Ultrasonic flowmeters are non-contact instruments suitable for measuring flow in difficult-to-reach and difficult-to-observe fluids and large pipes. They can be linked to a water level meter to measure flow in open water. Ultrasonic flowmeters do not require a measuring element to be installed in the fluid, so they do not alter the fluid's flow state or create additional resistance. Installation and maintenance of the instrument can be performed without disrupting production pipeline operations, making them ideal energy-saving flowmeters.
It is well known that current industrial flow measurement often faces difficulties measuring large pipe diameters and flow rates. This is because conventional flowmeters become more difficult to manufacture and transport as the pipe diameter increases, leading to increased costs, increased energy losses, and installation difficulties. Ultrasonic flowmeters eliminate these drawbacks. Because all types of ultrasonic flowmeters can be installed externally and measure flow non-contact, their cost is largely independent of the pipe diameter being measured. Unlike other types of flowmeters, which increase in cost significantly with increasing pipe diameter, larger pipe diameters offer a superior price-performance ratio compared to other types of flowmeters with the same functionality. Considered a superior instrument for measuring large-diameter flow, Doppler ultrasonic flowmeters can measure flow in two-phase media, making them suitable for measuring dirty flows such as sewers and sewage. In power plants, portable ultrasonic flowmeters are far more convenient than conventional pitot tube flowmeters for measuring large-diameter flow rates, such as turbine inlet flow and steam turbine circulating water flow. Ultrasonic flowmeters can also be used for gas measurement. The applicable pipe diameter ranges from 2 cm to 6 m, and they are suitable for applications ranging from open and culvert channels a few meters wide to rivers 500 m wide.
Furthermore, the flow measurement accuracy of ultrasonic flowmeters is virtually unaffected by parameters such as the measured fluid's temperature, pressure, viscosity, and density. Furthermore, ultrasonic flowmeters can be manufactured as non-contact and portable instruments, thus addressing the challenges of measuring the flow of highly corrosive, non-conductive, radioactive, and flammable and explosive media, which are difficult for other instruments to measure. Furthermore, due to its non-contact measurement characteristics, combined with appropriate electronic circuitry, a single instrument can accommodate a variety of pipe diameters and flow ranges. This adaptability of ultrasonic flowmeters is unmatched by other instruments. Ultrasonic flowmeters, with their aforementioned advantages, are gaining increasing attention and developing towards a series of universally compatible products. Standard, high-temperature, explosion-proof, and wet-type models with various acoustic channels are now available to suit flow measurement in various media, applications, and pipeline conditions.
The main drawbacks of ultrasonic flowmeters are that their measurable fluid temperature range is limited by the heat resistance of the ultrasonic transducer aluminum and the coupling material between the transducer and the pipeline, as well as incomplete raw data on the sound velocity of the measured fluid at high temperatures. Currently, ultrasonic flowmeters in my country can only measure fluids below 200°C. Furthermore, the measurement circuitry of ultrasonic flowmeters is more complex than that of conventional flowmeters. This is because, in typical industrial measurement, liquid flow velocities are often measured on the order of several meters per second, while the propagation speed of sound waves in liquids is approximately 1500 m/s. Therefore, changes in the measured fluid velocity (flow rate) can result in a maximum change in the sound velocity of only on the order of 10⁻³. If the accuracy of measuring flow velocity is required to be 1%, the accuracy of measuring sound velocity must be on the order of 10-5 to 10-6. Therefore, a complete measurement circuit is required to achieve this. This is also the reason why ultrasonic flow meters can only be put into practical use under the premise of rapid development of integrated circuit technology.