Vibration Multi-Sensor

Abstract

The invention relates to a device (1) and a method for determining and / or monitoring at least one process variable (P) of a medium (M). The device comprises a sensor unit (2) having a mechanically oscillatable unit (4), at least a first piezoelectric element (11a), a temperature detection unit (13) for determining and / or monitoring the temperature (T) of the medium (M), and an electronic unit (6). The device (1) is designed to excite the mechanically oscillatable unit (4) by means of an excitation signal (A), so that mechanical oscillations are performed, and to receive the mechanical oscillations of the oscillatable unit (4) and convert them into a first received signal (EA), to transmit a transmitted signal (S) and to receive a second received signal (ES), and the electronic unit (6) is designed to measure at least one process variable (P) based on the first received signal (EA) and / or the second received signal (ES), and to measure the temperature (T) of the medium based on a third received signal (ET) received by the unit (13).

Description

Technical Field

[0001] The invention relates to a device for determining and / or monitoring at least one process variable of a medium, comprising a sensor unit with a mechanically oscillatable unit, at least one piezoelectric element, a unit for determining and / or monitoring the temperature of the medium and an electronic unit. Furthermore, the invention relates to a method for determining and / or monitoring at least one process variable of a medium. The medium is located in a container, for example a vessel or a pipeline. Background Art

[0002] Vibration sensors are widely used in process and / or automation technology. In the case of a level measuring device, such a device has at least one mechanically oscillatable unit, such as, for example, an oscillating fork, a single fork tine or a membrane. The mechanically oscillatable unit is excited during operation by an exciter / receiver unit, which is usually in the form of an electromechanical transducer unit, so that mechanical oscillations are performed. The electromechanical transducer unit can be, for example, a piezoelectric drive or an electromagnetic drive. The corresponding field devices are produced in large quantities by the applicant and sold under the trademarks LIQUIPHANT and SOLIPHANT, for example. In principle, the basic measuring principle is known from a large number of publications. The exciter / receiver unit excites the mechanically oscillatable unit by an electrical excitation signal, so that mechanical oscillations are performed. Conversely, the exciter / receiver unit can receive the mechanical oscillations of the mechanically oscillatable unit and convert them into electrical receiving signals. The exciter / receiver unit is accordingly either a separate drive unit and a separate receiving unit, or a combined exciter / receiver unit.

[0003] In this case, the exciter / receiving unit is in many cases part of a feedback, electrical, oscillating circuit, by means of which the excitation of the mechanically oscillatable unit occurs, so that a mechanical oscillation is performed. For example, for a resonant oscillation, the oscillating circuit condition must be met, according to which the amplification factor is ≥ 1 and the sum of all phases occurring in the oscillating circuit is a multiple of 360. For the excitation and for meeting the oscillating circuit condition, a certain phase shift between the excitation signal and the receiving signal must be ensured. Therefore, usually, a predetermined value for the phase shift is set, thereby setting a desired value for the phase shift between the excitation signal and the receiving signal. To this end, the prior art offers the most diverse solutions, including both analog as well as digital methods, such as described, for example, in DE 10 2006 034 105 A1, DE 10 2007 013 557 A1, DE 10 2005 015 547 A1, DE 10 2009 026 685 A1, DE 10 2009 028 022 A1, DE 10 2010 030 982 A1 or DE 00 10 2010 030 982 A1.

[0004] Both the excitation signal and the received signal are characterized by a frequency ω, an amplitude A and / or a phase φ. Accordingly, changes in these variables are usually taken into account in order to determine a specific process variable. The process variable can be, for example, a material level, a predetermined material level or the density or viscosity of a medium and its flow rate. In the case of a vibrating limit level switch for liquids, for example, a distinction is made whether the oscillatable unit is covered by liquid or is oscillating freely. The two states, free state and covered state, are distinguished in this case, for example, based on different resonance frequencies and therefore on frequency shifts.

[0005] When the oscillatable unit is completely covered by the medium, the density and / or viscosity can only be determined by such a measuring device. With regard to determining the density and / or viscosity, different options are also described in the prior art, such as for example those disclosed in DE 10050299 A1, DE 10 2007 043 811 A1, DE 10057974 A1, DE 10 2006 033 819 A1, DE 10 2015 102 834 A1 or DE 10 2016 112 743 A1.

