JPS6215811B2 - - 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 to determine 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, according to Special Publication No. 52-25346,
two pressure extraction pipes that take pressure fluctuations out of the pipeline;
Flow rate measurement is provided with a communication pipe that connects both pressure take-off pipes so that the fluid in both pressure take-off pipes can freely reciprocate between the two pressure take-off pipes, and a detection element is placed in the communication pipe. The device is known (first conventional example).

Further, among conventional devices of this type, there is a device described in Japanese Patent Application Laid-open No. 48-30458 (second prior art example), which uses the pressure of a vortex to vibrate a diaphragm. This device is especially suitable for the third
According to the figure, a pressure sensitive plate is provided to detect the static pressure in the central passage 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 the second conventional device, in order not to disturb the Karman vortex street generated downstream of the vortex generating body, the pressure sensitive plate has a high spring constant as described above to reduce displacement of the pressure sensitive plate due to pressure fluctuations. It is integrally supported by a wide leaf spring support band. This wide leaf spring support band is fixed to the inner wall of the conduit.

By doing this, it is certain that the Karman vortex street generated downstream of the vortex generator 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.

Furthermore, when considering the incorporation of the second conventional example into the first conventional example, in the first conventional example, the condition is that the fluid in the communicating pipe can freely reciprocate. The fluid under the pressure plate is 2
The pressure fluctuations move freely between the two pressure take-off tubes, and as a result, the pressure fluctuations, rather than acting on the pressure plate,
It flows through the communication conduit below the pressure-sensitive plate, making measurement difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of these points, and an object of the present invention is to provide a Karman vortex flowmeter that can respond sensitively to minute pressure fluctuations even in a low flow velocity region where pressure fluctuations are small.

[Means for solving problems]

In order to achieve such an objective, the present invention
The diaphragm is formed from a predetermined portion of a plate-like member that remains after cutting off a predetermined portion into a predetermined shape, and the plate-like member further includes a pair of span band portions that support the diaphragm, and the span band portion. The vibrator formed of the diaphragm, the span band portion, and the frame configured in this manner is The frame portion is housed in a vibration chamber arranged outside the conduit so as to be fixed to the vibration chamber, and the vibration chamber is divided into two by a vibration plate, and one of the vibration chambers is divided into two by a vibration plate. is provided with a means for detecting the displacement of the diaphragm, and the other oscillation chamber is divided into two small chambers by symmetrically dividing the axis of rotation of the diaphragm into two by a protrusion, and the pressure is applied to each of the small chambers. The present invention is characterized in that an inlet for introducing fluctuation is provided, and a tension applying means is provided for applying tension to the span band portion.

[Effect]

By doing the above, it is possible to detect vortices while reducing the influence of contamination, etc., and also to reduce the mutual interference of vortices generated on both sides of the vortex generator, thereby eliminating the influence of external vibrations on the diaphragm. .

〔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 an AA cross-sectional view of the vortex generator in Figure 1, Figure 3 is an enlarged cross-sectional view of the vortex detection section viewed from the fluid flow direction, Figure 4 is a plan view of the vibrator, and Figure 5. 6 is a side sectional view of the vortex detection section, FIG. 6 is a configuration diagram of a displacement detection sensor that detects the displacement of a vibrator, and a characteristic diagram showing the characteristics of the sensor. FIG. 7 is a diagram showing another embodiment of the displacement detection sensor. FIG.

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, reference numeral 8 denotes a vibrator made of thin metal with a thickness of about 20 μm, which includes a diaphragm 9 on which vortex pressure acts, and a diaphragm 9 that is held on a line-symmetrical axis that includes its center of gravity. A pair of span bands 10a and 10b for causing torsional vibration and a frame 11 serving as a fixed end of the span bands are integrally molded from a single metal plate having a substantially constant thickness. Therefore, the mass of the diaphragm 9 is kept balanced with respect to its central axis. In addition, the span band 10a
The torsional spring constant determined by the dimensions 10b and 10b is designed to be as low as possible so that the diaphragm 9 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. Note that 11a 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 (not shown) having substantially the same shape corresponding to the shape of the vibrator 8.
By sequentially stacking the lower plate 13, the vibrator 8, and the upper plate 14 on top of the vibrator 5, the vibrator 8 is held, and a vibration chamber 16 and span band storage chambers 17a and 17b are formed.
The vibration chamber 16 is connected to the top 2 by the vibration plate 9 of the vibrator 8.
6. The lower chamber 19a, 19b is approximately divided into two chambers, and the chamber formed by the pressure receiving plate 9 and the lower plate 13 is provided at a position facing the rotation axis of the diaphragm 9 of the lower plate 13. The protrusion 18 bisects the chambers 19a and 19b, and the chambers 19a and 19b have holes 20a and 2, respectively.
It communicates with the slits 7a and 7b of the vortex generating body 2 via 0b. This protrusion 18 has chambers 19a, 19
The purpose is to prevent fluid flow between the protrusions 18 and diaphragm 9 and to transmit the pressure change of the vortex from the slit 7a or 7b to the diaphragm 9 without loss. It is desirable that the thickness be as small as possible without inhibiting the torsional vibration of the plate 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 Figure 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. A tension force is applied by pressing between the vibrator 8 and the protrusion 22, 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 upper surface of the room 9. That is, the optical system is entirely located within the chamber 26, thereby preventing direct contact with the fluid. Further, at the other end of this optical fiber, a light emitting element 27 and a light receiving element 28 are provided.
will be 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 generating body 2 (on the slit 7b side), the pressure near the slit 7b is lower than that near the slit 7a on the opposite side, so the pressure is communicated with the slit 7b. The pressure in the chamber 19b that is open is also lower than the pressure in the chamber 19a that communicates with the slit 7a on the opposite side. For example, if we consider the balance of forces around the rotational axis of the diaphragm 9 with reference to FIG.
In this case, the pressure applied to the lower surface of the chamber 19b is lower than that of the chamber 19a, so a clockwise moment corresponding to the pressure difference between the chambers 19a and 19b acts on the diaphragm 9. This causes the diaphragm 9 to rotate clockwise, but the amplitude of this rotation is regulated by the bottom and top surfaces of the oscillation chamber 16. Next, when a vortex is formed on the opposite side of the vortex generator, the pressure in the chamber 19a increases
Since the pressure is lower than the pressure b, the diaphragm 9 is displaced counterclockwise, but in this case as well, the amplitude is regulated by the bottom and top surfaces of the oscillation 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 torsional vibration does not occur. 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. Note that even if tension is applied to the span band in this manner, the torsional spring constant thereof is hardly affected, so that the vibration resistance can be improved without reducing the vortex detection sensitivity.

In this way, the vibrator 8 performs torsional vibration within the vibration chamber 16 as vortices are generated. It is important that the pressure change of the vortex be applied directly to the diaphragm 9 without loss. For this purpose, in the present invention, slits 7a and 7b are provided at the axial ends of the vortex generating body 2, so that the pressure change of the vortex can be controlled over the shortest distance between the chambers 19a and 19b.
is introduced into the chamber 19 by the protrusion 18.
The leakage between the chamber 26 and the chambers 19a and 19b is extremely small, and the gap between the periphery of the diaphragm 9 and the wall of the vibration chamber 16 also reduces the leakage between the chamber 26 and the chambers 19a and 19b, so that pressure can be received without loss. The pressure of the vortex acts on the plate (diaphragm), thereby making it possible to stably detect the vortex.

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 randomly arranged on the end face 31 facing the diaphragm 9, and the optical axis is aligned with the diaphragm 9.
They are placed almost perpendicularly to each other. As shown in FIG. 6b, the amount of reflected light from the diaphragm 9 decreases as the reflective 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, does not require optical axis adjustment, and has great practical effects. Note that, as described above, the optical system consisting of the optical fiber 23 and the reflective surface is connected to the vibration chamber 16.
Since the optical system is located in the room 26 and does not come into direct contact with the fluid, 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. This has the advantage of facilitating signal processing. 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 device of the second conventional example, the pressure sensitive plate is supported by a leaf spring support band having a high spring constant, so the resonance frequency of the pressure sensitive plate is very large.

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 a 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 device of the second conventional example, the resonance frequency of the pressure sensitive plate is very high, so 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 device of the second conventional example, there is a risk that the pressure sensitive plate may be destroyed by the applied pressure during resonance. This also occurs in the combination of the first conventional example and the second conventional example.

(3) In the present invention, the vibrator 8 consisting of the diaphragm 9, the span band parts 10a and 10b, and the frame part 11 has the frame part 11 in the vibration chamber 16 disposed outside the fluid conduit 1. The vibrating chamber 16 is fixedly housed in the vibrating chamber 16, and the vibrating chamber 16 is divided into two parts, and one vibrating chamber is provided with displacement detecting means for the vibrating plate 9, and the other vibrating chamber is provided with a displacement detecting means for the vibrating plate 9. are inlet ports 20a, 2 that introduce pressure fluctuations.
0b is provided.

By doing this, the vortex pressure change acting part (inlet ports 20a, 20b) and the diaphragm 9
displacement detection means are isolated by the diaphragm 9 itself.

Therefore, according to the present invention, the displacement detecting means of the diaphragm 9 is less likely to come into direct contact with the fluid, and vortices can be detected with less influence from contamination and the like.

(4) In the present invention, in that case, the other vibration chamber is divided into two by the projection 18 symmetrically about the rotation axis of the diaphragm 9 to form two small rooms 19a and 19b, and each small Inlet ports 20a and 2 for introducing pressure fluctuations into the chambers 19a and 19b, respectively
0b is provided.

By doing this, the vortices generated on both sides of the vortex generator 2 can be transmitted to each small room 19a, 1.
9b is introduced independently. Moreover, the pressure fluctuation caused by the vortex is caused by, for example, one of the inlet ports 20
Flow from a to the other inlet 20b is completely prevented by the protrusion 18.

Therefore, according to the present invention, the vortices generated on both sides of the vortex generator 2 have less mutual interference, and the pressure fluctuations caused by the vortices affect the entire diaphragm 9. Measurements can be performed with high detection sensitivity.

(5) 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. The vibration chamber is divided into two parts by the vibration plate, and one vibration chamber is provided with displacement detection means for the vibration plate, and the other vibration chamber is provided with a protrusion 1.
8 symmetrically divides the rotational axis of the diaphragm into two to form two small chambers 19a and 19b, and each of the small chambers is provided with an inlet for introducing the pressure fluctuation, and the span band A Karman vortex flowmeter characterized by comprising a tension applying means for applying tension to the section.