JP2004012159A - Vortex flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a vortex flowmeter having an improved S/N ratio and measuring reliability by the configuration which is hardly influenced by a noise N due to a vibration and so forth, without the decrease in sensitivity at a low flow velocity, while keeping the merit of an integrated shape. <P>SOLUTION: In the vortex flowmeter including a measuring conduit path in which a fluid flows, a columnar vortex generation body for generating a vortex in the fluid, and a lifting force detection part for detecting the lifting force acting on the vortex generation body, the vortex generation body has a prescribed width (d) in the direction perpendicular to the flowing direction of the fluid, and the lifting force detection part has a vane-like form, and is arranged parallel to the flowing direction of the fluid, behind the vortex generation body, in which L/d is in the range of from 0.5 to 2.5, where L is the distance from the upstream end part of the vortex generation body to the downstream end part of the lifting force detection part. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a Karman vortex detection unit structure in a vortex flowmeter.
[0002]
[Prior art]
With reference to FIGS. 7 to 10, an outline of the structure of a detection unit of the conventional vortex flowmeter disclosed in Japanese Patent Application Laid-Open No. 2002-48610 will be described. FIG. 7 is a sectional side view of a so-called two-body detector in which a vortex generator and a lift detector are separated from each other by a predetermined distance in the direction of fluid flow. FIG. 9 shows a piezoelectric bimorph for lift detection inside the vortex generator. FIG. 3 is a side sectional view of a so-called integrated detection unit in which a type sensor is embedded.
[0003]
In FIG. 7 showing the structure of the two-body detector, reference numeral 1 denotes a measurement pipe formed of synthetic resin, and 2 denotes a column-shaped vortex formed by extending from the inner wall 1a of the measurement pipe at right angles to the flow direction of the fluid F. The generator 3 is a vane-shaped lift detector, which is formed at a predetermined distance downstream of the vortex generator 2 and is also extended from the inner wall 1a of the measurement pipe, and 4 is a plate embedded in the lift generator. A piezoelectric bimorph-type sensor having the shape of
[0004]
FIG. 8 is an enlarged view of the detection unit structure of FIG. 7 as viewed from above. The vortex generator 2 has a substantially trapezoidal cross section, and is arranged such that the bottom side is orthogonal to the flow direction F on the upstream side. The lift generating unit 3 is in the shape of a thin plate vane, and is arranged so that its longitudinal direction is parallel to the flow direction F.
[0005]
When the width orthogonal to the flow on the upstream side of the vortex generator 2 is d, and the length of one cycle of the vortex is Lv, when the design is d / Lv = 0.28, the lift of the stable vortex is detected. it can. Furthermore, the distance L between the upstream end of the vortex generator 2 and the center of the lift detector 3 is set to be approximately L = 4d so that the lift detector 3 does not hinder the stable generation of the vortex. You.
[0006]
Next, in FIG. 9 showing the structure of the integral detection unit, reference numeral 1 denotes a measurement pipe made of a synthetic resin, and 2 denotes a measurement pipe extending from the inner wall 1a of the measurement pipe at right angles to the flow direction of the fluid F. The columnar vortex generator 4 is a piezoelectric bimorph sensor embedded in the vortex generator 2.
[0007]
FIG. 10 is an enlarged view of the detection unit structure of FIG. 9 as viewed from above. The vortex generator 2 has a substantially trapezoidal cross section, and is arranged such that the bottom side is orthogonal to the flow direction F on the upstream side. The piezoelectric bimorph type sensor 4 embedded in the vortex generator 2 is arranged so that the longitudinal direction is parallel to the flow direction F.
[0008]
[Problems to be solved by the invention]
In the two-body detection unit structure described with reference to FIGS. 7 and 8, if the distance between the vortex generator 2 and the lift detection unit 3 is short, a stable vortex becomes an obstacle to the generation, so that the predetermined It is necessary to keep a distance L, and there is a problem that the sensitivity decreases due to the attenuation of the vortex as it goes downstream. In addition, there is a problem that harmonics are easily superimposed on the vortex waveform as compared with the case of the integral type described later, and miscounting is easy at the time of vortex counting.
