JP3073595B2 - Electromagnetic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flow meter for measuring the flow rate of a conductive fluid such as water and sewage, chemicals, foods, chemical substances, slurries in which liquids and fine solids are mixed.

[0002]

2. Description of the Related Art There is an electromagnetic flowmeter that measures the flow rate of a conductive fluid using Fleming's law. In this electromagnetic flowmeter, a number of directions are set in a direction orthogonal to both the direction in which the conductive fluid flows and the direction of the magnetic field applied to the conductive fluid.
A voltage signal of 10 mV to several mV is generated. This voltage signal is generated in proportion to the flow rate of the conductive fluid flowing in the pipe.

Accordingly, the flow rate of the fluid can be measured by detecting and measuring the voltage signal as a flow rate signal.

FIG. 8 is a schematic sectional view of a main part of an electromagnetic flow meter. In FIG. 8, a conductive fluid flows through the inner surface of the pipe 1 whose inner surface is lined with an insulator from the front side to the back side of the paper surface or the reverse direction. Further, a pair of magnetic poles 4 made of a magnetic material having high magnetic permeability are arranged to face each other in the vertical direction in the drawing with the pipe 1 therebetween, and the exciting coil 2 is wound around each of the pair of magnetic poles 4. Have been. Then, a rectangular wave current flows from the AC power supply (not shown) to the pair of exciting coils 2. An upper magnetic path 5 (high-permeability material) and a lower magnetic path (high-permeability) (not shown) extending substantially perpendicular to the magnetic pole 4 are formed at the end of the magnetic pole 4 opposite to the pipe 1. . Further, a side magnetic path 6 extending substantially parallel to the magnetic pole 4 is provided at an end of the upper magnetic path 5 and the lower magnetic path.
(High magnetic permeability) is formed. And a pole piece 3, a magnetic pole 4, an upper magnetic path 5, a lower magnetic path, made of a magnetic material having a high magnetic permeability,
A magnetic circuit is formed by the side magnetic path 6, and a strong magnetic field is generated in the direction in which the fluid in the pipe 1 flows, that is, in the direction perpendicular to the axial direction of the pipe 1. Inside the pipe 1, electrodes 7 are arranged in a direction perpendicular to both the direction of the strong magnetic field and the flow direction of the fluid. Therefore, a flow signal e, which is proportional to the flow rate of the fluid and is expressed by the following equation (1), is generated at the electrode 7. e = BDV --- (1) where B is the magnetic flux density, D is the inner diameter (nominal diameter) of the pipe 1, and V is the flow velocity of the fluid. In the above equation (1),
If the pipe inner diameter D and the flow velocity V are determined, the value of the flow rate signal e is determined by the magnetic flux density B. Therefore, the configuration of the magnetic circuit greatly affects the value of the flow signal.

In general, the magnetic flux density Bo generated at the center of a parallel magnetic pole is represented by the following equation (2), where the excitation amount is IN (ampere turn), the magnetic pole interval is L, and k is a proportional constant. Bo = k4πIN / L --- (2) In general, the magnetic pole interval L is structurally determined and designed to be as small as possible. The relationship between the nominal diameter D of the pipe 1 and the magnetic pole interval L is expressed by the following equation (3). L = (1.2D + t) ± 2− (3) where the unit is mm. Further, t is approximately the thickness of the pipe 1, and is the sum of the thickness of the insulating lining and the thickness of the pipe. The value of t is the nominal diameter D
Is less than 50 mm, it is about 5 mm.

[0006] The amount of excitation IN is determined by the required magnetic flux density Bo.
Is determined to be obtained. Here, the proportional constant k is determined by the characteristics of the magnetic circuit.

