JP2002090191A - Flow measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low cost and highly accurate flow measuring device having a wide measuring range and easily applicable to a wide range of flow conditions. SOLUTION: The flow measuring device comprises a vortex generator 2, a pair of electromotive force measuring electrodes 4a and 4b provided at a downstream side of the vortex generator 2 for detecting the change of an induced electromotive force generated by the change of magnetic field when a Karman vortex 3 passes in the magnetic field, a magnetic field generating device 8 for generating the magnetic field, a detecting circuit 5 electrically connected with the pair of electromotive force measuring electrodes 4a and 4b for detecting the induced electromotive force to calculate a flow rate of fluid, and a reference potential measuring electrodes 6a and 6b each provided at both upstream and downstream sides of the pair of electromotive force measuring electrodes 4a and 4b and electrically connected with the detecting circuit 5 for allowing detection of the potential at each location, wherein uniform projections an recesses are provided on the inner wall of a measuring tube.

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 Conventionally, a Karman vortex flow rate measuring device is well known as a flow rate measuring device 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 the 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 changes 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. 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 electromotive force measuring 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 electromotive force measurement electrode 4b is provided on the downstream side of the vortex generator 2, but the electromotive force measurement electrode 4a
Is provided on the upstream side of the electromotive force measurement electrode 4b as a counter electrode of the electromotive force measurement electrode 4b, and at the same time, on the downstream side of the vortex generator 2. However, the electromotive force measurement electrode 4 shown in FIG.
a is integrated with the vortex generator 2.

Reference numeral 5 is electrically connected to the electromotive force measuring electrodes 4a and 4b, and detects the voltage between the electromotive force measuring electrodes 4a and 4b to calculate the flow rate of the fluid flowing through the measuring tube 1. A circuit 8 is a magnetic field generator provided around the measuring tube 1, and two magnets are sandwiched between the measuring tube 1 and the magnets, respectively.
The pole and the N pole are arranged facing each other. The magnetic field generator 8 is provided such 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 electromotive force measuring 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. This change in magnetic flux is caused by the electromotive force measurement electrodes 4a, 4
b to generate an induced electromotive force between
The number of voltage changes is proportional to the Karman vortex 3, and the flow rate can be calculated by counting the number of voltage changes detected by the detection circuit 5.

[0009]

However, in the above-mentioned conventional flow rate measuring device, the electromotive force generated between the electromotive force measuring electrodes 4a and 4b due to a change in the conductivity of the fluid or the degree of polarization of the electrodes. When a disturbance is applied to the flow or the magnetic field, noise is added to the magnetic field to be measured, and it is difficult to calculate an accurate flow rate. In particular, the electromotive force generated at the electromotive force measuring electrodes 4a and 4b is equal to 0. Since the voltage is as low as several mV to several mV, the input impedance must be set as high as several MΩ, and even a small amount of noise is picked up. Instead, it was difficult to accurately detect the flow rate. In addition, a fluid having a low conductivity originally has a low induced electromotive force and a low signal level, which makes it difficult to accurately detect a flow rate.

When the flow in the measurement pipe is laminar, the velocity distribution in the pipe is a parabola having the center of the pipe as a vertex. Even if the arrangement of the electrodes 4a and 4b is slightly displaced, an error occurs and it is difficult to detect the flow rate accurately. In addition, the Reynolds number Re = U which is a parameter representing the flow
L / υ (U: mean sectional velocity, L: representative length, υ: kinematic viscosity) decreases as the flow velocity decreases, and the flow transitions from turbulent flow to laminar flow. It changes depending on the state of the inner wall of the pipe, for example, the roughness and the shape of the inflow port. Therefore, it is desirable to perform measurement in a turbulent flow rather than a laminar flow.However, if the measurement flow rate changes from the flow rate range suitable for measurement, an unexpected error occurs, the frequency detection accuracy decreases, and the measurement accuracy decreases. descend.

In the laminar flow region, the generation of Karman vortices is unstable, and the proportionality between the frequency of occurrence of Karman vortices and the flow rate is not stable, so that the measurement accuracy is inherently low.

