DE102019114174A1 - Vibronic multi-sensor - Google Patents

Abstract

The present invention relates to a particularly computer-implemented method for the detection of gas bubbles in a liquid medium (M) with a sensor (1) with a mechanically oscillatable unit (4), comprising the following method steps, excitation of the oscillatable unit (4) with a first Excitation signal (11) for generating mechanical vibrations of the vibratable unit (4) according to a first predeterminable vibration mode (S1) of the vibratable unit (4), and receiving the mechanical vibrations from the mechanically vibratable unit (4) in the form of a first reception signal (X1 ), - Exciting the oscillatable unit (4) with a second excitation signal (12) for generating mechanical oscillations of the oscillatable unit (4) according to a second predeterminable oscillation mode (S2) of the oscillatable unit (4), and receiving the mechanical oscillations from the mechanically oscillatable unit (4) in the form of a second received signal (X2), - Determine n a first and second characteristic variable (f, A) of the first (X1) and second received signal (X2), - determining a ratio (V) of the first (f1, A1) and second characteristic variable (f2, A2), and- Generating a statement about the presence of gas bubbles based on the ratio (V) of the first (f1, A1) and second characteristic variable (f1, A1).

Description

The invention relates to a, in particular computer-implemented, method for the detection of gas bubbles in a liquid medium with a sensor with a mechanically oscillatable unit. The invention also relates to a computer program and a computer program product. The sensor is a device for determining and / or monitoring at least one process variable of the medium, in particular a vibronic sensor or a field device operating according to the Coriolis measuring principle. The medium is located in a container, for example in a container or in a pipeline. The process variable in turn is, for example, a fill level, in particular a specifiable fill level, a flow rate, the density or the viscosity of the medium.

Vibronic sensors are widely used in process and / or automation technology. In the case of fill level measuring devices, they have at least one mechanically oscillatable unit, such as an oscillating fork, a single rod or a membrane. During operation, this is excited to mechanical vibrations by means of a drive / receiver unit, often in the form of an electromechanical converter unit, which in turn can be, for example, a piezoelectric drive or an electromagnetic drive. Corresponding field devices are manufactured by the applicant in a large variety and sold, for example, under the name LIQUIPHANT or SOLIPHANT. The underlying measurement principles are known in principle from a large number of publications. The drive / receiver unit stimulates the mechanically oscillatable unit to produce mechanical oscillations by means of an electrical excitation signal. Conversely, the drive / receiver unit can receive the mechanical vibrations of the mechanically vibratable unit and convert them into an electrical received signal. The drive / receiver unit is accordingly either a separate drive unit and a separate receiver unit, or a combined drive / receiver unit.

In many cases, the drive / receiver unit is part of a feedback electrical oscillating circuit, by means of which the mechanically oscillatable unit is excited into mechanical oscillations. For example, for a resonant oscillation, the resonant circuit condition, according to which the gain factor ≥ 1 and all phases occurring in the resonant circuit result in a multiple of 360 °, must be fulfilled. A certain phase shift between the excitation signal and the received signal must be guaranteed to excite and fulfill the resonant circuit condition. Therefore, a specifiable value for the phase shift, that is to say a setpoint value for the phase shift between the excitation signal and the received signal, is often set. A wide variety of solutions, both analog and digital methods, have become known for this from the prior art, for example in the documents DE102006034105A1 , DE102007013557A1 , DE102005015547A1 , DE102009026685A1 , DE102009028022A1 , DE102010030982A1 or DE00102010030982A1 described.

Both the excitation signal and the received signal are characterized by their frequency ω, amplitude A and / or phase Φ. Accordingly, changes in these variables are usually used to determine the respective 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 the flow rate. In the case of a vibronic level switch for liquids, a distinction is made, for example, between whether the oscillatable unit is covered by the liquid or whether it oscillates freely. These two states, the free state and the covered state, are distinguished, for example, on the basis of different resonance frequencies, that is to say on the basis of a frequency shift.

