VIBRONIC MULTISENSOR

Abstract

A device for determining and/or monitoring a process variable of a medium includes a sensor unit having a mechanically oscillatable unit, a first piezoelectric element, a unit for determining and/or monitoring a temperature of the medium and an electronic system. The device is designed to excite the mechanically oscillatable unit and to receive the mechanical oscillations of the oscillatable unit, to convert them into a first receiving signal, to emit a transmission signal and to receive a second receiving signal, wherein the electronic system is designed to determine the process variable based on the first and/or second receiving signal. The unit for determining and/or monitoring the temperature includes a first and a second temperature sensor arranged at a distance from one another, and the electronic system is designed to determine the temperature of the medium based on a first and/or second temperature receiving signal.

Claims

1-14. (canceled)

15. A device for determining and/or monitoring at least one process variable of a medium, comprising a sensor unit including a mechanically oscillatable unit, at least one first piezoelectric element, and a unit for determining and/or monitoring a temperature of the medium; and an electronics unit, wherein the device is designed to excite the mechanically oscillatable unit via an excitation signal to produce mechanical oscillations, to receive the mechanical oscillations of the oscillatable unit and convert the received mechanical oscillations into a first receiving signal, and to transmit a transmission signal and to receive a second receiving signal, wherein the electronics unit is designed to determine the at least one process variable using the first receiving signal and/or second receiving signal (E.sub.S), wherein the unit for determining and/or monitoring the temperature includes a first temperature sensor and a second temperature sensor, wherein first and second temperature sensors are arranged at a distance from one another, and wherein the electronics unit is designed to determine the temperature of the medium by using a first and/or second temperature receiving signal of the first and/or second temperature sensor received by the unit electronics unit.

16. The device according to claim 15, wherein the sensor unit includes a first piezoelectric element and a second piezoelectric element, wherein the first and second piezoelectric elements are designed to excite the mechanically oscillatable unit to produce mechanical oscillations via an excitation signal and to receive the mechanical oscillations of the oscillatable unit and convert the received mechanical oscillations into a first receiving signal, wherein the first piezoelectric element is designed to emit a transmission signal, and wherein the second piezoelectric element is designed to receive the transmission signal in the form of a second receiving signal.

17. The device according to claim 16, wherein the mechanically oscillatable unit is a vibrating fork having a first oscillating element and a second oscillating element, and wherein the first piezoelectric element is at least partially arranged in the first oscillating element, and the second piezoelectric element is at least partially arranged in the second oscillating element.

18. The device according to claim 15, wherein the first temperature sensor is arranged and/or configured to detect a first temperature in a first end region, facing the medium, of the sensor unit, and the second temperature sensor is arranged and/or configured to detect a second temperature in a second end region, facing away from the medium, of the sensor unit.

19. The device according to claim 18, wherein the unit for determining and/or monitoring a temperature includes a rod-shaped housing element that is arranged such that a longitudinal axis of the rod-shaped housing element is parallel to a longitudinal axis of the oscillatable unit, and wherein the first temperature sensor is arranged in a first end region, facing the medium, of the housing element, and the second temperature sensor is arranged in a second end region, facing away from the medium, of the housing element.

20. A method for determining and/or monitoring at least one process variable of a medium, comprising: exciting, with an excitation signal, a sensor unit to oscillate mechanically; receiving mechanical oscillations by the sensor unit and converting the receive mechanical oscillations into a first receiving signal; emitting from the sensor unit transmission signal and receiving by the sensor unit a second receiving signal; determining the at least one process variable using the first and/or second receiving signals; and determining a first and/or a second value for at least one temperature by using a first and/or a second temperature receiving signal received by a first and/or second temperature sensor.

21. The method according to claim 20, wherein at least two different process variables are determined, wherein a first process variable is determined using the first receiving signal, and wherein a second process variable is determined using the second receiving signal.

22. The method according to claim 20, wherein the at least one process variable is a specifiable fill-level, a density, a viscosity, a sound velocity, or a variable derived from at least one of these variables.

