JP3736139B2 - Flow measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow rate measuring device that measures the flow rate of a gas or liquid (fluid) flowing in a pipe.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 60-40914 called a Karman vortex flow measuring device that detects the generation of Karman vortices by flowing fluid and calculates the flow rate from the Karman vortices. The ones described in are 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 vortex.
[0003]
However, a detection device used to detect changes in ultrasonic waves, vibrations, and the like has a problem that it is complicated, expensive, and large.
[0004]
In order to solve this problem, it has been proposed to use a magnetic field represented by Japanese Patent Laid-Open No. 5-172598 as means for detecting the generation of Karman vortices.
[0005]
Here, such a flow rate measuring apparatus will be described. FIG. 7 is a cross-sectional view showing the configuration of a conventional flow rate measuring device, and FIG. 8 is a cross-sectional view showing the conventional flow rate measuring device from a direction different from FIG.
[0006]
A vortex generator 6 for generating Karman vortices is installed in the pipe 1 through which the fluid passes. An electrode 4 is installed in the tube 1 on the downstream side in the fluid passage direction from the vortex generator 6. The vortex generator 6 also serves as a counter electrode for the electrode 4.
[0007]
At a predetermined position on the outer periphery of the tube 1, a magnetic field generating device 3 is provided that is composed of a magnet in which the S pole and the N pole are arranged to face each other so as to sandwich the tube 1. The magnetic field generator 3 is installed such that the magnetic field direction of the magnetic field generator 3 is perpendicular to the vortex generator 6 and the electrode 4.
[0008]
The vortex generator 6 and the electrode 4 are electrically connected to a calculation unit 5 that calculates the flow rate of the fluid.
[0009]
According to such a flow rate measuring device, an induced electromotive force is generated due to a magnetic field change caused by a change in the flow velocity of the fluid crossing between the vortex generator 6 and the electrode 4 along with the Karman vortex. If the frequency is counted by the calculation unit 5, the flow rate can be calculated.
[0010]
[Problems to be solved by the invention]
However, in the conventional flow rate measuring apparatus as described above, in order to detect the induced electromotive force accompanying the Karman vortex generation, a lot of noise is generated due to the disturbance of the fluid flow and the disturbance due to the vortex generation state. It becomes difficult to detect the flow rate.
[0011]
Here, it is conceivable to introduce a circuit for taking measures against noise. However, this complicates the structure of the apparatus and increases the cost.
[0012]
Furthermore, if the flow rate changes from the optimal flow rate for measurement, the accuracy of Karman vortex generation with respect to the flow rate decreases, or noise increases with the increase in flow rate, so the frequency detection accuracy decreases and the measurement range becomes narrow.
[0013]
When detection is performed using a direct current magnet in the magnetic field generator, the level changes due to performance degradation due to aging of the magnet or induced electromotive force due to polarization generated in the electrodes, making accurate flow rate detection difficult.
[0014]
Accordingly, an object of the present invention is to provide a flow rate measuring device having high measurement accuracy.
[0015]
Another object of the present invention is to provide a low-cost and highly accurate flow rate measuring device.
[0016]
Furthermore, an object of this invention is to provide the flow measuring device which has a wide measurement range.
[0017]
[Means for Solving the Problems]
In order to solve this problem, a flow measuring device according to the present invention includes a vortex generator that is installed in a pipe through which a conductive fluid flows, and that generates a Karman vortex toward the downstream side of the fluid, and a vortex generator Is installed on the outer circumference of the pipe on the downstream side in the fluid passage direction, and the magnetic field generated by the generated magnetic field traverses the inside of the pipe and the position perpendicularly intersecting the magnetic field generated by the magnetic field generating apparatus, and the fluid passes through the magnetic field. A pair of electrodes that detect an induced electromotive force due to a change in magnetic field, and a calculation unit that is electrically connected to the electrode and calculates a flow rate of a fluid flowing in the pipe from the induced electromotive force generated in the electrode. The first flow rate value is obtained from the induced electromotive force of the direct current component that changes in proportion to the flow rate, and the second flow rate value is obtained from the frequency of the alternating current component generated in a pulsed manner by the Karman vortex. Range of AC component detection When the outside as the measurement flow rate value of the first flow rate value, when the first flow rate value is within a range of AC component detection is obtained by a configuration in which the measurement flow rate value and the second flow rate value.
