Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti and Nb3Sn composite superconductors

IEC 61788-4:2016 specifies a test method for the determination of the residual resistance ratio (RRR) of Nb-Ti and Nb3Sn composite superconductors with Cu, Cu-Ni, Cu/Cu-Ni and Al matrix. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR value less than 350, and cross-sectional area less than 3 mm2. In the case of Nb3Sn, the specimens have received a reaction heat-treatment. This fourth edition cancels and replaces the third edition published in 2011. This edition constitutes a technical revision.

Supraleitfähigkeit - Teil 4: Messung des Restwiderstandsverhältnisses - Restwiderstandsverhältnis von Nb-Ti und Nb3Sn Verbundsupraleitern

Supraconductivité - Partie 4: Mesurage du rapport de résistance résiduelle - Rapport de résistance résiduelle des composites supraconducteurs de Nb-Ti et de Nb3Sn

L'IEC 61788-4:2016 spécifie une méthode d'essai pour la détermination du rapport de résistance résiduelle (RRR) des composites supraconducteurs de Nb-Ti et de Nb3Sn avec une matrice de Cu, Cu-Ni, Cu/Cu-Ni et Al. Cette méthode est destinée à être utilisée avec des éprouvettes de supraconducteurs présentant une structure monolithique avec une section rectangulaire ou circulaire, un RRR de valeur inférieure à 350 et une surface de section inférieure à 3 mm2. Dans le cas de Nb3Sn, les éprouvettes ont subi un traitement thermique de réaction. Cette quatrième édition annule et remplace la troisième édition parue en 2011. Cette édition constitue une révision technique.

Superprevodnost - 4. del: Meritve razmerja preostale upornosti - Preostala upornost za superprevodnike iz kompozita Nb-Ti in Nb3Sn (IEC 61788-4:2016)

Ta del standarda IEC 61788 opredeljuje preskusno metodo za določanje razmerja preostale upornosti
(RRR) za superprevodnike iz kompozita Nb-Ti in Nb3Sn z matrico Cu, Cu-Ni, Cu/Cu-Ni
in Al. Ta metoda je namenjena za uporabo z vzorci superprevodnikov z monolitno
strukturo s pravokotnim in okroglim prerezom, vrednostjo RRR, manjšo od 350, in prečnim
prerezom, manjšim od 3 mm2. V primeru Nb3Sn so vzorci
toplotno obdelani.

General Information

Status
Published
Publication Date
07-Apr-2016
Technical Committee
Drafting Committee
Current Stage
6060 - Document made available
Due Date
08-Apr-2016
Completion Date
08-Apr-2016

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SLOVENSKI STANDARD
SIST EN 61788-4:2016
01-julij-2016
1DGRPHãþD
SIST EN 61788-4:2011
Superprevodnost - 4. del: Meritve razmerja preostale upornosti - Preostala
upornost za superprevodnike iz kompozita Nb-Ti in Nb3Sn (IEC 61788-4:2016)

Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance

ratio of Nb-Ti and Nb3Sn composite superconductors (IEC 61788-4:2016)
Ta slovenski standard je istoveten z: EN 61788-4:2016
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN 61788-4:2016 en

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

---------------------- Page: 1 ----------------------
SIST EN 61788-4:2016
---------------------- Page: 2 ----------------------
SIST EN 61788-4:2016
EUROPEAN STANDARD EN 61788-4
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2016
ICS 17.200.20; 29.050 Supersedes EN 61788-4:2011
English Version
Superconductivity - Part 4: Residual resistance ratio
measurement - Residual resistance ratio of Nb-Ti and Nb3Sn
composite superconductors
(IEC 61788-4:2016)

Supraconductivité - Partie 4: Mesurage du rapport de Supraleitfähigkeit - Teil 4: Messung des

résistance résiduelle - Rapport de résistance résiduelle des Restwiderstandsverhältnisses - Restwiderstandsverhältnis

composites supraconducteurs de Nb-Ti et de Nb3Sn von Nb-Ti und Nb3Sn Verbundsupraleitern

(IEC 61788-4:2016) (IEC 61788-4:2016)

This European Standard was approved by CENELEC on 2016-02-23. 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 CEN-CENELEC

Management Centre 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 CEN-CENELEC Management Centre 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 61788-4:2016 E
---------------------- Page: 3 ----------------------
SIST EN 61788-4:2016
EN 61788-4:2016
European foreword

The text of document 90/359/FDIS, future edition 4 of IEC 61788-4, prepared by IEC/TC 90

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

EN 61788-4:2016.
The following dates are fixed:
(dop) 2016-11-23
• 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 standards conflicting with (dow) 2019-02-23
the document have to be withdrawn
This document supersedes EN 61788-4:2011.

