Coriolis mass flowmeter and method of operating same

Abstract

A method for determining variables affecting the total zero error of a Coriolis mass flowmeter, the method comprising: exciting a bending vibration mode of vibration; measuring a first total zero error (T) at a flow rate of zero; determining a first damping value (D) of the bending vibration mode of vibration; measuring an exciter-independent zero error (I) during a decay vibration of the bending vibration mode at a flow rate of zero; determining a first exciter-dependent contribution (E) to the first total zero error (T) using the first total zero error (T) and using the exciter-independent zero error (I); and determining a sensitivity coefficient (S) for the bending vibration mode using the first exciter-dependent contribution (E) to the total zero error (T) and using the first damping value (D).

Description

Technical Field

[0001] This invention relates to a Coriolis mass flow meter, a method for determining variables affecting the total zero-point error of the flow meter, a method for determining the total zero-point error, and the operation method thereof. Background Technology

[0002] The measuring tube of the Coriolis mass flow meter is excited by an exciter in a bending vibration mode, wherein the excitation ideally occurs in the symmetry of the bending vibration mode, and the mass flow through the measuring tube results in superposition with the next higher asymmetric bending vibration mode.

[0003] This causes a phase shift between the inlet and outlet sections of the vibration measuring tube, and measuring this phase shift can determine the mass flow rate.

[0004] In actual measuring tubes, due to manufacturing tolerances, the excitation may deviate from the symmetry of the vibration mode. As a result, the excitation will also proportionally excite the next higher asymmetric vibration mode, which will cause exciter-related zero-point error in flow measurement.

[0005] Furthermore, asymmetries caused by manufacturing tolerances can also occur in components other than the actuator. These asymmetries can cause zero-point errors unrelated to the actuator.

[0006] The total zero-point error is the sum of the contributions of the two aforementioned errors, from which the correlation of damping for the bending vibration mode can also be determined.

[0007] Therefore, the object of the present invention is to provide a method for accurately determining zero-point error, and to provide a Coriolis mass flow meter that can implement this method. Summary of the Invention

[0008] This objective is achieved by the method according to the invention and the Coriolis mass flow meter.

[0009] A first method according to the invention is used to determine variables affecting the zero-point error of a Coriolis mass flow meter, the flow meter comprising: at least one measuring tube mounted to be vibrate for conducting a medium; an exciter for exciting a bending vibration mode; at least two vibration sensors for detecting vibrations of the measuring tube; and at least one measurement and operation circuit for driving the exciter, detecting sensor signals from the vibration sensors, and determining a mass flow measurement value based on the sensor signals, wherein the method comprises: exciting vibrations of the bending vibration mode of the measuring tube; determining a total zero-point error with respect to a first medium in the measuring tube when the flow rate is zero; determining a damping value for the vibrations of the bending vibration mode of the first medium in the measuring tube; determining, when the flow rate is zero, an exciter-independent zero-point error with respect to the damped vibrations of the first medium in the bending vibration mode of the measuring tube, independent of the exciter; determining an exciter-related contribution to the total zero-point error based on the total zero-point error and based on the exciter-independent zero-point error; and determining a sensitivity coefficient for the bending vibration mode based on the exciter-related contribution to the total zero-point error and based on the damping value.

[0010] The sensitivity coefficient depends largely on the degree of symmetry disruption caused by the actuator, particularly the degree of symmetry disruption due to manufacturing tolerances. If the actuator's position relative to the measuring tube is fixed, the sensitivity coefficient will not actually change. Therefore, as long as the symmetry deviation between the measuring tube and the actuator remains constant, the sensitivity value, once determined, can be stored and used to determine the actuator-related zero-point error. In the intended use of the Coriolis mass flow meter, it can be assumed that the measuring tube is non-removably connected to the actuator throughout the entire service life of the device.

[0011] In the development of this invention, determining the damping value includes the quotient of the excitation current used to excite the vibration and the vibration amplitude thereby achieved.

