Berkert heralds breakthrough in flow meter management

Written by: Paul Fanning | Published:

Flow meters are a commonplace fixture in the industrial market. Their versatility and broad spectrum of applications have meant that magnetically-inductive devices have become established as the standard and are available in many versions, while devices based on ultrasound and coriolis principles are also seeing increases in application.

Despite this, it remains the case that traditional flow meters have significant weaknesses and limits of application, therefore making the choice of a suitable device for the respective measuring task a challenge.

Clearly the ideal flow meter would have certain core properties. It needs to cover the largest possible measurement range and perform the measuring task reliably throughout the entire life cycle, without excessively high operating expense. Low-maintenance devices are necessary to reduce downtimes. If a measurement is furthermore required without moving parts, as in the case of impellers or permanently mounted units such as vortex flow meters, this currently necessitates very complex and expensive procedures such as Coriolis technology, or solutions that are limited to media with specific properties.

It is for these reasons that Burkert Fluid Control Systems developed what its product manager sensors Volker Erbe describes as "a breakthrough in flow measurement" in the form of its new FLOWave technology.

FLOWave is based on Surface Acoustic Wave (SAW) technology. This uses wave propagation similar to that seen in seismic activities such as earthquakes. In the FLOWave sensors, the surface acoustic waves are excited on a pipe surface by a piezo-electric interdigital transducer specially developed by Bürkert for this purpose. As with an optical waveguide (e.g. a fibre optic cable), waves are sent on a zigzag path through the measured medium (fluid) using acoustic waveguide technology.

As stated, the main principle of this flowmeter is based on wave propagation forms similar to seismic waves, which start from an initial point of excitation and spread along the surface of a solid material. FLOWave uses at least four interdigital transducers which are located on the outside of the measuring tube and therefore have no direct contact with the liquid. Each transducer can act as a transmitter or a receiver.

These four interdigital transducers on the surface work together to achieve a more accurate measurement. Sensor numbers one and four send waves with the direction of flow, while sensors two and three send waves in the reverse direction. The comparison of single and multiple waves through the liquid allows excellent measurement performance and evaluations concerning the nature and properties of the liquid itself.

Thus, one transducer emits the wave, part of which travels directly to the first receiver, part of the same signal is transmitted through the liquid to the opposite side of the tube, where it splits again, with a proportion of the signal going to the second receiver and the remainder travelling through the liquid where the process repeats itself. Thus, a single excitation leads to a sequence of signals being received by two other transducers.

The absolute time for the wave to travel from the transmitter to the receiver depends mainly on the tube diameter and the type of liquid. The difference between the time of propagation in the forward and backward direction is proportional to the flow. The analysis of all the signals and comparisons based on different criteria such as amplitude, frequency and runtimes, allows evaluation of the quality of the measurement, the existence of gas bubbles or solids as well as the kind of liquid.

The first and most obvious advantage to this technology is that none of the components come into contact with the liquid and there are no flow restrictions inside the measuring tube.
Furthermore, the internal surface of the tube can be manufactured to the same surface finish as the rest of the pipeline, meaning that in terms of hygiene, cleaning and flow conditions, there is no difference to any other piece of straight pipe.

This measuring system currently provides very accurate flow and temperature data and the technology will, in the future; allow density measurement to be used to determine the mass flow rate. The principles behind this design enable the flowmeter to work with a stagnant liquid and so reliable flow figures are available even for the smallest flow volumes. The technology also enables it to recognise quick flow changes reliably, which makes it suitable for fast filling processes.

FLOWave also solves many of the issues associated with some high-end flowmeters, such as system vibration in the plant, magnetic and electrical effects as well as the conductivity of the liquid - none of these factors have any effect on the accuracy or reliability of the flow measurements; plus, the SAW technology also has the ability to distinguish between laminar and turbulent flows, a feature that will available later.

Not only does this revolutionary design come in a compact and simple design, but this flowmeter can also be installed in applications in any orientation without affecting performance.
The initial design, Type 8098, will comprise an all stainless steel body in four sizes, DN15, DN25, DN40 & DN50, fitted with a clamp connection to meet hygienic standards.

The flow meters of the FLOWave series thus far are specially qualified for hygienic applications and for the flow rate measurement of water with low conductivity. Extensive field tests that have been underway for some time demonstrate the potentials of the new SAW technology. In further development and expansion stages the new technology will then be extended to all other relevant applications.

Burkert is now necessary to make the product line based on this technology available for use in applications with the highest possible benefits. In addition, there will be continued development of the line with respect to the range of applications and functions, with the ultimate goal of a multi-parameter unit with high-end functionality and performance. Parallel to this development, FLOWave will be enhanced to include application-supporting functions and will then be available as a multi-parameter flow meter.

Says Volker Erbe: "From the end of September, we will have data for volume flow, temperature and density. From there, we will have information on mass flow and then density and concentration. This will open up a range of new applications for the technology."

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