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 61788-4:2016 was approved by CENELEC as a European

Standard without any modification.
---------------------- Page: 4 ----------------------
SIST EN 61788-4:2016
EN 61788-4:2016
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-815 - International Electrotechnical Vocabulary - -
(IEV) -- Part 815: Superconductivity
---------------------- Page: 5 ----------------------
SIST EN 61788-4:2016
---------------------- Page: 6 ----------------------
SIST EN 61788-4:2016
IEC 61788-4
Edition 4.0 2016-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 4: Residual resistance ratio measurement – Residual resistance ratio of
Nb-Ti and Nb Sn composite superconductors
Supraconductivité –
Partie 4: Mesurage du rapport de résistance résiduelle – Rapport de résistance
résiduelle des composites supraconducteurs de Nb-Ti et de Nb Sn
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20; 29.050 ISBN 978-2-8322-3129-6

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN 61788-4:2016
– 2 – IEC 61788-4:2016 © IEC 2016
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Principle .......................................................................................................................... 8

5 Apparatus ........................................................................................................................ 8

5.1 Material of measurement mandrel or of measurement base plate ............................ 8

5.2 Diameter of the measurement mandrel and length of the measurement base

plate ....................................................................................................................... 8

5.3 Cryostat for the resistance (R ) measurement ......................................................... 9

6 Specimen preparation ...................................................................................................... 9

7 Data acquisition and analysis .......................................................................................... 9

7.1 Resistance (R ) at room temperature ...................................................................... 9

7.2 Resistance (R or R ) just above the superconducting transition ............................ 9

2 2

7.2.1 Correction of strain effect ................................................................................ 9

7.2.2 Data acquisition of cryogenic resistance ........................................................ 10

7.2.3 Optional acquisition methods ......................................................................... 12

7.3 Correction on measured R of Nb-Ti composite superconductor for bending

strain .................................................................................................................... 12

7.4 Residual resistance ratio (RRR) ............................................................................ 12

8 Uncertainty and stability of the test method ................................................................... 12

8.1 Temperature ......................................................................................................... 12

8.2 Voltage measurement ........................................................................................... 12

8.3 Current ................................................................................................................. 13

8.4 Dimension ............................................................................................................. 13

9 Test report ..................................................................................................................... 13

9.1 RRR value ............................................................................................................ 13

9.2 Specimen .............................................................................................................. 13

9.3 Test conditions ..................................................................................................... 14

9.3.1 Measurements of R and R ........................................................................... 14

1 2

9.3.2 Measurement of R ........................................................................................ 14

9.3.3 Measurement of R ........................................................................................ 14

Annex A (informative) Additional information relating to the measurement of RRR ............... 15

A.1 Recommendation on specimen mounting orientation ............................................. 15

A.2 Alternative methods for increasing temperature of specimen above

superconducting transition temperature ................................................................ 15

A.3 Alternative measurement methods of R or R ..................................................... 15

2 2

A.4 Bending strain dependency of RRR for Nb-Ti composite superconductor .............. 18

A.5 Procedure of correction of bending strain effect .................................................... 21

Annex B (informative) Uncertainty considerations ................................................................ 23

B.1 Overview............................................................................................................... 23

B.2 Definitions............................................................................................................. 23

B.3 Consideration of the uncertainty concept .............................................................. 23

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SIST EN 61788-4:2016
IEC 61788-4:2016 © IEC 2016 – 3 –

B.4 Uncertainty evaluation example for TC 90 standards ............................................. 25

Annex C (informative) Uncertainty evaluation in test method of RRR for Nb-Ti and

Nb Sn composite superconductors ....................................................................................... 27

