JP2002031560A - Optical liquid level sensor - Google Patents

Abstract

(57) [Problem] To provide an optical liquid level sensor having a simple structure and capable of continuously detecting a level without being limited by the type of liquid to be measured. The liquid has a different refractive index from the liquid to be measured,
The level of the liquid is determined by a solid rod-shaped light guide formed such that the size of the rectangular cross section gradually decreases from one end located in the liquid toward the other end located in the air. A sensing unit 2 that detects light, a projection unit 3 that projects light toward the end surface of the one end or the other end is disposed on the one end or the other end, and the projection unit 3 is disposed on the other end. An emission unit is provided for emitting the light propagating from the one end side in the sensing unit to the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical liquid level sensor for optically detecting the liquid level of a liquid contained in a container or the like.

[0002]

2. Description of the Related Art Conventionally, as a liquid level sensor, for example, a water level sensor disclosed in Japanese Patent Application Laid-Open No. 8-14984 is known. This water level sensor has a sensor main body 101 as shown in FIG. 6 as a main part. The sensor main body 101 includes an inner hollow pipe 102 and an outer armature pipe 103. A stainless pipe 104 is spirally wound around the outer periphery of the hollow pipe 102. A plurality of through holes 105 are provided on the outer circumference of the exterior pipe 103.
Is provided. These through holes 105 are for introducing water into a chamber 106 between the hollow pipe 102 and the exterior pipe 103 and for discharging water in the chamber 106 to the outside. An optical fiber 107 for temperature measurement is inserted through the inside of the stainless steel tube 104.

[0003] The operation will be briefly described. In this water level sensor, a current is caused to flow through the stainless steel pipe 104 to generate heat, and the temperature of the temperature measuring optical fiber 107 inserted inside the stainless steel pipe 104 is increased.

In this state, when the chamber 106 of the sensor body 101 is submerged, the temperature of the temperature measuring optical fiber 107 decreases in a region below the level of the submerged liquid. An optical signal is incident on the optical fiber for temperature measurement 107 to generate Raman scattered light.

The level and frequency of the Raman scattered light change according to the temperature and length of the temperature measuring optical fiber 107. Therefore, by analyzing the Raman scattered light generated in the temperature measuring optical fiber 107, the length of the temperature measuring optical fiber 107 in the region where the temperature has decreased, that is, the water level can be clarified.

[0006]

However, the above-described conventional liquid level sensor has the following problems. First, the sensing part (stainless steel tube 10
Since 4) uses a metal material, the range of applicable liquids is limited. In addition, the stainless steel tube 104 is heated in advance to increase the temperature of the temperature measuring optical fiber 107 inserted therein.
It is not easy to keep the temperature of 4 constant. Further, where there is little change in water level or water flow, the hollow pipe 102
The surrounding liquid is heated, making continuous detection difficult. In addition, the formation of Raman scattered light and the circuit configuration for detecting its change become complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an optical liquid level sensor capable of continuously detecting a level without being limited by the type of liquid to be measured. Is to provide.

[0008]

SUMMARY OF THE INVENTION In order to achieve the object of the age, an optical liquid level sensor according to claim 1 has a refractive index different from that of a liquid to be measured, and has a rectangular cross section. A sensing unit for detecting a liquid level by a solid rod-shaped light guide formed so that the size of the liquid crystal becomes gradually smaller from one end arranged in the liquid toward the other end arranged in the air. Comprising, on the one end side or the other end side, a projection unit that projects light toward the end surface of the one end side or the other end side, and the sensing unit on the other end side from the one end side. According to the first aspect of the present invention, an emission unit that emits the propagated light to the outside is provided, and the sensing unit has a rectangular cross-section that is arranged in the liquid. From one end to the other end located in the air. Since a solid rod-shaped light guide formed so as to be used is used, light propagating from one end in the liquid toward the other end in the air repeats reflection at the boundary surface according to Snell's law. Propagate. At that time, the angle of incidence on the interface gradually increases. As a result, in the part in the air, most of the light is reflected on the boundary surface, but in the part in the liquid, reflection and refraction are performed. Therefore, the amount of light (intensity) emitted from the emission unit linearly corresponds to the length of the submerged portion, and a change in the liquid level can be detected.

