CN102269573B - Quasi-distributed composite structure strain and temperature detection system - Google Patents

Abstract

The invention relates to a quasi-distributed composite material structure strain and temperature detection system. The output light of a broadband light source enters the input end of a 2×2 optical fiber coupler through an optical fiber isolator; the output light of the 2×2 optical fiber coupler enters a 1×m optical fiber coupler. The input end of the switch; the output light of the 1×m optical switch enters the m×n network fiber grating sensor head; the reflected light of the m×n network fiber Bragg grating sensor head passes through the 1×m optical switch and the 2× 2 fiber couplers enter the input end of the optical fiber tunable FP filter; the output light of the optical fiber tunable FP filter passes through the photoelectric conversion module, signal amplifier, data acquisition card and computer successively, and the data is processed by the computer processing and display. The invention utilizes a fiber adjustable FP filter to realize wavelength demodulation of all sensing fiber grating reflected signal lights, and has the advantages of anti-electromagnetic interference, all-fiber type measurement, multiple measurement points for multiplexing, remote monitoring and non-destructive measurement, and the like.

Description

A quasi-distributed composite structure strain and temperature detection system

technical field

The invention relates to the technical field of fiber grating sensing, in particular to a quasi-distributed composite material structure strain and temperature detection system with multi-parameter and multi-point measurement functions. the

Background technique

A fiber grating is an optical element that establishes a certain spatial refractive index periodic distribution in an optical fiber, so that the propagation characteristics of light can be changed in it. A fiber grating is an optical element that establishes a certain spatial refractive index periodic distribution in an optical fiber, so that the propagation characteristics of light can be changed in it. When the broadband light is incident on the fiber Bragg grating, the central wavelength (Bragg wavelength) λ _B of the reflected light is given by the Bragg equation: λ _B = 2nΛ

Among them, n is the effective refractive index of the fiber core, and Λ is the grating period. Since the measured signal is wavelength coded when fiber grating is used for sensing measurement, how to simply, quickly and accurately demodulate the wavelength (change amount) is a crucial issue in the fiber grating sensing system. In the prior art, if a fiber grating is used to measure multiple points, a spectrometer is often used to measure the wavelength signal, so that the cost of wavelength signal demodulation is relatively high; and the number of measurement points is limited by the bandwidth of the light source; and when the light source When the output power is constant, the larger the number of measurement points, the lower the signal-to-noise ratio, resulting in larger measurement errors. Therefore, the current fiber grating point multi-parameter system is usually low in cost performance, difficult to realize remote monitoring, and poor in repeatability. At the same time, a large amount of useless data needs to be screened during measurement, and the signal-to-noise ratio of the measurement is not high, which affects the accuracy of the measurement. the

Contents of the invention

The technical problem to be solved by the present invention is to provide a quasi-distributed composite material structure strain and temperature detection system capable of real-time monitoring of the health status of the composite material structure. Remote monitoring and realization of non-destructive measurement, strong flexibility and other advantages. the

The technical solution adopted by the present invention to solve the technical problem is: provide a quasi-distributed composite material structure strain and temperature detection system, including broadband light source, optical fiber isolator, 2 × 2 optical fiber coupler, 1 × m optical switch, m ×n network fiber grating sensor head, optical fiber adjustable F-P filter, photoelectric conversion module, signal amplifier, data acquisition card and computer, the output light of the broadband light source enters the 2×2 optical fiber coupling through the optical fiber isolator The input end of the device; the output light of the 2×2 fiber coupler enters the input end of the 1×m optical switch through an output arm of the 2×2 fiber coupler; the 1×m optical switch The output light enters the m×n network fiber grating sensor head; the reflected light of the m×n network fiber Bragg grating sensor head enters through the 1×m optical switch and 2×2 fiber coupler in turn The input end of the optical fiber tunable F-P filter; the output light of the optical fiber tunable F-P filter enters the described signal amplifier after the described photoelectric conversion module; the signal amplifier will receive the signal After amplification, it is collected by the data acquisition card into the computer; the computer is connected with the 1×m optical switch. the

The fiber grating in the m×n network type fiber grating sensor head is a polarization maintaining fiber grating. the

In the 1×m optical switch, only one optical signal forms a path in a time period. the

