The Variation of Seebeck Voltage in Type E Thermocouple under Magnetic Field

• Main Authors: Pei-Chi Chang, 張珮琦
• Other Authors: Yung- Kang Kuo
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/87071519218043215612

碩士 === 國立東華大學 === 應用物理研究所 === 98 === In this thesis, the Seebeck voltages of E-type thermocouples (Constantan-Chromal) have been successfully calibrated under applied magnetic fields at low temperatures (T £ 35 K). The possible mechanisms of the field-induced variations in the Seebeck voltages are discussed. It is found that under applied magnetic field, the Seebeck voltages of E-type thermocouples show a significant variation, particularly at low temperatures (T < 10 K). The magneto- Seebeck voltage, defined as DV(H,T)/V(0,T), is found to be negative for temperatures below 10 K. However, DV(H,T)/V(0,T) is positive for temperatures above 10 K. A clear trend found in DV(H,T)/V(0,T) is that its absolute value gradually decreases with increasing temperature, and becomes negligible while the temperature is increased above 35 K. In the low temperature range, a peak feature in DV(H,T)/V(0,T) under weak magnetic fields was observed, being consistent with previously reported results in the literature. We argue that the observed phenomenon is presumably related to the transition from ferromagnetic state to spin glass state that occurs in Constantan at low T. Finally, we have fitted the calibrated DV(H,T)/V(0,T) results for E-type thermocouples, and the obtained fitting parameters were incorporated to LabVIEW to perform data acquisition and data processing. With such an effort, the field-dependent of various thermal properties on materials can be precisely measured.