08.04.2011
Within the EURAMET Project 827: „LDA based intercomparison of Anemometers” a Laser-Doppler-Anemometer (LDA) has for the first been used as a transfer standard in international comparison measurements. The LDA-measurement results enabled to verify the traceability of each involved national metrology institute for the unit flow velocity as well as to determine a reference value with the up to now lowest uncertainty in the field of anemometer calibration (0,2% - 0,3%).
International comparison measurements are essential for the validation of the lowest assignable uncertainties stated in the CMC (calibration and measurement capabilities) tables of the national metrology institutes and calibration facilities. The comparison measurements were organized by the PTB as pilot laboratory between six national calibration facilities and carried out with two transfer standards, one Laser-Doppler-Anemometer (fig. 1) and one small-sized ultrasonic anemometer. Together with previous comparison measurement results it has been shown that the comparability of calibration results is dependent on anemometer and calibration facility specific interactions.
In the air speed range between 0,5 m/s to 40 m/s for instance the comparison measurements based on the LDA as transfer standard 95% of the calibration results were comparable with the comparison reference value, whereas only 60% were comparable within an at least twofold uncertainty of the comparison measurement reference value for the ultrasonic anemometer with low but obviously not negligible interactions.
Thus for the validation of lowest assignable uncertainties on the highest possible metrological level the use of Laser-Doppler-Anemometers as transfer standards in comparison measurements has to be suggested.
Fig.1: PTB-Laser-Doppler-Anemometer used as transfer standard
Contact person:
Harald Müller, FB 1.4, AG 1.41, E-Mail:
harald.mueller(at)ptb.de