JP2002071405A - Flow measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow measurement apparatus which has a wide measurement range, can simply cope with wide fluid conditions, can be manufactured at a low cost, and has high measurement accuracy. SOLUTION: The flow measurement apparatus comprises a differential amplifier as a detecting circuit, and a pair of dummy electrodes 7a, 7b each of which is electrically connected to the detecting circuit 5 in the neighborhood of each electrode of a pair of electromotive force measurement electrodes 4a, 4b. External noise components induced by a pair of the electromotive force measurement electrodes 4a, 4b and a pair of the dummy electrodes 7a, 7b are compensated in the differential amplifier 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 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. 3 is a sectional view showing a configuration of a conventional flow measuring device.

As shown in FIG. 3, reference numeral 1 denotes a measuring tube through which a fluid having conductivity is passed, 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 electrode 4 for electromotive force measurement 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 6 is a magnetic field generating device provided around the measuring tube 1, and two magnets S
The pole and the N pole are arranged facing each other. The magnetic field generator 6 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 6. 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-described conventional flow rate measuring device, the electromotive force generated between the electromotive force measuring electrodes 4a and 4b is changed due to the change in the conductivity of the fluid, or the flow rate is changed. When a disturbance is applied to the magnetic field 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. Several mV to several m
Because of the low voltage of V, the input impedance must be set as high as several MΩ, which causes a small amount of noise to be picked up. Therefore, the influence of disturbance is large. Flow rate detection was difficult. 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 rate changes from the optimum flow rate for measurement, the frequency of the Karman vortex does not change in proportion to the change in the flow rate. Is disturbed, and the disturbance increases noise, so that measurement accuracy is reduced.

Further, when a permanent magnet is used as the magnetic field generator, the magnet changes with time to deteriorate the performance, and the polarization generated at the electrodes causes a reduction in the induced electromotive force, thereby lowering the signal level. In addition, accurate flow rate detection becomes difficult.

As described above, it is difficult for the conventional flow rate measuring apparatus to cope with all of the measuring conditions when the measuring conditions are variously changed, and the apparatus for cutting off the influence of such a disturbance, on the contrary, does not respond to the disturbance. There is a demand for the development of a device that removes the influence of disturbance with a simple device, which may cause such a problem.

In order to solve such a conventional problem, the present invention provides a high-precision flow measuring device which has a wide measuring range, can easily cope with a wide range of flow conditions, has a low cost and has a simple structure, and has a simple structure. The purpose is to provide.

[0014]

In order to solve such a problem, a flow rate measuring apparatus according to the present invention comprises a detection circuit provided with a differential amplifier circuit and a pair of electrodes for measuring a pair of electromotive force electrodes. A pair of pseudo-electrodes electrically connected to the detection circuit are provided one by one in the vicinity of, and a disturbance noise component induced by the pair of electromotive force measurement electrodes and the pair of pseudo-electrodes in the differential amplifier circuit. It is characterized by being offset.

[0015] Thus, a wide measurement range can be easily applied to a wide range of flow conditions, and a high-precision flow measurement can be performed with a low-cost and simple configuration.

[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 electrically connected to a power measurement electrode and including a detection circuit that detects an induced electromotive force to calculate a flow rate of a fluid, wherein the detection circuit includes a differential amplifier circuit and A pair of pseudo electrodes electrically connected to the detection circuit are provided near the respective electrodes of the electromotive force measurement electrodes, and a pair of electromotive force measurement electrodes and a pair of pseudo electrodes are provided in the differential amplifier circuit. Induced by the pseudo electrode The flow rate measurement device is characterized in that the disturbance noise component is canceled out, so even if the measurement conditions change, the fluctuation is canceled out using the differential amplifier circuit and the pseudo electrode. Therefore, it is possible to perform measurement in a wide measurement range, to easily cope with a wide range of flow conditions, and to perform high-precision flow measurement with a low-cost and simple configuration.

