Research of transient temperature measuring based on thin-film thermocouple and Wi-Fi wireless DAQ method

Abstract

The thin-film thermocouple temperature sensor is a new type of temperature sensor which was emerged with the development of thin-film materials. It features on a small heat capacity and a rapid response speed for transient temperature measurement on the surface of objects. The existing temperature data acquisition systems for filamentary thermocouples do not yet meet the conditions for distortion-free measurement of transient temperature signals in terms of sampling frequency and transmission rate. In addition, it is less flexible in terms of data transmission methods, while the cold end of the thermocouple compensation method has not yet compensated for the non-linear phenomenon of thermocouples, which affects the final measurement accuracy. This paper devised a wireless temperature data acquisition system for K-type thin-film thermocouples using a Wi-Fi wireless network to transmit sampling data, then applied the devised system as a data acquisition method to investigate the measurement of transient temperatures in conjunction with thin-film thermocouple sensors. The results of performance test indicated that the devised system is capable of transient temperature measurement of K-type thin-film thermocouples in the range of 0–650°C with a maximum sampling rate of 100 kHz, a temperature resolution of 0.16 degrees Celsius, an accuracy of 0.2% after non-linear compensation and the ability to measure transient temperature signals with a maximum frequency component of 25 kHz. Taken advantage of the devised wireless data acquisition system to measure the impulse response of a thin-film thermocouple sensor specimen, the meausured response curve is consistent with the law of first-order system, and the time constant of the sensor was obtained as approximately 1.16 ms. A comparison between the existing data acquisition apparatuses of type K thermocouple was made. The limitations of the devised system are also discussed.