JP2008145444A - Vibration measuring device and method for measuring viscosity of fluid led inside pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibration measuring device for measuring the viscosity of a fluid, led inside a pipe which is constituted, at the same time, as being suited also for the measurement of mass flow rate and the density of the fluid, and to make the accuracy of viscosity measurements improved by means of a Coriolis mass flowmeter-densitometer. <P>SOLUTION: The vibration measuring device includes a flow tube, having a lumen conducting a fluid which is clamped at an inlet end and an outlet end that can vibrate and which vibrates about a static position of rest, during operation to perform lateral deflections that cause periodic changes in the spatial position of the lumen. A sensor device forms a first sensor signal, representative of the inlet-side deflections of the flow tube, and a second sensor signal that indicates the outlet-side deflections of the flow tube; an excitation circuit forms exciting current, feeding an excitation arrangement. An evaluation circuit derives a density measured value that indicates the density of the fluid and derives a viscosity value that indicates the viscosity of the fluid, from at least one sensor signal and from the density measured value, on the basis of the excitation current. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vibration measuring device and a method for measuring the viscosity of a fluid guided in a pipe line.

  The Coriolis mass flow / density measuring device is preferably used to measure the mass flow and / or the density of the fluid guided in the conduit with high accuracy.

  The flexural vibration type Coriolis mass flow rate / density measuring device is a vibration measuring device as is well known, and this measuring device is designed to introduce fluid into at least one measuring tube inserted in a liquid-tight manner, in particular pressure-tight, into a pipe line. Have for. The measuring tube vibrates around a stationary state in multimode, in particular in bimode, with at least one frequency in the measuring operation. For this purpose, the measuring tube is excited by an electromechanical excitation device, usually in the first flexural vibration mode, as follows. That is, the Coriolis force is excited so as to be formed in the flowing fluid. When the measurement tube is linear, for example, the basic vibration mode of a flexible bar stretched with both sides fixed can be used as the first flexural vibration mode. This flexure bar has a single vibrating bell as is known. In particular, in a measurement tube curved in a U shape or Ω shape, the fundamental vibration mode of a bar stretched on one side is normally excited as the first flexural vibration mode.

  In this type of vibration type measuring apparatus, the second vibration mode is simultaneously excited based on the Coriolis force acting on the fluid fluid by the first flexural vibration mode. The amplitude of this second vibration mode also depends on the mass flow rate.

  In order to detect the mass flow rate, the vibration of the measuring tube at the inlet end and the vibration of the measuring tube at the outlet end are detected by corresponding sensor devices, and a first sensor signal representing the inlet vibration, It is converted into a second sensor signal representing the exit side vibration.

  Both detected vibrations have a second vibration mode superimposed on the first flexural vibration mode. This second vibration mode is a similar flexural vibration mode here, but out of phase with each other. This phase shift can accordingly be measured between the two sensor signals, and this phase shift is used as a measured quantity representing the mass flow rate in the Coriolis mass flow / density measuring device.

  In a Coriolis mass flow / density measuring device, the resonance frequency and / or the amplitude of the first flexural vibration mode usually depend measurable on the density of the fluid. Therefore, if the measurement tube is always excited at the resonance frequency of the first flexural vibration mode, this is a measure for the instantaneous density of the fluid.

  Vibrating measuring devices of the above-mentioned type, in particular Coriolis mass flow / density measuring devices, already belong to the prior art, and are described in US-A 4187721, US-A4801897, US-A4876879, US-A5648616, US-A5687100, US-A5796011, U.S. Pat. No. 6,006,609 and EP-A 866 319 describe a vibratory measuring device for measuring the mass flow rate and density of a fluid guided in a conduit. The vibration type measuring device includes a measurement value detector and a measurement device electronic circuit, and the measurement value detector includes at least one measurement tube inserted in a pipeline, an electromechanical excitation device, and a measurement tube. The measuring device electronic circuit has an excitation circuit and an evaluation circuit, and the measuring tube is oscillatingly stretched between the inlet end and the outlet end. And the measuring tube is vibrated relative to a stationary state by an adjustable excitation frequency in operation, the electromechanical excitation device spatially deflects the measuring tube and simultaneously The sensor device is elastically deformed to form a first sensor signal representing an inlet side deflection of the measuring tube and a second sensor signal representing an outlet side deflection of the measuring tube, and the excitation circuit includes the excitation circuit Forming the excitation current supplied to the excitation device The evaluation circuit transmits a mass flow rate value representing the mass flow rate of the fluid using the first sensor signal and a second sensor signal, and a density value representing the density of the fluid.

  Another physical parameter that is important for representing a flowing fluid is viscosity. Here, it is possible to distinguish between kinematic and dynamic as is well known.

Viscosity and density measurement for flowing fluids Vibration measuring devices also belong to the prior art. For example, U.S. Pat. No. 4,524,610 describes a vibration measuring device for measuring the viscosity of a fluid led to a conduit, which has a measurement value detector and a measuring device electronic circuit. ,
The measurement value detector includes a linear measurement tube inserted in a pipe line, an electromechanical excitation device, and a sensor device that responds to torsion of the measurement tube, and the measurement device electronic circuit is an excitation circuit. And the evaluation circuit, the measurement tube has a measurement tube lumen for guiding the fluid, and is stretched so as to vibrate between the inlet end and the outlet end, and the electromechanical excitation device includes: Forming a lateral deflection and / or torsion in the measuring tube, the sensor device forming a sensor signal representing the average torsion of the measuring tube, and the excitation circuit forming an excitation current supplied to the excitation device The evaluation circuit uses the sensor signal and the excitation current to form a viscosity measurement value representing the viscosity of the fluid.

  In this vibratory measuring device used as a density / viscosity measuring device, the measuring tube is alternately vibrated for density detection in the first flexural vibration mode described above, and for viscosity detection in the torsional vibration mode. Or simultaneously in both vibration modes but at different frequencies. Based on the torsional vibration performed by the measuring tube, a shear force is induced in the fluid, which counteracts the torsional vibration in a dampening manner.

