Electronic Vibration Multi-Sensor

Abstract

The present invention relates to a device (1) and a method for measuring and / or monitoring at least one process variable (P) of a medium (M). The device comprises a sensor unit (2) having a first mechanical vibration unit (4), at least one first piezoelectric element (11a), a unit (13) for measuring and / or monitoring the electrical conductivity (σ) and / or the capacitance (C) of the medium (M), and an electronic unit (6). The device (1) is designed to excite the mechanical vibration unit (4) to perform mechanical vibrations by means of an excitation signal (A), receive the mechanical vibrations of the vibration unit (4) and convert them into a first received signal (E A ), transmit a transmission signal (S), and receive a second received signal (E S ), and the electronic unit (6) is designed to measure at least one process variable (P) of the medium based on the first received signal (E A ) and / or the second received signal (E S ).

Description

Technical Field

[0001] The invention relates to 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 second piezoelectric element, a unit for determining and / or monitoring the temperature of the medium, and an electronics 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 in a vessel or in a pipeline. Background Art

[0002] Electronic vibration sensors are widely used in process and / or automation technology. In the case of a filling level measuring device, such a device has at least one mechanical oscillating unit, such as, for example, an oscillating fork, a single fork tooth or a diaphragm. Such an oscillating unit is excited during operation by means of an exciter / receiving unit, which is often in the form of an electromechanical transducer unit, so that mechanical oscillation is performed. The electromechanical transducer unit can be, for example, a piezoelectric drive or an electromagnetic drive. The corresponding field device is mass-produced by the applicant and sold, for example, under the trademarks LIQUIPHANT and SOLIPHANT. The basic measurement principle is generally known from a large number of publications. The exciter / receiving unit excites the mechanical oscillating unit by means of an electrical excitation signal so that mechanical oscillation is performed. Conversely, the exciter / receiving unit is capable of receiving the mechanical oscillations of the mechanical oscillating unit and converting them into electrical receiving signals. The exciter / receiving unit is correspondingly a separate drive unit and a separate receiving unit, or a combined exciter / receiving unit.

[0003] In this case, the exciter / receiving unit is in many cases part of a feedback circuit, an electrical circuit, an 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 an amplification factor ≥ 1 and all phases occurring in the oscillating circuit add up to a multiple of 360°. In order to excite and to meet the oscillating circuit condition, a certain phase shift between the excitation signal and the receiving signal must be ensured. Therefore, a predeterminable value for the phase shift is often 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 and digital methods, such as for example the methods described in DE102006034105A1, DE102007013557A1, DE102005015547A1, DE102009026685A1, DE102009028022A1, DE102010030982A1 or DE00102010030982A1.

[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 filling level, a predetermined filling level or the density or viscosity of the medium and its flow rate. In the case of an electronic vibrating limit switch for liquids, for example, it is distinguished whether the oscillatable unit is covered by liquid or is oscillating freely. The two states (i.e. the free state and the covered state) are distinguished in this case, for example, based on different resonance frequencies and thus on frequency shifts.

[0005] When the oscillatable unit is covered by the medium, the density and / or viscosity can thus only be ascertained with such a measuring device. With regard to determining the density and / or viscosity, different options are also described in the prior art, for example in those published 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 vibronic 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 situation 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 further processed appropriately in a unit superordinate to the device.

[0007] However, it is now the case that different measuring devices may have different measurement accuracies on the one hand. In addition, drift and / or aging effects may be very different in each case. Such effects can combine to make a given measurement or process monitoring and / or control quite difficult or inaccurate. In addition, it may be difficult to detect the condition of individual field devices in ongoing operation. Therefore, from German patent application No. 102018127526.9, which was not published as of the earliest filing date of the present application, a vibronic multi-sensor is known, by means of which both the vibronic measurement principle and the ultrasonic measurement principle can be applied to determine and / or monitor one or more process variables. Summary of the invention

[0008] Starting from the above-mentioned prior art, it is an object of the present invention to further expand the functionality of vibratory electronic sensors.

