Intercomparison of measurements on permanent magnets

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Industrial research and development

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
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ISSN 1018-5593
Commission of the European Communities
ber information
APPLIED METROLOGY
INTERCOMPARISON OF MEASUREMENTS
ON PERMANENT MAGNETS
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Commission of the European Communities
bcr information
APPLIED METROLOGY
INTERCOMPARISON OF MEASUREMENTS
ON PERMANENT MAGNETS
J. SIEVERTO, H. AHLERSO, J. LÜDKE(1)
L PARETIO, M. SOLZIO
(') Physikalisch­Technische Bundesanstalt
Bundesallee 100
D­3300 Braunschweig
(') Istituto Maspec
Via Chiavari 18
1­43100 Parma
Contract No 3336/1/0/143/89/11­BCR­D (30)
SYNTHESIS REPORT
tiduoe^ Λ^.ΡΟ t
Directorate­General
PARU EUROP, Biblioih. Science, Research and Development
1993 N.CËUR 15036 EN
01. Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General XIII
Telecommunications, Information Market and Exploitation of Research
L-2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of the Commission is responsible for the use which might be made of the following information
Catalogue number: CD-NA-15036-EN-C
ECSC — EEC — EAEC, Brussels · Luxembourg, 1993 III
Summary:
This report presents the results of a European intercom­
parison of measurements on permanent magnetic materials.
According to a decision taken at a meeting of experts in
Brussels in January 1989, the project consisted of two parts,
namely
(A) measurements on cylindrical specimens of AlNiCo and
NdFeB in a closed magnetic circuit corresponding to the
method described in IEC pubi. 404­5, and
(Β) measurements on spherical specimens of NdFeB in an
open magnetic circuit using vibrating sample or SQUID
magnetometers.
A total of 24 laboratories took part in the intercomparison.
Besides the AlNiCo and NdFeB specimens circulated for the
measurements, nickel reference s were circulated for
calibration purposes. For reasons of time and because of the
brittleness of the NdFeB specimens, it was not possible to
have one set of specimens passed through all laboratories.
Groups of two laboratories each received one set of speci­
mens, and the connections between the specimen sets had to be
made by means of the measurements made in the reference
laboratories, the Physikalisch­Technische Bundesanstalt,
Braunschweig, and the Istituto MASPEC, Parma.
The results of the intercomparisons are complex, but in
general it can be said that the agreement obtained was quite
good. The comparison between the two parts of the intercom­
parison using closed (A) and open (B) magnetic circuits for
the measurements, is restricted to the NdFeB material because
the AlNiCo specimens were not included in part B. The
difference between the Br results is relatively small,
whereas the differences in Hc, HcB and (BH)max results are
considerable which can be interpreted in the light of aging
of the NdFeB specimens due to the preparation process. CONTENTS
page
1. GENERAL 1
PART A: MEASUREMENTS IN A CLOSED MAGNETIC CIRCUIT 3
2. INTRODUCTION 3
3. CLOSED MAGNETIC CIRCUIT PRINCIPLE 3
4. PARTICIPANTS AND SETUPS INVOLVED 4
5. CIRCULATED SPECIMENS 8
5.1 Origin and properties
5.2 Calibration procedure using nickel 9
reference specimens
6. CONDITIONS AND PARAMETERS OF THE INTERCOMPARISON 13
6.1 Handling of specimens 14
6.2 Measurands and magnetizing conditions 1
6.3 Treatment of uncertainties5
7. REFERENCE LABORATORY MEASUREMENTS 17
7.1 Method of measurement
7.2 Results 18
7.3 Statistical considerations, uncertainties 21
8. RESULTS AND DISCUSSION 24
PART B: MEASUREMENTS IN AN OPEN MAGNETIC CIRCUIT ' 41
9. INTRODUCTION 41
10. OPEN MAGNETIC CIRCUIT PRINCIPLES 42 VI
page
11. PARTICIPANTS AND SETUPS INVOLVED 42
12. CIRCULATED SPECIMENS 45
12.1 Preparation and properties of NdFeB specimens 4
12.2 The calibration procedure using nickel
reference specimens8
13. CONDITIONS AND PARAMETERS OF THE INTERCOMPARISON 49
13.1 Handling of specimens 49
13.2 Measurands and magnetizing conditions 4
13.3 Treatment of uncertainties 51
14. REFERENCE LABORATORY MEASUREMENTS
14.1 Preliminary measurements
14.2 Statistical analysis5
14.3 Calibration 56
14.4 Measurements and results
15. RESULTS AND DISCUSSION 60
PART C: COMPARISON OF CLOSED- AND OPEN-CIRCUIT 69
MEASUREMENTS
16. COMPARISON AND DISCUSSION 69
17. CONCLUSIONS 70
References1 1. GENERAL
Following a proposal of the Physikalisch-Technische Bundes­
anstalt (PTB), Braunschweig, the Bureau of References (BCR)
invited European experts to participate in a meeting on
January 11th 1989 in Brussels in order to discuss a project
concerning an intercomparison of measurements on permanent
magnets. These materials play an increasingly important role
in modern technology, and are widely used in particular in
automobiles, household appliances and tools. Due to their
high density of energy new permanent magnets such as NdFeB
allow the volume of magnets to be decreased.
The experts indicated that there is an urgent need for such
an intercomparison. There are two main categories of measure­
ment methods applying to the problem we refer to, namely the
closed and the open magnetic circuit concept for magnetizing
the specimen and measuring it. The closed magnetic circuit
includes an electro-magnet between the poles of which the
specimen is arranged deliberately without any air gap. This
method is standardized in many countries and also as an IEC
standard /l/. The open magnetic circuit methods are usually
more sensitive, require smaller specimens and are therefore
mainly used in experimental labs. The specimen shape must
basically be of a rotational symmetry with reference to the
axis of the external field.
It was decided to include both closed circuit and open
circuit measurements in the intercomparison. The PTB was to
organize the two intercomparisons and to carry out the closed
circuit reference measurements. The measurements in an open t were to be made by the Istituto MASPEC, Parma. The
cylindrical specimens for the closed circuit were to be
supplied by Swift Magnets, UK, and Krupp Widia, Germany. Of
these specimens, a few were to be used by MASPEC to prepare
the smaller spherical specimens for the open circuit
measurements. The project was started in March 1990 and was completed,
after a prolongation due to delays resulting from problems
in some laboratories and postal delays, by the end of June
1992. Including the reporting laboratories, there were 20
laboratories participating in the closed circuit and 12 s participating in the open circuit audit, eight
of which took part in both exercises.
The following synthesis report includes information about the
conditions and all the results of the audit. During a meeting
of the participants held in October 1992 in Brussels, the
provisional issue of this report was discussed. This final
report includes the results of this discussion.