CN114252141A - Double-parameter detection digital sensing system and method based on optical fiber beat frequency technology - Google Patents
Double-parameter detection digital sensing system and method based on optical fiber beat frequency technology Download PDFInfo
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
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Abstract
The invention discloses a double-parameter detection digital sensing system and method based on an optical fiber beat frequency technology, and belongs to the technical field of information transmission. The system comprises: the device comprises a laser, a wavelength division multiplexer, a fiber laser resonant cavity, a vibration exciter control module, a photoelectric detector, data acquisition equipment and signal monitoring equipment; the invention realizes the measurement of double parameters by adopting different beat frequency signals with different sensitivity degrees to vibration and temperature, measures the low-frequency vibration by adopting the beat frequency of a polarization mode and measures the temperature information by adopting the beat frequency signal of a longitudinal mode, solves the problems that the traditional sensor can not detect the vibration signal below 1Hz and can not realize the measurement of double parameters, achieves the effect that the lowest detectable frequency is 0.25Hz and realizes the measurement of double parameters of vibration and temperature, and has the advantages of simple structure, high signal-to-noise ratio, high measurement precision, good stability and the like.
Description
Technical Field
The invention relates to a double-parameter detection digital sensing system and method based on an optical fiber beat frequency technology, and belongs to the technical field of information transmission.
Background
Vibration signal detection has been widely used in the fields of civil engineering, industrial engineering, engineering machinery, aerospace and the like. For applications such as seismic wave field monitoring, pipeline transmission, optical fiber hydrophones and the like, the low-frequency weak-energy vibration detection capability is very important due to the fact that the vibration frequency is low from Hz to sub-Hz and the energy is relatively weak. In addition, temperature variation is also an important factor for monitoring the engineering machinery, and is closely related to equipment failure. Therefore, the development of a high performance vibration sensor system with temperature detection and anti-electromagnetic interference capability, especially low frequency or weak energy vibration detection capable of operating in harsh environments, is very important to meet the requirements of the industry.
Compared with an electric sensor, the optical fiber vibration sensor has the inherent advantages of reliable operation, high precision, high sensitivity, strong anti-interference capability in severe environment and the like. Optical fiber vibration sensors are mainly of five types: Mach-Zehnder interferometers, Michelson interferometers, Fabry-perot (fp) cavity interferometers, Fiber Bragg Gratings (FBGs), Optical Frequency Domain Reflections (OFDRs), Optical Time Domain Reflections (OTDRs), and fiber lasers.
The optical fiber vibration sensor designed by a Mach-Zehnder interferometer by a scholars eliminates phase constraint in digital phase demodulation, enlarges the vibration detection range, and has the minimum detectable vibration frequency of 10 Hz. The researchers proposed a dynamic signal detection sensor based on a fiber-optics double-ring Michelson interferometer, which has good sensitivity to weak acoustic waves but has a minimum detectable vibration frequency of 500Hz, and studied a short kagomie hollow photonic crystal fiber all-fiber temperature insensitive vibration sensor based on an F-P interferometer, which has a minimum detectable vibration frequency of 1 Hz. In addition, the scholars have proposed a fiber grating sensor with pendulum structure, which uses wavelet transform method to avoid cross sensitivity of tilt and acceleration and realize the measurement of two parameters of tilt and acceleration, however, the sensor can only work under 32 Hz. The researchers have proposed a distributed vibration sensor based on OFDR and cross-correlation algorithms, which, although the accuracy is improved, has a minimum detectable frequency of 5 kHz. It has also been proposed by the authors that vibration and temperature measurements can be made by a polarized optical time domain reflectometer (P-OTDR) and a Raman Optical Time Domain Reflectometer (ROTDR), respectively. The uncertainty of the temperature measurement is 0.57 ℃, the vibration measurement at the minimum detection frequency is 100Hz, and there is cross sensitivity of temperature and vibration.