As the above-mentioned electromagnetic flow meter, there is, for example, one described in Japanese Patent Application Laid-Open No. 63-266313. According to Japanese Patent Application Laid-Open No. 63-266313, the length of the tip of the magnetic pole (the end face on the side of the pipe) in the pipe axis direction is shorter than the length of the magnetic pole in the portion where the excitation coil is wound in the pipe axis direction. ing. With this shape, the magnetic field is concentrated to prevent the leakage of the magnetic field to the external pipe, and the length of the flow meter in the pipe axial direction is reduced.

Further, similar to the above-mentioned electromagnetic flowmeter, there are a rectangular wave excitation electromagnetic flowmeter described in Japanese Patent Application Laid-Open No. 2-280012 and a residual magnetic type flowmeter described in Japanese Patent Application Laid-Open No. 62-179624. There is a calorimeter using an electromagnetic flow meter.

[0009]

However, in the above-mentioned conventional electromagnetic flowmeter, no consideration is given to the configuration for improving the characteristics of the magnetic circuit, and the proportionality constant k is a small value. (For example, 0.5 to 0.6). Therefore, in order to generate the required magnetic flux density Bo, it is necessary to increase the amount of excitation IN, and a large-sized excitation power supply is required. For this reason, the entire electromagnetic flowmeter has been increased in size and weight. SUMMARY OF THE INVENTION It is an object of the present invention to improve the characteristics of a magnetic circuit in an electromagnetic flowmeter, and to realize an electromagnetic flowmeter that can generate a flow signal of a sufficiently large value while being small and lightweight.

[0010]

The present invention is configured as follows to achieve the above object. The inner surface is lined with an insulator, and has a pipe through which a conductive fluid flows through the lined inner surface, a pair of magnetic poles, and a pair of coils wound around these magnetic poles, respectively. A magnetic circuit that generates an orthogonal magnetic field, and a pair of a magnetic circuit that is orthogonal to the axial line of the pipe and that is arranged in a direction that is orthogonal to the magnetic field generation direction line of the magnetic circuit and that generates a flow signal proportional to the flow rate of the conductive fluid. In the electromagnetic flowmeter provided with the electrodes, the distance between the magnetic poles is larger than the nominal diameter of the pipe, and the diameter of the magnetic pole at the end in the pipe direction is larger than the distance between the magnetic poles and the magnetic poles. In addition, the diameter of the portion of the magnetic pole around which the coil is wound is configured to be larger than the diameter of the end of the magnetic pole in the pipe direction. In addition, the inner surface is lined with an insulator, and a pipe through which a conductive fluid flows through the lined inner surface, a pair of magnetic poles, and a pair of coils wound around these magnetic poles, respectively, are provided in the axial direction of the pipe. A magnetic circuit that generates a magnetic field orthogonal to the line, and a magnetic circuit that is arranged in a direction that is orthogonal to the axial line of the pipe and orthogonal to the magnetic field generation direction line of the magnetic circuit and generates a flow signal proportional to the flow rate of the conductive fluid In a magnetic flowmeter provided with a pair of electrodes, the nominal diameter of the pipe is D, the distance between the magnetic poles is L, the diameter of the magnetic pole on the side in the pipe direction is d, and the coil of the magnetic pole is wound. Is dd and the unit is mm, the relationship between the interval L and the nominal diameter D is L = (1.2D + 5) ± 2, and the relationship between the interval L and the diameter d is 1.5L ≧ d ≧ 1.1L, and the relationship between the interval L and the diameter dd is 2L ≧ dd>
It is configured to be 1.5L. Preferably, in the above-mentioned electromagnetic flow meter, when the interval between the coils is Lc, the relationship between the interval L and the interval Lc is 1.8 ≧ Lc ≧ L
Is configured to be Preferably, the electromagnetic flowmeter is configured such that b / a satisfies 4 ≧ b / a ≧ 1, where a is the horizontal length of the coil cross section and b is the vertical length. Further preferably, in the electromagnetic flowmeter, an upper magnetic path or a lower magnetic path extending substantially perpendicular to the magnetic pole is formed at an end of the magnetic pole opposite to the pipe side, and an upper magnetic path or an end of the lower magnetic path is formed. A side magnetic path extending substantially parallel to the magnetic poles is formed in the portion.
And the inner diameter E is set so that 4L ≧ E ≧ 3.5L. More preferably, in the above-mentioned electromagnetic flowmeter, if the horizontal length of the coil cross section is a and the vertical length is b, the relationship between the magnetic pole interval L and the horizontal length a is 0.8
It is configured such that L ≧ a ≧ 0.5L and the relationship between the magnetic pole interval L and the vertical length b satisfies 3.2L ≧ b ≧ 0.5L.