C.1 Evaluation of uncertainty ....................................................................................... 27

C.2 Summary of round robin test of RRR of a Nb-Ti composite superconductor ........... 30

C.3 Reason for large COV value in the intercomparison test on Nb Sn composite

superconductor ..................................................................................................... 31

Bibliography .......................................................................................................................... 32

Figure 1 – Relationship between temperature and resistance.................................................. 8

Figure 2 – Voltage versus temperature curves and definitions of each voltage ...................... 10

Figure A.1 – Definition of voltages ........................................................................................ 17

Figure A.2 – Bending strain dependency of RRR value for pure Cu matrix of Nb-Ti
composite superconductors (comparison between measured values and calculated

values) .................................................................................................................................. 19

Figure A.3 – Bending strain dependency of RRR value for round Cu wires ............................ 19

Figure A.4 – Bending strain dependency of normalized RRR value for round Cu wires .......... 20

Figure A.5 – Bending strain dependency of RRR value for rectangular Cu wires ................... 20

Figure A.6 – Bending strain dependency of normalized RRR value for rectangular Cu

wires ..................................................................................................................................... 21

Figure C.1 – Distribution of observed r of Cu/Nb-Ti composite superconductor ............... 31

RRR

Table A.1 – Minimum diameter of the measurement mandrel for round wires ........................ 21

Table A.2 – Minimum diameter of the measurement mandrel for rectangular wires................ 21

Table B.1 – Output signals from two nominally identical extensometers ................................ 24

Table B.2 – Mean values of two output signals ..................................................................... 24

Table B.3 – Experimental standard deviations of two output signals ...................................... 24

Table B.4 – Standard uncertainties of two output signals ...................................................... 25

Table B.5 – COV values of two output signals ....................................................................... 25

Table C.1 – Uncertainty of each measurement ...................................................................... 30

Table C.2 – Obtained values of R , R and r for three Nb Sn samples ............................ 31

1 2 RRR 3
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SIST EN 61788-4:2016
– 4 – IEC 61788-4:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti and 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 61788-4 has been prepared by IEC technical committee 90:

Superconductivity.

This fourth edition cancels and replaces the third edition published in 2011. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) the unification of similar test methods for residual resistance ratio (RRR) of Nb-Ti and

Nb Sn composite superconductors, the latter of which is described in IEC 61788-11.

---------------------- Page: 10 ----------------------
SIST EN 61788-4:2016
IEC 61788-4:2016 © IEC 2016 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
90/359/FDIS 90/360/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 website under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 11 ----------------------
SIST EN 61788-4:2016
– 6 – IEC 61788-4:2016 © IEC 2016
INTRODUCTION

Copper, Cu/Cu-Ni or aluminium is used as matrix material in Nb-Ti and Nb Sn composite

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 and AC losses 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.

This part of IEC 61788 specifies the test method for residual resistance ratio of Nb-Ti and

Sn composite superconductors. The curve method is employed for the measurement of

the resistance just above the superconducting transition. Other methods are described in A.3.

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SIST EN 61788-4:2016
IEC 61788-4:2016 © IEC 2016 – 7 –
SUPERCONDUCTIVITY –
Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti and Nb Sn
composite superconductors
1 Scope

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

ratio (RRR) of Nb-Ti and Nb Sn composite superconductors with Cu, Cu-Ni, Cu/Cu-Ni and Al

matrix. This method is intended for use with superconductor specimens that have a monolithic

structure with rectangular or round cross-section, RRR value less than 350, and cross-

sectional area less than 3 mm . In the case of Nb Sn, the specimens have received a

reaction heat-treatment.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.

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

(available at: www.electropedia.org)
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

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

transition
Note 1 to entry: This note applies to the French language only.

Note 2 to entry: In this part of IEC 61788 for Nb-Ti and Nb Sn composite superconductors, the room temperature

is defined as 293 K (20 °C), and the residual resistance ratio is obtained in Formula (1), where the resistance (R )

at 293 K is divided by the resistance (R ) just above the superconducting transition.

r = (1)
RRR

Here r is a value of the residual resistance ratio, R is a value of the resistance measured in a strain-free

RRR 2
condition and zero external magnetic field.