[0009]
In the integrated detection unit structure described with reference to FIGS. 9 and 10, since the sensor is incorporated in the vortex generator, the problem of the two-body type is eliminated. However, the shape of the vortex generator 2 is trapezoidal (because the second moment of area is large), so that the plate-shaped piezoelectric bimorph-type sensor does not have sufficient sensitivity S, and there is a problem that the sensitivity is reduced at a low flow rate. In addition, since the vortex generator 2 has a large own weight, the vortex generator 2 is susceptible to noise N due to vibration or the like, so that there is a problem that the S / N is reduced.
[0010]
6A is a measurement waveform diagram at a low flow velocity of a two-body shape, FIG. 6B is a measurement waveform diagram at a high flow speed of the two-body shape, (1) is a detection signal waveform of the sensor, (2) is a filtering waveform of the detection signal, and ( 3) is a rectangular wave output waveform obtained by shaping the filtering waveform.
[0011]
As is clear from the comparison of the waveforms, the signal level of the sensor is small at the low flow velocity of (A), and a rectangular wave output cannot be obtained below the noise level. In the case of the high flow velocity shown in (B), noise due to vibration is superimposed greatly and pulse-like noise is superimposed on the rectangular wave output, which causes a count error when measuring the vortex frequency.
[0012]
In order to cope with such an integral problem, if the shape of the vortex generator is a vane shape applied to the two-body lift detector 3, vortices can be generated by the flow but can be generated stably. Therefore, stable flow measurement cannot be performed.
[0013]
An object of the present invention is to improve the S / N and improve the reliability of measurement by using a shape that is not affected by noise N due to vibration or the like, without reducing sensitivity at low flow rates while taking advantage of the advantages of the integral type. It is to implement a flow meter.
[0014]
[Means for Solving the Problems]
The configuration of the present invention that achieves such an object is as follows.
(1) In a vortex flowmeter including a measurement pipe through which a fluid flows, a column-shaped vortex generator for generating a vortex in the fluid, and a lift detector for detecting a lift acting on the vortex generator,
The vortex generator has a predetermined width (d) in a direction orthogonal to a flow direction of the fluid,
The lift detection unit has a vane-like form, is arranged behind the vortex generator in parallel with the flow direction of the fluid, and a downstream end of the lift detection unit from an upstream end of the vortex generator. A vortex flowmeter, wherein L / d is in the range of 0.5 to 2.5, where L is the distance to the part.
(2) The vortex flowmeter according to claim 1, wherein a piezoelectric bimorph-type sensor is embedded in the vane-like lift detection unit.
(3) The vortex flowmeter according to claim 1, wherein a strain gauge is attached or inserted to an opposing surface of the vane-shaped lift detector.
(4) The vortex flowmeter according to any one of claims 1 to 3, wherein the vane-shaped lift detector is integrally attached to a central portion behind the vortex generator.
(5) The vortex flowmeter according to any one of claims 1 to 3, wherein the vane-shaped lift detector is separated from the vortex generator at a predetermined distance from a central portion behind the vortex generator.
(6) The vortex flowmeter according to any one of claims 1 to 5, wherein both ends of the vortex generator are edge-processed.
(7) The vortex flowmeter according to any one of claims 1 to 6, wherein the measurement tube, the vortex generator, and the lift detector are integrally formed of synthetic resin.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an enlarged view of a detection unit showing an example of a vortex flowmeter to which the present invention is applied. FIG. 1 (A) is a top view and FIG. 1 (B) is a side sectional view.
