VIBRONIC MULTISENSOR

Abstract

Disclosed is a method for determining and/or monitoring at least two different process variables of a medium, wherein a sensor unit is excited to vibrate mechanically by means of an excitation signal, the mechanical vibrations are received from the sensor unit and are converted into a first reception signal, the sensor unit emits a transmission signal and receives a second reception signal, and a first process variable is determined on the basis of the first reception signal and a second process variable is determined on the basis of the second reception signal. Disclosed also is an apparatus configured to carry out a method according to the invention.

Claims

1-16. (canceled)

17. A method for determining and/or monitoring at least two different process variables of a medium, comprising: exciting a sensor unit to vibrate mechanically by means of an excitation signal; receiving mechanical vibrations by the sensor unit and converting the mechanical vibrations into a first reception signal; emitting from the sensor unit a transmission signal and receiving a second reception signal; and determining a first process variable on the basis of the first reception signal and determining a second process variable on the basis of the second reception signal.

18. The method according to claim 17, wherein the sensor unit is simultaneously supplied with the excitation signal and with the transmission signal and the excitation signal and the transmission signal are superimposed on one another, or wherein the sensor unit is alternately supplied with the excitation signal and with the transmission signal.

19. The method according to claim 17, wherein the excitation signal is an electrical signal having at least one specifiable frequency, including a sinusoidal or a rectangular signal.

20. The method according to claim 17, wherein the transmission signal is an ultrasonic signal, including a pulsed ultrasonic signal having at least one ultrasonic pulse.

21. The method according to claim 17, wherein the first process variable is a density of the medium and the second process variable is a sound velocity within the medium or a variable derived from the sound velocity within the medium.

22. The method according to claim 21, further comprising: determining a reference value for the density on the basis of the sound velocity; and comparing the reference value with the density determined from the first reception signal.

23. The method according to claim 17, further comprising: determining at least a third process variable of the medium.

24. The method according to claim 17, further comprising; determining on the basis of the first reception signal and the second reception signal and/or on the basis of the first process variable and the second process variable whether a deposit has formed on the sensor unit.

25. The method according to claim 17, further comprising: determining a drift and/or an aging of the sensor unit on the basis of the first and the second reception signal and/or on the basis of the first and the second process variable.

26. The method according to claim 17, further comprising: comparing with one another the first and the second reception signal, the first and the second process variable and/or a time profile of the first and the second reception signal and/or of the first and the second process variable.

27. The method according to claim 17, wherein in the determination and/or monitoring of at least one process variable or in the determination of a variable derived from at least one process variable and/or from at least one reception signal, an influence of a deposit, a drift and/or aging of the sensor unit on the first and/or the second reception signal is reduced or compensated for.

28. The method according to claim 17, further comprising: determining a first concentration of a first substance contained in the medium and a second concentration of a second substance contained in the medium on the basis of the first and the second reception signal and/or on the basis of the first and the second process variable.

29. A use of the method according to at least one of the preceding claims for monitoring a fermentation process or for monitoring an inversion of sugar.

30. An apparatus for determining and/or monitoring a first and a second process variable of a medium, wherein the apparatus is configured to: excite a sensor unit to vibrate mechanically by means of an excitation signal; receive mechanical vibrations by the sensor unit and convert the mechanical vibrations into a first reception signal; emit from the sensor unit a transmission signal and receive a second reception signal; and determine a first process variable on the basis of the first reception signal and determine a second process variable on the basis of the second reception signal.

31. The apparatus according to claim 30, wherein the sensor unit includes a mechanical-vibration-capable unit and at least a first piezoelectric element and a second piezoelectric element.

32. The apparatus according to claim 31, wherein the mechanical-vibration-capable unit is a tuning fork having a first and a second vibrating element, wherein the first piezoelectric element is at least partially arranged in one of the two vibrating elements, and wherein the first piezoelectric element is at least partially arranged in the first vibrating element and the second piezoelectric element is at least partially arranged in the second vibrating element.