[0006] Many process variables can be determined with vibration sensors and used to characterize a given process. However, in many cases, for comprehensive process monitoring and / or control, additional information about the process is required, in particular knowledge about other physical and / or chemical process variables and / or parameters. This can be handled, for example, by integrating other field devices into the process. The measured values ​​provided by the different measuring devices can then be appropriately further processed in the superordinated unit of the device.

[0007] However, the situation now is that different measuring devices can have different measurement accuracies on the one hand. In addition, drift and / or aging effects can be very different in each case. Such effects can make a given measurement or process monitoring and / or control very difficult or inaccurate. In addition, it is difficult to detect the condition of the individual field devices in operation. Therefore, from German patent application No. 102018127526.9 (unpublished as of the earliest filing date of the present application) a vibration multi-sensor is known, with which both the vibration measurement principle and the ultrasonic measurement principle can be used to determine and / or monitor one or more process variables. Summary of the invention

[0008] Starting from the above-mentioned prior art, the object of the present invention is to further expand the functionality of the vibration sensor.

[0009] This object is achieved by the device defined in claim 1 and by the method defined in claim 6 .

[0010] With regard to the device, the object is achieved by a device for determining and / or monitoring at least one process variable of a medium, the device comprising a sensor unit having a mechanically oscillatable unit, at least a first piezoelectric element and a temperature detection unit for determining and / or monitoring the temperature of the medium, and an electronic unit. The device is implemented to excite the mechanically oscillatable unit by an excitation signal so that mechanical oscillations are performed, receive the mechanical oscillations of the oscillatable unit and convert them into a first received signal, transmit a transmitted signal, and receive a second received signal. The electronic unit is in turn implemented to determine at least one process variable based on the first and / or second received signal, and to determine the temperature of the medium based on a third received signal received from the temperature detection unit.

[0011] The mechanically oscillatable unit is, for example, a membrane, a single fork tine, an arrangement of at least two oscillating elements or an oscillating fork. The at least one piezoelectric element can be arranged, for example, in the region of the oscillatable unit. On the one hand, it serves as an exciter / receiving unit for generating mechanical oscillations of the mechanically oscillatable unit, which are generated by the excitation signal. When the oscillatable unit is covered by a medium, the mechanical oscillations are in turn influenced by the properties of the medium, so that based on the first received signal representing the oscillation of the oscillatable unit, information about at least one process variable can be generated.

[0012] The piezoelectric element is also used to generate a transmission signal which is received in the form of a second reception signal. When the transmitted signal at least sometimes and partially passes through the medium on its path, it is also influenced by the physical and / or chemical properties of the medium and can be used accordingly to determine the process variable of the medium.

[0013] According to the invention, therefore, at least two measuring principles can be implemented in a single device. The sensor unit performs a mechanical oscillation on the one hand; in addition, a transmission signal is emitted. As a reaction to the mechanical oscillation and the transmission signal, two reception signals are received and can be evaluated, for example, with respect to at least two different process variables. In this case, the two reception signals can advantageously be evaluated independently of one another. According to the invention, therefore, the number of process variables that can be determined can be significantly increased, which results in a higher functionality of the sensor and additional fields of application.

[0014] Furthermore, the device of the invention comprises a temperature detection unit for determining and / or monitoring the temperature of the medium. The temperature detection unit comprises, for example, a temperature sensor. The temperature sensor can be operated, for example, by a temperature signal. Based on a third received signal received from the temperature detection unit, in particular from the temperature sensor, the temperature can be determined, for example, as a third process variable. The temperature has the greatest influence on the other process variables of the medium. By means of the supplementary determination and / or monitoring of the temperature, the measuring accuracy of the multi-sensor can be correspondingly significantly increased and the functionality of the sensors can be supplemented.

[0015] In an advantageous embodiment, the sensor unit comprises at least a first and a second piezoelectric element, wherein the first and the second piezoelectric element are embodied to excite the mechanically oscillatable unit by means of an excitation signal, so that a mechanical oscillation is performed, and to receive the mechanical oscillations of the oscillatable unit and convert them into a first received signal, wherein the first piezoelectric element is embodied to transmit the transmit signal, and wherein the second piezoelectric element is embodied to receive the transmit signal in the form of a second received signal. However, there may be more than two piezoelectric elements, which may be arranged at different positions relative to the oscillatable unit.

