DEVICE FOR MEASURING VISCOSITIES

Description

[0001] The invention relates to a device according to claim 1 and a method according to claim 8.

[0002] Devices for measuring the viscosity of fluids are used, for example, in industrial metrology.

[0003] For example, in EP 1 158 289 B1 and DE 10 2004 021 690 A1 devices for measuring the viscosity of a fluid are described, in which a pipe section of a measuring tube through which the fluid flows is excited to vibrations of a useful vibration mode and the viscosity of the fluid flowing through it is determined on the basis of the damping of the resulting vibration which depends on the viscosity.

[0004] US Patent 2008 / 0184813 A1 describes a mass flow meter designed to measure the mass flow rate and viscosity of a medium passing through at least one pipe. This is achieved by exciting the pipe at a first frequency to vibrate a first bending-displacement mode, exciting the pipe at a second frequency to vibrate the first bending-displacement mode, and determining the mass flow rate and viscosity based on a first vibration response measured during excitation at the first frequency and a second vibration response measured during excitation at the second frequency. US Patent 2008 / 0184813 A1 further describes how shear rates occurring in the pipe can be determined from the mass flow rate and a natural resonant frequency of the mass flow meter, and can be modified by changing the mass flow rate and / or the vibration mode.

[0005] Furthermore, DE 10 2004 021 690 A1 describes a Coriolis mass flow meter designed for use in applications where parameters of inhomogeneous fluids, e.g., two-phase or multiphase fluids, are to be determined. DE 10 2004 021 690 A1 describes a method in which a straight measuring tube is simultaneously or sequentially excited to lateral and torsional vibrations of different frequencies. The damping of the resulting lateral vibration, which depends essentially only on the viscosity of the fluid, and the damping of the resulting torsional vibration, which depends on both the viscosity and the inhomogeneity of the fluid, are measured. Intermediate values ​​are derived from these two measured damping values ​​and are then used to improve the measurement accuracy of parameters measured with the instrument, such as mass flow, density, or viscosity.This method is based on the fact that the viscosity of the fluid is identical for the two useful vibration modes excited to determine the intermediate values.

[0006] This method can detect and account for inhomogeneities. However, it cannot answer the crucial question, relevant to the flow behavior and rheology of fluids, of whether a fluid is a Newtonian fluid. Similarly, any shear rate dependence of a fluid's viscosity, if present, cannot be qualitatively detected or quantitatively determined using the measuring device described in DE 10 2004 021 690 A1.

[0007] It is an object of the invention to provide a device and a method with which shear rate-dependent viscosities of fluids can be determined.

[0008] The invention includes a device for measuring the viscosity of fluids according to claim 1.

[0009] A first advanced training is characterized by the fact that the evaluation device is designed in such a way that it can be used to determine viscosity values ​​based on at least two viscosity measurements determined at different shear rate values. a viscosity profile representing the viscosity of the fluid as a function of the shear rate is created, it recognizes whether the viscosity of the fluid exhibits a shear rate dependence, and / or, based on the viscosity measurements determined at the different shear rate values, it determines whether the fluid is a Newtonian fluid whose viscosity is essentially independent of the shear rate, or a shear-thinning fluid whose viscosity decreases with increasing shear rate, or a shear-thickening fluid whose viscosity increases with increasing shear rate.

[0010] According to a second further development, the device comprises a detection unit for detecting changes in the fluid and / or deviations in the viscosity of the fluid from the applicable specifications that occur during the measurement operation, which is designed in such a way that It compares the viscosity measurements determined at the measured shear rate values ​​or based on the viscosity profile with reference values, in particular predetermined target values ​​or predetermined target value ranges stored in a memory and / or viscosity measurements determined at one or more earlier times at shear rate values ​​determined by the device, and detects a change and / or deviation if at least one of the viscosity measurements deviates from the associated reference value by more than a predetermined tolerance, in particular a tolerance predetermined depending on the measurement accuracy of the viscosity measurement or a tolerance specified by the user.

[0011] An initial design is characterized by the fact that The excitation device includes a control device that regulates the amplitudes of the vibrations resulting from the excitation of the individual useful vibration modes to a constant value, and the measuring device is designed in such a way that it determines the damping on the basis of a measure determined by means of an energy demand measuring device for an energy demand required to maintain the resulting vibrations of constant amplitude when the respective useful vibration mode is excited.

[0012] A third advanced method is characterized by the fact that the calibration data for each useful vibration mode includes data determined in a preceding calibration procedure, whereby a viscosity measurement value is assigned to the damping measured during the measurement operation when the useful vibration mode is excited, and a shear rate value is assigned to each of the measured frequencies, which is essentially equal to 2π times the frequency of the resulting vibration of the respective pipe section.

[0013] A second embodiment is characterized in that the device comprises a measuring unit connected to the measuring device, which is designed in such a way that, during measuring operation, it determines a mass flow rate and / or a density of the fluid based on the vibration resulting from the excitation of at least one of the useful vibration modes.

[0014] A fourth further development is characterized by the fact that the useful oscillation modes have frequencies of less than or equal to 1600 Hz, in particular less than or equal to 1000 kHz, in particular less than or equal to 800 Hz, in particular from 100 Hz to 800 Hz.