Description

[0035] The invention is explained in greater detail with reference to the following figures. The following is shown:

[0036] FIG. 1: a schematic drawing of a vibronic sensor according to the prior art,

[0037] FIG. 2 a plurality of possible embodiments of a sensor unit that are known per se from the prior art and are suitable for carrying out the method according to the invention, and

[0038] FIG. 3 an illustration of an embodiment of the method according to the invention for detecting deposits in the region of the sensor unit.

[0039] In the figures, identical elements are respectively provided with the same reference signs.

[0040] FIG. 1 shows a vibronic sensor 1 having a sensor unit 2. The sensor has a mechanical-vibration-capable unit 4 in the form of a tuning fork, which is partially dipped into a medium M, which is located in a reservoir 3. The vibration-capable unit 4 is excited by the excitation/receiving unit 5 to vibrate mechanically and can, for example, be by means of a piezoelectric stack drive or bimorphic drive. Other vibronic sensors have, for example, electromagnetic driving/receiving units 5. It is possible to use a single driving/receiving unit 5, which serves to excite the mechanical vibrations and to detect them. However, it is also conceivable to implement one each, a driving unit and a receiving unit. FIG. 1 furthermore shows an electronic unit 6, by means of which the signal acquisition, evaluation and/or feeding takes place.

[0041] FIG. 2 shows, by way of example, various sensor units 2, which are suitable for carrying out a method according to the invention. The mechanical-vibration-capable unit 4 shown in FIG. 2a comprises two vibrating elements 9a, 9b, which are mounted on a base 8 and which are therefore also referred to as fork teeth. Optionally, a paddle may respectively also be formed on the end sides of the two vibrating elements 9a, 9b [not shown here]. In each of the two vibrating elements 9a, 9b, a cavity 10a, 10b, especially, a pocket-like cavity, is respectively introduced, in which at least one piezoelectric element 11a, 11b of the driving/receiving unit 5 is respectively arranged. Preferably, the piezoelectric elements 11a and 11b are embedded in the cavities 10a and 10b. The cavities 10a, 10b can be such that the two piezoelectric elements 11a, 11b are located completely or partially in the region of the two vibrating elements 9a, 9b. Such an arrangement along with similar arrangements are extensively described in DE102012100728A1.

[0042] Another possible exemplary embodiment of a sensor unit 2 is depicted in FIG. 2b. The mechanical-vibration-capable unit 4 has two vibrating elements 9a, 9b, which are aligned in parallel to one another and are configured here in a rod-shaped manner. They are mounted on a disk-shaped element 12 and can be excited separately from one another to vibrate mechanically. Their vibrations can likewise be received and evaluated separately from one another. The two vibrating elements 9a and 9b respectively have a cavity 10a and 10b, in which at least one piezoelectric element 11a and 11b is respectively arranged in the region facing the disk-shaped element 12. With respect to the embodiment according to FIG. 2b, reference is again furthermore made to the previously unpublished German patent application with reference number DE102017130527A1.

[0043] As shown schematically in FIG. 2b, according to the invention, the sensor unit 2 is supplied on the one hand with an excitation signal A in such a way that the vibration-capable unit 4 is excited to vibrate mechanically. The vibrations are generated by means of the two piezoelectric elements 11a and 11b. It is conceivable both for both piezoelectric elements to be supplied with the same excitation signal A and for the first vibrating element 11a to be supplied with a first excitation signal A.sub.1 and the second vibrating element 11b to be supplied with a second excitation signal A.sub.2. It is also conceivable for a first reception signal E.sub.A to be received on the basis of the mechanical vibrations, or for each vibrating element 9a, 9b to receive a separate reception signal E.sub.A1 or E.sub.A2.

[0044] In addition, a transmission signal S is emitted from the first piezoelectric element 11a and is received in the form of a second reception signal E.sub.S by the second piezoelectric element 11b. Since the two piezoelectric elements 11a and 11b are arranged at least in the region of the vibrating elements 9a and 9b, the transmission signal S passes through the medium M, provided that the sensor unit 2 is in contact with the medium M and is influenced accordingly by the properties of the medium M. The transmission signal S is preferably an ultrasonic signal, especially, a pulsed ultrasonic signal, especially, at least one ultrasonic pulse. However, it is also conceivable for the transmission signal S to be emitted by the first piezoelectric element 11a in the region of the first vibrating element 9a and to be reflected at the second vibrating element 9b. In this case, the second reception signal E.sub.S is received by the first piezoelectric element 11a. In this case, the transmission signal S passes through the medium M twice, which leads to a doubling of a transit time T of the transmission signal S.

