JP4679185B2 - Fiber Bragg Grating Physical Quantity Measuring Device and Fiber Bragg Grating Physical Quantity Measuring Method - Google Patents

Description

  The present invention relates to a fiber Bragg grating physical quantity measuring device that measures a physical quantity from a change amount of a reflected light wavelength from a fiber Bragg grating (FBG) sensor (hereinafter referred to as “FBG sensor”) that measures various physical quantities, and The present invention relates to a fiber Bragg grating physical quantity measuring method.

  In recent years, a large number of optical fiber sensing systems have been developed, designed to be applied to health monitoring of social infrastructures, etc. Technology is also being directed toward larger scales.

  A sensing system using an FBG sensor, which is one of those methods, inherits the common advantages of conventional optical sensing, and the slow measurement and response times and sensitivity that were the problems of conventional optical fiber sensing. The technology is expected to overcome the shortage.

  FIG. 10 shows a conventional FBG physical quantity measuring device. The FBG physical quantity measuring device 1 has a configuration in which one end of an optical fiber 3 is connected to a light source 2 and a plurality of FBG sensors 4 are provided on the optical fiber 3. The optical fiber 3 is configured by providing a plurality of optical branching devices 5 on the optical trunk line 3 a, and an optical branching path 3 b branches from each optical branching device 5. The FBG sensor 4 is provided in each optical branch path 3b. At this time, each FBG sensor 4 is configured to have different specific wavelength bands depending on the distance from each optical splitter 5 so that the specific wavelength bands of the FBG reflected light reflected from each other do not affect each other.

  A reflected light optical fiber 3c is connected to the optical branching device 5a on the light source 2 side, and a photodetector 6 is connected to an end of the reflected light optical fiber 3c. Further, the photodetector 6 and the light source 2 are connected to a control unit 7, and the control unit 7 is connected to a signal processing device 8.

  In such an FBG physical quantity measuring apparatus 1, a large number of FBG sensors 4 are provided by the optical fiber 3, and in order to be able to measure physical quantities at a large number of points, the light emitted from the light source 2 to each FBG sensor 4 is measured. A wavelength multiplexing system that obtains a physical quantity by receiving FBG reflected light of a plurality of wavelength bands with variable wavelength from the FBG sensor 4, and a plurality of times using the time difference of the FBG reflected light from the plurality of FBG sensors 4 using light as pulse light. Signal processing is performed by a time multiplexing method for obtaining a physical quantity in the FBG sensor 4.

  That is, broadband continuous light is emitted from the broadband light source 9 of the light source 2, and the wavelength tunable filter 11 is controlled by the scan execution unit 10 of the control unit 7 so that continuous light in a predetermined wavelength band is selectively transmitted. Further, a trigger signal is applied from the trigger signal application unit 12 to the optical pulse generator 13 in response to a command signal from the scan execution unit 10, and the continuous light having a predetermined wavelength band that has passed through the wavelength tunable filter 11 is converted into pulsed light. Each FBG sensor 4 is irradiated via the optical trunk line 3a, the optical branching unit 5 and the optical branching path 3b.

  For this reason, each FBG sensor 4 reflects FBG reflected light in a wavelength band corresponding to a physical quantity such as temperature and strain, and the light source 2 side via the optical branching path 3b, the optical branching unit 5 and the optical trunk line 3a. Light is received by the optical branching unit 5a. Then, each FBG reflected light is scanned for each wavelength in the photodetector 6, and a spectrum of each FBG reflected light is obtained and provided to the control unit 7 as reception data.

  The reception data of the FBG reflected light given to the control unit 7 is subjected to noise processing in the pulse integration circuit 14 and then given a time gate in the gate signal generation unit 15 to extract a pulse from the focused FBG sensor 4. The Further, the pulse from the focused FBG sensor 4 is digitized by the AD conversion device 16 and given to the wavelength center calculation unit 17 of the signal processing device 8 through the scanning unit.

  The wavelength center calculation unit 17 of the signal processing device 8 obtains the center of the wavelength region of each FBG reflected light, and the physical quantity conversion unit 18 converts the wavelength region center of each FBG reflected light into a physical quantity.

  Such physical quantity sensing using the FBG sensor 4 is performed based on the change in the reflection wavelength of light accompanying the change in the pitch of the Bragg diffraction grating formed in the fiber core of the FBG sensor 4. Examples of physical quantities to be sensed include physical quantities such as vibration, pressure, and water level measurement in addition to temperature and strain. A mechanism for converting the pitch change of the Bragg diffraction grating of the FBG sensor 4 into each physical quantity is an FBG physical quantity measuring device. 1 is a sensor.

  By the way, the principle of physical quantity sensing using the FBG sensor is based on a phenomenon in which the reflection wavelength is changed by an equal ratio due to the pitch change of the Bragg diffraction grating written in the optical fiber core.

  The number of connection points of the FBG sensor depends on the physical quantity range and the reflection wavelength band. If the physical quantity range is widened, the number of connection points decreases, and conversely, if the physical quantity range is narrow, the number of connection points can be increased, and these are always in a trade-off relationship. In order to solve this problem, there is a method in which the connection point of the FBG sensor is expanded to several hundreds of points in one system by using a multiplexing technique by wavelength multiplexing and time multiplexing.

  As an example of a system using these multiplexing techniques, after taking into account the reduction of the measurement time of the entire system, the reflected pulse trains of a plurality of FBG sensors discriminated by wavelength multiplexing are collectively converted into digital data by an AD converter. A measurement method for performing arithmetic processing by a computer is known (see, for example, Patent Document 1).

  However, in this example, as the number of FBG sensors increases and the time interval between pulses becomes longer, the amount of data to be captured increases, and as the number of FBG sensors increases, the amount of light is necessarily dispersed. The amount of reflected pulse light also becomes weak, leading to a decrease in S / N. As a result, measurement accuracy cannot be ensured. In order to ensure measurement accuracy, an averaging process of several hundred to several thousand times is required, so that the data amount is further increased. Since measurement is performed continuously, the processing capacity of the computer may be saturated in some cases, and it is necessary to reduce the amount of data to be processed as much as possible.

As an example of solving this problem, a time gate is provided for each pulse, and only necessary pulses are converted to digital data, and then data compression is performed by real-time averaging processing using a programmable logic device (PLD). A method is known in which the amount of data to be processed by the computer (the amount of data transferred to the computer) is minimized in advance (see, for example, Patent Document 2).
JP 2000-74742 A JP 2002-352369 A

  In the above-described prior art, when providing a time gate for each pulse of FBG reflected light, no specific means for knowing the exact return time of each individual pulse required is disclosed.

  In other words, in order to know the exact return time of each required pulse, it is considered that the optical fiber length and the connection position of the FBG sensor should be determined in advance at the design stage. When laying, the length of the optical fiber may be changed according to the field situation, and there are many cases where it does not become as designed in advance. Also, the length of the optical fiber itself is not as designed because an error of several percent occurs in the manufacturing process.

  As another method, there is a method using OTDR (Optical Time Domain Reflectometer). However, a conventional OTDR light source is generally an LD (laser diode) or the like, and even if the wavelength band of the LD is wide, for example, it is only about 1550 nm ± 20 nm. Therefore, the FBG sensor has a CL band (for example, 1530 to 1600 nm). ) Is not appropriate when the entire wavelength band is used. Although it is possible to technically widen the measurement system, it is inevitably expensive because it is an unnecessary function and no demand from the intended use of OTDR.

  The present invention has been made in view of such circumstances, and a fiber Bragg grating physical quantity measurement that can easily and accurately measure and obtain the reflection time information of the reflected light pulse of the FBG sensor at the initial stage of measurement. An object is to provide a device and a fiber bragg grating physical quantity measuring method.

In the invention according to claim 1, an optical fiber, a plurality of fiber Bragg grating sensors (FBG sensors) provided on the optical fiber, and a wavelength tunable filter for irradiating the FBG sensor with light in a required wavelength band A light source comprising: a light detector that receives reflected light from the FBG sensor and obtains received data; and a plurality of points by applying either or both of time division multiplexing and wavelength multiplexing based on the received data In an optical fiber Bragg grating apparatus comprising a physical quantity measuring means for measuring a physical quantity of an A / D converter, an AD conversion processing unit for converting an FBG reflected pulse obtained from the FBG sensor into a digital data string set of time and voltage, and the digital data string set Is a differential coefficient obtained with respect to steep slopes of rising and falling edges of the FBG reflection pulse And a time calculation processing unit for calculating the reflection time information of the FBG reflected pulse corresponding to over click sets provides fiber Bragg grating physical quantity measuring device and calculates the reflection time of the FBG reflected pulse.

  In the invention according to claim 2, the differential coefficient calculated from the FBG reflection pulse with the peak level of the differential coefficient peak group obtained for the rising and falling steep slopes of the FBG reflection pulse at the detection lower limit as a threshold value. Provided is a fiber Bragg grating physical quantity measuring device including a differential coefficient determination processing unit that determines only a threshold value of a differential coefficient peak group that exceeds the threshold value from a peak group.

  According to a third aspect of the present invention, there is provided a fiber Bragg grating physical quantity measuring device including a differential coefficient level ratio determining unit that compares and determines a relative ratio of peak levels of a differential coefficient pair with a predetermined threshold value.

  According to a fourth aspect of the present invention, there is provided a fiber Bragg grating physical quantity measuring device including a differential coefficient time width determination unit that compares and determines a time interval of a differential coefficient peak set with a threshold value based on a time width of the FBG reflection pulse. To do.

  According to a fifth aspect of the present invention, there is provided a fiber Bragg grating physical quantity measuring apparatus in which processing units of a digital data sequence set and a derivative coefficient sequence set are stored in a programmable logic device (PLD).

  According to a sixth aspect of the present invention, there is provided a fiber Bragg grating physical quantity measuring device provided with a low-pass filter before the AD conversion processing section.

