnetic" brass.
The relative magnetic permeability of some of these materials can vary significantly with the
applied magnetic field strength. In the majority of cases, these materials find application in the
ambient earth's magnetic field. This field in Europe is 35 A/m to 40 A/m, in the far East, it is
25 A/m to 35 A/m and in North America, it is 25 A/m to 35 A/m. However, at present, methods
of measurement are not available to determine the relative magnetic permeability of feebly
magnetic materials at such a low value of magnetic field strength.
Studies of the properties of feebly magnetic materials have been carried out, primarily with a
view to the production of improved reference materials. These studies have shown [1] that it
is possible to produce reference materials which have a substantially constant relative
magnetic permeability over the range from the earth's magnetic field to at least a magnetic
field strength of 100 kA/m.
Since conventional metallic materials can also be used as reference materials their relative
magnetic permeability can be determined using the reference method. It is important that the
magnetic field strength used during the determination of the relative magnetic permeability is
stated for all materials but in particular for conventional materials since the changes with
applied magnetic field can be large. This behaviour also needs to be considered when using
reference materials made from conventional materials to calibrate comparator methods. This
is because these methods use magnetic fields that vary through the volume of the material
being tested and this makes it difficult to know the relative magnetic permeability to use for
the calibration.
Where the effect of a feebly magnetic material on the ambient earth's magnetic field is critical,
the direct measurement of this effect using a sensitive magnetometer should be considered.
___________
Figures in square brackets refer to the bibliography.
– 6 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
MAGNETIC MATERIALS –
Part 15: Methods for the determination of the relative
magnetic permeability of feebly magnetic materials
1 Scope
This part of IEC 60404 specifies a solenoid method, a magnetic moment method, a magnetic
balance method and a permeability meter method for the determination of the relative
magnetic permeability of feebly magnetic materials (including austenitic stainless steel). The
magnetic balance and permeability meter methods are both comparison methods calibrated
using reference materials to determine the value of the relative magnetic permeability of the
test specimen. The relative magnetic permeability range for each of these methods is shown
in Table 1. The methods given are for applied magnetic field strengths of between 5 kA/m and
100 kA/m.
Table 1 – Relative magnetic permeability ranges for the methods described
Measurement method Relative magnetic permeability range
Solenoid 1,003 to 2
Magnetic moment 1,003 to 1,2
Magnetic balance 1,003 to 5
Permeability meter 1,003 to 2
NOTE 1 The relative magnetic permeability range given for the magnetic balance method covers the inserts
provided with a typical instrument. These can only be assessed at values for which calibrated reference materials
exist.
NOTE 2 For a relative magnetic permeability larger than 2, a reference material cannot be calibrated using this
written standard. A note of this is given in the test report explaining that the values measured using the magnetic
balance are for indication only.
The solenoid method is the reference method. The magnetic moment method described is
used mainly for the measurement of the relative magnetic permeability of mass standards.
Two comparator methods used by industry are described. These can be calibrated using
reference materials for which the relative magnetic permeability has been determined using
the reference method. When suitable, the magnetic moment method can also be used. The
dimensions of the reference material need to be given careful consideration when determining
the uncertainty in the calibration value due to self-demagnetization effects. See Annex A for
more information on correcting for self-demagnetization.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
IEC 2016
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-221,
IEC 60050-121 as well as the following apply.
3.1
self-demagnetization
generation of a magnetic field within a magnetized body that opposes the magnetization
3.2
demagnetize
to bring a magnetic material to a magnetically neutral state
3.3
feebly magnetic material
material that is essentially non-magnetic in character
4 Solenoid and magnetic moment method
4.1 General
The methods that are described in Clause 4 are reference methods for determining the
relative magnetic permeability of test specimens of feebly magnetic materials with a length to
diameter ratio of at least 10:1. When the relative magnetic permeability is less than 1,2, it is
possible to use a moment detection coil and a test specimen with a length to diameter ratio of
1:1. Both methods use similar equipment and involve similar calculations to determine the
relative magnetic permeability. The descriptions of both methods are therefore presented
together here with significant differences explained in the text.
