JP2012225687A - Temperature measurement system and temperature measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature measurement system achieving multipoint temperature measurement and temperature measurement of a wide range at low cost.SOLUTION: A temperature measurement system 10 includes one optical fiber 11, and FBGs 21, 22, 23 to 2n of the optical fiber 11 are respectively attached to sections 31, 32, 33 to 3n to be measured. A light source 12 connected to one end of the optical fiber 11 makes light of a wide band wider than a reflection band of each FBG and of continuous spectra incident on the optical fiber 11 as incident light. Measurement means 13 can measure a band including band width of a transmission spectrum transmitted through respective FBGs and measures the temperature of a corresponding section to be measured based on the movement distances of reflection spectra of respective FBGs indicated in the inputted transmission spectrum.

Description

  The present invention relates to a temperature measurement system and a temperature measurement method, and more particularly to a system and method for measuring the temperature of a measurement target part using an optical fiber on which an FBG is formed.

  In recent years, an optical fiber in which an FBG (fiber Bragg grating) is formed is used as a sensor for measuring temperature. The FBG is a diffraction grating in which the refractive index of the core of the optical fiber is changed by a predetermined length period (grating period) along the axial direction, and the incident light to the optical fiber depends on the grating period. It has a characteristic of reflecting light of a specific wavelength (Bragg wavelength) and transmitting the remaining light. When the FBG is thermally expanded in accordance with the temperature change, the grating period changes accordingly. Since the Bragg wavelength changes linearly with respect to the change in the grating period, the temperature can be measured based on the change amount of the Bragg wavelength. Further, if a plurality of FBGs are formed on one optical fiber, multipoint temperature measurement that measures temperatures at a plurality of locations can be performed. For example, Patent Document 1 discloses a temperature measurement system that uses a laser as a light source of incident light to an optical fiber and measures temperatures with a plurality of FBGs provided on an outer panel of an aircraft.

  Here, with reference to FIG. 7, a method of performing temperature measurement by FBG using a laser as a light source will be schematically described. In FIG. 7, a region denoted by reference numeral 100 indicates the FBG reflection spectrum when the measurement target part to be temperature-measured is at a given temperature. An area denoted by reference numeral 200 indicates a spectrum of incident light emitted by the laser, and its bandwidth is generally narrower than the bandwidth of the FBG reflection spectrum. When the part to be measured is at the above temperature, the FBG reflects the incident light indicated by reference numeral 200 at the reflection intensity S1. Further, when the temperature of the part to be measured rises and the FBG expands, the reflection spectrum of the FBG shifts to the longer wavelength side as indicated by the dashed-dotted region 110, and the reflection intensity of the reflected light changes from S1 to S2. To do. As described above, since the Bragg wavelength of the FBG changes linearly with respect to the change in the grating period, that is, the temperature change of the part to be measured, the temperature of the part to be measured is obtained based on the difference between the reflection intensities S1 and S2.

Special table 2009-516855 gazette

  When a plurality of FBGs are formed on one optical fiber and multipoint temperature measurement is performed, it is necessary to determine which FBG the reflected light is from. Therefore, the FBGs are generally formed so that their grating periods are different from each other, that is, the reflection bands of the FBGs are different from each other. Here, as described above, the bandwidth of the incident light emitted by the laser is narrow, and it is impossible to emit incident light corresponding to the reflection band of each FBG with a single laser. A plurality of lasers or wavelength tunable lasers are used as the light source. However, a laser is an expensive device compared with an LED or the like, and a wavelength variable laser is more expensive. Therefore, when performing multipoint temperature measurement using a laser as a light source as in the temperature measurement system described in Patent Document 1, the temperature is The problem is that the cost of the measurement system is high.

