Method for monitoring a coriolis mass flowmeter

Abstract

The invention relates to a method (100) for monitoring a Coriolis mass flowmeter having an oscillator with at least one measuring tube, the method comprising: - exciting (110) the oscillator in order to induce a flexural vibration of a first anti-symmetrical vibration mode by means of an excitation signal at a resonance frequency of the first anti-symmetrical vibration mode; - sensing (120) a vibration amplitude of the first anti-symmetrical vibration mode at the resonance frequency of the first anti-symmetrical vibration mode; - sensing (130) a time constant of a damped free vibration of the first anti-symmetrical vibration mode; and - determining (140) a modal elastic property of the oscillator with respect to the first anti-symmetrical vibration mode based on the vibration amplitude of the first anti-symmetrical vibration mode, the excitation signal and the time constant.

Description

Technical Field

[0001] The present invention relates to a method for monitoring a Coriolis mass flow meter having an oscillator having at least one measuring tube. Background Technology

[0002] The elastic properties of the measuring tube of a Coriolis mass flow meter are negatively affected by corrosive and abrasive media that erode the inner wall of the tube. Therefore, there is considerable interest in determining and monitoring the calibration or calibration factor of a Coriolis mass flow meter during operation. To this end, several solutions exist for determining the compliance of the measuring tube as a measure of the calibration factor, described in publications WO 2018 101 920A1, WO 2012062551A1, and the still unpublished patent application DE 10 2019 124 709.8. For simplicity, stiffness is always correspondingly covered where compliance is discussed below. The common feature of the above solutions is that they do not distinguish between specific modal compliances, but rather determine a compliance corresponding to the modal compliance of the useful mode or driving mode. However, the measurement effect is determined by the deformation of the measuring tube caused by the Coriolis force. This deformation is related to the modal compliance of the Coriolis mode, which has the opposite symmetry to the useful mode or driving mode. Therefore, if the useful mode or driving mode is symmetric about the transverse plane of the measuring tube, the Coriolis mode is antisymmetric. Thus, variations in the modal compliance of the Coriolis mode can only be conditionally derived from variations in the modal compliance of the useful mode or driving mode. This is reasonable when tube wall erosion is uniform, for example, that can occur due to corrosion, because in the case of uniform corrosion, the modal compliance of the driving mode and the Coriolis mode are highly correlated. Abrasive erosion is non-uniform, especially in the case of a given curved measuring tube, making it necessary to determine the correlation between the type of abrasive erosion and the nominal width of the measuring tube. Summary of the Invention

[0003] Therefore, the object of the present invention is to provide a method that can reliably monitor a flow meter independently of the wear type and independently of the nominal width of the flow meter.

[0004] According to the present invention, the objective of the present invention is achieved by the method according to the present invention.

[0005] The method according to the invention is used for monitoring a Coriolis mass flow meter having an oscillator having at least one measuring tube, wherein the method comprises:

[0006] The oscillator is excited by an excitation signal at the resonant frequency of the first antisymmetric vibration mode, so as to induce flexural vibration in the first antisymmetric vibration mode.

[0007] The amplitude of the first antisymmetric vibration mode at the resonant frequency of the first antisymmetric vibration mode is sensed.

[0008] The time constant of the decaying free vibration of the first antisymmetric vibration mode is sensed; and

[0009] Based on the vibration amplitude, excitation signal, and time constant of the first antisymmetric vibration mode, the modal elastic properties of the oscillator relative to the first antisymmetric vibration mode are determined.

[0010] Given the typical quality Q of an oscillator, excitation of a vibration mode at the oscillator's resonant frequency results in a quality-related resonance exaggeration. On the one hand, this is advantageous because if the exciter, despite being at a distance from the vibration node of the first antisymmetric vibration mode in the longitudinal direction of the measuring tube, is still located near the vibration node of the first antisymmetric vibration mode, this provides a basis for obtaining a usable signal of the antisymmetric vibration mode. On the other hand, without knowing the amplitude quality, conclusions cannot be drawn regarding the modal stiffness of the vibration mode.

