JPH01240822A - Optical vibration plate vortex current meter - Google Patents

Abstract

PURPOSE:To measure the flow velocity of a fluid of high or low temp. with high accuracy, by inserting a thin vibration plate in the flow of a fluid to detect the rotational vibration thereof as an electric signal by an optical means. CONSTITUTION:A rotary shaft 2 is supported in a freely rotatable and vibratile manner by the bearings 3a, 3b mounted on the flow passage walls 1a, 1b in a flow passage 1 and a vibration plate 4 composed of a thin plate having a square or rectangular shape is fixed to the rotary shaft 2 and vibrationally displaced around the rotary shaft 2 by the generation of a vortex. The rotational vibration of the vibration plate 4 is detected as the frequency of voltage change photoelectrically by a light emitter 8, a reflecting mirror 7 and a photoelectric converter 9 to measure the flow velocity of a fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diaphragm vortex current meter for measuring the flow velocity of a fluid.

Traditionally, as a means of measuring the flow velocity of a fluid,
A diaphragm vortex current meter is known. In other words, in this current meter, when an object such as a cylinder, a triangular bar, or a trapezoidal column, which has a flat front face perpendicular to the flow direction, is placed in the flow of fluid, the The flow separates from both sides of the front, generating Karman vortices with mutually counter-rotating circulation.If the number of solid bodies in the vortex is r, the width of the front facing the flow of the object is d, and the upstream flow velocity is U. , proportionality constant 5
The principle is that there is a relationship of U=rll/St using t (referred to as the Strouhal number).

Therefore, the vortex current meter based on this principle is shown in Fig. 7 of the attached drawings.
As shown in the figure, pressure holes 14a and 14b are formed on both sides of the plane of symmetry with respect to the flow direction The internal pressure is measured using a piezoelectric element or the like, whereby the frequency f of pressure fluctuations can be measured and the flow velocity U can be determined.

Alternatively, since the vortices Va and Vb are generated alternately from both sides of the front of the object 14, the force applied to the fixed object in the direction perpendicular to the flow varies.

Therefore, the flow velocity can also be determined from the frequency of this force fluctuation.

In this case, the fluctuating pressure is measured by guiding the pressure in the pressure holes 14a, 14b drilled in the object 14 to the pressure transducer 16 through the pressure pipes 15a, 15b, as shown in FIG. ing. That is, flow path 1
For example, a column 14 having a trapezoidal cross section is fixed so that its bottom surface is perpendicular to the flow direction X,
A vortex Va released from both sides toward the top surface
, Vb, for example, the pressure from pressure holes 14a, 14b drilled in each side wall of the column 14 is converted by a pressure electrical converter 16 through pressure conduits 15a, 15b. The frequency of vibration is detected as the frequency f of the electrical output, and from this frequency r, the flow velocity is determined through the number of vortices emitted per unit time in proportion to the flow velocity.

However, the pressure-to-electricity conversion sensitivity of the pressure-to-electricity converter 16 is not large, and therefore, the previously known vortex current meters based on pressure fluctuations cannot be used to measure gas flow velocities at high speeds of 10 m/s or more. Moreover, the pressure-electric transducer 16 cannot be used at high temperatures, and in addition, long pressure pipes 15a, 15b are required to lead pressure to the pressure-electric converter 16 shown in FIG. Since the pressure amplitude introduced into the pressure-electric transducer 16 is significantly reduced, the frequency characteristics are also changed, making it impossible to use the pressure at high temperatures.

Furthermore, the output electrical signal from the pressure-electric transducer 16 often does not have a regular sinusoidal waveform because the generation of Karman vortices is affected by upstream and downstream flow fluctuations, and therefore the output circuit 17 to remove unnecessary components.

Furthermore, since pressure is proportional to the square of velocity, there is a limit to the sensitivity of the pressure-electric transducer 16 of a conventional vortex current meter, and in the case of gas, the measured value is within a high speed range of 10 m/s or more. In addition, pressure is measured using piezoelectric elements, strain gauges attached to thin films that are displaced by pressure, or methods that measure the deformation of a film due to pressure by changes in capacitance. If it differs significantly from room temperature,
The temperature is outside the operating temperature range of the pressure-electric converter 16, and for this reason, it is almost impossible to accurately measure, for example, the flow rate of high-temperature gas.

In view of this, the present invention aims to solve the problem of conventional vortex current meters, which have various problems as described above, and in particular, conventional vortex current meters cannot be used when the flow velocity is small. If the flow has small pressure fluctuations, such as a hot gas flow, or is undesirable under high temperature conditions, it may be difficult to use other methods. In view of the current situation where flow velocity measurement in such a flow velocity range or high temperature gas is recently required, we have resolved these various problems and The object of the present invention is to provide a new current meter using eddy currents that satisfies the following requirements and has good measurement accuracy.

