EP1692466A2

EP1692466A2 - Coriolis mass flowmeter

Info

Publication number: EP1692466A2
Application number: EP04804715A
Authority: EP
Inventors: Christian Matt; Alfred Wenger; Michael Fuchs; Wolfgang Drahm
Original assignee: Endress and Hauser Flowtec AG; Flowtec AG
Current assignee: Endress and Hauser Flowtec AG
Priority date: 2003-12-12
Filing date: 2004-12-07
Publication date: 2006-08-23
Also published as: RU2006124841A; WO2005057137A9; WO2005057131A9; CA2547699A1; RU2348012C2; CA2547697A1; WO2005057137A2; EP1692467A2; CA2547697C; WO2005057131A2; RU2339007C2; CA2547699C; RU2006124840A; WO2005057137A3; WO2005057131A3

Abstract

Disclosed is a Coriolis mass flowmeter/density meter comprising at least one measuring tube (11) through which a two-phase or multiphase medium flows during operation thereof. A supporting means (12) of the Coriolis mass flowmeter/density meter is fixed to an inlet end and an outlet end of the measuring tube (11), thus clamping the same so as to allow the measuring tube (11) to vibrate. The measuring tube (11) is made to vibrate mechanically, particularly to perform bending vibrations, by means of an excitation system (13). The inventive Coriolis mass flowmeter/density meter further comprises means (141, 142) for generating test signals (xs1, xs2 ) representing vibrations at the inlet end and outlet end of the measuring tube (11). An electronic evaluation unit (2) generates an intermediate value (X'm) that is derived from the test signals (xs1, xs2) and represents an uncorrected mass flow rate as well as a corrected value (XK) for the intermediate value (X m), said corrected value being derived from the test signals (xs1, xs2), especially from a measured value (X?) which is also generated in the electronic evaluation unit (2) and represents a density of the medium. The electronic evaluation unit (2) additionally generates a measured value (Xm) representing a mass flow rate with the aid of the intermediate value (X'm) and the corrected value (XK).

Description

Description Coriolis mass flow meter

The invention relates to a Coriolis mass flow / density meter for a medium flowing in a pipeline, in particular two or more phases, and a method for generating a measured value representing a mass flow.

In process measurement and automation technology for measuring physical parameters of a fluid flowing in a pipeline, such as. the mass flow rate, the density and / or the viscosity, often used such measuring devices, by means of a vibration-type transducer used in the course of the fluid-carrying pipeline, flowed through by the fluid during operation and a measuring and operating circuit connected to it, reaction forces in the fluid, such as eg Coriolis forces corresponding to the mass flow rate, inertia forces corresponding to the density or friction forces corresponding to the viscosity, etc., and derived from these, generate the respective mass flow rate, a measurement signal representing the respective viscosity and / or the respective density of the fluid. Such sensors of the vibration type are, for example. in WO-A (0076880, WO-A 02/37063, WO-A 01/33174, WO-A 00/57141, WO-A 99/39164, WO-A 98O7009, WO-A 9516897, WO-A 88O3261, US 2003 ^ 0208325, US-B 65 13 393, US-B 65 05 519, US-A 6006 609, US-A 58 69 770, US-A 57 96,011, US-A 56 02 346, US-A 53 01 557, US-A 52 18 873, US-A 50 69 074, US-A 48 76 898, US-A 47 33 569 , US-A 46 60421, US-A 45 24 610, US-A 44 91 025, US-A 41 87 721, EP-A 553 939, EP-A 1 001 254 or EP- A 1 281 938.

To guide the fluid, the transducers each comprise at least one measuring tube held in a, for example tubular or box-shaped, support frame with a curved or straight tube segment which vibrate to generate the above-mentioned reaction forces, driven by an electro-mechanical excitation arrangement, during operation is left. In order to detect vibrations of the pipe segment, particularly on the inlet and outlet sides, the measuring sensors furthermore each have a physical-electrical sensor arrangement that reacts to movements of the pipe segment. In Coriolis mass flow meters for a medium flowing in a pipeline, the measurement of the mass flow is based, for example, on the fact that the medium flows through the measuring tube which is inserted into the pipeline and vibrates during operation is allowed to flow, whereby the medium experiences Coriolis forces. These in turn cause the inlet-side and outlet-side regions of the measuring tube to oscillate out of phase with one another. The size of these phase shifts serves as a measure of mass flow. The vibrations of the measuring tube are therefore detected by means of two vibration sensors of the aforementioned sensor arrangement which are spaced apart from one another along the measuring tube and converted into vibration measuring signals from whose mutual phase shift the mass flow is derived.

The US-A 41 87 721 already mentioned at the beginning mentions that the instantaneous density of the flowing medium can usually also be measured with Coriolis mass flowmeters, specifically on the basis of a frequency of at least one of the vibration measurement signals supplied by the sensor arrangement. In addition, a temperature of the fluid to be measured is usually also measured directly in a suitable manner, for example by means of a temperature sensor arranged on the measuring tube. It can therefore be assumed without further ado that - even if not expressly described - the density and temperature of the medium are measured using modern Coriolis mass flowmeters, especially since they are always used to compensate for measurement errors due to fluctuating fluid density are to be consulted, cf. in particular the already mentioned WO-A 02/37063, WO-A 99/39164, US-A 56 02 346 or also WO-A 00/36379.