[0011]

The distance between the magnetic poles is larger than the nominal diameter of the pipe, and the diameter of the magnetic pole at the end in the pipe direction is larger than the distance between the magnetic poles. Further, the diameter of the portion where the coil of the magnetic pole is wound is larger than the diameter of the end of the magnetic pole in the pipe direction. Thus, the magnetic flux center magnetic flux density in the electromagnetic flowmeter can be increased, and the flow signal can be increased without increasing the size of the coil excitation power supply. If the nominal diameter of the pipe is D, the distance between the magnetic poles is L, the diameter of the magnetic pole on the side in the pipe direction is d, the diameter of the portion where the magnetic pole coil is wound is dd, and the unit is mm The relationship between the distance L and the nominal diameter D is L = (1.2D + 5) ± 2, and the relation between the distance L and the diameter d is 1.5L ≧ d ≧ 1.1L
It is said. Further, the relationship between the interval L and the diameter dd is 2L ≧
dd> 1.5L. Thereby, the magnetic pole center magnetic flux density in the electromagnetic flowmeter can be further increased,
The flow rate signal can be increased without increasing the size of the coil excitation power supply.

[0012]

FIG. 1 is a sectional view of a main part of an electromagnetic flow meter according to an embodiment of the present invention. Members equivalent to those in the example of FIG. 8 are denoted by the same reference numerals. In addition, 8 is a lower magnetic path. First, the setting of the structural dimensions of the embodiment shown in FIG. 1 will be described. One embodiment of the present invention is an example of an electromagnetic flow meter satisfying the above expression (3).

At the tip of the magnetic pole 4, the magnetic flux is
There is an edge effect that bulges outward from the center line connecting the points 4 and 4. For this reason, when the distance L between the magnetic poles 4 (the magnetic pole distance) L is fixed and the diameter d of the tip end of the magnetic pole 4, that is, the pole piece 3 is changed, how the magnetic pole center magnetic flux density Bo becomes is I asked if it would change.

FIG. 2 is a graph showing the results of the above change, wherein the vertical axis represents the ratio between the magnetic flux density maximum value Bmax and the magnetic pole center magnetic flux density Bo, and the horizontal axis represents the ratio between the magnetic pole interval L and the magnetic pole piece diameter d. It is. From the curve Ca in FIG. 2, the magnetic flux density maximum value Bmax
D / L corresponding to the point P ₀ at which the ratio of the magnetic flux density Bo to the magnetic pole center becomes 0.9 is 1.1. Therefore, first,
The condition that d ≧ 1.1 L is obtained. Further, as shown in FIG. 3, if the angle at which the tip of the magnetic pole 4 is viewed from the center MC of the magnetic pole is 2θ, the magnetic flux density Bo at the center of the magnetic pole becomes the maximum θ.
Is the case where the product of sin ² θ × cos θ is maximum (see References, Toshinobu Chikagu, Magnetic Experimental Physics Course 17,
Kyoritsu Shuppan, 1968, pp. 52-56). When the maximum value of this equation is differentiated and obtained, θ = tan ⁻¹ √2 = 54.7
°, about 55 °. That is, since tan θ = d / L, the magnetic pole center magnetic flux density Bo becomes maximum when d / L = tan 55 ° = about 1.41. When θ exceeds 55 °, the magnetic flux density decreases, so that the condition of θ ≦ 55 ° is obtained. As described above, the dimension range of the pole piece diameter d is obtained by rounding the numerical values to obtain the following equation (4). 1.5L ≧ d ≧ 1.1L (4) Next, when the ratio between the pole piece diameter d and the diameter (magnetic pole diameter) dd of the magnetic pole 4 is changed, how the magnetic pole center magnetic flux density Bo becomes I asked if it would change. FIG. 4 is a graph showing the result of this change. The vertical axis represents the ratio between the maximum magnetic flux density Bmax and the magnetic pole center magnetic flux density Bo, and the horizontal axis represents the ratio between the magnetic pole diameter dd and the pole piece diameter d. From the curve Cb in FIG.
point P ₂ o is maximum corresponds to the d / dd = 0. 9. As a practical range, Bo / Bmax ≧ 0.9 is appropriate, and d corresponding to the points P ₁ and P ₃ where 0.9 is satisfied
/ Dd are 0.75 and 1.02. Therefore, d /
It turns out that dd is suitably 0.75 to 1.02.