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

cryogenic resistance.
---------------------- Page: 13 ----------------------
SIST EN 61788-4:2016
– 8 – IEC 61788-4:2016 © IEC 2016
(b)
(a)
T * T
IEC

The cryogenic resistance, R , is determined by the intersection, A, of two straight lines (a) and (b) at

temperature T .
Figure 1 – Relationship between temperature and resistance
4 Principle

The resistance measurement both at room and cryogenic temperatures shall be performed

with the four-terminal technique. All measurements are done without an applied magnetic field.

The target relative combined standard uncertainty of this method is defined as an expanded

uncertainty (k = 2) not to exceed 5 %.

The maximum bending strain induced during mounting and cooling the Nb-Ti specimen shall

not exceed 2 %. The measurement shall be conducted in a strain-free condition or in a

condition with allowable thermal strain for the Nb Sn specimen.
5 Apparatus
5.1 Material of measurement mandrel or of measurement base plate

Material of the measurement mandrel for a coiled Nb-Ti specimen or of the measurement

base plate for a straight Nb-Ti or Nb Sn 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 polyethylene terephthalate, polyester, polytetrafluoroethylene, etc.)

whose thickness is 0,1 mm or less.
5.2 Diameter of the measurement mandrel and length of the measurement base plate

The diameter of the measurement mandrel shall be large enough to keep the bending strain of

the specimen less than or equal to 2 % for the Nb-Ti specimen. The Nb Sn specimen on a

base plate shall be measured in a strain-free condition or a condition with allowable thermal

strain.
The measurement base plate shall be at least 30 mm long in one dimension.
Resistance
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SIST EN 61788-4:2016
IEC 61788-4:2016 © IEC 2016 – 9 –
5.3 Cryostat for the resistance (R ) measurement

The cryostat shall include a specimen support structure and a liquid helium reservoir for

measurement of the resistance R . The specimen support structure shall allow the specimen,

which is mounted on a measurement mandrel or a measurement base plate, to be lowered

into and raised 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 with a length of 30 mm or longer. The

specimen shall be instrumented with current contacts near each of its ends and a pair of

voltage contacts over its central portion. 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 should be taken during instrumentation

and installation of the specimen on the measurement mandrel or base plate so that no

excessive force, which may cause undesired bending strain or tensile strain, would be applied

to the specimen. Ideally, it is intended that the Nb Sn specimen be as straight as possible;

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

its as received condition.

The specimen shall be mounted on a measurement mandrel or on a measurement base plate

for these measurements. Both resistance measurements, R and R , shall be made on the

1 2
same specimen and the same mounting.
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 K ≤ T ≤ 308 K. A specimen current (I (A)) shall be applied so

m 1
2 2

that 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. Formula (2)

1 1 m
) at room temperature. The resistance (R )
below shall be used to calculate the resistance (R
m 1

at 293 K (20 °C ) shall be calculated using Formula (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 a

1 m,
pure Cu component.
(2)
R =
R = (3)
1+×0,00393 T – 293 
( )
 
7.2 Resistance (R or R ) just above the superconducting transition
2 2
7.2.1 Correction of strain effect

Under a strained condition of the Nb-Ti specimen, the measured cryogenic resistance, R , is

not a correct value for R . The corresponding correction of the strain effect is described in 7.3.

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SIST EN 61788-4:2016
– 10 – IEC 61788-4:2016 © IEC 2016
7.2.2 Data acquisition of cryogenic resistance

The specimen, which is still mounted as it was for the room temperature measurement, shall

be placed in the cryostat for electrical measurement specified in 5.3. Horizontal mounting of

the specimen is recommended in A.1. Alternate cryostats that employ a heating element to

sweep the specimen temperature are described in A.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.

During the acquisition phases of the low-temperature R measurements, a specimen current

2 2

(I ) shall be applied so that the current density is in the range 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 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)
(a)
20+
U U
0rev 20–
U *
IEC

NOTE 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

20+ 20– 0rev

measured at zero current is not shown coincident with U . Straight line (a) is drawn

...

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