How to Improve Accuracy of Existing Ultrasonic Water Meters

Abstract

In present paper, the focus is given to possible ways of increasing accuracy for existing ultrasonic time-of-flight water meters. We will consider transducers with coaxial reflectors working at laminar, transitional and turbulent regimes within their measurement range. Considering error curves of such meters, we can easily resume that they are non-linear and not simply corrected using only one polynomic function. Measurements in laboratory and field conditions demonstrate that there is a shift in the ultrasonic meter’s calibration factor. The deviation of readings starts at Re = 5 000–10 000 and the maximum value is reached at Re = 160. Great inaccuracies referred to the transition from laminar flow to turbulent take place abruptly, which lead to undesirable errors. To understand this phenomenon, the theoretical basis of ultrasonic measurements was analyzed and revealed that typical algorithm for determination of the calibration factor is very questionable since it contains simplified information about velocity profile distribution. Trying to fix this problem, we applied computational fluid dynamics (CFD) modelling of ultrasonic meters with different variants of flow straighteners. Ranges of applicability of a particular turbulence model for a correct description of the velocity profile and other flow parameters in metrological purposes have been evaluated. Due to applied techniques, the flow profile sensitivities of various meter configurations are investigated at different Reynolds numbers comparing to real experiments. To get an improved ultrasonic meter design recirculation zones and flow separation regions inside the flow transducer have been eliminated. As a result, the accuracy of the ultrasonic water meter has increased. Simulations demonstrated reasonable agreement to the error curves obtained on the calibration facility for a whole measurement range.

Investigation of the Correction Factor for Ultrasonic Flow Meters

“…The inaccuracy of the factor m is the largest component of the error for ultrasonic flowmeters, which can reach up to 5-10% and even more, especially in the lower part of the range [3]. This is because it's rather problematic to distinguish the ranges of applicability of one or another turbulence model for a correct representation of the velocity profile and other flow parameters for metrological purposes.…”

“…The known dependences [1][2][3][4] for mentioned corrections were obtained based on the assumption that the flow of the measuring medium is axisymmetric, and the trajectory of the ultrasonic beam lies in the plane passing through the axis of the pipeline. However, most industrial flow media have a distorted axial symmetry profile due to installation effects (such as spatial elbows) that are an integral part of any hydraulic system.…”

“…However, most industrial flow media have a distorted axial symmetry profile due to installation effects (such as spatial elbows) that are an integral part of any hydraulic system. In most cases, even the available straight pipe sections declared by the manufacturer before and after the meter are not enough to correct the axial asymmetry [3]. It should be noted that for accurate measurements mainly multipath ultrasonic meters are used.…”