JP2006284287A - Analog optical fiber sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive analog optical fiber sensor of a simple constitution. <P>SOLUTION: Changes in a liquid level are converted into mechanical displacements by a conversion part 1. The mechanical displacements are converted into optical intensity by a mechanism part 2 of a movable optical system to measure the optical intensity of measuring light. The mechanical displacements is measured by the measuring light by making reference to previously related reference light by a reference part 3 of a fixed optical system. In the mechanism part 2, emergent light of an incident and emergent part 2a for measurement of an optical fiber 4 for measurement is reflected by a vertically moving reflecting film 2b for measurement, and reflected light is made to return as measuring light from the incident and emergent part for measurement to the optical fiber for measurement. In the reference part 3, emergent light of an incident and emergent part 3a for reference of an optical fiber 5 for reference is reflected by a fixed reflecting film 3b for reference, and reflected light is made to return as reference light from the incident and emergent part for reference to the optical fiber for reference. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an analog type optical fiber sensor that detects a change in a measurement (monitoring) target such as a liquid level, temperature, and pressure by a change in light amount.

Conventionally, for example, an electric sensor for detecting a water level has been proposed, but this electric sensor converts a detection target such as a water level into a mechanical displacement, and the mechanical displacement is converted into a physical quantity by a differential transformer or a strain gauge. It is a system to convert. However, this type of electrical sensor requires an explosion-proof treatment to measure (detect) in the explosion-proof area, and a long-distance detection requires the use of an additional transmitter. There was a problem that required equipment costs.
As another example, there is an optical sensor that detects a change in light intensity. However, this optical sensor has a problem in that accurate measurement cannot be performed due to influences of fluctuations in the light source, optical transmission path loss, and the like.
As a conventional technique for solving these problems, an optical water level sensor (hereinafter referred to as “conventional example”) described in Japanese Patent Laid-Open No. 2001-91334 has been proposed. In this conventional example, when pressure is applied to a Bourdon tube provided in a case-like sensor head arranged at the bottom of the water, the Bourdon tube expands, and a pressure / strain conversion member bridged on the surface of the Bourdon tube or an optical type The strain sensor causes an optical change due to pressure proportional to the water level, this change is optically detected by a water level detector placed on the ground via an optical fiber, and a sensor head is placed by the signal processing unit. By finding the water level at a certain location, it is no longer affected by lightning strikes.
JP 2001-91334 A

According to the conventional example, it is possible to make it less susceptible to lightning strikes, and the water level is detected using a Bourdon tube, a pressure / strain conversion member, or an optical strain sensor, so that no power source or data transmission device is required. There is.
In the conventional optical fiber sensor including the above-described conventional example, there is an example in which FBG (Fiber Bragg Grating) using black reflection formed on the optical fiber is used. For example, when measuring the liquid level, a sensor thrown into the liquid receives a liquid pressure proportional to the liquid level at a sensitive part (such as a Bourdon tube, a diaphragm, or a bellows) and mechanically displaces. In FBG, the wavelength of reflected light is shifted according to the amount of strain generated by the mechanical displacement. The detector can detect the amount of shift and know the liquid level. At this time, the detector detects the phase shift amount with a complicated circuit configuration, so that the entire system becomes expensive.
An object of the present invention is to provide an analog optical fiber sensor that has a simple configuration and is inexpensive.