Compared with the complex optical demodulation method, the multi-longitudinal mode fiber laser sensor system has the advantages of simple structure, high sensitivity and low cost, and is widely accepted. By monitoring the frequency change of the beat signal rather than the wavelength shift of the laser, a very high sensing sensitivity can be observed.
The multi-longitudinal mode fiber laser sensor system based on the beat frequency sensing technology can demodulate parameters such as tension, pressure, temperature, vibration and the like by detecting the change of the beat frequency, such as Y.Guo, X.W.Mao, S.L.Song, Y.Ni, H.D.Wu, and X.F.Chen.Multi-longitudinal mode fiber laser digital demodulation-sensing system based on a multi-carrier modulation/modulation technique [ J ]. Optical Express,2020,28(21):31808 and 31820 disclose a multi-longitudinal mode fiber laser sensor system based on the digital vibration demodulation technology, which is composed of a laser, a wavelength division multiplexer, a fiber laser resonant cavity, a vibration exciter control module, a photoelectric detector and a general software radio. The system only realizes the measurement of single parameter, limits the application range, and monitors the vibration capability and the temperature change of the engineering machinery detection.
Disclosure of Invention
In order to solve the problems that the existing sensor cannot detect vibration signals below 1Hz and cannot realize double-parameter measurement, the invention provides a double-parameter detection digital sensing system and method based on an optical fiber beat frequency technology.
A first object of the present invention is to provide a two-parameter detection digital sensing system based on fiber beat frequency technology, said system comprising: the device comprises a laser, a wavelength division multiplexer, a fiber laser resonant cavity, a vibration exciter control module, a photoelectric detector, data acquisition equipment and signal monitoring equipment;
the laser, the wavelength division multiplexer, the optical fiber laser resonant cavity, the vibration exciter and the vibration exciter control module are sequentially connected; one end of the photoelectric detector is sequentially connected with the data acquisition equipment and the signal monitoring equipment, and the other end of the photoelectric detector is connected with one end of the wavelength division multiplexer connected with the laser;
the laser is used for generating laser, and the laser enters the fiber laser resonant cavity through the wavelength division multiplexer to generate resonance so as to generate multi-longitudinal-mode laser and polarization-mode laser;
the fiber laser resonator comprises: the temperature detection sensing element and the vibration detection sensing element are used for generating beat frequency signals with temperature and vibration sensing information;
the vibration exciter is controlled by the vibration exciter control module and is used for generating a vibration signal;
the photoelectric detector is used for performing photoelectric conversion on the multi-longitudinal-mode laser and the polarization-mode laser generated by the fiber laser resonant cavity and generating a plurality of beat frequency signals with sensing information, and comprises: longitudinal mode beat frequency signals and polarization mode beat frequency signals;
the data acquisition equipment is used for acquiring beat frequency signals output by the photoelectric detector; the signal monitoring equipment is used for signal monitoring and data processing.
Optionally, the fiber laser resonator includes: the fiber grating is used as a frequency-selective fiber grating, a rare earth-doped fiber, and a vibration sensing fiber grating;
one end of the fiber grating used for frequency selection is connected with the wavelength division multiplexer, the frequency of an optical signal output by the wavelength division multiplexer is selected, and the other end of the fiber grating used for vibration sensing is sequentially connected with the rare earth doped fiber and the fiber grating used for vibration sensing;
the rare earth doped optical fiber is the temperature detection sensing element, and the fiber bragg grating for vibration sensing is placed on the vibration exciter and is the vibration detection sensing element.
Optionally, the exciter control module comprises: a signal generator and a power amplifier; the signal generator, the power amplifier and the vibration exciter are connected in sequence.
Optionally, the data acquisition device includes a spectrum analyzer and a general software radio peripheral, and is configured to acquire a beat signal modulated with vibration sensing information and a beat signal modulated with temperature sensing information.
Optionally, the signal monitoring device is a computer, and a process of processing signal data by the computer includes:
and denoising the time-frequency signal of the polarization mode beat frequency modulated with the vibration sensing information, converting the time-domain signal subjected to denoising into a frequency-domain signal, and demodulating to obtain the vibration frequency.
