Method for operating a coriolis measuring device

Abstract

The invention relates to a method (100) for operating a Coriolis measuring device (1), comprising the following method steps: determining (101) an attenuation of a measuring tube vibration in the region of a first vibration sensor and in the region of a second vibration sensor; measuring (102) a first measuring variable by means of measuring signals from the first vibration sensor and from a third vibration sensor; measuring (103) a second mass flow by means of measuring signals from the second vibration sensor and from the third vibration sensor; determining (104) an influence of the attenuation on the first measuring variable and on the second measuring variable; forming (105) a difference between a measured value of the first measuring variable and a measured value of the second measuring variable; comparing (106) the difference with the determined attenuation of the measuring tube vibration.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for operating a Coriolis measuring device in an interference-resistant manner. BACKGROUND

[0002] In WO 98 / 52000 a Coriolis measuring device with higher reliability is proposed, in which for the purpose of sensing the measuring tube vibrations an arrangement of three such sensors is taught instead of two Coriolis sensors. If one sensor fails, the operation of the Coriolis measuring device can be maintained by the remaining sensors.

[0003] However, not only mechanical failures can affect the functionality of a Coriolis measuring device, but also adverse environmental conditions, such as local magnetic fields. SUMMARY

[0004] It is therefore an object of the present invention to propose a method for operating a Coriolis measuring device by which interferences can be detected.

[0005] This object is achieved by the method according to the independent claim 1.

[0006] In the method for operating a Coriolis measuring device for determining the mass flow and / or the density of a medium flowing through a pipe according to the invention, the Coriolis measuring device comprises:

[0007] at least one measuring tube having an inlet and an outlet, wherein the measuring tube is symmetrical with respect to a symmetry plane extending through the cross section of the measuring tube;

[0008] at least one vibration exciter for generating a measuring tube vibration,

[0009] wherein the measuring tube is designed to form a Coriolis mode with a vibration node in the region of the symmetry plane when a mass is flowing through,

[0010] wherein the Coriolis measuring device has a first vibration sensor, a second vibration sensor and a third vibration sensor, which are designed for sensing the measuring tube vibration, wherein the vibration sensors are each arranged at a different position along the center line of the measuring tube,

[0011] wherein the first vibration sensor is arranged on the inlet side of the measuring tube with respect to the vibration node, the second vibration sensor is arranged on the outlet side of the measuring tube with respect to the vibration node and the third vibration sensor is arranged in the region of the vibration node,

[0012] wherein the first vibration sensor and the second vibration sensor are arranged symmetrically with respect to the symmetry plane,

[0013] The method comprises the following method steps:

[0014] Determine the attenuation of the measuring tube vibrations,

[0015] measuring a first measured variable by means of the measurement signals from the first vibration sensor and from the third vibration sensor,

[0016] measuring a second measured variable by means of the measurement signals from the second vibration sensor and from the third vibration sensor,

[0017] determining the influence of the attenuation on the first measured variable and the second measured variable, and correcting the measured value of the first measured variable and the measured value of the second measured variable,

[0018] A difference is formed between the measured value of the first measured variable and the measured value of the second measured variable, thereby canceling out the influence of the mass flow on the difference,

[0019] The correspondence between the difference and the attenuation is checked.

[0020] The method steps listed do not necessarily have to be performed in the order shown. The order is essentially related to causal relationships. For example, the measurement of the first and second measured variables can also be carried out simultaneously.

[0021] The key point of the method is that the vibrations of the measuring tube in the area of ​​the first vibration sensor and in the area of ​​the second vibration sensor are damped or delayed relative to the vibration exciter by the medium, respectively. This can be attributed, for example, to the viscosity of the medium. When the measured variable is measured by the first and second vibration sensors by means of the difference between the measurement signals from the vibration sensors or the measured values ​​derived from the measurement signals, the contribution of this vibration damping or vibration delay no longer applies.

[0022] When measuring the measured variable using the first or second vibration sensor, respectively, together with a third vibration sensor, the contribution of the vibration damping remains valid even with suitable differentiation, since the third vibration sensor precisely follows the movement of the vibration exciter. This allows for the determination of a direct measured value for the symmetrical vibration damping. In the absence of substantial interference, this direct measured value for the symmetrical vibration damping corresponds to the expected value for the damping or phase delay.

