JPS6220489B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is a Karman vortex flow rate sensor that measures the flow velocity or flow rate of a fluid by detecting the vibration frequency of a Karman vortex street generated on the downstream side of a columnar object inserted into a fluid flow. Regarding meters (current meters).

In general, in this type of flowmeter, the Karman vortex street generated downstream of a columnar object becomes very weak in the low flow velocity region, so a highly sensitive detector is required to detect the vortex. Both methods that use highly sensitive heat rays and ultrasonic waves electrically amplify delicate analog signals, so the temperature characteristics and stability of the detector and detection circuit have a large effect on measurement accuracy and measurement range. That is, a detector used for detecting this kind of vortex in a low flow rate region is required to be less susceptible to these influences and to be highly sensitive.

As this type of Karman vortex flowmeter, the applicant proposed the following (Japanese Unexamined Patent Publication No. 80524/1983).

That is, FIG. 1 is an overall configuration diagram of this flowmeter, FIG. 2 is a sectional view taken along line A-A of the vortex generator shown in FIG. FIG. 4 is a plan view of the vibrator, and FIG. 5 is a side sectional view of the vortex detection section.

In FIG. 1, 1 is a conduit, 2 is a pair of vortex generators for generating a Karman vortex, and 3 is a vortex detector. As shown in FIG. 2, the vortex generator 2 is
It is composed of a pair of isosceles triangular upstream columnar bodies 4 and isosceles trapezoidal downstream columnar bodies 5, and these two columnar bodies 4 and 5 are inserted perpendicularly to the flow with a constant interval 6 between them. . Slits 7a and 7b are provided on both sides of the downstream columnar body 5 in the vicinity of its axial end, and are used to guide the pressure change of the generated vortex. In Fig. 4, 8 is a vibrator made of thin metal with a thickness of about 20μ, and a diaphragm 9 on which the pressure of the vortex acts.
A pair of span bands 10a and 10b for holding this diaphragm 9 on a line-symmetrical axis including its center of gravity to perform torsional vibration, and a frame portion 11 serving as a fixed end of this span band are held at approximately constant positions. It is made by integrally molding from a single thick metal plate.
The mass of the diaphragm 9 is kept balanced with respect to its central axis. In addition, span bands 10a and 10
The torsional spring constant determined by the dimension b is
It is designed to be as low as possible so that the diaphragm 9 can be displaced by a sufficient angle even in response to subtle pressure changes of the vortex, and its resonance frequency is also designed to be as small as possible. In addition, 1
1a and 11b are punched parts. In FIG. 3, a housing 12 houses the vibrator 8, and is composed of a lower plate 13 and an upper plate 14. The lower plate 13 and the upper plate 14 are provided with facing grooves having substantially the same shape corresponding to the shape of the vibrator 8.
By sequentially stacking the vibrator 8 and the upper plate 14, the vibrator 8 is held, and the vibration chamber 16 and the span band storage chambers 17a and 1 are
7b is formed. The vibration chamber 16 is divided into upper (26) and lower (19a, 19) by the vibration plate 9 of the vibrator 8.
b) The two rooms are divided into approximately two halves, and the room formed by the diaphragm 9 and the lower plate 13 is divided by a projection 18 provided on the lower plate 13 at a position opposite to the axis of rotation of the diaphragm 9. , rooms 19a and 19
It is divided into two halves, rooms 19a and 19b.
b communicate with the slits 7a, 7b of the vortex generator 2 via holes 20a and 20b, respectively.
The purpose of this protrusion 18 is to prevent fluid flow between the chambers 19a and 19b and to transmit the pressure change of the vortex from the slit 7a or 7b to the diaphragm 9 without loss. The gap with the plate 9 is preferably as small as possible without inhibiting the torsional vibration of the diaphragm 9, for example, about 0.1 to 0.2 mm. Furthermore, for the same purpose, it is desirable that the gap between the periphery of the diaphragm 9 and the oscillation chamber 16 is also approximately the same value. In FIG. 5, reference numeral 21 denotes an adjustment screw for applying tension to the span bands 10a and 10b, which is provided on the central axis of the span band 10b.
Tension is applied by pressing between the fixed portion on the peripheral edge of b and the protrusion 22 provided on the lower plate 13, and this tension prevents the vibrator 8 from flexural vibration. As shown in FIG. 3, 23 is a vibrator 8
It is a reflection type optical fiber for detecting the angular displacement of the room 26, and has two reciprocating optical paths 24 and 25, with each optical axis facing the upper surface of the diaphragm 9 of the vibrator 8 almost perpendicularly to the upper surface of the diaphragm 9 of the vibrator 8. It opens into the wall. That is, the optical system is entirely located within the chamber 26, thereby preventing direct contact with the fluid. Also, at the other end of this optical fiber,
A light emitting element 27 and a light receiving element 28 are provided. Note that 29 is a detection circuit section comprising the light emitting and light receiving elements 27 and 28, an amplification and shaping circuit (not shown) for the output signal of the light receiving element, and the like.

