Intelligent sensor techniques for fluctuating-temperature measurement (Self-diagnosis and adaptive compensation of sensor response)

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The research results are summarized as follows:(1) The purpose of this study is to improve the accuracy of general-purpose temperature sensors (commercially available thermistors) in fluctuating temperature measurement and to extend their applicability. First, heat transfer models reflecting the internal structures of plate-type and spherical thermistors were proposed to obtain theoretical frequency response to temperature fluctuations. Secondly, parameters dominating the response characteristics of the thermistor were extracted, and it was shown that the thermistor response can be approximated by a first-order system. Finally, a flexible response compensation technique for the thermistor was constructed, the development of which has been very difficult because the thermal time constant varies greatly depending on the flow velocity and physical properties of the fluid surrounding the thermistor. The technique utilized a two-thermocouple probe method --rational identification of thermal … More time constants and digital compensation for response delay-proposed by Tagawa et al. [Rev. Sci. Instrum. 69, 3370(1998)], and greatly improved the accuracy of fluctuating temperature measurement by the thermistor. Although the level of the improvement depends on the fluid type measured and the signal-to-noise ratio of temperature signals, the present response compensation technique worked successfully. As a result, the compensated thermistor became five to fifty times as fast as the uncompensated (original) one.(2) A novel technique for estimating in situ thermal time-constant values of temperature sensors in the frequency domain and for compensating the sensor outputs for the response delays is proposed. The scheme developed is complementary to the time-domain response-compensation ones previously reported by Tagawa et al. [Rev. Sci. Instrum. 69, 3370(1998)]. The scheme provides fast, simple and flexible data professing based on the fast Fourier transform (FFT) algorithm, and is potentially applicabale to the response compensation of various physical and chemical sensors.(3) Theoretical analysis of frequency response of fine-wire temperature sensors, e.g. fine-wire thermocouple and cold-wire, was performed, and the strict solution of the response was derived by treating rigorously the boundary condition of heat transport between the temperature sensing part and its adjoining support. The solution obtained is highly universal and can represent frequency response of temperature sensors such as a thermocouple and a cold-wire--these are very different in configuration and response characteristics--with a single equation. The validity of the theoretical solution was examined experimentally, and a widely applicable response compensation technique for fine-wire temperature sensors was developed based on the theoretical results. For example, identification of the complex response characteristics of cold-wire sensors and their response compensation, which have been considered to be quite a challenge, have became possible. In this procedure, any special apparatus for calibrating the dynamic response is unnecessary. The present response compensation technique can make 3.1μm tungsten cold-wire measurement well comparable to 0.63 μm platinum cold-wire, which is regarded as one of the fasted temperature sensors commercially available. Less