EP0917644A1 - Appareil magneto-inductif de mesure du debit de milieux en ecoulement - Google Patents

Appareil magneto-inductif de mesure du debit de milieux en ecoulement

Info

Publication number
EP0917644A1
EP0917644A1 EP98928187A EP98928187A EP0917644A1 EP 0917644 A1 EP0917644 A1 EP 0917644A1 EP 98928187 A EP98928187 A EP 98928187A EP 98928187 A EP98928187 A EP 98928187A EP 0917644 A1 EP0917644 A1 EP 0917644A1
Authority
EP
European Patent Office
Prior art keywords
magnetic field
magnetic
flow meter
electromagnet
meter according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98928187A
Other languages
German (de)
English (en)
Inventor
Ronald Van Der Pol
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Krohne Messtechnik GmbH and Co KG
Original Assignee
Krohne Messtechnik GmbH and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Krohne Messtechnik GmbH and Co KG filed Critical Krohne Messtechnik GmbH and Co KG
Publication of EP0917644A1 publication Critical patent/EP0917644A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/60—Circuits therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/584—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters constructions of electrodes, accessories therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/586—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters constructions of coils, magnetic circuits, accessories therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/588—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters combined constructions of electrodes, coils or magnetic circuits, accessories therefor

Definitions

  • the invention relates to a magnetic-inductive flow measuring device for flowing media, with a measuring tube, an electromagnetic which serves to generate an at least substantially perpendicular magnetic field to the measuring tube axis.
  • a measuring tube an electromagnetic which serves to generate an at least substantially perpendicular magnetic field to the measuring tube axis.
  • at least two measuring electrodes arranged along a connecting line running at least substantially perpendicular to the measuring tube axis and to the direction of the magnetic field, one current source serving to supply the electromagnet with a switched direct current and an evaluation circuit generating the measuring voltage of the measuring electrodes and generating a flow signal.
  • the basic principle of the magnetic-inductive flow meter for flowing media goes back to Faraday, who proposed in 1832 to use the principle of electrodynamic induction for flow velocity measurement.
  • Faraday's law of induction an electric field strength perpendicular to the direction of flow and the magnetic field is created in a flowing medium that carries charge carriers and flows through a magnetic field.
  • This law is used in a magnetic-inductive flow meter in that a magnet, regularly consisting of two magnetic coils, generates a magnetic field perpendicular to the direction of flow in the measuring tube.
  • each volume element of the flowing medium moving through the magnetic field with the field strength arising in this volume element makes a contribution to the measurement voltage tapped via the measurement electrodes.
  • the measuring electrodes are designed so that they are either galvanically or capacitively coupled to the flowing medium.
  • a special feature of the magnetic-inductive flow measuring devices is the proportionality between the measuring voltage and the flow velocity of the medium averaged over the cross-section of the tube, ie. H. between measuring voltage and volume flow.
  • Magnetic-inductive flowmeters were initially operated in the industrial sector with an alternating magnetic field.
  • the electromagnet for generating the magnetic field was connected to the existing AC voltage network, so that the magnetic field changes its strength essentially sinusoidally.
  • the fluctuations in the AC voltage network are immediate passed on to the electromagnet and thus went fully into the measuring accuracy of the electromagnetic flowmeter.
  • the known magnetic-inductive flowmeters which work with an alternating magnetic field, are problematic in that the measuring voltage applied to the measuring electrodes inevitably has the frequency of the alternating voltage network.
  • there are also mains frequency interference voltages at the measuring electrodes caused, for. B. by axial electrical currents in the flowing medium - caused, for example, by the grounding of pumps on the adjacent pipelines - which are superimposed on the measuring voltages arising according to Faraday's law of induction.
  • This problem leads to the fact that high measuring accuracies can hardly be guaranteed in the case of magnetic-inductive flow measuring devices which work with an alternating magnetic field, so that they can only be used to a limited extent in the industrial field.
  • Magnetic-inductive flowmeters which work with a switched magnetic direct field, have become increasingly popular since the mid-1970s. These devices avoid a large number of the problems associated with the magnetic-inductive flow measuring devices which work with an alternating field and thus enable very high measuring accuracies in the range of up to one per thousand.
  • the magnetic field measured via reference windings the current through the coil of the electromagnet is used to correct the measuring voltages applied to the measuring electrodes.
  • the starting point for this procedure is the assumption that in the steady state the strength of the magnetic field is directly proportional to the coil current.
  • the starting point chosen in the prior art is problematic in that a great deal of effort must be taken to ensure the proportionality between the strength of the current through, the electromagnets and the strength of the magnetic field, regardless of temperature, pressure, installation conditions, field frequency and service life.
  • the temperature changes the magnetic properties of the iron core, which is supposed to guide the magnetic field outside the flowing medium and is to ensure the highest possible magnetic field within the flowing medium.
  • An iron core must therefore be selected, the properties of which change as little as possible with temperature.
  • the material costs and the required material cross section for the iron core increase.