According to a second aspect of the present invention, there is provided the optical liquid level sensor according to the first aspect, wherein the emission portion is formed on the end face or the side peripheral face on the other end side. A light-receiving unit that receives light emitted from the light-emitting unit and the projection unit that projects light toward the end surface of the other end are disposed on the other end, and the end surface of the one end is formed as an inclined end surface. In addition, a specular reflection portion is provided on the inclined end surface so as to totally reflect the light projected and propagated from the projection portion and propagate the light toward the other end.

According to the second aspect of the invention, the light returned to the other end in the air by the mirror reflection portion provided at one end in the liquid reaches the other end while repeating reflection at the boundary surface. I do. Therefore, a change in the liquid level can be detected in a state where the projecting unit and the light receiving unit are concentratedly arranged on the other end side in the air.

According to a third aspect of the present invention, in the optical liquid level sensor according to the first aspect, the emission portion is formed on an end surface or a side peripheral surface of the other end. In addition, a light receiving unit that receives light emitted from the light emitting unit is disposed on the other end side, and a projection unit that projects light at a predetermined angle toward the end surface of the one end side is disposed on the one end side. It is characterized by the following.

According to the third aspect of the present invention, since the light is projected onto the one end side of the liquid at an inclined angle, the incident light is reflected toward the other end in the air while being reflected at the boundary surface. Can be changed. Therefore, a change in the liquid level can be detected.

According to a fourth aspect of the present invention, in the optical liquid level sensor according to the first aspect, the emission portion is formed on an end surface or a side peripheral surface of the other end. And a light receiving unit for receiving the light emitted from the light emitting unit is disposed on the other end side, and an end surface on the one end side is formed as an inclined end surface, and a projection unit for projecting light toward the inclined end surface is arranged. It is characterized by having been done.

According to the fourth aspect of the present invention, since one end surface in the liquid is formed to be inclined and light is projected toward the inclined end surface, the air is reflected while reflecting the incident light on the boundary surface. It can be directed to the other end inside. Therefore, a change in the liquid level can be detected.

The optical liquid level sensor according to the present invention has a refractive index different from that of the liquid to be measured, and the refractive index is arranged in the air from one end disposed in the liquid. A solid bar-shaped light guide formed so as to gradually decrease toward the end side constitutes a sensing unit for detecting a liquid level, and the one end side emits light at a predetermined angle toward the end surface on the one end side. And a light receiving unit that receives light emitted from the other end is disposed on the other end.

According to the fifth aspect of the present invention, the sensing portion is formed such that the refractive index gradually decreases from one end located in the liquid to the other end located in the air. Since a solid rod-shaped light guide is used, light incident from one end in the liquid propagates to the other end in the air while repeating refraction according to a change in refractive index according to Snell's law. At this time, in the submerged part, a part is radiated into the external liquid and the amount of propagating light decreases, but in the air, most is reflected on the boundary surface. Therefore, the amount of light (intensity) reaching the light receiving portion linearly corresponds to the length of the submerged portion, and a change in the liquid level can be detected.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the construction of an optical liquid level sensor according to a first embodiment of the present invention, wherein FIG. FIG. 3 is a sectional view taken along line A.

As shown in FIG. 1A, an optical liquid level sensor 1 according to a first embodiment includes a sensing section 2 having a predetermined length and one end of the sensing section 2 (hereinafter referred to as a "base end"). ) Is composed of a projecting unit 3 and a light receiving unit 4 arranged opposite to the end face of 2a, and a mirror reflecting unit 5 is provided at the other end (hereinafter referred to as "tip") 2b of the sensing unit 2. .

The sensing section 2 is made of a solid rod-shaped light guide having a refractive index different from that of the liquid to be measured, such as acrylic resin or glass, and has a rectangular cross section as shown in FIG. Has become. The size of the rectangular cross section is formed so as to be slightly smaller from the distal end 2b toward the proximal end 2a. That is, the vertical section along the length direction of the sensing unit 2 has a trapezoidal shape with long oblique sides.

