Study On The Preparation And Performance Of The T Type Thin-film Thermocouple

In pneumatic system, the transient temperatures are of great importance on theaccuracy control and measurement. As a kind of new temperature sensors, with thetypical two-dimension structure, thin-film thermocouples have the characteristics ofsmall heat capacity and short response time, which can satisfy the requirement ofreal-time temperature measurement. The air temperature ranges from-50℃-200℃inpneumatic system and T type (Cu/CuNi) thermocouples have the characteristics ofhigh precision, high stability and good linearity in low and medium temperaturemeasurement. Therefore, T type (Cu/CuNi) thin-film thermocouples were selected asthe test objects in this paper, and the subsequent studies were carried out onpreparation process, static and dynamic performances of the thermocouples.First of all, the preparation method of Cu/CuNi thin-film thermocouples bymagnetic sputtering was studied. Then, measurement and test on the microstructure,thickness, adhesive strength and electrical resistivity of Cu and CuNi thin films wouldbe carried out through SEM, Talystep, scratch test and four-point probe. Based on thetest results, the optimal preparation process was identified; deposition rate and criticalthickness of the thin films were also gained. Except that, the preparation and platingprocesses of SiO2barrier layer were studied, and through controlling the sputteringtime, a series of Cu/CuNi thin-film thermocouples with different thicknesses of0.5μm,1.0μm,1.5μm and2.0μm were fabricated.In addition, the static performance of Cu/CuNi thin-film thermocouples wasstudied theoretically and experimentally. Node method was adopted to static-calibratethe Cu/CuNi thin-film thermocouples with different thicknesses, and the sensitivities(thermoelectricity power ratio) obtained were respectively as46.49μV/℃,45.23μV/℃,44.32μV/℃and43.94μV/℃; based on electron-transportation theoryand size effect of metal thin film, the relationship between sensitivities and filmthicknesses of the thermocouples was deducted as that, when the film thickness islarger than the critical size, the sensitivity of thin-film thermocouple will increasewith the reciprocal of film thickness. The theoretical and static-calibrated resultscoincide, which provides a feasible approach to improve the static performance ofthin-film thermocouples.Finally, another study of dynamic performance of Cu/CuNi thin-filmthermocouples was carried out on theoretical analysis and calibration experiment. The charge and discharge temperatures were parameters to be measured; anone-dimension unsteady heat transfer model based on convection was established; thesimulation on the step temperature response of Cu/CuNi thin-film thermocouples wasimplemented according to the model; by the method of quick throwing, dynamiccalibration was made on the thermocouple with node thickness of1.0μm. Simulationand test results both showed that thin-film thermocouples were approximate toone-order inertial system, so time constant could reflect the dynamic characteristic.Theoretical and test results of time constant were very close, respectively as4.28msand7.89ms, from which the reliability of heat transfer model established could beexamined. The heat transfer model accords with the real temperature measurementand lays the theoretical foundation for the further research on dynamic characteristicenhancement of thin-film thermocouples.