SIST EN 61788-4:2008

Superconductivity -- Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors

This part of IEC 61788 covers a test method for the determination of the residual resistance ratio (RRR) of a composite superconductor comprised of Nb-Ti filaments and Cu, Cu-Ni or Cu/Cu-Ni matrix. This method is intended for use with superconductors that have a monolithic structure with rectangular or round cross-section, RRR less than 350, and cross-sectional area less than 3 mm2. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.4.

Supraleitfähigkeit -- Teil 4: Messungen des Restwiderstandsverhältnisses - Restwiderstandsverhältnis von Nb-Ti-Verbundsupraleitern

Supraconductivité -- Partie 4: Mesure de la résistivité résiduelle - Taux de résistivité résiduelle des supraconducteurs composites au Nb-Ti

Superprevodnost - 4. del: Meritve razmerja preostale upornosti - Preostala upornost za superprevodnike iz kompozita Nb-Ti (IEC 61788-4:2007)

General Information

• Status: Withdrawn
• Publication Date: 22-Nov-2007
• Withdrawal Date: 18-Aug-2014
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: I09 - Imaginarni 09
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 13-Aug-2014
• Due Date: 05-Sep-2014
• Completion Date: 19-Aug-2014
• Ref Project: EN 61788-4:2007 - Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors

Relations

• Replaces: SIST EN 61788-4:2002 - Superconductivity -- Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors
• Effective Date: 01-Jul-2010
• Replaced By: SIST EN 61788-4:2011 - Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors
• Effective Date: 29-Jan-2023
• Revised: SIST EN 61788-4:2011 - Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors
• Effective Date: 06-May-2014
• Revised: SIST EN 61788-4:2011 - Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors
• Effective Date: 25-Jan-2010
• Replaces: SIST EN 61788-4:2002 - Superconductivity -- Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors
• Effective Date: 29-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 61788-4:2008
01-januar-2008
1DGRPHãþD
SIST EN 61788-4:2002
Superprevodnost - 4. del: Meritve razmerja preostale upornosti - Preostala
upornost za superprevodnike iz kompozita Nb-Ti (IEC 61788-4:2007)
Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance
ratio of Nb-Ti composite superconductors
Supraleitfähigkeit - Teil 4: Messungen des Restwiderstandsverhältnisses –
Restwiderstandsverhältnis von Nb-Ti-Verbundsupraleitern
Supraconductivité - Partie 4: Mesure de la résistivité résiduelle - Taux de résistivité
résiduelle des supraconducteurs composites au Nb-Ti
Ta slovenski standard je istoveten z: EN 61788-4:2007
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN 61788-4:2008 en,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

EUROPEAN STANDARD
EN 61788-4

NORME EUROPÉENNE
July 2007
EUROPÄISCHE NORM

ICS 17.220.20; 29.050 Supersedes EN 61788-4:2001


English version


Superconductivity -
Part 4: Residual resistance ratio measurement -
Residual resistance ratio of Nb-Ti composite superconductors
(IEC 61788-4:2007)


Supraconductivité -  Supraleitfähigkeit -
Partie 4: Mesure Teil 4: Messungen
de la résistivité résiduelle - des Restwiderstandsverhältnisses –
Taux de résistivité résiduelle Restwiderstandsverhältnis
des supraconducteurs composites von Nb-Ti-Verbundsupraleitern
au Nb-Ti (IEC 61788-4:2007)
(CEI 61788-4:2007)




This European Standard was approved by CENELEC on 2007-07-01. 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, Bulgaria, 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


© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61788-4:2007 E

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EN 61788-4:2007 - 2 -
Foreword
The text of document 90/203/FDIS, future edition 2 of IEC 61788-4, prepared by IEC TC 90,
Superconductivity, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61788-4 on 2007-07-01.
This European Standard supersedes EN 61788-4:2001.
The main revisions are the replacement of "accuracy" by "uncertainty" and a change in Figure 1, where
the relationship between temperature and voltage is changed to the relationship between temperature
and resistance.
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) 2008-04-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-07-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61788-4:2007 was approved by CENELEC as a European
Standard without any modification.
__________

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- 3 - EN 61788-4:2007

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
1)
IEC 60050-815 - International Electrotechnical Vocabulary - -
(IEV) -
Part 815: Superconductivity





1)
Undated reference.