[0009] This object is achieved by a device as defined in claim 1 and by a method as defined in claim 7 .

[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, a conductivity / capacitance detection unit for determining and / or monitoring the conductivity and / or capacitance of the medium, and an electronic unit. The device is implemented to excite the mechanically oscillatable unit by means of an excitation signal so that a mechanical oscillation is performed, to receive the mechanical oscillations of the oscillatable unit and convert them into a first received signal, to transmit a sent signal, and to receive a second received signal. The electronic unit is further implemented to determine at least one process variable based on the first received signal and / or the second received signal, and to determine the conductivity and / or capacitance of the medium based on a third received signal received from the conductivity / capacitance detection unit.

[0011] The mechanically oscillatable unit is, for example, a diaphragm, a single fork tine, an arrangement of at least two oscillating elements or an oscillating fork. At least one piezoelectric element can be arranged, for example, in the region of the oscillatable unit. It serves on the one hand as an exciter / receiving unit for generating mechanical oscillations of the mechanically oscillatable unit, which are generated with the aid of an 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 oscillations of the oscillatable unit, information about at least one process variable can be generated.

[0012] The piezoelectric element further serves to generate a transmission signal which is received in the form of a second reception signal. When the transmission 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 a process variable of the medium.

[0013] According to the invention, at least two measuring principles can thus be implemented in a single device. On the one hand, the sensor unit performs a mechanical oscillation; in addition, a transmission signal is transmitted. As a reaction to the mechanical oscillation and to 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, the number of ascertainable process variables can thus be significantly increased, which leads to a higher functionality of the sensor and to additional fields of application.

[0014] Furthermore, the device of the invention comprises a conductivity / capacitance detection unit for determining and / or monitoring the conductivity and / or capacitance of the medium. This unit comprises, for example, a sensor unit which is implemented for registering at least one of the two variables. The sensor unit is excited by means of an additional electrical excitation signal and receives a third reception signal from the conductivity / capacitance detection unit. Based on the third reception signal, the conductivity and / or capacitance of the medium can then be ascertained as at least one further process variable. Due to the additional information about the conductivity and / or capacitance of the medium, the application field of the multi-sensor can be significantly improved and the functionality of the sensor is expanded.

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

[0016] In an additional advantageous embodiment, the mechanically oscillatable unit is an oscillating fork having a first oscillating element 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. For example, corresponding embodiments of the sensor unit are described 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, these two applications are comprehensively referenced. The embodiments of the sensor unit 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 diaphragm or in an additional oscillating element that is not used for electronic vibration excitation but is still also applied to the diaphragm.

[0017] A further embodiment of the device comprises that the conductivity / capacitance detection unit for determining and / or monitoring the conductivity and / or capacitance of the medium comprises a capacitive and / or conductive measuring probe having at least one probe electrode.

[0018] The conductivity and capacitive measuring principles are well known from the prior art. In the case of the conductivity measuring principle, for example, it is monitored whether there is an electrical contact between the probe electrode and the wall of the conductive container or the second electrode via the conductive medium. In the case of the capacitive measuring principle, on the contrary, the capacitance of the capacitor formed by the probe electrode and the wall of the container or the second electrode is ascertained.

[0019] Also known from the prior art are multi-sensors which are able to carry out conductivity measurements and capacitive measurements, such as are described, for example, in DE 10 2011 004 807 A1, DE 10 2013 102 055 A1, DE 10 2014 107 927 A1 or DE 10 2013 104 781 A1.

[0020] It is further advantageous if the measuring probe comprises a guard electrode. The use of a guard electrode is used, for example, to prevent disturbing effects of deposits in the region of the sensor unit on the measurement and is described in detail, for example, in DE 32 12 434 C2. Expanding on this, DE 10 2006 047 780 A1 describes a measuring probe with an amplification unit and a limiting element, which is insensitive to the formation of deposits over a large measuring range. In addition, DE 10 2008 043412 A1 describes as a subject a filling level measuring device with a memory unit in which limit values ​​for various media are stored.

