(A new time of flight) Acoustic flow meter using wide band signals and adaptive beamforming techniques

I Murgan,J L Ballester,B Reeb,I Candel,A Anghel,C Ioana,G Combes

doi:10.1088/1755-1315/49/6/062002

Abstract

In this paper we present the result of our research concerning the improvement of acoustic time of flight flow metering for water pipes. Current flow meters are based on the estimation of direct time of flight by matched filtering of the received and emitted signals by acoustic transducers. Currently, narrow band signals are used, as well as a single emitter/receptor transducer configuration. Although simple, this configuration presents a series of limitations such as energy losses due to pipe wall/water interface, pressure/flow transients, sensitivity to flow induced vibrations, acoustic beam deformations and shift due to changes in flow velocity and embedded turbulence in the flow. The errors associated with these limitations reduce the overall robustness of existing flow meters, as well as the measured flow rate range and lower accuracy. In order to overcome these limitations, two major innovations were implemented at the signal processing level. The first one concerns the use of wide band signals that optimise the power transfer throughout the acoustic path and also increase the number of velocity/flow readings per second. Using wide band signals having a high duration-bandwidth product increases the precision in terms of time of flight measurements and, in the same time, improves the system robustness. The second contribution consists in the use of a multiple emitter - multiple receivers configuration (for one path) in order to compensate the emitted acoustic beam shift, compensate the time of flight estimation errors and thus increase the flow meter's robustness in case of undesired effects such as the “flow blow” and transient/rapid flow rate/velocity changes. Using a new signal processing algorithm that take advantage of the controlled wide band content coming from multiple receivers, the new flow meters achieves a higher accuracy in terms of flow velocity over a wider velocity range than existing systems. Tests carried out on real scale experimental facility showed an increase in acoustic time of flight estimation, accuracy of 50% with respect to the existing measurements techniques based only on signal correlation.

Highlights

Nowadays, the technological processes monitoring in real time is a requirement for the most of the industrial activities, in particular those processes involving transient and/or turbulent water pipe flows
The acoustic flow metering basic principle is to compute the time of flight difference of the ultrasonic emitted waves, in the flow direction and the opposite direction
The principle of average flow velocity measurement is shown in figure 2, where we present the significance of the time of flight difference

Summary

Introduction

The technological processes monitoring in real time is a requirement for the most of the industrial activities, in particular those processes involving transient and/or turbulent water pipe flows. Of them is the measurement section that may not be sufficiently far with respect to a singularity as an elbow, in which case, the rule imposed by the flow standards measurement by time of flight: a distance of 10 diameters downstream and 5 diameters upstream the singularity is not respected [4]. In this context, the flow is not stabilized and time of flight measurement is not correct.

State of art

Experimental tests and results

Findings

Conclusions