WO2010074414A2

WO2010074414A2 - Liquid level measurement sensor formed by optical fiber

Info

Publication number: WO2010074414A2
Application number: PCT/KR2009/007075
Authority: WO
Inventors: 이종원
Original assignee: 한국항공우주연구원
Priority date: 2008-12-22
Filing date: 2009-11-30
Publication date: 2010-07-01
Also published as: WO2010074414A3; KR20100072671A

Abstract

The present invention relates to a liquid level measurement sensor formed by an optical fiber. The liquid level measurement sensor formed by an optical fiber applies reflection and refraction of light propagating inside the optical fiber when the optical fiber is immersed in liquid, wherein the optical fiber is wound in a periodic shape such as a helix or a trigonometric function waveform. The liquid level measurement sensor of the present invention comprises: an optical fiber; a light source which is coupled to one end of the optical fiber; an optical sensor which is coupled to the other end of the optical fiber; and a fixing member which is included on both ends of and/or on the middle part of the optical fiber.

Description

Oil level sensor made of optical fiber

The present invention relates to a level measurement sensor formed of an optical fiber, and more particularly, when the optical fiber wound in a periodic shape, such as a spiral or trigonometric waveform, is submerged in a liquid, reflection and refraction of light rays traveling inside the optical fiber are absorbed. The present invention relates to a surface measurement sensor formed of an applied optical fiber.

In general, optical level switches that apply reflection and refraction of light rays traveling inside a transparent medium are widely used throughout the industry.

Conventional optical level switch is a prism type surface switch (US Patent 7109513 B2, 5381022, Japanese Patent 2003-214926, 10-267731, 10-267730) and optical fiber type (Korea Patent 10-0187351-0000, Japanese Patent 04-125423) Etc. This method is effective to use as a switch to detect the position of the surface at a specific position but is not suitable for measuring continuously changing surface.

As a method of measuring continuously changing oil level by an optical method, a method of applying a wave guide (Korean Patent 10-0075777-0000, US Patent 7049622 B1, 6831290 B2, 6172377 B1) and a method of arranging a plurality of optical oil level switches (U.S. Patent 4954724, 3995168, Japanese Patent Laid-Open No. 2002021033) and the like. This approach has the disadvantage of requiring correction of the optical properties of the material constituting the wave guide, or the overall complexity of the measurement system.

Accordingly, there is a surface measuring sensor (Korea Patent 10-0789285-0000) formed by rolling a thin transparent film cut into polygons in various forms in an advanced manner, but since the axial rigidity of the sensor is relatively high, a flexible material such as rubber When the sensor is mounted inside the liquid storage container, if the strong impact such that the shape of the container is changed from the outside, the container may be perforated by the sensor.

In addition, by using a surface measuring sensor of a spiral or triangular or parallelogram prism composed of a thin film-like transparent material having a large number of prismatic oil level switches or flexible films, it is possible to measure continuously changing oil level. If the number of sensors is too large to complicate the system or the axial stiffness of the sensor increases and the external shock is applied to change the shape of the liquid storage container, the sensor itself may be damaged.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and a main object of the present invention is to reflect light rays traveling inside an optical fiber when the optical fiber wound in a periodic shape such as a spiral or trigonometric waveform is submerged in a liquid. It is an object of the present invention to provide a surface measuring sensor formed of an optical fiber with and refracting.

It is still another object of the present invention to provide a surface measuring sensor formed of an optical fiber which greatly reduces the axial rigidity by implementing the surface measuring sensor into an optical fiber molded into a periodic shape such as a spiral or trigonal waveform.

In order to achieve the above object, the oil level measurement sensor formed of the optical fiber of the present invention, the optical fiber; A light source coupled to one end of the optical fiber; And an optical sensor coupled to the other end of the optical fiber, wherein at least one of both ends or the interruption portion of the optical fiber is further provided with a fixing member.

At this time, the optical fiber is characterized in that formed of any one of a spiral or trigonometric waveform.

The light source may be attached to the transmission surface of the optical fiber, and the optical sensor may be attached to the reception surface of the optical fiber.