  • the distance between the pole pieces of the iron core can also be changed by a changing temperature, which in turn affects the proportionality between the strength of the current through the electromagnet and the strength of the magnetic field.
  • the distance between the pole pieces can also change due to pressure changes within the measuring tube. This can only be avoided by a particularly stable, costly mechanical construction of the electromagnetic flowmeter.
  • the installation conditions of the magnetic-inductive flow meter such as. B.
  • the magnetic properties of the screws and flanges used by the user have an influence on the course of the magnetic field lines between the pole pieces. This influence can be reduced by the fact that the magnetic-inductive flow meter is particularly long compared to the pipe diameter. This in turn creates higher costs.
  • the field frequency with which the polarity of the magnetic field is switched also has an influence on the strength of the magnetic field, since, as a result of inductances and eddy currents, it cannot always be assumed that the magnetic field is constant during the actual measuring time.
  • the influence of the eddy currents is not taken into account when assuming a linear relationship between the strength of the magnetic field and the strength of the current flowing through the electromagnet.
  • the invention is therefore based on the object of providing a magnetic-inductive flow measuring device for flowing media which works with a switched direct field, which ensures a higher measuring accuracy with a significantly reduced, mechanical design effort.
  • the previously derived and shown object is achieved in that at least one magnetic field sensor is arranged in the magnetic field of the electromagnet and the evaluation circuit has a processing circuit connected to the magnetic field sensor.
  • the magnetic field sensor delivers a particularly easy to evaluate signal when it is designed as a Hall sensor.
  • the output signal of a Hall sensor is directly proportional to the average strength of the magnetic field, i. H. the mean magnetic induction, over the area of the Hall sensor.
  • the magnetic field sensor is designed as a reference coil, the reference coil covering the entire cross-section mentioned.
  • the reference coil covering the entire cross-section mentioned.
  • a further advantageous embodiment of the magnetic inductive flow meter according to the invention is ensured in that the magnetic field sensor in is located in the immediate vicinity of the measuring tube between the pole pieces of the electromagnet.
  • This type of arrangement of the magnetic field sensor ensures that, as far as possible, it works independently of stray influences of the magnetic field which does not penetrate the flowing medium.
  • Hall sensors also have a temperature dependency, albeit to a much lesser extent, it is advantageous to arrange a temperature sensor in the vicinity of the magnetic field sensor, so that the output signal of the magnetic field sensor can be corrected using the temperature signal of this temperature sensor.
  • the shape of the magnetic field changes as a function of time
  • a plurality of magnetic field sensors are provided for the location-dependent measurement of the magnetic field.
  • the output signal of these different magnetic field sensors is then weighted according to their arrangement during further processing.
  • the valency distribution in the measuring volume of the flowing medium plays an important role and must be taken into account when correcting the measuring signal.
  • the above-mentioned distortions of the magnetic field occur in particular when ferromagnetic particles are present in the flowing medium or when the electromagnetic flowmeter is relatively short in terms of its diameter, so that the surrounding pipeline system or the flanges connected to it influence the shape of the Magnetic field.
  • the electromagnetic flowmeter according to the invention is characterized in that the evaluation circuit has a correction circuit correcting the flow signal and an output of the processing circuit is connected to an input of the correction circuit.
  • the measure mentioned makes it possible to correct the flow signal with the aid of the signals from the magnetic field sensor. For example, if the magnetic field is too strong compared to the desired magnetic field, the measuring voltage between the measuring electrodes is weighted less than if the magnetic field is too weak.
  • the correction just described is carried out particularly advantageously in that the correction circuit has an analog / digital converter which converts the flow signal and the output signal of the processing circuit is present at the reference input of the analog / digital converter. This configuration ensures that the flow signal is still corrected in the analog part of the evaluation circuit. This correction is carried out with very little effort and without delay.
  • the magnetic-inductive flow meter according to the invention is characterized in that the current source has a current regulator which regulates the direct current supplied to the electromagnet and an output of the processing circuit is connected to the setpoint input of the current regulator.
  • the aim of this embodiment is to keep the magnetic field monitored by the magnetic field sensor at a constant value independent of external influences. For the optimal case in which this constant maintenance is completely successful, no further corrective measures with regard to the flow signal are necessary.
  • magnetic field fluctuations due to external - even short-term - influences cannot really be ruled out, it is particularly advantageous to combine the second, particularly advantageous measure just explained with the already explained first, particularly advantageous embodiment of the electromagnetic flowmeter according to the invention.
  • a coil arranged in a magnetic field such as the reference coil
  • supplies a coil current that is proportional to the change in the magnetic flux over its area it is advantageous to provide the processing circuit for evaluating the reference coil signal with an integrator circuit.
  • This integrator circuit delivers as the output signal a signal which, apart from an unknown constant and known proportionality factors, corresponds to the magnetic flux and thus the average strength of the magnetic field.
  • the output signal of the integrator circuit is thus suitable for correcting the flow signal.
