JPS6215810B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention detects the vibration frequency of a Karman vortex street generated on the downstream side of a columnar object inserted into a fluid flow, and determines the fluid flow velocity or Related to Karman vortex flowmeters (current meters) that measure flow rates.

[Conventional technology]

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 minute 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.

By the way, as an example of a conventional device of this type in which a diaphragm is vibrated by the pressure of a vortex, there is a device described in Japanese Patent Laid-Open No. 48-30458. This device, in particular, according to its FIG.
A pressure sensitive plate is provided to detect the static pressure in the passage at the center of the vortex generated downstream of the vortex generator. In that case, the pressure-sensitive plate is integrally supported by a wide leaf spring support band, which has a high spring constant and is formed to reduce displacement of the pressure-sensitive plate due to pressure fluctuations. Ru.

[Problem that the invention seeks to solve]

In order not to disturb the Karman vortex street generated downstream of the vortex generator, such conventional devices use a wide plate with a high spring constant to reduce the displacement of the pressure sensitive plate due to pressure fluctuations, as described above. It is integrally supported by a spring support band. This wide leaf spring support band is fixed to the inner wall of the conduit.

By doing so, it is certain that the Karman vortex street generated downstream of the overgenerating body will not be disturbed by the displacement of the pressure sensitive plate.

However, for this purpose, the pressure sensitive plate must have a wide leaf spring support band to reduce its displacement due to pressure fluctuations.

However, especially in the low flow velocity region, the pressure change due to the generation of vortices is extremely small. Therefore, in such a conventional device, conversely, in a low flow rate region where pressure fluctuations are small, the pressure sensitive plate becomes unable to respond to minute pressure fluctuations, and therefore measurement becomes impossible in a low flow velocity region. problems arise.

Therefore, the present invention has been made in view of the above points, and provides a Karman vortex flowmeter that can respond sensitively to minute pressure fluctuations even in a low flow velocity region where pressure fluctuations are small, without disturbing the Karman vortex street. The purpose is to

[Means for solving problems]

In order to achieve such an objective, the present invention
A diaphragm is formed from a predetermined portion of a plate-like member that is cut off into a predetermined shape, and the plate-like member further includes a pair of spun band portions that support the diaphragm, and the spun band. the diaphragm, the diaphragm, the diaphragm, the diaphragm, the diaphragm, and the diaphragm. is housed in a vibration chamber disposed outside the fluid conduit such that the frame portion is fixed to the vibration chamber, and tension applying means for applying tension to the span band portion is provided. It is characterized by:

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention;
Figure 2 is a sectional view taken along line AA of the vortex generator in Figure 1;
The figure is an enlarged cross-sectional view of the vortex detection unit viewed from the fluid flow direction, Figure 4 is a plan view of the vibrator, Figure 5 is a side sectional view of the vortex detection unit, and Figure 6 detects the displacement of the vibrator. An explanatory diagram showing the displacement detection sensor and its characteristics. FIG. 7 is a configuration diagram showing another embodiment of the displacement detection sensor.

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
The diaphragm 9 is designed to be as low as possible so that it can be displaced by a sufficient angle even in response to minute 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 roughly divided into two halves by the diaphragm 9 of the vibrator 8 into two chambers, an upper 26 and a lower 19a, 19b, and the chamber formed by the diaphragm 9 and the lower plate 13 is divided into two by the diaphragm 9 of the vibrator 8. 1
A protrusion 18 provided at a position opposite to the rotation axis of the diaphragm 9 of No. 3 is divided into two chambers 19a and 19b, and the chambers 19a and 19b are connected to the vortex through holes 20a and 20b, respectively. Generator 2
It communicates with the slits 7a and 7b. 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 between the diaphragm 9 and the diaphragm 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 has a similar value. In FIG. 5, 21 is the span band 10
This is an adjustment screw for applying tension to a and 10b, and is provided on the central axis of the span band 10b.
Tension is applied by pressing between the fixed portion on the periphery of the oscillator 8 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, reference numeral 23 is a reflective optical fiber for detecting the angular displacement of the vibrator 8, and has two reciprocating optical paths 24 and 25, with each optical axis connected to the diaphragm of the vibrator 8. It opens into the wall of the room 26, facing almost perpendicularly to the top surface of the room 9. That is, the optical system is entirely located within the chamber 26, thereby preventing direct contact with the fluid. Furthermore, a light emitting element 27 and a light receiving element 28 are provided at the other end of this optical fiber. Note that 29 indicates the light emitting and light receiving elements 27 and 2.
8. A detection circuit section including an amplification and shaping circuit (not shown) for the output signal of the light receiving element.