[0016] In a further advantageous embodiment, the mechanically oscillatable unit is an oscillating fork having a first and a second oscillating element, 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. Corresponding embodiments of the sensor unit are described, for example, in DE102012100728A1 and in German patent application No.102017130527.0, which was not published as of the earliest filing date of the present application. In the context of the present invention, reference is made to both applications. The embodiments of the sensor units described in these two documents are examples of suitable structural embodiments of the sensor unit. For example, it is not absolutely necessary to arrange the piezoelectric element exclusively in the region of the oscillating element. On the contrary, the piezoelectric element can also be arranged in the region of the membrane or in an additional oscillating element that is not used for vibration excitation but is also applied to the membrane.

[0017] A further embodiment of the device comprises a temperature detection unit for determining and / or monitoring the temperature, which comprises a temperature sensor in the form of a resistance element or a thermocouple.

[0018] Advantageously, the temperature sensing unit for determining and / or monitoring the temperature is arranged in such a way that it has the best possible thermal coupling with the medium. In this case, the difference between the temperature of the medium and the temperature of the sensor unit is small. The temperature sensing unit should accordingly be arranged in an area of ​​the device which is at least sometimes and / or partially in contact with the medium. The temperature sensing unit can be arranged, for example, in the area of ​​or in the vicinity of the oscillatable unit. It is also advantageous if the sensor unit is embodied such that its thermal capacity is as small as possible. In this case, the response time of the temperature determination after a change in the temperature of the medium is short.

[0019] Another preferred embodiment of the device comprises a sensor unit, which comprises a unit for determining and / or monitoring the pressure and / or a unit for determining and / or monitoring the conductivity and / or capacitance of the medium. Due to the implementation of additional measuring principles in a single sensor, the application range of the sensor as well as the measuring accuracy can be further expanded and improved.

[0020] Furthermore, the object of the invention is achieved by a method for determining and / or monitoring at least one process variable of a medium, wherein

[0021] - the sensor unit is excited by the excitation signal so that a mechanical oscillation is performed,

[0022] - the mechanical oscillation is received by the sensor unit and converted into a first received signal,

[0023] - the sensor unit transmits a transmission signal and receives a second reception signal,

[0024] - Based on the first and / or second received signal, at least one process variable is determined, and based on the third received signal, the temperature of the medium is determined.

[0025] The method is particularly suitable for a device according to one of the above-described embodiments. On the one hand, as an option, the sensor unit can be operated simultaneously by the excitation signal and the transmission signal, wherein the excitation signal and the transmission signal are superimposed on each other. However, alternatively, the sensor unit can also be operated alternately by the excitation signal and the transmission signal.

[0026] The excitation signal is for example an electrical signal with at least one predetermined frequency, in particular a sinusoidal or rectangular signal. Preferably, the mechanically oscillatable unit is at least sometimes excited to perform a resonant oscillation. The mechanical oscillations are influenced by the medium surrounding the oscillatable unit, so that based on the received signal representing the oscillations, information about different properties of the medium can be obtained.

[0027] The transmitted signal is preferably an ultrasonic signal, in particular a pulsed ultrasonic signal, in particular at least one ultrasonic pulse. Therefore, an ultrasonic-based measurement method is performed as the second applied measurement method according to the present invention. The transmitted signal at least partially passes through the medium and its characteristics are affected by the medium. Accordingly, based on the second received signal, information about different media can also be obtained.

[0028] With the method of the invention, a plurality of different process variables can be determined by different measuring principles. In addition, in each case, the influence of temperature can be taken into account. The different process variables can advantageously be determined independently of one another, so that a comprehensive analysis of the process can be performed by a single measuring device. In addition, since the same sensor unit is used for a variety of measuring methods, the measuring accuracy can be significantly increased. In addition, based on different measuring principles, condition monitoring of the device can be performed. For this purpose, many embodiments of the method of the invention are possible, some of which are preferred variants are given below.

[0029] A preferred embodiment provides for determining at least two different process variables, wherein a first process variable is determined based on the first received signal, and wherein a second process variable is determined based on the second received signal.

