Development of Chinese Standard Type of Rhodium-Iron Resistance Thermometer

Abstract

New rhodium alloy wires with 0.52 % atomic of iron have been drawn, and several batches of RhFe thermometer with strain-free construction and helium-filled platinum capsule have been made using these new alloy wires and old alloy wires which were made in the 1980s in China. In one of the constructions, the coil of wire is inserted into twisted glass tubes, and in the other, it is laid in grooves on a fused-silica crossed frame. The resistance versus temperature relationship and interpolating characteristic of Chinese RhFe thermometer are similar to those of Tinsley 5187U thermometer from 1.5 K to 27 K. The resistance changes of most thermometers are less than that of equivalent to 0.2 mK at 4.5 K after they are exposed to fifty thermal cycles from room temperature to liquid helium temperature. This standard type of rhodium-iron resistance thermometer is now commercially available. Instead of the regular annealing temperature, which is $$750\,^{\circ }$$ C, two batches of RhFe thermometers are made with the annealing temperature of $$850\,^{\circ }$$ C and $$950\,^{\circ }$$ C. The interpolating characteristics of RhFe thermometers will be studied to find new calibration method.