In the present invention, the physical quantity to be detected (measured and monitored) is changed to mechanical displacement by the conversion unit, and the mechanical displacement is converted into light intensity by using the mechanism unit constituting the movable optical system, and used as measurement light. The measurement of the light amount of the measurement light corresponding to the mechanical displacement refers to the light amount of the reference light by the reference unit of the fixed optical system associated in advance.
In the present invention, the conversion unit such as a diaphragm, a bellows, a spring, and a Bourdon tube can be displaced following the displacement of a physical quantity to be detected such as a liquid level. The mechanism unit measures the amount of displacement of the conversion unit as a change in light intensity. For example, as a conversion method between displacement and light intensity, the reflection film attached to the displaced part is associated with the amount of reflected light of the convergent light incident on the reflection film.
The features of the present invention are as follows.
A first feature of the present invention is that a conversion unit that can be mechanically displaced in response to a change in a detection target, a mechanism unit that follows the mechanical displacement of the conversion unit, and a measurement optical fiber connected to the mechanism unit And a reference unit for compensating for fluctuations in the amount of light as a disturbance factor, and a reference optical fiber connected to the reference unit. A measurement input / output portion of the measurement optical fiber, a measurement reflective film (including a reflection mirror, a reflector, and the like) disposed to face the measurement input / output portion, and the measurement reflective film A measuring lens disposed between the measuring input and output unit, and the reference unit forms a pair with the mechanism unit and corresponds to the measuring input and output unit of the measuring optical fiber. A reference input / output portion of the reference optical fiber A reference reflection film (including a reflection mirror, a reflector, etc.) disposed opposite to the reference input / output portion and corresponding to the measurement reflection film, the reference reflection film and the reference film A reference lens that is disposed between the input and output portions and corresponds to the measurement lens is provided, and the reflective film for measurement can move following the mechanical displacement of the conversion portion. The reference reflective film is fixed by fixing means, and the light emitted from the measurement input / output part of the measurement optical fiber in the mechanism part is reflected by the measurement reflective film and becomes measurement light. The light emitted from the reference input / output portion of the reference optical fiber in the reference portion is reflected by the reference reflective film, and is guided to the measurement optical fiber from the measurement input / output portion. And see above Lies in the incidence and emission portions are intended to be guided to the reference optical fiber.
The second feature of the present invention is based on the first feature, wherein the mechanism portion and the reference portion are housed in a case, the conversion portion is made of a diaphragm, and this diaphragm is attached to the bottom of the case. The measuring reflecting film of the mechanism part is fixed to a holder which stands on the diaphragm and is exposed in the case.
The third feature of the present invention is based on the first feature, wherein the mechanism part and the reference part are housed in a case, the conversion part is made of a bellows, and the measurement reflective film of the mechanism part is the above-described one. Being mounted on the bellows.
The fourth feature of the present invention is based on the first feature, wherein the mechanism portion and the reference portion are housed in a case, and the conversion portion is formed of a bellows enclosing a sensitive substance. It has a sensitive part that extends outside the case, and the reflective film for measurement of the mechanism part is attached to the bellows.
A fifth feature of the present invention is based on any one of the first to fourth features, and the measurement optical fiber and the reference optical fiber are branched from a plurality of locations of the optical fiber connected to the OTDR via branch couplers. Therefore, it is possible to simultaneously measure multiple points.
The sixth feature of the present invention is based on the first feature, and is a movable reflection optical system that follows the mechanical displacement of the conversion unit, and does not follow the conversion unit in the vicinity of the mechanism unit. In addition, a reference unit that is a fixed reflection optical system having the same structure as the movable reflection optical system is installed, and a measurement light amount Pk that is a return light amount from the movable reflection optical system and a reference light amount that is a return light amount from the fixed reflection optical system. The measurement amount to be measured can be calculated by analog from the ratio (Pk / Ps) with Ps.

According to the present invention, an inexpensive system can be provided by a simple detection method for explosion-proof, electromagnetic noise, lightning, and the like.
According to the present invention, since the disturbance factor can be eliminated by making the light intensity ratio of the measurement light and the reference light correspond to each other, it is possible to detect with high accuracy.