However, if d / dd> 0.9, the magnetic flux density does not increase even if the pole piece diameter increases, so that d / dd
Is given by the following equation (5). 0.9 ≧ d / dd ≧ 0.75 (5) By substituting equation (4) into equation (5), dd becomes 2.0 L ≧ dd
≧ 1.22L, but from 0.9 ≧ d / dd to dd> d
And, under the condition of 1.5L ≧ d, the range of dd is approximately given by the following equation (6). 2.0L ≧ dd> 1.5L (6) FIG. 5 is a graph showing the relationship between the coil interval Lc / magnetic pole interval L and B0 / Bmax. In FIG. 5, (Ed
d) / 2L is the distance (E-dd) / 2 between the magnetic pole and the side magnetic path.
And the ratio between the magnetic pole interval L and (E-dd) / 2L = 1.
5 (curve Cc), 1.0 (curve Cd) and 0.75 (curve Ce) (where E is the inner diameter of the side magnetic path).

The magnetic flux generated by the two coils 2 does not always pass between the magnetic poles, but also has a leakage magnetic flux. Therefore, it is necessary to minimize this leakage magnetic flux. For this purpose, the distance Lc between the two coils 2 is
Can be effectively concentrated on the magnetic pole portion. However, in the electromagnetic flow meter, since the pipe 1 is provided between the magnetic poles 4 and the electrode 7 for extracting a flow signal and the seal fixing structure thereof are present, Lc <L cannot be physically satisfied. From FIG. 5, if Lc / L is 1.0 to 1.8, Bo /
Bmax value of 0.9 or more can be secured.
It can be seen that the magnetic flux created by can be effectively used without leaking. That is, the following equation (7) is obtained. 1.8 ≧ Lc ≧ L --- (7) By the way, when (E−dd) / 2L is small, of the magnetic fluxes generated by the exciting coil 2, compared with the magnetic flux passing between the magnetic poles 4,
The amount of magnetic flux leaking from the magnetic pole 4 to the side magnetic path 6 increases. That is, at (E-dd) /2L=0.75, the magnetic flux density at the magnetic pole center sharply decreases as Lc / L increases. From this, it is more practical to set (E-dd) / 2L to 1.0 or more. Therefore, the condition of the following equation (8) can be obtained. (E-dd) /2L≧1.0 --- (8) By substituting the equation (6) into the equation (8) and expressing the practical side magnetic path inner diameter E by the magnetic pole interval L, the following equation (9) is obtained. The following condition is obtained. 4.0L ≧ E ≧ 3.5L --- (9) Next, the horizontal length a and the vertical length b of the cross section of the exciting coil 2
Affects the shape of the magnetic circuit surrounding the coil 2. a> b
In the coil of (1), the flow direction dimension (distance between surfaces) of the fluid of the electromagnetic flowmeter becomes large, and the flowmeter becomes large. Further, in this case, since the winding diameter of the coil 2 increases, the impedance of the coil 2 increases, and the capacity of the coil excitation power supply also increases. FIG. 6 shows that the sectional area of the coil 2 is constant (a × b =
7 is a graph showing the relationship between the vertical length b / horizontal length a and the resistance of the coil 2 as constant. However, this is a case where the magnetic pole diameter dd is constant and the resistance of the coil 2 when b / a = 1 is 1.0. If the coil resistance of the electromagnetic flowmeter is reduced, the required power of the coil excitation power supply can be reduced, and the excitation power supply can be downsized. Also, the temperature rise of the electromagnetic flow meter can be reduced. From this viewpoint, it is better that b / a is larger than the curve Cf in FIG.