According to a second aspect of the present invention, the detecting circuit detects and amplifies the induced electromotive force generated between the pair of electromotive force measuring electrodes, and includes a pair of pseudo-phase amplifier circuits. A second positive-phase amplifier circuit for detecting and amplifying the induced electromotive force generated between the electrodes, wherein outputs of the first positive-phase amplifier circuit and the second positive-phase amplifier circuit are respectively input to a differential amplifier, and disturbance noise 2. The flow rate measuring device according to claim 1, wherein the components are canceled out, so that the detection signal can be amplified and processed, so that it can very easily cope with a wide range of flow rate conditions, and is low-cost and highly accurate. Can be.

(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 provided in a fluid to generate Karman vortices, and 3 is a rotating direction alternately at a frequency proportional to a representative dimension of the vortex generator 2. 4a and 4b are electromotive force measurement electrodes, 5 is a detection circuit that detects induced electromotive force and calculates a flow rate, and can cancel a signal of a disturbance noise component. 6 is a magnetic field generation. The devices 7a and 7b are pseudo electrodes for canceling disturbance noise components. Although not shown, the detection circuit 5 is provided with a differential amplifier circuit for removing disturbance noise components induced by the electromotive force measurement electrodes 4a and 4b from the detection signal. This will be described later. Note that the flow rate and the dimensional relationship between the members are very important in the generation of the Karman vortex 3, but in the present embodiment, for the sake of explanation, the width corresponding to the representative size of the vortex generator 2 is D as shown in FIG. The diameters of the electromotive force measuring electrodes 4a and 4b are da and db, the length of the electromotive force measuring electrodes 4a and 4b in the tube is h, the distance between the electromotive force measuring electrodes 4a and 4b is L, The width of the magnetic field generator is Dm.

The pseudo electrode 7a is provided near the electromotive force measuring electrode 4a, and the pseudo electrode 7b is provided near the electromotive force measuring electrode 4b. This is for detecting as much as possible the same noise component as the disturbance noise component induced in the electromotive force measuring electrodes 4a and 4b. The electromotive force measuring electrodes 4a and 4b are immersed in the fluid, but the pseudo electrodes 7a and 7b are not immersed in the fluid. The reason for not immersing in a fluid is that when immersed in a fluid, the pseudo electrode 7
This is because an electromotive force due to the Karman vortex 3 is also generated in a and 7b, and it becomes impossible to detect only a noise component. The shapes of the pseudo electrodes 7a and 7b are the same as those of the electrodes 4a and 4b for measuring electromotive force.
Any shape may be used as long as the same noise component as the disturbance noise component induced in the above can be faithfully detected.

Next, the above-described measuring tube 1, vortex generator 2, electrodes 4a and 4b for measuring electromotive force, and magnetic field generator 6 will be described in more detail.

First, if the inside diameter of the measuring tube 1 is too small, the influence of the boundary layer of the tube 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. Reynolds number in proper flow velocity range is 3,000
It is in the range of about 100,000.

Although the shape of the vortex generator 2 is a triangular prism in this embodiment, any shape may be used as long as it generates a Karman vortex street.
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, the measurement tube 1 having an inner diameter of φ7 mm was used in order to set the flow detection range to 1 L / min to 10 L / min. It was most effective to provide the vortex generator 2 composed of an isosceles triangular prism.

The two electromotive force measuring electrodes 4a and 4b 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, 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 permanent magnets constituting the magnetic field generator 6 are provided on both sides so as to sandwich the electromotive force measurement electrodes 4a and 4b from both sides of the measurement tube 1. The flow rate detection range is 1 L / min to 1
When it is set to 0 L / min, the magnetic field generator 6 needs to increase the magnetic flux density in the measuring tube 1 and uses a rare earth permanent magnet, which is a magnet having a width 1.5 times the vortex generator width.

By the way, the flow measuring device using the Karman vortex 3 ensures that the members arranged in such an arrangement stably generate the Karman vortex 3 and that noise is not generated due to turbulence in the fluid. In addition, it is necessary to carefully select the dimensions of each member, the Reynolds number of the fluid, and the like. That is,
These dimensions are based on a delicate balance in order to stably generate the Karman vortex 3 and prevent noise.