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INTERNATIONAL IEC


STANDARD 61788-4





Second edition
2007-04


Superconductivity –
Part 4:
Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti
composite superconductors
PRICE CODE
Commission Electrotechnique Internationale T
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

---------------------- Page: 5 ----------------------

– 2 – 61788-4 © IEC:2007(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5

1 Scope.6
2 Normative references .6
3 Terms and definition.6
4 Requirements .7
5 Apparatus.7
5.1 Material of measuring mandrel or of measuring base plate .7
5.2 Diameter of the measuring mandrel and length of the measuring base plate.7
5.3 Cryostat for the resistance, R , measurement .8
2
6 Specimen preparation.8
7 Data acquisition and analysis .8
7.1 Resistance (R ) at room temperature .8
1
7.2 Resistance (R *) just above the superconducting transition.8
2
7.3 Correction on measured R * for bending strain.11
2
7.4 Residual resistance ratio (RRR) .11
8 Uncertainty and stability of the test method .11
8.1 Temperature.11
8.2 Voltage measurement.11
8.3 Current.11
8.4 Dimension .12
9 Test report.12
9.1 RRR value.12
9.2 Specimen .12
9.3 Test conditions.12
9.3.1 Report of test conditions.12
9.3.2 Report of R .13
1
9.3.3 Report of R .13
2

14
Annex A (informative) Additional information relating to the measurement of RRR .
Annex B (informative) Statistical definitions .22

Figure 1 – Relationship between temperature and resistance .7
Figure 2 – Voltage versus temperature curves and definitions of each voltage.9
Figure A.1 – Bending strain dependency of RRR for pure Cu matrix of Nb-Ti composite
superconductors (comparison between measured values and calculated values) .15
Figure A.2 – Bending strain dependency of RRR for round Cu wires .15
Figure A.3 – Bending strain dependency of normalized RRR for round Cu wires .16
Figure A.4 – Bending strain dependency of RRR for rectangular Cu wires .16
Figure A.5 – Bending strain dependency of normalized RRR for rectangular Cu wires .17
Figure A.6 – Distribution of observed RRR of Cu/Nb-Ti composite superconductor .19
Figure A.7 – Definition of voltages .20

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61788-4 © IEC:2007(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________

SUPERCONDUCTIVITY –

Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti composite 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 61788-4 has been prepared by IEC technical committee 90:
Superconductivity.
This second edition cancels and replaces the first edition published in 2001. It constitutes a
technical revision. The main revisions are the replacement of “accuracy” by “uncertainty” and
a change in Figure 1, where the relationship between temperature and voltage is changed to
the relationship between temperature and resistance.
The text of this standard is based on the following documents:
FDIS Report on voting
90/203/FDIS 90/205/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 – 61788-4 © IEC:2007(E)
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61788 series, published under the general title Superconductivity,
can be found on the IEC website.
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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61788-4 © IEC:2007(E) – 5 –
INTRODUCTION
Copper is used as a matrix material in multifilamentary superconductors and works as an
electrical shunt when the superconductivity is interrupted. It also contributes to recovery of
the superconductivity by conducting heat generated in the superconductor to the surrounding
coolant. The cryogenic-temperature resistivity of copper is an important quantity, which
influences the stability of the superconductor. The residual resistance ratio is defined as a
ratio of the resistance of the superconductor at room temperature to that just above the
superconducting transition.
In this International Standard, the test method of residual resistance ratio of Nb-Ti composite
superconductors is described. The curve method is employed for the measurement of the
resistance just above the superconducting transition. Other methods are described in
Clause A.4.

