Patent Application
20240385025
The invention relates to a method for determining and/or monitoring a predeterminable fill level of a medium in a containment with a sensor comprising a sensor unit having a mechanically oscillatable unit in the form of an oscillatory fork and at least one piezoelectric element. The medium is located in a containment, for example, a container or a pipeline.
Vibronic sensors are widely used in process and/or automation technology. In the case of fill level measuring devices, such have at least one mechanically oscillatable unit, such as, for example, an oscillatory fork, a single tine or a diaphragm. Such is excited during operation by means of an exciting/receiving unit, frequently in the form of an electromechanical transducer unit, such that mechanical oscillations are executed. The electromechanical transducer unit can be, for example, a piezoelectric drive or an electromagnetic drive. Corresponding field devices are manufactured by the applicant in great variety and sold, for example, under the LIQUIPHANT and SOLIPHANT marks. The underpinning measuring principles are known, in principle, from a large number of publications. The exciting/receiving unit excites the mechanically oscillatable unit by means of an electrical excitation signal, such that mechanical oscillations are executed. Conversely, the exciting/receiving unit can receive the mechanical oscillations of the mechanically oscillatable unit and convert such into an electrical, received signal. The exciting/receiving unit is either separate exciting and receiving units, or one combined exciting/receiving unit.
In such case, the exciting/receiving unit is in many cases part of a fed back, electrical, oscillatory circuit, by means of which the exciting of the mechanically oscillatable unit occurs, such that mechanical oscillations are executed. For example, for a resonant oscillation, the oscillatory circuit state must be created, in which the amplification factor is >1 and all phases arising in the oscillatory circuit sum to a multiple of 360°. For exciting and fulfilling the oscillatory circuit state, a certain phase shift between the excitation signal and the received signal needs to be assured. Therefore, frequently a predeterminable value for the phase shift, thus, a desired value for the phase shift between the excitation signal and the received signal, is set. For this, the state of the art offers the most varied of solutions, including both analog as well as also digital methods, such as described, for example, in DE102006034105A1, DE102007013557A1, DE102005015547A1, DE102009026685A1, DE102009028022A1, DE102010030982A1 and DE00102010030982A1.
Both the excitation signal as well as also the received signal are characterized by a frequency ω, an amplitude A and/or a phase Φ. Correspondingly, changes in these variables are usually taken into consideration for determining the particular process variable. The process variable can be, for example, a fill level, a predetermined fill level, or the density or viscosity of the medium, as well as flow, e.g. flow rate. In the case of a vibronic limit level switch for liquids, for example, it is distinguished, whether the oscillatable unit is covered by the liquid or freely oscillating. These two states, the free state and the covered state, are distinguished, in such case, for example, based on different resonance- or eigen frequencies, thus, based on frequencies in the case of a predetermined phase shift between excitation signal and received signal.
Density and/or viscosity can, in turn, only be ascertained with such a measuring device, when the oscillatable unit is completely covered by the medium. For determining density and/or viscosity, likewise different options are provided by the state of the art, such as those described, for example, in DE10050299A1, DE102007043811A1, DE10057974A1, DE102006033819A1, DE102015102834A1 and DE102016112743A1.
Known from DE102012100728A1 and DE102017130527A1 are, additionally, various vibronic sensors, in the case of which the driving/receiving units in the form of piezoelectric elements are arranged, at least partially, within the oscillatable unit. With such and similar arrangements, advantageously, a plurality of process variables can be determined with a single sensor and used for characterizing different processes, such as described, for example, in WO2020/094266A1, DE102019116150A1, DE102019116151A1, DE02019116152A1, DE102019110821A1, DE102020105214A1 and DE102020116278A1.
In order to determine at least two different process variables by means of such a multisensor, the sensor unit is, on the one hand, excited by means of an excitation signal, such that mechanical oscillations are executed, and the mechanical oscillations of the sensor unit are received and converted into a first received signal. Additionally, a transmitted signal is transmitted from the sensor unit and a second received signal received. Based on the first received signal, then a first process variable can be ascertained, and, based on the second received signal, a second process variable can be ascertained. The piezoelectric element serves in the case of such multisensors as driving/receiving unit and for producing the mechanical oscillations by means of the excitation signal and for producing the transmitted signal.