[0015] Furthermore, the invention comprises a method for measuring viscosities according to claim 8.

[0016] A first further development of the method is characterized by the fact that the useful vibration modes have frequencies of less than or equal to 1600 Hz, in particular less than or equal to 1000 kHz, in particular less than or equal to 800 Hz, in particular from 100 Hz to 800 Hz.

[0017] Further development of the procedure is characterized by the fact that In the calibration procedure, reference measurements are performed for each of the individual useful vibration modes, in which the respective useful vibration mode is excited while the corresponding pipe section is filled with and / or through which a reference fluid flows, and the damping and the frequency of the vibration resulting from the excitation of the respective useful vibration mode are measured, wherein the reference measurements include reference measurements performed with Newtonian reference fluids of various known dynamic viscosities, and wherein a shear rate value is assigned to each of the measured frequencies, which is essentially equal to 2π times the frequency of the resulting vibration of the respective pipe section, and / or the reference measurements include reference measurements performed with non-Newtonian reference fluids with a viscosity dependent on the shear rate in a known manner, wherein the reference measurements in particularReference measurements are performed using reference fluids with elastic properties that vary in intensity relative to their viscous properties, and calibration data are determined for each useful vibration mode, from which a shear rate value and a viscosity measurement value are assigned to the damping and frequencies measured during the measurement operation when the respective useful vibration mode is excited.

[0018] A further development of the method is characterized by the fact that viscosity measurements are taken from at least two viscosity values ​​determined at different shear rate values. a viscosity profile representing the viscosity of the fluid as a function of the shear rate is created, it is recognized whether the viscosity of the fluid has a shear rate dependency, and / or it is determined, based on the viscosity measurements determined at the shear rate values, whether the fluid is a Newtonian fluid, a shear-thinning fluid or a shear-thickening fluid.

[0019] A further development of the method is characterized by the fact that changes in the fluid and / or deviations in the viscosity of the fluid from the applicable specifications that occur during the measurement operation are detected by The viscosity measurements determined at the measured shear rate values ​​are compared with reference values, in particular with specified target values, with specified target value ranges or with viscosity measurements determined at one or more earlier times at measured shear rate values, and a change and / or deviation is detected if at least one of the viscosity measurements deviates from the associated reference value by more than a specified tolerance, in particular a tolerance specified depending on the measurement accuracy of the viscosity measurement or a tolerance specified by the user.

[0020] The invention and further advantages will now be explained in more detail with reference to the figures in the drawing, in which an exemplary embodiment is shown; identical parts are provided with the same reference numerals in the figures. Fig. 1 shows: a device according to the invention; Fig. 2 shows: three exemplary useful vibration modes, each corresponding to a natural mode of a straight pipe section; Fig. 3 shows: an embodiment of a measuring system; Fig. 4 shows: a measuring system with four measuring tubes with curved pipe sections; and Fig. 5 shows: a measuring system with four measuring tubes with straight pipe sections.

[0021] Fig. 1 Figure 1 shows a device according to the invention for measuring the viscosity of fluids. The device comprises a Fig. 1 Measuring system 1, represented merely as a functional block, which comprises at least one measuring tube filled with a fluid or through which the fluid flows during measuring operation, and which has at least one pipe section that can be excited to vibrations.

[0022] Furthermore, the devices comprise an excitation device 3 for exciting at least two useful vibration modes of different frequencies, whereby at least one of the pipe sections is excited to vibrations, in particular to resonant vibrations, of the respective useful vibration mode. For this purpose, the excitation device 3 is designed such that, during measurement operation, at least one of the intended pipe sections can be excited to vibrations of a first useful vibration mode, and at least one of the intended pipe sections can be excited to vibrations of at least one further useful vibration mode. The individual useful vibration modes preferably correspond to natural vibration modes of the respective pipe section.Whether the excitation of the individual useful vibration modes and the evaluation of the resulting vibrations described below can be carried out simultaneously or must be carried out sequentially depends on the design of the pipe sections to be excited and the shape of the useful vibration modes.

[0023] To carry out the measuring method according to the invention, a measuring system 1 with only a single measuring tube and only a single tube section is sufficient. This section can be excited to vibrations of a first and at least one further useful vibration mode having a different frequency. An example of this is measuring systems with at least one measuring tube, which, for example, comprises at least one tube section that can be excited to torsional and / or bending vibrations.

[0024] In this respect, the measuring system 1 can, for example, comprise a straight pipe section 4 fixed at its opposite ends. Such a pipe section 4 can, for example, be excited to natural modes of vibration, which are lateral oscillations. The pipe section 4 is thereby excited to oscillate in a plane of vibration xy defined by its longitudinal axis x and an axis y perpendicular to its longitudinal axis x, during which it experiences displacements perpendicular to its longitudinal axis x. These natural modes of vibration comprise a Fig. 2 The first usable vibration mode, N1, is the fundamental vibration mode in which the displacement amplitudes occurring perpendicular to the longitudinal axis x form a single antinode. Furthermore, it includes a mode that is in Fig. 2The next higher, symmetrical harmonic of this natural mode, represented as the second useful vibration mode N2, forms three antinodes. Alternatively or additionally, straight pipe sections 4 can be excited to natural vibrations formed as torsional vibrations around a rotation axis running through the two fixed ends of the pipe section 4.

