The use of flow meters such as the 'Flowave' from Bürkert is ideal for precisely detecting the change between different liquids in food production. In rinsing processes in particular, the rapid differentiation between product and rinsing water ensures efficient process control. The device continuously measures the density factor, which is independent of the temperature. In this way, milk, for example, can be quickly and reliably distinguished from cleaning solution using this measured value. Compared to conventional time-controlled processes, this minimizes product waste and saves costs. At the same time, the effort required for waste water treatment is reduced, as fewer product residues end up in the waste water.

Non-contact flow measurement with SAW technology: The comparison of single to multiple shafts running through the liquid allows high measurement performance and additional evaluations regarding the type and properties of the liquids.

© Bürkert Fluid Control

The flowmeter works according to the 'Surface Acoustic Waves' (SAW) method. This technology uses wave propagation for flow measurement, such as occurs during seismic activities (e.g. earthquakes). The main part of the sensor consists of a measuring tube, on the surface of which interdigital transducers are arranged, which start the wave propagation when electrically excited. Four interdigital transducers are used, each of which can operate as a transmitter and receiver. If one is active as a transmitter, the two furthest away work as receivers. The surface waves generated on the pipe surface also couple out into the liquid. The decoupling angle depends on the liquid or the speed of the wave propagating in it. On the other side of the measuring tube, the waves couple back into the measuring tube and travel to the next interdigital transducer. In this way, the excitation of each interdigital transducer leads to a sequence of received signals at two others. Two interdigital transducers transmit in the direction of flow, two in the opposite direction. The volume flow rate is proportional to the time difference between the duration of the wave propagation in the forward and reverse directions. In this way, measured values can be determined by passing the liquid once or several times and comparing all the received signals. With the appropriate mathematical evaluation, they provide information about the fluid.

The importance of the density factor

The transition between beer or mixed alcoholic beverages and water can also be measured using this technology. As the propagation speed of the acoustic surface waves in the liquid increases when alcohol and sugar are added, the density factor of the liquid also increases in comparison to water. However, the pure density of the liquid hardly changes depending on the alcohol and sugar content, as sugar increases the density while alcohol reduces it. Therefore, the transition between beer or mixed alcoholic beverages and water is often very difficult to measure with conventional density meters.

The density factor, on the other hand, not only indicates media changes between product and water; liquids with different sugar contents can also be distinguished from one another. Furthermore, SAW technology makes it possible to obtain additional data from the medium: In addition to the temperature, the flow meter also automatically detects any gas bubbles and outputs the values as a percentage. Possible process faults can therefore be countered quickly and effectively.

Hygienic and low-maintenance

As the SAW technology does not require any sensor elements in the measuring tube, there are no pressure drops, sealing problems or dead spaces that impair cleaning. The sensors therefore meet the highest hygiene standards and facilitate the qualification and validation of production and cleaning processes. Data transmission of the 'Flowave' sensors is possible via the manufacturer's device platform 'EDIP' (Efficient Device Integration Platform) to all common fieldbuses.

Author:
Hendrik Faustmann is Product Manager at Bürkert Fluid Control Systems in Ingelfingen.