The specular reflector 5 is formed by inclining the end face of the tip 2b with respect to the longitudinal direction (the optical axis direction) of the sensing section 2 and subjecting the inclined end face to mirror processing. As a result, the light propagating from the base end 2a toward the front end 2b is totally reflected toward the boundary surface by the specular reflection unit 5, and the base end 2a is repeatedly reflected between the boundary surfaces.
Will propagate toward the side. In the first embodiment,
The end face of the base end 2a serves as an emission section for emitting light propagating from the tip 2b to the outside (the light receiving section 4).

The projection unit 3 may be configured to project the light emitted from the light emitting element directly to the end face of the base end 2a, or may be guided by an optical fiber and project the light to the end face of the base end 2a. The light receiving section 4 may be configured to directly receive the light emitted from the end face (emission section) of the base end portion 2a by the light receiving element, or may be configured to receive the light by an optical fiber and guide the light to the light receiving element.

Next, the operation of the optical liquid level sensor according to the first embodiment configured as described above will be described with reference to FIG. FIG. 2 is a diagram illustrating a use state of the optical liquid level sensor according to the first embodiment.

As shown in FIG. 2, the optical liquid level sensor 1 is disposed in the container 7 to detect the liquid level S of the liquid 8 contained in the container 7. The optical liquid level sensor 1 is arranged such that the base end 2 a of the sensing unit 2 is located in the air 9 and the distal end 2 b is located in the liquid 8. The liquid level S crosses an appropriate position of the sensing unit 2. Although the refractive index of the sensing unit 2 is different from that of the liquid 8, the refractive indexes of both are larger than the refractive index of the air 9.

Light is projected substantially vertically from the projection unit 3 toward the end face of the base end 2a. The sensing unit 2 includes a base end 2a
An optical waveguide having a divergent shape is formed toward the tip 2b. Therefore, the incident light projected on the base end portion 2 a travels substantially straight in the sensing section 2 and reaches the mirror reflection section 5. Since the specular reflector 5 is inclined at an angle to totally reflect the incident light with respect to the optical axis, the light incident on the specular reflector 5 is totally reflected toward the boundary surface of the sensing unit 2. Since the reflected light is incident on the boundary surface of the sensing unit 2 at an angle, reflection is repeated between the boundary surfaces of the sensing unit 2 so that the reflected light propagates toward the base end 2a.

At this time, the sensing part 2 is
, An optical waveguide that gradually narrows toward the base end portion 2a is formed.
It becomes larger toward the base end 2a.

In the section from the tip 2b to the liquid level S, the ratio of reflected light to refracted light is
Depends on the magnitude relationship of the refractive index and the angle of incidence on the boundary surface of the sensing unit 2, but a part of the light is emitted as refracted light into the liquid 8, and the amount of reflected light (propagating light) decreases accordingly. .

On the other hand, in the section from the liquid level S to the base end 2a, the outside is the air 9 and the angle of incidence on the boundary surface of the sensing unit 2 falls within the range of the critical angle.
Almost everything is reflected.

That is, the light level of the propagating light reaching the light receiving section 4 reflects the section length from the tip 2b to the liquid level S, so that the liquid level S can be detected. Moreover, this value has a linear correspondence relationship that the value decreases as the section length from the tip 2b to the liquid level S increases.

FIG. 3 shows an example of a liquid level detection characteristic. In FIG. 3, the horizontal axis is the liquid level (unit: mm).
And the vertical axis is the output value. As shown in FIG. 3, when the liquid level is near 0 (zero) and most of the outer periphery of the sensing unit 2 is air 9, the light receiving unit 4 includes the projection unit 3.
Since most of the outgoing light is incident, the output value indicates the maximum value (value 75 in the illustrated example). It is shown that the amount of light incident on the light receiving unit 4 decreases linearly with an increase in the liquid level, so that the output value also decreases linearly.

As can be understood from the above description, the liquid to be measured or the liquid having various refractive indexes can be changed by changing the inclination and the length of the oblique side of the trapezoid having a vertical cross section from the distal end 2b to the proximal end 2a. It can correspond to the surface level.

