SIST EN 61788-3:2007
(Main)Superconductivity -- Part 3: Critical current measurement - DC critical current of Ag- and/or Ag alloy-sheathed Bi-2212 and Bi-2223 oxide superconductors
Superconductivity -- Part 3: Critical current measurement - DC critical current of Ag- and/or Ag alloy-sheathed Bi-2212 and Bi-2223 oxide superconductors
This part of IEC 61788 covers a test method for the determination of the dc critical current of short and straight Ag- and/or Ag alloy-sheathed Bi-2212 and Bi-2223 oxide superconductors that have a monolithic structure and a shape of round wire or flat or square tape containing mono- or multicores of oxides. This method is intended for use with superconductors that have critical currents less than 500 A and n-values larger than 5. The test is carried out with and without an applying external magnetic field. For all tests in a magnetic field, the magnetic field is perpendicular to the length of the specimen. In the test of a tape specimen in a magnetic field, the magnetic field is parallel or perpendicular to the wider tape surface (or one surface if square). The test specimen is immersed either in a liquid helium bath or a liquid nitrogen bath during testing. Deviations from this test method that are allowed for routine tests and other specific restrictions are given in this standard.
Supraleitfähigkeit --Teil 3: Messen des kritischen Stromes - Kritischer Strom (Gleichstrom) von Ag- und/oder Ag-Legierung ummantelten oxidischen Bi-2212 und Bi-2223-Supraleitern
Supraconductivité -- Partie 3 : Mesure du courant critique - Courant critique continu des oxydes supraconducteurs Bi-2212 et Bi-2223 avec gaine Ag et/ou en alliage d'Ag
Superprevodnost - 3. del: Meritve kritičnega toka - Enosmerni kritični tok pri Bi-2212 in Bi-2223 oksidnih superprevodnikih, oklopljenih z Ag in/ali zlitinami Ag (IEC 61788-3:2006)
General Information
Relations
Standards Content (Sample)
SLOVENSKI SIST EN 61788-3:2007
STANDARD
januar 2007
Superprevodnost - 3. del: Meritve kritičnega toka - Enosmerni kritični tok pri
Bi-2212 in Bi-2223 oksidnih superprevodnikih, oklopljenih z Ag in/ali zlitinami
Ag (IEC 61788-3:2006)
(istoveten EN 61788-3:2006)
Superconductivity - Part 3: Critical current measurement - DC critical current of Ag-
and/or Ag alloy-sheathed Bi-2212 and Bi-2223 oxide superconductors (IEC 61788-
3:2006)
ICS 17.220.20; 29.050 Referenčna številka
SIST EN 61788-3:2007(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
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EUROPEAN STANDARD
EN 61788-3
NORME EUROPÉENNE
August 2006
EUROPÄISCHE NORM
ICS 17.220; 29.050 Supersedes EN 61788-3:2001
English version
Superconductivity
Part 3: Critical current measurement -
DC critical current of Ag- and/or Ag alloy-sheathed
Bi-2212 and Bi-2223 oxide superconductors
(IEC 61788-3:2006)
Supraconductivité Supraleitfähigkeit
Partie 3: Mesure du courant critique - Teil 3: Messen des kritischen Stromes -
Courant critique continu des oxydes Kritischer Strom (Gleichstrom) von
supraconducteurs Bi-2212 et Bi-2223 Ag- und/oder Ag-Legierung ummantelten
avec gaine Ag et/ou en alliage d'Ag oxidischen Bi-2212 und
(CEI 61788-3:2006) Bi-2223-Supraleitern
(IEC 61788-3:2006)
This European Standard was approved by CENELEC on 2006-06-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61788-3:2006 E
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EN 61788-3:2006 - 2 -
Foreword
The text of document 90/184/FDIS, future edition 2 of IEC 61788-3, prepared by IEC TC 90,
Superconductivity, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61788-3 on 2006-06-01.
This European Standard supersedes EN 61788-3:2001.
Modifications made to EN 61788-3:2001 mostly involve wording and essentially include no technical
changes.
