Superconductivity - Part 11: Residual resistance ratio measurement - Residual resistance ratio of Nb3Sn composite superconductors

IEC 61788-11:2011 covers a test method for the determination of the residual resistance ratio (RRR) of Nb3Sn composite superconductors. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR less than 350 and cross-sectional area less than 3 mm2, and have received a reaction heat-treatment. Ideally, it is intended that the specimens be as straight as possible; however, this is not always the case, thus care must be taken to measure the specimen in its as received condition. 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.3. This second edition cancels and replaces the first edition published in 2003. It constitutes a technical revision. The main revisions are the addition of two new annexes, 'Uncertainty considerations' (Annex B) and 'Uncertainty evaluation in test method of RRR for Nb3Sn' (Annex C).

Supraleitfähigkeit - Teil 11: Messung des Restwiderstandsverhältnisses - Restwiderstandsverhältnis von Nb3Sn-Verbundsupraleitern

Supraconductivité - Partie 11: Mesure du rapport de résistance résiduelle - Rapport de résistance résiduelle des supraconducteurs composites de Nb3Sn

La CEI 61788-11:2011 spécifie une méthode d'essai pour la détermination du rapport de résistance résiduelle (RRR) des supraconducteurs composites de Nb3Sn. Cette méthode est destinée à être utilisée avec des éprouvettes de supraconducteurs présentant une structure monolithique avec une section rectangulaire ou circulaire, un rapport RRR inférieur à 350 et une surface de section inférieure à 3 mm2, et qui ont reçu un traitement thermique de réaction. Dans l'absolu, il est prévu que les éprouvettes soient aussi droites que possible; cependant, ce n'est pas toujours le cas, c'est pourquoi il faut s'assurer que la mesure est effectuée sur des éprouvettes en l'état de livraison. Toutes les mesures sont effectuées sans appliquer de champ magnétique. La méthode décrite dans le corps de texte de la présente norme est la méthode de 'référence' et des méthodes d'acquisition facultatives sont présentées à l'Article A.3. Cette deuxième édition annule et remplace la première édition parue en 2003, dont elle constitue une révision technique. Les principales révisions sont l'ajout de deux nouvelles annexes, 'Considérations relatives à l'incertitude' (Annexe B) et 'Evaluation de l'incertitude de la méthode d'essai de RRR de Nb3Sn' (Annexe C).

Superprevodnost - 11. del: Meritve razmerja preostale upornosti - Preostala upornost za superprevodnike iz kompozita Nb3Sn

Ta del IEC 61788 zajema preskusno metodo za določevanje razmerja preostale upornosti (RRR) za superprevodnike iz kompozita Nb3Sn. Ta metoda je namenjena uporabi z vzorci superprevodnikov, ki imajo monolitno strukturo s pravokotnim ali okroglim prečnim prerezom, RRR manj kot 350 in prerezom manj kot 3 mm2 ter so bili reakcijsko toplotno obdelani. V idealnem primeru naj bi bili vzorci čim bolj ravni, ker pa ni vedno tako, je treba paziti, da se vzorec izmeri v dobljenem stanju. Vse meritve se izvajajo brez vnesenega magnetnega polja. Metoda, opisana v glavnem delu tega standarda, je »referenčna« metoda, izbirne metode so navedene v točki A.3.

General Information

Status
Withdrawn
Publication Date
25-Aug-2011
Technical Committee
Drafting Committee
Parallel Committee
Current Stage
9960 - Withdrawal effective - Withdrawal
Completion Date
11-Jan-2017

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SLOVENSKI STANDARD
SIST EN 61788-11:2011
01-oktober-2011
Superprevodnost - 11. del: Meritve razmerja preostale upornosti - Preostala
upornost za superprevodnike iz kompozita Nb3Sn