[0023] For example, the correspondence can be determined by calculating an expected value of the difference between the measured value of the first measurement variable and the measured value of the second measurement variable based on the attenuation and comparing it with the actual value of the difference, or by calculating an expected value of the attenuation obtained from the difference and comparing it with the determined attenuation value.

[0024] In one embodiment, the vibration exciter can be designed as a third vibration sensor, wherein the vibration exciter serves as a vibration sensor, for example, intermittently.

[0025] In one embodiment, the type of interference is determined if the difference deviates from the expected value. The presence of an asymmetry deviation of the measurement signal from the vibration sensor is checked from a reference value, with the check taking into account the amplitude of the measurement signal. For practical reasons, it is rare for the measurement signals from these vibration sensors to be completely symmetrical. Therefore, for example, when a Coriolis measuring device is put into operation, a reference value is determined for the asymmetry, which describes the initial state of the Coriolis measuring device.

[0026] If the amplitude of the measurement signal of the first or second vibration sensor does not correspond to the amplitude of the measurement signal of the other vibration sensor, this is considered to be an asymmetry. This correspondence can be determined, for example, by a limit value for this deviation. For example, if the deviation exceeds a limit value, this can be interpreted as a lack of correspondence.

[0027] In one embodiment, mass flow measurement is supported on a pair of vibration sensors that are undisturbed when asymmetry exists.

[0028] If the measurement signal amplitude of the first vibration sensor or the second vibration sensor does not correspond to the measurement signal amplitude of the other vibration sensor, this can be evaluated as an indication of a fault or a disturbance.

[0029] In one embodiment, the influence of the attenuation on the measured value of the undisturbed first or second measured variable is corrected.In this way, a mass flow measurement based on an undisturbed pair of vibration sensors can be performed with high accuracy.

[0030] In one embodiment, when determining the disturbed vibration sensor, the measurement signal amplitude of the third vibration sensor is taken into account in order to determine the plausibility of the measurement signal amplitudes of the first vibration sensor and the measurement signal amplitudes of the second vibration sensor.

[0031] In one embodiment, when a reference value for the deviation is present, the reduction in efficiency of the vibration exciter or vibration sensor is determined by measuring the non-correspondence between the difference and the attenuation, and in particular the compensated non-correspondence. This measure can be based on an absolute or relative deviation. For example, the reduction in efficiency can be caused by aging of the magnet of the vibration exciter. The reference value can be defined by a maximum deviation. A person skilled in the art will readily select a reasonable value.

[0032] The non-correspondence can be determined by calculating an expected value of the difference from the attenuation and comparing it to the actual value of the difference. The non-correspondence can be determined by calculating an expected value of the difference from the attenuation and comparing it to the determined attenuation value.

[0033] In one embodiment, the attenuation is determined by the ratio of the excitation current of the vibration exciter and the specific vibration amplitude of the vibration sensor.

[0034] In one embodiment, the first and second measured variables are phase differences or measured variables derived therefrom, such as time differences or mass flows, respectively.

[0035] In one embodiment, if the deviation has a time constant of less than one month, in particular less than one week, the interference is interpreted as being caused by an external magnetic field in the region of the vibration sensor.

[0036] In one embodiment, the vibration sensor and the vibration exciter each have a magnet system and a coil system, which are movable relative to one another parallel to the vibration direction.

[0037] A magnet system, comprising: at least one magnet; a coil system, the coil system comprising at least one coil.

[0038] In one embodiment, the Coriolis measuring device has an electronic measuring / evaluation circuit, which operates the vibration exciter, evaluates the measurement signals from the vibration sensor, carries out the method steps and calculates and provides the measurement values of the measured variables of the Coriolis measuring device.

[0039] In one embodiment, if the difference deviates from the expected value, a warning message is output. BRIEF DESCRIPTION OF DRAWINGS

[0040] The application will now be described with reference to exemplary embodiments.

[0041] Figure 1 An exemplary Coriolis measuring device according to the application is shown;

[0042] Figure 2 The influence on the measurement tube vibration is shown.