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. .

Next, detection of the number of displacements of the vibrator 8, that is, the vibration frequency, will be explained with reference to FIGS. 3, 6, and 7.

The vibration frequency is detected by detecting a change in the amount of light reflected from the upper surface of the diaphragm 9 using the optical fiber 23 in this case. That is, the optical fiber 23 has two optical paths 24 and 25, and these two optical paths are arranged randomly on the end face 31 facing the diaphragm 9, and the optical axis is connected to the diaphragm 9. They are arranged almost vertically facing each other. As shown in FIG. 6b, the amount of reflected light from the diaphragm 9 decreases as the reflection surface of the diaphragm rotates, so two optical pulse outputs are obtained with each reciprocating vibration of the oscillator. . Here, since the displacement of the vibrator 8 is substantially constant, the optical output is also substantially constant, and therefore the vortex frequency can be detected with a simple circuit configuration.
As described above, the method of detecting reflected light has a simple structure and does not require optical axis adjustment, and has great practical effects. Incidentally, as described above, the optical system consisting of the optical fiber 23 and the reflective surface is located within the chamber 26 of the vibration chamber 16 and does not come into direct contact with the fluid, so that it is possible to prevent the optical system from being contaminated.

In the above detection mechanism, the optical axis of the optical fiber 23 is provided almost perpendicular to the diaphragm 9;
As shown in FIG. 7, the optical axis of the optical fiber 23 is connected to the diaphragm 9.
The vibration plate 9 may be provided so as to be deviated in advance from the normal line by the maximum angular amplitude θm on the vibration surface. This method uses the part of the curve in Figure 6b where the slope is almost uniform, so as is clear from the figure, the detection sensitivity is good even for minute angular displacements, and the output signal is almost sinusoidal. Therefore, there is an advantage that signal processing becomes easy. In this case, it goes without saying that the peak value of the amount of reflected light moves to the right in FIG. 6b. Note that the configuration of this optical fiber is not limited to this embodiment, and any configuration may be used as long as it can effectively detect changes in the amount of reflected light.

〔Effect of the invention〕

As explained above, according to the present invention, the following advantages are achieved.

(1) In the present invention, the diaphragm 9 is formed from a predetermined portion of a single plate-like member that is cut off into a predetermined shape, and the diaphragm 9 is further supported on the plate-like member. A pair of span band parts 10a and 10b, and this span band part 10
A frame portion 11 that supports a and 10b is formed,
In addition, a rotation axis of the diaphragm 9 is formed by the span band parts 10a and 10b.

By doing so, the diaphragm 9
Spun band section 10 with extremely small spring constant
a and 10b, it can respond favorably to pressure fluctuations caused by Karman vortices.

Therefore, according to the present invention, measurement can be performed with sufficient sensitivity even in a low flow rate region with small pressure fluctuations.

(2) In the present invention, the diaphragm 9 is supported by the span band parts 10a and 10b.

By doing this, the spring constant of the span band portions 10a, 10b is small, so the resonant frequency of the diaphragm 9 becomes small.

On the other hand, in the above-mentioned conventional device (Japanese Unexamined Patent Publication No. 48-30458), the pressure sensitive plate is supported by a plate spring support band having a high spring constant, so the resonance frequency of the pressure sensitive plate is very high.

