JPH0228407Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to an electromagnetic flowmeter transmitter (hereinafter abbreviated as a transmitter when necessary), and is particularly suitable for use in a transmitter with a short distance between surfaces. Concerning useful ideas.

<Prior Art> Figure 1 shows the structure of a conventional transmitter. Figure a is a longitudinal cross-sectional view thereof, and figure b is a cross-sectional view at the center thereof. In the figure, 1 is a conduit through which the fluid to be measured flows. The axis of conduit 1 is the z-axis, the direction that crosses the z-axis at the center cross section of the conduit and is perpendicular to the plane of the paper is the x-axis, and the z-axis and x
Let the axis perpendicular to both the y-axis and the y-axis be the y-axis. 2 _a and 2 _b are rectangular excitation coils that apply a magnetic field in the y-axis direction to the fluid to be measured across the conduit 1, have a coil length l _c in the z-axis direction, and have a saddle shape on the outside of the conduit 1. It is located in 3 is a laminated core that serves as a return path for the magnetic field applied to the fluid to be measured. The laminated core 3 has an excitation coil _2a ,
2 It is arranged in a ring shape on the outside of _b . Reference numeral 4 denotes a cylindrical case which has the function of housing the excitation coils 2 _a and 2 _b , the laminated core 3, etc. in an airtight manner and connecting them to mating piping. 5 is conduit 1 and case 4
It is made of an insulating material that has the function of preventing a short circuit caused by the conduit 1 of the signal voltage generated in the fluid to be measured. The signal voltage generated in the fluid is detected by detection electrodes 6 _a and 6 _b arranged on the x-axis on the inner surface of the lining 5 in the central cross section. The inner diameter of the lining 5 is D, which is represented by the diameter. In use, the transmitter 7 constructed as described above is inserted and fixed between the pipes 8 _a and 8 _b . L is the distance between surfaces indicating the maximum length of the transmitter 7 in the z-axis direction.

The magnetic flux φ _p generated by the excitation coils 2 _a and 2 _b crosses the conduit 1 and the fluid to be measured, and follows a path returning to the laminated core 3, as shown in FIG. 1b.
However, as shown in FIG. 1a, some of the magnetic flux generated by the excitation coils 2 _a and 2 _b leaks to the outside of the case 4 of the transmitter 7 and crosses a part of the opposing pipes 8 _a and 8 _b . φ _l (only the upper half is shown, the magnetic flux φ _l in the lower half is not shown) is also present. Transmitter distance L
is large, even if a voltage is generated in the fluid to be measured due to the magnetic flux φ _l , the end face of the transmitter 7 and the detection electrode 6
Since the distance between the detection electrodes 6 _a and 6 _b is large, it does not contribute as a signal voltage to the detection electrodes 6 a and 6 b and does not cause an error. However, as the inter-plane distance L becomes shorter, the voltage caused by the magnetic flux φ _l also increases to the detection electrodes 6 _a and 6 _b . is detected and creates an error factor. In particular, depending on whether the inner surfaces of the pipes 8 _a and 8 _b to which the transmitter 7 is attached are conductive or insulating, the rate of the short-circuit effect in which the voltage generated due to the magnetic flux φ _l is short-circuited in the pipes differs. Moreover, this shorting effect depends on the conductivity of the fluid, with lower conductivity fluids being more likely to be shorted to the insulating inner surface of the piping. Furthermore, even if actual piping is initially insulative, the surface may become oxidized and become covered with an oxide film, or a grease-like insulator may adhere to the piping, causing it to become insulative. Conversely, even if the piping is initially coated with an insulating coating, the metal surface of the piping may become conductive as it wears away due to the flow of earth, sand, slurry, etc. Furthermore, even if the piping is covered with an insulating film, if the film is very thin, the voltage caused by the magnetic flux φ _l will be partially short-circuited due to capacitive coupling. Moreover, short circuits are not always uniformly distributed. Considering the above points comprehensively, in actual piping, no assumptions or predictions can be made regarding the properties of the inner surface of the piping and its changes over time. Further, due to differences in magnetic properties of the pipe material itself, the magnetic field distribution in the fluid to be measured by the transmitter 7 changes, causing an error in the flow rate signal.