[0043] Figure 3 An exemplary pair of measurement tubes is shown;

[0044] Figure 4 A sequence of an exemplary method according to the application is shown. DETAILED DESCRIPTION

[0045] Figure 1A side view of an exemplary Coriolis measuring device 1 is shown. It includes two measuring tubes 10; a fixing element 15; a support element 16 for supporting the measuring tubes; electronic measuring / operating circuitry 14 for operating the exciter and sensing the measurement signal generated by the sensor and used to provide a density or mass flow measurement; and a housing 17 for housing the electronic measuring / operating circuitry. The vibration exciter 11 and vibration sensor 12 are shown with dashed lines because they are arranged between the measuring tubes. The fixing elements 15 are designed to define the vibration nodes of the measuring tubes; these are known to those skilled in the art. The number and design of such fixing elements will be determined by those skilled in the art based on their needs.

[0046] The Coriolis measuring device has a first vibration sensor 12.1 on the inlet side, a second vibration sensor 12.2 on the outlet side, and a third vibration sensor 12.3. The third vibration sensor is positioned between the first and second vibration sensors relative to the measuring tube centerline 10.4 at the level of the vibration exciter 11. The third vibration sensor thus senses the vibration motion generated by the vibration exciter. In this case, the measuring tubes are each symmetrical about a symmetry plane 10.3, which extends through the measuring tube cross section, to produce a reflection at the symmetry plane.

[0047] The Coriolis measuring device is neither limited to two measuring tubes nor to straight measuring tubes. A Coriolis measuring device can have any number of measuring tubes, in particular only one measuring tube or four measuring tubes. The measuring tubes can also be arched.

[0048] Figure 2 The arrangement of the vibration sensors 12.1 to 12.3 and the vibration exciter 11 in the figure is purely schematic and serves only to illustrate the positioning along the center line of the measuring tube.

[0049] The solid line corresponds to an idealized measuring tube deformation without Coriolis effect, without damping effects, and only schematically taking into account the edge fixation.

[0050] The Coriolis effect in the mass flow through the measuring tube causes a deformation of the measuring tube vibration, as shown by the dashed line. For example, the Coriolis effect causes the measuring tube vibration to trail at the inlet side in the region of the first vibration sensor, but then causes the outlet side measuring tube vibration to lead in the region of the second vibration sensor, where the Coriolis effect is absent. This effect can be detected by determining the phase of the measurement signals from the vibration sensors. For example, the difference between the measurement signal phases can be used to measure the Coriolis effect and, therefore, determine the mass flow rate.

[0051] For example, vibration damping caused by the viscosity of the medium results in tailing of the first and second vibration sensors relative to the third vibration sensor or the vibration actuator. This phenomenon is known as symmetrical vibration damping. If the vibration damping effect of the medium or viscosity is known, the expected value of this tailing, or the corresponding phase delay or attenuation, can be determined. In this case, the ratio of the excitation current of the vibration actuator to the specific vibration amplitude of the vibration sensor is determined.

[0052] A first measured variable is measured using the measurement signals from the first and third vibration sensors, and a second measured variable is measured using the measurement signals from the second and third vibration sensors. The difference between the measured values ​​of the first and second measured variables is calculated, so that the effects of mass flow cancel each other out, leaving only the effect of symmetrical vibration damping without vibration interference. To cancel the effects of mass flow and amplify symmetrical vibration damping, for example, if the first and second measured variables are differences in the measurement signals from the vibration sensors, a difference between the first and second measured variables can be calculated. For example, the first measured variable can be the phase difference between first vibration sensor 12.1 and third vibration sensor 12.3, and the second measured variable can be the phase difference between third vibration sensor 12.3 and second vibration sensor 12.2. The difference between the first and second measured variables corresponds to the sum of the phases of the first and second vibration sensors minus twice the phase of the third vibration sensor. In addition to the phase difference, a derived measured variable, such as a time difference or mass flow, can also be used. In this way, a direct measurement of symmetrical vibration damping can be determined. In the absence of substantial disturbances, the direct measurement of this symmetrical vibration damping corresponds to the expected value of the damping or phase delay.

[0053] If the directly measured value and the expected value do not correspond, this can be interpreted as a disturbance. This can be caused, for example, by distortion of the measurement signal of the first or second vibration sensor caused by an external magnetic field. However, aging of the magnet of the first or second vibration sensor or the vibration actuator can also be the cause, for example.

