JPH102809A - Pressure detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure detector which has simple construction and which is easily minimize and lightened and which can detect fluid pressure in particular, hydraulic pressure and the like with desired accuracy. SOLUTION: A silica glass fiber to be a core is bent in U shape by heat processing and its both ends are specularly polished. Solution is prepared by dissolving tetrafluoroethylene-hexafluoropropylene-vinyliden fuluoride ternary copolymer in methylethylketone. Then, the fiber bent in U shape is dipped into this solution and taken out fiber is driednaturally to remove solvent. A clad of 20μm which comprises the ternary copolymer is formed. Both end of obtained optical fiber 2 are mounted through a through hole 41 of a fixture 4 and mounted to terminal parts 3a, 3b. A stainless steel made protecting cover 5 is mounted at a determined position of the fixture 4. The terminal, parts 3a, 3b are respectively connected with an optical power meter of white light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pressure detector using an optical fiber. Pressure detector of the present invention, pneumatic equipment, hydraulic equipment, piping of various chemical plants, reaction tanks, etc.
It can be used in load measuring devices, impact measuring devices, submersibles, and the like.

[0002]

2. Description of the Related Art Conventionally, there are various means for detecting pressure. The following various pressure detectors using an optical fiber have been developed. (1) Photoelastic element type pressure detector When pressure is applied to a transparent elastic body in one direction, it acts on light as a birefringent crystal due to deformation and distortion represented by a tensor ellipsoid. This phenomenon is referred to as a photoelastic effect, and the development of an optical fiber pressure gauge utilizing this effect is being promoted. This pressure gauge has a structure in which a polarizer, a quarter-wave plate for optical bias, a photoelastic element, and an analyzer are arranged between an input / output optical fiber with a rod lens set with the optical axis aligned. ing.

(2) Diaphragm reflection type pressure detector This pressure detector detects a change in the reflection of light due to the displacement of the diaphragm, and transmits the signal through an optical fiber. For example, there is a method in which reflected light when the pressure on both sides of the diaphragm is balanced and reflected light when the diaphragm is distorted by the pressure in the tank are measured, and the pressure is detected based on the difference. Also, there is an optical transmission line composed of three optical fibers, two of which are used for transmitting light from a light source and the other one for receiving reflected light from a diaphragm. In this method, two lights having different modulation frequencies are radiated to a diaphragm with two optical fibers, respectively, and after detecting the reflected light, the two are separated and compared to obtain a pressure signal.

(3) Liquid crystal filled probe type pressure detector Cholesteric liquid crystal C ₄₅ H ₇₈ O ₂ and nematic liquid crystal VL
In a mixture of -2055N, the pressure causes a change in the amount of light scattering. A blood pressure measurement device using a light scattering pressure detector utilizing this has been developed. According to the experiment, an extremely small pressure of 4 × 10 ⁴ Pa can be detected. However, this pressure sensor is disadvantageous in that it has a large temperature dependency, and it is necessary to perform temperature correction for practical use.

(4) Optical fiber function type acoustic pressure detector (optical fiber type hydrophone) The phase of the guided light propagating in the single mode optical fiber is changed by the stress or bending applied to the optical fiber. , Due to the photoelastic effect of strain. This phase change can be accurately detected by configuring an optical fiber interferometer. Specifically, a detector for measuring acoustic pressure using a Mach-Zehnder interferometer using a single mode optical fiber, that is, an optical fiber type hydrophone is being developed.

In this technique, a light beam emitted from a laser light source is split into two by a beam splitter, one of which is coupled to an optical fiber for signal detection and the other to an optical fiber for reference light. When an acoustic pressure signal is applied to a signal arm in which an optical fiber is wound in a coil shape, a phase change of guided light occurs in the signal arm. The signal light having undergone the phase change and the reference light from the reference arm are superimposed via a beam splitter, and optically homodyne-detected by a light-receiving element, whereby measurement can be performed with high sensitivity.

[0007]

As described above, pressure detectors based on various principles and configurations have been developed, but each has the following problems. In the pressure detector of (1),
A large number of component parts such as a photoelastic element, a polarizer, and an analyzer are required, the configuration becomes complicated, and miniaturization is difficult. Also,
Since the optical fiber cables for transmitting and receiving light are opposed to each other, there is a problem in ease of attachment to the pressure detection site. (2)
In the pressure detector described above, since a diaphragm is used, there is a limit to miniaturization. In the pressure detector of (3), the liquid is sealed, which involves special troublesomeness, has a large temperature dependency as described above, and has a limit in its heat-resistant temperature.
Further, the pressure detector of (4) has a complicated structure and is difficult to miniaturize.

The present invention solves the above-mentioned problem, and uses an optical fiber provided with a specific elastically deformable cladding on the outer peripheral surface of the core, and reduces the light transmission amount when an external force is applied to the cladding. An object of the present invention is to provide a pressure detector that detects a pressure by a decrease. The pressure detector of the present invention has a simple structure, and can be easily reduced in size and weight, and can detect the pressure of a fluid such as a hydraulic pressure with a required accuracy.

[0009]

According to a first aspect of the present invention, there is provided a pressure detector comprising an optical fiber comprising a core, an elastically deformable clad provided on an outer peripheral surface of the core, and connected to one end of the optical fiber. The optical fiber is constituted by a light source and light amount detecting means connected to the other end, and detects a pressure applied to at least a part of the optical fiber. Further, the pressure detector of the second invention is an optical fiber comprising a core and an elastically deformable clad provided on the outer peripheral surface of the core, a light reflecting means provided at one end of the optical fiber, and The optical fiber is constituted by a connected optical splitter / coupler, a light source connected to the optical splitter / coupler, and a light amount detecting means, and detects a pressure applied to at least a part of the optical fiber.

The material constituting the above-mentioned "core" is Ge, which is used as the core of a silica glass based optical fiber.
Quartz glass containing O ₂ can be used. Also, B used as a core of a multi-component optical fiber
SiO ₂ —N containing aO, GeO ₂ , ZrO _2, etc.
a like ₂ O-CaO-based and _{SiO 2 -Na 2 O-B 2} O 3 system glass may be used. Further, resins such as polymethyl methacrylate (PMMA), polystyrene and deuterated PMMA used as the core of the plastic optical fiber can be used.

The "elastically deformable clad" needs to have a refractive index slightly lower than that of the core. The degree of the elastic deformation depends on the pressure range to be measured, the method of applying force to the clad, and the like. Should be taken into account as required. Specifically, it can be set in consideration of the thickness of the clad, the elastic modulus of the material constituting the clad, the easiness of the change in the refractive index, and the like. Examples of the material constituting the clad include a fluororesin such as a tetrafluoroethylene-vinylidene fluoride copolymer and an acrylic resin such as PMMA and polychloroalkyl methacrylate.

As a constituent material of the clad, a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (a product of 3M, trade name "THV200P"), which is a kind of fluororesin, has heat resistance and corrosion resistance. It is particularly preferred in that it has. The method of coating these constituent materials on the outer peripheral surface of the core is not particularly limited.For example, by dissolving the constituent materials in an appropriate solvent, immersing the core in this solution, taking out and drying, and removing the solvent. Cladding can be easily formed.

The "light source" includes a semiconductor laser, a light emitting diode and the like. The "light amount detecting means" includes a PIN photodiode which generates a photocurrent upon incidence of light, a detection device using an avalanche photodiode which generates an avalanche effect upon incidence of light and causes optical amplification, or the like as a detection element. Can be used. These may be appropriately selected depending on the pressure range to be detected, the specific structure of the pressure detector, and the like.

The "light reflecting means" in the second invention includes, for example, one obtained by mirror-polishing one end of an optical fiber and then depositing silver or the like. In the case of the second invention, the light is sent from the light source to the “optical branching / coupling device”, and is incident on the optical fiber from the optical branching / coupling device. The incident light is reflected by the light reflecting means described above, and the reflected light is transmitted again to the optical branching coupler through the optical fiber, where it is separated from the incident light and sent to the light quantity detecting means, and the light quantity is reduced. Is detected.

The optical fiber has a double structure of a central core having a high refractive index and a cladding surrounding the core having a low refractive index. Then, the optical signal entering the core propagates inside the core while repeating total reflection at the boundary surface between the core and the clad. In the pressure detector of the present invention,
When pressure is applied to the cladding, the cladding undergoes elastic deformation, which compresses the cladding. This increases the density of the cladding and slightly increases its refractive index. As a result, the critical angle at the interface between the core and the cladding increases, and some light leaks from the core to the cladding, reducing the amount of light transmitted through the optical fiber.

That is, the greater the pressure applied to the cladding, the higher the density of the cladding and, as a result, the higher the refractive index. As a result, the critical angle becomes larger, the amount of light leaking to the cladding increases, and the light transmission amount becomes smaller. That is, a certain relationship occurs between the pressure applied to the optical fiber and the amount of transmitted light. It is the principle of the pressure detector of the present invention that the change in the light transmission amount is measured as in the third invention.

On the other hand, there are various conventional pressure detectors utilizing optical fibers as described above. But for example
In the pressure detectors of (1), (2) and (3), the pressure is sensed not by the optical fiber itself but by a photoelastic element other than the optical fiber, a diaphragm or a mixture of liquid crystals. Also, in the pressure detector of (4), a phenomenon in which the phase of the guided light propagating in the optical fiber changes due to the photoelastic effect due to deformation or distortion such as stress or bending applied to the optical fiber is applied. Things. As described above, although the pressure detector similarly uses an optical fiber, the pressure detector of the present invention applies a completely different principle from the conventional one.

Since the pressure detector of the present invention operates on the above principle, if light other than the light transmitted from the light source enters the cladding from the outside, it causes a malfunction. Therefore, it is preferable to provide a "light absorbing layer" on the outer peripheral surface of the clad as in the fourth invention. As a result, light from the outside is absorbed by the light absorbing layer and does not affect the inner cladding. This light absorbing layer can be formed by, for example, a method of depositing carbon on the surface of the clad. When the deposited carbon is used as a light absorbing layer, its thickness is 0.05 to
A thickness of about 0.3 μm is sufficient, and a thickness of about 0.1 μm functions sufficiently as a light absorbing layer.

In order to more reliably prevent the influence of external light, it is preferable to further provide a "light reflecting layer" on the outer peripheral surface of the light absorbing layer as in the fifth invention. The light reflecting layer can be formed by, for example, a method of depositing silver on the surface of the light absorbing layer. When the deposited silver is used as a light reflecting layer, its thickness is 0.05 to 0.3.
A thickness of about 0.1 μm is sufficient, and particularly, a thickness of about 0.1 μm sufficiently functions as a light reflection layer.

Although the optical fiber has a two-layer structure of a core and a clad, the optical fiber does not have sufficient strength. Therefore, it is not preferable that an excessive pressure other than the pressure to be detected is applied to the optical fiber. Therefore, it is preferable that this optical fiber be covered with a protective cover having a through-hole enough to allow the fluid to easily flow in and out. The shape and number of the through holes are not particularly limited as long as the protective cover can maintain sufficient strength. The through holes are preferably provided evenly on the wall surface of the protective cover so that pressure is applied to the optical fiber isotropically.

The material of the protective cover is not particularly limited, and metals such as stainless steel and aluminum, resins such as polyolefin, polyester and polyamide, glass and the like can be used. In these, processing is easy,
Stainless steel, which has a sufficient strength even when thin, and which can reduce the weight of the element portion of the pressure detector is preferable. It is preferable that the optical fiber and the protective cover have a configuration using an appropriate fixing tool or the like as shown in FIG. 1 described later.

Further, in the pressure detector of the present invention, it is preferable that the pressure is applied to the optical fiber isotropically as described above, so that more accurate pressure detection can be performed. Therefore, the pressure detector of the present invention is particularly suitable for detecting the pressure of a fluid such as a gas or a liquid. However, the fluid can be used for pressure detection of not only low-viscosity fluids such as water and oil but also fluids having a certain degree of fluidity such as clay and certain gel-like substances. Further, the pressure detector of the present invention, such as determining the correlation between the compressive stress and strain on the test object by compressing the optical fiber with the test object and the jig in the radial direction,
It can also be used when the test object is not a fluid.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. Example Commercially available quartz glass fiber (diameter; 50 μm, refractive index 1.4)
6) is prepared. This was bent into a U-shape having a width of 3 mm by thermal processing, cut off so that the height from the bottom to both ends of the U-shape was 80 mm, and the cut surfaces at both ends were mirror-polished. On the other hand, a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer was dissolved in methyl ethyl ketone to prepare a solution having a concentration of 0.07 g / cc. Next, the quartz glass fiber bent in a U-shape was immersed in this solution at room temperature for 10 minutes, and the quartz glass fiber taken out was air-dried to remove the solvent.

As described above, a cladding made of the above-mentioned copolymer having a thickness of 20 μm was formed on the outer peripheral surface of the quartz glass fiber. Thereafter, carbon was deposited on the outer peripheral surface of the clad to form a light absorbing layer having a thickness of about 0.1 μm.
Further, silver was deposited on the outer peripheral surface of the light absorbing layer to form a light reflecting layer having a thickness of about 0.1 μm. Both ends of the optical fiber processed as described above were inserted into through holes provided at predetermined positions of the fixed portion, and attached to the terminal portion. Further, a stainless steel protective cover was attached to the fixture, and an element portion of the pressure detector was manufactured.

FIG. 1 shows the element portion of the pressure detector of the present invention.
Shown in In FIG. 1, 1 is an element portion, 2 is an optical fiber formed in a U-shape, 3a and 3b are terminal portions, 4 is a fixture,
41 is a through hole provided in the fixture, 5 is a protective cover, and 51 is a through hole provided in the protective cover. Fixture 4
The protective cover 5 was also made of stainless steel, and the lower end of the protective cover 5 was fitted to a predetermined position of the fixture 4 and fixed by means such as adhesion or welding. The pressure detection fluid flows in or out of the through hole 51 provided in the protective cover 5. It should be noted that if the protective cover 5 can be firmly fixed to such an extent that the protective cover 5 is not easily detached by the fitting, there is no particular need to perform bonding, welding, or the like as described above. Further, the light absorbing layer and the light reflecting layer are not shown because the drawing is complicated.