  In the invention according to claim 7, an optical fiber, a plurality of FBG sensors provided on the optical fiber, and a light source including a wavelength tunable filter for irradiating light of a required wavelength band to these FBG sensors; A photodetector that receives reflected light from the FBG sensor and obtains received data, and a physical quantity that measures a physical quantity at multiple points by applying one or both of time division multiplexing and wavelength multiplexing based on the received data In a fiber Bragg grating device comprising a measuring means, an AD conversion processing unit that converts an FBG reflected pulse obtained from the FBG sensor into a digital data string set of time and voltage, and differential calculation of the digital data string set to calculate the above The FBG reflected pulse corresponding to the derivative peak set obtained with respect to the steep slope of the rising and falling edges of the FBG reflected pulse. A time calculation processing unit for calculating an irradiation time; and controlling the wavelength tunable filter so that the FBG reflected light is subjected to wavelength scanning at a predetermined number of detailed scanning points set in advance for the wavelength scanning range of the partial detailed scanning mode. And a wavelength in a pre-scan mode in which the scan range is wider than the wavelength scan range of the partial detail scan mode and wider than the scan interval of the partial detail scan mode with respect to the FBG reflected light A pre-scan parameter setting unit for setting a scan condition for scanning, and the wavelength scan in the pre-scan mode is executed prior to the wavelength scan in the partial detailed scan mode under the scan condition set by the pre-scan parameter setting unit. While controlling the tunable filter, The wavelength region center of the FBG reflected light is obtained from received data obtained by wavelength scanning in the pre-scan mode, and sections that can secure the number of detailed scanning points in the partial detail scan mode are provided on both sides of the obtained wavelength region center. A pre-scan unit that is determined as a wavelength scanning range in the partial detailed scan mode, a wavelength center calculation unit that obtains a wavelength region center of the FBG reflected light from reception data obtained by wavelength scanning in the partial detailed scan mode, and the wavelength center There is provided a fiber Bragg grating physical quantity measuring device comprising: a physical quantity converting unit that converts the center of the wavelength region of the FBG reflected light obtained by the calculating unit into a physical quantity.

In the invention according to claim 8, the step of receiving the reflected light from the plurality of FBG sensors provided on the optical fiber to obtain the received data, and any of time division multiplexing and wavelength multiplexing based on the received data Measuring a physical quantity at multiple points by applying one or both of them, an AD conversion step for converting an FBG reflected pulse obtained from the FBG sensor into a digital data string set of time and voltage, and differentiating the digital data string set A time calculation step processing unit for calculating time information corresponding to a derivative peak set obtained by calculating and obtaining the slope of the steep part of the rise and fall of the FBG reflection pulse, and the reflection time of the FBG reflection pulse A fiber Bragg grating physical quantity measuring method is provided.

  According to the present invention, it is possible to easily and accurately measure and obtain the reflection time information of the reflected light pulses of all the FBG sensors at the initial measurement stage.

  In addition, according to the present invention, it is possible to execute all processing by a digital circuit by processing using digital data. Therefore, the processing circuit can be processed at high speed, the output data can be compressed to only the minimum necessary information, the amount of data transferred to the computer and the software load can be reduced, and the processing speed of the entire system can be reduced. Can be improved.

  Furthermore, according to the present invention, it is possible to measure physical quantities at multiple points in a shorter time while ensuring the measurement accuracy of the physical quantities.

  Hereinafter, embodiments of a fiber Bragg grating physical quantity measuring device and a fiber Bragg grating physical quantity measuring method according to the present invention will be described with reference to the drawings.

[First Embodiment (FIGS. 1 to 6)]
FIG. 1 is a block diagram schematically showing a first embodiment of a fiber Bragg grating physical quantity measuring device according to the present invention.

First, the overall configuration will be described. As shown in FIG. 1, the fiber Bragg grating (FBG) physical quantity measuring device 20 has a configuration in which one end of an optical fiber 22 is connected to a light source 21 and a plurality of FBG sensors 23 are provided on the optical fiber 22. This optical fiber 22 is configured by providing a plurality of optical branching devices 24 on an optical trunk line 22 a, and an optical branching path 22 b branches from each optical branching device 24. The FBG sensor 23 is provided in series with each optical branch path 22b. An optical delay device 47 is provided in the optical trunk line 22a.

  A reflected light optical fiber 22c is connected to the optical branching device 24a on the light source 21 side, and a photodetector 25 is connected to an end of the reflected light optical fiber 22c. Further, the photodetector 25 and the light source 21 are connected to a common control unit 26, and the control unit 26 is connected to a signal processing device 27.

  The FBG sensor 23 is configured by providing a Bragg diffraction grating in the fiber core, and the pitch of the Bragg diffraction grating changes depending on physical quantities such as temperature, strain, vibration, pressure, and water level measurement. It has the property of reflecting FBG reflected light in the wavelength band. For this reason, the physical quantity can be obtained from the wavelength of the FBG reflected light. And each FBG sensor 23 is comprised so that it may become a different specific wavelength band according to the distance from each optical splitter 24 so that the specific wavelength band of the FBG reflected light which mutually reflects may not influence mutually.

  The light source 21 includes a broadband light source 28, a wavelength tunable filter 29, and an optical pulsing device 30. The broadband light source 28 and the wavelength tunable filter 29 are provided in a temperature adjustment unit 31 that provides a sufficiently stable temperature range for temperature-sensitive optical equipment. The broadband light source 28 has a function of generating broadband continuous light (CW: Continuous Wave), and the wavelength variable filter 29 has a function of receiving a broadband continuous light from the broadband light source 28 and selectively transmitting light in a predetermined wavelength band. The optical pulsing device 30 has a function of receiving light of a predetermined wavelength band from the wavelength tunable filter 29 and converting it into pulsed light. The light source 21 is configured to be able to irradiate each FBG sensor 23 provided in the optical fiber 22 with pulsed light in a predetermined wavelength band.

  The photodetector 25 receives the FBG reflected light from the FBG sensor 23, performs photoelectric conversion, and amplifies and shapes it to obtain received data as an electric pulse signal having a required signal intensity and bandwidth. A function of giving received data to the control unit 26.

  The control unit 26 includes a trigger signal application unit 32, a prescan unit 33, a partial detail scan unit 34, a prescan parameter setting unit 35, a pulse integration circuit 36, a gate signal generation unit 37, and an AD converter 38, and FBG reflected light. The wavelength scanning range of the light, that is, the wavelength band of the light transmitted by the wavelength tunable filter 29 and the transmission timing of the pulsed light generated by the optical pulsing device 30 based on the received data received from the photodetector 25. . At this time, the control unit 26 is configured to control the wavelength tunable filter 29 and the optical pulsing device 30 by two types of control modes, a pre-scan mode and a partial detailed scan mode.

  The trigger signal applying unit 32 has a function of controlling the timing of the pulsed light emitted from the light source 21 by giving a trigger signal to the optical pulsing device 30 and a function of giving timing information of the trigger signal to the gate signal generating unit 37. And have.

The pre-scan unit 33 controls the wavelength tunable filter 29 so as to execute wavelength scanning in the pre-scan mode to irradiate each FBG sensor 23 with light in a required wavelength band, and the trigger signal application unit 32 performs pre-scan. It has a function of controlling the optical pulsing device 30 by giving wavelength scanning timing information according to the mode.

The prescan unit 33 receives received data obtained by wavelength scanning in the prescan mode from the photodetector 25 via the pulse integration circuit 36, the gate signal generation unit 37, and the AD converter 38, and focuses on the FBG of interest. A function for obtaining the center of the wavelength region of the FBG reflected light from the sensor 23 and a section that can secure a predetermined number of detailed scanning points set in advance on both sides of the obtained center of the wavelength region are determined as the wavelength scanning range in the partial detail scanning mode. With functions.

The partial detail scanning unit 34 controls the wavelength variable filter 29 so that the wavelength scanning in the partial detailed scanning mode is executed for the wavelength scanning range in the partial detailed scanning mode determined by the prescanning unit 33 and is required for each FBG sensor 23 . And a function of controlling the optical pulse generator 30 by giving the trigger signal application unit 32 wavelength scanning timing information in the partial detailed scan mode. The partial detail scanning unit 34 also has a function of providing the signal processing device 27 with reception data of FBG reflected light obtained by wavelength scanning in the partial detail scanning mode.

  The prescan parameter setting unit 35 sets a scan condition such as a scan range and a scan point interval (scan interval) at the time of wavelength scanning in the prescan mode, and a function of giving the set scan condition to the prescan unit 33 And have.

  At this time, the scan range in the wavelength scan in the pre-scan mode is wider than the wavelength scan range in the partial detail scan mode, and the scan point interval (scan interval) in the wavelength scan in the pre-scan mode is the partial detail scan mode. The interval is wider than the interval (scan interval) between the scanning points in the wavelength scanning according to.

  In such a configuration, in this embodiment, a data storage unit 41 and a time calculation processing unit 42 are provided as means for accurately setting an AD conversion start trigger in advance. That is, in the present embodiment, the optical fiber 22 described above, a plurality of FBG sensors 23 provided on the optical fiber 22, and a wavelength tunable filter 29 for irradiating the FBG sensor 23 with light in a required wavelength band are provided. A light source 21 provided, a photodetector 25 that receives reflected light from the FBG sensor 23 to obtain received data, and a plurality of points by applying either or both of time division multiplexing and wavelength multiplexing based on the received data Physical quantity measuring means for measuring the physical quantity.

  In such a fiber Bragg grating device, an AD conversion device 38 as an AD conversion processing unit for converting an FBG reflected pulse obtained from the FBG sensor 23 into a digital data sequence set of time and voltage, and differential calculation of the digital data sequence set. And a time calculation processing unit 42 for calculating time information corresponding to the derivative peak set obtained with respect to the rising and falling steep part slopes of the FBG reflected pulse. It has a configuration having a function to calculate. Note that the processing units of the digital data sequence set and the derivative peak sequence set are housed in a programmable logic device (PLD).

  The time calculation processing unit 42 is connected to the AD converter 38 via the data storage unit 41, and includes a time series data set generation unit 43, an averaging processing unit 44, a smooth differentiation calculation processing unit 45, and a delay time calculation processing unit. 46 is provided.