23. The method according to claim 22, further comprising: compensating for an influence of the temperature of the medium on the first and/or second receiving signal or on the first and/or second process variable.

24. The method according to claim 23, further comprising detecting via the first temperature sensor a value for a first temperature in an end region, facing the medium, of the sensor unit; and/or detecting via the second temperature sensor a value for a second temperature in an end region, facing away from the medium, of the sensor unit, wherein a temperature is used in each case for determining one of the process variables.

25. The method according to claim 24, further comprising: compensating, by using the first and/or second temperature receiving signal, an influence of the temperature on at least one physical and/or chemical property of at least one component of the sensor unit, upon which property the at least one process variable depends.

26. The method according to claim 25, wherein a value for the first and/or second temperature is determined by using an electromechanical efficiency or a capacitance of at least one piezoelectric element of the sensor unit.

27. The method according to claim 26, wherein, for the first and/or second temperature, the value thereof determined by using the first and/or second temperature receiving signal and the value thereof determined by using the electromechanical efficiency or the capacitance are compared with one another, and wherein, in the case that a deviation between the values determined by means of the first and/or second temperature receiving signal and the values determined by using the electromechanical efficiency or the capacitance exceeds a specifiable limit value, a statement is made about the at least one piezoelectric element or the first and/or second temperature sensor.

28. The method according to claim 27, wherein a heat dissipation in the region of the sensor unit, is determined by using a difference between the values, determined by using the first and second temperature receiving signals, for the first and second temperature, and wherein, in the event that the difference exceeds a specifiable limit value, a warning is output.

Description

[0054] The invention is explained in greater detail with reference to the following figures, in which:

[0055] FIG. 1 shows a schematic drawing of a vibronic sensor according to the prior art,

[0056] FIG. 2 shows several 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

[0057] FIG. 3 shows a possible embodiment of a device according to the invention with a unit for determining the temperature of the medium.

[0058] In the figures, identical elements are respectively provided with the same reference signs.

[0059] FIG. 1 shows a vibronic sensor 1 having a sensor unit 2. The sensor has a mechanically oscillatable unit 4, in the form of a vibrating fork, which is partially dipped into a medium M which is located in a container 3. The oscillatable unit 4 is excited by the excitation/receiving unit 5 to mechanical oscillations and can, for example, be excited by means of a piezoelectric stack drive or bimorphic drive. Other vibronic sensors have electromagnetic drive/receiver units 5, for example. It is possible to use a single drive/receiver unit 5 which serves both to excite the mechanical oscillations and to detect them. However, it is conceivable as well to realize one each of a drive unit and a receiver unit. Furthermore, depicted in FIG. 1, is an electronics unit 6 by means of which the signal acquisition, evaluation, and/or feed takes place.

[0060] FIG. 2 shows, by way of example, various sensor units 2, which are suitable for carrying out a method according to the invention. The mechanically oscillatable unit 4 shown in FIG. 2a comprises two oscillating elements 9a, 9b, which are mounted on a base 8 and which are therefore also referred to as fork teeth. Optionally, a paddle [not shown here] may respectively also be formed on the end sides of the two oscillating elements 9a, 9b. In each of the two oscillating elements 9a, 9b, a cavity 10a, 10b, and, especially, a pocket-like cavity, is respectively introduced, in which at least one piezoelectric element 11a, 11b of the drive/receiver 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 oscillating elements 9a, 9b. Such an arrangement along with similar arrangements are extensively described in DE102012100728A1.

[0061] Another possible exemplary embodiment of a sensor unit 2 is depicted in FIG. 2b. The mechanically oscillatable unit 4 has two oscillating 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 oscillate mechanically. Their oscillations can likewise be received and evaluated separately from one another. The two oscillating 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 in turn further made to the previously unpublished German patent application with reference number DE102017130527A1.

