JPH02105020A - Optical liquid level sensor - Google Patents

Abstract

PURPOSE:To perform accurate measurement with a simple constitution by making the change of transmitted light quantity large with the change of the elongation of an optical fiber which is caused by the rise and fall of a float corresponding to a liquid level. CONSTITUTION:The optical fiber 3 having rubber-like elasticity whose length corresponds to the lowest water level is made to hang down from a cap 2 provided with an air vent hole on the upper end part of a cylindrical body 1. The lower end part of the optical fiber is attached to the float 4 which internally contacts with the cylindrical body. The change of the elongation of the optical fiber which is caused by the rise and fall of the float corresponding to the liquid level 5 can be known in such a constitution that the change of the transmitted light quantity between a light source 6 attached to the tip part of the optical fiber and a photodetector 7 provided at a position on the cap where the optical fiber penetrates is read with optical power 8. Thus, the change of the transmitted light quantity by the change of the elongation of the optical fiber which is caused the rise and fall of the float becomes large, so that the measurement can be accurately performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical liquid level sensor. More specifically, the present invention relates to an optical liquid level sensor using an optical fiber having rubber-like elasticity.

[Prior art] and [Problem to be solved by the invention]
Optical liquid level sensors used in water level gauges, etc. have conventionally used quartz or plastic optical fibers, and their method is to convert changes in water level into capacitance changes into frequency signals (Published by Denki Shoin). "Understanding Optical Fiber Application Technology," pages 204-212), or the end surface of the optical fiber and the liquid surface are made non-contact.

There are methods to determine the distance to the liquid surface by using the interference between the light emitted from the optical fiber and the returning light, which is reflected by the liquid surface.Although these methods are highly accurate, they require large systems. These problems include high technology, high cost, and complexity.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical liquid level sensor that has a simplified system and lower cost.

[Means to solve the problem]

An object of the present invention is to attach a float inscribed in the cylindrical body to the lower end of the optical fiber hanging from the upper end of the cylindrical body, and to prevent transmission due to changes in the elongation of the optical fiber caused by the rise and fall of the float corresponding to the liquid level. It has a structure that allows changes in the liquid level to be measured by an optical power meter connected to an optical fiber extending outside the cylindrical body, and the core material and cladding material of the optical fiber are crosslinkable with a glass transition temperature below room temperature. This is achieved by an optical liquid level sensor using a co-crosslinked product of a group-containing elastomer, the cladding material of which is covered with an elastomer protective material.

In the optical fiber used in the present invention, the core material and the cladding material are made of a co-crosslinked material of an elastomer containing a crosslinkable group whose glass transition temperature is below room temperature, and the cladding material is further coated with a protective material made of the elastomer. used.

In both cases, the glass transition temperature is below room temperature, preferably about 0°C.
A co-crosslinked product of a core material and a cladding material composed of the following elastomers having rubber-like elasticity is obtained by coextruding the core material and the cladding material using an elastomer containing a crosslinkable group or a mixture of it and a crosslinking agent. It is produced by a method in which a post-crosslinking reaction is carried out, or (2) a method in which the core material is extruded and treated under crosslinking conditions that do not allow the crosslinking reaction to be completed, and then the crosslinking reaction is completed immediately after the core material is coated with a cladding material.

Naturally, the core material and the cladding material are both excellent in transparency and have a difference in refractive index, that is, the former has a larger refractive index than the latter.

Specifically, as the core material, a crosslinkable group-containing acrylic elastomer having a refractive index no = 1.47 or more, preferably no = 1.475 to 1.492 is used.

Such a crosslinkable group-containing acrylic elastomer is an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms and/or an alkoxy group having 2 to 8 carbon atoms, as detailed in JP-A-61-184,507. About 1 to 30 mol%, preferably about 2 to 20 mol% of a monomer having a hydroxyl group, epoxy group, carboxyl group, reactive halogen group, amide group, or diene group as a crosslinking group is added to the alkoxyalkyl acrylate having an alkyl group. The crosslinkable group-containing monomer and its crosslinking method are as follows, for example.

