JPH03205513A - Detector of electromagnetic flow meter - Google Patents

Abstract

PURPOSE:To suppress a generation of error caused by the change of magnetic field distribution due to the difference in piping material of the other side by providing a casing made by non-magnetic body so as to surround a measuring tube, magnetic field generator and electrode, and arranging a magnetic shielding plate between the casing and exciting coil. CONSTITUTION:A detector of electromagnetic flow meter is arranged between the outside pipings 6, which is provided with the casing 1 formed by the non- magnetic body (stainless material, etc.) so as to surround the electrode 5 and magnetic field generator having a pair of upper/lower exciting coils 3a, 3b generating the magnetic field in the radial direction of measuring tube 4 and a core 2 made by non-magnetic body forming a return circuit for the magnetic field, and the magnetic shielding plates 7a,7b are provided between the exciting coils 3 and casing 1 so as to slightly set the position of exciting coils 3 apart from the measuring tube 4. A leaking magnetic flux to the outside of flow meter is thereby decreased, and the difference of magnetic field distribution of the flow meter inside between both cases of the magnetic and non-magnetic body materials is decreased, thereby the error can be reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to flow rate measurement of almost all types of conductive fluids, and the pressure drop can be ignored. This invention relates to the structure of an electromagnetic flowmeter detector suitable for control.

[Conventional technology]

As described in Japanese Patent Application Laid-Open No. 160019/1982, a conventional electromagnetic flowmeter consists of a measuring tube through which fluid passes, and an excitation coil wrapped around a magnetic pole that generates a magnetic field in the radial direction of the measuring tube. It consists of a magnetic field generator with a pair of magnetic field generators and a pair of electrodes installed on the measuring tube in a straight line perpendicular to the direction of the magnetic field and the axis of the measuring tube. It was connected to external piping via a flange. Therefore, only a casing made of non-magnetic material existed between the excitation coil and the external piping.

In the case of an electromagnetic flowmeter with this structure or a relatively large diameter, in the case of a small diameter, the casing itself is made of a ferromagnetic material, as described in Japanese Patent Application Laid-Open No. 58-641. It served as a return circuit for the magnetic field.

[Problem to be solved by the invention]

In the above conventional technology, when the diameter is large, only a non-magnetic casing exists between the excitation coil and the external piping, so the leakage magnetic flux to the outside of the flowmeter is large, compared to when the external piping is made of magnetic material. , the magnetic field distribution inside the flowmeter changes depending on the case of non-magnetic material, and even if the same flow rate is measured,
There was a drawback that different flow signal values were output.

If the diameter is small, the casing is made of ferromagnetic material, so the leakage magnetic flux to the outside is considered to be small, but the property of ferromagnetic material is that it has poor rust and corrosion resistance. It had the disadvantage of being susceptible to rust due to some external factor.

If the diameter is small, a ferromagnetic material is used to reduce the cost, ignoring rust prevention to some extent, and if the diameter is large, a non-magnetic material (such as stainless steel material) is used with emphasis on performance.

An object of the present invention is to obtain an electromagnetic flowmeter with small errors due to differences in mating piping materials and with high rust prevention properties.

[Means for Solving the Problems] In order to achieve the above object, the present invention has a measuring tube through which a fluid passes, and a set of upper and lower excitation coils and a core wound around magnetic poles, An electromagnetic flowmeter comprising: a magnetic field generating device that generates a magnetic field in a radial direction; and a pair of electrodes attached to the measuring tube and located on a line perpendicular to the direction of the magnetic field and the axial direction of the measuring tube. In the detector, a casing made of a non-magnetic material is installed to surround the measurement tube, magnetic field generator, and electrode, and a magnetic shield plate is installed between the casing and the excitation coil.

[Effect]

By inserting a magnetic shield plate between the excitation coil and external piping, leakage magnetic flux to the outside of the flowmeter is reduced.
A two-dimensional magnetic field that is almost uniform in the tube axis direction can be created only inside the flowmeter.

If the amount of magnetic flux leaking to the outside of the flowmeter is small, the difference in the magnetic field distribution inside the flowmeter will be small whether the external piping is made of magnetic material or non-magnetic material, and the same flow rate will be measured. The difference in flow rate output signal values becomes smaller when Therefore, errors caused by differences in the material of the external piping can be reduced.

