JP2002031551A - Flow rate measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate low-cost flow rate measurement device having a wide measurement range and complying with a wide flow rate condition. SOLUTION: In a measurement tube 1, through which conductive fluid flows, in the flow rate measurement device, a vortex generator 2 generating a Karman vortex 3 in the fluid is provided, while a pair of measurement electrodes 4a and 4b detecting a change in induced electromotive force generated by passage of the Karman vortex 3 through a magnetic field, a magnetic field generating device 8 generating a magnetic field, and a detection circuit 5 electrically connected to a pair of measurement electrodes 4a, 4b and detecting the induced electromotive force for finding a flow rate of the fluid are arranged on the downstream side beyond the vortex generator 2. On the upstream side and the downstream side of a pair of measurement electrodes 4a and 4b, reference potential measurement electrodes 6a and 6b electrically connected to the detection circuit 5 for measuring a potential difference between the upstream side and the downstream side are arranged each.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for measuring a flow rate of a gas or a liquid (hereinafter referred to as "fluid") flowing in a measuring tube.

[0002]

2. Description of the Related Art Hitherto, a Karman vortex flow rate measuring apparatus has been well known as a flow rate measuring apparatus for measuring a flow rate of a fluid flowing in a measuring pipe. This Karman vortex flow rate measuring device generates Karman vortices in a flowing fluid and counts the number of generated Karman vortices (hereinafter referred to as frequency) as described in, for example, Japanese Patent Application Laid-Open No. 60-40914. The flow rate is calculated from this frequency. This utilizes the phenomenon that the frequency of the Karman vortex is proportional to the flow rate. For this reason, the Karman vortex flow rate measurement device must count the frequency of Karman vortices. However, conventionally, as described in Japanese Patent Application Laid-Open No. 60-40914, the frequency is detected using ultrasonic waves or vibration. ing. When the Karman vortex flows down, it utilizes the fact that ultrasonic waves, vibrations, and the like incident thereon cause a change in frequency and phase.

However, in order to detect changes in ultrasonic waves, vibrations, and the like, there is a problem that a large, complicated, and expensive detecting device is required, although the size of the conduit itself is not so large. Was. Moreover, even with such expensive detectors, the accuracy of the flow rate depends primarily on the Karman vortex generation mechanism, and if the temperature or other disturbances affect the Karman vortex generation, the measurement accuracy is immediately increased. It was worse.

Therefore, in order to solve such a problem,
For example, as disclosed in JP-A-5-172598, it has been proposed to detect the frequency of Karman vortices using a magnetic field.

Therefore, such a conventional flow measuring device will be described. FIG. 2 is a cross-sectional view showing a configuration of a conventional flow measurement device.

As shown in FIG. 2, reference numeral 1 denotes a measuring tube through which a fluid having conductivity flows, and 2 denotes a vortex generator provided in the measuring tube 1. 3 is a Karman vortex generated by the vortex generator 2,
4a and 4b are measurement electrodes. On the downstream side of the vortex generator 2 placed in the flow, a pair of Karman vortex streets whose rotation directions are alternately reversed are generated at a frequency proportional to the representative dimension of the vortex generator 2. The measurement electrode 4b is provided on the downstream side of the vortex generator 2, while the measurement electrode 4a is provided on the upstream side of the measurement electrode 4b as a counter electrode of the measurement electrode 4b, and at the same time, on the downstream side of the vortex generator 2. However, the measurement electrode 4 a shown in FIG. 2 is integrated with the vortex generator 2.

A detection circuit 5 is electrically connected to the measurement electrodes 4a and 4b, detects a voltage between the measurement electrodes 4a and 4b, and calculates a flow rate of a fluid flowing in the measurement tube 1. Reference numeral 8 denotes a measurement tube. 1 is a magnetic field generating device provided around 1, wherein two magnets are disposed with a S-pole and an N-pole facing each other with a measurement tube 1 interposed therebetween. And the magnetic field generator 8
The magnetic field is provided so that the direction of the magnetic field from the north pole to the south pole is perpendicular to the axial direction of the vortex generator 2 and the measurement electrodes 4a and 4b.