[0025] Fig. 2 As an example, a third useful vibration mode N3, designed as a pure torsional vibration mode, is shown.

[0026] Alternatively, a measuring system 1 can be used that includes at least one pipe section with a different shape. Examples of this are measuring systems 1 that have at least one measuring tube comprising a curved, bent, U-shaped, V-shaped, and / or at least one Ω-shaped pipe section that can be excited to oscillations of a predefined useful vibration mode. Alternatively, the measuring system 1 can also comprise two or more measuring tubes connected in parallel or series in terms of flow direction, at least one of which has one or more pipe sections through which flow is series-connected and which can be excited to oscillations, whereby these pipe sections can also each have, for example, one of the aforementioned shapes.

[0027] Fig. 3Figure 1 shows, as an embodiment, a measuring system 1 comprising two substantially parallel measuring tubes 5, each having a pipe section 7 that is mechanically clamped at its opposite ends and, in the illustrated embodiment, curved and capable of being excited to vibration. In this embodiment, the useful vibration modes preferably include natural modes of the pipe sections 7, such as a fundamental mode and a higher-order mode of combined torsional-bending vibrations, in which the pipe sections 7 are excited to vibrate about a torsional axis passing through their clamped ends.

[0028] Fig. 4 Figure 1 shows a further embodiment of a measuring system 1 comprising four measuring tubes 5 connected parallel to each other in the direction of flow, each of which has a curved tube section 7 mechanically clamped at its opposite ends and capable of being excited to vibration. Fig. 5 As a further embodiment, a measuring system 1 is shown, comprising four measuring tubes connected parallel to each other in the flow direction, each of which has at least one straight tube section 4 mechanically clamped at its opposite ends and capable of being excited to vibration. The in Figs. 4 and 5 The illustrated measuring systems 1 are preferably operated such that two of the four measuring tubes form a pair of measuring tubes, the parallel tube sections 4 and 7 of which respectively are each subjected to vibrations, preferably to antiphase vibrations, at least one of which is in conjunction with Fig. 2 for straight pipe sections 4 or in conjunction with Fig. 3The useful vibration modes described for curved pipe sections 7 are excited. The method is preferably carried out and / or the pipe sections 4 and 7 are preferably designed such that the frequencies of the useful vibration modes of the pipe sections 4 and 7 of the two pairs of measuring tubes are different.

[0029] The excitation of the individual useful vibration modes of the pipe sections 4, 7 of the respective measuring system 1, which are capable of being excited to vibration, is preferably effected by one or more actuators D of the excitation device 3, each acting on a region of the respective pipe section 4, 7 selected according to the useful vibration mode to be excited. Actuators D commonly used today in Coriolis mass flow meters or density meters for exciting useful vibration modes, such as electrostatic, piezoelectric, or magnetic actuators D, are particularly suitable for this purpose. Such actuators D, as well as their number and arrangement required for exciting useful vibration modes, are known to those skilled in the art and are therefore not described in detail here. The excitation device 3 comprises, in the Fig. 1 and 3 The illustrated embodiment focuses on the center of the Fig. 3The drive D acting on the arc-shaped pipe sections 7 is preferably designed such that it excites the parallel pipe sections 7 to oscillations in opposite phase.

[0030] The device also includes a measuring device 9, which is configured to determine, for each of the useful vibration modes excited during measurement, the frequency and damping of the resulting vibration of at least one pipe section 4, 7 excited to vibrations of the respective useful vibration mode. As explained in detail below, there are embodiments of the device according to the invention in which it is necessary to also detect the amplitude of the resulting vibrations in addition to their frequencies. In this case, the measuring device 9 is configured to determine the frequency, amplitude, and damping of the resulting vibrations.

[0031] During measurement operation, the device performs measurements in each measurement cycle for at least two useful vibration modes of different frequencies, in which at least one pipe section 4, 7 is excited to vibrate in the respective useful vibration mode. During the excitation of the respective useful vibration mode, the resulting vibration of the excited pipe section 4 or pipe sections 4, 7 is preferably measured using at least one sensor S of the measuring device 9. Suitable sensors S, e.g., electrostatic, piezoelectric, or magnetic sensors, as well as their required number and arrangement in relation to the respective pipe section 4, 7 for detecting the resulting vibrations, are known from the prior art and are therefore not described in detail here. The sensors S can be, for example,They are designed and / or arranged in the same way as in Coriolis mass flow meters or density meters known from the prior art. In the case of the one described in... Fig. 1 and 3 In the illustrated embodiment, the measuring device 9 comprises two inlet and outlet sides in the area of ​​the legs of the Fig. 3 Seven sensors S are arranged in arc-shaped pipe sections for the measurement of their resulting vibrations.

