JP4844019B2 - Electromagnetic flow meter - Google Patents

Description

  The present invention mainly relates to a small-diameter electromagnetic flow meter, and more particularly to an electromagnetic flow meter in which the influence of eddy current generated inside a magnetic pole core is reduced and the frequency characteristics of a magnetic circuit are improved.

FIG. 9 is a diagram illustrating the principle configuration of an electromagnetic flow meter that has been generally used.
As shown in FIG. 9, when a uniform magnetic field having a magnetic flux density B is applied to a pipe having an inner diameter D, when a conductive liquid having an average flow velocity v flows, the magnetic field and the flow are perpendicular to each other. E = D ・ v ・ B
Electromotive force E is generated.

Volume flow Q is ^{Q = π · D 2/4} · v = π / 4 · D / B · E
Therefore, if the magnetic flux density B is constant, the flow rate Q is proportional to the electromotive force E. The electromagnetic flow meter detects the electromotive force E and measures the volume flow rate Q.

  FIG. 10 is a cross-sectional view showing the configuration of such an electromagnetic flow meter. In the figure, 1 is a measuring tube through which a conductive fluid to be measured flows, 2a and 2b are electrodes provided opposite to the outer periphery of the measuring tube, and 3a and 3b are also 90 ° at the outer periphery of the measuring tube. It is a columnar magnetic pole core provided facing the rotated position. A coil bobbin 5 around which a coil 4 is wound is disposed on the outer periphery of the magnetic pole core, and the magnetic pole core 3 is inserted into the coil bobbin 5.

  6a and 6b are signal lines connected to the tips of the electrodes 2a and 2b. In the illustrated example, the signal line 6b connected to the electrode 2b is located at the bottom (measurement tube) of the magnetic pole core 3b positioned on the lower side in the drawing. It passes through the through-hole 7 provided on the side of the electrode 2a, is drawn out to the electrode 2a side, is twisted with the signal line 6a connected to the tip of the electrode 2a, and is connected to a signal converter (not shown). A return core 8 is attached to the outside of the magnetic pole cores 3a and 3b and the coil bobbin 5, and functions as a return path for the magnetic field. The following patent documents are known as prior arts of such an electromagnetic flow meter.

JP 2004-294176 A

In the above-mentioned patent document, a cylindrical ferritic stainless steel material is used as the columnar magnetic pole core, and an electromagnetic pure iron material is inserted into the cylinder, thereby enabling high-frequency excitation and a high magnetic flux density.
However, in the above conventional example, the rise of the magnetic flux density is delayed by the eddy current generated in the magnetic pole core, the frequency characteristics of the magnetic circuit are not good, and the signal line 6b penetrates the magnetic pole core. The differential noise corresponding to the interlinkage area is generated only in the signal line 6b, and the convergence of the differential noise in the magnetic pole core is slow. Furthermore, if the differential noise does not sufficiently converge even during signal sampling, the differential noise remains on the signal line 6b. If there is a difference in the amount of noise between the signal line 6a and the signal line 6b, the noise component remains even after differential amplification, resulting in a problem that the zero shift amount increases.

  The present invention has been made to solve the above-described problems. The influence of eddy current generated in the magnetic pole core is reduced, the frequency characteristic of the magnetic circuit is improved, and the influence of differential noise on the signal line 6b is reduced. The purpose is to realize an electromagnetic flow meter that is small and has a small zero shift amount.

The present invention has been made to solve the above problems, and in the electromagnetic flow meter according to claim 1,
A pair of flow rate detection electrodes, a pair of cylindrical magnetic pole cores , one end of which is fixed to the outer periphery of the measuring tube and opposed to a position rotated 90 degrees with respect to the mounting direction of the electrodes, and this magnetic pole core is inserted And a coil bobbin formed shorter than the length of the magnetic pole core, applying a magnetic field to the conductive fluid flowing in the measurement tube, and based on the electromotive force generated in the flow rate detection electrode In the electromagnetic flow meter that outputs the generated flow rate signal, a hole formed to a depth that does not reach the measurement tube from the center on the other end side of the pair of cylindrical magnetic cores toward the measurement tube side; , One of the pair of columnar magnetic pole cores, the side of the magnetic pole core that is exposed when one end of the coil bobbin and the other end of the magnetic pole core are flush with each other , and the pair of flow rates Connected to detection electrode A signal line through hole penetrating the magnetic pole core and the hole in a direction perpendicular to the axial direction of the magnetic pole core is provided so that one of the signal lines can be drawn to the same side as the other signal line side. .

In claim 2 , in the electromagnetic flowmeter according to claim 1 ,
A screw is formed at the entrance of the hole.

In claim 3 , in the electromagnetic flowmeter according to claim 1 or 2 ,
A slit is provided in the magnetic pole core provided with the hole.

In claim 4 , in the electromagnetic flowmeter according to claims 1 to 3,
The hole of the magnetic pole core is filled with an insulating paste mixed with a soft magnetic metal powder or a resin mixed with a soft magnetic metal powder.

In claim 5 , in the electromagnetic flowmeter according to claim 4 ,
Prior to filling of the paste or resin mixed with the soft magnetic metal powder, an insulating layer is provided on the inner surface of the hole of the magnetic pole core by an insulating member.

In claim 6, in the electromagnetic flowmeter according to claim 4 or 5 ,
In the middle of the magnetic pole core, an axial center through hole is provided in a direction perpendicular to the axial center of the magnetic pole core, and a paste or resin mixed with the soft magnetic metal powder is used. To do.

As is apparent from the above description, the invention of claim 1 has the following effects.
In an electromagnetic flowmeter that outputs a flow rate signal generated based on an electromotive force generated in a flow rate detection electrode, the measurement tube reaches the measurement tube side from the center of the other end of the pair of cylindrical magnetic cores. A hole formed to a depth not to be fixed, and the magnetic pole core that is one of the pair of columnar magnetic pole cores and is exposed when one end of the coil bobbin and the other end of the magnetic pole core are flush with each other is fixed The magnetic pole core in a direction perpendicular to the axial direction of the magnetic pole core so that one of the signal lines connected to the pair of flow rate detection electrodes can be drawn to the same side as the other signal line side. And since the signal line through-hole penetrating the hole is provided, no eddy current is generated in the central part of the magnetic pole core.

  Further, the path through which the eddy current flows is limited to the outer periphery of the magnetic pole core, and when the signal line 6b is passed through the magnetic pole core, the area of the magnetic pole core in contact with the signal line is reduced. Further, the path through which the eddy current flows is limited to the outer periphery of the magnetic pole core and takes a long path, so the convergence of the eddy current is accelerated and the frequency characteristics of the magnetic circuit are improved.

  In addition, since the area of the magnetic pole core in contact with the signal line is reduced, the differential noise generated in the signal line 6b is reduced. As a result, the noise amount unbalance between the signal line 6a and the signal line 6b is reduced, and the zero shift amount is reduced.

According to the invention of claim 2, since the screw is formed at the entrance of the hole, the return core can be screwed to the magnetic pole.
According to the invention of claim 3, since the slit is provided in the magnetic pole core provided with the hole, the convergence of the eddy current can be further accelerated, and the frequency characteristic of the magnetic circuit can be improved.

According to the invention of claim 4, since the insulating paste in which the soft magnetic metal powder is mixed or the resin in which the soft magnetic metal powder is mixed is filled in the hole of the magnetic pole core, Convergence is faster and the effect on the rise of the magnetic field is reduced.
Also, since the paste or resin is mixed with soft magnetic metal powder, the influence of the decrease in the center magnetic flux density can be reduced and the maximum magnetic permeability can be increased as compared with the case where a hole is simply made in the center of the magnetic pole. be able to.

According to the invention of claim 5 ,
Prior to filling with the paste or resin mixed with the soft magnetic metal powder, an insulating layer is provided on the inner surface of the hole of the magnetic pole core by an insulating member, so that convergence of eddy current can be further accelerated.

According to the invention of claim 6 ,
Use a screw because a paste or resin that has an axial through hole in the middle of the magnetic pole core in a direction perpendicular to the axis of the magnetic core and mixed with the soft magnetic metal powder is used. The seat core can be fixed without any problem, and can function as a fixing member for the coil bobbin.

FIG. 1 is a sectional view showing an embodiment of the electromagnetic flowmeter of the present invention. In the figure, the same elements as those of the conventional example shown in FIG.
In the figure, 1 is a measuring tube, 2a and 2b are electrodes, and 3 is a magnetic pole core. The magnetic pole core 3 is inserted into the coil bobbin 5. Reference numerals 6a and 6b denote signal lines, and reference numeral 8 denotes a return core that functions as a magnetic field return path, and is attached to the outside of the magnetic pole core 3 and the coil 4.

  10a and 10b are holes provided at the centers of the columnar magnetic pole cores 3a and 3b, and these holes penetrate through a through hole (signal line through hole) 7 provided at the bottom (near the measuring tube) of the magnetic pole core 3b. It is formed to a depth that does not reach the measurement tube 1, and is formed so that the area of the magnetic pole core around the through hole 7 is small.

The inventors conducted experiments on measuring tubes having diameters of 2.5 mm, 5 mm, and 10 mm.
The diameter of the magnetic core is the same 10 mm regardless of the diameter, and the length is about 40 mm. The through-hole 7 provided in the magnetic pole core 3b is formed in the diameter direction at a position about 30 mm deep from the end of the magnetic pole core 3b. In addition, a hole having a diameter of 2.5 mm and a depth of 33 mm is formed in a magnetic core of a measuring tube having a diameter of 2.5 mm and 5 mm, and a hole having a diameter of 5 mm and a depth of 33 mm is formed in the magnetic core 3a and 3b of the measuring pipe having a diameter of 10 mm. The experiment was conducted.

FIG. 2 is an experimental result showing a comparative example in the case where a measureless magnetic core having no hole 10 and holes 10a and 10b are provided in the above-described measurement tube having a diameter.




According to the experiment
The corner frequency of the inductance is
The one with a diameter of 2.5mm is 195Hz for the non-countermeasure core
250Hz for magnetic pole core
230mm for 5mm diameter magnetic core
310Hz for magnetic pole core
The thing of 10mm in diameter is 260Hz in the magnetic pole core without countermeasures
320Hz for magnetic pole core

Zero shift amount is
The diameter of 2.5mm is -6.76cm / s for the non-countermeasured magnetic core.
-1.07 cm / s for magnetic pole core
The one with a diameter of 5 mm is -16.08 cm / s for the countermeasureless magnetic core.
-7.42 cm / s for magnetic pole core
10mm diameter is -10.12cm / s for magnetic core without countermeasures
-1.81 cm / s for magnetic pole core

The center magnetic flux density is 260 mA when direct current is passed through the coil.
The diameter of 2.5mm is 107.6milli-Tesla (mT) for the non-countermeasured magnetic core.
95.4 (mT) for magnetic pole core
59.3 (mT) for 5mm diameter core with no countermeasure magnetic core
51.8 (mT) for magnetic pole core
The diameter of 10 mm is 32.4 (mT) for the non-countermeasured magnetic core.
29.8 (mT) for magnetic pole core

It became. Here, focusing on the 2.5 mm diameter, by cutting out the inside of the magnetic core and reducing the magnetic core material in contact with the signal line penetrating the inside of the magnetic core, the corner frequency of the inductance is 195 Hz in the non-magnetic pole core. After the measures were taken, the frequency became 250 Hz, which was improved by about 30%.
Further, the zero shift amount was −6.76 cm / s before the countermeasure, but became −1.07 cm / s after the countermeasure, and when implemented, the zero shift amount was about 1/5.

Fig. 3 compares the absolute value of the peak of differential noise between a magnetic core with a 2.5mm caliber magnetic pole core with countermeasures (with holes) and no countermeasures (without holes). A signal waveform is shown. Although it was 33.8 mV before the countermeasure, it can be seen that the tail convergence is improved to 32.0 mV after the countermeasure.
FIG. 4 shows a comparison with a 10 mm aperture, and it can be seen that the tail of the peak of the differential noise is improved from 25 mV to 17.4 mV when the countermeasure is taken.

FIG. 5 shows an example in which a return hole and a magnetic pole core are coupled using screws or bolts using a round hole opened in the magnetic pole core as a pilot hole for a female screw.
The return core and the magnetic pole core may be coupled by press-fitting a pin or the like without cutting the female screw.
Moreover, as shown in the A-A cross-sectional view, by adding a slit in addition to the round hole, the portion where the overcurrent is generated is subdivided to reduce the overcurrent. As a result, the frequency characteristics of the magnetic circuit can be improved by further accelerating the convergence of the eddy current by subdividing the eddy current generation site and reducing the overcurrent.

  6 is a cross-sectional view showing an example in which an insulating paste or an insulating resin mixed with a soft magnetic metal powder is injected into the hole of the magnetic pole core shown in FIG. In this case, the mixing amount of the soft magnetic metal is determined by the required center magnetic flux density, but is adjusted so that the specific resistance value of the paste or resin is as high as possible even after mixing.

  According to the configuration of FIG. 6, the convergence of the eddy current is accelerated in the central part of the magnetic pole core, and the influence on the rise of the magnetic field is reduced. Further, the path through which most of the eddy current flows is limited to the outer periphery of the magnetic pole, and since a long path is taken, the convergence of the eddy current is accelerated and the frequency characteristics of the magnetic circuit can be improved.

As a result, the differential noise generated in the signal line 6b is reduced, and the noise amount imbalance between the signal lines 6a and 6b is reduced, so that the shift amount of the zero point can be reduced.
Furthermore, since soft magnetic metal powder is mixed in the insulating paste or the insulating resin, it functions as a magnetic pole. As a result, it is possible to reduce the influence of the decrease in the central magnetic flux density and increase the maximum magnetic permeability as compared with the case where the holes are simply drilled.

FIG. 7 shows another embodiment. In this example, an insulating varnish, silicon resin, or the like is injected before the soft magnetic metal powder is mixed in or before the resin is injected into the hole of the magnetic pole core. An insulating layer is formed between the magnetic pole core body and the magnetic pole core body. According to such a configuration, the convergence of eddy current can be further enhanced.

FIG. 8 shows still another embodiment. In this example, the hole 10 is formed in the magnetic pole core and the through hole 14 is formed in the diameter direction from the middle of the hole. As such a configuration,
A resin having a bonding effect is used as a resin mixed with soft magnetic metal powder to be injected into the hole, and the sheet core 8 is fixed by adhesion, and the coil bobbin 5 is also fixed together. According to the above-described configuration, the seat core can be easily fixed, and the adverse effect due to the vibration of the coil bobbin 5 can be eliminated and the measurement value can be stabilized.

  The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

It is sectional drawing of the electromagnetic flowmeter which shows an example of embodiment of this invention. It is an experimental result which shows the comparative example at the time of providing a countermeasure magnetic pole core which does not provide a hole, and a hole. The signal waveform which compared the peak value of a differential noise with what took the countermeasure to the magnetic pole core, and the magnetic core with no countermeasure is shown. The signal waveform which compared the peak value of a differential noise with what took the countermeasure to the magnetic pole core, and the magnetic core with no countermeasure is shown. It is sectional drawing of the electromagnetic flowmeter which shows another Example. It is sectional drawing of the electromagnetic flowmeter which shows another Example. It is sectional drawing of the electromagnetic flowmeter which shows another Example. It is sectional drawing of the electromagnetic flowmeter which shows another Example. It is a principle structure explanatory drawing of an electromagnetic flowmeter. It is sectional drawing which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measuring tube 2 Electrode 3 Magnetic pole core 4 Coil 5 Coil bobbin 6 Signal line 7 Through-hole 8 Sheet core (return core)
10 Hole 11 Paste or resin mixed with soft magnetic metal powder 12 Insulating member 13 Adhesive effect member

Claims (6)

A pair of flow rate detection electrodes, a pair of cylindrical magnetic pole cores , one end of which is fixed to the outer periphery of the measuring tube and opposed to a position rotated 90 degrees with respect to the mounting direction of the electrodes, and this magnetic pole core is inserted And a coil bobbin formed shorter than the length of the magnetic pole core, applying a magnetic field to the conductive fluid flowing in the measurement tube, and based on the electromotive force generated in the flow rate detection electrode In the electromagnetic flow meter that outputs the generated flow rate signal, a hole formed to a depth that does not reach the measurement tube from the center on the other end side of the pair of cylindrical magnetic cores toward the measurement tube side; , One of the pair of columnar magnetic pole cores, the side of the magnetic pole core that is exposed when one end of the coil bobbin and the other end of the magnetic pole core are flush with each other , and the pair of flow rates Connected to detection electrode A signal line through hole penetrating the magnetic pole core and the hole in a direction perpendicular to the axial direction of the magnetic pole core is provided so that one of the signal lines can be drawn to the same side as the other signal line side. Electromagnetic flow meter.   The electromagnetic flowmeter according to claim 1, wherein a screw is formed at an entrance of the hole. Electromagnetic flow meter according to claim 1 or 2, characterized in that the slits in pole core provided with said hole.   4. The electromagnetic flowmeter according to claim 1, wherein the magnetic core is filled with an insulating paste mixed with a soft magnetic metal powder or a resin mixed with a soft magnetic metal powder.   5. The electromagnetic flowmeter according to claim 4, wherein an insulating layer is provided on an inner surface of a hole formed in the magnetic pole core by an insulating member prior to filling of the paste or resin mixed with the soft magnetic metal powder. . In the middle of the magnetic pole core, an axial center through hole is provided in a direction perpendicular to the axial center of the magnetic pole core, and a paste or resin mixed with the soft magnetic metal powder is used. The electromagnetic flowmeter according to claim 4 or 5 .

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