A Weldless Approach for Thermocouple Fabrication Through Direct Ink Writing Technique

Thermocouples are abundantly used for temperature measurement in various applications because of their availability and reliability. In this research two different materials, carbon a semiconductor and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), an organic conductive polymer with silver as a common electrode were used to fabricate thermocouples through a weldless direct ink writing technique. Two different lengths were chosen for thermocouples to validate the effect of change in length on the performance of thermocouples. Each of the printed thermocouples is characterized and the sensitivity of thermocouples also known as the Seebeck coefficient are determined in a temperature range of up to 140°C. The Seebeck coefficients are found to be 16.6-17 μV/°C for PEDOT:PSS/Silver thermocouples and 15-17.8 μV/°C for carbon/silver thermocouples. These values are comparable to the recently reported numbers for the combination of the said materials. Furthermore, it was found that the Seebeck coefficient is not only material dependent but also influenced by the electrical properties of the printed thermocouples. Each type of printed thermocouple exhibits a stable and linear response towards the temperature change and is comparable to commercially available K-type thermocouple, however, the Seebeck coefficient reported is low when compared to K-type thermocouples due to material differences. Another key finding is the quick response and recovery time of the printed thermocouples as compared to sheath K-type thermocouples.