WO2021180623A1

WO2021180623A1 - Method for determining a calibration factor for a measuring tube, measuring tube pair, and coriolis measuring device having a measuring tube pair

Info

Publication number: WO2021180623A1
Application number: PCT/EP2021/055731
Authority: WO
Inventors: Hao Zhu; Wolfgang Drahm
Original assignee: Endress+Hauser Flowtec Ag
Priority date: 2020-03-10
Filing date: 2021-03-08
Publication date: 2021-09-16

Abstract

The invention relates to a method (100) for determining a calibration factor for a measuring tube for a Coriolis measuring device (1) having at least one interchangeable measuring tube (11), wherein the calibration factor depends on a rigidity of the measuring tube, wherein the measuring tube has a basic form in the absence of external forces, wherein a rigidity of the measuring tube is determined with respect to a deflection of the measuring tube from the basic form, wherein the measuring tube is produced from a material, wherein at least one of the following parameters of the measuring tube is used when determining the rigidity: external diameter (11.11), mass, wall thickness (11.12), at least one measured natural frequency of the measuring tube, area moment of inertia of a measuring tube cross section (11.13), modulus of elasticity of the material.

Description

Method for determining a calibration factor of a measuring tube, measuring tube pair and

Coriolis measuring device with a pair of measuring tubes

The invention relates to a method for determining a calibration factor of a measuring tube of a Coriolis measuring device, a measuring tube pair with measuring tubes with calibration factors determined according to the method, and a Coriolis measuring device with such a measuring tube pair.

For reasons of hygiene, for example, in the food industry or the pharmaceutical industry, it is necessary to change the medium of a flow meter or density meter to replace measuring tubes, as thorough cleaning would be too costly. Therefore, for example, Coriolis flowmeters with exchangeable measuring tubes or measuring tube pairs are also provided, see, for example, WO2019017891 A1.

So that a flow rate or density measurement can continue to be carried out with sufficient accuracy, the measuring tube pair is calibrated in order to establish a relationship between a measured Coriolis mode and a flow rate. Typically, the measuring tubes of a measuring tube pair have slightly different vibration behavior, which manifests itself in a zero point error. The calibration is based on the fact that a known flow rate of a known medium is fed to the measuring tube pair in order to determine vibration properties from it.

Calibrating the pair of measuring tubes is time-consuming and therefore expensive.

The object of the invention is therefore to propose a method for determining a calibration factor, a measuring tube pair and a Coriolis measuring device, the Coriolis measuring device being able to be set up robustly and quickly.

The object is achieved by the subjects of the independent claims 1, 8 and 14.

In a method according to the invention for determining a calibration factor of a measuring tube for a Coriolis measuring device with at least one exchangeable measuring tube, the calibration factor depends on a stiffness of the measuring tube, the measuring tube having a basic shape in the absence of external forces, the stiffness of the measuring tube against deflection of the measuring tube is determined from the basic shape, the measuring tube being made of a material, the method comprising the following method step:

Determination of the stiffness based on at least one of the following parameters of the measuring tube: Outside diameter, mass, wall thickness, at least one measured natural frequency of the measuring tube, area moment of inertia of a measuring tube cross-section, modulus of elasticity of the material, fixing positions of the measuring tube.

The calibration factor describes the relationship between a mass flow rate and a Coriolis-induced phase delay or time delay between measurement signals from two vibration sensors of a Coriolis measuring device. This phase delay or time delay is inversely proportional to a stiffness of the measuring tube.

In a finished Coriolis measuring device, measuring tubes are coupled to one another at fixing positions, so that fixing positions define nodes of measuring tube oscillations. In the case of known fixation positions, such knowledge can be used for a more precise determination of the calibration factor. The fixing positions are given, for example, by fixing elements.

In one embodiment, a computer with at least one processor and a storage device is provided, which computer implements the determination of the rigidity by means of software provided for this purpose, which software is stored in the storage device, at least one of the parameters being used as an input variable for the software, where an output of the software is the stiffness and / or the calibration factor.

In one embodiment, at least one physical relationship between at least one of the parameters and the rigidity is used to calculate the rigidity.

For example: f = 1 / (2 * pi) * sqrt (K / M) with f as the natural frequency, K as the oscillation constant and M as the mass of the measuring tube. The oscillation constant is dependent on a geometrical moment of inertia with respect to a measuring tube cross-section and a modulus of elasticity of the material used for measuring tube production, with the Coriolis-induced phase delay or time delay being inversely proportional to the square of the natural frequency at constant mass.

The method presented here is particularly advantageous when the requirements for measurement accuracy are somewhat reduced, so that an estimation or calculation of the calibration factor on the basis of physical relationships already provides sufficiently accurate results. Then there is no need for a laborious and time-consuming and therefore expensive measurement of the calibration factor. In one embodiment, artificial intelligence or machine learning is used to determine the rigidity and / or the calibration factor, the computer implementing the artificial intelligence or machine learning by means of the software.