Examples of technical changes introduced include the voltage lead diameter being smaller than 0,21 mm
and the mode of expression for magnetic field accuracy being ± 1 % and ± 0,02 T instead of 1 %. The
expression for magnetic field precision has been changed in the same way.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-03-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-06-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61788-3:2006 was approved by CENELEC as a European
Standard without any modification.
__________
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- 3 - EN 61788-3:2006
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application 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.
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year
IEC 60050-815 2000 International Electrotechnical Vocabulary - -
(IEV)
Part 815: Superconductivity
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INTERNATIONAL IEC
STANDARD 61788-3
Second edition
2006-04
Superconductivity –
Part 3:
Critical current measurement –
DC critical current of Ag- and/or Ag alloy-sheathed
Bi-2212 and Bi-2223 oxide superconductors
IEC 2006 Copyright - all rights reserved
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 the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale T
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
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– 2 – 61788-3 IEC:2006(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Normative reference .6
3 Terms and definitions .6
4 Principle .8
5 Requirements .8
6 Apparatus.8
7 Specimen preparation.9
8 Measurement procedure.10
9 Precision and accuracy of the test method.11
10 Calculation of results .12
11 Test report.13
Annex A (informative) Additional information relating to Clauses 1 to 10 .15
Annex B (informative) Magnetic hysteresis of the critical current of high-temperature
oxide superconductors.21
Bibliography.23
Figure 1 – Intrinsic U-I characteristic .14
Figure 2 – U-I characteristic with a current transfer component.14
Figure A.1 – Illustration of a measurement configuration for a short specimen of a few
hundred A class conductors .20
Figure A.2 – Illustration of superconductor simulator circuit .20
Table A.1 – Thermal expansion data of Bi-oxide superconductor and selected materials .19
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61788-3 IEC:2006(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
__________
SUPERCONDUCTIVITY –
Part 3: Critical current measurement –
DC critical current of Ag- and/or Ag alloy-sheathed
Bi-2212 and Bi-2223 oxide superconductors
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment
declared to be in conformity with an IEC Publication.
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.
International Standard IEC 61788-3 has been prepared by IEC technical committee 90:
Superconductivity.
This second edition cancels and replaces the first edition published in 2000. Modifications made
to the second version mostly involve wording and essentially include no technical changes.
Examples of technical changes introduced include the voltage lead diameter being smaller than
0,21 mm and the mode of expression for magnetic field accuracy being ±1 % and ±0,02 T
instead of 1 %. The expression for magnetic field precision has been changed in the same way.
The text of this standard is based on the following documents:
FDIS Report on voting
90/184/FDIS 90/190/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.
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– 4 – 61788-3 IEC:2006(E)
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 61788 consists of the following parts, under the general title Superconductivity:
Part 1: Critical current measurement – DC critical current of Cu/Nb-Ti composite super-
conductors
Part 2: Critical current measurement – DC critical current of Nb Sn composite super-
3
conductors
Part 3: Critical current measurement – DC critical current of Ag- and/or Ag alloy-sheathed
Bi-2212 and Bi-2223 oxide superconductors
Part 4: Residual resistance ratio measurement – Residual resistance ratio of Nb-Ti
composite superconductors
Part 5: Matrix to superconductor volume ratio measurement – Copper to superconductor
volume ratio of Cu/Nb-Ti composite superconductors
Part 6: Mechanical properties measurement – Room temperature tensile test of Cu/Nb-Ti
composite superconductors
Part 7: Electronic characteristic measurements – Surface resistance of superconductors at
microwave frequencies
Part 8: AC loss measurements – Total AC loss measurement of Cu/Nb-Ti composite
superconducting wires exposed to a transverse alternating magnetic field by a pickup
coil method
Part 9: Measurements for bulk high temperature superconductors – Trapped flux density of
large grain oxide superconductors
Part 10: Critical temperature measurement – Critical temperature of Nb-Ti, Nb Sn, and
3
Bi-system oxide composite superconductors by a resistance method
Part 11: Residual resistance ratio measurement – Residual resistance ratio of Nb Sn
3
composite superconductors
Part 12: Matrix to superconductor volume ratio measurement – Copper to non-copper volume
ratio of Nb Sn composite superconducting wires
3
Part 13: AC loss measurements – Magnetometer methods for hysteresis loss in Cu/Nb-Ti
multifilamentary composites
The committee has decided that the contents of this publication will remain unchanged until the
maintenance result 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.