However, as is well known, pressure fluctuations caused by Karman vortices increase in proportion to the square of the frequency at which such Karman vortices occur.

Therefore, in the present invention, since the resonance frequency of the diaphragm 9 is small, the resonance point of the diaphragm 9 is in the low frequency region, and therefore the pressure acting on the diaphragm 9 is small. Therefore, in the present invention, the diaphragm 9 is not destroyed by the applied pressure during resonance.

On the other hand, in the conventional device described above, since the resonance frequency of the pressure sensitive plate is very high, the resonance point of the pressure sensitive plate is in a high frequency region, and therefore the pressure acting on the pressure sensitive plate is large. Therefore, in the conventional device described above, there is a risk that the pressure sensitive plate may be destroyed by the applied pressure during resonance.

(3) In the present invention, the vibrator 8 consisting of the diaphragm 9, the span band parts 10a, 10b, and the frame part 11 has the frame part 11 in the vibration chamber 16 disposed outside the fluid conduit 1. It is housed in a fixed manner in the vibration chamber 16.

By doing this, the displacement of the diaphragm 9 is controlled by the vibration chamber 1 located outside the fluid conduit 1.
6, so it does not affect the fluid in the pipe.

Therefore, according to the present invention, no matter how large the displacement of the diaphragm 9 becomes, the Karman vortex street alternately generated within the conduit 1 is not disturbed.

(4) In the present invention, a tension applying means (consisting of screws 21 and protrusions 22 in the embodiment) is provided for applying tension to the span band portion 10b.

By doing this, deflection vibration of the vibrator 8 (ie, the diaphragm 9) is prevented.

Therefore, according to the present invention, the influence of external vibrations can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention;
Figure 2 is a sectional view taken along line AA of the vortex generator in Figure 1;
The figure is an enlarged cross-sectional view of the vortex detection unit viewed from the fluid flow direction, Figure 4 is a plan view showing the oscillator, Figure 5 is a side sectional view of the vortex detection unit, and Figure 6 is for detecting displacement of the oscillator. FIG. 7 is a configuration diagram showing another embodiment of the displacement detection sensor. Description of symbols 1...Pipe line, 2...Vortex generator, 3...Vortex detection section, 4...Upstream columnar body, 5...Downstream columnar body, 6...Gap, 7a, 7b...Slit, 8...Vibrator, 9...Vibration plate , 10a, 10b... Spun band, 11... Frame part, 11a, 11b... Punching part, 12... Housing, 13... Lower plate, 14... Upper plate, 15... Flange, 16... Vibration chamber, 17a, 1
7b... Spun band storage room, 19a, 19b, 2
6...Room, 18, 22...Protrusion, 20a, 20b...
Hole, 21...Screw, 23...Optical fiber, 24,2
5... Optical path, 27... Light emitting element, 28... Light receiving element, 2
9...Detection circuit section, 30...Vortex, 31...Optical fiber end face.

Claims (1)

[Claims] 1. A diaphragm that vibrates in response to pressure fluctuations that alternately occurs near both sides of a Karman vortex generator inserted into a fluid flow, and the vibration frequency of the diaphragm is used to determine the flow of the fluid. In a Karman vortex flowmeter for measuring flow rate, the diaphragm 9 is formed from a predetermined portion of a plate-shaped member that is cut off into a predetermined shape, and the diaphragm is further attached to the plate-shaped member. A pair of supporting span band parts 10a and 10b and a frame part 11 supporting the span band parts are formed, and the rotating shaft of the diaphragm is formed by the span band parts, and is configured in this way. A vibrator 8 consisting of a vibrating plate, a span band portion, and a frame portion is housed in a vibrating chamber 16 disposed outside the fluid conduit such that the frame portion is fixed to the vibrating chamber. A Karman vortex flowmeter characterized in that the span band section is further provided with tension applying means for applying tension to the span band portion.