JPH02236146A - Optical type liquid sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a highly sensitive sensor for measuring a mixing rate or the like for an alcohol/gasoline mixed fuel with an easier maintenance in a small size by forming a folded part of a glass optical fiber with a large caliber from a core alone. CONSTITUTION:A linear optical fiber 2' comprising a core alone is placed on a non-heat conductive die 3 to soften the fiber 2' by locally heating a corner part 14 with a small burner 15 or the like, so that the tip 16 of the fiber 2' bends by a dead load thereof. Then, an excess part of the fiber 2' is cut off to form a folded part 2c, which is fused by heat to fibers 2a and 2b comprising a core and a clad. Then, a light emitting element 3 and a photo detector 4 are inserted securely into a body 5 to form a sensor. When the folded part 2c of a sensor thus obtained is exposed into a liquid to be measured, a transmission loss increases according to a refractive index of the liquid. Thus, a mixing ratio of the liquid can be measured with a high sensitivity thereby enabling the obtaining of a small and easy to maintain sensor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used for measuring the mixing ratio, refractive index, etc. of alcohol/gasoline mixed fuel as an automobile fuel, for example.
This article relates to an optical liquid sensor and its manufacturing method. [Prior Art] Among this type of optical liquid sensor, the conventional technology related to an optical liquid sensor used for measuring the alcohol/gasoline mixture ratio will be explained. In the near future, it is expected that alcohol fuel will become popular as a vehicle fuel due to the need to prevent exhaust pollution and oil resources, and will be used in the form of an alcohol/gasoline mixed fuel. However, the mixing ratio is not constant and varies depending on the circumstances on the supply side or the use side. When this mixture ratio changes, engine parameters such as air-fuel ratio, ignition timing, and fuel supply speed must be adjusted accordingly to improve startability, combustion characteristics, fuel economy, and driveability.
Engine output and exhaust gas composition are impaired. As a result of repeated tests on actual vehicles, there has been a desire for a liquid sensor that can accurately measure this mixture ratio and has a simple structure. As such a liquid sensor, an optical liquid sensor shown in FIG. 11 is proposed in Japanese Patent Application Laid-Open No. 57-51920. This optical liquid sensor a consists of a quartz glass rod b, a light emitting element C and a light receiving element d arranged at both ends of the rod b. This glass rod b is connected to the fuel pipe e.
It is inserted into a header f provided midway through a seal g so that it is in contact with liquid. The measurement principle of this liquid sensor a is that, as shown in Figure 9, the refractive index of the fuel changes depending on the alcohol/gasoline mixture ratio, and when this refractive index changes, the interface between the glass rod b and the mixed fuel h This is an application of the fact that the amount of light that is refracted and transmitted into the mixed fuel changes. That is, the output of the light receiving element d is measured with respect to the light emitting element C having a constant output, and the mixture ratio is determined by comparing the output with the differential precipitance data. This optical liquid sensor has excellent responsiveness and is attracting attention. [Problems to be Solved by the Invention] Although the optical liquid sensor described in the prior art has excellent responsiveness, since the glass rod b is linear, each mode of light incident on the glass rod b is Depending on the angle of incidence at the point where most of it first reaches the interface with the liquid, it can be divided into those that are reflected and propagate through the glass rod b and those that are refracted and transmitted into the liquid. In order to make the relationship between the amount of light emitted from the liquid refractive index linear and to improve the measurement sensitivity, it is necessary to use a long glass rod b with a fairly large diameter, which increases the size of the liquid sensor (approx. There was a problem with the length (preferably 5c1 or more). Furthermore, since the glass rod b must be installed so as to pass through the liquid head 5 or the conduit, there is also the problem that it is not easy to replace or maintain the glass rod b if it becomes damaged or dirty. Ta. The present invention has been made in view of these problems with the conventional technology, and aims to provide an optical liquid sensor that is small, easy to maintain, and has good measurement sensitivity, and a method for manufacturing the same. It is something. [Means for Solving the Problems] In order to achieve the above object, the optical liquid sensor of the present invention folds a large diameter glass optical fiber in the opposite direction,
