IEC 61788-4:2011 pdf free download – superconductivity
5.3Cryostat for the resistance，R2,measurement
The cryostat shall include a specimen support structure and a liquid helium reservoir for theresistance，R2,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 R, shall be made on the same specimen andthe same mounting.
7.2.2 The specimen shall be slowly lowered into the liquid helium bath and cooled to liquidhelium temperature over a time period of at least 5 min.
7.2.3 During the acquisition phases of the low-temperature Rg*measurements, a specimencurrent (2) shall be applied so that the current density is in the range of 0,1 A/mm2 to10 A/mm2 based on the total wire cross-sectional area, and the resulting voltage (U(V)), 12(A),and specimen temperature (T (K)) shall be recorded. In order to keep the ratio of signal tonoise high enough，the measurement shall be carried out under the condition that theabsolute value of the resulting voltage above the superconducting transition exceeds 10 uV.An illustration of the data to be acquired and its analysis is shown in Figure 2.
7.2.6 The specimen voltage versus temperature curve shall be acquired with the rate oftemperature 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 thetransition into the normal state，up to a temperature somewhat less than 15 K. Then，thespecimen current shall be decreased to zero and the corresponding voltage，U20.,shall berecorded at a temperature below 15 K.
7.2.8 The specimen shall then be slowly lowered into the liquid helium bath and cooled tothe same temperature，within ±1 K, where the initial voltage signal u.was recorded.Aspecimen current，l2，with the same magnitude but negative polarity (polarity opposite thatused for the initial curve) shall be applied and the voltage uo- shail be recorded at thistemperature. The procedural steps 7.2.5 to 7.2.7 shall be repeated to record the voltageversus temperature curve with this negative current. In addition, the recording of U2o- shall bemade at the same temperature,within±1 K, where U20+ was recorded.