According to the present invention described above, the axial rigidity is negligibly small and the weight is very light, and when applied to the oil level sensor, a large prism having the same height as the height of the storage vessel containing the liquid in FIG. As shown in the drawing, the effect can be similar to that of measuring oil level, even when a strong external force acts to change the shape of the container inside a liquid storage container made of a flexible material such as rubber. Due to its rigidity, the possibility of the container being perforated can be ruled out.

1 is a view according to an embodiment of a surface measurement sensor formed of an optical fiber according to the present invention;

FIG. 2 illustrates a large prism partially submerged in a liquid according to one embodiment;

3 is a view showing a path of light propagating in and out of an optical fiber located in air;

4 is a view showing a path of light propagating in and out of an optical fiber located in a liquid;

5 is a view showing an application example installed in the liquid storage container according to an embodiment of the oil level sensor formed of the optical fiber according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view according to one embodiment of a surface measuring sensor formed of an optical fiber according to the present invention, Figure 2 is a view showing a large prism partially submerged in a liquid according to one embodiment, Figure 3 is an optical fiber located in the air 4 is a view illustrating a path of light propagating inside and outside, and FIG. 4 is a view illustrating a path of light propagating inside and outside an optical fiber located in a liquid, and FIG. 5 is an embodiment of a surface measuring sensor formed of an optical fiber according to the present invention. Figure 2 shows an application example installed in a liquid storage container.

The

oil level sensor

100, 200, or 300 according to the present invention includes the

optical fibers

110, 210, and 310 as shown in FIG. 1 or 5; Light sources (120, 220, 320) coupled to one end of the optical fiber (110, 210, 310); And optical sensors (130, 230, 330) coupled to the other ends of the optical fibers (110, 210, 310), at least one of both ends or the interruption of the optical fibers (110, 210, 310) The

fixing member

140, 240, 340 is further provided.

At this time, the optical fiber (110, 210, 310) is made of any one of a spiral or trigonometric waveform, the light source (120, 220, 320) is the transmission surface side of the optical fiber (110, 210, 310) A light source is attached to the light emitting side, and the

optical sensors

130, 230, and 330 are attached to the receiving side of the

optical fiber

110, 210, 310 (the light sensor is attached to receive the light). do.

The oil

level measurement sensor

100, 200, 300 is fixed using the

fixing members

140, 240, 340.

Consider a case where an optical fiber having a refractive index of n ₁ and a radius r of the constituent material is formed in the shape of an arc along the radius of curvature R formed by the centerline of the optical fiber, provided that the optical fiber does not form a closed curve in contact with itself.

When the optical fiber is located in the air having a refractive index of n ₂ as shown in FIG. 3, when the light is applied to the transmitting surface of the optical fiber, the amount of light reaching the receiving surface through the inside of the optical fiber is the diameter d, the radius of curvature R, and the refractive index of the optical fiber. Affected by n ₁ and n ₂ .

For the purpose of explanation, the refractive index n ₁ of the optical fiber is greater than the refractive index n ₂ of air in FIG. 3, the initial diameter of the light bundle incident on the optical fiber is the same as the diameter of the optical fiber, and the initial direction of the light bundle is about the centerline of the mineral oil. Suppose it is parallel to the tangent line.

In this way, imagine an imaginary concentric arc shape that is long on a semicircular cross-section along the diameter width of the fiber for ease of explanation at the initial condition where light bundles enter the optical fiber. In this concentric arc shape, the incident light rays coming into contact with the centerline of the optical fiber travel straight inside the optical fiber along line segment AB to reach the outer edge of the optical fiber and then reflect and / or refract. It can be seen from the Pythagorean theorem of FIG. 3 and the right triangle that the ray along this path holds the following two relations.

(Eq. 1)

(Eq. 2)

Under the same initial condition, the light rays entering the point F in contact with the outer edge of the optical fiber propagate along the outer edge of the optical fiber by total reflection.