According to the conventional flow rate measuring device, when the Karman vortex 3 generated by the vortex generator 2 flows down along with the flow, the flow velocity of the flow changes by the vortex velocity. Magnetic flux changes in the magnetic field applied by the magnetic field generator 8. Since this magnetic flux change causes an induced electromotive force between the measurement electrodes 4a and 4b, if this is detected by the detection circuit 5, the number of voltage changes is proportional to the Karman vortex 3, and the voltage change detected by the detection circuit 5 By counting the number of times, the flow rate can be calculated.

[0009]

However, in the above-mentioned conventional flow rate measuring device, when the conductivity of the fluid changes, the electromotive force generated between the measuring electrodes 4a and 4b changes, and the flow and the magnetic field change. When a disturbance is applied, noise is added to the magnetic field to be measured, and it is difficult to calculate an accurate flow rate. The low conductivity fluid originally has low induced electromotive force and low signal level, so that accurate flow rate detection has been difficult.

When the flow rate changes from the optimum flow rate for the measurement, the frequency of the Karman vortex 3 does not change in proportion to the change in the flow rate, and the proportional relationship is lost, so that the detection accuracy is reduced or the flow rate is increased. The flow is disturbed, and this disturbance increases the noise, thus reducing the measurement accuracy.

Further, when a permanent magnet is used as the magnetic field generator 8, the performance of the magnet deteriorates due to aging, and the polarization generated at the electrode causes a reduction in the induced electromotive force, thereby lowering the signal level. Therefore, accurate flow rate detection becomes difficult.

As described above, the conventional flow rate measuring device needs to detect and respond to various changes in the measurement conditions, but it is difficult to respond to all of the various measurement conditions. If a countermeasure device such as a filter circuit for noise suppression is incorporated, the overall structure of the device becomes complicated or the cost increases,
Secondary problems also occurred.

Accordingly, in order to solve such a conventional problem, an object of the present invention is to provide a low-cost, high-precision flow measuring device which has a wide measuring range, can cope with a wide range of flow conditions, and has a low cost. I do.

[0014]

In order to solve such a problem, a flow rate measuring apparatus according to the present invention is electrically connected to a detection circuit on the upstream and downstream sides of a pair of electrodes for measuring electromotive force. One reference potential measuring electrode for measuring the potential difference between the upstream side and the downstream side is provided, and the detection circuit calculates the flow rate by subtracting the potential difference from the induced electromotive force.

[0015] Thus, a wide measuring range can be met, a wide range of flow conditions can be met, and low-cost, high-precision flow measurement can be performed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An invention according to claim 1 of the present invention is provided in a measuring pipe through which a conductive fluid flows, and generates a Karman vortex in the fluid, and a downstream side of the vortex generator. A pair of electromotive force measuring electrodes for detecting a change in induced electromotive force generated by a magnetic field change generated when the Karman vortex passes through the magnetic field, a magnetic field generator for generating a magnetic field, and a pair of electromotive force A flow measurement device that is electrically connected to a power measurement electrode and includes a detection circuit that detects an induced electromotive force and calculates a flow rate of a fluid, and includes an upstream side and a downstream side of a pair of electromotive force measurement electrodes. Is provided with one reference potential measurement electrode electrically connected to the detection circuit for measuring the potential difference between the upstream side and the downstream side, and the detection circuit calculates the flow rate by subtracting the potential difference from the induced electromotive force. Flow rate measurement Because it is a device, even if the measurement conditions change, the change can be canceled out and the measurement can be performed.Therefore, measurement can be performed in a wide measurement range. Since no equipment is required, high-precision flow measurement can be performed at low cost.

According to a second aspect of the present invention, there is provided the flow rate measuring apparatus according to the first aspect, wherein the diameter of the reference potential measuring electrode is not more than 1/2 of the vortex generator width. The diameter of the reference potential measuring electrode is less than 1/2 of the representative dimension of the vortex generator, and is less than 1/2 in Reynolds number, approaching laminar flow, which almost disturbs the flow of Karman vortex street. In addition, since the vorticity component generated by the reference potential measuring electrode itself is small, and the change in flow velocity due to this is small and no change in magnetic flux occurs, the flow rate can be measured with high accuracy.

