JPH01224625A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To enable high-sensitivity detection by forming the detecting element of a vortex detector by using a high polymer piezoelectric film. CONSTITUTION:A vortex generation body 2 is fixed in a flow pipe 1 on its diameter by heat clamping and so sectioned in the shape of an isosceles triangular columnar body which has its bottom surface on an upstream side and its vortex on a downstream side. A rectangular recessed part 21 is bored in the flank of the vortex generation body 2 and a piezoelectric detecting element 3 is embedded in the recessed part 21 almost in level with the flank of the vortex generation body 2. This element is constituted by sticking electrodes 32 made of metal foil on both top and reverse surfaces of the high polymer piezoelectric film 31, and lead wires are connected to the electrodes 32 to output a piezoelectric signal. Here, fluid which flows under constant fluid pressure generate Karman vortexes by passing by the vortex generation body 2 and varying pressure caused by the vortex generation generates a thickness- directional voltage difference as a signal proportional to the vortexes between the films 31 on both flanks of the vortex generation body 2, and this signal is outputted as a flow rate signal by a signal processing means.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex flowmeter equipped with a vortex detector using a polymer piezoelectric film as a vortex detection element.

A conventional Karman vortex flowmeter has a main body that includes a flow tube, a vortex generator disposed in the flow tube, and a detector that detects the Karman vortex flowing out into the vortex generator in proportion to the flow. It has a simple configuration consisting of a vortex signal processing section and an eddy signal processing means that processes the vortex signal detected by the vortex detector to produce a flow rate signal, and has the advantage of measuring a wide flow rate range with a digital flow rate signal. It has become one of the mainstream.

As a vortex detection means in a vortex flow meter, there are two methods: one is to directly detect pt+% itself, which is generated in proportion to the flow velocity, and the other is to indirectly detect it from the fluctuating pressure caused by the generation of the vortex. Conventional vortex detection means Direct detection methods include detecting changes in flow caused by vortices from resistance changes in thermal detection elements or modulation by ultrasonic waves, while indirect detection methods detect fluctuating pressure caused by vortices from vortex generators. There are methods to determine the amount of strain and displacement using integrated or separate strain gauges, pressure elements, electrostatic electromagnetic or optical elements, etc. In the direct method, the sensing element detects direct waves. 41 Since the detection element comes into contact with a constant fluid, there are problems such as a decrease in detection sensitivity due to fine particles, sticky substances, etc. contained in the fluid over a long period of time. In fluid measurement systems,
Vortex flowmeters using detection elements such as strain gauges and piezoelectric elements are commonly used. Although strain gauges have lower sensitivity than piezoelectric elements, their low impedance makes them advantageous in signal processing. However, they have the disadvantage of lacking sensitivity in small areas, so in recent years, vortex flowmeters using piezoelectric elements have become more common. A method of detecting flow rate using a piezoelectric element is disclosed in Japanese Patent Laid-Open No. 59-97007, which was proposed by the present applicant.

This vortex flowmeter is made by pasting piezoelectric elements on both sides of a rectangular thin elastic base plate, and covering the pasted surface with a high-insulating ceramic material.The piezoelectric element plate receives the fluctuating pressure of the vortex. The elastic base material is inserted coaxially into a cylinder parallel to the flow direction, and after insertion, the detection element, which is fixed with an insulating material such as glass, is attached to a hollow shaft coaxially drilled in the vortex generator. A signal output from a piezoelectric element within a detection element in response to fluctuating pressure introduced through a through hole that is inserted with one end fixed while maintaining a slight gap and communicated with the fluid to be measured in the hollow chamber. The vortex flow rate signal is transmitted based on the vortex flow rate signal.

Problems with the conventional technique The piezoelectric element in the conventional technique described above is a solid element, transmits stress through an elastic base material, and is a high impedance element, so even after it is inserted into a cylinder, it is difficult to use a highly insulating material such as glass. Since it is insulated and fixed, the rigidity of the sensing element is increased.
The high-sensitivity piezoelectric element has the characteristics of +r+, and since high temperature treatment is required for sealing, productivity is poor and the piezoelectric element is expensive. Furthermore, since the piezoelectric element is solid, the detection area is also limited, which limits the range of application.

In order to solve the problems of the prior art mentioned above, the present invention uses a highly sensitive and flexible polymeric piezoelectric film as a vortex detection element. The purpose is to expand the applications of vortex flowmeters by taking advantage of their large piezoelectric properties in the thickness direction, and furthermore, by taking advantage of their high sensitivity and flexible characteristics, they can be used to develop inexpensive and highly sensitive vortex flowmeters (11). There are others whose purpose is to provide a meter.