[0030] A further preferred embodiment comprises compensating for the influence of the medium temperature on at least the first and / or the second received signal or on at least one process variable derived from the received signal.

[0031] Another embodiment of the method provides for obtaining information about the process that the medium undergoes based on the temperature of the medium. For example, based on the temperature determined in each case, a mixture of different media with different temperatures can be sensed and / or monitored. In this case, short-term fluctuations in the temperature of the mixture can occur suddenly, which can have a negative impact on the determination of specific process variables. Likewise, it can be detected whether a specific sensor is operated outside the permitted temperature operating range. Another possible task is to observe the cleaning process of the sensor. In the case of a cleaning process, different cleaning cycles can be sensed and / or monitored. Usually, the sensor unit is treated at high temperature, for example with hot steam, cold water flushing, which means that there are large changes in the temperature determined by the temperature detection unit used to determine and / or monitor the temperature. Likewise, as an option, the sensor unit is calibrated during individual process steps of the cleaning process, for example during a cold flushing process.

[0032] In a particularly preferred embodiment of the method according to the invention, the first value of the temperature is determined by means of a temperature detection unit for determining and / or monitoring the temperature, and / or wherein the second value of the temperature is determined based on the electromechanical efficiency of the first and / or second piezoelectric element. The temperature determination based on the electromechanical efficiency of the piezoelectric element is described in detail in DE 10 2016 120 326 A1, to which reference is made in its entirety in the context of the present invention.

[0033] The first and second temperature values ​​are then advantageously compared with one another.

[0034] It is also advantageous if a diagnosis of at least one component of the sensor unit is performed based on the comparison. The device is in particular a device according to the invention.

[0035] The diagnosis can include, for example, on the one hand, information about a temperature detection unit for determining and / or monitoring the temperature, or information about the condition of the first and / or second piezoelectric element. Advantageously, in this way, a plausibility check can be performed on the individual, applied measuring principles, in particular the two received signals, and the response signal received from the temperature detection unit for determining and / or monitoring the temperature.

[0036] Another particularly preferred embodiment comprises that at least one process variable is a predetermined fill level, density, viscosity, sound velocity or a variable derived from at least one of these variables. Particularly preferably, the density of the medium is determined based on the first received signal and the sound velocity within the medium is determined based on the second received signal. However, it should be understood that in this case, in addition to the explicitly mentioned process variables, other process variables and / or parameters accessible by means of the two performed measurements can also be determined and taken into account in order to characterize the specific process.

[0037] One embodiment of the method according to the invention provides that a reference value for the density is determined based on the speed of sound, wherein the reference value is compared with the density value determined from the first received signal. Preferably, based on the speed of sound determined from the second received signal, the concentration of a reference substance dissolved in a reference medium in a specifiable container is determined. Based on the concentration, a reference value for the density of the reference medium can be determined. Furthermore, a measured value for the density can be determined from the first received signal. The two density values ​​can be compared with one another. In particular, the density value determined from the first received signal can be adjusted based on the density reference value determined from the second received signal. In this way, adverse effects of the geometry of the container used on the vibration determination of the density can be compensated.

[0038] A particularly preferred embodiment comprises determining a first concentration of a first substance contained in the medium and a second concentration of a second substance contained in the medium based on the first and second received signals and / or based on the first and second process variables. In the prior art for such analysis of a medium of two different substances, two separate measuring devices are usually required, which provide different measured variables. In contrast, according to the invention, information about two different components in the medium can be reliably obtained by a single device.

[0039] A preferred application of the method relates to monitoring a fermentation process. During the fermentation process, sugars are converted into ethanol. In order to be able to ensure quality monitoring, it is necessary to determine both the concentration of sugars and the concentration of ethanol. According to the present invention, this is possible.

[0040] Finally, an advantageous embodiment of the method comprises determining, based on the first and second received signals and / or based on the first and second process variables, whether a deposit has formed on the sensor unit and / or whether a drift and / or aging of the sensor unit exists. Depending on a deposit on the probe unit, a drift or aging in the region of the sensor unit, the two received signals generally behave differently from one another. For example, based on a consideration of the two received signals over time and / or the process variables, the presence of a deposit, a drift or aging can be detected accordingly.