According to a third aspect of the present invention, the diameter of the electrode for measuring the electromotive force is not more than 1/2 of the width of the vortex generator. Because it is a device, the diameter of the electrode for measuring electromotive force is less than half of the typical size of the vortex generator, and when viewed in Reynolds number, it is 1
/ 2 or less, the nearby flow approaches a laminar flow, hardly disturbs the flow, does not destroy the flow of the Karman vortex street, and enables high-precision flow measurement.

According to a fourth aspect of the present invention, there is provided the flow rate measuring apparatus according to any one of the first to third aspects, wherein the electrodes for measuring the electromotive force have the same diameter. Since noise generated by the pair of electrodes for measuring electromotive force can be canceled and reduced by the detection circuit, the noise level can be reduced and the flow rate can be measured with high accuracy.

The invention according to claim 5 of the present invention is characterized in that the tube length of the electrode for measuring electromotive force is 2 to 2.5 times the width of the vortex generator. Since the flow measurement device described in (1) or (2) above, it is possible to measure only the induced electromotive force change at the center of the two generated Karman vortex streets and perform flow measurement with high accuracy.

The invention according to claim 6 of the present invention is the flow device according to any one of claims 1 to 5, wherein the lengths of the electrodes for measuring the electromotive force are the same in the tube. The noise level can be reduced by canceling the noise by the detection circuit, and the flow rate can be measured with high accuracy.

According to a seventh aspect of the present invention, the installation interval of the electrodes for measuring the electromotive force is 2 to 2.5 times the width of the vortex generator. The distance between the pair of electrodes for measuring electromotive force can be less than the distance between the vortex of the Karman vortex street and the number of Karman vortices existing between the electrodes for measuring electromotive force is less than one. By doing so, there is no change in the flow velocity or magnetic flux that causes noise, so that the noise level can be reduced, the frequency count can be easily performed, and the flow rate can be measured with high accuracy.

The invention according to claim 8 of the present invention is characterized in that the radial width of the magnetic field generator is 1.5 to 2 times the width of the vortex generator. Since the flow rate measuring device described in (1), the magnetic field generated in the measuring tube is concentrated only at the position where the Karman vortex is generated, and has an effect of reducing a noise component due to a vortex component generated on the side wall of the measuring tube.

(Embodiment) A flow rate measuring apparatus according to an embodiment of the present invention will be described below with reference to FIG. In addition, the same members as those of the conventional flow rate measuring device are denoted by the same reference numerals, and redundant description will be omitted. FIG. 1 is a sectional view showing a configuration of a flow measuring device according to an embodiment of the present invention.

As shown in FIG. 1, 1 is a measuring tube, 2 is a vortex generator which is provided in a fluid and generates Karman vortices, and 3 is a rotating direction alternately at a frequency proportional to a representative dimension of the vortex generator 2. 4a, 4b are electromotive force measuring electrodes, 5 is an induced electromotive force to calculate the flow rate, and a detection circuit that can invert and cancel the noise component signal by an inversion circuit. , 8 are magnetic field generators. If the inside diameter of the measuring tube 1 is too small, the influence of the boundary layer of the tube wall will affect the three rows of Karman vortices. If it is too large, the flow velocity will be slow and the three rows of Karman vortices will not be generated. The Reynolds number in an appropriate flow velocity range is in a range of about 3,000 to 100,000. Further, in the present embodiment, the shape of the vortex generator 2 is a triangular prism, but any shape may be used as long as it generates three rows of Karman vortices. The vortex generator 2 of the present embodiment is attached to the measurement tube 1 so that one side surface of the triangular prism is perpendicular to the flow. In the case of the flow measurement device of the present embodiment,
In order to set the flow rate detection range to 1 L / min to 10 L / min, the measuring tube 1 having an inner diameter of 7 mm was used. Under this condition, a vortex generated by a triangular prism having a width of 2 mm and a height of 3 mm and an isosceles triangular cross section was generated. Providing body 2 was most effective.

