CN107884477B - Acoustic emission detection system and detection method based on fiber bragg grating sensor - Google Patents
Acoustic emission detection system and detection method based on fiber bragg grating sensor Download PDFInfo
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Abstract
The invention provides an acoustic emission detection system and a detection method based on a fiber grating sensor, which comprises a tunable laser, the fiber grating sensor, a photoelectric detection module, a demodulation module and a servo system, wherein the tunable laser is connected with the fiber grating sensor; the photoelectric detection module converts reflected light of the fiber grating sensor into an electric signal, the servo system can adjust the wavelength of emergent light of the tunable laser according to the electric signal so as to adjust the intensity of the reflected light to the direction of a target intensity value, the electric signal output by the photoelectric detection module is transmitted to the demodulation module, and the demodulation module determines an acoustic emission signal according to the electric signal.
Description
Technical Field
The invention relates to the technical field of sensors, in particular to an acoustic emission detection system and method based on a fiber grating sensor.
Background
Acoustic emission refers to the phenomenon of a solid material releasing stored energy upon fracture to generate elastic waves. Since the frequency ranges of the acoustic emission signals generated by various materials are different, and the intensity of the acoustic emission signals generated when most materials are deformed and broken is very weak, so that the acoustic emission signals cannot be directly heard by human ears, the acoustic emission signals can be detected by means of sensitive electronic instruments.
Most of the existing acoustic emission detection systems adopt a piezoelectric ceramic sensor to detect acoustic emission signals generated by various materials. Although this acoustic emission detection system has the advantages of simple equipment, easy installation, and capability of being applied on-line in a wide range, the piezoelectric ceramic sensor has a large volume, and thus, it can only be installed outside a measured object such as a transformer, but not inside the measured object, which results in low detection sensitivity of the piezoelectric ceramic sensor for acoustic emission signals generated inside the measured object.
Based on this, the prior art proposes an acoustic emission detection system based on a fiber grating sensor, as shown in fig. 1, which includes a fiber grating sensor 10, a laser 11 and a demodulation system 12, where the fiber grating sensor 10 is disposed inside or on the surface of the monitored object 00 and is used to detect an acoustic emission signal generated by the monitored object 00, and especially under the condition of structural damage or impact, the central wavelength of reflected light of the fiber grating sensor 10 may shift under the action of the acoustic emission signal; the laser 11 is used for providing a light source for the fiber grating sensor 10, so that the fiber grating sensor 10 reflects the reflected light with a specific wavelength; the demodulation system 12 is configured to obtain the acoustic emission signal generated by the monitored object 00 according to the central wavelength offset of the reflected light and the corresponding relationship between the central wavelength offset and the acoustic emission signal.
The fiber grating sensor has small volume and light weight, so that the fiber with the fiber grating sensor can be arranged in the measured object to improve the sensitivity of the detection system. However, since the wavelength of the laser 11 may vary with ambient temperature, stress variations, vibrations, etc., the detection sensitivity and accuracy of the acoustic emission detection system may be affected or limited.
Disclosure of Invention
The embodiment of the invention provides an acoustic emission detection system and an acoustic emission detection method based on a fiber grating sensor, which are beneficial to improving the detection sensitivity, accuracy and anti-interference capability of the acoustic emission detection system.
The embodiment of the invention provides the following technical scheme:
an acoustic emission detection system based on a fiber grating sensor comprises a tunable laser, the fiber grating sensor, a photoelectric detection module, a demodulation module, a filter and a servo system;
the tunable laser is used for providing a light source for the fiber grating sensor, so that the incident light of the fiber grating sensor is the light with a specific wavelength in the light source;
the fiber grating sensor is used for detecting an acoustic emission signal of a monitored object, wherein the central wavelength of reflected light of the fiber grating sensor can deviate under the action of the acoustic emission signal generated by the monitored object;
the photoelectric detection module is used for detecting the reflected light of the fiber bragg grating sensor and converting the reflected light into an electric signal;
the servo system is used for judging whether the intensity of the reflected light is a target intensity value according to the electric signal, if not, the wavelength of the emergent light of the tunable laser is adjusted, so that the intensity of the reflected light is adjusted towards the direction of the target intensity value;
the electric signal output by the photoelectric detection module is transmitted to the demodulation module;
the demodulation module is used for determining the central wavelength offset of the reflected light or the intensity of the reflected light according to the electric signal and determining the acoustic emission signal generated by the monitored object according to the corresponding relation between the central wavelength offset and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal;
the servo system comprises at least one amplifier, and the amplifier is used for controlling the input of the tunable laser through a negative feedback signal to adjust the wavelength of emergent light of the tunable laser;
the filter is located on the negative feedback signal path, and the filter is used for filtering out signals of which the frequency is higher than a preset frequency in the electric signals so as to adjust the wavelength of emergent light of the tunable laser.
The preset frequency may be a x f, where f is the lowest frequency of acoustic emissions desired to be detected and a is less than 1, 1/2, 1/4, 1/10, 1/100, or 1/1000.
The detection system may include a control system for comparing the acoustic emission signal with reference data to obtain a health measure of the monitored object, the reference data including test data for acoustic emission signals generated by the monitored object at different levels of health.
The servo system may be configured to adjust at least one of the following according to a correspondence between the intensity of the reflected light and the wavelength of the light emitted by the tunable laser: the target intensity value, the wavelength of emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal.
The servo system can be used for obtaining the intensity of the reflected light under different wavelengths of the emergent light of the tunable laser by adjusting the wavelength of the emergent light of the tunable laser.
The detection system may comprise at least one temperature sensor;
the temperature sensor is used for detecting the environmental temperature data of the fiber bragg grating sensor;
the servo system is used for adjusting at least one of the following items according to the environment temperature data and the corresponding relation between the temperature and the wavelength of the tunable laser: the target intensity value, the wavelength of the emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal.
The grating in the fiber grating sensor can be one of or a combination of a phase shift grating, a chirped grating pair, a Fabry-Perot interference type grating fiber sensor, an overlapped grating or a partially overlapped grating, a cascade grating and a sampling fiber grating.
An acoustic emission detection method based on a fiber grating sensor comprises the following steps:
detecting an acoustic emission signal of the monitored object;
detecting reflected light of the fiber bragg grating sensor and converting the reflected light into an electric signal, wherein under the action of the acoustic emission signal, the central wavelength of the reflected light can be shifted;
judging whether the intensity of the reflected light is a target intensity value or not according to the electric signal;
if not, adjusting the intensity of the reflected light in the direction of the target intensity value, converting the reflected light into an electric signal, determining the central wavelength offset of the reflected light or the change of the intensity of the reflected light according to the electric signal, and determining the acoustic emission signal generated by the monitored object according to the corresponding relation between the central wavelength offset and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal.
Preferably, the method further comprises the following steps:
filtering out signals with the frequency higher than a preset frequency in the electric signals on a path of a negative feedback signal so as to adjust the wavelength of emergent light of the tunable laser;
adjusting at least one of the following items according to the corresponding relation between the intensity of the reflected light and the wavelength of the emergent light of the tunable laser: the target intensity value, the wavelength of emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal;
comparing the acoustic emission signals with reference data to obtain a health degree value of the monitored object, wherein the reference data comprises test data of the acoustic emission signals generated by the monitored object under different health degrees;
and judging whether the health degree value exceeds an early warning value, and if so, sending alarm information.
In the acoustic emission detection system and the acoustic emission detection method based on the fiber bragg grating sensor provided by the embodiment of the invention, the servo system can judge whether the intensity of the reflected light is the target intensity value according to the electric signal output by the photoelectric detection module, if not, the wavelength of the light emitted by the tunable laser is adjusted so that the intensity of the reflected light is adjusted towards the target intensity value, the electric signal output by the photoelectric detection module is transmitted to the demodulation module, the demodulation module determines the central wavelength offset of the reflected light or the intensity of the reflected light according to the electric signal, according to the method and the device, the acoustic emission signal generated by the monitored object is determined according to the central wavelength offset or the corresponding relation between the intensity of the reflected light and the acoustic emission signal, the wavelength of the tunable laser is adjusted by the servo system in the embodiment of the invention, so that the intensity of the reflected light is adjusted towards the direction of the target intensity value, and the detection sensitivity and the accuracy of the acoustic emission detection system are improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a conventional acoustic emission detection system based on a fiber grating sensor;
FIG. 2 is a schematic structural diagram of an acoustic emission detection system based on a fiber grating sensor according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of an acoustic emission detection system based on a fiber grating sensor according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a phase-shift grating in an acoustic emission detection system according to an embodiment of the present invention;
FIG. 5 is a reflection spectrum of a phase shift grating in an acoustic emission detection system according to an embodiment of the present invention;
fig. 6 is a flowchart of an acoustic emission detection method based on a fiber grating sensor according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments of the present invention are only a part of the embodiments of the present invention, and not all of the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides an acoustic emission detection system based on a fiber grating sensor, as shown in fig. 2, which comprises a tunable laser 21, a fiber grating sensor 22, a photoelectric detection module 23, a servo system 24, a filter 27 and a demodulation module 25.