  The time series data set generation unit 43 performs AD conversion of the FBG reflection pulse based on each parameter set with reference to the data file, and stores the FBG reflection pulse data until the specified average number of times is reached.

  In the averaging processing unit 44, the stored FBG reflection pulse is read, and data averaging calculation processing is performed. In the smooth differential calculation processing unit 45, the maximum value with respect to the time axis of each FBG reflected pulse is extracted, and a smoothed primary differential calculation is performed.

  In the delay time calculation processing unit 46, differential calculation of the smoothed FBG reflection pulse derivative digital data string set is performed, and the derivative peak obtained with respect to the steep slopes of the rising and falling edges of the FBG reflection pulse. Time information corresponding to the set is calculated.

  The operation of the time calculation processing unit 42 will be described with reference to FIGS. FIG. 2 is an operation explanatory diagram showing the timing time according to the present embodiment, and FIG. 3 is an explanatory diagram showing a differential coefficient obtained by smoothing differentiation of the reflected pulse according to the present embodiment.

  The continuous light output from the broadband light source 28 is transmitted only through a predetermined wavelength band by the wavelength tunable filter 29, and is converted into pulsed light by the optical pulse generator 30. The pulse light propagates through the line of the fiber 22 and is sent to the optical fiber 22a, which is two trunk lines, via the optical branching device 24a. A plurality of FBG sensors 23 are connected in series so that the reflected wavelength bands do not interfere with each other in the line of each optical fiber 22a branched in a branch shape. When the reflection wavelength band of the FBG sensor 23 matches, the light is reflected.

  The reflected pulse light passes through the original line of the optical fiber 22b, and is converted from an optical pulse to an electric pulse by the photodetector 25 via the optical branching device 24a. That is, the plurality of pulse lights reflected by the FBG sensor 23 connected to the line of each branch optical fiber 22a are time-delay set in advance by the optical delay device 47 connected between the lines of each branch optical fiber 22a. As a result, the pulse train is set at a set time interval, and is stored in the data storage unit 41 and reaches the time calculation processing unit 42 via the photodetector 25 and the control unit 26, respectively.

  The control unit 26 controls timing for converting continuous light into pulse light, wavelength scanning of the wavelength tunable filter 29, pulse reception timing to the photodetector, and the like. That is, the control unit 26 performs photoelectric conversion on the pulse train received by the photodetector, extracts only the pulse data using a time gate, and further converts it into digital data. The digital data is subjected to an averaging process for the required number of times in order to improve the S / N in the time arithmetic processing unit, and finally compressed to the minimum transfer data amount as 1 pulse = 1 data.

  As shown in FIG. 2, in this embodiment, based on the reference clock pulse c1, the reflected light pulse train c4 of all the FBG sensors 23 reaches the time arithmetic processing unit 42 before the next pulse light c2 is sent out. That is, the pulsed light passes through the wavelength tunable filter 29 set in a predetermined wavelength band in advance, and is reflected by the plurality of FBG sensors 23 having the reflected wavelengths overlapped. The reflected light pulse train c4 is received by the photodetector 25 at a predetermined time interval and converted into an electrical pulse train.

  Further, the electric pulse train is converted into digital data by the AD conversion processing unit 38 to form a digital data train set to which time information is added. In the present embodiment, as shown in FIG. 2, the time obtained by adding the offset time T1 of the optical pulsing device 30 and the design delay time T2 until the AD conversion start trigger c3 is set as the AD conversion operation start time Ta. Time information corresponding to the sampling rate of 38 is added to Ta.

  If the stop time of the AD conversion operation is, for example, the transmission timing of the next pulsed light c2, all the pulses of the reflected pulse train c4 can be converted into digital data without leaving them. These processes are repeated as many times as necessary, and the time arithmetic processing unit 42 performs the above-described averaging process of the digital data string set, thereby improving the S / N.

  Note that the AD conversion start trigger c3 described here is a time during which the reflected pulse of the shortest time in design is not returned. Further, the offset time from when the AD conversion device 38 receives the AD conversion start trigger c2 to when the AD conversion operation is actually started is treated as a constant, and is added to the design delay time T2 although not particularly specified.

  The averaged digital data sequence set is sent to the time calculation processing unit 42, and as shown in FIG. 3, for example, the rising steep portion slope d1 of the pulse waveform of the FBG reflection pulse d is positive on the calculation processing for smoothing differentiation. Then, the derivative peak sequence group e is obtained by sliding the derivative coefficients e1 and e2 indicating the peaks h1 and h2 and the time information as they are on the minus side of the falling steep part slope d2 to the minus side. At this time, the derivative coefficient peak can be calculated more accurately by using, for example, polynomial fitting.

  Subsequently, an intermediate value between peaks for each pulse of the derivative peak train set is calculated, and, as shown in FIG. 2, the time Tf1 to Tfn corresponding to the intermediate value is calculated with the AD conversion operation start time Ta as a base point. Ask. Alternatively, the times Tf1 to Tfn may be times corresponding to one of the peaks in the derivative coefficient peak set e described above.

  The AD conversion start trigger time, that is, the delay time of each FBG reflection pulse can be set using these times Tf1 to Tfn. At this time, for example, in order to AD-convert only the peak flat portion d3 of the pulse, since all the reflected pulses are reflected from one pulsed light, the time width of all the reflected pulses is constant, An appropriate time derived from the time width of the reflected pulse (treated as a constant) is subtracted from the times Tf1 to Tfn to obtain an AD conversion start trigger time, and from the time width of the pulse flat portion (this is also treated as a constant). What is necessary is just to set the sampling frequency of AD converter.

  FIG. 4 is a flowchart showing the above operation.

  First, each parameter of the FBG reflection pulse data is set with reference to the data file (S101), and AD conversion by the AD converter 38 is started (S102). The AD-converted time-series data is stored in the SDRAM as the data storage unit 41 (S103), and then AD conversion is stopped (S104). This AD conversion process is performed up to the designated average number of times (S105).

  Next, FBG reflection pulse data is read from the SDRAM (S106), and the data averaging calculation process is performed by the averaging processing unit 44 (S107). Data averaging calculation processing is performed up to the designated number of wavelength scans (S108, S109), thereby completing a predetermined number n of group measurements (S110).

  In the smooth differential calculation processing unit 45, the maximum value with respect to the time axis of each FBG reflection pulse is extracted (S111), and the above-described smoothed primary differential calculation is performed (S112). Then, the threshold value determination of the differential coefficient is performed in the delay time calculation processing unit 46 (S113), and then the differential coefficient comparison determination process is performed (S114).

  Based on the above processing, the AD trigger time shown in FIG. 2 is calculated (S115), the calculation result is overwritten in the data file (S116), and the processing is completed for all the groups of the designated fiber line. (S117, S118), the reflection time calibration is completed.

  According to the fiber Bragg grating physical quantity measuring device and the fiber Bragg grating physical quantity measuring method of the present embodiment, the time arithmetic processing unit 42 calculates a digital data sequence set averaged for each wavelength scan by smoothing differentiation, and reflects it. The level of the derivative with respect to the steep slope of the rising and falling edges of the pulse waveform is calculated. Then, threshold value determination processing is performed on the differential coefficient data string set calculated for each wavelength scan, and the AD conversion start trigger time for each FBG sensor can be accurately known.

  Therefore, when providing a time gate for each pulse of FBG reflected light, it is possible to obtain a specific means for knowing an accurate return time of each necessary pulse, and in the case where optical fiber cables are actually laid. Reliable time information can be obtained even when the length of the optical fiber is changed according to the situation at the site, the design is not complete, or an error occurs in the manufacturing process.

  In addition, since it is a process using digital data, it can be executed entirely by a digital circuit. Therefore, the processing circuit can be configured in a PLD (Programmable Logic Device) to perform high-speed processing. As a result, the output data can be compressed to only the minimum necessary information, the amount of data transferred to the computer and the software load can be reduced, and the processing speed of the entire system can be improved.

  Therefore, the reflection time information of the reflected light pulses of all the FBG sensors can be easily and accurately measured and acquired at the initial stage of measurement.

  In addition, an increase in the amount of transferred data and a decrease in processing speed associated with the data processing that occur when pulse train data is fetched in a batch are suppressed, and the digital data thus obtained is processed by a computer or the like. Thus, predetermined physical quantity information can be obtained.

  According to the present embodiment, the reflection time information of all the FBG reflection pulses can be easily and accurately obtained without using OTDR and the like, and after the reflection time information of the FBG reflection pulses is easily and accurately obtained, The wavelength scanning can be executed with high accuracy.

  FIG. 5 shows a scan interval when the pre-scan unit 33 shown in FIG. 1 executes wavelength scanning in the pre-scan mode and a scan interval when the partial detail scan unit 34 executes wavelength scanning in the partial detailed scan mode. It is a conceptual diagram which shows a relationship.

  In FIG. 5, the vertical axis indicates the light intensity Yi of the FBG reflected light received by the photodetector 25, and the horizontal axis indicates the wavelength Xi of the FBG reflected light received by the photodetector 25. In FIG. 2, the solid line indicates the spectrum A1 of the FBG reflected light from the FBG 7 of interest, the dotted line indicates the scanning point A2 for wavelength scanning in the partial detailed scanning mode, and the alternate long and short dash line indicates the scanning point A3 for wavelength scanning in the prescan mode. The two-dot chain line represents the design wavelength range A4 of the FBG 7 of interest.

  As shown in FIG. 5, the pre-scan parameter setting unit 35 sets the scan range A5 of the wavelength scan in the pre-scan mode as the entire design wavelength range A4 of the FBG 7, for example. Furthermore, the pre-scan parameter setting unit 35 obtains the maximum value of the wavelength region center A7 of the FBG reflected light, that is, the spectrum A1 of the FBG reflected light, as the interval (scan interval) A6 of the wavelength scanning point in the pre-scan mode. Set the interval so that Therefore, the scan point interval (scan interval) A6 of the wavelength scan in the prescan mode set by the prescan parameter setting unit 35 is an interval at which at least two scan points A3 exist on the spectrum A1 of the FBG reflected light. If it is. In other words, the interval (scan interval) A6 between the scanning points of the wavelength scanning in the pre-scan mode may be equal to or less than the half value of the distribution width A1d in the spectrum A1 of the FBG reflected light.