According to the first embodiment, since the sensing section 2 is made of only glass or acrylic resin, it has excellent erosion resistance, and there is no limitation on the type of liquid to be measured, and the liquid for a wide range of applications can be used. Surface level measurement becomes possible.

In FIG. 1, it is also possible to arrange only the light receiving section 4 on the end face of the base section 2a where the emission section is formed, and to arrange the projection section 3 on the side of the tip section 2b. That is, in the distal end portion 2b, the projection unit 3 is disposed so as to face the inclined end surface before the mirror surface processing, or the inclined end surface is stopped to make the end surface perpendicular to the optical axis similarly to the base end portion 2a, and the inclined surface is inclined with respect to the end surface. The projection unit 3 is arranged so as to project from the set angle. With this, the same operation and effect can be obtained.

FIG. 4 is a block diagram of an optical liquid level sensor according to a second embodiment of the present invention. In the present embodiment, in the first embodiment, the light emitting unit 41 is provided on the side peripheral surface of the base end 2a, and the light receiving unit 42 is arranged to face the light emitting unit 41. Others are the same as the first embodiment.

In the first embodiment, the projecting portion 3 and the light receiving portion 4 share the end face of the base portion 2a, and there is a problem in that the light receiving surface is sufficiently secured. According to the embodiment, there is an advantage that efficiency can be improved because the light receiving surface can be reliably obtained.

Next, FIG. 5 is a configuration diagram of an optical liquid level sensor according to a third embodiment of the present invention. As shown in FIG. 5, an optical liquid level sensor 11 according to the third embodiment includes a sensing unit 12 having a predetermined length and an end surface of one end (hereinafter, referred to as an “uppermost portion”) 12 a of the sensing unit 12. A light receiving unit 13 disposed opposite to the sensing unit 12;
And a projection unit 14 disposed opposite to the end face of the other end (hereinafter, referred to as the “lowest part”) 12b.

The sensing unit 12 has an uppermost portion 12a disposed in the air and a lowermost portion 12b disposed in the liquid. The sensing unit 12 is a solid rod-shaped light guide whose cross section is circular or rectangular, and has a refractive index different from that of the liquid to be measured. It is formed so as to gradually decrease from 12b toward the uppermost portion 12a. For example, the refractive index _{n 1} of the bottom 12b to 1.9, will gradually lowering the refractive index towards the upper, it is to the top 12a of the refractive index _{n 2} of about 1.7.

The light receiving section 13 may be configured so that light emitted from the end face of the uppermost portion 12a of the sensing section 12 is directly received by the light receiving element, or may be received by an optical fiber and guided to the light receiving element. Further, the projection unit 14 may be configured to directly project the light emitted from the light emitting element onto the end face of the lowermost part 12b of the sensing unit 12, but the light is guided by an optical fiber to form the lowermost part 12b.
It may be projected on the end face of the camera.

In the optical liquid level sensor 11, light is projected at an optimum angle from the projection unit 14 to the end surface of the lowermost part 12b arranged in the liquid of the sensing unit 12. The light incident on the sensing unit 12 travels toward the uppermost portion 12a while refracting according to the change in the refractive index. At this time, the incident light gradually refracts in the horizontal direction and spreads in the sensing unit 12, and thus reaches the boundary surface of the sensing unit 12 at an appropriate angle.

If this is called sensing light,
When the medium outside the sensing unit 12 is air, the sensing light is totally reflected and returns to the inside of the sensing unit 12. On the other hand, when the medium outside the sensing unit 12 is a liquid,
Since a part of the sensing light is emitted into the external liquid, the amount of reflected light is reduced.

Since only the sensing light which has been able to repeat such reflection up to the uppermost portion 12a reaches the light receiving portion 13, the intensity of the sensing light linearly corresponds to the liquid level of the liquid around the outside. And a change in the liquid level can be detected.

The linearity of the output can be changed by the allocation of the refractive index of the sensing unit 12, and the sensitivity can be changed by the amount of change in the refractive index. However, if the amount of change is too large, the sensing light cannot reach the uppermost portion 12a, so it is important to find the optimum amount of change in refractive index.
Further, the length of the sensing unit 12 can be freely set if the amount of change in the refractive index is made equal.