[0021] Another preferred embodiment of the device comprises that the sensor unit comprises a unit for determining and / or monitoring the pressure and / or a unit for determining and / or monitoring the temperature of the medium. Due to the implementation of additional measuring principles in a single sensor, the application range of the sensor and the measuring accuracy can be further expanded and improved.

[0022] 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

[0023] - the sensor unit is excited by means of an excitation signal so that a mechanical oscillation is performed,

[0024] - the mechanical oscillation is received by the sensor unit and converted into a first received signal,

[0025] - the sensor unit transmits a transmission signal and receives a second reception signal, and,

[0026] Based on the first received signal and / or the second received signal, at least one process variable is ascertained, and based on the third received signal, the conductivity and / or the capacitance of the medium is ascertained.

[0027] The method can be used in particular for an apparatus according to one of the above-described embodiments. On the one hand, one option is that the sensor unit is operated simultaneously by means of the excitation signal and by means of the transmission signal, wherein the excitation signal and the transmission signal are superimposed on each other. On the other hand, however, the sensor unit can alternate between operation by means of the excitation signal and operation by means of the transmission signal.

[0028] The excitation signal is, for example, an electrical signal having at least one predeterminable frequency, in particular a sinusoidal or rectangular electrical 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.

[0029] 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 properties are affected by the medium. Accordingly, based on the second received signal, information about different media can also be obtained.

[0030] With the method of the invention, a plurality of different process variables can be ascertained by means of different measuring principles. The different process variables can advantageously be determined independently of one another, so that a comprehensive analysis of the process can be performed by means of a single measuring device. Furthermore, since the same sensor unit is used for a plurality of measuring methods, the accuracy of the measurement can be significantly increased. In addition, condition monitoring of the device can be performed based on different measuring principles. For this purpose, many embodiments of the method of the invention are possible, of which some preferred variants are given below.

[0031] A preferred embodiment provides that at least two different process variables are ascertained, wherein the first process variable is ascertained based on the first received signal and wherein the second process variable is ascertained based on the second received signal.

[0032] Another preferred embodiment comprises that the at least one process variable is a predeterminable filling level, density, viscosity, speed of sound 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 speed of sound in the medium is determined based on the second received signal. However, it is to be understood that in addition to the process variables explicitly mentioned here, other process variables and / or parameters accessible by means of the twice performed measurements can likewise be determined and taken into account for characterizing a specific process.

[0033] An embodiment of the method of the invention provides for ascertaining a reference value for the density based on the speed of sound, wherein the reference value is compared with the value of the density ascertained from the first received signal. Preferably, the concentration of a reference substance dissolved in a reference medium in a predeterminable container is ascertained based on the speed of sound ascertained from the second received signal. From this concentration, a reference value for the density of the reference medium can then be ascertained. Additionally, a measured value for the density can be ascertained from the first received signal. The two values ​​for the density can be compared with one another. In particular, the value for the density ascertained from the first received signal can be adjusted based on the reference value for the density ascertained from the second received signal. In this way, it is possible to compensate for adverse effects of the geometry of the utilized container on the electronic vibration determination of the density.

[0034] Another preferred embodiment includes that the electrical impedance and / or the dielectric constant of the medium is ascertained. The electrical impedance and / or the dielectric constant can be ascertained based on the third received signal. For this, in particular, a conductivity / capacitance detection unit is used to determine and / or monitor the conductivity and / or capacitance of the medium.

[0035] A particularly preferred embodiment of the method according to the invention provides that at least the conductivity of the medium, the dielectric constant of the medium and / or the degree of coverage of a conductivity / capacitance detection unit for determining and / or monitoring the conductivity and / or capacitance of the medium are recorded as a function of time, wherein, based on the conductivity, dielectric constant and / or degree of coverage as a function of time, at least one process transpiring in a container containing the medium is monitored. The process can be, for example, a mixing process or a cleaning process. In this regard, reference is made to DE 10 2017 111 393 A1, to which reference is made in the context of the present invention, in particular to the method described therein.