Superconductivity - Part 11: Residual resistance ratio measurment - Residual resistance

ratio of Nb3Sn composite superconductors

Supraconductivité - Partie 11: Mesures de résistance résiduelle - Rapport de résistance

résiduelle des supraconducteurs composites de Nb3Sn
Ta slovenski standard je istoveten z: EN 61788-11:2011
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN 61788-11:2011 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 61788-11:2011
---------------------- Page: 2 ----------------------
SIST EN 61788-11:2011
EUROPEAN STANDARD
EN 61788-11
NORME EUROPÉENNE
August 2011
EUROPÄISCHE NORM
ICS 17.220; 29.050 Supersedes EN 61788-11:2003
English version
Superconductivity -
Part 11: Residual resistance ratio measurement -
Residual resistance ratio of Nb Sn composite superconductors
(IEC 61788-11:2011)
Supraconductivité - Supraleitfähigkeit -
Partie 11: Mesure du rapport de Teil 11: Messung des
résistance résiduelle - Restwiderstandsverhältnisses -
Rapport de résistance résiduelle des Restwiderstandsverhältnis von Nb Sn-
supraconducteurs composites de Nb Sn Verbundsupraleitern
(CEI 61788-11:2011) (IEC 61788-11:2011)

This European Standard was approved by CENELEC on 2011-08-15. 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, Croatia, 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
Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61788-11:2011 E
---------------------- Page: 3 ----------------------
SIST EN 61788-11:2011
EN 61788-11:2011 - 2 -
Foreword

The text of document 90/268/FDIS, future edition 2 of IEC 61788-11, prepared by IEC TC 90,

Superconductivity was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN 61788-11:2011.
The following dates are fixed:
(dop) 2012-05-15
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2014-08-15
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61788-11:2003.

The main revisions are the addition of two new annexes "Uncertainty considerations" (Annex B) and

"Uncertainty evaluation in test method of RRR for Nb Sn" (Annex C).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent

rights.
Endorsement notice

The text of the International Standard IEC 61788-11:2011 was approved by CENELEC as a European

Standard without any modification.
---------------------- Page: 4 ----------------------
SIST EN 61788-11:2011
- 3 - EN 61788-11:2011
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 - International Electrotechnical Vocabulary - -
(IEV) -
Part 815: Superconductivity
---------------------- Page: 5 ----------------------
SIST EN 61788-11:2011
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SIST EN 61788-11:2011
IEC 61788-11
Edition 2.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Superconductivity –
Part 11: Residual resistance ratio measurement – Residual resistance ratio of
Nb Sn composite superconductors
Supraconductivité –
Partie 11: Mesure du rapport de résistance résiduelle – Rapport de résistance
résiduelle des supraconducteurs composites de Nb Sn
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.220; 29.050 ISBN 978-2-88912-581-4
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN 61788-11:2011
– 2 – 61788-11  IEC:2011
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope ............................................................................................................................... 6

2 Normative references ....................................................................................................... 6

3 Terms and definitions ....................................................................................................... 6

4 Requirements ................................................................................................................... 7

5 Apparatus ......................................................................................................................... 7

5.1 Material of measuring base plate ............................................................................. 7

5.2 Length of the measuring base plate ......................................................................... 7

5.3 Cryostat for the resistance, R , measurement ......................................................... 7

6 Specimen preparation....................................................................................................... 8

7 Data acquisition and analysis .......................................................................................... 8

7.1 Resistance (R ) at room temperature ...................................................................... 8

7.2 Resistance (R ) just above the superconducting transition ...................................... 8

7.3 Residual resistance ratio (RRR) ............................................................................ 10

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 ............................................................................................................. 11

9 Test report...................................................................................................................... 11

9.1 RRR value ............................................................................................................. 11

9.2 Specimen .............................................................................................................. 11

9.3 Test conditions ...................................................................................................... 12

Annex A (informative) Additional information relating to the measurement of RRR ............... 13

Annex B (informative) Uncertainty considerations ................................................................ 15

Annex C (informative) Uncertainty evaluation in test method of RRR for Nb Sn ................... 19

Figure 1 – Relationship between temperature and resistance ............................................... 7

Figure 2 – Voltage (U) versus temperature (T) curves and definitions of each voltage ........... 9

Table B.1 – Output signals from two nominally identical extensometers ................................ 16

Table B.2 – Mean values of two output signals ..................................................................... 16

Table B.3 – Experimental standard deviations of two output signals...................................... 16

Table B.4 – Standard uncertainties of two output signals ...................................................... 17

Table B.5 – Coefficient of variations of two output signals..................................................... 17

Table C.1 – Uncertainty of each measurement ...................................................................... 20

Table C.2 – Obtained values of R , R and RRR for three Nb Sn samples............................ 21

1 2 3
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SIST EN 61788-11:2011
61788-11  IEC:2011 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 11: Residual resistance ratio measurement –
Residual resistance ratio of Nb Sn 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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61788-11 has been prepared by IEC Technical Committee 90:

Superconductivity.