A bilingual version of this publication may be issued at a later date.
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61788-3 IEC:2006(E) – 5 –
INTRODUCTION
In 1986 J.G. Bednorz and K.A. Mueller discovered that some Perovskite type Cu-containing
oxides show superconductivity at temperatures far above those which metallic superconductors
have shown. Since then, extensive R & D work on high-temperature oxide superconductors has
been and is being made worldwide, and its application to high-field magnet machines, low-loss
)
1
power transmission, electronics and many other technologies is in progress [1].
Fabrication technology is essential to the application of high-temperature oxide super-
conductors. Among high-temperature oxide superconductors developed so far, BiSrCaCu oxide
(Bi-2212 and Bi-2223) superconductors have been the most successful at being fabricated into
wires and tapes of practical length and superconducting properties. These conductors can be
wound into a magnet to generate a magnetic field of several tesla [2]. It has also been shown
that Bi-2212 and Bi-2223 conductors can substantially raise the limit of magnetic field
generation by a superconducting magnet [3].
In summer 1993, VAMAS-TWA16 started working on the test methods of critical currents in
Bi-oxide superconductors. In September 1997, the TWA16 worked out a guideline (VAMAS
guideline) on the critical current measurement method for Ag-sheathed Bi-2212 and Bi-2223
oxide superconductors. This pre-standardization work of VAMAS was taken as the base for the
IEC standard, described in the present document, on the dc critical current test method of
Ag-sheathed Bi-2212 and Bi-2223 oxide superconductors.
The test method covered in this International Standard is intended to give an appropriate and
agreeable technical base to those engineers working in the field of superconductivity
technology.
The critical current of composite superconductors like Ag-sheathed Bi-oxide superconductors
depends on many variables. These variables need to be considered in both the testing and the
application of these materials. Test conditions such as magnetic field, temperature and relative
orientation of the specimen and magnetic field are determined by the particular application. The
test configuration may be determined by the particular conductor through certain tolerances.
The specific critical current criterion may be determined by the particular application. It may be
appropriate to measure a number of test specimens if there are irregularities in testing.
––––––––––––––
)
1
The numbers in brackets refer to the bibliography.
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SUPERCONDUCTIVITY –
Part 3: Critical current measurement –
DC critical current of Ag- and/or Ag alloy-sheathed
Bi-2212 and Bi-2223 oxide superconductors
1 Scope
This part of IEC 61788 covers a test method for the determination of the dc critical current of
short and straight Ag- and/or Ag alloy-sheathed Bi-2212 and Bi-2223 oxide superconductors
that have a monolithic structure and a shape of round wire or flat or square tape containing
mono- or multicores of oxides.
This method is intended for use with superconductors that have critical currents less than 500 A
and n-values larger than 5. The test is carried out with and without an applying external magnetic
field. For all tests in a magnetic field, the magnetic field is perpendicular to the length of the
specimen. In the test of a tape specimen in a magnetic field, the magnetic field is parallel or
perpendicular to the wider tape surface (or one surface if square). The test specimen is
immersed either in a liquid helium bath or a liquid nitrogen bath during testing. Deviations from
this test method that are allowed for routine tests and other specific restrictions are given in this
standard.
2 Normative reference
The following referenced document is indispensable for the application 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 60050-815:2000, International Electrotechnical Vocabulary (IEV) – Part 815: Super-
conductivity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-815, several of
which have been repeated her for convenience, and the following apply.
3.1
critical current
I
c
maximum direct current that can be regarded as flowing without resistance
NOTE I is a function of magnetic field strength and temperature.
c
[IEV 815-03-01]
3.2
critical current criterion
I criterion
c
criterion to determine the critical current, I , based on the electric field strength, E or the
c
resistivity, ρ
-13
NOTE 1 E = 10 µV/m or E = 100 µV/m is often used as the electric field strength criterion, and ρ = 10 Ω·m or
-14
ρ = 10 Ω ·m is often used as the resistivity criterion.