  On the other hand, the wavelength scan in the partial detailed scan mode is a wavelength scan determined as a section in which the number of scanning points corresponding to the required accuracy of physical quantity measurement can be secured on both sides from the wavelength region center A7 obtained by the wavelength scan in the prescan mode. It is executed for the range A8. At this time, the interval (scan interval) A9 between the scanning points of the wavelength scanning in the partial detail scan mode is set according to the required accuracy of physical quantity measurement.

  FIG. 5 shows the wavelength region center A7 of the FBG reflected light obtained based on the received data on the two scanning points A3 when there are two scanning points A3 for wavelength scanning in the prescan mode on the spectrum A1 of the FBG reflected light. This is an example in the case where the wavelength scanning range A8 of the wavelength scanning by the partial detailed scanning mode is determined on both sides.

  On the other hand, the pulse integration circuit 36 of the control unit 26 is configured by a circuit such as a boxcar integrator or a gated integrator, and receives reception data output as an electric pulse signal of FBG reflected light from the photodetector 25 and receives received data. It has a function of executing a noise reduction process by obtaining a pulse area proportional to the pulse wave height, and a function of giving received data after the noise reduction process constituted by a pulse train of FBG reflected light to the gate signal generation unit 37.

  The gate signal generator 37 sets a time gate to extract an electric pulse signal of the FBG reflected light from the FBG 7 of interest from the pulse train of the FBG reflected light received from the pulse integration circuit 36, and the extracted FBG reflected light The function of giving the electrical pulse signal to the AD converter 38 as received data. That is, the gate signal generation unit 37 is required to correspond to the timing at which the FBG reflected light from the focused FBG 7 is received by the photodetector 25 based on the timing information of the trigger signal received from the trigger signal application unit 32. A time gate signal with a delay time of 1 is generated to detect only an electric pulse signal while the time gate signal is active.

  The AD converter 38 has a function of receiving the received data of the FBG reflected light from the focused FBG 7 from the gate signal generator 37 and AD-converting the received data to the pre-scan unit 33 or the partial detail scan unit 34.

  On the other hand, the signal processing device 27 includes a wavelength center calculator 39 and a physical quantity converter 40. The wavelength center calculator 39 receives the reception data of the FBG reflected light obtained by the wavelength scanning in the partial detailed scan mode from the partial detailed scan unit 34 of the control unit 26, and receives the center of the wavelength region of the FBG reflected light from the FBG 7 of interest. The function to ask for. As a method for the wavelength center calculator 39 to obtain the center of the wavelength region of the FBG reflected light, for example, by fitting the distribution of the spectrum, which is the reception data of the FBG reflected light, to a higher order expression such as a quadratic expression, A method for obtaining the maximum value is mentioned.

  The physical quantity conversion unit 40 has a function of converting the center of the wavelength region of the FBG reflected light into a physical quantity. Further, when the FBG physical quantity measuring device 20 dynamically measures the physical quantity to be converted with time, the physical quantity converting section 40 is provided with a function of giving a start instruction for the next wavelength scanning to the control section 26.

  Next, the operation of the FBG physical quantity measuring device 20 will be described.

  FIG. 6 is a flowchart showing a procedure for measuring a physical quantity by the FBG physical quantity measuring device 20 shown in FIG. 5, and the reference numerals with numerals in the figure indicate the steps of the flowchart.

  First, in step S1, the prescan parameter setting unit 35 sets the scan range R of the wavelength scan in the prescan mode over the entire design wavelength range of the FBG 7 to which attention is paid. Further, the prescan parameter setting unit 35 sets the scan interval of the wavelength scan in the prescan mode to a value obtained by dividing the scan range R by the set value N. Here, the set value N is set so that the value of the scan interval R / N is equal to or less than a half value of the spectrum distribution width of the FBG reflected light. Then, the prescan parameter setting unit 35 gives the scan range R and the scan interval R / N of the wavelength scan in the set prescan mode to the prescan unit 33.

  Next, in step S2, wavelength scanning in the pre-scan mode is executed an arbitrary number of times. That is, the pre-scan unit 33 controls the wavelength tunable filter 29 so that the wavelength scan is performed for the scan range R of the wavelength scan in the pre-scan mode received from the pre-scan parameter setting unit 35. Further, the pre-scan unit 33 gives a trigger signal application command to the trigger signal application unit 32 so as to control the timing of the pulsed light emitted from the light source 21.

  On the other hand, continuous light is given from the broadband light source 28 to the wavelength tunable filter 29. The wavelength tunable filter 29 selectively transmits continuous light in a wavelength band corresponding to the scan range R and supplies the continuous light to the optical pulse device 30. The optical pulsing device 30 converts continuous light in the wavelength band of the scan range R into pulsed light and transmits it into the optical fiber 22 at a timing corresponding to the trigger signal received from the trigger signal applying unit 32.

  For this reason, the pulsed light in the wavelength band of the scan range R propagates through the optical trunk line 22a and branches at each optical branching device 24, propagates through the optical branching path 22b, and is provided in series on the optical branching path 22b. The FBG sensor 23 is irradiated. Here, since the wavelength band of the pulsed light is set in the design wavelength range of the focused FBG sensor 23, the FBG sensor 23 in the same designed wavelength range as the focused FBG sensor 23 can respond to a physical quantity such as temperature. FBG reflected light in a certain wavelength band is generated.

  The FBG reflected light generated in the FBG sensor 23 propagates again through the optical branching path 22b, the optical branching device 24, and the optical trunk line 22a, and is guided from the optical branching device 24a on the light source 21 side to the reflected light optical fiber 22c. Then, the FBG reflected light guided to the reflected light optical fiber 22c is received by the photodetector 25, and is provided to the pulse integration circuit 36 of the control unit 26 as received data of an electrical signal by photoelectric conversion.

  The pulse integration circuit 36 receives the reception data output as the electric pulse signal of the FBG reflected light from the photodetector 25 and obtains a pulse area proportional to the pulse height of the reception data, and then performs a noise reduction process. Data is supplied to the gate signal generator 37.

  Based on the timing information received from the trigger signal application unit 32, the gate signal generation unit 37 sets a time gate signal with a certain delay time according to the position of the FBG 7 of interest, thereby generating a signal from the pulse integration circuit 36. The electric pulse signal of the FBG reflected light from the focused FBG 7 is extracted from the pulse train of the received FBG reflected light, and the extracted electric pulse signal of the FBG reflected light is given to the AD converter 38 as reception data.

  Further, the AD conversion device 38 performs AD conversion on the received data received from the gate signal generation unit 37 and supplies the AD data to the prescan unit 33.

  When wavelength scanning in the pre-scan mode is executed a plurality of times in order to maintain the calculation accuracy, the reception data of the FBG reflected light is repeatedly given to the pre-scan unit 33 by the same procedure.

  Next, in step S3, when the reception data of the FBG reflected light sufficient to maintain the calculation accuracy is obtained, the prescan unit 33 obtains the wavelength region center of the FBG reflected light, and both sides of the obtained wavelength region center. The section in which the required number of detailed scanning points set in advance can be secured is determined as the wavelength scanning range in the partial detailed scanning mode. Then, the pre-scan unit 33 gives the wavelength scan range in the determined partial detail scan mode to the partial detail scan unit 34.

  For this reason, in step S4, wavelength scanning in the partial detailed scan mode is executed an arbitrary number of times. That is, the partial detail scanning unit 34 controls the wavelength tunable filter 29 so as to execute wavelength scanning for the wavelength scanning range in the partial detailed scanning mode. Further, the partial detail scanning unit 34 gives a trigger signal application command to the trigger signal applying unit 32 so as to control the timing of the pulsed light emitted from the light source 21.

  On the other hand, continuous light is given from the broadband light source 28 to the wavelength tunable filter 29. The wavelength tunable filter 29 selectively transmits continuous light in a wavelength band corresponding to the wavelength scanning range in the partial detail scan mode to the optical pulse generator 30, and the optical pulse generator 30 uses the partial detail scan mode. The continuous light in the wavelength band of the wavelength scanning range at is converted into pulsed light and transmitted into the optical fiber 22.

  Therefore, similarly to the case of wavelength scanning in the pre-scan mode, reception data of FBG reflected light for the wavelength scanning range in the partial detailed scan mode is given to the partial detailed scan unit 34. Further, the partial detail scanning unit 34 gives the reception data of the FBG reflected light obtained by the wavelength scanning in the partial detail scanning mode to the wavelength center calculation unit 39 of the signal processing device 27.

  Therefore, in step S5, the wavelength center calculation unit 39 obtains the wavelength region center of the FBG reflected light from the focused FBG 7 based on the received data of the FBG reflected light obtained by the wavelength scanning in the partial detailed scan mode. This is given to the physical quantity converter 40.

  Further, in step S 6, the physical quantity conversion unit 40 converts the wavelength region center of the FBG reflected light received from the wavelength center calculation unit 39 into a physical quantity. For this reason, a physical quantity such as a temperature in the vicinity of the FBG sensor 23 of interest can be obtained. Then, the physical quantity conversion unit 40 gives a start command for the next wavelength scanning to the control unit 26 and the light source 21, and the physical quantity at each time is measured again by the procedure from step S2 to step S6.

  According to the FBG physical quantity measuring apparatus 20 as described above, a physical quantity with the required accuracy can be acquired without scanning the entire design wavelength range of the FBG sensor 23 of interest at a scan interval corresponding to the required accuracy of the physical quantity. For this reason, according to the FBG physical quantity measuring device 20, it is possible to measure physical quantities at multiple points in a shorter time while ensuring the measurement accuracy of the physical quantity, and it is possible to increase the measurement speed and measurement interval of the physical quantity. .

[Second Embodiment (FIGS. 2, 3, 7 and 8)]
FIG. 7 is a block diagram schematically showing a second embodiment of the physical quantity measuring device for fiber Bragg grating according to the present invention.

  As shown in FIG. 7, the fiber Bragg grating (FBG) physical quantity measuring device 20 has a configuration in which one end of an optical fiber 22 is connected to a light source 21 and a plurality of FBG sensors 23 are provided on the optical fiber 22. This optical fiber 22 is configured by providing a plurality of optical branching devices 24 on an optical trunk line 22 a, and an optical branching path 22 b branches from each optical branching device 24. The FBG sensor 23 is provided in series with each optical branch path 22b. An optical delay device 24 is provided in the optical trunk line 22a.

  A reflected light optical fiber 22c is connected to the optical branching device 24a on the light source 21 side, and a photodetector 25 is connected to an end of the reflected light optical fiber 22c. Further, the photodetector 25 and the light source 21 are connected to a common control unit 26, and the control unit 26 is connected to a signal processing device 27.

  The FBG sensor 23 is configured by providing a Bragg diffraction grating in the fiber core, and the pitch of the Bragg diffraction grating changes depending on physical quantities such as temperature, strain, vibration, pressure, and water level measurement. It has the property of reflecting FBG reflected light in the wavelength band. For this reason, the physical quantity can be obtained from the wavelength of the FBG reflected light. And each FBG sensor 23 is comprised so that it may become a different specific wavelength band according to the distance from each optical splitter 24 so that the specific wavelength band of the FBG reflected light which mutually reflects may not influence mutually.

  The light source 21 includes a broadband light source 28, a wavelength tunable filter 29, and an optical pulsing device 30. The broadband light source 28 and the wavelength tunable filter 29 are provided in a temperature adjustment unit 31 that provides a sufficiently stable temperature range for temperature-sensitive optical equipment. The broadband light source 28 has a function of generating broadband continuous light (CW: Continuous Wave), and the wavelength variable filter 29 has a function of receiving a broadband continuous light from the broadband light source 28 and selectively transmitting light in a predetermined wavelength band. The optical pulsing device 30 has a function of receiving light of a predetermined wavelength band from the wavelength tunable filter 29 and converting it into pulsed light. The light source 21 is configured to be able to irradiate each FBG sensor 23 provided in the optical fiber 22 with pulsed light in a predetermined wavelength band.

  The photodetector 25 receives the FBG reflected light from the FBG sensor 23, performs photoelectric conversion, and amplifies and shapes it to obtain received data as an electric pulse signal having a required signal intensity and bandwidth. A function of giving received data to the control unit 26.

  The control unit 26 includes a trigger signal application unit 32, a prescan unit 33, a partial detail scan unit 34, a prescan parameter setting unit 35, a pulse integration circuit 36, a gate signal generation unit 37, and an AD converter 38, and FBG reflected light. The wavelength scanning range of the light, that is, the wavelength band of the light transmitted by the wavelength tunable filter 29 and the transmission timing of the pulsed light generated by the optical pulsing device 30 based on the received data received from the photodetector 25. . At this time, the control unit 26 is configured to control the wavelength tunable filter 29 and the optical pulsing device 30 by two types of control modes, a pre-scan mode and a partial detailed scan mode.

  The trigger signal applying unit 32 has a function of controlling the timing of the pulsed light emitted from the light source 21 by giving a trigger signal to the optical pulsing device 30 and a function of giving timing information of the trigger signal to the gate signal generating unit 37. And have.

  The prescan unit 33 controls the wavelength tunable filter 29 to execute wavelength scanning in the prescan mode and irradiates each FBG 7 with light of a required wavelength band, and causes the trigger signal application unit 32 to use the prescan mode. It has a function of controlling the optical pulsing device 30 by giving timing information of wavelength scanning.

  The prescan unit 33 receives received data obtained by wavelength scanning in the prescan mode from the photodetector 25 via the pulse integration circuit 36, the gate signal generation unit 37, and the AD conversion device 38, and receives the FBG 7 of interest. A function for determining the center of the wavelength region of the FBG reflected light from the light source, and a function for determining a wavelength scanning range in the partial detail scan mode so that a predetermined number of detailed scanning points set in advance on both sides of the determined wavelength region center can be secured. Have

  The partial detail scanning unit 34 controls the wavelength variable filter 29 so as to execute wavelength scanning in the partial detailed scanning mode for the wavelength scanning range in the partial detailed scanning mode determined by the prescanning unit 33, and the required wavelength for each FBG 7. It has a function of irradiating light in a band, and a function of controlling the optical pulsing device 30 by giving the trigger signal application unit 32 timing information of wavelength scanning in the partial detailed scan mode. The partial detail scanning unit 34 also has a function of providing the signal processing device 27 with reception data of FBG reflected light obtained by wavelength scanning in the partial detail scanning mode.

  The prescan parameter setting unit 35 sets a scan condition such as a scan range and a scan point interval (scan interval) at the time of wavelength scanning in the prescan mode, and a function of giving the set scan condition to the prescan unit 33 And have.

  At this time, the scan range in the wavelength scan in the pre-scan mode is wider than the wavelength scan range in the partial detail scan mode, and the scan point interval (scan interval) in the wavelength scan in the pre-scan mode is the partial detail scan mode. The interval is wider than the interval (scan interval) between the scanning points in the wavelength scanning according to.

  In such a configuration, in this embodiment, a data storage unit 41, a time calculation processing unit 42, and a differential coefficient determination processing unit 48 are provided as means for accurately setting an AD conversion start trigger in advance. That is, in the present embodiment, the optical fiber 22 described above, a plurality of FBG sensors 23 provided on the optical fiber 22, and a wavelength tunable filter 29 for irradiating the FBG sensor 23 with light in a required wavelength band are provided. A light source 21 provided, a photodetector 25 that receives reflected light from the FBG sensor 23 to obtain received data, and a plurality of points by applying either or both of time division multiplexing and wavelength multiplexing based on the received data Physical quantity measuring means for measuring the physical quantity.

  Further, an AD conversion device 38 as an AD conversion processing unit for converting the FBG reflected pulse obtained from the FBG sensor 23 into a digital data string set of time and voltage, and a differential calculation of the digital data string set to rise and rise of the FBG reflected pulse A time calculation processing unit 42 that calculates time information corresponding to the derivative coefficient pair obtained for the steep slope of the falling edge.

  The time calculation processing unit 42 is connected to the AD converter 38 via the data storage unit 41, and includes a time series data set generation unit 43, an averaging processing unit 44, a smooth differentiation calculation processing unit 45, and a delay time calculation processing unit. 46 is provided.

  The time series data set generation unit 43 performs AD conversion of the FBG reflection pulse based on each parameter set with reference to the data file, and stores the FBG reflection pulse data until the specified average number of times is reached.

  In the averaging processing unit 44, the stored FBG reflection pulse is read, and data averaging calculation processing is performed. In the smooth differential calculation processing unit 45, the maximum value with respect to the time axis of each FBG reflected pulse is extracted, and a smoothed primary differential calculation is performed.

  In the delay time calculation processing unit 46, differential calculation of the smoothed FBG reflection pulse derivative digital data string set is performed, and the derivative peak obtained with respect to the steep slopes of the rising and falling edges of the FBG reflection pulse. Time information corresponding to the set is calculated.

  Further, the differential coefficient exceeding the threshold from the differential peak set calculated from the FBG reflected pulse, with the peak level of the differential peak set obtained for the rising and falling steep slopes of the FBG reflected pulse at the detection lower limit as a threshold. A differential coefficient determination processing unit 48 that determines only a peak set as a threshold is provided.

  This differential coefficient determination processing section 48 is a differential coefficient level ratio determination section 49 for comparing the relative ratio of the peak levels of the differential coefficient peak set with a predetermined threshold value with the differential coefficient level threshold determination section 49 for determining the threshold of the differential coefficient level. And a differential coefficient time width determination unit 51 that compares and determines the time interval of the differential coefficient peak set with a threshold value based on the time width of the FBG reflection pulse. Note that the processing units of the digital data sequence set and the derivative peak sequence set are housed in a programmable logic device (PLD).

  The operation of the time calculation processing unit 42 and the derivative determination processing unit 48 will be described with reference to FIGS. FIG. 2 is an operation explanatory diagram showing the timing time according to the present embodiment, and FIG. 3 is an explanatory diagram showing a differential coefficient obtained by smoothing differentiation of the reflected pulse according to the present embodiment.

  The continuous light output from the broadband light source 28 is transmitted only through a predetermined wavelength band by the wavelength tunable filter 29, and is converted into pulsed light by the optical pulse generator 30. The pulse light propagates through the line of the fiber 22 and is sent to the optical fiber 22a, which is two trunk lines, via the optical branching device 24a. A plurality of FBG sensors 23 are connected in series so that the reflected wavelength bands do not interfere with each other in the line of each optical fiber 22a branched in a branch shape. When the reflection wavelength band of the FBG sensor 23 matches, the light is reflected.

  The reflected pulse light passes through the original line of the optical fiber 22b, and is converted from an optical pulse to an electric pulse by the photodetector 25 via the optical branching device 24a. That is, the plurality of pulse lights reflected by the FBG sensor 23 connected to the line of each branch optical fiber 22a are time-delay set in advance by the optical delay device 47 connected between the lines of each branch optical fiber 22a. As a result, the pulse train is set at a set time interval, and is stored in the data storage unit 41 and reaches the time calculation processing unit 42 via the photodetector 25 and the control unit 26, respectively.

  The control unit 26 controls timing for converting continuous light into pulse light, wavelength scanning of the wavelength tunable filter 29, pulse reception timing to the photodetector, and the like. That is, the control unit 26 performs photoelectric conversion on the pulse train received by the photodetector, extracts only the pulse data using a time gate, and further converts it into digital data. The digital data is subjected to an averaging process for the required number of times in order to improve the S / N in the time arithmetic processing unit, and finally compressed to the minimum transfer data amount as 1 pulse = 1 data.

  As shown in FIG. 2, in this embodiment, based on the reference clock pulse c1, the reflected light pulse train c4 of all the FBG sensors 23 reaches the time arithmetic processing unit 42 before the next pulse light c2 is sent out. That is, the pulsed light passes through the wavelength tunable filter 29 set in a predetermined wavelength band in advance, and is reflected by the plurality of FBG sensors 23 having the reflected wavelengths overlapped. The reflected light pulse train c4 is received by the photodetector 25 at a predetermined time interval and converted into an electrical pulse train.

  Further, the electric pulse train is converted into digital data by the AD conversion processing unit 38 to form a digital data train set to which time information is added. In the present embodiment, as shown in FIG. 2, the time obtained by adding the offset time T1 of the optical pulsing device 30 and the design delay time T2 until the AD conversion start trigger c3 is set as the AD conversion operation start time Ta. Time information corresponding to the sampling rate of 38 is added to Ta.

  If the stop time of the AD conversion operation is, for example, the transmission timing of the next pulsed light c2, all the pulses of the reflected pulse train c4 can be converted into digital data without leaving them. These processes are repeated as many times as necessary, and the time arithmetic processing unit 42 performs the above-described averaging process of the digital data string set, thereby improving the S / N.

  By the way, in the present embodiment, wavelength discrimination is performed by transmitting only a predetermined FBG sensor reflection wavelength band in advance with the wavelength tunable filter 2 so that a plurality of FBG reflection pulses having different wavelength bands do not overlap and return. In fact, even in the same reflection wavelength band, some FBG reflection pulses may be out of the filter range of the wavelength tunable filter 29 due to manufacturing variations and differences in the ambient temperature of the laying site. Therefore, the wavelength tunable filter 2 scans a predetermined wavelength range at an appropriate wavelength interval in consideration of the wavelength variation of each reflected pulse in order to acquire the entire reflected pulse train. Similarly to the embodiment, the data is converted into a time and voltage digital data set sequence, this is repeated as many times as necessary, and the above-described digital data sequence set is averaged to improve S / N.

  That is, the digital data string set averaged for each wavelength scan is sent to the time arithmetic processing unit 42, and the derivative peak and time information shown in FIG. It is processed as an added derivative peak train set. In the differential coefficient determination processing unit 48, the peak level of the differential coefficient with respect to the rising and falling steep part slopes of the reflected pulse waveform at the detection lower limit level is calculated in advance and stored as a threshold value for each wavelength scanning. In the determination process of the differential coefficient level threshold determination unit 49 that extracts a differential coefficient peak exceeding this threshold value with respect to the calculated differential coefficient data stream group, the differential coefficient peak stream group consisting of the differential coefficient peak exceeding the threshold value and time information is obtained. Replaced. Further, the differential coefficient level comparison / determination unit 50 obtains only the differential coefficient having the maximum peak at the relative level with respect to the time axis from each of the replaced differential coefficient data string sets, and finally the differential coefficient time determination unit. In 51, a derivative peak sequence set including the maximum peak and time information is obtained. By this determination processing, it is possible to discriminate the peak portion of the derivative calculated from the reflected pulse and, for example, hum noise synchronized with the reference clock.

  The reflected pulse shape is close to a rectangular wave as shown in FIG. 4, and the slope shape of the steep part at the rise and fall of the pulse is approximate, and the relative level of these derivative peaks with respect to the slope of the steep part (derivative coefficient). When the peak levels h1 and h2 are compared, the ratio is close to 1. Using this, the differential coefficient peak sequence set determined by the differential coefficient level threshold determination unit 49 is sent to the differential coefficient level ratio determination unit 50, where the previous differential coefficient peak levels h1 and h2 are relatively compared, If an appropriate ratio is within a range of 1: 1 ± 0.1, for example, a threshold value that is normal is set in advance, and by performing a determination process, the reliability that the extracted derivative coefficient peak is calculated from the pulse is further improved. Can be increased.

  If the determination result is negative, it is expected that there is a problem with the FBG sensor 23, the optical fiber 22, or the like, and it can be applied as an abnormality detection means.

  Further, as described in the first embodiment, the differential coefficient level threshold determination unit 49 or the differential coefficient level ratio determination unit 50 performs the determination process using the fact that the width of all the reflected pulses is a fixed time length. The derivative peak train set is sent to the derivative coefficient time width determination unit 51, where the measured time value of the pulse width is stored in advance, and for this stored time, for example, 200 ns ± 10 ns is set as a threshold value. Compare the time interval of the peak of the derivative peak sequence set corresponding to the reflected pulse with this threshold value, and if it is within the threshold value, it is determined that it is normal and the extracted derivative coefficient is calculated from the pulse. The sex can be increased. If the determination result is negative, it is expected that there is a problem with the FBG sensor 24, the optical fiber 22, or the like, and it can be applied as an abnormality detection means.

  All processing using these digital data can be executed by a digital circuit. Therefore, the processing circuit can be configured in a PLD (Programmable Logic Device) to perform high-speed processing. As a result, the output data can be compressed to only the minimum necessary information, the amount of data transferred to the computer and the software load can be reduced, and the processing speed of the entire system can be improved.

  Note that the AD conversion start trigger c3 described here is a time during which the reflected pulse of the shortest time in design is not returned. Further, the offset time from when the AD conversion device 38 receives the AD conversion start trigger c2 to when the AD conversion operation is actually started is treated as a constant, and is added to the design delay time T2 although not particularly specified.

  The averaged digital data sequence set is sent to the time calculation processing unit 42, and as shown in FIG. 3, for example, the rising steep portion slope d1 of the pulse waveform of the FBG reflection pulse d is positive on the calculation processing for smoothing differentiation. Then, the derivative peak sequence group e is obtained by sliding the derivative coefficients e1 and e2 indicating the peaks h1 and h2 and the time information as they are on the minus side of the falling steep part slope d2 to the minus side. At this time, the derivative coefficient peak can be calculated more accurately by using, for example, polynomial fitting.

  Subsequently, an intermediate value between peaks for each pulse of the derivative peak train set is calculated, and, as shown in FIG. 2, the time Tf1 to Tfn corresponding to the intermediate value is calculated with the AD conversion operation start time Ta as a base point. Ask. Alternatively, the times Tf1 to Tfn may be times corresponding to one of the peaks in the derivative coefficient peak set e described above.

  The AD conversion start trigger time, that is, the delay time of each FBG reflection pulse can be set using these times Tf1 to Tfn. At this time, for example, in order to AD-convert only the peak flat portion d3 of the pulse, since all the reflected pulses are reflected from one pulsed light, the time width of all the reflected pulses is constant, An appropriate time derived from the time width of the reflected pulse (treated as a constant) is subtracted from the times Tf1 to Tfn to obtain an AD conversion start trigger time, and from the time width of the pulse flat portion (this is also treated as a constant). What is necessary is just to set the sampling frequency of AD converter.

  FIG. 8 is a flowchart showing the above operation.

  First, each parameter of the FBG reflection pulse data is set with reference to the data file (S201), and AD conversion by the AD converter 38 is started (S202). The AD-converted time-series data is stored in the SDRAM as the data storage unit 41 (S203), and then AD conversion is stopped (S204). This AD conversion process is performed up to the designated average number of times (S205).

  Next, the FBG reflection pulse data is read from the SDRAM (S206), and the data averaging calculation process is performed by the averaging processing unit 44 (S207). Data averaging calculation processing is performed up to the designated number of wavelength scans (S208, S209), thereby completing a predetermined number n of group measurements (S210).

  In the smooth differential calculation processing unit 45, the maximum value with respect to the time axis of each FBG reflection pulse is extracted (S211), and the above-described smoothed primary differential calculation is performed (S212). Then, the threshold value determination of the differential coefficient is performed in the delay time calculation processing unit 46 (S213), and then the differential coefficient comparison determination process is performed (S214).

  Then, the derivative determination processing unit 48 calculates the peak level of the derivative with respect to the rising and falling steep part slopes of the reflected pulse waveform at the detection lower limit level, and sets and stores the value as a threshold value (S215). ) In the determination process of the differential coefficient level threshold determination unit 49 for extracting the differential coefficient peak exceeding this threshold value for the differential coefficient data string set calculated for each wavelength scan, the fine coefficient peak and time information that exceeds the threshold value are determined. Replaced with coefficient peak train set.

  Further, the differential coefficient level comparison / determination unit 50 obtains only the differential coefficient having the maximum peak at the relative level with respect to the time axis from each of the replaced differential coefficient data string sets, and finally the differential coefficient time determination unit. In 51, a derivative peak sequence set including the maximum peak and time information is obtained. By this determination processing, it is possible to discriminate the peak portion of the derivative calculated from the reflected pulse and, for example, hum noise synchronized with the reference clock (S216).

  In addition, as described above, the reflected pulse shape is close to a rectangular wave, and the slope shape of the steep part at the rising and falling edges of the pulse is approximate, so the relative level of these derivative peaks with respect to the slope of the steep part (derivative coefficient). Using the fact that the peak levels h1 and h2 are compared and the ratio is a value close to 1, the differential coefficient level threshold determination unit 49 extracts the differential coefficient that is maximum at the relative level with respect to the time axis. (S217).

  Then, the differential coefficient peak sequence set determined as the threshold is sent to the differential coefficient level ratio determination unit 50, where the previous differential coefficient peak levels h1 and h2 are subjected to relative comparison determination (S217), for example, the ratio 1: 1 ± 0. If it is within 1, the determination process is performed based on the threshold setting of normal (S218, S219). Thereby, the reliability that the extracted derivative coefficient peak is calculated from the pulse can be further improved.

  Based on the above processing, the AD trigger time shown in FIG. 2 is calculated (S220), the calculation result is overwritten in the data file (S221), and the processing is completed for all the groups of the specified fiber line. (S222, S223), the reflection time calibration is completed.

  According to the fiber Bragg grating physical quantity measuring device and the fiber Bragg grating physical quantity measuring method of the present embodiment, the time arithmetic processing unit 42 calculates a digital data sequence set averaged for each wavelength scan by smoothing differentiation, and reflects it. The level of the derivative with respect to the steep slope of the rising and falling edges of the pulse waveform is calculated. Then, threshold value determination processing is performed on the differential coefficient data string set calculated for each wavelength scan, and the AD conversion start trigger time for each FBG sensor can be accurately known.

