JP2009063390A - Optical fiber humidity sensor and humidity detection system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical fiber humidity sensor having a simple structure, high sensitivity and a long signal transmission distance, requiring no troublesome optical setting, easy to mass-produce and low in cost, a humidity detection system using it and a dew point detection system. <P>SOLUTION: The bending loss change of a partially thinned-down constricted part 12 produced by the extension and contraction accompanying the humidity change of a humidity sensitive material 13 is detected as a change in the quantity of reflected light by an optical fiber 11 for the sensor equipped with the constricted part 12, the humidity sensitive material 13 fixed so as to apply bending to the constricted part 12 and extended and contracted by a humidity change and the reflection means 14 provided to the end surface near to the constricted part 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an optical fiber humidity sensor that detects humidity using an optical fiber, and a humidity detection system and a dew point detection system using the same, and more specifically, detects a bending loss of an optical fiber to detect humidity. The present invention relates to an optical fiber humidity sensor, a humidity detection system using the same, and a dew point detection system.

  Optical fiber sensors are expected to be used in a wide range of fields because of their excellent explosion-proof and electromagnetic noise resistance characteristics, and easy remote and multi-point monitoring. Optical fiber humidity sensors are also expected to be developed because of their advantages. It is rare.

Patent Literatures 1 to 7 describe humidity sensors using optical fibers.

Patent Document 1 discloses a sensor in which cobalt chloride, which reversibly discolors by absorbing and desorbing water vapor in the air, is fixed to the optical fiber tip with a transparent adhesive.

Patent Document 2 discloses a humidity sensor that measures an absorption spectrum of water using an infrared light source and a detector.

Patent Document 3 discloses a humidity sensor that measures absorption of evanescent waves by using a part of a clad of a plastic optical fiber as a moisture sensitive layer of a polyvinyl alcohol film in which deliquescent potassium acetate or the like is dissolved.

Patent Document 4 discloses a humidity sensor that measures absorption of evanescent waves by using a plastic optical fiber clad as a moisture-sensitive layer made of a cellulose-based polymer material such as hydroxyethyl cellulose.

Patent Document 5 discloses a humidity sensor that measures absorption of evanescent waves by using a clad of a plastic optical fiber as a moisture-sensitive layer in which a water-soluble acrylic polymer containing a copolymer and a deliquescent material are mixed. .

  Patent Document 6 discloses a humidity sensor that changes the amount of light incident on an optical fiber using a lens made of a substance that swells and changes reversibly with humidity.

Patent Document 7 discloses a humidity sensor that applies humidity detection material that expands and contracts in response to changes in humidity to the surface of an optical fiber equipped with an FBG, and detects the humidity by measuring the reflected wavelength of the FBG. Yes.
Japanese Patent Publication No. 06-011448 Japanese Patent Publication No. 05-209827 Japanese Patent Publication No. 05-060689 Japanese Patent Publication No. 2003-270141 Japanese Patent Publication No. 2003-130863 Patent Publication 2001-124868 Japanese Patent Publication No. 2005-351663

However, the humidity sensor that detects the discoloration of cobalt chloride disclosed in Patent Document 1 has a problem that it is expensive because a spectrum measuring device is required.

Moreover, in the humidity sensor which measures the infrared absorption spectrum currently disclosed by patent document 2, the infrared spectrum measuring apparatus was expensive, and there existed a problem that transmission distance was very short because the infrared transmittance | permeability of an optical fiber was low. .

Also, the humidity sensor disclosed in Patent Documents 3, 4, and 5 having a plastic fiber clad as a moisture sensitive layer has problems such as a short signal transmission distance and low sensitivity due to the plastic fiber.

In addition, the humidity sensor using a lens that is reversibly swelled by humidity disclosed in Patent Document 6 has a problem that precise optical setting is required and an error due to misalignment tends to occur.

Further, the humidity sensor using FBG disclosed in Patent Document 7 has a problem that it is expensive because a complicated device such as a wavelength meter and an optical spectrum analyzer is required to measure the wavelength change.

The present invention has been made in view of the above, and has as its purpose a simple structure, high sensitivity, a long signal transmission distance, no complicated optical setting, easy mass production, and low-cost optical fiber humidity. It is to provide a sensor and a humidity detection system and a dew point detection system using the sensor.

