Temperature detection method and system based on fiber grating temperature sensor

Abstract

The invention discloses a temperature detection method and system based on a fiber grating temperature sensor, low coherence light emitted by an SLD broadband light source is divided into first signal light and second signal light after passing through a coupler, the first signal light forms reference light, and the reference light is sent to an upper computer after being collected by a photoelectric detector; after the second signal light enters the fiber bragg grating temperature sensor through the optical circulator, part of the second signal light is reflected by the fiber bragg grating temperature sensor and returns to the optical circulator along the original path to form reflected light, and the reflected light is collected by the photoelectric detector and then sent to the upper computer; the other part of the second signal light penetrates through the fiber grating temperature sensor to form transmission light, and the transmission light is collected by the photoelectric detector and then sent to the upper computer; and the upper computer processes the reference light, the reflected light and the transmission light, calculates the power of the reference light, the power of the reflected light and the power of the transmission light, and obtains the corresponding real-time temperature from a pre-trained power-temperature relation table.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber measurement, and in particular relates to a temperature detection method and system based on an optical fiber grating temperature sensor. Background Art

[0002] Optical fiber temperature sensing technology is widely used in many important fields due to its anti-electromagnetic interference, high precision, and distributed measurement. In the petrochemical field, it can detect the temperature of oil wells and pipelines to effectively prevent leakage and dangerous situations; in the power industry, it can be used for temperature detection of cables and substation equipment to prevent overheating failures; in civil engineering, it can detect temperature changes in bridges and tunnels in real time to provide a reliable basis for structural safety assessment and maintenance; in the aerospace field, it can detect the temperature of aircraft engines to ensure safe operation.

[0003] At present, the temperature detection method based on fiber Bragg grating mainly adopts wavelength demodulation technology, which determines the temperature change by measuring the wavelength change of the reflected light of the fiber Bragg grating. However, wavelength demodulation technology requires complex demodulation equipment, such as spectrum analyzer, tunable narrowband light source, etc., which is expensive and has a slow demodulation speed, and cannot be used in some application scenarios with high cost and real-time requirements. Summary of the invention

[0004] In order to overcome one or more of the above-mentioned technical defects, the present invention provides a temperature detection method and system based on a fiber Bragg grating temperature sensor, which adopts an intensity demodulation method, detects the SLD broadband light source power, the fiber Bragg grating transmitted light power and the fiber Bragg grating reflected light power, and obtains the corresponding real-time temperature according to a pre-trained power-temperature relationship table. There is no need to configure complex demodulation equipment, the real-time demodulation speed is fast, the structure is simple and the cost requirement is low.

[0005] In a first aspect, the present invention provides a temperature detection method based on a fiber grating temperature sensor, comprising the steps of:

[0006] Controlling the SLD broadband light source to emit low-coherence light, the low-coherence light emitted by the SLD broadband light source is divided into a first signal light and a second signal light after passing through a coupler, the first signal light forms a reference light, and the reference light is collected by a photoelectric detector and sent to a host computer;

[0007] After the second signal light enters the fiber Bragg grating temperature sensor through the optical circulator, part of the second signal light is reflected by the fiber Bragg grating temperature sensor and returns to the optical circulator along the original path to form reflected light, which is collected by the photoelectric detector and sent to the host computer;

[0008] Another part of the second signal light passes through the fiber grating temperature sensor to form a transmitted light, which is collected by the photoelectric detector and sent to the host computer;

[0009] The host computer processes the reference light, reflected light and transmitted light, calculates the reference light power, reflected light power and transmitted light power, and obtains the corresponding real-time temperature from the pre-trained power-temperature relationship table.

[0010] Furthermore, the method further comprises the steps of:

[0011] The photoelectric detector converts the reference light signal into a reference light analog signal, converts the reflected light signal into a reflected light analog signal, converts the transmitted light signal into a transmitted light analog signal, and sends them to the host computer via the data acquisition card.

[0012] Furthermore, the method further comprises the steps of:

[0013] The data acquisition card converts the reference light analog signal from the photodetector into a reference light digital signal, converts the reflected light analog signal into a reflected light digital signal, converts the transmitted light analog signal into a transmitted light digital signal, and sends them to the host computer.

