Method and measuring device for determining the viscosity of a medium

Abstract

A method for determining a target measurement value (X) based on temporary damping measurements of an oscillation mode of a measuring tube, the target measurement value comprising the viscosity of a medium or a viscosity-related variable, the method comprising: exciting oscillations of the oscillation mode; detecting (110; 210) a series of temporary damping measurements for the measuring tube oscillation mode; and calculating (140; 240) the target measurement value (X); wherein the influence of cross-sensitivity to damping on the flow of the medium is corrected by determining (130; 230) a corrected damping measurement value based on the temporary damping measurement value, the corrected value corresponding to the damping when the medium is stationary, and determining the target measurement value based on the corrected damping measurement value, or by determining (112; 114) a temporary intermediate value of the damping-related variable based on the temporary damping measurement value, determining (132; 134) a corrected intermediate value corresponding to the intermediate value when the medium is stationary, and determining (142) the target measurement value based on the corrected intermediate value.

Description

Technical Field

[0001] The invention relates to a method for determining the viscosity of a medium based on the damping of the measuring tube oscillations of a Coriolis mass flow meter or a density measuring device with an oscillating measuring tube. The invention further relates to a measuring device for carrying out the method. Background Art

[0002] The determination of viscosity based on the damping of the measuring tube oscillations is known per se, for example as the subject of the published patent applications DE 100 20606 A1 and DE 10 2004 014 029 A1. Studies by the inventors of the present patent application have shown that above a critical flow rate or flow velocity, the damping has increasing fluctuations and the mean value of the damping increases. The damping is therefore influenced by the influence variable and not by the viscosity of the medium conducted in the measuring tube. It is therefore an object of the present invention to provide a method and a measuring device which enable reliable viscosity measurements even at large flows. This object is achieved by the method and the measuring device according to the invention. Summary of the invention

[0003] The method according to the invention is a method for determining a target measured value (X) of a medium flowing through a measuring tube based on a temporary damping measured value of at least one oscillation mode of the measuring tube, the target measured value comprising the viscosity of the medium or a viscosity-related variable, wherein the damping depends on the viscosity of the medium and has a cross-sensitivity to the flow rate of the medium, wherein the method comprises:

[0004] exciting oscillation of at least one oscillation mode;

[0005] detecting a series of temporary damping measurements for at least one measuring tube oscillation mode; and

[0006] Calculate the target measurement value (X);

[0007] It is characterized in that

[0008] Correcting the effect of the cross sensitivity of the damping on the flow rate of the medium by determining an adjusted damping measurement value corresponding to the damping in the case of a non-flowing medium based on the temporary damping measurement value, and determining the target measurement value based on the adjusted damping measurement value, or

[0009] The effect of the cross sensitivity of the damping on the flow rate of the medium is corrected by determining a temporary intermediate value of the damping-related variable based on the temporary damping measurement value, determining an adjusted intermediate value corresponding to the intermediate value in the case of a non-flowing medium, and determining the target measurement value based on the adjusted intermediate value.

[0010] In a refinement of the invention, the cross-sensitivity of the damping to a flow rate exceeding a critical rate value results in the damping increasing with the flow rate, and wherein the fluctuation of the temporary damping measurement value increases with the flow rate,

[0011] Therein, the influence of cross-sensitivity is corrected based on fluctuations of temporary damping measured values ​​or temporary intermediate values ​​and / or based on a function that depends on a flow parameter of the medium, wherein the flow parameter comprises values ​​of mass flow, volume flow, Reynolds number or flow, in particular temporary values ​​thereof.

[0012] In a refinement of the invention, the influence of cross-sensitivity is corrected based on fluctuations of the temporary damping measured value or the temporary intermediate value.

[0013] wherein a fluctuation of a temporary damping measurement value or a fluctuation of an intermediate value is determined, wherein the intermediate value is calculated based on the temporary damping measurement value;

[0014] wherein a fluctuation-related correction term for a temporary damping or intermediate value is determined, the temporary damping measurement value or the intermediate value being corrected with the correction term in order to obtain an adjusted damping value or an adjusted value;

[0015] Therein, the target measurement value is determined based on the adjusted damping value or the adjusted intermediate value.

[0016] In a development of the invention, the fluctuation-related correction term comprises a function of the standard deviation of the temporary damping measurement or of the intermediate variable.

[0017] In a development of the invention, the correction term is a linear function of the standard deviation, in particular proportional to the standard deviation, wherein the adjusted damping value or the adjusted intermediate value is obtained in particular by multiplication or by subtraction of the correction term.

[0018] In a refinement of the invention, a provisional damping mean of a plurality of damping measurement values ​​corrected with the correction term is formed to correct the provisional damping measurement value, or an intermediate mean of a plurality of intermediate values ​​corrected with the correction term is formed to correct the intermediate value.