Next, the operation will be explained.

For example, in FIG. 2, when a vortex 30 is generated above the vortex generator 2 (on the slit 7b side), the vortex 30
Since the pressure near the slit 7a on the opposite side is lower than that near the slit 7a on the opposite side, the pressure in the chamber 19b communicating with the slit 7b is also lower than the pressure in the chamber 19a communicating with the slit 7a on the opposite side. here,
For example, if we consider the balance of forces around the rotational axis of the diaphragm 9 with reference to FIG. In this case, since the chamber 19b is lower than the chamber 19a, a clockwise moment corresponding to the pressure difference between the chambers 19a and 19b acts on the diaphragm 9. The vibration plate 9 rotates clockwise, but the amplitude of this rotation is regulated by the bottom and top surfaces of the vibration chamber 16. Next, when a vortex is formed on the opposite side of the vortex generator, the pressure in the chamber 19a increases to the pressure in the chamber 19b.
, the vibration plate 9 is displaced counterclockwise, but in this case as well, its amplitude is regulated by the bottom and top surfaces of the vibration chamber 16, as described above. That is, the vibrator 8 performs one round of torsional vibration as a pair of vortices is generated, but the amplitude is regulated by the wall surface of the vibration chamber 16, so even if the pressure of the vortices changes, the amplitude remains almost constant. It will be preserved. Here, since the mass of the diaphragm 9 is substantially balanced around its central axis of rotation, inertial force due to external vibration is canceled out around the axis of rotation, and therefore no torsional vibration occurs. In addition, since tension is constantly applied to the span bands 10a and 10b, the vibrator 8 hardly follows external vibrations in the vertical direction, and from this point as well, it is possible to eliminate the influence of external vibrations. becomes. Furthermore, even if tension is applied to the span band in this way, it has almost no effect on its torsional spring constant, so it has the effect of improving vibration resistance without reducing vortex detection sensitivity. be.

However, as a result of various experiments and research conducted by the present inventors, as shown in FIG. and housing 1
2 (that is, the lower plate 13 and the upper plate 14), the tension of the span bands 10a and 10b changes greatly due to heat due to the difference in their coefficients of thermal expansion. Even in the case where the It turned out that it would go away.

An object of the present invention is to provide a Karman vortex flowmeter in which the tension of the span band of the diaphragm is always constant even when temperature changes occur.

According to the present invention, such a stop is a spring constant for the span band portion existing between the fixed end of the span band support member and the fulcrum of the span band provided in the storage chamber for storing the span band. This is achieved by pressing with a small spring member.

Next, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 6 is a side sectional view of one embodiment of the present invention, and FIG. 7 is an enlarged side sectional view of the main part thereof. In FIGS. 6 and 7, parts having the same functions as those in FIGS. 1 to 5 are given the same numbers, and their explanations will be omitted.

