Method of determining density measurement values and coriolis mass flowmeter for performing the method

Abstract

The invention relates to a method (100) for determining a density measurement of a medium by means of a Coriolis mass flow measuring transducer (10) having two oscillators (12, 14) and a pair of measuring tubes (12a, 12b, 14a, 14b) arranged one above the other. The measuring tubes (12a, 12b, 14a, 14b) are fluid-parallel and are guided into a collector (18) at an inlet side and an outlet side. Mounting the measuring transducer in a pipe causes mechanical stresses which can influence the oscillators via the collector. The medium is conducted in the measuring tubes. The method (100) comprises the following steps: (110) inducing at least one oscillation mode of the first oscillator and at least one oscillation mode of the second oscillator; (120) determining the natural frequency of each induced oscillation mode; (130) determining a respective temporary density measurement from the respective natural frequency; (140) determining a deviation between the temporary density measurements; and (150) determining a corrected density measurement by means of a model which determines and corrects the influence of the mechanical stresses on the density measurement on the basis of the deviation determination.

Description

Technical Field

[0001] The present invention relates to a method for determining a density measurement reading of a medium by means of a Coriolis mass flow transmitter having two oscillators installed in a pipeline, and to such a Coriolis mass flow transmitter for installation in a pipeline and for performing the method according to the invention. Background Technology

[0002] For example, a general-purpose flow meter is disclosed in DE 10 2015 104 931 A1. Transmitters of common origin are factory-calibrated and installed at the measurement point in a calibrated state. With this installation, a mechanical voltage can be applied to the transmitter, thereby minimizing the offset of the oscillator, which has a particular effect on frequency-dependent density measurements. Therefore, the object of the present invention is to find a remedy therein. Summary of the Invention

[0003] The method according to the invention is used to determine a density measurement reading of a medium by means of a Coriolis mass flow transmitter installed in a pipeline, the Coriolis mass flow transmitter having at least two oscillators, each oscillator comprising at least two measuring tubes oscillating relative to each other, wherein the measuring tube of the first oscillator extends above the measuring tube of the second oscillator, wherein the measuring tubes are arranged to flow parallel to each other and are guided into a collector at both the inlet and outlet sides, wherein the transmitter, installed in the pipeline, induces a mechanical voltage affecting the oscillators via the collector, wherein the medium is guided in the measuring tubes, and wherein the method comprises the following steps:

[0004] In each case, at least one vibration mode of the first oscillator and the second oscillator is excited;

[0005] Determine the natural frequencies of the vibration modes of the excitation;

[0006] In each case, a preliminary density measurement reading is determined based on its inherent frequency;

[0007] Determine the deviation between the initial density measurement readings;

[0008] The corrected density measurement readings are determined by using a model based on the influence of deviation determination and correction of mechanical voltage on density measurement.

[0009] In a more detailed study of the effects of mechanical voltage caused by the installation of transmitters at the measurement points, the inventors of this invention discovered that mechanical voltage has different effects on the two oscillators; that is, they are misaligned to varying degrees. This results in them producing different initial density values ​​for the medium passing through them. The degree of voltage-related misalignment can be determined and corrected according to this invention, provided that the deviation between the two initial density measurements is related to the absolute value of the misalignment condition.

[0010] In a further improvement of the invention, the model simulates the effect of mechanical voltage in the form of bending moment.

[0011] In a further improvement of the invention, the model simulates the effect of bending moment on the oscillator under the assumption that the bending moment has an axis extending perpendicular to the longitudinal axis of the transmitter and extending in the oscillation direction of the oscillator.

[0012] At most measurement points, the transmitter is arranged such that the measuring tube oscillates in the horizontal plane. That is, according to the above definition, the axis of the bending moment is also horizontal, especially if the transmitter is connected to a sag or over-supported section of pipe due to the gravitational effects caused by pipe support tolerances. This is perhaps the most common cause of installation-related misalignments, which can be corrected using the method according to the invention.

