CN102818531A - Dynamic strain measurement instrument based on multiple overlapped gratings - Google Patents

Dynamic strain measurement instrument based on multiple overlapped gratings Download PDF

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CN102818531A
CN102818531A CN2012103358692A CN201210335869A CN102818531A CN 102818531 A CN102818531 A CN 102818531A CN 2012103358692 A CN2012103358692 A CN 2012103358692A CN 201210335869 A CN201210335869 A CN 201210335869A CN 102818531 A CN102818531 A CN 102818531A
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gratings
dynamic strain
overlapping many
wavelength
many gratings
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CN102818531B (en
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杨远洪
马游春
杨明伟
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Beihang University
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Abstract

The invention provides a dynamic strain measurement instrument based on multiple overlapped gratings. The dynamic strain measurement instrument comprises the multiple overlapped gratings, a wideband light source, a tunable filter, a positioning coupler, an etalon, a photoelectric detector and a demodulation and control circuit. The multiple overlapped gratings are formed in a way that a plurality of sensing gratings with center wavelengths being distributed at equal intervals are inscribed in an overlapped manner in a same area on a sensing optical fiber by selecting different phase templates, wherein the center wavelengths of a fiber Bragg grating, which are inscribed in the overlapped together, are continuously distributed at equal intervals within a wavelength scanning range of the tunable filter, so that sensing information of the same physical quantity to be measured can be continuously obtained for a plurality of times within each wavelength scanning period, and a peak value position and wavelength variation of each sensing grating in the multiple overlapped gratings, namely reconfigurable original dynamic strain signals, can be recorded. Therefore, the purpose of improving a measurement bandwidth of the dynamic strain signals based on a grating demodulation system of the tunable filter can be realized. According to the dynamic strain measurement instrument provided by the invention, the sensed measurement bandwidth of the fiber Bragg grating based on the tunable filter can be effectively improved, so that the high-speed and high-precision simultaneous measurement requirement of the dynamic strain signals can be met.

Description

A kind of dynamic strain measurement appearance based on overlapping many gratings
Technical field
The present invention relates to a kind of dynamic strain measurement appearance, be mainly used in the sensing and the measurement of dynamic strain signal, belong to field of sensing technologies based on overlapping many gratings.
Background technology
Fiber grating can convert the variation (like stress, strain, vibration, temperature variation etc.) of external environment to the variation of self reflectance spectrum centre wavelength; After the suitable encapsulation of fiber grating process; Can be made into specific fiber-optic grating sensor; Fiber-optic grating sensor because have the electromagnetic interference of not receiving, characteristics such as volume is little, making is simple, wavelength sensitive, be widely used in remote optical sensing and optical communication field.
The technology that realizes the fiber grating demodulation at present has following several kinds usually, and they are spectral analysis technique, the length scanning technology based on tunable optic filter, boundary filter technological, non-equilibrium M-Z interferometer demodulation techniques and coupling grating demodulation method etc.Spectral analysis technique is owing to need a large amount of mathematical computations, and Wavelength demodulation speed is lower, can't adapt to the measurement of big bandwidth signal; Non-equilibrium M-Z interferometer demodulation techniques are owing to exist the zero drift problem to be only applicable to the measurement of Dynamic Signal at present; Optical filtering technology need be independent boundary filter and the detector of each sensing grating configuration; Be not easy to the multiplexing of a plurality of grating sensors, and cost is higher; Technological based on the length scanning of tunable optic filter owing to it has wavelength resolution height, wide, the strong practical applications widely that obtains of multiplexing capacity of measurement range; But that sells in the market exists the low problem of wavelength sweep rate again based on this method grating demodulation system, so can't satisfy the measurement demand of big Bandwidth Dynamic signal.
Influence mainly comprises following two aspects based on the reason of tunable optic filter grating demodulation systematic survey bandwidth:
(1) restriction of the tunable speed of tunable optic filter self, in order to guarantee laser instrument long term operation stability and reliability, existing fiber laser tuned speed based on tunable optic filter all arrives a few kHz magnitudes at 1Hz usually.