4.2 Principle
The relative magnetic permeability of a feebly magnetic test specimen is determined from the
magnetic polarization J and the corresponding magnetic field strength H measured using the
circuit shown in Figure 1 or Figure 5, using
J
= 1+
μ
r
H
μ
(1)
where
μ is the relative magnetic permeability of the test specimen (ratio);
r
-7
μ is the magnetic constant (4π × 10 ) (in H/m);
J is the magnetic polarization (in T);
H is the magnetic field strength (as calculated from the magnetizing current and the
magnetic field strength to current ratio (known as the coil constant) for the solenoid)
(in A/m).
– 8 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
N
N
Test specimen
R S
A
F
E
IEC 1691/12
Key
A current measuring device or ammeter
E d.c. supply
F flux integrator
N solenoid
N search coil or magnetic moment detection coil
R variable resistor (controlling magnetizing current)
S switch
Figure 1 – Circuit diagram for the solenoid method with withdrawal of test specimen
NOTE In Figure 1, the search coil N is replaced by a moment detection coil for the magnetic moment method.
IEC 2016
Air flux compensating coil
N
N
Test specimen
Flux coil
R
c
F
S
E
R
A
IEC
Key
A Current measuring device or ammeter
E d.c. power supply
F Flux integrator
N Solenoid
N Compensated search coil
R Variable resistor (controlling magnetizing current)
R Variable resistor (to adjust the output of the air flux compensating coil)
c
S Switch for reversing the current in the solenoid
Figure 5 – Circuit diagram for the solenoid method
with reversing of magnetizing current
4.3 Apparatus
4.3.1 Solenoid. The solenoid shall have a length to diameter ratio of not less than 10:1 or, in
the case of lower length, it shall contain coaxial supplementary coils at the ends or it shall
consist of a split pair coil system (Garrett [2]). The last two coil systems shall yield at least the
same degree of field homogeneity in the centre as is obtained with the long solenoid. The
coils shall be wound on non-magnetic, non-conducting formers. The winding shall have a
sufficient number of turns of wire to be capable of carrying a current that will produce a
magnetic field strength of 100 kA/m. The magnetic field to current ratio of the solenoid (known
as the coil constant) shall be determined with an uncertainty of ± 0,5 % or better, either by an
independent calibration or alternatively by measuring the magnetic field strength by means of
– 10 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
a calibrated Hall effect probe and by measuring the corresponding magnetizing current (using
the method described in 4.3.5).
NOTE 1 More than one solenoid (or split pair coil system) may be required to cover the complete range of
magnetic field strength.
NOTE 2 The optimal diameter of the solenoid depends upon the diameter of test specimens to be measured and
the sensitivity of the measurement. For measurements on bars up to 30 mm in diameter having a relative magnetic
permeability of 1,005, the internal diameter of the solenoid would be approximately 80 mm to accommodate the
requisite search coil.
4.3.2 Search coil for the solenoid method with withdrawal of test specimen. For the solenoid
method with withdrawal of test specimen, the search coil shall be wound on a non-magnetic,
non-conducting former. Typically, for test specimens up to 30 mm in diameter, the internal
diameter of the aperture in the search coil is 32 mm to allow test specimens to be freely
inserted and withdrawn. The length of the winding shall be 40 mm; end cheeks of between 75
mm and 80 mm diameter shall be fitted to the former. The winding can be, for example,
10 000 turns of 0,2 mm diameter insulated wire with interleaving as necessary.
NOTE The winding may can be tapped at intervals to facilitate the adjustment of the sensitivity of the measuring
system when determining the relative magnetic permeability of test specimens in the higher part of the permeability
range.
4.3.7 Search coil for the solenoid method with reversing of magnetizing current. For the
solenoid method with reversing of magnetizing current, the flux coil and the air flux
compensating coil shall each be wound on a non-magnetic, non-conducting former. The cross
section area of the flux coil shall be no more than ten times that of the test specimen and
there must be a sufficient number of turns for adequate resolution (typically >1 000 turns).
The flux coil should be no longer than 20 % of the test specimen length.
The flux coil and the air flux compensating coil are connected in series opposition to form a
compensated search coil. The length and effective area-turns of the flux coil and the air flux
compensating coil shall be nearly equal, with the area-turns of the air flux compensating coil
slightly larger than those of the flux coil so the compensating signal can be attenuated with a
variable resistor (R in Figure 5) to match the signal from the empty flux coil.
c
The air flux compensating coil shall be located a sufficient distance from the flux coil such that
there is no significant coupling to the magnetic flux of the test specimen. Coupling will change
the effectiveness of the compensation when a sample is present, and can cause significant
measurement error.