When using sensors of the type described, it has been found, however, that in the case of inhomogeneous media, in particular two-phase or multi-phase fluids, the vibration measurement signals derived from the vibrations of the measuring tube, in particular the phase shift mentioned, despite the viscosity and Density in the individual fluid phases as well as the mass flow rate are kept practically constant and / or are taken into account accordingly, are subject to considerable fluctuations and can therefore become completely unusable for the measurement of the respective physical parameter without remedial measures. Such inhomogeneous media can, for example, be liquids into which, as is practically unavoidable in metering or filling processes, a gas present in the pipeline, in particular air, is introduced or from which a dissolved fluid, e.g. Carbon dioxide, outgassing and leads to foam formation. Another example of such inhomogeneous media is wet or saturated steam.

Already in US-A 45 24 610 a possible cause of this problem for the operation of vibration type sensors is indicated, namely the fact that inhomogeneities entered by the fluid in the measuring tube, such as gas bubbles attach its inner wall and can influence the vibration behavior to a significant extent. In order to circumvent the problem, it is further proposed to install the measuring sensor in such a way that the straight measuring tube runs essentially vertically and thus prevents such disturbing, in particular gaseous, inhomogeneities from accumulating. However, this is a very special and, particularly in industrial process measurement technology, only very limitedly feasible solution. On the one hand, the pipeline into which the measuring sensor is to be inserted would have to be adapted to the latter, and not vice versa, which is probably not something that the user can get across. On the other hand, as already mentioned, the measuring tubes can also be those with a curved tube shape, so that the problem cannot be solved even by adapting the installation position. It has also been shown here that the aforementioned falsifications of the measurement signal cannot be significantly reduced even when using a vertically installed, straight measuring tube. In addition, the fluctuations of the measurement signal thus generated with flowing fluid cannot be prevented in this way either.

Similar causes as well as their effects on the measurement accuracy when determining the mass flow have also been discussed, for example, in JP-A 10-281846, WO-A 03O76880 or US-B 65 05,519. While a flow or fluid conditioning prior to the actual flow measurement is proposed in WO-A 03O76880 to reduce the measurement errors associated with two-phase or multi-phase fluids, both JP-A 10-281846 and US-B 65 05 519 a correction of the flow measurement based on the vibration measurement signals, in particular the mass flow measurement, is preferred, for example using previously trained, possibly also adaptive classifiers for the vibration measurement signals. The classifiers can be designed, for example, as a Kohonen map or neural network and the correction can be based either on a few parameters measured during operation, in particular the mass flow and density, and other features derived therefrom, or also using an interval of one or more oscillation periods Carry out vibration measurement signals.

The use of such a classifier has the advantage, for example, that compared to conventional Coriolis mass flow / density meters, no or only very slight changes are made to the sensor must, be it on the mechanical structure, on the excitation arrangement or the operating circuit controlling this, which are specially adapted to the special application.

[009] However, there is a considerable disadvantage of such classifiers, among others. in the fact that, compared to conventional Coriolis mass flow meters, considerable changes in the area of measured value generation are required, especially with regard to the analog-to-digital converter used and the microprocessors. As described in US-B 65 05 519, a sampling rate of about 55 kHz or more is necessary for sufficient accuracy for such a signal evaluation, for example when digitizing the vibration measurement signals, which may have a vibration frequency of about 80 Hz. In other words, the vibration measurement signals are to be sampled with a sampling ratio of well over 600: 1. In addition, the firmware stored and executed in the digital measuring circuit is correspondingly complex.

Another disadvantage of such classifiers can be seen in the fact that they train and accordingly on the measurement conditions actually prevailing in the operation of the sensor, be it the installation situation, the fluid to be measured and its mostly variable properties or other factors influencing the measurement accuracy must be validated. Due to the high complexity of the together. In the interplay of all these factors, the training and its validation can usually only be carried out individually on site and for each sensor, which in turn results in a considerable effort when the sensor is put into operation. In addition, it has also been shown that such classification algorithms, on the one hand due to the high level of complexity, and on the other hand as a result of the fact that a corresponding physical-mathematical model with technically relevant or comprehensible parameters is usually not explicitly available, classifiers have very little transparency and thus are often difficult to convey. In connection with this, considerable reservations can easily occur at the customer, whereby such acceptance problems can occur at the customer, in particular, if the classifier used is a self-adapting one, for example a neural network.

It is therefore an object of the invention to provide a corresponding Coriolis mass flow meter which measures the mass flow precisely even in the case of inhomogeneous, in particular multiphase, fluids. Another object is to specify a corresponding method for generating the measurement result.

To achieve this object, the invention consists in a Coriolis Mass flow meter, in particular Coriolis mass flow / density meter, for measuring a mass flow of a medium flowing in a pipeline, in particular a two-phase or multi-phase medium, which comprises Coriolis mass flow meter:

[013] at least one measuring tube inserted into the course of the pipeline and through which the medium flows during operation,

[014] a carrier means which is fixed to an inlet-side end and an outlet-side end of the measuring tube and thus clamps it so that it can vibrate,

An excitation arrangement which sets the measuring tube into mechanical vibrations, in particular bending vibrations, during operation,

Vibration sensors for generation

A first vibration measurement signal representing inlet-side vibrations of the measuring tube and

[018] A second vibration measurement signal representing outlet-side vibrations of the measuring tube, and

An evaluation electronics,

[020] which generates a first intermediate value derived from the vibration measurement signals, provisionally representing the mass flow to be measured and a correction value for the first intermediate value derived from the first intermediate value, and

[021] which uses the first intermediate value and the correction value to determine a mass flow measurement value which represents a mass flow to be measured,

Wherein the evaluation electronics generates the correction value using a second intermediate value derived from the first intermediate value, which represents a function value of a power function with the intermediate value as the basis and an exponent, especially a rational one, which is less than zero.

