A Novel Double Weighing Tank Approach for Precision Flow Measurement

Abstract

Water Flow Measurement Systems (WFMSs) are widely used for the measurement of flow rate of water flowmeters and also for the traceability purposes all over world. There exists basically two methods for the liquid (water) flow measurement namely gravimetric/ weighing and volumetric. Worldwide, weighing method as described in ISO 4185 is used in WFMS for calibration of different types of flowmeters. Last two decades have witnessed significant research contributions in the development of instrumentation and techniques. During these developments, special emphasis was placed on reducing the measurement errors enabling finally improving measurement uncertainty associated with flow calibration. Nowadays, flow standards of substantially low uncertainty, in the order of 0.05 % or better, are required for high accuracy flowmeters calibration wherein error and uncertainty contributions of standards transferred to meter under test (MUT) is considered almost negligible. The need of such highly accurate flow standards opens new lines for the research and developments in this field. In a static weighing method, the main sources of measurement uncertainty are collected mass, collection time (including diverter error), and density of water. The uncertainty of the collected water mass depends upon weighing balance s indication, drift, calibration, buoyancy correction, leaks and splashes, storage effects and evaporation of water. The collection time uncertainty depends upon timer calibration, timer actuation and diverter error. The uncertainty associated with density measurements depends upon the quality of tap water and its temperature. The associated measurement uncertainty can be improved by use of advanced instrumentation. However, it is not possible to reduce the diverter error only using better instrumentation but special mechanical designs are needed as used by several other researchers. In order to reduce the diverter error, a unique method/ technique of multiple weighing was proposed.