JPH04256811A - Karman vortex flowmeter and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to measure the flow speed and the flow rate of fluid to be measured with high accuracy by fixing the end part of the first flange having the free surface to which a strain detecting element is attached to the second flange holding a vortex detecting body. CONSTITUTION:A first flange 31 has a free surface 31a as a diaphragm. The entire surface of a fixed end part 31b is welded and fixed to a second flange 21 in an airtight manner. Therefore, the contact of a strain detecting element 12 and a fluid to be detected can be prevented. An upstream-side columnar body 23 and a force receiving part 33 constitute a Karman generating body in a broad meaning. At this time, the bending moment with respect to the free surface 31a on the side of a balance weight 35 caused by inertial force when a vortex detecting body 3 receives external vibration and the bending moment caused by inertial force on the side of the force receiving part 33 have the same magnitude in the reverse directions in this constitution. Thus, the inertial bending moment with respect to the free surface 31a when the vortex detecting body 3 receives the external vibration can be cancelled.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a Karman vortex flowmeter that measures the flow velocity of a fluid by detecting the frequency of the Karman vortex street generated on both sides of a vortex generator placed in the flow of a fluid to be measured. In particular, the present invention relates to a Karman vortex flowmeter that eliminates the influence of external vibrations and shocks, and a method for manufacturing the same.

0002

[Prior Art] As a conventional example of this type of Karman vortex flowmeter, as described in Japanese Patent Publication No. 58-4967, a stress detection section made of a piezoelectric element is used to generate a vortex using a sealed body such as a glass material. It is well known to have a structure in which the vortex generating body is insulated and sealed inside the body to detect pressure changes that occur in the cross section of the vortex generating body due to the action of alternating force due to the Karman vortex. Although the Karman vortex flowmeter has the advantage that the stress detection section is less likely to get dirty or deteriorate because the stress detection section and the fluid to be measured do not come into contact with each other, it is susceptible to various external vibration noises transmitted through the pipes. When this exists, vibrations in the same mode as the pressure of the vortex occur in the vortex generator, resulting in a disadvantage that the S/N ratio is small and accurate measurement cannot be performed.

[0003] As a solution to this drawback, the
There is a Karman vortex flowmeter equipped with a vibration compensator as described in Japanese Patent No. 3-32127. This Karman vortex flowmeter includes a vortex generator that extends into the pipe through the side wall of the pipe through which the fluid to be measured flows, and a vibration compensator that extends to the outside of the pipe. A first vibration sensor is embedded in the part where the vibration is located, and a second vibration sensor is embedded in the vibration compensator located outside the pipe, and the first vibration sensor is embedded in the vibration compensator located outside the pipe. The purpose is to electrically eliminate external vibration noise components contained in the output signal of the vibration sensor, and detect a signal with a frequency corresponding only to the frequency of the Karman vortex of the vortex generator.

0004

[Problems to be Solved by the Invention] In the Karman vortex flowmeter equipped with the conventional vibration compensation device as described above, there are two vibration sensors: a first vibration sensor inside the pipe and a second vibration sensor outside the pipe. Since external vibration noise is electrically canceled by performing predetermined calculations using output signals from multiple sensors, the characteristics of each vibration sensor and the subsequent measurement circuit affect measurement accuracy. Therefore, it is necessary to correct the output by taking into consideration variations in these sensor characteristics and circuit characteristics. Therefore, it is necessary to perform so-called actual flow adjustment, in which the output of the sensor is adjusted while actually causing the fluid to be measured to flow in the pipe and vibrating the vortex generator. This actual flow adjustment work is very complicated and requires skill, and as a result, there is a problem in that the cost of adjusting the Karman vortex flowmeter is extremely high.

The present invention was made in view of the above-mentioned problems, and its object is to be able to measure the flow velocity of a fluid to be measured with high precision without being affected by external vibrations or shocks, and to It is an object of the present invention to provide a Karman vortex flowmeter that does not require actual flow adjustment and a manufacturing method suitable for manufacturing the same.

[0006]

[Means for Solving the Problems] In order to solve this problem, the Karman vortex flowmeter according to the present invention includes a columnar section and a columnar column provided at one end of the column section so as to extend into the inside of the pipe. a force-receiving portion; a balance weight provided at the other end of the support portion such that its position can be adjusted along the axis of the support portion;
a first flange provided approximately at the center of the support column and having a free surface to which a strain detection element is attached, and an end of the first flange is connected to the conduit through a second flange. It is characterized by having a fixed vortex detector.

