EP3987253A1

EP3987253A1 - Method and device for ascertaining a flow parameter using a coriolis flow meter

Info

Publication number: EP3987253A1
Application number: EP20760755.7A
Authority: EP
Inventors: Thomas Chatzikonstantinou
Original assignee: Heinrichs Messtechnik GmbH
Current assignee: Heinrichs Messtechnik GmbH
Priority date: 2019-06-24
Filing date: 2020-06-24
Publication date: 2022-04-27
Also published as: US20220244084A1; CN114286926A; KR20220024747A; WO2020259762A1; DE102019116872A1

Abstract

The invention relates to a method for ascertaining a flow parameter of a medium, in particular the mass flow rate, using a Coriolis flow meter of a specified measurement device type and to a device which is suitable for said method. According to the method, the medium, which has a medium viscosity, flows through at least one measurement tube piece that is mechanically vibrated by a respective excitation signal, at least one measurement signal dependent on the flow parameter, in particular a phase shift, is ascertained in the vibration behavior of the respective measurement tube piece, and the flow parameter is determined from the at least one measurement signal while taking into consideration the dependency of the flow parameter on the medium viscosity, wherein a data field which is ascertained using an interpolation method, in particular a kriging method, and which indicates the dependency of the flow parameter on the medium viscosity is used in order to determine the flow parameter.

Description

Method and device for determining a flow parameter by means of a Coriolis flow measuring device

The invention relates to a method and a device for determining a

Flow parameters using a Coriolis flow meter.

Devices for Coriolis flow measurement are known from the prior art (see, for example, DE 20 2017 006 709 U1) and are used in particular to determine the mass throughput and / or the density of a fluid flowing through. Coriolis flowmeters have at least one measuring tube in a transducer through which the fluid, the mass flow rate and / or density of which is to be determined, flows. The at least one measuring tube is made to vibrate by means of a vibration exciter, while at the same time the vibrations of the measuring tube are measured by means of vibration sensors at separate measuring points. If no fluid flows through the measuring tube during the measurement, the measuring tube vibrates with the same phase at both measuring points. With fluid flowing through, however, it affects both

Measuring points due to occurring Coriolis forces to phase shifts that are a direct measure of the mass throughput, i.e. H. for the mass of the fluid flowing through the measuring tube in question per unit of time. In addition, the natural frequency of the measuring tube at the measuring points is directly dependent on the density of the fluid flowing through, so that its density can also be determined.

Coriolis flowmeters are used in many areas of technology, for example in pipeline billing measurements, in loading processes, for example when loading tankers with petroleum or gas, or in dosing processes.

The influence of the determinants mass flow and / or density on the measured variables phase shift or frequency depends not only on the type of Coriolis flow meter, but also on the temperature, pressure and viscosity of the medium to be measured. The use of a temperature Compensation known to correct temperature-related measurement errors of Coriolis flowmeters. For this purpose, the temperature of the fluid is attached at a suitable point on the Coriolis mass flow meter

Temperature sensor is continuously measured and density and / or mass flow are set in relation to a reference state, here a reference temperature, by means of mostly linear approximation formulas. Similarly, i.e. By means of mostly linear approximation formulas in relation to a reference state, here a reference pressure, the procedure is used to correct pressure-related measurement errors of Coriolis flowmeters. Coriolis mass flow meters usually do not have a pressure sensor, which is why, unlike the temperature, the pressure is not measured continuously but entered by the user, usually manually, on the electronic evaluation unit. Formulas for density and flow correction, e.g. by means of linear temperature and pressure compensation are known in the prior art.

In contrast to the case of temperature and pressure, the influence of viscosity on the measurement results of Coriolis mass flow meters is largely neglected in the prior art. In standard works of flow measurement technology such as in the book "Flow Measurement", Bela G. Liptak, CRC Press, ISBN

9780801983863, page 60, that there is only little documented information about the influence of viscosity on the accuracy of Coriolis flowmeters, but also that such inaccuracies have been reported without, however, being confirmed by documented test data.