Furthermore, the invention consists in a method for generating a first measured value representing a mass flow of a medium flowing in a pipeline by means of a Coriolis mass flow meter, in particular a Coriolis mass flow / density meter, which method comprises the following steps:

Causing vibrations, in particular bending vibrations, of a measuring tube of the Coriolis mass flow meter through which the medium flows in order to generate Coriolis forces,

Detecting the vibrations of the measuring tube and generating a first measurement signal representing vibrations on the inlet side and a second measurement signal representing vibrations on the outlet side for developing a mass flow temporarily representing intermediate value and for developing a correction value for the intermediate value

[026] wherein, for generating the correction value, the second intermediate value is derived from the first intermediate value, which represents a function value of a power function with the intermediate value as the base and an exponential, especially a rational one, which is less than zero, and

Correcting the intermediate value using the correction value.

[028] According to a first embodiment of the Coriolis mass flow meter of the invention

The evaluation electronics supplies a density measurement value, which is derived from the first and / or from the second vibration measurement signal and represents a density of the medium

The evaluation electronics also determine the correction value by means of the density measured value.

According to a second embodiment of the Coriolis mass flow meter of the invention, the evaluation electronics determine a deviation of the density of the medium from a predetermined reference density by means of the density measured value.

According to a third embodiment of the Coriolis mass flow meter of the invention, the evaluation electronics have a table memory in which digitized correction values dependent on the second intermediate value are stored, and the table memory supplies the correction value by means of a digital memory access address formed on the basis of the second intermediate value.

According to a first embodiment of the method of the invention, this comprises the following further steps:

Developing a second measured value representing a density of the medium on the basis of the measured signals and

Develop a correction value using the second measurement value.

An advantage of the invention is that in the Coriolis mass flow meter according to the invention, compared to a conventional Coriolis mass flow meter, only minor changes, essentially limited to the firmware, have to be made only in the usually digital evaluation electronics, while both in the sensor as in the generation and preprocessing of the vibration measurement signals, no or only minor changes are required. For example, the vibration measurement signals can still be sampled with a usual sampling ratio of well below 100: 1, especially about 10: 1. The invention and further advantageous refinements will now be explained in more detail with reference to exemplary embodiments which are shown in the figures of the drawing. Identical parts are provided with the same reference symbols in all figures; if clarity requires, reference numerals already mentioned are omitted in the following figures.

1 shows a perspective view of a Coriolis mass flow measuring device used to generate a mass flow measured value,

2 schematically shows, in the manner of a block diagram, a preferred embodiment of a measuring device electronics suitable for the Coriolis mass flow measuring device from FIG. 1, [039] FIG.

3 shows a perspective view in a first side view of an exemplary embodiment of a vibration-type measuring sensor suitable for the Coriolis mass flow meter of FIG. 1,

[041] FIG. 4 shows the sensor of FIG. 3 in perspective in a second side view and

5 shows an exemplary embodiment of an electro-mechanical excitation arrangement for the sensor of FIG. 3.

1 is a perspective view of a Coriolis mass flow meter 1, which is used to record a mass flow m of a medium flowing in a pipeline and to map it into a mass flow measurement value X that currently represents this mass flow; the pipeline is not shown for reasons of clarity. The medium can be practically any fluid substance, for example liquids, gases or vapors. For this purpose, the Coriolis mass flow measuring device 1 comprises a measuring sensor 10 of the vibration type and, as shown in FIG. 2, measuring device electronics 50 electrically connected to the measuring sensor 10. To accommodate the measuring device electronics 50, there is also an external sensor 10 attached electronics housing 200 provided. To detect the mass flow m, Coriolis forces are generated in the fluid flowing through by the measuring sensor 10, which is excited by the measuring device electronics 50 during operation, which are dependent on the mass flow m and which are measurable on the measuring sensor 10, that is to say they can be sensed and electronically evaluated , act back. In addition to generating the mass flow measurement value X, the Coriolis mass flow measurement device is also used to measure a density of the flowing medium and to determine a density measurement value X currently representing the density §. Preferably, the measuring device electronics 50 is also designed such that it operates a data processing unit, for example a programmable logic controller (PLC), a personal computer and / or a workstation, via data transmission system during operation of the Coriolis mass flow measuring device 1 , for example a fieldbus system, can exchange measurement and / or other operating data. Furthermore, the measuring device electronics 50 is designed in such a way that it can be supplied by an external energy supply, for example also via the aforementioned fieldbus system. In the event that the vibration measuring device is provided for coupling to a fieldbus, the measuring device electronics 50, in particular programmable, has a corresponding communication interface for data communication, for example. to send the measurement data to a higher-level programmable logic controller or a higher-level process control system.