[0041] Advantageously, the first and second received signals, the first and second process variables and / or the first and second received signals and / or the first and second process variables as a function of time are compared with one another. By comparison, the presence of an accumulation, a drift or an aging of the sensor unit can be indicated. Since at least two received signals or process variables are accessible, a high precision of the information about the accumulation, the drift or the aging can be achieved. Since according to the invention two different measurements are realized with a single sensor unit, the presence of an accumulation, a drift or an aging of the sensor unit can be reliably detected.

[0042] In a further particularly preferred embodiment, in the case of determining and / or monitoring at least one process variable, or in the case of determining a variable derived from at least one process variable and / or at least one received signal, the influence of the deposit, drift and / or aging of the sensor unit on the first and / or second received signal is reduced or compensated. Thus, in the case of determining and / or monitoring a specific process variable, the influence of the deposit, drift and / or aging of the sensor unit can be taken into account, so that the process variable can be determined without being influenced by the deposit, drift and / or aging. In order to reduce or compensate for such influences, for example, a suitable, in particular process-related algorithm can be provided, based on which a value of a specific process variable can be determined that is not corrupted by the influence of the deposit, drift and / or aging of the sensor unit. Thus, an increase in the measurement accuracy can be achieved, and a method for predictive maintenance is provided.

[0043] Furthermore, it should be noted that embodiments described in conjunction with the apparatus of the present invention may also be applied mutatis mutandis to the method of the present invention, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will now be explained in more detail based on the accompanying drawings, which are as follows:

[0045] Figure 1 is a schematic diagram of a vibration sensor according to the prior art,

[0046] Figure 2 are embodiments of sensor units known in the prior art and suitable for carrying out the method of the invention, and

[0047] Figure 3 is an embodiment of the device according to the invention having a device for determining the temperature of a medium.

[0048] In the drawings, identical elements have identical reference numerals. DETAILED DESCRIPTION

[0049] Figure 1A vibration sensor 1 with a sensor unit 2 is shown. The sensor has a mechanically oscillatable unit 4 in the form of an oscillating fork, which is partially immersed in a medium M located in a container 3. The oscillatable unit 4 is excited by an exciter / receiving unit 5, so that the oscillatable unit 4 performs mechanical oscillations, and can be, for example, a piezoelectric stack or a bimorph driver. Other vibration sensors use, for example, an electromagnetic exciter / receiving unit 5. A single exciter / receiving unit 5 can be used, which is used both for exciting and for detecting mechanical oscillations. Likewise, it is possible to choose to implement separate drive units and separate receiving units. In addition, Figure 1 An electronics unit 6 is shown, via which signal recording, evaluation and / or feeding takes place.

[0050] As an example, Figure 2 Detailed Description of the Invention Different sensor units 2 are shown which are suitable for carrying out the method according to the invention. Figure 2 The mechanically oscillatable unit 4 shown in a comprises two oscillating elements 9a, 9b, which are also referred to as fork teeth, applied on a base 8. In addition, optionally, in each case, a paddle (not shown) can be formed at the end of the two oscillating elements 9a, 9b. In each of the two oscillating elements 9a, 9b, a particularly bag-shaped hollow space 10a, 10b is provided in each case, in which at least one piezoelectric element 11a, 11b of the exciter / receiving unit 5 is arranged in each case. Preferably, the piezoelectric elements 11a and 11b are cast in the hollow spaces 10a and 10b. In this case, the hollow spaces 10a, 10b can be formed so that the two piezoelectric elements 11a, 11b are located completely or partially in the region of the two oscillating elements 9a, 9b. This arrangement and similar arrangements are described in detail in DE102012100728A1.

[0051] Figure 2 b shows another example of an embodiment of the sensor unit 2. In this case, the mechanically oscillatable unit 4 comprises two parallel rod-shaped oscillating elements 9a, 9b, which are mounted on a disk-shaped element 12 and can be excited independently of one another to perform mechanical oscillations, and in this case the oscillations can likewise be received and evaluated independently of one another. The two oscillating elements 9a and 9b in each case have a hollow space 10a and 10b, in each case at least one piezoelectric element 11a, 11b is arranged in the region facing the disk-shaped element 12. Figure 2 For example b, reference is made to DE 10 2017 130 527 A1, which was not published as of the earliest filing date of the present application.

