JP2006047018A - Level gauge using optical fiber sensor, level, manometer, and thermometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a level gauge, level, manometer, and thermometer using it, which do not depending on the refractive index of measuring target liquid, capable of measuring the liquid level not discretely but continuously. <P>SOLUTION: The liquid level gauge is constituted of: an optical fiber sensor 9 spliced with a sensor part 4 of a hetero-core part 30 being mode regulation releasing part at its tip part; a light source 1 for light emitting into the core of the optical fiber sensor 9; a signal detector 6 being the direct intensity of returned light to the light source 1 while receiving mutual action with external at the sensor part 4. By measuring the intensity of returned light from the tip of the sensor part 4, at least a part of which is dipped into the measurement objective liquid LQ, the liquid level LS of the objective liquid LQ is measured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid level gauge, a level indicator, a pressure gauge, and a thermometer using a tip-type optical fiber sensor that detects the state of the outside world at the tip of an optical fiber.

For example, Non-Patent Document 1 reports a liquid level meter using an optical fiber.
FIG. 14 is a schematic diagram showing a configuration of a liquid level meter using the above optical fiber.
The optical fiber 200 is composed of a core 201 and a clad 202 covering the outer periphery thereof. The core 201 is periodically provided with regions 203 having different refractive index distributions.
This is based on the principle of a long-period grating (LPG), and by providing a periodic refractive index distribution (grating) in the fiber, a cladding mode (the propagation light wave L _CL existing in the cladding is measured). Energy) and the substance attached to the cladding. That is, a loss can be caused in the propagating light wave L _CL depending on the concentration (refractive index) of the substance adhering to the cladding and its area. That is, the position (liquid level) of the liquid level LS of the liquid to be measured can be measured by measuring the loss of the propagating light wave L _CL .

  However, when the grating is provided in the fiber, the intervals are discrete, and a typical grating period is 100 μm to 1 mm. This feature means that the liquid level that can be measured can only take discrete values when used as a liquid level gauge.

Also, the liquid that can cause loss due to LPG must have a refractive index close to the refractive index of the cladding of the optical fiber, and the measurable refractive index range is 1.4 to 1.456. Therefore, for example, since the refractive index of water is about 1.333, the above measurement range means that only a considerably limited liquid can be measured.
Sanfraz Khaliq, Stephen W. James, and Ralph P Tatam, Fiber-optic liquid-level sensor using a long-period grating, Optics Letters, Vol. 26, No. 16, August 15, 2001.

  The problem to be solved is that it is difficult to measure the liquid level continuously, not discretely, regardless of the refractive index of the liquid to be measured.

  The liquid level meter according to the present invention includes an optical fiber portion that transmits light in the core, and a light transmissive member that is fusion-bonded to a tip of the optical fiber portion, and includes at least light transmitted by the optical fiber portion. A fiber optic sensor having a mode regulation release unit that partially guides the outside of the core to release the regulation of the mode of the light, and returns the light whose mode regulation is released to the core, and the optical fiber sensor Connected to an end of the optical fiber portion of the optical fiber sensor, and a light source that emits light to the core of the optical fiber sensor, and the core in response to an interaction between the mode specification release portion and the outside of the mode specification release portion A light detection unit that detects the direct intensity of the return light that has returned to the light source through the above, and in a state where at least a part is immersed in the liquid to be measured from the tip of the mode regulation release unit Return light intensity By measuring, for measuring the liquid level of the measurement object liquid.

In the liquid level gauge of the present invention, preferably, the mode regulation canceling portion is a hetero core portion having a core diameter different from that of the core of the optical fiber portion.
Alternatively, preferably, the mode regulation canceling portion is a hetero core portion made of only a clad.

Furthermore, it is preferable that the surface of the hetero core portion further includes a metal film that generates surface plasmons by reflection of light in the hetero core portion on the surface.
Further, preferably, the surface of the hetero core part selectively reacts with the liquid to be measured outside the hetero core part, and changes corresponding to the reaction are caused in the hetero core part. The detection drug that brings to the light is fixed.
More preferably, the light in the hetero core part is reflected on the surface of the end part opposite to the end part fusion-bonded to the optical fiber part of the hetero core part. It further has a reflection part returning to the optical fiber part side.

  The liquid level meter according to the present invention includes an optical fiber portion that transmits light in the core, and a light transmissive member that is fusion-bonded to the tip of the optical fiber portion, and the light transmitted by the optical fiber portion. A plurality of optical fiber sensors having a mode specification releasing unit that guides at least a part of the light to the outside of the core to release the specification of the mode of the light, and returns the light whose mode specification has been released to the core; A light source that is connected to an end of the optical fiber sensor on the optical fiber side and emits light to the core of the optical fiber sensor, and an interaction between the mode specification release unit and the outside of the mode specification release unit. A light detection unit that detects the direct intensity of the return light that has been received and returned to the light source side through the core, and each mode regulation canceling unit of the plurality of optical fiber sensors includes a liquid to be measured. It against the liquid level The liquid to be measured is measured by measuring the intensity of the return light in a state where at least a part is immersed in the liquid to be measured from the tip of any one of the mode regulation release portions. Measure the liquid level.

  In addition, the level according to the present invention includes an optical fiber portion that transmits light in the core and a light-transmitting member that is fusion-bonded to the tip of the optical fiber portion, and the optical fiber portion transmits light. A mode regulation canceling unit that guides at least a part of the light to the outside of the core to cancel the regulation of the mode of the light, and returns the light whose mode regulation has been released to the core; Three optical fiber sensors arranged so as to be spaced apart from each other; a light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor; A light detection unit that detects the direct intensity of the return light that has returned to the light source side through the core in response to the interaction with the outside of the mode specification release unit in the mode specification release unit; Each posture is fixed In a state in which a mode regulation release portion is contained in a container and a measurement target liquid contained in the container, and at least a part of the mode regulation release portion is immersed in the measurement target liquid By measuring the intensity of the return light, the liquid level of the liquid to be measured for each mode regulation release unit is measured, and the inclination of the liquid surface of the liquid to be measured with respect to the three optical fiber sensors is measured. .

  In addition, the level according to the present invention includes an optical fiber portion that transmits light in the core and a light-transmitting member that is fusion-bonded to the tip of the optical fiber portion, and the optical fiber portion transmits light. A mode regulation canceling unit that guides at least a part of the light to the outside of the core to cancel the regulation of the mode of the light, and returns the light whose mode regulation has been released to the core; Two optical fiber sensors arranged so as to be spaced apart from each other; a light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor; A light detection unit that detects the direct intensity of the return light that has returned to the light source side through the core in response to the interaction with the outside of the mode specification release unit in the mode specification release unit; Each posture is fixed In a state in which a mode regulation release portion is contained in a container and a measurement target liquid contained in the container, and at least a part of the mode regulation release portion is immersed in the measurement target liquid By measuring the intensity of the return light, the liquid level of the liquid to be measured with respect to the two optical fiber sensors obtained by measuring the liquid level of the liquid to be measured for each mode regulation release unit, The inclination of the liquid surface of the liquid to be measured is measured from the shape of the container and the volume of the liquid to be measured.

