RU2161778C1 - Electromagnetic flowmeter - Google Patents

Abstract

FIELD: measurement of flow rate of conducting liquids in pipelines. SUBSTANCE: flowmeter has pipeline section made of nonmagnetic and nonconducting material, two excitation coils provided with common axle perpendicular to channel axis, several pairs of electrodes positioned in central section of pipeline along its perimeter, and magnetic casing embracing pipeline with excitation coils from the outside. Two auxiliary excitation coils with common axle coinciding with axis of flowmeter channel are mounted on pipeline equidistantly from central section of channel in which electrodes are arranged. Flowmeter provides for measurement of flow rate by electromagnetic method in pipelines of large diameters with channel filled not completely and in pressure pipelines when measuring flow rate of multiphase media, for example, pulp. EFFECT: enhanced accuracy of measurement. 3 dwg

Description

 The invention relates to instrumentation, in particular to the field of flow measurement by an electromagnetic method, and can be used to measure the flow of electrically conductive fluids in pressure-free pipelines (with a varying level of filling of the channel with a measured liquid).

 Known electromagnetic flow meters for measuring the flow rate of electrically conductive liquids having a pipe section of non-magnetic material, an electromagnetic system (inductor) consisting of a magnetic circuit and excitation coils, electrodes in contact with the measured liquid, and a measuring device [1].

 The disadvantage of such flowmeters is the low sensitivity to changes in the level of filling the channel with the measured medium and therefore their low measurement accuracy.

 This disadvantage is partially eliminated in the electromagnetic flowmeter [2], designed to measure flows with a channel not completely filled.

 The electromagnetic flowmeter [2] also has a pipeline section made of non-magnetic and non-conductive material, two excitation coils having a common axis perpendicular to the channel axis, and a magnetic casing enclosing the pipeline with excitation coils. In contrast to [1], the flow meter [2] has not one, but several pairs of electrodes, for example, two or three pairs located in the central section of the pipeline along its perimeter. With the help of a controlled switching device of the flow meter, programmatically switching the excitation coils to the power source is carried out: alternating, consonant and counterclosing of both coils. Depending on the circuit for switching on the coils, a different distribution of the magnetic field is created in the flowmeter channel.

 The flowmeter measuring device is multi-channel with the number of channels corresponding to the number of electrode pairs.

 The operation of an electromagnetic flowmeter is based on the interaction of a moving conductive fluid with a magnetic field, obeying the law of electromagnetic induction. A feature of the known flowmeter [2] is as follows. When a stream moves along a channel in a liquid, an electric field arises, which is determined by the flow rate, the distribution of the magnetic field in the channel, and the "live" cross section, i.e. the cross-sectional area of the fluid flow. In this case, the magnetic field of excitation periodically changes depending on the different circuit of the inclusion of coils. The signals recorded by the pairs of electrodes are amplified in the measuring device of the flow meter and stored. Thus, a database is prepared for magnetic fields formed by the various switching of the coils to the power source. Further, the computing device, using a special algorithm, calculates the average flow rate and the area of the "live section", and therefore the volumetric flow rate of the measured medium.

 An electromagnetic flow meter [2] is the closest analogue to the flow meter made according to the invention. The disadvantage of the flow meter [2] is the low sensitivity to changes in the "live" flow cross section. This is because the magnetic field formed by the excitation coils, the axis of which is vertical and perpendicular to the axis of the channel, creates a potential electric field in the fluid flow. The dependence of the electric field in the flowmeter channel on the change in the boundary conditions, i.e. from a change in the level of filling the channel with liquid, it is determined only by the heterogeneity of the distribution of the magnetic field along the vertical axis, caused by a change in the component of the magnetic field directed along the axis of the channel. When the arrangement of coils of the magnetic field component used in the flowmeter [2], directed along the axis of the channel, is small and is determined by the length of the inductor along the generatrix of the pipeline. The shorter the inductor along the channel, the higher this component, i.e. the higher the sensitivity of the flow meter to a change in the level of filling the channel, however, this decreases the sensitivity of the flow meter to the flow rate, because decreases the component of the magnetic field directed vertically, i.e., perpendicular to the lines connecting the pairs of electrodes. It should be noted here that with a free flow of fluid through a pipeline with a change in flow rate, the “live” flow section changes almost proportionally to it and its average speed almost does not change.

 The flowmeter made according to the invention is free from this drawback: it is highly sensitive both to the flow rate and to the change in the area of the "live" section of the flow.

 The proposed electromagnetic flow meter is characterized in that it additionally has two excitation coils with a common axis coinciding with the axis of the flow meter channel. These additional coils are located on the pipeline, are turned towards each other and are equidistant from the central section of the channel in which the electrodes are located.

 The design and operation of the flowmeter are illustrated in FIG. 1, 2 and 3.

 In FIG. 1 shows the design of the flow meter, where 1 is a section of the pipeline made of non-magnetic and non-conductive material; 2 - flowmeter housing, which is simultaneously a magnetic circuit; 3 and 3 '- two excitation coils located on the pipeline, their common axis coincides with the axis of the channel, and the plane of the turns are parallel to the cross section of the channel; 4 and 4 '- two excitation coils, their common axis is perpendicular to the channel axis; 5 and 5 '- a pair of electrodes located along the diameter of the channel, connecting their line perpendicular to the axis of the channel; 6 and 6 '- a pair of electrodes located along a chord parallel to the line of electrodes 5 and 5'.