  • the processing circuit has a high-pass filter in addition to evaluating the reference coil signal, it is ensured that only the time-varying portions of the measurement signal of the magnetic field sensor are taken into account in the output signal of the processing circuit. After an integration, this is suitable through a High-pass filter filtered measurement signal of the magnetic field sensor especially for correcting the flow signal of the magnetic-inductive flow meter according to the invention.
  • FIG. 1 schematically shows an embodiment of a magnetic inductive flow meter according to the invention
  • Fig. 2 shows a circuit of an embodiment of the supply of
  • Electromagnets of a current source serving flow meter according to the invention
  • FIG. 1 of the drawing an embodiment of a magnetic-inductive flow meter for flowing media is shown.
  • This exemplary embodiment has a measuring tube 1, an electromagnet 2 used to generate a magnetic field running perpendicular to the measuring tube axis, and two along one running perpendicular to the measuring tube axis and to the magnetic field direction Connecting line arranged measuring electrodes 3, 4, one of the supply to the electromagnet 2 serving with a switched direct current power source 5 and the measurement voltage of the measurement electrodes 3, evaluating 4, a flow signal -Create, the evaluation circuit 6.
  • the evaluation circuit 6 characterized that two magnetic field sensors 7, 8 are arranged in the magnetic field of the electromagnet 2 and the evaluation circuit 6 has a processing circuit 9 connected to the magnetic field sensors 7, 8.
  • the embodiment of a magnetic-inductive flowmeter shown in FIG. 1 has two magnetic field sensors 7, 8, which are designed as reference coils and are arranged between the pole pieces 10, 11 of the electromagnet 2.
  • the magnetic field sensors 7, 8 can, as already mentioned, also be designed as Hall sensors.
  • the reference coils are preferably to be designed such that their diameter corresponds to the diameter of the coils 12, 13 of the electromagnet 2, so that the portion of the magnetic field which penetrates the flowing medium also passes through the reference coils.
  • the evaluation circuit 6 of the exemplary embodiment shown in FIG. 1 for an electromagnetic flowmeter according to the invention has a correction circuit 14 which corrects the measurement voltage between the measurement electrodes and outputs a flow signal and which is connected to an input of an output of the processing circuit 9.
  • the correction circuit 14 thus has at its disposal a signal proportional to the strength of the magnetic field, on the basis of which the correction circuit 14 corrects the flow signal according to the following equation:
  • correction circuit 14 has an analog / digital converter 16 which converts the measuring voltage between the measuring electrodes 3, 4 and is amplified by a differential amplifier 15 Output signal of the processing circuit 9 is present via a reference input.
  • the current source 5 of the exemplary embodiment of a magnetic inductive flow meter according to the invention shown in FIG. 1 has a current regulator 17 which regulates the direct current supplied to the electromagnet 2, with an output of the processing circuit 9 having the setpoint input of the current regulator 17 is connected so that the current through the coils 12, 13 of the electromagnet 2 is controlled so that the strength of the magnetic field generated by the electromagnet 2 remains constant regardless of external influences.
  • the actual supply of the coils 12, 13 of the electromagnet 2 takes place via a reversible H circuit 18 within the current source 5.
  • the processing circuit 9 has at least one integrator circuit 19 and preferably a high-pass filter 20 for evaluating the reference coil signal.
  • the exact function of the integrator circuit 19 and the high-pass filter 20 will be explained in more detail later with reference to FIGS. 3 and 4.
  • the current source 5 shown only schematically in FIG. 1 is shown in detail in FIG. 2 as a circuit.
  • the current source 5 has a current regulator 17 and an H circuit 18.
  • the H circuit 18 is controlled by a clock generator 21 to generate the switched direct field and has four electronic switches 22 to control the coil 12 shown here for the sake of simplicity.
  • a controllable constant current source 23 is used as the current source in the actual sense in the current source 5 shown in FIG. 2.
  • This controllable constant current source 23 is controlled by the current regulator 17, which has an integrator 25 that can be erased via an electronic switch 24 and is preferably arranged in the processing circuit 9 a resistor 26 and an electronic switch 27 is connected.
  • the input of the integrator 25 is connected via an electronic switch 28 to the output of a magnetic field sensor 7 designed as a reference coil.
  • the course of the strength of the magnetic field which is preferably averaged over the magnetic field cross section, ie the course of the magnetic induction B, is the.
  • the relatively low field frequency when the magnetic field is switched over means that the magnetic induction no longer changes in the measuring intervals shown hatched in FIG. 3, during which the measuring voltage is recorded. In this case, it is sufficient to correct the measuring voltage applied to the measuring electrodes if the stroke of the magnetic induction B is used for the correction.
  • the stroke of the magnetic induction B results in a simple manner as follows I :
  • Uref reference voltage of the reference coil.
  • FIG. 4 shows the case in which the field frequency for switching the direct field is so high that the magnetic induction B has not yet reached saturation at the end of a measuring interval.
  • Fig. 4a shows the case in which the field frequency for switching the direct field is so high that the magnetic induction B has not yet reached saturation at the end of a measuring interval.
  • FIG. 4b shows the integrated reference voltage of the reference coil also changes within the measurement intervals shown hatched in FIG. 4.
  • Fig. 4c The signal obtained, as shown in Fig. 4d), again gives a signal for magnetic induction B, which is then also suitable for the correction of the measuring voltage applied to the measuring electrodes, if this occurs during the measuring interval. valle still changes.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Measuring Volume Flow (AREA)