With reference to FIGS. 1-3, the analog type optical fiber sensor S1 which concerns on the 1st Embodiment of this invention is demonstrated.
The optical fiber sensor S1 detects (measures) a change in a measurement target (temperature, pressure, liquid level, etc.) that is a detection target.
An optical fiber sensor S1 illustrated in FIG. 1 includes a conversion unit 1, a mechanism unit 2, a reference unit 3, a measurement optical fiber 4, and a reference optical fiber 5.
In the illustrated example, the conversion unit 1 is made of a diaphragm, and this diaphragm is attached in the attachment hole 6 a at the bottom of the case 6. The diaphragm 1 is mechanically displaceable in response to a change in the detection target. When the detection target is at the liquid level of the liquid W, the diaphragm 1 is deformed into a mountain shape corresponding to an increase or decrease in the liquid level, or is shown from the mountain shape. It is possible to return to the original shape shown in FIG.
The mechanism unit 2 follows the mechanical displacement of the diaphragm 1. The mechanism unit 2 includes a measurement input / output unit 2a of the measurement optical fiber 4, a measurement reflection film 2b disposed to face the measurement input / output unit, the measurement reflection film, and the measurement input / output unit. And a measuring lens 2c disposed between the two portions. The light emitted from the measurement input / output part 2a of the measurement optical fiber 4 is reflected by the measurement reflection film 2b through the measurement lens 2c, and becomes measurement light and enters the measurement input / output part. The measurement reflective film 2 b is fixed to the upper end surface of the rod-shaped holder 7. The holder 7 stands on the inner surface of the diaphragm 1 and the upper end side is exposed in the case. In the holder 7, the diaphragm 1 is deformed by the magnitude of the liquid pressure of the liquid W. Accordingly, the measurement reflective film 2b moves up and down following this operation.
For this reason, the light emitted from the measurement entrance / exit section 2a is condensed by the measurement lens 2c and becomes convergent light, reaches the measurement reflective film 2b, is reflected there, and the reflected light is measured again as measurement light. The amount of light that is coupled to the incident / exit section is uniquely determined for each focal point (front focal point, rear focal point) depending on the position of the reflective film for measurement.
One end of the measurement optical fiber 4 is connected to the measurement input / output part 2a, and the other end is drawn from the upper part of the case 6 to the outside of the case and communicates with the detector 9 (FIG. 3).
The reference unit 3 is disposed in the installation space of the mechanism unit 2, that is, in the case 6, and compensates for fluctuations in light quantity due to disturbance factors (transmission loss, temperature variations of the mechanism unit 2 and the reference unit 3, etc.). It is. The reference unit 3 includes a reference input / output unit 3a connected to the reference optical fiber 5, a reference reflective film 3b disposed opposite to the reference input / output unit, the reference reflective film, and a reference And a reference lens 3c disposed between the light entrance and exit portions. The reference reflective film 3b is fixed to the case 6 via a holder 8 which is a fixing means.
For this reason, the light emitted from the reference entrance / exit section 3a is collected by the reference lens 3c and becomes convergent light, reaches the reference reflective film 3b, is reflected there, and the reflected light is again used as reference light. The amount of light coupled to the reference entrance / exit section is uniquely determined by fixing the position of the reference reflective film.
A reference incident / exit section 3a is connected to one end of the reference optical fiber 5, the other end is drawn from the upper part of the case 6 to the outside of the case, and the other end is connected to the detector 9 (FIG. 3).

The relationship between the mechanism part 2 and the reference part 3 is demonstrated.