In order to eliminate these inconveniences, it is possible to increase the distance L between the surfaces of the transmitter 7 , but this results in an increase in manufacturing costs, especially in response to the recent demands for economic efficiency and miniaturization and weight reduction. I can't.

<Purpose of the invention> In view of the above-mentioned prior art, an object of the present invention is to obtain a highly accurate transmitter that is not affected by the mating piping even when the distance between the surfaces of the transmitter is short.

<Structure of the invention> The structure of the invention that achieves this object is an electromagnetic flowmeter transmitter having a magnetic field generating means disposed outside a conduit through which a fluid to be measured flows and applies a magnetic field to the fluid to be measured. The electromagnetic flowmeter transmitter is characterized in that it includes auxiliary magnetic field generating means that generates an auxiliary magnetic field in a direction that cancels the magnetic field at an end of the magnetic field generating means in the axial direction.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings. Note that the same parts as in the prior art are denoted by the same reference numerals, and redundant explanations will be omitted as necessary.

FIG. 2 is a perspective view showing one embodiment of the present invention. For simplicity, in FIG. 2, the conduit 1, laminated core 3, case 4, and lining 5 in FIG. 1 are omitted, and only the essential parts of the present invention are shown. 2
_a and _2b are excitation coils that apply a main magnetic field to the fluid to be measured, and have the same configuration as that shown in FIG. Excitation coil 2 _a in the z-axis direction of conduit 1,
Auxiliary magnetic field generators 9 and 10 are provided at the downstream end of _2b .
However, auxiliary magnetic field generating sections 11 and 12 having a similar configuration are also arranged at the upstream end. The auxiliary magnetic field generating section has a roughly arc shape, and this is located near the ends of the rectangular excitation coils 2 _a and 2 _b in the z-axis direction.
They are arranged along the outer periphery of the conduit 1 symmetrically with respect to the z-axis plane including the axis.

FIG. 3 is a diagram showing the configuration of the auxiliary magnetic field generator. The auxiliary magnetic field generator includes an auxiliary core and an auxiliary coil. The auxiliary core 91 has an arcuate shape with a radius of curvature γ, and has magnetic poles 92 and 93 at its ends and in the middle, respectively. This auxiliary core 9
1 is made by punching out and laminating several silicon steel plates. The thickness of the stack depends on the diameter, but a thickness of about 10 mm to 20 mm is sufficient. An auxiliary coil 94 is wound around the center of the auxiliary core 91, and by passing a current through this, an auxiliary magnetic flux φ _s is generated from the magnetic poles 92 and 93 in the y-axis direction. The auxiliary coil 94 is connected in series with the excitation coils 2 _a and 2 _b , and the polarity is selected so that the auxiliary magnetic flux φ _s cancels the main magnetic flux φ _p . Regarding the other auxiliary magnetic field generating units 10, 11, and 12, the polarity of each auxiliary coil is similarly selected so that the auxiliary magnetic flux φ _s cancels the main magnetic flux φ _p . The magnitude of the auxiliary magnetic flux φ _s can be adjusted by changing the number of turns of the auxiliary coil.

The magnetic flux density at the end of the transmitter 7 is significantly reduced by the auxiliary magnetic flux φ _s generated by the auxiliary magnetic field generator configured in this manner. FIG. 4 is a magnetic flux density curve showing an example of the effect of reducing magnetic flux density according to the present invention. The curve in this figure is point P in Figure 1b (X=0.9R, R:D/2)
It shows the z-axis dependence of the magnetic flux density at . The horizontal axis indicates the z-axis at the x point, and the vertical axis indicates the magnetic flux density at each point on the axis. The solid line indicates when there is no auxiliary magnetic flux φ _s , and the dotted line indicates when there is auxiliary magnetic flux φ _s . Even with the auxiliary magnetic flux φ _s , the magnetic flux density near the center hardly decreases, but the magnetic flux decreases significantly near the end face of the transmitter. For example, if the coil length l _c is the diameter D
The magnetic flux density at point P on the end face of a transmitter with a face-to-face distance L of 1.5D is about 10% of the central magnetic field, but when this auxiliary magnetic field generator is added, it becomes 1. %. Note that the distribution of the magnetic field can also be changed by changing the length of the arc of the auxiliary core or increasing the number of its magnetic poles.

As explained above, by adding an auxiliary magnetic field generating section, the magnetic flux density near the end face of the transmitter can be significantly reduced, which reduces the voltage generated in the fluid to be measured and the inner surface of the mating piping. The distance between the surfaces can be significantly shortened compared to the conventional method. Furthermore, since the magnetic field near the end face of the transmitter remote from the detection electrodes 6 _a and 6 _b is canceled, the reduction in the signal voltage as a whole is small.

In the explanation so far, we have explained the fan-shaped core shown in Fig. 3 as the auxiliary core that constitutes the auxiliary magnetic field generating section, but with such a shaped auxiliary core, the effect of reducing the magnetic field near the auxiliary core is large. The reduction effect near the tube axis is small. FIG. 5 shows an embodiment of an auxiliary core that increases the reduction effect near the tube axis. As shown in this figure, the magnetic poles 131, 13 of the auxiliary coil
By providing the positions of 2, 141, and 142 point-symmetrically with respect to the tube axis, the reduction effect at the center can be increased.

FIG. 6 shows an embodiment using a ring-shaped core 15 as the auxiliary core. The structure is such that auxiliary coils 16 _a and 16 _b are wound around a part of the ring-shaped core 15 to provide a reduction effect by utilizing the magnetic flux φ _s leaking inside from each part of the ring-shaped core.

In these embodiments, a case has been described in which a magnetic field is created by flowing an excitation current, but in the case of a DC excitation type transmitter, a permanent magnet can also be used as an auxiliary magnetic field generating section.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, it is possible to create a transmitter between short surfaces in which less magnetic flux leaks into the measured fluid portion outside the end face of the transmitter. . Therefore, the magnetic force of the mating piping,
It is possible to obtain a highly accurate oscillator that is independent of electrical characteristics and unaffected by the conductivity of the fluid. Particularly in the case of large-diameter transmitters, the use of short planes leads to a reduction in manufacturing costs, which is of great industrial benefit.

[Brief explanation of the drawing]

FIG. 1 is an example of a conventional transmitter, FIG. 2 is a perspective view of a transmitter according to the present invention, FIG. 3 is an example showing the configuration of an auxiliary magnetic field generating section, and FIG. 4 is a diagram showing a magnetic flux density according to the present invention. A magnetic flux density curve showing the attenuation effect, FIG. 5 shows a first modified embodiment of the auxiliary magnetic field generating section, and FIG. 6 shows a second modified embodiment of the auxiliary magnetic field generating section. 1... Conduit, 2 _a , 2 _b ... Excitation coil, 4...
Case, _6a , _6b ...detection electrode, 7 ...transmitter,
8 _a , 8 _b ... Piping, 9, 10, 11, 12... Auxiliary magnetic field generating section.

Claims (1)

[Scope of utility model registration request] In an electromagnetic flowmeter transmitter having a magnetic field generating means disposed outside a conduit through which a fluid to be measured flows and applying a magnetic field to the fluid to be measured, the magnetic field is canceled at an end of the magnetic field generating means in the axial direction of the conduit. An electromagnetic flowmeter transmitter characterized by comprising an auxiliary magnetic field generating means for generating an auxiliary magnetic field in a direction.