(1) Hydroxyl group-containing vinyl monomer hydroxyalkyl (meth)acrylate, hydroxyalkoxyacrylate, N-methylolacrylamide, etc. These copolymers are polyisocyanates such as hexamethylene diisocyanate, polycarboxylic acids such as adipic acid, methoxymethyl (2) Epoxy group-containing vinyl monomer allyl glycidyl ether, glycidyl (meth)acrylate, etc. These copolymers are crosslinked with a crosslinking agent such as alkoxymethyl melamine such as melamine, and polyamines such as diethylenetriamine and m-phenylenediamine. (3) Carboxyl group-containing vinyl monomers such as acrylic acid, methacrylic acid, itaconic acid, etc. The copolymer is crosslinked by a method using a polyepoxide such as ethylene glycol diglycidyl ether, a crosslinking agent such as 1,4-butanediol, or 1,1,1-trimethylolpropane, or by heating.(4) Reactive halogen Group-containing vinyl monomers such as 2-chloroethyl vinyl ether, monochloroacetic acid, etc. These copolymers are crosslinked with crosslinking agents such as polyamines such as diethylene triamine, polycarbamates, etc. (5) Amide group-containing vinyl monomers acrylamide, methacryl (6) Diene monomers divinylbenzene, pentadiene, vinylcyclohexene, butadiene, cyclopentadiene, methylbutadiene, ethylene glycol diacrylate, propylene glycol Methods using sulfur such as di(meth)acrylate, organic peroxides such as benzoyl peroxide and dicumyl peroxide, azo compounds such as azobisisobutyronitrile, crosslinking agents such as divinylbenzene and triallyl cyanurate, or heating. On the other hand, the cladding material has a lower refractive index than the core material, generally a refractive index no=1.
34 to 1.41 is used. Specifically, IH
, IH-trifluoroethyl (meth)acrylate, I
H, IH, 3H-tetrafluoropropyl (meth)acrylate, IH, LH.

Side chain such as 5H-octafluoropentyl (meth)acrylate -〇〇〇 (CH,)n (CF, )mX
A fluorine-containing monomer that lowers the glass transition temperature, such as (meth)acrylate having (X = H or F), alone or about 1 to 30 mol%, preferably about 5 to 20
A copolymer of about 1 to 30 mol %, preferably about 2 to 20 mol % of the crosslinking group-containing monomer is used together with mol % of ethyl acrylate, butyl acrylate, methyl methacrylate, etc.

Manufacture of optical fiber using each of these materials.

(1) A method of co-extruding a core material material and a cladding material material, and then co-crosslinking the coextruded product by heating or irradiating it with light to impart a chemical bond to the interface between the core material layer and the cladding material layer, or ( 2) After the core material is extruded and treated under crosslinking conditions in which the crosslinking reaction is not completed, i.e. after applying heat or light irradiation to the extrudate in such a way that the crosslinking reaction is not completed.

This is carried out by immediately coating the cladding material using an extrusion coating method, dipping method, etc., and then heating or irradiating it again to cause co-crosslinking and impart a chemical bond thereto.

Therefore, the copolymers used as the core material and the cladding material are copolymerized with the same type of crosslinkable group-containing monomers,
Those that can be crosslinked by the same type of crosslinking method are preferred.

Thereafter, the surface of the cladding material is coated with an elastomer protective material for the purpose of protecting it from external factors and improving the intensity of blocking light that may enter from the outside. Such protective materials are made using, for example, ethylene-propylene copolymer rubber, nitrile rubber, etc. Specifically, they are coated with an elastomer solution containing compounding agents such as crosslinking agents depending on the type of elastomer used. This is done by heating and thermally crosslinking. These protective materials can also be formed by photocrosslinking.

In this case, unsaturated bonds in the protective material are utilized,
A photopolymerization initiator and, if necessary, a sensitizer and a polyfunctional photopolymerizable monomer or oligomer are added thereto, and photocrosslinking can be carried out by irradiation with light.