3 and 4 show an exemplary embodiment of a physical-electrical transducer arrangement of the vibration type serving as a measuring sensor 10. The structure and the mode of operation of such a converter arrangement are known per se to the person skilled in the art and, for example. also described in detail in US-A 60 06 609.

[047] For guiding the fluid to be measured, the measuring sensor 10 comprises at least one measuring tube 13 having an inlet end 11 and an outlet end 12 of predeterminable measuring tube lumen 13A which is elastically deformable in operation and of a predeterminable nominal diameter. Elastic deformation of the measuring tube lumen 13A means here that in order to generate internal fluid forces and thus describing the fluid, a spatial shape and / or a spatial position of the measuring tube lumen 13A is changed cyclically, in particular periodically, within a range of elasticity of the measuring tube 13, cf. , for example US-A 48 01 897, US-A 5648 616, US-A 57 96 011 and / or US-A 60 06 609. It should also be expressly pointed out at this point that although the sensor in Embodiment includes only a single, straight measuring tube, practically any of the Corioils mass flow rate measuring sensors described in the prior art can be used to implement the invention instead of such a vibration-type measuring sensor, especially one of the bending vibration type with only or at least partially in a bending mode vibrating, curved or straight measuring tube. Particularly suitable are, for example, vibration-type sensors with two curved measuring tubes through which the medium to be measured flows in parallel, as they do for example, are also described in detail in EP-A 1 154243, US-A 53 01 557, US-A 57 96 011, US-B 65 05 519 or WO-A 02/37063. Further suitable embodiments for such transducer arrangements serving as measuring sensors 10 are, for example. WO-A 02/099363, WO-A 02/086426, WO-A 95T6 897, US-A 56 02 345, US-A 55 57 973 or US-A 53 57 811. The material for the measuring tube 13 used is, for example. Titanium alloys particularly suitable. Instead of titanium alloys, other materials commonly used for such, in particular also for curved, measuring tubes, such as, for example,. stainless steel, tantalum or zirconium etc. can be used.

The measuring tube 13, which communicates in the usual manner on the inlet side and the outlet side with the pipeline supplying or discharging the fluid, is clamped in a rigid, in particular flexurally and torsionally rigid, support frame 14 so that it can vibrate , Instead of the box-shaped support frame 14 shown here, of course, other suitable carrier means, such as. Pipes running parallel or coaxial to the measuring tube can be used.

The support frame 14 is fixed to the measuring tube 13 on the inlet side by means of an inlet plate 213 and from the slave side by means of an outlet plate 223, both of which are pierced by corresponding extension pieces of the measuring tube 13. Furthermore, the support frame 14 has a first side plate 24 and a second side plate 34, which two side plates 24, 34 are each fixed to the inlet plate 213 and to the outlet plate 223 such that they run practically parallel to and from the measuring tube 13 and from one another are arranged at a distance, cf. Fig. 3. Thus, facing side surfaces of the two side plates 24, 34 are also parallel to each other. A longitudinal rod 25 is fixed to the side plates 24, 34, spaced apart from the measuring tube 13, which serves as a balancing mass which counteracts the vibrations of the measuring tube 13. The longitudinal rod 25 extends, as shown in FIG. 4, practically parallel to the entire oscillatable length of the measuring tube 13; however, this is not mandatory, the longitudinal bar 25 can of course also be made shorter, if necessary. The support frame 14 with the two side plates 24, 34, the inlet plate 213, the outlet plate 223 and the longitudinal rod 25 thus has a longitudinal center line that runs practically parallel to a measuring tube central axis 13B virtually connecting the inlet end 11 and the outlet end 12.

3 and 4 is indicated by the heads of the drawn screws, I that the aforementioned fixing of the side plates 24, 34 to the inlet plate 213, to the outlet plate 223 and to the longitudinal rod 25 can be done by screwing; it can however, other suitable types of fastening known to those skilled in the art can also be used.

In the event that the sensor 10 is to be detachably mounted with the pipeline, the measuring tube 13 has a first flange 19 formed on the inlet side and a second flange 20 on the outlet side, cf. Fig. 1; instead of the flanges 19, 20, for example. other pipe connection pieces for detachable connection to the pipe may be formed, such as. the so-called triclamp connections indicated in FIG. 3. If necessary, the measuring tube 13 can also be connected directly to the pipeline, for example. be connected by means of welding or brazing etc.

To generate the Coriolis forces mentioned, the measuring tube 13 is vibrated in the so-called useful mode during operation of the measuring sensor 10, driven by an electro-mechanical excitation arrangement 16 coupled to the measuring tube, at a predefinable oscillation frequency, in particular a natural resonance frequency can be predetermined elastically deformed, the natural resonance frequency also being dependent on a density of the fluid. In the exemplary embodiment shown, the vibrating measuring tube 13 is spatially, in particular laterally, deflected from a static idle position, as is customary in such transducer arrangements of the bending vibration type. The same applies in practice to those transducer arrangements in which one or more curved measuring tubes perform cantilever vibrations around a corresponding longitudinal axis that connects the respective inlet and outlet ends, or to those transducer arrangements in which one or more straight measuring tubes merely have bending vibrations in a single oscillation - Execution level.