[0012] In the development of this invention, determining the damping value includes determining the time constant of the damped vibration of the bending vibration mode.

[0013] In the development of this invention, determining the exciter-related contribution to the total zero-point error includes the difference between the total zero-point error and the zero-point error independent of the exciter.

[0014] In the development of this invention, determining the sensitivity coefficient involves dividing the exciter-related contribution to the total zero-point error by the damping value.

[0015] In a further development of the invention, the method also includes determining an updated exciter-independent zero-point error, the method comprising: exciting vibrations of a bending vibration mode with respect to a second medium in a measuring tube; measuring a second total zero-point error with respect to the second medium in the measuring tube when the flow rate is zero; determining a second damping value with respect to the second medium in the measuring tube; and determining an updated exciter-independent zero-point error based on the second total zero-point error, the second damping value, and a sensitivity coefficient.

[0016] According to the development of the present invention, determining the media-related third total zero-point error of the Coriolis mass flow meter based on previously determined influencing variables includes: determining a third damping value for vibration in a bending vibration mode; and calculating the third total zero-point error based on the third damping value, the sensitivity coefficient of the bending vibration mode, and a zero-point error independent of the exciter.

[0017] In the development of this invention, the third total zero-point error includes the sum of the zero-point error independent of the exciter and the third exciter-related contribution to the total zero-point error.

[0018] In the development of this invention, the exciter-related contribution to the third total zero-point error includes the product of the sensitivity coefficient and the third damping value.

[0019] The present invention also relates to a modular Coriolis mass flow meter having a replaceable measuring tube assembly. In these devices, the symmetry deviation between the exciter and the measuring tube changes each time the measuring tube assembly is replaced. Therefore, it is preferable to determine a new sensitivity coefficient after replacing the measuring tube assembly, for example as defined in the third method according to the invention.

[0020] A second method according to the invention is used to operate a modular Coriolis mass flow meter, the modular Coriolis mass flow meter comprising: at least one measuring tube mounted to be vibrating for conducting a medium; an exciter for exciting a bending vibration mode; at least two vibration sensors for detecting the vibration of the measuring tube; and at least one measurement and operation circuit for driving the exciter, detecting sensor signals from the vibration sensors, and determining a mass flow measurement value based on the sensor signals, wherein the Coriolis mass flow meter includes a base module and a replaceable measuring tube module, wherein the measuring tube module includes the measuring tube and a first component of the exciter and each of the two vibration sensors, wherein the base module includes the measurement and operation circuit, a housing with a housing for the measuring tube module, and a second component of the exciter and each of the two vibration sensors, wherein the method comprises: connecting the measuring tube module to the base module such that the first and second components of the exciter and the two sensors are in an operating position relative to each other in each case; and determining a sensitivity coefficient and a zero-point error independent of the exciter using the first method according to the invention.

[0021] In the development of this invention, the method for operating the modular Coriolis mass flow meter further includes: determining the total zero-point error by means of a second method according to the invention.

[0022] The Coriolis mass flow meter according to the invention is equipped with: at least one measuring tube, which is mounted to be vibrate for conducting a medium; an exciter for exciting a bending vibration mode; at least two vibration sensors for detecting the vibration of the measuring tube; and at least one measurement and operation circuit for driving the exciter, detecting sensor signals from the vibration sensors, and determining a mass flow measurement value based on the sensor signals, wherein the measurement and operation circuit is configured to perform at least one of the methods according to the invention. Attached Figure Description

[0023] The invention will now be explained in more detail with reference to the exemplary embodiments shown in the accompanying drawings. In the drawings:

[0024] Figure 1a An exemplary embodiment of the basic module of the Coriolis mass flow meter according to the present invention is shown;

[0025] Figure 1b An exemplary embodiment of the measuring tube assembly of a Coriolis mass flow meter according to the present invention is shown;

[0026] Figure 1c It shows having Figure 1a and Figure 1b An exemplary embodiment of the Coriolis mass flow meter according to the present invention, showing the components;

[0027] Figure 2a Exemplary measurement data for determining the zero-point error of a Coriolis mass flow meter are shown;

[0028] Figure 2b A graph showing the contribution to the zero-point error is provided.

[0029] Figure 2c A plot showing the updated zero-point error independent of the exciter is presented;

[0030] Figure 3a A flowchart illustrating an exemplary embodiment for determining variables affecting zero-point error is shown;

[0031] Figure 3b A flowchart illustrating an exemplary embodiment for updating zero-point errors independent of the exciter is shown;

[0032] Figure 3c A flowchart illustrating an exemplary embodiment for determining the total zero-point error is shown; and

[0033] Figure 3d A flowchart illustrating an exemplary embodiment for operating a modular Coriolis mass flow meter is shown. Detailed Implementation

[0034] Figures 1a to 1c An exemplary embodiment of the Coriolis mass flow meter 100 shown includes a base module 110 and a replaceable measuring tube assembly 140.

[0035] The basic module 110 includes a housing 120 in which a measuring chamber 122 is formed. The measuring chamber receives the measuring tube 141 of the measuring tube assembly 140. The measuring chamber 122 has an opening 124 through which the measuring tube 141 can be introduced into the measuring chamber 144. An excitation coil 112 and two sensor coils 114 and 116 are arranged on the wall of the measuring chamber 122. The basic module also includes a measurement and operation circuit 118 to which the excitation coil 112 and the sensor coils 114 and 116 are connected.

[0036] The measuring tube assembly 140 includes not only a U-shaped measuring tube 141 but also a mounting plate 148. The measuring tube 141 is rigidly connected to the mounting plate and can be fixed within the housing body 120. Furthermore, the measuring tube assembly 140 includes an excitation magnet 142 and two sensor magnets 144 and 146. The excitation magnet 142 is positioned at the apex of the U-shaped measuring tube 141, while the sensor magnets 144 and 146 are symmetrically positioned relative to the excitation magnet on the inlet and outlet sides of the straight measuring tube section. Ideally, in the installed state of the measuring tube assembly 140, the excitation magnet 142 is perfectly aligned with the excitation coil 112, such that the excitation of bending vibrations through the exciter formed by the excitation coil 112 and the excitation magnet 142 occurs symmetrically with respect to the transverse plane of the measuring tube, and the measuring tube 141 and the sensors formed by the sensor coil and the sensor magnets have mirror symmetry with respect to the transverse plane of the measuring tube. However, due to manufacturing tolerances, slight symmetry deviations may occur, which can lead to zero-point errors in mass flow measurement.

[0037] Figure 2a Exemplary measurement data for determining zero-point error is shown, wherein, for this purpose, a mass flow rate measurement is performed once when the mass flow rate is zero, i.e., while the active exciter maintains vibration in the bending vibration usage mode, to determine the total zero-point error T, and once during vibration decay in the exciter-off condition to determine the exciter-independent zero-point error I. The difference between the total zero-point error T and the exciter-independent zero-point error I is the exciter-related zero-point error E. Simultaneously with the measurement of the zero-point error, a damping value D for the vibration of the measuring tube in the bending vibration mode is determined, for example, based on the ratio of excitation current to vibration amplitude.

[0038] Figure 2b This illustrates how to determine the zero-point error during an ongoing measurement operation based on the above measurement results. It is assumed here that the exciter-related portion E of the zero-point error depends on, and specifically is proportional to, the damping D. The proportionality constant is the sensitivity coefficient S, which can be obtained from the above measurements by dividing the difference between the total zero-point error T and the exciter-independent zero-point error by the damping value, i.e.:

[0039] S:=E / D=(TI) / D

[0040] The sensitivity coefficient S corresponds to the slope of the increased straight line in the graph. For example, if the characteristics of the medium flowing through the measuring tube change, a new damping value D' is established, and the new total zero-point error T' is obtained according to the following formula: T':=I+E'=I+S D'.