As is well known, polymer piezoelectric films are made of polymer electret obtained by polarization treatment of polar polymers such as polyvinylidene fluoride (PVDF), polymers and ferroelectric ceramics. A composite electret 1 obtained by polarizing a mixture of fine particles or a composite type in which ceramic particles are embedded in a single layer in a plastic film are in practical use. PVDF in the former is (-CH
.

It is known that -CF2-)n polymer has β-crystalline PVDF, in which the dipoles of CF and CF are oriented in the same direction, and when polarized at high temperature, it exhibits large piezoelectric properties in the stretching direction and thickness direction. In addition, mechanically, the flexibility of the polymer, the processability, φ fins, sound η and p impedance are low, and electrically, the voltage output coefficient (k constant) is higher than that of PZT.
(zirconate titanate 3-4), BaTi0. (barium titanate) etc. solid pressure 1' (from τ element, equivalent to -1
; is large and Q is small, so mechanical resonance is less likely to occur and a detection element with excellent S/H can be obtained. The latter composite material also has similar properties. Gold Jfi box electrodes are attached to both sides of the polymer piezoelectric film in the above, and conductive wires are welded to the electrode foils and a /B force is applied.

FIG. 1 shows an example of the outline construction of the vortex flow meter of the present invention.
) Figure is a view of the flowmeter as seen from behind the flow, Figure (c) is (
b) It is a sectional view taken along the line CC in the figure.

Are you talented at drawings? 1 is a cylindrical flow tube, and the vortex generator 2 is fixed on the inner diameter of the flow tube 1 by a flexible fit or the like, and the cross-sectional shape is a two-dimensional shape with the bottom on the upstream side and the apex on the downstream side. It is a columnar body in the shape of an equilateral triangle.

A rectangular recess 21 is bored in the side surface of the vortex generator, and the piezoelectric detection element 3 is buried in the recess 21 so as to be substantially flush with the side surface of the vortex generator 2. . The piezoelectric detection element 3 has electrodes 32 made of gold λIIt foil on both the front and back surfaces of the polymer piezoelectric film 31, as shown in FIG.
is attached, and a lead wire 34 is led out from the electrode 32.
Outputs piezoelectric signals. The entire detection element including the polymer piezoelectric film 31, electrodes 32, and part of the lead wires 34 is covered with a thin insulating film 33.

Next, the operation of the piezoelectric detection element 3 buried in the recessed part 21 of the vortex generator 2 and covered with insulation as described above will be described.

Fluid flowing under a constant fluid pressure generates a Karman vortex by passing through the vortex generator, and due to the fluctuating pressure caused by this vortex generation, there is a gap in the thickness direction between the polymer piezoelectric films 31 on both sides of the vortex generator 2. A voltage difference is generated as a signal proportional to the eddy, and this is output as a flow rate signal by a signal processing means (not shown).

FIG. 2 shows a vortex generator having the same external dimensions as the vortex generator 2 shown in FIG. , which shows the shape of a vortex generator that shows an attempt to improve the pressure conduction method for the piezoelectric detection element 3 in order to enable more sensitive vortex detection. FIG. 3B is a cross-sectional view taken along arrows EE in FIG. 3B, which is a partial side sectional view, and FIG. That is, the concave portions 2 are formed on both side slopes of the vortex generating body 2 having an isosceles triangular cross section.
Open cavity 23 is formed by boring cavity 23 with an area smaller than 1.
By communicating the opening groove 22 formed vertically along the long side with respect to the opening cavity 23, and maintaining the pressure inside the opening cavity 23 at the same pressure as the downstream pressure of the vortex generating body 2. , an alternating pressure is applied to the piezoelectric detection element 3 buried in the recessed part 21 from both the front and back surfaces, and not only the thickness effect of the polymer piezoelectric film 31 but also the piezoelectric output in the stretching direction, which has a high piezoelectric effect, can be used as a detection signal. .

FIG. 3 shows that the piezoelectric detection element 3 is not embedded in the vortex generator 2, but is alternately arranged in the cross section of the flow path Av composed of the side surface of the vortex generator 2 and the flow tube 1 as vortices are generated. Taking advantage of the fact that a flow velocity change occurs and a pressure difference is generated, the flow tube wall 11 in the vicinity opposite to the side surface of the vortex generator 2 is moved along the flow tube wall 11 so that it becomes flush with the flow tube wall 11. This figure shows another vortex flowmeter which is buried in the same manner as shown in FIG. The view (b) is a cross section taken along the arrow F-F in the figure (,), and the signal voltage of the piezoelectric detection element 3.3 is
The signal is guided inside the flow tube 1 along the wall surface 11 via a terminal 34 outside the flow tube to a signal processing means (not shown).

FIG. 4 shows a vortex generator 2 in which the piezoelectric detection element 3 of the present invention is applied to a suitable vortex generator previously proposed by the present applicant, and FIG. G-line sectional view, (b
) is a partial side view of the vortex generator 2, in which the vortex generator is viewed from the flow direction.

