METHOD FOR ASCERTAINING A PHYSICAL PARAMETER OF A CHARGED LIQUID

Abstract

A method for the measurement of a physical parameter of a liquid by means of a 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, comprises: determining at least one current value of a vibration parameter of the flexural vibration mode; determining a measurement value of the physical parameter according to the current value of the vibration parameter, wherein the measurement value is compensated in respect of the resonator effect according to a current value for the natural frequency of the flexural vibration mode and according to the sound velocity of the liquid conducted in the measuring tube, wherein the value for the sound velocity is provided independently of the vibrations of the measuring tube.

Claims

1-16. (canceled)

17. A method for determining a measurement value of a physical parameter of a liquid using a sensor having a measuring tube for conducting the liquid, wherein the measuring tube can be excited to vibrate in a flexural vibration mode, the method comprising: conducting the liquid in the measuring tube; determining a current value of a vibration parameter of the flexural vibration mode; determining a measurement value of the physical parameter as a function of the current value of the vibration parameter; and compensating the measurement value with respect to a resonator effect as a function of a current value for a natural frequency of the flexural vibration mode and of a sound velocity of the liquid conducted in the measuring tube, wherein a value for the sound velocity of the liquid is provided independently of the vibrations of the measuring tube.

18. The method according to claim 17, wherein the physical parameter is a density or a mass flow value of the liquid conducted in the measuring tube, wherein the associated vibration parameter is a vibration frequency or a time delay proportional to the mass flow rate between signals of two vibration sensors arranged offset from one another in a longitudinal direction of the at least one measuring tube.

19. The method according to claim 17, wherein the value for the sound velocity of the liquid is provided by an external sensor, or an externally determined value for the sound velocity of the liquid is stored in a data memory and is read out from the data memory to calculate the physical parameter.

20. The method according to claim 17, wherein a density correction term K.sub.i for a preliminary density value ρ.sub.i has the following form on the basis of that of the natural frequency of an f.sub.i-mode: $K_i:=\left(1+\frac{r}{{\left(\frac{g.Math.c}{f_i}\right)}^2-b}\right),$ wherein: r and g are media-independent constants; f.sub.i is a natural frequency of the f.sub.1 mode; b is a scaling constant such that r/b<1 and/or b=1; g is a proportionality factor that is a function of a diameter of the measuring tube between a resonance frequency f.sub.res of the liquid and the sound velocity c of the liquid such that f.sub.res=g.Math.c.

21. The method according to claim 20, wherein the following applies to a density error E.sub.ρi of the preliminary density value ρ.sub.i on the basis of the natural frequency of the f.sub.i-mode:
E.sub.ρi:=K.sub.i−1, wherein a mass flow rate error E.sub.m of a preliminary mass flow value is proportional to the density error E.sub.ρi of the preliminary density value based on the flexural vibration mode f1:
E.sub.m:=k.Math.E.sub.ρ1, wherein the proportionality factor k is not less than 1.5 and not more than 3, wherein a mass flow correction term K.sub.m is determined as:
K.sub.m:=1+E.sub.m.

22. The method according to claim 21, wherein a mass flow correction term K.sub.m is estimated as: $K_m:=1+a_1.Math.{\left(\frac{4\pi .Math.f_c}{c}.Math.r_t\right)}^2,$ wherein a.sub.1 is a constant, f.sub.c is the vibration frequency at which the flow rate measurement was performed, r.sub.t is the radius of the measuring tube or of the measuring tubes, and c is a value for the sound velocity of the liquid contained in the measuring tube.

23. The method according to claim 17, wherein a measurement value of the physical parameter is determined as a function of the current value of the vibration parameter on the assumption that device parameters included in the calculation of the physical parameter were determined taking the resonator effect into account.

24. The method according to claim 20, wherein a corrected density value ρ.sub.corr is determined as: ${\rho }_{\mathrm{corr}}=\frac{{\rho }_i}{K_i}.$

25. The method according to claim 21, wherein a corrected mass flow value {dot over (m)}.sub.corr is determined as ${\stackrel{.}{m}}_{\mathrm{corr}}=\frac{{\stackrel{.}{m}}_v}{K_m},$ wherein a preliminary mass flow value {dot over (m)}.sub.v is determined by multiplying a time flow-proportional delay Δt between the signals of two vibration sensors by a calibration factor calf.

