JPS5950315A - Electromagnetic flow meter - Google Patents

Abstract

PURPOSE:To suppress the generation of leaked magnetic flux of an energizing coil, and to reduce a rise time of an energizing current, by providing a leaked magnetic flux suppressing means of the energizing coil, which is provided between a magnetic pole and a feedback magnetic path body, and is constituted of a nonmagnetic conductive material for surrounding a part of the outside circumference of the energizing coil without forming a closed circuit for surrounding the whole outside circumference of the energizing coil. CONSTITUTION:A block 7 for suppressing a leaked magnetic flux phiL of an energizing coil 4 is provided between a magnetic pole 3 and a feedback magnetic path body 6. The block 7 is constituted of a nonmagnetic and conductive material and surrounds the greater part of the outside circumference of the energizing coil 4, but does not form a closed circuit for surrounding the whole outside circumference of the energizing coil because it has a cut part 8. The suppressing body 7 is cut by at least one piece so that the closed circuit running along the outside circumference of the energizing coil 4 is not constituted, therefore, it has no effect for reducing a main magnetic flux phiM. That is to say, since it can reduce an hourly variation of the main magnetic flux phiM in a sampling time ts, it can reduce an electromagnetic induced noise containing in a signal fetched from an electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic flowmeter that utilizes Faraday's law of electromagnetic conduction, and more particularly to an electromagnetic flowmeter that applies a DC magnetic field whose polarity changes periodically to a fluid.

This type of electromagnetic flowmeter has conventionally applied a father-flow magnetic field generated by an alternating current excitation method to the fluid in the measuring tube. By adopting a DC excitation method in which the value changes periodically, such as a square wave excitation method, in an electromagnetic flowmeter, the stability of the zero point when the fluid does not flow can be greatly improved compared to the case of an AC excitation method. I can do it. This improvement in stability is achieved because by using a DC magnetic field, electromagnetic induction noise caused by temporal changes in the magnetic field can be theoretically reduced. However, in reality, the electromagnetic induction noise cannot be reduced to zero as theoretically possible. The reason for this is that eddy currents are induced in the iron core, outer casing, etc. that constitute the magnetic circuit. In Figure 1, the horizontal axis is time and the vertical axis is excitation voltage.

FIG. 3 is a waveform chart of various quantities of an electromagnetic flowmeter with a magnetic flux density of 1. (3) is the excitation current of the square wave excitation method'), B1 is the magnetic flux in the flow rate measuring tube constituting the electromagnetic flowmeter, and B2 is the magnetic flux which will be described later with reference to FIG. tμ is the rise or fall time of the excitation current I, tBFi is the sampling time for obtaining the output signal of the electromagnetic flowmeter, and T is one cycle of the excitation current (2). In the square wave excitation method,
The flow rate is measured using the output signal of the electromagnetic flowmeter corresponding to a period during which the temporal change in the magnetic flux density in the measuring tube becomes small to a certain extent, for example, the sampling time ts. As mentioned above, the electromagnetic induction noise included in this sampling time tB does not become zero, but it is desirable to reduce it as much as possible.

The following three methods can be considered to reduce this electromagnetic induction noise.

A. A method of devising the material and structure of the flowmeter to reduce eddy currents induced in the iron core, outer casing, etc.

B. Decrease the excitation frequency. That is, a method of increasing the excitation period T shown in FIG.

A method of shortening the rise time of the C2 excitation subcurrent, that is, the time tμ in FIG.

Method A can be expected to be effective to some extent, but there are problems with production and cost. Although method B is effective in reducing induced noise, the number of measurements within a certain period of time is reduced, resulting in poor responsiveness. Method C is slightly inferior to method B in terms of reducing induced noise, but is superior to method B in terms of responsiveness. As a means of concretely implementing method C, the magnetic flux density distribution in the measurement tube is designed so that it becomes a dog in the area where the signal extraction electrode is installed, and the magnetomotive force of the magnetic field generator that crosses the measurement tube is reduced. . In this way, the excitation current can be made smaller by the number of turns of the excitation coil, so the rise time tlt of the excitation current I can be made smaller. However, if this is done, a new problem arises in that the measurement results are affected by drift.