The density and / or viscosity, in turn, can only be determined with such a measuring device if the oscillatable unit is covered by the medium. In connection with the determination of the density and / or viscosity, different possibilities have also become known from the prior art, such as those in the documents DE10050299A1 , DE102007043811A1 , DE10057974A1 , DE102006033819A1 , DE102015102834A1 or DE102016112743A1 revealed.

In the case of measuring devices working according to the Coriolis measuring principle, which are used, for example, to determine and / or monitor the mass flow rate or the density, a measuring tube, which is held in a housing module and can oscillate and communicates with a pipeline, is used as an oscillating unit Rest position, in particular bending vibrations, is excited. The underlying measurement principles are also known from a large number of publications and, for example, in US-A 47 93 191 , the US-A 48 23 614 , the * US-A 48 31 885 , the US-A 56 02 345 , the US-A 2007/0151368 , the US-A 2010/0050783 , the WO-A 96/08697 , the WO-A 2009/120222 or the WO-A 2009/120223 described in detail and in detail.

A problem with sensors based on mechanical vibrations relates to the presence of gas bubbles in different media. Gas bubbles have a major influence on the viscoelastic properties of liquids. Correspondingly, there may be unwanted changes in the oscillation frequency of the oscillatable unit that are not related to the process variable being considered, and thus falsified measured values for the respective process variable.

A wide variety of causes can be responsible for the formation of gas bubbles in liquid media, such as stirring or pumping in the process, outgassing of dissolved air after a pressure drop in the medium, or a change in the medium temperature. Gas bubbles are particularly common in fresh water or aqueous solutions. Gas bubbles that are distributed in the medium and also separated on a surface of the respective sensor unit of the sensor, which includes the oscillatable unit, play a role.

From the DE102015122661A1 For example, a method for determining a physical parameter of a liquid laden with gas for a Coriolis flow measuring device has become known. The oscillatable unit is excited to mechanical oscillations in two different oscillation modes, which depend to varying degrees on gas bubbles present within the medium. The influence of the gas bubbles on the measurement can be determined and corrected from the ratio of the values calculated for the density and / or the mass flow rate in the two oscillation modes.

The present invention is based on the object of enabling reliable measuring operation of a sensor with an oscillatable unit in a simple manner in the event of gas bubble formation.

This object is achieved by the method according to claim 1, by the computer program according to claim 15 and the computer program product according to claim 16.

• - Anregen der schwingfähigen Einheit mit einem ersten Anregesignal zur Erzeugung von mechanischen Schwingungen der schwingfähigen Einheit gemäß einer ersten vorgebbaren Schwingungsmode der schwingfähigen Einheit, und Empfangen der mechanischen Schwingungen von der mechanisch schwingfähigen Einheit in Form eines ersten Empfangssignals,
• - Anregen der schwingfähigen Einheit mit einem zweiten Anregesignal zur Erzeugung von mechanischen Schwingungen der schwingfähigen Einheit gemäß einer zweiten vorgebbaren Schwingungsmode der schwingfähigen Einheit, und Empfangen der mechanischen Schwingungen von der mechanisch schwingfähigen Einheit in Form eines zweiten Empfangssignals,
• - Bestimmen einer ersten und zweiten charakteristischen Größe des ersten und zweiten Empfangssignals,
• - Bestimmen eines Verhältnisses der ersten und zweiten charakteristischen Größe, und
• - Generieren einer Aussage über das Vorhandensein von Gasblasen anhand des Verhältnisses der ersten und zweiten charakteristischen Größe.