It is a composite body consisting of 1.2.3 elements 24.25.26. The first element 24 is a cross-sectional view of an isosceles triangle having an apex on the upstream side, the second element 25 has a side parallel to the bottom of the first element 24, and the third element 26 has a side parallel to the second element 25. It is a T-shaped element with a vertical plate 261 parallel to the flow from the symmetrical position of its sides, each plane being separated by an equal distance lvQ, and all widths d seen in the flow direction being equal. Along the fluid flow, the combined vortex generator generates a strong vortex with the same effect as a single vortex generator, resulting in fluctuating pressure acting on both sides of the vertical plate 261.

In the present invention, this fluctuating pressure is detected by a piezoelectric detection element 3 disposed within the vertical plate 261, and the piezoelectric detection element 3 has both ends inserted into a rectangular through hole 262 penetrating the vertical plate 261. , upper and lower ends 2621 of the through hole 262
The piezoelectric detection element 3 is a beam with the end portions 2621 serving as both fixed portions, and the middle portion freely responds to the fluctuating pressure of the vortex. The shape of the flow tube 1 to which the vortex generator 2 described above is attached can be either circular or rectangular in cross section, considering that the vortex generator is an element constituting a vortex flowmeter. it is obvious.

FIG. 5 shows another invention in which a vortex detection plate 35 is disposed on the downstream side of the vortex generator 2, and the flow tube 1 is equipped with a rectifying grid 52 as shown in FIG. The main body is axially symmetrical, and is narrowed by a continuous curved surface 53 from a large-diameter inlet 51 with a rectangular cross section toward the rear, and continues to a small-diameter outlet 54 with a constant rectangular cross section. A flow tube 1 having a circular cross section as shown in FIG. 1 may be used. The vortex detection plate 35 is shown in FIG.
FIG. 1(b) is an example of the piezoelectric detection element 3 shown in FIG.
The upper part is fixed to the holding base 561 of the lower fixing boss 56 by screws etc.
51, adjust the position of the upper fixing boss 55 so that the length of the vortex detection plate 35 in the flow tube 5 becomes L correctly, and fix the upper part of the vortex detection plate 35 to the upper fixing boss 55 with screws or the like. do. (c) is a diagram showing another embodiment of the embodiment shown in (b), unlike the embodiment shown in (b) where the vortex detection plate 35 is fixed at the upper and lower ends of the flow tube 5. , which is elastically supported at the bottom and fixed only at the top. In the figure, upper and lower fixing bosses 57 and 58
are fixed to the upper and lower walls (not shown) of the outflow portion 54 of the flow tube 5, and this interval is determined by the end of the metal rod 61 that protects and supports the vortex detection plate 35 with a slight gap on both sides. It is determined by the position of a plate-shaped stopper 611 provided in the section.

On the outer side of the stopper 611 of the metal rod 61, there are upper and lower fixing bosses 57 and 58 which are clamped and fixed to the stopper 611 and screws 612. The vortex detection plate 35 is fixed at the upper fixed boss 57, and its lower end is attached to a spring plate 62 supported at both ends by metal rods 61, 61 at the lower part of the lower boss 58.
It is elastically supported by a presser plate 63 made of an insulator fixed to the center of the holder, and is stretched with a certain elasticity.

The vortex detection plate 35 shown in FIGS. (b) and (C) described above is basically supported at both ends and has excellent vibration resistance.

FIG. 6 is an exploded perspective view showing the configuration of a vortex flowmeter in order to easily attach the vortex detection plate 35 to the flow tube 5 according to the present invention, and the flow tube 5 is shown in FIG. The flow tube shown is
The same reference numerals as in FIG. 5 are given to parts having the same functions as in FIG. 5, and explanations of each component will be omitted. A vortex generator insertion hole 541 and a vortex detection extraction insertion hole 542 are provided in the earthen wall of the outflow portion 54.
and each of the insertion holes 541 and 542
The vortex generating body 2 and the vortex detection plate 35 integrally fixed to the plate-like body 71 as the sensing unit 70 are inserted through the vortex generator 2 and the vortex detection plate 35 are housed in a predetermined positional relationship with respect to the flow tube 5, and the vortex flowmeter The flange 7 of the sensing unit 70
11.712.713 to the flange 81 of the amplifier unit 80
1. Flange 5 of flow tube 5 along with 812 (not shown) and 813
44° 545 and the screw 8 overlapping the fixing screw part 543
They are integrally fixed by screwing means such as No. 14. 6th
In the figure, the vortex generator 2 and the vortex detection plate 35 are arranged side by side in the sensing unit 70, but the first
If the piezoelectric detection element 3 is built into the vortex generating body 2 shown in FIGS. The insertion/extraction hole 542 is also unnecessary.