[0041] Figure 3aThe flowchart below summarizes the procedure of an exemplary embodiment 10 of the method according to the present invention, which begins with an excitation 11 of bending vibration. Then, the total zero-point error T is determined 12, and the damping value D is determined 13. Next, the zero-point error I, independent of the exciter when the exciter is turned off, is determined 14. Based on the aforementioned variables, the exciter-related contribution E to the zero-point error is determined 15, and the sensitivity coefficient S is determined 16.

[0042] Figure 2b The sensitivity coefficient S remains constant as long as the symmetry deviation between the actuator and the measuring tube does not change. This is generally true for Coriolis mass flow meters with a fixed measuring tube throughout operation. However, for modular units, this is only true when the measuring tube assembly is replaced. The corresponding effective sensitivity coefficient S can be stored in the measurement and operation circuitry, just like the actuator-related zero-point error I, and can be used to calculate the total zero-point error during ongoing measurement operations.

[0043] Even if the zero-point error I, which is independent of the actuator, is more stable, it can still change. Therefore, it is recommended to update the zero-point error I, independent of the actuator, occasionally, especially when there are significant changes in the dielectric properties. This procedure will refer to... Figure 2c The following explanation is provided. When the flow rate is zero, the total zero-point error T'' and the damping value D'' are detected. Therefore, the updated exciter-independent zero-point error can be calculated as follows:

[0044] I':=T'-E'=T'-S D'.

[0045] Then, the updated zero-point error I'', independent of the exciter, is stored and replaced with the previously used value.

[0046] Figure 3b A simplified flowchart of an exemplary embodiment 20 for updating zero-point error independent of the exciter is shown: after determining the total zero-point error T' when the flow rate is zero (21) and determining the damping value D' (22), the zero-point error independent of the exciter can be determined based on T', D' and the known value S (23).

[0047] Assuming the variables affecting the total zero-point error T, namely the sensitivity coefficient S and the zero-point error I independent of the exciter, are known, then during the ongoing measurement operation, the following can be used at any time: Figure 3c The method of exemplary embodiment 30 in the embodiment determines the total zero-point error based on simple damping measurement, wherein, after determining the current damping value D'', the current total zero-point error T'' can be determined according to the following formula: T'' := I + E'' = I + S D''.

[0048] The different names of variable X as X' and X'' simply mean that the value of the variable can come from different measurements.

[0049] Figure 3d Finally, a method 40 for operating a modular measuring device is shown, for example in... Figure 1a As shown in Figure 1d. The method begins by mounting the measuring tube assembly onto the base module. Then, using... Figure 3a The exemplary embodiment of the present invention uses method 10 to determine the variables affecting the zero-point error. During the measurement operation, then, according to... Figure 3c The total zero-point error T is determined according to the method 30 of the present invention in an exemplary embodiment. If necessary, it can be determined according to... Figure 3b Exemplary embodiment 20 updates the zero-point error I, which is independent of the exciter.

Claims

1. A method for determining variables affecting the total zero-point error of a Coriolis mass flow meter, the Coriolis mass flow meter comprising: At least one measuring tube, said at least one measuring tube being mounted to vibrate for use as a conductive medium; An exciter for exciting bending vibration modes; At least two vibration sensors are used to detect the vibration of the measuring tube; The method includes at least one measurement and operation circuit, which is used to drive the exciter, detect a sensor signal from the vibration sensor, and determine a mass flow measurement value based on the sensor signal, wherein the method comprises: Excite the vibration of the bending vibration mode of the measuring tube; When the flow rate is zero, measure the first total zero-point error with respect to the first medium in the measuring tube; Determine a first damping value for the vibration relating to the bending vibration mode of the first medium in the measuring tube; When the flow rate is zero, determine the exciter-independent zero-point error of the first medium in the measuring tube during the damped vibration of the bending vibration mode; A first actuator-related contribution to the first total zero-point error is determined based on the first total zero-point error and based on the actuator-independent zero-point error; and The sensitivity coefficient for the bending vibration mode is determined based on the first exciter-related contribution to the total zero-point error and based on the first damping value.