Further, WO-A9516897 describes a radial vibration type vibration measuring device used as a Coriolis mass flow rate / density / viscosity meter, and this measuring device measures the viscosity of a fluid guided in a pipe line. This vibration measuring device has a measurement value detector and a measuring device electronic circuit,
The measurement value detector includes a linear measurement tube inserted in a pipe line, an electromechanical excitation device, and a sensor device that responds to an axially symmetric variation of the measurement tube. The electromechanical excitation device has an excitation circuit and an evaluation circuit, the measurement tube has a measurement tube lumen for guiding a fluid, and is oscillatingly stretched between an inlet end and an outlet end. Forms an axisymmetric deformation and / or a lateral deflection in the measuring tube, the sensor device forms a sensor signal representing the deformation of the measuring tube, and the excitation circuit generates an excitation current supplied to the excitation device. And the evaluation circuit uses the sensor signal and the excitation current to form a viscosity measurement representative of the viscosity of the fluid.

  In a Coriolis mass flow / density / viscosimeter, the measuring tube is first signaled in an axisymmetric radial vibration mode to detect viscosity and mass flow. In this axially symmetric radial vibration mode, the measurement tube wall is deformed so as to remain elastic and the measurement tube centroid remains substantially statically stationary. Furthermore, the measuring tube is excited at least occasionally in the secondary vibration mode, which is used to detect the density and pressure of the fluid. The secondary vibration mode may be, for example, the first flexural vibration mode.

  WO-A9516897 describes that a radial vibration type vibration measuring device can be used for measurement of fluid mass flow rate and viscosity. However, for mass flow measurement, this device has been applied exclusively to gaseous gases. That is, the effect of viscosity damping is particularly large on the amplitude of the second vibration mode which depends on the mass flow rate, and this second vibration mode is substantially detected by the sensor at a viscosity already slightly higher than water. Can not do.

  US-A 5,359,881 further describes a method for measuring the viscosity of a flowing fluid. In this method, a flexural vibration type Coriolis mass flow / density measuring device is used to detect the mass flow rate, and additionally, a pressure difference along the flow direction in the flowing fluid is detected to detect the viscosity. .

  Furthermore, US Pat. No. 5,253,533 and US Pat. No. 6,606,609 describe flexural vibration type Coriolis mass flow / density detectors. This detector can detect the viscosity of the fluid in addition to the mass flow rate and / or density. The Coriolis mass flow / density detectors each have a linear measuring tube that is vibrated in the same torsional vibration mode simultaneously with the first flexural vibration mode during the measurement operation, thereby at least partly. Torsional vibration is performed around the longitudinal axis of the measuring tube.

  During the operation of such Coriolis mass flow measurement, until now it has been substantially detected only by the excitation current measurement, only for the compensation of the primary measurement, i.e. for the compensation of the mass flow measurement and the density measurement. Viscosity was detected incorrectly due to the output as an additional viscosity measurement.

  It is an object of the present invention to provide a vibration measuring device for accurately measuring the viscosity of a fluid guided in a conduit, which device is also suitable for measuring the mass flow rate and density of a fluid. Constitute. Furthermore, this invention makes it a subject to provide the method of improving the precision of the viscosity measurement using a Coriolis mass flow rate / density measuring apparatus.

  The problem is that the vibration type measuring device has a measured value detector and a measuring device electronic circuit, and the measured value detector forms at least one measuring tube inserted in a pipe line and generates vibration in the measuring tube. And a sensor device for detecting a spatial deflection of the measuring tube, the measuring device electronic circuit having an exciting circuit and an evaluation circuit, the measuring tube having a measuring tube lumen for guiding fluid Lateral direction deflection that is vibrated and stretched between the inlet side end and the outlet side end and periodically changes the spatial position of the measurement tube lumen by vibrating with respect to the stationary state during operation. The sensor device generates a first sensor signal representing a lateral deflection in the inlet direction of the measurement tube and a second sensor signal representing a lateral deflection in the outlet side of the measurement tube, and the excitation circuit is connected to the excitation device. Forming the excitation current to be supplied and Circuit sends the density measurement value representing the fluid density is solved by an apparatus for forming a viscosity value representing the viscosity of the fluid based on at least one of the sensor signals and density measurements and the excitation current. Another problem is that a viscous friction is formed in the fluid by causing the measurement tube to vibrate in a stationary state by causing the measurement tube to vibrate with respect to a stationary state through an excitation device, and the vibration generated from the measurement tube is At least partially flexural vibration, detecting an excitation current supplied to an excitation device that vibrates the measuring tube, detecting at least one sensor signal representative of the bending vibration of the measuring tube, detecting the detected excitation current and at least one This is solved by a method of forming a viscosity measurement that represents the viscosity by means of a density measurement based on one sensor signal.

  According to a first advantageous configuration of the vibratory measuring device according to the invention, the evaluation circuit uses the first sensor signal and / or the second sensor signal to form an estimate for the speed of movement of the fluid. Here, this fluid motion causes viscous friction.

  According to a second advantageous configuration of the vibration measuring device according to the invention, the evaluation circuit uses the excitation current to form a friction measurement representing the viscous friction in the fluid.

  According to a third advantageous configuration of the vibratory measuring device according to the invention, the evaluation circuit uses the friction value and the estimated value to form a quotient value, which is the damping of the vibration measuring tube acted on by viscous friction. Represents.

  According to the fourth configuration of the vibration type measurement apparatus of the present invention, an elastic deformation of the measurement tube lumen is generated in the measurement tube based on the spatial deflection.

  According to the fifth configuration of the vibration type measuring apparatus of the present invention, twist is generated around the longitudinal axis of the measuring tube in the measuring tube based on the spatial deflection.

  According to the sixth configuration of the present invention, the vibratory measuring device delivers a mass flow measurement value representing the instantaneous mass flow rate of the fluid.

  According to the seventh configuration of the present invention, the vibratory measuring device delivers a density measurement value representing the instantaneous density of the fluid.

  According to an advantageous first configuration of the method of the invention, the quotient value is divided by the correction value to form a viscosity measurement.

  According to an advantageous second configuration of the method of the invention, the quotient value is squared to form a viscosity measurement.

  The basic technical idea of the invention consists of the measured excitation current and the lateral direction of the measuring tube, which is always detected during operation of the described type of vibration measuring device, in particular the flexural vibration type Coriolis mass flow / density measuring device. Deriving the viscosity from the deflection, in particular the vibrations detected at the inlet and / or outlet side for mass flow measurement.

  An advantage of the present invention is that a conventional flexural vibration type Coriolis mass flow / density detector can be used for its realization, and in that case it does not need to be modified in terms of its mechanical structure. That is. Therefore, the method of the present invention can be realized in a Coriolis mass flow / density measuring apparatus that has already been used.