Because of the constantly increasing demands on the accuracy of Coriolis flowmeters, the viscosity of the fluid to be measured is increasingly cited as a possible source of error (see e.g. "Factors Affecting Coriolis

Flowmeters ”, Chris Mills, NEL, March 25, 2014). On the other hand, however, the influence of viscosity on the measurement results of Coriolis mass flow meters is hardly given any importance in practice. E.g. A review of the operating instructions of leading manufacturers of Coriolis mass flow meters shows that they have so far transferred the viscosity values of the fluid to be measured to the electronic

The evaluation unit of the Coriolis mass flow meter does not include or to process. This should be noted even though considerable measurement errors occur, especially with low Reynolds numbers, which can amount to several percentage points, especially if - as is regularly the case - water is used as the calibration medium. This effect is particularly pronounced when using a device calibrated with water when used for a fluid with high to very high viscosity. The same applies to very large Coriolis flowmeters, such as those used at large loading terminals for hydrocarbons or bitumen. But also with small ones

Viscosities and at the same time very small mass flow rates of the fluid, e.g. small Coriolis flowmeters that are used in the kilogram per hour range, measurement errors based on the influence of viscosity should not be neglected.

WO 2015/086224 A1 discloses a density measuring device, in particular a Coriolis mass flow / density measuring device, in which it is proposed not to use the resonance frequency of the measuring transducer measuring tube for measuring the density or the mass flow rate of the fluid flowing through a transducer, but a different frequency, which should result in a preferred phase shift. The optimal measurement frequency leads to independence from the influence of viscosity on the measurement result. The optimal phase shift angle can be determined experimentally and / or with simulation calculations.

When assessing the prior art, it is stated in WO 2015/086224 A1 that the damping of the useful oscillations caused by dissipation of oscillation energy in heat is another influencing variable that does not readily affect the resonance frequency serving as the useful frequency

influence negligible extent or to which the density measuring device can have a certain cross-sensitivity. Changes in the damping and the associated changes in the corresponding resonance frequency are to a considerable extent also due to changes in the transducer in an intact transducer

Determines the viscosity of the medium to be measured, and this in such a way that the respective resonance frequency decreases with increasing viscosity despite the constant density. It was suggested to change the resonance frequency correct by first using the measuring device electronics to determine the viscosity of the fluid flowing through the measuring transducer from the measuring signals of the measuring transducer. The measured variable to be determined - here the density value of the fluid - can be determined using the viscosity measured value as well as a correspondingly extended characteristic curve function, namely also the change in the resonance frequency caused by changes in viscosity.

DE 100 20 606 A1 discloses devices and methods for Coriolis flow measurement which allow the viscosity to be determined and, at the same time, the density and mass flow rate of the fluid flowing through to be measured.

No. 5,027,662 A discloses a Coriolis flow measuring device in which, in certain embodiments, a damping dependent on the viscosity is taken into account in order to determine the mass flow. Flierfür is the attenuation from the

Measured values are determined without the viscosity values being determined themselves.

It is stated as known from “Numerical Simulations of Coriolis Flow Meters for Low Reynolds Number Flows” (Vivek Kumar and Martin Anklin, Endress + Hauser FLOWTEC Journal of Metrology Society India, Vol 26, No 3, 2011, pp. 225-235) that there is a need to correct the measured values of Coriolis flowmeters at low Reynolds numbers and that this is done according to the manufacturer's own information using the Reynolds number. The Reynolds number is indirectly proportional to the dynamic viscosity and proportional to the

Flow rate of the fluid and the nominal diameter of the measuring tube. This means that the Reynolds number is only a similarity parameter and, as such, is very useful in many applications in flow technology, but due to the further dependencies, it is not sufficient to take into account the influence especially of the viscosity in Coriolis flowmeters. This viscosity compensation based on the Reynolds number is due to the structure of the Coriolis flow meter, i.e. e.g. independent of the shape of the measuring tubes, the housing and the material, since a correction function according to the Reynolds number is different in size and with

Coriolis flowmeters equipped with different loops treated in the same way if they move into correctly relevant Reynolds areas during operation, although the flow conditions are in the

Significantly change measuring tubes depending on their shape or size in particular. Depending on the speed and viscosity, these can be relatively large or very small Coriolis flowmeters.