[0014] In a second aspect, the present invention further provides a temperature detection system based on a fiber Bragg grating temperature sensor, which is used to implement the above-mentioned temperature detection method based on a fiber Bragg grating temperature sensor, comprising an SLD broadband light source, a coupler, an optical circulator, a fiber Bragg grating temperature sensor, a photodetector and a host computer, wherein one end of the coupler is connected to the SLD broadband light source, and the other end is respectively connected to the optical circulator and the photodetector; the other end of the optical circulator is respectively connected to the fiber Bragg grating temperature sensor and the photodetector, the output end of the fiber Bragg grating temperature sensor is connected to the photodetector, and the output end of the photodetector is connected to the host computer;

[0015] The SLD broadband light source is used to provide broadband low-coherence light;

[0016] The coupler is used to divide the broadband low-coherence light emitted by the SLD broadband light source into a first signal light and a second signal light, wherein the first signal light is a reference light and enters the photodetector; and the second signal light enters the optical circulator;

[0017] The optical circulator is used to isolate the interference of the reflected light on the reference light;

[0018] The fiber grating temperature sensor is used to reflect part of the second signal light into reflected light with different wavelengths according to changes in ambient temperature;

[0019] The photoelectric detector is used to convert the collected reference light signal, reflected light signal and / or transmitted light signal into a reference photoelectric signal, a reflected photoelectric signal and / or a transmitted photoelectric signal;

[0020] The host computer is used to process the reference photoelectric signal, the reflected photoelectric signal and / or the transmitted photoelectric signal from the photodetector, calculate the reference light power, the reflected light power and the transmitted light power, and obtain the corresponding real-time temperature from a pre-trained power-temperature relationship table.

[0021] Furthermore, it also includes a data acquisition card for converting the reference light analog signal, the reflected light analog signal and / or the transmitted light analog signal into corresponding reference light digital signals, reflected light digital signals and / or transmitted light digital signals, and sending them to the host computer.

[0022] Furthermore, the splitting ratio of the coupler is 95:5.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The invention discloses a temperature detection method and system based on a fiber grating temperature sensor. The method comprises the following steps: controlling an SLD broadband light source to emit low-coherence light. The low-coherence light emitted by the SLD broadband light source is divided into a first signal light and a second signal light after passing through a coupler. The first signal light forms a reference light. The reference light is collected by a photoelectric detector and then sent to a host computer. After the second signal light enters the fiber grating temperature sensor through an optical circulator, part of the second signal light is reflected by the fiber grating temperature sensor and returns to the optical circulator along the original path to form reflected light. The reflected light is collected by the photoelectric detector and then sent to the host computer. Another part of the second signal light passes through the fiber grating temperature sensor to form transmitted light. The transmitted light is collected by the photoelectric detector and then sent to the host computer. The host computer processes the reference light, the reflected light and the transmitted light, calculates the reference light power, the reflected light power and the transmitted light power, and obtains the corresponding real-time temperature from a pre-trained power-temperature relationship table. Different from the traditional fiber Bragg grating wavelength demodulation method, the present invention adopts the intensity demodulation method, which detects the SLD broadband light source power, the fiber Bragg grating transmitted light power and the fiber Bragg grating reflected light power, and obtains the corresponding real-time temperature according to the pre-trained power-temperature relationship table. There is no need to configure complex demodulation equipment, the real-time demodulation speed is fast, the structure is simple and the cost requirement is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 A schematic diagram of the structure of a temperature detection system based on a fiber Bragg grating temperature sensor according to an embodiment;

[0027] Figure 2 A flow chart of a temperature detection method based on a fiber Bragg grating temperature sensor according to an embodiment;

[0028] Figure 3A spectrum diagram of reference light of the temperature detection method based on the fiber grating temperature sensor described in the embodiment;

[0029] Figure 4 A spectrum diagram of transmitted light of the temperature detection method based on the fiber Bragg grating temperature sensor described in the embodiment;

[0030] Figure 5 A spectrum diagram of reflected light of the temperature detection method based on the fiber grating temperature sensor described in the embodiment;

[0031] Marking description: 100, SLD broadband light source; 200, coupler; 300, optical circulator; 400, fiber Bragg grating temperature sensor; 500, photodetector; 600, host computer; 700, data acquisition card. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0035] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0036] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] The present application embodiment provides a temperature detection system based on a fiber Bragg grating temperature sensor, such as Figure 1 , including an SLD broadband light source 100, a coupler 200, an optical circulator 300, a fiber Bragg grating temperature sensor 400, a photodetector 500 and a host computer 600. One end of the coupler 200 is connected to the SLD broadband light source 100, and the other end is respectively connected to the optical circulator 300 and the photodetector 500; the other end of the optical circulator 300 is respectively connected to the fiber Bragg grating temperature sensor 400 and the photodetector 500, the output end of the fiber Bragg grating temperature sensor 400 is connected to the photodetector 500, and the output end of the photodetector 500 is connected to the host computer 600.