[0045] In addition to these two embodiments shown of an apparatus 1 according to the invention, numerous other variants are also conceivable, which likewise fall within the present invention. For example, for the embodiments according to figures FIG. 2a and FIG. 2b, it is possible to use only one piezoelectric element 11a, 11b and to arrange it at least in one of the two vibrating elements 9a, 9b. In this case, the piezoelectric element 9a serves to generate the excitation signal and the transmission signal S, and to receive the first E.sub.1 and the second reception signal E.sub.2. In this case, the transmission signal is reflected at the second vibrating element 9b without piezoelectric element 11b.

[0046] Another exemplary possibility is depicted in FIG. 2c. Here, a third piezoelectric element 11c is provided in the region of the membrane 12. The third piezoelectric element 11c serves to generate the excitation signal A and to receive the first reception signal E.sub.1; the first 11a and the second piezoelectric element 11b serve to generate the transmission signal S or to receive the second reception signal E.sub.2. Alternatively, it is possible, for example, to generate the excitation signal A and the transmission signal S and receive the second reception signal E.sub.2 with the first 11a and/or the second piezoelectric element 11b, wherein the third piezoelectric element 11c serves to receive the first reception signal E.sub.1. It is also possible to generate the transmission signal S with the first 11a and/or the second piezoelectric element 11b and the excitation signal A with the third piezoelectric element 11c and to receive the first E.sub.1 and/or the second reception signal E.sub.2 with the first 11a and/or the second piezoelectric element 11b. In the case of FIG. 2c, it is also possible for other embodiments to dispense with the first 11a or the second piezoelectric element 11b.

[0047] Yet another possible embodiment of the apparatus 1 is the subject matter of FIG. 2d. Starting from the embodiment of FIG. 2b, the apparatus comprises a third 9c and a fourth vibrating element 9d. However, the latter do not serve to generate vibrations. Rather, a third 11c and a fourth piezoelectric element 11d are respectively arranged in the additional elements 9c, 9d. In this case, the vibronic measurement is carried out by means of the first two piezoelectric elements 11a, 11b and the ultrasonic measurement by means of the other two piezoelectric elements 11c, 11d. Here as well, a piezoelectric element, e.g., 11b and 11d, can be dispensed with depending on the measurement principle. For reasons of symmetry, however, it is advantageous to always use two additional vibrating elements 9c, 9d.

[0048] In principle, the first E.sub.A and the second reception signal E.sub.S result according to the invention from different measurement methods and can be evaluated independently of one another with respect to different process variables P.sub.1 and P.sub.2. This results in a higher degree of accuracy with regard to the determination of the various available process variables and in a greater number of determinable variables. A comprehensive and precise characterization of the respective process is accordingly possible.

[0049] An advantageous embodiment of the method according to the invention includes the determination of the concentration of two different substances contained in the medium. In order to be able to determine a first concentration of a first substance and a second concentration of a second substance, which are both contained in the same medium, two different process variables or process parameters must be determined independently of one another. According to the invention, the two necessary process variables or process parameters can be determined by means of two independent measurement methods, but by means of the same sensor unit. This leads to increased accuracy with regard to the determination of the two concentrations and.

[0050] A preferred application in this context consists in monitoring a fermentation process. In this case, sugar is converted to ethanol. An exemplary possibility for determining the two concentrations and of sugar and ethanol consists in determining the density p of the medium M on the basis of the first reception signal and the sound velocity of the medium on the basis of the second reception signal.

[0051] Another preferred application consists in monitoring an inversion of sugar or an invert sugar. In this case, the proportion to which a sugar mixture, generally household sugar, has converted to glucose or fructose is monitored. In this case, the two concentrations of glucose and fructose can also be determined on the basis of the first and second reception signals.