Effects As mentioned above, in the vortex flowmeter of the present invention having a vortex detection element using a polymer piezoelectric film, it is possible to detect excessively fluctuating pressure in comparison with a conventional strain gauge or a vortex flowmeter using a solid piezoelectric element. , enables highly sensitive detection not available with strain gauges, makes it possible to take advantage of flexible properties not found in solid piezoelectric elements, and improves vibration resistance properties that were not possible with conventional elements. Since the piezoelectric polymer film itself is a vibration-resistant member due to its low Q, it can be realized without special consideration. In this respect, the fifth
The double-end supported vortex detection plates shown in Figures (, ), (b), and (c) are less affected by external vibrations that are seen in conventional cantilever strain gauge systems, and in particular, It is possible to realize a vortex flowmeter with excellent vibration resistance in gas measurement, etc., and since it is made of inexpensive material, it is possible to provide an inexpensive vortex flowmeter.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the vortex flowmeter according to the present invention, in which (a) is a sectional view taken along the line A-A in FIG. The view is (c) and the view is (b).
A sectional view taken along the line C-C in the figure, (d) is a diagram showing details of the piezoelectric detection element, and FIG. 2 is a diagram showing the structure of a vortex generator as another embodiment of the present invention. ) is a cross-sectional view taken along line E-E in figure (b), figure (b) is a cross-sectional view taken along line D-D in figure (a), and FIG. 3 is a view showing another embodiment of the present invention. ,(a) The figure is
Figure (b) is a cross-sectional view taken along the line F-F in figure (a), and Figure 4 is a diagram showing another embodiment of the present invention. (b) is a sectional view taken along the line G-C in figure (b).
) is a partial side view of the vortex generator, FIG. 5 is a diagram showing another embodiment of the present invention, FIG. 5(b) is a diagram showing an example of the vortex detection plate 35 in FIG. C) The figure shows another example,
(d) is a sectional view taken along the line - in FIG. FIG. 1.5...flow tube, 2...vortex generator, 3.35...
Piezoelectric detection element, 31... Polymer piezoelectric film, 32.
··electrode. 33... Insulating film, 34... Lead wire. Figure 1 Figure 2 Figure 6 (0) (b+ Figure 5 (0) (b) (C)

Claims (1)

[Claims] 1. A flow tube through which a fluid to be measured flows, a vortex generator disposed in the flow tube to oppose the flow, and a Karman generated from the vortex generator in accordance with the flow of the fluid. A vortex flowmeter comprising a vortex detector that detects fluctuating pressure due to vortices, and which determines the flow rate from the vortex signal detected by the vortex detector, characterized in that the detection element of the vortex detector is made of a polymer piezoelectric film. A vortex flowmeter with a 2. The shape of the vortex generator is a columnar body with an isosceles triangular cross section, with the bottom facing the flow and the apex located on the downstream side, and both sides of the polymer piezoelectric film are covered with a flexible insulating film such as a resin film. A vortex flowmeter characterized in that piezoelectric detection elements are embedded flush with both slopes of a vortex generator. 3. Opening passes through at least part of the slopes on both sides of the vortex generating body having an isosceles triangular cross section to form a cavity, and the opening cavity is electrically connected to an opening groove bored vertically along the top side; The vortex flowmeter according to claim 2, wherein the opening groove communicates with the fluid to be measured. 4. A vortex flowmeter characterized in that a polymer piezoelectric film is insulated and pasted on both inner walls of the flow tube near the cross section of the flow tube including the vortex generator. 5. The shape of the vortex generator has a first element whose cross section is an isosceles triangle with an apex on the upstream side, a second element whose sides are parallel to the base of the first element and have the same length, and a second element whose cross section is an isosceles triangle with an apex on the upstream side. In a composite vortex generator having a T-shaped third element having sides parallel to the element and a T-shaped third element having a vertical plate parallel to the flow from a symmetrical position of the side, each side is in the form of a column with equal distances between the elements, A vortex flowmeter characterized in that a polymer piezoelectric film whose both sides are insulated is disposed within the vertical plate of the third element. 6. A polymer piezoelectric film is placed parallel to the flow at a flow tube diameter position parallel to the vortex generator downstream of the vortex generator, and reinforced by insulating treatment with resin coating on both sides. Features of vortex flowmeter. 7. The flow tube is an axially symmetrical body in which a large-diameter inlet with a constant rectangular cross section equipped with a rectifying grid is constricted by a continuous curved surface toward the rear and connected to a small-diameter outlet with a constant rectangular cross section, and the main body is A vortex flowmeter characterized in that at least a portion of the upper surface of the small-diameter outflow portion is opened, and the vortex generator and vortex detector according to claim 2, 3, 5, or 6 are installed as a unit in an insertable manner in the opening. .