Optionally, the rare earth doped fiber is an erbium-doped fiber.
The second objective of the present invention is to provide a double-parameter detection digital sensing method based on the fiber beat frequency technology, which is implemented based on the above double-parameter detection digital sensing system based on the fiber beat frequency technology, and includes:
s1: the laser generates laser light;
s2: the wavelength division multiplexer transmits laser to a fiber laser resonant cavity, resonance occurs in the fiber laser resonant cavity, and longitudinal mode laser and polarization mode laser are generated;
s3: the temperature signal acts on the temperature detection sensing element and modulates the optical signal in the fiber laser resonant cavity, and the vibration signal acts on the vibration detection sensing element and modulates the optical signal in the fiber laser resonant cavity;
s4: the modulated optical signal is reflected back to the wavelength division multiplexer and enters the photoelectric detector, and a plurality of beat frequency signals for modulating temperature or vibration are generated on the photoelectric detector;
s5: transmitting the longitudinal mode beat frequency signal modulated with the temperature sensing information and the polarization mode beat frequency signal modulated with the vibration sensing information to the data acquisition equipment;
s6: and the signal monitoring equipment is used for carrying out signal monitoring and data processing on the beat frequency signals acquired by the data acquisition equipment.
Optionally, the data acquisition process includes: the method comprises the steps of adopting a radio frequency spectrum analyzer and a general software radio peripheral to collect beat frequency signals modulated with vibration sensing information, and collecting beat frequency signals modulated with temperature sensing information by the radio frequency spectrum analyzer.
Optionally, the process of processing data by the signal monitoring device includes:
and denoising the time-frequency signal which is acquired by the radio frequency spectrometer and is modulated with the polarization mode beat frequency of the vibration sensing information, converting the time-domain signal subjected to denoising into a frequency-domain signal, and demodulating to obtain the corresponding vibration frequency.
Optionally, the noise reduction method includes: and (3) a variational modal decomposition method.
The invention has the beneficial effects that:
the double-parameter detection digital sensing system and the method based on the optical fiber beat frequency technology realize the measurement of double parameters by utilizing different sensitivity degrees of different beat frequency signals to vibration and temperature, namely measuring low-frequency vibration by using polarization mode beat frequency and measuring temperature information by using longitudinal mode beat frequency signals, thereby solving the problem that the traditional sensing system cannot realize the measurement of the double parameters of vibration and temperature; the invention can adopt a time-frequency module of a frequency spectrograph to collect vibration signals of polarization mode beat frequency, and utilizes a variation mode to demodulate and reduce noise, thereby realizing the detection of the vibration frequency of 0.25Hz at the lowest and solving the problem that the current sensor can not detect the vibration signals below 1 Hz; in addition, the sensing system of the invention also has the advantages of simple structure, high signal-to-noise ratio, high measurement precision, good stability and the like.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic diagram of a two-parameter digital sensing system based on fiber beat frequency technology in a preferred embodiment of the present invention.
FIG. 2 is a schematic diagram of the structure of the fiber laser resonator for generating polarization mode beat frequency and longitudinal mode beat frequency according to the preferred embodiment of the present invention.
FIG. 3 is a schematic diagram of demodulation of a time-frequency signal based on polarization mode beat frequency vibration in the preferred embodiment of the present invention.
Fig. 4 is a schematic diagram of detecting a vibration signal for a polarization mode beat frequency in a preferred embodiment of the present invention, where a (a) is an actually acquired time-frequency signal diagram, a (B) is a time-frequency signal diagram after noise reduction, and B is an actually demodulated frequency signal diagram.
Fig. 5 is a diagram illustrating the variation of the beat frequency of different polarization modes and the amplitude of the same vibration signal.
Fig. 6 is a schematic diagram of a demodulation frequency of a vibration signal in a preferred embodiment of the present invention, where a is a vibration frequency acquired and demodulated by using a time-frequency module of a frequency spectrometer, and B is a vibration frequency acquired and demodulated by using a software-based radio peripheral.