FIG. 1 schematically shows an oscillating measuring device used to detect the viscosity η of a fluid guided through a conduit (not shown), and a viscosity measurement value X _η representing the viscosity η of the fluid is formed. Is done.

Furthermore, the vibration measuring device advantageously determines, for example, simultaneously the fluid density ρ and the mass flow rate m in addition to the viscosity η, and correspondingly obtains a density measurement value X _ρ representing the density _ρ and a mass flow value representing the mass flow rate m. to convert to X _m.

  For this purpose, the vibration measuring device is advantageously configured as a Coriolis mass flow / density measuring device. The structure of a Coriolis mass flow / density measuring device for measuring this type of mass flow m and / or density ρ is disclosed in US Pat. Nos. 4,187,721, 4,876,879, 5,648,616, referred to at the beginning, Nos. 5687100, 5796011, and European Patent Application No. 866 319.

  In order to detect the aforementioned parameters describing the fluid, ie viscosity η, density ρ, and possibly mass flow m, the oscillating measuring device is fluid-tightly inserted (especially pressure-tight) into the conduit. It has a measured value pickup 10 of the formula.

  Furthermore, the vibration type measuring device has a measuring device electronic circuit 50 which is used for driving the measuring value pickup 10 and for forming the aforementioned measuring value. If the vibratory measuring device is designed to be coupled to a serial fieldbus in particular, the measuring device electronic circuit 50 has a corresponding communication interface for data communication so that, for example, measurement data can be stored in a higher-level memory. Sent to the program control unit or the upper process guide system. Of course, the measuring device electronics 50 can be accommodated in a correspondingly not shown electronics casing in a manner known to those skilled in the art.

  2 and 3 show an embodiment of a vibration type physical-electric conversion device used as the measurement value pickup 10. The structure of this type of conversion device is described in detail, for example, in US Pat. No. 6,006,609. Furthermore, for example, the Coriolis measurement flow rate / density measurement device “PROMASS I” series manufactured by the present applicant can be used as the aforementioned conversion device.

  The measurement value pickup 10 has a measuring tube 13 having a linear input side end 11 and an output side end 12, and this measuring tube is elastically deformable with a predetermined measuring tube inner diameter 13 A and a predetermined rating. Width. The measurement tube 13 is stretched in a rigid support frame 14 covered by the casing 100 so as to vibrate. The elastic deformation of the measuring tube inner diameter 13A here means that the fluid is conducted during the driving of the measurement pickup 10 in order to form a stress describing the fluid, ie Coriolis force, mass inertial force and / or shear force. This means that the spatial shape and / or the spatial position of the measuring tube inner diameter 13A is changed cyclically (especially periodically) as predetermined within the elastic region of the measuring tube 13. See, for example, U.S. Pat. Nos. 4,801,897, 5,648,616, 5,796,011, and / or 6,006,609. For example, a titanium alloy is particularly suitable as the material of the measuring tube 13. Instead of titanium alloys, other commonly used materials for bendable measuring tubes, such as stainless steel or zirconium, can also be used.

  The support frame 14 is fixed to the input side plate 213 covering the measurement tube 13 at the input side end 11, and is similarly fixed to the output side plate 223 covering the measurement tube at the output side end 12. ing. Further, the support frame 14 has a first support plate 24 and a second support plate 34, and these two support plates 24, 34 are fixed to the input side plate 213 and the output side plate 223. These plates are substantially parallel to the measuring tube 13, spaced from the measuring tube and spaced from each other. See FIG. 2 for this. The mutually facing sides of the two support plates 24, 34 are therefore also parallel to each other.

  A longitudinal stub 25 is preferably secured to the support plates 24, 34 at a distance from the measuring tube 13, which is used as a compensating mass that eliminates vibrations of the measuring tube 13. The longitudinal stub 25 is actually parallel to the entire length of the oscillating measuring tube 13, as shown in FIG. However, this is not necessarily so, and the longitudinal stub 25 can of course be made shorter if necessary.

  Thus, the support frame 14 with the two support plates 24, 34, the input side plate 213, the output side plate 223, and possibly the longitudinal stub 25, has a longitudinal center of gravity line. The barycentric line extends in parallel to the measurement tube longitudinal axis 13B in which the input side end 11 and the output side end 12 are virtually connected.

  2 and 3 show that the above-described support plates 24 and 34 are screwed to the input side plate 213 and the output side plate 223 by the illustrated screw head. However, other suitable fixing methods implemented by those skilled in the art may be applied to this.

  According to FIG. 2, the measured value pickup 10 further comprises an electromechanical excitation device 16. This electromechanical excitation device is used for spatially deflecting the measuring tube 13 from a stationary position during driving and elastically deforming it in a predetermined manner.

  As shown in FIG. 4, the excitation device 16 includes a T-shaped rigid lever device 15, which has a bending resistance and a bracket 154 fixed to the measuring tube. And a yoke 163. The yoke 163 is fixed to the end portion of the bracket 154 spaced from the measuring tube 13 in the same manner with bending resistance, and is oriented in the transverse direction with respect to the measuring tube longitudinal axis 13B. . As the bracket 154, for example, a metal disk that accommodates the measurement tube in the hole is used. In another suitable embodiment, an alternative lever device 15 is shown in the aforementioned US Patent Application No. 6006609.

  The lever device 15 is preferably arranged to act on the measuring tube 13 at approximately the center of the input end 11 and the output end 12, as can be seen easily from FIG. 2, so that the measuring tube 13 is in operation. On average, it has the maximum lateral deflection state.

  To drive the lever device 15, the excitation device 16 of FIG. 4 includes a first excitation coil 26 and a first permanent magnet 27 corresponding thereto, a second excitation coil 36 and a second permanent coil corresponding thereto. The two exciting coils 26 and 36 are detachably fixed to the support frame 14 below the yoke 163 on both sides of the measuring tube 13. The two excitation coils 26, 36 are electrically connected in series. However, these coils can of course be connected in parallel if necessary.