[0018]
This makes it possible to measure the flow rate with high accuracy. In addition, since a circuit for noise suppression is unnecessary, it is possible to measure the flow rate with high accuracy at low cost. Furthermore, since it is possible to detect the flow rate exceeding the range of the Karman vortex generation flow rate value, it is possible to measure the flow rate over a wide range.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, a vortex generator that is installed in a pipe through which a fluid having conductivity flows and generates a Karman vortex toward the downstream side of the fluid, and a fluid passing direction of the vortex generator A magnetic field generator installed on the outer periphery of the pipe on the downstream side, where the generated magnetic field crosses the inside of the pipe, and a magnetic field change when the fluid passes through the magnetic field installed at a position perpendicular to the magnetic field generated by the magnetic field generator. A pair of electrodes for detecting the induced electromotive force due to the liquid crystal, and a calculation unit that is electrically connected to the electrode and calculates the flow rate of the fluid flowing in the pipe from the induced electromotive force generated at the electrode, the calculation unit being proportional to the flow rate The first flow rate value is obtained from the induced electromotive force of the direct current component that changes and the second flow rate value is obtained from the frequency of the alternating current component generated in a pulsed manner by Karman vortex. First when out of range This is a flow rate measurement device that uses the flow rate value as the measured flow rate value, and when the first flow rate value is within the range of AC component detection, the second flow rate value as the measured flow rate value, making it possible to measure the flow rate with high accuracy. It has the effect of becoming. In addition, since a circuit for countermeasures against noise is not required, the flow rate can be measured with high accuracy at low cost. Furthermore, since it is possible to detect the flow rate exceeding the range of the generated flow value of the Karman vortex, the flow rate can be measured over a wide range.
[0020]
The invention according to claim 2 of the present invention is the correction value calculated from the second flow rate value when the first flow rate value is within the range of AC component detection. This is a flow measurement device that uses the first flow rate value as the measurement flow rate value, calculates the flow rate of the fluid from the AC component, and responds to changes in magnetic flux density and changes in electrode resistance that change the DC component of the induced electromotive force over time. Since the correction can be performed, the flow rate can be measured with higher accuracy.
[0021]
The invention according to claim 3 of the present invention is the flow measurement device according to claim 1 or 2, wherein the calculation unit determines that the device is abnormal when the correction value exceeds a predetermined value. It has the effect that the reliability can be improved.
[0022]
According to a fourth aspect of the present invention, in the first, second, or third aspect of the invention, the vortex generator is a flow rate measuring device installed perpendicular to the magnetic field direction of the magnetic field generator. The Karman vortex train generated from the body moves downstream while occupying the direction of the magnetic field, so the change in the Karman vortex velocity with respect to the fluid flow velocity is accurately detected as a change in the frequency of the pulsed AC component. It has the effect that it becomes possible to do.
[0023]
According to a fifth aspect of the present invention, in the first, second, third, or fourth aspect of the invention, the magnetic field generator is a flow rate measuring device made of a permanent magnet, and an electric power generator for excitation is not required. As a result, the apparatus can be reduced in size, saved in power, and reduced in cost.
[0024]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.
[0025]
1 is a cross-sectional view showing a configuration of a flow rate measuring device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing a configuration of the flow rate measuring device according to an embodiment of the present invention from a direction different from FIG. FIG. 3 is a graph showing the relationship between the flow rate and the induced electromotive force, FIG. 4 is a graph showing the induced electromotive force that changes in a pulse shape with the generation of Karman vortex, and FIG. 5 is a calculation unit of the flow rate measuring device of FIGS. FIG. 6 is a flowchart showing the flow of flow rate calculation processing in the calculation unit of the flow rate measuring device of FIGS. 1 and 2.
[0026]
As shown in FIG. 1 and FIG. 2, for example, the inside of a tube 1 having an inner diameter of φ10 mm and through which conductive liquid or gas (collectively referred to as “fluid” in this specification) flows, A vortex generator 2 that is located in the fluid and generates Karman vortex streets in the fluid is installed. The vortex generator 2 has, for example, an isosceles triangular prism shape with a width of 2.2 mm and a height of 3 mm. However, the vortex generator may have any shape as long as it can generate a Karman vortex street.