FIG. 7 shows the relationship between b / a and the magnetic flux density at the magnetic pole center (curve C) when the intensity of excitation is about 340 AT.
9 is a graph showing the relationship (curve Ch) between g) and b / a and the maximum magnetic flux density in the magnetic path. As shown in FIG.
Is changed, the center magnetic flux density of the magnetic pole and the maximum magnetic flux density in the magnetic path change even if the excitation amount is constant, and in particular, the maximum magnetic flux density in the magnetic path changes significantly. From this, it is possible to know the optimum shape that can minimize the loss in the magnetic circuit by changing the coil cross-sectional shape b / a.

When b / a is increased, the maximum magnetic flux density in the magnetic path is increased, and magnetic saturation of the magnetic pole portion is easily caused. Therefore, it is necessary to design with care so that the magnetic flux density in the magnetic path is not saturated. Usually, b / a is within the range shown by the following equation (10) in order to reduce the distance between the surfaces of the flow meter and to reduce the size of the excitation power supply. b / a = 1.0 to 4.0 --- (10) Normally, since the value of a is put between the magnetic pole and the side magnetic path, (Ed
d) / 2 is 50 to 80%. Therefore, 0.8
If (E-dd) /2≧a≧0.5 (E-dd) / 2 and (E-dd) / 2 is approximately 1.0, the following equation (1)
The condition of 1) is obtained. 0.8L ≧ a ≧ 0.5L --- (11) From the expressions (10) and (11), the following expression (12) is obtained. 3.2L ≧ b ≧ 0.5L --- (12) As described above, the optimum shape of the magnetic circuit of the electromagnetic flowmeter can be represented as a function of the magnetic pole interval L represented by the equation (3). . Therefore, if the diameter D is set,
The magnetic pole interval L is determined by the equation (3), and the equations (4) to (1)
2) determines the optimal shape of the magnetic circuit. Thus, it is possible to realize an electromagnetic flowmeter capable of obtaining a sufficiently large flow signal without increasing the size of the excitation power supply.

A conventional example is disclosed in Japanese Patent Application Laid-Open No. 63-266.
No. 313 (hereinafter simply referred to as a gazette), the structural dimensions of the device described in the gazette are the same as those shown in FIGS.
(However, since the specific dimensional values are not described in the above publication, they were inferred from the accompanying drawings of this publication.) First, FIG.
In the case of the apparatus disclosed in the publication, d / L is about 0.15 and about 0.17, which is significantly different from the present invention. Next, in FIG. 4, in the case of the device disclosed in the publication, d / dd
Are about 0.3 and about 0.35, which are also significantly different from the present invention. In addition, in FIG. 5, in the case of the apparatus disclosed in the publication, Lc / L is about 1.44, which is equivalent to the present invention, but (E-dd) / 2L is about 0.46. Are very different. 6 and 7, in the case of the apparatus disclosed in the publication, b / a is about 3.6, which is the same as in the present invention. Thus, it can be understood that the structure of the device disclosed in the above publication and the embodiment of the present invention are greatly different.

Next, for an electromagnetic flow meter using a pipe having a nominal diameter D of 5 mm, the structural dimensions calculated according to the equations (3) to (12) are shown in Table 1 below.