26. The method according to claim 22, wherein a corrected mass flow value {dot over (m)}.sub.corr is determined as ${\stackrel{.}{m}}_{\mathrm{corr}}=\frac{{\stackrel{.}{m}}_v}{K_m},$ wherein a preliminary mass flow value {dot over (m)}.sub.v is determined by multiplying a time flow-proportional delay Δt between the signals of two vibration sensors by a calibration factor calf.

27. The method according to claim 17, wherein a measurement value of the physical parameter is determined as a function of the current value on the assumption that device parameters included in the calculation of the physical parameter were determined while disregarding the resonator effect, wherein a correction is made for the effect of the resonator effect on the determination of the device parameters.

28. The method according to claim 20, wherein an initial density correction term K.sub.0,i for the f.sub.i-mode is to be determined as: $K_{0,i}:=\left(1+\frac{r}{{\left(\frac{g.Math.c_0}{f_{0,i}}\right)}^2-b}\right),$ wherein c.sub.0 is the sound velocity of the medium used in determining the coefficients for measuring the density of the medium used and f.sub.0,i designates the observed natural frequency of the fi mode.

29. The method according to claim 28, wherein the corrected density is calculated according to: ${\rho }_{\mathrm{corr}}={\rho }_i.Math.\frac{K_{0,i}}{K_i}$

30. The method according to claim 20, wherein an initial mass flow correction term K.sub.0,m is calculated according to: $K_{0,m}:=\left(1+\frac{2.Math.\tau }{{\left(\frac{g.Math.c_0}{f_{0,i}}\right)}^2-b}\right),$ wherein c.sub.0 is the sound velocity of the medium used in determining the coefficients for measuring the density of the medium used and f.sub.0,i designates the observed natural frequency of the f.sub.i-mode.

31. The method according to claim 17, wherein an initial mass flow correction term K.sub.0,m is calculated according to: $K_{0,m}:=1+a_1.Math.{\left(\frac{4\pi .Math.f_{0,c}}{c_0}.Math.r_t\right)}^2,$ wherein a.sub.1 is a constant, f.sub.0,c is the oscillation frequency at which the measurement was carried out to determine the calibration factor calf r.sub.t is the radius of the measuring tube, and c.sub.0 is the sound velocity of the liquid used in determining the calibration factor.

32. The method according to claim 30, wherein a corrected mass flow measurement value is calculated according to: ${\stackrel{.}{m}}_{\mathrm{corr}}={\stackrel{.}{m}}_v.Math.\frac{K_{0,m}}{K_m},$ wherein K.sub.m is the current mass flow correction term, K.sub.0,m is the initial mass flow correction term and {dot over (m)}.sub.v is a preliminary mass flow value determined by multiplying a time flow-proportional delay Δt between the signals of two vibration sensors by a calibration factor calf.

33. The method according to claim 31, wherein a corrected mass flow measurement value is calculated according to: ${\stackrel{.}{m}}_{\mathrm{corr}}={\stackrel{.}{m}}_v.Math.\frac{K_{0,m}}{K_m},$ wherein K.sub.m is the current mass flow correction term, K.sub.0,m is the initial mass flow correction term and {dot over (m)}.sub.v is a preliminary mass flow value determined by multiplying a time flow-proportional delay Δt between the signals of two vibration sensors by a calibration factor calf.