(2) restriction of signals collecting and processing speed; Keeping under the constant condition of scanning wavelength resolution; The switching rate of A/D and D/A is directly proportional with the wavelength sweep rate of tunable optic filter, and the data-handling capacity of demodulating system has limited the raising of A/D SF, and under the constant condition of A/D SF; Can only reduce wavelength scanning range and wavelength resolution with the raising wavelength sweep rate, but this can influence the multiplexing capacity and the demodulation accuracy of demodulating system again.
Summary of the invention
Technology of the present invention is dealt with problems: overcome the deficiency of prior art, propose a kind of dynamic strain measurement appearance based on overlapping many gratings, to satisfy the measurement demand to big Bandwidth Dynamic strain signal based on the grating demodulation system of tunable optic filter.
The present invention solves the problems of the technologies described above the technical scheme that is adopted: a kind of dynamic strain measurement appearance based on overlapping many gratings; The a plurality of centre wavelengths that it is characterized in that utilizing overlapping inscription equally distributed sensor fibre grating 5 or adopt the parallel method that connects many overlapping many gratings to design sensors such as various stress, strain or impact shock in wavelength scanning range based on fiber grating; The same measurand of a plurality of fiber gratings that overlap perception simultaneously; The variable quantity of each grating centre wavelength is directly proportional with the size of measurand; And based on grating demodulation system under the effect of triangular wave D/A converter 11 and high-voltage drive 12 the output continuous narrow linewidth wavelength of wideband light source 1 with tunable optic filter 2; Output wavelength is through getting into overlapping many gratings 5 and etalon 6 respectively behind the coupling mechanism 3; Isolator 4 is used for the reflected signal of isolation standard tool 6; The transmission spectrum of the reflectance spectrum of overlapping many gratings 5 and etalon 6 gets into photodetection 7 respectively, the electric signal of exporting through multichannel synchronous serial A/D converter 8 real-time synchronous acquisition photodetectors 7 at last; The work schedule and the output waveform that are used to control A/D converter 8 and D/A converter 11 based on the demodulation of FPGA and control circuit 10; Receive and handle the signal of A/D converter 8 simultaneously in real time; And the data that will handle in real time send to computing machine 9 through interface (PCI, USB or network interface) and further handle, and computing machine 9 is main accomplishes resolving and reconstruct of each sensing grating peak wavelength in overlapping many gratings of each length scanning cycle; Calculate the D/A controlling value of each length scanning overlapping many gratings and corresponding scanning voltage of each peak wavelength of etalon in the cycle in real time based on the demodulation of FPGA and control circuit 10 peak extraction algorithm capable of using; Because the centre wavelength of each output peak value of etalon immobilizes; And the peak wavelength of overlapping many grating outputs will move to long wave or shortwave direction under the dynamic strain effect; Computing machine 9 can calculate the variation of each sensing grating centre wavelength in overlapping many gratings through calculating the variable quantity of overlapping many grating 5 each peak relative standard tools 6 each peak value centers; In addition because each sensing grating centre wavelength uniformly-spaced evenly distribution on frequency domain in overlapping many gratings 5; And the output wavelength of tunable optic filter 2 is continuous linear distribution on time domain; So the result that resolves of each sensing grating centre wavelength also is spacedly distributed on time domain continuously in overlapping many gratings, with each sensing grating centre wavelength in overlapping many gratings to resolve that the result combines by the scanning sequency of wavelength be restructural dynamic strain information.
Because overlapping many gratings all have the output of sensing grating response spectra in tunable optic filter forward and backward wave long scan process; In order to realize uniformly-spaced gathering the purpose of dynamic strain signal; Each length scanning cycle all need be resolved the sensing grating response spectra of positive and negative both direction simultaneously; Evenly distribute for the centre wavelength that realizes each grating in overlapping many gratings simultaneously, the centre wavelength of each sensing grating in overlapping many gratings should be chosen according to the computes result:
λ B [ i ] = λ S + [ i - 1 2 ] × λ E - λ S n - - - ( 1 )
In the formula: λ B [i]Be the centre wavelength of i sensing grating;
λ SLength scanning starting point for tunable optic filter;
λ ELength scanning terminal point for tunable optic filter;
N is the total number of sensing grating.