The mechanism part 2 and the reference part 3 form a pair, have the same structure, and are provided in the case 6 adjacent to each other. The measurement input / output unit 2a, the measurement reflective film 2b, and the measurement lens 2c in the mechanism unit 2 correspond to the reference input / output unit 3a, the reference reflective film 3b, and the reference lens 3c in the reference unit 3, respectively. . However, the measurement reflective film 2b and the reference reflective film 3b have different mounting states. That is, the measurement reflective film 2b moves up and down in accordance with the mechanical displacement of the diaphragm 1, but the mechanism part 2 and the reference part 3 are different in that the reference reflective film 3b is fixed. Due to this difference, the reflected light that returns to the measurement incident / exit section 2a is a measurement light because it detects a change in the amount of light, and the reflected light that returns to the reference input / output section 3a is a reference light because it is constant. .
In other words, the reflected light that is reflected by the measurement reflective film and returns to the measurement input / output part 2a of the measurement optical fiber 4 changes its light amount (light intensity) every time the position of the measurement reflective film 2b changes. It becomes.
When the diaphragm 1 is displaced and the measurement reflective film 2b is raised from the position of FIG. 1, the measurement reflective film approaches the measurement input / output part 2a, and reflected light (return light from the measurement reflective film). The amount of reflected light decreases, and conversely, the amount of reflected light decreases by moving away from the measurement entrance / exit section 2a.
On the other hand, since the reference reflective film 3b is fixed, the focal point of the reference lens 3c with respect to the reference reflective film is not changed. The returning reflected light has a constant light amount (light intensity) and becomes reference light.
By detecting the intensity of the measurement light based on the relative ratio between the measurement light quantity and the reference light quantity and obtaining the displacement of the liquid level of the liquid W, accurate detection can be performed.
Of course, the amount of light (measurement light and reference light) returning to the measurement input / output unit 2a and the reference input / output unit 3a is affected by disturbance factors (transmission loss, temperature fluctuations of the mechanism unit 2 and the reference unit 3, etc.). Although easily changed, since both the measurement light and the reference light are similarly changed, the relative ratio does not change.
The relative ratio will be described.
Since the reflected light amount, the displacement of the diaphragm 1, the liquid pressure, and the liquid level of the liquid W have the relationship shown in FIG. 2, the liquid level can be detected by measuring the reflected light amount. That is,
As shown in FIG. 2, the liquid pressure of the liquid W (FIG. 1) and the liquid level are in a proportional relationship, and when the liquid pressure increases, the diaphragm 1 is displaced, so the liquid pressure and the displacement of the diaphragm are in a proportional relationship. Furthermore, the change in the amount of reflected light (measured light amount) follows the displacement of the diaphragm.
From this, the liquid level can be obtained from the amount of reflected light.
The amount of returning light (measurement light and reference light) varies under the influence of the disturbance factors. Even if the liquid level is obtained from the light amount of the measurement light measured by the mechanism unit 2, it is necessary to exclude fluctuations due to disturbance factors from the light amount in order to enable more accurate detection.
Therefore, in the vicinity of the mechanism unit 2 that is a reflection optical system (movable reflection optical system) that follows the mechanical displacement of the diaphragm 1, the movable reflection optical system is not linked to the movable unit (diaphragm 1 in the example of FIG. 1). A reference unit 3, which is a reflection optical system (fixed reflection optical system) similar to the system, is installed, and a return light amount (measurement light amount) Pk from the movable reflection optical system and a return light amount (reference light amount) Ps from the fixed reflection optical system, By calculating the ratio (Pk / Ps), a more accurate liquid level can be obtained.
As a result, both the above-described reflection optical systems (movable reflection optical system and fixed reflection optical system) are affected by disturbance factors (for example, even if the light source fluctuates or is transmitted over a long distance) Even if the coupling efficiency fluctuates due to fluctuations, fluctuations in the amount of reflected light act in the same way on any reflective optical system with the same configuration and cancel each other, so the fluctuations affect the relative ratio. There is no.