Therefore, the present invention provides (1) a partially narrowed constriction, a moisture-sensitive material that expands and contracts due to a change in humidity so as to bend the constriction, and a reflecting means on the end surface near the constriction. An optical fiber humidity sensor comprising the optical fiber for sensor (11) provided is provided.

  (2) An optical fiber humidity sensor is provided in which the moisture sensitive material 13 is polyamide resin (nylon) or hair.

(3) The incident side of the constricted portion is fixed to a base made of a material having a larger coefficient of thermal expansion than the moisture-sensitive material, and the reflective side of the constricted portion is fixed to one end of the moisture-sensitive material. The other end is fixed to the pedestal, and the position where the moisture sensitive material is fixed to the pedestal substantially cancels the thermal expansion of the moisture sensitive material by the sum of the thermal expansion of the optical fiber for the sensor and the pedestal. An optical fiber humidity sensor is provided.

(4) The optical fiber humidity sensor is characterized in that the material of the moisture sensitive material is nylon and the material of the pedestal is polyvinylidene fluoride.

(5) The optical fiber humidity sensor, a transmission optical fiber that performs optical transmission between the optical fiber humidity sensor and the measurement unit, and a light emitting unit that generates measurement light to be supplied to the optical fiber humidity sensor There is provided a humidity detection system comprising: a light receiving unit that receives measurement light that has undergone a change in light quantity by the optical fiber humidity sensor; and an arithmetic processing unit that converts the output of the light receiving unit into humidity.

(6) A temperature sensor for acquiring temperature data necessary for temperature compensation or dew point calculation is added to the humidity detection system, and the calculation is performed based on the temperature dependence data of the reflected light amount acquired in advance. There is provided a humidity detection system characterized in that a temperature correction or dew point calculation is performed by a processing means.

Moreover, (7) The humidity detection system characterized by the said temperature sensor being an optical fiber type temperature sensor using the bending loss of a constriction part is provided.

Further, (8) a light having a specific wavelength is demultiplexed into a specific optical fiber humidity sensor, and a combined / demultiplexed filter that combines the reflected light from the optical fiber humidity sensor; A plurality of optical fiber humidity sensors arranged in the transmission optical fiber, a light emitting means for generating measurement light having a plurality of wavelengths to be supplied to the optical fiber humidity sensor, and a plurality of light quantity changes received by the optical fiber humidity sensor A wavelength branching filter for branching the measurement light consisting of a plurality of wavelengths into each wavelength, a plurality of the light receiving means for receiving the branched light of each wavelength, and the calculation for converting the outputs of the plurality of light receiving means into humidity A multipoint humidity detection system comprising a processing means.

Furthermore, (9) the optical fiber humidity sensor and the optical fiber temperature sensor for acquiring temperature data necessary for temperature compensation or dew point calculation are arranged as a set in the transmission optical fiber. Provide a multi-point humidity detection system

According to the present invention, an optical fiber humidity sensor and a humidity detection system using the same can be realized with a simple structure, high sensitivity, a long signal transmission distance, no need for complicated optical setting, and easy mass production.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a basic configuration diagram of an optical fiber humidity sensor according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes a humidity sensor, a sensor optical fiber 11 having a constricted portion 12 and a reflecting mirror 14 that are partially narrowed, a moisture sensitive material 13 that expands and contracts in response to changes in humidity, and a moisture sensitive material fixing portion 15. Consists of.

The sensor optical fiber 11 is preferably a single mode fiber in order to obtain a response with good linearity, and is preferably adapted to an optical communication wavelength band such as a 1.5 μm band and a 1.3 μm band in terms of transmission distance and cost. It is.

The constricted portion 12 serves to give the sensor optical fiber 11 a bend with a large curvature with a small force and good reproducibility. The narrower the central diameter of the constricted portion 12, the higher the sensitivity. Hereinafter, the central diameter of the constricted portion 12 is referred to as a constricted diameter. However, if the constricted diameter is too thin, the light output tends to be non-linear, so an excessively constricted diameter is not desirable. For example, in the case of a normal single mode fiber having a cladding diameter of 125 μm and an MFD (mode field diameter) of about 10 μm (wavelength: 1.55 μm), the constriction diameter is desirably in the range of 50 to 90 μm. When the constricted diameter is 90 μm or more, light leakage due to bending is small, and when it is 50 μm or less, light leakage is large even without bending, and the light output tends to be nonlinear and unstable. The sensitivity also depends on the fixed interval of the sensor optical fiber 11, and the sensitivity becomes higher as the fixed interval becomes narrower.