[0032] To determine the damping of the vibration resulting from the excitation of the respective useful vibration mode, which depends on the viscosity of the fluid filling or flowing through the respective pipe section 4, 7, the device, in particular its measuring device 9, can be designed, for example, such that it determines the damping in the manner described in US 2004 / 0255648 A1 based on the vibration quality of the respective pipe section 4, 7, which can be derived, for example, from the width of the resonance peak of the respective useful vibration mode.

[0033] Alternatively, it can be designed such that it determines the damping in each case, based on the energy required to maintain the respective useful vibration mode, in a manner described, for example, in EP 1 158 289 B1 or in DE 10 2004 021 690 A1 in conjunction with mass flow meters. This embodiment is described in Fig. 1As shown, the excitation device 3 is preferably controlled via a control device 11 connected to the measuring device 9 and the excitation device 3 such that it regulates the amplitudes of the vibration of the respective pipe section 4, 7, measured by the sensors S and resulting from the excitation of the respective useful vibration mode, to a constant value. The energy required to maintain the resulting vibration at a constant amplitude depends on the damping, which in turn depends on the viscosity of the fluid. Accordingly, a measure of the energy required for this purpose, corresponding to the viscosity-dependent damping, is determined by means of a suitably designed energy consumption measuring device 13.

[0034] The excitation of the useful vibration modes preferably occurs at a frequency corresponding to the resonance frequency of the respective useful vibration mode. The excitation of the resonance frequency is achieved, for example, in a manner known from the prior art. For this purpose, the device is preferably designed such that it maximizes the amplitude of the resulting vibration measured by the sensors S by appropriately controlling the drive frequency and / or controls a phase shift between excitation and the resulting vibration to a value corresponding to the resonance by appropriately controlling the drive frequency.

[0035] According to the invention, the device comprises an evaluation unit 15, which is configured to determine a shear rate value and a viscosity measurement value for each of the useful vibration modes excited during measurement operation, based on calibration data stored in a memory 17. The shear rate value and the viscosity measurement value are determined based on the frequency and damping, and, if necessary, also the amplitude, of the vibration resulting from the excitation of the respective pipe section 4, 7. The shear rate values ​​and the viscosity measurement values ​​are determined based on the calibration data such that the viscosity measurement values ​​correspond to the dynamic viscosity of the fluid at a static shear rate corresponding to the associated shear rate value.

[0036] Excitation of the respective vibration mode causes an oscillatory movement of the excited pipe section 4, 7. This generates shear waves in the fluid flowing through or within the pipe section, which penetrate the fluid to a certain depth h, originating from a pipe wall of the respective pipe section. The penetration depth h is regularly dependent on the frequency of the resulting vibration, as well as on the dynamic viscosity and density of the fluid, and can be determined, for example, according to: h = η 2 πρf The viscosities can be estimated, where η denotes the dynamic viscosity, f the frequency of the resulting vibration, and ρ the density of the fluid. The viscosity-dependent damping of the vibration resulting from the excitation of the respective useful vibration mode increases with the increasing penetration depth h, corresponding to the viscosity. Accordingly, viscosities can be measured with devices according to the invention that lie within a range of values ​​in which the penetration depth h changes depending on the viscosity. This is the case as long as the penetration depth h is less than the pipe radius of the pipe section 4, 7. The pipe sections 4, 7 of the measuring tubes 5 regularly have radii in the centimeter or decimeter range. Therefore, the penetration depth h in devices according to the invention is also significantly less than the pipe radius of the respective pipe section at low frequencies, e.g., frequencies in the range of 100 Hz to 1000 Hz.

[0037] In devices according to the invention, the dimensions of the pipe section(s) 4, 7, as well as their lengths or partial lengths deflected during excitation of the respective useful vibration mode, are preferably dimensioned such that the frequencies and damping of the vibrations resulting from the excitation of the individual useful vibration modes exhibit no or only a slight dependence on the amplitude of the resulting vibration of the respective pipe section 4, 7. This offers the advantage that the amplitude of the resulting vibrations does not need to be measured during operation, nor does it need to be taken into account when determining the shear rate values ​​and the viscosity measurements.Where this is not possible, the amplitudes of the resulting vibrations must be measured using the measuring device 9 and taken into account when determining the shear rate values ​​and the viscosity measurements based on calibration data that reflect the existing amplitude dependence of the measurements.

[0038] The calibration data are preferably determined in a preliminary calibration procedure. According to a first variant, reference measurements are performed for each of the individual useful vibration modes using Newtonian reference fluids of various known dynamic viscosities and non-Newtonian reference fluids with a viscosity dependent on the shear rate in a known manner. During these reference measurements, the individual useful vibration modes are excited while the respective pipe section 4, 7 is filled with the reference fluid or while the reference fluid flows through the respective pipe section 4, 7. The frequency and damping, as well as, if necessary, the amplitude of the resulting vibration, are measured for each of the useful vibrations using the measuring device 9. The calibration data are then derived from these measurements and stored in the memory 17 assigned to the evaluation unit 15.

[0039] The devices according to the invention can be used to determine the dynamic viscosities of fluids exhibiting essentially exclusively viscous properties, such as oils. For these fluids, the measured damping represents a direct measure of the dynamic viscosity. For this application, the reference measurements are preferably performed using reference fluids exhibiting essentially exclusively viscous properties. The reference measurements performed with these Newtonian reference fluids yield calibration data that reflect the dependence of the measured damping on the dynamic viscosity of the fluid. Based on this calibration data, the respective corresponding viscosity measurement value can be assigned to the damping values ​​measured during operation.