The optical fiber sensor S1 is connected to the detector 9 shown in FIG.
In the detector 9 shown in the figure, laser light emitted from a laser diode (LD) 9a as a light source is divided into two via a branching coupler 9d1. One of the branched lights is guided to the measurement optical fiber 4 and the other light is guided to the reference optical fiber 5. One of the lights is returned to the detector as measurement light and passes through the branch coupler 9 d 2 to be the first photodiode. (PD1) is input to 9b1, and is converted from an optical signal to an electrical signal by this photodiode and output to the arithmetic processing unit 9c. The other is returned to the detector as reference light and passes through the branching coupler 9d3 to the second. This is input to the photodiode (PD2) 9b2, and is converted from an optical signal to an electric signal by the photodiode and output to the arithmetic processing unit. The arithmetic processing unit obtains a relative ratio (measurement light amount / reference light amount), and the ratio Is input to the formula for calculating the analog physical quantity (for example, water depth in this example) prepared in advance, and the calculated value displayed in analog is Display unit via the interface (I / F) is displayed (not shown.).

The detection action of the analog type optical fiber sensor S1 will be described.
The laser light oscillated from the detector 9 is divided into two, and one light guided to the measurement optical fiber 4 of the optical fiber sensor S1 is emitted from the measurement input / output part 2a of the mechanism part 2 as measurement light. Then, the light is condensed by the measurement lens 2c and becomes convergent light and is incident on the measurement reflective film 2b. Then, the measurement light reflected by the measurement reflection film 2b is coupled to the measurement input / output unit 2a, and returns as the first photodiode (PD1) 9b1 in the detector 9 via the measurement optical fiber 4 and the branch coupler 9d2. Is converted into an electric signal and input to the arithmetic processing unit 9c. The other light guided to the reference optical fiber 5 is emitted from the reference entrance / exit section 3a of the reference section 3 as reference light, and then condensed by the reference lens 3c to become convergent light, which is the reference reflective film 3b. Is incident on. Then, the reference light reflected by the reference reflective film 3b is coupled to the reference incident / exit section 3a, and returns as the second photodiode (PD2) 9b2 in the detector 9 via the reference optical fiber 5 and the branch coupler 9d3. Is converted into an electric signal and input to the arithmetic processing unit 9c.
When the measurement reflective film 2b of the mechanism unit 2 is in the normal state shown in FIG. 1 (measurement temperature is within a normal range), the reflected light reflected by the measurement reflective film of the mechanism unit 2 becomes measurement light. Then, the light is guided to the measuring optical fiber 4 and reaches the detector 9, and the reflected light reflected by the reference reflecting film 3 b of the reference unit 3 becomes the reference light, and is guided to the reference optical fiber 5 and reaches the detector 9. Finally, from the relative ratio (measured light quantity / reference light quantity) calculated by the arithmetic processing unit 9c, a preset measurement amount (in this example, the liquid surface displacement amount) of the measurement target is calculated in an analog manner, and the calculated value By this, it can be confirmed that the level of the liquid level is in a normal state.
When the liquid level of the liquid W rises from the normal state shown in FIG. 1 and the diaphragm 1 is deformed into a mountain shape by the liquid pressure, the measurement reflective film 2b rises in conjunction with this deformation. The position gradually approaches the measurement lens 2c, and the measurement light reflected by the measurement reflection film 2b returns to the measurement input / output unit 2a, but the measurement optical fiber 4 changes in the state where the amount of the return light changes. The light is received by the first photodiode 9b1 of the detector 9 through the branch coupler 9d2. On the other hand, since the reference light is not affected by the displacement of the diaphragm 1, the amount of the return light based on this displacement does not change from the normal time, and the second light of the detector 9 is passed through the reference optical fiber 5 and the branch coupler 9d3. Light is received by the photodiode 9b2.
In the first and second photodiodes 9b1 and 9b2, the received measurement light and reference light are converted into electrical signals and output to the arithmetic processing unit 9c, and the arithmetic processing unit previously calculates the relative ratio (measurement light amount / reference light amount). The set measurement amount (in this example, the amount of displacement of the liquid level) is calculated in an analog manner, and it can be confirmed from the calculated value that the level of the liquid level is abnormal.
As described above, in the optical fiber sensor S1, the mechanical displacement of the diaphragm 1 is converted into a change in the reflected light amount (measured light amount) by the mechanism unit 2, the change is measured by the detector 9, and the liquid level is in a normal state. Or it is detected whether it is in an abnormal state. In order to reduce the measurement error based on the disturbance factor, the physical quantity at the liquid level is calculated from the ratio between the amount of measurement light from the mechanism unit 2 and the amount of reference light from the reference unit 3 having the same configuration as the mechanism unit. Is calculated in an analog fashion.

FIG. 4 shows the configuration of a multi-point detection system that can perform multi-point simultaneous measurement using an OTDR (Optical Time Domain Reflect meter) 11 as a detector connected to a plurality of optical fiber sensors S1.
In the illustrated multipoint detection system, the optical fiber 10 connected to the OTDR 11 at one end has a plurality of optical fiber sensors S1 connected to the other end by a bus.
In each optical fiber sensor S1, laser light emitted from the OTDR 11 is divided into two by branch couplers 12 and 13, one of which is guided to the mechanism unit 2 via the branch coupler 12 and each measurement optical fiber 4, and is used as measurement light. The other is guided to the reference unit 3 via the branch coupler 13 and each reference optical fiber 5 to be used as reference light.
In this multi-point detection system, since the OTDR 11 that detects the light intensity-modulated signal light and measures the Rayleigh scattered light on the line of the optical fiber 10 is used as a detector, the state of each optical fiber sensor S1 connected by the bus is collectively displayed. Can be measured.
By using the OTDR 11, long distance and multipoint measurement can be realized at low cost by using a general optical measuring instrument used for laying the optical fiber 10. In addition, when the OTDR 11 is used as a detector, not only can a multipoint measurement be performed on one fiber line, but a long-distance monitoring system can be configured at a low cost by combining a reflective optical switch.

