Ultrasonic Flow Measurement Using Two Asymmetric ‘Sing-Around’ Paths

Abstract

A novel approach to non-invasive ultrasonic flow-metering is described. The use of two asymmetric ‘sing-around’ (or frequency difference) paths avoids the problem of temperature dependence inherent in conventional flowmeters. The new system transmits two beams of ultrasound in bursts of 0.5 to 1.5μs duration at 2 MHz through the metered medium to two receiver transducers, one upstream and one downstream. The flow velocity is derived from the measured ‘sing-along’ frequencies of the two paths of different lengths and distance between the two receivers; the frequencies are independent of the temperature-dependent velocity of sound. The accuracy for water flow at 2 m/s was about 2%. The pipe material must be ultrasonically conducting and the fluid must be sonically homogeneous. Flow direction can be identified easily. The high frequency used gives shorter counting intervals, so better response. Less beam divergence also results. Good matching of transducers to the fluid was needed to allow high frequency operation.