Coriolis flow meter

Abstract

The invention relates to a Coriolis flowmeter (1) comprising a measuring tube (2), an excitation system for exciting the measuring tube (2), a sensor system (4) for detecting the mechanical vibrations of the measuring tube (2), wherein the sensor system (4) is configured to generate at least one first sensor signal s1 and a second sensor signal s2, and a measuring and / or operating circuit (5), in particular formed by means of at least one microprocessor, wherein the measuring and / or operating circuit (5) is configured to operate the excitation system with an excitation signal, wherein the measuring and / or operating circuit (5) comprises a filter with a filter coefficient a, which is configured to receive the first sensor signal s1 and to generate a filtered first sensor signal s1*, wherein the measuring and / or operating circuit (5) comprises a second filter (7b) with a filter coefficient b,which is configured to receive the second sensor signal s2 and to generate a filtered second sensor signal s2*, wherein the measuring and / or operating circuit (5) is configured to receive the filtered first sensor signal s1* and the second sensor signal s2, wherein the measuring and / or operating circuit (5) comprises a control circuit (15) which is configured to control the filter coefficient a and / or b from the filtered first sensor signal s1* and the second sensor signal s2 such that a control criterion is satisfied, wherein the measuring and / or operating circuit (5) is configured to generate a first measured value representing the process quantity from the filter coefficient a and / or b.

Description

The invention relates to a Coriolis flowmeter for determining a process variable of a flowable medium that varies over time.Field devices in process measurement technology with a measurement pickup of the vibration type and in particular Coriolis flow meters have been known for many years. The basic structure of such a measuring device is described, for example, in EP 1 807 681 A1, reference being made to the full extent of the structure of a field device of the generic type within the scope of the present invention to this publication.Typically, Coriolis flow measuring devices have at least one or more oscillatory measuring tubes, which can be set into oscillation by means of an oscillation exciter. These oscillations are transmitted over the tube length and are varied by the type of flowable medium located in the measuring tube and its flow rate. One oscillation sensor or in particular two oscillation sensors spaced apart from one another can record the varied oscillations in the form of a sensor signal or a plurality of sensor signals at another point of the measuring tube. From the sensor signal or the sensor signals, a measuring and / or operating circuit can then determine the mass flow, the viscosity and / or the density of the flowing medium.For the determination of the mass flow ≅ it is usual to use the following formula:Here, f is the driving frequency of the excitation signal, Δφ is the phase difference between two measured sensor signals, and k is a calibration factor. With this approach, the mass flow can be determined very accurately for stable flows. The disadvantage of this is that the measuring system is no longer in a harmonic operating mode in the event of disturbed conditions, such as occur, for example, in the case of polyphases in the medium, and thus in the case of a driver frequency and amplitude which is unstable over time, and the above formula is no longer sufficiently accurate or even invalid. Furthermore, a time offset can occur between the determined phase difference Δφ and the driver frequency f, i.e. the driver frequency f assumed for the measured value of the process variable does not correspond to the driver frequency f actually present at the time of measuring the sensor signals for determining the phase difference Δφ. This leads to a corruption of the determined process variable.The object of the invention is thus to remedy the problem.The object is achieved by the Coriolis flowmeter according to claim 1.The Coriolis flowmeter according to the invention for determining a process variable of a flowable medium that varies over time, comprising:a measuring tube for guiding the medium;an excitation system for exciting the measuring tube to mechanical oscillations;a sensor system for detecting the mechanical oscillations of the measuring tube, wherein the sensor system is configured to generate at least a first sensor signal and a second sensor signal,a measuring and / or operating circuit, formed in particular by means of at least one microprocessor, wherein the measuring and / or operating circuit is configured to operate the exciter system with an exciter signal, wherein the measuring and / or operating circuit comprises a first adaptive filter with a filter coefficient a, which is configured to receive the first sensor signal and to generate a filtered first sensor