A light emitting element is provided at the starting end of the outward path of this optical fiber, a light receiving element is provided at the end of the incoming path, and the folded part of the optical fiber is exposed as a detection part, and most of the outgoing path and return path is an optical system that is sealed and stored inside the main body. The liquid sensor is a liquid sensor in which the outgoing and returning paths of an optical fiber are made up of a core and a cladding, and the folded portion has a portion consisting only of the core, or the folded portion has a portion where the core is exposed. A method for manufacturing an optical liquid sensor in which the folded part consists of only a core is to form a folded part with an optical fiber made of only a core, and to have an outgoing path and a return path made of the core and cladding at both ends of the folded part. There is a manufacturing method that involves fusing and then sealing the outbound and return routes inside the main body. In addition, as a method for manufacturing an optical liquid sensor in which the folded portion has a portion where the core is exposed, an optical fiber consisting of a core and a cladding is bent to form an outgoing path, a return path, and a folded portion, and at least one of the folded portions is There is a manufacturing method in which one turning point is brought into contact with a glass corrosive solution to partially corrode the glass to expose the core, and then the forward and return paths are sealed and housed within the main body. [Function] The folded part of the optical fiber has a lot of transmission loss, and measurement is possible because the degree of this transmission loss changes according to changes in the refractive index of the liquid. However, if the part consisting only of the core or the core is exposed If there is a part that is exposed, this transmission loss will increase and the measurement sensitivity will increase. The reason for using large-diameter optical fibers is to distinguish them from small-diameter communication cables in the sense that, unlike communication cables that minimize transmission loss, measurements cannot be made without a certain amount of transmission loss. According to a manufacturing method in which a folded part is formed with an optical fiber consisting only of the core, and an outgoing path and a return path made of the core and cladding are fused to both ends of this folded part, optical fibers in which the entire folded part consists only of the core It becomes a sensor. Further, according to a manufacturing method in which an optical fiber consisting of a core and a cladding is bent to form an outward path, a return path, and a folded portion, and at least one folding point of the folded portion is brought into contact with a glass corrosive liquid to partially corrode, It is an optical optical sensor with the core of the folded part partially exposed. [Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a sectional view of the optical liquid sensor of the present invention, FIG. 2 is a bottom view of the optical liquid sensor of FIG. 1, and FIGS. 3 and 4 are enlarged views of the folded portion. In FIG. 1, an optical liquid sensor 1 consists of a large-diameter glass optical fiber 2, a light emitting element 3 and a light receiving element 4 at both ends of the optical fiber 2, and a zero body 5 housing them. The optical fiber 2 is formed of an outgoing path 2a, a returning path 2b, and a folded portion 2C, which are approximately parallel (may be slightly inclined in a pattern). This folded part 2C comes into contact with the liquid and constitutes a detection part. There is a lot of transmission loss in this folded portion 2C, and the amount of transmission loss is influenced by the refractive index of the liquid, which is important because it determines the measurement sensitivity. Note that the shape of the folded portion 2C is not limited to the U-shape with a straight bottom as shown in the figure, but may be a semicircular U-shape. In FIG. 3, the outgoing path 2a and the incoming path 2b are composed of a core 6 with a high refractive index and a cladding 7 with a low refractive index, but the entire folded part 2C is composed of only the core 6. ．． In addition, in Fig. 4, "outward route 2"
Most of the return path 2b and the folded portion 2c are composed of the core 6 and the cladding 7, but the folded point 2d of the folded portion 2C is composed of the core 6 partially exposed. There is. In the example of FIG. 4, the core 6 is exposed at the left and right folding points 2d, but the core 6 may be exposed at either the left or right folding point 2d.
Further, the folded portion 20 may be intermediate between those shown in FIGS. 3 and 4. Further, the material of this optical fiber 2 is glass-based such as quartz glass or multi-component glass. The material, especially the refractive index, is selected based on the range of change in the refractive index of the liquid being measured. The diameter of this optical fiber 2 is not one < 0.1 m like that for ordinary communication cables, but
A larger diameter one is selected. Preferably 0 because a certain amount of transmission loss is required, shape stability and workability.
．． Those with a length of 5 m or more are used. The light emitting element 3 is at the starting end of the outgoing path 2a, and the light receiving element 4 is at the starting end of the outgoing path 2b.
