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Final report on EURAMET project No. 827: LDA-based intercomparison of anemometers

A regional air speed comparison between six EURAMET laboratories used an ultrasonic anemometer and a laser Doppler anemometer (LDA) at air speeds between 0.2 m s−1 and 40 m s−1. Based on periodic calibrations at the pilot laboratory (PTB), the uncertainty contributed to the comparison by the LDA was 0.2% and the uncertainty contributed by the ultrasonic anemometer depended on the air speed and varied between 2.95% and 0.11%. The degrees of equivalence between the participants were notably better for the laser Doppler anemometer data than for the ultrasonic anemometer data. For example, using the 95% chi-squared consistency check, 16 of the original 59 participant data points were removed as discrepant from the ultrasonic data set, but only one point was discrepant in the LDA data. A possible explanation is that the LDA is non-intrusive and therefore does not alter the velocity field in the wind tunnel whereas the ultrasonic device does produce blockage effects. The results of this comparison (and prior EURAMET and CIPM comparisons) indicate a need for more attention to blockage effects during air speed calibrations and their effect on air speed uncertainty statements. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).