A three-dimensional ultrasonic anemometer for indoor environmental applications

When faced with the task of monitoring the indoor environment of a coal mine shaft, obtaining air velocity measurements is beneficial in considerations such as environmental impact, energy consumption and safety. To fulfill this demand, our research focuses on the design, construction and characterization of an economical three-dimensional ultrasonic anemometer, as well as the evaluation of its performance in combination with a Kalman filter algorithm. Our instrument was characterized using a wind tunnel in a process that included sixteen runs to both examine the distortion of the measurements caused by the sensor structure, and then to calibrate its response to changes in speed and direction of the incoming airflow, and three runs to assess the performance of the calibrated instrument. The results showed the instrument capable of obtaining wind velocity at a maximum frequency of 20Hz, with measurement accuracy of ±(5° ± 1% FS) in orientation and ±(0.8 m/s ± 4% FS) in wind speed, under reference conditions of 9 m/s wind speed and up to 15° from the horizontal wind incidence. The implementation of the Kalman filter resulted in improved accuracy of the wind direction measurement and enabled the anemometer to recursively extract the average velocity of highly-turbulent air currents.