A certain amount of light emitted from the light emitting element 3 is placed at the end of the
The amount of light transmitted through the optical fiber 2 is measured by the light receiving element 4 and output. The zero body 5 consists of a holder 8 made of corrosion-resistant metal and an adapter 9 made of acrylic. The holder 8 has a hexagonal shape as a whole, and a mounting screw 8a is machined at the bottom thereof (see Figs. 1 and 2). Using this mounting screw 8a, attach the entire optical liquid sensor l to a pipe or the like so that the detection part is in contact with the liquid. Further, two holes 8b are machined in this holder 8, and the optical fiber 2 is inserted into these holes 8b and sealed with an adhesive 10 or the like. The adapter 9 accommodates the light emitting element 3 and the light receiving element 4, is inserted into the holder 8, and is fixed to the holder 8 with epoxy resin or the like. Next, the operation of the above-mentioned optical liquid sensor 1 will be explained based on FIG. 5. For comparison, a fifth (a) case in which the entire folded portion 2C consists of a core 6 and a cladding 7 and a fifth (b) case in which the entire folded portion 2c consists of a core 6 will be explained. In FIG. 5(a), the light from the outgoing path 2a is reflected at the interface between the core 6 and the cladding 7 and reaches the folded portion 2C.
The light that reaches the folded part 2c has a small incident angle, and the light that is less than the critical angle ΦCi determined by the ratio of the refractive index of the core 6 and the cladding 7 reaches the cladding 7 as refracted and transmitted light. Furthermore, in order to reach the liquid 12, it is necessary that the angle be less than or equal to the critical angle ΦC, which is determined by the ratio of the refractive index of the cladding 7 and the liquid l2. Then, when the refractive index of the liquid l2 approaches the refractive index of the cladding 7, the critical angle Φc8 becomes large, the amount of refracted and transmitted light increases, the transmission loss becomes large, and the output of the light receiving element 4 becomes small. When the refractive index of the liquid 12 moves away from the refractive index of the cladding 7, the critical angle ΦC becomes smaller, the amount of refracted and transmitted light decreases, the transmission loss decreases, and the output of the light receiving element 4 increases. Therefore, the output of the light-receiving element 4 changes according to the change in the refractive index of the liquid 12, making it possible to measure the mixing ratio and the like. However, the incident angle of the refracted and transmitted light between the core 6 and the cladding 7 increases by the curvature of the folding point 2d, and the probability that the refracted and transmitted light will be transmitted from the cladding 7 to the liquid l2 becomes low. In FIG. 5(b), for the folded portion 2c consisting of only the core 6, all light below the critical angle ΦC determined by the ratio of the refractive index of the core 6 and the liquid l2 becomes refracted and transmitted light. Measurement sensitivity improves. Then, the probability of the light being refracted and transmitted is determined by the critical angle ΦC according to the change in the refractive index of the liquid l2.
The output of the light-receiving element 4 changes when the measurement sensitivity increases depending on the change in , and it is possible to measure the mixing ratio, etc. Further, the degree of this change also depends on the ratio of the portion consisting only of the core 6 in the folded portion 2c. 6(a), 6(b), 6(c), and 6(d) are diagrams showing a method of manufacturing the optical liquid sensor shown in FIG. 3, in which the entire folded portion consists only of a core. In FIG. 6(a), a straight optical fiber 2' consisting only of a core is placed on a non-thermal conductive mold 13, and the corner portion 14 is locally heated with a small burner 15 or the like to form the optical fiber 2'. Soften. The tip l6 of the optical fiber 2' bends approximately 90 degrees under its own weight. Next, as shown in FIG. 6(b), the root portion l8 of the optical fiber 2' is rotated 90 degrees counterclockwise so that it follows the side surface of the mold l3. Then, replace the new corner l9 with the small burner 1.