In the case of application of vibronic sensors with oscillatable units in the form of oscillatory forks for determining and/or monitoring a predeterminable fill level, e.g. a limit level, of a medium in a containment, it must be reliably detected, whether the mechanically oscillatable unit is covered with the respective medium or not. Such is especially important in the case of safety-critical applications, for example, in the case of applications, which require that the utilized measuring device have a certain safety integrity level (SIL). Based on an evaluation of the frequency of the received signal representing the mechanical oscillations of the mechanically oscillatable unit, however, an exact determination concerning the degree of covering, e.g. a complete covering, of the mechanically oscillatable unit is in some cases insufficiently exactly possible. The ascertained covering is influenced, for example, by various measurement parameters, such as the reigning temperatures or the density of the medium.
Therefore, an object of the invention is to improve the accuracy of measurement of vibronic, limit level sensors.
The object is achieved by a method for determining and/or monitoring at least first and second process variables of a medium in a containment with a sensor having a sensor unit with a mechanically oscillatable unit in the form of an oscillatory fork and at least one piezoelectric element, comprising:
According to the invention, information concerning state of the sensor unit is ascertained based on the second received signal.
By means of the excitation signal, the oscillatable unit produces mechanical oscillations, which are influenced by the properties of the medium, when the oscillatable unit is covered by medium. Correspondingly, based on the first received signal and according to the vibronic measuring principle, information can be ascertained concerning the predeterminable fill level.
The transmitted signal is transmitted and received by a component of the sensor unit, for example, the one or more piezoelectric elements. For example, the transmitted signal propagates along a measurement path extending between the two oscillatory elements of the oscillatable unit embodied in the form of an oscillatory fork, or along a measurement path between one oscillatory element and an additional component of the sensor unit, or between the sensor unit and a wall of the containment. In this way, the transmitted signal passing at least at times and sectionally through the medium is influenced by the physical and/or chemical properties of the medium, especially medium in the region of the sensor unit, and can by means of the ultrasonic measuring principle correspondingly be taken into consideration for determining information concerning state of the sensor unit. For example, the presence of medium in a region between the two oscillatory elements of the oscillatable unit can be detected reliably. Depending on structural embodiment of the sensor unit and the one or more piezoelectric element or elements relative to the oscillatory elements, in given cases, also a degree of covering of the oscillatable unit with the medium can be ascertained. Also the presence of a blockage of the oscillatable unit by a deposit or by a solid body present in the medium can be detected. On the whole, thus, a comprehensive state monitoring of the sensor unit is possible based on an evaluation of the second received signal.
Because two measuring principles are implemented in a single device, the accuracy of measurement relative to the detecting of the predeterminable fill level, thus the limit level detection, can be significantly improved. Based on the second received signal, according to the invention, information concerning state of the sensor unit, especially concerning covering, or degree of covering, of the oscillatable unit with the medium, can be gained. Moreover, it is, additionally, possible, based on the first and second received signals, to ascertain various other process variables of the medium.
In an embodiment of the method, the excitation signal and/or the transmitted signal are/is an electrical signal having at least one predeterminable frequency, especially a sinusoidal, a rectangular, a trapezoidal, a triangular or a sawtooth-shaped signal. For example, the excitation signal can be so selected that the oscillatable unit by means of the excitation signal is excited to execute resonant oscillations.
Also for the transmitted signal, various, different options are possible. Thus, advantageously, the transmitted signal is a pulsed signal, especially a signal having a predeterminable, preferably constant, pulse width.
In an additional embodiment of the method of the invention, the transmitted signal is a signal of variable frequency using frequencies within a predeterminable frequency interval. Preferably within this frequency interval, a so-called frequency sweep is performed, in the case of which the frequency varies successively within the predeterminable frequency interval. Also, a pulsed frequency sweep can serve as transmitted signal.
As already discussed, the information with reference to state of the sensor unit can be, for example, information concerning a covering, especially a degree of covering, of the oscillatable unit with medium. Likewise, deposits in the region of the sensor unit can be detected. Moreover, in an additional embodiment, the information with reference to state of the sensor unit is information concerning a blockage in the region of the sensor unit.
In an advantageous embodiment, an amplitude of the second received signal is ascertained. The information with reference to state of the sensor unit can thus, advantageously, be generated based on an amplitude detection.
In an additional advantageous embodiment of the method of the invention, a frequency of the first received signal is ascertained.