The computer controls the serial number of the light-passing optical path and the light-passing time of the 1×m optical switch, or the computer controls the 1×m optical switch by using a time-averaged measurement method. the

The wavelength of the optical fiber tunable F-P filter corresponds to the peak characteristic wavelength (i.e. the sensing signal wavelength) of the fiber grating of the m×n network fiber grating sensor head, and at this time the data acquisition card A maximum analog electrical signal will be received, and after analog-to-digital conversion, the computer can identify and change the maximum signal and realize signal demodulation. the

The fiber grating of the m×n network type fiber grating sensor head is installed to the point to be measured of the measured object by surface sticking or internal embedding. the

A refractive index matching liquid is installed on the other output arm of the 2×2 fiber coupler. the

Beneficial effect

Owing to having adopted above-mentioned technical scheme, the present invention has following advantage and positive effect compared with prior art:

(1) The present invention only needs one fiber grating to realize simultaneous measurement of strain and temperature, and does not need expensive wavelength demodulation equipment such as a spectrometer. The grating wavelength can be accurately calculated according to the output value of the photoelectric conversion module, and then combined with Compared with the initial wavelength, the amount of wavelength shift can be obtained, so as to know the size of the measured object. the

(2) The present invention utilizes the computer to control the light-through time of the light-through optical path i (i is an integer, i=1, 2..m) of a 1×m optical switch, and can prolong the light-through time of the path when key monitoring is required time to ensure the reliability of monitoring. the

(3) The 1×m optical switch in the present invention has m paths in total, wherein there are n fiber grating sensing heads in series in the i-th path, and the spatial resolution of the measurement can be determined according to the measurement needs, and the minimum can reach the length of the fiber grating That is 1cm. the

(4) In the present invention, when the fiber grating is modulated by the measured parameter and its peak characteristic wavelength drifts, since the wavelength of the fiber tunable F-P filter corresponds to the peak characteristic wavelength of the fiber Bragg grating, the output light of the fiber tunable F-P filter reaches the maximum response, After photoelectric conversion and analog-to-digital conversion, the maximum signal can be identified by the computer, that is, demodulation is realized, and it has the advantages of fast demodulation speed and no double value problem. the

(5) The technical level of the optical fiber and components used in the present invention is very mature, the manufacture is convenient and feasible, and can be widely used in various fields. The practical application in detection and long-term monitoring is of great significance. the

Description of drawings

Fig. 1 is a schematic structural view of the present invention. the

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application. the

The embodiment of the present invention relates to a quasi-distributed composite material structure strain and temperature detection system, as shown in Figure 1, including a broadband light source 1, an optical fiber isolator 2, a 2×2 optical fiber coupler 3, a refractive index matching liquid 4, 1×m optical switch 5, m×n network fiber grating sensor head 6, fiber tunable F-P filter 7, photoelectric conversion module 8, signal amplifier 9, data acquisition card 10 and computer 11, the broadband light source 1 The output light enters the input end of the 2×2 fiber coupler 3 through the fiber isolator 2; part of the output light of the 2×2 fiber coupler 3 enters through an output arm of the 2×2 fiber coupler 3 The refractive index matching liquid 4 is used to reduce the interference signal light, and the other part enters the input end of the 1×m optical switch 5 through the other output arm of the 2×2 fiber coupler 3; the 1 The output light of the ×m optical switch 5 enters the m×n network fiber grating sensor head 6; the reflected light of the m×n network fiber Bragg grating sensor head 6 sequentially passes through the 1×m optical switch 5 and 2×2 fiber coupler 3 enter the input end of the fiber tunable F-P filter 7; the output light of the fiber tunable F-P filter 7 enters the signal after passing through the photoelectric conversion module 8 Amplifier 9; after the signal amplifier 9 amplifies the signal received, it is collected in the computer 11 by the data acquisition card 10, and the computer 11 carries out data processing and display; the computer 11 is connected with the computer 11 The 1×m optical switch 5 is connected. the

The fiber grating in the network fiber grating sensor head 6 in the present invention is a polarization maintaining fiber grating. For a fiber grating built on a polarization-maintaining fiber, when broadband light is incident on the polarization-maintaining fiber grating, there are two peak center wavelengths in its reflection spectrum, which correspond to the reflection wavelengths on the fast axis and the slow axis, respectively expressed as:

λ _Bx = 2Λn _x ,

λ _By = _2Λny ,

Among them, n _x and _ny are the effective refractive index of the fast axis and slow axis of the fiber core respectively, and Λ is the grating period.