The tunable laser 21 is a laser that can continuously change the output wavelength of laser light within a certain range. In the embodiment of the present invention, the tunable laser 21 is used to provide a light source for the fiber grating sensor 22, so that the incident light of the fiber grating sensor 22 is light with a specific wavelength.
The fiber grating sensor 22 is disposed inside or on the surface of the monitored object 20 for detecting acoustic emission signals generated by the monitored object 20. In which the center wavelength of the light reflected by the fiber grating sensor 22 is shifted by the acoustic emission signal generated by the monitored object 20.
The photo-detection module 23 is used for detecting the reflected light of the fiber grating sensor 22 and converting the reflected light signal into an electrical signal. The photo detection module 23 includes, but is not limited to, a photo detector.
The servo system 24 is configured to determine whether the intensity of the reflected light of the fiber grating sensor 22 is a target intensity value according to the electrical signal output by the photoelectric detection module 23, and if not, adjust the wavelength of the light emitted by the tunable laser 21 to adjust the intensity of the reflected light of the fiber grating sensor 22 in the direction of the target intensity value, and transmit the electrical signal output by the photoelectric detection module 23 to the demodulation module 25.
The demodulation module 25 is configured to determine a central wavelength offset of the reflected light of the fiber grating sensor 22 or an intensity of the reflected light according to the electrical signal output by the photoelectric detection module 23, and determine an acoustic emission signal generated by the monitored object 20 according to a correspondence between the central wavelength offset and the acoustic emission signal or a correspondence between the intensity of the reflected light and the acoustic emission signal.
The servo system 24 comprises at least one amplifier for adjusting the wavelength of the light emitted by the tunable laser 21 by controlling the input of the tunable laser 21 through a negative feedback signal. The servo system 24 controls the wavelength of the emergent light of the tunable laser 21 through primary negative feedback; the servo system 24 can also control the wavelength of the emergent light of the tunable laser 21 through secondary negative feedback or multiple times of negative feedback;
the filter 27 is located on a path of the negative feedback signal, and the filter 27 is used for filtering out a signal higher than a preset frequency so as to adjust the wavelength of emergent light of the tunable laser.
The filter 27 may be one or more, including but not limited to, a specific circuit or a non-circuit device or unit dedicated to performing the filtering function and separately installed in the signal path. The filter 27 may also have other functions. The filter 27 may be a whole or may be formed by circuit or non-circuit devices or units distributed in different parts of the path of the negative feedback signal, and the respective filter characteristics of these different devices or units may be different, so that when the filter characteristics are considered as a whole, the effect of filtering out signals above a predetermined frequency is achieved. The filtering out of the signal higher than the preset frequency does not mean to completely eliminate the signal of the corresponding frequency, but means to attenuate the signal intensity of the corresponding frequency band to a certain degree, which can be achieved by the technology in the art, so that the interference can be reduced compared with the case of no attenuation.