signal, wherein the measuring and / or operating circuit (5) comprises a second adaptive filter with a filter coefficient b, which is configured to receive the second sensor signal s2 and to generate a filtered second sensor signal s2*, wherein the measuring and / or operating circuit comprises a regulator circuit, which is configured to receive the filtered first sensor signal s1* and the filtered second sensor signal s2*, or to receive a variable derived from the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, wherein the controller circuit is configured to control the filter coefficient a and / or the filter coefficient b such that a control criterion is fulfilled, starting from the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, or from a variable derived from the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, wherein the measurement and / or operating circuit is configured to generate a first measurement value representing the process variable from the filter coefficient a and / or from the filter coefficient b.This has the result that the first measured value representing the process variable (e.g. mass flow, viscosity, density) is no longer determined analytically, but rather results from the two sensor signals and the filter coefficient a and / or b determined via the control. With the aid of the regulation of the adaptive first filter via the filter coefficient a and the adaptive second filter via the filter coefficient b, for example, in such a way that the filtered first sensor signal s 1* corresponds to the filtered second sensor signal s 2* within tolerance limits, it is achieved that the information of the first measured value representing the process variable is projected onto the filter coefficient a and / or b. The filter coefficient a and / or the filter coefficient b accordingly describes or describe the influence of the process variable to be determined on the sensor signal and is therefore or are proportional thereto. If the first measured value representing the process variable is determined as a function of the filter coefficient a and / or the filter coefficient b, not only the measurement error is reduced, but also the need for a time-accurate synchronization of the driver frequency f with the phase difference Δp is reduced. Thus, dynamic zero shifts are prevented from occurring in the case of strong frequency fluctuations.Advantageous embodiments of the invention are the subject matter of the dependent claims.In one embodiment, the controller circuit is configured to ascertain the filter coefficient a and / or the filter coefficient b by means of a least mean squares algorithm and / or by means of a normalized least mean squares algorithm and / or by means of a recursive least squares algorithm and / or a linear or nonlinear gradient method.The controller circuit is preferably arranged close to the sensor system in the local area, so that the sensor signal travels only a short distance up to the controller circuit. The sensor signal is furthermore preferably provided directly after the generation at the regulator circuit, so that no time delay occurs which otherwise occurs when the sensor signal first has to pass through the electronic components in order to form the phase difference.In one embodiment, the controller circuit comprises a PID controller which is configured to control the filter coefficient a and / or the filter coefficient b on the basis of the filtered first sensor signal s 1* and the filtered second sensor signal s 2* or the variable derived from the filtered first sensor signal s 1* and the filtered second sensor signal s 2* such that the control criterion is fulfilled.One configuration provides that the process variable comprises the mass flow of the medium.One embodiment provides that the excitation signal has a driver frequency f, wherein the driver frequency f does not enter into the determination of the first measured value representing the mass flow of the medium.In one embodiment, the control criterion includes a deviation between the filtered first sensor signal s 1* and the filtered second sensor signal s 2* assuming a sensor signal setpoint value or being less than a sensor signal limit value.In one embodiment, the measuring and / or operating circuit is configured to determine a phase difference Δφ between the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, wherein the derived variable corresponds to the phase difference Δφ.One embodiment provides that the control criterion comprises that the phase difference Δφ corresponds to a phase difference setpoint value and / or less than a phase difference limit value.One embodiment provides that a calibration factor k, determined in particular at the factory, is additionally included in the generation of the first measurement value representing the process variable, in particular the mass flow.One configuration provides that the measurement and / or operating circuit is configured to determine a current