JPS6257207B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a Karman vortex flowmeter that measures the flow velocity or flow rate of a fluid by detecting the frequency of Karman vortex streets generated on both downstream sides of a columnar object inserted into a fluid flow.

[Conventional technology]

Generally, in this type of flowmeter, the Karman vortex street generated downstream of a columnar object becomes very weak in the low flow velocity region, and therefore a highly sensitive detector is required to detect the vortex. Highly sensitive vortex detectors include devices that use hot wires, for example, but since these devices electrically amplify minute analog signals, the temperature characteristics and stability of the detector and detection circuit depend on the measurement accuracy and measurement range. The detection circuit has to be complicated in order to prevent temperature compensation and error differences due to electromagnetic noise, which reduces reliability and increases cost. Among conventional devices of this kind, a device that uses the pressure of a vortex to displace a diaphragm to facilitate signal processing and reduce the effects of ambient temperature and electromagnetic noise is disclosed in Japanese Utility Model Publication No. 46-21501, for example. There is a device. This is a system in which a vibration chamber is provided inside the vortex generator, and a vibrator consisting of a flat object with one end fixed to the wall of the vibration chamber is attached.The flow velocity or flow rate is determined from the vibration frequency of the vibrator. It is something to be measured.

[Problems to be solved by the invention]

This device has the advantage of a simple structure because it directly detects pressure changes caused by the generation of vortices as displacement or force. Especially in the low flow velocity region, the pressure change due to the generation of vortices is extremely small, so it is impossible to distinguish between vibrations caused by vortices and external vibrations, and therefore the vortex frequency cannot be detected accurately. The disadvantage is that it cannot be done. This invention was made in view of the above, and is a Karman vortex that is less affected by temperature and electromagnetic noise and is equipped with a detection means that can accurately detect only vibrations caused by vortices without being affected by external vibrations even in low flow velocity regions. The purpose is to provide a flow rate (current velocity) meter.

[Means to solve the problem]