Because overlapping many gratings can not guarantee that in manufacturing process the centre wavelength of each sensing grating is spacedly distributed fully in the wavelength scanning range of tunable optic filter; And each centre wavelength of sensing grating can take place to move around to shortwave and long wave direction under the effect of dynamic strain; The nonlinear sweep of tunable optic filter also can cause the unequal interval of sensing grating output spectra to distribute in addition; Dynamic strain signal for correct reconstruct measurand; Demodulation and control circuit (10) based on FPGA need the real-time peak that calculates overlapping many gratings of each length scanning cycle and etalon; And result of calculation sent to computing machine (9), result of calculation should comprise the position t of each sensing grating centre wavelength in length scanning cycle n, the overlapping many gratings NiAnd the peak of etalon; Because the centre wavelength that the peak of etalon is corresponding immobilizes, thereby computing machine (9) can calculate the variation delta λ of each sensing grating centre wavelength according to the position of each sensing grating centre wavelength in overlapping many gratings with respect to the change in location of etalon Ni, again according to each sensing grating centre wavelength dynamic strain sensitivity coefficient k in overlapping many gratings iBe the dynamic strain information of restructural measurand, n scan period dynamic strain signal should be by reconstruct shown in the following formula:
Δ ϵ n = { ( t n 1 , Δ λ n 1 k 1 ) , ( t n 2 , Δ λ n 2 k 2 ) , · · · , ( t ni , Δ λ ni k i ) } - - - ( 2 )
In the formula: Δ ε nBe n the dynamic strain information that the scan period obtained;
t NiBe i sensing grating peak in n overlapping many gratings of scan period;
Δ λ NiIt is the center wavelength variation amount of i sensing grating in n overlapping many gratings of scan period;
k iDynamic strain sensitivity coefficient for i sensing grating in overlapping many gratings.
Principle of the present invention: the overlapping many gratings that adopt among the present invention are through selecting for use the phase mask with different centre wavelengths to repeat to inscribe made at the same position of sensor fibre; It mainly has following characteristics: (1) time synchronized property, the i.e. heat transfer agent of all sensing gratings that overlap perception simultaneously measurand; (2) compact conformation is because the grating of the sensing that is useful on all is scribed at the same sensitive position of sensor fibre.Based on the measuring instrument of these overlapping many gratings mainly by the overlapping many gratings that are used for dynamic strain measurement with forms based on grating demodulation system two parts of tunable optic filter and wideband light source, the overlapping many gratings that are used for dynamic strain measurement are on the same sensitive zones of same optical fiber, to repeat to inscribe a plurality of centre wavelengths equally distributed fiber grating also in wavelength scanning range.Because in overlapping many preparing gratings process; Grating of every increase all can have influence on centre wavelength and the reflectivity thereof of having inscribed grating; This inscription technological requirement to overlapping many gratings is higher, thereby limited the number that it can overlapping grating, in order further to improve the measurement bandwidth of dynamic strain and to guarantee demodulation accuracy; Can increase the number of each length scanning cycle sensing grating through the parallel mode that connects many overlapping many gratings, thereby realize more gratings purpose of sensing simultaneously.At each length scanning in the cycle; Sensor based on above overlapping many gratings can uniformly-spaced obtain a plurality of sensing grating output spectras continuously; After the variation and time sequencing reconstruct through each sensing grating centre wavelength of real-time resolving according to the appearance of sensing grating output spectra; Can obtain more dynamic strain heat transfer agent; Thereby can be in the measurement purpose that keeps realizing under the constant condition of tunable optic filter sweep speed big bandwidth signal; The present invention need not to improve sweep speed and the scanning step of tunable optic filter and need not reduce the wavelength scanning range of tunable optic filter, thereby can on the basis of existing wavelength resolution and multiplexing capacity, realize the sensing and the measurement of big Bandwidth Dynamic strain signal.
The present invention compared with prior art advantage is:
(1) the present invention adopts a plurality of centre wavelengths uniformly-spaced equally distributed overlapping many gratings in the tunable optic filter wavelength scanning range to design the dynamic strain sensing device; Can effectively improve existing measurement bandwidth, have advantages such as the demodulating system wavelength resolution is high, measurement range is wide, multiplexing capacity is strong simultaneously concurrently based on tunable optic filter grating demodulation system.
(2) type of dynamic strain sensor that the present invention is based on overlapping many gratings can link together through same optical fiber with a plurality of employing monochromatic light grid sensor designed and make up sensing; Thereby measure demand, the range of application and the dirigibility that can effectively improve grating sensing when can satisfy existing low frequency small-signal high frequency dynamic strain signal is arranged again.
Description of drawings
Fig. 1 is that the dynamic strain measurement instrument system that the present invention is based on overlapping many gratings is formed;
Fig. 2 the present invention is based on the overlapping dynamic strain measurement appearance demodulation principle of having inscribed two overlapping many gratings of centre wavelength, wherein: (a) be the sensing grating output spectra under the dynamic strain effect of overlapping many gratings; (b) be the pectination output spectra of etalon; (c) be the scanning voltage of tunable optic filter;
The dynamic strain sensing principle of a plurality of sampling gratings of overlapping inscription on the single sensor fibre of Fig. 3;
Fig. 4 adopts two to be carved with the parallel dynamic strain sensing principle that connects of overlapping many grating fibers;
The overlapping many gratings of Fig. 5 the present invention are each cycle sensing grating reflectance spectrum under the sinusoidal dynamic strain effect of 100Hz;
The wavelength change reflectance spectrum in sinusoidal dynamic strain each cycle of signal of 100Hz after Fig. 6 reconstruct of the present invention.
Among the figure: 1-width light source; The 2-tunable optic filter; The 3-fiber coupler; The 4-isolator; The overlapping many gratings of 5-; The 6-etalon; The 7-photodetector; The 8-A/D converter; The 9-computing machine; 10-is based on demodulation and the control circuit of FPGA; The 11-D/A converter; The 12-high-voltage drive.
Embodiment
To combine accompanying drawing and instance that the present invention is done further detailed description below.
As shown in Figure 1, based on the dynamic strain measurement appearance of overlapping many gratings mainly comprise wideband light source 1, tunable optic filter 2, fiber coupler 3, isolator 4, overlapping many grating 5, etalon 6, photodetector 7, A/D converter 8, computing machine 9, based on demodulation and control circuit 10, D/A converter 11 and the high drive amplifying circuit 12 of FPGA; Wideband light source 1 optional usefulness has the power light source of higher gain flatness (bandwidth is greater than 40nm among the figure; Wavelength coverage 1520nm ~ 1560nm; General power is greater than 10mW); Wideband light source will be through becoming the laser of narrow linewidth behind the tunable optic filter 2; The output linewidth of the tunable optic filter of selecting for use should be superior to 0.01nm, and to guarantee the demodulation accuracy of demodulating system, tunable optic filter 2 will periodically be exported the narrow-linewidth laser of linear change under the effect of triangular voltage sweep voltage; The wavelength of narrow-linewidth laser is in the variation of 1520nm ~ 1560nm scope intercycle property; Triangular voltage sweep voltage is produced through D/A converter 11 and high-voltage drive 12 by demodulation and the control circuit 10 based on FPGA, and the narrow linewidth output wavelength is through getting into overlapping many gratings 5 and etalon 6 respectively behind the coupling mechanism 3, and isolator 4 is used for the reflected signal of isolation standard tool 6; Get into photodetection 7 respectively through the reflection wave of the many gratings 5 of lap over and the transmitted wave of etalon 6; The electric signal of exporting through A/D converter 8 real-time synchronous acquisition photodetectors 7 again; A/D converter 8 adopts multipath high-speed synchronous serial A/D; Can effectively improve based on the demodulation of FPGA and the multi-channel parallel data-handling capacity of control circuit 10 through this design, reduce the A/D conversion, be convenient to the expansion of more demodulation passages based on the demodulation of FPGA and the demand of control circuit 10 input and output pins.The work schedule and the output waveform that are used to control A/D converter 8 and D/A converter 1 based on the demodulation of FPGA and control circuit 10; Receive and handle the signal of A/D converter 8 simultaneously in real time; The data that to handle in real time at last send to computing machine 9 through interface (PCI, USB or network interface) and further handle, and each sensing grating peak wavelength resolves and reconstruct in computing machine 9 main completion overlapping many gratings of each length scanning cycle; Shift to an earlier date algorithm based on the demodulation of FPGA and control circuit 10 peak values capable of using and calculate each length scanning position of the corresponding scanning voltage of each peak wavelength in overlapping many gratings and the etalon in the cycle in real time; Because the centre wavelength of each output peak value of etalon immobilizes; And the peak wavelength of each sensing grating output will move to long wave or shortwave direction under the dynamic strain effect in overlapping many gratings; Computing machine 9 can calculate the variation of each overlapping many gratings centre wavelength through calculating the variable quantity of overlapping many grating 5 each peak relative standard tools 6 each peak value centers.