With regard to the method, the object is achieved by a method, in particular a computer-implemented method, for the detection of gas bubbles in a liquid medium with a sensor with a mechanically oscillatable unit, comprising the following method steps:

• - Exciting the oscillatable unit with a first excitation signal for generating mechanical vibrations of the oscillatable unit according to a first predeterminable oscillation mode of the oscillatable unit, and receiving the mechanical vibrations from the mechanically oscillatable unit in the form of a first received signal,
• - Exciting the oscillatable unit with a second excitation signal for generating mechanical oscillations of the oscillatable unit according to a second predeterminable oscillation mode of the oscillatable unit, and receiving the mechanical oscillations from the mechanically oscillatable unit in the form of a second received signal,
• - determining a first and second characteristic variable of the first and second received signal,
• - determining a ratio of the first and second characteristic variables, and
• - Generating a statement about the presence of gas bubbles on the basis of the ratio of the first and second characteristic variables.

The oscillatable unit is part of a sensor unit of the sensor for determining and / or monitoring at least one process variable of a medium. In the case of a vibronic sensor, the oscillatable unit is, for example, a single rod or an oscillating fork. In the case of a flow meter, on the other hand, the oscillatable unit is given by a measuring tube. The first and second excitation signals are each an electrical signal with a predeterminable first or second frequency, in particular a sinusoidal or a square-wave signal. The mechanically oscillatable unit is preferably excited at least temporarily to resonate oscillations. The mechanical vibrations are influenced by the medium surrounding the vibratable unit, so that conclusions can be drawn about various properties or process variables of the medium on the basis of a received signal representing the vibrations.

However, the first and second received signals are also influenced by the presence of gas bubbles. However, since the influence of the gas bubbles on the first and second received signal is different, a statement about the presence of gas bubbles can be made based on the evaluation of the ratio of the two characteristic quantities of the two received signals in the two different oscillation modes. The method is advantageously very easy to implement. No complex structural measures or additional sensor units are necessary. Rather, it only needs the excitation of the oscillatable unit with two different excitation signals to generate two different vibration modes. The two oscillation modes can be excited simultaneously, that is to say superimposed on one another, or alternately, in particular sequentially.

In one embodiment of the invention, the first oscillation mode is a fundamental oscillation mode of the oscillatable unit. In this regard, it is advantageous if the mass distribution, rigidity and / or geometry of the oscillatable unit is / are chosen such that the fundamental oscillation mode is at a frequency f ₁ <1.5 kHz.

A further particularly preferred embodiment includes that the second oscillation mode is selected in such a way that the oscillations of the oscillatable unit are influenced by the formation of gas bubbles in the area of the mechanically oscillatable unit. The higher oscillation mode is therefore deliberately selected with a view to detecting the gas bubbles. The respective process variable is then preferably determined and / or monitored on the basis of a different oscillation mode.

With regard to the second oscillation mode, it is advantageous if the higher oscillation mode is selected such that the frequency of the second oscillation mode lies in a frequency range in which a natural frequency of the gas bubbles lies. The natural frequency or the resonance frequency of gas bubbles depends, among other things, on the, in particular physical and / or chemical properties of the medium and on the bubble size. If the sensor is operated at frequencies which are in the range of the resonance frequency of the gas bubbles occurring, the vibration energy of the sensor is absorbed by the gas bubbles and a resonance vibration of the vibratable unit is very strongly damped or no longer possible.

The second oscillation mode is preferably a first, higher oscillation mode of the oscillatable unit.

Another embodiment of the invention includes that the first and second characteristic variables of the first and second received signals are a frequency, an amplitude, or a variable derived from at least the frequency or the amplitude.

A particularly preferred embodiment includes that in the event that the ratio of the first and second characteristic variable is zero or a slope of the ratio of the first and second characteristic variable as a function of time exceeds a predeterminable limit value, the presence of gas bubbles is concluded. If gas bubbles are present, it is no longer possible to excite the vibratable unit in an vibration mode influenced by the gas bubbles, for example the second vibration mode. It is no longer possible to detect a frequency or amplitude for the corresponding second received signal.

Another particularly preferred embodiment includes that in the event that the ratio of the first and second characteristic variable is greater than zero or a slope of the ratio of the first and second characteristic variable as a function of time falls below a predeterminable limit value, it is concluded that there are no gas bubbles.