In order to achieve such an objective, the present invention
A diaphragm is provided that vibrates in response to pressure fluctuations that occur alternately near both sides of a Karman vortex generator inserted into a fluid flow, and the diaphragm is in mass balance with respect to a rotation axis that includes its center of gravity. The Karman vortex flowmeter is configured to hold the diaphragm with at least one pair of span bands, optically detect the vibration displacement of the diaphragm with at least one pair of emitting and light-receiving elements, and measure the flow rate of the fluid from the vibration frequency of the diaphragm. The light emitting and light receiving elements are disposed so as to be offset from the diaphragm by the maximum angular amplitude of 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 vortex detection signal processing circuit diagram, FIG. 7 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. 8 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 71 and 72 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 101 and 102 for causing torsional vibration and a frame 11 serving as a fixed end of the span bands are integrally formed from a single metal plate of approximately constant thickness. , the mass of the diaphragm 9 is kept balanced with respect to its central axis. In addition, span bands 101, 10
The torsional spring constant determined by the time dimension of 2 is
It is designed to be as low as possible so that the diaphragm 9 is 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 111 and 112 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. 13, the vibrator 8, and the upper plate 14, the vibrator 8 is held, and a vibration chamber 16 and span band storage chambers 17a and 17b are formed. Vibration chamber 16
is the upper 26 and lower 19 by the diaphragm 9 of the vibrator 8.
1,192 The chamber is divided into two chambers, and is further formed by the pressure receiving plate 9 and the lower plate 13. Yotsute room 19
The chambers 191 and 192 communicate with the slits 71 and 72 of the vortex generator 2 through holes 201 and 202, respectively. The purpose of this protrusion 18 is to prevent fluid flow between the chambers 191 and 192 and to transmit the pressure change of the vortex from the slit 71 or 72 to the diaphragm 9 without loss. 9
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, reference numeral 21 denotes an adjustment screw for applying tension to the span bands 101 and 102, which is provided on the central axis of the span band 102. Lower plate 13
Apply tension by pressing between the protrusions 22 provided on the
This tension prevents flexural vibration of the vibrator 8. In FIG. 3, 23 is a light emitting element, and 24 is a light receiving element, each of which is arranged to face the upper surface of the diaphragm 9, and whose optical axis passes through the central axis of rotation of the diaphragm 9. . Reference numeral 25 denotes a detection circuit unit for driving the light emitting and light receiving elements 23 and 24 and processing the output signals, and as shown in FIG. 26 and a comparator 27 that converts this signal into pulses. 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 72 side), the pressure near the slit 72 is lower than that near the slit 71 on the opposite side, so that the vortex 30 is connected to the slit 72. The pressure in the chamber 192 that communicates with the slit 71 on the opposite side is also lower than the pressure in the chamber 191 that communicates with the slit 71 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 chamber 192 is lower than that of chamber 191, so a clockwise moment corresponding to the pressure difference between chambers 191 and 191 acts on 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 diaphragm 16. Next, when a vortex is formed on the opposite side of the vortex generator, the pressure in room 191 is reduced to
2, 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 torsional vibration does not occur. In addition, since tension is constantly applied to the span bands 101 and 102, the vibrator 8 hardly follows external vibrations in the vertical direction, and from this point of view 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 tension chamber 16 as vortices are generated, and in order to make this vibration occur regularly in a wide vortex frequency range ranging from 10Hz to 1KHz, for example. Therefore, it is important to make the pressure change of the vortex act directly on the diaphragm 9 without loss. For this purpose, in the present invention, slits 71 and 72 are provided at the axial ends of the vortex generating body 2, so that the pressure change of the vortex can be controlled between the chambers 191 and 192 through the shortest distance.
is introduced into the chamber 19 by the protrusion 18.
Since the leakage between the chamber 1 and the chamber 192 is extremely small, and the gap between the periphery of the diaphragm 9 and the wall of the vibration chamber 16 reduces the leakage between the chamber 28 and the chambers 191 and 192, the pressure receiving plate can be installed without loss. (diaphragm)
The pressure of the vortex acts on the vortex, which makes 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 described with reference to FIGS. 3, 6, 7, and 8. In this case, the vibration frequency is detected by the light emitting element 23.
The light receiving element 24 detects a change in the amount of light reflected from the upper surface of the diaphragm 9. The amount of light reflected from the diaphragm 9 decreases as the reflection surface of the diaphragm rotates, as shown in FIG. 7B. In other words, the amount of reflected light is maximum when the displacement angle θ=0, and from θ=0 to θ=
+θm (plus maximum displacement angle) and θ=-θm
(minus maximum displacement angle). In that case, θ=0 to θ=+θm,
The amount of change in light amount when θ=-θm is ΔL. The output signal (that is, the amount of received light) of the light receiving element 24 changes twice as the diaphragm 9 vibrates back and forth, as shown in FIG. 7C. In other words, the light receiving element 24
When the diaphragm 9 vibrates clockwise in FIG. 7A, the amount of received light increases from θ=-θm to θ=0, decreases from θ=0 to θ=+θm, and , when the diaphragm 9 returns to vibration in the counterclockwise direction, it increases again from θ=+θm toward θ=0, and decreases again from θ=0 toward θ=−θm. As a result, as described above, the light receiving element 24
The amount of received light changes twice as the diaphragm 9 vibrates in one round trip, and the amplitude of the change in the amount of received light is ΔL, which is the same as the amount of change in the amount of reflected light. Here, since the displacement of the vibrator 8 is substantially constant, the optical output is also substantially constant, and an output of about 1 V can be obtained from the light receiving element 24 even in a low flow rate region. Therefore, the vortex frequency can be detected with a simple circuit configuration in which this output is simply waveform-shaped by the comparator 27. As described above, the optical system consisting of the light emitting/receiving element and the reflecting surface is located within the chamber 28 of the vibration chamber 16 and does not come into direct contact with the fluid, so it is possible to prevent the optical system from being contaminated. The detection mechanism shown in FIG. 7A shows the basic configuration of the present invention in which the light emitting element 23 and the light receiving element 24 are arranged so that the maximum amount of reflected light can be obtained when the diaphragm 9 is in a horizontal position. Therefore, in FIG. 7A, the center line M of the angle formed by the light emitting element 23 and the light receiving element 24 is located perpendicular to the diaphragm 9. In FIG. In response to such a principle configuration, in one embodiment of the present invention, as shown in FIG.
3. The light receiving element 24 is biased in advance with respect to the diaphragm 9 by a maximum angular amplitude θm. In this case, the amount of light reflected from the diaphragm 9 increases as the reflection surface of the diaphragm rotates, as shown in FIG. 9B. In other words, the amount of reflected light is minimum when the displacement angle θ = -θm (minus maximum displacement angle), and when θ = -θm
It increases from θ=+θm (plus maximum displacement angle), and becomes maximum when θ=+θm. In that case, the amount of change in light amount from θ=-θm to θ=+θm is ΔL ₀ . This amount of change in light amount ΔL ₀ is approximately 2 of the amount of change in light amount ΔL in the principle configuration shown in FIG. 7A.
times, that is, ΔL ₀ ≒2ΔL. Then, the output signal of the light receiving element 24 (that is, the amount of light received) is
As shown in FIG. C, it changes only once as the diaphragm 9 vibrates once back and forth. In other words, when the diaphragm 9 vibrates clockwise in FIG. 9A, the amount of light received by the light receiving element 24 increases from θ=-θm to θ=0 and from θ=0 to θ=+θm. , θ=
The maximum value is reached at +θm, and when the diaphragm 9 returns to vibration in the counterclockwise direction, from θ=+θm to θ
=0 and decreases from θ=0 to θ=−θm, respectively. As a result, as described above, the light receiving element 24
The amount of received light changes only once with one round-trip vibration of the diaphragm 9, and the amplitude of change in the amount of received light is the same as the amount of change in the amount of reflected light, ΔL ₀ (≒2
ΔL). Therefore, in the detection mechanism shown in FIG. 8, the amplitude of change in the amount of light received by the light receiving element is twice that of the detection mechanism shown in FIG. Moreover, since the amount of received light changes only once with one round-trip vibration of the diaphragm 9, the signal processing is much easier than with the detection mechanism shown in FIG. 7A, which changes twice. It becomes easier.