The excitation arrangement 16 is used to generate an excitation force F acting on the measuring tube 13 exe by converting an electrical excitation power P fed in by the measuring device electronics 50. The excitation power P serves practically exe exe only to compensate for the power component extracted from the vibration system via mechanical and fluid-internal friction. To achieve the highest possible efficiency, the excitation power P is set as precisely as possible so that exe practically the vibrations of the measuring tube 13 in the useful mode, for example. that of a fundamental resonance frequency are maintained. For the purpose of transmitting the excitation force F to the measuring tube 13, the exe excitation arrangement 16, as shown in FIG. 5, has a rigid, electromagnetically and / or electrodynamically driven lever arrangement 15 with a boom 154 fixed to the measuring tube 13 and with it a yoke 163. The yoke 163 is on an end of the arm 154 spaced from the measuring tube 13 is also fixed in a manner that is resistant to bending, in such a way that it is arranged above the measuring tube 13 and transversely to it. As a boom 154, for example. serve a metallic disc, which receives the measuring tube 13 in a bore. For further suitable designs of the lever arrangement 15, reference is made to the already mentioned US-A 6006 609. The lever arrangement 15 is T-shaped and arranged, see. Fig. 5 that it acts approximately in the middle between inlet and outlet ends 11, 12 on the measuring tube 13, whereby this experiences its greatest lateral deflection in the middle in operation.

5 comprises a first excitation coil 26 and an associated first permanent magnetic armature 27 and a second excitation coil 36 and an associated second permanent magnetic armature 37. The two excitation coils, which are preferably connected electrically in series, for driving the lever arrangement 15 26, 36 are on both sides of the measuring tube 13 below the yoke 163 on the support frame 14, in particular releasably, fixed so that they interact with their associated armature 27 and 37 during operation. If necessary, the two excitation coils 26, 36 can of course also be connected in parallel with one another. As shown in FIGS. 3 and 5, the two armatures 27, 37 are fixed to the yoke 163 so that they are spaced apart from one another in such a way that during operation of the sensor 10 the armature 27 is practically from a magnetic field of the excitation coil 26 and the armature 37 is practically from a magnetic field Exciter coil 36 passes through and is moved due to corresponding electrodynamic and / or electromagnetic force effects. The movements of the armatures 27, 37 generated by the magnetic fields of the excitation coils 26, 36 are transmitted from the yoke 163 and from the arm 154 to the measuring tube 13. These movements of the armatures 27, 37 are designed such that the yoke 163 is alternately deflected from its rest position in the direction of the side plate 24 or in the direction of the side plate 34. A corresponding axis of rotation of the lever arrangement 15 parallel to the already mentioned measuring tube center axis 13B can, for example. through the boom 154.

[056] The support frame 14 further comprises a holder 29 for the electromechanical excitation arrangement 16, in particular detachably connected to the side plates 24, 34, in particular for holding the excitation coils 26, 36 and possibly individual components of a magnetic brake arrangement 217 mentioned below.

[057] Finally, the sensor 1 has a sensor housing 100 surrounding the measuring tube and support frame, which protects them from harmful environmental influences. The sensor housing 100 is with a neck-like transition piece provided, on which the electronics housing 200 housing the measuring device electronics 50 is fixed, cf. Fig. 1.

[058] In the measuring sensor 10 of the exemplary embodiment, the lateral deflections of the vibrating measuring tube 13 firmly clamped at the inlet end 11 and at the outlet end 12 simultaneously cause an elastic deformation of its measuring tube lumen 13A, which is practically formed over the entire length of the measuring tube 13. Furthermore, due to a torque acting on the lever arrangement 15 at the same time as the lateral deflections, a rotation about the central axis 13B of the measuring tube is forced in the measuring tube 13, so that the measuring tube 13 practically oscillates in a mixed bending vibration torsion mode serving as a useful mode. The rotation of the measuring tube 13 can be designed such that a lateral deflection of the end of the arm 154 spaced from the measuring tube 13 is either the same as or opposite to the lateral deflection of the measuring tube 13. The measuring tube 13 can thus execute torsional vibrations in a first bending vibration torsion mode corresponding to the same direction or in a second bending vibration torsion mode corresponding to the opposite direction. Then, in the case of the sensor 10 according to the exemplary embodiment, the natural fundamental resonance frequency of the second bending vibration torsion mode is, for example. 900 Hz almost twice as high as that of the first bending vibration torsion mode.

[059] In the event that the measuring tube 13 is to perform operational vibrations only in the second bending vibration torsion mode, a magnetic brake arrangement 217 based on the eddy current principle is integrated in the excitation arrangement 16, which serves to stabilize the position of the mentioned axis of rotation. By means of the magnetic brake arrangement 217, it can thus be ensured that the measuring tube 13 always vibrates in the second bending vibration torsion mode and thus any external disturbing influences on the measuring tube 13 do not lead to a spontaneous change to another, especially not to the first, bending vibration torsion mode. Details of such a magnetic brake arrangement are described in detail in US-A 60 06 609.

At this point, it should also be mentioned that in the measuring tube 13 deflected in this way in accordance with the second bending vibration torsion mode, the imaginary central axis 13B of the measuring tube is slightly deformed and thus spans not a plane but a slightly curved surface during the vibrations. In addition, a surface lying in this area, from the center of the measuring tube central axis recorded trajectory the smallest curvature of all trajectory described by the measuring tube center axis.