2. The method according to claim 1, wherein, Determining the first damping value includes the quotient of the excitation current used to excite the vibration and the resulting vibration amplitude.

3. The method according to claim 1, wherein, Determining the first damping value includes determining the time constant of the damped vibration of the bending vibration mode.

4. The method according to any one of claims 1 to 3, wherein, Determining the first exciter-related contribution to the first total zero-point error includes forming the difference between the first total zero-point error and the zero-point error independent of the exciter.

5. The method according to any one of claims 1 to 3, wherein, Determining the sensitivity coefficient involves dividing the first exciter-related contribution to the first total zero-point error by the first damping value.

6. The method according to any one of claims 1 to 3, further comprising determining an updated exciter-independent zero-point error, including: Excite the vibration of the bending vibration mode with respect to the second medium in the measuring tube; When the flow rate is zero, measure the second total zero-point error with respect to the second medium in the measuring tube; Determine a second damping value for the second medium in the measuring tube; The updated, actuator-independent zero-point error is determined based on the second total zero-point error, the second damping value, and the sensitivity coefficient.

7. The method according to any one of claims 1 to 3, further comprising determining a third total zero-point error of the Coriolis mass flow meter, wherein, The method includes: Determine the third damping value of the vibration of the bending vibration mode with respect to the third medium in the measuring tube; and The third total zero-point error is calculated based on the third damping value, the sensitivity coefficient of the bending vibration mode, and the zero-point error independent of the exciter.

8. The method according to claim 7, wherein, The third total zero-point error includes the sum of the zero-point error independent of the exciter and the third exciter-related contribution to the total zero-point error.

9. The method according to claim 8, wherein, The third exciter-related contribution to the total zero-point error includes the product of the sensitivity coefficient and the third damping value.

10. A method for operating a modular Coriolis mass flow meter, the modular Coriolis mass flow meter comprising: At least one measuring tube, said at least one measuring tube being mounted to vibrate for use as a conductive medium; An exciter for exciting bending vibration modes; At least two vibration sensors are used to detect the vibration of the measuring tube; The method includes at least one measurement and operation circuitry for driving the exciter, detecting sensor signals from the vibration sensors, and determining mass flow measurement values ​​based on the sensor signals. The Coriolis mass flow meter comprises a base module and a replaceable measuring tube module. The measuring tube module includes the measuring tube and a first component for each of the exciter and the two vibration sensors. The base module includes the measurement and operation circuitry, a housing with a housing for the measuring tube module, and a second component for each of the exciter and the two vibration sensors. The method includes: The measuring tube module is connected to the base module such that the first and second components of the exciter and the two sensors are in an operating position relative to each other in each case; and the sensitivity coefficient and the zero-point error independent of the exciter are determined using the method according to any one of claims 1 to 6.

11. The method of claim 10, further comprising: The third total zero-point error is determined by the method according to any one of claims 7 to 9.

12. A Coriolis mass flow meter, comprising: At least one measuring tube, said at least one measuring tube being mounted to vibrate for use as a conductive medium; An exciter for exciting bending vibration modes; At least two vibration sensors are used to detect the vibration of the measuring tube; And at least one measurement and operation circuit, the at least one measurement and operation circuit being used to drive the exciter, to detect sensor signals from the vibration sensor, and to determine mass flow measurement values ​​based on the sensor signals, wherein the measurement and operation circuit is configured to perform at least one of the methods according to any one of claims 1 to 9 and the methods according to claim 10 or 11.

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