Method for determining physical parameters of charged liquids

Abstract

The method (100) according to the invention allows the determination of a measured value of a physical parameter of a liquid with the aid of a sensor, the sensor having at least one measuring tube for conducting the liquid, wherein the measuring tube can be excited to vibrate in at least one flexural vibration mode, wherein the method comprises the following steps: determining at least one current value of a vibration parameter of the flexural vibration mode (110); determining a measured value of a physical parameter (120) based on the current value of the vibration parameter, wherein the measured value is compensated with respect to a resonator effect based on the current value of the natural frequency of the flexural vibration mode and on the sound velocity of the liquid conducted in the measuring tube, wherein the value of the sound velocity is provided independently of the vibration of the measuring tube.

Description

Technical Field

[0001] The invention relates to a method for determining a physical parameter of a liquid by means of a sensor, the sensor having at least one measuring tube for conducting the liquid, wherein the measuring tube comprises an inlet-side end section and an outlet-side end section, wherein the sensor has at least one inlet-side fastening device and an outlet-side fastening device, by means of which the measuring tube is fastened in one of the end sections, respectively, wherein the measuring tube can be excited to vibrate between the two fastening devices, wherein the mass flow rate and the density of the liquid can be determined based on the vibration characteristics of the measuring tube. However, the measured values ​​of the mass flow rate and the measured values ​​of the density have cross-sensitivities with respect to the sound velocity or the compressibility of the liquid. It is therefore desirable to compensate for these cross-sensitivities. Background Art

[0002] The first publication of patent application DE 10 2015 122 661 A1 discloses a method for determining the density or mass flow rate of an aerated liquid by means of a sensor having a measuring tube with a plurality of flexural vibration modes with different natural frequencies. A preliminary density value is determined on the basis of the natural frequencies of two flexural vibration modes, assuming a resonance of the aerated liquid relative to the measuring tube, enabling the determination of the speed of sound and then the determination of corrected density and mass flow values.

[0003] The above methods based on the so-called multi-frequency technique provide satisfactory results where measurements of aerated liquids are involved, which have a significantly reduced sound velocity compared to the pure liquid phase. When the sound velocity is too high, the multi-frequency technique is not feasible.

[0004] As the requirements for measuring accuracy increase, the resonator effect becomes more important even in the case of media with high sound velocities; therefore, this should also be taken into account when determining measured values ​​for pure liquids. The object of the present invention is to provide a method and a measuring device which correct the influence of the resonator effect also for such media. Summary of the invention

[0005] According to the invention, this object is achieved by a method for determining a measured value of a physical parameter of a liquid by means of a sensor and by a measuring device for determining a measured value of a physical parameter of a liquid.

[0006] The method according to the invention is a method for determining a measured value of a physical parameter of a liquid with the aid of a sensor, the sensor having at least one measuring tube for conducting the liquid, wherein the measuring tube in each case has an inlet-side end section and an outlet-side end section, wherein the sensor has at least one inlet-side fastening device and an outlet-side fastening device, by means of which the measuring tube is fastened in one of the end sections, respectively, wherein the measuring tube can be excited to vibrate between the two fastening devices in at least one flexural vibration mode, wherein the method comprises the following steps: determining at least one current value of a vibration parameter of the flexural vibration mode; determining a measured value of the physical parameter based on the current value of the vibration parameter, wherein the measured value is compensated with respect to a resonator effect based on the current value of the natural frequency of the flexural vibration mode and the sound velocity of the liquid conducted in the measuring tube, wherein a value of the sound velocity is provided independently of the vibration of the measuring tube.

[0007] In a development of the invention, the vibration parameter comprises a natural frequency of a flexural vibration mode, wherein the physical parameter comprises a density of the liquid conducted in the measuring tube.

[0008] In a development of the invention, the vibration parameter comprises a time delay proportional to the mass flow rate between signals of two vibration sensors arranged offset relative to one another in the longitudinal direction of the measuring tube, wherein the physical parameter comprises the mass flow rate of the liquid conducted in the measuring tube.