[0007] When the diameter of the pipe to which the Karman vortex flow meter is attached is small, the force receiving part of the vortex detector is connected to the downstream columnar part of the vortex generating body consisting of the upstream columnar body and the downstream columnar body. It can be used as a body. If the diameter of the pipe to which the Karman vortex flowmeter is installed is large,
An opening passing through both side surfaces of the downstream columnar body and an insertion hole communicating with the opening are formed in the downstream columnar body, and the force-receiving part of the vortex detector is inserted into the insertion hole. It is desirable to keep the vortex generator independent from the vortex generator. Furthermore, the strain detection element of the vortex detector is provided with a pair of electrodes facing each other, one of which is two dividing electrodes arranged symmetrically with respect to a plane including the axes of the force receiving part and the pipe line, and the other is a pair of electrodes facing each other. is one common electrode corresponding to this partial electrode, and it is possible to configure the structure so that outputs are respectively taken out between this common electrode and each of the aforementioned partial electrodes.

[0008] Furthermore, the method for manufacturing a Karman vortex flowmeter according to the present invention includes: a support section; a columnar force receiving section provided at one end of the support section extending into the interior of the conduit; an upstream vortex detector comprising a balance weight provided at an end and a first flange having a free surface to which a strain sensing element is attached; and a second flange having a second flange to which the first flange is fixed at one end. A method for manufacturing a Karman vortex flowmeter comprising a side columnar body, the method comprising: providing a protrusion at an end of the first flange, bringing the protrusion into contact with a flange of the upstream columnar body; and the second flange are sandwiched between block-shaped electrodes, the first flange and the second flange are pressed through the electrodes, and electricity is applied between the electrodes, so that the second flange is The first flange and the second flange are welded by heating and melting the contact portion between the protrusion and the second flange.

[0009]

[Operation] In the Karman vortex flowmeter according to the present invention, if we consider the case where external vibration is applied to the vortex detector, the inertia force due to the external vibration in the direction perpendicular to the axis of the vortex detector will be on the balance weight side of the vortex detector. and the force-receiving section side at the same time. Therefore, the vortex detector is arranged so that the bending moment of inertia on the balance weight side and the bending moment of inertia on the force receiving part side with respect to the free surface of the first flange of the vortex detector are the same magnitude and in opposite directions. If it is supported by the end of the first flange, the output signal from the strain detection element attached to the free surface will have external vibration noise components canceled. On the other hand, since the pressure caused by the Karman vortex acts only on the force-receiving portion of the vortex detector, the accurate vortex frequency corresponding to the generation of the Karman vortex can be detected from the strain detection element attached to the free surface of the first flange. can be detected.

Further, according to the method of manufacturing a Karman vortex flowmeter according to the present invention, the protrusion provided at the end of the first flange of the vortex detector and the part of the second flange that contacts the protrusion. Since the current is concentrated in the area, welding can be completed in a short time. Therefore, residual stress due to heat generation during welding is not generated on the free surface of the first flange of the vortex detection body to which the strain detection element is attached. Therefore, the free surface of the vortex detector reliably responds to pressure changes due to the Karman vortices.

[0011]

[Embodiment] A first embodiment of the Karman vortex flowmeter according to the present invention will be described with reference to FIGS. 1 to 6. FIG. 1 is a schematic diagram of the first embodiment. In the figure, 1 is a pipe through which the fluid to be measured flows, 2 is a base screwed to the side wall of the pipe 1, and 3 is a vortex detector fixed to the side wall of the pipe 1 via the base 2. It is. The base 2 mainly includes a second flange 21 as a part fixed to the outer periphery of the side wall of the conduit 1, and a second
a support part 22 provided at the center of the flange 21 and fitted into the side wall; and an upstream columnar body 23 for supporting Karman vortex generation provided extending from the support part 22 into the inside of the conduit 1.
and a support portion 24 located at the tip of the upstream columnar body 23 and fitted into an opposing portion of the side wall of the conduit 1. Each of the support parts 22 and 24 is fitted into the side wall of the conduit 1 via each O-ring 4 and 5 in order to provide vibration isolation to the upstream columnar body 23.