[0036] Particularly preferred embodiments include ascertaining 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 received signal and the second received signal and / or based on the first process variable and the second process variable. In the prior art for such an analysis of a medium for two different substances, as a rule, two separate measuring devices are usually required, which provide different measured variables. According to the invention, on the contrary, information about two different components in the medium can be reliably obtained by means of a single device.

[0037] 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. This is possible according to the invention.

[0038] Finally, an advantageous embodiment of the method comprises finding out, based on the first received signal and the second received signal and / or based on the first process variable and the second process variable, whether a deposit has formed on the sensor unit and / or whether a drift and / or aging of the sensor unit exists. The two received signals typically behave differently from one another depending on a deposit on the probe unit, a drift in the region of the sensor unit or aging. For example, the presence of a deposit, a drift or aging can be detected based on taking into account the two received signals and / or the process variables as a function of time, respectively.

[0039] 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. Based on the comparison, the presence of a deposit, a drift or an aging of the sensor unit can then be indicated. Since at least two received signals or process variables are accessible, a high accuracy of the information about the deposit, drift or aging can be achieved. Since two different measurements are achieved with a single sensor unit according to the invention, the presence of a deposit or a drift or an aging of the sensor unit can be reliably detected.

[0040] A further preferred embodiment of the method comprises determining, based on the electrical conductivity, capacitance, electrical impedance and / or dielectric constant of the medium, based on at least one variable derived from at least one of these variables or based on at least one of these variables as a function of time, whether deposits have formed on the sensor unit and / or whether drift and / or aging of the sensor unit exists.

[0041] In this case, advantageously, based on the first and second received signals and / or based on the first process variable and the second process variable ascertained first information and based on the conductivity, capacitance, electrical impedance and / or dielectric constant of the medium, based on at least one variable derived from at least one of these variables and / or based on at least one of these variables as a function of time, deposits on the sensor unit and / or drift and / or aging of the sensor unit are compared with one another. In this way, information about deposits, drift and / or aging of the sensor unit can be redundantly determined and, in given cases, a plausibility check can be performed.

[0042] Advantageously, therefore, based on the comparison, a condition monitoring of at least one component of the sensor unit is performed.

[0043] In an additional 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 deposits, drifts and / or aging of the sensor unit on at least the first received signal and / or the second received signal is reduced or compensated. Thus, the influence of deposits, drifts and / or aging of the sensor unit can be taken into account in the case of determining and / or monitoring a specific process variable, so that the process variable can be determined without being influenced by the presence of deposits, drifts and / or aging. For example, in order to reduce or compensate for the influence, a suitable, in particular process-related algorithm can be supplied, based on which the value of a specific process variable that is not destroyed by the influence of deposits, drifts and / or aging of the sensor unit is ascertainable. Thus, an improved measurement accuracy can be achieved and a method for predictive maintenance can be provided.

[0044] In another preferred embodiment, the thickness and / or conductivity of the deposit on the sensor unit is ascertained. The thickness and / or conductivity of the deposit can be ascertained, for example, based on the ascertained conductivity and the ratio of the measurement signals of the probe electrode and the guard electrode.

[0045] Furthermore, it should be noted that the 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

[0046] The invention will now be explained in more detail based on the accompanying drawings, which show the following:

[0047] Figure 1 is a schematic diagram of an electronic vibration sensor according to the prior art,

[0048] Figure 2 is an embodiment of a sensor unit known in the prior art and suitable for carrying out the method of the invention, and

[0049] Figure 3 It is an embodiment of the device of the present invention.

[0050] In the drawings, the same elements are provided with the same reference numerals. DETAILED DESCRIPTION

[0051] Figure 1An electronic 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 means of 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 electronic 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 the mechanical oscillations and for their detection. Likewise, one option is to implement separate drive units and separate receiving units. In addition, Figure 1 An electronics unit 6 is shown, by means of which the signal registration, evaluation and / or feeding takes place.

[0052] As an example, in Figure 2 Detailed Description of the Invention Various 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 FIG. 1 comprises two oscillating elements 9a, 9b, which are also referred to as fork teeth, applied on a base 8. Optionally, in addition, in each case, a paddle (not shown) can be formed at the end of the two oscillating elements 9a, 9b. In each case, a particularly bag-shaped hollow space 10a, 10b is provided in each of the two oscillating elements 9a, 9b, wherein in each case at least one piezoelectric element 11a, 11b of the exciter / receiving unit 5 is arranged. 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 created so that the two piezoelectric elements 11a, 11b are completely or partially located in the region of the two oscillating elements 9a, 9b. Such an arrangement and similar arrangements are described in detail in DE 10 2012 100 728 A1.

[0053] Another example of an embodiment of the sensor unit 2 is shown in Figure 2 b. The mechanically oscillatable unit 4 in this case comprises two parallel rod-shaped oscillating elements 9a, 9b which are mounted on a disk-shaped element 12 and can be excited separately from one another to perform mechanical oscillations, and in this case the vibrations can likewise be received and evaluated separately from one another. In each case, the two oscillating elements 9a and 9b have a hollow space 10a and 10b, wherein in each case at least one piezoelectric element 11a, 11b is arranged in the region facing the disk-shaped element 12. Figure 2 b, reference is made to DE102017130527A1 which was not published as of the earliest filing date of the present application.

[0054] like Figure 2As schematically shown in FIG. 1 , according to the invention, the sensor unit 2 is supplied with an excitation signal A in such a way that the oscillatable unit 4 is excited in such a way that a mechanical oscillation is performed. In this case, the oscillation is generated by means of two piezoelectric elements 11a and 11b. The same excitation signal A can be supplied to both piezoelectric elements, or the first oscillating element 11a can be supplied with a first excitation signal A1 and the second oscillating element 11b can be supplied with a second excitation signal A2. Likewise, one option is to receive a first received signal E based on the mechanical oscillation. A , or a separate received signal E A1 、E A2 Received by oscillating elements 9a, 9b.

[0055] Furthermore, the transmission signal S is transmitted from the first piezoelectric element 11a, which 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, the transmission signal S passes through the medium M when the sensor unit 2 is in contact with the medium M and is affected by the properties of the medium M accordingly. Preferably, the transmission signal S is in particular a pulsed ultrasonic signal, which specifically has at least one ultrasonic pulse. Likewise, however, another option is that the transmission 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 is received by the first piezoelectric element 11a. In this case, the transmission signal S passes through the medium M twice, which results in the travel time τ of the transmission signal S being doubled.

[0056] In addition to the two illustrated embodiments of the device 1 of the invention, many other variations are possible which also fall within the scope of the invention. Figure 2 a and Figure 2 b can use only one piezoelectric element 11a, 11b and arrange it 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.

[0057] Figure 2c shows another embodiment by way of example. In this case, a third piezoelectric element 11c is provided in the region of the diaphragm 12. The third piezoelectric element 11c is used to generate an excitation signal A and to receive a first reception signal E1, whereas the first piezoelectric element 11a and the second piezoelectric element 11b are used to generate a transmission signal S and to receive a second reception signal E2. Alternatively, for example, the first piezoelectric element 11a and / or the second piezoelectric element 11b may 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 may be used to generate the transmission signal S and the third piezoelectric element 11c may be used to generate the excitation signal A, and the first piezoelectric element 11a and / or the second piezoelectric element 11b may 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.

[0058] Another embodiment of the device 1 is shown in Figure 2 d. This device is based on Figure 2 b and comprises a third oscillating element 9c and a fourth oscillating element 9d. However, these oscillating elements are not 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, electronic vibration measurement is performed with the help of the first two piezoelectric elements 11a, 11b and ultrasonic measurement is performed with the help of the other two piezoelectric elements 11c, 11d. In this case as well, for each measuring principle, one of the piezoelectric elements, for example 11b and 11d, can be omitted. However, for reasons of symmetry, it is always advantageous to use two additional oscillating elements 9c, 9d.

[0059] 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 is incorporated herein by reference in the context of the present invention.