【Effect of the invention】

As explained above, in the present invention, as shown in FIG. 8, the light emitting and light receiving elements are installed so as to be offset from the diaphragm by the maximum angular amplitude of the diaphragm, so that the amount of light received by the light receiving element changes. Since the amplitude is twice that of the configuration shown in FIG. 7A, the sensitivity is improved even to minute angular displacements of the diaphragm 9.
The amount of light received is 1 due to one round trip vibration of the diaphragm 9.
Since the detection mechanism changes only once, signal processing becomes easier compared to the detection mechanism of FIG. 7A, which changes twice.

[Brief explanation of the drawing]

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. is a side sectional view of the vortex detection unit, FIG. 6 is a processing circuit diagram of a vortex detection signal, FIG. 7C is a different characteristic diagram for explaining the characteristics of the sensor, FIG. 8 is a configuration diagram showing one embodiment of the present invention of the displacement detection sensor, and FIG. 9A is the displacement detection sensor shown in FIG. 8. Schematic configuration diagram, Figure 9B
and FIG. 9C are different characteristic diagrams for explaining the characteristics of the sensor. 2... Vortex generator, 8... Vibrator, 9... Vibration plate, 101, 102... Spun band, 23...
Light emitting element, 24... Light receiving element.

Claims (1)

[Claims] 1. A diaphragm that vibrates in response to pressure fluctuations that alternately occur near both sides of a Karman vortex generator inserted into a fluid flow, and the diaphragm is connected to a rotation axis that includes the center of gravity of the diaphragm. The vibration displacement of the diaphragm is optically detected by at least one pair of emitting and light receiving elements, and the flow rate of the fluid is determined from the vibration frequency of the diaphragm. A Karman vortex flowmeter for measuring , characterized in that the emitting and light receiving elements 23 and 24 are installed to be offset from the diaphragm 9 by the maximum angular amplitude (θm) of the diaphragm. Vortex flow meter.