The dimensional relationship will be described. For example, the measurement electrode diameters da, of the electromotive force measurement electrodes 4a, 4b
It is preferable that db is 1/2 or less of the vortex generator width D. This is because the Reynolds number near the flow is 1/2
This is because the flow becomes stable below, the flow for generating the Karman vortex 3 is hardly disturbed, and the flow of the Karman vortex street is not destroyed. When the measurement electrode diameters da and db of the electromotive force measurement electrodes 4a and 4b are the same, noise generated at the electromotive force measurement electrodes 4a and 4b can be relatively reduced. That is, the flow disturbed by the electromotive force measurement electrode 4a flows down the streamline while the turbulence is diffused, and flows into the electromotive force measurement electrode 4b. However, when the measurement electrode diameters da and db are different, Fluid resistance and peeling conditions at the electrodes are different, the surrounding flow becomes complicated and the noise increases, but the noise is relatively suppressed because of the same diameter.

Furthermore, since the inner diameter of the measuring tube 1 is about 3 to 4 times the vortex generator width D because the flow and the size are appropriately balanced, the electromotive force measuring electrodes 4a and 4a are used.
4b, the length h in the measuring electrode tube is set to 2 to 2.5 of the vortex generator width D.
When it is doubled, the vicinity of the tip of the electromotive force measuring electrodes 4a and 4b becomes the minimum height that completely surrounds exactly two Karman vortex streets, and only the induced electromotive force change at the center of the generated Karman vortex street is measured. The flow rate can be measured with high accuracy. If the tube lengths h of the electromotive force measurement electrodes 4a and 4b are the same, the electromotive force measurement electrodes 4a
Disturbance noise due to disturbances other than the Karman vortex 3, such as a vortex flowing out from the tip of 4b, can be canceled by the detection circuit 5, the noise level can be reduced, and the flow rate can be measured with high accuracy.

When the distance L between the electrodes 4a and 4b for measuring the electromotive force is set to be 2 to 2.5 times the width D of the vortex generator, the distance L between the electrodes 4a and 4b for measuring the electromotive force becomes equal to Kalman. The number of Karman vortices 3 existing between the electrodes 4a and 4b for measuring the electromotive force can be reduced to less than the distance between the vortices 3 of the vortex street.
It is possible to reduce the noise level, to make one of the Karman vortices 3 correspond to one of the detection signals, to facilitate the frequency counting, and to reduce the noise level. Accurate flow measurement can be performed. 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 known from the study of Strouhal. If you count it as one of the signals,
By measuring the frequency of the Karman vortex street, the flow rate of the fluid flowing in the measurement tube 1 can be calculated.

The magnetic field generator width D of the magnetic field generator 6
When m is 1.5 to 2 times the vortex generator width D, the magnetic field generated in the measuring tube 1 is concentrated only at the position where the Karman vortex 3 is generated, and the noise component due to the vorticity component generated on the side wall of the measuring tube 1 Can be reduced. As described above, the flow rate measuring device of the present embodiment employs 1.5 times.

Next, a description will be given of a detection circuit of the flow rate measuring apparatus according to the present embodiment having such a configuration and its detection operation. FIG. 2 is a block diagram of a detection circuit according to one embodiment of the present invention. In FIG. 2, 8a, 8b, 8
c, 8d, 8e are operational amplifiers, 9 is a comparator, and 10 is a bandpass filter. 11 is a resistor, 12 is a coupling capacitor.

The operational amplifier 8a has a positive-phase input terminal coupled to the coupling capacitor 12, and a negative-phase input terminal connected to the resistor 1
1 constitutes a first positive-phase amplifier circuit which is negatively fed back through the first positive-phase amplifier circuit. The electromotive force measuring electrode 4a is connected to the coupling capacitor 12, and the electromotive force measuring electrode 4b is connected to the negative-phase input terminal via the resistor 11 for providing an input potential. Similarly, the operational amplifier 8
b, a second positive-phase amplifier circuit whose positive-phase input terminal is coupled to the coupling capacitor 12 and whose negative-phase input terminal is negatively fed back via the resistor 11. The pseudo electrode 7a is connected to the coupling capacitor 12, and the pseudo electrode 7b is connected to the negative-phase input terminal via the resistor 11 for providing an input potential. The amplification factor of the first positive-phase amplifier circuit and the second positive-phase amplifier circuit is determined by the ratio of the two resistors 11 connected to the negative-phase input terminal, that is, the resistor 11 for giving an input potential and the negative feedback Are amplified by the ratio of the resistor 11. Thereby, the electromotive force measuring electrodes 4a and 4b and the pseudo electrode 7a,
The induced electromotive force generated in 7b is amplified to a predetermined signal level.

