WO2010121631A1 - Débitmètre électromagnétique et procédé de fonctionnement de celui-ci - Google Patents

Débitmètre électromagnétique et procédé de fonctionnement de celui-ci Download PDF

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Publication number
WO2010121631A1
WO2010121631A1 PCT/EP2009/002936 EP2009002936W WO2010121631A1 WO 2010121631 A1 WO2010121631 A1 WO 2010121631A1 EP 2009002936 W EP2009002936 W EP 2009002936W WO 2010121631 A1 WO2010121631 A1 WO 2010121631A1
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WO
WIPO (PCT)
Prior art keywords
flowmeter
electrodes
period
magnetic field
measurement
Prior art date
Application number
PCT/EP2009/002936
Other languages
English (en)
Inventor
Søren NIELSEN
Original Assignee
Siemens Aktiengesellschaft
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 Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Priority to PCT/EP2009/002936 priority Critical patent/WO2010121631A1/fr
Publication of WO2010121631A1 publication Critical patent/WO2010121631A1/fr

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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

Definitions

  • Electromagnetic flowmeter and method of operation thereof are Electromagnetic flowmeter and method of operation thereof
  • the present invention relates to electromagnetic flowmeters for measurement of fluid flow rate, and in particular, to condition monitoring in such flowmeters.
  • Electromagnetic flowmeters utilize the principle of electrodynamic induction for flow rate measurement of a fluid medium.
  • a magnetic field is generated across a measuring section of the flowmeter pipe through which the medium flows, which, by operation of
  • Such an electromagnetic flowmeter is, in principle, a black box. If there is no differential electrode signal, it is assumed that there is no flow. That is, there is no way to monitor operational failures which may lead to no differential electrode signal, for example, when there is a short circuit of the electrodes, or when no current is flowing through the coils in the magnetic circuit.
  • the object of the present invention is to provide an improved electromagnetic flowmeter and method of operation thereof.
  • the above object is achieved by the features of the present invention as set forth in claims 1 and 8.
  • the differential electrode signal is proportional to the flow velocity only if the magnetic field is stable. Therefore, for a given pulse of the magnetic field accurate flow measurements would be possible only for a time period when the magnetic field is stable.
  • the underlying idea of the present invention is that, by measuring the differential electrode signal in the period when the magnetic field is stabilizing, it is possible to monitor the health of the flowmeter. During this period, the differential electrode signal is dominated by the rate of change of the magnetic field. Hence a measurement of the differential electrode signal during this period would make it possible to verify if the coil current is resulting in the magnetic field, which again is resulting in the differential electrode signal.
  • the flowmeter comprises a flow measurement module adapted for determining flow rate of said fluid based on measurement of said differential electrode signal during a second period within the duration of said pulse, said second period corresponding to a time interval within said pulse after said magnetic field has stabilized.
  • the differential electrode signal is proportional to the flow rate during the second period, and hence it is possible to accurately measure the fluid flow rate during this period.
  • the condition monitoring module is adapted to determine an operational condition as abnormal when said differential electrode signal measured during said first period is lesser than a reference value. It is shown herein that under normal operating conditions, i.e., when there is current in the magnetic coils and the electrodes are not short circuited, the differential electrode signal would shows a high peak value at the beginning of the pulse. The absence or reduction of this value (with respect to a reference value) can therefore be used to indicate an abnormal operational condition.
  • the condition monitoring module is further adapted for measurement of individual potentials of each of said electrodes with respect to ground within the duration of said first period, and determining an operational condition of said flowmeter based upon a comparison of the measured individual potentials of said electrodes with respect to ground. This can be used to check balance of electrode to ground impedance through the fluid medium
  • Electrode surface contamination electrode surface contamination
  • each electrode of said pair of electrodes is provided with an electrode cable made with a loop of equal area and identical turn direction and positioned such that said magnetic field passes through said loops of said electrode cables.
  • the flowmeter further comprises means for displaying the determined operational condition of said flowmeter.
  • the flowmeter comprises a microprocessor adapted to execute said condition monitoring module and said flow measurement module.
  • the microprocessor can be advantageously programmed to process the differential electrode signal during the first and second periods distinctly. The durations of the first and second periods can be preprogrammed into the microprocessor.
  • FIG 1 is a schematic diagram of an electromagnetic flowmeter having a condition monitoring module according to one embodiment of the present invention
  • FIG 2 is a graphical representation of the variation of the measured differential electrode signal during one pulse of the magnetic field
  • FIG 3 is a schematic diagram of an electromagnetic flowmeter arrangement according to a further embodiment of the present invention for monitoring electrode to ground impedance through the fluid medium, and
  • FIGS 4A and 4B are graphical representations of the variation of the individual electrode potentials of the measuring electrodes with respect to ground during one pulse of the magnetic field.
  • an electromagnetic flowmeter 10 includes a measurement tube 12 extending along an axis 40.
  • the measurement tube 12 defines a passage for flow of a fluid media 14 whose flow rate is to be measured.
  • the fluid 14 to be measured is electrically conductive, at least to a slight extent.
  • Measuring electrodes 16 and 18 are arranged on opposite sides of the measurement tube 12.
  • a non-conducting liner 38 may be disposed along the inner surface of the measurement tube 12 to prevent the electrodes 16 and 18 from being short circuited.
  • a magnetic circuit comprising coils 44 and 46 that are excitable by a pulsed alternating current signal 49 from a current source 48.
  • the pulsed current signal 49 is generated to have a substantially constant value during one pulse of the current signal 49, approaching a square waveform.
  • the excitation of the coils 44 and 46 results in a pulsed magnetic field 42 of alternating polarity that is oriented perpendicularly to the direction of flow of the fluid 14.
  • charge carriers in the fluid media 14 migrate to the measuring electrodes 16 and 18 of opposite polarity thus building up a potential difference across the electrodes 16 and 18.
  • Flow measurement means 24, such as a differential amplifier amplifies this potential difference (i.e. the difference in the output signals 22 and 20 from the measuring electrodes 16 and 18 respectively) and provides a differential electrode signal 26.
  • the differential electrode signal 26 is proportional to the flow velocity of the fluid 14 (averaged over the cross- sectional area of the measurement tube 12) when the magnetic field 42 has stabilized (i.e., becomes constant). However, when the magnetic field 42 is in the process of stabilizing, the differential electrode signal 26 is a function of both the fluid velocity and the rate of change of magnetic flux d ⁇ /dt.