The vortex detector 3 mainly consists of a first flange 31 fixed to the surface of the second flange 21;
The strut portion 3 extends from the flange 31 in the inner and outer directions of the conduit 1.
2, a force receiving part 33 which functions as a Karman vortex generating body and a detecting body, which is located at the tip of this force receiving part 33 and is fitted into the center of the support part 24 of the base 2 via an O-ring 6. It consists of a support part 34 and a balance weight 35 which has approximately the same mass as the force receiving part 33 and is provided at the tip of the support part 32 so that its position can be adjusted along the axial direction. Note that all of the above-mentioned constituent members constituting the vortex detector 3 are coaxial. Further, the O-ring 6 is used for vibration isolation for the end portion of the force-receiving portion 33. Further, the first flange 31 has a free surface 31a as a diaphragm, and the fixed end 31
The entire circumference of b is hermetically welded and fixed to the second flange 21. Therefore, it is possible to prevent the strain detection element 12 as a sensor from coming into contact with the fluid to be measured, and the sensor is less likely to become dirty or deteriorate.

Now, FIG. 2 is a sectional view taken along line A-A in FIG. The long base sides of the equilateral trapezoid in the cross section of the force section 33 are approximately the same length and are closely opposed to each other. These upstream columnar bodies 23 and force receiving portions 33 are
It constitutes a Karman generator in a broad sense, with the force receiving part 33 corresponding to a main part that generates a vortex, and the upstream columnar body 23 corresponding to a sub part supporting vortex generation. Note that the arrow Q indicates the flow direction of the fluid to be measured. What is important here is that when the vortex detector 3 receives external vibrations or shocks (hereinafter simply referred to as external vibrations), the bending moment (hereinafter referred to as inertial bending) on the balance weight 35 side with respect to the free surface 31a is caused by inertial force. moment) and
The bending moment due to the inertia force on the force receiving portion 33 side is configured to have the same magnitude and in opposite directions. In other words, the balance weight 3 has dimensions and weight roughly determined in advance so that the above conditions are met.
5 is finely adjusted in position. Thereby, the bending moment of inertia regarding the free surface 31a when the vortex detector 3 receives external vibration can be canceled.

FIG. 3 is a schematic diagram showing the above, in which the bending moment of inertia M1 regarding the free surface 31a
is due to the inertial force of each part indicated by the arrows acting on the lower part of the support column 32 and the force receiving part 33, and similarly, the inertial bending moment M2 is due to the inertia force of each part indicated by the arrow acting on the upper part of the support column 32 and the balance weight 35. This is due to the inertial force of each part, and the inertial bending moments M1 and M2 have the same magnitude and opposite directions with respect to the free surface 31a. In addition, FIG. 4 shows the bending moment M with respect to the free surface 31a of the force (vortex force) due to the Karman vortex indicated by the arrow that acts only on the force receiving part 33.
FIG. As is clear from the diagram,
The output of the strain detection element 12 fixed to the free surface 31a has a frequency corresponding only to the frequency of the Karman vortex, with the influence of external vibration removed.

Returning to FIG. 1 again, the strain detection element 12 is a ring-shaped piezoelectric element, and is attached to the upper surface of the free surface 31a. As shown in FIG. 5, which is a front view, and FIG. 6, which is a back view, this strain sensing element is constructed with a piezoelectric material sandwiched between the electrodes 12a and 12b, which are indicated by hatching.
, 12c, and 12d. Each electrode 12a, 12b is
A plane including each axis of the support portion 32 and the pipe line 1, that is, X
Fixed to the outer surface are two polarizing electrodes arranged symmetrically with respect to the plane perpendicular to the plane of the paper containing -X. Further, the electrode 12d is a common electrode corresponding to each of the electrodes 12a and 12b, which are divided electrodes, and is fixed to the inner surface. Note that the electrode 12c fixed to the outer surface in FIG.
is integrated with the electrode 12d, which is a common electrode, and serves as an output extraction section. That is, since it is difficult to take out the output from the inner electrode 12d, the output is taken out from between the electrode 12d via the electrically equivalent outer electrode 12c. As is clear from the above explanation, the piezoelectric element 12 acts on the force receiving part 33 shown in FIG.
- An output signal corresponding only to the alternating force in the Y direction (lift direction), in other words, only to the flow rate of the fluid from which the influence of external vibrations has been removed, is taken out in a form doubled by a well-known electronic circuit. become. This helps improve measurement sensitivity and accuracy.

Next, a second embodiment of the Karman vortex flowmeter according to the present invention will be explained based on FIGS. 7 to 9. This second embodiment is particularly suitable when the pipe line to which the vortex flowmeter is attached has a large diameter. The first embodiment described above has a simple structure and has the excellent effect of being able to remove external vibration noise, and is extremely useful when the diameter of the pipe through which the fluid to be measured flows is small. It is. However, when the pipe diameter becomes extremely large, the dimensions of the force-receiving part of the vortex detector also become longer, which lowers its natural frequency and causes resonance and malfunction when high-frequency external vibrations are applied. There is a risk of it being stored away. This is due to the fact that the force receiving part of the vortex detector has a function as a vortex generator.