[0013] In a further improvement of the invention, the effective density measurement reading is determined as the average of the preliminary density measurement readings or the average of the preliminary density measurement readings weighted by the corresponding flow rate through the measuring tube of the oscillator, wherein the corrected density measurement reading is determined based on the effective density measurement reading and a correction term determined based on the deviation.

[0014] In a further improvement of the invention, in each case, the corrected density measurement readings are determined based on both the preliminary density value and the correction term assigned to them, which is determined based on the deviation.

[0015] In a further improvement of the invention, at least one correction term includes a polynomial of the deviation, particularly a first- or second-order polynomial.

[0016] In a further improvement of the invention, at least one correction term is added to the effective density measurement reading.

[0017] In a further improvement of the invention, it is checked whether the medium is single-phase, wherein the density measurement reading corrected by the model is determined only for single-phase media.

[0018] In a further improvement of the invention, in each case, a first bending vibration mode of the oscillator is excited, wherein a preliminary density measurement reading is determined based on the natural frequency of this bending vibration mode.

[0019] In a further improvement of the invention, the deviation between the corrected density measurement reading and the actual density of the medium does not exceed 0.5 kg / m³. 3 Especially not exceeding 0.3 kg / m 3 Especially not exceeding 0.2 kg / m 3 .

[0020] A Coriolis mass flow transmitter according to the invention for installation in a pipeline comprises: at least two oscillators, each oscillator comprising at least two measuring tubes capable of oscillating relative to each other, wherein, in the installed state, the measuring tube of the first oscillator extends above the measuring tube of the second oscillator, wherein the measuring tubes are arranged to flow parallel to each other and are guided into a collector at the inlet and outlet sides, wherein the installation of the transmitter in the pipeline causes a mechanical voltage affecting the oscillators via the collector, wherein the measuring tubes are used to conduct a medium whose density will be determined by the Coriolis mass flow transmitter, and wherein the Coriolis mass flow transmitter further comprises measurement and operation circuitry for performing the method according to the invention using the Coriolis mass flow transmitter. Attached Figure Description

[0021] The invention will now be explained in more detail with reference to the exemplary embodiments shown in the accompanying drawings. The drawings are shown below:

[0022] Figure 1 Example voltage distribution in a transmitter;

[0023] Figure 2 : Graphs of preliminary and corrected density measurement readings under variable mechanical voltage;

[0024] Figure 3 A flowchart illustrating an exemplary embodiment of the method according to the present invention; and

[0025] Figure 4 Exemplary embodiments of the method according to the present invention. Detailed Implementation

[0026] Figure 1 Exemplary simulation results are shown for the mechanical voltage in a general-purpose transmitter at its installation location in a pipeline, in the case where bending moment is introduced into transmitter 10 due to tolerances in the pipeline support. Figure 1 Only one-quarter of the transmitter 10 is shown in the diagram, where it can be assumed that the mechanical voltage in the unshown portion is formed to be substantially mirror-symmetrical with respect to the voltage distribution in the one-quarter shown relative to the transverse and longitudinal planes of the transmitter. Quantitative details are not important in the voltage representation. The only important point to note is that a larger mechanical voltage appears in the bright display area of ​​the component compared to the dark display area.

[0027] The transmitter 10 includes an external oscillator 12 with two parallel-guided curved measuring tubes and an internal oscillator 14 with two parallel-guided curved measuring tubes, wherein the measuring tubes on the inlet and outlet sides are respectively guided into collectors 18, which are supported by flanges 20 for mounting the transmitter 10 in a pipeline. The two collectors 18 are connected to each other by rigid support tubes 16.

[0028] In this regard, it is only necessary to note that the mechanical voltage introduced onto the measuring tube of the external oscillator 12, compared to the internal oscillator 14, results in a larger range of voltage-dependent offsets, as directly illustrated by the comparison of the highlighted areas. Therefore, the external oscillator 12 may be expected to exhibit stronger voltage-dependent offset conditions compared to the internal oscillator 14.