Fig. 7 is a graph of the demodulation results for a 0.25Hz to 5000Hz dynamic signal in a preferred embodiment of the invention.
FIG. 8 is a schematic diagram of the change of the beat frequency of the longitudinal mode when different vibration signals are applied in the preferred embodiment of the present invention.
FIG. 9 is a schematic diagram of the variation of the beat frequency of the longitudinal mode at different temperatures in the preferred embodiment of the present invention.
FIG. 10 is a schematic diagram of time-frequency and demodulation frequency of the change of the beat frequency of the polarization mode when the temperature of the same vibration signal changes.
Fig. 11 is a schematic diagram of signal demodulation stability in a preferred embodiment of the present invention.
Description of the labeling: 1-a laser; 2-wavelength division multiplexer; 3-fiber laser resonator; 31-fiber grating; 32-rare earth doped fiber; 33-fiber grating; 4-a vibration exciter; 5-a power amplifier; 6-a signal generator; 7-a photodetector; 8-a data acquisition device; 9-computer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The first embodiment is as follows:
the embodiment provides a dual-parameter detection digital sensing system based on an optical fiber beat frequency technology, which comprises: the device comprises a laser, a wavelength division multiplexer, a fiber laser resonant cavity, a vibration exciter control module, a photoelectric detector, data acquisition equipment and signal monitoring equipment;
the laser, the wavelength division multiplexer, the optical fiber laser resonant cavity, the vibration exciter and the vibration exciter control module are sequentially connected; one end of the photoelectric detector is sequentially connected with the data acquisition equipment and the signal monitoring equipment, and the other end of the photoelectric detector is connected with one end of the wavelength division multiplexer connected with the laser;
the laser is used for generating laser, and the laser enters the fiber laser resonant cavity through the wavelength division multiplexer to generate resonance so as to generate multi-longitudinal-mode laser and polarization-mode laser;
the fiber laser resonator comprises: the temperature detection sensing element and the vibration detection sensing element are used for generating beat frequency signals with temperature and vibration sensing information;
the vibration exciter is controlled by the vibration exciter control module and is used for generating a vibration signal;
the photoelectric detector is used for performing photoelectric conversion on the multi-longitudinal-mode laser and the polarization-mode laser generated by the fiber laser resonant cavity and generating a plurality of beat frequency signals with sensing information, and comprises: longitudinal mode beat frequency signals and polarization mode beat frequency signals;
the data acquisition equipment is used for acquiring beat frequency signals output by the photoelectric detector; the signal monitoring equipment is used for signal monitoring and data processing.
Example two:
the present embodiment provides a dual-parameter detection digital sensing system based on fiber beat frequency technology, referring to fig. 1, the system includes:
laser instrument 1, wavelength division multiplexer 2, fiber laser resonant cavity 3, vibration exciter 4, power amplifier 5, signal generator 6, photoelectric detector 7, data acquisition equipment 8, computer 9, fiber laser resonant cavity 3 includes rare earth doping optic fibre 32 and central wavelength assorted fiber grating 31 and fiber grating 33, fiber grating 31 and fiber grating 33 pass through rare earth doping optic fibre 32 and connect, fiber grating 33 is arranged in on the vibration exciter 4 by signal generator 6 and power amplifier 5 control, refer to fig. 2, and wherein, rare earth doping optic fibre 32 is the sensing element of temperature detection, and fiber grating 33 is the sensing element of vibration detection, and fiber grating 31 plays the frequency-selecting function.