process state from the filter coefficient a and / or from the filter coefficient b and optionally output it.One configuration provides that the current process state comprises the presence of gas bubbles in the medium.One embodiment provides that the measuring and / or operating circuit is configured to:in a first operating mode, a second measured value representing the process variable is determined and output as a function of a phase difference Δφ between the first sensor signal or the filtered first sensor signal s 1* and the filtered second sensor signal s 2* and the driver frequency f,in a second operating mode, the first measured value representing the process variable is determined and output as a function of the filter coefficient a and / or the filter coefficient b.In one embodiment, the measuring and / or operating circuit is configured to switch from the first operating mode into the second operating mode if a deviation between the first measured value and the second measured value assumes a setpoint value and / or lies outside a tolerance range.In one embodiment, the measuring and / or operating circuit is configured to determine the presence of gas bubbles by comparing a signal representing the first measured value and a signal representing the second measured value.One embodiment provides that the measuring and / or operating circuit is configured to:determining a second measured value representing the process variable, in particular the mass flow, as a function of a phase difference Δφ between the filtered first sensor signal s 1* or first sensor signal and the filtered second sensor signal s 2* or second sensor signal s 2 and the driver frequency f,correcting the second measured value as a function of the filter coefficient a and / or the filter coefficient b, or the first measured value, andoutputting the corrected second measured value.In one embodiment, the first filter is designed such that the mathematical relationship between the first sensor signal and the filtered first sensor signal can be described using a transfer function H(s)=(1-a·s) with a Laplace index s.In one embodiment, the first filter is designed such that the mathematical relationship between the first sensor signal s1and the filtered first sensor signal s1*can be described with a Laplace index s via a transfer function H(s)=(1-a·s) / (1+as).In one embodiment, the first filter is designed such that the mathematical relationship between the first sensor signal s1and the filtered first sensor signal s1*is determined via a transfer function H(s)=(1+a) / 2+(1-a) / 2·z -1, where z is a z-variable of a discrete system.In one embodiment, the second filter is designed such that the mathematical relationship between the second sensor signal s2and the filtered second sensor signal s2*can be described using a transfer function H(s)=(1+b·s) with a Laplace index s.In one embodiment, the second filter is designed such that the mathematical relationship between the second sensor signal s2and the filtered second sensor signal s2*is calculated via a transfer function H(s)=(1-b) / 2+(1+b) / 2·z -1, where z is a z-variable of a discrete system.In one embodiment, the second filter is designed such that the mathematical relationship between the second sensor signal s2and the filtered second sensor signal s2*is calculated via a transfer function H(s)= 1⁄2+1 1⁄2*z -1, where z is a z variable of a discrete system.One embodiment provides that the second filter is designed such that the mathematical relationship between the second sensor signal s 2 and the filtered second sensor signal s 2* can be described via a transfer function H(s)=1.One embodiment provides that a=b.One configuration provides that the first adaptive filter and / or the second adaptive filter are, in particular each, an all-pass filter.The invention is explained in more detail with reference to the following figures. It shows: FIG. 1 shows a diagram of a Coriolis flowmeter according to the prior art; and FIG. 2 : a diagram of two Coriolis flow meters according to the invention.FIG. 1 shows a diagram of a Coriolis flowmeter 1 according to the prior art. The Coriolis flowmeter 1 for ascertaining a process variable of a flowable medium that varies over time comprises a measuring tube 2 for guiding the medium. Exactly one straight measuring tube 3 is depicted. However, the use of bent and / or multiple measuring tubes is already known. The core idea of the invention can be applied to any shape and number of measuring tubes.An exciter system 3 for exciting the measuring tube 2 to mechanical oscillations is in effect with the measuring tube 2. One or more excitation coils per measuring tube are suitable for this purpose, which is arranged by means of a holding device on the measuring tube, in the housing of the Coriolis flowmeter or an arrangement specifically provided for this purpose in the housing interior. The excitation coil is normally in effect with a magnet arranged directly on the measuring tube