  Further, when the temperature change range of the measured part is wide, the thermal expansion amount of the FBG when the temperature rises also increases, so that the reflection spectrum of the FBG may shift to a region 120 indicated by a two-dot chain line in FIG. . In such a case, the spectrum 200 of the incident light emitted from the laser is not included in the band of the reflection spectrum, and the reflection on the FBG does not occur, so that it becomes impossible to measure the temperature. To avoid this problem, it is necessary to use a tunable laser or change the material of the optical fiber to reduce the thermal expansion amount of the FBG. The cost of the temperature measurement system increases. That is, a temperature measurement system that performs multipoint temperature measurement using a laser as a light source, and a temperature measurement system that performs temperature measurement of a measured part having a large temperature change range using a laser as a light source are difficult to construct at low cost It had the problem of being.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a temperature measurement system that realizes multi-point temperature measurement and wide-range temperature measurement at low cost.

  The temperature measurement system according to the present invention includes an optical fiber having an FBG that changes the wavelength of reflected light with respect to incident light and the wavelength of transmitted light with respect to incident light in accordance with the temperature of the measured part, and the incident light is incident on the optical fiber. In a temperature measurement system including a light source that performs measurement and a measurement unit that measures the temperature of the measurement target based on reflected light or transmitted light, the light source has a bandwidth that is wider than the bandwidth of the reflection spectrum of the FBG and is continuous. Light having a specific spectrum is incident on the optical fiber as incident light, and the measuring means measures the temperature of the measured part based on the change in the position of the FBG reflection spectrum or the change in the position of the FBG transmission spectrum. It is characterized by doing.

  Since the incident light emitted from the light source is a broadband light having a bandwidth wider than the reflection spectrum bandwidth of the FBG and having a continuous spectrum, a plurality of FBGs are used in accordance with the spectrum bandwidth of the incident light. Is possible. In addition, since the incident light has a wide band, the measurable temperature range is expanded regardless of whether the FBG is single or plural. Since the measurement means measures the reflection spectrum or transmission spectrum of the FBG, when the wavelength band corresponding to the bandwidth of the spectrum of the incident light is measured, the reflection spectrum of the FBG can be found within that band, and the position of this spectrum The amount of change in temperature can be obtained based on the amount of change in. In other words, even if a single light source is used, the bandwidth that can be measured is widened. As in the case where a laser is used as a light source, a plurality of light sources are used, and the wavelength of incident light is variable. Do not need. Moreover, when making incident light into a broadband, cheap apparatuses, such as LED, can be used as a light source, for example. Therefore, in the temperature measurement system, multipoint temperature measurement and wide-range temperature measurement can be performed at low cost.

  The optical fiber may have a plurality of FBGs. Further, the measuring means may measure the temperature of the corresponding measured part based on the amount of change in the position of the transmission spectrum of the FBG. In general, when measuring the reflection spectrum of the FBG, both the light source and the measuring means are connected to one end of the optical fiber, so that a circulator or the like for guiding the reflected light from the FBG to the measuring means is required. On the other hand, when measuring the transmission spectrum of the FBG, a light source is connected to one end of the optical fiber and a measuring means is connected to the other end, so that transmitted light can be input to the measuring means without the need for a circulator or the like. . That is, when measuring a transmission spectrum, the configuration of the temperature measurement system can be simplified.

  The measuring unit may measure the temperature of the corresponding measurement target part based on the amount of change in the position of the reflection spectrum of the FBG. In the temperature measurement system having a plurality of FBGs, when the reflection spectrum of the FBG is measured, if the optical fiber is broken in the middle, the reflected light from the FBG after the broken point will not reach the measuring means. Therefore, it is possible to identify the presence / absence of a disconnection and the location of the disconnection.

  The temperature measurement system according to the present invention can be used as a vehicle sensor for measuring the temperature of a vehicle. In this case, the vehicle has a plurality of measured parts, and the optical fiber is provided in the measured parts. A plurality of FBGs.

  The temperature measuring method according to the present invention includes an optical fiber having an FBG that changes the wavelength of reflected light with respect to incident light and the wavelength of transmitted light with respect to incident light in accordance with the temperature of the part to be measured, and incident light on the optical fiber. In a temperature measurement method for measuring the temperature of a part to be measured using a temperature measurement system comprising a light source incident on the light source and a measuring means for measuring the temperature of the part to be measured based on reflected light or transmitted light. Are provided in the measured portion, the step of causing the light source to enter the optical fiber as light having a continuous spectrum that is wider than the bandwidth of the reflection spectrum of the FBG, and the reflection means reflects the FBG. Measure the transmission spectrum of the spectrum or FBG, and based on the change in the position of the reflection spectrum or the change in the position of the transmission spectrum, It is characterized in that comprising the step of calculating the temperature of the measuring unit.