[0011] In the development of this invention, the exciter is offset only slightly relative to the center in the longitudinal direction relative to the length of the measuring tube, and thus always remains near the vibration node of the first antisymmetric vibration mode. A suitable position for the exciter is, for example, offset from the center of the measuring tube by 2.5% of the tube length. To apply the method according to the invention, a precaution should be taken such that the exciter is arranged to be offset from the center of the measuring tube by, for example, at least 0.5% of the tube length, and especially not less than 1% of the tube length. When the oscillator is excited using the eigenfrequency of the symmetrical drive mode, especially the f1 mode, the asymmetrical mounting of the exciter creates a phase difference between the vibrations of the two vibration sensors, which, if not considered and compensated for, can lead to zero-point errors in flow measurement. Therefore, it is advantageous if the symmetry disruption due to the asymmetrical mounting remains limited. For example, the exciter is thus offset in the longitudinal direction from the center of the measuring tube by no more than 5% of the tube length.

[0012] In the development of this invention, modal quality is initially determined based on time constant, wherein then the determination of the modal elastic properties of the oscillator is carried out based on vibration amplitude, excitation signal and quality, wherein the resonant frequency of the vibration mode under consideration can be further included in the determination of quality.

[0013] In the development of this invention, the resonant frequency of the oscillator is further included in the determination of the modal elastic properties of the oscillator.

[0014] In the development of this invention, the change in the modal elastic properties of the oscillator is determined by comparing it with at least one reference value of the modal stiffness.

[0015] In the development of this invention, the mass flow meter is characterized by a calibration factor (calf) used to determine the mass flow measurement value, which is proportional to the calibration factor and the time difference between the in-phase points of the signals from the two vibration sensors of the flow meter, wherein the method according to the invention further includes: adjusting the calibration factor calf based on changes in the modal elastic properties of the oscillator.

[0016] In a further development of the present invention, the method includes: sensing a series of values ​​of the modal elastic properties, and determining the trend of the modal elastic properties or the trend of the calibration factor calf.

[0017] In a further development of the present invention, the method further includes: determining a period of time during which the modal elastic properties or calibration factor calf remain within the allowable range; and if the period of time is below the limit value, signaling the period of time or outputting an alarm signal, wherein the period of time is in particular not less than one week, for example not less than one month, and further, for example not less than one quarter.

[0018] In a further development of the present invention, the method further includes: determining the modal elastic properties of at least one additional vibration mode;

[0019] Calculate the current relationship between the modal elastic properties of the first antisymmetric vibration mode and the modal elastic properties of the other vibration mode.

[0020] In a further development of the invention, the method includes: evaluating the current relationship between the modal elastic properties of a first antisymmetric vibration mode and the modal elastic properties of the other vibration mode.

[0021] In a further development of the present invention, the method further includes: determining the wear degree and type of at least one measuring tube of the oscillator based on the relationship between the modal elastic properties of the first antisymmetric vibration mode and the modal elastic properties of the other vibration mode.

[0022] In the development of this invention, modal elastic properties include the modal flexural stiffness or modal flexibility of the oscillator.

[0023] In the development of this invention, the first different vibration mode includes a first symmetrical flexural vibration mode and / or a second symmetrical flexural vibration mode. Attached Figure Description

[0024] The invention will now be explained in more detail based on the exemplary embodiments shown in the accompanying drawings.

[0025] In the attached diagram:

[0026] Figure 1a: A schematic diagram of an exemplary embodiment of a Coriolis mass flow meter for implementing the method according to the present invention;

[0027] Figure 1b : Figure 1a A schematic diagram of an electromechanical transducer of an exemplary embodiment of a Coriolis mass flow meter;

[0028] Figure 2 Vibration mode diagram of Coriolis mass flow meter;

[0029] Figure 3 A flowchart of a first exemplary embodiment of the method according to the present invention;

[0030] Figure 4 A graph showing the relationship between changes in calibration factors and changes in modal compliance of the driving modes; and

[0031] Figure 5 : A flowchart of a second exemplary embodiment of the method according to the present invention. Detailed Implementation