[0027]
A pair of electrodes 4 are disposed opposite to the vortex generator 2 on the downstream side in the fluid passage direction. Further, on the outer periphery of the tube 1, there is provided a magnetic field generator 3 composed of a magnet in which the S pole and the N pole are arranged to face each other with the tube 1 interposed therebetween. The electrode 4 is disposed at a position perpendicular to the magnetic field generated by the magnetic field generator 3. Thus, an induced electromotive force is generated in the electrode 4 due to a change in the magnetic field when the Karman vortex of the fluid generated by the vortex generator 2 crosses the magnetic field. The vortex generator 2 is installed perpendicular to the magnetic field direction of the magnetic field generator 3.
[0028]
A calculation unit 5 that calculates the flow rate of the fluid flowing in the tube 1 from the magnitude of the induced electromotive force obtained in this way is electrically connected to both electrodes of the electrode 4.
[0029]
Next, the operation of the flow rate measuring apparatus having such a configuration will be described.
The fluid flowing in the tube 1 passes through the magnetic field generated by the magnetic field generator 3. At this time, an induced electromotive force proportional to the flow rate is generated between the electrodes 4 according to Faraday's law as shown in FIG.
[0030]
Therefore, if this induced electromotive force is detected, the flow rate of the fluid flowing in the pipe 1 can be calculated.
[0031]
In addition, Karman vortices are periodically generated by the vortex generator 2 in the fluid flowing in the tube 1. The vortex generation period is proportional to the flow velocity, as is known from the study of Strouhal. Further, since the rotation speed of the generated Karman vortex street is different from the velocity of the fluid, when the Karman vortex street passes through the magnetic field generator 3, as shown in FIG. 4, the change in velocity is pulsed as the change in induced electromotive force. Appear in the shape.
[0032]
Therefore, if the frequency that changes in a pulse shape in proportion to the flow rate is counted, the flow rate of the fluid flowing in the pipe 1 can be calculated.
[0033]
As described above, the flow rate of the fluid flowing in the tube 1 can be calculated from the induced electromotive force of the DC component that changes in proportion to the flow rate and the frequency of the AC component that is generated in a pulsed manner.
[0034]
In the case of the flow rate measuring device of the present embodiment, in order to set the flow rate detection range to 1 L / min to 7 L / min, the magnetic field generator 3 has a rare earth permanent magnet in order to increase the magnetic flux density at the center of the pipe. A magnet is used as a magnet having a width of ½ of the tube diameter (5 mm × 5 mm × 3 mm, magnetic flux density 1 (T)). In addition, an induction electromotive force of about 100 mV is obtained between the electrodes 4.
[0035]
However, since the magnitude of the induced electromotive force to be obtained needs to be set according to the magnitude of noise depending on the installation state and the circuit configuration, it is preferable to appropriately set the magnetic flux density of the magnet used in the magnetic field generator 3 accordingly.
[0036]
Next, signal processing of the induced electromotive force obtained will be described with reference to FIGS.
[0037]
As shown in FIG. 5, the induced electromotive force obtained is processed by being divided into a DC component proportional to the flow rate and a pulsed AC component accompanying Karman vortex generation. The DC component of the induced electromotive force is smoothed and A / D converted, and then calculated as a flow value according to a predetermined calculation formula. In the case of the present embodiment, from the voltage value E (mV) obtained from the direct current component, the proportional relationship of the flow rate Q (L / min) is, according to Faraday's law, the magnetic flux density in the pipe is B, the average speed is v, If the tube diameter is D,
E = B × v × D
Therefore, when converted to an equation for determining the flow rate Q,
Q = E × ((D / 2) ² × π) / (B × D)
Then, the tube diameter D = 10 (mm) and the magnetic flux density B = 1 (T) in this condition are substituted, and further, the flow rate Q (L / min) = speed v (m / s) × tube cross-sectional area A (m ² ) Therefore, the desired flow rate value (first flow rate value) Q1 is
Q1 = E × ((10 × 10 ⁻³ / 2) ² × π)
/ 1/10 × 10 ⁻³ × ^{60/10 −3}
= 470 × E
Can be obtained as
[0038]
Further, in the present invention, in order to correct a change such as demagnetization of the magnetic flux density B that changes with time, a correction value C for correcting the flow rate value is multiplied by comparison with the flow rate calculation value Q2 of the AC component, It is calculated by the following formula.
