Method for operating an electronic vibration sensor

Abstract

The invention relates to a method for determining and / or monitoring a predeterminable fill level of a medium (2) in a container (2a) by means of an electronic vibration sensor (1) having at least one sensor unit (3) having a mechanically vibratable unit (4), comprising the following method steps: - exciting the mechanically vibratable unit (4) to mechanically vibrate by means of an excitation signal (U A ) and receiving the mechanical vibrations in the form of a reception signal (U E ), - determining an amplitude (A) and a frequency (f) of the reception signal (U E ), - comparing the frequency (f) and the amplitude (A) of the reception signal (U E ) with predeterminable frequency limit values (f ref ) and predeterminable amplitude limit values (A ref ), and - determining when the predeterminable fill level has been reached on the basis of the comparison.

Description

Technical Field

[0001] This invention relates to a method for determining and / or monitoring a predetermined fill level of a medium in a container using an electronic vibration sensor having at least one sensor unit with a mechanically vibrating element. In addition to determining the predetermined fill level of the medium, the electronic vibration sensor can also be used to determine the flow rate, density, or viscosity of the medium. The container is, for example, a tank or pipe. Background Technology

[0002] Electronic vibration sensors are commonly used in process and / or automation engineering. In the case of filling level measuring devices, they have at least one mechanically vibratory unit, such as, for example, a vibrating fork, a single rod, or a diaphragm. In operation, this is excited to generate mechanical vibration by means of a drive / receiver unit, typically in the form of an electromechanical transducer unit, which can be, for example, a piezoelectric actuator or an electromagnetic actuator.

[0003] Various corresponding field devices are manufactured by the applicant and, in the case of filling level measuring devices, are distributed under names such as LIQUIPHANT or SOLIPHANT. The underlying measurement principle is known in principle from numerous publications. A drive / receiver unit excites a mechanically vibrating unit to induce mechanical vibration via an electrical excitation signal. Conversely, a drive / receiver unit can receive the mechanical vibration of the mechanically vibrating unit and convert it into an electrical received signal. The drive / receiver unit can be a separate drive unit and a separate receiver unit, or a combined drive / receiver unit.

[0004] In many instances, the drive / receiver unit is thus part of an electro-resonant feedback circuit, by which a mechanically vibrating unit is excited to produce mechanical vibration. For example, resonance must be achieved by satisfying the resonant circuit condition that the amplification factor is ≥1 and all phases appearing in the resonant circuit result in multiples of 360°.

[0005] To excite and satisfy the resonant circuit conditions, a defined phase shift between the excitation and received signals must be ensured. The predetermined value of the phase shift, thus the setpoint of the phase shift between the excitation and received signals, is frequently set. For this purpose, various solutions, both analog and digital methods, are known from the prior art. In principle, the phase shift can be set, for example, by using a suitable filter, or it can be adjusted to a predetermined setpoint value using a control loop. For example, DE102006034105A1 discloses the use of an adjustable phase shifter. In contrast, DE102007013557A1 describes the additional integration of an amplifier with an adjustable amplification factor for additional control of the vibration amplitude. DE102005015547A1 proposes the use of an all-pass filter. The phase shift can also be adjusted using so-called frequency search, as disclosed in DE102009026685A1, DE102009028022A1, and DE102010030982A1. However, the phase shift can also be adjusted to a predetermined value using a phase-locked loop (PLL). The excitation method based on this forms the subject of DE102010030982A1.

[0006] Both the excitation and received signals are characterized by their frequency ω, amplitude A, and / or phase Φ. Therefore, changes in these variables are typically used to determine the process variables under discussion, such as a predetermined fill level of the medium in the tank, or the density and / or viscosity of the medium, or the flow rate of the medium through the pipe. For example, in the case of an electronically vibrating fill level switch for a liquid, a distinction is made between whether the vibrating element is covered by the liquid or vibrates freely. These two states, free and covered, are therefore distinct—for example, based on different resonant frequencies, i.e., frequency shifts. If the vibrating element is covered by the medium, the density and / or viscosity can only be determined using measuring devices such as those described in documents DE10050299A1, DE102007043811A1, DE10057974A1, DE102006033819A1, or DE102015102834A1.

[0007] To ensure the reliable operation of electronic vibration sensors, many methods are known to be used to perform sensor condition monitoring, such as those described in documents DE102005036409A1, DE102007008669A1, DE102017111392A1, or DE102017102550A1. Summary of the Invention

[0008] The purpose of this invention is to expand the application areas of electronic vibration sensors.

[0009] According to the present invention, this objective is achieved by a method for determining and / or monitoring a predetermined filling level of a medium in a container by means of an electronic vibration sensor having at least one sensor unit having a mechanically vibrating element, the method comprising the following steps:

[0010] - The mechanically vibrating unit is excited by an excitation signal to generate mechanical vibration, and the mechanical vibration is received in the form of a receiving signal.

[0011] - Determine the amplitude and frequency of the received signal.

[0012] - Compare the frequency and amplitude of the received signal with predetermined frequency and amplitude limits, and

[0013] - Determine the attainment of a pre-determined fill level based on comparison.

[0014] According to the present invention, reference values ​​are defined for amplitude and frequency, and the amplitude and frequency of the received signal are compared in each case using these reference values.

[0015] Consideration of the two variables, amplitude and frequency, leads to expanded possibilities in making statements about the process variables. For example, changes in frequency or amplitude can be attributed to different causes. Additional consideration of other corresponding characteristic variables makes it possible to distinguish between different possible causes of change. Many embodiments are possible in this regard, some of which are particularly preferred variants as follows:

[0016] In one embodiment, the frequency is checked to see if it exceeds or falls below a predetermined frequency limit. In another embodiment, the amplitude is similarly checked to see if it exceeds or falls below a predetermined amplitude limit.

[0017] One embodiment includes recording the frequency and / or amplitude of the received signal as a function of time. In this way, the time progression of the sensor can also be observed. Therefore, the method according to the invention further advantageously enables, in particular, predictive maintenance.

[0018] One embodiment of the method according to the invention includes the following: when the frequency changes, particularly when the value exceeds or falls below a predetermined frequency limit while the amplitude remains substantially constant, this indicates that the vibrating element is covered by liquid. If only the frequency changes while the amplitude remains substantially constant, it can therefore be inferred that a predetermined filling level has been reached.

[0019] Another embodiment provides that when the amplitude changes, particularly when the value exceeds or falls below a predetermined amplitude limit, this indicates that the vibrating element is covered by foam or that there is sediment in the medium. The present invention advantageously enables the detection of foam and sediment that are typically undetectable or can only be detected with greater effort using conventional evaluation methods.

[0020] In this scenario, with the frequency remaining substantially constant, it is advantageous to infer the deposition of precipitates in the region of the vibrating unit. This is particularly advantageous if an electronic vibration sensor is used to determine the minimum limiting level in the container. In this case, for example, precipitates in the bottom region of the container can be detected, which may distort statements about the limiting level. Therefore, having an accurate knowledge of the presence of precipitates in the bottom region allows for a more accurate determination of the limiting level.

[0021] Alternatively, advantageously, when the frequency changes, if the value specifically does not exceed or falls below a predetermined frequency limit, it is inferred that there is sediment or foam covering in the medium. Conversely, a small change in frequency, however, where the value does not exceed or fall below the frequency limit, is an indicator that foam or sediment is dissolved in the medium.

[0022] In one embodiment of the method, the amplitude reference value and / or frequency reference value are each values ​​of amplitude and / or frequency that correspond to the resonant vibration of the vibrating element in its fundamental mode and in air. For example, these reference values ​​may be determined during the production of the respective sensor and stored, for example, in a storage unit, database, or data table. The reference values ​​then correspond to the sensor's delivery state. However, they may also be determined at the customer's location and after installation in the respective container. By determining the reference value for each sensor individually, the typical variance of these values ​​caused by manufacturing tolerances can be directly offset.

[0023] Within the scope of the method according to the invention, the following is also advantageous: if the mechanically vibrating unit is excited to produce mechanical resonant vibration in a fundamental mode, wherein the received signal represents the resonant vibration of the vibrating unit in the fundamental mode.

[0024] Finally, another embodiment includes a vibratory unit that is a vibratory fork having a membrane and two vibratory rods attached to the membrane.

