Performance analysis of present cup anemometers

Abstract

The cup anemometer, wind speed sensor developed by T.R. Robinson in the 19th century, remains today as the best option in relation to important scientific and economic sectors such as the meteorology sector or the wind energy sector. Despite the great advances reached by new technologies as sonic anemometry, LIDAR or SODAR, the cup anemometer is the most demanded wind speed sensor thanks to its balance between the accuracy, reliability, endurance and the cost. In the present paper, the work carried out in relation to this instrument at the IDR/UPM Institute is briefly summarized, and then the results from the last research testing campaigns are included. The output signal of the first class cup anemometers such as Thies CLIMA First Class, Thies CLIMA 4.3350, and Vector Instruments is analyzed to obtain insights on the instrument accuracy. It is found that three accelerations of the rotor are converted into a pulsed output signals, leading to some error if that is not taken into account. Besides, the way the output signal is registered in order to correlate the output frequency with the wind speed has proven to be also a source of error. Two ways of extracting the output frequency, namely by Counting Pulses (CP), and by using FFT are compared. Results indicate that the wind speed errors are six times larger in the case of using FFT.