In the above embodiments, the liquid to be measured was not touched. However, for example, the level of a gasoline tank, the level of a liquid having a different refractive index from the sensing section, such as a blue panel or an LPG, can be detected.

[0043]

As described above, according to the present invention,
Since a rod-shaped light guide is used for the sensing unit and the liquid level can be detected by a change in the amount of light in the light receiving unit, the range of the liquid to be measured can be expanded, and continuous detection is also possible. In addition, since there is no mechanical structure and no heat generating portion, the durability is improved. Furthermore, since a linear output is obtained for the liquid level,
The detection accuracy is improved. In addition, since the sensing part has a rod shape, if there is a hole where the sensing part can be inserted,
Can be set and measured. Therefore, according to the present invention, an optical liquid level sensor excellent in usability can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical liquid level sensor according to a first embodiment of the present invention. (A) is an external view configuration diagram. FIG. 2B is a sectional view taken along line AA in FIG. 1.

FIG. 2 is a diagram illustrating a use state of the optical liquid level sensor according to the first embodiment.

FIG. 3 is a diagram illustrating an example of a liquid level detection characteristic;

FIG. 4 is a configuration diagram of an optical liquid level sensor according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical liquid level sensor according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional optical liquid level sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical liquid level sensor 2 Sensing part (light guide) 2a Base end part 2b Tip part 3 Projection part 4 Light receiving part 5 Mirror reflection part 7 Container 8 Liquid 9 Air 11 Optical liquid level sensor 12 Sensing part (Guide) 12a Uppermost part 12b Lowermost part 13 Light receiving part 14 Projecting part 41 Light emitting part 42 Light receiving part

Continued on the front page (72) Inventor Isao Takiguchi 1500 Onjuku, Susono-shi, Shizuoka Yazaki Sogyo Co., Ltd. F-term (reference) 2F014 AB02 AB03 FA02

Claims (5)

[Claims] 1. A liquid having a different refractive index from a liquid to be measured,
The level of the liquid is determined by a solid rod-shaped light guide formed such that the size of the rectangular cross section gradually decreases from one end located in the liquid toward the other end located in the air. A sensing unit for projecting light toward the one end side or the other end side is disposed on the one end side or the other end side, and the sensing unit is disposed on the other end side. An optical liquid level sensor, comprising: an emission unit that emits light that has propagated from the one end side to the outside. 2. The optical liquid level sensor according to claim 1, wherein the emission section is formed on an end surface or a side peripheral surface of the other end, and the emission section is provided on the other end side. A light receiving unit for receiving the emitted light and the projection unit for projecting light toward the other end surface are disposed, and the one end surface is formed as an inclined end surface, and the inclined end surface is projected from the projection unit. An optical liquid level sensor, further comprising: a specular reflection unit that totally reflects the transmitted light and propagates the light toward the other end. 3. The optical liquid level sensor according to claim 1, wherein the emission section is formed on the end face or the side peripheral face on the other end side, and the emission section from the emission section is provided on the other end side. An optical liquid level sensor, comprising: a light receiving unit that receives the emitted light; and a projecting unit that projects light at a predetermined angle toward the end surface of the one end on the one end side. 4. The optical liquid level sensor according to claim 1, wherein the emission section is formed on an end face or a side peripheral face on the other end side, and the emission section from the emission section is provided on the other end side. An optical liquid level, comprising: a light receiving unit that receives the emitted light; and an end surface on the one end side is formed as an inclined end surface, and a projection unit that projects light toward the inclined end surface is arranged. Sensor. 5. It has a refractive index different from the liquid to be measured,
A sensing section for detecting a liquid level by a solid rod-shaped light guide formed such that its refractive index gradually decreases from one end side arranged in liquid to the other end side arranged in air. A projection unit that projects light at a predetermined angle toward the end surface of the one end side is arranged on the one end side, and a light receiving unit that receives light emitted from the other end side is arranged on the other end side. An optical liquid level sensor, characterized in that: