JP7119989B2 - Temperature measuring device and its measuring method - Google Patents

Description

The present invention relates to a temperature measuring device and its measuring method, and more particularly to a temperature measuring device capable of measuring fluid temperature using an optical fiber and its measuring method.

Optical fibers, which are excellent in long-distance transmission, electrical noise resistance, explosion-proof performance, etc., have been widely used not only in the field of communication but also in the field of sensing for measuring physical quantities.
Generally, an optical fiber is composed of a dielectric material consisting of a core that propagates light and a concentric clad that covers the core. Light is transmitted using the phenomenon. Since such an optical fiber has optical characteristics and temperature dependence as its characteristics, various temperature measuring devices using these characteristics have been proposed.

First, temperature measurement devices that use optical characteristics are represented by OTDR (Optical Time Domain Reflectometry) sensors, which use scattering phenomena such as Raman scattering and Brillouin scattering that occur when a strong incident light is introduced into an optical fiber. ing. This is because the wavelength of these backscattered lights depends on the temperature of silicon dioxide, which is the constituent material of the optical fiber.
Patent document 1 is not a temperature measurement device, but a cantilever type scanning optical fiber is continuously vibrated from an initial frequency substantially separated from the resonance frequency of the optical fiber itself so as to approach the resonance frequency, and light is irradiated. and collects the backscattered light in time series.

A temperature measuring device using temperature dependence is represented by an FBG (Fiber Bragg Grating) sensor. (for example, Patent Document 2). This is because the wavelength of the reflected light reflected from the plurality of diffraction gratings formed in the core changes due to the distortion of the optical fiber itself caused by temperature.

As shown in FIG. 11, in the FBG sensor, a periodic diffraction grating 54 having a larger refractive index than the core 51 is formed in the core 51 of the optical fiber, and a protective coating such as an ultraviolet curing resin is formed on the outer circumference of the clad 52. 53 are provided. In this type of sensor, of the incident light propagating in the core 51, the light whose spacing of the diffraction grating 54 matches the half wavelength of the incident light is Bragg-reflected as reflected light in the direction opposite to the direction of travel, and the diffraction grating 54 is transmitted in the direction of travel as transmitted light. The condition for Bragg reflection is expressed by the following equation.
λ=2n・Λ
is the Bragg wavelength (reflected light wavelength), n is the refractive index of the core 51, and .LAMBDA. is the refractive index modulation period (interval of the diffraction grating 54).

Patent No. 5043182 JP-A-10-141922

An FBG sensor that performs multi-point sensing using a single light source and a single light receiver has more temperature measurement points per optical fiber than an OTDR sensor that performs continuous distributed sensing on a line. In particular, it is highly superior in situations where multi-point measurement is performed in a narrow space.
However, since the FBG sensor measures the temperature using the strain of the optical fiber itself caused by the environmental temperature in which it is placed, it can There is a possibility that the fluid temperature cannot be accurately detected while maintaining the measurability.

Therefore, in order to clarify the above problem, the present inventor created a temperature measurement experimental device using an FBG sensor and conducted a verification experiment.
An experimental device is composed of a blower whose wind speed can be adjusted step by step and an FBG sensor stretched in front of the blower port of this blower, and the measured value and the The measured temperature difference from the true value and the vibration frequency of the FBG sensor were measured.
12 and 13 show the verification results. FIG. 12 is a graph showing the correlation between the elapsed time and the measured temperature difference, and FIG. 13 is a graph showing the correlation between the wind speed and the vibration frequency of the optical fiber.
As shown in FIG. 12, a region in which the measured temperature difference, so-called measurement noise, increases extremely occurs corresponding to a specific elapsed time. Further, as shown in FIG. 13, although the vibration frequency of the FBG sensor has a linear tendency proportional to the wind speed, a region where the vibration frequency is fixed at a constant value occurs corresponding to a specific wind speed.

The above verification experiments revealed the following problems.
As shown in FIG. 14, when an optical fiber is in fluid with velocity, the optical fiber oscillates up and down in a direction orthogonal to the wind direction. This is due to Karman vortices that are alternately generated vertically from the upper and lower surfaces to the rear surface of the optical fiber, and the optical fiber periodically vibrates in the vertical direction due to the pressure difference between the upper and lower surfaces. When the vibration of the optical fiber (self-excited vibration) caused by the Karman vortices approaches the inherent vibration frequency (eigenfrequency) of the structure of the optical fiber itself, the generated frequency of the Karman vortices becomes the peculiar frequency of the optical fiber. Since the frequency is forcibly attracted (so-called rocking phenomenon), the self-excited vibration of the optical fiber resonates with the frequency of Karman vortex generation, resulting in a difference between the natural frequency of the optical fiber and the frequency of Karman vortex generation. The self-excited oscillations of the optical fiber tend to be further amplified in the peripheral frequency band where .

That is, in order to improve the measurement accuracy of the FBG sensor for fluid temperature, it is necessary to suppress the amplification of the self-excited vibration due to the resonant vibration of the FBG sensor and the Karman vortices.
However, at present, no effective and concrete improvement measures have been proposed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a temperature measuring device, a measuring method, and the like capable of improving the accuracy of temperature measurement in a fluid while maintaining multi-point measurement capability.

The temperature measuring device according to claim 1 comprises an optical fiber having a temperature sensing portion extending in the axial direction and supported portions formed at both ends of the temperature sensing portion, a light source for outputting light to the optical fiber, and the sensor. In a temperature measuring device capable of measuring fluid temperature, the temperature sensing part is arranged in a fluid having a velocity, and the natural vibration of the optical fiber is measured. is set to a frequency outside the frequency band of the Karman vortices generated from the temperature sensing part.

In this temperature measuring device, since the temperature sensing portion is arranged in fluid having a velocity, the fluid temperature can be measured at multiple points using reflected light reflected from the temperature sensing portion.
Since the natural frequency of the optical fiber is set to a frequency outside the frequency band of the Karman vortices generated from the temperature sensing part, the frequency band corresponding to the frequency of the Karman vortices generated in the measurement environment is Therefore, it is possible to forcibly and structurally avoid the rocking phenomenon that is attracted to the natural frequency of the optical fiber, and to suppress the occurrence of distortion in the optical fiber due to the resonance vibration between the optical fiber and the Karman vortex.

The invention of claim 2 is the invention of claim 1, wherein the optical fiber has a metal coating for changing the natural frequency of the optical fiber on the surface of the temperature sensing part, and the thickness of the metal coating is set in association with the frequency band of the Karman vortices.
According to this configuration, the natural frequency of the optical fiber can be adjusted while suppressing expansion and contraction of the optical fiber by using the metal coating corresponding to the protective coating.

The invention of claim 3 is the invention of claim 2, wherein the optical fiber has a core and a clad covering the core, and the thickness of the metal coating is smaller than the diameter of the optical fiber. It is characterized by being
According to this configuration, it is possible to achieve both measurement accuracy and measurement responsiveness.

The invention of claim 4 is the invention of claim 2 or 3, wherein a film is provided to cover the surface of the supported portion, and the film thickness of the film is formed to be larger than the film thickness of the metal film. and
According to this configuration, by thinning the metal film of the temperature sensing portion, it is possible to increase the adjustment range of the natural frequency while improving the measurement response. Moreover, by thickening the coating of the supported portion, the support rigidity of the optical fiber can be ensured.

According to a fifth aspect of the present invention, in the first aspect of the invention, a tension applying means capable of adjusting the tension of the optical fiber is provided at the end of the optical fiber opposite to the processing means, and the tension applying means It is characterized in that tension is applied to the optical fiber so that the natural frequency of the fiber can be removed from the frequency band of the Karman vortices.
According to this configuration, it is possible to increase the adjustment range of the natural frequency with a simple configuration.

