JPH11287679A - Ultrasonic vortex flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive, using an ultrasonic receiver, modulation signals derived from a stable Karman vortex and to reduce sneak path noises. SOLUTION: An ultrasonic vortex generator 18 has a vortex generator 5 provided in a line 4, and has an ultrasonic wave transmitter and receiver 6, 7 with piezoelectric elements 6a, 7a mounted on detection mounting holes 19, 20 in a housing 3 across an area wherein a Karman vortex is generated. The piezoelectric elements 6a, 7a are pointed in different directions so that an ultrasonic signal of a detection beam with R1 such that the transmission beam width T of the ultrasonic transmitter 6 overlaps with the reception area of the ultrasonic receiver 7 orthogonally intersects the vortex generator 5 and passes near the center of the line 4. Therefore, the stable Karman vortex can be detected which occurs near the center o of the line 4 in which an almost uniform distribution of flow rates of the fluid for measurement is achieved in a turbulent region wherein the Karman vortex is produced, and the accuracy of measuring flow rate can be enhanced by stabilizing the amount of phase modulation of the ultrasonic waves. Also, by limiting the received beam width R1 , sneak path noises are reduced and S/N ratio can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic vortex flowmeter for measuring a flow rate of a fluid to be measured in a pipe based on a generation cycle of Karman vortices.

[0002]

2. Description of the Related Art An example of a conventional ultrasonic vortex flowmeter is described below.
This will be described with reference to FIGS. As shown in FIGS. 6 and 7, the ultrasonic vortex flow meter 1 is configured to vortex the fluid so as to traverse a pipe 4 in a housing 3 connected to a pipe 2 through which a fluid to be measured (the flow direction is indicated by a thick arrow) flows. A generator 5 is provided. A pair of ultrasonic transceivers 6 and 7 are orthogonal to the vortex generator 5 on the tube wall of the housing 3 with a Karman vortex generation region generated downstream of the vortex generator 5 due to the flow of the fluid to be measured. Installed as

In the ultrasonic transmitters / receivers 6, 7, the piezoelectric elements 6a, 7a are inserted into mounting holes 8, 9 provided on the outer peripheral portion of the housing 3, respectively, and screwed, welded, or bonded to the housing 3. Is pressed through an elastic body 11 such as silicon rubber by the lid member 10 fixed by the
The tube wall forming 7b is tightly fixed (joined) via an acoustic bonding agent 12 such as an adhesive or grease.

[0004] As shown in FIG. 8, the schematic configuration of the flow rate measuring circuit of the ultrasonic vortex flow meter 1 is as follows.
(Piezoelectric element 6a) and the phase comparison circuit 14, and the ultrasonic receiver 7 (piezoelectric element 7a) is connected to the phase comparison circuit 14 via the amplification circuit 15;
Are connected to the conversion circuit 16. In the figure, reference numeral 17 denotes a power supply circuit.

Next, the operation of the ultrasonic vortex flowmeter 1 will be described.

The piezoelectric element 6a of the ultrasonic transmitter 6 vibrates by an electric signal from the transmission circuit 13, and oscillates ultrasonic waves into the fluid to be measured in the pipe 4 via the acoustic bonding agent 12 and the vibration propagation section 6b. I do. This ultrasonic wave propagates through the fluid to be measured in the conduit 4,
After being modulated by the Karman vortex K generated in the wake of the vortex generator 5 by the flow of the fluid to be measured, it is received by the piezoelectric element 7a via the vibration propagating portion 7b and the acoustic bonding agent 12 and converted into an electric signal. .

[0007] The electric signal is amplified by the amplifier circuit 12 and input to the phase comparison circuit 14. The phase comparison circuit 14 compares the phase of the signal including the modulation by the Karman vortex K from the ultrasonic receiver 7 with the phase of the original signal from the oscillation circuit 13 and detects the modulation by the Karman vortex K to detect the Kalman vortex. Vortex K
Is output as a modulated signal having a frequency equal to the generation cycle of Since the frequency of the modulation signal is proportional to the flow rate of the fluid to be measured, the conversion circuit 16 processes this modulation signal and outputs a pulse signal representing the flow rate of the fluid to be measured. The measured flow rate of the fluid to be measured can be obtained by processing this pulse signal by various arithmetic and control circuits (not shown).