[0052] like Figure 2As schematically shown in FIG. 1 , according to the invention, the sensor unit 2 is provided with an excitation signal A on the one hand, so that the oscillatable unit 4 is excited and thus performs mechanical oscillations. In this case, the oscillations are generated by the two piezoelectric elements 11a and 11b. The two piezoelectric elements can be provided with the same excitation signal A, or the first oscillating element 11a can be provided with a first excitation signal A1 and the second oscillating element 11b can be provided with a second excitation signal A2. Likewise, it is possible to select a first reception signal E based on the mechanical oscillations. A , or each oscillating element 9a, 9b receives a separate reception signal E A1 、E A2 .

[0053] In addition, the transmission signal S is transmitted from the first piezoelectric element 11a, and the transmission signal S is received by the second piezoelectric element 11b as a second reception signal E S Since the two piezoelectric elements 11a and 11b are arranged at least in the region of the oscillating elements 9a and 9b, when the sensor unit 2 is in contact with the medium M, the transmitted signal S passes through the medium M and is correspondingly affected by the characteristics of the medium M. Preferably, the transmitted signal S is in particular a pulsed ultrasonic signal, in particular having at least one ultrasonic pulse. Likewise, however, it is also possible to select that the transmitted signal S from the first piezoelectric element 11a is transmitted in the region of the first oscillating element 9a and reflected on the second oscillating element 9b. In this case, the second received signal E S Received by the first piezoelectric element 11a. In this case, the transmission signal S passes through the medium M twice, which results in the propagation time τ of the transmission signal S being doubled.

[0054] In addition to the two illustrated embodiments of the device 1 of the present invention, many other variations are possible, which also fall within the scope of the present invention. Figure 2 a and Figure 2 In the embodiment of FIG. 1 , only one piezoelectric element 11a, 11b may be used, and such a piezoelectric element may be arranged in at least one of the two oscillating elements 9a, 9b. In this case, the piezoelectric element 11a is used to generate the excitation signal and the transmission signal S, and to receive the first reception signal E1 and the second reception signal E2. In this case, the transmission signal is reflected on the second oscillating element 9b lacking the piezoelectric element 11b.

[0055] Figure 2c shows another embodiment by way of example. In this case, the third piezoelectric element 11c is arranged in the area of ​​the membrane 12. The third piezoelectric element 11c is used to generate an excitation signal A and receive a first reception signal E1, while the first piezoelectric element 11a and the second piezoelectric element 11b are used to generate a transmission signal S and receive a second reception signal E2. Alternatively, for example, the first piezoelectric element 11a and / or the second piezoelectric element 11b can be used to generate the excitation signal A and the transmission signal S, and to receive the second reception signal E2, wherein the third piezoelectric element 11c is used to receive the first reception signal E1. Similarly, the first piezoelectric element 11a and / or the second piezoelectric element 11b can be used to generate the transmission signal S, the third piezoelectric element 11c can be used to generate the excitation signal A, and the first piezoelectric element 11a and / or the second piezoelectric element 11b can be used to receive the first reception signal E1 and / or the second reception signal E2. Similarly in Figure 2 c, in other embodiments, the first piezoelectric element 11 a or the second piezoelectric element 11 b may be omitted.

[0056] Another embodiment of the device 1 is Figure 2 d. The device is based on Figure 2 b, and comprises a third oscillating element 9c and a fourth oscillating element 9d. However, these cannot be used to generate oscillations. Instead, the third piezoelectric element 11c and the fourth piezoelectric element 11d are arranged in the additional elements 9c, 9d, respectively. In this case, the vibration measurement is carried out by the first two piezoelectric elements 11a, 11b, and the ultrasonic measurement is carried out by the other two piezoelectric elements 11c, 11d. In this case as well, one piezoelectric element, for example 11b and 11d, can be omitted for each measuring principle. However, for reasons of symmetry, it is advantageous to always use two additional oscillating elements 9c, 9d.

[0057] The first received signal E A and the second received signal E S are generated by 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 German patent application No. 102018127526.9, which was unpublished as of the earliest filing date of the present application and to which reference is made in its entirety in the context of the present invention.