  • FIG 2 depicts a curve 50 showing a typical variation of the differential electrode signal E 0 (V), represented along the axis 52 with time t(ms) represented along the axis 54.
  • the curve 50 is herein discussed within the duration Pi of one pulse of the magnetic field.
  • the magnetic flux increases rapidly (i.e. d ⁇ /dt is very high at the start of the pulse) , due to which the differential electrode signal has a very steep spike from a negative value to a positive peak value E D (p ea k) at the beginning of the pulse.
  • the rate of change of magnetic flux d ⁇ /dt subsequently decreases till the time the magnetic field stabilizes. Till the time the magnetic field stabilizes (i.e. till d ⁇ /dt becomes zero), the differential electrode signal is a function of both, the rate of change of flux d ⁇ /dt and the flow velocity of the fluid, the rate of change of magnetic flux being the more dominant factor.
  • the period before the magnetic flux has stabilized is indicated by ti.
  • differential electrode signal gradually decreases with time till the curve 50 becomes asymptotic with the time axis 54.
  • differential electrode signal is proportional to the flow velocity of the fluid, till the onset of the next pulse of the magnetic field which is of opposite polarity.
  • the present invention proposes to utilize the first period ti for condition monitoring of the flowmeter.
  • the second period t 2 may be utilized for flow measurement.
  • the differential electrode signal By measuring the differential electrode signal during the first period ti when the magnetic field is stabilizing, it is possible to monitor the health of the flowmeter. For example, if individual potentials of each of said electrodes (16, 18) with respect to ground or the differential electrode signal is measured to be zero in the first period ti, it indicates an operational failure, arising, for example, when no current flows through the magnetic coils, or measuring electrodes are partially or fully short circuited, which may take place if the liner is destroyed or, if there is a deposit of a conductive layer on the liner. This makes it possible for appropriate remedial action or repair work.
  • an abnormal operational condition may be indicated whenever individual potentials of each of said electrodes (16, 18) with respect to ground or the differential electrode signal measured in the first period ti is lesser than a predetermined reference value.
  • the differential electrode signal would show a high peak value E D( p eak ) at the beginning of the pulse. The absence or any reduction in this peak value can therefore be used to indicate an abnormal operational condition.
  • the proposed flowmeter 10 includes a condition monitoring module 30, executed, for example, by a microprocessor 28, for determining an operational condition of the flowmeter 10 by measuring the differential electrode signal 26 for a first period in the duration of a pulse of the magnetic field 42 when the magnetic field 42 is stabilizing, as discussed referring to FIG 2. Based upon the measured differential electrode signal during this first period, the operational status of the flowmeter, or any abnormality thereof, can be notified to the user via display means 36. As an example, the display means 36 may simply include an LED with an ON/OFF function to indicate whether or not the flowmeter is functioning normally. Determination of flow rate of the fluid is carried out by a flow measurement module 32 executed by the microprocessor 28 by measurement of the differential electrode signal 26 during the second period of the pulse.
  • the flow measurement module 32 calibrates the differential electrode signal 26 measured during the second period to units of flow velocity or flow rate, and provides an output to output circuitry 34.
  • the condition monitoring module and the flow measurement module may be implemented by preprogramming durations of the first and second periods in the pulse into the microprocessor 28.
  • the first period would correspond to a time interval within a pulse before the magnetic field has stabilized.
  • the second period would correspond to a time interval within the pulse after the magnetic field has stabilized.
  • condition monitoring module may be extended to check balance of electrode to ground impedance through the fluid media. This can be achieved by measuring each individual electrode potential with respect to ground during the first period ti of the pulse, when the magnetic field is stabilizing, and comparing these measured individual electrode potentials with respect to ground.
  • FIG 3 shows an exemplary arrangement for carrying out the same.
  • the measuring electrodes 16 and 18 arranged on opposite sides of the measurement tube 12 are provided with electrode cables that are made with respective loops 156 and 158.
  • These loops 156 and 158 have equal area and identical turn directions, and are positioned such that the magnetic field 42 passes through the loops 156 and 158.
  • the arrangement described herein advantageously provides an enhanced signal for measurement of electrode potential with respect to ground that may be used for determining the operational condition by comparison to a reference value.
  • FIG 4A shows the variation of the potential of the electrode 16 with respect to the ground (represented by curve 70) in the duration Pi of a pulse of the magnetic field, wherein the axis 72 represents the potential Ei 6 (V) of the electrode 16 with respect to ground and the axis 74 represents time t(ms) .
  • the electrode potential of the electrode 16 with respect to ground has a very steep spike from a negative value to a positive peak value E 16 (p ea k) at the beginning of the pulse.
  • E 16 p ea k
  • the loops 156 and 158 are of equal area and have identical turn directions, under normal operating conditions, a similar variation can be observed with respect to the potential of the electrode 18 with respect to ground during the pulse Pi, as depicted by the curve 80 in FIG 4B, wherein the axis 82 represents the potential Ei 8 (V) of the electrode 18 with respect to ground and the axis 84 represents time t(ms).
  • the individual electrode potentials Ei 6 and Ei 8 should be substantially equal, although not exactly equal in value.
  • the potentials Ei 6 and Ei 8 cannot be fully identical as the effect of the varying field in the fluid will add to one of the signals 22 and 22 and be subtracted from the other.
  • the condition monitoring module 30 can be adapted to determine an abnormal operational condition (such as, a possible short circuit in one of the electrodes or an electrode surface contamination) in case of any inequality in the measured individual electrode potentials (i.e, the signals 20 and 22 measured individually) during the first period t x , beyond an accepted tolerance limit.
  • an abnormal operational condition such as, a possible short circuit in one of the electrodes or an electrode surface contamination
  • the present invention provides an electromagnetic flowmeter and a method of operation thereof.
  • the proposed flowmeter comprises a measurement tube defining a passage for carrying a fluid whose flow is to be measured.
  • a magnetic circuit is provided having a pair of coils excitable by a pulsed alternating current signal to generate a pulsed magnetic field oriented perpendicularly to a direction of flow of said fluid.
  • a pair of electrodes is positioned on opposite sides of said measurement tube.
  • the proposed flowmeter further comprises a condition monitoring module adapted for determining an operational condition of the flowmeter based upon measurement of individual potentials of each of said electrodes with respect to ground or upon measurement of a differential electrode signal obtained from a difference between output signals of said electrodes. This measurement is carried out during a first period within the duration of one pulse of said magnetic field, said first period corresponding to a time interval within said pulse before said magnetic field has stabilized.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