Used overlapping many gratings need to confirm the number of sensing grating and the interval of centre wavelength thereof according to the requirement of dynamic strain measurement bandwidth and the sweep speed of tunable optic filter among Fig. 1; Calculate the centre wavelength of each grating in overlapping many gratings again through formula (1); At last through selecting for use corresponding preparing grating template to inscribe; Because overlapping many gratings need carry out pretension and fix before carrying out the dynamic strain sensing; The centre wavelength of each grating will move to the long wave direction under the effect of pretension simultaneously; Thereby can take place to further relatively and zoom out in the top and the bottom of tunable optic filter triangular voltage sweep voltage, cause the unequal interval sampling of intersection, this problem can be eliminated through the scanning bias voltage of adjustment tunable optic filter.
As shown in Figure 2; Be demodulation principle based on the dynamic strain measurement appearance of overlapping many gratings; 4 sensing grating reflectance spectrums that Fig. 2 (a) exports in the single tunable optic filter length scanning cycle for overlapping many gratings of overlapping two centre wavelengths; Wherein in forward scan and reverse scan process, produce two sensing grating reflectance spectrums respectively; The centre wavelength of sensing grating reflectance spectrum is corresponding with two sensing grating centre wavelengths in overlapping many gratings, owing to overlapping many gratings are inscribed in the identical zone of sensor fibre, thereby has close sensing sensitivity; The demodulation result of each scan period 4 sensing grating reflectance spectrum is consistent with the scope of dynamic strain; Just the time of each sensing grating reflectance spectrum appearance is spacedly distributed successively, and overlapping many gratings are under the dynamic stress effect, and 4 sensing grating reflectance spectrums will move to shortwave or long wave direction simultaneously; The demodulation result of 4 sensing grating reflectance spectrums just can realize 4 times of measurements to the dynamic strain signal of wavelength sweep rate after reconfiguring according to the order of formula (2) and time, thereby reaches the purpose of raising based on tunable optic filter grating demodulation systematic survey bandwidth.Fig. 2 (b) is the pectination output spectra of etalon; Each pectination output spectra be spaced apart fixing 800pm; Because the centre wavelength of each output spectra of etalon receives Influence of Temperature very little; Thereby can be used as reference wavelength, the Real-time and Dynamic that is used for overlapping many gratings is demarcated, and can effectively improve the demodulation accuracy of grating centre wavelength.Fig. 2 (c) is the scanning voltage of tunable optic filter, and the bias voltage through changing sweep waveform and the amplitude of scanning voltage can change the scope of tunable optic filter scanning wavelength.
As shown in Figure 3; For select for use the different phase mask plate to come the method for designing of a plurality of sensing gratings of overlapping inscription at the same position of sensor fibre; Keep sensor fibre motionless in overlapping many gratings inscription process, has inscribed first sensing grating after, use phase mask plate instead and carry out the inscription second time with different centre wavelengths; Or directly select for use phase mask plate to inscribe with a plurality of sensing gratings; To accomplish the inscription work of a plurality of sensing gratings, move left and right will take place in the reflectance spectrum centre wavelength of each sensing grating in overlapping many gratings under the tension and compression effect of dynamic stress, move the result shown in the little figure among Fig. 2 (a).
As shown in Figure 4; For adopting the parallel two type of dynamic strain sensor methods for designing that are carved with overlapping many gratings that connect; This design can be reduced in the negative effect that a plurality of sensing grating of overlapping inscription is brought on the same optical fiber; To improve the number of used sensing grating in the dynamic strain sensing; The overlapping many grating reflection spectrum signal of two-way can get into independently photodetector respectively, also can get into same photodetector through directional coupler and carry out signals collecting and processing, because all sensing grating centre wavelengths of using all are uniformly-spaced equally distributed in the wavelength scanning range of tunable optic filter; Need requirement unified distribution, do not have the overlapping problem of wavelength according to formula (1).