An analog type optical fiber sensor S2 according to the second embodiment will be described with reference to FIG.
The optical fiber sensor S2 shown in FIG. 5 is for temperature measurement.
The optical fiber sensor S2 is different from the optical fiber sensor S1 shown in FIG. 1 in which the conversion unit 1 that mechanically displaces relative to the liquid surface is a diaphragm in that a conversion unit 21 that mechanically displaces with respect to temperature uses a bellows. ing.
The main feature of the optical fiber sensor S2 is that the converter 21 is a bellows, and all other components except the converter are substantially the same as the components of the optical fiber sensor S1 shown in FIG. Mechanism part 22 (measurement input / output part 22a, measurement reflection film 22b, measurement lens 22c), reference part 23 (reference input / output part 23a, reference reflection film 23b, reference lens 23c) in the optical fiber sensor S2, The optical fiber 24 for measurement, the optical fiber 25 for reference, and the case 26 are all the mechanical unit 2 (measurement input / output unit 2a, measurement reflective film 2b, measurement lens 2c), and reference unit 3 (see FIG. 1). The reference incident / exit section 3a, the reference reflection film 3b, the reference lens 3c), the measurement optical fiber 4, the reference optical fiber 5 and the case 6 are respectively supported.
Hereinafter, the characteristics of the optical fiber sensor S2 will be mainly described.
The bellows 21 includes an accordion-shaped displacement portion 21a, a conduit portion 21b, and a temperature sensing portion 21c, and a temperature sensitive material (organic liquid, vapor, etc.) that is a sensitive material is enclosed therein. A displacement portion 21a is connected to one end of the conduit portion 21b, and a temperature sensing portion 21c is connected to the other end. The displacement portion 21a and the conduit portion 21b are accommodated in the case 26, and the other end side of the conduit portion extends outside the case. A reflective film 22b for measurement of the mechanism portion 22 is attached to the upper surface of the displacement portion 21a. The displacement part 21a can be expanded and contracted in the vertical direction of FIG. 5, and the measurement reflective film 22b can be moved up and down through an expansion and contraction operation.
The temperature sensing unit 21 c can sense a temperature change that is a detection target (measurement target) outside the case 26. A sensitive substance such as an organic liquid filled in the bellows 21 undergoes a volume change according to a temperature change through the temperature sensitive part 21c, and the displacement part 21a mechanically moves (stretches) following this change.

The detection action of the analog type optical fiber sensor S2 will be described.
When the measurement reflective film 22b of the mechanism unit 22 is in the normal state shown in FIG. 5 (measurement temperature is within a normal range), the reflected light reflected by the measurement reflective film of the measurement unit 22 becomes measurement light. The reflected light reflected by the reference reflective film 3b of the reference section 23 is guided to the detector and guided to the reference optical fiber 25 to reach the detector. Then, from the relative ratio (measured light quantity / reference light quantity) calculated by the arithmetic processing unit, a measurement amount (temperature displacement amount in this example) that is set in advance is calculated in an analog manner, and the temperature is calculated based on the calculated value. It can be confirmed that it is in a normal state.
The measurement reflective film 22b rises from the normal state shown in FIG. The process by which the measurement reflective film 22b rises will be described. When the measurement temperature rises, this temperature rise reaches the temperature-sensitive substance through the temperature-sensing part 21c, and the volume of the temperature-sensitive substance increases, following the volume change. The pressure of the temperature sensitive substance in the displacement portion 21a rises, so that the measurement reflective film 22b rises, the position gradually approaches the measurement lens 22c, and the measurement light reflected by the measurement reflective film 22b. Returns to the measurement input / output unit 22a, but is output to the detector 9 through the measurement optical fiber 24 in a state in which the amount of the return light is changed, and the reference light is not affected by the displacement of the bellows 21. Therefore, the amount of the return light based on this displacement is input to the detector via the reference optical fiber 25 without changing from the normal time. After that, the calculation unit of the detector calculates the measurement amount (temperature displacement amount in this example) of the measurement target set in advance from the relative ratio (measurement light amount / reference light amount), and calculates the temperature based on the calculated value. Can be confirmed to be abnormal.

According to the analog type optical fiber sensor S2, since the bellows 21 is used as the conversion unit, a temperature change can be detected with a simple configuration and at a low cost.
The conversion unit is not limited to the bellows 21, and may be, for example, a piston.

Although the diaphragm 1 is used in the analog type optical fiber sensor S1 shown in FIG. 1 as the conversion unit, it is not limited to this example.
For example, as shown in FIG. 6, an analog optical fiber sensor S3 using a bellows 31 as a conversion unit may be used. Since the configuration and operation of the optical fiber sensor S3 are the same as the configuration and operation of the optical fiber sensor S1 except for the bellows 31, the description thereof is omitted.

  The conversion unit is not limited to the above-described diaphragm or bellows, and may be a spring, a Bourdon tube, or the like in combination with them.

