JPS6147517A - Karman vortex flowmeter - Google Patents

Abstract

PURPOSE:To allow the titled flowmeter to operate with sufficient sensitivity even in the case of gas of which the signal component is weak and, at the same time, to enhance the strength thereof against the vibration of a pipe while allowing the same to have a large S/N ratio, by modulating the quantity of the reflected light or transmitted light of an optical fiber by the flow of the fluid in a communication port. CONSTITUTION:Karman vortexes alternately flows to the downstream side along both sides of a sensor body 10 and differential pressure DELTAP is alternately generated transitionally in both sides of the sensor body 10 and, corresponding to this differential pressure DELTAP, a seal diaphragm 30 is bent and the oil F in a communication port 13 flows right and left, and a flag 22 and an optical fiber 16 also flows and vibrates right and left. Light enters the optical fiber 16 from the upper end thereof and is emitted to a reflective mirror 21 from the end surface thereof and a part thereof is reflected to be again returned to the optical fiber 16. Because of the relative shift vibration of the end surface 20 and the reflective mirror 21, this return light is modulated at Karman vortex frequency (f) and, by calculating this Karman vortex frequency (f), the flow amount and flow velocity in a pipe 1 are calculated. The oil F is sealed in order to prevent the seal diaphragm 30 from largely bending by the change in static pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a Karman vortex flow meter or current meter that uses light.

Conventional technology The Karman vortex flowmeter or flowmeter, which uses light, has great advantages such as being resistant to electromagnetic induction and having no inherent explosion hazard, so it is rapidly being developed. The inventor focused on this point and conducted extensive research, and in 1930,
``Mechanical light modulation device'' as described in Patent Application Publication No. 033522 (Japanese Patent Application No. 15481/1989)
4) was proposed. This device calculates the Karman vortex frequency from the loss of light due to bending of the optical fiber. According to the results of this study, when the fluid to be measured is a liquid, the vortex has a large number S.

It was found that it is possible to obtain a sufficient S ratio. However, when the fluid is a gas, the vortex shield S is small,
It was also discovered that there was a problem with the S ratio.

The inventor conducted further research and invented a "mechanical light modulator" with even greater sensitivity. The contents of this "mechanical light modulation device" are described in detail in Patent Application No. 145188 filed in 1982 by the same applicant as the present application. This device improves sensitivity by taking into account the effect of optical fiber misalignment. However, even with this device, when the fluid is gas and the device is used in an environment where the pipes vibrate strongly, it has been found that problems remain in the S ratio and the device is not perfect.

When the density of the fluid is ρ and the flow velocity is V, the lift force corresponding to the signal S of the Karman vortex is proportional to ρv72.

When the measured fluid changes from liquid to gas, the density ρ becomes approximately 1/10
It goes down to 00. Even if the gas flow rate is increased by one order of magnitude, the gas ρV
2/2 becomes 1/io of liquid. On the other hand, vibrations of a pipe through which a fluid flows, which corresponds to the noise N, are not much different from those of a liquid even if it is a gas, so the S/c ratio is much worse in the case of a gas. This is why gaseous Karman vortex flowmeters are inherently difficult.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional circumstances.
Therefore, the object of the present invention is to provide a new Karman vortex flowmeter using light, which operates with sufficient sensitivity even when the shield number S is a weak gas, is resistant to pipe vibrations, etc., and has a large S ratio. It's about getting the measure. - Structure of the Invention In order to achieve the above object, the Karman vortex flowmeter according to the present invention has a Karman vortex generator inserted perpendicularly to the fluid flow or a vortex sensor inserted in its wake from both sides of the sensor body. This pressure is introduced into a communication port provided in the vortex sensor, and the amount of light reflected or transmitted through the optical fiber is modulated by the flow of fluid within the communication port.

Practical Examples of the Invention Next, preferred embodiments of the present invention will be specifically explained with reference to the drawings.

FIG. 1 shows a schematic cross-section of a Karman vortex flowmeter using one embodiment of the present invention. In the figure, fluid flows in the pipe 1 from left to right in the direction of the arrow.