  Therefore, when providing a time gate for each pulse of FBG reflected light, it is possible to obtain a specific means for knowing an accurate return time of each necessary pulse, and in the case where optical fiber cables are actually laid. Reliable time information can be obtained even when the length of the optical fiber is changed according to the situation at the site, the design is not complete, or an error occurs in the manufacturing process.

  In addition, since it is a process using digital data, it can be executed entirely by a digital circuit. Therefore, the processing circuit can be configured in a PLD (Programmable Logic Device) to perform high-speed processing. As a result, the output data can be compressed to only the minimum necessary information, the amount of data transferred to the computer and the software load can be reduced, and the processing speed of the entire system can be improved.

  Therefore, the reflection time information of the reflected light pulses of all the FBG sensors can be easily and accurately measured and acquired at the initial stage of measurement.

  In addition, an increase in the amount of transferred data and a decrease in processing speed associated with the data processing that occur when pulse train data is fetched in a batch are suppressed, and the digital data thus obtained is processed by a computer or the like. Thus, predetermined physical quantity information can be obtained.

  According to the present embodiment, the reflection time information of all the FBG reflection pulses can be easily and accurately obtained without using OTDR and the like, and after the reflection time information of the FBG reflection pulses is easily and accurately obtained, The wavelength scanning can be executed with high accuracy. This operation will be described with reference to FIGS. 5 and 6 described above.

  FIG. 5 shows the scan interval when the pre-scan unit 33 shown in FIG. 7 performs wavelength scanning in the pre-scan mode, and the partial detailed scan unit 34 performs wavelength scanning in the partial detailed scan mode, as in the first embodiment. It can be applied as a conceptual diagram showing the relationship with the scan interval when executing.

  In FIG. 5, the vertical axis indicates the light intensity Yi of the FBG reflected light received by the photodetector 25, and the horizontal axis indicates the wavelength Xi of the FBG reflected light received by the photodetector 25. In FIG. 2, the solid line indicates the spectrum A1 of the FBG reflected light from the FBG 7 of interest, the dotted line indicates the scanning point A2 for wavelength scanning in the partial detailed scanning mode, and the alternate long and short dash line indicates the scanning point A3 for wavelength scanning in the prescan mode. The two-dot chain line represents the design wavelength range A4 of the FBG 7 of interest.

  As shown in FIG. 5, the pre-scan parameter setting unit 35 sets the scan range A5 of the wavelength scan in the pre-scan mode as the entire design wavelength range A4 of the FBG 7, for example. Furthermore, the pre-scan parameter setting unit 35 obtains the maximum value of the wavelength region center A7 of the FBG reflected light, that is, the spectrum A1 of the FBG reflected light, as the interval (scan interval) A6 of the wavelength scanning point in the pre-scan mode. Set the interval so that Therefore, the scan point interval (scan interval) A6 of the wavelength scan in the prescan mode set by the prescan parameter setting unit 35 is an interval at which at least two scan points A3 exist on the spectrum A1 of the FBG reflected light. If it is. In other words, the interval (scan interval) A6 between the scanning points of the wavelength scanning in the pre-scan mode may be equal to or less than the half value of the distribution width A1d in the spectrum A1 of the FBG reflected light.

  On the other hand, the wavelength scan in the partial detailed scan mode is a wavelength scan determined as a section in which the number of scanning points corresponding to the required accuracy of physical quantity measurement can be secured on both sides from the wavelength region center A7 obtained by the wavelength scan in the prescan mode. It is executed for the range A8. At this time, the interval (scan interval) A9 between the scanning points of the wavelength scanning in the partial detail scan mode is set according to the required accuracy of physical quantity measurement.

  FIG. 5 shows the wavelength region center A7 of the FBG reflected light obtained based on the received data on the two scanning points A3 when there are two scanning points A3 for wavelength scanning in the prescan mode on the spectrum A1 of the FBG reflected light. This is an example in the case where the wavelength scanning range A8 of the wavelength scanning by the partial detailed scanning mode is determined on both sides.

  On the other hand, the pulse integration circuit 36 of the control unit 26 is configured by a circuit such as a boxcar integrator or a gated integrator, and receives reception data output as an electric pulse signal of FBG reflected light from the photodetector 25 and receives received data. It has a function of executing a noise reduction process by obtaining a pulse area proportional to the pulse wave height, and a function of giving received data after the noise reduction process constituted by a pulse train of FBG reflected light to the gate signal generation unit 37.

  The gate signal generator 37 sets a time gate to extract an electric pulse signal of the FBG reflected light from the FBG 7 of interest from the pulse train of the FBG reflected light received from the pulse integration circuit 36, and the extracted FBG reflected light The function of giving the electrical pulse signal to the AD converter 38 as received data. That is, the gate signal generation unit 37 is required to correspond to the timing at which the FBG reflected light from the focused FBG 7 is received by the photodetector 25 based on the timing information of the trigger signal received from the trigger signal application unit 32. A time gate signal with a delay time of 1 is generated to detect only an electric pulse signal while the time gate signal is active.

  The AD converter 38 has a function of receiving the received data of the FBG reflected light from the focused FBG 7 from the gate signal generator 37 and AD-converting the received data to the pre-scan unit 33 or the partial detail scan unit 34.

  On the other hand, the signal processing device 27 includes a wavelength center calculator 39 and a physical quantity converter 40. The wavelength center calculator 39 receives the reception data of the FBG reflected light obtained by the wavelength scanning in the partial detailed scan mode from the partial detailed scan unit 34 of the control unit 26, and receives the center of the wavelength region of the FBG reflected light from the FBG 7 of interest. The function to ask for. As a method for the wavelength center calculator 39 to obtain the center of the wavelength region of the FBG reflected light, for example, by fitting the distribution of the spectrum, which is the reception data of the FBG reflected light, to a higher order expression such as a quadratic expression, A method for obtaining the maximum value is mentioned.

  The physical quantity conversion unit 40 has a function of converting the center of the wavelength region of the FBG reflected light into a physical quantity. Further, when the FBG physical quantity measuring device 20 dynamically measures the physical quantity to be converted with time, the physical quantity converting section 40 is provided with a function of giving a start instruction for the next wavelength scanning to the control section 26.

  Next, the operation of the FBG physical quantity measuring device 20 will be described.

  FIG. 6 is a flowchart showing a procedure for measuring a physical quantity by the FBG physical quantity measuring device 20 shown in FIG. 5, and the reference numerals with numerals in the figure indicate the steps of the flowchart.

  First, in step S1, the prescan parameter setting unit 35 sets the scan range R of the wavelength scan in the prescan mode over the entire design wavelength range of the FBG 7 to which attention is paid. Further, the prescan parameter setting unit 35 sets the scan interval of the wavelength scan in the prescan mode to a value obtained by dividing the scan range R by the set value N. Here, the set value N is set so that the value of the scan interval R / N is equal to or less than a half value of the spectrum distribution width of the FBG reflected light. Then, the prescan parameter setting unit 35 gives the scan range R and the scan interval R / N of the wavelength scan in the set prescan mode to the prescan unit 33.

  Next, in step S2, wavelength scanning in the pre-scan mode is executed an arbitrary number of times. That is, the pre-scan unit 33 controls the wavelength tunable filter 29 so that the wavelength scan is performed for the scan range R of the wavelength scan in the pre-scan mode received from the pre-scan parameter setting unit 35. Further, the pre-scan unit 33 gives a trigger signal application command to the trigger signal application unit 32 so as to control the timing of the pulsed light emitted from the light source 21.

  On the other hand, continuous light is given from the broadband light source 28 to the wavelength tunable filter 29. The wavelength tunable filter 29 selectively transmits continuous light in a wavelength band corresponding to the scan range R and supplies the continuous light to the optical pulse device 30. The optical pulsing device 30 converts continuous light in the wavelength band of the scan range R into pulsed light and transmits it into the optical fiber 22 at a timing corresponding to the trigger signal received from the trigger signal applying unit 32.

  For this reason, the pulsed light in the wavelength band of the scan range R propagates through the optical trunk line 22a and branches at each optical branching device 24, propagates through the optical branching path 22b, and is provided in series on the optical branching path 22b. The FBG sensor 23 is irradiated. Here, since the wavelength band of the pulsed light is set in the design wavelength range of the focused FBG sensor 23, the FBG sensor 23 in the same designed wavelength range as the focused FBG sensor 23 can respond to a physical quantity such as temperature. FBG reflected light in a certain wavelength band is generated.

  The FBG reflected light generated in the FBG sensor 23 propagates again through the optical branching path 22b, the optical branching device 24, and the optical trunk line 22a, and is guided from the optical branching device 24a on the light source 21 side to the reflected light optical fiber 22c. Then, the FBG reflected light guided to the reflected light optical fiber 22c is received by the photodetector 25, and is provided to the pulse integration circuit 36 of the control unit 26 as received data of an electrical signal by photoelectric conversion.

  The pulse integration circuit 36 receives the reception data output as the electric pulse signal of the FBG reflected light from the photodetector 25 and obtains a pulse area proportional to the pulse height of the reception data, and then performs a noise reduction process. Data is supplied to the gate signal generator 37.

  Based on the timing information received from the trigger signal application unit 32, the gate signal generation unit 37 sets a time gate signal with a certain delay time according to the position of the FBG 7 of interest, thereby generating a signal from the pulse integration circuit 36. The electric pulse signal of the FBG reflected light from the focused FBG 7 is extracted from the pulse train of the received FBG reflected light, and the extracted electric pulse signal of the FBG reflected light is given to the AD converter 38 as reception data.

  Further, the AD conversion device 38 performs AD conversion on the received data received from the gate signal generation unit 37 and supplies the AD data to the prescan unit 33.

  When wavelength scanning in the pre-scan mode is executed a plurality of times in order to maintain the calculation accuracy, the reception data of the FBG reflected light is repeatedly given to the pre-scan unit 33 by the same procedure.