[0029] Figure 2 The measurement results confirmed this expectation. Figure 2 The display shows density measurement readings during the installation of a mass flow transmitter in the pipeline, where the start-up voltage increases over time. The transmitter is filled with air under normal conditions, therefore it must measure approximately 1.2 kg / m³. 3 The density.

[0030] Curve (a) shows the initial density measurement reading of the external oscillator, while curve (b) shows the initial density measurement reading of the internal oscillator. As expected, the density reading of the external oscillator deviates more from the setpoint compared to the internal oscillator.

[0031] Finally, curve (c) shows the density measurement reading corrected by the method according to the invention, which satisfactorily corresponds to the set point.

[0032] Now based on Figure 3 The flowchart of the exemplary embodiment shown explains the method according to the invention in more detail. Method 100 begins by exciting at least one vibration mode (110) of a first oscillator and a second oscillator, wherein, generally, the fundamental mode of bending vibration is excited, i.e., the mode in which the excited mode has no vibration nodes and has the lowest natural frequency of all vibration modes of the corresponding oscillator. In a second step, the corresponding natural frequency of the excited vibration mode is determined (120). A preliminary density measurement reading is then determined based on the corresponding natural frequency (130). For a transmitter installed without voltage, the two preliminary density measurement readings should be substantially the same. However, if a deviation exists and it can be ruled out that this deviation has other causes, such as gas loading of the liquid medium, the deviation indicates the effect of mechanical voltage on the density measurement. Therefore, in the next step, the deviation between the preliminary density values ​​is determined (140). Based on this, a corrected density measurement reading is finally determined by a model based on the deviation to determine and correct the effect of mechanical voltage on the density measurement (150). Typically, the correction function can be a polynomial of the difference between the density measurement readings, where sufficient measurement accuracy can be achieved by a linear function of the deviation or a second-order polynomial. The process using a linear term is explained below, but it can be used accordingly with a polynomial.

[0033] Initially, the corrected partial density measurement readings for each oscillator can be determined according to the following formula.

[0034] ρ corr,i =ρ vorl.i +a i ·ρ diff +b i ,

[0035] Where i = 1, 2 are the indices of the first or second oscillator, ρ vorl,i This is the preliminary density measurement reading of the corresponding oscillator, where a i and b i These are oscillator-specific coefficients, where ρ diff This is the deviation between the initial density measurement readings. The corrected portion of the density measurement reading ρ obtained from the oscillator. vorl,i They should be roughly matched. The density measurement reading ρ is used as a calibration. corr Then, the two density component readings ρ were measured. corr,i The average value can be output, optionally weighted by the corresponding mass flow rate through the measuring tube of the oscillator.

[0036] The density measurement reading corrected by the method according to the present invention deviates from the actual density of the medium by no more than 0.5 kg / m³. 3 Especially not exceeding 0.3 kg / m 3 Especially not exceeding 0.2 kg / m 3 .

[0037] Figure 4 An exemplary embodiment of the transmitter 10 according to the invention shown includes an external oscillator 12 having two parallel-guided curved measuring tubes 12a, 12b and an internal oscillator 14 having two parallel-guided curved measuring tubes 14a, 14b, wherein the measuring tubes on the inlet and outlet sides are respectively guided into a collector 18, which supports a flange 20 for mounting the transmitter 10 in a pipeline. The two collectors 18 are connected to each other by a rigid support tube 16.

[0038] To excite the bending vibration of the measuring tubes of oscillators 12 and 14, each oscillator's transmitter has an electric exciter (not shown here) that acts between the measuring tubes of the respective oscillator. Furthermore, each oscillator's transmitter has inlet-side and outlet-side electric vibration sensors to detect the vibration of the oscillator's measuring tube. The details are known in principle to those skilled in the art and are explained in more detail, for example, in DE 10 2015 104 931 A1.

[0039] The transmitter according to the invention further includes a measurement and operation circuit 32 with a computing unit to drive the exciter, detect the signal from the vibration sensor, and perform the method according to the invention.