[0039]
Q1 = 470 × E × C
The correction value C is initially given C = 1 and repeatedly measured as described below, whereby a converged value can be obtained for each measurement condition.
[0040]
Further, the AC component of the induced electromotive force is calculated as a flow rate value according to a predetermined calculation formula after the frequency f is counted by the comparator through the amplifying unit and then averaged by the number of counts.
[0041]
In the case of the present embodiment, the proportional relationship between the frequency of Karman vortex generation and the flow velocity is generally the frequency f (Hz), the flow velocity v (m / s), the diameter d (m) of the vortex generator, and the proportionality constant St. (Strawhal number)
f = St × v / d
As required.
[0042]
Here, the Reynolds number Re is
Re = v · d / ν
(Ν is the kinematic viscosity coefficient of water, v is the velocity, d is the diameter of the vortex generator)
It is.
[0043]
Since the flow rate of water is measured in this embodiment, the kinematic viscosity coefficient ν is
ν = 1.004 × 10 ⁻⁶ m ² / s (20 ° C., 1 atm)
The diameter d of the vortex generator is 2.2 mm, and the flow rate Q is 1 to 7 (L / min).
[0044]
When obtaining the Reynolds number Re from the relationship of the flow rate Q (L / min) = velocity v (m / s) × Kandan area A (m ^2),
Re = v · d / ν = 2.3 × 10 ^{2 to} 3.4 × 10 ³
It becomes.
[0045]
By the way, in the range of this Reynolds number, the Strouhal number can be given as St = 0.2.
[0046]
St = 0.2
Therefore, when converted into an equation for obtaining the flow rate Q,
Q = f × ((D / 2) ² × π) × d / St
When this condition is substituted, the flow rate value (second flow rate value) Q2 (L / min) is
Q2 = 0.05 × f
It can obtain | require by the type | formula of.
[0047]
In the above embodiment, Q = 1 to 7 (L / min) and ν = 1.004 × 10 ⁻⁶ m ² / s of water have been described, but Re = 10 ² to 10 ⁵ . Since the Strouhal number St = 0.2 in the range, the above-described calculation formula can be used in common, and a measurement of approximately Q = 500 (L / min) is possible if the liquid is equivalent to water.
[0048]
Even outside the range of the Reynolds number, if the Strouhal number St is selected according to the flow rate Q and the kinematic viscosity coefficient ν, a wider range of measurement can be made possible.
[0049]
By the way, in the flow rate measuring apparatus configured as described above, as shown in the flowchart of FIG. 6, the obtained flow rate values Q1 and Q2 are processed in the relationship between the upper limit set value and the lower limit set value for AC component detection.
[0050]
Here, as shown in the relationship between the vortex generation frequency and the flow rate shown in FIG. 9, the relationship between the vortex generation frequency and the flow rate is linear in the large flow rate portion and the small flow rate portion in the flow rate range to be measured. Sex is reduced.
[0051]
This is because, as shown in the relationship between the S / N of the electromotive force signal and the flow rate in FIG. 10, the S / N of the obtained electromotive force signal decreases in the large flow rate portion and the small flow rate portion of the flow rate range to be measured. It is.
[0052]
This decrease in S / N in the large flow rate portion causes turbulent flow in the fluid due to the increase in flow rate, preventing vortex generation and simultaneously increasing noise components and lowering the S / N level.
[0053]
Further, the S / N decrease in the small flow rate portion is caused by the decrease in the signal level due to the decrease in the vortex velocity due to the decrease in the flow rate, so that the S / N level also decreases.
[0054]
Therefore, in this embodiment, the S / N value level of the induced electromotive force necessary on the circuit that can ensure the flow rate detection accuracy is set to 10 dB, the lower limit value of the small flow rate portion is set to 2 L / min, and the large flow rate portion The upper limit is set to 7 L / min.
[0055]
However, the set flow rate value is desirably set appropriately because the signal level to be input and processed varies greatly depending on changes in circuit conditions and the like.
[0056]
As shown in FIG. 6, first, two flow rate values Q1 and Q2 are calculated (step S1), and it is determined whether or not the flow rate value Q1 is greater than or equal to a lower limit set value for AC component detection (step S2).