Another embodiment of the method according to the invention includes that a process variable of the medium is determined on the basis of the first received signal on the basis of the first received signal. The process variable is preferably a fill level, in particular a predeterminable fill level, a flow rate, the density or the viscosity of the medium. In particular, the determination of the density of the medium shows a sensitive dependence on the presence of gas bubbles in the respective liquid.

It is advantageous if the process variable is only determined when there are no gas bubbles.

It is also advantageous if, during a time interval in which gas bubbles are present, a value for the process variable that was last determined before the formation of the gas bubbles is output, and / or a current value in each case during a time interval in which there are no more gas bubbles determined value for the process variable is output.

Another particularly preferred embodiment includes that process monitoring is carried out on the basis of the ratio of the first and second characteristic variables. The presence of gas bubbles can also be desired in certain processes and monitored or verified by means of the method according to the invention.

For example, fermentation or a disinfection process can advantageously be monitored by means of the method according to the invention. The presence of gas bubbles during individual process steps is absolutely necessary for such processes. The inventive method can on the one hand provide information about the actual presence of the gas bubbles. In addition, a point in time can also be determined at which there are no more gas bubbles. On the basis of this point in time, for example, further process steps can then be initiated or process variables of the medium can be determined and / or monitored.

The object on which the invention is based is further achieved by a computer program for detecting gas bubbles in a liquid medium with computer-readable program code elements which, when executed on a computer, cause the computer to execute at least one embodiment of the method according to the invention.

The object on which the invention is based is also achieved by a computer program product with a computer program according to the invention and at least one computer-readable medium on which at least the computer program is stored.

It should be pointed out that the configurations described in connection with the method according to the invention can also be applied mutatis mutandis to the computer program according to the invention and the computer program product according to the invention, and vice versa.

• 1 eine schematische Skizze eines (a) vibronischen Sensors und (b) eines nach dem Coriolis-Messprinzip arbeitendes Feldgerät gemäß Stand der Technik,
• 2 eine schematische Darstellung des Einflusses von Gasblasen auf das Empfangssignal,
• 3 Diagramme der Frequenz des ersten und zweiten Empfangssignals sowie des Verhältnisses der ersten und zweiten Frequenz je als Funktion der Zeit, und
• 4 Diagramme der Amplitude des ersten und zweiten Empfangssignals sowie des Verhältnisses der ersten und zweiten Amplitude je als Funktion der Zeit.

The invention is explained in more detail with reference to the following figures. It shows:

• 1 a schematic sketch of a (a) vibronic sensor and (b) a field device operating according to the Coriolis measuring principle according to the prior art,
• 2 a schematic representation of the influence of gas bubbles on the received signal,
• 3 Diagrams of the frequency of the first and second received signal and of the ratio of the first and second frequency as a function of time, and
• 4th Diagrams of the amplitude of the first and second received signal and of the ratio of the first and second amplitude as a function of time.

In the figures, the same elements are provided with the same reference numerals.

1a shows a vibronic sensor 1 with a sensor unit 2 with a vibratory unit 4th in the form of a vibrating fork, which are used in particular to determine and / or monitor a, in particular predeterminable, fill level, the density and / or the viscosity of the medium. The mechanically oscillating unit 4th partially immersed in a medium M. one that is in a container 3 is located, and is by means of the excitation / reception unit 5 excited to mechanical vibrations, which in turn can be, for example, a piezoelectric stack or bimorph drive. Other vibronic sensors have, for example, electromagnetic drive / receiving units 5 . It is possible to have a single drive / receiver unit 5 to use, which serves to excite the mechanical vibrations and to detect them. However, it is also conceivable to implement a drive unit and a receiving unit. Is shown in 1 also an electronics unit 6th , by means of which the signal acquisition, evaluation and / or feeding takes place.