The signal from the air flux compensating coil shall be adjusted to exactly cancel the signal
from the empty flux coil. With no sample present, apply the highest magnetizing current to be
used in the test, reset the flux integrator, reverse the magnetizing current, and adjust the
variable resistor R to obtain the minimum output from the compensated coil set N . Repeat
c 2
as necessary until the output is as low as can be adjusted.
4.3.3 Moment detection coil. For much shorter solid right cylinders with a length to diameter
ratio of 1:1, a moment detection coil with a homogeneous sensitivity over the volume of the
test specimen shall be used for measuring the magnetic dipole moment of the cylinder (see
Figure 2). The magnetic polarization is calculated from
j
J= (2)
V
where
J is the magnetic polarization (in T);
j is the magnetic dipole moment (in Wbm);
V is the volume of the test specimen (in m ).
IEC 2016
The moment detection coil can be a solenoid with additional homogenizing windings close to
the ends of the coil.
Test specimen
Moment detection coil
Compensation coil
Magnetizing solenoid
IEC 1692/12
Figure 2 – Coil system for the determination
of the magnetic dipole moment
The measurement of the magnetic moment of short cylinders with a length to diameter ratio of
1:1 shall be restricted to materials having a relative permeability smaller than μ = 1,2. If this
r
condition is not met, the magnetic field strength inside the test specimen and the polarization
become inhomogeneous and this will produce significant errors in the measured relative
magnetic permeability.
In the region μ = 1,003 to 1,2, a linear correction for the effect of the self-demagnetizing field
r
is appropriate. See Annex A for more information.
NOTE Typically, weight pieces of the classes E , E and F according to OIML R111-1 (2004) [3] fall into this
1 2 1
range.
For this correction, equation (A.2) of Annex A is to be used together with the value of the
magnetometric self-demagnetization factor N as obtained from reference [6].
m
For example, for a cylindrical sample with a 1:1 aspect ratio, values of the relative correction
to the applied magnetic field for different relative magnetic permeabilities due to self-
demagnetization are given in Table 2.
Table 2 – Cylindrical sample with a 1:1 aspect ratio
µ N ∆H/H
r m
1,000 1 0,311 6 0,003 %
1,007 0,311 4 0,22 %
1,2 0,309 3 6,2 %
ΔH/H is the relative correction of the magnetic field strength and N is the magnetometric
m
self-demagnetization factor.
This is discussed in more detail in Annex A.
– 12 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
4.3.4 Flux integrator. The flux integrator shall be an electronic charge integrator or similar
device, calibrated with an uncertainty of ± 0,5 % or better.
4.3.5 Current measuring device. The current measuring device shall consist of a calibrated
resistor connected in series with the magnetizing circuit and a calibrated digital voltmeter.
The magnetizing current shall be determined from the measurement of the voltage developed
across the resistor. The combined uncertainties of the resistor and voltmeter shall be such
that the magnetizing current can be determined with an uncertainty of ± 0,2 % or better.
Alternatively, an ammeter calibrated with an equivalent uncertainty can be used.
4.3.6 Micrometer. The micrometer for measuring the transverse dimensions of the test
specimen for the solenoid method shall be calibrated. For the magnetic moment method, the
volume is required and appropriate dimensional measurements shall be made.
4.4 Test specimen for the solenoid method
The test specimen shall consist of a round or rectangular bar, or a number of strips or wires
having a total cross-sectional area of at least 100 mm . The maximum cross-sectional area
shall be determined by the diameter of the central aperture of the search coil. Allowance shall
be made for the easy insertion and withdrawal of the test specimen without disturbing the
position of the search coil.
To avoid significant errors introduced by self-demagnetization, the length to equivalent
diameter ratio of the test specimen shall be not less than 10:1. When corrections for self-
demagnetization are required see Annex A.
For example, values are given in Table 3 for a rod of circular cross section with an aspect
ratio of 10:1, a diameter of 30 mm and a search coil with an effective average diameter of
52,2 mm. The relative corrections to the applied magnetic field strength and the magnetic
polarization for different relative magnetic permeabilities due to self-demagnetization are
shown.
