High-speed sound
Ultrasonic flow measurement systems: Access without contact

Ultrasonic technology provides a method for performing non-contact flow measurement. The advantages are obvious. Low pressure loss, the absence of moving mechanical parts and the resulting immunity to contamination and corrosion are factors that are especially significant in the chemical industry.
Flow measurement is not all that difficult, and the process control and measurement industry offers a variety of solutions to accomplish the task. However, the job becomes a bit more challenging particularly when pure fluids are involved and an unadulterated measurement result must be provided in both flow directions if possible. Another hurdle arises if measurements need to be taken on a pipe that has no provision for holes to mount sensors. In these situations, ultrasonic flow measurement systems are the solution of choice. Why? Because they provide non-contact measurement, they operate independent of the medium being measured, and they facilitate external clamp-on installation. How does ultrasonic flow measurement work? There are two basic measurement principles: the Doppler principle and the transit time differential principle. In both cases, a piezo-ceramic converter, which is mounted on the pipe wall, generates ultrasonic waves that are sent into the fluid at an angle to the direction of flow. When the Doppler principle is used, the frequency shift of the ultrasonic waves, which are reflected from stray particles in the fluid, is analyzed. Only one piezo signal converter, which transmits and receives using a time offset, is required. Using the transit time differential principle, two piezo-ceramic converters are used, which are positioned at an angle to the direction of flow. The converters alternatively send or receive pulseshaped ultrasonic wave packets upstream and downstream.