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– 6 – 61788-4 © IEC:2007(E)
SUPERCONDUCTIVITY –

Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti composite superconductors



1 Scope
This part of IEC 61788 covers a test method for the determination of the residual resistance
ratio (RRR) of a composite superconductor comprised of Nb-Ti filaments and Cu, Cu-Ni or
Cu/Cu-Ni matrix. This method is intended for use with superconductors that have a monolithic
structure with rectangular or round cross-section, RRR less than 350, and cross-sectional
2
area less than 3 mm . All measurements are done without an applied magnetic field.
The method described in the body of this standard is the “reference” method and optional
acquisition methods are outlined in Clause A.4.
2 Normative references
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, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity
3 Terms and definition
For the purpose of this document, the terms and definitions given in IEC 60050-815 and the
following apply.
residual resistance ratio
RRR
the ratio of resistance at room temperature to the resistance just above the superconducting
transition.
In this standard for Nb-Ti composite superconductors, the room temperature is defined as
20 °C, and the residual resistance ratio is obtained in equation (1) below where the resistance
(R ) at 20 °C is divided by the resistance (R ) just above the superconducting transition.
1 2
R
1
RRR = (1)
R
2
Figure 1 shows schematically a resistance versus temperature curve acquired on a specimen
while measuring the cryogenic resistance. Draw a line in Figure 1 where the resistance
sharply increases (a), and draw also a line in Figure 1 where the temperature increases but
the resistance remains almost the same (b). The value of resistance at the intersection of
these two lines, A, is defined as resistance (R ) just above the superconducting transition.
2

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61788-4 © IEC:2007(E) – 7 –

Resistance
(b)
A
R
2
(a)
0
T
T*
c
IEC  970/01

Figure 1 – Relationship between temperature and resistance

4 Requirements
The resistance measurement both at room and cryogenic temperatures shall be performed
with the four-terminal technique.
The target relative combined standard uncertainty of this method is that the coefficient of
variation (COV) in the intercomparison test shall be 5 % or less.
The maximum bending strain, induced during mounting the specimen, shall not exceed 2 %.
5 Apparatus
5.1 Material of measuring mandrel or of measuring base plate
Material of the measuring mandrel for a coiled specimen or of the measuring base plate for a
straight specimen shall be copper, aluminium, silver, or the like whose thermal conductivity is
equal to or better than 100 W/(m⋅K) at liquid helium temperature (4,2 K). The surface of the
material shall be covered with an insulating layer (tape or a layer made of mylar, polyester,
teflon, etc.) whose thickness is 0,1 mm or less.
5.2 Diameter of the measuring mandrel and length of the measuring base plate
Diameter of the measuring mandrel shall be large enough to keep bending strain of the
specimen less than or equal to 2 %.
The measuring base plate shall be at least 30 mm long in one dimension.

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– 8 – 61788-4 © IEC:2007(E)
5.3 Cryostat for the resistance, R , measurement
2
The cryostat shall include a specimen support structure and a liquid helium reservoir for the
resistance, R , measurement. The specimen support structure shall allow the specimen,
2
which is mounted on a measurement mandrel or a measurement base plate, to be lowered
and raised into, and out of, a liquid helium bath. In addition, the specimen support structure
shall be made so that a current can flow through the specimen and the resulting voltage
generated along the specimen can be measured.
6 Specimen preparation
The test specimen shall have no joints or splices, and shall be 30 mm or longer. The distance
between two voltage taps (L) shall be 25 mm or longer. A thermometer for measuring
cryogenic temperature shall be attached near the specimen.
Some mechanical method shall be used to hold the specimen against the insulated layer of
the measurement mandrel or base plate. Special care shall be taken during instrumentation
and installation of the specimen on the measurement mandrel or on the measurement base
plate so that there is no excessive force, which may cause undesired bending strain or tensile
strain, being applied to the specimen.
The specimen shall be instrumented with current contacts near each end of the specimen and
a pair of voltage contacts over a central portion of the specimen. The specimen shall be
mounted on a measurement mandrel or on a measurement base plate for these measure-
ments. Both resistance measurements, R and R , shall be made on the same specimen and
1 2
the same mounting.
7 Data acquisition and analysis
7.1 Resistance (R ) at room temperature
1
T (°C)), where T satisfies
The mounted specimen shall be measured at room temperature (
m m
the following condition, 0 ≤ T ≤ 35. A specimen current (I (A)) shall be applied so that the
m 1
2 2
current density is in the range of 0,1 A/mm to 1 A/mm based on the total wire cross-
sectional area, and the resulting voltage (U (V)), I and T shall be recorded. Equation (2)
1 1 m
below shall be used to calculate the resistance (R ) at room temperature. The resistance (R )
m 1
at 20 °C (293 K) shall be calculated using equation (3) for a wire with Cu matrix. The value of
R shall be set equal to R , without any temperature correction, for wires that do not contain
1 m
a pure Cu component.
U
1
R = (2)
m
I
1
R
m
R = (3)
1
[]1 + 0,00393 × ()T – 20
m