As described above, the roughness state of the inner wall of the pipe greatly affects the transition from laminar flow to turbulent flow and from turbulent flow to laminar flow, thereby changing the measurable range and the measurement accuracy itself. Greatly affected by However, in the conventional flow measuring device, the influence of the condition of the inner wall of the measuring pipe on the Karman vortex measurement is not recognized, but rather, a very smooth wall is used to reduce the flow path resistance. Was.
For this reason, there is a problem that the Reynolds number at which transition from laminar flow to turbulent flow becomes very high, the lower limit of the flow rate that can be measured with high accuracy becomes high, and the measurement range becomes very narrow.

Further, when a permanent magnet is used as the magnetic field generator, the magnet may change with time and the performance may deteriorate.
The polarization generated in the electrodes causes a reduction in the induced electromotive force, which lowers the signal level and makes accurate flow rate detection difficult.

As described above, the conventional flow rate measuring device has a narrow measuring range, and when the flow rate to be measured greatly changes, a measurement error is likely to occur. And the cost is high. In addition, there is a problem that disturbance is easily picked up.

Therefore, 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 having a wide measuring range, excellent noise resistance, and low cost. .

[0016]

In order to solve such a problem, a flow measuring device according to the present invention is characterized in that a uniform unevenness is provided on an inner wall surface of a measuring tube.

As a result, it is possible to provide a wide measuring range, excellent noise resistance, low cost, and high accuracy.

[0018]

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 detection circuit electrically connected to the power measurement electrode and detecting the induced electromotive force to calculate the flow rate of the fluid; and a detection circuit electrically connected to the upstream and downstream sides of the pair of electromotive force measurement electrodes. The flow measurement device is provided with one reference electrode capable of detecting the potential at each position, and the flow measurement device is characterized in that uniform unevenness is provided on the inner wall surface of the measurement tube, Karman vortex with uniform unevenness Can be generated in Joteki, good noise immunity for eliminating noise components in the reference electrode,
Measurement can be performed in a wide measurement range, low cost,
High accuracy can be achieved.

According to a second aspect of the present invention, the unevenness is provided on a separate member attached to the inner wall surface of the measuring tube, so that the flow rate can be measured. The measurement can be performed in a wide measurement range without complicating the pipe, and it is possible to manufacture a low-cost flow measuring device which is easy to manufacture.

According to a third aspect of the present invention, the separate member has conductivity and is provided so as to be in contact with a part of the reference potential measuring electrode. Since the flow rate measuring device is described, the water contact area of the measurement reference electrode can be increased, the noise resistance can be improved, and the flow rate can be measured with high accuracy.

According to a fourth aspect of the present invention, since the flow rate measuring device according to the first to third aspects is characterized in that the separate member is a coil spring, a member having uniform unevenness can be manufactured at low cost. Can be manufactured.

According to a fifth aspect of the present invention, at least a part of the coil spring has a pitch smaller than the diameter of the reference potential measuring electrode, and the reference potential measuring electrode is inserted between the pitches. The flow rate measuring device according to any one of claims 1 to 4, wherein the contact is made by the close contact force of the coil spring, so that the contact with the measurement reference electrode can be stably and firmly maintained. A flow measurement device can be stably provided.

(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 electrodes for measuring an electromotive force, 5 is a detection circuit which detects an induced electromotive force and calculates a flow rate, and has a differential amplifier circuit and can cancel a signal of a noise component. , 6a and 6b are reference potential measuring electrodes, 8
Is a magnetic field generator, and 9a and 9b are members having the same shape and uniform asperities as the conduit of the measuring tube 1. In this embodiment, a coil spring that can be provided at low cost is used.

Incidentally, the shape of the vortex generator 2 which is a key to generate the Karman vortex 3 is a triangular prism in the present embodiment. However, any shape may be used as long as the Karman vortex street can be generated stably. The vortex generator 2 is attached to the measuring tube 1 so that one side of the triangular prism is perpendicular to the flow.
In addition, in the case of the flow rate measuring device of the present embodiment, the flow rate detection range is 1 L / min to 10
In order to set L / min, a measuring tube 1 having an inner diameter of φ7 mm is employed.
The vortex generator 2 composed of a triangular prism having an isosceles triangular cross section of mm was the most effective.