[0019] In a development of the invention, the intermediate value comprises a provisional target measured value which is calculated based on the damping measured value without correction for cross-sensitivities, wherein the adjusted intermediate value in particular serves as the target measured value.

[0020] In an improved solution of the present invention, the target measurement value X as the viscosity measurement value or the viscosity-related variable measurement value may be i Described as the adjusted damping value D' i The linear function X i =F(D' i ),

[0021] where the intermediate value is determined as a function of the temporary damping measurement Z i =G(D i ),

[0022] where the target measurement is determined as a function of the adjusted intermediate value X i =H(Z' i ),and

[0023] Among them, the following apply:

[0024] |(H(G(D' i ))-F(D' i )) / F(D i )|=E, wherein E<0.05, in particular, E<0.02, in particular, E>0.01.

[0025] In a development of the invention, the influence of the cross-sensitivity is corrected on the basis of a function which is dependent on the flow parameter.

[0026] In an improved embodiment of the invention, a correction term is determined as a function of a flow parameter and a critical value SK of the flow parameter in order to correct cross sensitivity, wherein the critical value of the flow parameter corresponds to the value of the flow parameter at a critical flow rate, and wherein for values ​​of the flow parameter exceeding the critical flow parameter, the function is essentially a linear function of the flow parameter.

[0027] In a development of the invention, the target variable comprises the viscosity, the Reynolds number, the mass flow, the volume flow and / or the density of the medium, wherein the mass flow, the volume flow and / or the density are corrected with respect to the cross-sensitivity to the viscosity.

[0028] The measuring device for determining a target variable of a flowable medium according to the present invention comprises: at least one oscillating measuring tube for conducting a medium; at least one exciter for exciting the oscillation of the measuring tube; at least one sensor for detecting the oscillation of the measuring tube and outputting an oscillation-related signal; and a measuring and operating circuit for driving the exciter and processing the oscillation-related signal; wherein, according to the present invention, the measuring and operating circuit is configured to perform the method according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention is explained in more detail below based on the exemplary embodiments shown in the accompanying drawings. As shown below:

[0030] Figure 1 is a schematic diagram of an exemplary embodiment of a measuring device according to the present invention;

[0031] Figure 2 is a schematic diagram showing damping as a function of flow rate;

[0032] Figure 3 is a flow chart of a first exemplary embodiment of a method according to the present invention;

[0033] Figure 4 is a flow chart of a second exemplary embodiment of a method according to the invention. DETAILED DESCRIPTION

[0034] Figure 1 The exemplary embodiment of the measuring device 1 according to the invention shown comprises an oscillator 10, which comprises a pair of oscillating measuring tubes 14, which run in parallel and extend between an inlet-side flange 11 and an outlet-side flange 12, wherein each flange comprises a flow divider or collector in which the measuring tube 14 opens. 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 damped in the oscillation frequency range of the useful bending oscillation mode 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, so that the frequency of the useful bending oscillation mode is approximately established. The oscillator 10 is excited to oscillate by an electrodynamic exciter 17, which acts between the two measuring tubes 14, wherein the oscillations are detected by two oscillation sensors 18, 19 detecting the relative movement of the measuring tubes 14 relative to one another. The exciter 17 is operated by an operating and evaluation circuit 30, wherein the latter also detects and evaluates the signals of the oscillation sensors in order to determine density measurement values ​​and possibly mass flow measurement values. According to the invention, the operating and evaluation circuit 30 is likewise configured to carry out the method according to the invention, namely in particular to determine a provisional damping measurement value of the measuring tube oscillation and to calculate therefrom an adjusted damping measurement value. Figure 1 Unlike the illustrated example, the operating and evaluation circuit can also comprise a plurality of modules separated in space. Thus, the damping can also be calculated in a remote computing module, to which the required raw data are transmitted, for example, wirelessly.

[0035] Figure 2 Typical damping measurements of the measuring tube oscillations of a Coriolis mass flowmeter as a function of the liquid flow rate are shown. An observable value proportional to the damping is, for example, the ratio of the excitation current to the oscillation amplitude, wherein the oscillation amplitude is detected by an electromagnetic sensor as an induced voltage proportional to the rate, which is normalized by the oscillation frequency. The fluctuation or standard deviation of the damping is constant over a wide flow range, but increases with increasing flow in a first approximation linearly from a threshold value, wherein the mean value of the damping also increases approximately linearly above the threshold value. For a measuring sensor of size DN 25, the threshold value corresponds to a flow rate of several m / s, for example of about 4 m / s. There are two methods according to the invention for determining a rate-independent or adjusted damping value at a flow rate above a threshold value starting from the observed damping measurements. Firstly, a correction term can be determined based on the standard deviation of the temporary damping values ​​in order to obtain an adjusted damping value, as described with reference to Figure 3Second, when a flow rate threshold is exceeded, a correction term may be determined based on the difference between the current flow rate and the threshold, as shown in FIG. Figure 4 Described in more detail.

[0036] Refer to the following Figure 3 A first exemplary embodiment 100 of a method according to the invention is explained. In a first method step 110, a series of temporary damping measurements {X' 1,i}, for example as the ratio of the excitation current to the oscillation amplitude. In a second step 120, a temporary damping measurement {X' 1,i The standard deviation σ1({X' 1,i In the third step 130, the adjusted damping value X1 ({X' 1,i},σ1), wherein, for example, a correction term is subtracted from the mean of the temporary damping measurements, the correction term being a function of the standard deviation σ1, in particular the correction term being a linear function of the standard deviation σ1. A viscosity value X2(X1) can then be calculated 140 based on the adjusted damping value X1. This can be a dynamic viscosity η or a kinematic viscosity ν, wherein the latter also includes a density measurement of the medium. Finally, the viscosity is also included in the other variables X N (eg the Reynolds number Re), which is calculated based on the mass flow and the previously determined dynamic viscosity 150. The Reynolds number can then in turn be included in the correction of the mass flow measurement value accordingly, as described, for example, in EP 1 055 102 B1.

[0037] The first exemplary embodiment includes also Figure 3 Therefore, the temporary damping measurement {X' 1,i} is converted 112 to a temporary intermediate value of a variable derived from damping {X' 2,i}({X' 1,i In the subsequent step 122, the temporary intermediate value {X' 2,i The standard deviation σ2({X' 2,i In the third step 132, the adjusted intermediate value X2 ({X' 2,i},σ2), where, for example, from the temporary intermediate value {X' 2,i} minus a correction term, which is a function of the standard deviation σ2, and in particular, a linear function of the standard deviation σ2. For example, the adjusted intermediate value can represent the viscosity of the medium. Using the adjusted intermediate value X2, 142 other derived variables X can be determined N , such as the Reynolds number Re. In other alternatives, according to the intermediate variable {X' 2,i}({X' 2,i}), initially the temporary intermediate variable {X'2,i}Convert 114 to temporary target measurement value {X' N,i In the subsequent step 124, the temporary target measurement value {X' 2,i The standard deviation σ N ({X' N,i}), then in a further step 134, according to X N ({X' N,i},σ N ), determine the adjusted target measurement value X N , where, for example, from the temporary target measurement {X' N,i} minus the correction term, which is the standard deviation σ N function of , in particular, the correction term is the standard deviation σ N For example, the adjusted target measurement value X N It can represent the Reynolds number Re.

[0038] Refer to the following Figure 4 A second exemplary embodiment 200 of the method according to the invention is explained. In a first method step 210, a series of temporary damping measurement values ​​X are detected. N And calculate their mean<X‘1> ({X' 1,i In a further step 220, when a temporary damping measurement value {U i (X' 1,i}, calculate the value of flow parameter U i The mean In particular, the flow parameter may in particular comprise a flow rate, a mass flow rate or a volume flow rate.

[0039] In a further step 230, the average of the temporary damping measurements is calculated based on<X‘1> The adjusted damping value X1 is determined by subtracting the correction term from the mean of the temporary damping measurements as the mean of the flow parameters exceeding the critical flow parameter SK A function of wherein the correction term is a monotonic function exceeding a critical flow parameter. If the flow rate is selected as the flow parameter, a typical value of the critical flow parameter for a device of nominal size DN 25 is, for example, 3 m / s to 5 m / s. The specific value will be determined experimentally depending on the device. Based on the adjusted damping value X1, the influence of the measured variable X2 associated therewith, such as viscosity, on the flow parameter can be determined in a further step 240, and the viscosity can also be adjusted accordingly. Based on the above-mentioned variations of the first exemplary embodiment, a person skilled in the art can conceive variations of the second exemplary embodiment.

Claims

1. A method for determining a target measurement value X of a medium flowing through a measuring tube based on a temporary damping measurement value of at least one oscillation mode of the measuring tube, the target measurement value comprising the viscosity of the medium or a viscosity-related variable, wherein: The damping depends on the viscosity of the medium and has cross-sensitivity to the flow rate of the medium, and the method comprises: exciting oscillation of at least one oscillation mode; For the at least one measuring tube oscillation mode, detecting (110; 210) a series of temporary damping measurement values; and Calculate (140; 240) the target measurement value X; It is characterized in that Correcting the effect of the cross sensitivity of the damping on the flow rate of the medium by determining (130; 230) an adjusted damping measurement corresponding to the damping in the case of a non-flowing medium based on the temporary damping measurement, and determining the target measurement based on the adjusted damping measurement, or Correcting the effect of the cross sensitivity of the damping on the flow rate of the medium by determining (112; 114) a temporary intermediate value of a damping-related variable based on the temporary damping measured value, determining (132; 134) an adjusted intermediate value corresponding to the intermediate value in the case of a non-flowing medium, and determining (142) the target measured value based on the adjusted intermediate value, wherein a cross sensitivity of the damping to a flow rate exceeding a critical rate value causes the damping to increase with the flow rate, and wherein fluctuations in the temporary damping measure increase with the flow rate, Therein, the influence of the cross sensitivity is corrected based on fluctuations of the temporary damping measurement value or the temporary intermediate value and / or based on a function that depends on a flow parameter of the medium, wherein the flow parameter comprises a value of a mass flow, a volume flow, a Reynolds number or a flow rate.

2. The method according to claim 1, wherein: The flow parameter comprises a mass flow rate, a volume flow rate, a Reynolds number or a temporary value of the flow rate.

3. The method according to claim 1, wherein: correcting the effect of the cross sensitivity based on fluctuations of the temporary damping measurement value or the temporary intermediate value, wherein a fluctuation of the temporary damping measurement value or a fluctuation of the temporary intermediate value is determined, wherein the temporary intermediate value is calculated based on the temporary damping measurement value; wherein a fluctuation-related correction term is determined for the temporary damping measurement value or the temporary intermediate value, the temporary damping measurement value or the temporary intermediate value being corrected by means of the fluctuation-related correction term in order to obtain an adjusted damping value or an adjusted intermediate value; Therein, the target measurement value is determined based on the adjusted damping value or based on the adjusted intermediate value.

4. The method according to claim 3, wherein: The fluctuation-related correction term comprises a function of the standard deviation of the temporary damping measurement or intermediate variable.

5. The method according to claim 4, wherein: The fluctuation-related correction term is a linear function of the standard deviation, wherein the adjusted damping value or the adjusted intermediate value is obtained by multiplication with the fluctuation-related correction term or by subtraction from the fluctuation-related correction term.

6. The method according to claim 5, wherein: The fluctuation-related correction term is proportional to the standard deviation.

7. The method according to any one of claims 3 to 6, in, forming a temporary damping mean of a plurality of damping measurements corrected with the fluctuation-related correction term so as to correct the temporary damping measurements, or Therein, an intermediate mean of a plurality of temporary intermediate values ​​corrected with the fluctuation-related correction term is formed in order to correct the temporary intermediate value.

8. The method according to any one of claims 1 to 6, wherein: The temporary intermediate values ​​include temporary target measurement values ​​calculated based on the damping measurement values ​​without correction for the cross sensitivity, wherein the adjusted intermediate values ​​serve as target measurement values.

9. The method according to any one of claims 1 to 6, in, A target measurement value X can be used as a viscosity measurement value or a viscosity-related variable measurement value. i Described as the adjusted damping value D' i The linear function X i =F(D' i ), The temporary intermediate value is determined as a function Z of the temporary damping measurement value. i =G(D i ), The target measurement value is determined as a function X of the adjusted intermediate value. i =H(Z' i ),and Among them, the following apply: |(H(G(D' i ))-F(D' i )) / F(D i )|=E, where E<0.

05.

10. The method according to claim 9, wherein: E<0.02。 11. The method according to claim 10, wherein: E>0.01。 12. The method according to claim 1, wherein: The influence of the cross-sensitivity is corrected based on a function that depends on the flow parameter.

13. The method according to claim 12, wherein: A correction term is determined as a function of the flow parameter and a critical value of the flow parameter in order to correct the cross sensitivity, wherein the critical value of the flow parameter corresponds to the value of the flow parameter at a critical flow rate, wherein for values ​​of the flow parameter exceeding a critical flow parameter SK, the function is essentially a linear function of the flow parameter.

14. The method according to any one of claims 1 to 6, wherein: The target measured values ​​include the viscosity, the Reynolds number, the mass flow, the volume flow and / or the density of the medium, wherein the mass flow, the volume flow and / or the density are corrected with respect to a cross-sensitivity to the viscosity.

15. A measuring device for determining a target measured value of a flowable medium, comprising: at least one oscillating measuring tube for conducting a medium; at least one exciter for exciting oscillations of the measuring tube; at least one sensor for detecting oscillations of the measuring tube and for outputting an oscillation-related signal; as well as a measuring and operating circuit for driving the actuator and for processing the oscillation-related signal; It is characterized in that The measurement and operation circuit is configured to perform a method according to any one of claims 1 to 14 .

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