An Uncertainty Analysis of the NIST Airspeed Standards

The National Institute of Standards and Technology (NIST) provides calibration services for airspeed instrumentation. This document describes the uncertainty of the NIST airspeed standards. An extensive component analysis of the system was performed. The standard for airspeed measurement at NIST is a fiber optic Laser Doppler Anemometer (LDA), which is calibrated with known velocities produced by a rotating disk. Airspeed calibrations are performed in a wind tunnel which has a test cross section of 1.5 m by 2.1 m over a range of speeds from 0.15 m/s to 40 m/s. Over this range, the airspeed uncertainty is found to be a function of airspeed and the expanded uncertainty at 95% confidence level, i.e. k = 2, in m/s can be expressed by the root-sum-square of 0.0048V and 0.0068 m/s, where V is airspeed in m/s. This gives a maximum uncertainty of 4.6% at the lowest airspeed of 0.15 m/s and a minimum uncertainty of 0.48% at the highest speed of 40 m/s.