In the ultrasonic vortex flowmeter in which the generation frequency of the Karman vortex is detected using ultrasonic waves as described above, the state of the Karman vortex greatly affects the detection accuracy of the generated frequency, and as a result, The flow measurement system will be affected.

The state of the Karman vortex generated by the vortex generator will be described with reference to FIGS. 9 and 10. FIG. FIG. 9 shows an outline of the pipe 4 perpendicular to the fluid flow direction viewed from the downstream side of the vortex generator, and FIG. 10 shows an outline of a cross section of the pipe 4 parallel to the fluid flow direction. In the figure, reference numeral 5 denotes a vortex generator, and arrows indicate the flow direction and size of the fluid in each part.

In the vicinity of the center of the pipeline 4, the flow velocity is large as shown in FIG.
As a result, Karman vortices having substantially the same period and having a large flow velocity in the ultrasonic transmission / reception direction are two-dimensionally generated in parallel to a plane perpendicular to the axis of the vortex generator 5 (see the arrows shown by solid lines in FIGS. 9 and 10). . However, since the flow velocity decreases as the distance from the center of the pipe 4 to the pipe wall decreases, the cycle near the pipe wall is slower than the vortex generation cycle near the pipe center, and the pipe wall and the vortex generator As a result, a turbulence surrounding the vortex generator 5 called a horseshoe vortex occurs due to the effect of the contact portion (FIGS. 9 and 10).
Medium, see broken line arrow).

This horseshoe vortex is slower than the Karman vortex near the center of the pipeline and is generated at an irregular period. Therefore, the ultrasonic waves received by the ultrasonic receiver are not only modulated by the Karman vortex but also generated by the horseshoe vortex. , The modulated signal detected by the phase comparison circuit 14 is a signal in which a plurality of waveforms having different frequencies are superimposed, and it is not possible to obtain only the generation period of the Karman vortex necessary for the flow meter rule.

Also, the horseshoe vortex complicates the flow three-dimensionally and causes disturbances in the generation of Karman vortices. Therefore, Karman vortices generated near the tube wall must maintain a stable two-dimensional period. , Which further complicates the modulated signal. Therefore, the ultrasonic transmitter / receiver is placed near the center of the pipeline so that the ultrasonic wave is not modulated by the horseshoe vortex or the Karman vortex generated by the horseshoe vortex. Detection can be performed stably, and the measurement accuracy of the flow rate can be enhanced.

[0013]

In order to measure a very small flow rate using the above-mentioned conventional ultrasonic vortex flowmeter 1, the flow velocity (Reynolds number) of the fluid to be measured is increased to the Karman vortex generation region. It is necessary to generate a stable Karman vortex, and therefore, it is necessary to set the diameter D of the conduit 4 to be sufficiently small.

However, the ultrasonic transceivers 6 and 7
From the viewpoint of securing the performance stability of the piezoelectric element, the piezoelectric elements 6a and 7a
Is difficult to reduce appropriately. For this reason, the dimension D of the ultrasonic transceivers 6 and 7 had to be relatively larger than the diameter D of the pipe 4 (see FIG. 7).

As shown in FIG. 7, the ultrasonic wave oscillated from the ultrasonic transmitter 6 propagates through the fluid in the pipe 4 with the directivity (expansion) of a predetermined transmission beam width T, and receives the ultrasonic wave. It is received within a predetermined detection beam width _R0 of the piezoelectric element 7a of the detector 7. Ultrasonic transceivers 6 and 7 with respect to diameter D of conduit 4
If the width H of the (piezoelectric elements 6a, 7a), that is, the dimension along the axial direction of the vortex generator 5, is large, the piezoelectric element of the ultrasonic receiver 7
The detection beam width R ₀ according to 7 a becomes larger than the diameter D of the pipe 4.

