JP2002071404A - Flow measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow measurement apparatus which can be manufactured at a low cost, has high measurement accuracy, and a wide measurement range dealing with wide fluid conditions. SOLUTION: A vortex producing body 2 for producing Karman's vortexes 3 is arranged in a vortex measurement pipe 1 in which fluid passes, and electrodes 4a, 4b having mutually the same shape are arranged in the downstream position from the vortex producing body 2 to measure induced electromotive forces. A magnetic field generating apparatus 6 composed of a magnet in which N-poles and S-poles are arranged facing each other so as to hold the vortex measurement pipe 1 is arranged on the outer periphery of the vortex measurement pipe 1. The magnetic field generating apparatus 6 is arranged such that the direction of the magnetic field is perpendicular to the vortex producing body 2 and the electrodes 4a, 4b for measuring induced electromotive forces. A circuit 5 for detecting the flow rate of the fluid is electrically connected to the electrodes 4a, 4b. The detection circuit 5 is composed of a differential amplifier, a positive-phase amplifier, or the like, in which a reference potential is constituted of a high impedance circuit.

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 fluid such as gas or liquid flowing in a pipe.

[0002]

2. Description of the Related Art Conventionally, a flow rate measuring device for measuring a flow rate of a fluid flowing in a pipe detects a Karman vortex generated by the flowing fluid, and calculates a flow rate from the Karman vortex. The one described in JP-A-60-40914 is generally used. In this Karman vortex flow rate measuring apparatus, ultrasonic waves, vibrations, and the like are used as means for detecting the generated Karman vortices.

[0003] However, a detecting device used for detecting changes in ultrasonic waves and vibrations is complicated and expensive.
Or it has a problem that it becomes large.
In order to solve this problem, as a means for detecting the occurrence of Karman vortex, a method using a magnetic field as described in Japanese Patent Application Laid-Open No. 5-172598 has been proposed.

Next, such a flow measuring device will be described. FIG. 4 is a sectional view of a conventional flow measuring device. A vortex generator 2 for generating Karman vortices 3 is provided in a vortex measurement tube 1 through which a fluid passes. In the vortex measuring tube 1 downstream of the vortex generator 2 in the fluid passage direction, an electrode 4b is provided.
Is installed. The vortex generator 2 also functions as the electrode 4a as a counter electrode to the electrode 4b. At a predetermined position on the outer periphery of the vortex measurement tube 1, a magnetic field generator 6 including a magnet having an S pole and an N pole opposed to each other so as to sandwich the vortex measurement tube 1 is provided. The magnetic field generator 6 is installed so that the magnetic field direction of the magnetic field generator 6 is perpendicular to the vortex generator 2 and the electrodes 4a and 4b.

A detection circuit 5 for detecting the flow rate of the fluid is electrically connected to the electrodes 4a and 4b integrated with the vortex generator 2. According to such a flow rate measuring device, the flow rate can be calculated by the detection circuit 5 counting the frequency due to the change in the flow velocity of the fluid that crosses between the vortex generator 2 and the electrodes 4a and 4b with the Karman vortex 3. become.

[0006]

However, in the conventional flow measuring device as described above, in order to detect the induced electromotive force accompanying the occurrence of Karman vortex, changes in the conductivity of the fluid and the electromotive force at each flow velocity are detected. Changes In addition, many influences due to disturbance noise occur, and it is difficult to accurately detect a flow rate in response to a change in measurement conditions. Further, when the flow rate changes from the flow rate optimal for measurement, the accuracy of the Karman vortex generation with respect to the flow rate decreases, and noise increases with the increase in the flow rate, so that the frequency detection accuracy decreases and the measurement accuracy decreases. When performing detection using a permanent magnet in the magnetic field generator, the signal level is reduced due to a decrease in performance due to the aging of the magnet and a decrease in induced electromotive force due to polarization generated in the electrodes, making accurate flow rate detection difficult. . Further, in the case of a fluid having a low conductivity, the signal level is reduced due to a decrease in the induced electromotive force, which makes it difficult to accurately detect a flow rate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a flow rate measuring apparatus which can obtain high measurement accuracy at low cost and can detect a flow rate in a wide range corresponding to a wide range of fluid conditions.

[0008]

In order to solve this problem, a flow measuring device according to the present invention is provided in a vortex measuring tube through which a fluid having conductivity flows, and a Karman vortex is provided on the downstream side of the fluid. A pair of electrodes installed on the outer periphery of the tube on the downstream side of the vortex generator in the fluid passage direction and detecting induced electromotive force due to a magnetic field change when the fluid passes through the magnetic field; A flow measurement device electrically connected to an electrode and including a detection circuit that calculates a flow rate of the fluid flowing through the pipe from an induced electromotive force generated in the electrode, wherein the pair of electrodes for measuring the induced electromotive force is provided. In the same shape and at the same position.

As a result, it is possible to realize a flow rate measuring device which can obtain high measurement accuracy at low cost and can detect a flow rate in a wide flow rate range in accordance with a wide range of fluid conditions.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 is a vortex generator which is installed in a vortex measurement tube through which a conductive fluid flows, and generates a Karman vortex toward the downstream side of the fluid;
A pair of electrodes installed on the outer periphery of the pipe on the downstream side of the vortex generator in the fluid passage direction and detecting induced electromotive force due to a magnetic field change when the fluid passes through the magnetic field, and electrically connected to the electrodes, A flow measuring device provided with a detection circuit for calculating a flow rate of a fluid flowing in a pipe from generated induced electromotive force, wherein a pair of electrodes for measuring induced electromotive force are arranged at the same position in the same shape. is there.