[0038] The SLD broadband light source 100 is used to provide broadband low-coherence light; the coupler 200 is used to divide the broadband low-coherence light emitted by the SLD broadband light source 100 into a first signal light and a second signal light, the first signal light is a reference light, and enters the photodetector 500; the second signal light enters the optical circulator 300. The SLD broadband light source 100 can provide broadband low-coherence light with Gaussian distribution, providing conditions for fiber grating intensity demodulation. Specifically, the splitting ratio of the coupler 200 is 95:5, 95% of the light enters the optical circulator 300, and 5% of the light directly enters the photodetector 500 as the reference light from the SLD broadband light source 100.

[0039] The fiber grating temperature sensor 400 is used to reflect part of the second signal light into reflected light with different wavelengths according to the change of the ambient temperature; the optical circulator 300 is used to isolate the interference of the reflected light on the reference light, so that the reflected light can be completely collected by the photodetector 500. Specifically, the wavelength of the reflected light reflected by the fiber grating temperature sensor 400 changes with the change of the ambient temperature.

[0040] The photodetector 500 is used to convert the collected reference light signal, reflected light signal and / or transmitted light signal into a reference photoelectric signal, a reflected photoelectric signal and / or a transmitted photoelectric signal; the host computer 600 is used to process the reference photoelectric signal, the reflected photoelectric signal and / or the transmitted photoelectric signal from the photodetector 500, calculate the reference light power, the reflected light power and the transmitted light power, monitor the power in real time, demodulate the power, and obtain the corresponding real-time temperature from a pre-trained power-temperature relationship table.

[0041] In one embodiment, a data acquisition card 700 is further included, which is used to convert the reference light analog signal, the reflected light analog signal and / or the transmitted light analog signal into corresponding reference light digital signals, reflected light digital signals and / or transmitted light digital signals, and send them to the host computer 600.

[0042] Based on the above-mentioned temperature detection system based on fiber Bragg grating temperature sensor, the embodiment of the present application also provides a temperature detection method based on fiber Bragg grating temperature sensor, such as Figure 2 , including the steps of:

[0043] S1. Control the SLD broadband light source to emit low-coherence light. The low-coherence light emitted by the SLD broadband light source is divided into a first signal light and a second signal light after passing through a coupler. The first signal light forms a reference light. The reference light is collected by a photodetector and sent to a host computer. The splitting ratio of the coupler is 95:5, 5% of the light enters the photodetector, and 95% of the light enters the optical circulator.

[0044] S2. After the second signal light enters the fiber Bragg grating temperature sensor through the optical circulator, part of the second signal light is reflected by the fiber Bragg grating temperature sensor and returns to the optical circulator along the original path to form reflected light. The reflected light is collected by the photoelectric detector and sent to the host computer.

[0045] S3. Another part of the second signal light passes through the fiber grating temperature sensor to form transmitted light, which is collected by the photoelectric detector and sent to the host computer.

[0046] S4. The host computer processes the reference light, reflected light and transmitted light, calculates the reference light power, reflected light power and transmitted light power, and obtains the corresponding real-time temperature from the pre-trained power-temperature relationship table.

[0047] In one embodiment, the steps further include:

[0048] The photoelectric detector converts the reference light signal into a reference light analog signal, converts the reflected light signal into a reflected light analog signal, converts the transmitted light signal into a transmitted light analog signal, and sends them to the host computer via the data acquisition card.

[0049] In one embodiment, the steps further include:

[0050] The data acquisition card converts the reference light analog signal from the photodetector into a reference light digital signal, converts the reflected light analog signal into a reflected light digital signal, converts the transmitted light analog signal into a transmitted light digital signal, and sends them to the host computer.