[0054] Figure 3An exemplary pair of measuring tubes 10 of a Coriolis measuring device according to the present invention is shown. The device comprises a first vibration sensor 12.1, a second vibration sensor 12.2, a third vibration sensor 12.3, and a vibration exciter 11, wherein the third vibration sensor and the vibration exciter are co-located relative to the measuring tube centerline 10.4. The vibration exciter is designed to cause the measuring tubes of the pair to vibrate relative to each other. In this way, the forces generated in the measuring tubes cancel each other out, enabling low-vibration operation. As indicated herein, the vibration sensor and the vibration exciter can each comprise a coil system 13.2 and a magnet system 13.1, respectively, which are movable relative to each other and designed to interact electromagnetically. For example, the coil system can be arranged on the first measuring tube and follow its vibrational motion, while the magnet system can be arranged on the second measuring tube and follow its vibrational motion. During vibration excitation, forces are exerted on the associated magnet systems by the coil currents. During vibration detection, the relative motion induces electromagnetic induction in the coil system, which can be used as a measurement signal. Possible arrangements and embodiments of vibration sensors and vibration exciters in connection with the at least one measuring tube are known to a person skilled in the art.

[0055] Figure 4 The sequence of an exemplary method according to the present invention is illustrated.

[0056] The method 100 comprises the following method steps:

[0057] In method step 101 , the damping of the measuring tube vibration is determined.

[0058] In method step 102 , a first measured variable is measured by means of measurement signals from the first vibration sensor and from the third vibration sensor.

[0059] In method step 103 , a second measured variable is measured by means of the measurement signals from the second vibration sensor and from the third vibration sensor,

[0060] In method step 104 , the influence of the attenuation on the first measured variable and the second measured variable is determined.

[0061] In method step 105 , a difference is formed between the measured value of the first measured variable and the measured value of the second measured variable,

[0062] In method step 106 , the difference is compared with an expected value derived from the attenuation.

[0063] The method steps listed do not necessarily have to be performed in the order presented. The order is inherently related to causality.

[0064] The essence of the method is that the vibrations of the measuring tube in the area of ​​the first vibration sensor and in the area of ​​the second vibration sensor are damped or delayed relative to the vibration exciter by the medium, respectively. This can be attributed, for example, to the viscosity of the medium. When the measured variable is measured by the first vibration sensor and the second vibration sensor by means of a difference formed between the measurement signals from the vibration sensors or between measured values ​​derived from the measurement signals, the contribution of this vibration damping or vibration delay no longer applies. When the measured variable is measured by the first vibration sensor or the second vibration sensor, respectively, together with a third vibration sensor, the contribution of this vibration damping does not cease to apply, because the third vibration sensor strictly follows the movement of the vibration exciter. In this respect, see also Figure 2 If the attenuation is known, an expected value for the delay or attenuation in the region of the first vibration sensor and in the region of the second vibration sensor can be determined. The expected value for the attenuation can be determined by the ratio of the excitation current of the vibration actuator to the specific vibration amplitude of the vibration sensor.