The laser 1 is used for generating laser, the laser enters the fiber laser resonant cavity 3 through the wavelength division multiplexer 2, and resonates in the fiber laser resonant cavity to generate multi-longitudinal mode and polarization mode laser. In this embodiment, the rare-earth doped fiber 32 in the resonant cavity is not heated, and only the vibration signal is applied to the fiber grating 33 in the resonant cavity. The fiber grating 33 at the end of the laser resonator is placed on the vibration exciter 4 controlled by the signal generator 6 and the power amplifier 5 as a vibration sensor. Multi-longitudinal mode and polarization mode lasers are generated in the laser cavity. Photoelectric signal conversion is carried out on the photoelectric detector 7, and a plurality of beat frequency signals with sensing information are generated, wherein the beat frequency signals comprise longitudinal mode beat frequency signals and polarization mode beat frequency signals. And (3) enabling the polarization mode beat frequency signal with the vibration sensing information to reach the data acquisition equipment 8, including a radio frequency spectrum analyzer or a general software radio peripheral, and carrying out signal monitoring and data processing by using a computer 9.
In this embodiment, the laser 1 outputs laser with a wavelength of 1480nm, the laser enters the fiber laser resonator 3 through the wavelength division multiplexer 2 with a wavelength of 1480nm &1550nm, and the fiber laser resonator 3 generates multi-longitudinal mode laser and polarization mode laser, and meanwhile, the rare earth doped fiber 32 is a sensing element for temperature detection, the fiber grating 33 is a sensing element for vibration detection, and the fiber grating 31 plays a role in frequency selection.
In practical applications, the laser 1 and the wavelength division multiplexer 2 may also use other parameters, such as a pump source with a wavelength of 980nm, a wavelength division multiplexer with a wavelength of 980nm &1550nm, etc. The fiber laser cavity 3 may also use other parameter devices, such as a faraday mirror instead of another fiber grating as a vibration sensing element, or other array structures capable of generating multi-longitudinal mode laser, such as frequency division multiplexing, wavelength division multiplexing, etc., which are not limited in this application.
In the present embodiment, the fiber gratings 31 and 33 are two fiber gratings (FBGs) with center wavelengths matched and a reflectivity of about 93%, wherein the FBG center wavelength and the 3dB bandwidth are 1549.753nm, 1549.769nm, 0.242nm and 0.229nm, respectively; an erbium doped fiber with a length of 0.8m and an absorption coefficient of 37.8dB/m at 1532 nm.
In practical application, the FBG may use other parameters according to requirements, such as a 1552nm or 1554nm FBG, the erbium-doped fiber may also use other absorption coefficients with different lengths, such as a length of 5m and an absorption coefficient of 13dB/m at 1532nm, parameters of components in the fiber laser resonator are not specifically required, as long as a polarization mode beat frequency and a multi-longitudinal mode beat frequency can be formed in the resonator, and other rare earth-doped fibers with a gain amplification effect are also suitable, such as the ytterbium-doped fiber.
The data acquisition device 8 of the embodiment includes a radio frequency spectrum analyzer and a general software radio peripheral, and other devices for data acquisition may also be used, such as a data acquisition card based on a Labview platform.
In the embodiment, the variation mode method is adopted to perform noise reduction and demodulation to obtain the vibration signal, and other methods for noise reduction and demodulation, such as Empirical Mode Decomposition (EMD), may also be applicable.
Different sensing parts of the fiber laser resonant cavity 3 can realize the measurement of different parameters.
In this embodiment, the process of processing the demodulation result of detecting the vibration signal by using the fiber grating 33 is as follows:
a laser with multiple longitudinal modes is generated in the laser cavity. The wavelength of which can be expressed as
Where n is the effective index of refraction in the cavity, L is the effective cavity length of the entire laser, and m represents the number of modes of the laser.