This effect can also be expected by coating the casing itself with a ferromagnetic material, but this will impair rust prevention.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

The electromagnetic flowmeter detector consists of a measuring tube 4 with an insulating lining on the inner surface, a magnetic field generated in the radial direction of the measuring tube,
A magnetic field generator having a lower set of excitation coils 3 and a core 2 made of a magnetic material serving as a return circuit for the magnetic field, and an inner surface of the measuring tube 4 located on a straight line orthogonal to each of the magnetic field direction and the tube axis direction. It consists of a pair of electrodes 5 attached to a casing 1 and a casing 1 that fixes the whole, and is installed between external piping 6. A magnetic shield plate 7 is attached between the excitation coil 3 and the casing 1 at a position of the excitation coil as shown in FIG. Further, the flow rate signal from the electrode 5 is taken out to the outside of the detector via a flow rate signal line and connected to a converter.

As described above, the present invention has the following advantages over conventional electromagnetic flowmeters:
This can be achieved by simply moving the exciting coil 3 slightly away from the measuring tube 4 and inserting the magnetic shield plate 7.

Next, the operation of the present invention will be explained using FIGS. 3 and 4. FIGS. 3 and 4 show the results of numerical analysis of the magnetic field distribution within the detector, and respectively represent the magnetic field distribution between the electrodes (in the X direction) and the magnetic field distribution in the tube axis direction (in two directions). As can be seen from the figure, when there is no shield plate, the difference between the magnetic field distribution when the external piping material is non-magnetic and the magnetic field distribution when it is magnetic is very large, but when there is a shield plate, the difference is very large. is getting smaller. The electromotive force generated between the electrodes, which is detected as a flow rate signal, depends on the magnetic field distribution inside the detector if the measured flow velocity distribution is the same. Therefore, if the change in the magnetic field distribution when changing the piping material is small, Measurement errors due to differences in piping materials are reduced.

FIG. 5 is a perspective view showing the shape of a magnetic shield plate in another embodiment of the present invention. As shown in the figure, if a shield plate is installed to surround the part where the current flows in the direction of expanding the magnetic field in the direction of the tube axis, the amount of leakage of magnetic flux in the direction of the tube axis will be reduced, and errors due to differences in external piping materials will be reduced. becomes smaller.

FIG. 6 is also a perspective view showing the shape of a magnetic shield plate in another embodiment of the present invention. The area is smaller than that of the shield plate shape shown in FIG. 2, and it is located only on the outside of the part where current flows in the direction of expanding the magnetic field in the tube axis direction. Even with such a shield shape, since the main portion that spreads the magnetic field in the tube axis direction is shielded, it is possible to suppress errors due to differences in the external piping material, although this is not as great as the shape shown in FIG. 2.

〔Effect of the invention〕

According to the present invention, the difference between the magnetic field distribution inside the detector when the external piping material to which the flowmeter is attached is made of magnetic material and the magnetic field distribution when it is made of non-magnetic material is small, so flow measurement due to differences in the external piping material is reduced. The error can be reduced.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an electromagnetic flowmeter detector according to an embodiment of the present invention, Fig. 2 is a perspective view showing the shape of a magnetic shield plate according to the present invention, and Fig. 3 is a numerical analysis of magnetic field distribution between electrodes. FIG. 4 is an explanatory diagram of the results, and FIG. 4 is an explanatory diagram of the numerical analysis results of the magnetic field distribution in the tube axis direction. FIGS. 5 and 6 are perspective views showing the shape of the magnetic shield plate of other embodiments of the present invention. be. 1...Casing, 2...Core, 3, 3a, 3b・
・・Exciting coil, 4・Measuring tube, 5・Electrode, 6・
... External piping, further 1 ■ Senior 3 Diagram 4 Diagram K (ntsunkuno

Claims (1)

[Scope of Claims] 1. A magnetic field generating device that includes a measurement tube through which a fluid passes, and a set of upper and lower excitation coils and a core wound around magnetic poles, and generates a magnetic field in the radial direction of the measurement tube; An electromagnetic flowmeter detector comprising a pair of electrodes attached to the measuring tube and located on a straight line orthogonal to each of the direction of a magnetic field and the tube axis direction of the measuring tube, the measuring tube, the magnetic field generating device. An electromagnetic flowmeter detector, characterized in that a casing made of a non-magnetic material is installed to surround the electrode, and a magnetic shield plate is installed between the casing and the excitation coil.