[0016]
FIG. 2 is an overall structural view of a vortex flowmeter to which the present invention is applied, (A) is an upper sectional view, (B) is a side sectional view, and (C) is a front view as viewed from the downstream side (arrow P). It is. FIG. 3 is an enlarged view of the vortex generator 2, the lift detector 3, and the piezoelectric bimorph sensor 4. In this embodiment, a unit in which the vortex generator 2 and the lift detection unit 3 are integrated into a hole 1b formed in the measurement pipeline 1 is inserted from outside the pipeline.
[0017]
As is clear from FIGS. 1A, 2A and 3, the vortex generator 2 and the lift detector 3 are integrally formed in a T-shape when viewed from above, A thin vane-shaped lift detecting unit 3 as a vertical rod portion is connected in parallel with the flow direction to a central portion behind a horizontal rod portion having a function of a vortex generator (becoming a separation point of a flow) at right angles. The piezoelectric bimorph type sensor 4 is embedded in the lift detecting section.
[0018]
Hereinafter, the features of the detection unit structure of the vortex flowmeter of the present invention will be described with reference to the enlarged view of FIG.
The structure of the vortex generator 2 is a plate-shaped column orthogonal to the flow direction and has a predetermined width d. The function as the vortex generator is the same as that of the trapezoidal vortex generator described with reference to FIGS. 7 to 10, and is designed to have d / Lv = 0.28.
[0019]
The structure of the lift detecting unit 3 is the same as that of the lift detecting unit in the two-body type shown in FIGS. 7 and 8, and is a thin plate vane-shaped column arranged in parallel with the flow.
The feature of the present invention resides in that the plate-shaped vortex generator 2 and the vane-shaped lift detector are arranged very close to each other, and a structure equivalent to the integral type shown in FIGS. 9 and 10 is realized as a whole.
[0020]
When the distance between the upstream end of the vortex generator 2 and the downstream end of the lift detecting unit 3 is L, the range of the close arrangement between the two to produce the effect of the present invention is L / d of 0.5 to 0.5. It is in the range of 2.5.
[0021]
If this condition is satisfied, even if the vortex generator 2 and the vane-shaped lift detection 3 are physically two bodies, it can be considered that they are substantially an integrated structure.
FIG. 4 is an enlarged view of a detection unit showing another embodiment of the present invention, and has a structure in which a vortex generator 2 and a vane-like lift detection unit 3 are separated into two parts close to each other. , L / d in the range of 0.5 to 2.5 are the same as in the integrated structure of FIG.
[0022]
The present invention eliminates the disadvantages of the two-body type and the one-body type by adopting a structure in which the shape of the lift detection unit 3 is disposed immediately after the vortex generator 2 having high detection sensitivity while maintaining the shape of the thin plate vane. However, it is possible to exhibit the effect of incorporating only the advantages.
[0023]
FIG. 5 is a waveform diagram showing measurement results of the structure of the present invention under substantially the same conditions as those of the conventional two-body structure described in FIG. 5A is a measurement waveform chart at a low flow rate, FIG. 5B is a measurement waveform chart at a high flow rate, (1) shows a detection signal waveform of the sensor, (2) shows a filtering waveform of the detection signal, and (3) shows a filtering waveform. It is a shaped rectangular wave output waveform.
[0024]
As is clear from the comparison of the waveforms, the comparison between FIG. 5A and FIG. 6A shows that a stable rectangular wave output waveform can be obtained without a decrease in the sensor signal level even at a low flow rate. I have.
[0025]
Furthermore, as is clear from the comparison between FIG. 5B and FIG. 6B, at a high flow velocity, there is little harmonic noise due to the turbulence of the flow, there is no superposition of pulse-like noise on the rectangular wave output, and S / N can be measured.
[0026]
In the embodiment described above, the vortex generator 2 is exemplified as a flat plate. However, in order to improve the separation of the vortex, both edges are tapered in the flow direction as shown by a dotted line 5 in FIG. Alternatively, although not shown, it is also possible to perform a process of adding R.