[0009] In a development of the invention, the current measured value of the sound velocity of the liquid is provided by an external sensor, in particular an ultrasonic sensor.

[0010] In a development of the invention, an externally determined value for the speed of sound of the liquid is stored in a data memory and is read out from the data memory in order to calculate the physical parameter.

[0011] In a further development of the invention, the measured value of the physical parameter is determined from the current value of the vibration parameter on the assumption that the system parameters included in the calculation of the physical parameter are valid, wherein in particular the system parameters are determined taking into account resonator effects.

[0012] In a refinement of the invention, the measured value of the physical parameter is determined based on the assumption that the device parameters included in the calculation of the physical parameter are determined while ignoring the resonator effect, wherein a correction for the influence of the resonator effect occurs when determining the device parameters.

[0013] The initial density value of the fluid ρ i Based on the natural frequency f of the fi mode i The relationship is described as:

[0014]

[0015] Among them, c 0i 、c 1i and c 2i is a device parameter, here in the form of a mode correlation coefficient.

[0016] However, the above method does not take into account the influence of the resonator effect, i.e. the influence of the vibrating liquid in the measuring tube. The closer the resonant frequency of the vibrating liquid is to the natural frequency of the flexural vibration mode, the stronger the influence of the natural frequency. The resonant frequency of the liquid depends on its sound velocity. In the improved solution of the present invention, the mode-specific correction term K of the preliminary density value is i It is therefore a function of the quotient of the liquid sound velocity and the natural frequency of the mode used to determine the preliminary density measurement.

[0017] In an improved solution of the present invention, the preliminary density value ρ i The correction term K i Based on f i The natural frequencies of a mode have the following form:

[0018]

[0019] in

[0020]

[0021] Among them, r and g are constants independent of the medium, and f i Yes i The natural frequency of the mode, ρ corr is the corrected density and b is a scaling constant, wherein in particular: r / b<1, in particular r / b<0.9 and / or b=1. In the above equation, g is in particular the resonant frequency f of the liquid res The proportionality factor between the velocity of sound in the liquid and the diameter of the measuring tube is a function of the following:

[0022] f res =g·c

[0023] For example, for a double-tube measuring device of DN 50 or DN 100, the value of g is approximately 21 or 8.5.

[0024] The sound velocity c of the liquid can be stored, for example, as a predetermined value in a data memory, optionally together with a temperature correction, and read out therefrom, or it can be provided by an external sensor, for example an ultrasonic sensor.

[0025] In a refinement of the invention, the following applies to the density error E of the preliminary density value based on the natural frequency of the fi mode: ρi :

[0026] E ρi:=K i -1,

[0027] Among them, the mass flow rate error E of the preliminary mass flow value m The density error E from the preliminary density value based on the flexural vibration mode f1 p1 Proportional, that is to say:

[0028] E m :=K·E ρ1 ,

[0029] The proportional factor k is not less than 1.5 and not greater than 3. In the currently preferred embodiment of the present invention, the proportional factor is k=2.

[0030] The following correction term K applies to the mass flow rate: m :

[0031] K m :=1+E m ,

[0032] therefore

[0033]

[0034] The corrected mass flow rate is obtained as As

[0035]

[0036] Here, the preliminary mass flow value is determined in a known manner by multiplying the time delay Δt between the signals of the two vibration sensors by a calibration factor calf.

[0037] The determination of the mass flow rate correction term as described here also follows the procedure in the multi-frequency technique, whereby the mass flow rate correction term is conveniently estimated via the density correction term, since the density correction term must be determined anyway in order to determine the value of the velocity of sound of the liquid. However, if the value of the velocity of sound is provided externally, the mass flow rate correction term K can also be calculated independently of the density correction term. m Estimated to be:

[0038]

[0039] In this case, a1 is a constant and f c is the vibration frequency at which the measurement is performed, r t is the radius of the measuring tube or tubes, and c is the speed of sound in the medium under consideration.

[0040] The above correction term K i and K m The interpretation is only in determining the device parameter cji This is valid under the assumption that the resonator effect of the reference medium is taken into account. If this is not the case, the device parameter c ji Or the calf will be determined too low.

[0041] Therefore, according to a refinement of the invention, the influence of the resonator effect in the determination of the device parameters must be corrected subsequently. This can ideally be done using the data of the medium used to determine the device parameters. The corresponding initial density correction term K for the fi mode is 0，i will be defined as:

[0042]

[0043] In this case, c0 is the medium sound velocity used to determine the coefficient for measuring the density of the medium used, and f 0,i is the observed natural frequency of the fi mode.

[0044] In this case, the corrected density is calculated according to the following equation:

[0045]

[0046] The same applies to mass flow measurement, for which failure to take into account the resonator effect when determining the calibration factor calf will subsequently be corrected.

[0047] There are two alternatives for determining the initial mass flow correction term K: 0，m and the correction term K used to determine the current mass flow rate m .

[0048] First, based on the initial density correction term:

[0049]

[0050] Where c0 is the medium sound velocity used to determine the coefficient for measuring the density of the medium used, and f 0,i represents the observed natural frequency of the fi mode.

[0051] Secondly, based on the conditions for determining the calibration factor calf:

[0052]

[0053] In this case, a1 is a constant and f 0,c is the oscillation frequency at which the measurement is performed to determine the calibration factor calf, r t is the radius of the measuring tube or tubes, and c0 is the sound velocity of the liquid used to determine the calibration factor.

[0054] Then the following applies for the corrected mass flow rate:

[0055]

[0056] Among them, K m is the current mass flow correction term, K 0,m is one of the two initial mass flow correction terms, and is the preliminary mass flow measurement.

[0057] The device according to the invention is used for determining a measured value of a physical parameter of a liquid, in particular by means of a method according to the invention, wherein the device comprises a sensor having: at least one measuring tube for conducting the liquid, wherein the measuring tube in each case has an inlet-side end section and an outlet-side end section, wherein the sensor has at least one inlet-side fastening device and one outlet-side fastening device, by means of which the measuring tube is in each case fastened in one of the end sections, wherein the measuring tube can be excited to vibrate in at least one flexural vibration mode between the two fastening devices, and at least one exciter for exciting the measuring tube in at least one flexural vibration mode. The measuring device further comprises an operating and evaluation circuit configured to: drive an exciter; acquire a signal from at least one vibration sensor; determine at least one current value of a vibration parameter of the flexural vibration mode based on the sensor signal; and determine a measured value of a physical parameter based on the current value of the vibration parameter, wherein the operating and evaluation circuit is configured to compensate the measured value with respect to a resonator effect based on a current value of a natural frequency of the flexural vibration mode and a sound velocity of a liquid conducted in the measuring tube, wherein the value of the sound velocity is provided independently of the vibration of the measuring tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will now be described in more detail based on the exemplary embodiments shown in the drawings. In the drawings:

[0059] Figure 1 is a schematic diagram of an exemplary embodiment of a measuring device according to the present invention;

[0060] Figure 2a is a flow chart of a first exemplary embodiment of a density measurement method according to the present invention;

[0061] Figure 2b is a flow chart with sub-steps according to a first exemplary embodiment of a method according to the present invention;

[0062] Figure 3a is a flow chart of a second exemplary embodiment of a method for mass flow measurement according to the present invention; and

[0063] Figure 3bis a flow chart with sub-steps of a second exemplary embodiment of a method according to the invention. DETAILED DESCRIPTION

[0064] Figure 1 The exemplary embodiment of the measuring device 1 according to the invention shown in comprises an oscillator 10 which comprises a pair of oscillating measuring tubes 14 which extend in parallel and between an inlet end flange 11 and an outlet end flange 12, wherein the flanges each comprise a flow divider or collector into which the measuring tubes 14 open. The flow dividers are connected to one another by a rigid housing 15, so that the oscillations of the flow dividers accommodating the measuring tubes are effectively suppressed in the oscillation frequency range of the useful bending vibration modes of the oscillator. The measuring tubes 10 are rigidly connected to an inlet-side node plate 20 and an outlet-side node plate 21, wherein the node plates define the oscillation nodes of the oscillator 10 formed by the two measuring tubes 14 and thus define to a large extent the frequencies of the useful bending vibration modes, except for the density dependence. The oscillator 10 is excited to oscillate by an electrodynamic exciter 17 acting between the two measuring tubes 14, wherein the oscillations are detected by means of two oscillation sensors 18, 19 which capture the relative movements of the measuring tubes 14 relative to one another. The exciter 17 is operated by an operating and evaluation circuit 30 which also captures and evaluates the signal from the oscillating sensor in order to determine a density or mass flow value corrected with respect to the resonator effect.

[0065] The influence of the resonator effect will now be explained in more detail based on density measurements of two media, namely water and carbon tetrachloride.

[0066] The natural frequency f of the fluid based on the fi mode i The initial density value ρ i The relationship is described as:

[0067]

[0068] Among them, c 0i 、c 1i and c 2i are device-specific, mode-dependent coefficients. The above coefficients are usually initially determined immediately after the production of the measuring device, wherein the vibration frequencies of the flexural vibration modes, in particular the vibration frequencies of the f1 mode, are determined for a medium of known density. Air at normal pressure and 20°C and water at 20°C are often used as media.

[0069] Table 1 shows the observed frequencies of the f1 mode for an exemplary measurement apparatus for these media and carbon tetrachloride.

[0070] medium density f1 c f0 f1 apparent density Resonator Effect Density error [kg / m3] [Hz] [m / s] [Hz] [kg / m3] [kg / m3] [kg / m3] 20℃ air 1.2 300 340 1994 1.22 0.02 0.00 Water at 20°C 1000 250 1482 8689 1000.69 0.69 0.00 <![CDATA[CCl4 at 20 °C]]> 1590 230.057 926 5429 1592.39 2.39 1.30

[0071] Table 1

[0072] Table 1 also indicates the density of the medium vibrating on the measuring tube, the speed of sound c and the resulting resonant frequency. In the column "f1 apparent density" the apparent density value is given, which is due to the f1 frequency in the measuring device, which was taken into account in the initial determination of the coefficients if the resonator effect is neglected in the current density measurement. The contribution of the resonator effect to the apparent density is specified in the column "Resonator effect".

[0073] The column "Density Error" summarizes the prior art situation, according to which not only the coefficient c 0i 、c 1i and c 2i The resonator effect is neglected both in the initial determination of and in the density measurement. Instead, the coefficients are chosen so that a target density of 1.2 kg / m^3 for air and 1000 kg / m^3 for water is obtained. The measurement error for these two media is therefore zero, while the measurement error for carbon tetrachloride is 1.3 kg / m^3.

[0074] Table 2 shows the coefficient c used to determine the density obtained based on the natural frequency of the first flexural vibration mode without considering the resonator effect. 01 to c 21 , where the natural frequency f of the liquid based on the fi mode i The initial density value ρ i The relationship is given here as:

[0075]

[0076] Insofar as the values ​​of the density of air and the density of water are pre-assigned as reference densities during calibration, the values ​​of the measured apparent density or preliminary density match the target values ​​of the density of these two media. However, for carbon tetrachloride there is a deviation of 1.3 kg / m^3. If the influence of the resonator effect on the initial calibration is taken into account and with the aid of the initial density correction term K 0i is used for subsequent corrections and is additionally included in the density correction term K i In correction to the current density measurement, it will then be possible to determine the correct medium density, as indicated in the last column of Table 2.

[0077]

[0078] Table 2

[0079] Based on f i The preliminary or apparent density value ρ of the natural frequency of the mode i Density correction term K i Has the following form:

[0080]

[0081] Among them, r and g are constants independent of the medium, and f i Yes i The natural frequency of the mode, ρ corr is the corrected density, and b is a scaling constant, wherein in particular: r / b<1, in particular r / b<0.9, and / or b=1. In the above equation, g is the resonant frequency f of the liquid res The proportionality factor with the sound velocity of the liquid is in particular a function of the diameter of the measuring tube, for which the following applies:

[0082] f res =g·c

[0083] The speed of sound c of the liquid can be stored, for example, as a predefined value in a data memory, optionally together with a temperature correction, and can be read out therefrom.

[0084] The corresponding initial density correction term K of the fi mode 0，i Will be determined as:

[0085]

[0086] In this case, c0 is the medium sound velocity used to determine the coefficient for measuring the density of the medium used, and f 0,i is the observed natural frequency of the fi mode.

[0087] In this case, the subsequent corrected density is calculated according to the following equation:

[0088]

[0089] Finally, Table 3 shows the coefficient c for determining the density obtained based on the natural frequency of the first flexural vibration mode taking into account the resonator effect. 01_sos to c 21_sos .

[0090] In this case, neglecting the resonator effects during the measurement operation leads to a preliminary density ρ i There is a considerable error.

[0091] medium c01_sos C11_sos C21_sos Initial density Corrected density [kg / m3] [kg / m3] 20℃ air -2270.3 2,06E+08 -87214.7 1.2232734 1.200 Water at 20°C 1000.6934 1000.000 Carbon tetrachloride at 20°C 1592.3937 1590.000

[0092] Table 3:

[0093] In this case, the corrected density ρ is determined according to the following equation corr :

[0094]

[0095] where the density correction term Ki is given previously as:

[0096]

[0097] The agreement between the corrected density values ​​and those from the literature is very good.

[0098] refer to Figure 2a and Figure 2b The flow chart in describes a first exemplary embodiment 100 of a method according to the invention, wherein the exemplary embodiment 100 is used for density measurement.

[0099] In a first step 110, as Figure 2a As shown, the current value of the natural frequency of the fundamental flexural vibration mode or f1 mode is determined.

[0100] In a second step 120, the density measurement is determined as a function of the current value of the natural frequency vibration parameter.

[0101] The second step 120 comprises Figure 2b The sub-steps shown in .

[0102] First, in a first sub-step 122 , a preliminary density measurement value ρ1 is determined based on the current value of the natural frequency f1 .

[0103] In the device used in this exemplary embodiment, the coefficient c is obtained by taking into account the resonator effect. 01_sos to c 21_sos Therefore, in the measuring mode, only the resonator effects in the current measurement need to be corrected. For this purpose, in a second substep 124, the value of the sound velocity of the liquid currently conducted in the measuring tube is provided, for example, from a data memory.

[0104] In a third sub-step 126 , a density correction term K1 is determined based on the value of the natural frequency f1 and the speed of sound c of the liquid.

[0105] Finally, in a fourth sub-step 128, a corrected density measurement ρ is calculated by dividing the preliminary density measurement ρ1 by K1. corr .

[0106] If the coefficient c is determined without taking into account the resonator effect 01 、c 11 、c 21 , then it will still need to be multiplied by the initial density correction term K 0.1 , in order to subsequently compensate for this error.

[0107] refer to Figure 3a and Figure 3bThe flow chart shown in describes a second exemplary embodiment 200 of a method according to the invention, wherein the exemplary embodiment 200 is used for mass flow measurement.

[0108] In a first step 210, as Figure 3a As shown, the current value of the time delay Δt proportional to the mass flow rate is determined between the rest position passages of the two vibration sensors on the measuring tube.

[0109] In a second step 220, the mass flow measurement is determined as a function of the current value of the time delay.

[0110] The second step 220 comprises Figure 3b The sub-steps shown in .

[0111] First, in a first sub-step 222, a preliminary mass flow value is determined based on the current value of the time delay Δt by multiplying the calibration factor calf In the apparatus used in this exemplary embodiment, the calibration coefficient calf is obtained in consideration of the resonator effect.

[0112] Therefore, in measurement mode, only the resonator effect in the current measurement needs to be corrected.

[0113] For this purpose, in a second substep 224 , the value of the speed of sound c of the liquid currently conducted in the measuring tube is provided, for example, from a data memory.

