Technology Ultrasonic flowmeters

Ultrasonic flowmeters - Principle and advantages

Principe de mesure du débitmètre à ultrasons

Baxir develops ultrasonic flowmeters using the transit-time difference principle. This technology requires at least one pair of transducers connected to an electronic device named a transmitter. The ultrasonic transducers are installed on either side of the pipe, on a diametral plane. The axial distance between them - D - is calculated by the transmitter based on the application physical characteristics such as pipe diameter, type of fluid, etc.

Driven by the flowmeter, those transducers alternately emit and receive ultrasounds. Their travel time is measured in both directions: from the transducer A upstream to B downstream and vice versa. When ultrasounds travel through the fluid, their velocity is affected by the flow. Consider a swimmer crossing a river from point A upstream to point B downstream: his A to B run with the current will be faster than his B to A return run against the current.

Principe de mesure du débitmètre à ultrasons

The same physical laws apply for ultrasounds: travel time Tab with the flow will be faster than travel time Tba against the flow. The travel times are measured in micro or milliseconds, their difference in nanoseconds.

The velocity measured by the transducers - V - is directly proportional to the travel time difference and calculated based on the application physical characteristics and travel times. This measured velocity is then converted to an average fluid velocity - Vavg - with fluid mechanics algorithms. The Kh coefficient is based on the Reynolds number, the fluid viscosity and the pipe roughness. Finally, the flow - Q - is the integration of the average flow velocity on the section.

This technology offers numerous advantages:

- non-intrusive ultrasonic sensors
- bidirectional and precise measurement
- measurement possible on most homogeneous liquids
- easy and quick installation
- no pipe modification or stoppage of the industrial process
- no pressure drop
- no contact with the fluid
- no mechanical wear as there are no moving parts
- no calibration or annual maintenance