JPH07128102A - Karman vortex flowmeter - Google Patents

Abstract

PURPOSE:To improve not only stabilization of a measured value but a measuring accuracy by eliminating scattering of an output signal of a piezoelectric element. CONSTITUTION:A piezoelectric unit 20 has a structure in which leads 22a, 22b, 22c are connected to electrodes 21a, 21b, 21c of a piezoelectric element 21 and an entirety is covered with an insulator 22. In this case, the element 21 is the same as a conventional example except a point that only a circular part of an electrode of a back surface side is not provided. The insulator 22 is selected from a polybutylene terephthalate or polyphenylene sulfide. Accordingly, when a strain occurs at the unit 20 together with a diaphragm upon reception of a force based on Karman vortex, scattering of its output signal is suppressed. Further, the insulator 22 has small difference of thermal expansion coefficient from that of the element 21 even in the case of any of the materials, and hence temperature characteristics of the output signal of the element is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a detection rod that receives a force based on a Karman vortex, and a diaphragm that causes strain, and a piezoelectric element for strain detection is electrically insulated on the surface of the diaphragm. The present invention relates to a fixed Karman vortex flowmeter, in particular, an improved Karman vortex flowmeter that stabilizes the output signal of a piezoelectric element and thus maintains and improves the measurement accuracy.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIGS. FIG. 5 is a side sectional view of the conventional example, and FIG. 6 is a transverse sectional view of the hole of the vortex generator with respect to the section AA of FIG. In FIG. 5, reference numeral 1 is a conduit through which the measurement fluid flows. Reference numeral 2 denotes a vortex generator, which is inserted into the pipe 1 so as to penetrate along the diameter thereof, and the penetrating portion is an upstream columnar body 11 having a triangular cross section,
Cylindrical protrusions 25, 26 for promoting the generation of Karman vortices are integrally formed at the upper and lower fitting positions of the pipe 1 and the downstream column 12 having a trapezoidal cross section. In addition, pipeline 1
O-rings, which are not labeled, are inserted at the fitting points above and below and for both fluid sealing and vibration isolation.
Reference numeral 3 denotes a vortex detector, which comprises a disk-shaped diaphragm 3a, a mandrel 3b extending inward in the axial direction, and a threaded rod extending outwardly. The mandrel 3b has two stages, the small diameter portion on the tip side is located inside the hole 28 formed in the columnar body 12, and the cushioning material 4 is inserted at the root of the small diameter portion for preventing resonance. It Insulating plate 6, piezoelectric element 8, insulating plate 9 and disc spring are mounted on the upper surface of diaphragm 3a in the order that they fit into the threaded rod.
9 are stacked and fixed by screwing the balance weight 10. Here, the piezoelectric element 8 detects a minute displacement of the lower rod-shaped portion of the vortex detector 3 as a displacement of the diaphragm 3a, converts it into an electric signal, and outputs it. Balance weight 10
Has a function of canceling the influence of vibration factors other than the Karman vortex received by the vortex detector 3, for example, the vibration of the conduit 1 as well as the function of the nut for fixing the screw.

In FIG. 5, when the fluid flows to the right in the conduit 1, a Karman vortex is generated in the vicinity of the columnar body 12 by the upstream side columnar body 11 and the downstream side columnar body 12, and this generated Karman The change in fluid pressure caused by the vortex is transmitted to the mandrel 3b at the tip of the vortex detector 3. The transmission of this pressure change is such that in FIG. 6, the pressure guiding hole 13 is penetrated through the columnar body 12 at a position corresponding to the mandrel 3b so as to communicate with the hole 28 of the columnar body 12 at a right angle to the flow and parallel to the paper surface. Through. Now, the small displacement of the rod-shaped part of the vortex detector 3 including the mandrel 3b is converted into the displacement of the diaphragm 3a, and then the piezoelectric element
The signal is converted into a corresponding electric signal by the 8 and output.