Next, the electrodes 4a and 4b for measuring the electromotive force, which are the center of the electromotive force measurement, are provided on the downstream side of the vortex generator 2.
Are mounted parallel to each other so as to be orthogonal to both the axis and the direction of flow. Therefore,
When a streamline passing through the electromotive force measurement electrode 4a is drawn, the streamline always passes through the electromotive force measurement electrode 4b. N-poles and S-poles of the permanent magnets constituting the magnetic field generator 8 are provided so as to sandwich the electromotive force measuring electrodes 4a and 4b from both side surfaces of the measuring tube 1. Since the magnitude of the induced electromotive force is proportional to the magnetic flux density, it is necessary to increase the magnetic flux density of the magnetic field generator 8. In the present embodiment in which the flow rate detection range is 1 L / min to 10 L / min, the rare earth permanent magnet is used. A magnet having a width 1.5 times the width of the vortex generator 2 is adopted.

Next, the reference potential measuring electrodes 6a and 6b measure the respective potentials on the upstream and downstream sides of the electromotive force measuring electrodes 4a and 4b, and measure the potential difference between the upstream position and the downstream position. Things. Reference potential measuring electrodes 6a, 6b
Are arranged in parallel with the electromotive force measuring electrodes 4a and 4b. At this time, the stream lines drawn through the reference potential measuring electrodes 6a, 6b always correspond to 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.

As described above, in this embodiment, in order to set the flow rate detection range from 1 L / min to 10 L / min, the measuring tube 1 having an inner diameter of 7 mm is employed.
This is because the inner diameter of the measurement tube 1 has an important relationship with the flow rate in order to generate the Karman vortex 3 stably. If the inside diameter is too small, the influence of the boundary layer of the pipe wall affects the Karman vortex street, and if it is too large, the flow velocity becomes slow and the Karman vortex street does not occur. As described above, the Karman vortex 3 is generated stably, and the proportional relationship between the generation frequency of the Karman vortex 3 and the flow rate is established when the flow of the fluid to be measured is a turbulent flow. It can be expressed by Reynolds number. That is, the Reynolds number in an appropriate flow velocity range is in the range of about 3,000 to 100,000. However, the Reynolds number in this appropriate flow velocity region changes depending on the shape of the inner wall of the measurement tube 1. In particular, the vicinity of the critical Reynolds number of 2,320 to Reynolds number 3,000 is the transition region between laminar flow and turbulent flow. To enable measurement in that Reynolds number region, the inner wall surface upstream of the vortex generator 2 must be used. Must be uniformly roughened to generate turbulence stably.

For this reason, in the present embodiment, a coil spring 9a is provided in the measurement tube 1 on the upstream side of the vortex generator 2 and a coil spring 9b is also provided on the downstream side in order to provide uniform unevenness. Has been established. Since the coil springs 9a and 9b are wound at a predetermined pitch, they are the most excellent materials for providing uniform roughness, and are extremely easy to assemble and manufacture, and have excellent predictability of the effect. In this manner, the unevenness is not directly formed on the inner wall surface of the measuring tube 1 but the measuring tube 1
Are formed as coil springs 9a and 9b, which are separate members, without complicating the configuration of the pipeline, facilitating manufacture, and providing roughness to the inner wall surface of the measurement tube 1 at low cost.

The coil springs 9a and 9b are made of a conductive material, and are provided in contact with the reference potential measuring electrodes 6a and 6b. This contact improves the performance of the reference potential measuring electrodes 6a and 6b as the reference potential measuring electrodes. If at least a part of the pitch of the coil springs 9a, 9b is shorter than the diameter of the reference potential measuring electrodes 6a, 6b, the reference potential measuring electrodes 6a, 6b are inserted between the pitches, and Due to the adhesion, stable and strong contact can be achieved. Also, the coil springs 9a,
If a close contact spring is used for 9b, the water contact area can be increased even with the same spring length, which is efficient. Further, the reference potential measurement electrodes 6a and 6b, the coil spring 9
a, 9b so that the reference potential measuring electrode 6 is not deformed.
It is desirable that the materials and wire diameters of the coil springs 9a and 9b and the coil springs 9a and 9b be the same as those of the reference potential measuring electrodes 6a and 6b.