In order to solve this problem, the present invention aims to solve this problem by measuring the flow rate of a fluid in a plane perpendicular to the direction of the flow. , a diaphragm consisting of a thin plate having a square or rectangular shape is arranged, and this diaphragm is supported by a rotating shaft having a small diameter and mounted on an axis symmetrical with respect to the flow direction,
This rotary shaft is supported in the vicinity of its upper and lower ends so that it can rotate and vibrate, and when the diaphragm is supported so that it can rotate and vibrate in the fluid flow via the rotary shaft, this rotary plate The vortices mutually generated over time from both side edges cause the thin plate to rotate and vibrate around the rotational axis, but this rotational vibration is converted into rotational vibration of a minute reflecting mirror attached to the rotational axis. , optically measure the rotational vibration of this reflecting mirror, extract this optical vibration as a change in voltage photoelectronically, measure the frequency of this voltage change, and determine the proportional relationship that exists between this frequency and the flow velocity. This method is characterized in that the flow velocity is determined from the following.

In this way, in the present invention, by using one plate as the diaphragm, it is possible to reduce the moment of inertia of the vibrating part, and therefore, even in a small flow velocity region, the diaphragm is By performing rotational vibration, using heat-resistant materials for the diaphragm and rotating shaft, and preventing the bearings that support the rotating shaft from being exposed to high-temperature gas, or by using pivot bearings, etc. It is also possible to measure the flow velocity of high temperature gas, and
By measuring the frequency of the diaphragm as an electrical frequency using optical means, the measurement can be made with high precision.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to FIGS. 1 to 6 of the accompanying drawings showing embodiments thereof.

First, FIGS. 1 and 2 schematically illustrate the principle of measurement according to the present invention and an embodiment of the present invention that operates based on this principle.
Inside a channel 1 having a suitable cross section, for example a rectangular cross section, each channel is formed in a plane that includes its central axis and is perpendicular to the opposing channel walls 1a and 1b. A rotating shaft 2 made of a metal rod or metal tube with a small diameter is arranged in a direction perpendicular to the walls 1a, lb, and this rotating shaft 2 is connected to a bearing attached to each channel wall 1a, lb. It is rotatably supported via 3a and 3b. Further, a diaphragm 4 made of a thin plate having a square or rectangular shape is fixed to the rotating shaft 2 on its negative surface along the axis of symmetry in the longitudinal direction.

In this way, when a fluid having a flow velocity υ is caused to flow in the direction of the arrow X from the upstream side of the flow path 1, the rotation axis of the diaphragm 4
Vortices Va and Vb are generated alternately from both sides in the direction of , and as they go downstream, these vortices Va and Vb have a certain interval in the direction parallel to the flow and in the direction perpendicular to the flow, respectively. This creates a so-called Karman vortex street that is asymmetrically spaced at regular intervals. Furthermore, due to these Karman vortex streets, a pressure corresponding to the vortex street is generated on the diaphragm 4. In this case, since the vortices Va and Vb are generated alternately as described above, the diaphragm 4 is oscillatedly displaced around the center of the rotating shaft 2, and as shown by the broken line in FIG. vibrate.

Moreover, in this case, the vortex Va.

Vb is arranged at regular intervals downstream, but the mounting of the diaphragm 4 upstream of the vortex row is influenced by fluctuations in the upstream flow, and the diaphragm 4 is arranged at irregular intervals. In addition, it sometimes vibrates with a large amplitude.

In the present invention, a splitter 5 and a diaphragm 4 are installed downstream of the diaphragm 4 in order to prevent signals that affect the measurement of the fluid flow velocity U from appearing in the measurement output as much as possible.
A stopper or stopper bar 6 having an appropriate shape is provided to prevent the vibration rotational amplitude from exceeding a certain value.

Further, as shown in FIG. 2, the rotating shaft 2 has one end extending outward through one channel wall 1a of the channel 1, and a small reflecting mirror 7 is provided in this extension. is fixed. This reflecting mirror 7 receives light emitted from a light emitter (light emitting diode) (LED) 8 installed nearby,
This reflected light is received by a light-receiving electrical converter (photoelectric device) 9 such as a photodiode installed near the reflecting mirror 7, and in this way, the reflected light is reflected by the reflecting mirror 7. Using light, the rotational vibration of the diaphragm 4 is converted into an electrical output that varies depending on the rotational frequency. That is, the frequency of this electrical output is the vortex Va, Vb
This corresponds to the rotational frequency of the diaphragm 4 due to 6.Furthermore, in the present invention, taking into account the measurement of the flow velocity of high-temperature gas, the rotating shaft 2 shown in FIG. Considering that bearings 3a and 3b, such as ball bearings, are not highly reliable for long-term use under high temperatures, as shown in FIG. , a pivot bearing 11a is attached to each channel wall 1a, lb.
, llb and these pivot bearings 11a, l
The rotating shaft 2 is rotatably supported by the rotary shaft 2, and at the same time, the light emitter 8, the reflecting mirror 7, and the light-receiving electrical converter 9 are also appropriately installed inside the outer box 12, etc., so that they can be cooled. It is something to put. In this way, cooling of the channel 1 itself is not required even when measuring the flow velocity of high-temperature gas.