[061] In order to detect the deformations of the measuring tube 13, the measuring sensor 10 further comprises a sensor arrangement 60 which, by means of at least one first sensor 17 which reacts to vibrations of the measuring tube 13, generates a first, in particular analog, vibration measurement signal sl which represents it. The sensor 17 can, for example. be formed by means of a permanent magnetic armature, which is fixed to the measuring tube 13 and interacts with a sensor coil held by the support frame 14. Particularly suitable as sensors 17 are those which, based on the electrodynamic principle, detect a speed of the deflections of the measuring tube 13. However, it is also possible to use acceleration-measuring electrodynamic or also path-measuring resistive or optical sensors. Of course, other sensors known to the person skilled in the art and suitable for the detection of such vibrations can also be used. The sensor arrangement 60 further comprises a second sensor 18, in particular identical to the first sensor 17, by means of which it supplies a second vibration measurement signal s2, which also represents vibrations of the measuring tube 13. In this embodiment, the two sensors 17, 18 are spaced apart from one another along the measuring tube 13, in particular at an equal distance from the center of the measuring tube 13, in such a way that by means of the sensor arrangement 60 both the inlet side and the outlet side side vibrations of the measuring tube 13 are recorded locally and mapped into the corresponding vibration measurement signals sl or s2. The first and possibly the second vibration measurement signal sl or s2, which usually each have a signal frequency corresponding to an instantaneous vibration frequency of the measuring tube 13, are fed to the measuring device electronics 50, as shown in FIG. 2.

To make the measuring tube 13 vibrate, the excitation arrangement 16 is fed by means of a likewise oscillating excitation current i of adjustable amplitude and excitation frequency f that can be set in such a way that the excitation coils 26, 36 flow through them in operation exe and in a corresponding manner required to move the armature 27, 37 magnetic fields are generated. The excitation current i can exe, for example. be sinusoidal or rectangular. The excitation frequency f of the excitation current exe i is preferably selected and set so exe in the measuring sensor shown in the exemplary embodiment that the laterally oscillating measuring tube 13 oscillates as exclusively as possible in the second bending vibration torsion mode. [063] To generate and adjust the excitation current i, the measuring device comprises Electronics 50 a corresponding driver circuit 53, which is controlled by a frequency control signal y representing the excitation frequency f to be set and by an exe FM the amplitude exc control signal y representing the amplitude of the excitation current i to be set. The driver circuit can, for example. be realized by means of a voltage-controlled AM oscillator and a downstream voltage-to-current converter; instead of an analog oscillator, for example. a numerically controlled digital oscillator for setting the excitation current i can also be used exe. [064] For generating the amplitude control signal y, for example. an amplitude control circuit 51 integrated in the measuring device AM electronics 50 serves to update the amplitude control signal y on the basis of the instantaneous amplitude of at least one of the two sensor signals s, s and on the basis of a corresponding constant or variable amplitude reference value W; if necessary, a momentary amplitude of the excitation current i can also be used to generate the amplitude control signal y. exe AM Such amplitude control circuits are also known to the person skilled in the art. As an example of such an amplitude control circuit, reference is again made to Coriolis mass flow meters of the "PROMASS I" series. Their amplitude control circuit is preferably designed so that the lateral vibrations of the measuring tube 13 to a constant, that is, from. ?.

Density, β, independent, amplitude can be controlled.

[066] Furthermore, the frequency control signal y can be supplied by a corresponding frequency FM control circuit 52 which, for example. on the basis of at least the sensor signal s and on the basis of a frequency-representative direct voltage serving as a corresponding frequency reference value W 1 2. The frequency control circuit 52 and the driver circuit 53 are preferably connected to form a phase control loop, which is used in the manner known to the person skilled in the art to use a phase difference, measured between at least one of the sensor signals s, s and the one to be set or the measured one Er- 1 2 excitation current i, constantly adjust the frequency control signal y to a momentary resonance FM frequency of the measuring tube 13. The construction and use of such phase locked loops for operating measuring tubes at one of their mechanical resonance frequencies is, for example. described in detail in US-A 48 01 897. Of course, other frequency control circuits known to those skilled in the art can also be used, such as. are also described in US-A 45 24 610 or US-A 48 01 897. Furthermore, regarding the use of such frequency control Circuits for sensors of the type described refer to the "PROMASS I" series already mentioned. Further circuits suitable as driver circuits can also be found, for example, in US Pat. No. 5,869,770 or also in US Pat. No. 5,505,519.

According to a further embodiment of the invention, the amplitude control circuit 51 and the frequency control circuit 52 are realized by means of a digital signal processor DSP provided in the measuring device electronics 50 and by means of program codes implemented accordingly and running therein. The program codes can, for example. be stored persistently or permanently in a non-volatile memory EEPROM of a microcomputer 55 which controls and / or monitors the signal processor and, when the signal processor DSP is started, in a, eg. volatile data memory RAM of the measuring device electronics 50 integrated in the signal processor DSP can be loaded. Suitable signal processors for such applications are, for example. those of the type TMS320VC33, such as those offered by Texas Instruments Inc. on the market.