The invention of claim 6 is the invention of claim 5, wherein the temperature sensing part is formed so as to be able to detect temperatures at a plurality of positions and is arranged between a pair of frames extending in the longitudinal direction of the vehicle body in the engine room of the vehicle. and the tension applying means is arranged on either one of the pair of frames.
According to this configuration, it is possible to accurately measure the temperature in the engine room of the vehicle with a simple configuration.

A temperature measuring method according to claim 7 comprises: an optical fiber having a temperature sensing portion extending in an axial direction and supported portions formed at both ends of the temperature sensing portion; a light source for outputting light to the optical fiber; In a temperature measurement method capable of measuring fluid temperature using a processing means for processing reflected light generated in a warm part, the frequency band of Karman vortices generated from the optical fiber placed in the fluid is determined based on the velocity of the fluid. a frequency calculation step for calculating; and a frequency setting step of setting the frequency to be previously out of the frequency band of the Karman vortices generated from the temperature sensing part.

Since this temperature measurement method has a frequency calculation step of calculating the frequency band of the Karman vortices generated from the optical fiber placed in the fluid based on the velocity of the fluid, the fluid temperature is reflected from the temperature sensing part. In the measurement using the reflected light, it is possible to calculate the frequency band corresponding to the generation frequency of the Karman vortices under the measurement environment.
When the natural frequency of the optical fiber is included in the frequency band of the Karman vortices when the temperature sensing part is placed in the fluid, the natural frequency of the optical fiber is the frequency of the Karman vortices generated from the temperature sensing part. Since it has a frequency setting step that preliminarily sets the frequency to be outside the band, the locking phenomenon in which the frequency band of the Karman vortices is attracted to the natural frequency of the optical fiber is forcibly and structurally avoided under the measurement environment. It is possible to suppress the occurrence of strain in the optical fiber due to resonance vibration between the optical fiber and the Karman vortices.

According to the temperature measurement device and the measurement method of the present invention, by changing the natural frequency of the optical fiber without affecting the measurement performance, the temperature measurement accuracy in the fluid is improved while maintaining the multi-point measurement capability. can do.

1 is a block diagram showing the overall configuration of a temperature measuring device according to Example 1; FIG. It is explanatory drawing of the optical fiber used for a temperature measuring device. It is a table|surface which shows the relationship between the thickness of a metal film, and a Young's modulus. It is a front view of the engine room in which the optical fiber is arranged. It is a bottom view of the engine room in which the optical fiber is arranged. 4 is a perspective view of an optical fiber mounting portion; FIG. 4 is a flow chart showing a procedure of temperature measurement processing; It is a graph which shows the correlation of the elapsed time and measured temperature difference which concern on a temperature measuring device. It is a graph which shows the correlation of the wind speed and the vibration frequency of an optical fiber which concern on a temperature measuring device. FIG. 2 is a view corresponding to FIG. 2 according to Example 2; It is explanatory drawing of the FBG sensor which concerns on a prior art. It is a graph which shows the correlation of the elapsed time and measured temperature difference which concern on the verification experiment of a prior art. FIG. 10 is a graph showing the correlation between the wind speed and the vibration frequency of the optical fiber according to the verification experiment of the prior art; FIG. It is a figure which shows the relationship between the optical fiber arrange|positioned in the fluid, and a Karman vortex.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated based on drawing. The following description of preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its applications or uses.

Embodiment 1 of the present invention will be described below with reference to FIGS. 1 to 9. FIG.
The temperature measurement device 1 according to the first embodiment is a temperature measurement device based on the premise of an FBG (Fiber Bragg Grating) sensor that utilizes the temperature dependence of optical fibers.
As shown in FIG. 1, the temperature measuring device 1 of the first embodiment mainly includes an optical fiber 10, a light source 2, a circulator 3, a processing means 4, and the like.
For convenience of explanation, a single optical fiber 10 is shown, but the number of optical fibers 10 may be one, or a plurality of them depending on the measurement environment.
It should be noted that the following description of the temperature measuring device 1 includes the description of the temperature measuring method.