[0040] Furthermore, the reference measurements performed with the non-Newtonian reference fluids yield calibration data, from which a shear rate value can be assigned to each of the measured frequencies or the measured frequencies and amplitudes, which corresponds to the shear rate at which the reference fluid has the dynamic viscosity corresponding to the associated viscosity measurement.

[0041] Furthermore, the devices according to the invention can also be used to determine the dynamic viscosities of fluids that, in addition to purely viscous properties, also exhibit elastic properties. In these fluids, the damping comprises both a component dependent on the dynamic viscosity and a component attributable to energy losses caused by the elastic properties of the fluid. In these fluids, even in Newtonian fluids, the damping may, under certain circumstances, depend on the frequency or on the frequency and amplitude. This dependence will be stronger the greater the component of the damping attributable to the elastic properties of the fluid. Conversely, in these fluids, the shear rate value associated with a viscosity measurement may also depend on the dynamic viscosity of the fluid and / or on the ratio of the viscous to the elastic properties of the fluid.This is preferably taken into account when recording the calibration data by performing reference measurements with reference fluids that have elastic properties that vary considerably in relation to their viscous properties. Using these reference fluids, the dependencies of the damping measured during operation on the dynamic viscosity and frequency or frequency and amplitude, as well as the dependence of the shear rate values ​​on the measured damping and frequency or frequency and amplitude, can be determined based on the reference measurements performed with these fluids, depending on the ratio of the viscous and elastic properties of the reference fluids.Alternatively or additionally, the calibration data for this application preferably comprise data obtained from reference measurements carried out with at least one reference fluid that is identical to the fluid whose shear rate-dependent viscosity is to be determined with the device according to the invention, or is as similar as possible to it, in particular with regard to its viscoelastic properties.

[0042] In devices according to the invention, where the penetration depth h of the shear wave is significantly smaller, preferably at least ten times smaller, than the tube radius of the respective tube section 4, 7, it can be approximately assumed that shear forces develop in the fluid to which the rule established by W.P. Cox and E.H. Merz for oscillation viscometers is applicable, at least approximately. This rule states that the magnitude of a complex viscosity |η*| of a fluid measured with an oscillation viscometer at a specific oscillation frequency ω corresponds to the magnitude of the dynamic viscosity |η| of the fluid at a static shear rate fstat corresponding to the oscillation frequency ω. The complex viscosity η* measured in oscillation viscometers is composed of a contribution attributable to the elastic properties and a contribution attributable to the viscous properties of the fluid.

[0043] When applying this rule to devices according to the invention, the damping values ​​measured with devices according to the invention are each interpreted as a measured quantity corresponding to the complex viscosity measured in an oscillation viscometer and are used as a measure of the dynamic viscosity of the fluid at a static shear rate corresponding to the frequency of the resulting oscillation.

[0044] In this respect, the evaluation device 15 is preferably designed in such a way that it determines the viscosity measurement value on the basis of the damping of the resulting vibration of the respective pipe section 4, 7 determined during the excitation of the respective useful vibration mode and the corresponding shear rate value on the basis of the frequency of the resulting vibration of the respective pipe section 4, 7.

[0045] In these devices, the rule derived by W.P. Cox and E.H. Merz for oscillation viscometers is preferably applied as described above when deriving the calibration data. In this case, the calibration data for each useful vibration mode includes data that assign the corresponding viscosity measurements to the damping values ​​of the resulting vibration of the respective pipe section 4, 7, determined during the excitation of the respective useful vibration mode, and the shear rate values ​​to the frequencies of the resulting vibration of the respective pipe section 4, 7. The calibration data can be determined, for example, in a significantly simplified calibration procedure in which only the dependencies of the damping values ​​on the corresponding viscosity measurements are determined, and the shear rate values ​​are essentially set equal to 2π times the frequency of the resulting vibrations. For this purpose, for example,Reference measurements are performed exclusively with Newtonian reference fluids of known, shear-rate-independent viscosity. Reference measurements with reference fluids of known shear-rate-dependent viscosity are not required in this case.

[0046] By applying the rule of WP Cox and EH Merz, acceptable measurement accuracies can be achieved for fluids with predominantly viscous properties, especially when the device is designed in such a way that the damping and frequencies of the vibrations resulting from the excitation of the respective useful vibration modes are essentially independent of the amplitude of the resulting vibrations.

[0047] Devices according to the invention are preferably designed by appropriately dimensioning the dimensions of the pipe sections, in particular their cross-sectional areas, their wall thicknesses and their lengths or partial lengths deflected to excite the individual useful vibration modes, such that the frequencies of the useful vibration modes relevant for the measured shear rate values ​​cover a frequency range that makes it possible to measure dynamic viscosities in a shear rate range in which viscosities of non-Newtonian fluids typically change depending on the shear rate.