As shown in FIG. 7, the ultrasonic transceivers 6, 7
FIG. 11 shows the positional relationship between the detected beam width R ₀ and the vortex generated by the vortex generator when the vortex generators are arranged facing each other. In this case, the ultrasonic wave is modulated by the unstable horseshoe vortex near the upper and lower pipe walls of the vortex generator 5 in the pipeline 4 and the Karman vortex disturbed by the horseshoe vortex in addition to the periodic modulation received by the Karman vortex. As a result, the modulation signal indicating the modulation amount of the ultrasonic wave detected by the phase comparison circuit 14 varies due to the influence, and only the generation period of the Karman vortex is not obtained, and the measurement accuracy of the flow rate is reduced. . As shown in FIG. 7, when the detection beam width R ₀ is larger than the diameter D of the pipe 4, the beam is oscillated from the piezoelectric element 6 a of the ultrasonic transmitter 6 and propagates through the pipe wall of the housing 3. Without being modulated by the flow of the fluid to be measured, the signal (wraparound noise) directly received by the piezoelectric element 7a of the ultrasonic receiver 7 increases and the S / N ratio deteriorates.

FIG. 12 shows the piezoelectric elements of the ultrasonic transceivers 6 and 7.
When the width H of 6a, 7a is larger than the diameter D of the conduit 4, the output waveform A of the phase comparison circuit 14 (vortex signal waveform which is a modulation signal waveform due to the flow of the fluid to be measured) and the output pulse of the waveform shaping circuit 16 The waveform B is shown. From FIG. 12, it is found that the output waveform A (vortex signal waveform) varies due to the detection of unstable flow turbulence near the pipe wall and the influence of wraparound noise, etc., and the ultrasonic wave is modulated purely by the Karman vortex alone. It can be seen that a stable sine wave is not obtained, and the output pulse waveform B obtained by pulsing the output waveform A is missing. By calculating the flow rate of the fluid to be measured based on the output pulse waveform B having a missing waveform, the measurement accuracy of the flow rate decreases.

The present invention has been made in view of the above points, and eliminates the need for a stable Kalman vortex by eliminating the modulation of ultrasonic waves by a horseshoe vortex or a Karman vortex disturbed by a horseshoe vortex. It is an object of the present invention to provide an ultrasonic vortex flowmeter capable of receiving a modulation signal due to a vortex and reducing sneak noise.

[0019]

In order to solve the above-mentioned problems, a first aspect of the present invention is to provide a pair of ultrasonic transceivers having a vortex generator provided in a pipe through which a fluid to be measured flows and having a piezoelectric element. Is disposed so as to sandwich the generation region of the Karman vortex generated by the vortex generator of the conduit, and the flow rate of the fluid to be measured is determined based on the generation period of the Karman vortex detected by the ultrasonic transceiver. In the ultrasonic vortex flowmeter to be measured, one of the pair of ultrasonic transceivers has an ultrasonic transmission region, and the vortex generator at an overlapping portion of the other ultrasonic reception region of the pair of ultrasonic transceivers. The pair of ultrasonic transceivers are offset from each other so that the width in the axial direction is smaller than the width of the ultrasonic receiving surface of the other piezoelectric element.

With this configuration, the width of the overlapping portion between the ultrasonic transmission region and the ultrasonic reception region in the axial direction of the vortex generator is smaller than when a pair of ultrasonic transceivers are arranged opposite to each other. Become smaller.

The offset arrangement described in claim 1 means that the pair of ultrasonic transceivers do not face each other so as to sandwich the center of the pipeline, or that the positions in the axial direction of the vortex generator are not equal. That is, they are arranged so as to satisfy one of the conditions.

According to a second aspect of the present invention, a vortex generator is provided in a conduit through which a fluid to be measured flows, and a pair of superconducting members each including a piezoelectric element and a vibration propagating portion joined to the piezoelectric element by an acoustic bonding agent. An ultrasonic wave transmitter / receiver is disposed so as to sandwich a generation region of the Karman vortex generated by the vortex generator in the conduit, and the fluid to be measured is determined based on a generation period of the Karman vortex detected by the ultrasonic transmitter / receiver. In the ultrasonic vortex flowmeter that measures the flow rate, the width in the axial direction of the vortex generator body joint portion between the piezoelectric element and the vibration propagating portion of at least one of the pair of ultrasonic transceivers by the acoustic bonding agent is set. The width of the piezoelectric element in the axial direction of the vortex generator is made smaller.