  The pressure gauge according to the present invention includes an optical fiber portion that transmits light in the core, and a light-transmitting member that is fusion-bonded to the tip of the optical fiber portion, and transmits the light transmitted by the optical fiber portion. An optical fiber sensor having a mode definition canceling unit that guides at least a part of the light to the outside of the core to cancel the definition of the mode of the light, and returns the light whose mode is canceled to the core; and the optical fiber A light source connected to an end of the optical fiber portion of the sensor and emitting light to the core of the optical fiber sensor, and receiving an interaction with the outside of the mode prescription release portion in the mode prescription release portion, A light detection unit that detects the direct intensity of the return light that has returned to the light source via the core, a container that holds the mode regulation release unit fixed therein, and a measurement target that is enclosed in the container With liquid The container has a mechanism in which the liquid level of the liquid to be measured fluctuates according to an external pressure, and the intensity of the return light in a state where at least a part is immersed in the liquid to be measured from the tip of the mode regulation release unit. Is measured, and the liquid level of the liquid to be measured is measured and converted into the external pressure.

  The thermometer according to the present invention includes an optical fiber portion that transmits light in the core, and a light transmissive member that is fusion-bonded to the tip of the optical fiber portion, and transmits the light transmitted by the optical fiber portion. An optical fiber sensor having a mode definition canceling unit that guides at least a part of the light to the outside of the core to cancel the definition of the mode of the light, and returns the light whose mode is canceled to the core; and the optical fiber A light source connected to an end of the optical fiber portion of the sensor and emitting light to the core of the optical fiber sensor, and receiving an interaction with the outside of the mode prescription release portion in the mode prescription release portion, A light detection unit that detects the direct intensity of the return light that has returned to the light source through the core, a container that holds the mode regulation release unit fixed therein, and is enclosed in the container, According to temperature And measuring the intensity of the return light in a state in which at least a part is immersed in the liquid to be measured from the tip of the mode regulation release unit. The liquid level is measured and converted into the temperature.

  According to the liquid level meter of the present invention, the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core is not discrete regardless of the refractive index of the liquid to be measured. The liquid level can be measured continuously.

  In addition, according to the level of the present invention, by combining a plurality of optical fiber sensors provided with a mode regulation release unit at the tip of the optical fiber unit that transmits light in the core, regardless of the refractive index of the liquid to be measured, The liquid level can be measured continuously, not discretely, and the inclination of the liquid level of the liquid to be measured can be measured.

  In addition, according to the pressure gauge of the present invention, the liquid level of the liquid to be measured varies depending on the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core and the external pressure. In combination with a container having a mechanism, the liquid level can be continuously measured and converted into an external pressure, not discretely, regardless of the refractive index of the liquid to be measured.

  In addition, according to the thermometer of the present invention, the liquid to be measured whose liquid level fluctuates according to the temperature of the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core and the temperature of the atmosphere. In combination, the liquid level can be continuously measured and converted into temperature, not discretely, regardless of the refractive index of the liquid to be measured.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment FIG. 1 is a schematic configuration diagram of a liquid level meter using a tip type optical fiber sensor according to this embodiment, and a sensor unit provided at the tip of the optical fiber sensor is connected to a liquid to be measured. It is an apparatus for measuring the position (liquid level) of the liquid level when immersed in the tip from the tip side.
A liquid level meter 100 shown in FIG. 1 includes a light source 1, an optical branching device 2, an optical fiber sensor 9, a reference light detector 5, a signal detector 6, and a measurement calculator 7.
One embodiment of the light detection unit in the present invention corresponds to the signal detector 6.

The light source 1 is connected to the optical branching device 2 by an optical fiber portion 20d, and the signal detector 6 is connected to the optical branching device 2 by an optical fiber portion 20e.
The optical fiber sensor 9 is connected to the optical fiber portion 20b through the optical fiber connector 3, and this optical fiber portion 20b is further connected to the optical branching device 2.
The reference light detector 5 is connected to the optical branching device 2 through the optical fiber portion 20c.

  The optical fiber sensor 9 has a sensor unit 4 at one end of the optical fiber unit 20a. The other end of the optical fiber portion 20a is connected to the optical fiber portion 20b via the optical fiber connector 3.

  Each of the optical fiber portions 20a to 20e is configured using an optical fiber. A single mode optical fiber or a multimode optical fiber may be used for the optical fibers constituting the optical fiber portions 20a to 20e. The optical fibers constituting the optical fiber portions 20a to 20e may be of different types.

  The lengths of the optical fiber portions 20a to 20e can be determined as appropriate. For example, when the liquid level of the liquid to be measured is measured in a laboratory or laboratory, the length may be several tens of centimeters. When it is necessary to increase the distance between the light source 1 and the sensor unit 4, for example, the length of the optical fiber unit 20b or the optical fiber unit 20d may be increased. Depending on the form of use, each of the optical fiber portions 20a to 20e can be several hundred meters long.

The signal detector 6 and the measurement calculator 7, and the light source 1 and the measurement calculator 7 are connected by signal lines, respectively.
For example, as shown in FIG. 1, the light source 1, the reference light detector 5, the signal detector 6, and the measurement computing unit 7 may be combined into a measuring device 8.

As the light source 1, both a multi-wavelength light source that emits light including light of a plurality of wavelengths and a single wavelength light source that emits monochromatic light of an arbitrary wavelength can be used. As the multi-wavelength light source, for example, a white light source is used, and as the single-wavelength light source, for example, a light emitting diode (Light Emitting Diode: LED) or a laser diode (Laser Diode: LD) is used.
The light source 1 outputs light LT 1 for measurement using the optical fiber sensor 9 to the optical branching device 2.

The optical branching device 2 is realized by a device such as an optical fiber coupler that, when light is incident on one input port, branches and outputs the light to a plurality of output ports.
In this embodiment, a 2 × 2 optical fiber coupler that has two input ports and two output ports and is manufactured by a fusion drawing method is used. In this 2 × 2 optical fiber coupler, light input to one input port is branched to two output ports and output.
In this optical fiber coupler, if the input / output direction of light is changed, the output port functions as an input port, and the input port functions as an output port.

  For the optical fiber connector 3, for example, a commercially available connector used for connecting optical fibers is used. The optical fiber connector 3 is used for connection between the optical fiber portion 20a of the optical fiber sensor 9 and the optical fiber portion 20b. When the optical fiber sensor is manufactured by providing the sensor part 4 directly at the tip of the optical fiber part 20b, the optical fiber connector 3 is unnecessary.

The optical fiber sensor 9 causes the LT2 light input from the light source 1 through the optical branching device 2, the optical fiber unit 20b, and the optical fiber unit 20a to interact with the external environment of the optical fiber sensor 9 in the sensor unit 4, and As a situation, the liquid level LS of the measurement target liquid LQ is detected.
Details of the configuration and function of the optical fiber sensor 9 will be described later.