As shown in FIG. 2, the element section 1 of the pressure detector shown in FIG. 1 is mounted on a predetermined portion of a hydraulic pipe of a hydraulic press, one of the terminals is connected to a white light source, and the other is connected to an optical power source. Connected to meter. In FIG. 2, 6 is a white light source, 7 is an optical power meter, 8 is a hydraulic pipe of a hydraulic press, and 81 is a branch of the hydraulic pipe.

In FIG. 2, the lower pipe is connected to a hydraulic pump, and the upper pipe is connected to a hydraulic mechanism for driving a piston. Then, the oil flows in the direction of the arrow, flows in and out of the through holes 51 provided in the protective cover 5 of the element portion 1 mounted on the edge of the branch portion 81, and comes into contact with the optical fiber. The terminals 3a, 3b and the white light source 6 and the optical power meter 7 are connected by an optical fiber. The element portion 1 is fixed by fitting a screw provided on the outer periphery of the fixture 4 to a screw provided on the inner surface of the end of the branch portion 81 of the hydraulic pipe 8. There was no oil leakage from the mounting site.

Thereafter, the hydraulic press was operated while changing the hydraulic pressure. At the same time, the oil pressure was also detected by a conventional Bourdon tube pressure gauge, and the relationship between the indicated value and the indicated value of the optical power meter of the pressure detector of this embodiment was examined. As a result, a good linear relationship was confirmed as shown in FIG. Further, even when the pressure was increased or decreased, no hysteresis phenomenon was observed, and good reproducibility was exhibited.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention in accordance with the purpose and application. For example, the type of the core, the type of the material constituting the clad, the shape and size of the optical fiber, and the like can be appropriately changed. Also,
It can also be used as a pressure detector in the case of the type of the pressure-detected fluid to be detected or a means for transmitting a force other than fluid. In any case, the pressure can be easily and simply detected by confirming the correlation with the indicated value of another appropriate pressure detector such as the Bourdon tube pressure gauge described above.

[0030]

According to the first and second aspects of the present invention, it is possible to obtain a pressure detector which has a simple structure, is small in size and light in weight, has excellent mountability to a pressure-receiving portion, and has excellent reliability. it can. In this pressure detector, information can be transmitted by an optical fiber, so that remote monitoring and remote control can be performed without being affected by electromagnetic induction disturbance or the like. In addition, since electricity is not used, there is an advantage that explosion-proof treatment is not required.

Further, according to the present invention, as in the third invention, the change in the amount of light transmission in the optical fiber is measured, and the measurement is extremely easy. Further, by providing the light absorbing layer of the fourth invention or further providing the light reflecting layer of the fifth invention, a more reliable pressure detector can be obtained without being affected by external light at all. You can also.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an element portion of a pressure detector of the present invention in an embodiment.

FIG. 2 shows a pressure detector of the present invention in an embodiment.
It is explanatory drawing at the time of measuring the hydraulic pressure of the hydraulic piping of a hydraulic press machine.

FIG. 3 shows the output of the pressure detector of the present invention in the embodiment;
It is a graph which shows the correlation with the output of the conventional Bourdon tube pressure gauge.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1; Element part of a pressure detector, 2; U-shaped optical fiber, 3a, 3b; Terminal part, 4; Fixing tool, 41; Through hole provided in fixing tool, 5; A through hole provided in the protective cover, 6; a white light source, 7; an optical power meter, 8; a hydraulic pipe, 81;

Claims (5)

[Claims] 1. An optical fiber comprising a core, an elastically deformable cladding provided on an outer peripheral surface of the core, a light source connected to one end of the optical fiber, and a light amount detecting means connected to the other end. And a pressure detector for detecting a pressure applied to at least a part of the optical fiber. 2. An optical fiber comprising a core and an elastically deformable cladding provided on the outer peripheral surface of the core, light reflecting means provided at one end of the optical fiber, and optical branching coupling connected to the other end. A pressure detector comprising: a light source connected to the optical branching coupler; and a light amount detecting means, and detecting a pressure applied to at least a part of the optical fiber. 3. The pressure according to claim 1, wherein a pressure is detected based on a difference between a light amount measured by the light amount detection unit when no pressure is applied to the optical fiber and when a pressure to be detected is applied. Detector. 4. The pressure detector according to claim 1, wherein a light absorbing layer is provided on an outer peripheral surface of the clad. 5. The pressure detector according to claim 4, wherein a light reflecting layer is provided on an outer peripheral surface of the light absorbing layer.