Extension wire system for thin film ceramic thermocouples

Metallic wire thermocouples and thin film thermocouples, often require the use of a wire of the same composition but less expensive to extend the signal to the data acquisition system. Ceramic thin film thermocouples exhibit thermoelectric powers that are an order of magnitude larger than metal-based thermocouples. Their extremely low thermal mass coupled with a profile that is well below the boundary layer thickness makes these sensors ideal for aerospace applications. However, ceramic film thermocouples are somewhat limited in that the voltage signals collected at room temperature using common data acquisition systems would be altered by the introduction of a third thermocouple junction at some intermediate temperature when using traditional extension wires. This leads to unwanted voltages that can affect calibration and lead to considerable error in temperature measurement. Since extension wire for thin film ceramic thermocouples does not currently exist, an extension wire system was developed specifically for ceramic thermoelements based on alloys of indium-tin- oxide. We describe the methodology used to develop an extension wire for ceramic thin film thermocouples based on Cu-Ni alloys and the optimal compositions of Cu-Ni alloys that yield a zero emf when coupled to indium-tin-oxide reference electrodes. The requirements for an extension wire system for ceramic thermocouples are also described within the paper.