In 1b again is a Coriolis meter 1 shown according to the prior art, which is an example of two measuring tubes 7a , 7b , a housing module 8th with a carrier 9 and a casing 10 and one on the inlet side 11a and process connection on the outlet side 11b disposes. Other configurations of generic field devices have different numbers of measuring tubes 7th . Using the two process connections 11a , 11b can the field device 1 be integrated into an existing pipeline, which is not shown here for the sake of simplicity. The carrier 4th is designed in the form of a laterally at least partially open, especially tubular support cylinder and with the two measuring tubes 7a , 7b connected. The measuring tubes 7a , 7b are also from the casing 10 surround. Usually it is on the carrier 9 also a neck tube (not shown here) for connecting an electronics unit 6th attached, which is used, for example, for signal acquisition, evaluation and feeding.

In the area of the inlet side 11a and process connection on the outlet side 11b an inlet-side and an outlet-side (not visible) distributor piece are integrated, which distributor pieces are integrated with the carrier 9 and with the two measuring tubes 7a , 7b are mechanically connected, and which the flowing medium M. from the pipeline (not visible) onto the two measuring tubes 7a , 7b to distribute. The two measuring tubes 7a , 7b are further by means of several coupling elements ( 10 ; here only one is marked) mechanically coupled with each other.

Each of the two measuring tubes 9a , 9b causes mechanical vibrations during operation. Furthermore, at least one is on at least one measuring tube 9a , 9b Acting electromechanical, in particular electro-dynamic, exciter arrangement (not visible here) for generating and / or maintaining mechanical vibrations of the measuring tube 11a , 11b shown, as well as at least one on vibrations of the measuring tubes 11a , 11b responsive vibration sensor arrangement (also not visible) to the Generating at least one vibration measurement signal representing the vibrations of the measuring tubes.

Dabei ist f_1,vac die Resonanzfrequenz der schwingfähigen Einheit 4 in der Grundschwingungsmode im Vakuum bzw. an Luft und S ist die von der Geometrie der schwingfähigen Einheit 4 abhängige Empfindlichkeit der schwingfähigen Einheit 4.Gas bubbles in a liquid medium have a great influence on the viscoelastic properties of the liquid. As a result, gas bubbles also have a major influence on the mechanical vibrations of the vibratable unit 4th characterizing received signal X have, as in 2 illustrated for the case of a vibronic sensor. The frequency change Δf / f _{1 is shown} as a function of the frequency f for oscillations of the oscillatable unit 4th for example in the fundamental mode. The frequency f ₁ in the fundamental mode depends on the density ρ of the liquid M. from. In the case that it is a Newtonian liquid without gas bubbles, the following applies for the frequency change Δf / f _{1, vac,} for example: $$\frac{\mathrm{<figure-callout\; id="1"\; label="\Delta \; f\; f"\; filenames="DE102019114174A1\_0003.png"\; state="\{\{state\}\}">\Delta </figure-callout>}f}{f_{}}=\sqrt{\frac{1}{1+\mathrm{S.}\cdot \rho }-1}.$$

Here, f _{1, vac is} the resonance frequency of the oscillatable unit 4th in the fundamental oscillation mode in vacuum or in air and S is that of the geometry of the oscillatable unit 4th dependent sensitivity of the oscillatable unit 4th .

In case of 2 the same vibratory unit dives 4th now twice in the same medium M. a, in a first case in the medium M. Gas bubbles are present (squares) and in the second case there are no gas bubbles (triangles). With the medium M. For the example shown here, it is water. While for frequencies f <fp the frequency change for both cases is the same, it comes for frequencies f> f _P to significant deviations. The change in frequency in the event of gas bubbles being present is significantly greater than the change in frequency for the same medium M. without gas bubbles. The frequency fp describes a critical limit frequency, from which the vibration behavior of the vibratable unit 4th is influenced by the presence of the gas bubbles. If the sensor is operated at frequencies f> fp, in particular at frequencies which are in the range of the natural frequency of the gas bubbles occurring in each case, the oscillation energy of the sensor is increased 1 absorbed by the gas bubbles and a resonance oscillation of the oscillatable unit 4th is not possible anymore.

In the case of media in the form of aqueous solutions, the natural frequency f _G of gas bubbles can be calculated according to the following equation, for example: $$f_G=\frac{1}{2\pi \alpha }{\left(\frac{3\gamma p_{\mathrm{A.}}}{\rho }\right)}^{\frac{1}{2}}$$

Here, a is the radius of the gas bubbles, γ the polytropic coefficient, p _A the process pressure and ρ the density of the liquid. For a pressure p _A = 1 bar, the gas bubble frequency is f _G = 6520 / D Hz, where D is the diameter of the gas bubbles in millimeters. If the sensor is operated at frequencies which are in the range of the resonance frequency of the gas bubbles occurring, the vibration energy of the sensor is absorbed by the gas bubbles and a resonance vibration of the vibratable unit is very weak or no longer possible.

The respective maximum gas bubble size in water depends on the Archimedean force that drives the bubbles out of the liquid and on the adhesion of the gas bubbles to the surface of the sensor unit 2 , especially the vibratory unit 4th . At a process pressure p _A = 1 bar, gas bubbles generally have a diameter d from 2-3mm up before it from the surface of the sensor unit 2 be replaced. Operation of a sensor is therefore essential for this application 1 Possible undisturbed at frequencies f <2kHz. For frequencies f> 2kHz, on the other hand, there is a considerable influence from the gas bubbles.

In the event that by means of the sensor 1 the concentration ρ of the medium M. is to be determined, the presence of gas bubbles is particularly critical. With a variance of the oscillation frequency f due to gas bubbles of 1-2%, there is already a gas bubble-induced measurement error of approx. 10%. However, such an order of magnitude for the measurement error is not acceptable in the area of density determination in process measurement technology.

Similar considerations apply to the case of a Coriolis measuring device 1 with a measuring tube 7th as a vibratory unit

The method according to the invention now allows the reliable detection of gas bubbles in liquid media. For this purpose, the oscillatable unit 4,7 is activated by means of two different excitation signals I1 and I2 in two different modes of vibration S1 and S2 stimulated. For each of the two received signals X1 and X2 a characteristic variable is then determined and based on the ratio V the characteristic quantities made a statement about the presence of gas bubbles.

Two possible exemplary configurations for the method according to the invention are shown in the figures 3 and 4th illustrated.

In case of 3 is the characteristic size of the received signals X1 and X2 given by the frequency f1 and f2, respectively. The first vibration mode S1 is therefore the fundamental oscillation mode with the frequency f1 and the second oscillation mode S2 is the first higher oscillation mode with the frequency f2.

For the example shown, the oscillatable unit 4, 7 is designed such that the fundamental oscillation mode is at a natural frequency f _{1, vac} <1.5 kHz and the first higher oscillation mode is at a natural frequency f _{2, vac} ~ 9f _{1, vac} . In this way, gas bubbles with diameters d> 0.5mm can be reliably detected.

3a shows the first frequency f ₁ of the first received signal X1 as a function of time t , where f _{1, vac} = 1000Hz, and where the medium is M. fresh fresh water. In the medium M. air bubbles are deposited on the oscillatable unit 4,7 with increasing time. When the air bubbles reach a certain size, they are detached from the surface of the oscillatable unit 4, 7. This leads to a gas bubble-induced reduction in the first frequency f ₁ from 752Hz to 744Hz. After the gas bubbles from the medium M. have left (approx. 14h) the first frequency increases f ₁ back to the original one in the medium M. corresponding to the immersed state, value of 752 Hz, which it reaches after a period of Δt = 14h.

The course of the second frequency f ₂ of the second received signal X2 is, also as a function of time t , in 3b shown. The gas bubbles temporarily lead to a break in or to a strong damping of the vibrations in the second vibration mode. However, the mere presence of the second oscillation mode as a criterion for the presence of gas bubbles is not reliable. For the period of time Δt = 4h-14h, the oscillatable unit 4, 7 can indeed be in the second oscillation mode S2 be stimulated; however, there is still a reduction in the first frequency at the same time f ₁ in the first vibration mode S1 compared to the case without gas bubbles, so that a determination of the respective process variable using the first oscillation mode S1 is not yet reliably possible. Rather, a reliable determination of a process variable is only possible after a period of time Δt = 14h.