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61788-3 IEC:2006(E) – 7 –
NOTE 2 For short high temperature oxide superconductor specimens, less sensitive criteria than those shown in
Note 1 are sometimes used.
[IEV 815-03-02, modified]
3.3
n-value (of a superconductor)
exponent obtained in a specific range of electric field strength or resistivity when the
n
voltage/current U-I curve is approximated by the equation U ∝ I
n
NOTE In the case for high temperature oxide superconductors, the equation U ∝ I does not hold in a wide range of U.
[IEV 815-03-10, modified]
3.4
quench
uncontrollable and irreversible transition of a superconductor or a superconducting device from
the superconducting state to the normal conducting state
NOTE A term usually applied to superconducting magnets.
[IEV 815-03-11]
3.5
Lorentz force (on fluxons)
force applied to fluxons by a current
NOTE 1 The force per unit volume is given by J x B, where J is a current density, and B is a magnetic flux density.
NOTE 2 "Lorentz force" is defined in IEV 121-11-20.
[IEV 815-03-16]
3.6
current transfer (of composite superconductor)
phenomenon that a dc current transfers spatially from filament to filament in a composite
superconductor, resulting in a voltage generation along the conductor
NOTE In the I measurement, this phenomenon appears typically near the current contacts where the injected
c
current flows along the conductor from periphery to inside until uniform distribution among filaments is accomplished.
3.7
constant sweep rate method
a U-I data acquisition method where a current is swept at a constant rate from zero to a current
above I while continuously or frequently and periodically acquiring U-I data
c
3.8
ramp-and-hold method
a U-I data acquisition method where a current is ramped to a number of appropriately distributed
points along the U-I curve and held constant at each one of these points while acquiring a
number of voltages and current readings
3.9
Bi-2212 and Bi-2223 oxide superconductors
oxide superconductors with layered structure containing CuO sheets and chemical formulae,
2
Bi Sr CaCu O ( x = ~ 8) and (Bi,Pb) Sr Ca Cu O ( x = ~10 ), respectively
2 2 2 x 2 2 2 3 x
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– 8 – 61788-3 IEC:2006(E)
4 Principle
The critical current of a composite superconductor is determined from a voltage (U) - current (I)
characteristic measured at a certain value of a static applied magnetic field strength (magnetic
field) and at a specified temperature in a liquid cryogen bath at a constant pressure. To get a U-I
characteristic, a direct current is applied to the superconductor specimen and the voltage
generated along a section of the specimen is measured. The current is increased from zero and
the U-I characteristic generated is recorded. The critical current is determined as the current at
which a specific electric field strength criterion (electric field criterion) (E ) or resistivity criterion
c
(ρ ) is reached. For either E or ρ , there is a corresponding voltage criterion (U ) for a specified
c c c c
voltage tap separation.
5 Requirements
The target precision of this method is a coefficient of variation (standard deviation divided by the
average of the critical current determinations) that is less than 5 % for the measurement at 0 T
and near 4,2 K or 77 K.
The use of a common current transfer correction is excluded from this test method. Furthermore,
if a current transfer signature is pronounced in the measurement, then the measurement shall be
considered invalid.
It is the responsibility of the user of this standard to consult and establish appropriate safety and
health practices and to determine the applicability of regulatory limitations prior to use. Specific
precautionary statements are given below.
Hazards exist in this type of measurement. Very large direct currents with very low voltages do
not necessarily provide a direct personal hazard, but accidental shorting of the leads with
another conductor, such as tools or transfer lines, can release significant amounts of energy and
cause arcs or burns. It is imperative to isolate and protect current leads from shorting. Also the
energy stored in the superconducting magnets commonly used for the background magnetic
field can cause similar large current and/or voltage pulses or deposit large amounts of thermal
energy in the cryogenic systems, causing rapid boil-off or even explosive conditions. Under
rapid boil-off conditions, cryogens can create oxygen-deficient conditions in the immediate area
and additional ventilation may be necessary. The use of cryogenic liquids is essential to cool the
superconductors to allow the transition into the superconducting state. Direct contact of skin
with cold liquid transfer lines, storage Dewars or apparatus components can cause immediate
freezing, as can direct contact with a spilled cryogen. If improperly used, liquid helium storage
Dewars can freeze air or water in pressure vent lines and cause the Dewar to over-pressurize
and fail despite the common safety devices. It is imperative that safety precautions for handling
cryogenic liquids be observed.
6 Apparatus
6.1 Measurement holder material
The measurement holder shall be made from an insulating material or from a conductive
non-ferromagnetic material that is either covered or not covered with an insulating layer.
The critical current may inevitably depend on the measurement holder material due to the strain
induced by the differential thermal contraction between the specimen and the measurement
holder.
The total strain induced in the specimen at the measuring temperature shall be minimized to be
within ±0,1 %. If there is an excess strain due to the differential thermal contraction of the
specimen and the holder, the critical current shall be noted to be determined under an excess
strain state by identification of the holder material.
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61788-3 IEC:2006(E) – 9 –
Suitable measurement holder materials are recommended in A.3.1. Any one of these may be
used.
When a conductive material is used without an insulating layer, the leakage current through the
holder shall be less than 1 % of the total current when the specimen current is at I (see 9.5).
c
6.2 Measurement holder construction
The holder shall have a flat surface on which a straight specimen can be placed.
The current contact shall be rigidly fastened to the measurement holder to avoid stress
concentration in the region of transition between the holder and the current contact. It is
important to have no difference in level between the mounting surfaces of the current contacts
and the specimen holder.
6.3 Measurement set up
The apparatus to measure the U-I characteristic of the superconductor specimen consists of a
specimen probe, a test cryostat, a magnet system and a U-I measurement system.
The specimen probe, which consists of a specimen, a measurement holder and a specimen
support structure, is inserted in the test cryostat filled with liquid cryogen. In some cases the
cryostat contains a superconducting solenoid magnet and its support structure to apply a
magnetic field to the specimen. The U-I measurement system consists of a dc current source, a
recorder and necessary preamplifiers, filters or voltmeters, or a combination thereof.
A computer assisted data acquisition system is also allowed.
7 Specimen preparation
7.1 Reaction heat treatment
Reaction heat treatment shall be carried out according to the manufacturer's specification which
includes reaction temperature, period and atmosphere, oxygen partial pressure, specimen
warming and cooling rates, specimen protection method against mechanical strain, examination
of deformation and surface condition of specimen and error limits which shall not be exceeded.
Temperature variations within the furnace shall be controlled such as not to exceed those limits.
Reaction heat treatment can be skipped when it has already been carried out by the
manufacturer.
7.2 Specimen mounting for measurement
After the reaction heat treatment, the ends of the specimen shall be trimmed to suit the
measurement holder.
When using resistivity criteria for the critical current determination, the total cross-sectional area
S of the specimen shall be determined to an accuracy of 5 %.
The specimen shall be mounted to the flat surface of the holder and both ends shall be soldered
to the current contact blocks (see Clause A.5 for solder material).
For the test in magnetic fields, a low-temperature adhesive (such as epoxy) shall be used to
bond the specimen to the measurement holder to reduce specimen motion against the Lorentz
force.
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– 10 – 61788-3 IEC:2006(E)
For a tape specimen, the bond shall be strong enough to keep the specimen in place against the
Lorentz force, in the case where the applied magnetic field is perpendicular to the specimen
surface.
The length of a specimen to be measured shall be defined as follows:
L = 2 × L + L + 2 × L ≥ 5 × W (1)
1 2 3
L , L, L ≥ W (2)
2 3
where
L is the distance between the voltage taps;
L is the length of a specimen to be measured;
1
L is the length of the soldered part of the current contact;
2
L is the shortest distance from a current contact to a voltage tap;
3
W is the width or diameter of a specimen to be measured.
For a specimen with a large current-carrying capacity, narrow tape, or round wire, L
...
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