The compensation based on the Reynolds number gives the impression of validity for all devices, regardless of the manufacturer. However, this is not the case, because with the compensation based on the Reynolds number, important local ones remain

Effects that are related to the specifics of the device type and the

Influence measurement accuracy, disregarded, e.g. Locally different diameters of the measuring tubes over the course of the measuring tube, local wrinkles in the wall of the measuring tubes caused by measuring tube bending processes, locally different surface quality of the inside of the measuring tubes, but also other effects, all of which, together with the shape of the measuring tubes, the velocity profile of the flow along of the measuring tubes. A constant, undisturbed velocity profile of the flow along the measuring tubes cannot therefore be assumed. In addition, with the measuring principle of Coriolis flowmeters, due to the unsteady, i.e. dynamic fluid structure leads to interactions between the fluid to be measured, the structure of the Coriolis flow meter and its surroundings. For such unsteady physical phenomena there is one

Compensation by means of the Reynolds number, which is only a static similarity parameter by its definition, is fundamentally not expedient.

EP 1 281 938 B1 discloses taking into account the viscosity of the fluid in order to correct an intermediate value determined for the mass flow rate of a fluid. For this purpose, the viscosity is measured and from that which is representative for the viscosity

Measurement signal and the intermediate value, a further measurement signal representative of the Reynolds number is generated, based on which the intermediate value is then corrected. Thus, the Reynolds number is ultimately decisive, which brings with it the problems already described above with regard to the accuracy of the measured value. From EP 1725839 B1 a Coriolis flow measuring device is known, during the operation of which the viscosity of the fluid flowing through the measuring device is taken into account in order to compensate for measurement errors in the mass flow measurement. The

Viscosity value is determined during operation or is determined in advance as a specified reference viscosity and entered manually from a remote control room or on site, knowing the medium to be measured. To determine the actual mass flow, a first intermediate value for the mass flow is offset against a correction value. The correction value in turn is calculated from the specified or measured viscosity value and a second intermediate value, the second intermediate value corresponding to a damping of the vibrations of the measuring tube that is dependent on an apparent viscosity of the medium carried in the measuring tube. To determine the correction value, the deviation of the apparent viscosity determined via the second intermediate value from the specified or measured viscosity is taken into account. The connection between the

The correction value and the second intermediate value can be mapped with a clear relationship in a table memory of a measuring device electronics. The

Table memory has a set of digital correction values, e.g. in the

Calibration of the Coriolis flow meter has been determined. A measured second intermediate value is compared with the default values stored in the table memory for the second intermediate value and the closest of these is used to determine the correction value.

It is generally known from the prior art for the measurement

determine the relevant relationship between phase shift and mass flow by calibrating the Coriolis flow meter. When

In the prior art, the calibration medium used is almost exclusively water. Disregarding general flow-induced non-linearities, this is

The relationship for water is almost linear in most cases, which is why, according to the prior art, the linear relationship between phase angle and

Mass flow is taken over and represented by means of a proportionality constant, the so-called device parameter. This device parameter, sometimes too

Device constant called, is usually also on the nameplate of each produced Coriolis flow meter. Device constants of devices of the same size and type do not differ significantly from one another.

If, as is the rule in the prior art, measurements are carried out with fluids of other viscosities using a device calibrated with water, measurement errors can result that easily exceed the accuracy of the device based on the calibration medium water by a factor of ten or more . The following is an exemplary table which, depending on the viscosity of the medium and the uncorrected mass flow rate, shows the measurement errors in percent that would result if the viscosity of the measurement medium, which deviates from the calibration medium water, is neglected for the measurement result.

The first column shows the uncorrected mass flow values and the first line shows the viscosity values of the measuring medium.

In a Coriolis flow meter type available on the market, for example, compared to calibration with water (viscosity 1 mPas) when measuring 20,000 kg / h of a liquid with a viscosity of 590 mPas, the error is -1.03%. In order to obtain the correct mass flow rate value, the measured

Add flow rate 1.03%.

