Abstract
The calibration results of 61 commercially available air flow velocimeters over the velocity range of 0.05 to 1m/s are presented. The calibration was performed with the towing carriage system which is the national standard for low range air velocity. The effect of the residual flow along the rail on the calibration result was estimated experimentally. It is proved that the calibration uncertainty was sufficiently minimal.
The error of the thermal type velocimeters showed vast scattering against the standard velocity. It was found that the error was due to the following facts. (1) The velocity standards of the manufacturers are inconsistent with the national standard. (2) The secular change is fairly large. (3) The sensitivity significantly changes below 0.2m/s.
When the flow velocity changed from zero to 0.5m/s, most of the thermal type velocimeters showed longer response time than those stated in their specification.