[0021]

[Table 1]

However, in Table 1, since the nominal diameter D and the magnetic pole interval L are fixed values, the columns of the dimension range and the average dimension are blank. The ratio of the nominal diameter D to L is also omitted. Further, the numerical value of the dimension range in each item is a dimension range obtained by substituting L into Expressions (4) to (12). The average dimension is an average value of the upper limit and the lower limit indicated in the dimension range. Then, an appropriate design size was determined based on the size range and the average size. Thereby, the dimensions of each part of the magnetic circuit can be made an effective shape without waste. For example, in the magnetic circuit of the electromagnetic flow meter in one embodiment of the present invention, the magnetic pole center magnetic flux density is 1.1 gauss / AT per unit excitation, and the proportional constant k =
0.9 was obtained. Proportional constant k of the device in the conventional example
Is 0.5 to 0.6, so in the case of the embodiment of the present invention, the value of the proportionality constant is about twice that of the conventional example.
As a result, the magnitude of the flow signal can be reduced to about 1.5 to
It can be 1.8 times. Therefore, it is possible to realize an electromagnetic flowmeter capable of obtaining a large flow signal without increasing the size of the excitation power supply. Further, if the magnitude of the flow signal is equal to that of the conventional example, the coil excitation power supply can be reduced to about １ ／ of that of the conventional example, and the size can be greatly reduced.

Note that, of the above equations, the equations (3), (4),
Even with a structural size that satisfies only the condition (5), it is possible to realize an electromagnetic flowmeter that can obtain a large flow signal without increasing the size of the excitation power supply. Further, from the conditions of the equations (3), (4), and (5), L> D, d> L,
It can be seen that dd> d. That is, it is possible to realize an electromagnetic flowmeter capable of obtaining a large flow signal without increasing the size of the excitation power supply even if the structural dimensions satisfy the condition of the following expression (13). dd>d>L> D --- (13)

[0024]

As described above, according to the electromagnetic flowmeter of the present invention, the interval between the magnetic poles is larger than the nominal diameter of the pipe, and the diameter of the magnetic pole at the end in the pipe direction is the magnetic pole. And the diameter of the portion of the magnetic pole around which the coil is wound is larger than the diameter of the end of the magnetic pole in the pipe direction. As a result, the characteristics of the magnetic circuit in the electromagnetic flowmeter are improved, the magnetic pole center magnetic flux density is increased, and an electromagnetic flowmeter that can generate a flow signal with a sufficiently large value while being small and lightweight can be realized.

The nominal diameter of the pipe is D, the distance between the magnetic poles is L, the diameter of the magnetic pole at the end in the pipe direction is d, and the diameter of the portion where the magnetic pole coil is wound is dd. mm, the relationship between the interval L and the nominal diameter D is L = (1.2D
+5) ± 2, and the relationship between the interval L and the diameter d is 1.5 L
If ≧ d ≧ 1.1L and the relationship between the interval L and the diameter dd is 2L ≧ dd> 1.5L, the characteristics of the magnetic circuit in the electromagnetic flowmeter are further improved, and the magnetic pole center It is possible to realize an electromagnetic flowmeter that can generate a flow signal of a larger value while having a higher magnetic flux density and a small size and light weight.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an electromagnetic flow meter according to an embodiment of the present invention.

FIG. 2 shows a pole piece diameter d / pole interval L and a pole center magnetic flux density B.
6 is a graph showing a relationship with o.

FIG. 3 is an explanatory diagram of an angle when a tip of a magnetic pole is viewed from a center of the magnetic pole.

FIG. 4 shows pole piece diameter d / pole diameter dd and pole center magnetic flux density B
6 is a graph showing a relationship with o.

FIG. 5 is a graph showing a relationship between a coil interval Lc / a magnetic pole interval L and a magnetic pole center magnetic flux density Bo.

FIG. 6 is a graph showing a relationship between a coil section vertical length b / horizontal length a and a coil resistance value.