La présente invention porte sur un débitmètre électromagnétique et sur un procédé de fonctionnement de celui-ci. Le débitmètre proposé (10) comprend un tube de mesure (12) définissant un passage pour transporter un fluide (14) dont l'écoulement doit être mesuré. Un circuit magnétique est disposé, lequel a une paire de bobines (44, 46) aptes à être excitées par un signal de courant alternatif pulsé (42), pour générer un champ magnétique pulsé (42) orienté perpendiculairement à une direction d'écoulement dudit fluide (14). Une paire d'électrodes (16, 18) est disposée sur des côtés opposés dudit tube de mesure (12). Le débitmètre proposé (10) comprend en outre un module de surveillance de condition (30) apte à déterminer une condition de fonctionnement du débitmètre (10) en fonction d'une mesure de potentiels individuels de chacune desdites électrodes (16, 18) par rapport à une masse ou lors de la mesure d'un signal d'électrode différentiel (26) obtenu à partir d'une différence entre des signaux de sortie (22, 20) desdites électrodes (16, 18). Cette mesure est effectuée au cours d'une première période (t1) à l'intérieur de la durée (P1) d'une impulsion dudit champ magnétique (42), ladite première période (t1) correspondant à un intervalle de temps à l'intérieur de ladite durée (P1) de l'impulsion avant que ledit champ magnétique (42) ne soit stabilisé.
PCT/EP2009/002936 2009-04-22 2009-04-22 Débitmètre électromagnétique et procédé de fonctionnement de celui-ci WO2010121631A1 (fr)