[0025] In summary, this invention allows for the precise determination and / or monitoring of pre-determined fill levels using electronic vibration sensors, which can be implemented very easily. Because both frequency and amplitude are considered simultaneously, more accurate determination of process variables is possible, and various negative factors affecting the determination of process variables—such as the presence of, for example, foam or sediment—can be detected, and their influence on the statements made can therefore be eliminated. Attached Figure Description

[0026] Please refer to the following attached figures. Figure 1 The invention and its advantages are described in more detail with reference to Figure 3. In the figure:

[0027] Figure 1 An electronic vibration sensor according to the prior art is shown;

[0028] Figure 2 The vibratory unit of an electronic vibration sensor in the form of a vibrating fork is shown; and

[0029] Figure 3 shows a diagram illustrating the frequency and amplitude of different media used to illustrate the process according to the present invention. Detailed Implementation

[0030] Figure 1 An electronic vibration sensor 1 is shown. A sensor unit 3, having a vibrating element 4, is depicted in the form of a vibrating fork, partially immersed in a medium 2 located in a container 2a. Mechanical vibration is excited in the vibrating element 4 by an excitation / receiving unit 5, and the vibrating element can be, for example, a piezoelectric stack driver or a dual piezoelectric wafer driver. However, it is naturally understood that other embodiments of the electronic vibration sensor also belong to the present invention. Furthermore, an electronic unit 6 is shown by means of which signal detection, signal evaluation, and / or signal supply are performed.

[0031] Figure 2 A side view of a vibratory unit 4 in the form of a vibrating fork is shown, which is integrated, for example, into an electronic vibration sensor 1 sold by the applicant under the name LIQUIPHANT. The vibrating fork 4 includes two vibrating rods 8a and 8b integrally formed on a membrane 7, and blades 9a and 9b integrally formed at the ends of each of the vibrating rods 8a and 8b. The vibrating rods 8a and 8b, together with the blades 9a and 9b, are generally referred to as fork tips. To mechanically vibrate the mechanically vibratory unit 4, a force is applied to the membrane 8 by means of a drive / receiver unit 5 securely mounted on the side of the membrane 8 opposite to the vibrating rods 7a and 7b. The drive / receiver unit 5 is an electromechanical transducer unit and includes, for example, a piezoelectric element or also an electromagnetic actuator [not shown]. The drive unit 5 and the receiver unit are constructed as two separate units or as a combined drive / receiver unit. In the case where the drive / receiver unit 5 includes a piezoelectric element 9, the force applied to the membrane 7 is achieved by applying an excitation signal U, for example, in the form of an AC voltage. A The change in the applied voltage causes a change in the geometry of the drive / receiver unit 5 (i.e., contraction or relaxation within the piezoelectric element), thus affecting the excitation signal U. AThe application of AC voltage causes the membrane 7, which is firmly bonded to the drive / receiver unit 5, to vibrate. Conversely, the mechanical vibration of the vibrating unit is transmitted via the membrane to the drive / receiver unit 5 and converted into an electrical received signal U. E Then it can be based on the received signal U E For example, based on the received signal U E The amplitude A, frequency f, or phase is used to determine the predeterminable filling level of medium 2 in container 2a.

[0032] The method according to the invention allows for significantly higher accuracy in determining pre-determined fill levels in expanded application areas. Various preferred embodiments are illustrated in Figure 3 by way of example in this scenario.

[0033] In the first step, reference values ​​f for amplitude and frequency are determined. ref A ref In this process, the vibrating unit 4 is excited to generate resonant vibrations in the air. To determine a predetermined fill level during continuous operation, the vibrating unit 4 uses an excitation signal U... A The excited entity generates mechanical vibrations in a fundamental mode, and the received signal U represents the oscillation. E The data is received and evaluated with respect to frequency f and amplitude A. The values ​​f and A are compared with the corresponding reference value f. ref A ref Compare, and for example, determine the measured value f, A with the reference value f. ref A ref The deviation, or check whether the frequency f and / or amplitude A exceed or fall below the predetermined limit value f respectively. ref Or A ref .

[0034] Figure 3 shows an example diagram of frequency f and amplitude A, where, for different cases, the frequency f and amplitude A are shown as a function of the immersion depth t of the vibrating element 4 in the medium 2. When the liquid medium 2 covers the vibrating element 4, the frequency f changes, while the amplitude A remains largely constant or changes only slightly, such as... Figure 3a As shown.