Two electrodes 4a and 4b for measuring the electromotive force are attached to the downstream side of the vortex generator 2 side by side so as to be orthogonal to the axis of the vortex generator 2 and the flow. At this time, if a streamline passing through the measurement electrode 4a is drawn, the streamline always passes through the measurement electrode 4b of the electromotive force. N-poles and S-poles of permanent magnets constituting the magnetic field generator 8 are provided on both sides so as to sandwich the measurement electrodes 4a and 4b from both sides of the measurement tube 1. When the flow rate detection range is set to 1 L / min to 10 L / min, the magnetic field generator 8 needs to increase the magnetic flux density in the measuring tube 1 and uses a rare earth permanent magnet, and is 1.5 times the vortex generator width. The width of the magnet.

Reference numerals 6a and 6b denote reference potential measuring electrodes which measure the potentials of the electromotive force measuring electrodes 4a and 4b on the upstream and downstream sides, respectively, and measure the potential difference between the upstream position and the downstream position. You can do it. Reference potential measurement electrode 6
a and 6b are provided in parallel with four measurement electrodes 4a and 4b. At this time, the stream lines drawn through the reference potential measuring electrodes 6a, 6b are always the electromotive force measuring electrodes 4a, 4b.
You will pass through. Therefore, the four electrodes completely have a positional relationship upstream and downstream of one flow.

The Karman vortex flow rate measuring apparatus is designed so that each member arranged in such an arrangement stably generates the Karman vortex 3 and does not generate noise due to turbulence generated in the measuring tube 1. In addition, it is necessary to carefully select the representative dimensions of each member, the Reynolds number of the fluid, and the like.

In FIG. 1, the dimensions of each member are D, the width corresponding to the representative dimension of the vortex generator 2, the diameters of the measurement electrodes 4a, 4b are da, db, and the reference potential measurement electrodes 6a, 6 respectively.
b is dc, dc, the length of the measuring electrodes 4a, 4b in the tube is h, the distance between the measuring electrodes 4a, 4b is L, the magnetic field generator 8
Is Dm. As described below, these dimensions are based on a delicate balance relationship for stable generation of the Karman vortex 3 and prevention of noise.

For example, the diameter dc of the reference potential measuring electrodes 6 a and 6 b is selected to be 以下 or less of the width D which is a representative dimension of the vortex generator 2. Thereby, the reference potential measuring electrode 6
Considering the diameter dc of a and 6b, the Reynolds number is 1 /
In the vicinity of 2 or less, the flow approaches a laminar flow, and the generation of the Karman vortex 3 is not disturbed. Further, the reference potential measuring electrodes 6a, 6
The vorticity component generated by b itself also decreases. With such a change in the flow velocity, a change in the magnetic flux hardly occurs between the measurement electrodes 4a and 4b, so that the flow rate can be measured without reducing the measurement accuracy.

The diameters da, d of the measuring electrodes 4a, 4b
It is preferable that b is also １ ／ or less of the vortex generator width D. This is because the Reynolds number becomes １ ／ or less, and the flow in the vicinity approaches laminar flow, so that the flow that generates the Karman vortex 3 is hardly disturbed, and the flow of the Karman vortex street is not destroyed. . Then, the measurement electrodes 4a,
When the diameters da and db of the electrodes 4b are the same, noise generated at the measurement electrodes 4a and 4b of the electromotive force can be reduced. That is, the flow disturbed by the measurement electrode 4a flows down the streamline while the turbulence is diffused, and flows into the measurement electrode 4b. However, when the diameters da and db have different diameters, the fluid resistance and the peeling state of both electrodes are reduced. In contrast, the surrounding flows become separate and complicated flows and the noise increases, but the noise is relatively suppressed because they have the same diameter. Moreover, in the present embodiment, the diameter d
a and db are made the same to make the noise components almost the same, and the detecting circuit 5 is provided with an inverting circuit. After the noise component signal from one electrode is inverted by the inverting circuit,
By canceling both the processed noise component signals, the noise level is further reduced from the viewpoint of signal processing.

