P3E-4 Transducer Design for Liquid Custody Transfer Ultrasonic Flowmetering

Liquid custody transfer (LCT) monitoring demands accurate measurement of flow at a relatively wide temperature range. Transit-time ultrasonic flowmeters, built as a one-piece "drop-in" flowcell with wetted transducers (i.e., transducers that are in contact with fluids), have provided a solution. In the applications of ultrasonic flowmetering to LCT, the desired accuracy and potential exposure to harsh environments impose challenges to ultrasonic transducer design in terms of sensitivity, bandwidth, safety and temperature tolerance. This paper concerns the above design aspects of ultrasonic transducers, including both transducer elements and passive buffers, for transit-time ultrasonic flowmetering in the context of LCT applications. Two types of transducer elements have been investigated in combination with potential backings and buffers. In order to achieve the desired high accuracy across a wide temperature range, the real time-of-flight in the buffers is measured via the so-called pulse-echo technique and is used for compensation to realize an exact time-of-flight in the liquid path. Both solid buffer design and bundled waveguide buffer design have been proposed and compared. MHz-range ultrasonic transducers have been designed for transit-time ultrasonic flowmetering with a high accuracy of 0.15% in flow measurement and an exposure to fluid temperature applications of -40degC to 140degC The performance of the transducers is theoretically modeled and optimized. Prototypes have been built and tested in water. Pulse-echo with a high signal-to-noise ratio (SNR) of more than 20dB has been achieved in ultrasonic buffers by properly designing the dimensions and mechanical features.