[0052] The density p can be determined, for example, on the basis of the following equation:

[00001]$\rho =\frac{1}{S}.Math.\left[{\left(\frac{F_0}{F_{Med}}\right)}^2-1\right]$

[0053] Here, F.sub.Med is the vibration frequency of the vibration-capable unit 4 in the medium M, F.sub.0 is the reference frequency of the vibration-capable unit 4 in vacuum or in air, and S describes the sensitivity of the sensor unit 2. The vibration frequency of the vibration-capable unit 4 in the medium M, F.sub.Med, can be determined directly on the basis of the first reception signal E.sub.A.

[0054] The sound velocity v.sub.M of the medium M can in turn be determined from the distance L between the first 11a and the second piezoelectric element 11b, which serve as transmitting unit and receiving unit, along with the transit time T of the transmission signal S from the first 11a to the second piezoelectric element 11b according to the following equation:

[00002]$v_M=\frac{L}{\tau }$

[0055] The dependence of the density p and the sound velocity v.sub.M is illustrated in FIG. 3a. FIG. 3a shows for this purpose a schematic drawing of a vibration-capable unit 4 in the form of a tuning fork with two vibrating elements 9a and 9b arranged at a distance L from one another. For the following consideration, it is furthermore assumed that a deposit of thickness h has formed in the region of the vibrating elements 9a and 9b.

[0056] FIG. 3b shows the sound velocity v.sub.M, which was calculated on the basis of the measured transit time T and on the basis of the distance L between the two vibrating elements 9a and 9b, for a medium M with a density p of 2.0 g/cm.sup.3 at a temperature of 20° C. As the deposit increases, or as the thickness h of the deposit increases, the measured sound velocity v.sub.M increases.

[0057] FIG. 3c again shows the density p, calculated on the basis of the measured vibration frequency f of the vibration-capable unit 4, at a temperature of 20° C. as a function of the deposit thickness h. The density p also increases with increasing thickness h of the deposit, but the slopes of the density p and of the sound velocity v.sub.M are respectively different depending on the thickness h of the deposit.

[0058] Hereinafter, a preferred exemplary embodiment for compensating or reducing the influence of a deposit on the determination of a process variable P.sub.1-P.sub.3 is illustrated. The following considerations apply analogously to the case in which a drift and/or aging of the sensor unit 2 occurs. It should furthermore be pointed out that the compensation of the influence of the deposit described here is merely one of many ways of compensating for the influence of a deposit. Accordingly, the present invention is by no means limited to the exemplary embodiment indicated below.

[0059] In order to compensate for the influence of a deposit, a variable FM derived from at least one process variable can be determined. In the present case, the variable FM is determined on the basis of the sound velocity v.sub.M and the density p according to

[00003]$FM=\frac{v_m}{{\rho }^n}$

[0060] This variable is shown in FIG. 3d for the case of n=0.5. As can be seen from the graph, the influence of a deposit of thickness h on the variable FM is negligible. If a process variable P.sub.1-P.sub.3 is calculated on the basis of the variable FM, the calculation takes place essentially without the influence of a deposit.

LIST OF REFERENCE SIGNS

[0061] 1 Vibronic sensor [0062] 2 Sensor unit [0063] 3 Reservoir [0064] 4 Vibration-capable unit [0065] 5 Driving/receiving unit [0066] 6 Electronic unit [0067] 8 Base [0068] 9a, 9b Vibrating elements [0069] 10a, 10b Cavities [0070] 11a 11b Piezoelectric elements [0071] 12 Disk-shaped element [0072] M Medium [0073] P.sub.1-P.sub.3 Process variables [0074] A Excitation signal [0075] S Transmission signal [0076] E.sub.A First reception signal [0077] E.sub.S Second reception signal [0078] ΔΦ Specifiable phase shift [0079] p Density of the medium [0080] v Viscosity of the medium [0081] v.sub.M Sound velocity of the medium [0082] T Transit time [0083] a First substance [0084] b Second substance [0085] C.sub.a Concentration of the first substance [0086] C.sub.b Concentration of the second substance [0087] L Distance between the two fork teeth [0088] H Thickness of the deposit on the sensor unit