[0023] With this configuration, the acoustic bonding agent allows the entire surface of the piezoelectric element of the ultrasonic transceiver to be joined to the vibration propagating part that is combined with the piezoelectric element.
The width of at least one of the ultrasonic wave transmission region and the ultrasonic wave reception region in the axial direction of the vortex generator is reduced.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. In the following description, the same parts as those in the conventional example shown in FIGS. 6 to 8 are denoted by the same reference numerals, and only different parts will be described in detail.

As shown in FIG. 1, in the ultrasonic eddy flow meter 18 according to the present embodiment, the piezoelectric elements 6 of the ultrasonic transceivers 6 and 7 are arranged.
a, 7a mounting holes 19, 20
A predetermined transmission beam oscillated from the piezoelectric element 6a of the ultrasonic transmitter 6 is offset by a predetermined angle with respect to the axial direction of the vortex generator 5, and a part of the piezoelectric elements 6a and 7a face each other. the ultrasonic waves and reception area of the piezoelectric element 7a of the ultrasonic receiver 7 having directivity width T of the (spread) wraps (overlapping) orthogonal ultrasonic detection beamwidth R ₁ is an axial direction of the vortex generator 5 Then, it passes near the center of the pipe 4.

Further, the ultrasonic transceivers 6 and 7 are connected to the pipe 4 where the detected beam width R ₁ is substantially uniform in the turbulent flow region where Karman vortices are generated in the pipe 4. Are arranged so as to pass through a region near the center of the image. More specifically, based on FIG. 2 showing a flow velocity distribution in a circular pipe,
The detection beam has a large flow velocity and a substantially constant area, that is, 0.35D from the center of the pipe 4 in the axial direction of the vortex generator.
(D: the diameter of the conduit 4) is limited within the range.

Next, the operation of the present embodiment configured as described above will be described.

As shown in FIGS. 6 to 8, the ultrasonic wave oscillated from the ultrasonic transmitter 6 propagates with a directivity (expansion) having a predetermined transmission beam width T, and a part of the ultrasonic wave is transmitted through the pipeline. The light is propagated through the fluid to be measured in 4, modulated by the Karman vortex K, and received by the ultrasonic receiver 7. At this time, since the detection area of the Karman vortex 4 is limited to the detection beam width R ₁ to wrap the receiving area of the transmission beam width T and the ultrasonic receiver 7, the conduit 4 which flow velocity distribution is substantially uniform A stable Karman vortex generated near the center can be detected, and the modulation signal detected by the phase comparison circuit 14 can be stabilized.

Further, by limiting the detection beam width R ₁ by the piezoelectric element 7a ultrasonic receivers 7, an ultrasonic transmitter 6
The signal (wraparound noise) oscillated from the piezoelectric element 6a and propagated on the side wall of the housing 3 and directly received by the ultrasonic receiver 7 is reduced, and the S / N ratio is improved.

As described above, by not receiving the ultrasonic wave modulated by the horseshoe vortex or the Karman vortex disturbed by the horseshoe vortex, the modulation signal (the output waveform of the phase comparison circuit 14) is not received.
Together to stabilize, by improving the S / N ratio by reducing the ultrasonic wave echo noise only housing 3 in the detection beam width R ₁ by ultrasonic waves do not include a region that would propagate, By stabilizing the output waveform of the phase comparison circuit 14 and the output pulse waveform of the waveform shaping circuit 16, the measurement accuracy of the flow rate can be improved.

FIG. 3 shows an ultrasonic vortex flowmeter according to this embodiment.
18 shows an output waveform C of the phase comparison circuit 14 and an output pulse waveform D of the waveform shaping circuit 16. Output waveform C shown in FIG.
Also, it can be seen that the output pulse waveform D is very stable with no waveform loss compared to the output waveform A and the output pulse waveform B shown in FIG.

