Page 1 of 14 IGHEM 2008 - Milano Session 4 Paper 6 IGHEM 2008 – MILANO 3 rd -6 th September International Conference on Hydraulic Efficiency Measurements Presentation of optimized integration methods and weighting corrections for the acoustic discharge measurement Thomas Tresch thomas.tresch@hslu.ch Bruno Lüscher bruno.luescher@hslu.ch Thomas Staubli thomas.staubli@hslu.ch Lucerne University of Applied Sciences and Arts Technikumstrasse 21, CH-6048 Horw, Switzerland Abstract According to the appendix of the IEC 60041standard the volume flux Q in a conduit can be determined with the acoustic discharge measurement method by integrating averaged individual path velocity readings. This is done by applying a simplified Gauss-Jacobi integration method, where the individual path readings are weighted and added up. This integration method is then summarized for circular and rectangular sections. The IEC 60041 has the following limitations: First, by assuming a uniform velocity profile, the method cannot cope well with truly turbulent velocity profiles, which fall off at the boundary layers near the wall. To overcome this limitation Voser [3] proposed a modified integration method called OWICS (Optimal Weighted Integration for Circular Sections) with slightly modified optimum sensor positions and weighting coefficients, thus reducing the integration error by 0.1 up to 0.2 percent. Second, the method uses fixed weighting of the averaged path velocities and thus the need for very accurate positioning of the acoustic transducers with respect to the prescribed distances d i of the acoustic paths to the pipe centre. Voser [3] also suggested to include the actual, measured path positions for determination of the weighting coefficients and hereby reducing the positioning error strongly. Third, the method is only documented for 4-path configurations in one or two crossed planes. In this paper the following issues are presented in a compact way: 1) General formula for determining the positions and weighting for rectangular and circular cross sections. This includes for both cases uniform and turbulent velocity profiles for a varying number of paths from two to nine. The numerical values are also given in a table. 2) The correction formula for the modified weighting for all cases is derived in a generic way, allowing to apply the correction for an arbitrary number of paths. 3) Simulations show the improvement for different configurations for a selected number of malpositioned acoustic paths. Peter Gruber peter.gruber@rittmeyer.com Rittmeyer Ltd CH - 6340 Baar, Switzerland