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 8×8 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, resulting in larger measurement range and better signal-to-noise-ratio (SNR). The UFM fabricated consists of a pipe with an inner diameter of 146mm with a flush-mounted 2D-phased array, embedded in a 3D-printed waveguide structure. The configuration was tested in a calibrated flow rig at various gas flow velocities. The received amplitudes without sound drift compensation, i.e. the transmitted waves emitted at beam steering angles of 30° and -30° reduce by 39% and 26%, respectively, when the flow velocity was ramped up to a maximum of 41 m/s. The amplitudes only dropped by 13% in both cases at the maximum flow velocity of 41 m/s when the sound drift compensation was turned on. Our results prove that using a phased-array will significantly increase the measurement range of gas flow meters.