As shown in FIG. 2, the optical fiber 10 includes a core 11, a clad 12 formed with a lower refractive index than the core 11 and covering the core 11, and a higher refractive index than the core 11. It comprises a plurality of diffraction gratings 13 formed and formed in the core 11, a metal coating 14 covering the cladding 12, an attachment coating 15 (coating), and the like.
The core 11 and the clad 12 are made of a transparent dielectric (such as glass) and have a diameter of 125 μm, for example.

The optical fiber 10 has a temperature sensing portion 10a extending in the optical axis direction on which a plurality of diffraction gratings 13 are formed, and a pair of supported portions 10b corresponding to both ends of the temperature sensing portion 10a.
The temperature sensing part 10a is arranged in a fluid (space), which is a measurement target area, so as to have an intersecting angle (for example, 90°) with respect to the traveling direction of the fluid. The pair of supported portions 10b are supported by a fixed member in order to stretch the temperature sensing portion 10a in a non-contact state.
In this embodiment, a pair of supported portions 10b are supported by a fixed member via a tension applying means 5, which will be described later.

As shown in FIG. 2, a plurality of periodic diffraction gratings 13 are formed in the temperature sensing portion 10a.
When the interval of the diffraction grating 13 is Λ and the refractive index of the core 11 is n, the wavelength (Bragg wavelength) λ of reflected light from the diffraction grating 13 can be expressed by the following equation (1).
λ=2n·Λ (1)
The portion of the diffraction grating 13 corresponding to the wavelength λ corresponds to the sensor portion for measuring the fluid temperature, and it is possible to form a plurality of sensor portions with different intervals Λ of the diffraction grating 13 on the single temperature sensing portion 10a. be.

The metal coating 14 covers the surface of the clad 12 corresponding to the temperature sensitive portion 10a so as to have a constant thickness. This metal coating 14 is formed of a nickel coating, and has a film thickness (for example, 10 μm) in which the natural frequency fi of the optical fiber 10 deviates from the frequency band A corresponding to the generation frequency of Karman vortices under the measurement environment. is set to
The attachment coating 15 covers the surface of the clad 12 corresponding to the supported portion 10b so as to have a constant thickness. In this embodiment, the attachment coating 15 is made of a material different from that of the metal coating 14 and is set to have the same film thickness.

As shown in FIG. 1, the light source 2 is composed of a broadband wavelength light source and continuously outputs light to an optical fiber 10 . The circulator 3 guides the incident light to the temperature sensing portion 10 a of the optical fiber 10 , separates the reflected light Bragg-reflected from the diffraction grating 13 toward the light source 2 side from the mixed light, and guides it to the processing means 4 . It controls the waveguide direction.
The processing means 4 receives the reflected light reflected from the diffraction grating 13 (sensor section) and calculates the temperature at the position corresponding to the diffraction grating 13 based on the Bragg wavelength λ of the input reflected light and the temperature characteristic coefficient k. is doing. Assuming that the Bragg wavelength at the reference temperature Ta° C. is λa and the Bragg wavelength at the temperature Tb° C. higher than the reference temperature is λb, the following equation (2) holds.
Tb−Ta=(λb−λa)/k (2)
The temperature characteristic coefficient k is, for example, 10 pm/°C.

尚、Ｅは、ヤング率、Ｉは、断面２次モーメント、ρは、平均密度、Ａは、断面積、Ｌは、長さ、Ｔは、張力である。 Next, the basic idea of the temperature measuring device 1 according to this embodiment will be described.
In the temperature measurement device 1, when the natural frequency fi of the optical fiber 10 is included in the frequency band A of the Karman vortices under the measurement environment, the natural frequency fi is removed from the frequency band A. Performing a number change process.
The natural frequency fi of the optical fiber 10 can be expressed by the following equation (3).

E is the Young's modulus, I is the geometrical moment of inertia, ρ is the average density, A is the cross-sectional area, L is the length, and T is the tension.

A case where the natural frequency fi of the basic optical fiber calculated using equation (3) is, for example, 72 Hz and the wind velocity range under the measurement environment is, for example, 0 m/s to 15 m/s will be described.
Note that the metal coating 14 and the attachment coating 15 are omitted from the basic optical fiber.
Since the Karman vortex generation frequency exhibits a linear characteristic as a physical property in proportion to the flow velocity, the Karman vortex generation frequency and the natural frequency fi of the fundamental optical fiber substantially match at a wind speed of about 11 m/s. In the region around the wind speed of 11 m/s, specifically, in the region of wind speeds from about 9 m/s to 12 m/s, a rocking phenomenon occurs in which the frequency of Karman vortices is forcibly attracted to the natural frequency of the fundamental optical fiber. The self-excited oscillation of the fundamental optical fiber resonates at the frequency of the Karman vortices. Therefore, the natural frequency fi of the optical fiber is forcibly removed from the region of the wind speed of about 9 m / s to 12 m / s, that is, the frequency band A of about 60 Hz to 80 Hz including the frequency of 72 Hz, and the rocking phenomenon in the frequency band A avoids the occurrence of

The natural frequency changing process is at least one of the film thickness setting process and the tension setting process.
In the film thickness setting process, a nickel metal film 14 having a film thickness of 10 μm is provided on the outer circumference of the clad 12 .
As a result, the Young's modulus E in equation (3) can be increased by 92.2 Gpa, and the natural frequency fi of the optical fiber 10 is forcibly removed from the frequency band A. As shown in the table of FIG. 3, the Young's modulus E can be increased by increasing the thickness of the nickel metal coating 14. Therefore, the thickness of the metal coating 14 is appropriately set according to the frequency band A. ing.
Also, the material of the metal film 14 can be arbitrarily selected according to the measurement environment, such as copper or gold. can.

In the tension setting process, tension applying means 5 for increasing the tension T applied to the temperature sensing portion 10a is provided (see FIGS. 4 to 6).
As a result, the tension T in equation (3) can be increased, and the natural frequency fi of the optical fiber 10 is removed from the frequency band A. As the tension applying means 5, for example, a sticking means such as a tape can be used. The supported portion 10b is supported by the fixed member while a predetermined tension T is applied to the temperature sensing portion 10a using the tension applying means 5. As shown in FIG.
If the film thickness of the metal film 14 is thicker than the predetermined thickness, there is a possibility that measurement responsiveness may be hindered. Therefore, in removing the natural frequency fi of the optical fiber 10 from the frequency band A, if the thickness of the metal coating 14 exceeds a predetermined thickness, the thickness of the metal coating 14 is limited to a predetermined thickness. , the tension applying means 5 is additionally used to increase the tension T of the temperature sensing portion 10a.
The same applies when the film thickness is restricted based on the spatial tolerance.

Next, an example of a measurement environment in which the optical fiber 10 is arranged will be described.
In this embodiment, the ambient temperature between the lower end of the engine room, specifically between the oil pan and the undercover, is detected while the vehicle is running in a wind tunnel test or the like.
As shown in FIGS. 4 to 6, in the engine room of the vehicle V, a transversely mounted engine 21, a transmission 22 arranged adjacent to the left side of the engine 21, and a front suspension (not shown) are supported, and the front end and a pair of left and right engine support members 24 ( frame) and an undercover (not shown) that covers the bottom of the engine room.
In the drawings, the direction of arrow F indicates the front in the longitudinal direction of the vehicle, the direction of arrow L indicates the left in the width direction of the vehicle, and the direction of arrow U indicates the upper direction in the vertical direction of the vehicle.

The three optical fibers 10 are arranged between the oil pan and the undercover of the engine 21 so as to be orthogonal to each other in the front-rear direction, and the left end thereof is connected to the base end portion of the left engine support member 24 via the tension applying means 5. The right midway portion is supported by the base end portion of the right engine support member 24 via the tension applying means 5 . The tension T set by the tension setting process is applied to the portion of each optical fiber 10 sandwiched between the tension applying means 5 .
Since the diameter of the optical fiber 10 (145 μm) is equal to the distance between the oil pan and the undercover (17.5 mm, for example), it has little effect on the flow field.
If the diameter of the optical fiber 10 is 1 mm (occupying about 5% of the space interval), it is within the spatial allowable range. and the panel insulator (approximately 23.3 mm), the interval between the catalyst and the tunnel insulator (approximately 25.1 mm), etc. (both not shown).

Next, an example of temperature measurement operation by the temperature measurement device 1 will be described with reference to the flowchart shown in FIG. In the figure, Si (i=1, 2, . . . ) indicates each step.

As shown in the flowchart of FIG. 7, in S1, measurement conditions such as the physical properties of the optical fiber 10, the wind speed range under the measurement environment, and the ambient temperature are set, and the process proceeds to S2 (frequency calculation step).
In S2, the natural frequency fi of the optical fiber 10 is calculated using Equation (3), and then the process proceeds to S3. In S3, after calculating the frequency band A corresponding to the occurrence frequency of the Karman vortices, the process proceeds to S4.

In S4, it is determined whether or not the natural frequency fi of the optical fiber 10 is out of the frequency band A of the Karman vortices.
As a result of the determination in S4, if the natural frequency fi is out of the frequency band A, the optical fiber 10 is arranged at the measurement position of the fluid whose temperature is to be measured (S5).
After S5, multi-point temperature measurement is performed by the temperature measuring device 1 (S6), and the process ends.
If the result of determination in S4 is that the natural frequency fi does not deviate from the frequency band A, the natural frequency changing process is executed for the optical fiber 10 (S7), and the process returns to S2.
In the natural frequency changing process of S7 (frequency setting step), first, the film thickness setting process is executed, and when the film thickness of the metal coating 14 exceeds a predetermined thickness, the tension setting process is executed.

Next, the operation and effects of the temperature measuring device 1 will be described.
In order to explain the operation and effects, a temperature measurement experimental apparatus using the temperature measurement apparatus 1 of Example 1 was created and a verification experiment was conducted. In this verification experiment, the experimental device was configured with a blower whose wind speed can be adjusted stepwise and an optical fiber 10 stretched in front of the blower port of the blower, and the wind speed was increased over time. , the measured temperature difference between the measured value and the true value and the vibration frequency of the optical fiber 10 were measured.

8 and 9 show the verification results.
8 is a graph showing the correlation between the elapsed time and the measured temperature difference, and FIG. 9 is a graph showing the correlation between the wind speed and the vibration frequency of the optical fiber.
As shown in FIG. 8, compared with the conventional FBG sensor (see FIG. 12), the measured temperature difference due to measurement noise is eliminated. Further, as shown in FIG. 9, the locking phenomenon in the frequency band A of the Karman vortices is eliminated, and the vibration frequency of the optical fiber 10 has linear characteristics regardless of the wind speed.

According to this temperature measuring device 1, since the temperature sensing portion 10a is arranged in a fluid having a velocity, the fluid temperature can be measured at multiple points using reflected light reflected from the temperature sensing portion 10a. .
Since the natural frequency fi of the optical fiber 10 is set to a frequency outside the frequency band A of the Karman vortex generated from the temperature sensing part 10a, the frequency band A corresponding to the generation frequency of the Karman vortex under the measurement environment is attracted to the natural frequency fi of the optical fiber 10 can be forcibly and structurally avoided, and the occurrence of strain in the optical fiber 10 due to resonance vibration between the optical fiber 10 and the Karman vortices can be suppressed. be able to.

The optical fiber 10 has a metal coating 14 for changing the natural frequency fi of the optical fiber 10 on the surface of the temperature sensing portion 10a, and the thickness of the metal coating 14 is set in association with the frequency band A of the Karman vortices. Therefore, the natural frequency fi of the optical fiber 10 can be adjusted while suppressing the expansion and contraction of the optical fiber 10 using the metal coating 14 corresponding to the protective coating.

The optical fiber 10 has a core 11 and a clad 12 covering the core 11, and the thickness of the metal coating 14 is smaller than the diameter of the optical fiber 10, so both measurement accuracy and measurement response are achieved. can do.

A tension applying means 5 capable of adjusting the tension T of the optical fiber 10 is provided at the end of the optical fiber 10 opposite to the processing means 4, and the tension applying means 5 adjusts the natural frequency fi of the optical fiber 10 to the frequency band of the Karman vortices. Since the tension T that can be removed from A is applied to the optical fiber 10, the adjustment range of the natural frequency fi can be increased with a simple configuration.

The temperature sensing part 10a is arranged between a pair of engine support members 24 which are formed so as to be able to detect temperatures at a plurality of positions and which extend forward and backward in the engine room of the vehicle V. Since they are respectively arranged on the support members 24, the temperature in the engine room of the vehicle V can be accurately measured with a simple configuration.

This temperature measurement method has a frequency calculation step of calculating the frequency band A of the Karman vortices generated from the optical fiber 10 placed in the fluid based on the velocity of the fluid. When measuring using the reflected light, it is possible to calculate a frequency band A corresponding to the frequency of occurrence of Karman vortices under the measurement environment.
When the natural frequency fi of the optical fiber 10 is included in the frequency band A of the Karman vortices when the temperature sensing portion 10a is placed in the fluid, the natural frequency fi of the optical fiber 10 is the Karman frequency fi generated from the temperature sensing portion 10a. Since there is a frequency setting step for setting a frequency that is preliminarily deviated from the frequency band A of the vortex, the locking phenomenon in which the frequency band A of the Karman vortex is attracted to the natural frequency fi of the optical fiber 10 under the measurement environment is prevented. This can be forcibly and structurally avoided, and the occurrence of strain in the optical fiber 10 due to resonance vibration between the optical fiber 10 and the Karman vortices can be suppressed.

Next, an optical fiber 10A according to Example 2 will be described with reference to FIG.
In addition, the same code|symbol is attached|subjected to the member similar to Example 1. As shown in FIG.
In Example 1, the metal coating 14 and the attachment coating 15 have the same film thickness, whereas in Example 2, the metal coating 14 and the attachment coating 15A have different thicknesses.

The metal coating 14 covers the surface of the clad 12 corresponding to the temperature sensitive portion 10a so as to have a constant thickness. A plurality of periodic diffraction gratings 13 are formed in the temperature sensing portion 10a.
The mounting film 15A is formed to be thicker than the metal film 14, and covers the surface of the clad 12 corresponding to the supported portion 10b so that the thickness increases toward the end portion.
In this embodiment, the attachment coating 15A is made of the same material as the metal coating 14. As shown in FIG.

As a result, the mounting film 15A is provided to cover the surface of the supported portion 10b, and the film thickness of the mounting film 15A is formed to be larger than the film thickness of the metal film 14, so that the metal film of the temperature sensing portion 10a can be made thinner. It is possible to increase the adjustment range of the natural frequency fi while improving the responsiveness. Moreover, by increasing the thickness of the attachment coating 15A of the supported portion 10b, the support rigidity of the optical fiber 10 can be ensured.

Next, a modified example in which the above embodiment is partially changed will be described.
1) In the above embodiments, the metal coating and the mounting coating are directly coated on the outer periphery of the core and the clad. An optical fiber coated with a protective coating such as an ultraviolet curable resin may be coated with a metal coating to change the natural frequency. In addition, the protective coating may be not a single layer, but a multi-layer coating such as a primary coating and a secondary coating.

2) In the above embodiment, the temperature in the engine room was measured using three optical fibers capable of multi-point measurement. Any fluid space having a flow velocity can be applied.
A single optical fiber may be used, or a plurality of optical fibers may be used together.
Complete Karman vortices are generated when the Reynolds number is in the range of about 80 to about 300, approximately periodic Karman vortices are generated in the range of 300 to 3×10 ⁵ , and periodic Karman vortices are generated in the range of more than 3×10 ⁶ . Therefore, it is preferable to apply it to a fluid space that satisfies the above Reynolds number.

3) In the above embodiments, nickel, copper, and gold were used as examples of the metal coating, but other metals may be used. Although 10 μm, 20 μm, and 30 μm are shown as examples of film thickness, the present invention is not limited to these.

4) In the above embodiment, an example of the optical fibers arranged in a direction perpendicular to the flow direction of the running wind has been explained, but at least the optical fibers have a crossing angle with respect to the flow direction of the running wind. I wish I could.

5) In addition, without departing from the spirit of the present invention, a person skilled in the art can implement the above-described embodiment in a form in which various modifications are added or in a form in which each embodiment is combined. Any modifications are also included.

1 Temperature measuring device 2 Light source 4 Processing means 5 Tension applying means 10, 10A Optical fiber 10a Temperature sensing part 10b Supported part 11 Core 12 Cladding 14 Metal coating 15, 15A Mounting coating 24 Engine support member V Vehicle

Claims (7)

An optical fiber having a temperature sensing portion extending in an axial direction and supported portions formed at both ends of the temperature sensing portion, a light source for outputting light to the optical fiber, and processing the reflected light generated by the temperature sensing portion. A temperature measuring device capable of measuring fluid temperature, comprising a processing means for
the temperature sensing portion is placed in a fluid having a velocity, and
A temperature measuring device, wherein the natural frequency of the optical fiber is set to a frequency outside the frequency band of Karman vortices generated from the temperature sensing portion. The optical fiber has a metal coating on the surface of the temperature sensing part for changing the natural frequency of the optical fiber,
2. The temperature measuring device according to claim 1, wherein the film thickness of said metal coating is set in relation to the frequency band of said Karman vortices. The optical fiber has a core and a clad covering the core,
3. The temperature measuring device according to claim 2, wherein the thickness of said metal coating is smaller than the diameter of said optical fiber. providing a coating covering the surface of the supported portion;
4. The temperature measuring device according to claim 2, wherein the thickness of said coating is formed to be larger than the thickness of said metal coating. A tension applying means capable of adjusting the tension of the optical fiber is provided at the end of the optical fiber opposite to the processing means,
2. The temperature measuring device according to claim 1, wherein said tension applying means applies tension to said optical fiber so as to remove the natural frequency of said optical fiber from the frequency band of said Karman vortices. The temperature sensing part is formed to detect temperatures at a plurality of positions and is disposed between a pair of frames extending in the longitudinal direction of the vehicle body in the engine room of the vehicle,
6. The temperature measuring device according to claim 5, wherein said tension applying means is arranged on either one of said pair of frames. An optical fiber having a temperature sensing portion extending in an axial direction and supported portions formed at both ends of the temperature sensing portion, a light source for outputting light to the optical fiber, and processing the reflected light generated by the temperature sensing portion. In a temperature measurement method capable of measuring fluid temperature using a processing means to
a frequency calculation step of calculating a frequency band of Karman vortices generated from the optical fiber arranged in the fluid based on the velocity of the fluid;
Next, when the natural frequency of the optical fiber is included in the frequency band of Karman vortices when the temperature sensing portion is placed in the fluid, the natural frequency of the optical fiber is set to the Karman vortex generated from the temperature sensing portion. a frequency setting step of setting a frequency that is preliminarily deviated from the frequency band of the vortex;
A temperature measurement method, comprising:

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