  FIG. 2 shows a characteristic example of the sensor optical fiber 11 when the constriction diameter 12 and the fixed interval are changed. The sensor optical fiber 11 with high sensitivity shown in (a) produces a bending loss of 10 dB with a displacement of only 40 μm, and the sensor optical fiber 11 with low sensitivity shown in (b) produces a bending loss of approximately 10 dB with a displacement of about 3 mm. That is, the displacement width of the sensor optical fiber 11 is Min. 40 μm to Max. It can be adjusted within a range of 3 mm, and a bending loss of about 10 dB can be obtained at any displacement width. Therefore, by applying the sensor optical fiber 11 having a displacement width matched to the expansion / contraction amount of the bellows 13, the dynamic range of the measurement can be about 10 dB.

Reference numeral 13 denotes a moisture-sensitive material that expands and contracts in response to changes in humidity. As shown in FIG. 1, the fixing portion 15 fixes the sensor optical fiber 11 to the sensor optical fiber 11 so that the sensor optical fiber 11 is bent around the constricted portion 12. . The shorter the interval between the fixing portions 15, the higher the sensitivity. However, from the viewpoint of linear response and ease of manufacture, a length of about 10 to 30 mm is usually desirable. As for the degree of bending of the constricted portion 12, the bending loss is preferably about 5 to 10 dB at the maximum from the viewpoint of linear response.

  As a specific material of the moisture sensitive material 13, for example, a fibrous or ribbon-like polyamide resin (nylon) or hair is suitable. Nylon has an advantage of 0.6% expansion and contraction with respect to a change in relative humidity of 0 to 100% and excellent durability. On the other hand, since the hair has a large expansion and contraction of 1%, it becomes a highly sensitive humidity sensor. For example, 6-nylon having a length of 10 mm has an expansion / contraction of 60 μm with respect to a change in relative humidity of 0 to 100%. As described with reference to FIG. 2, since the constricted portion 12 causes a bending loss change of 10 dB when the expansion / contraction amount is in the range of 40 μm to 3 mm, it is obvious that these materials can be used as the moisture sensitive material 13.

  The fixing portion 15 that fixes the moisture-sensitive material 13 to the sensor optical fiber 11 is not particularly limited as long as it is a lightweight fixing method that does not affect the bending of the sensor optical fiber 11. Alternatively, the moisture-sensitive material 13 and the sensor optical fiber 11 may be directly fixed with an adhesive, or caulking or adhesive fixing using a fine metal ring or the like may be used.

The reflecting mirror 14 also needs to be lightweight so as not to hinder the bending operation of the constricted portion 12, and is preferably formed directly on the end face of the sensor optical fiber 11 by film forming means such as sputtering or vapor deposition. The distance from the center of the constricted portion 12 to the reflecting mirror 14 is desirably shorter for weight reduction, and is usually 10 mm or less.

  As described above, the narrowed portion 12 that is partially narrowed, the moisture-sensitive material 13 that is fixed so as to bend the narrowed portion 12, and expands and contracts in response to a change in humidity, and is formed on the end face close to the narrowed portion 12. By configuring the sensor optical fiber 11 including the reflecting means 14, it is possible to realize a humidity sensor that does not require complicated setting of optical components, is easily mass-produced, has high sensitivity, and is inexpensive.

The operation of the optical fiber humidity sensor of this embodiment will be described with reference to FIGS.

FIG. 2 shows changes in the bending of the humidity sensor 1 accompanying changes in humidity. (B) As shown in the intermediate humidity, the moisture sensitive material 13 is fixed so as to bend the sensor optical fiber 11 including the constricted portion 12 appropriately, and the measurement light is incident thereon. As the humidity increases, the moisture-sensitive material 13 extends, so that the bending of the sensor optical fiber 11 decreases due to the fiber elasticity, and the leakage light in the constricted portion 12 decreases, and becomes minimum at a humidity of 100%. On the other hand, when the humidity is lowered, the moisture-sensitive material 13 is contracted, the bending of the constricted portion 12 is increased, and the leakage light is increased, and becomes maximum at a humidity of 0%. Therefore, a change in relative humidity can be detected by measuring this change in leakage light as a change in reflected light intensity.