[0027]
Further, in the above-described embodiment, a structure in which the piezoelectric bimorph-type sensor is embedded inside the vane-like lift detecting unit 3 as a sensor for detecting the lift is illustrated. However, the present invention is not limited thereto. A structure in which a vane-shaped lift detector is attached to or inserted into both sides of a vane lift detecting section (a thin plate having strain gauges on both sides is embedded in the vane) may be used.
[0028]
The vortex flowmeter of the present invention shown in FIGS. 1 and 2 has a configuration in which a unit in which a vortex generator 2 and a lift detector 3 are integrated into a hole 1 b formed in a measurement pipe 1 is inserted from outside the measurement pipe. Although illustrated as an example, as illustrated in FIGS. 7 to 10, it is also possible to adopt a structure in which the measurement conduit, the vortex generator, and the lift detection unit are integrally molded of a synthetic resin.
[0029]
【The invention's effect】
As is apparent from the above description, according to the present invention, the following effects can be expected.
(1) By forming the lift detecting portion in a vane shape, the secondary moment of area around the piezoelectric bimorph type sensor (case) can be reduced, and vortex detection sensitivity can be increased.
(2) Since the weight of the detection unit can be reduced, noise due to vibration can be reduced.
(3) Since the pressure fluctuation in the portion immediately after the separation of the vortex can be detected, a clean vortex waveform with few harmonics can be detected.
(4) From this, it is possible to improve the detection reliability such as measurement in a lower flow region and improvement in vibration resistance.
[Brief description of the drawings]
FIG. 1 is an enlarged view of a detection unit in a vortex flowmeter to which the present invention is applied.
FIG. 2 is an overall structural diagram of a vortex flowmeter to which the present invention is applied.
FIG. 3 is an enlarged top view of a vortex generator and a lift detector in a vortex flowmeter to which the present invention is applied.
FIG. 4 is an enlarged top view of a vortex generator and a lift detector according to another embodiment of the present invention.
FIG. 5 is a measurement waveform diagram in the vortex flowmeter of the present invention.
FIG. 6 is a measurement waveform diagram in a conventional integrated detection unit structure.
FIG. 7 is a side sectional view of a conventional two-body detector.
FIG. 8 is an enlarged view of a vortex generator and a lift detection unit when the detection unit of FIG. 7 is viewed from above.
FIG. 9 is a side sectional view of a conventional integrated detection unit.
FIG. 10 is an enlarged view of the vortex generator when the detection unit in FIG. 9 is viewed from above.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Measurement pipeline 1a Pipe inner wall 1b Hole 2 Vortex generator 3 Lift detector 4 Piezoelectric bimorph sensor

Claims (7)

In a vortex flowmeter including a measurement pipe through which a fluid flows, a column-shaped vortex generator that generates a vortex in the fluid, and a lift detection unit that detects a lift acting on the vortex generator,
The vortex generator has a predetermined width (d) in a direction orthogonal to a flow direction of the fluid,
The lift detecting unit has a vane-like form, and is arranged behind the vortex generator in parallel with a flow direction of the fluid,
Wherein the distance from the upstream end of the vortex generator to the downstream end of the lift detector is L, and L / d is in the range of 0.5 to 2.5. Total. The vortex flowmeter according to claim 1, wherein a piezoelectric bimorph-type sensor is embedded in the vane-like lift detection unit. The vortex flowmeter according to claim 1, wherein a strain gauge is attached or inserted to a surface of the vane-shaped lift detection unit facing the surface. The vortex flowmeter according to any one of claims 1 to 3, wherein the vane-shaped lift detection unit is integrally attached to a central portion behind the vortex generator. The vortex flowmeter according to any one of claims 1 to 3, wherein the vane-shaped lift detector is separated from the vortex generator by a predetermined distance from a central portion behind the vortex generator. The vortex flowmeter according to any one of claims 1 to 5, wherein both ends of the vortex generator are edge processed. The vortex flowmeter according to any one of claims 1 to 6, wherein the measurement tube, the vortex generator, and the lift detection unit are integrally formed of a synthetic resin.

Images