Claims

1. A method (100) for determining a density measurement reading of a medium by means of a Coriolis mass flow transmitter (10) installed in a pipeline, said transmitter having at least two oscillators (12, 14), each of said at least two oscillators comprising at least two measuring tubes oscillating relative to each other, wherein, The measuring tubes (12a, 12b) of the first of the at least two oscillators extend above the measuring tubes (14a, 14b) of the second of the at least two oscillators, wherein the measuring tubes (12a, 12b, 14a, 14b) are arranged for parallel flow and guided into the collector (18) at the inlet and outlet sides, wherein the installation of the transmitter in the pipeline causes a mechanical voltage that affects the at least two oscillators through the collector, wherein the medium is guided in the measuring tubes, and wherein the method (100) includes the following steps: (110) Excite at least one vibration mode of the first oscillator and the second oscillator; (120) Determine the natural frequencies of the excited vibration modes; (130) Determine preliminary density measurement readings based on their respective natural frequencies; (140) Determine the deviation between the initial density measurement readings; (150) A model is used to determine the corrected density measurement reading, the model being based on the deviation to determine and correct the effect of mechanical voltage on the density measurement.

2. The method according to claim 1, wherein, The model simulates the effect of the mechanical voltage in the form of bending moment.

3. The method according to claim 2, wherein, The model simulates the effect of the bending moment on the at least two oscillators, assuming that the bending moment has an axis extending perpendicular to the longitudinal axis of the transmitter and extending in the direction of oscillation of the at least two oscillators.

4. The method according to claim 2 or 3, wherein, The effective density measurement reading is determined as the average of the initial density measurement readings or the average of the initial density measurement readings weighted by the corresponding flow rates of the measurement tubes of the at least two oscillators, wherein the corrected density measurement reading is determined based on the effective density measurement reading and a correction term, the correction term being determined based on the deviation.

5. The method according to claim 2 or 3, wherein, In each case, the corrected density measurement readings are determined based on both the initial density value and the correction term assigned to them, which is determined based on the deviation.

6. The method according to claim 4, wherein, At least one correction term includes a polynomial of the deviation.

7. The method according to claim 4, wherein, At least one correction term includes a first-order or second-order polynomial.

8. The method according to claim 4, wherein, At least one correction term is added to the effective density measurement reading.

9. The method according to claim 1 or 2, wherein, Check whether the medium is single-phase, wherein the density measurement reading corrected by the model is determined only for single-phase media.

10. The method according to claim 1 or 2, wherein, In each case, the first bending vibration mode of the at least two oscillators is excited, and a preliminary density measurement reading is determined based on the natural frequency of this bending vibration mode.

11. The method according to claim 1 or 2, wherein, The deviation between the corrected density measurement reading and the actual density of the medium shall not exceed 0.5 kg / m³. 3 .

12. The method according to claim 1 or 2, wherein, The deviation between the corrected density measurement reading and the actual density of the medium shall not exceed 0.3 kg / m³. 3 .

13. The method according to claim 1 or 2, wherein, The deviation between the corrected density measurement reading and the actual density of the medium shall not exceed 0.2 kg / m³. 3 .

14. A Coriolis mass flow transmitter (10) for installation in a pipeline, comprising: At least two oscillators (12, 14), each of the at least two oscillators comprising at least two measuring tubes (12a, 12b, 14a, 14b) capable of oscillating relative to each other, wherein, in the installed state, the measuring tube (12a, 12b) of the first oscillator of the at least two oscillators extends above the measuring tube (14a, 14b) of the second oscillator of the at least two oscillators, wherein the measuring tubes (12a, 12b, 14a, 14b) are arranged for parallel flow and guided into the collector (18) on the inlet and outlet sides. The installation of the transmitter in the pipeline can induce a mechanical voltage that affects the at least two oscillators (12, 14) via the collector (18), wherein the measuring tubes (12a, 12b, 14a, 14b) are used to conduct the medium whose density is to be determined by the Coriolis mass flow transmitter (10), wherein the Coriolis mass flow transmitter further includes a measuring and operating circuit having a computing unit (32) for performing the method according to any one of claims 1 to 13 using the Coriolis mass flow transmitter.

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