Based on the amplitude and/or frequency of the first and/or second received signal, in especially easy manner, different pieces of information concerning the sensor unit can be derived. In the case of such an evaluation of the received signals, advantageously, no especially high requirements need to be placed on electronic components or evaluation mechanisms. Some especially preferred variants are set forth in the following. It is understood, however, that besides the described embodiments, various other embodiments can be used, which likewise fall within the scope of the invention.
Concerning evaluation of the second received signal as regards amplitude and/or frequency, advantageously, if the frequency of the first received signal exceeds or subceeds a predeterminable frequency limit value, and the amplitude of the second received signal subceeds a predeterminable amplitude limit value, then it is determined that a blockage is present in the region of the sensor unit.
Likewise advantageously, if the predeterminable limit level is a maximum fill level of medium in the containment, and if the amplitude of the second received signal exceeds a predeterminable limit value, then it is determined that the maximum fill level has been reached.
Alternatively, advantageously, if the predeterminable limit level is a minimum fill level of medium in the containment, and if the amplitude of the second received signal subceeds a predeterminable limit value, then it is determined that the minimum fill level has been reached. In the case of a so-called MIN switch, the covered state represents the safe state. For example, in the case of media of high viscosity, it can happen that no reliable information concerning the limit level is possible based on the first received signal. Blockings of the oscillatable unit by the, especially viscous, medium or otherwise by particles present in the medium must in such case be safely excluded, and this is possible by means of the invention.
Finally, another embodiment of the method of the invention includes that the excitation signal and the transmitted signal are periodically, alternately produced. In this way, the state monitoring of the sensor unit can be performed continuously.
Alternatively, advantageously in another embodiment, the transmitted signal is produced at predeterminable, especially periodic, points in time. In such case, the state of the sensor unit is checked as required.
Quite especially advantageous is when the exciting of the mechanically oscillatable unit by means of the excitation signal is interrupted, when the transmitted signal is transmitted and the second received signal received. In this way, the presence of medium between the two oscillatory elements of the oscillatory fork can be ascertained especially reliably.
In the case of the sensor unit in the form of an oscillatory fork with two oscillatory elements and at least one piezoelectric element, wherein the piezoelectric element is arranged, at least partially, within an oscillatory element, such preferably concerns an embodiment of a sensor unit according to DE102012100728A1 and DE102017130527A1. Comprehensive reference is taken to the two applications in the context of the present invention. The embodiments of the sensor unit described in the two documents are, however, only examples of possible structural embodiments of the sensor unit.
The invention and advantageous embodiments thereof will now be explained in greater detail based on the appended drawing, the figures of which show as follows:
In the figures, equal elements are provided with equal reference characters.
Another example of a possible embodiment of a sensor unit 2 is shown in
As shown schematically in
Moreover, additionally, for example, emanating from the first piezoelectric element 11a, a transmitted signal T can be transmitted, which is received by the second piezoelectric element 11b in the form of a second received signal RT. Since the two piezoelectric elements 11a and 11b are arranged at least in the region of the oscillatory elements 9a and 9b, the transmitted signal T passes through the medium M and is correspondingly influenced by the properties of the medium M, when the sensor unit 2 is in contact with the medium M. Likewise, it is, however, an option that the transmitted signal T is transmitted from the first piezoelectric element 11a in the region of the first oscillatory element 9a and is reflected on the second oscillatory element 9b. In such case, the second received signal RT is received by the first piezoelectric element 11a. The transmitted signal T passes, in such case, two times through the medium M.
Besides these two illustrated embodiments of an apparatus 1 of the invention, numerous other variants are possible, which likewise fall within the scope of the invention. For example, it is possible for the embodiments of
Another possibility is shown, by way of example, in
Likewise it is possible to produce the transmitted signal T with the first 11a and/or second piezoelectric element 11b and the excitation signal E with the third piezoelectric element 11c and to receive the first received signal RE and/or second received signal RT with the first 11a and/or second piezoelectric element 11b. Also in the case of
Another possible embodiment of the apparatus 1 is shown in
According to the invention, information concerning state of the sensor unit 2 is generated based on the transmitted signal T. Preferably, the sensor unit 2 is embodied in such a manner that the at least one piezoelectric element 11a is arranged, at least partially, in an internal volume of the oscillatable unit 4, especially, at least partially, within an oscillatory tine 9a of the oscillatable unit 4. Such a sensor unit 2 is shown schematically in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 126 092.2 | Oct 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/076341 | 9/22/2022 | WO |