Abstract

Cet appareil magnéto-inductif de mesure du débit de milieux en écoulement comprend un tube de mesure (1), un électro-aimant (2) qui sert à générer un champ magnétique au moins sensiblement perpendiculaire à l'axe du tube de mesure, au moins deux électrodes de mesure (3, 4) situées le long d'une ligne de liaison au moins sensiblement perpendiculaire à l'axe du tube de mesure et à l'orientation du champ magnétique, une source de courant (5) pour alimenter l'électro-aimant (2) en courant direct et un circuit d'évaluation qui évalue les tensions de mesure des électrodes de mesure (3, 4) et qui génère un signal indicateur du débit. Selon l'invention, l'appareil magnéto-inductif de mesure du débit de milieux en écoulement se caractérise en ce qu'au moins un capteur (7, 8) du champ magnétique est monté dans le champ magnétique de l'électro-aimant (2) et en ce que le circuit d'évaluation (6) comprend un circuit de traitement (9) relié au capteur (7, 8) du champ magnétique.
EP98928187A 1997-04-04 1998-04-01 Appareil magneto-inductif de mesure du debit de milieux en ecoulement Withdrawn EP0917644A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE19713751 1997-04-04
DE1997113751 DE19713751A1 (de) 1997-04-04 1997-04-04 Magnetischinduktives Durchflußmeßgerät für strömende Medien
PCT/EP1998/001884 WO1998045670A1 (fr) 1997-04-04 1998-04-01 Appareil magneto-inductif de mesure du debit de milieux en ecoulement