If you take into account the fact that Coriolis available on the market

Flowmeters are specified with accuracies of 0.1% or even 0.05%, it is immediately apparent that the viscosity of the measuring medium influences the accuracy of the devices by a factor of 5, 10 or even more. As mentioned before, this one depends

The phenomenon does not depend on the Reynolds number, but is different depending on the

Measuring device type, so that with other measuring device types (e.g. with different measuring tube shapes), completely different errors will occur in terms of numbers.

The creation of tables of the type shown above with a for the

Viscosity compensation with sufficient resolution is problematic in practice, since this would be associated with a correspondingly high number of measurements and / or simulations. Thirty-six measurements and / or simulations are required for the very rough error table shown above, which is only valid for a specific Coriolis flowmeter type, which is very time-consuming and costly.

The problem presented also arises when, in contrast to the usual procedure, a calibration medium other than water is used.

The invention is based on the technical problem, a method and a

To provide a device of the type mentioned at the outset, which allow an improved consideration of the influence of the viscosity on the measurement result. In particular, the new method and the new device should be practical, economical and as precise as possible.

This problem is solved in terms of the method with the features of claim 1, in terms of the device of the type mentioned with the

characterizing features of claim 6 solved. Advantageous embodiments result from the dependent claims.

In a method for determining a flow parameter of a medium, in particular a mass flow, by means of a Coriolis flow measuring device, the medium having a medium viscosity accordingly flows through at least one measuring tube piece, which is mechanically controlled by means of an excitation signal Vibrations is excited. At least one measurement signal that is dependent on the flow parameter, in particular a phase shift, is determined in the vibration behavior of the respective measurement pipe section, with the at least one

Measurement signal of the flow parameters is determined taking into account the dependence of the flow parameter on the medium viscosity, with for

Determination of the flow parameter a data field which is determined by means of an interpolation method and shows the dependency of the flow parameter on the medium viscosity is used.

In particular, the method according to the invention can be implemented in such a way that the interpolation method for determining a data field is applied to a basic data set determined experimentally and / or by simulation. The

Basic data set can be stored in the form of a table, for example, in

Coriolis flowmeter itself or in an external memory. The

Basic data set can e.g. can be generated experimentally through tests with media of different viscosity or through simulation calculations or a combination of both methods. The basic data set can consist of a small number of data, since a large number of measurements but also of simulations is generally not sensible for economic or practical reasons. A basic data set that is as small as possible is desirable, since a separate data field or characteristic field should be determined for each type of measuring device.

The basic data set can be, for example, a table in which, for certain viscosity values, flow parameter values that have not yet been measured taking into account the influence of viscosity, e.g. Mass flow values, the respective error is specified that arises compared to a device type calibrated with water or another calibration medium. Such an exemplary basic data set is shown in the introduction to the description. Of course he can

Basic data set also have a different structure with other data, as long as this results in the dependency of the mass flow rate or the other

determining flow parameters of the medium viscosity results. In particular, the basic data set can also show the errors in absolute values instead of Specify percentages. As a further alternative, instead of values representing errors, it is also possible to specify already corrected mass flow values.

The same naturally also applies to the data fields or characteristic fields that are generated with the aid of the interpolation method. So much for the following

Description in connection with basic data sets, data fields or

If the speech is based on the indication of errors in percent, the same applies to alternative structures which indicate the error in a different way or which indicate mass flow values that have already been corrected.

Instead of the mass flow rate of the medium, the density of the medium flowing through the Coriolis flow measuring device can also be measured as a flow parameter, for example. As far as the following statements refer to the

Referring to mass flow, this can also be done in an analogous manner for others

Flow parameters such as the density, apply. For density measurements e.g. a suitable data field can also be generated and used by means of the interpolation, with which viscosity-related error of the density measurement relative to a

Reference density measurement established and the measured values can be corrected.

With the interpolation method, a data field of higher data density that is sufficiently fine for the required accuracy is generated from the basic data set with a relatively low data density or number of data. The data field can be in the form of a table or a characteristic field. So much for the following presentation of the

Method according to the invention and the device according to the invention of

If a map is assumed for the sake of easier readability, this also applies correspondingly to tables or other forms of data fields.