34. A measuring device for determining a measurement value of a physical parameter of a liquid, the measuring device comprising: a sensor having: a measuring tube for conducting the liquid, wherein the measuring tube has an inlet-side end section and an outlet-side end section; an inlet-side fastening device and an outlet-side fastening device with which the measuring tube is fastened in one of the respective end sections, wherein the measuring tube is embodied to be excited to vibrate between the two fastening devices in at least one flexural vibration mode; an exciter for exciting vibrations of the measuring tube in at least one vibration mode; and a vibration sensor for detecting vibrations in the at least one flexural vibration mode; and an operating and evaluation circuit which is configured to: drive the exciter; capture signals of the at least one vibration sensor; determine at least one current value of a vibration parameter of the flexural vibration mode on the basis of the sensor signals; and determine a measurement value of the physical parameter as a function of the current value of the vibration parameter, wherein the operating and evaluation circuit is configured to compensate the measurement value in respect of the resonator effect as a function of a current value for a natural frequency of the at least one flexural vibration mode and of the sound velocity of the liquid conducted in the measuring tube, wherein the value for the sound velocity is provided independently of vibrations of the measuring tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention will now be described in greater detail on the basis of the exemplary embodiment shown in the figures. The following are shown:

[0030] FIG. 1 shows a schematic representation of an exemplary embodiment of a measuring device according to the present disclosure;

[0031] FIG. 2a shows a flow diagram of a first exemplary embodiment of the method for density measurement according to the present disclosure;

[0032] FIG. 2b shows a flow diagram with sub-steps of the first exemplary embodiment of the method according to the present disclosure;

[0033] FIG. 3a shows a flow diagram of a second exemplary embodiment of the method according to the invention for mass flow measurement; and

[0034] FIG. 3b shows a flow diagram with sub-steps of the second exemplary embodiment of the method according to the present disclosure.

DETAILED DESCRIPTION

[0035] The exemplary embodiment of a measuring device 1 according to the invention shown in FIG. 1 comprises an oscillator 10 which comprises a pair of oscillatory measuring tubes 14 which run parallel and extend 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 oscillations of the flow dividers accommodating the measuring tubes are effectively suppressed in the range of oscillation frequencies of useful bending vibration modes of the oscillator. The measuring tubes 14 are rigidly connected to an inlet-side node plate 20 and an outlet-side node plate 21, wherein the node plates define oscillation nodes of the oscillator 10 formed by the two measuring tubes 14, and thus largely define the frequencies of the useful flexural vibration modes except for the density dependency. 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 capturing relative movements of the measuring tubes 14 with respect to each other. The exciter 17 is operated by an operation and evaluation circuit 30, wherein the latter also captures and evaluates the signals from the oscillation sensors in order to determine a density or mass flow value corrected in relation to the resonator effect.

[0036] The effect of the resonator effect will now be explained in more detail on the basis of the density measurement for two media, namely water and carbon tetrachloride.

[0037] The relationship of a preliminary density value ρ.sub.i of a fluid on the basis of the natural frequency f.sub.i of an f.sub.i-mode is described as:

[00011]${\rho }_i=c_{0i}+c_{1i}\frac{1}{f_i^2}+c_{2i}\frac{1}{f_i^4},$

where c.sub.0i, c.sub.1i, and c.sub.2i are device-specific mode-dependent coefficients. The above coefficients are usually initially determined immediately following production of the measuring devices, wherein the vibration frequencies of the flexural vibration modes, in particular for the f1 mode, are determined for media of known density. Air at normal pressure and 20° C. and water at 20° C. are frequently used as the media.

[0038] Table 1 shows the observed frequencies of the f1 mode of an exemplary measuring device for these media and for carbon tetrachloride.

TABLE-US-00001 TABLE 1 f1 appar- Resona- Dens- Dens- ent tor ity ity: f1 c f0 density effect error Medium [kg/m3] [Hz] [m/s] [Hz] [kg/m3] [kg/m3] [kg/m3] Air at 20° 1.2 300 340 1994 1.22 0.02 0.00 C. Water at 1000 250 1482 8689 1000.69 0.69 0.00 20° C. CCl.sub.4 at 1590 230.057 926 5429 1592.39 2.39 1.30 20° C.

[0039] Table 1 also indicates the density, the sound velocity c, and the resulting resonance frequency for the medium vibrating against the measuring tube. An apparent density value is given In the “f1 apparent density” column, which density value would result due to the f1 frequency in a measuring device for which the resonator effect had been taken into account in the initial determination of the coefficients if the resonator effect is disregarded in the current density measurement. The contribution of the resonator effect to the apparent density is specified in the “resonator effect” column.