[0057]
When the flow rate value Q1 falls below the lower limit set value, the flow rate value Q1 is immediately selected (step S3), and that value is set as the measured flow rate value. If the flow rate value Q1 is equal to or higher than the lower limit set value, it is determined whether the flow rate value Q1 is equal to or lower than the upper limit set value for AC component detection (step S4).
[0058]
When the flow rate value Q1 exceeds the upper limit set value, the flow rate value Q1 is selected (step S3), and that value is set as the measured flow rate value. Further, when the flow rate value Q1 is equal to or lower than the upper limit set value, that is, when the flow rate value Q1 is within the preset flow rate range, the flow rate value Q2 is selected (step S5), and that value is the measured flow rate value. It is said.
[0059]
Here, when the flow rate value Q1 is within a preset flow rate range, the flow rate value Q2 can be set as the measured flow rate value. However, in the present embodiment, if the flow rate value Q2 is selected, For example, the correction value C is calculated from the induced electromotive force E of the DC component (step S6). Here, the correction value C is calculated by the following equation.
[0060]
C = Q2 / (0.1 × E)
Then, it is determined whether or not the obtained correction value C is equal to or less than a preset value (here, 0.5) in order to detect a decrease in induced electromotive force due to an increase in electrode resistance or a decrease in magnetic field strength. (Step S7).
[0061]
When the correction value C exceeds 0.5, it is detected as an equipment abnormality (for example, abnormality of the electrode 4 due to deterioration with time, abnormality of magnetic force drop of the magnetic field generator 3) (step S8), and the correction value C is If it is 0.5 or less, the correction value C is stored (step S9), and the flow rate value Q1 is selected (step S3).
[0062]
In this embodiment, the device abnormality is determined to be 0.5 or more of the value of 1/2 reduction of the initial condition from the detection level of the electromotive force signal of the circuit used, but the S / N ratio of the detection circuit This value is set as appropriate for reasons such as amplification and amplification.
[0063]
Thus, according to the flow rate measuring apparatus of the present embodiment, the flow rate value Q1 is derived from the induced electromotive force of the direct current component that changes in proportion to the flow rate, and the flow rate value is derived from the frequency of the alternating current component generated in a pulsed manner by the Karman vortex. Q2 is obtained, and when the flow rate value Q1 is outside the range of AC component detection, the flow rate value Q1 is set as the measured flow rate value. When the flow rate value Q1 is within the range, the flow rate value Q1 is set as the measured flow rate value from the correction value C calculated from the flow rate value Q2. Therefore, the flow rate can be measured with high accuracy.
[0064]
In addition, since a circuit for noise suppression is unnecessary, it is possible to measure the flow rate with high accuracy at low cost.
[0065]
Furthermore, since it is possible to detect the flow rate exceeding the range of the Karman vortex generation flow rate value, it is possible to measure the flow rate over a wide range.
[0066]
When the flow rate value Q1 is within the range of AC component detection, if the flow rate value Q1 is set as the measured flow rate value from the correction value C calculated from the flow rate value Q2, the flow rate of the fluid is calculated from the AC component, and the induction Correction for changes in magnetic flux density and changes in electrode resistance that change the DC component of power over time can be performed, and flow measurement can be performed with higher accuracy.
[0067]
When the correction value C obtained from the flow rate value Q2 and the induced electromotive force E of the DC component exceeds a predetermined value, it is determined that the device is abnormal, so that the reliability of the apparatus can be improved.
[0068]
Since the vortex generator 2 is installed perpendicularly to the magnetic field direction of the magnetic field generator 3, the Karman vortex street generated from the vortex generator 2 advances toward the downstream side while occupying the direction of the magnetic field. It becomes possible to accurately detect the change in the traveling speed of the Karman vortex with respect to the flow velocity as the change in the frequency of the pulsed AC component.
[0069]
Since a permanent magnet is used for the magnetic field generator 3, a power generator for exciting the object is not necessary, and the apparatus can be reduced in size, power consumption, and cost.
[0070]
【The invention's effect】
As described above, according to the present invention, the flow rate of the fluid having conductivity is calculated from both the DC component of the induced electromotive force that is proportional to the flow rate and the AC component of the induced electromotive force that is generated in a pulsed manner when the Karman vortex is generated. Therefore, it is possible to obtain an effective effect that the flow rate can be measured with high accuracy.