Therefore, in the second embodiment, the force-receiving portion of the vortex detector is made independent from the vortex generator, thereby making it possible to apply it to a large diameter pipe. FIG. 7 is a schematic configuration diagram of the second embodiment, FIG. 8 is a cross-sectional view of the second embodiment as seen from the direction B-B in FIG. 7, and FIG. 9 is a cross-sectional view of the vortex generator portion of the base. be. Note that constituent members similar to those described in the first embodiment are given the same numbers and explanations are omitted.

In FIGS. 7 and 8, 7 is a base having a vortex generator made of two columnar bodies, and 9 is a circuit box fixing member, each of which is fixed to the conduit 1. Base 7
includes a second flange 71 screwed to the conduit 1, a support portion 72 fitted into the side wall of the conduit 1, and this support portion 72.
An upstream columnar body 73 with a triangular cross section and an isosceles trapezoidal cross section downstream columnar body 75 which are provided to extend into the interior of the conduit 1 and constitute a vortex generator, and a support part 72 of the side wall of the conduit 1 and a support portion 74 that is fitted into and fixed to a location facing the support portion 74 with a screw. Then, the second flange 71 of the base 7
The end of the first flange 31 of the vortex detector 3 is welded and fixed to the surface of the vortex detector 3, and a circuit box 76 surrounding the vortex detector 3 is provided. Furthermore, a circuit board 8 to which leads for extracting signals from the strain detection element 12 of the vortex detector 3 are connected is installed at the top of the circuit box 76 . Note that an O-ring 10 is inserted between the side surface of the circuit box 76 and the side surface of the circuit box fixing member 9 to make the circuit portion airtight. In particular, the downstream columnar body 75, which can be said to be the main part of the vortex generator, has openings 75b and 75c penetrating both side surfaces thereof, and communicates with these openings 75b and 75c along the axis of the columnar body 75. An insertion hole 75a is provided. In addition, the vortex detector 3 is
The end of the first flange 31 is welded to the surface side of the second flange 71 of the base 7, and the length dimension is such that it reaches the center of the conduit 1. Part 3
3 is inserted into the insertion hole 75a of the downstream columnar body 75. Note that the lower end of the force receiving portion 33 is supported and fixed within the insertion hole 75a by an O-ring 5.

In the second embodiment configured as described above, the Karman vortex is detected as follows. That is, as shown in FIG. 9, which is a cross-sectional view of the vortex generator portion of the base 7, when the Karman vortex 13 is generated by the upstream columnar body 73 and the downstream columnar body 75, the opening 7 of the downstream columnar body 75
The pressure on the opening 75b side becomes lower than the pressure on the 5c side, and the force receiving part 33 of the vortex detector 3 deforms toward the opening 75b. Since Karman vortices are generated alternately in the vicinity of both side surfaces of the downstream columnar body 75, the force receiving portion 33 is arranged along Y-Y in the figure.
It will vibrate in the direction. Since this vibration of the force receiving part 33 deforms the free surface 31a of the vortex detector 3, the free surface 31a
A voltage signal corresponding to the vortex frequency can be obtained from the strain detection element 12 attached to the surface of a. Note that even when external vibration is applied, the external vibration noise can be canceled by the bending moment due to the inertial force acting on the portion above the free surface 31a of the vortex detector 3, as in the first embodiment described above. Can be done.

As is clear from the above description, according to the second embodiment of the Karman vortex flowmeter according to the present invention, the force receiving portion 33 of the vortex detector 3 is inserted into the insertion hole 75a of the downstream columnar body 75. The vortex detector 3
Even if the diameter of the conduit 1 is large, it is possible to reduce the size of the force receiving part 33 of the vortex detector 3 and set the natural frequency of the detection part to be high. It has the advantage that it will not malfunction even if vibration is applied. Furthermore, even when measuring flow rates for multiple channels with different diameters, one vortex detector 3 can be used in common, eliminating the need to manufacture vortex detectors of different sizes for each channel diameter. , Therefore, manufacturing costs can be reduced.

