Ultrasonic Flowmeters

Ultrasonic Flowmeters

Ultrasonic flowmeters measure volumetric flow by transmitting ultrasonic signals through the process medium and evaluating how flow changes the signal transit time. In the differential transit-time method, signals traveling with the flow arrive sooner than signals traveling against it; the measured time difference is proportional to flow rate. This principle is applicable to a wide variety of gases and liquids and does not rely on the fluid’s electrical conductivity.

Ultrasonic technologies are available as in-line meters and as clamp-on systems. In-line sensors are typically selected when traceable and guaranteed accuracy is required, supported by factory calibration and robust industrial mechanical design. Clamp-on sensors mount externally on the pipe wall, enabling temporary measurement campaigns or retrofits without interrupting the process - useful where shutdowns are costly or where access to wetted parts is undesirable.

Benefits include measurement that is independent of pressure, density, temperature, conductivity, and viscosity for homogeneous fluids, combined with a free pipe cross-section that avoids pressure loss. The absence of moving parts reduces wear mechanisms and supports long service life, while the choice of in-line or clamp-on construction allows a fit to either permanent metering or diagnostic/verification use.

Typical applications include water and industrial utility networks, large-diameter pipelines, and chemical transfer lines where non-intrusive installation or low-maintenance operation is valued. For aggressive fluids and high-pressure duties, clamp-on arrangements can provide a measurement solution without exposing sensors to the medium. In hydrocarbon and LNG value chains, ultrasonic metering is widely used for high-accuracy custody transfer and allocation, including dedicated LNG metering solutions.

Engineering considerations include maintaining a fully developed and stable velocity profile, managing entrained gas or solids that can attenuate ultrasound, and ensuring proper acoustic coupling and pipe data for clamp-on installations. Pipe material, lining, wall thickness, and temperature gradients influence the acoustic path and must be accounted for during setup. For in-line meters, short inlet-run requirements can simplify layout, but upstream disturbances and swirl should still be evaluated during design.

Field Instruments & Controls, Inc. an exclusive authorized representative of sales and service for Endress+Hauser.