[0048] This frequency range can be estimated, at least approximately, using the aforementioned application of the rule by W.P. Cox and E.H. Merz. To measure dynamic viscosities in a shear rate range of less than or equal to 10,000 Hz with devices according to the invention, vibration modes with frequencies below 1600 Hz are preferably excited. Preferably, vibration modes with frequencies less than or equal to 1000 Hz, and even more preferably less than or equal to 800 Hz, are excited. For example, dynamic viscosities in a shear rate range on the order of 600 Hz to 5000 Hz can be measured using vibration modes with frequencies in the frequency range of 100 Hz to 800 Hz.

[0049] The devices according to the invention offer the advantage that, based on the viscosity measurements they determine, it can be established whether the fluid exhibits a shear rate-dependent viscosity. Furthermore, any shear rate dependence of the viscosity that may be present can be quantitatively determined and / or evaluated. The associated additional information can be determined by the operator of the device based on the viscosity measurements and the corresponding shear rate values. Alternatively, this information can also be determined by the device and made available via an output unit 19. For this purpose, the evaluation unit 15 is preferably designed such that, based on the viscosity measurements determined at least two different shear rate values, it recognizes whether the fluid exhibits a shear rate-dependent viscosity.For this purpose, it is sufficient to check whether at least two viscosity measurements taken at different shear rate values ​​differ from each other by more than a specified minimum deviation.

[0050] Alternatively or additionally, the evaluation unit 15 is preferably configured to generate a viscosity profile representing the viscosity of the fluid as a function of the shear rate, based on viscosity measurements obtained at least two different shear rate values. If a sufficient number of viscosity measurements obtained at sufficiently different shear rate values ​​are available, the profile can be generated directly from the viscosity measurements and the corresponding shear rate values. Alternatively or additionally, the profile can be determined using a mathematical function that describes the functional dependence of the viscosity of non-Newtonian fluids on the shear rate.In this case, two viscosity measurements determined at different shear rate values ​​are sufficient to create a meaningful profile from which the shear rate dependence of the fluid's viscosity can be extrapolated even for shear rate ranges for which no viscosity measurements have been determined.

[0051] Alternatively or additionally, the evaluation unit 15 is preferably designed such that it determines, on the basis of the viscosity measurements determined at the different shear rate values ​​or the profile derived therefrom, whether the fluid is a Newtonian fluid whose viscosity is essentially independent of the shear rate, or a shear-thinning fluid whose viscosity decreases with increasing shear rate, or a shear-thickening fluid whose viscosity increases with increasing shear rate.

[0052] Furthermore, the viscosity measurements taken with the device according to the invention can also be used to detect changes in the viscosity of the fluid and / or deviations in the viscosity of the fluid from applicable specifications that occur during the ongoing measurement operation.

[0053] Just as with the previously described determination of additional information, the detection of these changes and / or deviations can also be carried out by the operator of the device using the viscosity measurements. Alternatively, this detection can also be performed by a detection device 21 connected to or integrated into the device and displayed accordingly or output in another way. The function of the detection device 21 can be carried out, for example, by a PC equipped with appropriate software, a microprocessor, or similar device. Alternatively, the detection device 21 can be designed as a component of the evaluation unit 15, as shown here.

[0054] Detection is preferably carried out by the device performing viscosity measurements at successive intervals, determining at least two viscosity values ​​and the corresponding different shear rate values ​​in each measurement. Subsequently, the viscosity values ​​determined for the shear rate values ​​are compared with reference values ​​stored in a memory 23 assigned to the detection unit 21.

[0055] The reference values ​​can, for example, include predefined target values ​​or target value ranges for the fluid, specifying the desired viscosity of the fluid at certain shear rates. In this case, the detection device 21 detects a deviation from the specifications defined by the target values ​​if at least one of the viscosity measurements deviates from the corresponding target value or target value range by more than a predefined tolerance. The predefined tolerance can be, for example, a tolerance determined by the measurement accuracy of the viscosity measurements or a tolerance defined in another way, such as a user-defined tolerance. Alternatively or additionally, the comparison can, of course, also be performed using a viscosity profile generated from the measured viscosity values ​​and the corresponding shear rate values.The latter enables the detection of deviations even when the target values ​​or target value ranges are only known for shear rates or shear rate ranges that differ from the shear rate values ​​at which the viscosity measurements were determined.

[0056] Alternatively or additionally, the reference values ​​can include specific viscosity measurements taken during one or more measurements previously performed by the device at measured shear rate values. In this case, the detection device 21 detects a change in the viscosity of the fluid over time if at least one of the current viscosity measurements deviates from the corresponding reference value measured at an earlier time and stored in memory 23 by more than a tolerance dependent on the measurement accuracy of the viscosity measurements or a user-defined tolerance.

[0057] The additional information and the detection of deviations and / or changes in the viscosity of the fluid are particularly advantageous when the device according to the invention is also used to measure other measured variables, such as mass flow and / or density, and / or when the viscosity measurements determined by it are used to compensate for viscosity-dependent measurement errors of density and / or mass flow measurements.