In one embodiment, the software maps a neural network, the neural network being trained with a large number of different measuring tubes, the parameters of which are determined, the measuring tubes differing in pairs in at least one parameter.

In one embodiment, the neural network is trained with a large number of different measuring tubes, the parameters of which are determined, the measuring tubes differing in pairs in at least one parameter.

In one embodiment, the measuring tube has at least three magnets which are fastened along a measuring tube center line on an outside of a measuring tube wall, the number and arrangement of the magnets being taken into account when calculating the calibration factor.

In one embodiment, the measuring tube is manufactured by means of a hydroforming process, a measuring tube lumen being subjected to water under high pressure, the measuring tube wall being pressed against a tool that surrounds the measuring tube circumferentially.

In this way, the outer diameter is known with high accuracy, and by weighing the measuring tube, a wall thickness of the measuring tube wall can be calculated with high accuracy with the mass thus determined and with a known mass density of the material used to manufacture the measuring tube. Thus, for example, a geometrical moment of inertia of a measuring tube cross-section can then be determined.

The measuring tube is preferably made of a plastic or a metal such as stainless steel.

A measuring tube pair according to the invention comprises two measuring tubes each with a calibration factor determined according to one of the preceding claims, a deviation of the calibration factors of the measuring tubes from a mean value of the calibration factors being less than 3% and in particular less than 1% of the mean value.

In this way, the pair of measuring tubes is balanced and causes little interference in measuring operation.

In one embodiment, the measuring tubes of the measuring tube pair are set up to oscillate against one another, the projections of the measuring tubes on a central plane being the same. In one embodiment, the measuring tubes are each connected on the inlet side and on the outlet side by means of at least one fixing element.

In one embodiment, the measuring tubes of the measuring tube pair each have at least three magnets which are fastened along a measuring tube center line to an outside of a measuring tube wall, the magnets of the measuring tubes facing away from one another.

In one embodiment, the measuring tubes each follow a U-shape.

In this way, the inlet and outlet of the measuring tubes are arranged on the same side and can therefore be quickly connected to a pipeline. In one embodiment, the measuring tube pair has a distributor and a collector, which are set up to connect the measuring tube pair to the pipeline.

A Coriolis measuring device according to the invention for determining a density or a mass flow rate of a medium flowing through a pipeline comprises:

At least one exchangeable measuring tube pair according to the invention, at least one vibration exciter for generating measuring tube vibrations, at least two vibration sensors for detecting measuring tube vibrations of the measuring tubes of the measuring tube pair;

An electronic measuring / operating circuit for operating the vibration exciter, for acquiring measurement signals from the vibration sensors and for providing measured values of density or mass flow, the pair of measuring tubes being detachably attached to the pipeline, the attachment being accomplished, for example, by means of a clamp mechanism or a coupling is.

In one embodiment, the vibration exciter and the vibration sensors each have a coil system with a coil and each have a magnet system with a magnet. In one embodiment, the magnets attached to the measuring tubes are each a magnet of a vibration sensor or vibration exciter.

In one embodiment, the Coriolis measuring device has a distributor and a collector, which are set up to connect the pair of measuring tubes to the pipeline.

The invention is described below using exemplary embodiments. 1 describes an exemplary measuring tube of a Coriolis measuring device and explains an exemplary method according to the invention;

2 shows an exemplary measuring tube pair according to the invention;

3 outlines an exemplary Coriolis measuring device according to the invention with a measuring tube pair according to the invention.

4 outlines an exemplary method according to the invention.

1 outlines an exemplary measuring tube 11 of a Coriolis measuring device which, as shown here, can be U-shaped. The measuring tube has a measuring tube wall 11.1 with an outside 11.14, which measuring tube wall encloses a measuring tube lumen 11.2. The measuring tube has an outside diameter of 11.11. the measuring tube wall has a wall thickness 11.12, see the measuring tube cross-section 11.13 shown. The measuring tube wall does not have to follow a round shape in a measuring tube cross-section, as shown here, but can also follow an oval or angular shape.

Measuring tubes, which are intended for replacement, can be produced by means of a hydroforming process, the measuring tube lumen being pressed under high pressure against a tool surrounding the measuring tube with water or another liquid medium such as an oil, the outer wall forming the shape assumes a mating surface of the tool. In the case of measuring tubes which are produced by means of such a method, the outer shape and, in particular, in the case of measuring tubes with round cross-sections, the outer diameter is known with a high degree of accuracy. Uncertainties of the outside diameter of less than 0.1 mm are achieved. By weighing the measuring tube, if the mass density is known, it is then also possible to deduce a wall thickness, the measuring accuracy being essentially limited by the weighing accuracy.