As shown in FIGS. 2 and 4, the two permanent magnets 27 and 37 are fixed to the yoke 163 at a distance from each other. When the measurement value pickup 10 is driven, the permanent magnet 27 is mainly used as an excitation coil. The permanent magnet 37 is penetrated mainly by the magnetic field of the exciting coil 36 and moves based on the action of a corresponding electromagnetic force. For this purpose, the excitation device 16 is fed by a unipolar or bipolar excitation current i _exc sent from a corresponding excitation circuit 50A of the measuring device electronic circuit 50, and the excitation coils 26, 36 conduct this current when driven, correspondingly. A magnetic field is formed on the permanent magnets 27 and 37. This excitation current is likewise oscillating and has an adjustable amplitude and an adjustable excitation frequency f _exc . The excitation current i _exc appears as, for example, harmonic vibration, triangular vibration, or rectangular vibration. In particular, the only excitation frequency f _exc of the excitation current i _exc corresponds to the instantaneous mechanical resonance frequency of the measuring tube 13 that conducts the fluid, as in a conventional vibration measuring device.

The movements of the permanent magnets 27 and 37 formed by the magnetic fields of the exciting coils 26 and 36 are transmitted to the measuring tube 13 through the yoke 163 and the bracket 154. This movement of the permanent magnets 27, 37 is performed so that the yoke 163 is alternately deflected from the rest position in the direction of the support plate 24 or the support plate 34 by means of the only excitation frequency f _exc . The axis of rotation of the lever device 15 parallel to the corresponding measuring tube longitudinal axis 13B extends, for example, through the bracket 154.

  Advantageously, the support frame 14 further comprises a bearing member 29 for the electromagnetic exciter 16 detachably connected to the support plates 24, 34, which in particular will be described below with the excitation coils 26, 36 and possibly below. Used to support the individual components of the magnet support device 217.

  As described above, the excitation device 16 excites the measurement value pickup 10 when it is driven, and is used to mechanically vibrate the measurement tube 13 around the stationary position. As a result, the measuring tube generates at least a lateral deflection (oscillating deflection in the lateral direction).

  In the measurement value pickup 10 of this embodiment, the deflection in the lateral direction is simultaneously performed by the measurement tube inner diameter 13A of the measurement tube 13 fixedly stretched at the input side end portion 11 and the output side end portion 12 as described above. Generate elastic deformation. In this case, the deformation of the measuring tube inner diameter 13A actually acts over the entire length of the measuring tube 13.

  Further, the measurement tube 13 is at least partially twisted and rotated simultaneously with the lateral deflection based on the tensioned state of the measurement tube and the moment acting on the measurement tube 13 via the lever device 15. The rotation of the measuring tube 13 is performed so that the lateral deflection of the bracket end spaced from the measuring tube 13 is the same or opposite to the lateral deflection of the measuring tube 13. . In other words, the torsional vibration of the measuring tube 13 is generated in the first torsion mode corresponding to the former case, or in the second torsion mode corresponding to the latter case. At that time, in the measurement value pickup 10 of this embodiment, the natural frequency (for example, 900 Hz) of the second torsion mode is almost twice as high as that of the first mode.

  If the torsional vibration is performed only in the second torsional mode in response to the drive of the measuring tube 13, a magnet support device 217 based on the vortex principle is advantageously incorporated in the excitation device 16. This device is used in particular for adjusting and / or stabilizing the position of the axis of rotation depending on the instantaneous density of the fluid. For this reason, the magnet support device 217 guarantees that the measurement tube 13 always vibrates in the second torsion mode, and in any case, an external disturbance influence on the measurement tube 13 causes the other torsion mode (first mode) to enter. Does not cause spontaneous police box. Details of this type of magnet support device are described in detail, for example, in US Pat. No. 6,006,609. Furthermore, the use of this type of magnet support device is known from the "PROMASS I" series of measurement pickups described above.

Advantageously, for the measured value pickup 10, according to this embodiment, the excitation frequency f _exc is adjusted, the excitation is carried out exclusively in the second torsion mode, and the first mode is correspondingly suppressed accordingly. However, if necessary, excitation can be performed in the first torsion mode.

  According to FIG. 1, the measurement value pickup 10 has a further sensor device 60, which detects the instantaneous spatial deflection of the measuring tube 13 and produces a corresponding analog signal. For this purpose, the sensor device 60 has a first sensor 17 responsive to the deflection of the measuring tube 13 causing the first lateral oscillation on the input side and the deflection of the measuring tube 13 causing the second lateral oscillation on the output side. And a second sensor 18 responsive to. As shown in FIG. 2, the two sensors 17 and 18 are fixedly arranged on the support frame 14 at a distance from each other along the measurement tube 13. These sensors are in particular arranged at the same distance with respect to the center of the measuring tube 13 and are fixedly arranged on the support frame 14, in particular on the support plate 24 or 34.

  As the sensors 17 and 18, velocity-measuring electrodynamic sensors are preferably used. However, a distance measurement type, acceleration measurement type electrodynamic sensor, or optical sensor can also be used. Of course, other deflection responsive sensors known to those skilled in the art may be used as the sensors 17,18.

Through the sensors 17 and 18, the sensor device 60 outputs a first sensor signal x _s1 representing the lateral deflection on the input side and a second sensor signal x _s2 representing the lateral deflection on the output side during driving. Form.

The sensor signals x _s1 , x _s2 are supplied to a programmable evaluation circuit 50B of the measuring device electronics 50 as shown in FIG. This evaluation circuit is used in particular for the formation of the measured viscosity value _Xη and the measured density value _Xρ . According to an advantageous embodiment of the present invention, evaluation circuit 50B is further formed mass flow measurement value X _m.

The two measurement signals x _s1 and x _s2 each have one signal frequency corresponding to the excitation frequency f _exc .

The sensor device 60 preferably further comprises an amplifier circuit, which is used to adjust the two sensor signals x _s1 and x _s2 to the same amplitude. A suitable amplitude control circuit is shown, for example, in US Pat. No. 5,648,616 or EP-A-866319.

The adjustment of the excitation frequency f _exc is preferably performed by the phase control loop of the excitation circuit 50A, as is commonly done with this type of excitation device. The structure of this type of phase control loop and its use in adjusting the mechanical resonance frequency are described in detail in US Pat. No. 4,801,897.

  Of course, a frequency control circuit for adjusting the mechanical resonance frequency of a vibration measuring device of the above-mentioned type, known to other persons skilled in the art, may be used. See U.S. Pat. Nos. 4,524,610 and 4,801,897 for this. Furthermore, the use of this type of frequency control circuit for a vibration measuring device of the type described above is shown in the aforementioned "PROMASS I" series.