[0071]
In addition, according to the present invention, since a circuit for noise suppression is not necessary, it is possible to obtain an effective effect that the flow rate can be measured with high accuracy at low cost.
[0072]
Furthermore, according to the present invention, it is possible to detect the flow rate exceeding the range of the generated flow value of the Karman vortex, so that it is possible to obtain an effective effect that the flow rate can be measured over a wide range.
[0073]
When the first flow rate value is within the range of AC component detection, if the first flow rate value is the measured flow rate value from the correction value calculated from the second flow rate value, the fluid flow rate is calculated from the AC component, Since it is possible to correct for changes in magnetic flux density and changes in electrode resistance that change the DC component of the induced electromotive force over time, it is possible to obtain an effective effect of enabling flow measurement with higher accuracy. .
[0074]
If the correction value exceeds a predetermined value, it is possible to improve the reliability of the apparatus if it is determined that the device is abnormal.
[0075]
If the vortex generator is installed perpendicularly to the magnetic field direction of the magnetic field generator, the Karman vortex train generated from the vortex generator will travel downstream while occupying the direction of the magnetic field. It is possible to obtain an effective effect that it is possible to accurately detect the change in the traveling speed of the current as the change in the frequency of the pulsed AC component.
[0076]
If the magnetic field generator is composed of permanent magnets, an exciting power generator is not required, so that it is possible to obtain an effective effect that the device can be reduced in size, reduced in power consumption, and reduced in cost.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a flow rate measuring apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a configuration of a flow rate measuring apparatus according to an embodiment of the present invention from a direction different from FIG. 3 is a graph showing the relationship between the flow rate and the induced electromotive force. FIG. 4 is a graph showing the induced electromotive force that changes in a pulse shape as Karman vortices are generated. FIG. 5 is an operation of the flow rate measuring device shown in FIGS. FIG. 6 is a flow chart showing the flow of flow rate calculation processing in the calculation unit of the flow rate measuring device of FIGS. 1 and 2. FIG. 7 is a cross-sectional view showing the configuration of a conventional flow rate measuring device. 8 is a cross-sectional view showing a conventional flow rate measuring device from a direction different from FIG. 7. FIG. 9 is a graph showing the relationship between vortex generation frequency and flow rate. FIG. 10 is a relationship between S / N of electromotive force signal and flow rate. Graph [Explanation of symbols]
1 Tube 2 Vortex Generator 3 Magnetic Field Generator 4 Electrode 5 Arithmetic Unit

Claims (5)

A vortex generator installed in a pipe through which a fluid having electrical conductivity flows, and generating a Karman vortex toward the downstream side with respect to the fluid;
A magnetic field generator installed on the outer periphery of the tube on the downstream side in the fluid passage direction of the vortex generator, and a generated magnetic field crossing the tube;
A pair of electrodes that are installed at positions perpendicularly intersecting with the magnetic field generated by the magnetic field generator and detect an induced electromotive force due to a magnetic field change when the fluid passes through the magnetic field;
A calculation unit that is electrically connected to the electrode and calculates a flow rate of the fluid flowing in the pipe from an induced electromotive force generated in the electrode;
The calculation unit obtains a first flow rate value from an induced electromotive force of a direct current component that changes in proportion to the flow rate, and obtains a second flow rate value from a frequency of an alternating current component generated in a pulsed manner by Karman vortex. When the flow rate value is outside the range of AC component detection, the first flow rate value is set as the measured flow rate value. When the first flow rate value is within the range of AC component detection, the second flow rate value is set as the measured flow rate value. A characteristic flow rate measuring device. The calculation unit, when the first flow rate value is within an AC component detection range, uses the first flow rate value as a measured flow rate value based on a correction value calculated from the second flow rate value. 1. The flow rate measuring device according to 1. The flow rate measuring apparatus according to claim 1, wherein the arithmetic unit determines that the device is abnormal when the correction value exceeds a predetermined value. The flow rate measuring device according to claim 1, wherein the vortex generator is disposed perpendicular to a magnetic field direction of the magnetic field generator. 5. The flow rate measuring device according to claim 1, 2, 3, or 4, wherein the magnetic field generator is made of a permanent magnet.

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