The reference light detector 5 detects the reference light LT5 branched from the light LT1 from the light source by the light branching device 2.
The reference light detector 5 is realized by, for example, a photodiode or a spectrum analyzer (spectrometer).
The reference light LT5 detected by the reference light detector 5 is used as a reference (reference) for canceling instability such as temporal fluctuation of the light LT1 from the light source 1, and for example, the reference light detector 5 is a measurement computing unit 7. The reference signal SGr obtained by detecting the reference light LT5 is transmitted to the measurement calculator 7. Therefore, the reference light detector 5 is not necessary if the measurement does not take into account the stability of the light source 1, and an output port for branching light to the reference light detector 5 in the optical branching device 2 is also necessary. Absent.

The signal detector 6 receives the return light returned to the light source 1 side through the optical fiber unit 20b and the optical branching device 2 due to the interaction with the external environment (external environment) of the optical fiber sensor 9 in the optical fiber sensor 9. The light is received through the optical fiber portion 20e.
The intensity of the return light is detected by the signal detector 6. That is, the signal detector 6 detects the direct intensity of the return light from the optical fiber sensor 9.
The signal detector 6 transmits a data signal SG 1 of the detected light intensity to the measurement calculator 7.

  As the signal detector 6, for example, a spectrum analyzer or a light receiving circuit using a photodiode is used, and these detectors are used depending on the type of the light source 1. For example, when a white light source is used as the light source 1, a spectrum analyzer is used to detect the intensity of each wavelength of light included in the light from the white light source. When a single wavelength light source such as an LED or LD is used as the light source 1, a light receiving circuit using a photodiode is sufficient. A light receiving circuit using a photodiode is sometimes called a power meter.

The measurement computing unit 7 is realized by, for example, a processing circuit such as a CPU (Central Processing Unit) and a program for driving the processing circuit.
The measurement computing unit 7 calculates the measurement value of the measurement target using the optical fiber sensor 9 based on the data signal SG1 transmitted from the signal detector 6. In other words, the measurement computing unit 7 obtains information on the intensity of light represented by the data signal SG1 by the predetermined calculation using this intensity, the presence of the measurement object in the external environment of the optical fiber sensor 9, its concentration, acidity, etc. Convert to characteristic information. A program for conversion according to such a measurement purpose is included in the measurement calculator 7.

  In order to automate the measurement, a control signal SG2 may be output from the measurement computing unit 7 to the light source 1 so that the measurement computing unit 7 controls on / off of the light source 1 and intensity / type of light. .

Hereinafter, the optical fiber sensor 9 will be described in detail.
2A to 2C show the configuration of the optical fiber sensor 9 according to the first embodiment, and are longitudinal sectional views in the vicinity of the sensor portion 4 of the optical fiber sensor 9. FIG. 2A to 2C show optical fiber sensors in which the structure of the sensor unit 4 is different.
The optical fiber sensor 9 according to the present embodiment includes an optical fiber portion 20 a and a sensor portion 4.
The optical fiber portion 20a includes a core 21 and a clad 22 laminated around the core 21. Light from the light source 1 enters the core 21.
In addition, the sensor unit 4 according to the present embodiment includes a hetero core unit 30, a metal film 50, and a reflective film 60.

One embodiment of the mode regulation releasing unit in the present invention is the hetero core unit 30. One embodiment of the reflecting portion in the present invention is the reflecting film 60.
The optical fiber sensor 9 according to the present embodiment is compared with the length of the optical fiber portion 20a of several millimeters to several tens of millimeters at the end opposite to the end disposed on the light source 1 side of the optical fiber portion 20a. Short hetero cores 30 are connected. Therefore, the optical fiber sensor 9 is a tip-type optical fiber sensor in which the hetero core portion 30 constituting the sensor portion 4 exists at the tip.

2A and 2B show a hetero-core portion 30 having a core 31 and a clad 32 stacked around the core 31, like the optical fiber portion 20a. A hetero core portion 30 in which the diameter bl of the core 31 is smaller than the diameter al of the core 21 of the optical fiber portion 20a is shown in FIG. 2A, and the hetero core portion 30 in which the diameter bl is larger than the diameter al. This is shown in FIG.
Thus, since the diameter bl of the core 31 is different from the diameter al of the core 21 of the optical fiber portion 20a, the core 31 and the clad 32 are referred to as a hetero core portion.
The refractive index of the core 21 is slightly larger than the refractive index of the clad 22, and the refractive index of the core 31 is slightly larger than the refractive index of the clad 32.
Each of the core 31 and the clad 32 is a light transmissive member and can transmit light.

In the hetero core portion 30 shown in FIG. 2A, the diameter bl of the core 31 is sufficiently smaller than the diameter al of the core 21, and for example, it is assumed that al = 50 μm and bl = 3 μm.
In the hetero core section 30 shown in FIG. 2B, the diameter bl of the core 31 is sufficiently larger than the diameter al of the core 21, and for example, it is assumed that al = 50 μm and bl = 90 μm.
Further, the length cl of the hetero core portion 30 is set to several mm to several tens mm, for example.

  Further, as shown in FIG. 2C, for example, a light transmissive member 300 having a refractive index equivalent to that of the cladding 22 of the optical fiber portion 20a and capable of transmitting light is used instead of the hetero core portion 30. It can also be used. Such a light transmissive member 300 can also be regarded as a kind of hetero-core portion having a core diameter bl of zero.

The optical fiber portion 20a and the hetero core portion 30 or the light transmissive member 300 are coaxially joined along the longitudinal direction at an interface 40a orthogonal to the longitudinal direction. When joining the hetero core part 30 to the optical fiber part 20a, the core 31 of the hetero core part 30 and the core 21 of the optical fiber part 20a are in contact with each other.
For the above-mentioned joining, it is preferable to use a general-purpose fusion technique by electric discharge.

As the optical fiber part 20a and the hetero core part 30, either a single mode optical fiber or a multimode optical fiber can be used, and these may be used in combination.
In the following, for example, an optical fiber portion 20a using a multimode optical fiber (manufactured by Osaki Electric Co., Ltd.) having a core diameter al of about 50 μm is used as a single mode optical fiber (manufactured by Newport, F-SA, having a core diameter bl of about 3 μm). The case where the hetero-core part 30 using the above is joined will be described as an example.

Due to the presence of the hetero core portion 30, at least a part of the light transmitted through the core 21 of the optical fiber portion 20a leaks to the outside of the core 21 at the interface 40a. At least a part of the leaked light guided to the outside of the core 21 travels in the cladding 32 of the hetero core portion 30. At this time, in the clad 32 of the hetero core part 30, the light mode regulation in the core 21 of the optical fiber part 20a is canceled and broken.
The definition of the light mode in the hetero-core unit 30 is canceled because the type of optical fiber used as the optical fiber unit 20a and the hetero-core unit 30 is a single-mode optical fiber or a multi-mode optical fiber. Regardless of whether it occurs.

FIG. 3 is a schematic diagram illustrating the configuration and operation of the sensor unit 4.
The hetero core part 30 of the sensor part 4 according to the present embodiment is formed with a metal film 50 so as to cover the surface side.
As the metal film 50, for example, a chromium (Cr) film is formed on the outer surface of the hetero core 30 by vapor deposition, and a gold (Au) film is formed on the chromium film by vapor deposition. A metal film 50 is formed as a laminated film. The film thickness of the chromium film is, for example, about several nm, and the film thickness of the gold film is, for example, about several tens of nm.