  Next, in step S3, when the reception data of the FBG reflected light sufficient to maintain the calculation accuracy is obtained, the prescan unit 33 obtains the wavelength region center of the FBG reflected light, and both sides of the obtained wavelength region center. The section in which the required number of detailed scanning points set in advance can be secured is determined as the wavelength scanning range in the partial detailed scanning mode. Then, the pre-scan unit 33 gives the wavelength scan range in the determined partial detail scan mode to the partial detail scan unit 34.

  For this reason, in step S4, wavelength scanning in the partial detailed scan mode is executed an arbitrary number of times. That is, the partial detail scanning unit 34 controls the wavelength tunable filter 29 so as to execute wavelength scanning for the wavelength scanning range in the partial detailed scanning mode. Further, the partial detail scanning unit 34 gives a trigger signal application command to the trigger signal applying unit 32 so as to control the timing of the pulsed light emitted from the light source 21.

  On the other hand, continuous light is given from the broadband light source 28 to the wavelength tunable filter 29. The wavelength tunable filter 29 selectively transmits continuous light in a wavelength band corresponding to the wavelength scanning range in the partial detail scan mode to the optical pulse generator 30, and the optical pulse generator 30 uses the partial detail scan mode. The continuous light in the wavelength band of the wavelength scanning range at is converted into pulsed light and transmitted into the optical fiber 22.

  Therefore, similarly to the case of wavelength scanning in the pre-scan mode, reception data of FBG reflected light for the wavelength scanning range in the partial detailed scan mode is given to the partial detailed scan unit 34. Further, the partial detail scanning unit 34 gives the reception data of the FBG reflected light obtained by the wavelength scanning in the partial detail scanning mode to the wavelength center calculation unit 39 of the signal processing device 27.

  Therefore, in step S5, the wavelength center calculation unit 39 obtains the wavelength region center of the FBG reflected light from the focused FBG 7 based on the received data of the FBG reflected light obtained by the wavelength scanning in the partial detailed scan mode. This is given to the physical quantity converter 40.

  Further, in step S 6, the physical quantity conversion unit 40 converts the wavelength region center of the FBG reflected light received from the wavelength center calculation unit 39 into a physical quantity. For this reason, a physical quantity such as a temperature in the vicinity of the FBG sensor 23 of interest can be obtained. Then, the physical quantity conversion unit 40 gives a start command for the next wavelength scanning to the control unit 26 and the light source 21, and the physical quantity at each time is measured again by the procedure from step S2 to step S6.

  According to the FBG physical quantity measuring apparatus 20 as described above, a physical quantity with the required accuracy can be acquired without scanning the entire design wavelength range of the FBG sensor 23 of interest at a scan interval corresponding to the required accuracy of the physical quantity. For this reason, according to the FBG physical quantity measuring device 20, it is possible to measure physical quantities at multiple points in a shorter time while ensuring the measurement accuracy of the physical quantity, and it is possible to increase the measurement speed and measurement interval of the physical quantity. .

[Third Embodiment (FIG. 9)]
FIG. 9 is a diagram showing an equivalent circuit of a low-pass filter 60 that attenuates high-frequency noise and the like as the third embodiment of the present invention.

  In the first and second embodiments described above, since the AD conversion processing unit 11 is based on a computer, high frequency noise may be mixed into the input signal from a digital device or the like. For this reason, by connecting the low-pass filter 60 that optimizes the frequency band to be cut to the input stage of the AD converter, it is possible to suppress the influence of high-frequency noise mixed in the electric pulse train signal (input signal).

  According to this embodiment, since erroneous detection such as high-frequency noise mixed in the electric pulse train signal can be suppressed, individual pulses can be detected with higher accuracy.

The block diagram which shows the apparatus by 1st Embodiment of this invention. Action | operation explanatory drawing which shows the timing time by 1st Embodiment of this invention. Explanatory drawing which shows the differential coefficient obtained by carrying out the smoothing differentiation of the reflected pulse by 1st Embodiment of this invention. The flowchart which shows the FBG reflection time calculation effect | action by 1st Embodiment of this invention. Explanatory drawing at the time of wavelength scanning execution in the prescan mode by 1st Embodiment of this invention. 5 is a flowchart showing a wavelength scanning operation according to the first embodiment of the present invention. The figure which shows the structure which shows the apparatus by 2nd Embodiment of this invention. The flowchart which shows the FBG reflection time calculation effect | action by 2nd Embodiment of this invention. The circuit diagram which shows the low-pass filter equivalent circuit applied for FBG reflection time calculation by 3rd Embodiment of this invention. The block diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Fiber Bragg grating (FBG) physical quantity measuring device 21 Light source 22 Optical fiber 22a Optical trunk line 22b Optical branching path 22c Optical fiber 23 for reflected light FBG sensor 24, 24a Optical branching device 25 Photodetector 26 Control part 27 Signal processing device 28 Broadband Light source 29 Variable wavelength filter 30 Optical pulse converter 31 Temperature adjustment unit 32 Trigger signal application unit 33 Pre-scan unit 34 Partial detailed scan unit 35 Pre-scan parameter setting unit 36 Pulse integration circuit 37 Gate signal generation unit 38 AD converter 39 Wavelength center Calculation unit 40 Physical quantity conversion unit 41 Data storage unit 42 Time calculation processing unit 43 Time series data set generation unit 44 Averaging processing unit 45 Smooth differential calculation processing unit 46 Delay time calculation processing unit 47 Optical delay device 48 Derivative coefficient determination processing unit 49 Threshold determination unit 50 Derivative coefficient level ratio determination unit 5 1 Derivative coefficient time width determination unit 60 Low-pass filter

Claims (8)

An optical fiber, a plurality of fiber Bragg grating sensors (FBG sensors) provided on the optical fiber, a light source including a wavelength tunable filter for irradiating the FBG sensor with light in a required wavelength band, and the FBG A photodetector that receives reflected light from the sensor and obtains received data, and a physical quantity measuring unit that measures a physical quantity at multiple points by applying one or both of time division multiplexing and wavelength multiplexing based on the received data In an optical fiber Bragg grating apparatus, an AD conversion processing unit that converts an FBG reflection pulse obtained from the FBG sensor into a digital data string set of time and voltage, and differential calculation of the digital data string set to perform the FBG reflection FBG corresponding to the derivative peak sets obtained for steep portion slope of the rise and fall of the pulse Morphism and a time calculation processing unit for calculating the reflection time information of the pulse, the FBG reflected pulse fiber Bragg grating physical quantity measuring device and calculates the reflection time. The peak level of the derivative peak set obtained for the rising and falling steep slopes of the FBG reflection pulse at the detection lower limit is used as a threshold value, and the threshold value exceeds the threshold value from the derivative peak set calculated from the FBG reflection pulse. The fiber Bragg grating physical quantity measuring device according to claim 1, further comprising a differential coefficient determination processing unit that determines only a differential coefficient peak set as a threshold value. The fiber Bragg grating physical quantity measuring device according to claim 1, further comprising a differential coefficient level ratio determination unit that compares and determines a relative ratio of peak levels of the differential coefficient pair with a predetermined threshold. Fiber Bragg according to any one of claims 1 having the comparison determines the derivative time width determination unit at the threshold where the time interval of the derivative peak group based on the time width of the FBG reflected pulse until 3 Grating physical quantity measuring device. The digital data sequence sets and derivative peak series of sets of processing unit, a fiber Bragg grating physical quantity measuring apparatus according to any one of claims 1 matches the programmable logic in the device (PLD) to 4. The fiber Bragg grating physical quantity measuring device according to claim 1, wherein a low-pass filter is provided upstream of the AD conversion processing unit. An optical fiber, a plurality of FBG sensors provided on the optical fiber, a light source including a wavelength tunable filter for irradiating the FBG sensor with light in a required wavelength band, and reflected light from the FBG sensor Fiber Bragg comprising: a photodetector that receives light and obtains received data; and a physical quantity measuring unit that measures a physical quantity at multiple points by applying one or both of time division multiplexing and wavelength multiplexing based on the received data In the grating device, an AD conversion processing unit that converts the FBG reflected pulse obtained from the FBG sensor into a digital data string set of time and voltage, and a rise and fall of the FBG reflected pulse by differentially calculating the digital data string set Time calculation for calculating the reflection time of the FBG reflection pulse corresponding to the derivative peak set obtained with respect to the steep part inclination of A processing unit, and a partial detailed scanning unit that controls the wavelength tunable filter so as to execute wavelength scanning at a predetermined number of detailed scanning points set in advance for the wavelength scanning range of the partial detailed scanning mode with respect to the FBG reflected light; A scan condition for wavelength scanning in the pre-scan mode is set with respect to the FBG reflected light so that the scan range is wider than the wavelength scan range of the partial detail scan mode and wider than the scan interval of the partial detail scan mode. A pre-scan parameter setting unit; and controlling the wavelength tunable filter so that the wavelength scan in the pre-scan mode is executed prior to the wavelength scan in the partial detailed scan mode under the scan condition set by the pre-scan parameter setting unit. To the pre-scan mode The partial detailed scan mode includes a section in which the center of the wavelength region of the FBG reflected light is obtained from the received data obtained by the wavelength scan and the number of detailed scanning points in the partial detailed scan mode can be secured on both sides of the obtained wavelength region center. A pre-scan unit that is determined as a wavelength scanning range in the above, a wavelength center calculation unit that obtains a wavelength region center of the FBG reflected light from reception data obtained by wavelength scanning in the partial detailed scan mode, and a wavelength center calculation unit And a physical quantity conversion unit for converting the center of the wavelength region of the reflected FBG light into a physical quantity. Receiving reflected light from a plurality of FBG sensors provided on an optical fiber to obtain received data, and applying one or both of time division multiplexing and wavelength multiplexing based on the received data to obtain multiple points Measuring the physical quantity of the FBG, converting the FBG reflected pulse obtained from the FBG sensor into a digital data string set of time and voltage, and differentially calculating the digital data string set to rise of the FBG reflected pulse And a time calculation step processing unit that calculates time information corresponding to the derivative peak set obtained with respect to the steep slope of the fall, and calculating the reflection time of the FBG reflection pulse. Bragg grating physical quantity measurement method.

Images