[0058] If a pipe section 4, 7 of a device according to the invention, through which fluid flows, is excited to oscillate by means of the excitation device 3, Coriolis forces arise in the pipe section 4, 7 through which fluid flows, and these forces affect the resulting vibration mode of the pipe section 4, 7. In the embodiments shown here, this leads to the vibrations detected by the sensors S provided on the inlet and outlet sides of the respective pipe section 4, 7 exhibiting frequencies corresponding to the resulting vibration mode, which are phase-shifted relative to each other by a phase shift that depends on the mass flow rate. This phase shift can thus be determined, for example, by means of a measuring unit 25 connected to the corresponding sensors S, which then determines the mass flow rate based on the measured phase shift.Alternatively or additionally, the device can be used for density measurement. In this case, at least one pipe section 4, 7 of the measuring system 1 is excited to oscillate at a resonance frequency by means of the excitation device 3 and the control device 11. The density-dependent resonance frequency is determined by means of the measuring unit 25 connected to the vibration sensors S, and the density of the fluid is determined from this. If the measuring device is also operated as a density measuring device, this offers the advantage that the viscosity measurements corresponding to the dynamic viscosities can be converted into viscosity measurements corresponding to the associated kinematic viscosity based on the measured density. At the same time, density and viscosity measurements can be used to correct density-dependent measurement errors in the viscosity measurements and / or viscosity-dependent measurement errors in the measured densities. Reference symbol list

[0059] 1 Measuring system 15 Evaluation unit 3 Pathogen facility 17 memory 4 Pipe section 19 Output unit 5 Measuring tube 21 Detection device 7 Pipe section 23 memory 9 Measuring device 25 Unit of measurement 11 Control device 13 Energy demand measuring device

Claims

1. A device for measuring viscosities of fluids with a complex viscosity, which comprises one part attributable to elastic properties and one part attributable to viscous properties, and with its part attributable to viscous properties being large compared to its part attributable to elastic properties, with - a measuring system (1) with at least one measuring tube (5) filled with a fluid or with a fluid flowing through it in measuring mode, which has at least one tube section (4, 7) which can be caused to oscillate, - an excitation device (1) for initiating at least two useful oscillation modes with different frequencies, in which at least one of the tube sections (4, 7) is in each case caused to oscillate, in particular to perform resonant oscillations, in the respective useful oscillation mode, - a measuring device (3), which is configured to determine, for each of the at least two useful oscillation modes initiated in measuring mode, a frequency and a damping of the resultant oscillation of at least one tube section (4, 7) which is caused to oscillate in the respective useful oscillation mode, - wherein a tube radius and a length or partial length of each tube section (4, 7) deflected when the respective useful oscillation mode is initiated are dimensioned in such a way that the frequencies and the dampings of the oscillations which result when the individual useful oscillation modes are initiated do not have a dependency on the amplitude of the resultant oscillation, and - wherein the tube section (4) which can be caused to perform useful oscillations or the tube sections (4, 7) which can be caused to perform useful oscillations each have a tube radius greater than or equal to ten times the penetration depth (h) to which shear waves formed in the fluid originating from a tube wall of the respective tube section (4, 7) penetrate into the fluid when the respective tube section (4, 7) is caused to oscillate in the respective useful oscillation mode, and - a deflection device (15) which is configured in such a way that it determines a viscosity measured value based on calibration data saved in a storage device (17) for each of the at least two useful oscillation modes initiated in measuring mode based on the damping of the resultant oscillation of the respective tube section (4, 7) determined upon their excitation and a shear rate value based on the frequency of the resultant oscillation of the respective tube section (4, 7), wherein the viscosity measured value of the dynamic viscosity of the fluid corresponds to a static shear rate corresponding to the shear rate value.

2. The device as claimed in claim 1, in which the evaluation device (15) is configured in such a way that, based on at least two viscosity measured values determined at different shear rate values, - it creates a viscosity profile reflecting the viscosity of the fluid as a function of the shear rate, - it detects whether the viscosity of the fluid is dependent on the shear rate, and / or - it determines, based on the viscosity measured values determined at the different shear rate values, whether the fluid is a Newtonian fluid, the viscosity of which is essentially independent of the shear rate, or a shear-thinning fluid, the viscosity of which decreases as the shear rate rises, or a shear-thickening fluid, the viscosity of which increases as the shear rate rises.

3. The device as claimed in claims 1 and 2, with a detection device (21) for detecting changes in the fluid and / or deviations in the viscosity of the fluid from specifications applicable to this during measuring mode, which is configured in such a way that - it compares the viscosity measured values determined at the measured shear rate values or viscosity measured values determined based on the viscosity profile with reference values, in particular with specified target values saved in a storage device (23) or with specified target value ranges and / or with viscosity measured values saved in a storage device (23) determined at one or more earlier time points at shear rate values determined by the device, and - a change and / or deviation is / are detected if at least one of the viscosity measured values deviates from the corresponding reference value by more than a specified tolerance, in particular a tolerance specified as a function of the measurement accuracy of the viscosity measurement or a tolerance specified by the user.

4. The device as claimed in claims 1 to 3, in which - the excitation device (3) comprises a control device (11), which regulates each amplitude of the oscillations which result when the individual useful oscillation modes are initiated to a constant value, and - the measuring device (3) is configured in such a way that it determines dampings in each case based on a value determined using an energy requirement measuring device (13) for an energy requirement necessary for a constant amplitude for maintaining the resultant oscillations when the respective useful oscillation mode is initiated.