FIG. 3 is an example showing the relationship between the reflected light intensity of the humidity sensor according to the configuration of this embodiment and the humidity displayed by a commercially available digital hygrometer. The optical fiber 11 used is a single mode optical fiber having an MFD of 9.5 μm and a cutoff wavelength of 1280 nm, and the constricted diameter is 80 μm. The moisture sensitive material 13 was a 6-nylon stranded wire having a thickness of 0.2 mm and a length of 22 mm. A semiconductor laser having a wavelength of 1.3 μm was used for the light emitting element 4.

  The reflected light amounts of this sensor at 100% and 0% were -16.65 dBm and -23.01 dBm, respectively, and the measurement dynamic range was 6.36 dB. The amount of reflected light decreased monotonically from -16.65 dBm to -23.01 dBm, and the relationship between the humidity displayed by the hygrometer and the reflected light intensity was close to linear and could be approximated well by a second order polynomial.

  FIG. 4 shows a schematic configuration of a sensor in which the first embodiment is developed and the influence of bending loss due to temperature change is reduced. In this embodiment, the incident side of the constricted portion 12 is fixed to the pedestal 16 by the sensor optical fiber / pedestal fixing portion 17. One end of the moisture sensitive material 13 is fixed by the reflection side of the constricted portion 12 and the sensor optical fiber / humid sensitive material fixing portion 15. The other end is fixed by the base 16 and the moisture sensitive material / base fixing part 18. The base 16 is made of a material having a larger coefficient of thermal expansion than that of the moisture sensitive material 13.

The operation will be described by taking as an example the case where the moisture sensitive material is 6-nylon having a thermal expansion coefficient of 8 × 10 ⁻⁵ and the base 16 is polyvinylidene fluoride having a thermal expansion coefficient of 13 × 10 ⁻⁵ . The fiber length between the sensor optical fiber / moisture sensitive material fixing part 15 and the sensor optical fiber / base fixing part 17 is Lf, and the base 16 between the sensor optical fiber / base fixing part 17 and the moisture sensitive material / base fixing part 18 is used. If the length of the moisture sensitive material 13 between the moisture sensitive material fixing part 15 and the moisture sensitive material / pedestal fixing part 18 is Lh, the length will be bundled if the change in the coefficient of thermal expansion between (Lf + Lp) and Lh is almost equal. The influence of the temperature change of the bending loss of the portion 12 is almost eliminated.
The length satisfying such conditions is about 32 mm for Lp and about 52 mm for Lh when Lf is 20 mm.

  Another advantage of the present embodiment is that the length of the moisture sensitive material 13 can be made longer than the fiber length Lf between the sensor optical fiber / moisture sensitive material fixing portion 15 and the sensor optical fiber / pedestal fixing portion 17. The sensitivity of the bending loss in the constricted portion 12 is higher as Lf is shorter, and the amount of expansion / contraction of the moisture sensitive material accompanying the change in humidity is larger as Lh is longer. Therefore, if designed so that Lf is short and Lh is long, a highly sensitive humidity sensor can be obtained.

  The operation of the optical fiber humidity detection system of this embodiment will be described with reference to FIG.

  In the figure, reference numeral 2 denotes an optical fiber for transmission for transmitting light to the humidity sensor unit 1 and guiding reflected signal light to the measuring unit 3. The main components of the measuring unit 3 are a light emitting element 4, an optical coupler 5, a light receiving element 6, an optical isolator 7, and an arithmetic processing circuit 8. The light-emitting element 4 is a light source that can be incident on an optical fiber, and in order to transmit a signal to a remote location, the wavelength band is preferably a communication wavelength band such as a 1.5 μm band and a 1.3 μm band. A semiconductor laser in the communication wavelength band can be used.

Since these main components of the measuring unit 3 can be purchased commercially at low cost, an inexpensive humidity detection system can be configured.

The measurement light emitted from the light emitting element 4 passes through the optical isolator 7 and the optical coupler 5, is sent to the optical transmission fiber 2, and enters the humidity sensor 1. After a part of the light leaks at the constricted part 12, the measurement light is reflected by the reflection mirror 14, leaks the light again at the constricted part 12, reaches the optical coupler 5 through the transmission optical fiber 2, and receives the light receiving element 6. Is received. A part of the light returning to the light emitting element 4 side is blocked by the optical isolator 7. If a relational expression between humidity and reflected light intensity is input to the arithmetic processing circuit 8 in advance and the output of the light receiving element 6 is calculated, the relative humidity can be detected.