For the adjustment of the excitation current i _exc , a corresponding amplifier circuit is used, as is usually done with this type of vibration measuring device. This amplifier circuit is controlled by a frequency setting signal representing the excitation frequency f _exc to be adjusted and an excitation current setting signal representing the amplitude of the excitation current i _exc to be adjusted. The frequency setting signal is, for example, a DC voltage sent from the above-described frequency control circuit, and this DC voltage has an amplitude representing a frequency.

In order to form the excitation current i _exc , the excitation circuit 50A has a corresponding amplitude control circuit which forms at least one of the two sensor signals x _s1 and x _s2 via the instantaneous amplitude. , to form the excitation current setting signal via the amplitude reference value W ₁ of the constant or variable accordingly. In some cases, the instantaneous amplitude of the excitation current i _exc can also be used to form the excitation current setting signal. This type of amplitude control circuit is likewise well known to those skilled in the art. As an example of this type of amplitude control circuit, the "PROMASS I" series of Coriolis mass flow measuring devices is cited again. The amplitude control circuit of this measuring device is advantageously configured such that the vibration of each measuring tube is controlled to a constant amplitude, i.e. an amplitude independent of density, in the first flexural vibration mode.

  The process for determining the viscosity η of the fluid according to the present invention will be described in detail below using the example of the measurement value pickup 10 described above. Conceptual viscosity should be understood to mean both dynamic and kinematic viscosity of the fluid. This is because these viscosities can be easily converted into each other depending on the density measured in the same manner when the vibration type measuring device is driven. Further, instead of the viscosity η, the reciprocal thereof, that is, the fluidity of the fluid can be obtained.

  As described above, in the vibration type measurement apparatus including at least one measurement tube that oscillates, the spatial deflection of each measurement tube causes the movement of the fluid that generates a shearing force. The shearing force in the fluid is determined by the viscosity η of the fluid, and acts as a friction loss on the oscillating measuring tube in a damping manner.

It has been found that the damping i acting on the deflection can be alternatively evaluated by the ratio i _exc / θ between the excitation current i _exc and the velocity of the fluid motion θ that generates shear forces that cannot actually be measured directly. Here, the attenuation of the deflection is determined together with a damping component attributed to the friction of the viscosity in the fluid, and the viscosity is determined using this. In addition to the excitation current i _exc , the aforementioned fluid motion speed θ is also detected in order to determine the viscosity η accordingly.

  In the process described in the aforementioned U.S. Pat. No. 4,524,610, the velocity [theta] is evaluated by the drive movement performed by the drive lever. This drive movement accordingly affects the torsional rotation of the measuring tube. This drive lever substantially corresponds to the lever device 15.

  For the purpose of viscosity measurement, the lever device 15 is only suitable for a limited range in order to detect the velocity θ via a measurement value pickup of the type described above. One reason is that, as described above, the position of the rotation axis of the lever device 15 is variable, and the actual state must always be detected accordingly. Another is that this type of lever device is often not provided at the location of a measurement value pickup of the type described above, in particular a Coriolis mass flow / density pickup.

According to the basic idea of the present invention, the velocity θ is therefore not detected directly by the lever device 15 of the measurement value pickup 10 but is obtained from the sensor signals x _s1 and x _s2 sent from the sensor device 60.

The use of the sensor signals x _s1 and x _s2 for the measurement of the viscosity η means that the velocity of the fluid motion causing viscous friction θ and the measurement tube 13 reproducible at least in the operating region of the measurement value pickup 10 of the type described above. It is based on the recognition that instantaneous lateral deflection is linearly related. Assuming good approximation, X _θ = K ₁ · X _V (1)
Holds. Here, X _V is a velocity measurement value derived from the sensor signals x _s1 and x _s2 and instantaneously represents the lateral deflection velocity of the measuring tube 13, and X _θ is an evaluation of the velocity θ of the fluid motion. A value that acts on viscous friction in the fluid, and K ₁ is a calibration measure for the proportionality factor to be determined.

The velocity measurement X _V may be the only sensor signal x _s1 or x _s2 or a signal value derived from the two sensor signals x _s1 , x _s2 , in particular the sum of the signals x _s1 + x _s2 (eg instantaneous Signal amplitude). If the sensors 17, 18 are arranged symmetrically with respect to the center of the measuring tube 13 and the sensor signals x _s1 , x _s2 have the same signal amplitude or an equally controlled signal amplitude as described above, According to this embodiment, the signal sum x _s1 + x _s2 is proportional to the lateral deflection at the center of the measuring tube 13.

To form the evaluation value X _theta for the speed theta, evaluating circuit 50B is 5, it has an input stage 51, as shown schematically in FIG. 6, the stage sensor signals x _s1, x _A first measurement circuit 511 for digitally processing _s2 is provided, where a velocity measurement value _XV is formed. Such a measuring circuit for measuring the signal amplitude is shown, for example, in US Pat. No. 5,648,616 or EP-A-866319.

As schematically shown in FIG. 6, the input stage 51 further includes a multiplier 512 that is used to implement equation (1). The multiplier multiplies the proportional coefficient K ₁ is applied first and the speed measurement value X _V is applied to the input side is transmitted from the measurement circuit 511 to a second input of the evaluation value X as an output _{Send θ} .

The relationship formed by equation (1) is determined by a corresponding calibration measurement for each actual implementation of the measurement value pickup 10 and incorporated into the measurement value electronic circuit 50. To determine the proportionality factor K _1, the actual speed is determined in rotation at the center of the calibration measurement for example measuring tube 13, are set relationship to the sensor signals x _s1, x _s2 is formed at the same time. Furthermore, the proportionality factor K ₁ is numerically calculated for a series of measurement pickups, for example by the finite element method well known to those skilled in the art.

In particular, when the fluid to be measured is a non-Newtonian fluid, the influence of the instantaneous mass flow rate on the velocity θ must be taken into account when determining the evaluation value _Xθ . That is, in a non-Newtonian fluid, the shear force decreases as the mass flow rate m increases.

When calibrating the measurement pickup 10, typically two or more different fluids with known parameters, such as density ρ, mass flow m, viscosity η, and / or temperature, are sequentially passed through the measurement pickup 10. The corresponding measured value pickup 10 response, for example the instantaneous excitation current i _exc and / or the instantaneous excitation frequency f _exc, is measured. Response measurements pickup 10 which is measured adjusted parameters and respective mutual implicating accordingly, for example, proportional coefficient K ₁ is formed. The obtained calibration constant is stored in the table memory of the evaluation circuit 50B in the form of digital data, for example. These data are used as analog adjustment values for the corresponding calculation circuit. Here, it is pointed out that calibration of the measurement value pickup is well known to those skilled in the art, and detailed description thereof is omitted.

The vibration of the measurement tube 13 is attenuated not only by a damping component attributed to viscous friction but also by a damping component that does not actually depend on the fluid. This damping component is caused by the frictional force and acts on the material in the excitation device 16 and the measuring tube 13, for example. In other words, the measured excitation current i _exc represents the friction force and / or the entire friction force of the measurement value pickup 10. When the fluid viscosity η is determined, the fluid-independent damping component is correspondingly eliminated from the ratio Δi _exc / θ. Therefore, the ratio between the excitation current component Δi _exc and the velocity θ corresponding to the damping component of the excitation current i _exc due to viscous friction must be obtained.

In order to form the excitation current component Δi _exc , and thus the friction measurement value X _Δi representing viscous friction, during the driving of the vibration measuring device, the input stage 51 determines from the excitation current i _exc or the excitation current measurement value representing the instantaneous excitation current. The corresponding no-load current measurement K _i0 is subtracted. This no-load current measurement represents the aforementioned frictional force of the excitation device 16. For this purpose, the input stage 51 has a second measuring circuit 513, in particular performing digital processing, as schematically shown in FIG. 6, which is applied to the reduced input side. Subtract the no-load current measurement value K _i0 applied to the reduction input side from the excitation current i _exc or the excitation current measurement value, and send the friction measurement value X _Δi to the output side.

Similarly, the no-load current measured value K _i0 is obtained during calibration of the vibration type measuring device, for example, after the contents of the measuring tube 13 are discharged or during a period in which only air is conducted, and is stored in the measuring device electronic circuit 50 accordingly. Must be adjusted. For those skilled in the art, other physical parameters that affect the no-load current measurement K _i0 when necessary, such as the instantaneous temperature of the measuring tube and / or the fluid, are calibrated during the calibration of the no-load current measurement K _i0 . It is also clear that this must be taken into account.

In order to form a quotient value X _Δi / X _θ corresponding to the damping component Δi _exc / θ attributed to viscous friction in the fluid, the evaluation circuit 50B further includes a first functional block as shown in FIG. This block is used to divide the measured friction value X _Δi applied to the dividend input side by the evaluation value X _θ applied to the divisor input side.

When the viscosity η is obtained by the measurement value pickup of the above-mentioned type, in addition to the excitation current i _exc and the velocity θ, the vibration frequency and fluid density ρ of the measurement tube 13 must be taken into consideration. See U.S. Pat. No. 4,524,610 for this.

For this purpose, the evaluation circuit 50B further comprises a second functional block 53, which has a corresponding value depending on the fluid density ρ and the excitation frequency f _exc by means of the density measurement value X _ρ and the excitation frequency measurement value X _f . Used to form the correction value X _{ρ, f} .

The density measurement value X _ρ and the excitation frequency X _f are measurement values that are normally obtained when driving the vibration type measurement device of the above-described type, particularly the Coriolis mass flow rate / density measurement device. For example, U.S. Pat. Nos. 4,187,721, 4,524,610, 4,876,879, 5,648,616, 5,687,100, or European Patent Application No. 866,139. Please refer to the book. Therefore, it is easily understood that the measured values X _f and X _ρ can be used for detecting the viscosity η of the present invention.

As for the correction value X _{ρ, f} , the following equation is realized by the function block 53 as a good approximation, particularly in the measurement tube 13 that vibrates as described above. That is, _{Xρ, f} = _Xρ · _Xf (2)
Holds.

If the distance measuring sensor is used as the sensors 17 and 18, the correction value X _[rho, its squared value X _f ² it is used in place of the simple excitation frequency measurements X _f in order to obtain the _f. That is, the functional block 53 is provided with a further multiplier or a squarer in addition to the multiplier for the equation (2).

According to FIG. 5, the quotient value X _Δi / X _θ and the correction value X _{ρ, f} are supplied to the third functional block 54 of the evaluation circuit 50B, and again the quotient value X _Δi / X _θ and the correction value X _The measured viscosity X _η is formed by _{ρ and f} .

According to an advantageous embodiment of the invention, the viscosity η is determined on the basis of the following equation:
_{X η = (K 2 / X} ρ, f) · (X Δi / X θ) 2 (3)
Here K ₂ is a constant that depends on the square of the constant determined by calibration, especially nominal width of the measuring tube 13.

It has been found that the measured viscosity X _η determined by equation (3) more accurately matches the actual viscosity η the lower the viscosity η and / or the higher the fluid density ρ. Further, in the embodiment of the present invention, the viscosity η can be accurately obtained as the rated width of the measuring tube 13 increases.

According to another advantageous embodiment of the method according to the invention, in order to detect an accurate viscosity measurement X _η , in particular when the viscosity η is greater than 5 Pas (= Pascal second) and / or the measuring tube 13 When the rated width is smaller than 8 mm, detection is performed based on the following equation.

Equation (4) actually represents a universal means of measurement value pickup that excites one or more measurement tubes to produce torsional vibration about the measurement tube longitudinal axis. For measurement pickup 10 of this embodiment, the value of the constant _{K 3} is present in the range of, for example, from 0.24 to 0.25. In particular, in the measurement tube that generates the torsional vibration as described above in the operating range of the measurement value pickup of the above-described type, the equation (4) indicates that the viscosity-dependent frictional force acting in the fluid is applied to the excitation current component Δi _exc. This takes into account the fact that the influence is gradually reduced towards the longitudinal axis of the measuring tube in the radial direction. Constant K ₃ is a coefficient actually representing a square component of the aforementioned diminishing. When the excitation current component Δi _{exc and} thus the friction measurement value X _Δi go to a very small value, the equation (4) is transferred to the equation (3).

In order to implement equation (3) or equation (4), the functional block 54 comprises a divider 541 according to the preferred embodiment of the invention shown in FIGS. This divider has a dividend input side for the quotient value X _Δi / X _θ and a divisor input side for the correction values X _{ρ, f} , thereby forming a first intermediate value. Furthermore, the functional block 54 comprises a calculation stage 542 and a multiplier 543, the calculation stage having a first input for the first intermediate value and forming a second intermediate value proportional to the viscosity η. Multiplier for converting the second intermediate value by multiplying the constant K ₂ to the viscosity measured value X _eta applied to the first input.

To implement equation (3), the calculation stage 542 is configured as a multiplier according to another embodiment of the present invention, which is schematically illustrated in FIG. This multiplier converts the first intermediate value as the output of the divider 541 by the quotient value X _Δi / X _θ applied to the second input side of the calculation circuit 542 to obtain the second intermediate value. Used for.

To implement equation (4), calculation stage 542, according to another embodiment of the present invention, for the corresponding square root for the difference in roots of equation (4) and the term subtracting the roots. And a corresponding squarer. Furthermore, the calculation stage 542 is used to multiply the square value formed using the squarer by the constants K ₃ , K ₄ and the correction value X _{ρ, f} , thereby forming a second intermediate value. The

Furthermore, it is known that the evaluation of the velocity θ described above depends slightly on the fluid density ρ according to the equation (1). As a result, K ₁ = K ₁ (ρ) (5)
Holds.

According to research, the proportionality coefficient K ₁ is obtained by the following equation in consideration of density dependence for the measurement value pickup 10 of this embodiment. That _{K 1 = K 1,0 / [1} + K 5 · (X ρ -ρ 0)] (6)
Holds. Where ρ0 is the adjusted density or measuring the density of the calibration fluid used in the calibration of the measurement pickup 10, K _{1, 0} is the proportionality factor of the measuring tube to conduct fluid for calibration, K ₅ is The calibration constant depends on the rated width of the measuring tube 13.

Similar to the equation (1), K _1,0 = X _{ρ, 0} / X _{V, 0} for the proportional coefficient K _1,0 (7)
Holds. Here, X _{ρ, 0} is a first calibration measurement value representing the velocity θ of the measurement tube 13 that conducts the calibration fluid, and X _{V, 0} is a second calibration derived from the sensor signal x _s1 . It is a measured value, and represents the lateral deflection speed of the measuring tube 13 that conducts the calibration fluid.

  Equation (6) is implemented by the function block 514 of the input stage 51, as schematically shown in FIG.

Multiplier 512 by the function block 52,53,54,514 and the above-mentioned case to be utilized in the formation of viscosity measurements X _eta is a well known technique to those skilled in the art, a microcomputer provided in the example evaluating circuit 50B Accordingly, it is realized by a program code that is executed by being incorporated therein. The above equations (1), (2), (3), (4), (6) are converted into corresponding functional blocks, and the equations (1), (2), (3), (4), (6) The formation of the program code for the microcomputer used for realizing the above is well-known to those skilled in the art and will not be described in detail here. Of course, these equations can easily be represented in the evaluation circuit 50B by analog and / or digital calculation circuits which are configured in a discrete manner in whole or in part. Correspondingly, the input stage 51 can also be realized via the aforementioned microcomputer, in which the sensor signals x _s1 and x _s2 and the detected excitation current i _exc can be converted into corresponding digital signals by an analog-digital converter. It is also clear. Reference is made in particular to EP-A 866 319 in this regard.

In particular, the measurement value pickup 10 according to this embodiment causes torsional rotation, and the ratio Δi _exc / v between the excitation current component Δi _exc and the excitation current i _exc is normalized to a comparative viscosity of about 4 Pas. This is a value that reaches 90%. That is, the measured value pickup 10 has a very high sensitivity to the viscosity η.

It is also possible to use other measurement value pickups known to those skilled in the art for measuring the viscosity η, for example a pickup with a measuring tube curved in a helical shape. Further, as described above, the viscosity η can be appropriately measured by using a vibration type measurement value pickup having a curved measurement tube or a curved measurement tube. This is described, for example, in US Pat. Nos. 5,648,616 or 5,796,011. This type of measurement pickup has, for example, the ratio Δi _exc / i _exc in the range of about 70% to 80% in relation to the aforementioned comparative viscosity.

It is the schematic of the vibration type measuring device for fluids. It is the figure which showed the 1st side surface of one Example of the measurement value pick-up 10 of the vibration type measuring apparatus of FIG. It is the figure which showed the 2nd side surface of the measured value pickup of FIG. FIG. 3 is an enlarged partial view of the measurement value pickup of FIG. 2. It is the schematic which shows the format of the block circuit of the element of the evaluation circuit of the vibration type measuring apparatus of FIG. FIG. 6 is a schematic block circuit diagram of an embodiment of the evaluation circuit of FIG. 5. FIG. 6 is a schematic block circuit diagram of an embodiment of the evaluation circuit of FIG. 5. FIG. 6 is a schematic block circuit diagram of an embodiment of the evaluation circuit of FIG. 5. FIG. 6 is a schematic block circuit diagram of an embodiment of the evaluation circuit of FIG. 5.

Explanation of symbols

  50 measuring device electronic circuit, 10 measured value pickup, 13 measuring tube, 14 support frame, 16 excitation device, 17, 18 sensor, 100 casing

Claims (28)