  According to the present invention, in the temperature measurement system, multipoint temperature measurement and wide-range temperature measurement can be performed at low cost.

It is the schematic which shows the structure of the temperature measurement system which concerns on Embodiment 1 of this invention. FIG. 3 is a schematic diagram showing a configuration of an FBG in the temperature measurement system according to the first embodiment. 3 is a graph showing a reflection spectrum of each FBG in the temperature measurement system according to the first embodiment. It is a graph which shows the transmission spectrum input into a measurement means in the temperature measurement system which concerns on Embodiment 1, (a) shows a steady state spectrum, (b) shows the state which the temperature change produced. It is the schematic which shows the structure of the temperature measurement system which concerns on Embodiment 2 of this invention. It is the schematic which shows the structure of the vehicle sensor using the temperature measurement system which concerns on Embodiment 3 of this invention. It is a graph for demonstrating the conventional temperature measuring method.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 schematically shows a configuration of a temperature measurement system 10 according to the first embodiment. The temperature measurement system 10 includes a single optical fiber 11, a light source 12 connected to one end of the optical fiber 11, and measurement means 13 connected to the other end of the optical fiber 11. Further, n FBGs (fiber Bragg gratings) 21, 22, 23,..., 2n are formed in the middle of the optical fiber 11, and these FBGs are subjected to n measurement targets for temperature measurement. It is provided in each of the measurement units 31, 32, 33, ..., 3n. As will be described later, the temperature of each measured part can be measured by the corresponding FBG. That is, the temperature measurement system 10 performs multi-point temperature measurement for measuring the temperatures of a plurality of measured parts using a single optical fiber 11.

  Next, the configuration will be described with reference to the FBG 21 shown in FIG. As shown in FIG. 2, the optical fiber 11 includes a core 11a through which incident light L1 input from a light source 12 (see FIG. 1) propagates, and a clad 11b that covers the outer periphery of the core 11a. The FBG 21 is a diffraction grating in which the refractive index of the core 11a is changed by a predetermined length period (grating period) Λ1 along the axial direction, and emits light of a specific wavelength (Bragg wavelength) with respect to the incident light L1. The reflected light L2 is reflected and the remaining light is transmitted as transmitted light L3. The optical fiber 11 is made of a material such as quartz glass, for example, and has a positive coefficient of thermal expansion. As an example, the formation of each FBG is performed by irradiating the core 11a of the optical fiber 11 with ultraviolet rays or the like.

  The grating period Λ1 is one of the elements that define the Bragg wavelength of the FBG 21, and the Bragg wavelength changes linearly with respect to the amount of change of the grating period Λ1. That is, when the temperature of the part to be measured 31 rises and the FBG 21 expands, the grating period Λ1 also increases, and accordingly, the Bragg wavelength shifts to the long wavelength side. On the contrary, when the temperature of the measured part 31 decreases and the FBG 21 contracts, the grating period Λ1 also decreases, and accordingly, the Bragg wavelength shifts to the short wavelength side. Therefore, it becomes possible to measure the temperature of the part to be measured 31 based on the shift amount of the Bragg wavelength. Here, since the transmitted light L3 transmitted through the FBG 21 is obtained by removing the reflected light L2 from the incident light L1, the shift amount of the Bragg wavelength can be obtained from both the reflection side and the transmission side.