The interpolation method does not have to be part of the measuring method according to the invention but can be carried out in advance, e.g. during calibration or after

Calibration of the measuring device type can be used. The resulting data field can be stored as a table or as a map for all Coriolis flowmeters of the calibrated measuring device type, e.g. in the measuring device electronics unit of each Coriolis flowmeter or in an external unit, and for the actual measurement be used. The measuring method is characterized by the fact that it uses the data field used with interpolation for the actual measurement. However, it is also possible for the interpolation method to be used during the measurement for an evaluation during or after the determination of the at least one measurement signal. In this case it is external or in the Coriolis flowmeter itself

Basic data set stored.

The medium viscosity can, for example, be entered manually on the Coriolis flowmeter or made available for measurement in some other way, e.g. by means of a measurement on the medium. The medium viscosity can also depend on pressure or temperature, which is also true for the process according to the invention

can be taken into account.

The inventive method can also be carried out so that the

Interpolation method is used when calibrating the device type. In this case, the finished map can already be used in the specific Coriolis flow meter, e.g. be stored in a measuring device electronics unit or in an external unit.

The interpolation method used can also be a combination of individual interpolation methods, e.g. linear interpolation or interpolation with higher degree polynomials. Any suitable interpolation method can be used. An interpolation method in the context of the method according to the invention is to be understood as any method that is capable of one

Starting from the basic data set, generating a data field that is as fine as possible and, ideally, complete, with the aid of which the influence of the medium viscosity can be taken into account when measuring the flow parameters, in particular the mass flow rate. In particular, when using a Coriolis flow meter, the device type of which has been calibrated with a calibration medium that differs from the measuring medium, in particular water, a viscosity-related measurement deviation compared to the calibration medium can be determined and the correct flow parameter, in particular the mass flow, can be determined for each medium. The method according to the invention can be carried out in a particularly advantageous manner in that at least kriging is also used as the interpolation method.

Kriging, also known as Krigen, is a descendant of Danie Krige

Interpolation method, which is known in the prior art in connection with geostatistical methods and outside of geostatistics as Gaussian process regression. In geostatistics, stochastic methods are used

Characterization and estimation of data used, for example, to determine the distribution of surface temperatures in land areas or bodies of water. For this purpose, measured values are recorded at individual points in the area to be examined, which are then used as starting points for a spatial interpolation. Any number of estimated values can be determined from a finite number of measured values, which should represent reality as precisely as possible.

In the kriging method, spatial variance is taken into account in geostatistics, and semivariograms are used to determine this. The measured values used for the calculation are weighted in such a way that the estimation error variance is as low as possible, which is a good thing compared to other interpolation methods

is a particular advantage with regard to the accuracy of the estimate of the intermediate values. With kriging, in comparison to other interpolation methods, in particular also to higher-grade polynomials, a higher degree of accuracy can generally be achieved, particularly with a small number of data points, that is to say with a small basic data set. In contrast to alternative interpolation methods, however, the result of Kriging cannot be in a closed form, e.g. as a polynomial. Kriging is complex and usually uses inversion and multiplication of several matrices. Since kriging is therefore very computationally and memory-intensive, it should be avoided to use kriging to resolve a coarse basic data set as finely as desired. Rather, it can be for one in terms of time as well

Storage requirement-optimized procedure can be advantageous to get a refined matrix from the basic data set by means of kriging in a first stage, eg refined by a factor of 5, 10 or 100, and for a further refinement between the values obtained by means of kriging other, less complex ones

To use interpolation methods. The result of the less elaborate

Interpolation method can then again be in a closed form, e.g. linear.

The following is an exemplary embodiment of the invention

Procedure presented using figures.

1 shows again the table already listed in the introduction to the description with experimentally determined by measurements and / or simulation methods

percentage deviations of the measured uncorrected, i.e. based on a calibration of the measuring device with water, mass flow values in kg / h of actual mass flow values, which result when the

Medium viscosity (here in mPas) of the medium flowing through a Coriolis flowmeter of the calibrated measuring device type. The table thus shows a basic data set with a data volume for which measurements or

Simulation calculations still represent a reasonable expense.