5, etc., and bend the tip l6 approximately 90 degrees under its own weight. Then, in FIG. 6(C), when the excess portion of the optical fiber 2' is cut, a U-shaped folded portion 2C with a straight bottom is formed. Then, the outward paths 2a and 2b consisting of the core and the cladding are brought into contact with both ends of the folded part 2c, and are thermally fused to the folded part 2c using a burner 15 or the like to form the optical fiber 2. Next, in FIG. 6(d), the surface of this optical fiber 2 is coated with a thin layer of epoxy resin, and the hole 8 of the main body 5 is
Insert into a. Furthermore, the light emitting element 3 and the light receiving element 4 are also zero bodies 5.
Insert it inside and fix it with epoxy resin. FIGS. 6(e) and 6(f) are diagrams showing another method of manufacturing the optical liquid sensor shown in FIG. 3, in which the entire folded portion consists only of a core. First, in FIG. 6(e), a straight optical fiber 2'
One end of the optical fiber 2 is held horizontally by a grasping arm 20b that is rotatable relative to the fixed arm 20a of the holder 2o, for example, and the corner portion 14 is heated with a small burner 15 or the like to soften the optical fiber 2. The tip l6 of the optical fiber 2' is approximately 9o due to its own weight.
It bends frequently. Next, as shown in FIG. 5(r), the gripping arm 20b of the holder 20 is rotated 90 degrees counterclockwise to vertically hold the root portion 18 of the optical fiber 2'.
The new corner l9 is locally heated with a small burner 15, etc., and the tip l6 is bent 90 degrees by its own weight. Thereafter, the excess portion of the optical fiber 2' is cut in the same manner to obtain a U-shaped optical fiber 2' with a straight bottom. According to the above manufacturing method, since the outward path 2a, the I path 2b and the folded portion 2C are made separately, products of the same thickness can be manufactured.
Stable quality can be ensured with little variation in measurement precision for each product.

7(a), (b), and (c) show an optical liquid sensor 1 in which the core at the folding point shown in FIG. 4 is partially exposed.
FIG. In FIG. 7(a), first, an optical fiber 2 having a U-shaped folded portion 2C'2 with a straight bottom surface is manufactured from a straight optical fiber consisting of a core and a cladding. Then, masking such as painting is applied to areas other than the folding point 2d (the area indicated by the dashed line). Next, in FIG. 7(b), the folded portion 2C of the optical fiber 2 is immersed in a glass corrosive agent such as hydrofluoric acid. Then, as shown in FIG. 7(c), only the folding point 2d is corroded and the core is exposed. According to the above manufacturing method, the folded portion 2C in which the core is partially exposed can be formed relatively easily. Next, a case will be described in which the optical liquid sensor 1 of the present invention is applied to measuring the alcohol/gasoline mixture ratio. FIG. 8 is a sectional view of the detection device 2l. Detector it21
is provided with a fuel passage 22, and an optical liquid sensor 1 for measuring the fuel in this fuel passage 22 and a temperature detector 23 are built in parallel. Furthermore, the print base 124 is also built-in, making it compact. For example, if an optical fiber with a diameter of 0.75 m is used and the width of the U-shaped folded portion is 5-1, the optical liquid sensor 1 can be downsized to a length of about 25 m. Therefore, the detection device 220 as a whole can be made small, about 40 mm square or less. Next, the measurement accuracy of the optical fiber 2 in the case of measuring the alcohol/gasoline mixture ratio will be explained based on FIG. 9 and FIG. Figure 9 is a graph showing changes in refractive index in response to changes in alcohol concentration, and Figure 10 is a graph showing an example of the output of an optical optical analyzer with a folded portion consisting only of a core.