  FIG. 6 shows a configuration in which the embodiment of the humidity detection system shown in FIG. 5 is developed to improve temperature characteristics and detect dew point. In the figure, 31 is a temperature sensor. In order to make the best use of the characteristics of the optical fiber sensor system, for example, an optical fiber temperature sensor disclosed in Japanese Patent Application Laid-Open No. 2007-24527 is desirable as the temperature sensor. 31 examples are shown. However, it is also possible to use a general sensor such as a thermocouple or a platinum resistor. In this case, the signal transmission path differs depending on the type of the temperature sensor. For example, the optical fiber temperature sensor 31 is an optical fiber, For thermocouples, this is the compensating conductor. Similarly, the temperature measuring unit is adapted to the type of temperature sensor.

  The temperature dependence of the output of the humidity sensor 1 measured in advance is input to the arithmetic processing circuit 8, and the temperature dependence is corrected using the temperature data measured by the temperature sensor 31. It is an accurate humidity detection system that is not affected.

  Further, if the dew point is calculated by the arithmetic processing circuit 8 using the acquired humidity and temperature data, a dew point detection system can be obtained.

  FIG. 8 shows a schematic configuration of a multipoint humidity detection system according to the fifth embodiment of the present invention. Hereinafter, the operation of the system will be described. The light source 21 is a light source that emits a plurality of wavelengths, such as an ASE light source or a tunable laser, and the light emitted from the light source 21 passes through the optical isolator 7 and the two optical couplers 5 to the transmission optical fiber 2. Incident. A part of the light emitted from the optical isolator 7 is branched by the optical coupler 5 and incident on the power monitor light receiving element 24 for monitoring the light intensity change of the light source 21 and used as data for correcting the fluctuation of the light source.

In the system of this embodiment, each humidity sensor 1 is identified by measuring each humidity sensor 1 with light of a different wavelength. When the measurement light including a plurality of different wavelengths to reach the demultiplexing filters 22-1 is branched only to the humidity sensor 1-1 side light of the wavelength lambda _1, the light of the remaining wavelength above a transmission optical fiber 2 move on. The wavelength assigned to each humidity sensor 1- (1 to n) is branched, such as λ ₂ in the multiplexing / demultiplexing filter 22-2 and λ ₃ in the multiplexing / demultiplexing filter 22-3. The light of each wavelength reflected by each humidity sensor 1-(1 to n) is multiplexed again to the transmission optical fiber 2 via the multiplexing / demultiplexing filter 22, and reaches the wavelength branching filter 23 via the optical coupler 5. The light is branched into each wavelength by the wavelength branching filter 23 and is incident on the assigned light receiving element 6.

If a relational expression between humidity and reflected light intensity is input in advance to the arithmetic processing circuit 8 and the output data of each light receiving element 6 is subjected to arithmetic processing, the humidity of each humidity sensor 1- (1-n) can be detected.

By using light λ _{1 to} λ _n of different wavelengths for identification of each humidity sensor 1-(1 to n) and receiving light in parallel by a plurality of light receiving elements PD _{1 to} PD _n assigned to each wavelength, Shorter and real-time measurement is possible.

The various components such as the transmission optical fiber 2, the optical coupler 5, the optical isolator 7, the multiplexing / demultiplexing filter 22, the wavelength branching filter 23, and the light receiving element 6 are inexpensive and reliable developed for optical communication. Therefore, it is possible to configure an inexpensive and highly reliable system.

  The example in which only the humidity sensor 1 is disposed has been described above, but a configuration in which a plurality of pairs of the humidity sensor 1 and the optical fiber temperature sensor are disposed in the transmission optical fiber 2 is also possible. In this case, if each sensor is identified by assigning different wavelengths to all the humidity sensors 1 and the optical fiber temperature sensors, the temperature correction function and the dew point calculation function can be obtained with the same configuration. Point humidity sensor system can be configured

  Although the invention has been described with reference to specific embodiments, various modifications may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. Such changes and modifications are also within the technical scope of the present invention.

It is a figure which shows schematic structure of 1st Example of this invention. It is a figure which shows the example of a characteristic of the optical fiber for sensors. It is a side view explaining operation | movement of a humidity sensor. It is a figure which shows the example of a measurement of the relationship between the reflected light intensity of a humidity sensor, and humidity. It is a figure which shows schematic structure of 2nd Example of this invention. It is a figure which shows schematic structure of 3rd Example of this invention. It is a figure which shows schematic structure of 4th Example of this invention. It is a figure which shows schematic structure of 5th Example of this invention.

Explanation of symbols

1: Humidity sensor 2: Transmission optical fiber 3: Measuring unit 4: Light emitting element 5: Optical coupler
6: light receiving element 7: optical isolator 8: arithmetic processing circuit 11: sensor optical fiber 12: constricted part 13: moisture sensitive material 14: reflection mirror 15: sensor optical fiber / moisture sensitive material fixing part 16: pedestal 17: sensor Optical fiber / pedestal fixing unit 18: moisture sensitive material / pedestal fixing unit 20: multipoint measuring unit 21: light source 22- (1-n): multiplexing / demultiplexing filter 23: wavelength branching filter 24: light receiving element 31 for power monitoring : Temperature sensor

Claims (9)

On the end face close to the narrow part (12), the moisture-sensitive material (13) that expands and contracts due to humidity change fixed so as to bend the narrow part (12), and the narrow part (12) An optical fiber humidity sensor comprising a sensor optical fiber (11) provided with a reflecting means (14).   The optical fiber humidity sensor according to claim 1, wherein the moisture sensitive material (13) is a polyamide resin (nylon) or hair.   The incident side of the constricted portion (12) is fixed to a base (16) made of a material having a larger coefficient of thermal expansion than the moisture sensitive material (13), and the reflective side of the constricted portion (12) is fixed to the moisture sensitive material (13). The other end of the moisture sensitive material (13) is secured to the pedestal (16), and the position where the moisture sensitive material (13) is secured to the pedestal (16) is the moisture sensitive material ( 13. The optical fiber humidity sensor according to claim 1, wherein the thermal expansion of 13) is substantially offset by the sum of thermal expansion of the optical fiber for sensor (11) and the pedestal (16).   4. The optical fiber humidity sensor according to claim 3, wherein the material of the moisture sensitive material is nylon and the material of the pedestal is polyvinylidene fluoride. The optical fiber humidity sensor, a transmission optical fiber (2) for performing optical transmission between the optical fiber humidity sensor and the measurement unit (3), and a light emitting means for generating measurement light to be supplied to the optical fiber humidity sensor (4), a light receiving means (6) for receiving measurement light having undergone a change in light quantity by the optical fiber humidity sensor, and an arithmetic processing means (8) for converting the output of the light receiving means (6) into humidity. Humidity detection system characterized by that. A temperature sensor (31) for acquiring temperature data necessary for temperature compensation or dew point calculation is added to the humidity detection system, and the calculation processing means is based on the temperature dependence data of the reflected light amount acquired in advance. 4. The humidity detection system according to claim 3, wherein temperature correction or dew point calculation is performed in (8).   The humidity detection system according to claim 6, wherein the temperature sensor (31) is an optical fiber temperature sensor using a bending loss of the constricted portion (12).   The light of a specific wavelength is demultiplexed to the specific optical fiber humidity sensor, and the reflected light from the optical fiber humidity sensor is multiplexed and the multiplexed / demultiplexed filter (22) is passed through. A plurality of optical fiber humidity sensors arranged in the transmission optical fiber (2), light emitting means (21) for generating measurement light having a plurality of wavelengths to be supplied to the optical fiber humidity sensor, and the optical fiber humidity A wavelength branching filter (23) for branching measurement light comprising a plurality of wavelengths subjected to a change in the amount of light by the sensor to each wavelength; a plurality of light receiving means (6) for receiving the branched light of each wavelength; A multipoint humidity detection system comprising the arithmetic processing means (8) for converting the output of the light receiving means (6) into humidity.   A plurality of sets of the optical fiber humidity sensor and the optical fiber temperature sensor (31) for acquiring temperature data necessary for temperature compensation or dew point calculation are arranged in the transmission optical fiber (2) as a set. Multi-point humidity detection system.

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