Because of the Karman vortex generator 2 inserted at right angles to the flow,
A regular Karman vortex 3 is generated within a certain flow rate range. The vortex 3 is detected by the vortex sensor A according to the present invention installed on the downstream side, and the flow rate in the shivibe 1 is determined from the generation frequency of the vortex 3. 2
2 is a flag, which will be explained later.

FIG. 3 shows another practical example of the invention, in which the vortex sensor according to the invention has been disposed of in the Karman vortex generator 2' itself.

FIG. 2(a) is an enlarged sectional view showing the first embodiment of the vortex sensor A when cut along line B-B' in FIG. 1 and viewed in the direction of the arrow. FIG. 2 Φ) shows a side view of the vortex sensor A. However, in (b), pipe 1 is omitted.

In Fig. 2 (a) and (b), vortex sensor A for vortex detection is shown.
It is composed of a flag part 9 and a flat sensor body 10 inserted into the flow. The flag part 9 is fixed to the pipe 1 with a screw 11. 12 is rO for leak prevention
It is J-ring Patsukin. Countersink recesses 14 and 15 are formed from the left and right sides approximately at the center of the sensor body 10, and the bottoms communicate with each other to form a communication port 13. An optical fiber 16 is attached to the center of the flag portion 9 and sensor body 10. The upper end of the optical fiber <16 is Fel-/L/1
7 and is centered. Remove screw 18 and inject adhesive 19. By adjusting the screw 18, the optical fiber 16 is solidified with the lower end surface 20 of the optical fiber 16 properly exposed.

A reflecting mirror 21 is attached to the sensor body 10 facing the end surface 20 of the optical fiber 16. Hikari 7 Aino (16
A standard product with a core diameter of 50 μm and a cladding diameter of 125 μm is suitable. When properly assembled, exactly half of the end face 20 is covered by the reflecting mirror 21. The gap between the end face 20 and the reflecting mirror 21 is preferably 0.1 mm or less.

With such a small gap, 5o% of the light emitted from the end face 2o is reflected and enters the optical fiber 16.
! 'ru. A flag 22 is attached to the optical fiber 16 as necessary.
is installed. It is desirable that the 7-piece plug 22 be installed in a position that blocks the communication port 13.

The entire lower half of the sensor body 10 of the vortex sensor A is wrapped in a seal diaphragm 30 and welded at 31 and 32 parts.

Damping oil F is introduced into the space inside the sensor body lo through the oil sealing port 33, and the port #34 is sealed.

The sealing diaphragm 3o may be welded to and around the groove 5 which closes the individual recess 14,15. Also.

The shapes of the individual recesses 14 and 15 and the communication opening 13 do not necessarily have to be circular.

Next, to explain the first practical example of the present invention, Karman vortices alternately flow downstream on both sides of the sensor body 1o. Therefore, a transient pressure difference ΔP is alternately generated on both sides of the senna body 1o. Accordingly, the seal diaphragm 3o is bent, and the oil F in the communication port 13 flows left and right. Flag 22 accordingly. The optical fiber 16 also flows left and right and vibrates.

Light from an optical connector (not shown) enters from the upper end surface of the optical fiber 16, exits from the end surface 20 to the reflecting mirror 2, and part of it is reflected and returns to the optical fiber 16 again. End face 2
This return light is modulated by the Karman vortex frequency f due to the relative deviation vibration between the mirror 21 and the mirror 21. Now, find the Karman vortex frequency f.

The flow rate or flow velocity in the pipe 1 is determined. Although oil F is not indispensable, the main reason for sealing it in is to prevent the seal diaphragm 30 from flexing due to changes in hydrostatic pressure even if the pressure of the fluid to be measured changes. . At the same time, the damping of the vibration system is moderated, and the end face 201
It also serves to prevent cloud formation due to dew condensation on the reflecting mirror 21. It also helps to reduce 7-Renel reflection loss.

Lower limit frequency fX of measurement frequency, differential pressure Δ of extremely low frequency below
When P is added, oil F also flows at an extremely low frequency,
Fill the gap 23 between the flag 22 and the communication port 13 with oil F.
passes freely, and the flag 22 hardly bends. Therefore, at very low frequencies, the light is hardly modulated.

It has the property of a bypass filter, not responding to unnecessary extremely low frequencies. This property is desirable in practice.