In this embodiment, the working process of the acoustic emission detection system is as follows: the fiber grating sensor 22 continuously reflects the light emitted by the tunable laser 21, once the monitored object 20 generates an acoustic emission signal, the central wavelength of the light reflected by the fiber grating sensor 22 shifts, the intensity of the reflected light changes, the fiber coupler 26 transmits the reflected light of the fiber grating sensor 22 to the photoelectric detection module 23 through another fiber, and the photoelectric detection module 23 converts the reflected light signal with the shifted central wavelength into an electrical signal and transmits the electrical signal to the servo system 24 and the demodulation module 25 after detecting the reflected light signal; the servo system 24 obtains the intensity of the reflected light of the fiber grating sensor 22 according to the intensity of the electrical signal, and judges whether the intensity of the reflected light is a target intensity value, if not, the control amplifier controls the input of the tunable laser 21 through a negative feedback signal to adjust the wavelength of the emitted light of the tunable laser 21, so that the intensity of the reflected light of the fiber grating sensor 22 is adjusted towards the direction of the target intensity value; the input to the tunable laser 21 may be a voltage or a current; the demodulation module 25 determines the variation of the electrical signal according to the electrical signal output by the photoelectric detection module 23, the variation of the electrical signal reflects the shift of the central wavelength of the grating reflected light or the variation of the intensity of the reflected light in the fiber grating sensor 22, and then determines the acoustic emission signal generated by the monitored object, which is reflected by the shift of the central wavelength or the variation of the intensity of the reflected light, according to the corresponding relationship between the shift of the central wavelength and the acoustic emission signal or the corresponding relationship between the variation of the intensity of the reflected light and the acoustic emission signal.
It can be known from the above technical solutions that, in the acoustic emission detection system based on the fiber grating sensor provided in the embodiment of the present invention, the servo system may determine whether the intensity of the reflected light is the target intensity value according to the electrical signal output by the photodetection module, if not, adjust the wavelength of the emitted light of the tunable laser, so as to adjust the intensity of the reflected light in the direction of the target intensity value, the electrical signal output by the photodetection module is transmitted to the demodulation module, the demodulation module determines the central wavelength offset of the reflected light or the intensity of the reflected light according to the electrical signal, and determines the acoustic emission signal generated by the monitored object according to the corresponding relationship between the central wavelength offset and the acoustic emission signal or between the intensity of the reflected light and the acoustic emission signal, in the embodiment of the present invention, the intensity of the reflected light is adjusted in the direction of the target intensity value by adjusting the wavelength of the tunable laser through the servo system, the sensitivity and the accuracy of the acoustic emission detection system for detecting the emitted light are improved.
In the acoustic emission detection system, an optical fiber coupler 26 is connected between the tunable laser 21 and the fiber grating sensor 22, as shown in fig. 2, wherein the connection relationship between the tunable laser 21, the fiber grating sensor 22, the optical fiber coupler 26 and the photoelectric detection module 23 is as follows:
the light-emitting end of the tunable laser 21 is connected to one end of an optical fiber, so that the light emitted from the tunable laser 21 can reach the fiber grating sensor 22 at the other end of the optical fiber through the optical fiber, the grating in the fiber grating sensor 22 can reflect the reflected light with a specific wavelength, and the fiber coupler 26 can divide the reflected light of the grating of the fiber grating sensor 22 into another optical fiber. The other optical fiber is provided with a photoelectric detection module 23, namely one end of the other optical fiber is connected with the optical fiber coupler 26, and the other end of the other optical fiber is connected with the photoelectric detection module 23. Furthermore, one end of the servo system 24 is connected to the photodetection module 23, the other end is connected to the input end of the tunable laser 21, and the demodulation module 25 is connected to the output end of the photodetection module 23.
It should be noted that the amplifier in the servo system 24 may be an operational amplifier, an instrumentation amplifier, or other amplifiers, and the embodiment of the present invention is not limited thereto. In addition, after the servo system 24 in this embodiment adjusts the wavelength of the tunable laser 21, the intensity of the reflected light of the fiber grating sensor 22 approaches the target intensity value, so that the photoelectric detection module 23 can detect the optical signal more sensitively, thereby improving the detection sensitivity of the acoustic emission detection system.
It should be further noted that the sensitivity of the fiber grating sensor 22 is closely related to the slope of the linear region of the slope of the grating reflection spectrum, and the larger the slope of the linear region of the slope of the reflection spectrum is, the larger the output light power jitter amplitude is, the higher the sensitivity of the fiber grating sensor 22 is. The grating in the fiber grating sensor 22 in this embodiment may be a phase-shift grating, the phase-shift grating includes a plurality of discontinuous structures with periodically varying refractive indexes, a reflection spectrum of the phase-shift grating is as shown in fig. 5, an abscissa W in fig. 5 represents a wavelength, an ordinate R represents a reflectivity, an extremely narrow recess is introduced in the middle of the reflection spectrum of the phase-shift grating, and a bandwidth of the recess is in picometer order. In a specific application, the reflected light λ of the fiber grating sensor 22 can be adjusted0Is locked on the slope a of the middle recess of the phase-shifted grating reflection spectrum to achieve high sensitivity of the fiber grating sensor 22. Each type of fiber grating sensor has different reflection spectrum characteristics, but all the fiber grating sensors have ideal working sections with larger slope of linear region of reflection spectrum slope similar to slope A in figure 5, and will reflect light lambda0Is locked within the desired operating range, which helps to achieve higher sensitivity.
The servo system 24 in this embodiment may adjust at least one of the following items according to the correspondence between the intensity of the reflected light and the wavelength of the light emitted from the tunable laser 21: the target intensity value, the wavelength of emergent light of the tunable laser 21 and the positive and negative polarities of the negative feedback signal. The servo system 24 can adjust the wavelength of the light emitted from the tunable laser 21 to obtain the intensity of the reflected light at different wavelengths of the light emitted from the tunable laser 21.
Under different conditions, for example, different temperatures, the wavelength of the light reflected by the fiber grating sensor 22 may be different for the same wavelength of incident light, and may deviate from the ideal operating range. According to the corresponding relation between the intensity of the reflected light and the wavelength of the emergent light of the tunable laser 21, the target intensity value is adjusted, and the tunable laser is obtainedOne or more of the wavelength of the light emitted from the optical device 21 and the positive and negative polarities of the negative feedback signal will contribute to the reflected light λ of the fiber grating sensor 220Is locked to a particular desired operating region. When the positive and negative polarities of the negative feedback signal are changed, a new negative feedback can be formed to make the reflected light lambda of the fiber grating sensor 220Is locked in the linear region of the reflection spectrum slope of opposite slope.
The correspondence between the intensity of the reflected light and the wavelength of the light emitted from the tunable laser 21 may be obtained by historical empirical values, or may be obtained by other methods. For example, the servo system 24 controls the wavelength of the outgoing light of the tunable laser 21 to change within a certain range, and the photodetection module 23 monitors the intensity of the reflected light of the fiber grating sensor 22, so that the intensity of the reflected light at different wavelengths of the outgoing light of the tunable laser 21, that is, the corresponding relationship between the wavelength of the tunable laser 21 and the intensity of the reflected light of the fiber grating sensor 22, can be obtained.
Based on some embodiments, as shown in fig. 3, the acoustic emission detection system in this embodiment may further include a control system 28 connected to the output of the demodulation module 25, wherein the control system 28 is configured to compare the acoustic emission signal demodulated by the demodulation module 25 with reference data to obtain the degree of health value of the monitored object 20, and the reference data includes test data of the acoustic emission signal generated by the monitored object 20 under different health degrees. In addition, the control system 28 may also be configured to determine whether the health degree value exceeds the warning value, and if so, start the warning system to prompt the monitor to maintain the monitored object 20, so as to avoid major accidents.
In addition, the acoustic emission detection system in this embodiment may further include a correction module, where the correction module is configured to correct the offset of the center wavelength according to the influence value of the environmental noise on the offset of the center wavelength of the reflected light of the fiber grating sensor 22, or correct the offset of the intensity of the reflected light according to the influence value of the environmental noise on the offset of the intensity of the reflected light of the fiber grating sensor 22, so as to improve the accuracy of the demodulated acoustic emission signal, and thus, the health degree value of the monitored object 20 can be better evaluated.
On the basis of some embodiments, the preset frequency is a × f, where f is the lowest frequency of the acoustic emission desired to be detected, and a is less than 1, 1/2, 1/4, 1/10, 1/100, or 1/1000, although the embodiment of the present invention is not limited thereto, and the value of a may be set according to practical situations.
On the basis of some embodiments, the acoustic emission detection system in the present embodiment comprises at least one temperature sensor for detecting ambient temperature data of the fiber grating sensor 22; the servo system 24 may adjust at least one of the following according to the ambient temperature data detected by the temperature sensor and the temperature versus wavelength correspondence of the tunable laser 21: the target intensity value, the wavelength of the light emitted by the tunable laser 21, and the positive and negative polarities of the negative feedback signal.
