Ultrasonic phased array for sound drift compensation in gas flow metering

We present an ultrasonic transit-time gas flow meter (UFM) that features a 40-kHz 2D-phased array for transmitting ultrasonic sound waves up- and downstream to two single element receivers. This allows us to electronically compensate for the well-known parasitic sound drift effect, and, thus, increasing the measurement range by improving the signal-to-noise-ratio (SNR). A regular double-path UFM consists of at least two inclined sound paths to measure the propagation times up- and downstream. However, with increasing flow velocity the sound drift effect reduces the SNR and therefore limits the measurement range. Previous work used rotating [Mylvaganam, TUFFC, 1989] or shifting [Kupnik, IUS, 2006] the ultrasonic transducers to compensate for this parasitic effect. In this work, we consider whether an ultrasonic phased array as a transmitter can be utilized instead. For large diameter flowmeters with ultrasonic transducers, operating at lower frequencies for low attenuation, the array approach not only increases the measurement range but also allows new flowmeter operation modalities, such as adaptive beam steering and off-center measurements for more accurate meter factor determination.