  Although not shown in FIG. 2, FBGs 22, 23,..., 2n are arranged on the downstream side of the FBG 21 in the direction in which the incident light L1 propagates (see FIG. 1). The transmitted light transmitted through is sequentially incident on the downstream FBG. These FBGs have the same configuration as the FBG 21 and are used to measure the temperatures of the corresponding measured parts 32, 33,..., 3n, respectively, but have different grating periods Λ2, Λ3,. .., Λn, that is, each FBG is formed so as to reflect light having different Bragg wavelengths. Describing in more detail using FIG. 3, the FBGs 21, 22,..., 2n reflect the reflected light of the reflection spectra 41, 42,. The grating period of each FBG is selected so that the corresponding reflection spectrum is located in a wavelength band that is separated from each other, so that it is possible to determine which FBG the reflected light and transmitted light are from.

  Referring back to FIG. 1, the light source 12 is a device that emits broadband light including the reflection spectra 41, 42,..., 4n (see FIG. 3) of the FBGs 21, 22,. For example, an LED that emits white light is used. Here, the white light emitted by the LED refers to light having a spectrum in which ultraviolet light (invisible), light having a wavelength corresponding to purple to red (visible), and infrared light (invisible) are continuously connected. That is, the light emitted from the light source 12 as the incident light L1 (see FIG. 2) to the optical fiber 11 is not limited to colorless light, and may include various colors of light according to the spectrum bandwidth. . On the other hand, the measuring means 13 is a device that measures the intensity of light within a predetermined band using a compound eye optical element MOS or CCD, and can measure the emission band of the incident light L1 emitted from the light source 12. Yes. As apparent from the fact that the measuring means 13 is connected to the opposite side of the light source 12, the temperature measuring system 10 measures the temperature of each measured part based on the transmitted light transmitted by each FBG. It is.

Next, a method for measuring the temperatures of the parts to be measured 31, 32, 33,..., 3n using the temperature measurement system according to the first embodiment of the present invention will be described.
As shown in FIG. 1, first, FBGs 21, 22, 23,..., 2n are provided on the corresponding measured parts 31, 32, 33,. Incident light L 1 is incident on the fiber 11. When the incident light L1 is incident, the FBG 21 located on the most upstream side reflects the reflected light L2 (see FIG. 2) corresponding to the Bragg wavelength, and the remaining light is downstream as the transmitted light L3 (see FIG. 2). Permeate to the side. Similarly, the FBGs 22, 23,..., 2n reflect the reflected light corresponding to the Bragg wavelength with respect to the transmitted light from the upstream FBG, and transmit the remaining light. Finally, the light transmitted through all the FBGs is input to the measuring means 13 and monitored.

  Here, the transmitted light transmitted by each FBG is obtained by removing the reflected light from the light incident from the upstream side. The light source 12 emits broadband light including the reflection spectrum of each FBG in the bandwidth, and the measuring means 13 can measure the emission band of the light emitted from the light source 12. That is, as shown in FIG. 4A, the transmission spectrum 50 that passes through all the FBGs and is input to the measuring means 13 includes the spectra 51, 52,..., 5n reflected by each FBG. The measurement means 13 can recognize these spectra as waveforms. Since the reflection spectra 51, 52,..., 5n are separated from each other in the transmission spectrum 50, the corresponding FBGs are determined based on the wavelength band in which they are located. FIG. 4A shows a steady state before a temperature change occurs in each measured part.

  In the temperature measurement system 10 that monitors the transmission spectrum 50 as described above, the case where the temperature of the measured part 31 decreases and the temperature of the measured part 32 increases will be described below. When the temperature of the measured part 31 decreases from the steady state shown in FIG. 4A, the corresponding FBG 21 contracts and the Bragg wavelength shifts to the short wavelength side. Further, when the temperature of the measured part 32 rises, the corresponding FBG 22 expands and the Bragg wavelength shifts to the long wavelength side. Therefore, as shown in FIG. 4B, the transmission spectrum 50 input to the measuring means 13 (see FIG. 1) moves to the position where the reflection spectrum 51 corresponding to the measured part 31 is indicated by reference numeral 51 ′. Then, the reflection spectrum 52 corresponding to the part to be measured 32 is moved to the position indicated by reference numeral 52 ′. Since the measurement means 13 can recognize the reflection spectrum in each FBG as a waveform, the temperature change amount of the measured portions 31 and 32 is based on the movement amount of the reflection spectra 51 and 52, specifically, the reflection spectrum 51. , 52 on the basis of the movement amount of the peak position of the waveform, or the movement amount of the waveform at a predetermined intensity.