[0032] Figure 1a The Coriolis mass flow meter 1 shown includes an oscillator 8 having substantially parallel, curved measuring tubes 10 and an exciter 11 acting between the measuring tubes 10 in the flow direction to excite the measuring tubes 10, thereby causing them to flex and vibrate in opposite directions relative to each other. The exciter 11 is arranged to be offset from the center of the measuring tube by approximately 2.5% of the measuring tube length L in the longitudinal direction relative to the center of the measuring tube. Therefore, when the oscillator is excited using the exciter 11, if the excitation of the oscillator occurs at the resonant frequency of a first antisymmetric vibration mode, sufficient asymmetric force is applied to excite the first antisymmetric vibration mode to resonate, which is referred to as the f2 mode or the first Coriolis mode. Furthermore, the Coriolis mass flow meter 1 has two vibration sensors 12.1 and 12.2, which are arranged symmetrically in the longitudinal direction relative to the center of the measuring tubes 10 to detect the relative motion of the measuring tubes 10 vibrating in opposite directions relative to each other. A measuring tube 10 extends between two shunts 16 that fluidly combine the measuring tube 10 and are respectively connected to a flange 18 for mounting the Coriolis mass flow meter 1 in a pipe. A rigid support tube 60 connecting the shunts to each other extends between the shunts 16 to suppress opposing vibrations of the shunts 16 within the frequency range of opposing flexural vibration modes of the measuring tubes 10. The support tube also carries an electronic housing 80 containing a measuring and operating circuit 77 configured to operate the flow meter and implement the method according to the invention.

[0033] like Figure 1b As shown, the exciter 11 and vibration sensor 12 are specifically designed as electric transducers, each having an excitation magnet 14 or a sensor magnet 14.1 and an excitation coil 13 or a sensor coil 13.1, respectively, which are mechanically connected to one of the measuring tubes 10 opposite to each other. The excitation coil 13 is configured to be supplied with an alternating current by an operating circuit 77, the frequency of which corresponds to the instantaneous eigenfrequency of the flexural vibration mode to be excited. The generated magnetic field alternately produces attractive and repulsive forces on the excitation magnet 14, thereby setting the measuring tubes 10 to vibrate in opposite directions. Therefore, the relative motion of the sensor magnet 14.1, which vibrates with the measuring tube 10, relative to the sensor coil 13.1 induces a voltage in the sensor coil 13.1, which depends particularly on the relative velocity of the measuring tubes relative to each other. The measurement and operation circuit 77 is configured to sense and evaluate the induced voltage in order to determine the relative velocity or deflection of the vibration sensors 12.1, 12.2 or the measuring tube 10, and the modal deflection of the measuring tube 10 for different vibration modes.

[0034] Figure 2 The pattern-dependent deflection of the measuring tube is schematically illustrated. Curve a A This shows the bending curve of the measuring tube in the first symmetrical vibration mode, also known as the driving mode or f1 mode. Curve a C1 The bending line of the measuring tube in the first Coriolis mode or the first antisymmetric vibration mode is shown, wherein if the mass flow passes through the measuring tube vibrating in the first symmetric vibration mode, the measuring tube is deflected by the Coriolis force. The first antisymmetric vibration mode has a vibration node in the center of the tube at z=0 in the longitudinal direction of the measuring tube. The exciter at this position will not be able to excite the vibration of the first antisymmetric vibration mode. Therefore, the exciter is offset here relative to the center by about 2.5% of the measuring tube length, that is, about 5% of half the measuring tube length. The measuring tube length is therefore the length of the centerline of the measuring tube between the inlet-side splitter 16 and the outlet-side splitter 16, following the bending line of the measuring tube, the measuring tube 10 is fixed in the inlet-side splitter 16 and the outlet-side splitter 16 through their ends. At the offset position, if the exciter applies an excitation force F at the resonant frequency of the first antisymmetric vibration mode... E Then the exciter can excite the first antisymmetric vibration mode.

[0035] The position of the vibration sensor is symmetrically selected about the center of the measuring tube in the longitudinal direction, such that the deflection X of the vibration sensor... S1 X S2 Sufficient measurement signals are generated in both the drive mode and the first antisymmetric vibration mode. Furthermore, Figure 2 The diagram shows the curved line a used for the second antisymmetric vibration mode or the second Coriolis mode.C2 Wherein, if the mass flow through the measuring tube vibrates in the second symmetrical drive mode (not shown here), i.e., mode f3, the measuring tube deflects. Similarly, if the exciter applies an excitation force F at the resonant frequency of the second Coriolis mode... E This can stimulate the second Coriolis pattern.

[0036] For example, due to the high modal quality Q between 1000 and 10000, the amplitude of the vibration modes of an oscillator or its measuring tube exhibits strong resonant exaggeration. To infer the modal stiffness or compliance of each mode, the modal quality Q is determined in addition to the vibration amplitude at the corresponding resonant frequency. For this purpose, the decay curve of the corresponding vibration mode can be sensed, especially after the excitation force has been cut off. Using the quality Q and the excitation force F... E Normalized vibration amplitude is a measure of modal compliance.

[0037] The modal compliance of the first antisymmetric vibration mode affects the calibration factor calf. By a first approximation, the calibration factor calf is inversely proportional to this modal compliance, and the mass flow rate dm / dt is correlated with the time delay Δt between the zero-crossing points of the two vibration sensors, i.e.:

[0038] dm / dt=calf·Δt

[0039] Therefore, by using the method according to the invention to monitor the modal compliance of the first antisymmetric vibration mode, it is possible to directly monitor and correct the calibration factor calf, or to verify the mass flow rate measurement value dm / dt.

[0040] use Figure 3 The method steps of a first exemplary embodiment 100 according to the present invention are explained. Method 100 can be implemented, for example, continuously, periodically, or in a situation-controlled manner, wherein the triggering situation can be, for example, a user request or the determination of a change in another monitored variable of the measuring device.

[0041] Method 100 begins by utilizing the resonant frequency ω of the first antisymmetric vibration mode. c1 Modal excitation signal F c1 The 110 oscillator is excited to flexural vibration in a first antisymmetric vibration mode. This first antisymmetric vibration mode is either a first Coriolis mode or an f2 mode, as combined with... Figure 2 The explanation given.

[0042] In the steady state of this first antisymmetric vibration mode, the sensing 120 of the amplitude Xc1 of the first antisymmetric vibration mode occurs at its resonant frequency. For this purpose, the velocity-proportional induced voltage of the electrodynamic vibration sensor is evaluated at the resonant frequency of the first antisymmetric vibration mode.

[0043] Then, the time constant τ of the decaying free vibration of the first antisymmetric vibration mode of 130 was sensed. c1 For this purpose, the excitation signal at the resonant frequency of the first antisymmetric vibration mode is partially or completely cut off, and the amplitude of the damped induced voltage of the vibration sensor is sensed at the resonant frequency.

[0044] Finally, based on the oscillator's vibration amplitude, excitation signal, and time constant, the modal elastic properties of the 140 oscillator relative to the first antisymmetric vibration mode are determined. For this purpose, for example, the modal quality Q can initially be determined based on the time constant. c1 Modal quality Q c1 For example, it can be determined as follows:

[0045]

[0046] Where, ω c1 It is the resonant frequency of the vibration mode under consideration.

[0047] Then, the modal elastic properties of the oscillator are determined based on the vibration amplitude, excitation signal, and modal quality.

[0048] Modal elastic properties can be, for example, modal compliance N. c1 Its relationship with modal vibration amplitude X c1 Divided by modal mass Q c1 and modal excitation signal F c1 The amplitude is proportional, that is:

[0049] N c1 =K c1 ·X c1 / (F c1 ·Q c1 ), where K c1 It is a specific mode constant.

[0050] Modal compliance N determined in this way c1 Compared with reference value N c1-0 By comparing 150, the changes in the modal elastic properties of the oscillator can be determined, where the reference value represents, for example, the state when the mass flow meter is started.

[0051] As mentioned above, the calibration factor calf of a mass flow meter is essentially related to the modal compliance N. c1 Inversely proportional. In this respect, the calibration factor calf can also be used as the elastic property to be monitored for the first antisymmetric vibration mode, wherein the calibration factor calf can be determined as follows: calf = K calf / N c1 K calf It is a scaling factor specific to the equipment.

[0052] The calibration factor calf depends on the modal compliance N. c1 The adjustment of the variation 160 also enables accurate mass flow measurement even under given measuring tube wear conditions. Under a given modified modal compliance N... c1 In this case, after repeated adjustments to the calibration factor, a trend analysis of the calibration factor calf can be performed 170, and under the assumption of the same media properties, a prediction of the remaining service life 180 can be provided, which is related to the latest point in time when the flow meter can still be operated. The following is combined with... Figure 4 Let me explain the details further.

[0053] Furthermore, the method according to the invention can be advantageously combined with the method for monitoring the state of a measuring tube according to International Publication WO 2012 062551A1, which teaches the monitoring of the modal compliance N of a first symmetric driving mode. a This can be determined, in particular, independently of quality, through excitations other than resonance. The current modal compliance N of the first symmetric driving mode. a Compared to, for example, a brand new state or a reference state N after authentication. a-0 The relative deviation ΔN a It is also an indicator that measures changes within the tube. Figure 4 The relative deviation ΔN of the modal compliance of the first symmetric driving mode a The relative deviation Δcalf of the calibration factor is related. Test series have shown that, depending on the cause of the variation in the measuring tube, the two monitored variables Δcalf and ΔN... a The relationship presents two distinct scenarios. Both scenarios share a common starting point (0,0) for the measuring tubes under the reference state. In the case of corrosion, the walls of the measuring tubes are subjected to essentially uniform attack, causing a uniform change in the moment of inertia across all measuring tube cross-sections. Therefore, the modal stiffness of the relevant vibration modes is uniformly affected, resulting in a difference between Δcalf and ΔN under a given corrosion condition. a There is a very good correlation between them. This corrosion condition is... Figure 4 The midline b is indicated by a cross-shading. In contrast, a different picture emerges for a given wear condition. Wear typically occurs in heterogeneous media, including liquids with solid loads. Different spatial distributions of wear can occur depending on the Reynolds number, concentration, density distribution, and size distribution, where, during its initiation, in… Figure 4 Above the midline a Figure 4 The linear trajectory within the region indicated by the midpoint line is used to monitor the variables Δcalf and ΔN. aThe first approximation was observed. Since these two conditions are clearly distinct from each other, this provides plant operators with a means to identify wear and corrosion processes in measuring devices at an early stage, based on Δcalf and ΔN. a The relationship identifies the type of material erosion. Therefore, if a pair of values ​​(Δcalf, ΔN) a If the value is above line a, it is assumed to be wear, while if this pair of values ​​is below line b, it indicates corrosion. Figure 5 A flowchart of a second exemplary embodiment 200 of the method according to the invention for implementing this aspect of the invention is shown.

[0054] The first method steps are similar to those of the first exemplary embodiment, until the amplitude Xc1 of the first antisymmetric vibration mode and its decay time τ are determined. c1 and at the resonant frequency ω c1 The associated excitation signal F c1 Determine the calibration factor 240 calf. Modal compliance N of the first symmetric vibration mode. a The determination of 250 occurs in parallel with this. As described in WO 2012 062551A1, this can be similar to the determination of modal compliance at resonance in the first exemplary embodiment, or the determination of modal compliance independent of quality using excitations outside of resonance. In fact, the modal compliance N used to determine the calibration factor calf and the first symmetric vibration mode is... a Measurements can be performed simultaneously because vibrations can be excited in a superposition manner. If the calibration factor calf and modal compliance N are obtained... a The current value, then the relative deviation Δcalf and ΔN a The relationship between them 260 arises from their respective reference values, where the relative deviation of variable x is determined by Δx = (xx) ref ) / x ref To determine, where x is the calibration factor calf or modal compliance N. a , and where x ref This refers to the state of the corresponding variables when the flow meter starts up. The evaluation of the relationship 270 then occurs in the form of a classification, where it is determined whether the relationship indicates corrosion or abrasion. Only when the determined abrasion has reached a certain level, for example if... Figure 4 The value pairs in the diagram must be located outside the inner elliptical arc i for reliable classification to be implemented. Using the duration of the trajectory of the required value pair from the inner elliptical arc i to the intermediate elliptical arc ii, it is possible to infer when the value pair will reach its critical wear limit, which is represented, for example, by the outer elliptical arc iii. This point in time can be provided as notification for planned maintenance actions. Furthermore, if the time before reaching the critical wear limit is less than, for example, a quarter and / or a month's limit, an alarm can be generated.

[0055] In an exemplary embodiment, the modal elastic properties of the oscillator are described as the modal compliance of the oscillator or measuring tube. Of course, modal flexural stiffness or the calibration factor calf can be similarly used to model or describe wear.