Next, the operation of the flow measuring device according to the present embodiment having such a configuration will be described. The fluid to be measured flowing through the measuring tube 1 is disturbed by the coil spring 9a and becomes turbulent. In this state, a Karman vortex street proportional to the flow velocity is stably generated by the vortex generator 2.
When the Karman vortex street crosses the magnetic flux passing through the portion surrounded by the electromotive force measuring electrodes 4a and 4b, a magnetic field change occurs, and the induced electromotive force is regularly generated in the electromotive force measuring electrodes 4a and 4b in a pulse shape. I do. Since the potential difference in the vicinity is measured by the reference potential measurement electrodes 6a and 6b with which the coil springs 9a and 9b are in contact, the measurement conditions (DC components other than Karman vortex and disturbance noise components) are reflected. The reference potential difference between the electromotive force measuring electrodes 4a and 4b can be measured. By canceling the reference potential difference signal and the electromotive force signal in the detection circuit 5, signals other than noise components and Karman vortex streets can be easily obtained. Can be deleted.

As described above, in this embodiment, since the coil springs 9a and 9b for forming uniform irregularities on the inner wall surface of the measuring tube are provided, the Karman vortex 3 is generated stably, thereby increasing the measuring range. It can be manufactured at low cost because it is spread, has excellent noise resistance, and is mounted with a separate member.

[0033]

As described above, the flow rate measuring device of the present invention is provided with unevenness of uniform roughness on the inner wall surface in the measuring pipe through which the fluid flows, and is provided with the reference electrode. A Karman vortex can be stably generated, and noise components are eliminated by the reference electrode, so that it has excellent noise resistance, can be measured in a wide measurement range, and can be made low-cost and highly accurate.

Further, since the unevenness is provided on a separate member mounted on the inner wall surface of the measuring tube, the flow measuring device of the present invention can be manufactured at low cost without complicating the measuring tube.

In the flow rate measuring apparatus of the present invention, the separate member has conductivity and is provided so as to be in contact with a part of the reference potential measuring electrode. This makes it possible to improve the noise resistance and measure the flow rate with high accuracy.

Further, in the flow rate measuring device of the present invention, since the separate member is a coil spring, a member having uniform unevenness can be manufactured at low cost.

Further, in the flow rate measuring device of the present invention, the pitch is formed to be smaller than the diameter of the reference potential measuring electrode in the coil spring, and the reference potential measuring electrode is inserted and brought into contact by the adhesion force of the coil spring. Since the contact with the reference electrode can be kept stable and strong, a high-accuracy flow measurement device can be stably realized.

[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]

 DESCRIPTION OF SYMBOLS 1 Measurement tube 2 Vortex generator 3 Karman vortex 4a, 4b Electromotive force measurement electrode 5 Detection circuit 6a, 6b Reference potential measurement electrode 8 Magnetic field generator 9a, 9b Coil spring

Continued on the front page (72) Inventor Kazushi Kasahara 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Person Takashi Ehara 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Yasumasa Fukami 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (5)

[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 A detection circuit that detects the induced electromotive force and calculates the flow rate of the fluid, and is electrically connected to the detection circuit on the upstream side and the downstream side of the pair of electrodes for measuring the electromotive force. What is claimed is: 1. A flow measuring device provided with one reference electrode capable of detecting a potential, wherein uniform unevenness is provided on an inner wall surface of the measuring tube. 2. The flow measuring device according to claim 1, wherein the unevenness is provided on a separate member mounted on an inner wall surface of the measuring tube. 3. The flow rate measuring device according to claim 1, wherein the separate member has conductivity and is provided so as to be in contact with a part of the reference potential measuring electrode. 4. The flow measuring device according to claim 1, wherein said separate member is a coil spring. 5. A pitch not exceeding the diameter of the reference potential measuring electrode is formed on at least a part of the coil spring.
5. The flow rate measuring device according to claim 1, wherein the reference potential measuring electrode is inserted between the pitches and brought into contact by the adhesion force of the coil spring.