Formation of a protective material coating using such a photocrosslinkable elastomer can also be carried out by sequentially applying coating and light irradiation treatment to the surface of the co-crosslinked material of the core material and cladding material, as in the case of thermal crosslinking. It can also be carried out by a coextrusion method.

In this case, the core material, the cladding material, and the protective material are triple-coextruded and immediately photocrosslinked to photocrosslink the protective material, and then the core material and the cladding material are thermally crosslinked. Specifically, for example, each material is coextruded from a triple die into a reflective tube with a mirror-finished inner surface equipped with a mercury lamp.

After photo-crosslinking the protective material by irradiating it with ultraviolet light in a nitrogen gas atmosphere, it is introduced into a horizontal infrared furnace to undergo primary thermal crosslinking of the core material and cladding material, and finally, it is wound up on a drum and subjected to secondary thermal crosslinking. It is done by

An optical liquid level sensor configured using such an optical fiber is
A float inscribed in the cylindrical body is attached to the lower end of the optical fiber hanging from the upper end of the cylindrical body, and the highest water level is when the optical fiber does not stretch. Changes in the amount of transmitted light due to changes in the elongation of the liquid can be measured using an optical power meter connected to an optical fiber extending outside the cylindrical body.

Since various aspects of the optical liquid level sensor according to the present invention are shown in FIGS. 1 to 3 of the drawings, these will be explained.

In the embodiment shown in FIG. 1, an optical fiber 3 having rubber-like elasticity and having a length corresponding to the lowest water level is suspended from a lid 2 with an air vent hole (not shown) at the upper end of a cylindrical body 1. The lower end of this optical fiber is connected to a float 4 inscribed in the cylindrical body.
It is attached to.

Changes in the elongation of the optical fiber caused by the rise and fall of the float corresponding to the liquid level 5 are transmitted between the light source 6 attached to the tip of the optical fiber and the light receiving element 7 provided at the position where the optical fiber passes through the lid. A configuration is adopted in which changes in the amount of light are read by an optical power meter 8.

In the embodiment shown in FIG. 2, the light source 6 and the light-receiving element 7 are mounted on the lid body 2 with an air vent hole M! It has been done.

Since the optical fiber 3, which has rubber-like elasticity, is bent into a U-shape by the float 4 and buried, the elongation of the optical fiber changes even with the same displacement of the float, compared to the embodiment shown in Fig. 1. Since it is large, the sensitivity is further improved.

Note that an optical power meter 8 is connected to the light receiving side.

In the embodiment shown in FIG. 3, the light source 6 and the light receiving element 7 are also
are installed on the lid body 2 with an air vent hole, and these are attached to each end of the reflection plate 9 installed on the upper surface side of the float 4 and the Y-shaped optical fiber 3' having rubber-like elasticity. The light receiving element measures the amount of light emitted from the light source and reflected by the reflector.

In each of these representative embodiments, the light-receiving element (and light source) installed in the lid with an air vent hole is provided with a groove in which the connector thereof is attached.
It is glued into the groove with adhesive. Furthermore, in the embodiment shown in FIG. 1, a connector for connecting this connector is attached to the tip end of the optical fiber.

Although LDs (laser diodes), which have high brightness but are also expensive, are also used as light sources, LEDs are generally optimal. Further, as a light receiving element serving as a photoelectric conversion element, a Si photodiode, a Si phototransistor, a PIN photodiode, etc. are used.

An optical fiber is fixed to a float using a polyethylene hollow sphere or the like by making a groove in the upper part of the hollow sphere, passing the optical fiber through the groove, and bonding it with epoxy resin or the like. Further, as the reflecting plate installed on the upper surface side of the float, a glass plate, a transparent plastic plate, a metal plate, a mirror, etc. are used.

The cylindrical body in which the float is inscribed generally has a diameter of about 20 to
Made of vinyl chloride resin with an inner diameter of approximately 50mm.

A material made of polycarbonate or polyethylene is used, and a float having a diameter approximately 1 to 5 mm smaller than the inner diameter is inscribed therein.