[0051] After the low-coherence light emitted by the SLD broadband light source passes through the coupler, 95% of the light is transmitted forward into the optical circulator, and 5% of the light is collected by the photodetector as reference light and sent to the host computer through the data acquisition card. The host computer obtains the spectrum of the reference light (i.e., the spectrum of the SLD broadband light source), such as Figure 3 , where the real-time power and wavelength of the reference light are Gaussian distributed.

[0052] In one embodiment, the training power-temperature relationship table includes:

[0053] After 95% of the light is transmitted forward into the optical circulator, it is output to the fiber grating temperature sensor. Part of the light passes through the fiber grating temperature sensor to form transmitted light and is collected by the photoelectric detector. It is sent to the host computer through the data acquisition card. The host computer obtains the spectrum of the transmitted light, such as Figure 4 , where t n and t n+1 is the adjacent time, t n+1 The temperature at time t is greater than n The temperature at the moment, the higher the temperature, the larger the wavelength of the reflected light, t n and t n+1 The transmission spectra at time t correspond to the original SLD broadband light source spectrum in the figure minus t n The solid peak wave under the logo and the original SLD broadband light source spectrum minus t n+1 The dotted spike wave under the logo. Figure 4 It can be seen that before the reflected light wavelength reaches the peak of the broadband spectrum, if the output power of the light source remains unchanged, as the temperature rises, the reflected light wavelength continues to shift to the right and the transmitted light power continues to decrease, that is, the larger the area dug out in the spectrum graph.

[0054] The transmission spectrum is the incident light spectrum minus the reflection spectrum. Figure 4 is the change of the transmission spectrum at adjacent moments, the area of ​​the peak wave corresponds to the reflected light power, and the vertical axis represents the wavelength. The reflection wavelength range of the fiber Bragg grating changes with temperature, and the amplitudes of different wavelengths in the broadband light source are also different; at t n and t n+1 At different times, the area where the SLD broadband light source spectrum is reflected and the size of its corresponding area are different.

[0055] Under different ambient temperatures, light of different specific wavelengths is reflected by the fiber Bragg grating temperature sensor when passing through it, and returns to the optical circulator along the original path to form reflected light, which is collected by the photoelectric detector and sent to the host computer through the data acquisition card. The host computer obtains the spectrum of the reflected light. Figure 5 , where t n and t n+1 is the adjacent time, t n+1 The temperature at time t is greater than n The temperature at the moment is given by Figure 5 It can be seen that before the reflected light wavelength reaches the peak of the broadband spectrum, if the output power of the light source remains unchanged, as the temperature rises, the reflected wavelength continues to shift to the right and the power of the reflected light continues to rise.

[0056] The spectrum of the SLD light source is quasi-Gaussian, and the reflectivity of the fiber Bragg grating is quasi-Gaussian with the wavelength λ of the incident light. The peak reflectivity is R0, and the reflected light power P Reflect With the incident light power P In The relationship is:

[0057] P Reflect =P In ×R(λ)

[0058] Among them, R(λ) represents the reflectivity function, which satisfies the Gaussian distribution and is defined as:

[0059]

[0060] Where, σ is the reflection spectrum width of the fiber Bragg grating, λ B is the Bragg center wavelength (the reflection wavelength of the fiber Bragg grating at 0°C).

[0061] The reference light is 5% of the incident light, that is, the reference light power P Ref =5%P In , we can get:

[0062]

[0063] Combined with the temperature dependence of the Bragg wavelength:

[0064] λ=λ B +a T T

[0065] Among them, a T is the temperature sensitivity coefficient of the fiber Bragg grating, T is the temperature, and the comprehensive result is:

[0066]

[0067] After the incident light passes through the fiber Bragg grating temperature sensor, it is divided into reflected light and transmitted light. The transmitted light power PPass is the incident light power P In Part of can be expressed as:

[0068] P Pass =P In -P Reflect

[0069] Similarly, we can get:

[0070]

[0071] That is, the reference optical power, reflected optical power, and transmitted optical power are correlated with the temperature (positively or negatively correlated). The temperature is monitored by professional temperature regulating equipment (such as a high and low temperature box) and the reference optical power, reflected optical power, and / or transmitted optical power are recorded to obtain a power-temperature relationship table.