By the way, the piezoelectric element 8 and the insulating plates 6 and 7
Will be described in more detail. FIG. 3 is a conventional piezoelectric element, (a) is a plan view thereof, and (b) is a rear view thereof. In FIG. 3 (a), an arcuate electrode 8a is arranged on the lower side and an arcuate electrode 8b is arranged on the upper side symmetrically with respect to the horizontal axis passing through the center of the piezoelectric element 8. The tongue-shaped electrode 8c shown at the right end is
This is the folded back portion of the annular electrode 8c in FIG. 3 (b). The arc of each electrode 8a, 8b and the ring of electrode 8c correspond.
In Fig. 5, the force due to Karman vortex perpendicular to the paper is
A bending moment about the horizontal axis contained in the paper is applied to the diaphragm 3a. This bending moment causes bending strain in the diaphragm 3a, and in response thereto, the piezoelectric element 8 outputs a voltage signal. That is, each electrode 8 of FIG.
Distortions of the same magnitude and different signs are generated in a and 8b, and voltages of the same magnitude and different signs are generated between the electrodes 8a and 8c and between the electrodes 8b and 8c. Based on each of these voltages, a calculation circuit (not shown) calculates the flow velocity and flow rate.

FIG. 4 is a plan view of one of the insulating plates relating to the conventional piezoelectric element, and FIG. 4 (b) is a plan view of the other. One insulating plate 6 is the rear side of the piezoelectric element 8 (Fig. 3).
(See (b)), and the other insulating plate 7 comes into contact with the upper surface side of the piezoelectric element 8 (see FIG. 3 (a)). The insulating plate 6 has no electrodes, but the insulating plate 7 is provided with electrodes 7a, 7b, 7c.
Electrodes 7a, 7b, 7c of insulating plate 7 and electrodes 8a, 8b, 8c of piezoelectric element 8
(Tongue part) overlap and make contact with each electrode
The voltage signal from the piezoelectric element 8 is taken out from the ends of the straight portions of 7a, 7b, 7c. The electrode 7c is for grounding.

[0006]

In the conventional example, when the piezoelectric element 8 is distorted together with the diaphragm 3a due to the force based on the Karman vortex, the electrode 8c and the insulating plate on the back side of the piezoelectric element 8 are distorted.
Electrodes 8a, 8b, 8c on the upper surface side of the piezoelectric element 8 between the upper surface of 6 and
And the electrodes 7a, 7b, 7c of the insulating plate 7 may slip or the contact area may vary. This is
Variations occur in the output signal of the piezoelectric element, which in turn results in unstable measured values and reduced measurement accuracy.

The problem to be solved by the present invention is to solve the above problems of the prior art, improve the output signal of the piezoelectric element so as not to cause variations, stabilize the measurement value, and improve the measurement accuracy. The purpose is to provide a Karman vortex flowmeter designed for the purpose.

[0008]

A Karman vortex flowmeter according to claim 1 is a detection rod that receives a force based on the Karman vortex,
In a flowmeter in which a strain-producing diaphragm is integrally configured, and a piezoelectric element for strain detection is provided on the surface of the diaphragm in an electrically insulated manner, the piezoelectric element has a lead wire connected to each electrode. The whole is covered with an insulator.

A Karman vortex flowmeter according to a second aspect is the flowmeter according to the first aspect, wherein the insulating material is engineering plastic polybutylene terephthalate. A Karman vortex flowmeter according to a third aspect is the flowmeter according to the first aspect, wherein the insulator is polyphenylene sulfide of engineering plastic.

[0010]

In the Karman vortex flowmeter according to any one of claims 1 to 3, since the entire piezoelectric element is covered with the insulator, the piezoelectric element is deformed together with the diaphragm under the force due to the Karman vortex. When tapped, there is no slippage or variation in contact area between the electrode and the electrode of the insulating plate unlike in the conventional example. Moreover,
Since the output signal of the piezoelectric element is taken out through the lead wire connected to the electrode, the variation of the output signal is suppressed.

Particularly, in the Karman vortex flowmeter according to the second or third aspect, since the insulator is polybutylene terephthalate or polyphenylene sulfide, respectively, the difference in the coefficient of thermal expansion from the piezoelectric element is small, and it depends on the temperature change. The distortion of the piezoelectric element is reduced, and the temperature characteristic of the output signal of the piezoelectric element is suppressed.

