Field of the invention

The invention concerns an ultrasonic probe for measurement of temperature of liquids, both at rest and flowing, applicable in medicine, pharmaceutics or food processing industry.

Comparison with prior art

In many domains, where there is a risk of the liquid contamination, the liquid is strictly separated from the ambient environment. It is so in medicine, pharmaceutics and food processing industry. The liquids are transported either in closed plastic containers or bags or sets of plastic tubes - all this equipment is disposable. For various purposes it is often necessary to measure the temperature of the transported liquid. Direct measurement by means of insertion of the measuring probe into the liquid is ruled out as it creates a contamination risk. Placing a contact probe on the outer surface brings distortion into the measured values as both the heat resistance of the container material and the ambient temperature are indefinable. Because of the above mentioned reasons it is also not suitable to measure the temperature using infra-red radiation measurement.

There exists a solution as specified in US 7404671 patent. It describes measuring temperature inside closed containers using acoustic waves. The solution is based on measuring changes in the velocity of acoustic waves propagation depending on the temperature of the surfaces of closed containers in contact with the measured medium or depending on the temperature of the medium closed in such containers. Acoustic waves are transmitted and received by means of closer unspecified transducers transforming electric waves into acoustic waves of unspecified frequency, amplitude and energy. According to the text of the said patent, the acoustic transducers are placed on the container outer surface, inside of its walls or on its inner surface. The said patent presents

i several methods of measurement: using one transducer working alternately as a transmitter and a' receiver; using two transducers with one working as a transmitter; or using more, circularly arranged, transducers, in which case it is possible to choose the required ratio of transmitters and receivers. All the signals brought to the transducers as well as those received by them are further processed in a computer system according to methods specified in the invention documentation. The final output is then the information on temperature changes in the measured medium. The disadvantage of this solution is the fact that it does not deal with the spatial arrangement (layout) of the transducers with regard to the fact that a flowing medium affects the propagation of acoustic waves differently as compared to one at rest, especially when the flux axis is not perpendicular to that of the transmitted acoustic waves. The said patent does not deal at all with the transducers placement over the container surface, although this aspect may affect significantly the feasibility of the measurement.

In the case of measuring temperature by means of two transducers placed on the outer surface of a container, the said patent',deals with measuring the container inner surface temperature using acoustic .waves of various frequencies, unspecified in the patent. The patent also mentions^, for this set-up, a solution when the temperature of the medium (water, in this case) is measured directly. The acoustic waves pass through the container wall and continue through the measured medium. Consequently, the delay of the acoustic waves is identified. This delay is caused by thermal changes which alter the acoustic qualities of the measured medium. The disadvantage of this solution is the fact that the acoustic waves pass both through the material of the container (undesirable signal) and the measured medium (desirable signal), the intensity of which is directly proportional to the material density and the energy of the acoustic waves passing both through the container material and measured medium. The propagation of acoustic waves is also significantly affected by the frequency of the waves. In cases of unfavourable combinations of the container wall material and measured medium various interactions of the desirable and undesirable signals occur, distorting or even preventing correct evaluation of the signal delay in relation to the temperature of the measured medium. In such case, measurement according to the invention becomes greatly complicated or even impossible.

The solution presented in US 7266989 patent describes a multi-function sensor based on the principle of sound waves propagation. The sensor consists of two parts. The first, open part is in direct contact with the liquid and allows measurement of at least two of its physical quantities. The second part consists of two hermetically sealed chambers. One of them contains the reference liquid of known composition and pressure. Both the open and sealed parts are identical. Each of them is equipped with a pair of acoustic transducers (one serving as a transmitter, the other as a receiver), used to measure changes in the velocity of sound waves in a liquid according to the liquid temperature and pressure, respectively. The second, hermetically sealed chamber is also equipped with a pair of acoustic transducers, one of which serves as a transmitter, the other as a receiver, in this case in an arrangement that allows ambient liquid pressure measurement. The contacts of the transmitting transducers are connected to electronic circuits generating electric waves which become acoustic waves in the transducers. These waves are, with a certain delay according to the temperature and pressure, respectively detected by the receiving transducers and converted into electric signals. By further processing of the measured values, time delays between transmitting and receiving the acoustic waves is identified. By means of a computer, the information is then transformed into temperature and pressure readings. The advantage of this solution is great accuracy of the temperature and pressure measurement. Immersion of the measuring sensor into the measured liquid is required as it has to be in direct contact with the liquid, which is to be seen as a disadvantage.

The object of US 4483630 patent is an ultrasonic thermometer using an acoustic pulse reflection for measuring high temperatures and temperature profiles. The basis is a magnetostrictive transducer which transforms the actuation electric signals into acoustic waves in the coil core, which it transmits and consequently it transforms the reflected acoustic waves back into an electric signal in the core. The coil is wound around an already mentioned metal core of a longish shape. On one side, the core protrudes several lengths of the coil off the winding. The exposed part of the core features several circumferential grooves creating discontinuities in the core. The pulses generated by the magnetostrictive transducer gradually pass through the entire core. At the discontinuities and at the ends of the core, the acoustic waves reflect. The reflected acoustic waves return to the magnetostricive transducer where they retroactively create electric signal, which is then further processed. The delay of the reflections depends on the temperature of the exposed part of the core which is in contact with the measured environment. The measured environment brings the core on its own temperature. According to the patent, the thermometer must be in direct contact with the environment, which may be unsuitable in many cases; in the intended field of use, i.e. measurements of metallurgical processes temperatures, however, it is quite appropriate.