Therefore, an object of the present invention is to provide an electromagnetic flowmeter equipped with a means for suppressing the leakage magnetic flux of the excitation coil of the magnetic flux generation means that crosses the measurement tube of the electromagnetic flowmeter and reducing the rise time of the excitation current. It is about providing.

The electromagnetic flowmeter of the present invention includes a pair of magnetic poles arranged on opposite sides of a flow rate measuring tube so that magnetic flux crosses the flow rate measuring tube, and a pair of magnetic poles for exciting the respective magnetic poles. An excitation coil, a return magnetic path body for the magnetic flux that has crossed the flow rate measurement tube, and a closed circuit that is provided between the magnetic pole and the return magnetic path body and surrounds the entire outer periphery of the excitation coil without forming a closed circuit. and a leakage magnetic flux suppressing device for the excitation coil, which is made of a non-magnetic proprietary material and surrounds at least a portion of the outer periphery of the excitation coil.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, a flow rate measuring tube 2 made of, for example, an insulating material is shown.
A pair of magnetic poles 3 are disposed on opposite sides of the magnetic pole 3, and each magnetic pole 3 is excited by an excitation coil 4. The magnetic flux φ, generated when the magnetic pole 3 is excited, crosses the measuring tube 2 as a main magnetic flux. An electrode 5 is provided from the measuring tube 2 to output a measured value. The flow rate ° is determined from a known formula showing the correlation between the velocity of the fluid flowing in the measuring tube 2, the main magnetic flux φ□l 'j'fL pole 5, and the electromotive force emitted from the pole 5. Reference numeral 6 denotes a return magnetic path body made of a magnetic material that forms two return paths for the magnetic flux, and also serves as protection and magnetic shielding inside the flowmeter. A block 7 for suppressing leakage magnetic flux φL of the excitation coil 4 is provided between the magnetic pole 3 and the return magnetic path body 6. This block 7 is made of a non-magnetic and conductive material and has, for example, the planar shape shown in FIG. 3A. That is, although it surrounds most of the outer periphery of the exciting coil 4, it does not form a closed circuit that surrounds the entire outer periphery of the exciting coil because it has the dividing portion 8.

The planar shape of the block 7 can also be as shown in FIG. 3B and Mr. a0. This block 7 is generally referred to as a leakage magnetic flux suppressor, and can be constructed of, for example, a thin steel plate, a copper or aluminum plate, or a block of these materials.

Next, the effects of the device shown in FIG. 2 will be explained. The inductance L of the excitation coil 4 is expressed by the following equation.

L=φ/■ (1) Here, I is the excitation current, and φ is the total amount of the generated magnetic flux.φ=φ1+φ1 (2). φM is a magnetic flux that crosses the measuring tube 2 shown in FIG. 2, and is a magnetic flux that is directly involved in the output signal of the electromagnetic flow meter output from the electric current & 5.

φ1 is the leakage magnetic flux of the excitation coil 4, and is not related to the magnitude of the electromotive force emitted from the electrode 5. 1 When the polarity of the excitation current I is reversed as shown in Fig. 1, the leakage magnetic flux φ1 of the excitation coil 4 is a measurement that shows a change in the main magnetic flux φ if it is assumed that the leakage flux suppressor 7 does not exist. It changes with the same waveform as the in-tube Ω magnetic flux density B1.However, if the leakage magnetic flux suppressor 7 exists, an eddy current is induced in the suppressor 7 according to the change in the leakage magnetic flux φ, so the leakage magnetic flux φ1 is It changes as shown in Figure 1B2.

To be more specific, the magnitude of the leakage magnetic flux 9 after a sufficient period of time has passed after the polarity of the excitation current changes is hardly affected by the presence of the suppressor 7, but when the excitation current changes. The presence of the suppressor makes φ significantly smaller at the time of the increase. That is, at the time when the excitation current is changing, the inductance of the M coil 4 becomes small.If the inductance L of the coil becomes small, the rise time t7 of the excitation current becomes short.On the other hand, when the suppressor 7 is divided into at least one piece on the outer periphery of the excitation coil 4 so as not to form a closed circuit (see Fig. 3A), so it does not have the effect of reducing the main magnetic flux φM. That is, as shown in Fig. 1 sampling time t
Since the temporal change in the main magnetic flux φ between the electrodes 5 and 8 can be reduced, the electromagnetic induction noise contained in the signal output from the electrodes 5 can be reduced.

