Types and designs of ultrasonic flow meters: clamp-on and insertion

We currently offer several types of ultrasonic sensors, which can be installed directly in the pipe or come pre-installed in a measuring tube. We distinguish two subgroups of these sensors, depending on whether they are used with the Doppler effect method or the signal transit time method:

■ Externally mounted sensors, "clamp-on" type«

■ Insertion sensors

Externally mounted sensors, "clamp-on" type«

Sound waves can pass through matter without causing any harmful effects. Thanks to this property, sound waves are very useful for applications in medical diagnostics, materials testing, and flow measurement. Regarding flow measurement, this property allows the sensor to be located outside the pipe and does not necessarily have to be in contact with the fluid. We usually refer to devices mounted in this way as externally mounted sensors (see figure below). One characteristic of externally mounted sensors is that the ultrasonic waves always pass through the entire central diameter of the pipe because the pipe wall allows the ultrasonic waves to pass through.

Fig.: Externally mounted sensors are attached directly to the outside of the pipe. A special mounting rail facilitates precise positioning.

Insertion sensors

Sensors in direct contact with the fluid are known as "insertion or immersion sensors." Insertion sensors are used when the pipe is made of materials such as granular concrete, which do not allow sound waves to pass through. They are also used in multi-path flow meters with transit-time signal measurement systems, meaning they measure acoustic paths other than the one passing through the pipe's mid-plane. Dual-path acoustic systems are an example of this. Multi-path systems offer better linear performance and are less susceptible to disturbances in the flow velocity profile.

Fig.: The insertion sensors are immersed in the fluid. The sensor mounting bracket is welded to the pipe wall. Photo: "Prosonic How" insertion sensors, by E+H.

In-line measuring tube/sensor:

Ultrasonic sensors can be attached directly to the pipe (externally mounted sensors) or welded to the pipe wall (insertion sensors). Therefore, prefabricated measuring tubes are not essential for ultrasonic flow meters. A measuring tube essentially acts as a support for the sensors.

Fig.: Prefabricated measuring tube with four insertion sensors and two acoustic measuring paths. Photo: E+H "Prosonic Flow" in-line flow meter.

Prefabricated measuring tubes (see previous figure) are ideal for transferring measurement accuracies determined in the laboratory directly to the execution site. An in-line sensor consists of a complete prefabricated measuring tube with pre-installed insertion sensors. Configurations of this type typically employ in-line sensors with a multipath system consisting of two, three, or five sensor pairs.