[069] It is practically self-evident that at least the sensor signal s and possibly also the sensor signal s convert into corresponding digital signals for processing in the signal processor DSP by means of corresponding analog-to-digital converters A / D. are to be converted, cf. see EP-A 866 319 in particular. If necessary, control signals are output by the signal processor, such as, for example. convert the amplitude control signal y or AM the frequency control signal y, if necessary in a corresponding manner digital-to-analog to FM. [070] As shown in FIG. 2, the vibration measurement signals x, x are also fed to a measurement sl s2 circuit 21 of the measurement device electronics. The measuring circuit 21 serves to determine a measured value corresponding to the mass flow to be measured in the manner known per se to the person skilled in the art on the basis of a phase difference detected between the two, possibly suitably conditioned, vibration measurement signals x, x de- sl2. Conventional, especially digital, measuring circuits can be used as the measuring circuit 21 for this purpose, which determine the mass flow on the basis of the vibration measuring signals x, x, cf. in this regard in particular the aforementioned WO-A 02/37063, WO-A 99/39164, US-A 5648 616, US-A 50 69 074. Of course, other Coriolis mass flow-through known to those skilled in the art Suitable measuring circuits are used for measuring devices, which measure phase and / or time differences between the vibration measurement signals x, x and evaluate them accordingly. The measuring circuit 21 can also advantageously be realized by means of the signal processor DSP. As already mentioned at the beginning, inhomogeneities in the flowing medium, for example gas bubbles entrained in liquids or foam layers formed, can lead to the fact that the measured value determined in a conventional manner, assuming a homogeneous medium, does not yet match the actual mass flow rate sufficiently precisely, ie it must be corrected accordingly; This previously determined measured value, which temporarily represents the mass flow, is therefore referred to as a first intermediate value X ', from which the mass flow measured value X, which represents the mass flow sufficiently sufficiently, is in turn derived from m. m

[072] It has already been discussed in the prior art that such inhomogeneities, due to the measuring principle, result primarily in a change in the density measured by the flowing medium. Further investigations by the inventors, however, led to the surprising finding that the correction of the intermediate value X ', contrary to what is stated in the prior art, can be carried out on the one hand using fewer, very easy-to-determine correction factors, which can be directly determined by the operator measured parameters, in particular the measured density and the provisionally measured mass flow rate, can be derived. On the other hand, the correction can be carried out using the predetermined density measured value X§ and the predetermined intermediate value X 'with a computational effort that is very small in comparison to the rather complex computing methods mentioned at the beginning. [073] For precise measurement of the mass flow, a corresponding correction value X is derived from the intermediate value X by means of the evaluation electronics 2 and the mass flow measurement value X is calculated using the correction value X to m K, the intermediate value X ', especially digitally. For example, the correction can be carried out in a simple manner based on the functional equation [074] [which is the coded mathematical formula] (1)

[075] take place.

[076] According to the invention, the evaluation electronics derive a second intermediate value X from the intermediate value X 'm, which purifies a functional value of a power function, X' 2 m ⁿ , with the intermediate value X 'as the basis and an, especially rational, exponent n presented that is less than zero, ie the second intermediate value X should have the functional relationship: X = KJX "with n <0 (2) 2 K m

[078], where K is an adaptation or scaling of the coefficient of the intermediate value X K 2, which is determined in advance, for example individually when calibrating the Coriolis mass flow meter 1 or also device-specific, and, for example. in the non-volatile memory EEPROM, can be stored digitally. According to one embodiment of the invention, the exponent n is greater than -1, for example. -0.5 or -0.25. According to a further development of the invention, the evaluation electronics are used to store the measured density value X§ and a previously determined or timely measured reference density value K§, which is stored, for example, as a constant value when the Coriolis mass flow meter is put into operation or in Operation from external, to which Coriolis mass flow meter can be transmitted, a deviation 0 § of the density _ \ of the medium from a predetermined reference density is determined. To generate the correction value X, the deviation 0 K determined in this way becomes the second intermediate value X based on the functional equation

X = H B X (3) K 2

[081] offset.

Knowing the fluid to be measured, the reference density value K @ can be entered manually, for example on site or from a remote control room, or sent from an external density meter to the measuring device electronics, for example via fieldbus.

According to one embodiment of the invention, the reference density value K _ is determined using a density measurement value XH likewise stored in the measuring device electronics, the stored density measurement value Xi representing a density, o, o of the medium, which at homogeneous medium or when medium is assumed to be homogeneous. According to a further development of this embodiment of the invention, the measured density value X§ stored as the reference density value Kß is used for the subsequent correction of an intermediate value X ′ previously determined in the case of an inhomogeneous medium. This embodiment of the invention can, for example, in a particularly advantageous manner. be used in a metering or filling process in which flow conditions in the measuring tube differ considerably from one another within a batch in a short time sequence, in particular also when the measuring tube is not completely filled, and in which on the other hand primarily the totalized over an entire batch mass flow, ultimately the total mass of the bottled is of interest. [084] Using Eq. (2) Eq. (3) the correction value (X) in a simple K manner based on the functional equation [085] [the encoded mathematical formula is] (4)

[086] can be determined.