US 4683750 patent presents yet another solution, describing measurement of sample surface warming. It is based on measuring the deviation of an externally generated acoustic wave above the measured sample. The acoustic wave is directed to the sample surface in line with a modulated light beam. The absorption of the light by the tested sample causes periodical warming of its surface and immediate environment. Air in contact with the surface of the sample gradually warms and creates a periodical phase shift in the reflected acoustic wave. This phase shift is detected and provides a direct measurement of periodical surface warming. The advantage of the invention is the possibility of non-contact measurement of the surface of the sample with great spatial accuracy. The essential disadvantage is in the fact that only the temperature of the surface of the sample is measured, the method does not allow to measure the temperature inside the sample.

The principle of the invention

The principle of the invention of probe for ultrasonic liquid temperature measurement is based on the premise that the liquid is contained in a plastic- elastic container. Such materials only carry a minimum amount of sound waves, thus the measurement is not distorted. There are two piezoelectric ultrasonic transducers abutting on the outer surface of the container. One of them is a mechanical waves transmitter, the other one is a mechanical waves receiver. Their mutual position (opposite each other) and their position relative to the surface is constant. Although the measurement is done without any contact with the liquid whose temperature is being measured, thanks to the fact that the working areas of the piezoelectric transducers fit tightly the container surface and thanks to their exactly defined mutual position there is no risk of distortion of the acquired values. The plastic-elastic material of the container, too, contributes to the measurement accuracy as it only allows the ultrasonic waves to spread for very short distances. Thus the ultrasonic waves may travel perpendicularly through the container wall into the measured liquid and then again from the liquid into the opposite sensor; however, they cannot pass along the container wall from one sensor into the other, thus distorting the measurement.

In order to prevent distortion of the measured values it is also necessary to make sure that neither the transmitter nor the receiver width may exceed the inner dimensions of the container. That way it is ensured that all the ultrasonic mechanical waves transferred from the transmitter into the mechanical waves receiver pass through the liquid and are affected by its temperature. To minimize the ambient temperature influence, it is advisable that the transmitter and receiver be fitted with thermal or sound insulation on their outer surface.

It is possible to further increase the accuracy of the measurement by applying thermal insulation also on the container wall outer surface in the measurement area, thus minimizing the effects of ambient temperature.

To secure ideal adherence of the transmitter and receiver to the outer surface of the container, it is suitable to apply immersion gel to the contact areas of the transmitter and receiver.

According to the invention, the probe may be used for measuring the temperature of a liquid at rest, placed in a container or a bag, as well as for measuring liquids flowing through a hose/tube, provided that all those containers are made of plastic-elastic materials.

Description of the figures in the drawing

Figure 1 shows a cross-section of a two-piece casing fitted with piezoelectric transducers and with a container, in this case a hose/tube inserted to it, Figure 2 shows a cross-section of the casing closed, with the piezoelectric transducers pushed to the hose, and Figure 3 shows a longitudinal section of the latter.

Description of the exemplary embodiment

The container wall 1 is represented by the wall of a hose/tube made of plastic-elastic material with piezoelectric transducers abutting on its outer surface. One of them is the mechanical waves transmitter Pl_ and the other is the mechanical waves receiver P2. The transmitter Pi and the receiver P2 are mounted in holders created for that purpose in the two-piece casing 3 and connected by cables 4 with an evaluating unit (not depicted). Both parts of the two-piece casing 3 are joined by a hinge 3JL on one side and by bolted joint 32 on the other. The transmitter Pl and the receiver P2 keep a stable position relative to the container wall l_ as well as a stable position opposite each other. The widths of the transmitter Pi and the receiver P2 do not exceed the inner dimensions of the container J_. The transmitter PJ _. and the receiver P2 are equipped with a thermal or sound insulation 2 on their outer surfaces, continuing also on the surface of the container wall L To improve the contact of the transmitter PJ_ and the receiver P2 with the surface of the container wall i, immersion gel has been applied on the surfaces of the transmitter PJ and the receiver P2 that are in contact with the container wall L

The open two-piece casing 2 is placed on a selected spot on the plastic hose/tube surface 1, closed by turning in the hinge 3J_ and locked by means of the bolted joint 32. The grip of the two-piece casing and the pressure of the liquid in the hose will press the wall of the hose i towards the transmitter PJ and the receiver P2. The distance between the transmitter PJL and the receiver P2 determines the suitable diameter of the hose/tube. It is advantageous, if the . . transmitter PJ _. is capable of generating acoustic pulses of the length of 0.04-0.2 ns with the energy up to 300 μJ and the receiver P2 is capable of receiving them and transforming them into electric signal. Prior to the first application, it is recommended to calibrate the mutual cooperation of the transmitter PJ _. and the receiver P2 at a known liquid temperature. If, in the following measurement, a hose/tube of identical wall i (both of identical thickness and of identical plastic- elastic material) is used and identical liquid is being measured, repeated calibration is not necessary. By means of cables 4, the transmitter Pi and the receiver P2 are connected to an evaluation unit, which is neither depicted here, nor is it a subject of this invention. The device determines the energy and frequency of the ultrasonic mechanical waves transmitted by the transmitter PJ _. and also it receives and amplifies the electric signal from the receiver P2. The electric signal on the receiver is a result of transformation of mechanical waves transmitted by the transmitter PL The device then evaluates the time delay between the moment the signals are sent by the transmitter Pi and received by the receiver P2. The difference then serves to state the temperature of the specific measured liquid.

Industrial applicability

The invention allows industrial application in all fields where it is necessary to measure the temperature of liquids strictly separating the liquid from the measuring probes, both for flowing liquids and liquids at rest.