As described above, in the present invention, the rotation frequency of the diaphragm 4 is extracted as the frequency of the electrical output. Conventionally, as means for measuring the frequency of the electrical output,
As already explained based on FIGS. 7 and 8, the frequency of the pressure fluctuation is detected as the frequency of the electrical output, and from this frequency, the number of vortices released per unit time is calculated in proportion to the flow velocity U. The flow velocity was determined through the . However, the pressure-to-electricity conversion sensitivity of the pressure-to-electricity converter 16 is not large;
Furthermore, as shown in FIG. 8, in order to guide the pressure to the pressure-electric transducer 16, long pressure pipes 15a and 15b are used to take it out of the flow path, so the amplitude of the pressure introduced to the pressure-electric transducer 16 is The frequency characteristics were significantly reduced, and therefore the frequency characteristics were changed, making it impossible to use them at high temperatures.

In contrast, in the present invention, minute pressure fluctuations caused by the vortices Va and Vb are detected as rotational vibrations of the diaphragm 4, and this rotational vibration is detected by a reflecting mirror 7 fixed to the rotating shaft 2 that is integral with the diaphragm 4. This optical rotational vibration is converted into an optical rotational vibration of Since the diaphragm 4 is designed to be extracted as an electric signal that fluctuates in the vortex Va.

Since the rotational vibration closely follows the changing micro-pressure of VB, it not only makes it possible to measure low-speed flow velocities that were impossible to measure with conventional vortex current meters, but also makes it possible to This also makes it possible to measure the flow velocity of high-temperature gas, which has been difficult to measure.

Hereinafter, the present invention will be explained using numerical examples thereof.

Numerical value Example 1 In a -like flow velocity U between parallel flat plate channel walls, the thickness is 0.2 mm, the length is 112 mm, the width is 80 mm, 6
0mm.

An optical diaphragm vortex current meter according to the present invention was installed in which a rotary plate 4 made of several types of titanium, such as 40 mm in diameter, was attached to a rotary shaft 2 in the center of the channel width so that it could rotate and vibrate freely.

In addition, in order to investigate the effectiveness of the splitter plate 5, the diaphragm 4 in the case where the splitter plate 5 with a length of 401 mm and a thickness of 4 ends was installed behind the diaphragm 4 with a width of 52 mm with an interval of 5InI11. The temporal change in the output of the light-receiving electric converter (photodiode) 9 was measured when the reflector 7 was used. The results are shown in Figure 4(a) and (
b) is shown. That is, FIG. 5A shows the results without the splitter plate 5, and FIG. 2B shows the results with the splitter plate 5 installed. By comparing these figures, it can be seen that when the splitter plate 5 is installed according to the present invention, the output signal almost contains only the fundamental frequency, proving the effectiveness of the splitter plate 5. There is.

In addition, the plate width d of the diaphragm 1 is 80 mm, 60 mm, and 4.
0 mm, the width of each channel is 3.7 times the plate width, the Strouhal number is St, the optically measured frequency is f, and St is 5t=fd/U.

The results of measuring the relationship between the Strouhal number St determined from the equation and the flow velocity U are shown in FIG.

From this figure, the Strouhal number St is constant at 0.184 when the flow velocity is between 10 m/s and 1 m/s.
It can be seen that the present invention has a good accuracy as a measurement of flow velocity and therefore has a wide range of applications.

Next, place a 15 mm x 15 tube in the center of a 50 mm diameter circular tube.
A square rotary plate 4 with a diameter of 1 mm was made from titanium with a thickness of 0.21 mm, placed in the center of a circular tube with a diameter of 50 mm, and fixed to a rotating shaft 2 made of a circular tube with a diameter of 1 mm. Furthermore, as shown in FIG. 2, this rotating shaft 2 is extended so as to protrude outside the circular tube, and a small reflecting mirror 7 is attached to the extended part of this rotating shaft 2, and a light emitter is installed. The rotation frequency of the rotating shaft 2 was determined from the output signal of the light receiving electrical converter (photodiode) 9 via the light receiving electrical converter (photodiode) 8 and the light receiving electrical converter (photodiode) 9.

This measurement result is expressed as the average flow velocity U! of the fluid in the circular pipe. The relationship between R and the frequency of the electrical signal is shown in a diagram as shown in Figure 6.