Under the same initial conditions, the incident light rays coming into contact with the inside of the optical fiber go straight inside the optical fiber along the line segment PQ to reach the outside of the optical fiber and then reflect and / or refract. For the rays along this path, it can be seen from the Pythagorean theorem for FIG. 3 and the right triangle that the following relation holds.

(Eq. 3)

(Eq. 4)

It can be seen that the following conditions must be satisfied from Equation 4 and Snell's Law in order for all the light bundles incident on the optical fiber to be totally reflected.

(Eq. 5)

In summary, the following is obtained.

(Equation 6)

The equation can be rewritten as follows.

(Eq. 7)

here

ego

to be.

When the radius r optical fiber is bent on an arc, if the radius of curvature R formed by the centerline of the optical fiber satisfies the above condition (Equation 6), the light beam is incident into the optical fiber parallel to the tangent to the centerline of the optical fiber. It can be seen that both are totally reflected and propagate inside the optical fiber as shown in

rays

510 and 520, as shown in FIG.

If the radius of curvature R formed by the centerline of the optical fiber bent in a circular arc is smaller than the right side of Equation (6), only a part of the bundle of light incident into the inside of the optical fiber is totally reflected and the remainder is partially parallel to the tangent to the centerline of the optical fiber. It can be seen that the light propagates inside the optical fiber.

Now consider the case where the optical fiber satisfying the equal sign of Equation 6 in air is immersed in the liquid whose refractive index is between n ₁ and n ₂ as shown in FIG. 4. If the refractive index of this liquid is n ₃ , the following holds between the refractive indices of the optical fiber, liquid and air.

(Eq. 8)

If the critical path at which total reflection occurs inside the optical fiber submerged in liquid is called line segment ST, the following equation holds.

(Eq. 9)

here

ego

It can be seen from Snell's law for the critical path that total reflection occurs and the following conditions must be satisfied.

(Eq. 10)

In summary, the following relational expression is obtained.

(Eq. 11)

here

to be.

If an optical fiber with a radius of curvature of R and an index of refraction n ₁ is immersed in a liquid with a smaller refractive index n ₃ , the total and partially reflected light bundles that enter the inside of the fiber parallel to the tangent to the center line of the fiber The ratio of the part reflected by can be calculated from the above equation (11).

The light bundle of the totally reflected portion propagates as it is totally reflected inside the optical fiber, and in the remaining light bundle, some light is emitted into the liquid as shown in FIG. 4 whenever reflection occurs at the liquid contact surface from the inside of the optical fiber.

Refractions

511, 512, 521, 522 are lost and only the rest are reflected to propagate inside the optical fiber.

In other words, in the light bundle (line segment SF region) located outside the point S based on the initial position of the initial light bundle, total internal reflection always occurs inside the optical fiber. It spreads.

In contrast, in the bundle of rays (line segment PS region) located inside the point S based on the initial position of the bundle of rays, the partial loss due to refraction is repeated whenever reflected inside the optical fiber. At this time, in the light bundle located at the line segment PS based on the initial position of the initial light bundle, the total loss due to refraction is relatively small even if the light rays closer to the point S are repeated, and the light rays closer to the point P are more refractious as the light rays closer to the point P are repeated. The total loss caused by this is relatively large.

In order to apply the principles described above to the sensor for measuring the surface of the present invention is to present the shape of the optical fiber (110, 210, 310) formed in a spiral or trigonometric waveform.

For example, when the helical

optical fibers

110, 210, 310 are located in a container containing liquid as shown in FIG. 5, the

optical fibers

110, 210 through the transmission surface of the

optical fibers

110, 210, 310 are provided. The light bundle incident on the inside of the fiber 310 is totally reflected at the portion of the

optical fiber

110, 210, 310 which is in contact with the air, and propagates inside the

optical fiber

110, 210, 310.

As the light bundle propagates as described above reaches a portion of the

optical fibers

110, 210 and 310 located at the interface between air and liquid, a part of the light bundles is totally reflected to propagate inside the

optical fibers

110, 210 and 310. As the rest is reflected, as shown in FIG. 4, the light is propagated repeatedly through the

optical fiber

110, 210, 310 while being repeatedly attenuated by the loss due to

partial refraction

511, 512, 521, 522 into the liquid. .

A ratio of the initial cross-sectional area of the light bundle portion propagated by total internal reflection of the inside of the

optical fiber

110, 210, 310 to the initial cross-sectional area of the initially incident light bundle regardless of contact with the liquid is a The ratio of the initial cross-sectional area of the bundle of light propagating as it is repeatedly attenuated by the loss due to partial refraction into the liquid each time it is reflected is 1-a.

The average intensity of the light bundle propagating through the internal reflection of the

optical fiber

110, 210, 310 regardless of contact with the liquid maintains the initial intensity b as long as there is no loss of other forms.

On the other hand, the average intensity c of the light bundle propagating as it is repeatedly attenuated at a rate of m by partial refraction into the liquid while propagating one spiral number in contact with the liquid is the

optical fiber

110, 210, 310 submerged in the liquid. In the case where the number of helixes in the region is n, it is expressed as

(Eq. 12)

The average intensity P of the light bundles reaching the

optical sensors

130, 230, and 330 attached to the receiving surface is expressed by the following equation unless other losses are considered.

(Eq. 13)

In the oil

level measurement sensor

100, 200, 300 according to the present invention, at the

optical fiber

110, 210, 310 located in the air 500, light bundles propagating inside the

optical fiber

110, 210, 310 are provided. The whole is totally reflected, and in the portion of the optical fiber (110, 210, 310) submerged in the liquid 600, a part of the light bundle propagating inside the optical fiber (110, 210, 310) is totally reflected and the rest is reflected in the liquid each time It is repeatedly attenuated by the loss due to partial refraction of the optical fiber (110, 210, 310) propagates inside.

Since the

optical fibers

110, 210, and 310 formed into a spiral or trigonal wave shape are attenuated at a specific ratio m every one cycle of the

optical fibers

110, 210, and 310 in a liquid submerged portion, The number of attenuation cycles may be inverted from the luminous intensity values P measured by the

photosensors

130, 230 and 330 located at the receiving surface of the ends of the

optical fibers

110, 210 and 310 with respect to the unit luminous intensity of the light bundle. To recapitulate this equation (13), we get

(Eq. 14)

here,

= Number of shape cycles in a fiber part submerged in liquid (not necessarily an integer)

= Average intensity of light bundles reaching the optical sensor attached to the receiver

= Ratio of the initial cross-sectional area of the light bundle propagated by total reflection inside the optical fiber to the initial cross-sectional area of the initially incident light bundle regardless of contact with liquid.

= Average intensity of the initial bundle of light incident on the optical fiber at the transmitting surface

= A light bundle corresponding to (1-a) inside an optical fiber formed into a helical or trigonometric shape submerged in a liquid, and part of the optical fiber, except for light that is refracted into the liquid and leaked during the reflection process over one cycle. Proportion of reflected light

Since the number of shape cycles n of the

optical fiber

110, 210, 310 submerged in the liquid is calculated from Equation 14, the interface between the air 500 and the liquid 600 in the container storing the liquid, namely It is possible to accurately measure the position of the surface.

While the present invention has been illustrated and described with respect to preferred embodiments, the invention is not limited to the above-described embodiments, and is commonly used in the field of the invention without departing from the spirit of the invention as claimed in the claims. Anyone with a variety of variations will be possible.

Claims

Optical fiber;

A light source coupled to one end of the optical fiber; And

An optical sensor coupled to the other end of the optical fiber;

It is made, including

At least one of the both ends or the stop of the optical fiber is a surface measurement sensor formed of an optical fiber, characterized in that further provided.
The method of claim 1, wherein the optical fiber,

A surface measuring sensor formed of an optical fiber, characterized in that formed in any one of a spiral or trigonometric waveform.
The method according to claim 1 or 2,

And the light source is attached to the transmission surface of the optical fiber, and the optical sensor is attached to the reception surface of the optical fiber.