The difference between the peak center wavelengths of two fiber gratings on different axes is:

Δλ=2ΛΔn

Among them, Δn=n _{x -ny} , so a polarization maintaining fiber grating has two characteristic reflection peaks, and the drift of the peak wavelength has a good linear relationship with the strain and temperature changes. Based on the drift value, the strain and temperature to be measured are calculated, so as to achieve the purpose of simultaneously measuring two parameters with one sensor head. Among them, the parameters such as the peak reflection wavelength, bandwidth, and reflectivity of the polarization-maintaining fiber grating should match each other, and the wavelength is within the adjustable wavelength range of the fiber FP tunable filter, so that fast and accurate demodulation can be achieved.

In the present invention, only one optical signal of the 1×m optical switch 5 forms a path in a time period, that is to say, the 1×m optical switch 5 has m paths in total, and only one optical signal can form a path in a certain period of time. A path can be formed in any other optical path in the next period of time. Since only one optical path forms a path in a certain period of time, all the optical power entering the optical switch enters this channel, making the optical power of this measurement channel and the optical power of the signal light reflected by the fiber Bragg grating reach the maximum, so the measured signal-to-noise Relatively large, high measurement accuracy. The computer 11 can control the serial number and the light-passing time of the light-passing optical path of the 1×m optical switch 5, and can also control the described 1×m optical switch 5 by using the time-equal measurement method. The two control methods only need to be based on The actual measurement requirements and goals can be determined, and the computer 11 is remotely connected to the 1×m optical switch 5 through an optical fiber, so that the computer 11 can control the 1×m optical switch 5, thereby realizing the purpose of remote monitoring. the

The wavelength of the fiber tunable F-P filter 7 corresponds to the peak characteristic wavelength of the fiber grating of the m×n network fiber grating sensor head 6 . When the grating is modulated by the measured parameter and its peak characteristic wavelength drifts, since the wavelength of the fiber tunable F-P filter 7 corresponds to the fiber Bragg grating peak characteristic wavelength of the m×n network fiber grating sensor head 6, the fiber tunable F-P The output light of the filter 7 reaches the maximum response, and the maximum signal can be identified by the computer 11 after photoelectric conversion and analog-to-digital conversion, that is, demodulation is realized, so that the present invention has the advantages of fast demodulation speed and no double value problem. the

The fiber grating of the m×n network type fiber grating sensor head 6 is used as a sensitive element of the measured parameter, and can be mounted to the measured point of the measured object by surface sticking or internal embedding, so as to realize non-destructive measurement Purpose. the

The specific embodiment of the present invention is as follows: (1) when selecting and determining the broadband light source, the light source with larger power spectral density should be selected, generally should be greater than-20dB/nm, to ensure that the light power incident on the sensor grating is larger, Make the signal optical power reflected by the sensing fiber grating larger to improve the measurement accuracy; (2) When selecting each fiber grating, the determination of its wavelength is very important, especially the selection of the reflection peak characteristic wavelength interval of the fiber grating, should take into account The size of the measurement points and the measurement range requirements of each point. To meet the requirements of the measurement range, select a series of fiber gratings with a small interval between the characteristic wavelengths of the reflection peaks as the fiber gratings that make up the network fiber grating sensor head, and realize the quasi-distribution of more measurement points when the bandwidth of the light source is constant. (3) When selecting an optical switch, m is the number of parallel optical paths, and theoretically m can be infinite; (4) When installing and integrating a network-type fiber grating sensor head, the number of parallel measurement channels should be equal to the number of optical paths The number of channels of the switch is matched to avoid or reduce the waste of optical power and increase the measurement efficiency. n is the maximum number of gratings that can be arranged in series on the same road. n is determined by the peak characteristic wavelength interval and the bandwidth of the light source. Taking the light source bandwidth of 80nm as an example, if the FBG wavelength interval is 2nm, a total of 40 FBGs can be connected in series for simultaneous sensing. Since the sensing head contains m×n fiber gratings, real-time measurement of m×n points of the composite material structure can be realized. the

It is not difficult to find that the present invention uses a single fiber grating to realize simultaneous measurement of two parameters of strain and temperature, and uses a fiber tunable F-P filter to realize wavelength demodulation of all sensor fiber grating reflected signal light, which is a cost-effective A quasi-distributed measurement system for strain and temperature in composite structures. The invention also has the advantages of anti-electromagnetic interference, all-fiber type measurement, multiple measurement points, remote monitoring and non-destructive measurement. the

It should be noted that the quasi-distributed composite material structural strain and temperature detection system implemented in the present invention can also be used to measure other parameters such as structural load and magnetic field strength. the

Claims (6)

1. A quasi-distributed composite material structure strain and temperature detection system, including broadband light source (1), optical fiber isolator (2), 2 × 2 optical fiber coupler (3), 1 × m optical switch (5), m ×n network fiber grating sensing head (6), fiber tunable FP filter (7), photoelectric conversion module (8), signal amplifier (9), data acquisition card (10) and computer (11), its features In that, the output light of the broadband light source (1) enters the input end of the 2×2 fiber coupler (3) through the fiber isolator (2); the output of the 2×2 fiber coupler (3) The light enters the input end of the 1×m optical switch (5) through an output arm of the 2×2 fiber coupler (3); the output light of the 1×m optical switch (5) enters the m ×n network fiber grating sensor head (6); the reflected light of the m×n network fiber grating sensor head (6) passes through the 1×m optical switch (5) and 2×2 optical fibers in sequence Coupler (3) enters the input end of described optical fiber tunable FP filter (7); The output light of described optical fiber tunable FP filter (7) enters after described photoelectric conversion module (8) Described signal amplifier (9); Described signal amplifier (9) gathers in the described computer (11) by described data acquisition card (10) after the signal amplification of receiving; Described computer (11) ) is connected with the 1 × m optical switch (5); the fiber grating in the m × n network fiber grating sensing head (6) is a polarization-maintaining fiber grating; when the broadband light is incident on the polarization-maintaining For fiber gratings, there are two peak center wavelengths in the reflection spectrum, corresponding to the reflection wavelengths on the fast axis and the slow axis, expressed as: λ _Bx = 2Λn _x , λ _By = 2Λn _y , where n _x and n _y are respectively is the effective refractive index of the fast axis and slow axis of the fiber core, Λ is the grating period; the difference between the two peak center wavelengths on different axes is: Δλ=2ΛΔn, where Δn=n _{x -ny} , so a polarization maintaining fiber The grating has two characteristic reflection peaks, and the drift of the peak wavelength has a good linear relationship with the strain and temperature changes. The purpose of the sensor head measuring two parameters at the same time; wherein, the peak reflection wavelength, bandwidth, and reflectivity of the polarization-maintaining fiber grating match each other, and the wavelength is within the adjustable wavelength range of the fiber-tunable FP filter, achieve fast and accurate demodulation. 2. The quasi-distributed composite material structure strain and temperature detection system according to claim 1, characterized in that, only one path of the optical signal of the 1×m optical switch (5) forms a path in a time period . 3. quasi-distributed composite material structure strain and temperature detection system according to claim 1, is characterized in that, described computer (11) controls the serial number of the light-passing optical path of described 1 * m optical switch (5) and light-through time, or the computer (11) controls the 1×m optical switch (5) using a time-equal measurement method. 4. quasi-distributed composite material structure strain and temperature detection system according to claim 1, is characterized in that, the wavelength of described optical fiber tunable F-P filter (7) and described m * n network type fiber grating The peak characteristic wavelength of the optical fiber grating of the sensing head (6) corresponds. 5. quasi-distributed composite material structure strain and temperature detection system according to claim 1, is characterized in that, the optical fiber grating of described m * n network type optical fiber grating sensing head (6) utilizes surface sticking or internal buried The imported method is installed to the point to be measured of the target to be measured. 6. The quasi-distributed composite material structure strain and temperature detection system according to claim 1, characterized in that a refractive index matching liquid is installed on the other output arm of the 2×2 fiber optic coupler (3) (4).