It is sectional drawing which shows the analog type optical fiber sensor which concerns on 1st Embodiment in this invention, Comprising: It is a figure which has a liquid level in a normal state. It is a figure which shows the correlation in the relationship between the amount of reflected light and the displacement of a diaphragm, the relationship between a hydraulic pressure and the displacement of a diaphragm, and the relationship between a hydraulic pressure and a liquid level. It is a figure which shows the structure of the detector which has a photodiode. 1 is a configuration diagram showing a multipoint detection system in which a plurality of analog type optical fiber sensors according to the present invention are connected. FIG. It is a block diagram which shows the analog type optical fiber sensor which concerns on the 2nd Embodiment in this invention, Comprising: It is a figure which has temperature in a normal state. It is a block diagram which shows the analog type optical fiber sensor which concerns on 3rd Embodiment in this invention, Comprising: It is a figure which has a liquid level in a normal state.

Explanation of symbols

S1, S2, S3 Analog optical fiber sensor 1 Diaphragm (conversion unit)
21, 31 Bellows (conversion part)
21a Displacement part 21b Conduit part 21c Temperature sensing part 2,22 Mechanism part 2a, 22a Measurement input / output part 2b, 22b Measurement reflection film 2c, 22c Measurement lens 3,23 Reference part 3a, 23a Reference input / output part 3b , 23b Reference reflective film 3c, 23c Reference lens 4, 24 Measurement optical fiber 5, 25 Reference optical fiber 6, 26 Case 7 Holder 8 Holder (fixing means)
9 Detector 10 Optical fiber 11 OTDR (Detector)
12,13 Branch coupler

Claims (6)

A conversion unit that can be mechanically displaced in response to a change in a detection target, a mechanism unit that follows the mechanical displacement of the conversion unit, a measurement optical fiber connected to the mechanism unit, and an installation space of the mechanism unit And a reference unit for compensating for fluctuations in the amount of light caused by disturbance, and a reference optical fiber connected to the reference unit,
The mechanism section includes a measurement input / output unit of the measurement optical fiber, a measurement reflective film disposed opposite to the measurement input / output unit, and the measurement reflective film and the measurement input / output unit. Each with a measuring lens placed between them,
The reference part forms a pair with the mechanism part, and is arranged opposite to the reference input / output part of the reference optical fiber corresponding to the measurement input / output part of the measurement optical fiber and the reference input / output part. Therefore, the reference reflective film corresponding to the measurement reflective film and the reference reflective film and the reference input / output portion are disposed, and correspond to the measurement lens. Each with a reference lens,
The reflective film for measurement is movable following the mechanical displacement of the conversion unit,
The reference reflective film is fixed by a fixing means,
The light emitted from the measurement input / output part of the measurement optical fiber in the mechanism part is reflected by the measurement reflective film, and becomes measurement light and is guided from the measurement input / output part to the measurement optical fiber. Yes,
The light emitted from the reference incident / exit section of the reference optical fiber in the reference section is reflected by the reference reflective film, and is guided as reference light from the reference incident / exit section to the reference optical fiber. An analog type optical fiber sensor characterized by that.   The mechanism part and the reference part are housed in a case, the conversion part is made of a diaphragm, and this diaphragm is attached to the bottom part of the case, and the reflection film for measurement of the mechanism part is erected on the diaphragm. 2. The analog optical fiber sensor according to claim 1, wherein the analog optical fiber sensor is fixed to a holder exposed in the case.   The analog part according to claim 1, wherein the mechanism part and the reference part are housed in a case, the conversion part is made of a bellows, and the reflection film for measurement of the mechanism part is mounted on the bellows. Type optical fiber sensor.   The mechanism part and the reference part are housed in a case, and the conversion part is composed of a bellows enclosing a temperature sensitive substance, and the bellows has a temperature sensitive part extending outside the case, 2. The analog optical fiber sensor according to claim 1, wherein the reflection film for measurement of the mechanism portion is attached to the bellows.   The measurement optical fiber and the reference optical fiber are branched from a plurality of positions of the optical fiber connected to the OTDR via a branch coupler, whereby multiple points can be simultaneously measured. 5. The analog type optical fiber sensor according to any one of 4 above.   A mechanism unit that is a movable reflection optical system that follows the mechanical displacement of the conversion unit, and a reference unit that is a fixed reflection optical system that does not follow the conversion unit in the vicinity of the mechanism unit and has the same structure as the movable reflection optical system The measurement amount of the measurement object is analogized from the ratio (Pk / Ps) of the measurement light amount Pk that is the return light amount from the movable reflection optical system and the reference light amount Ps that is the return light amount from the fixed reflection optical system. 2. The analog type optical fiber sensor according to claim 1, which can be calculated.

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