5. The device as claimed in claims 1 to 4, in which the calibration data determined for each useful oscillation mode comprises data determined during an upstream calibration process, which is used to assign a viscosity measured value to the dampings measured in measuring mode when the useful oscillation mode is initiated and to assign a shear rate value to each measured frequency, which is essentially equal to 2π the frequency of the resultant oscillation of the respective tube section (4, 7).

6. The device as claimed in claims 1 to 5, with a measuring unit (25) connected to the measuring device (9), which is configured in such a way that it determines a mass flow and / or a density of the fluid in measuring mode based on the oscillation which results when at least one of the useful oscillation modes is initiated.

7. The device as claimed in claims 1 to 6, in which the useful oscillation modes have frequencies of less than or equal to 1600 Hz, in particular less than or equal to 1000 kHz, in particular less than or equal to 800 Hz, in particular from 100 Hz to 800 Hz.

8. A method for measuring viscosities of a fluid with a complex viscosity, which comprises one part attributable to elastic properties and one part attributable to viscous properties, and with its part attributable to viscous properties being large compared to its part attributable to elastic properties, in which measurements are carried out for at least two useful oscillation modes of a different frequency, in which - in each case at least one tube section (4, 7) of at least one measuring tube (5) of a measuring system (1) filled with a fluid and / or with fluid flowing through it is caused to oscillate using an excitation device (3), in particular to perform resonant oscillations, in the respective useful oscillation mode, - a frequency and a damping of the resultant oscillation of at least one tube section (4, 7) caused to oscillate in the respective useful oscillation mode are determined, - wherein a tube radius and a length or partial length of each tube section (4, 7) deflected when the respective useful oscillation mode is initiated are dimensioned in such a way that the frequencies and the dampings of the oscillations which result when the individual useful oscillation modes are initiated do not have a dependency on the amplitude of the resultant oscillation, and - wherein the tube section (4) which can be caused to perform useful oscillations or the tube sections (4, 7) which can be caused to perform useful oscillations each have a tube radius greater than or equal to ten times the penetration depth (h) to which shear waves formed in the fluid originating from a tube wall of the respective tube section (4, 7) penetrate into the fluid when the respective tube section (4, 7) is caused to oscillate in the respective useful oscillation mode, and - a viscosity measured value is determined based on calibration data determined during a calibration process for each of the at least two initiated useful oscillation modes based on the damping of the resultant oscillation of the respective tube section (4, 7) determined upon their excitation and a shear rate value based on the frequency of the resultant oscillation of the respective tube section (4, 7), wherein the viscosity measured value of the dynamic viscosity of the fluid corresponds to a static shear rate corresponding to the shear rate value.

9. The method as claimed in claim 8, in which the useful oscillation modes have frequencies less than or equal to 1600 Hz, in particular less than or equal to 1000 kHz, in particular less than or equal to 800 Hz, in particular from 100 Hz to 800 Hz.

10. The method as claimed in claims 8 and 9, in which - reference measurements are performed for each of the individual useful oscillation modes during the calibration process, in which the respective useful oscillation mode is initiated while the corresponding tube section (4, 7) is filled with the one reference fluid and / or has the reference fluid flow through it, and the damping and the frequency of the oscillation which results when the respective useful oscillation mode is initiated are measured, - wherein the reference measurements comprise reference measurements performed with Newtonian reference fluids with a varying known dynamic viscosity, and - wherein each of the measured frequencies is assigned a shear rate value, which is essentially equal to 2π the frequency of the resultant oscillation of the respective tube section (4, 7) and / or the reference measurements comprise reference measurements performed with non-Newtonian reference fluids with a viscosity that is dependent in a known way on the shear rate, - wherein the reference measurements comprise reference measurements performed in particular using reference fluids with elastic properties which vary greatly relative to their viscous properties, and - for each useful oscillation mode calibration data is determined which is used to assign a shear rate value and a viscosity measured value to the dampings and frequencies measured in measuring mode when the respective useful oscillation mode is initiated.

11. The method as claimed in claims 8 to 10, in which, based on at least two viscosity measured values determined at different shear rate values, - a viscosity profile reflecting the viscosity of the fluid as a function of the shear rate is created, - it is detected whether the viscosity of the fluid is dependent on the shear rate, and / or, - based on the viscosity measured values determined at the shear rate values, it is determined whether the fluid is a Newtonian fluid, a shear-thinning fluid or a shear-thickening fluid.

12. The method as claimed in claims 8 to 11, in which changes to the fluid and / or deviations in the viscosity of the fluid from specifications applicable to this during measuring mode are detected by - comparing the viscosity measured values determined at the measured shear rate values with reference values, in particular with specified target values, with specified target value ranges or with viscosity measured values determined at measured shear rate values at one or more earlier time points, and - detecting a change and / or deviation if at least one of the viscosity measured values deviates from the corresponding reference value by more than a specified tolerance, in particular a tolerance specified as a function of the measurement accuracy of the viscosity measurement or a tolerance specified by the user.