〔Effect of the invention〕

Since the optical liquid level sensor according to the present invention has a large change in the amount of transmitted light due to the change in elongation of the optical fiber caused by the vertical movement of the float corresponding to the liquid level, it can measure the amount more accurately, and is structurally Since it is simple, the system can be made smaller and lower in price.

〔Example〕

Next, the present invention will be explained with reference to examples.

Example core material: Ethyl acrylate-2-hydroxyethyl acrylate (molar ratio 27:1) copolymer mixed with 6.8% by weight (NGO10H equivalent ratio 1.2) of hexamethylene diisocyanate (crosslinked product) 100% modulus of: 62.OKgf/aJ) Clad material: IH, IH, 5H-octafluoropentyl acrylate-ethyl acrylate-2-hydroxyethyl acrylate (molar ratio 17.5:6:
2) A mixture of terpolymer and 6.8% by weight of hexamethylene diisocyanate (100% modulus of cross-linked product = 53.1 Kgf/aJ) Protective material: EPDM (Japanese Synthetic Rubber Products EP24) mixed with 2
A toluene solution to which sulfur was added in an amount of
After heating at 100°C for 8 minutes), the cladding material was coated and heated at 100°C for 60 minutes to complete the crosslinking reaction between the two, and then the above protective material was coated and heated at 120°C for 3 minutes.
A protective material layer was formed by heating and crosslinking for 5 minutes. The obtained optical fiber has a core material diameter of 0.924 mm, a cladding material layer diameter of 1.00 mm, a protective material layer diameter of 2.02 mm, a tensile strength of 140 Kgf/cd, an elongation of 220%, and a hardness ( JIS
A) It has a physical property value of 63.

Using such an optical fiber, an optical liquid level sensor of the embodiment shown in FIG. 2 was manufactured.

A high-intensity LED (wavelength: 660 nm) is used as the light source, and a Si photodiode is used as the light receiving element.
-01) is installed on the lid. A polyethylene hollow sphere with a diameter of 46+ m and a weight of 60 g is used as the float, and the U-shaped bent portion of the optical fiber is fixed with adhesive.

The total length of the optical fiber used here was 1 m, and the distance between the bottom surface of the lid and the top surface of the float (= length of the variable part of the optical fiber) was 47 cm, and these were housed in a polycarbonate cylinder with an inner diameter of 50 mm. ing.

The lower end of this cylindrical body is open, so we put it into a water tank, measured the rate of change in light intensity with respect to fiber elongation, obtained the following values, and found a correlation between the two. Ta.

lliA1'μl Metaplasia 0 1.00 10 0.94 20 0.88 30 0.82 40 0.77 50 0.70 60 0.64 Note that when the optical fiber is stretched due to a change in the water level We also checked the amount of sinking of the float (difference in depth between the water surface and the lower end of the float), but almost no difference was observed even at 60% elongation, which was a 2L2cm displacement (decrease) from the water level of 47ci+. This is because a sufficiently heavy float was used.

[Brief explanation of the drawing]

1 to 3 are longitudinal sectional views of one embodiment of the optical liquid level sensor according to the present invention. (Explanation of symbols) 1......Cylindrical body 2......Lid 3.3', 3''...Optical fiber 4. ...Thrift...L...Float 5...Liquid level 6...Light source 7... . . . Light receiving element 10 . . . Reflector plate

Claims (1)

[Claims] 1. A float inscribed in the cylindrical body is attached to the lower end of the optical fiber hanging from the upper end of the cylindrical body, and changes in the amount of transmitted light due to changes in the elongation of the optical fiber caused by the rise and fall of the float corresponding to the liquid level are reflected outside the cylindrical body. It has a structure that allows liquid level changes to be measured by an optical power meter connected to an extended optical fiber, and the core material and cladding material of the optical fiber are co-crosslinked elastomers containing crosslinkable groups whose glass transition temperature is below room temperature. An optical liquid level sensor using a cladding material covered with an elastomer protective material.