Search

Ultrasound is an emerging technology that can be applied to monitor food processes. However, ultrasonic techniques are usually limited to research activities within a laboratory environment and they are not extensively used in industrial processes. The aim of this paper is to describe a novel ultrasonic sensor designed to monitor physical–chemical changes that occur in wines stored in industrial tanks. Essentially, the sensor consists of an ultrasonic transducer in contact with a buffer rod, mounted inside a stainless steel tube section. This structure allows the ultrasonic sensor to be directly installed in stainless steel tanks of an industrial plant. The operating principle of this design is based on the measurement of ultrasonic velocity of propagation. To test its proper operation, the sensor has been used to measure changes of concentration in aqueous samples and to monitor the progress of a malolactic fermentation of red wines in various commercial wineries. Results show the feasibility of using this sensor for monitoring malolactic fermentations in red wines placed in industrial tanks.

This article explains how a multi-frequency ultrasonic beam path is split due to passing through dispersive materials and the implications that it has in flow measurement using a Clamp-on ultrasonic flowmeter. The importance of knowing this phenomenon is because dispersive materials are commonly used in the manufacture of transducer wedges and plastic pipes. Splitting of the ultrasonic beam path occurs when the incident angle is not normal to the surface of the pipe and a coupling wedge is necessary. The diffraction angle is produced at the boundaries among materials with different propagation velocities (according to Snell’s law), and furthermore, in dispersive materials, the propagation speed depends on frequency. Therefore, when the excitation signal contains several frequential components, each frequency travels with a different velocity. Under this circumstance, different diffraction angles are produced for each frequency at the boundaries between materials. As a result of splitting the path, the ultrasonic beam widens and the reception transducer aperture becomes too small to receive all the frequential components contained in the ultrasonic beam. Thus, when the ultrasonic beam is carried by the liquid flowing inside the pipe, the reception transducer receives different frequential contributions, producing change in its spectral composition. As a consequence of the mixing of these frequencies, the reception signal is modulated in phase and amplitude. Moreover, modulation will change as a function of frequential composition that is combined at the reception transducer. This is the origin of the linearity error in Clamp-on ultrasonic flowmeters.

Ultrasonic properties of materials present a strong dependence on temperature and in turn the ultrasonic velocity of propagation in the material under test. It is precisely for this reason that most ultrasonic measurements are often carried out with thermostated samples by using either water tanks or climate chambers. This approach is viable in a laboratory and when the measured or characterized samples are relatively small. However, this procedure is highly improbable to be applied when in situ measurements in industrial environments must be performed. This goes for the case of, for example, ultrasonic velocity measurements in wine while it is performing malolactic fermentation inside a tank of hundreds of thousands of litres. In this paper two different practical approaches to temperature compensation are studied. Then, the two temperature compensation methods are applied to the measured ultrasonic velocity values along a whole malolactic fermentation process. The results of each method are discussed.

Many ultrasonic sensors intended for non-destructive testing include a plastic or metal element, known as buffer rod, between the ultrasonic transducer and the material under analysis. Buffer rods are often terminated in the form of a conical tip for ultrasonic inspection of liquid-like substances. The conical tip is carefully shaped in a 45?? angle to favour the in phase reception of all the components of the ultrasonic wave reflected at the buffer tip, obtaining thus a maximum amplitude measurement signal. The effect of the buffer rod cone angle on measurement signals is studied in this work. A straightforward approximate formula for the effect of the error angle on measurement signal amplitude is used. Simulations are performed using a two-dimensional finite differences tool. Measurements are conducted with the same operating conditions and buffer rod materials and dimensions as those defined for both approximate formula evaluation and simulations. Thus, a comparison of the approximate formula, simulation and measurement results are established. Furthermore, the significance of some parameters such as ultrasonic transducer operating frequency and diameter, and buffer rod material are also analysed. The obtained results show that significant loss of the measurement signal amplitude is found only for cone error angles beyond the range of usual machining errors.