As a result, the flow rate can be measured with high accuracy at low cost. Further, the flow rate can be detected in a wide flow rate range in accordance with a wide range of fluid conditions.

According to a second aspect of the present invention, in the first aspect of the invention, the reference potential of the circuit for amplifying the electromotive force generated in the pair of electrodes for measuring the induced electromotive force is constituted by a high impedance circuit. The stable detection is performed without attenuating the weak electromotive force generated in (1).

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a flow rate measuring device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a dimensional ratio of each part of the flow rate measuring device according to an embodiment of the present invention.

As shown in FIG. 1 and FIG.
A vortex generator 2 which has a 7 mm inner diameter and in which a fluid such as a liquid or gas having conductivity flows and which is located in the fluid and generates a Karman vortex 3 in the fluid is installed. ing. The vortex generator 2 has a width of 2 mm, for example.
It has a triangular prism shape with a height of 3 mm. However, the vortex generator may have any shape as long as the Karman vortex street 3 can be generated.

On the downstream side of the vortex generator 2 in the fluid passage direction, a pair of electrodes 4a and 4b for measuring induced electromotive force are arranged having the same shape. Further, a magnetic field generator 6 composed of a magnet in which an S pole and an N pole are opposed to each other is provided on the outer periphery of the vortex measurement tube 1 so as to sandwich the vortex measurement tube 1 therebetween. Electrode 4
The diameters da and db of a and 4b are 以下 or less of the vortex generator width D, and the tube length h of the electrodes 4a and 4b is 2 to 2 of the vortex generator width D.
The distance L between the electrodes 4a and 4b is 2.5 times the width D of the vortex generator.
The width Dm of the magnetic field generator 6 is 1.5 to 2 times that of the vortex generator 2. The electrodes 4a and 4b are
It is arranged at a position perpendicular to the magnetic field generated by the magnetic field generator 6. Thereby, a regular induced electromotive force is generated in the electrodes 4a and 4b by the change in the magnetic field when the Karman vortex 3 of the fluid generated by the vortex generator 2 crosses. Here, since the electrodes 4a and 4b are arranged in the same shape and at the same position, the induced electromotive force due to the magnetic field change when the Karman vortex of the fluid passes can be reliably detected.

Next, the operation of the flow measuring device having such a configuration will be described. The fluid flowing in the vortex measurement tube 1 passes through the magnetic field generated by the magnetic field generator 6.
At this time, the Karman vortex generated by the vortex generator 2 has a proportional relationship with the flow velocity, as is known from the study of Strouhal. Therefore, the flow rate of the fluid flowing through the vortex measurement tube 1 can be calculated by counting the periodically changing Karman vortex frequency proportional to the flow rate.

In the case of the flow measuring device according to the present embodiment, the magnetic field generating device 6 is provided with a magnetic field generating device 6 for increasing the magnetic flux density in the vortex measuring tube in order to set the flow detecting range to 1 L / min to 10 L / min. And a rare-earth permanent magnet having a width 1.5 times the width of the vortex generator.

FIG. 3 is a block diagram of a detection circuit according to one embodiment of the present invention. In FIG. 3, the induced electromotive force generated in the induced electromotive force measurement electrodes 4a and 4b is amplified to a predetermined signal level by removing a common-mode signal by a differential amplifier constituted by operational amplifiers 7a and 7b. . Further, the signal is amplified to a signal level that can be detected by the comparator 8 by the positive-phase amplifier constituted by the operational amplifier 7c. The induced electromotive force generated each time the Karman vortex crosses the electrodes 4a and 4b for measuring the induced electromotive force is amplified by the differential amplifier and the positive-phase amplifier, and then shaped by the comparator 8 to be output. A rectangular wave that changes periodically in proportion to the flow rate can be obtained. 9 is a bandpass filter,
10 is a resistor, 11 is a capacitor.

By the way, the reference potential of the differential amplifier and the positive-phase amplifier is given by converting a potential obtained by dividing the power supply voltage Vcc by a voltage follower using an operational amplifier 7c into a high impedance. Therefore, electrode 4
The weak induced electromotive force generated in a and 4b can also be reliably detected.

[0020]

As described above, according to the present invention, it is possible to easily realize a flow rate measuring apparatus which has a high measuring accuracy at a low cost and has a wide measuring range corresponding to a wide range of fluid conditions.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a dimensional ratio of each part of the flow measuring device according to the embodiment of the present invention.

FIG. 3 is a block diagram of a detection circuit according to one embodiment of the present invention;

FIG. 4 is a cross-sectional view of a conventional flow measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vortex measuring tube 2 Vortex generator 3 Karman vortex 4a, 4b Electrode for measuring induced electromotive force 5 Detection circuit 6 Magnetic field generator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference)

Claims (2)

[Claims] 1. A vortex generator which is installed in a pipe through which a conductive fluid flows, and generates a Karman vortex toward the downstream of the fluid, and the pipe at a downstream side of the vortex generator in a fluid passage direction. A pair of electrodes installed on the outer periphery of the tube and detecting an induced electromotive force due to a change in the magnetic field when the fluid passes through the magnetic field, and electrically connected to the electrodes; A flow measurement device comprising a detection circuit for calculating the flow rate of the fluid flowing through the
A flow rate measuring device, wherein the pair of electrodes for measuring the induced electromotive force are arranged at the same position in the same shape. 2. The flow rate measuring device according to claim 1, wherein a reference potential of a circuit for amplifying the electromotive force generated in the pair of electrodes for measuring an induced electromotive force is constituted by a high impedance circuit.