The fiber grating 33 sensor for vibration sensing, the reflection wavelength of which can be expressed as:
λB＝2neffΛ
wherein λ isBIs a Bragg wavelength of neffThe effective refractive index of the fiber grating, Λ is the grating period. Because the fiber bragg grating is a part of the cavity of the fiber laser sensor, only the laser mode reflected by the FBG sensor can be transmitted in the fiber laser cavity, and the laser mode of the fiber laser cavity is also the laser mode reflected by the FBG sensor. Therefore, the temperature of the molten metal is controlled,
λB＝λm
when an external strain is applied to the fiber grating, the wavelength variation of the fiber grating can be expressed as:
ΔλB＝2neff×ΔΛ
where Δ Λ represents the change in grating period, proportional to the external strain. Therefore, the temperature of the molten metal is controlled,
ΔλB＝Kεε
wherein, Δ λBAnd KεThe grating center wavelength displacement and the strain sensing coefficient are respectively, and the formula shows that the total strain of the strain sensor is in direct proportion to the change of the FBG center wavelength. When a vibration signal is applied, the dynamic microstrain caused by the vibration signal can be expressed as:
ε＝Ad cos(2πfdt)
in the formula, AdAmplitude of dynamic microstrain, fdIs the frequency of the vibration signal. The frequency of the beat signal is:
n is the serial number of the beat signal, and c is the speed of light. In combination with the above formula, one can obtain:
when the FBG sensor is subjected to dynamic micro-strain, the corresponding reflection wavelength of the FBG changes, and the frequency of the beat frequency signal is as follows:
the formula is introduced and simplified to obtain:
from the above equation, it can be seen that the frequency variation of the beat signal is related to the dynamic microstrain of the application. Since the frequency variation of the beat signal is related to the wavelength variation of the FBG sensor, the sensing system can detect the dynamic micro-strain.
In the demodulation, the vibration signal is denoised and demodulated by the method of fig. 3. In the present embodiment, a polarization mode beat frequency of 122.4MHz is used to measure a 0.25Hz vibration signal applied to the exciter 4, which is generated by the signal generator 6 and amplified by the power amplifier 5, and the noise reduction decomposition is performed by the variation modal decomposition, which can be referred to fig. 3. It should be noted that, in practical applications, polarization mode beats of other frequencies can be used for vibration detection.
Fig. 4 is a schematic diagram of detecting a 0.25Hz vibration signal for a beat frequency of a 122.4MHz polarization mode in an embodiment, where fig. 4a (a) is a time-frequency signal actually acquired, fig. 4a (B) is a time-frequency diagram after noise reduction, and fig. 4B is a vibration frequency actually demodulated.
Fig. 5 is a schematic diagram showing the relationship between the beat frequency of different polarization modes and the amplitude of the same vibration signal.
In this embodiment, the vibration frequency obtained by demodulating the vibration signal collected by the radio frequency spectrum analyzer is shown in fig. 6A, and it can be seen that the system provided in this embodiment can measure the vibration signal by using the polarization mode beat signal, and the lowest detected vibration frequency is 0.25 Hz. In addition, the vibration frequency obtained by demodulating the vibration signal acquired by the general software radio peripheral is shown in fig. 6B, and it can be seen that the system provided by the embodiment can realize not only low-frequency vibration but also high-frequency vibration.
Fig. 7 shows the accuracy result of demodulating the dynamic signal of 0.25Hz to 5000Hz by using the system of the present invention, and it can be seen that the lowest resolution of the system in this embodiment to the frequency can reach 0.25Hz, that is, the lowest signal frequency capable of being demodulated is 0.25Hz, which has very high accuracy.
In addition, fig. 8 shows the variation of the multi-longitudinal mode beat frequency when the vibration frequency varies from 0.25Hz to 5000Hz, and it can be seen that the multi-longitudinal mode beat frequency does not vary significantly, which indicates that the longitudinal mode signal is not sensitive to the vibration signal. It should be noted that, when the frequency of the actual vibration device is not limited, the detection range can be further expanded by using the method.
Example three:
in this embodiment, on the basis of the second embodiment, when the vibration signal is not applied to the resonator, and only the rare-earth doped fiber 32 in the resonator is heated, the temperature changes from 0 to 80 ℃, the measurement is performed by the platinum resistor, and the longitudinal mode beat frequency is selected to be 1102.373MHz, and the longitudinal mode beat frequencies of other frequencies can also be used for detecting the temperature. And (3) sending the longitudinal mode beat frequency signal with the temperature sensing information to the data acquisition equipment 8, which comprises a radio frequency spectrum analyzer or a general software radio peripheral, and carrying out signal monitoring and data processing by using a computer 9. The variation of the longitudinal mode beat frequency with temperature in this embodiment is schematically shown in fig. 9, which illustrates that the longitudinal mode signal insensitive to the vibration signal can be used for temperature detection.
Example four:
in the embodiment, on the basis of the second embodiment, vibration measurement in different temperature environments is realized. A 1Hz vibration signal is applied to the fiber grating 33 in the resonant cavity while the erbium doped fiber 32 in the resonant cavity is heated to a temperature varying from 0 to 80 c. Because the polarization mode beat frequency is more sensitive to the vibration signal, the polarization mode beat frequency signal can be used for realizing the detection of vibration, and the longitudinal mode beat frequency signal can be used for realizing the detection of temperature. The vibration signals detected at different temperatures are shown in fig. 10A, and the vibration signals demodulated at different ambient temperatures can be seen from fig. 10B. It can be seen that the change in temperature does not affect the detection of the vibration signal.
When the temperature is kept constant, an experiment is carried out on the demodulation stability of the dynamic signal with the vibration frequency of 1Hz, in the experiment, the result is tested every 5 minutes within 100 minutes, as shown in FIG. 11, the highest offset is only 0.00036Hz, and the performance of the vibration sensor system is stable.
It can be seen from the above embodiments that the polarization mode beat frequency is suitable for vibration testing, and vibration demodulation is not affected by external temperature. The multi-longitudinal-mode beat frequency has good temperature sensing performance and is not influenced by external vibration, so that a vibration and temperature dual-parameter sensing system is realized, and the precision and the sensitivity are high and do not interfere with each other.
Example five:
the embodiment provides a method for double-parameter detection digital sensing based on an optical fiber beat frequency technology, which is implemented based on a double-parameter detection digital sensing system based on the optical fiber beat frequency technology in the first embodiment, and includes:
s1: the laser generates laser light;
s2: the wavelength division multiplexer transmits laser to a fiber laser resonant cavity, resonance occurs in the fiber laser resonant cavity, and longitudinal mode laser and polarization mode laser are generated;
s3: the temperature signal acts on the temperature detection sensing element and modulates the optical signal in the fiber laser resonant cavity, and the vibration signal acts on the vibration detection sensing element and modulates the optical signal in the fiber laser resonant cavity;
s4: the modulated optical signal is reflected back to the wavelength division multiplexer and enters the photoelectric detector, and a plurality of beat frequency signals for modulating temperature or vibration are generated on the photoelectric detector;
s5: transmitting the longitudinal mode beat frequency signal modulated with the temperature sensing information and the polarization mode beat frequency signal modulated with the vibration sensing information to the data acquisition equipment;
s6: and the signal monitoring equipment is used for carrying out signal monitoring and data processing on the beat frequency signals acquired by the data acquisition equipment.
Some steps in the embodiments of the present invention may be implemented by software, and the corresponding software program may be stored in a readable storage medium, such as an optical disc or a hard disk.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A two-parameter detection digital sensing system based on fiber beat frequency technology, the system comprising: the device comprises a laser, a wavelength division multiplexer, a fiber laser resonant cavity, a vibration exciter control module, a photoelectric detector, data acquisition equipment and signal monitoring equipment;
the laser, the wavelength division multiplexer, the optical fiber laser resonant cavity, the vibration exciter and the vibration exciter control module are sequentially connected; one end of the photoelectric detector is sequentially connected with the data acquisition equipment and the signal monitoring equipment, and the other end of the photoelectric detector is connected with one end of the wavelength division multiplexer connected with the laser;
the laser is used for generating laser, and the laser enters the fiber laser resonant cavity through the wavelength division multiplexer to generate resonance so as to generate multi-longitudinal-mode laser and polarization-mode laser;
the fiber laser resonator comprises: the temperature detection sensing element and the vibration detection sensing element are used for generating beat frequency signals with temperature and vibration sensing information;
the vibration exciter is controlled by the vibration exciter control module and is used for generating a vibration signal;
the photoelectric detector is used for performing photoelectric conversion on the multi-longitudinal-mode laser and the polarization-mode laser generated by the fiber laser resonant cavity and generating a plurality of beat frequency signals with sensing information, and comprises: longitudinal mode beat frequency signals and polarization mode beat frequency signals;
the data acquisition equipment is used for acquiring beat frequency signals output by the photoelectric detector; the signal monitoring equipment is used for signal monitoring and data processing.