In the embodiment shown in FIG. 4, the cross-sectional area of the portion of the magnetic pole 3 facing the measuring tube 2 is set to be υ larger than the cross-sectional area of the magnetic pole surrounded by the excitation coil 4, and the magnetic pole surface, which is a dog of this cross-sectional area, and the return magnetic path body A leakage magnetic flux suppressor 7 is provided between the magnet 6 and the magnet 6. Fourth
The leakage magnetic flux suppressor 2 shown in the figure has a block shape, and the magnetic pole 3
It is weighed in Figure 1. The leakage magnetic flux suppressor 7 shown in FIG. 5 is attached to a return magnetic path body 6 which is a plate-shaped body.

The embodiment shown in FIG. 6 has a coil body 7 as a leakage magnetic flux suppressor.
a is used. This coil body 7a is provided between the magnetic pole 3 and the return magnetic path body 6, and its shape Fi is shown in FIG. 6A. The coil body 7a is wound so as not to form a closed circuit surrounding the outer periphery of the excitation coil 4, and is wound so as to form a coil surface through which leakage magnetic flux passes. The terminals of this coil may be short-circuited so as not to reduce the total current induced in the coil due to leakage magnetic flux, or may be connected through an appropriate load. Furthermore, it may be connected in series with the exciting coil 4 so as to cancel the leakage 4iM flux φL of the exciting coil 4. The embodiment shown in FIG. 7 is basically the same as the embodiment shown in FIG.

The difference from FIG. 6 is that the leakage flux suppressing coil body 7a is
It has the shape shown in the perspective view of A and is fixed to the magnet +6i3. Figure 6.

The embodiment shown in FIG. 7 has the same effect as the embodiment shown in FIG.

[Brief explanation of the drawing]

1N is a waveform diagram for explaining the principle of the device of the present invention, FIG. 2 is a sectional view of 1 implementation order U of the device of the present invention, and FIGS. 3A to 3C are leakage magnetic flux suppressors shown in FIG. 2. FIGS. 4 and 5 are respectively sectional views of other embodiments of the apparatus of the present invention; FIGS. 6 and 7 are sectional views of still other embodiments of the apparatus of the present invention, and FIG. 6A FIGS. 4r and 7h are perspective views of the leakage magnetic flux suppressor shown in FIGS. 6 and 7, respectively. 2...Flow rate measuring tube, 3...Magnetic pole, 4...Exciting coil, 5...Induced voltage extraction electrode, 6...Return magnetic path body,
7, 2a... Leakage magnetic flux suppressor. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 4 Figure 5 Figure 6A

Claims (3)

[Claims] (1) A pair of magnetic poles arranged on opposite sides of the flow rate measuring tube so that magnetic flux crosses the flow rate measuring tube, and a pair of excitation coils for exciting each of the magnetic poles; In an electromagnetic flowmeter including a return magnetic path body for magnetic flux that traverses a flow rate measurement tube, the magnetic flow meter is provided between the magnetic pole and the return magnetic path body, without forming a closed circuit surrounding the entire outer periphery of the excitation coil. An electromagnetic flowmeter characterized by comprising means for suppressing leakage magnetic flux of the excitation coil, which is made of a non-magnetic conductive material surrounding at least a portion of the outer periphery of the excitation coil. (2) The leakage magnetic flux suppressing means is fixed to the magnetic pole surface or the return magnetic path body surface between the magnetic pole and the return magnetic path body, surrounds the outer periphery of the excitation coil, and has at least one The electromagnetic flowmeter according to claim 1, characterized in that the electromagnetic flowmeter includes a block body or a plate-like body having two dividing points. (3) The leakage magnetic flux suppressing means includes a coil provided between the magnetic pole and the return magnetic path body, and this coil is wound so as to form a closed circuit surrounding the entire outer periphery of the excitation coil. An electromagnetic flowmeter characterized in that the magnetic flowmeter is wound so as to form a closed circuit crossed by the leakage magnetic flux of the excitation coil.