The National Institute of Standards and Technology (NIST) uses a laser Doppler anemometer (LDA) as a working standard for airspeed calibrations in the range 0.15 m/s to 75 m/s (0.34 to 168 miles/hour). We report improved procedures for calibrating the LDA that reduced its uncertainty from 0.26% to 0.10% at airspeeds above 1 m/s. (Uncertainties are stated with the coverage factor k=2 which corresponds to a 95 % confidence level.) The calibration uses a rotating disk with known dimensions at several known rotation frequencies, thereby tracing the LDA to the primary standards of length and time. We also improved the LDA signal-to-noise ratio in NISTs wind tunnel, particularly at higher air speeds, by replacing a water seeding system with an oil seeding system. New software automates the airspeed setting, oil-seeding rate, data-collection time, and instrument averaging time.
Proceedings Title: Measurement Science Conference Proceedings
Conference Dates: March 22-26, 2010
Conference Location: Pasadena, CA
Pub Type: Conferences
atomizers, airspeed calibrations, laser Doppler anemometer, primary standards