New Primary Standards for Air Speed Measurement at NIST
Vern E. Bean, J. M. Hall
NIST has changed its primary standard for air speed measurements from a Pitot tube to a fiber optic laser Doppler anemometer (LDA). In earlier times, the Pitot tube was adapted as the primary standard instrument because it is a direct application of accepted theory and there were no other primary instruments with which to compare measurements until the recent development of the fiber optic LDA. Since the LDA measures air speed by measuring the speed of very small particles entrained in the air stream, it is feasible to calibrate it with a known speed reference such as a light scattering particle on the edge of a spinning disk. NIST now calibrates its LDA system by a particle of known speed, a 5 micron diameter tungsten wire mounted at a measured radius on the perimeter of a disk rotating at a measured rate. The uncertainty of the LDA measurement is 0.006 m/s with a coverage factor of 2. The LDA is now used to assess the performance of the Pitot tube in the overlap air speed range.
Proceedings of the 1999 NCSL Conference
July 11-15, 1999
National Conference of Standards Laboratories International
air speed, anomemetry, pitot tube, primary standards
and Hall, J.
New Primary Standards for Air Speed Measurement at NIST, Proceedings of the 1999 NCSL Conference
(Accessed December 3, 2023)