The use of tunable laser 21 emitting light of different wavelengths at different temperatures helps to lock the center wavelength of the reflected light from the fiber grating sensor 22 to a specific desired operating region. According to the corresponding relation between the temperature and the wavelength of the emergent light of the tunable laser 21, the target intensity value is adjusted, and one or more of the wavelength of the emergent light of the tunable laser 21 and the positive and negative polarities of the negative feedback signal are favorable for enabling the reflected light lambda of the fiber grating sensor 22 to be reflected0Is locked to a particular desired operating region.
The correspondence between the temperature and the wavelength of the light emitted from the tunable laser 21 may be obtained by historical empirical values, or may be obtained by other methods. For example, at a specific temperature, the servo system 24 controls the wavelength of the light emitted from the tunable laser 21 to change within a certain range, and the photodetection module 23 monitors the intensity of the light reflected by the fiber grating sensor 22, so as to measure the corresponding relationship between the specific temperature and the wavelength of the light emitted from the tunable laser 21.
In the embodiment of the present invention, the fiber grating sensor 22 is an acoustic emission sensor based on a fiber bragg grating, and the fiber bragg grating is a refractive index circumference which is generated in the fiber core and is arranged along the axial direction of the fiber coreThe periodically varying structure, as shown in FIG. 4, has a refractive index different between the darker part and the lighter part, and reflects only light λ with a specific wavelength0Light of other wavelengths will continue to propagate through the grating and along the fiber.
Since the acoustic emission signal is a mechanical wave, the mechanical wave causes a jitter of the fiber grating wavelength, i.e. the reflected light λ of the fiber grating sensor 22 is affected by the acoustic emission signal0The optical signal is detected by the photoelectric detection module 23 and converted into an electrical signal, and the corresponding acoustic emission signal is demodulated by the demodulation system 24 according to the electrical signal, so that the acoustic emission signal generated by the monitored object 20 can be obtained.
The sensitivity of the fiber grating sensor 22 is closely related to the slope of the linear region of the slope of the grating reflection spectrum, and the larger the slope of the linear region of the slope of the reflection spectrum is, the larger the output optical power jitter amplitude is, the higher the sensitivity of the fiber grating sensor 22 is. The grating in the fiber grating sensor 22 may be a phase-shift grating, the phase-shift grating includes a plurality of discontinuous structures with periodically varying refractive index, the reflection spectrum of the phase-shift grating is as shown in fig. 5, the abscissa W in fig. 5 represents wavelength, and the ordinate R represents reflectivity, an extremely narrow recess is introduced in the middle of the reflection spectrum of the phase-shift grating, and the bandwidth of the recess is in picometer order. In a specific application, the reflected light λ of the fiber grating sensor 22 can be adjusted0Is locked on the slope a of the middle recess of the phase-shifted grating reflection spectrum to achieve high sensitivity of the fiber grating sensor 22.
Of course, the present invention is not limited thereto, and the grating in the fiber grating sensor 22 in the present embodiment may be one or a combination of a phase-shifted grating (pi-FBG), a chirped grating (CFBG), a chirped grating pair (CFBG pairs), a Fabry-Perot type grating fiber sensor (Fabry-Perot), an overlapped grating or a partially overlapped grating (super-overlapped FBG), a cascaded grating (cascaded grated FBGs with/without spacing in between), and a sampled fiber grating (sampled grated FBGs).
The embodiment of the present invention further provides an acoustic emission detection method based on a fiber grating sensor, which is applied to the acoustic emission detection system based on the fiber grating sensor provided in any of the above embodiments, as shown in fig. 6, and includes:
s601: detecting an acoustic emission signal of a monitored object by a fiber grating sensor, wherein under the action of the acoustic emission signal, the central wavelength of reflected light of the fiber grating sensor can be shifted.
S602: and detecting the reflected light of the fiber bragg grating sensor through a photoelectric detection module, and converting the reflected light into an electric signal.
S603: and judging whether the intensity of the reflected light is a target intensity value or not through a servo system according to the electric signal, and if not, entering S604.
S604: and adjusting the wavelength of emergent light of the tunable laser so as to adjust the intensity of the reflected light to the direction of the target intensity value.
S605: and determining the central wavelength offset of the reflected light or the intensity of the reflected light through a demodulation module according to the electric signal, and determining the acoustic emission signal generated by the monitored object according to the corresponding relation between the central wavelength offset and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal.