[0058] Furthermore, according to the invention, the temperature of the medium can be determined and / or monitored. Figure 3 As shown, the device according to the invention has a temperature detection unit for determining and / or monitoring the temperature. Figure 3 Shows something like Figure 2A temperature detection unit 13 is arranged between the two oscillating elements 9a and 9b of the oscillatable unit 4 (embodied in the form of an oscillating fork) for determining and / or monitoring the temperature T of the medium. The temperature detection unit 13 comprises a temperature sensor 14, for example in the form of a resistance element or a thermocouple.

[0059] Alternatively, the temperature detection unit 13 for determining and / or monitoring the temperature may be arranged, for example, in the region of the oscillating elements 9 a , 9 b or in the region of the base 8 .

[0060] Reference Mark List

[0061] 1 Vibration sensor

[0062] 2 Sensor unit

[0063] 3 Container

[0064] 4 Oscillating units

[0065] 5 Exciter / Receiver Unit

[0066] 6 Electronic unit

[0067] 8 Base

[0068] 9a, 9b Oscillating element

[0069] 10a, 10b Hollow space

[0070] 11a, 11b Piezoelectric element

[0071] 12 Disc-shaped element

[0072] 13. Temperature detection unit for determining and / or monitoring temperature

[0073] 14 Temperature Sensor

[0074] M Medium

[0075] P Process parameter

[0076] T Temperature

[0077] A Excitation signal

[0078] S Transmit signal

[0079] E A First received signal

[0080] E S The second received signal

[0081] E T The third received signal

[0082] ΔΦ Predeterminable phase shift

Claims

1. A device (1) for determining and / or monitoring at least two different process variables (P1, P2) of a medium (M), the device (1) comprising: A sensor unit (2) comprising: a mechanically oscillatable unit (4), at least a first piezoelectric element (11a) and a second piezoelectric element (11b), a temperature detection unit (13) for determining and / or monitoring the temperature (T) of the medium (M), and Electronic unit (6), wherein the mechanically oscillatable unit (4) is an oscillatory fork having a first oscillatory element (9a) and a second oscillatory element (9b), wherein the first piezoelectric element (11a) is at least partially arranged in the first oscillating element (9a), wherein the second piezoelectric element (11b) is at least partially arranged in the second oscillating element (9b), The first piezoelectric element (11a) and the second piezoelectric element (11b) are implemented to excite the mechanical oscillatory unit (4) through an excitation signal (A), so that mechanical oscillation is performed, and receive the mechanical oscillation of the oscillatory unit (4) and convert it into a first receiving signal (E A ), wherein the first piezoelectric element (11a) is implemented to emit a transmission signal (S) as an ultrasonic signal, The second piezoelectric element (11b) is implemented to receive a second receiving signal (E S ), and The electronic unit (6) is implemented to receive the first received signal (E A ) to determine the density of the medium (M) as a first process variable, The electronic unit (6) is implemented to receive the second received signal (E S ) to determine the sound velocity of the medium (M) as a second process variable (P2), The electronic unit (6) is implemented to receive a third received signal (E) from the temperature detection unit (13) based on the third received signal (E T ) to determine the temperature (T) of the medium (M) as a third process variable, and The electronic unit (6) is designed to compensate for the effect of the temperature (T) of the medium (M) on the first received signal (E A ) and / or the second received signal (E S ), The electronic unit (6) is designed to determine a reference value for the density of the medium (M) based on the determined sound velocity and compare the reference value with a value based on the first received signal (E A ) is compared with the value of the density determined by 2. The device (1) according to claim 1, in, The temperature detection unit (13) for determining and / or monitoring the temperature comprises a temperature sensor (14) in the form of a resistance element or a thermocouple.

3. The device (1) according to claim 1 or 2, in, The electronic unit (6) is embodied to determine a first value of the temperature (T) by means of a temperature detection unit (13) for determining and / or monitoring the temperature (T), wherein the electronic unit (6) is implemented to determine the second value of the temperature (T) based on the electromechanical efficiency of the first piezoelectric element (11a) and / or based on the electromechanical efficiency of the second piezoelectric element (11b), wherein the electronic unit (6) is embodied to compare the first value and the second value of the temperature (T) with each other, and Therein, the electronic unit (6) is designed to perform a diagnosis of at least one component of the sensor unit (2) based on the comparison.

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