Next, a method of manufacturing a Karman vortex flowmeter according to the present invention will be explained based on FIGS. 10, 11, and the above-mentioned FIG. 1. Note that FIG. 10 is a sectional view of a main part of the first flange of the vortex detector, and FIG. 11 is a diagram for explaining the outline of the manufacturing method. One of the Karman vortex flowmeters to which the manufacturing method of the present invention is applied has the configuration shown in FIG. Force receiving part 33 that functions as a body
and a vortex detector 3 having a first flange 31, and the vortex detector 3 is fixed by welding the first flange 31 to the second flange 21.

In the Karman vortex flowmeter constructed as described above, the points to be considered when welding the first flange 31 and the second flange 21 are as follows when conventional full-circumference arc welding is used. This will be explained using an example. First, in the case of full-circumference arc welding, the periphery of the fixed part 31b of the first flange 31 of the vortex detector 3 is sequentially welded so as to go around the first flange 31. and second
There is a problem in that local thermal strain occurs at the welded part with the flange 21, and as a result, the axis of the upstream columnar body 23 and the axis of the force receiving part 33, which functions as the downstream columnar body, are likely to tilt. . If there is an inclination of this axis, not only will it have a negative effect on the generation of Karman vortices, but there is also a risk that the proportional relationship between the vortex frequency and the flow velocity will be disrupted. Secondly, since the time required for welding is long, residual stress is likely to be generated on the free surface 31a of the first flange 31 to which the strain sensing element 12 is attached, which may cause variations in the sensor output.

Therefore, in the method of manufacturing a Karman vortex flowmeter according to the present invention, the first flange 31 of the vortex detector 3 is
A protrusion is provided on the fixed portion 31b of the vortex detector 3, and the vortex detector 3 is disposed with the second flange 21 of the upstream columnar body 23 using only this protrusion, and resistance welding is performed using this protrusion. Figure 1
0 is a sectional view of a main part of the first flange 31 of the vortex detector 3. FIG. As shown in the figure, an annular projection 31c having a trapezoidal cross section is provided on the lower surface side of the fixing portion 31a of the first flange 31. To perform resistance welding using this projection 31c, as shown in FIG. 11, first place the lower electrode member 15a of the lower electrode 15 having a split structure inside the guide 14 of the welding device, The positioning pin 16 and spring 17 are inserted into the lower electrode member 15b, and the lower electrode member 15b is attached. Next, using the positioning pin 16 as a guide, the second flange 21 of the upstream columnar body 23 is attached to the lower electrode member 15.
Further, the vortex detector 3 is arranged so that only the protrusion 31c of the first flange 31 is in contact with the second flange 21, and the upper electrode member 18b and the upper electrode 18a are placed on top of the vortex detector 3. Attach. These operations maintain the horizontality of the first flange 31 of the vortex detector 3 and the second flange 21 of the upstream columnar body 23 during welding, so that The inclination with the force receiving part 33 having the function of . In this state, a force of, for example, 300 kgf is applied from above and below to the electrodes 18 and 15 for 2 seconds, and a current of 12.5 kA is applied for 20 msec during the pressurization.
By flowing c, the protrusion 3 of the first flange 31 of the vortex detector 3
1c and the second flange 21 of the upstream columnar body 23, current and pressure are concentrated, and due to the contact resistance, exothermic melting occurs, and welding is completed in a short time of 2 seconds. In this embodiment, the protrusion 31c of the first flange 31 has a trapezoidal cross-sectional shape, but any cross-sectional shape may be used as long as the current and pressing force are concentrated on the protrusion 31c.
For example, it may be a semicircle or a triangle.

As is clear from the above description, according to the method of manufacturing a Karman vortex flowmeter according to the present invention, the vortex detector 3
Since the first flange 31 of the first flange 31 can be welded without causing distortion due to processing, the inclination of the axis can be kept small, and therefore,
The generation of vortices and the variation in the proportionality constant between vortex frequency and flow velocity can be suppressed within a certain range. Furthermore, when detecting the strain generated on the free surface 31a of the first flange 31 due to the pressure of the vortex, since no residual stress or strain remains, symmetrical strain occurs, and the variation in left and right outputs is reduced. small. Furthermore, since the heat generation time during welding is short and the transmission of heat is small, welding can be performed after, for example, bonding a strain detection element such as a piezoelectric element to the free surface 31a of the first flange 31. It has the effect of being easy to work with and having a good yield.