or via a holding device on the measuring tube. However, exciter systems differing therefrom are also known. Thus, the exciter system can also be in mechanical contact with the measuring tube 2 and can be designed and configured to transmit its own oscillation behavior directly or indirectly to the measuring tube 2. The nature of the exciter system 3 is not essential to the invention, however.The Coriolis flowmeter 1 further comprises a sensor system 4 for detecting the mechanical oscillations of the measuring tube 2. the sensor system 4 usually comprises two sensor coils per measuring tube, which each act with a magnet arranged on the measuring tube 2 or a further measuring tube (not shown). The sensor coils can-likewise like the excitation coils-be arranged in the housing interior of the housing by means of a holding device on the measuring tube 2, in the housing (not shown) of the Coriolis flowmeter 1 or an arrangement (not shown) provided specifically for this purpose. The sensor coils are usually arranged offset with respect to one another in the direction of flow of the medium. The excitation coil is arranged between the two sensor coils in the direction of flow of the medium. However, sensor systems differing therefrom are also known. Thus, the mechanical oscillations of the measuring tube 2 can also be detected via optical sensors. The characteristic of the sensor system 4 is not essential to the invention. The sensor system 4 is configured to generate at least one first sensor signal s 1 and one second sensor signal s 2, wherein the first sensor signal s 1 and the second sensor signal s 2 describe the current oscillation behavior of the measuring tube 2 at two different positions offset in the flow direction.In the depicted embodiment, the sensor system 4 comprises two sensor coils and the excitation system an excitation coil. The positioning of the two sensor coils and the excitation coil is chosen for the purpose of a clearer illustration of the diagram and does not correspond to an arrangement which is actually necessary for implementing the invention. The first sensor signal s 1 is provided at one of the two sensor coils and the second sensor signal s 2 is provided at the corresponding other sensor coil.The exciter system 3 and the sensor system 4 are connected to a measurement and / or operating circuit 5 comprising, in particular, at least one microprocessor and electronic components (for example comprising a transistor, an electrical resistor, a capacitor, a mixer, a filter and / or a microcontroller). In the embodiment depicted, the excitation signal can be described by I exc= I 0. cos(2πft), the excitation current being a maximum excitation coil current and I exc the current excitation coil current dependent on time. The driving frequency f and the excitation amplitude I 0 are adjustable variables. The control unit 6 is configured to provide the excitation amplitude I 0 and the temporally varying (periodic) portion of the excitation signal-in the form of cos(2πft)-to a mixer 16, which generates the excitation signal from the two parts and forwards it to the excitation system 3. Furthermore, the control unit 6 is in electrical connection with four further mixers 9 a- d. The control unit 6 is configured to provide a cos(2πft) signal at the mixers 9 a, 9 cand a sin(2πft) signal at the mixers 9 b, 9 c. Furthermore, the control unit 6 is configured to transmit the current driver frequency f to a computing unit 8. The arithmetic unit 8 is likewise part of the measurement and / or operating circuit 5 and is configured to determine the mass flow ≅ at least as a function of the provided driver frequency f. A mathematical equation suitable for this is introduced in the introduction to the description. The driver frequency f is output or enters into the determination of further process variables.The first sensor signal s1can be described by s1= ≅ 1· cos(2πft+φ 1). Here, φ 1 is the first phase and ≅1 is the first signal amplitude. The first sensor signal s 1 is applied to the mixers 9 a, 9 bfor frequency conversion, in particular multiplicative mixers. The mixer 9 ais configured to apply a sinusoidal component to the first sensor signal s 1. Thus, the mixer 9 acan be configured, for example, to multiply the first sensor signal s 1 by a sine function sin(2πft). The mixer 9 bis configured to apply a cosine component to the first sensor signal s 1. Thus, the mixer 9 bmay be configured to multiply the first sensor signal s 1 by a cosine function cos(2πft). The result of the two mixers 9 a, 9 bis provided to a filter 10 a, 10 b, respectively. The filters 10 a, 10 bmay be programmable low-pass filters, for example. These can be configured to eliminate the 2f component of the sensor signal. Furthermore, the filters 10 a, 10 bare set up to limit the bandwidth of the received sensor signal in order to reduce the noise component. The filtered results are provided to a computing unit 11 a, which is suitable and configured to execute an