[0062] 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 oscillatable unit 4 is excited to oscillate mechanically. The oscillations are generated by means of the two piezoelectric elements 11a and 11b. It is conceivable that the same excitation signal A be applied to both piezoelectric elements, as well as that a first excitation signal A.sub.1 be applied to the first oscillating element 11a and a second excitation signal A.sub.2 be applied to the second oscillating element 11b. It is also conceivable for a first receiving signal E.sub.A to be received on the basis of the mechanical oscillations, or for each oscillating element 9a, 9b to receive a separate receiving signal E.sub.A1 or E.sub.A2.

[0063] In addition, a transmission signal S is emitted from the first piezoelectric element 11a and is received in the form of a second receiving 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 oscillating 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, and, 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 oscillating element 9a and to be reflected at the second oscillating element 9b. In this case, the second receiving 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.

[0064] In addition to these two embodiments shown of an apparatus 1 according to the invention, numerous other variants are also conceivable, which likewise fall under 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 oscillating 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 receiving signal E.sub.2. In this case, the transmission signal is reflected at the second oscillating element 9b without piezoelectric element 11b.

[0065] 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 receiving 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 receiving 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 receiving 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 receiving 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 receiving 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.

[0066] 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 oscillating element 9d. However, the latter do not serve to generate oscillations. 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 upon the measurement principle. For reasons of symmetry, however, it is advantageous to always use two additional oscillating elements 9c, 0d.

[0067] The first E.sub.A and second E.sub.S receiving signals result from different measuring methods and can be evaluated independently of one another with respect to at least one process variable P. In this regard, reference is made to the previously unpublished German patent application with the reference number 102018127526.9, to which reference is made in full within the scope of the present invention.

[0068] Furthermore, according to the invention, the temperature T can be determined very accurately and reliably, and the influence thereof on the particular determined process variables can be compensated for. For this purpose, the device according to the invention has a unit for determining and/or monitoring the temperature, as illustrated in FIG. 3. For the shown example, the sensor unit 2 is designed analogously to the variant from FIG. 2a. Between the two oscillating elements 9a and 9b, the unit 13 is arranged for determining and/or monitoring the temperature T of the medium, which comprises a rod-shaped housing element 14 in which a first temperature sensor 15a and a second temperature sensor 15b are arranged spaced apart from one another. The temperature sensors can be designed, for example, in the form of resistance elements or thermocouples. The first temperature sensor 15a is configured to determine a first temperature T1 in an end region B1, facing the medium M, of the sensor unit 2, while the second temperature sensor 15b is configured to determine a second temperature T2 in an end region B2, facing away from the medium M, of the sensor unit 2. The first and second temperatures T1 and T2 usually differ from one another due to different temperatures of the medium and the environment. In order to be able to determine all available process variables highly accurately, knowledge of the spatially resolved temperature profile of the sensor unit 2 is therefore of great importance. Because of the determination of the temperature at different positions, the achievable measurement accuracy of the multisensor 1 can be considerably increased, and, moreover, a further diagnostic function can be provided.

[0069] Alternative variants not presented separately here for a device 1 according to the invention can, for example, be such that at least one temperature sensor 15a, 15b is arranged in the region of an oscillating element 9a, 9b or in the region of the base 8. It is also conceivable to use more than two temperature sensors 15 which are positioned at a distance from one another.

LIST OF REFERENCE SIGNS

[0070] 1 Vibronic sensor [0071] 2 Sensor unit [0072] 3 Container [0073] 4 Oscillatable unit [0074] 5 Drive/receiver unit [0075] 6 Electronics unit [0076] 8 Base [0077] 9a, 9b Oscillating elements [0078] 10a, 10b Cavities [0079] 11a, 11b Piezoelectric elements [0080] 12 Disk-shaped element [0081] 13 Unit for determining and/or monitoring the temperature [0082] 14 Rod-shaped housing element [0083] 15, 15a, 15b Temperature sensors [0084] M Medium [0085] P Process variable [0086] T, T1, T2 Temperatures [0087] A Excitation signal [0088] S Transmission signal [0089] E.sub.A First receiving signal [0090] E.sub.S Second receiving signal [0091] E.sub.T Third receiving signal [0092] Δϕ Specifiable phase shift