[087] The aforementioned m functions, which serve to generate the mass flow measurement value X, symbolized by Eq. (1) to (4) can be at least partially implemented in an evaluation stage 54 of the measuring device electronics 50. The evaluation stage 54 can, for example, advantageously. also by means of the signal processor DSP or, for example. can also be realized by means of the above-mentioned microcomputer 55. The creation and implementation of corresponding algorithms which correspond to the previously described equations or which simulate the functioning of the amplitude control circuit 51 or the frequency control circuit 52, as well as their translation into program codes which can be executed in such signal processors is known per se to the person skilled in the art and therefore requires no detailed explanation. Of course, the aforementioned equations can also be easily or completely represented in the measuring device electronics 50 by means of corresponding, discretely constructed, analog and / or digital computing circuits. According to a further embodiment of the invention, the evaluation electronics 2 furthermore have a table memory in which a set of digital correction values X previously determined, for example during the calibration of the Coriolis mass flow rate measuring device, is stored. These correction values X are accessed via a memory address derived by means of the second intermediate value X currently valid K, ι K, ι. The correction value X can, for example. can be determined in a simple manner by comparing the K currently determined intermediate value X with corresponding preset values for the intermediate value X entered in the table memory and then reading out that correction value X which corresponds to the intermediate value X closest to the K, ι 2 coming preset value. A programmable read-only memory, ie an EPROM or an EEPROM, can serve as the table memory. The use of such a table storage has among other things the advantage that the correction value X is very quickly available for K 2 after the calculation of the intermediate value X at runtime. In addition, the correction values X entered in the table memory can be very precisely beforehand using a few calibration measurements, for example. κ, ι based on Eq. (2) and using the least squares method.

Claims

Expectations

1. Coriolis mass flow meter, esp. Coriolis mass flow meter / density meter, for measuring a mass flow of a medium flowing in a pipeline, in particular two or more phases, which comprises Coriolis mass flow meter:

- at least one measuring tube (11) inserted into the course of the pipeline and through which the medium flows during operation,

[003] a carrier means (12) which is fixed at an inlet-side end and an outlet-side end of the measuring tube (11) and thus clamps it so that it can vibrate,

An exciter arrangement (13) which sets the measuring tube (11) in operation in mechanical vibrations, in particular bending vibrations,

- Vibration sensors (141, 142) for generating

[006] ~ an inlet-side vibration of the measuring tube (11) representing the first vibration measurement signal (x) and sl

A second vibration measurement signal (x) representing outlet-side vibrations of the measuring tube (11), and s2

[008] - an evaluation electronics (2),

- The one derived from the Schwirigungsmeßsignalen (x, x), a preliminary to the sl s2 mass flow to be measured representing first intermediate value (X ') and a derived from the first intermediate value (X') correction value mm (X) for the first Intermediate value (X ') generated, and K m

[010] - which uses the first intermediate value (X ') and the correction value (X) to determine an m K mass flow measurement value (X) which represents a mass flow to be measured, [011] - the evaluation electronics determining the correction value (X) using K generates a second intermediate value (X) m 2 derived from the first intermediate value (X '), which has a function value of a power function, X' ⁿ , with the interwoven value (X ') as the basis and a, especially rational , Pure exponent (s) that is less than zero. 2. Coriolis mass flow meter according to Claim 1,

[013] - in which the evaluation electronics (2) provide a density measurement value (X§) derived from the first and / or from the second vibration measurement signal (x, x) and representing a density of the medium s2 and - In which the evaluation electronics (2) also determines the correction value (X) by means of the K density measurement value (X). 3. Coriolis mass flow meter according to the preceding claim, wherein the evaluation electronics (2) by means of the density measurement value (X) determines a deviation (0 β) of the density of the medium from a predetermined reference density and the correction value (X ) based on the functional equation K

[The encoded mathematical formula is]

Determined.

4. Coriolis mass flow meter according to the previous Anspmch, in which the evaluation electronics (2) the correction value (X) based on a polynomial K

[The encoded mathematic formula is]

Determined.

5. Coriolis mass flow meter according to one of the preceding claims, in which the evaluation electronics (2) determine the mass flow measurement value (X) based on the function equation [022] [is the coded mathematical formula]

Determined.

6 Coriolis mass flow meter according to one of the preceding claims, in which the evaluation electronics (2) have a table memory in which digitized correction values dependent on the second intermediate value (X) are stored, the table memory containing the correction value (X) by means of a digital memory access address formed on the basis of the second intermediate value (X). 7. A method for generating a first measured value (X) m representing a mass flow of a medium flowing in a pipeline by means of a Coriolis mass flow meter, in particular a Coriolis mass flow / density meter, which method comprises the following steps:

Causing vibrations, in particular bending vibrations, of a measuring tube (11) of the Coriolis mass flow meter through which the medium flows, for generating Coriolis forces,

- Detecting the vibrations of the measuring tube (11) and generating a first measuring signal (x) representing vibrations on the inlet side and a second measuring signal (x) representing vibrations on the outlet side for s2 developing an intermediate value (X ') temporarily representing the mass flow and for developing a correction value (X) for the thread K sword value (X ') m

[028] ~ whereby for generating the correction value (X) is derived from the first intermediate value (X ') m the second intermediate value (X), which is a function value of a power function, X' ", with the intermediate value (X ') as the basis and represents a, especially mm rational, exponent (n) which is less than zero, and [029] - correcting the intermediate value (X ') by means of the correction value (X) m K

8 A method according to claim 6, comprising the following further steps:

- Developing a second measured value (Xß) representing a density of the medium on the basis of the measured signals (x, x) and sl s2

- Development of a correction value (X) using the second measured value (X§).

[033]