[0035] On the other hand, if a change in amplitude A can be detected, especially if it exceeds a predetermined amplitude limit value A... ref Therefore, it can be inferred that vibration unit 4 is covered by foam or that there are sediments in the medium, such as Figure 3b As shown. Without additional consideration, it will be impossible to distinguish between the freely vibrating vibrating unit 4 and the coverage of foam or sediment. This would cause considerable problems, as it might not be possible to accurately display the reaching of predetermined limit values.

[0036] Furthermore, in order to distinguish directly between sediment and foam, it may be helpful to consider the frequency f, for example, when the amplitude A changes, such as... Figure 3b In this case, if the frequency f remains substantially constant, then, for example, there may be deposits in the region of the vibrating unit 4. On the other hand, if a change in frequency f is also detected, but does not exceed a predetermined limit of frequency, it can be inferred, for example, that there are deposits in medium 2 or that the vibrating unit 4 is covered with foam.

[0037] In addition to the possibilities mentioned, many further embodiments of the method according to the invention can be envisioned, which allow further conclusions to be drawn from considerations regarding the determination of the frequency and amplitude of statements about the limiting level, and these also belong to the invention.

[0038] Figure Labels

[0039] 1. Electronic vibration sensor

[0040] 2. Medium

[0041] 2a Container

[0042] 3 Sensor Units

[0043] 4 Vibrating Units

[0044] 5. Drive / Receive Unit

[0045] 6 electronic units

[0046] 7. Membrane

[0047] 8a, 8b Vibration rods

[0048] 9a, 9b blades

[0049] U A stimulus signal

[0050] U E Received signal

[0051] f frequency

[0052] f ref Frequency reference value

[0053] A amplitude

[0054] A ref Amplitude reference value

[0055] a freely vibrating vibrating unit

[0056] b. Vibrating unit covered by a medium

[0057] t is the immersion depth of the vibrating unit.

Claims

1. A method for determining and / or monitoring a predetermined filling level of a medium (2) in a container (2a) using an electronic vibration sensor (1), said electronic vibration sensor (1) having at least one sensor unit (3) having a mechanically vibrating unit (4), said method comprising the following steps: - Using the excitation signal (U A The mechanically vibrating unit (4) is excited to generate mechanical vibration, and receives a signal (U) E The mechanical vibration is received in the form of ) - Determine the received signal (U) E The amplitude (A) and frequency (f) of the wave. - The received signal (U) E The frequency (f) and amplitude (A) of the frequency (f) are related to the predetermined frequency limit value (f). ref ) and a predetermined amplitude limit (A) ref ) for comparison, and - The predetermined fill level is determined based on the comparison. in, When the frequency (f) changes while the amplitude (A) remains constant, this indicates that the mechanically vibrating unit (4) is covered by a liquid, and / or In the case of a change in amplitude (A), this indicates that the mechanically vibrating unit (4) is covered with foam or that there are deposits in the medium (2).

2. The method according to claim 1, in, Check whether the frequency (f) exceeds or falls below the predetermined frequency limit value (f). ref ).

3. The method according to claim 1, in, Check whether the amplitude (A) exceeds or falls below the predetermined amplitude limit value (A). ref ).

4. The method according to any one of claims 1-3, in, The received signal (U) E The frequency (f) and / or amplitude (A) of the ) are recorded as a function of time.

5. The method according to claim 1, in, When the value exceeds or falls below the predetermined frequency limit value (f) ref If the amplitude (A) remains constant, this indicates that the mechanically vibrating unit (4) is covered by liquid.

6. The method according to claim 1, in, When the value exceeds or falls below the predetermined amplitude limit (A) ref In this case, it indicates that the mechanically vibrating unit (4) is covered with foam or that there are deposits in the medium (2).

7. The method according to claim 1, in, With the frequency (f) remaining constant, it is inferred that the deposits are deposited in the region of the mechanically vibrating unit (4).

8. The method according to claim 1, in, When the frequency (f) changes, Wherein, the value does not exceed or is lower than the predetermined frequency limit value (f) ref ), inferring that there are precipitates or foam covering in the medium (2).

9. The method according to any one of claims 1-3, in, The predetermined amplitude limit value (A) ref ) and / or the predetermined frequency limit value (f ref Each of these values ​​represents the amplitude (A) and / or the frequency (f), which correspond to the resonant vibration of the mechanically vibrating unit (4) in the basic mode and in air.

10. The method according to any one of claims 1-3, in, The mechanically vibrating unit (4) is a vibrating fork with a membrane and two vibrating rods attached to the membrane.

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