Preliminary Intercomparison of Anemometer Calibration Systems at Very Low Speeds between the National Standard Laboratories in Japan and the USA

Abstract

An international comparison of air speed standards has been conducted by Japan and the USA using anemometers. The national standard for low air speed measurement in Japan uses a tow carriage system with a laser-based speed determination system. In the USA, a specially designed low-speed wind tunnel equipped with a laser Doppler anemometer comprises the national standard. Two anemometers, one thermal and one ultrasonic, were selected as the transfer standards, and these were tested in the air speed range of 0.1 to 1m / s. The results showed the two national standards to agree within the calibration uncertainties which were nominated to be between 1% and 9%. The results also indicated that the thermal anemometer used in this program had a transient characteristic and a sensitivity to the atmospheric pressure that required special analysis and data handling procedures. These characteristics and the procedures implemented are discussed and explanations are given that should improve future testing.