In the working process of the acoustic emission detection system, the fiber grating sensor can continuously reflect light with a specific wavelength in emergent light of the tunable laser, once an acoustic emission signal is generated by a monitored object, the central wavelength of the light reflected by the fiber grating sensor can shift, the fiber coupler transmits reflected light of the fiber grating sensor to the photoelectric detection module through optical fibers, and the photoelectric detection module converts the reflected light signal after the central wavelength shifts into an electric signal and transmits the electric signal to the servo system and the demodulation module after detecting the reflected light signal;
the servo system obtains the intensity of the reflected light of the fiber grating sensor according to the intensity of the electric signal, judges whether the intensity of the reflected light is a target intensity value, and if not, controls the amplifier to control the input (input voltage or input current) of the tunable laser through a negative feedback signal to adjust the wavelength of the emergent light of the tunable laser so as to adjust the intensity of the reflected light of the fiber grating sensor to the direction of the target intensity value;
the demodulation module compares the electric signal output by the photoelectric detection module with a standard electric signal to obtain the variation of the electric signal, determines the offset of the central wavelength of the grating reflected light in the fiber grating sensor or the intensity of the reflected light according to the variation of the electric signal, and then determines the acoustic emission signal generated by the monitored object according to the corresponding relation between the offset of the central wavelength and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal.
From the above technical solutions, the acoustic emission detection method based on the fiber grating sensor provided in the embodiments of the present invention, the servo system can judge whether the intensity of the reflected light is the target intensity value according to the electric signal output by the photoelectric detection module, if not, the wavelength of the emergent light of the tunable laser is adjusted so that the intensity of the reflected light is adjusted towards the direction of the target intensity value, the electric signal output by the photoelectric detection module is transmitted to the demodulation module, determining the central wavelength offset of the reflected light or the intensity of the reflected light by a demodulation module according to the electrical signal, and determining the acoustic emission signal generated by the monitored object according to the corresponding relation between the central wavelength offset and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal.
In addition, the acoustic emission detection method in the present embodiment further includes: and comparing the acoustic emission signals with reference data through a control system to obtain the health degree value of the monitored object, wherein the reference data comprises test data of the acoustic emission signals generated by the monitored object under different health degrees.
Further, the acoustic emission detection method in this embodiment further includes: and judging whether the health degree value exceeds the early warning value through the control system, if so, starting the alarm system to send alarm information to prompt a monitor to maintain the monitored object, and avoiding major accidents.
In addition, the acoustic emission detection method in this embodiment may further include: correcting the offset of the central wavelength according to the influence value of environmental noise on the offset of the central wavelength of the reflected light of the fiber grating sensor or correcting the offset of the intensity of the reflected light according to the influence value of the environmental noise on the offset of the intensity of the reflected light of the fiber grating sensor by a correction module; the accuracy of the demodulated acoustic emission signals is improved, and therefore the health degree value of the monitored object can be better evaluated.
Further, when the acoustic emission detection system further includes at least one temperature sensor, the acoustic emission detection method in this embodiment may further include: the temperature sensor detects the environmental temperature data of the fiber bragg grating sensor; the servo system adjusts at least one of the following items according to the environment temperature data detected by the temperature sensor and the corresponding relation between the temperature and the wavelength of the tunable laser: the target intensity value, the wavelength of the emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal.