[0032] Then, for measurement of the minute flow rate, even if the reduced diameter D of the pipe 4, without reducing the size of the ultrasonic receiver 7, it is possible to obtain a desired detection beamwidth R _1, The S / N ratio is high, and a stable modulation signal can be detected to increase the flow rate measurement accuracy. Thereby, the performance stability of the piezoelectric element of the ultrasonic receiver 7 is easily secured,
It is possible to prevent a reduction in manufacturing and assembling workability due to downsizing, and prevent an increase in manufacturing cost.
Further, it is not necessary to manufacture piezoelectric elements of each size according to the measured flow rate, so that components can be shared and the manufacturing cost can be reduced.

[0033] In the above embodiment, by detecting a stable modulated signal by limiting a detection beam width R ₁ of the ultrasonic only near the center of the pipe 4, to enhance the measurement system of the flow rate For example, as shown in FIG. 4, an ultrasonic transceiver is used so that a detection beam width R ₂ overlapping with a transmission beam width T avoids a portion affected by a horseshoe vortex near the end of the vortex generator 5. By arranging the sixth and seventh piezoelectric elements 6a and 7a, it is possible to detect a modulation signal to some extent stable with respect to the above-described conventional technology, and it is possible to improve the flow measurement accuracy.

[0034] In the above embodiment, the piezoelectric element 6a of ultrasonic transducers 6 and 7, but so as to limit the detection beam width R ₁ by the mounting angle of 7a, the present invention is not limited to this, for example, By appropriately disposing acoustic mask means for blocking the transmission path of the ultrasonic wave between the piezoelectric elements 6a and 7a,
It is also possible to limit the detection beam width R ₁ in the vicinity of the center portion of the pipe 4.

In this case, as shown in FIG. 5, for example, a piezoelectric element 7a is provided at the center of the bottom (vibration propagation section 7b) of the mounting hole 9 on the reception side of the ultrasonic transmitters / receivers 6, 7 arranged facing each other.
By projecting a bonding portion 21 smaller than the ultrasonic receiving surface of the piezoelectric element 7a and the ultrasonic receiving surface of the piezoelectric element 7a via an acoustic bonding agent 22,
7b as an acoustic mask means,
Can limit the detection beam width R ₁ near the center portion of the conduit 4 can achieve effects similar to the above embodiment, the effect. In addition, by projecting a joint at the bottom (vibration propagation portion 6b) of the mounting hole 8 on the transmission side to reduce the joint with the piezoelectric element 6a, the beam width on the transmission side is reduced, and the detection beam width is reduced. Can be limited. FIG.
The same parts as those shown in FIG. 7 are denoted by the same reference numerals.

[0036]

As described above in detail, according to the ultrasonic eddy flow meter according to the first aspect, one ultrasonic transmission region of the pair of ultrasonic transceivers and the ultrasonic transmission region of the pair of ultrasonic transceivers are used. A pair of ultrasonic transceivers are offset from each other so that the width of the overlapping portion with the other ultrasonic receiving area in the vortex generator axial direction is smaller than the width of the ultrasonic receiving surface of the other piezoelectric element. The arrangement allows the width of the overlapping portion of the ultrasonic transmission area and the ultrasonic reception area in the axial direction of the vortex generator to be smaller than the case where the pair of ultrasonic transceivers are arranged opposite to each other. Therefore, even if the diameter of the conduit is reduced, the field of the ultrasonic beam can be reduced without reducing the size of the piezoelectric element. It is possible to prevent a decrease in workability and prevent an increase in manufacturing cost. Further, it is not necessary to manufacture piezoelectric elements of each size according to the measured flow rate, so that components can be shared and the manufacturing cost can be reduced.