This second edition cancels and replaces the first edition published in 2003. It constitutes a

technical revision. The main revisions are the addition of two new annexes, "Uncertainty

considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for Nb Sn"

(Annex C).
---------------------- Page: 9 ----------------------
SIST EN 61788-11:2011
– 4 – 61788-11  IEC:2011
The text of this standard is based on the following documents:
FDIS Report on voting
90/268/FDIS 90/279/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.

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 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.
---------------------- Page: 10 ----------------------
SIST EN 61788-11:2011
61788-11  IEC:2011 – 5 –
INTRODUCTION

Copper or aluminium is used as stabilizer material in multifilamentary Nb Sn superconductors

and works as an electrical shunt when the superconductivity is interrupted. It also contributes

to recovery of the superconductivity by conducting the heat generated in the superconductor

to the surrounding coolant. The resistivity of copper used in the composite superconductor in

the cryogenic temperature region 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 for the residual resistance ratio of Nb Sn

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.3.
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SIST EN 61788-11:2011
– 6 – 61788-11  IEC:2011
SUPERCONDUCTIVITY –
Part 11: Residual resistance ratio measurement –
Residual resistance ratio of Nb Sn composite superconductors
1 Scope

This part of IEC 61788 covers a test method for the determination of the residual resistance

ratio (RRR) of Nb Sn composite superconductors. This method is intended for use with

superconductor specimens that have a monolithic structure with rectangular or round cross-

section, RRR less than 350 and cross-sectional area less than 3 mm , and have received a

reaction heat-treatment. Ideally, it is intended that the specimens be as straight as possible;

however, this is not always the case, thus care must be taken to measure the specimen in its

as received condition. 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.3.
2 Normative references

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.

IEC 60050-815, International Electrotechnical Vocabulary – Part 815: Superconductivity

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050-815 and the

following apply.
3.1
residual resistance ratio
RRR

the ratio of resistance at room temperature to the resistance just above the superconducting

transition

NOTE In this standard for Nb Sn composite superconductors, the room temperature is defined as 293°K (20°C),

and the residual resistance ratio is obtained in Equation (1) below, where the resistance (R ) at 293°K is divided

by the resistance (R ) just above the superconducting transition.
RRR = (1)

Figure 1 shows schematically a resistance versus temperature curve acquired on a specimen while measuring

cryogenic resistance. Draw a line in Figure 1 where the resistance sharply increases (a), and draw also a line in

Figure 1 where the resistance increases gradually (b) with temperature. The value of resistance at the intersection

of these two lines at T=T *, A, is defined as resistance (R ) just above the superconducting transition.

c 2
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SIST EN 61788-11:2011
61788-11  IEC:2011 – 7 –
(b)
(a)
Temperature
T *
IEC 1603/11
Temperature T * is that at the intersection point.
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 defined as an expanded

uncertainty (k = 2) not to exceed 10°% based on the coefficient of variation (COV) of 5°% in

the intercomparison test (see Clause C.2).
5 Apparatus
5.1 Material of measuring base plate

Material of the measuring base plate shall be copper, aluminum, 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 polyethylene terephthalate, polyester, polytetrafluoroethylene, etc.) whose thickness

is 0,1°mm or less.
5.2 Length of the measuring base plate
The measuring base plate shall be at least 30°mm long in one dimension.
5.3 Cryostat for the resistance, R , measurement

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,

which is mounted on 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

Resistance
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SIST EN 61788-11:2011
– 8 – 61788-11  IEC:2011

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 base plate. Special care shall be taken during instrumentation and

installation of the specimen on the measurement base plate so that no excessive force, which

may cause undesired bending strain or tensile strain, shall be 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 base plate for these measurements. Both resistance measure-

ments, R and R , shall be made on the same specimen and the same mounting.
1 2
7 Data acquisition and analysis
7.1 Resistance (R ) at room temperature

The mounted specimen shall be measured at room temperature (T (K)), where T satisfies

m m

the following condition 273 ≤ T ≤ 308. A specimen current (I (A)) shall be applied so that

m 1
2 2

the 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.

1 1 m

Equation°(2) below shall be used to calculate the resistance (R ) at room temperature. The

resistance (R ) at 293 K shall be calculated using equation (3) for a wire with Cu stabilizer.

The value of R shall be set equal to R , without any temperature correction, for wires that do

1 m
not contain a pure Cu component.
R = (2)
R = (3)
[1+ 0,00393⋅ (T − 293)]
7.2 Resistance (R ) just above the superconducting transition

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.

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

current (I ) shall be applied so that the current density is in the range of 0,1°A/mm to

10 A/mm based on the total wire cross-sectional area and the resulting voltage (U(V)), I (A),

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

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SIST EN 61788-11:2011
61788-11  IEC:2011 – 9 –

absolute value of 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.
(b)
(a)
20+
20–
0rev
2– IEC 1604/11

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 . Voltages U * and U * with asterisk are those at the intersection points.

2+ 2-
Figure 2 – Voltage (U) versus temperature (T) curves
and definitions of each voltage

7.2.4 When the specimen is in superconducting state and test current (I ) is applied, two

voltages shall be measured nearly simultaneously: U (the initial voltage recorded with a

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

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+ 0rev
< 1 % (4)
where U is the average voltage for the specimen in the normal state at cryogenic
temperature, which is defined in 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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SIST EN 61788-11:2011
– 10 – 61788-11  IEC:2011

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 into the normal state, up to a temperature somewhat less than 25 K. Then, the

specimen current shall be decreased to zero and the corresponding voltage, U , shall be

20+
recorded at a temperature below 25 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

specimen current, I , with the same magnitude but negative polarity (polarity opposite that

used for the initial curve) shall be applied and the voltage U shall be recorded at this

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 voltages 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 raised gradually and almost linearly with temperature increase.

U * and U * in Figure 2 shall be determined at the intersection of these two lines for the

2+ 2–
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
| U −U |
2+ 2
U = (5)

7.2.11 A valid R measurement requires that the shift of thermoelectric voltage be within

acceptable limits during the measurements of the U and U . Thus, the following condition

2+ 2–
shall be met for a valid measurement,
|∆ −∆ |
+ −
< 3 % (6)
where ∆ and ∆ are defined as ∆ = U – U and ∆ = 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

superconducting transition.
R = (7)
7.3 Residual resistance ratio (RRR)
The RRR shall be calculated using Equation°(1).
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SIST EN 61788-11:2011
61788-11  IEC:2011 – 11 –
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°K,

while holding the specimen, which is mounted 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

When the current is directly applied to the specimen with a programmable DC current source,

the specimen test current shall be determined with a standard uncertainty not to exceed

0,3°%.

When the specimen test current is determined from a voltage-current characteristic of a

standard resistor by the four-terminal technique, the standard resistor, with a relative

combined standard uncertainty not to exceed 0,3°%, shall be used .

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.
8.4 Dimension

The distance along the specimen between the two voltage taps, (L), shall be determined with

a relative combined standard uncertainty not to exceed 5°%.
9 Test report
9.1 RRR value
The obtained RRR value shall be reported as
RRR(1±U ) (n = ∙∙∙ ), (8)

where U = 2u (k = 2) is the expanded relative uncertainty with u denoting the uncertainty, k

re r r

is a coverage factor and n is the sampling number. It is desired that n be larger than 4 so that

the normal distribution can be assumed for the estimation of the standard deviation. If n is not

sufficiently large, a square distribution shall be assumed. In case of n = 1 the analytic method

described in Annex C shall be used with b/R = 1,46 × 10 estimated from the
intercomparison test.
9.2 Specimen

The test report for the result of the measurements shall also include the following items, if

known:
a) manufac
...

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