 In FIG. 2 shows the distribution of the magnetic field in the channel caused by various pairs of field coils. In FIG. 2a shows the distribution of the magnetic field formed by two excitation coils, the common axis of which is perpendicular to the axis of the channel, where 1 is the pipeline, 2 is the casing and simultaneously the magnetic circuit, 4 and 4 'are the excitation coils, whose common axis is perpendicular to the axis of the channel, 5 and 5' - electrodes located along the channel diameter, 6 and 6 '- electrodes located along the chord, 7 - magnetic field lines. In FIG. 2b shows the distribution of the magnetic field in the channel, formed by the excitation coils, the common axis of which coincides with the axis of the channel, where 1 is the pipeline, 2 is the casing and simultaneously the magnetic circuit, 3 and 3 'are the excitation coils, the common axis of which coincides with the axis of the channel, 7 - magnetic field lines. In FIG. 2c shows the distribution of the magnetic field in the central section of the channel (where the electrodes are located), formed by two excitation coils, the common axis of which coincides with the axis of the channel, where 1 is the pipeline, 2 is the body and simultaneously the magnetic circuit, 5 and 5 'is a pair of electrodes located along the diameter of the channel, 6 and 6'- a pair of electrodes located along the chord, 8 is the radial component of the magnetic field.

 In FIG. 3 shows a flowmeter diagram, where 1 is the pipeline, 3 and 3 'are the excitation coils, the common axis of which coincides with the axis of the channel, 4 and 4' are the excitation coils, whose common axis is perpendicular to the channel axis, 5 and 5 'are the pair of electrodes located by channel diameter, 6 and 6 '- a pair of electrodes located along the chord, 9 - switch, 10 - power supply, 11 - measuring channel of a signal taken from a pair of electrodes 5 and 5', 12 - measuring channel of a signal taken from a pair of electrodes 6 and 6 ', 13 - calculator.

 The operation of the flowmeter is as follows.

 If the liquid level in the channel is between full filling and half of the channel cross-section, then the flow rate is measured by processing signals taken from a pair of electrodes that are located along the channel diameter (5 and 5 ', Fig. 3). If the filling level is below the location of the electrodes 5 and 5 ', then the signal from them will be absent due to the open electrodes of the electrically conductive liquid. In this case, the flow measurement is carried out by processing signals taken only from a pair of electrodes that are located along the chord (6 and 6 ', Fig. 3) and are washed by the measured medium.

 Flow measurement is carried out with two modes of switching on the excitation coils, which are created alternately. When coils are connected to the power source, the axis of which is perpendicular to the axis of the channel, a mainly vertical component of the magnetic field is formed in the central section of the channel (see Fig. 2a); in this case, the signal excited at the electrodes is determined by the average flow rate and does not depend much on the channel filling level. The signal taken from the electrodes is stored by the calculator. Then the excitation coils 3 and 3 'are turned off and the power supply 10 is connected to the coils 4 and 4', the common axis of which coincides with the axis of the channel (Fig. 3). Since these coils are turned towards each other, a significant radial component of the magnetic field appears in the central section of the channel, which changes sharply along the radius of the pipe, rapidly decreasing to the center of the channel to zero (see Figs. 2b and 2c). The signal arising from the interaction of this magnetic field with the fluid flow is highly sensitive to changes in the channel filling level and the velocity of the measured medium. When the channel is completely filled, the signal between the electrodes 5 and 5 'is equal to zero due to the complete symmetry of the electric field relative to the line 5-5'. As the liquid level decreases, the signal at the electrodes 5 and 5 'increases and reaches a maximum value when the level approaches the line connecting the pair of electrodes in question. In that case, if the liquid level drops below the location of the electrodes 5 and 5 ', then the flow rate and level are measured by the signals taken from the electrodes 6 and 6'. The received signal is stored by the calculator. Based on the measurement results of the signals corresponding to the two power supply modes of the excitation coils, the volumetric flow rate of the liquid and the filling level of the channel are calculated.

 Using the proposed solution allows you to expand the functionality of the electromagnetic method of flow measurement: to measure the flow rate at a changing level of the filling of the pipeline channel with high sensitivity both to the flow rate and to the change in the area of the "live" flow section.

Sources of information
1. Kremlin P.P. Flowmeters and counters of quantity, "Mechanical Engineering", L. 1989, pp. 408-434.

 2. U.S. Patent No. 5,301,556, 1994, FLOW MEASURING APPARATUS.

Claims (1)

 An electromagnetic flow meter containing a portion of the pipeline made of non-magnetic and non-conductive material, a first pair of field coils having a common axis perpendicular to the channel axis, several pairs of electrodes located in the central section of the pipe along its perimeter, and a magnetic body enclosing the pipe with the field coils outside , characterized in that it contains a second pair of coils having a common axis coinciding with the axis of the channel located on the pipeline and equidistant from the central channel, while two modes of inclusion of pairs of excitation coils are created alternately.

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