To verify high accuracy of a new type flow-metering system based on the measurements of line velocity profiles, eliminating Profile Factors, calibration tests of “UDF”, the flow-metering system by ultrasonic pulse-Doppler profile-velocimetry, were conducted at national standard loops worldwide, including the National Institute of Standard Technology (NIST) of the U.S. Department of Commerce, the National Metrology Institute of Japan (NMIJ) of the National Institute of Advanced Industrial Science and Technology (AIST) in Japan, the Nederlands Meetinstituut (NMI) in Netherlands, and the Centro National de Metrologia (CENAM) in Mexico. The deviations of UDF to the standard loops in the calibration tests for water were found between −0.23% and +0.26% at NIST, 0.1% and 0.4% at NMIJ, and −0.52% and +0.59% at NMI in terms of the average values of each measurement. Following improvements to the UDF System, the calibration tests at CENAM exhibited the deviations between −0.18% and +0.23% and the expanded uncertainty with ±0.21%.

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