[0012]

Embodiments of the Karman vortex flowmeter according to the present invention will be described below with reference to the drawings. This embodiment is different from the conventional example in the insulating structure of the piezoelectric element.
FIG. 1 is a plan view of the piezoelectric element unit of the embodiment, and FIG. 2 is a side sectional view of the piezoelectric element unit. The piezoelectric element unit 20 has a structure in which lead wires 22a, 22b, 22c are connected to the electrodes 21a, 21b, 21c of the piezoelectric element 21, respectively, and the whole is covered with an insulator 22. Here, the electrodes 21a, 21b, and 21c of the piezoelectric element 21 are the electrodes 8a and 8c of the piezoelectric element 8 of the conventional example.
It is the same except that b, 8c and the ring portion of 8c on the back side are not provided. The insulator 22 is selected from engineering plastic polybutylene terephthalate or polyphenylene sulfide.

Now, the entire piezoelectric element 21 is covered with the insulator 22 and configured as the piezoelectric element unit 20, which does not come into contact with the insulating plate. Therefore, the piezoelectric element unit 20 receives the force based on the Karman vortex, and the piezoelectric element unit 20 together with the diaphragm 3a. When 20 is distorted, the respective electrodes 21a, 21b, 21c do not slip or vary in contact area between the electrodes of the insulating plate, unlike in the conventional example. Moreover, the output signal is the lead wires 22a, 22b, 2 connected to the electrodes 21a, 21b, 21c.
Since it is taken out through 2c, the variation of the output signal is suppressed. Furthermore, the insulator 22 is small in the coefficient of thermal expansion from the piezoelectric element 21 in any of the above-described materials, the distortion of the piezoelectric element due to temperature change is small, and the temperature characteristic of the output signal of the piezoelectric element is small. It can be suppressed. Incidentally, the expansion coefficient of the piezoelectric element is 1 × 10 ^-5 , and that of polybutylene terephthalate and polyphenylene sulfide is 1.7 × 10 ^-5 , respectively.

[0014]

In the Karman vortex flowmeter according to any one of claims 1 to 3, since the entire piezoelectric element is covered with the insulator, the piezoelectric element is distorted together with the diaphragm by the force based on the Karman vortex. When this occurs, there is no slippage or variation in contact area between the electrode and the electrode of the insulating plate, unlike in the conventional example. Moreover, since the output signal of the piezoelectric element is taken out through the lead wire connected to the electrode, the variation of the output signal is suppressed. Therefore, the simple measure of covering the entire piezoelectric element with an insulator can stabilize the measurement value of the flow rate measurement and thus maintain and improve the measurement accuracy.

Particularly, in the Karman vortex flowmeter according to claim 2 or 3, the insulator is polybutylene terephthalate,
Alternatively, since polyphenylene sulfide is used, the coefficient of thermal expansion is small, the distortion of the piezoelectric element due to temperature change is small, and the temperature characteristic of the output signal of the piezoelectric element is suppressed. Therefore, the influence of the temperature change is suppressed, and the stabilization of the measured value of the flow rate measurement, and thus the maintenance and improvement of the measurement accuracy are supported.

[Brief description of drawings]

FIG. 1 is a plan view of a piezoelectric element unit according to an embodiment of the present invention.

FIG. 2 is a side sectional view of the same piezoelectric element unit.

FIG. 3A is a plan view of a conventional piezoelectric element,
(b) Rear view

FIG. 4 is a plan view of one of the insulating plates related to the conventional piezoelectric element, and (b) is a plan view of the other.

FIG. 5 is a side sectional view of a conventional example.

FIG. 6 is a transverse sectional view of a hole portion of a vortex generator in a conventional example.

[Explanation of symbols]

 1 Pipeline 2 Vortex Generator 3 Vortex Detector 3a Diaphragm 3b Detection Rod 20 Piezoelectric Unit 21 Piezoelectric Element 21a, 21b, 21c Electrode 22 Insulator 23a, 23b, 23c Lead Wire

Claims (3)

[Claims] 1. A detection rod which receives a force based on a Karman vortex,
In a flowmeter in which a strain-producing diaphragm is integrally configured, and a piezoelectric element for strain detection is provided on the surface of the diaphragm in an electrically insulated manner, the piezoelectric element has a lead wire connected to each electrode. The Karman vortex flowmeter, characterized in that it is entirely covered with an insulator. 2. The Karman vortex flowmeter according to claim 1, wherein the insulating material is engineering plastic polybutylene terephthalate. 3. The Karman vortex flowmeter according to claim 1, wherein the insulator is an engineering plastic polyphenylene sulfide.