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Application Number Priority Date Filing Date Title
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2618584C1 (ru) * 2016-02-26 2017-05-04 Акционерное общество научно-исследовательский институт теплоэнергетического приборостроения "НИИТеплоприбор" Электромагнитный преобразователь расхода
EP2972123B1 (fr) * 2013-03-14 2020-12-09 Micro Motion, Inc. Débitmètre magnétique avec réglage automatique basé sur impédance complexe détectée

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5370000A (en) 1991-07-04 1994-12-06 Fischer & Porter Company Magnetic flowmeter with fault detection
US20020145417A1 (en) * 2001-04-10 2002-10-10 Helmut Brockhaus Magnetoinductive flowmeter and magnetoinductuve flow-measuring process
WO2007033697A1 (fr) * 2005-09-21 2007-03-29 Siemens Aktiengesellschaft Procede pour faire fonctionner un dispositif electromagnetique de mesure de debit, et dispositif electromagnetique de mesure de debit correspondant

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5370000A (en) 1991-07-04 1994-12-06 Fischer & Porter Company Magnetic flowmeter with fault detection
US20020145417A1 (en) * 2001-04-10 2002-10-10 Helmut Brockhaus Magnetoinductive flowmeter and magnetoinductuve flow-measuring process
WO2007033697A1 (fr) * 2005-09-21 2007-03-29 Siemens Aktiengesellschaft Procede pour faire fonctionner un dispositif electromagnetique de mesure de debit, et dispositif electromagnetique de mesure de debit correspondant

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2972123B1 (fr) * 2013-03-14 2020-12-09 Micro Motion, Inc. Débitmètre magnétique avec réglage automatique basé sur impédance complexe détectée
RU2618584C1 (ru) * 2016-02-26 2017-05-04 Акционерное общество научно-исследовательский институт теплоэнергетического приборостроения "НИИТеплоприбор" Электромагнитный преобразователь расхода

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