FIG. 7 is a graph showing the relationship between the coil section vertical length b / horizontal length a and the magnetic pole center magnetic flux density and the maximum magnetic flux density in the magnetic path.

FIG. 8 is a sectional view of a main part of a conventional electromagnetic flow meter.

[Description of Signs] 1 Piping 2 Exciting coil 3 Magnetic pole piece 4 Magnetic pole 5 Upper magnetic path 6 Side magnetic path 7 Electrode 8 Lower magnetic path a Exciting coil cross-sectional horizontal length b Exciting coil cross-sectional vertical length D Piping nominal diameter d Magnetic pole piece diameter dd Magnetic pole diameter E Side magnetic path inner diameter L Magnetic pole interval Lc Excitation coil interval

Claims (6)

(57) [Claims] 1. A pipe having an inner surface lined with an insulator, a pipe through which a conductive fluid flows on the lined inner surface, a pair of magnetic poles, and a pair of coils respectively wound around the magnetic poles. A magnetic circuit that generates a magnetic field orthogonal to the axial line of the
It is arranged in a direction perpendicular to the magnetic field generation direction line of the magnetic circuit,
A pair of electrodes for generating a flow signal proportional to the flow rate of the conductive fluid, the distance between the magnetic poles is larger than the nominal diameter of the pipe, and the end of the magnetic pole in the pipe direction The diameter of the portion is larger than the distance between the magnetic poles, and the diameter of the portion where the coil of the magnetic pole is wound is larger than the diameter of the end of the magnetic pole in the pipe direction. Electromagnetic flow meter. 2. A pipe having an inner surface lined with an insulator and having a conductive fluid flowing through the lined inner surface, a pair of magnetic poles, and a pair of coils wound around the magnetic poles, respectively. A magnetic circuit that generates a magnetic field orthogonal to the axial line of the
It is arranged in a direction perpendicular to the magnetic field generation direction line of the magnetic circuit,
An electromagnetic flowmeter having a pair of electrodes for generating a flow signal proportional to the flow rate of the conductive fluid, wherein the nominal diameter of the pipe is D, the distance between the magnetic poles is L, and the end of the magnetic pole is in the pipe direction. Assuming that the diameter is d, the diameter of the portion where the magnetic pole coil is wound is dd, and the unit is mm, the relationship between the interval L and the nominal diameter D is L = (1.2D + 5) ± 2,
The relationship between the interval L and the diameter d is 1.5L ≧ d ≧ 1.1L, and the relationship between the interval L and the diameter dd is 2L ≧ dd>
An electromagnetic flowmeter having a volume of 1.5 L. 3. The electromagnetic flowmeter according to claim 2, wherein the distance between the coils is Lc, where Lc is the distance between the coils.
An electromagnetic flowmeter, wherein the relationship with c is 1.8 ≧ Lc ≧ L. 4. The electromagnetic flow meter according to claim 2, wherein b / a is 4 ≧ b / a ≧ 1 where a is a horizontal length of the coil cross section and b is a vertical length. An electromagnetic flowmeter characterized by the following. 5. An electromagnetic flowmeter according to claim 2, wherein an upper magnetic path or a lower magnetic path extending substantially perpendicular to the magnetic pole is formed at an end of the magnetic pole opposite to the pipe side. At the end of the magnetic path or the lower magnetic path, a side magnetic path extending substantially parallel to the magnetic pole is formed. When the inner diameter of the side magnetic path is E, the relationship between the magnetic pole interval L and the inner diameter E is 4L ≧ E ≧ An electromagnetic flowmeter characterized by being 3.5 L. 6. The electromagnetic flowmeter according to claim 5, wherein a horizontal length of the coil cross section is a, and a vertical length of the coil cross section is b.
The relationship between the magnetic pole interval L and the lateral length a is 0.8L ≧ a ≧
0.5 L, and the relationship between the magnetic pole interval L and the length b in the longitudinal direction is 3.2 L ≧ b ≧ 0.5 L.