Noise thermometry in crystal growth facilities for the International Space Station (ISS)

Abstract

AbstractAlthough noise thermometry is an established technique for absolute temperature measurement, several aspects needed to be clarified before this method can be employed for temperature measurement in a space furnace at 1800°C. First, the electrical insulation resistance for sheathed sensors with different insulation materials were measured. Five test sensors with outer diameters of 3.2 mm or less were fabricated and tested. The measurements clearly show a significant advantage for the pyrolytic boron nitride (pBN) insulation compared to Hafnium oxide. The electrical insulation resistance values at 1800°C for the sensors with HfO2 were below 10 Ω, whereas pBN‐insulated test sensors exhibited values of more than 600 Ω for the same diameter. Furthermore, no difference has been found between the resistance of bent and straight sensors. Based on these results a miniaturised and bent noise thermometer with a diameter of 3.2 mm having a pBN insulation was fabricated. This sensor and additional control thermocouples were subjected to performance tests up to 1800°C in a space‐compatible furnace. All sensor readings exhibited a consistent figure during the tests. The noise thermometer, however, showed always the highest reading indicating that noise thermometry is an appropriate method for accurate measurements of absolute temperatures, even in the harsh environment of a compact multi‐zone space furnace.