A kriging method is now used as the interpolation method on the basic data set of the table according to FIG. On the basis of the relatively small number of output values, the data field is completed so that a data field with a significantly increased resolution is achieved, as is exemplified, for example, from the table in FIG. 2. There are several possibilities for the specific application of kriging to a basic data set, as shown in the table according to FIG. 1. The kriging process can in principle be programmed by the user himself. However, suitable kriging software can be purchased or is even available free of charge, including the source code. In particular, there is the option of integrating suitable additional functions in spreadsheet programs such as Microsoft Excel®, such as the XonGrid add-in, which at the time of filing this application under http://xongrid.sourceforge.net/ was available and among others

Interpolation methods also offered by kriging.

Finally, reference is also made to the comments on kriging in the publication “Optimal methods for the interpolation of environmental variables in geographic

Information systems "by P.A. Burrough in Geographica Helvetica 1990 no. 4, pp. 159-160.

The refined table according to FIG. 2 obtained by means of kriging also shows in the first column the mass flow rate in kg / h that would be measured with a Coriolis flow meter calibrated with water without taking the medium viscosity into account. This mass flow is referred to below as the calibration medium mass flow. The media viscosity in mPas is listed in the first line.

The following can be read from the data field as an example: If a calibration medium mass flow rate of 110,000 kg / h, i.e. 110 tons per hour, measured, this would mean an error of -0.6% with an actual medium viscosity of 600 mPas. This means that the actual measuring medium mass flow rate is 0.6% higher than the calibration medium mass flow rate, namely 110,000 kg / h * 1, 006 = 110,660 kg / h.

The data field can be further refined as required, e.g. by further application of the kriging method or preferably by less complex interpolation methods, such as linear interpolation or higher-grade

Polynomials.

Fig. 3 shows one from the table. Fig. 2 a developed characteristic diagram, as it can be used for a measurement taking into account the medium viscosity.

The characteristics map according to FIG. 3 or the table according to FIG. 2 can be stored in advance in a memory of a measuring device electronics of the Coriolis flow measuring device for further processing or for consideration in the evaluation. Alternatively, it is also possible to use the basic data set or a relatively rough one in the measuring device electronics Store data field and during or after the measurement the kriging method or other interpolation method, optionally also in combination, in the

Use evaluation software.

Claims

1. A method for determining a flow parameter of a medium, in particular a mass flow, by means of a Coriolis flow measuring device of a certain type of measuring device, in which

- the medium having a medium viscosity flows through at least one measuring tube piece which is excited to mechanical vibrations by means of an excitation signal,

- At least one measurement signal that is dependent on the flow parameter, in particular a phase shift, in the vibration behavior of the respective

Measuring tube piece, is determined and

- From the at least one measurement signal, the flow parameters below

Consideration of the dependence of the flow parameter on the

Medium viscosity is determined, with an interpolation method determined by means of an interpolation method, the dependence of the

Flow parameters of the medium viscosity indicating data field is used.

2. The method according to claim 1, characterized in that the

Interpolation method for determining a data field is applied to a basic data set determined experimentally and / or by simulation.

3. The method according to claim 1 or 2, characterized in that the interpolation method is used in the calibration of the device type.

4. The method according to claim 1 or 2, characterized in that the interpolation method is used in an evaluation during or after the determination of the at least one measurement signal.

5. The method according to any one of the preceding claims, characterized

characterized in that at least kriging is also used as the interpolation method.

6. Device for determining a flow parameter of a medium, in particular a mass flow, by means of a Coriolis flow measuring device, comprising

a) a measuring transducer, wherein the measuring transducer is a for the flow of a fluid

specific measuring tube, a vibration exciter for generating measurement signals in the form of mechanical vibrations on the measuring tube and vibration sensors for detecting the vibrations of the measuring tube, and

b) a measuring device electronics unit, the measuring device electronics unit being set up to be transmitted from the measuring transducer to the measuring device electronics unit

To determine a measured value for the desired flow parameter from measurement signals,

characterized in that

c) the measuring device electronics unit is set up, the method according to one of

Claims 1 to 5 to carry out.

7. The device according to claim 6, characterized in that the

The measuring device electronics unit has a data memory with a data field which shows the dependency of the flow parameter on the medium viscosity, the data field being generated using an interpolation method.

8. The device according to claim 6, characterized in that the

Interpolation method is a kriging method.