IEC 61788-4 2011 pdf free download – Superconductivity – Part 4: Residual resistance ratio measurement – Residual resistance ratio of Nb-Ti composite superconductors.
4Requirements
The resistance measurement both at room and cryogenic temperatures shall be performedwith the four-terminal technique.
The target relative combined standard uncertainty of this method is defined as an expandeduncertainty (k = 2) not to exceed 5 % based on the coefficient of variation (CoV) of 2,5 % inthe intercomparison test (see Clause c.2).
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 astraight specimen shall be copper, aluminium, silver,or the like whose thermal conductivity isequal to or better than 100 Wi(m-K) at liquid helium temperature (4,2 K). The surface of thematerial shall be covered with an insulating layer (tape or a layer made of polyethyleneterephthalate , polyester, polytetrafluoroethylene , 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 thespecimen less than or equal to 2 %.
The measuring base plate shall be at least 30 mm long in one dimension.
5.3Cryostat for the resistance,R, measurement
The cryostat shall include a specimen support structure and a liquid helium reservoir for theresistance，Re,measurement. The specimen support structure shall allow the specimen,which is mounted on a measurement mandrel or a measurement base plate，to be loweredand raised into，and out of, a liquid helium bath. In addition， the specimen support structureshall be made so that a current can flow through the specimen and the resulting voltagegenerated 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 distancebetween two voltage taps (L) shall be 25 mm or longer. A thermometer for measuringcryogenic temperature shall be attached near the specimen.
Some mechanical method shall be used to hold the specimen against the insulated layer ofthe measurement mandrel or base plate. Special care shall be taken during instrumentationand installation of the specimen on the measurement mandrel or on the measurement baseplate 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 anda pair of voltage contacts over a central portion of the specimen. The specimen shall bemounted on a measurement mandrel or on a measurement base plate for these measure-ments.Both resistance measurements，Rand Rg, shall be made on the same specimen andthe same mounting.
7 Data acquisition and analysis
7.1 Resistance(1) at room temperature
The mounted specimen shall be measured at room temperature (Tm(K)), where Tm satisfiesthe following condition,273 ≤ Tm ≤308. A specimen current (l1(A)) shall be applied so thatthe current density is in the range of 0,1 A/mm2 to 1 A/mm2 based on the total wire cross-sectional area, and the resulting voltage(U1 (V)), l and Tm shall be recorded. Equation(2)below shall be used to calculate the resistance (Rm) at room temperature.The resistance(R)at 293 K (20 C) shall be calculated using equation(3) for a wire with Cu matrix.The value ofRshall be set equal to Rm, without any temperature correction, for wires that do not containa pure Cu component.IEC 61788-4 pdf download.