Search

The effect of magnetic fields on the sensitivity of a type E thermocouple made from thin wires of chromel and constantan has been measured from 5 to 115 K in magnetic fields up to 9 T. In general, the field-induced change in sensitivity depends non-monotonically on the field. Above ∼7.4 K the sensitivity changes between 2% and −6% but increases sharply below this temperature even in weak magnetic fields of the order of 0.1 T. Magnetization measurements of the thermocouple elements indicate a ferromagnetic ordering in chromel and constantan at T ≈53 K and ≈19 K, respectively. The magnetization data for constantan suggest a re-entrant spin-glass transition at T ∼10 K.

A magnetic moment sensitivity of 10 −10 A-m 2 is provided with a low-cost apparatus within a temperature range 4.2 to 300 K and a field range 0 to 1 T. Cryogenic subsystem includes a modified transport LHe dewar and removable insert of 45 mm in diameter only. Therefore a special cryostat and LHe refilling are avoided. The dewar capacity yields a 6 days operation and the top-loading insert allows rapid (3 min typical) sample replacement without insert warming. Two Au:Fe/Chromel thermocouples provide sample temperature accuracy of 0.1 K with 0.05 K resolution. The sample is moved with a hydraulic piston driven by a fluid-flow pump. Both manual and personal computer controlled measurements are possible.

Chromel–AuFe0.07% thermocouples are widely used to measure small temperature differences down to liquid-He temperatures. In this work we present the thermopower S of two chromel–AuFe0.07% thermocouples over an extended temperature range from 1.5 K to 200 K in magnetic fields up to 7 T. For low temperatures T

This paper discusses some serious discrepancies which arose between temperature measurements, as determined by calibrated, commercial temperature sensors, during the course of experiments designed to calibrate some locally-fabricated gold/chromel thermocouples. The three commercially-calibrated sensors were: a platinum resistor, a germanium resistor; and a silicon diode. The most serious discrepancies which occurred were between the results employing the silicon diode calibration, and the results from any of the other calibrations. We comment upon the procedures employed to achieve a reasonably self-consistent temperature calibration, and the suitability of the properties of gold/chromel thermocouples, for measurements over an extended range of cryogenic temperatures.

The Au-0.03at% Fe/Chrornel P thermocouple was calibrated between 1 and 300 K to monitor the temperature of freely vibrating specimens in measurements of elastic energy dissipation. In the intermediate temperature range (50–23 K) the calibration points were obtained by means of a miniature sealed cell containing oxygen, which gave three fixed points: the O 2 triple point, 54.3610 K; the β-γ transition, 43.802 K; and the α-β transition, 23.873 K.