As will be described in detail later, light in the hetero core portion 30 is reflected at the boundary between the hetero core portion 30 and the metal film 50 to generate surface plasmons.
For example, the metal film 50 may be formed using other metals such as silver (Ag) and aluminum (Al).

In the first embodiment, the reflective film 60 is further provided on the surface of the end portion of the hetero core portion 30 opposite to the end portion that is fusion-bonded to the optical fiber portion 20a.
The reflective film 60 is formed by evaporating silver, for example.
The thickness dl of the reflective film 60 is set to a thickness that can sufficiently reflect the light in the hetero-core portion 30 toward the optical fiber portion 20a. For example, the film thickness dl is about several hundred nm.
The reflection film 60 may be formed using a substance other than a metal such as silver as long as the light in the hetero core part 30 can be sufficiently reflected toward the optical fiber part 20a.
Since the tip of the hetero core 30 is mirror-like by the reflective film 60, the light in the hetero core 30 is easily reflected at the tip, so that more light returns to the optical fiber 20a side. become.

Here, measurement of the position (liquid level) of the liquid level LS of the liquid LQ to be measured by the liquid level meter 100 according to the present embodiment will be described.
The optical fiber sensor 9 having the metal film 50 for generating surface plasmon can be used for measuring the liquid level of liquids having various physical and chemical characteristics. An example of measuring the liquid level is given below.

As shown in FIGS. 1 and 3, the sensor unit 4 according to this embodiment is immersed in a measurement target liquid LQ such as a glycerin aqueous solution from the tip side of the sensor unit.
In this state, measurement light is emitted from the light source 1.
As shown in FIG. 1, the light LT1 emitted from the light source 1 enters the optical branching device 2 through the optical fiber portion 20d.

  The light LT1 is branched into two lights by the light branching device 2. One light LT2 reaches the sensor unit 4 via the optical fiber unit 20b and the optical fiber unit 20a of the optical fiber sensor 9. The other light LT5 enters the reference light detector 5 as the reference light through the optical fiber portion 20c.

In the core 21 of the optical fiber portion 20a, the light LT2 is transmitted as light in which a plurality of modes are formed due to the normal properties of the optical fiber. The mode of light transmitted by the optical fiber portion 20a can also be schematically taken as the light reflection angle at the boundary between the core 21 and the clad 22. When the light mode is regarded as a reflection angle, the reflection angle of the light in the optical fiber portion 20a can be considered as a very large number of discrete angles.
In the present embodiment, since the measurement is performed using the intensity change of the light incident on the optical fiber portion 20a from the light source 1, it is sufficient to consider only the combined light intensity of the mode group for one wavelength.

  When light having various modes passes through the interface 40a and enters the clad 32 of the hetero-core portion 30, the mode is released and the mode is destroyed. In other words, in the hetero core 30, light is transmitted at various reflection angles at the boundary between the clad 32 and the metal film 50. This is because various conditions (core diameter, refractive index, refractive index distribution) that determine the mode form change when light enters the hetero-core portion 30, and fiber that is one factor for mode formation. This is probably because the length of the hetero core portion 30 is insufficient. Therefore, when light defined in a certain mode is incident on the hetero core 30, the mode is deregulated, the mode is destroyed, and the light is reflected at various reflection angles. It leaks into the clad 32.

  At this time, as shown in FIG. 3, the leaked light is reflected at the boundary between the clad 32 and the metal film 50 of the hetero core 30. At this time, due to a phenomenon called an evanescent interaction, an interaction occurs between the light in the clad 32 and the metal film 50, a change appears on the spectrum as an optical loss, the reflectivity changes, and in most cases In some cases, the reflectance of light decreases and the intensity of reflected light decreases.

The change in reflectance described above may occur even when the metal film 50 is not present. However, when the metal film 50 is provided, as shown in FIG. 3, surface plasmon resonance (Surface Plasmon resonance).
Resonance (SPR) phenomenon causes the energy of the light to be taken and lost to create the surface plasmon resonance wave SPW, so that the change in reflectance can be made larger and the measurement of the change in light intensity can be facilitated. be able to. Regarding the surface plasmon resonance phenomenon, for example, refer to documents such as “Kasai,“ Biosensor using surface plasmon resonance (SPR) ”protein nucleic acid enzyme, Vol. 37, No. 15 (1992) p2977-2984”. I want.

  When the metal film 50 exists, the reflectance of light in the clad 32 changes according to the refractive index and light absorption rate of the substance in contact with the metal film 50. When the metal film 50 is not present, the reflectance changes according to the refractive index and light absorption rate of the substance attached to the outer surface of the clad 32. Therefore, by measuring the intensity of the light reflected by the hetero core 30, it is possible to know characteristics such as the refractive index and the light absorption rate of the substance existing in the external environment of the sensor unit 4, so that the sensor unit is immersed. It is possible to measure the liquid level of the measurement target liquid LQ.

  By reflecting the light whose mode is broken at the boundary between the metal film 50 and the clad 32, it is possible to generate the interaction between the light and the outside of the sensor unit 4 at various reflection angles, that is, in more conditions. Become.

  The light that has entered the clad 32 of the hetero core portion 30 from the optical fiber portion 20 a and has become a mode-disrupted light is transmitted to the tip of the hetero core portion 30 while being reflected at the boundary with the metal film 50. Since the reflection film 60 is provided on the interface 40b at the tip of the hetero core 30 so as to be a mirror surface, the light is reflected at the interface 40b and is reflected again at the boundary with the metal film 50, and then the optical fiber portion 20a. Return to the side. In this way, by reflecting the light whose mode is broken at the tip of the sensor unit 4 and returning it, the return light that has returned to the optical fiber unit 20a only passes through the hetero core unit 30 in one direction. Compared with light, the light contains more information on mutual interference.

The return light LT3 returned to the core 21 of the optical fiber part 20a after interaction with the outside of the sensor part 4 in the hetero core part 30 is returned to the optical fiber part 20b as the return light LT4 shown in FIG. The optical branching device 2 is reached via
The return light LT4 is branched into two lights by the optical branching device 2. One branched light LT6 reaches the signal detector 6 via the optical fiber portion 20e.

  The signal detector 6 detects the intensity of the light LT6. Since there is a correlation between the intensity of the light LT6 and the intensity of the return light LT3, the intensity change of the return light LT3 can be known by detecting the intensity change of the light LT6.

Based on the information on the intensity of the light LT6 included in the data signal SG1 transmitted from the signal detector 6, the measurement calculator 7 obtains in advance the characteristics of the known liquid to be measured and the intensity of the light LT6 as described above. The liquid level of the liquid to be measured is measured using the correlation. At this time, the data from the signal detector 6 and the data from the reference light detector 5 are compared, and a calculation for correcting the light fluctuation of the light source 1 is performed.
The above correlation is stored as a lookup table in a storage device such as a memory (not shown). The measurement computing unit 7 accesses this memory as appropriate to obtain the correlation between the characteristics of the measurement object and the intensity of the light LT6.