The same and similar parts in the various embodiments of the present specification may be referred to each other. Some devices and some methods disclosed for the embodiments correspond to each other and can be referred to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. An acoustic emission detection system based on a fiber grating sensor is characterized by comprising a tunable laser, the fiber grating sensor, a photoelectric detection module, a demodulation module, a filter and a servo system;
the tunable laser is used for providing a light source for the fiber grating sensor, so that the incident light of the fiber grating sensor is the light with a specific wavelength in the light source;
the fiber grating sensor is used for detecting an acoustic emission signal of a monitored object, wherein the central wavelength of reflected light of the fiber grating sensor can deviate under the action of the acoustic emission signal generated by the monitored object;
the photoelectric detection module is used for detecting the reflected light of the fiber bragg grating sensor and converting the reflected light into an electric signal;
the servo system is used for judging whether the intensity of the reflected light is a target intensity value according to the electric signal, if not, the wavelength of the emergent light of the tunable laser is adjusted to enable the intensity of the reflected light to be adjusted towards the direction of the target intensity value, and therefore the central wavelength of the reflected light falls into an ideal working section, wherein the ideal working section is a section with a larger slope of a linear region of a reflection spectrum slope;
the electric signal output by the photoelectric detection module is transmitted to the demodulation module;
the demodulation module is used for determining the central wavelength offset of the reflected light or the intensity of the reflected light according to the electric signal and determining the acoustic emission signal generated by the monitored object according to the corresponding relation between the central wavelength offset and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal;
the servo system comprises at least one amplifier, and the amplifier is used for controlling the input of the tunable laser through a negative feedback signal to adjust the wavelength of emergent light of the tunable laser;
the filter is positioned on a path of the negative feedback signal and is used for filtering out signals with the frequency higher than a preset frequency in the electric signals so as to adjust the wavelength of emergent light of the tunable laser;
the servo system is used for adjusting at least one of the following items according to the corresponding relation between the intensity of the reflected light and the wavelength of the emergent light of the tunable laser: the target intensity value, the wavelength of emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal.
2. The inspection system of claim 1 further comprising a control system for comparing the acoustic emission signals to reference data to obtain a health metric for the monitored object, the reference data including test data for acoustic emission signals generated by the monitored object at different levels of health.
3. The detection system according to claim 1, wherein the servo system is configured to obtain the intensity of the reflected light at different wavelengths of the emitted light from the tunable laser by adjusting the wavelength of the emitted light from the tunable laser.
4. The detection system of claim 1, further comprising at least one temperature sensor;
the temperature sensor is used for detecting the environmental temperature data of the fiber bragg grating sensor;
the servo system is used for adjusting at least one of the following items according to the environment temperature data and the corresponding relation between the temperature and the wavelength of the tunable laser: the target intensity value, the wavelength of the emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal.
5. The detection system according to claim 1, wherein the grating in the fiber grating sensor is one or a combination of a phase-shift grating, a chirped grating, a fabry-perot interference type grating fiber sensor, an overlapped grating, a cascade grating, and a sampling fiber grating.
6. An acoustic emission detection method based on a fiber grating sensor, which is applicable to the acoustic emission detection system based on the fiber grating sensor as claimed in any one of claims 1 to 5, the method comprises:
detecting an acoustic emission signal of the monitored object;
detecting reflected light of the fiber bragg grating sensor and converting the reflected light into an electric signal, wherein under the action of the acoustic emission signal, the central wavelength of the reflected light can be shifted;
judging whether the intensity of the reflected light is a target intensity value or not according to the electric signal;
if not, adjusting the intensity of the reflected light so as to adjust the intensity of the reflected light to the direction of the target intensity value, so that the central wavelength of the reflected light falls into an ideal working section, wherein the ideal working section is a section with a larger slope of a linear region of a reflection spectrum slope;
filtering out signals with the frequency higher than a preset frequency in the electric signals on a path of a negative feedback signal so as to adjust the wavelength of emergent light of the tunable laser; determining the central wavelength offset of the reflected light or the intensity of the reflected light according to the electric signal, and determining an acoustic emission signal generated by the monitored object according to the corresponding relation between the central wavelength offset and the acoustic emission signal or the corresponding relation between the intensity of the reflected light and the acoustic emission signal;
judging whether the intensity of the reflected light is a target intensity value or not according to the electric signal; if not, adjusting the intensity of the reflected light so that the intensity of the reflected light is adjusted towards the direction of the target intensity value comprises: adjusting at least one of the following items according to the corresponding relation between the intensity of the reflected light and the wavelength of the emergent light of the tunable laser: the target intensity value, the wavelength of emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal.
7. The method of claim 6, further comprising:
adjusting at least one of the following items according to the corresponding relation between the intensity of the reflected light and the wavelength of the emergent light of the tunable laser: the target intensity value, the wavelength of emergent light of the tunable laser and the positive and negative polarities of the negative feedback signal;
and comparing the acoustic emission signals with reference data to obtain the health degree value of the monitored object, wherein the reference data comprises test data of the acoustic emission signals generated by the monitored object under different health degrees.
8. The method of claim 7, further comprising:
and judging whether the health degree value exceeds an early warning value, and if so, sending alarm information.
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