[0065] Reference Mark List

[0066] 1 Coriolis measurement device

[0067] 10 Measuring tube

[0068] 10.1 Entry

[0069] 10.2 Export

[0070] 10.3 Symmetry plane

[0071] 10.4 Measuring the centerline of the tube

[0072] 11. Vibration exciter

[0073] 12.1 First Vibration Sensor

[0074] 12.2 Second Vibration Sensor

[0075] 12.3 Third Vibration Sensor

[0076] 13.1 Magnet System

[0077] 13.2 Coil System

[0078] 14 Electronic measurement / operation circuits

[0079] 15 Fixing elements

[0080] 16 Support elements

[0081] 17 Housing

[0082] 100 methods

[0083] 101 Determine attenuation

[0084] 102 Measure the first measured variable

[0085] 103 Measuring the second measured variable

[0086] 104 Determining the Effects of Attenuation

[0087] 105 Creating Differences

[0088] 106 Comparing Differences

Claims

1. A method (100) for operating a Coriolis measuring device (1) to determine the mass flow rate and / or density of a medium flowing through a pipeline, the Coriolis measuring device comprising: at least one measuring tube (10) having an inlet (10.1) and an outlet (10.2), wherein the measuring tube is symmetrical about a symmetry plane (10.3) extending through a cross section of the measuring tube; at least one vibration exciter (11) for generating vibrations of the measuring tube, wherein the measuring tube forms a Coriolis mode having a vibration node in the region of the symmetry plane when a mass flows through it, The Coriolis measuring device comprises a first vibration sensor (12.1), a second vibration sensor (12.2) and a third vibration sensor (12.3), wherein the first vibration sensor (12.1), the second vibration sensor (12.2) and the third vibration sensor (12.3) are designed to sense vibrations of the measuring tube, wherein the vibration sensors are respectively arranged at different positions along the center line (10.4) of the measuring tube, The first vibration sensor is arranged on the inlet side of the measuring tube relative to the vibration node, the second vibration sensor is arranged on the outlet side of the measuring tube relative to the vibration node, and the third vibration sensor is arranged in the region of the vibration node. wherein the first vibration sensor and the second vibration sensor are arranged symmetrically with respect to the symmetry plane; The method (100) includes the following steps: determining (101) the attenuation of the vibration of the measuring tube, measuring (102) a first measurement variable by means of measurement signals from the first vibration sensor and from the third vibration sensor, measuring (103) a second measurement variable by means of the measurement signals from the second vibration sensor and from the third vibration sensor, determining (104) the effect of the attenuation on the first measured variable and the second measured variable, forming (105) a difference between the measured value of the first measured variable and the measured value of the second measured variable, thereby cancelling out the effect of the mass flow on the difference, The correspondence between the difference and the attenuation is checked (106).

2. The method according to claim 1, in, Determine the type of interference in case of non-correspondence, Therein, a measurement signal from the vibration sensor is checked for the presence of a deviation of the asymmetry from a reference value for the asymmetry, wherein the checking takes into account the amplitude of the measurement signal.

3. The method according to claim 2, in, When said deviation is present, the mass flow measurement is supported by a pair of vibration sensors (12.1, 12.2, 12.3) which are not disturbed.

4. The method according to claim 3, in, The influence of the attenuation on the measured value of the undisturbed first or second measured variable is corrected.

5. The method according to claim 4, in, When determining the disturbed vibration sensor, the amplitude of the measurement signal of the third vibration sensor (12.3) is used to determine the plausibility of the amplitudes of the measurement signals of the first vibration sensor and the second vibration sensor.

6. The method according to any one of claims 2 to 5, in, When a reference value for the deviation is present, the reduction in efficiency of the vibration exciter (11) or the vibration sensor (12.1, 12.2) is determined based on a measure of the non-correspondence between the difference and the attenuation and compensated for.

7. The method according to any one of claims 1 to 5, in, The damping is determined by the ratio of the excitation current of the vibration exciter (11) to the specific vibration amplitude of the vibration sensor (12.1, 12.2, 12.3).

8. The method according to any one of claims 1 to 5, in, The first measured variable and the second measured variable are each a phase difference or a measured variable derived therefrom.

9. The method according to claim 8, in, The measured variable derived from the first measured variable and the second measured variable is a time difference or a mass flow rate.

10. The method according to any one of claims 2 to 5, in, If the time constant of the deviation is less than one month, the disturbance is interpreted as being caused by an external magnetic field in the region of the vibration sensor.

11. The method according to claim 10, in, The time constant is less than one week.

12. The method according to any one of claims 1 to 5, in, The vibration sensor (12.1, 12.2, 12.3) and the vibration exciter (11) each have a magnet system (13.1) and a coil system (13.2), which are movable relative to each other parallel to the vibration direction.

13. The method according to any one of claims 1 to 5, in, The Coriolis measuring device (1) has an electronic measuring / operating circuit (14) which operates the vibration exciter, evaluates the measurement signal from the vibration sensor, carries out the method steps, and calculates and provides a measured value of a measured variable of the Coriolis measuring device.

14. The method according to any one of claims 1 to 5, in, If the difference between the measured value of the first measured variable and the measured value of the second measured variable deviates from an expected value of the difference between the measured value of the first measured variable and the measured value of the second measured variable, a warning message is output.

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