Liquid flow measurement using silicone polymer wedge clamp-on ultrasonic transducers

Accurate liquid flow measurement is vital to many industries, and the benefits and limitations of ultrasonic transit-time clamp-on measurements are well understood. The ultrasonic transducers used in high quality clamp-on systems tend to be high cost items, containing an ultrasonic wedge of machined polyether ether ketone plastic (PEEK). PEEK is used because of its consistency and favourable ultrasonic properties of relatively low attenuation and consistent ultrasonic wave velocity over a wide range of frequencies. The viability of a new, high performance and low cost design of clamp-on ultrasonic transducers is described, made from a silicone based polymer moulded inside a shell and directly bonded to the active piezoelectric element. In addition to the reduced material and production cost, the new transducers have good thermal stability, consistency, conform well to the surface of the pipe. Tests were performed on a flow rig and on calibration blocks for thermal stability tests, showing that the sensors are of comparable performance to quality devices constructed using PEEK wedges.