[0114] In a third sub-step 226, the mass flow correction term K is determined based on the value of the natural frequency fc at which the flow measurement occurs and the speed of sound c of the liquid according to the following equation: m :

[0115]

[0116] Among them, a1 is a constant, and r t is the radius of the measuring tube or tubes.

[0117] Finally, in a fourth sub-step 228, the preliminary mass flow value is used to Divide by K m To calculate the corrected mass flow value Right now:

[0118]

[0119] If the calibration factor calf is not determined taking into account the resonator effect, then the initial mass flow correction term K will also need to be multiplied. 0,m , in order to subsequently compensate for this error.

Claims

1. A method for determining a measured value of a physical parameter of a liquid by means of a sensor, the sensor having at least one measuring tube for conducting the liquid, wherein: The measuring tube can be excited to vibrate in at least one flexural vibration mode, wherein the method comprises the following steps: determining at least one current value of a vibration parameter of the flexural vibration mode; determining a measured value of said physical parameter based on said current value of said vibration parameter, wherein the measured value is compensated with respect to the resonator effect as a function of the current value of the natural frequency of the flexural vibration mode and the speed of sound of the liquid conducted in the measuring tube, wherein the value of the speed of sound is provided independently of the vibration of the measuring tube; where the following applies to the density error E of the preliminary density value based on the natural frequency of the fi mode: ρi : E ρi :=K i -1, wherein a measured value of the physical parameter is determined from the current value based on the assumption that device parameters are included in the calculation of the physical parameter and the resonator effect is ignored, wherein a correction is made for the influence of the resonator effect when determining the device parameters; Among them, the density correction term K of the initial density value ρi i Based on f i The natural frequencies of a mode have the following form: Among them, r and g are constants independent of the medium, and f i is the f i The natural frequency of the mode, and b is a scaling constant, where: r / b<1, and / or b=1, in the above equation, g is the resonant frequency f of the liquid res is a proportionality factor between the sound velocity of the liquid and is a function of the diameter of the measuring tube, where the following applies: res =g·c; Among them, the initial density correction term K of the fi mode is 0，i Determined as: where c0 is the speed of sound of the medium used to determine the coefficient for measuring the density of the medium used, and f 0,i represents the observed natural frequency of the fi mode; where the corrected density is calculated according to the following equation:

2. The method according to claim 1, wherein An external sensor provides a current measurement of the speed of sound of the liquid, or An externally determined value of the speed of sound of the liquid is stored in a data memory, from which it is read out in order to calculate the physical parameter.

3. The method according to claim 2, wherein: An ultrasonic sensor provides a current measured value of the speed of sound of the liquid.

4. The method according to claim 1, wherein: r / b<0.9。 5. A measuring device for determining a measured value of a physical parameter of a liquid by means of a method according to any one of claims 1 to 4, in, The measuring device comprises a sensor having: at least one measuring tube for conducting the liquid, wherein the measuring tube has an inlet-side end section and an outlet-side end section, at least one inlet-side fastening device and an outlet-side fastening device, by means of which the measuring tube is fastened to one of the end sections, respectively, wherein the measuring tube can be excited to vibrate in at least one flexural vibration mode between the two fastening devices, at least one exciter for exciting the measuring tube to vibration in at least one flexural vibration mode, at least one vibration sensor for detecting vibrations in at least one flexural vibration mode; and Wherein, the measuring device further comprises an operating and evaluating circuit, wherein the operating and evaluating circuit is configured to: driving the exciter; capturing a signal of the at least one vibration sensor; determining at least one current value of a vibration parameter of the flexural vibration mode based on the sensor signal; and determining a measured value of said physical parameter based on said current value of said vibration parameter, Therein, the operating and evaluation circuit is configured to compensate the measured value with respect to resonator effects as a function of the current value of the natural frequency of the flexural vibration mode and the sound velocity of the liquid conducted in the measuring tube, wherein the value of the sound velocity is provided independently of the vibration of the measuring tube.

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