The operational amplifiers 8c and 8d constitute a differential amplifier circuit, amplify the output from the first positive-phase amplifier circuit in the positive phase, and cancel the output from the second positive-phase amplifier circuit.
At the same time as the in-phase signal of the disturbance noise component is removed, the signal is amplified to a signal level that can be detected by the comparator 9. Then, in the present embodiment, the waveform is shaped by the comparator 9 through the band pass filter 10, and this signal is output.
Therefore, the induced electromotive force generated each time the Karman vortex 3 crosses the electromotive force measuring electrodes 4a and 4b is amplified and noise components are removed by the first positive-phase amplifier circuit, the second positive-phase amplifier circuit, and the differential amplifier circuit. After that, the waveform is shaped into a rectangular wave by the comparator 9 and output as a train of rectangular waves (pulses) proportional to the flow rate. As described above, in the present embodiment, one of the Karman vortices 3 is made to correspond to one of the pulses. Therefore, by counting the output frequency, it is possible to easily measure the flow rate with high accuracy.

The operational amplifier 8e is negatively fed back to the negative-phase input terminal to form a voltage follower. This circuit has an extremely high input impedance and a low output impedance. Therefore, even if the induced electromotive force generated in the electromotive force measuring electrodes 4a and 4b is weak, the disturbance noise component is canceled by the differential amplifier circuit composed of the operational amplifiers 8a and 8b, and the magnetic field change caused by the Karman vortex 3 Only measurable.

As described above, the flow rate measuring apparatus according to the present embodiment includes the noise canceling amplifier circuit including the first positive-phase amplifier circuit, the second positive-phase amplifier circuit, and the differential amplifier circuit, and the pseudo electrode. The noise canceling amplifier circuit can cancel out the disturbance noise components, and even if the measurement conditions change, the fluctuations can be canceled out and the measurement can be performed. , And low-cost, high-precision flow measurement.

[0035]

As described above, since the flow rate measuring apparatus of the present invention is provided with the pseudo electrode and the differential amplifier circuit, even if the measurement conditions change, the fluctuations are canceled out for the measurement. Since it is possible to perform measurement in a wide measurement range, it is possible to easily cope with a wide range of flow conditions, and it is possible to perform high-precision flow measurement at low cost without disturbing the flow.

Since the flow rate measuring device of the present invention includes the first positive-phase amplifier circuit and the second positive-phase amplifier circuit, it can easily cope with a wide range of flow conditions by amplifying the detection signal, and can reduce the cost. Thus, the flow rate can be measured with high accuracy.

[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 block diagram of a detection circuit according to one embodiment of the present invention;

FIG. 3 is a cross-sectional view showing a configuration of a conventional flow measuring 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 6 Magnetic field generator 7a, 7b Pseudo electrode 8a, 8b, 8c, 8d, 8e Operational amplifier 9 Comparator 10 Bandpass filter 11 Resistor 12 Coupling capacitor D Vortex generator width Dm Magnetic field generator width da, db Measurement electrode diameter h Measurement electrode tube length L Measurement electrode interval

──────────────────────────────────────────────────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 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 flow rate measuring device comprising a detection circuit that detects the induced electromotive force and calculates the flow rate of the fluid, wherein the detection circuit is provided with a differential amplifier circuit,
A pair of pseudo electrodes electrically connected to the detection circuit are provided near each of the pair of electromotive force measurement electrodes, respectively, and the pair of electromotive force measurement in the differential amplifier circuit. A disturbance noise component induced by the use electrode and the pair of pseudo electrodes is offset. 2. A first positive-phase amplifier circuit for detecting and amplifying an induced electromotive force generated between the pair of electrodes for measuring an electromotive force, and an electromotive force generated between the pair of pseudo electrodes. A second positive-phase amplifier circuit for detecting and amplifying power, wherein outputs of the first positive-phase amplifier circuit and the second positive-phase amplifier circuit are respectively input to the differential amplifier to cancel disturbance noise components The flow rate measuring device according to claim 1, wherein: