The well-known transit time ultrasonic flow measuring method is based on determining of the difference in transit time of high frequency sound pulses that are transmitted along and against the flow stream. Having this information, the flowmeter can calculate average flow velocity and then the flowrate. The principle of measurement is simple but determining the true average velocity is difficult, especially to obtain custody transfer measurement accuracy in one-path ultrasonic flowmeters. This paper proposes an improvement of the mentioned flow measuring method. For this purpose it is not necessary to use extra devices complicating a design and causing additional pressure drop. The object in view is achieved by entering necessary correction during flowrate calculation. For that the stage-by-stage estimation of the flow profile correction factor, which considers a difference between average velocity along the sound path and average velocity for pipe cross-section is carried out depending on the flow regime. Correction is based on the offered original processing algorithm which in turn relies on the mathematical model of ultrasonic flowmeter, considering except for velocity distribution profile also influence of a pipeline wall roughness. Thus, even having only one pair of piezoelectric transducers, the improved method allows to increase an accuracy of flow measurement in the wide range covering laminar, transitive and turbulent flow modes.

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