Publications (1)

Publication Number Publication Date
EP0917644A1 true EP0917644A1 (fr) 1999-05-26

Family

ID=7825329

Family Applications (1)

Application Number Title Priority Date Filing Date
EP98928187A Withdrawn EP0917644A1 (fr) 1997-04-04 1998-04-01 Appareil magneto-inductif de mesure du debit de milieux en ecoulement

Country Status (5)

Country Link
EP (1) EP0917644A1 (fr)
JP (1) JP2000511647A (fr)
AU (1) AU8012798A (fr)
DE (1) DE19713751A1 (fr)
WO (1) WO1998045670A1 (fr)

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DE19907864A1 (de) * 1999-02-23 2000-09-14 Krohne Messtechnik Kg Magnetisch-induktives Durchflußmeßgerät
DE10026052B4 (de) * 2000-05-25 2005-03-17 Forschungszentrum Rossendorf E.V. Verfahren und Anordnung zur kontaktlosen Bestimmung von räumlichen Geschwindigkeitsverteilungen in nicht-kugelförmigen elektrisch leitfähigen Flüssigkeiten
DE10254268A1 (de) * 2002-11-21 2004-06-09 Abb Patent Gmbh Verfahren zum Betrieb einer induktiven Durchflussmesseinrichtung, sowie induktive Durchflussmesseinrichtung selbst
DE10347878A1 (de) * 2003-10-10 2005-05-04 Abb Patent Gmbh Magnetisch-induktives Messgerät für strömende Stoffe und Verfahren zu dessen Herstellung
DE102004057680A1 (de) * 2004-11-29 2006-06-01 Endress + Hauser Flowtec Ag Verfahren zur Funktionsüberwachung eines Magnetisch Induktiven Durchflussmessaufnehmers
DE102008034565A1 (de) * 2008-07-24 2010-02-04 Siemens Aktiengesellschaft Elektromagnetischer Durchflussmesser sowie Verfahren zum Betrieb eines elektromagnetischen Durchflussmessers
RU2596863C2 (ru) * 2010-08-03 2016-09-10 ГОУЭНС Ли Электромагнитный расходомер
CN201964914U (zh) * 2010-12-22 2011-09-07 上海威尔泰工业自动化股份有限公司 一种可以检测磁场和磁导率的电磁流量计传感器
DE102013014016B4 (de) * 2013-08-26 2015-08-06 Krohne Messtechnik Gmbh Verfahren zum Betreiben eines magnetisch-induktiven Durchflussmessgeräts
DE102015120103B4 (de) * 2015-11-19 2018-09-13 Krohne Ag Verfahren zur Durchflussmessung durch ein magnetisch-induktives Durchflussmessgerät
DE102017112950A1 (de) 2017-06-13 2018-12-13 Krohne Messtechnik Gmbh Magnetisch-induktives Durchflussmessgerät und Verfahren zum Betreiben eines magnetisch-induktiven Durchflussmessgerätes
DE102019133460A1 (de) * 2019-12-06 2021-06-10 Endress+Hauser Flowtec Ag Magnetisch-induktives Durchflussmessgerät
DE102020114515A1 (de) 2020-05-29 2021-12-02 Endress+Hauser Flowtec Ag Magnetisch-induktive Durchflussmessvorrichtung
DE102021130339A1 (de) 2021-11-19 2023-05-25 Endress+Hauser Flowtec Ag Magnetisch-induktive Durchflussmessgerät
DE102022121407A1 (de) * 2022-08-24 2024-02-29 Krohne Messtechnik Gmbh Testvorrichtung für ein modulares magnetisch-induktives Durchflussmessgerät, Testverfahren für eine solche Testvorrichtung, Testvorrichtung für ein monolithisches magnetisch-induktives Durchflussmessgerät und Testverfahren für eine solche Testvorrichtung

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Also Published As

Publication number Publication date
WO1998045670A1 (fr) 1998-10-15
AU8012798A (en) 1998-10-30
JP2000511647A (ja) 2000-09-05
DE19713751A1 (de) 1998-10-08

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