[0072] The present invention provides a temperature detection method and system based on a fiber grating temperature sensor. Different from the traditional fiber grating wavelength demodulation method, the present invention adopts an intensity demodulation method, which detects the SLD broadband light source power, the fiber grating transmitted light power and the fiber grating reflected light power, and obtains the corresponding real-time temperature according to a pre-trained power-temperature relationship table, thereby realizing accurate demodulation of temperature information. There is no need to configure complex demodulation equipment, the real-time demodulation speed is fast, the structure is simple and the cost requirement is low, and the method is suitable for application scenarios with strict requirements on cost, sampling time and sampling accuracy.

[0073] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A temperature detection method based on a fiber Bragg grating temperature sensor, characterized in that: Includes steps: Controlling the SLD broadband light source to emit low-coherence light, the low-coherence light emitted by the SLD broadband light source is divided into a first signal light and a second signal light after passing through a coupler, the first signal light forms a reference light, and the reference light is collected by a photoelectric detector and sent to a host computer; After the second signal light enters the fiber Bragg grating temperature sensor through the optical circulator, part of the second signal light is reflected by the fiber Bragg grating temperature sensor and returns to the optical circulator along the original path to form reflected light, which is collected by the photoelectric detector and sent to the host computer; Another part of the second signal light passes through the fiber grating temperature sensor to form a transmitted light, which is collected by the photoelectric detector and sent to the host computer; The host computer processes the reference light, reflected light and transmitted light, calculates the reference light power, reflected light power and transmitted light power, and obtains the corresponding real-time temperature from the pre-trained power-temperature relationship table.

2. The temperature detection method based on fiber Bragg grating temperature sensor according to claim 1, characterized in that: Also includes the steps: The photoelectric detector converts the reference light signal into a reference light analog signal, converts the reflected light signal into a reflected light analog signal, converts the transmitted light signal into a transmitted light analog signal, and sends them to the host computer via the data acquisition card.

3. The temperature detection method based on fiber Bragg grating temperature sensor according to claim 2, characterized in that: Also includes the steps: The data acquisition card converts the reference light analog signal from the photodetector into a reference light digital signal, converts the reflected light analog signal into a reflected light digital signal, converts the transmitted light analog signal into a transmitted light digital signal, and sends them to the host computer.

4. A temperature detection system based on a fiber Bragg grating temperature sensor, used to implement the temperature detection method based on a fiber Bragg grating temperature sensor according to any one of claims 1 to 3, characterized in that: It includes an SLD broadband light source, a coupler, an optical circulator, a fiber Bragg grating temperature sensor, a photodetector and a host computer. One end of the coupler is connected to the SLD broadband light source, and the other end is connected to the optical circulator and the photodetector respectively; the other end of the optical circulator is connected to the fiber Bragg grating temperature sensor and the photodetector respectively, the output end of the fiber Bragg grating temperature sensor is connected to the photodetector, and the output end of the photodetector is connected to the host computer; The SLD broadband light source is used to provide broadband low-coherence light; The coupler is used to separate the broadband low-coherence light emitted by the SLD broadband light source into a first signal light and a second signal light, wherein the first signal light is a reference light and enters the photodetector; The second signal light enters the optical circulator; The optical circulator is used to isolate the interference of the reflected light on the reference light; The fiber grating temperature sensor is used to reflect part of the second signal light into reflected light with different wavelengths according to changes in ambient temperature; The photoelectric detector is used to convert the collected reference light signal, reflected light signal and / or transmitted light signal into a reference photoelectric signal, a reflected photoelectric signal and / or a transmitted photoelectric signal; The host computer is used to process the reference photoelectric signal, the reflected photoelectric signal and / or the transmitted photoelectric signal from the photodetector, calculate the reference light power, the reflected light power and the transmitted light power, and obtain the corresponding real-time temperature from a pre-trained power-temperature relationship table.

5. The temperature detection system based on fiber Bragg grating temperature sensor according to claim 4, characterized in that: It also includes a data acquisition card for converting the reference light analog signal, the reflected light analog signal and / or the transmitted light analog signal into corresponding reference light digital signals, reflected light digital signals and / or transmitted light digital signals, and sending them to the host computer.

6. The temperature detection system based on fiber Bragg grating temperature sensor according to claim 4, characterized in that: The splitting ratio of the coupler is 95:5.

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