  According to the liquid level meter according to the present embodiment, the optical fiber sensor provided with the mode regulation release unit at the tip of the optical fiber unit that transmits light in the core, regardless of the refractive index of the liquid to be measured, The liquid level can be measured continuously, not discretely.

(Example)
A liquid level detection response experiment of the optical fiber sensor was performed using the liquid level meter according to the present embodiment.
First, the optical fiber sensor was fixed to a stage jig movable perpendicularly to the liquid surface, moved from above to below, and immersed in the liquid from the tip side of the sensor portion of the optical fiber sensor. This operation is equivalent to the liquid level rising and falling with respect to the optical fiber sensor.
The liquid used for the measurement is a 50% glycerin aqueous solution (refractive index: 1.398), the length of the sensor part of the used optical fiber sensor is 10 mm, and a chromium film of 5 nm and a gold film of 20 nm are formed on the surface of the sensor part. A metal film as a laminated film was formed.

FIG. 4 (a) shows a spectrum obtained by quantifying the normalized light intensity with respect to the wavelength when immersed in the liquid from the front end side of the optical fiber sensor using a white light source and a spectrum analyzer. This corresponds to the case where the sensor portions are immersed 0 mm, 6.75 mm, 9.00 mm, 11.25 mm, and 13.5 mm, respectively.
When the sensor part is gradually immersed in a 50% aqueous glycerin solution, the intensity of light decreases around a specific wavelength region (660 nm). This phenomenon is peculiar to SPR, and the wavelength at which light is most reduced is called the resonance wavelength.

FIG. 4 (b) shows the light propagation intensity when a light emitting diode and a photodiode having a peak wavelength of 660 nm are used as a light source and a photodetector, respectively, and the sensor part is immersed in a 50% aqueous glycerin solution at intervals of 0.8 mm. It is the figure which plotted the relative output equivalent to to inundation depth.
A monotonous decrease in light was observed with increasing depth of immersion in the sensor section.

Second Embodiment FIG. 5 is a schematic diagram showing the configuration of a liquid level meter according to this embodiment.
Similarly to the liquid level meter according to the first embodiment, the optical fiber sensor 9, the optical branching device 2, the light source, the measuring device 8 including the signal detector and the measurement arithmetic unit, and the reference light detector 5 are included.
Here, the optical fiber sensor 9 includes a plurality of optical fiber sensors, and sensor units (4a, 4b, 4c,. 4n) is arranged at different heights with respect to the liquid level LS of the liquid to be measured by the fiber fixing jigs FF1 and FF2.
In the above configuration, the liquid level of the measurement target liquid is measured by measuring the intensity of the return light from the sensor unit in a state where at least a part of the sensor unit is immersed in the measurement target liquid. Can do.

According to the liquid level meter according to the present embodiment, the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core allows the discrete measurement regardless of the refractive index of the liquid to be measured. Instead, the liquid level can be measured continuously.
In order to measure the liquid level with high accuracy using the tip type optical fiber sensor, it is necessary to suppress the length of the sensor unit to about several tens of millimeters. However, as in the present embodiment, a plurality of optical fibers are used. By arranging the sensors at different heights, the liquid level can be measured for each sensor unit, and the dynamic range of the liquid level measurement can be expanded.

Third Embodiment FIG. 6A is a schematic diagram showing the configuration of a level according to this embodiment, and FIG. 6B is a plan view showing the arrangement configuration of a fiber fixing jig and a sensor unit.
Similarly to the liquid level meter according to the first embodiment, the optical fiber sensor 9, the optical branching device 2, the light source, the measuring device 8 including the signal detector and the measurement arithmetic unit, and the reference light detector 5 are included.
Here, the level according to the present embodiment has three optical fiber sensors. The sensor portions (4a, 4b, 4c), which are hetero-core portions, which are the mode regulation release portions of the three optical fiber sensors, are housed in the container CN1 with their relative postures fixed by the fiber fixing jig FF3. Has been. Specifically, for example, as shown in FIG. 6 (b), it is arranged and fixed at every known angle (for example, an angle of 120 °) on the outer peripheral portion of the substantially cylindrical fiber fixing jig FF3.

  The container CN1 is sealed with the fiber fixing jig FF3 as a lid, and encloses a quantity of liquid (measuring liquid) such that the liquid level comes to the middle of each sensor part (4a, 4b, 4c). As the liquid to be used, anything such as water or oil may be used. Since this uses SPR as the sensing principle, various types, various concentrations and various refractive indexes can be obtained by changing the thickness of the metal film. It is because it can respond to a liquid. However, it is desirable to prevent the liquid from adhering to the sensor parts (4a, 4b, 4c) by using a volatile liquid such as ethanol or a liquid having low viscosity.

The three optical fiber sensors connected to the sensor units (4a, 4b, 4c) are connected to the optical branching device 2 including an optical coupler and an optical switch, respectively. The optical branching device 2 is connected to the measuring device 8 and can detect the optical signal of each sensor unit (4a, 4b, 4c) independently.
The reference fiber and the reference light detector 5 connected to the reference fiber are provided to cancel light loss due to instability of the light source or bending caused in the transmission line fiber from the sensor signal. Therefore, it is effective when measuring from a remote location or when the light intensity of the light source fluctuates greatly.

By measuring the intensity of the return light from each sensor part (4a, 4b, 4c) in a state where at least a part is immersed in the liquid to be measured from the tip of each sensor part (4a, 4b, 4c), The liquid level of the liquid to be measured is measured for each sensor unit (4a, 4b, 4c), and the inclination of the liquid level LS of the liquid to be measured with respect to the three optical fiber sensors is measured. By this inclination, the inclination of the level can be measured.
For example, the inclination of the liquid level LS can be measured for each of the initial state and the measurement target state, and how much the measurement target state is inclined with respect to the initial state can be measured.

FIG. 7A is a schematic diagram when it is assumed that the level shown in FIGS. 6A and 6B is inclined in a certain direction.
Assume that an inclination I has occurred from an initial state indicated by a dotted line to an inclined state indicated by a solid line. At this time, the liquid level LS once fluctuates, but eventually becomes steady and becomes a horizontal plane. For this reason, the positions where the sensor portions (4a, 4b, 4c) of the respective optical fiber sensors are in contact with the liquid surface change.

FIG. 7B shows a coordinate system of the fiber fixing jig FF3. The dotted and solid X marks CP in the figure indicate the contact points with the liquid level of each sensor. In this coordinate system, when the level (fiber fixing jig) is tilted, it seems that the liquid level is relatively tilted from the initial state (dotted line) to the tilted state (solid line).
Since the xy plane in FIG. 7B corresponds to a diagram viewed from the upper part of the level, the coordinates thereof are not changed, and only the values in the z-axis direction are changed. That is, only the liquid level information of the three optical fiber sensors changes.
Since the plane can be obtained if the values of the coordinates of the three points are known, the inclined plane can be obtained by sensing the liquid level information on the z-axis of the three points and combining it with the value of the xy coordinates, which is a constant.
In order to obtain the direction and the magnitude of the inclination, two angles (the angle formed with the θ1: xy plane, θ2: arc degree on the xy plane) may be obtained. Specifically, the normal of the inclined plane is obtained, and the angle with the plane in the initial state is obtained.

  According to the level of the present embodiment, a plurality of optical fiber sensors each provided with a mode regulation release unit at the tip of an optical fiber unit that transmits light in the core are combined, so that they are discrete regardless of the refractive index of the liquid to be measured. It is possible to measure the liquid level continuously and measure the inclination of the liquid surface of the liquid to be measured.

Fourth Embodiment FIG. 8A is a schematic diagram showing the configuration of a level according to this embodiment, and FIG. 8B is a plan view showing the arrangement configuration of a fiber fixing jig and a sensor unit.
Similar to the level according to the third embodiment, the optical fiber sensor 9, the optical branching device 2, the light source, the signal detector, the measuring device 8 including the measurement arithmetic unit, and the reference light detector 5 are provided.
Here, the level according to the present embodiment has two optical fiber sensors. The sensor part (4a, 4b) which is a hetero core part which is each mode regulation release part of two optical fiber sensors is housed in the container CN2 with its relative posture fixed by the fiber fixing jig FF4. Yes. Specifically, for example, as shown in FIG. 8 (b), it is arranged and fixed at a known angle (for example, an angle of 90 °) at the outer periphery of the substantially cylindrical fiber fixing jig FF4. .
In addition, the shape of the container is a spherical shape such as a round bottom flask, and the surface area of the liquid level LS is always maintained even when an inclination occurs. In the case of a round-bottomed container, provide a foundation to stabilize the leveling.

  In the level of the present embodiment, the liquid surface is tilted from the xyz coordinates (liquid level) detected by the sensor units of the two optical fiber sensors and the volume of the liquid (measuring liquid) enclosed in the container CN2. A plane can be obtained.

  According to the level of the present embodiment, a plurality of optical fiber sensors each provided with a mode regulation release unit at the tip of an optical fiber unit that transmits light in the core are combined, so that they are discrete regardless of the refractive index of the liquid to be measured. It is possible to measure the liquid level continuously and measure the inclination of the liquid surface of the liquid to be measured.

Fifth Embodiment FIG. 9 is a schematic diagram of a pressure gauge such as a barometer or a water pressure system according to this embodiment.
Similar to the liquid level meter according to the first embodiment, the optical fiber sensor 9, the optical branching device 2, the light source, the signal detector, and the measurement computing unit including the sensor unit 4 including the hetero core unit 30 serving as the mode regulation canceling unit. And a reference light detector 5.
The sensor unit 4 (mode regulation release unit) is fixed and accommodated in the container CN3 by the fiber fixing jig FF5.
Further, the measurement target liquid LQ is sealed in the container CN3.
Here, the container CN3 has a mechanism in which the liquid level LS of the measurement target liquid LQ varies according to an external pressure such as atmospheric pressure or water pressure. For example, when the bottom surface of the container CN3 has a diaphragm structure DF, the bottom surface of the container CN3 is deformed when pressure (atmospheric pressure, water pressure) is applied, and thereby the liquid level LS of the measurement target liquid LQ enclosed therein varies. To do.
Here, by measuring the intensity of the return light from the sensor unit 4 in a state where at least a part of the sensor unit 4 (mode regulation release unit) is immersed in the measurement target liquid LQ, the measurement target liquid LQ is measured. Measure liquid level and convert to external pressure. The inside of the container has a constricted shape at the top, so that minute changes in the shape of the diaphragm can be converted into large fluctuations in the liquid level and observed.

  According to the pressure gauge of the present embodiment, a mechanism in which the liquid level of the liquid to be measured fluctuates according to the external pressure and the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core The liquid level can be continuously measured and converted into an external pressure, not discretely, regardless of the refractive index of the liquid to be measured.

Sixth Embodiment FIG. 10 is a schematic diagram of a thermometer according to this embodiment.
Similar to the liquid level meter according to the first embodiment, the optical fiber sensor 9, the optical branching device 2, the light source, the signal detector, and the measurement computing unit including the sensor unit 4 including the hetero core unit 30 serving as the mode regulation canceling unit. And a reference light detector 5.
The sensor unit 4 (mode regulation release unit) is fixed and accommodated in the container CN4.
Further, in the container CN4, a liquid TL having a thermal expansion property such as alcohol or white kerosene is enclosed. Depending on the temperature of the atmosphere, the volume of the liquid TL for thermal expansion changes, and the liquid level LS varies.
By measuring the intensity of the return light from the sensor unit 4 in a state where at least a part of the tip of the sensor unit 4 (mode regulation release unit) is immersed in the liquid TL to be measured for thermal expansion, The liquid level of the liquid TL to be measured is measured and converted into temperature.

  According to the thermometer of the present embodiment, the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core, and the liquid to be measured whose liquid level varies according to the temperature of the atmosphere In combination, regardless of the refractive index of the liquid to be measured, the liquid level can be measured continuously, not discretely, and converted into temperature.

Seventh Embodiment FIGS. 11 (a) to 11 (c) are longitudinal views of a sensor portion of an optical fiber sensor applicable to the liquid level gauge, level, pressure gauge, and thermometer according to the first to sixth embodiments. It is sectional drawing of a direction.
The sensor unit of the optical fiber sensor according to the present embodiment is different from the sensor unit shown in FIGS. 2A to 2C in that a detection drug immobilization film 500 is used instead of the metal film 50. ing. FIGS. 11A to 11C correspond to FIGS. 2A to 2C, respectively, and show different structures of the hetero core portion 30, respectively. The same components are denoted by the same reference numerals, and detailed description thereof is omitted.

  The detection drug immobilization film 500 is realized by, for example, a film formed by a sol-gel method or a polymer film. For example, forming the detection drug-immobilized film 500 as a porous film having extremely fine pores at the molecular level reacts the detection drug immobilized on the detection drug-immobilized film 500 and the measurement object more effectively. It is preferable in terms of possible.

As the detection agent, for example, a functional dye such as a pH indicator for detecting an acid or a base, or a chemical such as a metal indicator for detecting a specific metal can be used.
These detection drugs can be immobilized on the detection drug immobilization film 500 by mixing when forming the detection drug immobilization film 500 by the sol-gel method, or chemically fixed on the detection drug immobilization film 500. It can also be converted.

The detection drug as described above selectively reacts with a specific detection target depending on the type. By this reaction, a phenomenon such as absorption of light of a specific wavelength or generation of fluorescence occurs depending on the characteristics of the detection target (for example, whether it is an acid or a base).
In accordance with the phenomenon such as light absorption and fluorescence, changes such as spectrum change and intensity change are brought to the light in which the mode inside the hetero core 30 is broken.
Therefore, the signal detector 6 detects the spectral change and intensity change of the return light LT6 of the light subjected to the interaction based on the reaction between the detection agent and the detection target, thereby detecting the presence of the detection target, that is, the measurement target. It becomes possible to know characteristics such as pH, type, and the like.

As described above, according to the sensor unit of the present embodiment, the detection drug that reacts with a specific measurement object is immobilized on the hetero core 30 by the detection drug immobilization film 500. Therefore, it becomes possible to selectively measure the measurement object according to the type of detection drug, and it is possible to perform measurement with higher sensitivity and higher accuracy.
Since the detection drug is immobilized on the sensor unit 4 side, for example, detection and quantification of a measurement target contained in a gas as well as a liquid can be performed as in detection of ammonia.
As described above, various sensors such as a refractive index sensor, a concentration sensor, and a pH measurement sensor can be realized by changing the type of detection drug.