A more reliable statement about the presence of gas bubbles is possible by considering the ratio V of the two frequencies f ₁ and f ₂ , as in 3c shown. In the period of time Δt = 4h-14h the ratio is V the first f ₁ and second frequency f2 first zero and then has a considerable slope. Only after a period of Δt = 14h does the gradient of the ratio flatten out V and converges to a constant value V> 0.

The same considerations can be applied to the case where the amplitude A is used as the characteristic variable instead of the frequency f. This case is exemplary for the same application of a sensor immersed in fresh fresh water 1 in 4th shown.

4a shows the first amplitude A ₁ of the first received signal X1 as a function of time t . There is a temporary, gas-bubble-induced decrease in the first amplitude A ₁ . After Δt = 14h the first has amplitude A ₁ reaches its original value, which corresponds to the absence of gas bubbles. The second amplitude A ₂ on the other hand ( 4b) temporarily collapses or is heavily damped. Only based on the ratio V the first A ₁ and second amplitude A ₂ can gas bubbles in the medium M. can be reliably detected, as in 4c illustrated. In the period of time Δt = 4h-14h the ratio is V the first A ₁ and second amplitude A ₂ first zero and then has a significant slope. Only after a period of Δt = 14h does the gradient of the ratio flatten out V and converges towards a constant value.

In the event of 4th it is assumed that the amplitudes of the first and second excitation signals I1 and I2 are kept constant. Alternatively, it would also be conceivable to change the amplitudes A ₁ and A ₂ of the two received signals X1 and X2 keep constant. In this case, the relationship can be evaluated V the amplitudes of the two excitation signals I1 and I2 at. Another possibility is the evaluation of a normalized amplitude A _nor = X / I, which is derived from the quotient of the amplitudes of the received signal X and the excitation signal I. The use of a normalized amplitude is advantageously independent of the amplitude of the excitation signals used in each case I1 and 12th .

List of reference symbols

1

Vibronic sensor

2

Sensor unit

3

container

4th

Vibratory unit of a vibronic sensor

5

Drive / receiver unit

6th

Electronics unit

7.7a, 7b

oscillatable unit of a Coriolis measuring device

8th

Housing module

9

carrier

10

Cladding

11a, 11b

Process connections

M.

medium

S1, S2

Modes of vibration

1,11,12

Excitation signals

X, X1, X1

Received signals

f ₁ , f ₂

first, second frequency

A ₁ , A ₂

first, second amplitude

f _G

Natural frequency of the gas bubbles

f _P

critical frequency

ρ

Density of the medium

V

relationship

t

time

S.

sensitivity

d

Diameter of the gas bubbles

a

Radius of the gas bubbles

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102006034105 A1 [0003]
• DE 102007013557 A1 [0003]
• DE 102005015547 A1 [0003]
• DE 102009026685 A1 [0003]
• DE 102009028022 A1 [0003]
• DE 102010030982 A1 [0003]
• DE 00102010030982 A1 [0003]
• DE 10050299 A1 [0005]
• DE 102007043811 A1 [0005]
• DE 10057974 A1 [0005]
• DE 102006033819 A1 [0005]
• DE 102015102834 A1 [0005]
• DE 102016112743 A1 [0005]
• US 4793191 A [0006]
• US 4823614 A [0006]
• US 4831885 A [0006]
• US 5602345 A [0006]
• US 2007/0151368 A [0006]
• US 2010/0050783 A [0006]
• WO 96/08697 A [0006]
• WO 2009/120222 A [0006]
• WO 2009/120223 A [0006]
• DE 102015122661 A1 [0009]

Claims (16)

