Ultrasonic cross-correlation flowmeters

Cross correlation transit-time measuring instrumentation can be accurate to a few parts per million depending upon the sensing technology. When ultrasonic sensors are used to measure fluid flow the accuracy is primarily determined by the fluid properties and flow profile. In multiphase mixtures, very large changes of acoustic attenuation can occur and this originally provided the impetus to produce the ultrasonic cross-correlation flowmeter. In its basic form the instrument measures the flow velocity by determining the transit time of changes of acoustic impedance, due to flow disturbances, between two parallel ultrasonic beams spaced a known distance apart. Since only the transit time is measured between two fixed marker beams, the measurement is largely unaffected by wide variations in the speed of sound in the fluid and the fluid properties. The correlation signal processor used in all trials reported in this paper was a commercially available instrument specifically designed for accurate transit time determination and velocity tracking and is based on a multichannel design system. The measurable transit time range was from 0.5 ms to 400 ms corresponding to a velocity range of 0.1 m/s to 80 m/s for a sensor spacing of 40 mm. This instrument can also process phase and amplitude modulation data simultaneously so that fluids varying from single phase to multiphase can be metered