[0060] Furthermore, according to the invention, the conductivity σ and / or the capacitance C of the medium can be determined and / or monitored. To this end, the device of the invention has a conductivity / capacitance detection unit 13 for determining and / or monitoring the conductivity σ and / or the capacitance C, which has a capacitive and / or conductive measuring probe 14, such as Figure 3 shown. Figure 3 Shows something like Figure 2a. Arranged between the two oscillating elements 9a and 9b of the oscillatable unit 4, which is realized in the form of an oscillatory fork, is a conductivity / capacitance detection unit 13, which serves to determine and / or monitor the conductivity σ and / or the capacitor C of the medium M and has a capacitively and conductively operating measuring probe 14, which has a sensor electrode 15 and a guard electrode 16 coaxially surrounding the sensor electrode 15. Arranged in each case between the two electrodes 15 and 16 and between the measuring probe 14 and the mechanically oscillatable unit 4 is an insulating layer 17.

[0061] Reference numerals list

[0062] 1 Electronic vibration sensor

[0063] 2 Sensor unit

[0064] 3 Container

[0065] 4 Oscillating units

[0066] 5 Exciter / Receiver Unit

[0067] 6 Electronic unit

[0068] 8 Base

[0069] 9a,9b Oscillating element

[0070] 10a,10b Hollow space

[0071] 11a,11b Piezoelectric element

[0072] 12 Disc-shaped element

[0073] 13 Conductivity / capacitance detection unit for determining and / or monitoring conductivity or capacitance

[0074] 14 Capacitance and / or conductivity measuring probes

[0075] 15 Sensor electrodes

[0076] 16 Guard electrode

[0077] 17 Insulation layer

[0078] M Medium

[0079] P Process variable

[0080] σ Conductivity

[0081] C Capacitor

[0082] A Excitation signal

[0083] S Send signal

[0084] E A First received signal

[0085] E S The second received signal

[0086] E L / C The third received signal

[0087] ΔΦ Predetermined phase shift

Claims

1. A device (1) for determining and / or monitoring at least one process variable (P) of a medium (M), comprising A sensor unit (2), the sensor unit (2) comprising: a mechanically oscillatable unit (4), at least a first piezoelectric element (11a) and a second piezoelectric element (11b), a conductivity / capacitance detection unit (13) for determining and / or monitoring the conductivity (σ) and / or capacitance (C) of the medium (M), and Electronic unit (6), in, 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), and 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 mechanically oscillatable unit (4) by means of an excitation signal (A) so that mechanical oscillation is performed, receive the mechanical oscillation of the mechanically oscillatable unit (4) and convert the mechanical oscillation into a first received signal (E A ), wherein the first piezoelectric element (11a) is implemented to transmit a transmission signal (S) which is an ultrasonic signal, The second piezoelectric element (11b) is implemented to receive a second received signal (E S ), receiving the transmission signal (S) in the form of The conductivity / capacitance detection unit (13) comprises a capacitive and / or conductive measuring probe (14) having at least one probe electrode (15). The conductivity / capacitance detection unit (13) is located between the first oscillating element (9a) and the second oscillating element (9b). The electronic unit (6) is implemented as follows: based on the first received signal (E A ) to find out the first process variable (P1), wherein the first process variable (P1) is a predeterminable filling level, a density or a viscosity of the medium (M), The electronic unit (6) is implemented as follows: based on the second received signal (E S ) to ascertain the speed of sound in the medium (M) as a second process variable (P2), and The electronic unit (6) is implemented as follows: based on the third receiving signal (E) received from the conductivity / capacitance detection unit (13), L / C ) to determine the conductivity (σ) and / or the capacitance (C) of the medium (M).

2. The device (1) according to claim 1, in, The measuring probe (14) comprises a guard electrode (16).

3. The device (1) according to claim 1, in, The sensor unit (2) comprises a unit for determining and / or monitoring the pressure (p) of the medium (M) and / or a unit for determining and / or monitoring the temperature (T) of the medium (M).

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