As can be seen from this diagram, the flow rate is 8 + m/s and 1.
5II/s, the relationship between flow velocity and frequency is perfectly linear, and the optical diaphragm vortex velocimeter according to the invention can be used as a vibrating droplet velocimeter for low flow velocities. It is clear that he is well suited to be

The present invention has the above-mentioned structure and operation, and therefore can measure low gas velocities and high-temperature gas flow velocities, which are impossible to measure with conventional vortex movement needles. A thin diaphragm fixed to a rotating shaft at the center is placed in the flow so that it can rotate even in response to minute pressure fluctuations. The frequency of the rotational vibration of the diaphragm is extracted as an electrical signal by optical means, and the flow velocity of a fluid such as a gas or liquid at a low velocity, for example, 10II/s or less, is measured under conditions where the fluid is high or low temperature. Even if there is, it is possible to measure the fluid. Therefore, the present invention provides the following advantages in various plants:
For example, it is widely used in various fields, such as for measuring the flow velocity of high-temperature gas and corrosive gas for semiconductor manufacturing.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the principle of the present invention, and the second section is the first section.
FIG. 3 is a schematic perspective view showing a somewhat specific configuration of an embodiment of the optical diaphragm vortex current meter according to the present invention, which is made based on the principle shown in FIG. Similar schematic perspective views, FIGS. 4(a) and 4(b), show another embodiment of a current meter according to the invention in which the meter is modified to be suitable for measuring the flow rate of hot fluids. Figure 5, a diagram comparing the effects of the splitter plates used, shows a current velocity meter according to the present invention in which diaphragms with three different widths were used to measure flow velocities of approximately 10 n/s or less. Figure 6 is a diagram showing the relationship between the flow velocity and the Strouhal number in the case of the present invention, and the average flow velocity when the flow velocity of a fluid flowing in a circular pipe is measured by the eddy flow needle movement according to the present invention, and its optical measurement. FIG. 7 is a diagram showing the relationship between the frequency of the electrical output by the means, FIG. 7 is a schematic diagram showing an example of a conventionally known eddy current hand movement, and FIG. FIG. DESCRIPTION OF SYMBOLS 1... Flow path, 2... Rotating shaft, 3a, 3b... Bearing, 4... Vibration plate, 5... Split plate, 6... Stopper, 7... Reflector, 8 ...Light emitter, 9...
・Light receiving electrical converter, lla,, 11b... Pivot bearing, 12... Outer box 6 Figure 1 Figure 2 Figure 1b 3b AA Figure 1n 1b Figure 4(b) LJ with slot plate ( m/s) Um (m/sl Fig. 8 Fig. 7)

Claims (1)

[Claims] 1. As a vortex generator having a certain area extending in a direction generally perpendicular to the direction of the flow in the flow of the fluid whose flow velocity is to be measured. It consists of a diaphragm, a rotating shaft that supports the diaphragm so that it can rotate freely, and an optical measurement means for measuring the rotational vibration of the rotating plate. A fixed reflecting mirror, a light emitter for emitting light toward the reflecting mirror, a light receiver for receiving the reflected light from the reflecting mirror, and light based on the rotational vibration of a diaphragm received by the light receiver. An optical diaphragm vortex current meter comprising an electronic measuring means for electronically measuring the rotational vibration of light reflected from a radiator through a reflecting mirror as a frequency of voltage change. . 2. The optical diaphragm vortex current meter according to claim 1, wherein the diaphragm is composed of a thin plate made of a material such as titanium, aluminum or plywood. 3. The optical diaphragm vortex current meter according to claim 1 or 2, wherein the rotating shaft supporting the diaphragm so as to freely rotate and vibrate is supported by a bearing, for example, a ball bearing. 4. The optical diaphragm vortex current meter according to claim 1 or 2, wherein the rotating shaft rotatably supporting the diaphragm is supported by a pivot bearing placed outside the fluid flow. 5. When the fluid is made to flow between a pair of opposing channel walls, in the flow direction of the fluid from the axis of rotation of the diaphragm, during the wake, parallel to the channel walls and at a distance from them. Install a plate-shaped splitter plate with the
The rotational vibration of the diaphragm should be as close to a sine wave as possible,
The optical diaphragm vortex current meter according to any one of claims 1 to 4, which improves the accuracy of frequency measurement. 6. In order to prevent the diaphragm from vibrating at a frequency different from the main frequency due to a temporary increase in amplitude due to irregular generation of vortices or fluctuations included in the flow, The optical diaphragm vortex current meter according to any one of claims 1 to 5, further comprising a stopper that prevents the rotational amplitude from exceeding a certain value. 7. The optical diaphragm vortex current meter according to any one of claims 1 to 6, wherein the bearing of the rotating shaft and the optical measuring means are arranged outside the flow of the fluid and are completely cut off from the flow. . 8. The optical diaphragm vortex current meter according to claim 7, wherein the bearing of the rotating shaft and the optical measuring means are arranged in the cooling means.