Table 3 – Circular cross section rod with an aspect ratio of 10:1
µ N ∆H/H ∆J/J
r f
1,000 1 0,004 927 0,000 % 1,49 %
1,007 0,004 931 0,003 % 1,49 %
1,2 0,005 054 0,101 % 1,53 %
2 0,005 541 0,554 % 1,68 %
ΔH/H is the relative correction of the magnetic field strength, N is the fluxmetric self-
f
demagnetization factor and ΔJ/J is the relative correction of the magnetic polarization.
This is discussed in more detail in Annex A.
IEC 2016
4.5 Procedure
4.5.1 Cross-sectional area of test specimen. The cross-sectional area of the test specimen
shall be established from a number of measurements of each dimension. For a test specimen
for the solenoid method, the diameter or transverse dimensions shall be measured by means
of a calibrated micrometer (see 4.3.6) at approximately 10 mm intervals along the central
40 mm of length. The mean cross-sectional area, expressed in square metres, shall be
calculated from the mean dimensions, with an uncertainty of ± 0,5 %. The difference between
the greatest and least cross-sectional areas shall not exceed ± 0,5 % of the mean area.
For a test specimen for the magnetic moment method, the determination of the volume is
required and sufficient dimensional measurements shall be made so that this can be
determined with an uncertainty of ± 0,71 % (this is the square root of the sum of the squares
of 0,5 % for the cross section and 0,5 % for the length).
4.5.2 Calibration of flux integrator. The calibration of the flux integrator shall be established
with an uncertainty of ± 0,5 % or better. In order to do this, the secondary winding of a
calibrated mutual inductor is connected in series with the search coil and flux integrator and
the current flowing in the primary winding of the mutual inductor is changed to give the
change in magnetic flux required. From the integrator reading, equation (3) is used to
determine the calibration constant of the integrator.
kΦ = M∆I
IR
(3)
where
k is the calibration constant of the flux integrator;
Φ is the flux integrator reading (in Wb);
IR
M is the mutual inductance for the calibration (in H);
∆I is the change in primary current in the mutual inductor (in A).
NOTE It is important that the total winding resistance at the input of the integrator is the same for calibration and
measurements on the test specimen. To avoid the possibility of coupling of the search coil or moment coil to the
mutual inductor, a non-inductive resistance equivalent to the secondary of the mutual inductor can be placed in
series with the search coil or the moment coil.
4.5.3 Demagnetization of test specimen. The test specimen shall be demagnetized
immediately prior to the measurement from a magnetic field strength of not less than 20 kA/m
by the slow reversal of a gradually reducing direct current or a gradually reducing alternating
current (for the frequency, see next paragraph), provided the magnetic field produced by the
latter can completely penetrate the test specimen. Test specimens which have been subjected
to a higher magnetic field strength shall be demagnetized from a suitably high magnetic field
before measurement. The effectiveness of the demagnetization shall be checked by inserting
the test specimen into the search coil or moment detection coil and, with no current flowing,
withdrawing the test specimen and observing the reading on the flux integrator. There shall be
either a zero reading or an insignificantly small reading on the flux integrator.
In order that the magnetic field may completely penetrate the test specimen, the frequency of
reversal shall not exceed 0,5 Hz for a cross-section of 10 mm × 10 mm and 0,1 Hz for a
cross-section of 20 mm × 20 mm. Some materials may also display magnetic viscosity effects
so that even slower reversals are required to ensure complete demagnetization. In cases of
doubt, the effect of slower and more rapid reversals shall be compared.
The magnetizing current to produce the required magnetic field strength shall be calculated
from the magnetic field strength to current ratio previously determined for the solenoid (see
4.3.1).
– 14 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
At low values of magnetic field strength, the earth's magnetic field may be significant. It is
recommended that the axis of the solenoid is aligned in a horizontal plane in a direction
normal to the horizontal component of the earth's magnetic field.
The magnetic polarization shall be measured by inserting the demagnetized test specimen
into the search coil or moment detection coil, adjust the magnetizing current to the required
value taking care not to overshoot, zero the flux integrator, withdraw the test specimen and
record the integrator reading. Care shall be taken to withdraw the test specimen from the
search coil or moment detection coil to a position where it no longer has an influence on the
search coil or moment detection coil, as indicated by the integrator reading.
For the solenoid method, the complete measurement procedure shall be repeated with the
other end of the test specimen inserted into the search coil. Either the two integrator readings
shall be averaged or used separately, depending on the customer's requirement.