[0056] In addition to the first symmetrical flexural vibration mode, the second symmetrical flexural vibration mode, also known as the f3 mode, can also be used as another mode.

Claims

1. A method for monitoring a Coriolis mass flow meter (100), The Coriolis mass flow meter includes: An oscillator having at least one measuring tube; Exciter; And two oscillation sensors; The method includes: The oscillator is excited by means of the exciter, using an exciter signal of the resonant frequency of the first antisymmetric vibration mode, so as to induce flexural vibration (110) of the first antisymmetric vibration mode. The exciter is offset from the center in the longitudinal direction of the measuring tube. Wherein, the exciter is offset relative to the center of the measuring tube in the longitudinal direction by no more than 5% of the length of the measuring tube, so as to limit the symmetry disruption caused by the asymmetrical installation of the exciter, which causes a phase difference between the vibrations of the two oscillation sensors when the oscillator is excited using the eigenfrequency of the symmetrical drive mode. Sensing the vibration amplitude (120) of the first antisymmetric vibration mode at the resonant frequency of the first antisymmetric vibration mode; The time constant (130) of the decaying free vibration of the first antisymmetric vibration mode is sensed; and Based on the vibration amplitude of the first antisymmetric vibration mode, the excitation signal, and the time constant, the modal elastic properties of the oscillator relative to the first antisymmetric vibration mode are determined (140).

2. The method (100) according to claim 1, wherein, The exciter is offset from the center of the measuring tube in the longitudinal direction by at least 0.5% of the length of the measuring tube.

3. The method (100) according to claim 2, wherein, The exciter is offset from the center of the measuring tube in the longitudinal direction by not less than 1% of the length of the measuring tube.

4. The method (100) according to claim 1, wherein, The modal quality is initially determined based on the time constant, and then the modal elastic properties of the oscillator are determined based on the vibration amplitude, the excitation signal, and the quality.

5. The method (100) according to claim 1, wherein, The resonant frequency of the oscillator is also included in the determination of the modal quality of the oscillator.

6. The method (100) according to any one of claims 1-5, wherein, The change in the modal elastic property of the oscillator is determined by comparison with at least one reference value of the modal elastic property (150).

7. The method (100) according to any one of claims 1-5, in, The mass flow meter is characterized by a calibration factor calf, which is used to determine the mass flow measurement value, the mass flow measurement value being proportional to the calibration factor and the time difference between the in-phase points of the signals of the two oscillating sensors of the flow meter; The method (100) further includes: The calibration factor calf(160) is adjusted depending on the change in the modal elastic properties of the oscillator.

8. The method according to claim 7, wherein, The method further includes: A series of values ​​of the modal elastic property are sensed, and the trend of the modal elastic property or the trend of the calibration factor calf is determined (170).

9. The method according to claim 8, wherein, The method further includes: The time period (180) during which the modal elastic properties or the calibration factor calf remain within the allowable range; and If the time period is below the limit value, then the time period is sent by signal, and / or an alarm signal is output.

10. The method according to claim 9, wherein, The time period shall be no less than one week.

11. The method according to claim 10, wherein, The time period shall be no less than four weeks.

12. The method according to claim 11, wherein, The time period shall be no less than eight weeks.

13. The method (100) according to any one of claims 1-5, further comprising: Determine the modal elastic properties of at least one additional vibration mode (250); Calculate the current relationship between the modal elastic properties of the first antisymmetric vibration mode and the modal elastic properties of the other vibration mode (260).

14. The method (100) according to claim 13, further comprising: Evaluate the current relationship between the modal elastic properties of the first antisymmetric vibration mode and the modal elastic properties of the other vibration mode (270).

15. The method of claim 13, further comprising: Based on the relationship between the modal elastic properties of the first antisymmetric vibration mode and the modal elastic properties of the other vibration mode, the wear degree and type of the at least one measuring tube of the oscillator are determined.

16. The method according to any one of claims 1-5, wherein, The modal elastic properties include modal flexural stiffness, modal flexibility, or calibration factor calf.

17. The method according to claim 13, wherein, The additional vibration modes include a first symmetrical flexure vibration mode and / or a second symmetrical flexure vibration mode.

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