The element that limits the amplitude of the flag 22, t:+ end face 20 near the measurement lower limit frequency fz is the stiffness of the seal diaphragm 3°. The larger the effective diameter of the seal diaphragm 3o is, and the thinner the plate thickness, the higher the sensitivity.

If the seal diaphragm 30 and oil F are removed, the only thing that limits the amplitude is the resistance to bending of the optical fiber 16), and the highest sensitivity is achieved, but the end face 20 and reflector 21 become dirty due to aging. Due to cloud cover, it can only be used for laboratory purposes and is limited to 71:D applications.

The main amplitude limiting factor at high frequencies is the mass of the oil F flowing from side to side within the communication port 13. As mentioned above,
The lift force that causes the oil F to vibrate is proportional to the square of the flow velocity V. The Kalman frequency f is proportional to the flow velocity (T). - The alternating force required to vibrate a constant mass of oil in the communication port 13 with a constant amplitude is also the square of the Kalman frequency f, which is the flow rate ■
Since it is proportional to the square of
remains constant, almost unchanged. This property is a highly desirable property. In particular, the seal diaphragm 30
In order to prevent fatigue damage, the smaller the deflection of the seal diaphragm 30, the better. In the case of a core diameter of 50 μm, it is sufficient that the swinging portion of the flag 22 is 1 μm, so the seal diaphragm 30 can be bent to a degree of 1 μm, so there is no fear of fatigue. The adjustment of the amplitude in the high frequency range depends on the hole diameter of the communication port 13, the countersink diameter, the oil viscosity, etc. If the width W of the sensor body 1O is large, the mass of the oil F in the communication port 13 increases, and the amplitude in the high frequency range becomes undesirable. The horizontal vibration of the pipe causes vibration of the oil F. In response to this, the flag 22 also makes a fake vibration and generates a noise amount N. Width W
The smaller the better. The smaller the difference between the density ρ0 of the oil F and the density ρ of the fluid to be measured, the stronger the pipe becomes resistant to vibration. When the fluid to be measured is a liquid, the difference in density from the oil F is small, so the noise N due to pipe vibration is small. In the case of gas, the difference is large, so it is inevitably weak against pipe vibration.The density of the flag 22 is surprisingly close to the density ρ0 of the oil F. Since the density of the oil F is 1 in ρ0 (g, /e''), it is desirable to use a thin plate of plastic.If you pay attention to the material of the flag in this way, the deviation between the end face 20 and the reflector 21 due to the mounting orientation can be kept within a few microns. Therefore, readjustment is not necessary even if the mounting orientation changes.

If the light-receiving optical fiber is installed concentrically in the oil sealing port 33 and the end faces are brought close to each other by removing the reflector 21, the amount of light passing through the light-receiving optical fiber will be modulated by the Zn vibration of the end face. It's obvious that it's flag 22 in Figure 2.
If the reflector 22 is lowered to the lower blade while the position @ is left as is, and at the same time the optical fiber is extended and the end face 20 is lowered to the lower blade, the optical fiber will have a mechanical lever effect. Compared to the vibration amplitude of the end face 22, the amplitude of the end face 20 is larger υ, and the deflection is expanded. The 0 flag 22, which is useful in applications where the flow rate is small and the signal is weak, is not essential. Without this, the optical fiber will not be able to follow the flow of the oil F, and the amplitude will only decrease.

FIG. 4(a) is an enlarged sectional view of the main part of the second embodiment of the present invention, and FIG. 4(b) and (C) are side views thereof.
The major difference from the first embodiment shown in the figure is that the optical fiber 16 is fixed, whereas the reflecting mirror 21 vibrates.

In FIG. 4, the optical fiber 16 is fixed to the sensor body 10 with an adhesive 19. Exactly half of the end face 20 is covered by the reflector 21. The reflector 21 is the flag 22.
It is attached to the The flag 22 is placed in a position to block the communication port 13, and its periphery is welded to the sensor body 10 with a screw. A large number of slits 24 are inserted so that the oil F in the communication port 13 flows from side to side due to the Karman vortex 19, which allows it to bend with a slight force. It is also easy to install a light-receiving optical fiber in the oil inlet 33 to modulate the amount of light reflected to the optical fiber 16 by the Kármán vortex frequency, thereby changing the amount of light that passes through the optical fiber to a modulating type.