algorithm. The algorithm can be, for example, an iterative algorithm, in particular a coordinate rotation digital computer algorithm, with which mathematical functions can be executed. The algorithm is designed and configured to ascertain the first phase φ 1 and the first signal amplitude ≅1. The first signal amplitude ≅1can be output or used for the determination of a further process variable.The second sensor signal s2 can be described by s2= ≅ 2· cos(2πft+φ 2). Here, φ 2 is the second phase and ≅2 is the second signal amplitude. The second phase φ 2 is offset from the first phase φ 1 by a phase difference Δφ when the medium is flowing. The second sensor signal s 2 is applied to the, in particular multiplicative, mixers 9 c, 9 d. The mixer 9 cis configured to apply a sinusoidal component to the second sensor signal s 2. Thus, the mixer 9 acan be configured, for example, to multiply the second sensor signal s 2 by a sine function sin(2πft). The mixer 9 bis configured to apply a cosine component to the second sensor signal s 2. Thus, the mixer 9 bmay be configured to multiply the second sensor signal s 2 by a cosine function cos(2πft). The result of the two mixers 9 c, 9 dis provided to a filter 10 c, 10 d, respectively. The filters 10 c, 10 dmay be low-pass filters, for example. The filtered results are provided to a computing unit 11 b, which is configured to execute an algorithm. The algorithm can be, for example, an iterative algorithm, in particular a coordinate rotation digital computer algorithm, with which mathematical functions can be executed. The algorithm is designed and configured to ascertain the second phase φ 2 and the second signal amplitude ξ2. The second signal amplitude ≅2can be output or used for the determination of a further process variable. The first phase φ 1 and the second phase φ 2 are each provided to a filter 12 a, 12 b. The filters 12 a, 12 bare configured to reduce the respective noise components of the determined phases. The filters 12 a, 12 bmay be low-pass filters, for example.The measuring and / or operating circuit 15 also has a subtractor 13. The first phase φ 1 and the second phase φ 2 enter the subtracter 13. The subtractor 13 is configured to determine the phase difference Δφ-which is proportional to the mass flow ≅-between the first phase φ 1 and the second phase φ 2 and to provide it to a calculation unit 8. The arithmetic unit 8 is configured to determine the mass flow ≅ as a function of the phase difference Δφ and the provided driver frequency f. The mass flow ≅ is determined based on the equation ≅ = k·tan(Δφ / 2) / 2πf.FIG. 2 shows a diagram of two Coriolis flow meters according to the invention. The first configuration is depicted by the dashed lines and the second configuration is depicted by the solid lines.According to the first embodiment, the first sensor signal s 1 is provided at a first adaptive filter 7 a. The first filter 7 acan be an all-pass filter. The allpass filter is a signal processing filter which passes all frequencies equally well but which changes the phase relationship between the different frequencies. The first filter 7 ais configured to receive the first sensor signal s 1 and to generate a filtered first sensor signal s 1*. In this case, the transfer function H(s) with which the first sensor signal s1 is converted into the filtered first sensor signal s1* is considered to be H(s)=(1-a·s). S is the Laplace index.Alternatively, the mathematical relationship between the first sensor signal s 1 and the filtered first sensor signal s 1* can also be described with a Laplace index s via a transfer function H(s)=(1-a·s) / (1+as).Alternatively, the mathematical relationship between the first sensor signal s 1 and the filtered first sensor signal s 1* can be described by means of a transfer function H(s)=(1+a) / 2+(1-a) / 2·z -1. In this case, z is a z variable of a discrete system.According to the first embodiment, the second sensor signal s 2 is provided at a second adaptive filter 7 b. The second filter 7 bmay likewise be an all-pass filter. The allpass filter is a signal processing filter which passes all frequencies equally well but which changes the phase relationship between the different frequencies. The second filter 7 bis configured to receive the second sensor signal s 2 and to generate a filtered second sensor signal s 2*. In this case, the transfer function H(s) with which the second sensor signal s 2 is transferred into the filtered second sensor signal s 2* is considered to be H(s)=(1+b·s). S is likewise the Laplace index.Alternatively, the mathematical relationship between the second sensor signal s2and the filtered second sensor signal s2*can be described via a transfer function H(s)=(1-b) / 2+(1+b) / 2·z -1. In this case, z is a z variable of a discrete system.Alternatively, the mathematical relationship between the second sensor signal s 2 and the filtered second sensor signal s 2* can be described via a transfer function H(s)= 1⁄2+1 1⁄2*z -1. In this case, z is a z variable of a discrete system.Alternatively, the mathematical relationship between the second sensor signal s 2 and the filtered second sensor signal s 2* can be described via a transfer function H(s)=1.The measuring and / or operating circuit 5 has a regulator circuit 15 which is configured to regulate the filter coefficient a and / or the filter coefficient b on the basis of the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, or a variable derived from the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, in such a way that a regulation criterion is fulfilled. The control criterion can be a deviation between the filtered first sensor signal s 1* and the filtered second sensor signal s 2*, which deviation has to assume a sensor signal setpoint value or which deviation has to be smaller than a sensor signal limit value. The controller circuit 15 can be configured according to the invention to determine the filter coefficient a and / or the filter coefficient b by means of a least mean squares algorithm and / or by means of a normalized least mean squares algorithm and / or by means of a recursive least squares algorithm and / or a linear or nonlinear gradient method.Alternatively, the controller circuit 15 can comprise a PID controller which is configured to control the filter coefficient a and / or the filter coefficient b on the basis of the filtered first sensor signal s 1* and the filtered second sensor signal s 2* or the variable derived from the filtered first sensor signal s 1* and the filtered second sensor signal s 2* such that the control criterion is fulfilled.The measuring and / or operating circuit 5 comprises a computing unit 14, which is configured to generate a first measured value for the current mass flow through the pipeline from the filter coefficient a and / or the filter coefficient b. For the determination of the first measured value representing the mass flow, a calibration factor k is additionally used, which is determined in particular at the factory. The equation a=k·m F or b=k·m F. applies. The driver frequency f is therefore not included in the determination of the first measurement value representing the mass flow of the medium.Alternatively or additionally, the measuring and / or operating circuit 5, in particular the arithmetic unit 14, can be configured to determine a current process state from the filter coefficient a and / or from the filter coefficient b and optionally output it. An example of the process state to be detected is the presence of gas bubbles in the medium.In the second embodiment, the measuring and / or operating circuit 5 is configured to determine a phase difference Δφ between the filtered first sensor signal s 1* and the filtered second sensor signal s 2*. For this purpose, the first sensor signal s 1 is provided at the adaptive first filter, where it is filtered. The filtered sensor signal s*1 passes through the mixers 9 a, 9 b, where it is mixed as described for the prior art. After the mixing, the filtered first sensor signal s*1applied with a sine component passes through a filter 10 a. The filter 10 ais configured to eliminate the 2 fcomponent of the mixed sensor signal s* 1 and to reduce the noise component.It is then provided at a computing unit 11 a, which is configured to determine the first signal amplitude ξ*1of the filtered first sensor signal. The filtered first sensor signal s*1applied with a cosine component passes through a filter 10 b. The filter 10 bis likewise configured, like the filter 10 a, to eliminate the 2 f component of the mixed sensor signal s* 1 and to reduce the noise component. It is then provided to a computing unit 11 b, which is configured to determine the filtered first phase φ* 1 of the filtered first sensor signal. The filtered first phase φ* 1 continues to pass through a filter 12a before being provided to a subtractor 13.For the determination of the phase difference Δφ, the second sensor signal s 2 is provided to an adaptive second filter 7 bwhere it is filtered. The filtered sensor signal s*1 passes through the mixers 9 c, 9 d, the filters 10 c, 10 d, the arithmetic unit 11 band the filter 12 b. The processing of the filtered second sensor signal s 2* corresponds to the processing described in the description of the figures. The determined second phase φ 2 is provided at the subtractor. The subtractor 13 is configured to determine the phase difference Δφ between the filtered first phase φ* 1 and the second phase φ 2 and to provide it to the control unit 15. The control unit 15 is configured to control the filter coefficient a such that the phase difference Δφ corresponds to a phase difference setpoint value and / or less than a phase difference limit value. Specifically, the filter coefficient a and / or the filter coefficient b is controlled so that the phase difference Δφ is minimum or zero. Likewise as in the previous embodiment, the computing unit 14 is configured to determine the measured values representing the mass flow as a function of the filter coefficient a and / or the filter coefficient b and a calibration factor kA third embodiment combines the processes of the two previous embodiments and incorporates them into different operating modes. In a first operating mode, a second measured value representing the process variable is determined as a function of a phase difference Δφ between the first sensor signal s 1 or the filtered first sensor signal s 1* and the second sensor signal s 2 or the filtered second sensor signal s 2* and the driver frequency f and is optionally output. The second measured value can be the mass flow. In a second operating mode, the first measured value representing the process variable is determined as a function of the filter coefficient a and / or the filter coefficient b and optionally output. The measuring and / or operating circuit 5 is configured to switch from the first operating mode into the second operating mode if a deviation between the first measured value and the second measured value assumes a setpoint value and / or lies outside a tolerance range. The second measurement value can be corrected as a function of the filter coefficient a and / or the filter coefficient b or the first measurement value and the corrected second measurement value can be output.LIST OF REFERENCE CHARACTERS1 Coriolis flowmeter 2 measuring tube 3 exciter system 4 sensor system 5 measuring and / or operating circuit 6 control unit 7 all-pass filter 8 arithmetic unit 9 imixer 10 ifilter 11 i arithmetic unit 12 ifilter 13 subtractor 14 arithmetic unit 15 regulator circuit 16 mixerReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 1 807 681 A1

[0002]

Claims

Coriolis flowmeter (1) for determining a process variable of a flowable medium that varies over time, comprising: - a measuring tube (2) for guiding the medium; - an exciter system (3) for exciting the measuring tube (2) to mechanical oscillations; - a sensor system (4) for detecting the mechanical oscillations of the measuring tube (2), wherein the sensor system (4) is configured to generate at least a first sensor signal s1 and a second sensor signal s2, - a measurement and / or operating circuit (5) formed in particular by means of at least one microprocessor, wherein the measurement and / or operating circuit (5) is configured to operate the exciter system with an exciter signal, wherein the measurement and / or operating circuit (5) comprises a first adaptive filter (7a) with a filter coefficient a, the measuring and / or operating circuit (5) comprising a second adaptive filter (7b) having a filter coefficient b, which filter coefficient is configured to receive the second sensor signal s2 and to generate a filtered second sensor signal s2*, wherein the measuring and / or operating circuit (5) comprises a regulator circuit (15), which is configured to receive the filtered first sensor signal s1* and the filtered second sensor signal s2*, or a variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2*, wherein the regulator circuit (15) is configured to receive the filtered first sensor signal s1* and the filtered second sensor signal s2*, based on the filtered first sensor signal s1* and the filtered second sensor signal s2*, or a variable derived from the filtered first sensor signal s 1* and the filtered second sensor signal s 2* to control the filter coefficient a and / or the filter coefficient b in such a way that a control criterion is fulfilled, wherein the measuring and / or operating circuit (5) is configured to generate a first measured value representing the process variable from the filter coefficient a and / or from the filter coefficient b.Coriolis flowmeter according to Claim 1, wherein the controller circuit (15) is designed to ascertain the filter coefficient a and / or the filter coefficient b by means of a least mean squares algorithm and / or by means of a normalized least mean squares algorithm and / or by means of a recursive least squares algorithm and / or a linear or nonlinear gradient method.Coriolis flowmeter according to claim 1, wherein the controller circuit (15) comprises a PID controller, which is configured to control the filter coefficient a and / or the filter coefficient b based on the filtered first sensor signal s1* and the filtered second sensor signal s2* or the variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2* such that the control criterion is fulfilled.Coriolis flowmeter according to one of the preceding claims, wherein the process variable comprises the mass flow of the medium.Coriolis flowmeter according to claim 4, wherein the excitation signal has a driver frequency, wherein the driver frequency does not enter into the determination of the first measured value representing the mass flow of the medium.Coriolis flowmeter according to one of the preceding claims, wherein the control criterion comprises a deviation between the filtered first sensor signal s1* and the filtered second sensor signal s2* assuming a sensor signal setpoint value or being less than a sensor signal limit value.Coriolis flowmeter according to one of the preceding claims, wherein the measuring and / or operating circuit (5) is configured to ascertain a phase difference Δφ between the filtered first sensor signal s1* and the filtered second sensor signal s2*, wherein the derived variable corresponds to the phase difference Δφ.The Coriolis flowmeter of claim 7, wherein the control criterion comprises the phase difference Δφ corresponding to a phase difference set point and / or less than a phase difference threshold.Coriolis flowmeter according to one of the preceding claims, wherein the generation of the first measured value representing the process variable, in particular the mass flow, additionally includes a calibration factor k, determined in particular at the factory.Coriolis flowmeter according to one of the preceding claims, wherein the measuring and / or operating circuit (5) is configured to determine a current process state from the filter coefficient a and / or from the filter coefficient b and optionally output it.The Coriolis flowmeter of claim 10, wherein the current process state comprises the presence of gas bubbles in the medium.Coriolis flowmeter according to one of Claims 4 to 11, wherein the measuring and / or operating circuit (5) is set up to: - determine and output a second measured value representing the process variable in a first operating mode as a function of a phase difference Δφ between the first sensor signal s1 or the filtered first sensor signal s1* and the filtered second sensor signal s2* and the driver frequency f, - determine and output the first measured value representing the process variable in a second operating mode as a function of the filter coefficient a and / or the filter coefficient b.Coriolis flowmeter according to claim 12, wherein the measuring and / or operating circuit (5) is configured to switch from the first operating mode into the second operating mode if a deviation between the first measured value and the second measured value assumes a setpoint value and / or lies outside a tolerance range.Coriolis flowmeter according to claim 13, wherein the measuring and / or operating circuit (5) is configured to determine the presence of gas bubbles by comparing a signal representing the first measured value and a signal representing the second measured value.Coriolis flowmeter according to one of the preceding claims, wherein the measuring and / or operating circuit (5) is configured to: - determine a second measured value representing the process variable, in particular the mass flow, as a function of a phase difference Δφ between the filtered first sensor signal s1* or first sensor signal s1 and the filtered second sensor signal s2* or the second sensor signal s2 and the driver frequency f, - correct the second measured value as a function of the filter coefficient a and / or b, or the first measured value, and - output the corrected second measured value.Coriolis flowmeter according to one of the preceding claims, wherein the first filter is designed in such a way that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be written with a Laplace index s via a transfer function H(s) = (1 - a · s).Coriolis flowmeter according to one of Claims 1 to 15, wherein the first filter is designed in such a way that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be written with a Laplace index s via a transfer function H(s) = (1 - a · s) / (1 + as).Coriolis flowmeter according to one of Claims 1 to 15, wherein the first filter is designed in such a way that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be described via a transfer function H(s) = (1 + a) / 2 + (1 - a) / 2 · z -1 where z is a z variable of a discrete system.Coriolis flowmeter according to one of the preceding claims, wherein the second filter is designed in such a way that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be written with a Laplace index s via a transfer function H(s) = (1 + b · s).Coriolis flowmeter according to one of Claims 1 to 18, wherein the second filter is designed in such a way that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described via a transfer function H(s) = (1-b) / 2 + (1 + b) / 2 · z -1 where z is a z variable of a discrete system.Coriolis flowmeter according to one of Claims 1 to 18, wherein the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described via a transfer function H(s) = 1⁄2 + 1⁄2 * z -1 where z is a z variable of a discrete system.Coriolis flowmeter according to one of Claims 1 to 18, wherein the second filter is designed in such a way that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described via a transfer function H(s)=1.The Coriolis flowmeter of any preceding claim, wherein a = b.Coriolis flowmeter according to one of the preceding claims, wherein the first adaptive filter and / or the second adaptive filter, in particular each, is an all-pass filter.

Images