Eighth Embodiment FIGS. 12 (a) to 12 (c) are longitudinal views of a sensor portion of an optical fiber sensor applicable to the liquid level gauge, level, pressure gauge, and thermometer according to the first to sixth embodiments. It is sectional drawing of a direction.
The sensor part of the optical fiber sensor according to the present embodiment is different from the sensor part shown in FIGS. 2A to 2C in that the metal film 50 is not provided. FIGS. 12A to 12C correspond to FIGS. 2A to 2C, respectively, and show different structures of the hetero core portion 30, respectively. The same components are denoted by the same reference numerals, and detailed description thereof is omitted.

  When the optical fiber sensor according to the present embodiment is used, the reflective film 60 is not provided at the tip of the hetero core 30. Even without the reflective film 60, the light in the hetero core 30 is reflected to the optical fiber 20a side to some extent due to the difference in refractive index between the hetero core 30 and the outside outside.

  In an optical fiber type sensor, in order to detect the characteristics of the external situation of the sensor, it is only necessary to allow the light in the optical fiber to interact with the outside. When sensitivity and selectivity are not required, a metal film is used. 50 and the detection agent immobilization film 500 are not necessary. Therefore, even when the sensor 4 unit is realized using only the hetero core unit 30 as shown in FIGS. 12A to 12C, it is possible to detect the characteristics of the external situation.

  Even in the case of an optical fiber sensor in which only the hetero-core part 30 is fusion-bonded to the optical fiber part 20a, the detection mode can be made linear by losing the light mode in the hetero-core part 30. .

Ninth Embodiment FIG. 13 is a schematic configuration diagram of a liquid level meter using a tip-type optical fiber sensor according to the present embodiment.
The tip-type optical fiber sensor liquid level meter 100a according to the present embodiment has substantially the same configuration as that of the liquid level meter 100 according to the first embodiment. The apparatus 2a is connected, and the optical fiber branching apparatus 2a is different in that the reference fiber 4r and the reference light detector 5 are connected.
As described above, the propagating light LT51 is guided to the reference fiber 4r using the two optical branching devices (2, 2a). A reflection film is formed at the tip of the reference fiber 4r in the same manner as the sensor unit 4, and the light guided to the reference fiber 4r is reflected to be returned light LT52. The return light LT53 that has passed through the optical splitter 2a is guided to the reference light detector 5, where it is detected and the light intensity is measured. The reference light detector 5 is connected to the measurement calculator 7 and transmits a reference signal SGr obtained by detecting the reference light to the measurement calculator 7.

A reference fiber is introduced to reduce the effects caused by bending applied to the fiber. In implementation, the reference fiber is configured along a position as close as possible to the fiber of the sensor unit 4. By this, an equivalent bending is given to a sensor part and a reference fiber, and a bending loss can be made equivalent. In this way, the bending loss can be corrected by comparing the light intensities detected from the sensor unit and the reference fiber and performing a calculation process.
The configuration other than the above is the same as that of the first embodiment, and the optical fiber sensor in which the mode regulation release unit is provided at the tip of the optical fiber unit that transmits light in the core, regardless of the refractive index of the liquid to be measured, The liquid level can be measured continuously, not discretely. The configuration in which the two optical branching devices according to the present embodiment are connected and the reference fiber is provided can be applied to each of the above embodiments.

  The liquid level gauge, level, pressure gauge, and thermometer according to each of the above embodiments does not require electric power at the portion that directly contacts the liquid to be measured, and therefore has excellent electrical explosion resistance and flammability resistance, and transmits information by light. Therefore, remote monitoring is possible, and it is possible to construct a sensor unit that is small and light, and by using a configuration of a light emitting diode and a photodiode, it is possible to perform measurement with high real-time performance on the order of milliseconds, As a liquid level gauge, it is possible to measure the liquid level that rises and falls continuously with high accuracy, and the level can measure the inclination with high accuracy.

In addition, this invention is not limited to said embodiment and its modification.
For example, in each of the above embodiments, a non-adhesive (hydrophobic) cover member may be attached to the sensor portion of the optical fiber sensor to protect it. In this case, the liquid level is in contact with the sensor unit at any liquid level.
In addition, various modifications can be made without departing from the spirit of the present invention.

The liquid level meter of the present invention can adjust the liquid levels of various liquids, various concentrations, and various refractive indexes according to the type of metal film 50 and the type of detection drug immobilized on the detection drug immobilization film 500. It can be applied to a liquid level meter that measures with high accuracy.
Further, the level of the present invention can be applied to a level that detects a highly accurate inclination.
The pressure gauge of the present invention can be applied to a pressure gauge that measures pressure such as atmospheric pressure or water pressure with high accuracy.
Moreover, the thermometer of this invention is applicable to the thermometer which measures temperature with high precision.

FIG. 1 is a schematic configuration diagram of a liquid level meter using a tip type optical fiber sensor according to a first embodiment of the present invention. 2A to 2C are longitudinal sectional views in the vicinity of the sensor portion of the optical fiber sensor according to the first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating the configuration and operation of the sensor unit according to the first embodiment of the present invention. FIG. 4 (a) is a spectrum in which the normalized light intensity when immersed in the liquid from the front end side of the sensor part in the embodiment is shown with respect to the wavelength, and FIG. 4 (b) is a relative value of the sensor part. It is the figure which plotted the output with respect to the inundation depth. FIG. 5 is a schematic diagram showing the configuration of a liquid level meter according to the second embodiment of the present invention. FIG. 6A is a schematic diagram showing a configuration of a level according to the third embodiment of the present invention, and FIG. 6B is a plan view showing an arrangement configuration of a fiber fixing jig and a sensor unit. FIG. 7 (a) is a schematic diagram assuming that the level shown in FIGS. 6 (a) and 6 (b) is inclined in a certain direction, and FIG. 7 (b) shows the coordinate system of the fiber fixing jig. Yes. FIG. 8A is a schematic diagram showing a configuration of a level according to the fourth embodiment of the present invention, and FIG. 8B is a plan view showing an arrangement configuration of a fiber fixing jig and a sensor unit. FIG. 9 is a schematic view of a pressure gauge according to the fifth embodiment of the present invention. FIG. 10 is a schematic diagram of a thermometer according to a sixth embodiment of the present invention. FIGS. 11A to 11C are cross-sectional views in the longitudinal direction in the vicinity of the sensor portion of the optical fiber sensor according to the seventh embodiment of the present invention. 12A to 12C are cross-sectional views in the longitudinal direction in the vicinity of the sensor portion of the optical fiber sensor according to the eighth embodiment of the present invention. FIG. 13 is a schematic configuration diagram of a liquid level gauge using a tip-type optical fiber sensor according to the ninth embodiment of the present invention. FIG. 14 is a schematic diagram of a liquid level gauge using a conventional optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source 2, 2a ... Optical branching device 3 ... Optical fiber connector 4, 4a, 4b, 4c ... 4n ... Sensor part 4r ... Reference 3 illumination fiber 5 ... Reference light detector 6 ... Signal detector (light detection means) )
7 ... Measurement calculator (measuring means)
DESCRIPTION OF SYMBOLS 9 ... Tip type optical fiber sensor 20a-e ... Optical fiber part 21, 31 ... Core 22, 32 ... Cladding 30 ... Hetero core part 50 ... Metal film 60 ... Reflective film 100 ... Tip type optical fiber sensor liquid level meter 500 ... Detection drug immobilization film CN1 to CN4 container VDF diaphragm structure LQ liquid to be measured LS liquid level LT, LT1 to LT6, LT51 to LT53 optical FF1 to FF5 fiber fixing jig SG1 data signal SG2 control signal SGr ... reference signal SPW ... surface plasmon resonance wave TL ... thermal expansion liquid to be measured