In the case of hydroforming, a round shape in the measuring tube cross-section is advantageous.

A geometrical moment of inertia of the measuring tube wall can be calculated from a known measuring tube cross-section. With material properties such as the modulus of elasticity, the rigidity of the measuring tube can then be determined with the area moment of inertia. The rigidity allows a conclusion to be drawn about a calibration factor, which shows a relationship between the measured mass flow rate and a Coriolis-induced phase delay or time delay between measurement signals from two vibration sensors of a Coriolis measuring device. According to the invention, the calibration factor is not calculated by measuring by means of a mass flow rate, but based on the knowledge of physical, measuring tube-specific variables.

The exchange of measuring tubes can be important in food applications, for example, in order to avoid contamination when the food to be measured changes, for example.

2 outlines an exemplary measuring tube pair 10 according to the invention in a top view and in a side view, in which calibration factors of the measuring tubes were determined by means of the method according to the invention, measuring tubes 11 of a measuring tube pair being selected on the basis of the determined calibration factors. The deviations of the calibration factors of the measuring tubes of a measuring tube pair from an average value of the calibration factors are preferably less than 3% and preferably less than 1% of the average value.

In this way, it is possible to pair suitable measuring tubes in order to form particularly balanced measuring tube pairs and to enable low-interference measuring operation.

As shown here, the measuring tubes are arranged in relation to one another and held or clamped by means of two fixing elements 12. This fixation defines vibration nodes of measuring tube vibrations and thus influences the calibration factor. Alternatively, only one fixing element or more than two fixing elements can be used.

Distributors 18.1 and collectors 18.2 are set up to bring together measuring tube volumes and to connect the measuring tubes to a pipeline 20.

A fastening element 10.1 is provided to enable the pair of measuring tubes to be connected to a holder of a Coriolis measuring device provided for this purpose.

If the measuring tubes have a shape other than a U-shape, the person skilled in the art will adapt the fixing elements, distributors and collectors accordingly if necessary. Distributors and collectors can advantageously be part of the measuring tube pair, since when the measuring tube pair is exchanged, for example, because of a media change, distributors and collectors should also be exchanged.

As shown here, the measuring tubes can have magnets 17.1, which are set up to complete vibration exciters 13 or vibration sensors 14 when installed in a Coriolis measuring device, see FIG. 3.

As shown schematically and by way of example in FIG. 3, the exchangeable measuring tube pair is arranged in such a way that magnets 17.1 are arranged with associated coils 16.1 of coil systems 16 and thus form vibration exciters 13 or vibration sensors 14. As shown here, the measuring tube pair can be attached to one for this by means of a fastening element provided holder of the Coriolis measuring device be manually detachable attached. The fastening can be ensured, for example, by means of a snap, clamp or snap lock.

The connection of the measuring tubes 11 or collectors 18.2 or distributors 18.1 to the pipeline 20 can also be ensured by means of a manually releasable fastening, for example likewise by means of a snap, clamp or snap lock.

An electronic measuring and operating circuit 15 is set up to operate vibration exciters, to acquire and evaluate measurement signals from the vibration sensors and to create and output measured values for mass flow and / or density of a medium flowing through the pipeline. The electronic measuring / operating circuit is usually arranged in a housing (not shown) and connected to the vibration sensors or vibration exciters via electrical connections.

Vibration sensors and vibration exciters include a coil system 16 with at least one coil 16.1 and a magnet system with at least one magnet, with the excitation of measuring tube vibrations and their detection by means of electromagnetic interaction of coils and magnets assigned to one another.

4 outlines an exemplary method 100 according to the invention, an exemplary computer 30 being supplied with parameters of the measuring tube via an input 30.1, and the computer outputting values for the rigidity and / or the calibration factor of a measuring tube via an output 30.2. The input can be, for example, a keyboard or an interface to a device for determining the parameters. The output can be, for example, a screen or an interface to another computer or to a storage device. A processor 31 processes the parameters by means of software 33 stored on a storage device 32 of the computer and calculates values for the rigidity and / or the calibration factor of a measuring tube.