In FIG. 3, the Karman vortex generator 2' also serves as a sensor body. Bellows 30' in place of the seal diaphragm
Oil F is sealed using . Thus, the sealing element is not necessarily a diaphragm. The material is not limited to metal either. In general, the force of the bellows 30' is the force on the diaphragm z
The sensor can also be designed with low stiffness, resulting in high sensitivity.

FIG. 5 shows an embodiment of the WS3 of the present invention.

The pressure in the individual depressions 14 and 15 is the communication port 13 outside the pipe.
will lead you to. 22 is a flag, and this effect is the same as described above. In gas flow rate measurement, the upper limit frequency fIr of the measurement frequency is several kHz. Care must be taken when using the 8th line, as the loss at the pressure inlet to the communication port 13 will increase.

When oil F is sealed as shown in FIG. 2, a resonant frequency in the ordinary sense does not appear. There should be a resonance frequency due to the stiffness of the seal diaphragm 30 and the mass of the oil F, but a peak value appears due to the damping of the oil F. However, the sensitivity increases if the force is set close to the measurement lower limit frequency f4 or at an even lower frequency.

It is not essential to block the pressure inlet with a sealing element or to seal oil inside it. Practical performance is only 1 shibeta.

Effects of the Invention The present invention is constructed and operates as described above. According to the second aspect of the present invention, a sufficiently large Karman vortex frequency signal can be obtained even when measuring the flow rate of gas with a small signal component S. The N1 pipe is highly resistant to vibration and has a simple structure, making it highly reliable.
An inexpensive Karman vortex flowmeter can be obtained, which has great practical effects.

The amplitude of the moving part is less than a few micrometers, and there is virtually no vibration, which helps improve reliability. Needless to say, it is not subject to electromagnetic induction.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one basic principle of the present invention, and FIG. 2(a) shows a first embodiment of the vortex sensor according to the present invention.
FIG. 2(b) is an enlarged cross-sectional view cut along the line and viewed in the direction of the arrow, and FIG. 2(b) is a side view of the vortex sensor shown in FIG. 2(a).
The figure is another basic principle diagram of the present invention, and FIG. 4(a) is an enlarged sectional view of the main part showing the second embodiment of the present invention.
) is a side view of the second embodiment, and FIG. 5 is an enlarged sectional view of essential parts showing the third embodiment of the present invention. 1 @11-pipe, 2.2'... Karman vortex generator, 3... Karman vortex, 9... flange part, 10...
・Sensor body, 12---0 ring packing, 13・
・Communication hole, 14.15 ・Individual hollow, 16...
- Optical fiber, 17... φ ferrule, 19-... Adhesive, 2011Φ - End face of optical fiber 16, 21-- Reflection m, 22- Own flag, 23... Gats 7', 3
0-...Seal diaphragm, 33--Oil filling port, 34...Ball, A...Vortex sensor, F...Dumping oil Fig. 1 ρ Fig. 3 Fig. 4 Ko (C)

Claims (6)

[Claims] (1) The pressure on both sides of the sensor body of the Karman vortex generator inserted at right angles to the fluid flow or the vortex sensor inserted in its wake is guided to the communication port provided in the vortex sensor, and the pressure is guided into the communication port provided in the vortex sensor. A Karman vortex flowmeter characterized by modulating the amount of light reflected or transmitted through an optical fiber by the flow of fluid. (2) The Karman vortex flow rate according to claim (1), further characterized in that the optical fiber is made to protrude into the communication port, and the amount of reflected light or the amount of transmitted light is modulated by bending of the optical fiber. Total. (3) Claim (1) or (2) further characterized in that a flag is attached to the optical fiber.
Karman vortex flowmeter as described in section. (4) A Karman vortex flow rate according to claim (1), further characterized in that a flag is provided at the communication port, and the amount of reflected light or the amount of light passing through the optical fiber is modulated by deflection of the flag. Total. (5) The Karman vortex flowmeter according to claims (1) to (4), further characterized in that the pressure introduction port is closed with a sealing element (diaphragm, bellows, etc.). (6) The Karman vortex flowmeter according to claim (5), further characterized in that oil is sealed in the region blocked by the sealing element.