Claims (11)

An optical fiber that transmits light in the core;
A light transmissive member fused and bonded to the tip of the optical fiber portion, and at least part of the light transmitted by the optical fiber portion is guided to the outside of the core to cancel the regulation of the mode of the light; An optical fiber sensor having a mode regulation canceling unit for returning the light whose regulation is canceled into the core;
A light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor;
A light detection unit that detects the direct intensity of the return light that has returned to the light source side through the core in response to the interaction with the outside of the mode specification release unit in the mode specification release unit;
A liquid level meter that measures the liquid level of the measurement target liquid by measuring the intensity of the return light in a state where at least a part of the mode regulation release unit is immersed in the measurement target liquid. The liquid level meter according to claim 1, wherein the mode regulation release unit is a hetero core unit having a core diameter different from that of the core of the optical fiber unit. The liquid level gauge according to claim 1, wherein the mode regulation canceling portion is a hetero core portion made only of a clad. The liquid level meter according to claim 2, further comprising a metal film that generates surface plasmons on the surface of the hetero core portion by reflection of light in the hetero core portion on the surface. A detection agent that selectively reacts with the liquid to be measured outside the hetero-core portion on the surface of the hetero-core portion and brings a change corresponding to the reaction to the light in the hetero-core portion The liquid level meter according to claim 2 or 3, wherein is fixed. The light in the hetero core portion is reflected on the surface of the end portion of the hetero core portion opposite to the end portion fusion-bonded to the optical fiber portion to the optical fiber portion side. The liquid level meter according to any one of claims 2 to 5, further comprising a reflecting portion to be returned. An optical fiber that transmits light in the core;
A light transmissive member fused and bonded to the tip of the optical fiber portion, and at least part of the light transmitted by the optical fiber portion is guided to the outside of the core to cancel the regulation of the mode of the light; A plurality of optical fiber sensors having a mode regulation releasing unit for returning light into which the regulation is released into the core;
A light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor;
A light detection unit that detects the direct intensity of the return light that has returned to the light source side through the core in response to the interaction with the outside of the mode specification release unit in the mode specification release unit;
Each mode regulation release portion of the plurality of optical fiber sensors is arranged at different heights with respect to the liquid surface of the liquid to be measured,
A liquid level meter that measures the liquid level of the measurement target liquid by measuring the intensity of the return light in a state in which at least a part is immersed in the measurement target liquid from any tip of the mode regulation release unit. An optical fiber that transmits light in the core;
A light transmissive member fused and bonded to the tip of the optical fiber portion, and at least part of the light transmitted by the optical fiber portion is guided to the outside of the core to cancel the regulation of the mode of the light; Three optical fiber sensors, each of which has a mode regulation canceling portion for returning the light of which the regulation has been canceled into the core, and the mode regulation canceling unit is disposed so as to have a predetermined interval;
A light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor;
A light detection unit that detects direct intensity of return light that has returned to the light source side through the core in response to an interaction with the outside of the mode specification release unit in the mode specification release unit;
A container for fixing the relative posture and accommodating each mode regulation release portion therein;
A liquid to be measured contained in the container,
By measuring the intensity of the return light in a state in which at least a part is immersed in the measurement target liquid from the tip of each mode definition release unit, the liquid level of the measurement target liquid for each mode specification release unit is determined. Measure and measure the inclination of the liquid level of the liquid to be measured with respect to the three optical fiber sensors. An optical fiber that transmits light in the core;
A light transmissive member fused and bonded to the tip of the optical fiber portion, and at least part of the light transmitted by the optical fiber portion is guided to the outside of the core to cancel the regulation of the mode of the light; Two optical fiber sensors, each of which has a mode regulation release unit for returning the light of which the regulation is released into the core, and the mode regulation release unit is arranged so as to open a predetermined interval;
A light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor;
A light detection unit that detects direct intensity of return light that has returned to the light source side through the core in response to an interaction with the outside of the mode specification release unit in the mode specification release unit;
A container for fixing the relative posture and accommodating each mode regulation release portion therein;
A liquid to be measured contained in the container,
By measuring the intensity of the return light in a state in which at least a part is immersed in the measurement target liquid from the tip of each mode definition release unit, the liquid level of the measurement target liquid for each mode specification release unit is determined. The level of the liquid level of the measurement target liquid is measured from the liquid level of the measurement target liquid with respect to the two optical fiber sensors obtained by measurement, the shape of the container, and the volume of the measurement target liquid. An optical fiber that transmits light in the core;
A light transmissive member fused and bonded to the tip of the optical fiber portion, and at least part of the light transmitted by the optical fiber portion is guided to the outside of the core to cancel the regulation of the mode of the light; An optical fiber sensor having a mode regulation canceling unit for returning the light whose regulation is canceled into the core;
A light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor;
A light detection unit that detects direct intensity of return light that has returned to the light source side through the core in response to an interaction with the outside of the mode specification release unit in the mode specification release unit;
A container for fixing and accommodating the mode regulation release portion;
A liquid to be measured enclosed in the container,
The container has a mechanism in which the liquid level of the liquid to be measured varies according to external pressure,
The liquid level of the measurement target liquid is measured by measuring the intensity of the return light in a state in which at least a part is immersed in the measurement target liquid from the tip of the mode regulation release unit, and converted into the external pressure. Pressure gauge. An optical fiber that transmits light in the core;
A light transmissive member fused and bonded to the tip of the optical fiber portion, and at least part of the light transmitted by the optical fiber portion is guided to the outside of the core to cancel the regulation of the mode of the light; An optical fiber sensor having a mode regulation canceling unit for returning the light whose regulation is canceled into the core;
A light source connected to an end of the optical fiber sensor on the optical fiber part side and emitting light to the core of the optical fiber sensor;
A light detection unit that detects direct intensity of return light that has returned to the light source side through the core in response to an interaction with the outside of the mode specification release unit in the mode specification release unit;
A container for fixing and accommodating the mode regulation release portion;
A liquid to be measured that is sealed in the container and has a liquid level that varies according to the temperature of the atmosphere,
The liquid level of the measurement target liquid is measured and converted into the temperature by measuring the intensity of the return light in a state in which at least a part is immersed in the measurement target liquid from the tip of the mode regulation release unit. thermometer.

Images