7.2 Resistance (R *) just above the superconducting transition
2
Under a strained condition of the specimen, the measured cryogenic resistance, R *, is not a
2
correct value for R . The corresponding correction of the strain effect will be described in 7.3.
2
7.2.1 The specimen, which is still mounted as it was for the room temperature measurement,
shall be placed in the cryostat for electrical measurement specified under 5.3. Alternate
cryostats that employ a heating element to sweep the specimen temperature are described in
Clause A.2.

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61788-4 © IEC:2007(E) – 9 –
7.2.2 The specimen shall be slowly lowered into the liquid helium bath and cooled to liquid
helium temperature over a time period of at least 5 min.
7.2.3 During the acquisition phases of the low-temperature R * measurements, a specimen
2
2
current (I ) shall be applied so that the current density is in the range of 0,1 A/mm to
2
2
10 A/mm based on the total wire cross-sectional area, and the resulting voltage (U(V)), I (A),
2
and specimen temperature (T (K)) shall be recorded. In order to keep the ratio of signal to
noise high enough, the measurement shall be carried out under the condition that the
absolute value of the resulting voltage above the superconducting transition exceeds 10 μV.
An illustration of the data to be acquired and its analysis is shown in Figure 2.
U
(b)
U*
2+
A
(a)
U
0+
U
20+
U
20–
U
0rev
0
T
U
0–
U*
2–
IEC  971/01

Voltages with subscripts + and – are those obtained in the first and second measurements under positive and
negative currents, respectively, and U and U are those obtained at zero current. For clarity, U is not
20+ 20– 0rev
shown coincident with U .
0–
Figure 2 – Voltage versus temperature curves and definitions of each voltage
7.2.4 When the specimen is in superconducting state and test current (I ) is applied, two
2
voltages shall be measured nearly simultaneously, U (the initial voltage recorded with a
0+
positive current polarity) and U (the voltage recorded during a brief change in applied
0rev
current polarity). A valid R * measurement requires that excessive interfering voltages are not
2
present and that the specimen is initially in the superconducting state. Thus, the following
condition shall be met for a valid measurement:
U − U
0+ 0 rev
< 1 % (4)
U
2
where U is the average voltage for the specimen in the normal state at cryogenic
2
temperature, which is defined at 7.2.10.
7.2.5 The specimen shall be gradually warmed so that it changes to the normal state
completely. When the cryostat for the resistance measurement specified under 5.3 is used,
this can be achieved simply by raising the specimen to an appropriate position above the
liquid helium level.