[0040] The “density error” column summarizes the situation of the prior art, according to which the resonator effect is disregarded not only in the initial determination of the coefficients c.sub.0i, c.sub.1i, and c.sub.2i but also in the density measurement. The coefficients are rather selected such that the target density of 1.2 kg/m{circumflex over ( )}3 for air and the target density of 1000 kg/m{circumflex over ( )}3 for water are obtained. The measurement error for these two media is thus zero, while for carbon tetrachloride it is 1.3 kg/m{circumflex over ( )}3.

[0041] Table 2 shows the coefficients c.sub.0i to c.sub.2i for determining the density obtained on the basis of the natural frequency of the first flexural vibration mode without taking into account the resonator effect, wherein the relationship of a preliminary density value ρ.sub.i of a liquid based on the natural frequency f.sub.i of an f.sub.i-mode is given here as:

[00012]${\rho }_i=c_{0i}+c_{1i}\frac{1}{f_i^2}+c_{2i}\frac{1}{f_i^4}$

[0042] Insofar as the density values of air and water were prespecified as reference densities during the calibration, the values of a measured apparent or preliminary density match the target value for density for these two media. However, for carbon tetrachloride, there is a deviation of 1.3 kg/m{circumflex over ( )}3. If the influence of the resonator effect on the initial calibration is taken into account and used for subsequent correction by means of an initial density correction term K.sub.0i and additionally included in the correction of the current density measurement by means of a density correction term K.sub.i, it will be possible to determine a correct media density, as indicated in the last column of Table 2.

TABLE-US-00002 TABLE 2 Measured Subsequent apparent density correction Medium c01 c11 c21 [kg/m3] [kg/m3] Air at 20° C. −2268.8 2.06E+08 −87156.2 1.2 Water at 20° C. 1000 Carbon tetrachloride 1591.3036 1590.013265 at 20° C.

[0043] The density correction term K.sub.i for the preliminary or apparent density values ρ.sub.i on the basis of that of the natural frequency of the f.sub.i-mode has the following form:

[00013]$K_i:=\left(1+\frac{r}{{\left(\frac{g.Math.c}{f_i}\right)}^2-b}\right),$

where r and g are media-independent constants, f.sub.i is the natural frequency of the f.sub.i-mode, ρ.sub.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 a proportionality factor, which is in particular a function of the diameter of the measuring tube, between a resonance frequency f.sub.res of the liquid and the sound velocity of the liquid, wherein the following applies:

f.sub.res=g.Math.C

[0044] The sound velocity c of the liquid can, for example, be stored as a prespecified value, optionally with temperature correction, in a data memory and read out therefrom.

[0045] The corresponding initial density correction term K.sub.0,i for the f.sub.i-mode is to be determined as:

[00014]$K_{0,i}:=\left(1+\frac{r}{{\left(\frac{g.Math.c_0}{f_{0,i}}\right)}^2-b}\right),$

In this case, c.sub.0 is the sound velocity of the medium used in determining the coefficients for measuring the density of the medium used and f.sub.0,1 is the observed natural frequency of the f.sub.i-mode.

[0046] In this case, the subsequently corrected density is to be calculated according to:

[00015]${\rho }_{\mathrm{corr}}={\rho }_i.Math.\frac{K_{0,i}}{K_i}$

[0047] Finally Table 3 shows the coefficients c.sub.01_sos to c.sub.21_sos for determining the density obtained on the basis of the natural frequency of the first flexural vibration mode taking into account the resonator effect.

[0048] In this case, disregarding the resonator effect during measurement operation leads to considerable errors in the preliminary density ρ.sub.i.

TABLE-US-00003 TABLE 3 Preliminary Corrected density density Medium c01_sos C11_sos C21_sos [kg/m3] [kg/m3] Air at 20° C. −2270.3 2.06E+08 −87214.7 1.2232734 1.200 Water at 20° C. 1000.6934 1000.000 Carbon tetrachloride 1592.3937 1590.000 at 20° C.
In this case, the corrected density ρ.sub.corr is to be determined according to:

[00016]${\rho }_{\mathrm{corr}}\text{.Math.=}\frac{{\rho }_i}{K_i}$

wherein the density correction term K.sub.i as previously given is as:

[00017]$K_i:=\left(1+\frac{r}{{\left(\frac{g.Math.c}{f_i}\right)}^2-b}\right).$

Agreement between the corrected density values and the values in the literature is very good.