A method, in particular a computer-implemented method, for the detection of gas bubbles in a liquid medium (M) with a sensor (1) with a mechanically oscillatable unit (4), comprising the following method steps, - excitation of the oscillatable unit (4) with a first excitation signal (11 ) for generating mechanical vibrations of the vibratable unit (4) according to a first predeterminable vibration mode (S1) of the vibratable unit (4), and receiving the mechanical vibrations from the mechanically vibratable unit (4) in the form of a first received signal (X1), Exciting the oscillatable unit (4) with a second excitation signal (12) for generating mechanical vibrations of the oscillatable unit (4) according to a second predeterminable oscillation mode (S2) of the oscillatable unit (4), and receiving the mechanical oscillations from the mechanically oscillatable unit (4) in the form of a second received signal (X2), - determining a first and second n characteristic quantity (f, A) of the first (X1) and second received signal (X2), - determining a ratio (V) of the first (f ₁ , A ₁ ) and second characteristic quantity (f ₂ , A ₂ ), and - Generating a statement about the presence of gas bubbles based on the ratio (V) of the first (f ₁ , A ₁ ) and second characteristic variable (f ₁ , A ₁ ). Procedure according to Claim 1 , wherein the first oscillation mode (S1) is a fundamental oscillation mode of the oscillatable unit (4). Procedure according to Claim 2 , the mass distribution, rigidity and / or geometry of the oscillatable unit (4) being / are selected such that the fundamental oscillation mode (S1) is at a frequency f ₁ <1.5 kHz. Method according to at least one of the preceding claims, wherein the second oscillation mode (S2) is selected such that the oscillations of the oscillatable unit (4) are influenced by the formation of gas bubbles in the area of the mechanically oscillatable unit (4). Procedure according to Claim 4 , the second oscillation mode (S2) being selected such that the frequency (f2) of the second oscillation mode (S2) lies in a frequency range in which a gas bubble natural frequency (f _G ) of the gas bubbles lies. Procedure according to Claim 4 or 5 , the second oscillation mode (S2) being a first higher oscillation mode of the oscillatable unit (4). Method according to at least one of the preceding claims, wherein the characteristic variable (f, A) of the first (X1) and second received signal (X2) is a frequency (f), an amplitude (A), or one of at least the frequency (f) or the amplitude (A) derived quantity. Method according to at least one of the preceding claims, wherein in the case that the ratio (V) of the first (f ₁ , A ₁ ) and second characteristic variable (f ₂ , A ₂ ) is zero, or a slope of the ratio (V) of first (f ₁ , A ₁ ) and second characteristic variable (f ₂ , A ₂ ) as a function of time (t) exceeds a predeterminable limit value, it is concluded that gas bubbles are present. Method according to at least one of the Claims 1 - 7th , where in the case that the ratio (V) of the first (f ₁ , A ₁ ) and second characteristic quantities (f ₂ , A ₂ ) is greater than zero or a slope of the ratio (V) of the first (f ₁ , A ₁ ) and the second characteristic variable (f ₂ , A ₂ ) as a function of time (t) falls below a predeterminable limit value, it is concluded that there are no gas bubbles. Method according to at least one of the preceding claims, wherein a process variable of the medium (M) is determined on the basis of the first received signal (X1). Method according to at least one of the preceding claims, wherein the process variable is only determined in the event that no gas bubbles are present. Method according to at least one of the preceding claims, wherein during a time interval in which gas bubbles are present, a value for the process variable last determined before the formation of the gas bubbles is output, and / or during a time interval in which there are no more gas bubbles present, in each case a currently determined value for the process variable is output. Method according to at least one of the preceding claims, process monitoring being carried out on the basis of the ratio (V) of the first (f ₁ , A ₁ ) and second characteristic variables (f ₁ , A ₁ ). Procedure according to Claim 12 , whereby a fermentation or a disinfection process is monitored. Computer program for the detection of gas bubbles in a liquid medium with computer-readable program code elements which, when executed on a computer, the computer cause a method according to at least one of the preceding claims to be carried out. Computer program product with a computer program Claim 14 and at least one computer-readable medium on which at least the computer program is stored.

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