The procedure is repeated as necessary to determine the given measurement repeatability.
NOTE Small fluctuations of the magnetizing current or of the ambient magnetic field can induce large instabilities
in the measured flux. To avoid this, a compensation coil can be used.
The weight of the specimen can change the direction of the search coil axis used in the
solenoid method by a small amount during the withdrawal of the specimen, which leads to an
additional induced voltage in the search coil. Therefore the search coil should be fixed very
rigidly or mechanically decoupled from the movement of the specimen.
Electrostatic charging of the search coil or moment coil during the withdrawal of the specimen
can disturb the flux measurements and should be prevented. A copper shielding might be
effective to avoid signal contributions from electrostatic charges.
4.5.4 Measurement of magnetic polarization with withdrawal of the test specimen. The
magnetic polarization shall be measured by inserting the demagnetized test specimen into the
search coil or moment detection coil, adjust the magnetizing current to the required value
taking care not to overshoot, zero the flux integrator, withdraw the test specimen and record
the integrator reading. Care shall be taken to withdraw the test specimen from the search coil
or moment detection coil to a position where it no longer has an influence on the search coil
or moment detection coil, as indicated by the integrator reading.
The weight of the specimen can change the direction of the search coil axis used in the
solenoid method by a small amount during the withdrawal of the specimen, which leads to an
additional induced voltage in the search coil. Therefore the search coil should be fixed very
rigidly or mechanically decoupled from the movement of the specimen.
Electrostatic charging of the search coil or moment coil during the withdrawal of the specimen
can disturb the flux measurements and should be prevented. A copper shielding might be
effective to avoid signal contributions from electrostatic charges.
Small fluctuations of the magnetizing current or of the ambient magnetic field can induce large
instabilities in the measured flux. To avoid this, a compensation coil can be used.
4.5.5 Measurement of magnetic polarization with reversing of magnetizing current. The
magnetic polarization shall be measured by inserting the demagnetized test specimen into the
center of the compensated search coil, adjust the magnetizing current to the required positive
value taking care not to overshoot, zero the flux integrator, reverse the magnetizing current to
the same amplitude as the positive value taking care not to overshoot, and record the
integrator reading. The reading represents two times the magnetic polarization due to the
current reversal.
NOTE The use of an air flux compensating coil and compensating resistor allows the air flux enclosed by the flux
coil to be cancelled out so that magnetic polarization can be measured directly (see 4.3.7).
IEC 2016
4.5.6 Averaging over the two sample directions. For the solenoid method, the complete
measurement procedure shall be performed two times, once with one end of the test
specimen inserted into the search coil and again with the other end inserted into the search
coil. Either the two integrator readings shall be averaged or used separately, depending on
the customer’s requirement.
4.5.7 Repeatability. The procedure is repeated as necessary to determine the measurement
repeatability.
4.6 Calculation
For the solenoid method with withdrawal of test specimen, the magnetic polarization shall be
calculated using Equation (4):
Φ
IR
Φ
IR
J=
J= (4)
NA NA
s
S
For the solenoid method with reversing of magnetizing current, the magnetic polarization shall
be calculated using Equation (7):
Φ
IR
J=
(7)
2NA
S
where
J is the magnetic polarization (in T);
Φ is the flux integrator reading corrected in accordance with the integrator calibration (in
IR
Wb);
A is the cross sectional area of the test specimen (in m );
s
N is the number of turns of the search coil.
For the magnetic moment method, the magnetic dipole moment shall be calculated using
equation (5):
−1
H
j=Φ ⋅
(5)
IR
I
where
j is the magnetic dipole moment (in Wbm);
Φ is the flux integrator reading corrected in accordance with the integrator calibration (in
IR
Wb);
H/I is the coil constant (magnetic field strength to current ratio) of the moment coil system
(in (A/m)/A).
The magnetic polarization, J, shall then be calculated using equation (2).
If necessary, see Annex A for the calculation of corrections for self-demagnetization. In that
case, the relative magnetic permeability of the test specimen shall be calculated from the
following equation:
– 16 – IEC 60404-15:2012+AMD1:2016 CSV
IEC 2016
J
μ = 1+
r
H
μ
(6)
where
μ is the relative magnetic permeability of the test specimen (ratio);
r
-7
μ is the magnetic constant (4π × 1
...
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