A three-path ultrasonic flowmeter for small-diameter pipelines

An ultrasonic flowmeter has been developed which incorporates a single transmitting transducer and lens system producing a diverging ultrasound beam detected by three widely spaced receiving transducers. This enables measurements to be made with three ultrasound paths in pipelines of relatively small diameter. Volume flow rate is evaluated from measurements of the difference in phase angle between the received signals under 'flow' and 'no-flow' conditions. A separate cross-flow ultrasound system is used to correct measurements for variations in sound velocity with temperature. For fully developed turbulent flow, the measured phase differences are linearly related to flow rate as predicted by theoretical analysis of the system. The meter compares the flow rates derived from the phase-angle differences for three paths. Agreement of all flow rates indicates that fully developed turbulent flow exists, as present during calibration, and a weighted mean flow-rate is determined and displayed. In other cases warning is given that a reliable measurement of the flow rate cannot be made.