FPGAによる抵抗線温度計用の周波数補償システムのデジタル化

概要

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In this study, the frequency compensator for the cold-wire thermometer was digitised by employing a FPGA (Field Programmable Gate Array) device. The frequency response of the thermometer sensor indicates a first-order lag at a high frequency range (100Hz~) and a low frequency range (0.01~10Hz) due to the time constants related to the heat capacity of the cold-wire and its prongs, respectively. To compensate the attenuation property of the sensor, the first-order lead characteristic was realized by adopting the bilinear transformation. As a preliminary step to implement on the FPGA device, the frequency response characteristic of the digital compensator was evaluated through the computer simulation. The first-order lead characteristic was realized with an uncertainty of less than 0.13% by configuring the bit length of the digital filter coefficients adequately. The accuracy of compensator in the low frequency range was verified by wind tunnel experiments applying sinusoidal temperature fluctuations to the temperature sensor. It was confirmed that the temperature signals were appropriately compensated by the present method with an uncertainty of less than 1.0%.
2010-01-31