In FIGS. 6 and 7, 30 is a tensioning mechanism for applying tension to the span bands 10a and 10b, 31 is a compression spring, 32 is a cap, and 33 is a light resin presser that presses the span band 10b. It is formed into a cylindrical shape with a bottom.
A rectangular protrusion 35 provided at the bottom of this presser 33 is guided by a rectangular guide hole 34 provided in the upper plate 14 so as not to rotate when the spring is compressed. 10b and the protrusion 22 provided on the lower plate 13 to apply tension, and this tension causes the vibrator 8 to
deflection vibration is prevented. In addition, spring 3
1 is housed in the cylindrical body of the presser 33, and the cap 3
2 prevents it from falling off.

As mentioned above, in FIG. 6, when vortices are generated alternately on both sides of the vortex generating body 2, the diaphragm 9 is It rotates in the direction in which the side where the vortex is generated is pulled, and as a result, one reciprocating vibration is obtained with the generation of a pair of vortices. This vibration change is transmitted through the optical fiber 2.
3. It is detected by an optical displacement detection means consisting of a light emitting element 27 and a light receiving element 28, and the waveform is shaped by the detection circuit section 29 to obtain a pulse output corresponding to the vortex frequency.

By the way, when there is a sudden temperature change, the oscillator 8
Since there is a transient temperature difference between the housing 12 and the housing 12 (that is, the upper plate 14 and the lower plate 13), the length of the span band changes due to the difference in thermal expansion even if these materials are the same. However, in the present invention, as described above, since the span band is pre-deflected and tension is applied by the compression spring 31 with a small spring constant, the variation in length due to thermal expansion can be absorbed.
In addition, since the tension is kept almost constant, the span band will not be damaged or its vibration resistance will not deteriorate due to external vibrations.

As explained above, according to the present invention, since the span band of the vibrator is configured to be pressed by a spring, the tension of the span band remains constant regardless of temperature changes, and as a result, the tension of the span band remains constant regardless of temperature changes. Therefore, there is an advantage that there is no reduction in vibration resistance or damage to the span band.

[Brief explanation of the drawing]

Figure 1 is an overall configuration diagram of the flowmeter proposed by the applicant, and Figure 2 is a diagram of the vortex generator shown in Figure 1.
A sectional view, FIG. 3 is an enlarged cross-sectional view of the vortex detection section viewed from the fluid flow direction, FIG. 4 is a plan view showing the vibrator, FIG. 5 is a side sectional view of the vortex detection section, and FIG. FIG. 7 is a side cross-sectional view of one embodiment of the present invention, and FIG. 7 is an enlarged side cross-sectional view of the main part thereof. DESCRIPTION OF SYMBOLS 1... Pipeline, 2... Vortex generator, 3... Vortex detection section, 8... Vibrator, 9... Vibration plate, 10a, 10
b... Spun band, 11... Frame, 11a, 1
1b...Punching part, 12...Housing, 13
... lower plate, 14 ... upper plate, 15
...Flange, 16...Vibration chamber, 17a, 17b
...Spun band storage room, 19a, 19b, 26
...Room, 18, 22...Protrusion, 20a, 20b
... hole, 21 ... screw, 23 ... optical fiber,
24, 25... optical path, 27... light emitting element, 28...
...Light receiving element, 29...Detection circuit unit, 30...Tension applying mechanism, 31...Compression spring, 32...Cap, 33...Press element.

Claims (1)

[Claims] 1. A vibrating member that vibrates in response to pressure fluctuations that occur alternately near both sides of a Karman vortex generator inserted into a fluid flow is mounted in a span band so that its mass is balanced with respect to the rotation axis that includes its center of gravity. hold,
A spring member with a small spring constant presses the span band portion that exists between the fixed end of the member that supports the span band and the fulcrum of the span band provided in the storage chamber that stores the span band. Karman vortex flow meter.