  As described above, the incident light L1 emitted from the light source 12 has a bandwidth wider than the bandwidth of the reflection spectra 51, 52,..., 5n of the FBGs 21, 22, 23,. Since broadband light having a spectrum is used, a plurality of FBGs can be provided in accordance with the spectrum bandwidth of the incident light L1. In addition, since the incident light L1 has a wide band, the measurable temperature range is expanded regardless of whether the FBG is single or plural. In order to measure the transmission spectrum 50 that has passed through the FBGs 21, 22, 23,..., 2n, the measuring means 13 measures the wavelength band corresponding to the bandwidth of the spectrum of the incident light L1. , 5n can be found, and the amount of change in temperature can be determined based on the amount of change in the position of these spectra. In other words, even if a single light source 12 is used, the measurable bandwidth is widened. As in the case where a laser having a narrow emission band is used as a light source, a plurality of light sources or a wavelength of incident light is used. Is not required to be variable. In addition, when the incident light L1 has a wide band, for example, an inexpensive device such as an LED can be used as the light source 12. Therefore, the temperature measurement system 10 can perform multi-point temperature measurement and wide-range temperature measurement at low cost.

  In addition, since the measuring means 13 measured the temperatures of the corresponding measured parts 31, 32, 33,..., 3n based on the transmission spectra 50 that passed through the FBGs 21, 22, 23,. The configuration of the temperature measurement system 10 is simplified. Specifically, when connecting the measurement means 13 to the reflection side, that is, the light source 12 side, it is common to require a device such as a circulator to guide the reflected light from each FBG to the measurement means. When the temperature measurement is performed based on the transmission spectrum 50 as in the temperature measurement system 10, the light source 12 may be connected to one end side of the optical fiber 11 and the measurement means 13 may be connected to the other end side, and a circulator or the like is required. do not do.

Embodiment 2. FIG.
Next, a temperature measurement system according to Embodiment 2 of the present invention will be described. The temperature measurement system according to the second embodiment is connected to the reflection side, whereas the measurement means 13 in the temperature measurement system 10 according to the first embodiment is connected to the transmission side, that is, the opposite side of the light source 12. It is comprised so that. In the embodiments described below, the same reference numerals as those shown in FIGS. 1 to 4 are the same or similar components, and thus detailed description thereof is omitted.

  As shown in FIG. 5, the temperature measurement system 60 includes the same optical fiber 11 and light source 12 as those in the first embodiment. In addition, a circulator 62 for branching light propagating from the FBG 21 side to the light source 12 side to the optical fiber 61 is connected between the light source 12 and the FBG 21 located on the most upstream side. Measuring means 13 is connected to the tip. That is, the temperature measurement system 10 in the first embodiment monitors the transmission spectrum 50 (see FIG. 4) that has passed through the FBGs 21, 22, 23,..., 2n, and the reflection spectra 51, 52,. .., 4n, while the temperature of the measured part is measured based on the amount of change in the position of 5n, the temperature measurement system 60 monitors the reflection spectra 41, 42,..., 4n shown in FIG. The temperature is measured based on these movement amounts. Other configurations and temperature measurement methods are the same as those in the first embodiment.

  As described above, even if the measuring means 13 is connected to the reflection side of the FBGs 21, 22, 23,..., 2n, the same effect as in the first embodiment can be obtained. Further, when the measuring unit 13 is connected to the reflection side, for example, if the optical fiber 11 is disconnected between the FBG 21 and the FBG 22, the measuring unit 13 includes FBGs 22, 23,. Therefore, it is possible to determine whether or not there is a disconnection and to identify the disconnection location.