Embodiment 1
Below mainly have overlapping many gratings of two sensing gratings to realize that 4 times of measuring methods to the dynamic sinusoidal strain signal of tunable optic filter sweep speed are illustrated to overlapping inscription; Fig. 2 has provided the demodulation principle based on the dynamic strain measurement appearance of overlapping many gratings; Wavelength scanning range with tunable optic filter is an example from 1535nm～1555nm; In overlapping many gratings the centre wavelength of two sensing gratings by formula (1) choose; Corresponding two sensing grating centre wavelengths are respectively 1540nm, 1550nm; The centre wavelength of each sensing grating is spaced apart 10nm; Wavelength sweep rate with tunable optic filter is that 500Hz is an example; The dynamic strain sensing device that adopts overlapping many gratings design the forward in each tunable optic filter length scanning cycle and reverse scan process respectively can the same sensing point of double acquisition measurand, adds up to 4 times to pass on a skill from a master to a single disciple the sensitization grid the measurement bandwidth of obtainable measurand, the actual information frequency acquisition that the overlapping many gratings dynamic strain sense measuring device of correspondence is obtained should be 2kHz; The measurement bandwidth of measured signal has just improved 4 times; The output power spectrum of scanning wavelength and overlapping many gratings is as shown in Figure 2, has provided the triangular voltage sweep voltage of demodulating system overlapping many grating reflection spectrums and tunable optic filter in forward and reverse scan process among the figure, and wavelength scanning range is 1535nm～1555nm.Fig. 5 has provided the sinusoidal dynamic strain reflectance spectrum of 4 100Hzs of overlapping many gratings under 500Hz forward and the effect of reverse scan voltage; Can know by Fig. 5; 4 corresponding same tested dynamic strain signals of sensing grating output spectra, the peak of sensing grating output reflection spectrum demonstrates periodic sinusoidal variations.Fig. 6 is that 4 sinusoidal dynamic strain reflectance spectrums are pressed the later wavelength change reflectance spectrum of formula (2) reconstruct among Fig. 5; Sensing grating output reflection spectrum has become 20 by 5 of single sensing grating; Promptly obtained 4 times of dynamic strain signals collecting and counted, thereby effectively improved the measurement bandwidth of dynamic strain signal to the tunable optic filter sweep speed.
In a word, the present invention need not to select the expensive humorous wave filter of high-speed adjustable for use and need not reduce wavelength scanning range, thereby can on the basis that does not influence original wavelength resolution and multiplexing capacity, realize the more measurement of high-bandwidth signals.This method can effectively improve the measurement bandwidth based on the tunable optic filter optical fiber grating sensing, can satisfy the dynamic strain signal to high speed and the high-precision demand of measuring simultaneously.
The present invention does not set forth the known technology that part belongs to those skilled in the art in detail.

Claims (6)

1. dynamic strain measurement appearance based on overlapping many gratings is characterized in that: comprise wideband light source (1), tunable optic filter (2), fiber coupler (3), isolator (4), overlapping many gratings (5), etalon (6), photodetector (7), A/D converter (8), computing machine (9), based on demodulation and control circuit (10), D/A converter (11) and the high drive amplifying circuit (12) of FPGA; Said overlapping many gratings (5) are to repeat to inscribe a plurality of sensing gratings with different centre wavelengths at sensor fibre the same area, and each centre wavelength of overlapping many gratings (5) is spacedly distributed tunable optic filter (2) wavelength scanning range planted agent; Demodulation and control circuit (10) based on FPGA pass through D/A converter (11) and high-voltage drive (12) control wideband light source (1) and the continuous wavelength of tunable optic filter (2) output, get into overlapping many gratings (5) and etalon (6) respectively behind this output wavelength process coupling mechanism (3); Isolator (4) is used for the reflected signal of isolation standard tool (6); Get into photodetection (7) respectively through the reflection wave of the many gratings of lap over (5) and the transmitted wave of etalon (6), deliver in the demodulation and control circuit (10) based on FPGA through the electric signal of A/D converter (8) synchronous acquisition photodetector (7) output in real time again; The signal that receives A/D converter (8) in real time based on demodulation and the control circuit (10) of FPGA; The peak of overlapping many gratings of each length scanning cycle (5) and etalon (6) in the signal calculated; And result of calculation sent to computing machine (9), be used to control the work schedule and the output waveform of A/D converter (8) and D/A converter (11) simultaneously based on the demodulation of FPGA and control circuit (10); Because the centre wavelength of each output peak value of etalon (6) immobilizes; And the peak wavelength of overlapping many gratings (5) output will move to long wave or shortwave direction under the dynamic strain effect; Computing machine (9) can calculate the variation of each sensing grating centre wavelength in overlapping many gratings (5) through calculating the variable quantity of each peak of peak relative standard tool (6) of each sensing grating in overlapping many gratings (5); In addition because each centre wavelength of overlapping many gratings (5) uniformly-spaced evenly distribution on frequency domain; And the output wavelength of tunable optic filter (2) is continuous linear distribution on time domain; The result that resolves of each centre wavelength of overlapping many gratings (5) also is spacedly distributed on time domain continuously, with each centre wavelength of overlapping many gratings (5) to resolve that the result combines by the scanning sequency of wavelength be restructural dynamic strain information.
2. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings, it is characterized in that: a plurality of sensing gratings with different centre wavelengths are chosen according to following formula in said overlapping many gratings (5):
λ B [ i ] = λ S + [ i - 1 2 ] × λ E - λ S n
In the formula: λ B [i]Be the centre wavelength of i sensing grating;
λ SLength scanning starting point for tunable optic filter;
λ ELength scanning terminal point for tunable optic filter;
N is the total number of sensing grating.
3. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings; It is characterized in that: in order further to improve the measurement bandwidth of dynamic strain; In said overlapping many gratings (5), also can promptly overlapping many gratings have all been inscribed on every sensor fibre through the parallel production method that connects many overlapping many gratings; Again with the parallel stiff end that is connected to the dynamic strain measurement device of many sensor fibres; Be used for the purpose of the synchronous sensing of same measurand with the more gratings of realization, but all sensing grating centre wavelengths of using need be unified to choose in the many overlapping many gratings of connection that walk abreast, choosing method is:
λ B [ i ] = λ S + [ i - 1 2 ] × λ E - λ S n
In the formula: λ B [i]Be the centre wavelength of i sensing grating;
λ SLength scanning starting point for tunable optic filter;
λ ELength scanning terminal point for tunable optic filter;
N is the total number of sensing grating.
4. a kind of dynamic strain measurement appearance based on overlapping many gratings according to claim 1 is characterized in that: the process of said computing machine (9) reconstruct dynamic strain information is: the variation delta λ that calculates each sensing grating centre wavelength according to each sensing grating peak in overlapping many gratings with respect to the change in location of etalon output peak value Ni, again according to each sensing grating centre wavelength dynamic strain sensitivity coefficient k in overlapping many gratings iBe the dynamic strain information of restructural measurand, n scan period dynamic strain signal should be by reconstruct shown in the following formula:
Δ ϵ n = { ( t n 1 , Δ λ n 1 k 1 ) , ( t n 2 , Δ λ n 2 k 2 ) , · · · , ( t ni , Δ λ ni k i ) }
In the formula: Δ ε nBe n the dynamic strain information that the scan period obtained;
t NiBe i sensing grating peaks of n overlapping many gratings of scan period;
Δ λ NiIt is the wavelength change of i sensing grating of n overlapping many gratings of scan period;
k iDynamic strain sensitivity coefficient for i sensing grating of overlapping many gratings.
5. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings; It is characterized in that: said A/D converter (8) adopts multipath high-speed synchronous serial A/D; Can effectively improve based on the demodulation of FPGA and the multi-channel parallel data-handling capacity of control circuit (10) through this design; Reduce the A/D conversion to based on the demodulation of FPGA and the demand of control circuit (10) input and output pin, be convenient to the expansion of more demodulation passages.
6. a kind of dynamic strain measurement appearance according to claim 1 based on overlapping many gratings; It is characterized in that: said tunable optic filter (2) adopts the mode of triangular wave or sinusoidal wave symmetrical scanning; And can change output wavelength through the bias voltage and the peak-to-peak value scope of adjustment sweep waveform, on frequency domain so that the output wavelength of each sensing grating is spacedly distributed in overlapping many gratings (5) as far as possible.
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CN109798925A (en) * 2019-01-15 2019-05-24 太原理工大学 A kind of adjustable matched FBG demodulating equipment of range
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