In a vibration measuring device for measuring the viscosity of a fluid guided in a pipe line,
The vibration measurement device has a measurement value detector (10) and a measurement device electronic circuit (50),
The measurement value detector (10) includes at least one measurement tube (13) inserted in a pipe, an excitation device (16) for generating vibration in the measurement tube (13), and the measurement tube (13). Sensor device (60) for detecting the spatial deflection of
The measuring device electronic circuit (50) has an excitation circuit (50A) and an evaluation circuit (50B),
The measurement tube (13) has a measurement tube lumen (13A) for guiding a fluid, and is stretched to be able to vibrate at an inlet side end and an outlet side end, and vibrates with respect to a stationary state during operation. Causing lateral deflection that periodically changes the spatial position of the measurement tube lumen (13A),
The sensor device (60) includes a first sensor signal (x _s1 ) representing the inlet side lateral deflection of the measuring tube (13) and a second sensor signal (x representing the outlet side lateral deflection of the measuring tube (13). _s2 ),
The excitation circuit (50A) forms an excitation current (i _exc ) supplied to the excitation device (16),
The evaluation circuit (50B) sends a density measurement value (X _ρ ) representing the fluid density, and an excitation current (i _exc ) is _{generated from} at least one sensor signal (x _s1 , x _s2 ) and the density measurement value (X _ρ ). A vibration type measuring device that forms a viscosity measurement value (X _η ) representing the viscosity of a fluid based on Mass flow measurement value from the evaluation circuit (50B) representing the instantaneous mass flow rate of the fluid (X _m) is sent, the vibration-type measuring device according to claim 1. The vibration type measuring device according to claim 2, wherein the evaluation circuit (50B) forms the viscosity measurement value (X _η ) using the mass flow rate measurement value (X _m ). The evaluation circuit (50B) sends an excitation frequency measurement value (X _f ) representing an excitation frequency (f _exc ) that vibrates the measurement tube (13), and the excitation frequency measurement value (X _f ) and density measurement value (X The vibration type measuring device according to any one of claims 1 to 3, wherein the viscosity measurement value (X _η ) is formed using a correction value (X _{ρ, f} ) obtained based on _ρ ). The evaluation circuit (50B) uses at least one sensor signal (x _s1 , x _s2 ) to form an estimate (X _θ ) for the speed of motion acting on the viscous friction of the fluid. The vibration type measuring apparatus according to claim 1. The evaluation circuit (50B) forms a viscosity measurement (X _η ) based on a signal amplitude derived from at least one sensor signal (x _s1 , x _s2 ). Vibration type measuring device. The evaluation circuit (50B) _obtains the attenuation amount of the vibration of the measuring tube (13) acting on the viscous friction by using at least one sensor signal (x _s1 , x _s2 ) and the excitation current (i _exc ). The vibration type measuring apparatus according to claim 1, wherein a viscosity measurement value (X _η ) representing the viscosity of the fluid is formed based on the amount of attenuation. The vibration type measuring apparatus according to any one of claims 1 to 7, wherein the evaluation circuit (50B) uses the excitation current (i _exc ) to form a friction measurement value (X _Δi ) representing the viscous friction of the fluid. The evaluation circuit (50B) uses the excitation current (i _exc ) to form a friction measurement value (X _Δi ) representing the viscous friction of the fluid, and further uses the friction measurement value (X _Δi ) and the estimated value (X _θ ). The vibration-type measuring device according to claim 8, wherein a quotient value (X _Δi / X _θ ) is formed, and the quotient value represents a damping amount of the vibration measuring tube (13) caused by viscous friction.   10. The vibration type measuring device according to claim 1, wherein an elastic deformation of the measurement tube lumen (13A) is formed in the measurement tube (13) that vibrates laterally with respect to a stationary state. .   11. The vibration type measuring device according to claim 1, wherein a torsion is formed in the vibrating measurement tube (13) around the longitudinal axis (13 </ b> B) of the measurement tube.   12. A torsional vibration mode is formed in part around the measuring tube axis (13B) during operation in order to form viscous friction in the fluid of the measuring tube (13). Vibration measuring device.   Sensor device (60) comprises a first sensor (17) responsive to lateral deflection of the inlet side of the measuring tube (13), said sensor delivering at least one signal. The vibration type measuring apparatus according to any one of the above.   14. The sensor device (60) comprises a second sensor (18) responsive to lateral deflection on the outlet side of the measuring tube (13), said sensor delivering at least one signal. The vibration type measuring apparatus according to any one of the above.   The vibration type measuring device according to any one of claims 1 to 14, wherein the measuring tube (13) is configured in a straight line.   16. The vibration type measuring device according to claim 1, wherein the measuring tube (13) is bent. Evaluating circuit (50B) sends mass flow measurement value representative of the instantaneous mass flow rate of the fluid (X _m), the vibration-type measuring device according to any one of claims 1 to 16. Flow through the pipeline using a flexural vibration type Coriolis mass flow / density measuring device that sends a mass flow measurement (X _m ) representing the Coriolis mass flow of the fluid and a density measurement (X _ρ ) representing the density of the fluid. In a method for measuring the viscosity of a fluid,
Viscous friction is formed in the fluid by causing the measurement tube (13) through which the fluid flows to vibrate by causing the measurement tube to oscillate with respect to a stationary state via the excitation device (16). The vibration generated from is at least partially a flexural vibration,
Detecting an excitation current (i _exc ) supplied to an excitation device (16) for vibrating the measurement tube (13);
Detecting at least one sensor signal (x _s1 , x _s2 ) representing the flexural vibration of the measuring tube (13);
Forming a viscosity measurement value (X _η ) representing the viscosity with a density measurement value (X _ρ ) based on the detected excitation current (i _exc ) and at least one sensor signal (x _s1 , x _s2 ). A method for measuring the viscosity of a fluid flowing through a pipeline.   19. The method according to claim 18, wherein the measuring tube is deflected laterally to deform the measuring tube lumen (13A) elastically. _19. Estimating (X _θ ) representing the velocity of motion of the fluid acting on viscous friction from at least one sensor signal (x _s1 , x _s2 ) to form a viscosity measurement (X _η ). Or the method of 19. _21. A method according to any one of claims 18 to 20, wherein a friction measurement (X [ _{Delta] i} ) representing viscous friction is derived from the excitation current ( _iexc ) to form a viscosity measurement (X [ _eta] ). The method of claim 21, wherein the friction measurement (X _Δi ) is divided by the estimate (X _θ ) to form a quotient value (X _Δi / X _θ ) to form a viscosity measurement (X _η ). . The measurement tube (13) is vibrated at an excitation frequency (f _exc ) to form a viscosity measurement (X _η ) to form an excitation frequency measurement (X _f ) representing the excitation frequency. The method according to any one of the above. In order to form a viscosity measurement (X _η ), a correction value (X _{ρ, f} ) that depends on the density of the fluid and the excitation frequency is formed from the density measurement (X _ρ ) and the excitation frequency measurement (X _f ). 24. The method of claim 23. 25. The method according to claim 24, wherein a viscosity measurement (X [ _eta] ) is formed from the quotient value (X [Delta] _i / x [ _theta] ) and the correction value (X [ _{rho], f} ). 26. The method of claim 25, wherein the quotient value (X [Delta] _i / X [ _theta] ) is divided by a correction value (X [ _{rho], f} ) to form a viscosity measurement (X [ _eta] ). Using at least one sensor signal (x _s1 , x _s2 ) and the excitation current (i _exc ), the amount of vibration attenuation of the measuring tube (13) acting on the viscous friction is obtained, and the fluid is further calculated based on the obtained amount of attenuation. 27. A method according to any one of claims 18 to 26, wherein a viscosity measurement value (X [ _eta] ) representing the viscosity of is formed. Forming a viscosity measurement (X _η ) based on a signal value, eg a signal amplitude, representing a lateral deflection of the oscillating measuring tube (13) derived from the at least one sensor signal (x _s1 , x _s2 ) 28. The method according to any one of items 18 to 27.

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