In an exemplary embodiment, artificial intelligence or machine learning is used to determine the rigidity and / or the calibration factor, the computer 30 implementing the artificial intelligence or machine learning by means of the software. For example, the software maps a neural network, the neural network being trained with a large number of different measuring tubes 11, the parameters of which are determined, the measuring tubes differing in pairs in at least one parameter. List of reference symbols

1 Coriolis measuring device

10 Measuring tube pair 10.1 Fastening element 11 Measuring tube

11.1 Measuring tube wall 11.11 Outside diameter 11.12 Wall thickness 11.13 Measuring tube cross-section 11.14 Outside of the measuring tube wall

11.2 Measuring tube lumen 12 fixing element

13 vibration exciter

14 vibration sensors 15 electronic measuring / operating circuit

16 Coil system 16.1 Coil 17 Magnet system

17.1 Magnet 18.1 Distributor

18.2 Collectors

19 Attachment

20 pipeline

30 computers 30.1 Input

30.2 edition

31 processor

32 storage device 33 software

100 procedures

Claims

1. Method (100) for determining a calibration factor of a measuring tube for a Coriolis measuring device (1) with at least one exchangeable measuring tube (11), the calibration factor depending on a rigidity of the measuring tube, the measuring tube having a basic shape in the absence of external forces, wherein a stiffness of the measuring tube with respect to a deflection of the measuring tube from the basic shape is determined, wherein the measuring tube is made of a material, the method comprising the following method step:

Determination of the rigidity on the basis of at least one of the following parameters of the measuring tube: outer diameter (11.11), mass, wall thickness (11.12) of a measuring tube wall (11.1), at least one measured natural frequency of the measuring tube, area moment of inertia of a measuring tube cross-section (11.13), modulus of elasticity of the material, fixing positions of the Measuring tube.

2. The method (100) according to claim 1, wherein a computer (30) with at least one processor (31) and a storage device (32) is provided, which computer is used to determine the rigidity and / or the calibration factor by means of software (33 ) converts which software is stored in the storage device, at least one of the parameters being used as an input variable for the software, an output variable of the software being the rigidity and / or the calibration factor.

3. The method (100) according to claim 1 or 2, wherein at least one physical relationship between at least one of the parameters and the stiffness is used to calculate the stiffness.

4. The method according to claim 1 or 2, wherein artificial intelligence or machine learning is used to determine the stiffness and / or the calibration factor, the computer (30) implementing the artificial intelligence or machine learning by means of the software.

5. The method according to claim 4, wherein the software (33) maps a neural network, the neural network being trained with a plurality of different measuring tubes (11), the parameters of which are determined, with measuring tubes differing in pairs in at least one parameter.

6. The method according to any one of the preceding claims, wherein the measuring tube (11) has at least three magnets (17.1) which are attached along a measuring tube center line on an outer side (11.14) of the measuring tube wall (11.1).

7. The method according to any one of the preceding claims, wherein the measuring tube (11) is manufactured by means of a hydroforming process, wherein a measuring tube lumen (11 .2) is acted upon with a liquid such as water or an oil under high pressure, the measuring tube wall against the measuring tube extensively enclosing tool is pressed.

8. Measuring tube pair (10) comprising two measuring tubes (11) each with a calibration factor determined according to one of the preceding claims, wherein a deviation of the calibration factors of the measuring tubes from a mean value of the calibration factors is less than 3% and in particular less than 1% of the mean value.

9. The measuring tube pair (10) according to claim 8, wherein the measuring tubes (11) of the measuring tube pair are set up to oscillate against one another, the projections of the measuring tubes on a central plane being the same.

10. Measuring tube pair according to claim 8 or 9, wherein the measuring tubes (11) are connected on the inlet side and on the outlet side by means of at least one fixing element (12).

11. Measuring tube pair according to one of Claims 8 to 10, the measuring tubes each having at least three magnets, which are fastened along a measuring tube center line on an outside of a measuring tube wall (11.1), the magnets of the measuring tubes particularly facing away from each other.

12. Pair of measuring tubes according to one of claims 8 to 11, whereby the measuring tubes each follow a U-shape.

13. Measuring tube pair according to one of claims 8 to 12, wherein the measuring tube pair has a distributor and a collector which are set up to connect the measuring tube pair to the pipeline.

14. Coriolis measuring device (1) for determining a density or a mass flow rate of a medium flowing through a pipeline (20) comprising:

At least one exchangeable measuring tube pair (10) with two measuring tubes (11) according to one of Claims 8 to 12, at least one vibration exciter (13) for generating measuring tube vibrations, at least two vibration sensors (14) for detecting measuring tube vibrations of the measuring tubes of the measuring tube pair;

An electronic measuring / operating circuit (15) for operating the vibration exciter, for acquiring measurement signals from the vibration sensors and for providing measured values of density or mass flow, the measuring tube pair being detachably attached to the pipeline (20), with a fastening (19 ) is accomplished for example by means of a clamping mechanism or a coupling.

15. Coriolis measuring device according to claim 14, wherein the vibration exciter and the vibration sensors each have a coil system (16) with at least one coil (16.1) and each have a magnet system (17) with at least one magnet (17.1).

16. Coriolis measuring device (1) according to claim 15 with a measuring tube pair (10) according to claim 11, wherein the magnets attached to the measuring tubes are each a magnet of a vibration sensor or vibration exciter.