[0025]

As explained above, the Karman vortex flowmeter according to the present invention has the following superior effects compared to the conventional technology. (1) It is possible to accurately measure flow rate and flow rate without being affected by external vibrations or shocks. (2) Since actual flow adjustment is not required, troublesome work can be avoided and costs can be reduced. (3) Since the output of the strain detection element corresponds only to the flow rate, the structure of the flowmeter is simplified, such as eliminating the need for an electronic circuit for vibration compensation, resulting in high reliability and low cost. Furthermore, by using the method for manufacturing the Karman vortex flowmeter according to the present invention, residual stress is not generated on the free surface of the vortex detector to which the strain detection element is attached, so that more accurate flow rate measurement is possible. A possible Karman vortex flow meter can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a first embodiment of a Karman vortex flowmeter according to the present invention.

[Figure 2] A-A sectional view in Figure 1

[Figure 3] Schematic diagram of inertia bending moment due to external vibration

[
Figure 4: Schematic diagram of bending moment due to vortex force

[Figure 5] First
Surface view of the piezoelectric element in the example of

[Fig. 6] Back view of the piezoelectric element in the first embodiment

FIG. 7 is a schematic configuration diagram of a second embodiment of the Karman vortex flowmeter according to the present invention.

[Figure 8] BB sectional view in Figure 7

[Figure 9] A-A sectional view in Figure 7

FIG. 10 is a sectional view of a main part of a vortex detector used in the method for manufacturing a Karman vortex flowmeter according to the present invention.

FIG. 11 is a diagram for explaining the method for manufacturing the Karman vortex flowmeter according to the present invention.

[Explanation of symbols]

1 Pipeline 2 Base 21 Second flange 23 Upstream columnar body 3 Vortex detector 31 First flange 31a Free surface 31b Fixed end 31c protrusion 32 Strut part 33 Force receiving part 35 Balance weight 7 Base 71 Second flange 73 Upstream columnar body 75 Downstream columnar body 75a Insertion hole 75b Opening 75c opening 12 Strain detection element 12a　　　Electrode 12b Electrode 12c Electrode 12d Electrode

Claims (5)

[Claims] 1. A Karman vortex flowmeter that measures the flow velocity of a fluid by detecting a Karman vortex street generated downstream of a vortex generator vertically inserted into a pipe through which a fluid to be measured flows, comprising: A columnar force-receiving section provided at one end of the support section to extend into the inside of the pipe, and a balance weight provided at the other end of the support section so as to be adjustable in position along the axis of the support section. and a first flange provided approximately at the center of the support section and having a free surface to which a strain detection element is attached, and an end of the first flange connects to the pipe line through the second flange. A Karman vortex flowmeter characterized in that it is equipped with a vortex detector fixed to. 2. The Karman vortex flowmeter according to claim 1, wherein the vortex generator has a second flange to which the first flange is fixed at one end, and one end of the force receiving portion is inserted into the other end. A Karman vortex flowmeter comprising: an upstream columnar body made up of the force-receiving portion; and a downstream columnar body made of the force-receiving portion. 3. The Karman vortex flowmeter according to claim 1, wherein the second flange to which the first flange is fixed, and an upstream side provided extending from the second flange into the inside of the pipe line. A columnar body and a downstream columnar body are provided, and the downstream columnar body has an opening passing through both sides thereof, and an insertion hole communicating with the opening along the axis of the downstream columnar body. A Karman vortex flowmeter characterized in that the force receiving part of the vortex detector is inserted into the insertion hole. 4. The Karman vortex flowmeter according to claim 1, wherein the strain detection element of the vortex detector includes a pair of electrodes facing each other, one of which includes the respective axes of the force receiving portion and the conduit. two polarizing electrodes arranged symmetrically with respect to the plane,
A Karman vortex flowmeter characterized in that the other electrode is a common electrode corresponding to the partial electrode, and outputs are taken out between the common electrode and each of the partial electrodes. 5. A support section, a columnar force-receiving section provided at one end of the support section so as to extend into the inside of the conduit, a balance weight provided at the other end of the support section, and a strain detection element attached. A Karman vortex flowmeter comprising: a vortex detector comprising a first flange having a free surface attached to the flange; and an upstream columnar body having a second flange at one end to which the first flange is fixed. The manufacturing method includes providing a protrusion at an end of the first flange, bringing the protrusion into contact with the second flange, and sandwiching the first flange and the second flange between block-shaped electrodes. The first flange and the second flange are pressed through the electrode, and electricity is applied between the electrodes to generate heat and melt the contact portion between the protrusion of the first flange and the second flange. A method of manufacturing a Karman vortex flowmeter, characterized in that the first flange and the second flange are welded.