According to the ultrasonic vortex flowmeter of the second aspect,
The width of the piezoelectric element in at least one of the pair of ultrasonic transceivers and the vibration propagating portion in the vortex generator axial direction of the joining portion by the acoustic bonding agent is larger than the width of the piezoelectric element in the vortex generator axial direction. Since the size is reduced, at least any one of the ultrasonic transmission region and the ultrasonic reception region is compared with the case where the entire surface of the piezoelectric element of the ultrasonic transceiver is joined to the vibration propagation portion forming a pair with the piezoelectric element by the acoustic bonding agent. The width of the vortex generator in the axial direction can be reduced. Therefore, even if the diameter of the conduit is reduced, the field of the ultrasonic beam can be reduced without reducing the size of the piezoelectric element. It is possible to prevent a decrease in workability and prevent an increase in manufacturing cost. Further, it is not necessary to manufacture piezoelectric elements of each size according to the measured flow rate, so that components can be shared and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view across a pipeline of an ultrasonic vortex flowmeter according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a flow velocity distribution in a circular pipe.

FIG. 3 is a graph showing an output waveform of a phase comparison circuit and an output pulse waveform of a waveform shaping circuit of the apparatus of FIG. 1;

FIG. 4 is a schematic diagram showing an arrangement of a piezoelectric element of an ultrasonic transceiver in a longitudinal section crossing a pipeline of an ultrasonic vortex flowmeter according to a modification of the embodiment shown in FIG. 1;

FIG. 5 is a vertical cross-sectional view across a conduit of an ultrasonic vortex flowmeter according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view of a conventional ultrasonic vortex flow meter.

FIG. 7 is a vertical cross-sectional view of the ultrasonic vortex flow meter of FIG.

8 is a block diagram showing a schematic configuration of a flow measurement circuit of the ultrasonic vortex flow meter of FIG.

FIG. 9 is a vertical cross-section across a pipeline showing the state of Karman vortices generated by the vortex generator.

FIG. 10 is a longitudinal section along a pipeline showing a state of Karman vortices generated by the vortex generator.

FIG. 11 is a vertical cross-section across a pipeline showing a positional relationship between a detected beam width of an ultrasonic wave and a vortex generated by a vortex generator in the conventional example shown in FIG. 6;

12 is a graph showing an output waveform of a phase comparison circuit and an output pulse waveform of a waveform shaping circuit of the ultrasonic vortex flowmeter of FIG. 6;

[Explanation of symbols]

 4 Pipeline 5 Vortex generator 6 Ultrasonic transmitter 7 Ultrasonic receiver 6a, 7a Piezoelectric element 6b, 7b Vibration propagation section 12 Acoustic bonding agent 18 Ultrasonic vortex flow meter

Claims (2)

[Claims] 1. A vortex generator is provided in a conduit through which a fluid to be measured flows, and a pair of ultrasonic transceivers having a piezoelectric element are sandwiched between generation regions of Karman vortices generated by the vortex generator in the conduit. In the ultrasonic vortex flowmeter that measures the flow rate of the fluid to be measured based on the generation cycle of the Karman vortex detected by the ultrasonic transceiver, one of the pair of ultrasonic transceivers The ultrasonic transmission region, the width in the axial direction of the vortex generator body of the overlapping portion of the other ultrasonic receiving region of the pair of ultrasonic transceiver, than the width of the ultrasonic receiving surface of the other piezoelectric element. The ultrasonic vortex flowmeter, wherein the pair of ultrasonic transceivers are offset from each other so as to be small. 2. A vortex generator is provided in a pipe through which a fluid to be measured flows, and a pair of ultrasonic transceivers each including a piezoelectric element and a vibration propagating unit joined to the piezoelectric element by an acoustic bonding agent are connected to the pipe. An ultrasonic wave that is arranged so as to sandwich a generation region of a Karman vortex generated by the vortex generator, and that measures a flow rate of the fluid to be measured based on a generation period of the Karman vortex detected by the ultrasonic transceiver. In the vortex flowmeter, the width of the piezoelectric element in at least one of the pair of ultrasonic transceivers and the vibration propagating part in the axial direction of the vortex generator body may be determined by the vortex of the piezoelectric element. An ultrasonic vortex flowmeter characterized in that the width is smaller than the width in the axial direction of the generator.