Embodiment 3 FIG.
Next, a case where the temperature measurement system according to Embodiment 3 of the present invention is applied as a vehicle sensor applied to an electric vehicle, a hybrid car, or the like will be described as an example.
As shown in FIG. 6, the vehicle sensor 70 is formed by sequentially connecting a battery 72 a provided at the front portion of the vehicle 71, parts 72 b and 72 c in the room of the vehicle 71, and the like with the optical fiber 11. . That is, the battery 72a and the above-described parts 72b and 72c correspond to the measured parts in the first and second embodiments, and the FBGs 21 to 23 are provided for these parts. In addition, a vehicle control unit (not shown) is connected to the measuring means 13, and based on the temperature measurement results using the FBGs 21 to 23, the operation of devices such as a warning light indicating the operating status of the battery and an auto air conditioner is performed. Be controlled. Other configurations and temperature measurement methods are the same as those in the first embodiment.
As described above, the temperature measurement system according to the present invention can also be applied as the vehicle sensor 70. In this case, if one optical fiber 11 is laid in the vehicle 71, multipoint temperature measurement can be performed, so that temperature management at a plurality of locations can be performed with a simple configuration.

  Although the temperature measurement system according to the first to third embodiments is configured to perform multipoint temperature measurement, the temperature measurement system is not limited to a plurality of measurement target parts, and is used for temperature measurement of one measurement target part. It is also possible to use it. The present invention has an effect that a measurable temperature range can be expanded by using a broadband light source and a measuring unit capable of measuring the emission band of the light source. It is common regardless of the number. Therefore, unlike the case where a laser is used as a light source, there is no problem that the emission band of the light source deviates from the reflection spectrum of the FBG and the temperature cannot be measured.

  10, 60 Temperature measurement system, 11 Optical fiber, 12 Light source, 13 Measuring means, 21, 22, 23,..., 2n FBG, 31, 32, 33,. , 71 Vehicle, 72a Battery (measured part), 72b, 72c Vehicle interior part (measured part), L1 incident light, L2 reflected light, L3 transmitted light.

Claims (6)

An optical fiber having an FBG that changes the wavelength of reflected light with respect to incident light and the wavelength of transmitted light with respect to the incident light in accordance with the temperature of the part to be measured;
A light source that makes the incident light incident on the optical fiber;
In a temperature measurement system comprising a measuring means for measuring the temperature of the part to be measured based on the reflected light or the transmitted light,
The light source is incident on the optical fiber as incident light with light having a bandwidth wider than that of the reflection spectrum of the FBG and having a continuous spectrum;
The temperature measuring system is characterized in that the measuring means measures the temperature of the part to be measured based on the change amount of the position of the reflection spectrum of the FBG or the change amount of the position of the transmission spectrum of the FBG.   The temperature measurement system according to claim 1, wherein the optical fiber includes a plurality of the FBGs.   The temperature measurement system according to claim 1, wherein the measurement unit measures a temperature of the corresponding measurement target part based on a change amount of a position of a transmission spectrum of the FBG.   The temperature measurement system according to claim 1, wherein the measurement unit measures a temperature of the corresponding measurement target part based on a change amount of a position of a reflection spectrum of the FBG. A vehicle sensor that measures the temperature of a vehicle using the temperature measurement system according to any one of claims 1 to 4,
The vehicle has a plurality of measured parts,
The said optical fiber is a sensor for vehicles which has several FBG provided in these measured parts. An optical fiber having an FBG that changes the wavelength of reflected light with respect to incident light and the wavelength of transmitted light with respect to the incident light in accordance with the temperature of the part to be measured;
A light source that makes the incident light incident on the optical fiber;
In a temperature measurement method for measuring the temperature of the measured part using a temperature measurement system provided with a measuring means for measuring the temperature of the measured part based on the reflected light or the transmitted light,
Providing the FBG in the portion to be measured;
Injecting into the optical fiber as the incident light light having a continuous spectrum and a bandwidth wider than the bandwidth of the FBG reflection spectrum by the light source;
A step of measuring a reflection spectrum of the FBG or a transmission spectrum of the FBG by the measuring means, and calculating a temperature of the measured part based on a change amount of the position of the reflection spectrum or a change amount of the position of the transmission spectrum; A temperature measurement method comprising:

Images