[0049] A first exemplary embodiment 100 of the method according to the invention is described with reference to the flow diagrams in FIGS. 2a and 2b, wherein the exemplary embodiment 100 serves for density measurement.

[0050] In a first step 110, as shown in FIG. 2a, a current value of the natural frequency of the basic flexural vibration mode or f1 mode is determined.

[0051] In a second step 120, a density measurement value is determined as a function of the current value of the natural frequency vibration parameters.

[0052] The second step 120 comprises the sub-steps shown in FIG. 2b.

[0053] Firstly, in a first sub-step 122, a preliminary density measurement value ρ.sub.i is determined on the basis of the current value of the natural frequency f.sub.1.

[0054] In the device used in this exemplary embodiment, the coefficients c.sub.01_sos to c.sub.21_sos were obtained taking into account the resonator effect. In measuring mode, therefore, corrections only need to be made for the resonator effect in the current measurement. For this purpose, in a second sub-step 124, a value for the sound velocity of the liquid currently conducted in the measuring tube is provided, for example from a data memory.

[0055] In a third sub-step 126, the density correction term K.sub.1 is determined on the basis of the value for the natural frequency f1 and the sound velocity c of the liquid.

[0056] Finally, in a fourth sub-step 128, a corrected density measurement value ρ.sub.corr is calculated by dividing the preliminary density measurement value ρ.sub.1 by K.sub.1.

[0057] If the coefficients c.sub.01, c.sub.11, c.sub.21 were not determined taking into account the resonator effect, then multiplication by an initial density correction term K.sub.0.1 will still need to be carried out in order to subsequently compensate for this error.

[0058] A second exemplary embodiment 200 of the method according to the invention is described with reference to the flow diagrams shown in FIGS. 3a and 3b, wherein the exemplary embodiment 200 serves for mass flow measurement.

[0059] In a first step 210, as shown in FIG. 3a, a current value of the time delay Δt proportional to the mass flow rate is ascertained between the rest position passages of two vibration sensors on the measuring tube.

[0060] In a second step 220, the mass flow measurement value is determined as a function of the current value of the time delay.

[0061] The second step 220 comprises the sub-steps shown in FIG. 3b.

[0062] Firstly, in a first sub-step 222, on the basis of the current value of the time delay Δt a preliminary mass flow value {dot over (m)}.sub.v is determined by multiplying by a calibration factor calf. In the device used in this exemplary embodiment, the calibration coefficient calf was obtained taking into account the resonator effect.

[0063] In measuring mode, therefore, corrections only need to be made for the resonator effect in the current measurement.

[0064] For this purpose, in a second sub-step 224, a value for the sound velocity c of the liquid currently conducted in the measuring tube is provided, for example from a data memory.

[0065] In a third sub-step 226, the mass flow correction term K.sub.m is determined on the basis of the value for the natural frequency fc at which the flow measurement takes place and the sound velocity c of the liquid according to:

[00018]$K_m:=1+a_1.Math.{\left(\frac{4\pi .Math.f_c}{c}.Math.r_t\right)}^2,$

where a.sub.1 is a constant and r.sub.t is the radius of the measuring tube or of the measuring tubes.

[0066] Finally, in a fourth sub-step 228, a corrected mass flow value {dot over (m)}.sub.corr is calculated by dividing the preliminary mass flow value {dot over (m)}.sub.v by K.sub.m, i.e.:

[00019]${\stackrel{.}{m}}_{\mathrm{corr}}\text{.Math.=}\frac{{\stackrel{.}{m}}_v}{K_m}.$

[0067] If the calibration factor calf was not determined taking into account the resonator effect, then multiplication by an initial mass flow correction term K.sub.0,m will also need to take place in order to subsequently compensate for this error.