2. The dual parameter sensing digital sensor system, as set forth in claim 1, wherein said fiber laser resonator comprises: fiber grating used for frequency selection, rare earth doped fiber, and fiber grating used for vibration sensing;
one end of the fiber grating used for frequency selection is connected with the wavelength division multiplexer to perform frequency selection on the optical signal output by the wavelength division multiplexer, and the other end of the fiber grating used for vibration sensing is sequentially connected with the rare earth doped fiber and the fiber grating used for vibration sensing;
the rare earth doped optical fiber is the temperature detection sensing element, and the fiber bragg grating for vibration sensing is placed on the vibration exciter and is the vibration detection sensing element.
3. The dual parameter sensing digital sensor system of claim 1, wherein said exciter control module comprises: a signal generator and a power amplifier; the signal generator, the power amplifier and the vibration exciter are connected in sequence.
4. The dual parameter sensing digital sensor system, as set forth in claim 1, wherein said data acquisition device comprises a spectrum analyzer and a general purpose software radio peripheral for acquiring beat signals modulated with vibration sensing information and beat signals modulated with temperature sensing information.
5. The dual parameter sensing digital sensor system, according to claim 1, wherein said signal monitoring device is a computer, and said computer processes signal data by a process comprising:
and denoising the time-frequency signal of the polarization mode beat frequency modulated with the vibration sensing information, converting the time-domain signal subjected to denoising into a frequency-domain signal, and demodulating to obtain the vibration frequency.
6. The dual parameter sensing digital sensing system of claim 2, wherein said rare earth doped fiber is an erbium doped fiber.
7. A double-parameter detection digital sensing method based on an optical fiber beat frequency technology, which is implemented based on the double-parameter detection digital sensing system based on the optical fiber beat frequency technology of claim 1, and comprises:
the method comprises the following steps: the laser generates laser light;
step two: the wavelength division multiplexer transmits laser to a fiber laser resonant cavity, resonance occurs in the fiber laser resonant cavity, and longitudinal mode laser and polarization mode laser are generated;
step three: the temperature signal acts on the temperature detection sensing element and modulates the optical signal in the fiber laser resonant cavity, and the vibration signal acts on the vibration detection sensing element and modulates the optical signal in the fiber laser resonant cavity;
step four: the modulated optical signal is reflected back to the wavelength division multiplexer and enters the photoelectric detector, and a plurality of beat frequency signals for modulating temperature or vibration are generated on the photoelectric detector;
step five: transmitting the longitudinal mode beat frequency signal modulated with the temperature sensing information and the polarization mode beat frequency signal modulated with the vibration sensing information to the data acquisition equipment;
step six: and the signal monitoring equipment is used for carrying out signal monitoring and data processing on the beat frequency signals acquired by the data acquisition equipment.
8. The method of claim 7, wherein the data acquisition process comprises: the method comprises the steps of adopting a radio frequency spectrum analyzer and a general software radio peripheral to collect beat frequency signals modulated with vibration sensing information, and collecting beat frequency signals modulated with temperature sensing information by the radio frequency spectrum analyzer.
9. The method of claim 8, wherein the processing of the data by the signal monitoring device comprises:
and denoising the time-frequency signal which is acquired by the radio frequency spectrometer and is modulated with the polarization mode beat frequency of the vibration sensing information, converting the time-domain signal subjected to denoising into a frequency-domain signal, and demodulating to obtain the corresponding vibration frequency.
10. The method of claim 9, wherein the noise reduction demodulation method is: and (3) a variational modal decomposition method.
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