Abstract
In this study, the compensator for the cold-wire thermometer was digitized by employing a FPGA (Field Programmable Gate Array) device. The cold-wire thermometer involved the frequency response of a first-order lag in a high-frequency range (100Hz〜) and a low-frequency range (0.01〜10Hz) due to the thermal time constants related to the cold-wire and its prongs, respectively. The bilinear transformation was utilized to design a digital filter with the first-order lead characteristic. As the characteristic roots of the thermometer depend on temperature and velocity fields, the temperature signals were compensated through updating the filter coefficients based on the instantaneous temperature and velocity fluctuations. Consequently, the present method made it possible to realize the high-accuracy temperature measurements by using the cold-wire thermometer in unsteady flows. It was verified that the temperature signals at the low frequency were appropriately compensated with an uncertainty of less than 5.5%.