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– 10 – 61788-4 © IEC:2007(E)
7.2.6 The specimen voltage versus temperature curve shall be acquired with the rate of
temperature increase maintained between 0,1 K/min and 10 K/min.
7.2.7 The voltage versus temperature curve shall continue to be recorded during the
transition and into the normal state, up to a temperature somewhat less than 15 K. Then the
specimen current shall be decreased to zero and the corresponding voltage, U , shall be
20+
recorded at a temperature below 15 K.
7.2.8 The specimen shall then be slowly lowered into the liquid helium bath and cooled to
the same temperature, within ±1 K, where the initial voltage signal U was recorded. A
0+
specimen current, I , with the same magnitude but negative polarity (polarity opposite that
2
used for the initial curve) shall be applied and the voltage U shall be recorded at this
0–
temperature. The procedural steps 7.2.5 to 7.2.7 shall be repeated to record the voltage
versus temperature curve with this negative current. In addition, the recording of U shall be
20–
made at the same temperature, within ±1 K, where U was recorded.
20+
7.2.9 Each of the two voltage versus temperature curves shall be analyzed by drawing a line
(a) through the data where the absolute value of voltage sharply increases with temperature
(see Figure 2) and drawing a second line (b) through the data above the transition where the
voltage is nearly constant with temperature. U * and U * shall be determined at the
2+ 2–
intersection of these two lines for the positive and negative polarity curves respectively.
7.2.10 The corrected voltages, U and U , shall be calculated using the following
2+ 2–
equations, U = U *– U and U = U *– U . The average voltage, U ,⎯shall be defined
2+ 2+ 0+ 2– 2– 0– 2
as
| U − U |
2 + 2
−
U =   (5)
2
2
7.2.11 A valid R * measurement requires that the shift of thermoelectric voltage be within
2
acceptable limits during the measurements of the U and U . Thus, the following condition
2+ 2–
shall be met for a valid measurement,
| Δ − Δ |
+ −
< 3% (6)
U
2
where Δ and Δ are defined as Δ = U – U and Δ = U – U . If the R * measurement
+ – + 20+ 0+ – 20– 0– 2
does not meet the validity requirements in 7.2.4 and this subclause, then improvement steps
either in hardware or experimental operation shall be taken to meet these requirements
before results are reported.
7.2.12 Equation (7) shall be used to calculate the measured resistance (R *) just above the
2
superconducting transition.
U
2
*
R =  (7)
2
I
2

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61788-4 © IEC:2007(E) – 11 –
7.3 Correction on measured R * for bending strain
2
If there is no pure Cu component in the superconductor, then R shall be set equal to R *.
2 2
For a specimen with a pure Cu component, the bending strain shall be defined by
ε = 100 × (h/r) (%), where h is a half of the specimen thickness and r is the bending radius. If
b
the bending strain is less than 0,3 %, then no correction is necessary, and R shall be set
2
equal to R *.
2
If neither of the above two situations applies, then the resistance R just above the
2
superconducting transition under the strain-free condition shall be estimated by
L
*
R = R − Δ ρ × (8)
2
2
S
Cu
where Δρ is defined below and S and L are defined in 8.4. The increase in the resistivity of
Cu
pure copper at 4,2 K due to tensile strain, ε(%), is expressed by
–12 –14 2;
Δρ (Ωm) = 6,24 × 10 ε − 5,11 × 10 ε ε ≤ 2 % (9)
The calculation of equation (9) shall be carried out assuming that the equivalent tensile strain
ε is (1/2) ε and (4/3π) ε for rectangular and round wires, respectively. The bending strain
b b
dependency of residual resistance ratio for pure copper is described in A.1.
7.4 Residual resistance ratio (RRR)
The RRR shall be calculated using Equation (1).
8 Uncertainty and stability of the test method
8.1 Temperature
The room temperature shall be determined with a standard uncertainty not to exceed 0,6 °C,
while holding the specimen, which is mounted on the measuring mandrel or on the measuring
base plate, at room temperature.
8.2 Voltage measurement
For the resistance measurement, the voltage signal shall be measured with a relative
standard uncertainty not to exceed 0,5 %.
8.3 Current
The specimen test current shall be determined from a voltage-current characteristic of a
standard resistor by the four-terminal technique.
A four-terminal standard resistor, with a relative combined standard uncertainty not to exceed
0,3 %, shall be used to determine the specimen test current.
The fluctuation of d.c. specimen test current, provided by a d.c. power supply, shall be less
than 0,5 % during every resistance measurement.

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– 12 – 61788-4 © IEC:2007(E)
8.4 Dimension
The d
...