In Figure 9, the refractive index decreases as the alcohol concentration increases, although it varies depending on the liquid temperature. Therefore, using a multi-component glass optical fiber with a core of 1.62 (refractive index of the cladding being 1.55), which is higher than the highest value of the refractive index of the entire alcohol concentration range, allows measurement of the entire alcohol concentration range. However, in FIG. 10, if the folded portion 2b is composed of a core and a cladding,
As shown by the solid line, the gradient becomes gentler and the degree of perturbation becomes duller. Therefore, if the entire folded portion 2d is made up of only the core as shown in FIG. 3 or 4, the gradient becomes steeper and the perturbation becomes sharper, as shown by the dotted line in FIG. 1θ. The glass material, especially the core, can be selected depending on the type of alcohol to be measured, the concentration range, and the measurement sensitivity. [Effects of the Invention] Since the present invention is configured as described above, it produces the following effects. A large-diameter glass optical fiber is folded back in the opposite direction, and the folded section is used as a detection section in contact with the liquid, making it possible to downsize the entire optical optical sensor and simplify maintenance and inspection. Furthermore, the forward and return paths of the optical fiber are made up of a core and a cladding, and the folded portion has a portion consisting only of the core, or the folded portion has a portion where the core is exposed, so that measurement sensitivity can be improved. Can be done. A manufacturing method includes forming a folded part with an optical fiber consisting only of a core, fusing an outgoing path and a returning path consisting of a core and a cladding to both ends of this folded part, and then sealing and storing the outgoing path and the returning path in the main body. This allows you to easily produce a core with an exposed core of uniform thickness. Further, an optical fiber consisting of a core and a cladding is bent to form an outward path, a return path, and a folded portion, and at least one folding point of the folded portion is brought into contact with a glass corrosive liquid to partially corrode the core to expose the core. Then, by using a manufacturing method in which the outward and return paths are sealed and stored inside the main body, it is possible to easily manufacture a device in which the core is partially exposed.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the optical liquid sensor of the present invention, FIG. 2 is a bottom view of the optical liquid sensor of FIG. 1, FIGS. 3 and 4 are enlarged views of the folded part, and FIG. 5 is an optical Fig. 6 is a diagram showing the manufacturing method of the optical liquid sensor shown in Fig. 3, Fig. 7 is a diagram showing the manufacturing method of the optical liquid sensor shown in Fig. 4, and Fig. 8 is a diagram showing the manufacturing method of the optical liquid sensor shown in Fig. 4. A cross-sectional view of a detection device when the optical liquid sensor of the invention is applied to the measurement of alcohol/gasoline mixture ratio, FIG. 9 is a graph showing changes in refractive index according to changes in alcohol concentration, and FIG. FIG. 11 is a graph showing an example of the output of an optical optical sensor with a folded portion made of only a single piece, and FIG. 11 is a cross-sectional view of a conventional optical liquid sensor. The explanations of the main symbols in the drawings are as follows. 2... Optical fiber 2a - Outward path 2b - Return path 2c - Turning section (detection section) 3... Light emitting element Figure 4... Light receiving element 6... Core 7... Clad. Patent Applicant: Hitachi, Ltd. TAC Wire Co., Ltd. Agent: Yoshiyuki Kaji, Patent Attorney Figure 7 (a) (b) Column 8 (C) 3rd [21 (a) Figure 4 (b) Figure 9 Figure 10

Claims (4)

[Claims] (1) A large diameter glass optical fiber is folded back in the opposite direction, a light emitting element is provided at the beginning of the outgoing path of this optical fiber, a light receiving element is provided at the end of the incoming path, and the folded part of the optical fiber is exposed as a detection part, Most of the outward and return paths are optical liquid sensors sealed and housed in the main body, the outbound and return paths of the optical fiber are comprised of a core and a cladding, and the folded portion has a portion consisting only of the core. Optical liquid sensor. (2) A folded part is formed of an optical fiber consisting only of a core, an outgoing path and a return path consisting of a core and a cladding are fused to both ends of the folded part, and then the outgoing path and the returning path are sealed and stored in the main body. 1. The method for manufacturing an optical liquid sensor according to 1. (3) A large diameter glass optical fiber is folded back in the opposite direction, a light emitting element is provided at the beginning of the outgoing path of this optical fiber, a light receiving element is provided at the end of the incoming path, and the folded part of the optical fiber is exposed as a detection part, Most of the outward and return paths are optical liquid sensors sealed and housed within the main body, the outbound and return paths of the optical fiber are comprised of a core and a cladding, and the folded portion has a portion where the core is exposed. Optical liquid sensor. (4) An optical fiber consisting of a core and a cladding is bent to form an outward path, a return path, and a folded portion, and at least one folding point of the folded portion is brought into contact with a glass corrosive liquid to partially corrode the core to expose the core. 4. The method of manufacturing an optical liquid sensor according to claim 3, wherein the outgoing and returning paths are sealed and stored in the main body.