Further, the length h in the tube of the measuring electrodes 4a, 4b
Is set to 2 to 2.5 times the vortex generator width D, the flow and size balance is appropriately adopted as the inner diameter of the measurement tube 1 to about 3 to 4 times the vortex generator width D. 4a, 4b
Near the tip of the Karman vortex street is the minimum height that completely surrounds the two Karman vortex streets. Only the induced electromotive force change at the center of the generated Karman vortex street can be measured, and the flow rate can be measured with high accuracy. . When the lengths h of the measuring electrodes 4a and 4b are the same, noise caused by disturbances other than the Karman vortex 3, such as vortices flowing out from the tips of the measuring electrodes 4a and 4b, can be canceled by the detection circuit 5, thereby reducing the noise level. Can,
The flow rate can be measured with high accuracy.

When the installation interval L of the measurement electrodes 4a and 4b is set to be 2 to 2.5 times the width D of the vortex generator, a pair of measurement electrodes 4a and 4b
The distance L between the Karman vortices 3 of the Karman vortex street and the Karman vortex 3 can be made smaller than the distance between the measurement electrodes 4a and 4b. The noise level is reduced, and one of the Karman vortices 3 is detected as a detection signal (pulse) 1
The frequency can be easily counted, and the flow rate can be measured with high accuracy.

When the width Dm of the magnetic field generator 8 in the radial direction of the tube is set to 1.5 to 2 times the width D of the vortex generator, the magnetic field generated in the measuring tube 1 is concentrated only at the position where the Karman vortex 3 is generated. As a result, a noise component due to a vorticity component generated on the side wall of the measurement tube 1 can be reduced. As described above, the flow rate measuring device of the present embodiment employs 1.5 times.

With the flow rate measuring apparatus having the above-described arrangement, when the Karman vortex street crosses the magnetic flux passing through the portion surrounded by the measurement electrodes 4a and 4b, a magnetic field change occurs, and the measurement electrodes 4a and 4b are regulated. The induced electromotive force is generated in a pulse form. Since the potential difference in the vicinity is measured by the reference potential measuring electrodes 6a and 6b, the reference potential between the measurement electrodes 4a and 4b reflecting the measurement conditions (DC components and disturbance noise components other than the Karman vortex 3) in the vicinity is measured. The potential difference can be measured, and by canceling this reference potential difference signal with the electromotive force signal in the detection circuit 5, noise components and signals other than the Karman vortex street can be easily eliminated.

Next, the operation of the flow measuring device according to the present embodiment having such a configuration will be described. The fluid flowing in the measuring tube 1 flows down in the magnetic field applied by the magnetic field generator 8. At this time, the Karman vortex street generated in the vortex generator 2 has a proportional relationship between the frequency of the Karman vortex 3 and the flow velocity, as is known from the study of Strouhal. Therefore, if the frequency of the Karman vortex 3 is counted, the flow rate of the fluid flowing in the measurement tube 1 can be calculated.

[0037]

As described above, in the flow rate measuring apparatus according to the first aspect of the present invention, one reference potential measuring electrode is provided on each of the upstream and downstream sides of the electromotive force measuring electrode, and Since the flow rate is calculated by subtracting the potential difference from the electric power, even if the measurement conditions change, the measurement can be performed without the change, so that the measurement can be performed in a wide measurement range, and the measurement can be performed in a wide flow rate range. Since no equipment such as a filter circuit for reducing noise is required, low-cost, high-precision flow measurement can be performed.

In the flow rate measuring device according to the second aspect, since the diameter of the reference potential measuring electrode is not more than half the width of the vortex generator, the Karman vortex street is hardly disturbed and generated by the reference potential measuring electrode. The vorticity component is small, and the flow rate can be measured with high accuracy.

In the flow rate measuring device according to the third aspect, since the diameter of the electrode for measuring electromotive force is not more than 1/2 of the width of the vortex generator, the flow in the vicinity is a laminar flow of Karman vortices generated. The flow rate can be measured with high accuracy without substantially disturbing the flow and without destroying the Karman vortex.

In the flow rate measuring device according to the fourth aspect, since the diameters of the electrodes for measuring the electromotive force are the same, the noise generated at the pair of electrodes for measuring the electromotive force can be canceled out by the detection circuit and reduced. Therefore, the noise level can be reduced and the flow rate can be measured with high accuracy.

In the flow rate measuring device according to the fifth aspect, since the length of the electrode for measuring the electromotive force is 2 to 2.5 times the width of the vortex generator, the center of the two generated Karman vortex rows is generated. The flow rate can be measured with high accuracy by measuring only the induced electromotive force change.

In the flow rate measuring apparatus according to the sixth aspect, since the lengths of the electrodes for measuring the electromotive force are the same, noise can be canceled by the detection circuit to reduce the noise level, and the flow rate can be measured with high accuracy. It becomes possible.

In the flow rate measuring device according to the seventh aspect, the interval between the electrodes for measuring the electromotive force is 2 to 2.5 times the width of the vortex generator. It is possible to reduce the noise level by reducing the Karman vortex that exists between the electrodes for measuring the electromotive force to less than one space between the vortices in the row. In addition, the frequency count can be easily performed with one Kalman vortex as one pulse, and the flow rate can be measured with high accuracy.

In the flow rate measuring device according to the eighth aspect, since the width of the magnetic field generator in the radial direction of the tube is 1.5 to 2 times the width of the vortex generator, the magnetic field generated in the measurement tube generates Karman vortices. Noise components due to vortices generated on the side wall of the measurement tube.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a flow measurement device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a conventional flow measurement device.

[Explanation of symbols]

 Reference Signs List 1 Measurement tube 2 Vortex generator 3 Karman vortex 4a, 4b Measurement electrode 5 Detection circuit 6a, 6b Reference potential measurement electrode 8 Magnetic field generator D Vortex generator width Dm Magnetic field generator width da, db, dc Measurement electrode diameter h Measurement Electrode tube length L Measurement electrode interval

Claims (8)

[Claims] 1. A vortex generator which is provided in a measurement tube through which a fluid having conductivity flows and generates a Karman vortex in the fluid; and a vortex generator provided downstream of the vortex generator, wherein the Karman vortex passes through a magnetic field. A pair of electromotive force measurement electrodes for detecting a change in induced electromotive force generated by a magnetic field change occurring when the magnetic field is generated, a magnetic field generator for generating the magnetic field, and electrically connected to the pair of electromotive force measurement electrodes It is a flow rate measuring device provided with a detection circuit for detecting the induced electromotive force and calculating the flow rate of the fluid, wherein the upstream and downstream sides of the pair of electrodes for electromotive force measurement, the detection circuit, One reference potential measurement electrode for measuring the potential difference between the upstream side and the downstream side which is electrically connected is provided, and the detection circuit calculates the flow rate by subtracting the potential difference from the induced electromotive force. Features Flow measurement device. 2. The flow rate measuring apparatus according to claim 1, wherein the diameter of the reference potential measuring electrode is not more than half the width of the vortex generator. 3. The method according to claim 1, wherein the diameter of the electromotive force measuring electrode is one of the vortex generator width.
The flow rate measuring device according to claim 1 or 2, wherein the flow rate is equal to or less than / 2. 4. The flow measuring device according to claim 1, wherein the electrodes for measuring the electromotive force have the same diameter. 5. The flow rate measuring device according to claim 1, wherein the length of the tube for measuring the electromotive force is 2 to 2.5 times the width of the vortex generator. 6. The flow rate measuring device according to claim 1, wherein the electrodes for measuring the electromotive force have the same length in the tube. 7. The flow rate measuring device according to claim 1, wherein the interval between the electrodes for measuring the electromotive force is 2 to 2.5 times the width of the vortex generator. 8. The flow rate measuring device according to claim 1, wherein the width of the magnetic field generator in the radial direction of the tube is 1.5 to 2 times the width of the vortex generator.