Boiler heating surface fiber bragg grating sensor with temperature compensation

Abstract

The invention belongs to the technical field of optical fiber sensor detection, and particularly relates to a boiler heating surface optical fiber grating sensor with temperature compensation, which comprises a packaging shell and a packaging cavity, the packaging shell is composed of an inner layer, a middle layer and an outer layer, the inner layer is made of a zirconia ceramic tube, the middle layer is a titanium alloy elastic bracket, and the packaging cavity is arranged in the packaging shell; the main grating is fixedly arranged in the packaging cavity and is used for sensing the closing temperature and the thermal collision strain; the reference grating is suspended in the packaging cavity, is in the same temperature field as the main grating, isolates strain and is used for corresponding environment temperature; wherein the main grating and the reference grating are located on the same axis, and an isolating layer is arranged between the reference grating and the main grating, so that errors caused by local temperature excursion are avoided; and the optical fiber is electrically connected with the main grating and the reference grating and is used for signal transmission. By adopting the double-grating compensation design, the cross sensitivity of temperature and strain is effectively eliminated, and the temperature measurement precision is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fiber optic sensor detection, and particularly relates to a fiber Bragg grating sensor for boiler heating surfaces with temperature compensation. Background Technique

[0002] Fiber Bragg grating (FBG) sensors are new sensors that use optical fibers as carriers to measure and transmit physical quantities. Due to their many advantages such as high pressure resistance, electromagnetic field interference resistance, good insulation, small size, light weight, insensitivity to environmental changes, high sensitivity, and easy integration, they have been widely used in the field of vibration testing.

[0003] Fiber grating sensors are a type of wavelength modulation optical sensor with two functions: detecting and transmitting the quantity to be measured. They use optical fibers as the transmission medium. When the environmental parameters where the fiber grating is located change, the transmission characteristics of light waves will change accordingly. Using this characteristic of fiber gratings, parameters such as temperature, stress, vibration, and humidity can be measured. In actual work, fiber grating sensors are often exposed to environments with temperature changes, and the temperature sensitivity coefficient of fiber optic sensors is relatively large compared to other environmental parameters. This makes temperature one of the important reasons affecting the measurement accuracy of FBG sensors, especially more obvious in environments with large temperature changes.

[0004] With the wide application of FBG sensors, the demand for fiber grating sensors with high precision, high efficiency, and wide application range is becoming more urgent. To compensate for the drift of the central wavelength of FBG sensors caused by temperature and improve the measurement accuracy of fiber grating sensors, scholars at home and abroad have made a lot of efforts. Currently, the most commonly used temperature compensation method is to connect a temperature sensor in series beside the FBG sensor used for measurement, and it is considered that the temperature measured by the temperature sensor is the temperature of the FBG sensor. By subtracting the temperature of the temperature sensor, the compensated measurement signal is obtained.

[0005] In the prior art, traditional grating fiber optic sensors cannot distinguish between temperature and strain interference, are prone to drift at high temperatures, are complex to install and have a short lifespan. Only through single grating measurement, they are significantly affected by temperature-strain cross-sensitivity, with complex compensation algorithms and low reliability; for example, the dual grating parallel structure requires additional demodulation equipment and the packaging is not suitable for the harsh environment of boilers, resulting in poor long-term stability. Summary of the Invention

[0006] Aiming at the difficulties and deficiencies in the temperature detection of boiler heating surface tubes in the prior art, a fiber Bragg grating sensor with an integrated temperature compensation function is provided to solve the problem of temperature-strain cross-interference in the high-temperature environment of boiler heating surfaces and achieve high-precision and long-term stable temperature monitoring.

[0007] A fiber Bragg grating sensor for boiler heating surfaces with temperature compensation includes: The encapsulation housing is composed of an inner layer, a middle layer, and an outer layer. The inner layer is made of a zirconia ceramic tube, the middle layer is a titanium alloy elastic support for buffering mechanical stress caused by boiler vibration, and the outer layer is made of a 316L stainless steel shell with an Al2O3 anti-corrosion coating sprayed on its surface, which is resistant to acid-base corrosion and high-pressure steam scouring; The encapsulation cavity is arranged inside the encapsulation housing; The main grating is fixedly arranged inside the encapsulation cavity for sensing the closing temperature and thermal collision strain; The reference grating is suspended inside the encapsulation cavity. It is in the same temperature field as the main grating but isolates strain for corresponding to the ambient temperature; Among them, the main grating and the reference grating are on the same axis, and an isolation layer is arranged between the reference grating and the main grating to make the ambient temperature difference between the two gratings ≤ 0.1 °C, avoiding errors introduced by local temperature drift; The optical fiber is electrically connected to the main grating and the reference grating for signal transmission.

[0008] Preferably, the isolation layer is nano-aerogel.

[0009] Preferably, an isolation adhesive layer is filled between the encapsulation cavity and the encapsulation housing, and the material of the isolation adhesive layer is aerogel or high-temperature silicone grease.

[0010] Preferably, for the reference optical fiber, an elastic buffer layer is arranged at one end, and the elastic buffer layer adopts a combined design of a titanium alloy corrugated pipe + disc spring.

[0011] Preferably, in the frequency domain, the measured signal of the fiber Bragg grating sensor contains both the true signal and also contains interference components caused by temperature fluctuations Therefore, there is: (1) k Ts —Cross-sensitivity coefficient; Another temperature sensor is additionally attached to the side adjacent to the fiber Bragg grating sensor. In the frequency domain, compared with the strain signal, the temperature signal is an absolute low-frequency component. Therefore, the monitored temperature signal is used as the reference temperature signal of the measured signal. Design a high-pass filter that is adapted to the energy distribution range of the temperature signal monitored by the reference temperature sensor in the frequency domain. The passband and stopband frequencies are respectively: (2) (3) Ωsh is the stopband frequency; Ωph is the passband frequency; A(f i ) is the temperature signal monitored by the temperature sensor at frequency fi The amplitude at; E is the energy of the temperature signal monitored by the temperature sensor; Preferably, the high-pass filter uses a Butterworth filter or a Chebyshev filter.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. By adopting a double-grating compensation design, the present invention effectively eliminates the cross-sensitivity between temperature and strain and improves the temperature measurement accuracy.

[0013] 2. By adopting special packaging materials and heat dissipation designs, the present invention ensures the stability and reliability of the sensor in high-temperature and strongly corrosive environments.

[0014] 3. By optimizing the sensor structure and demodulation algorithm, the present invention reduces the production cost and maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of the present invention.

[0016] In the drawings: 10 - optical fiber, 20 - packaging shell, 30 - isolation adhesive layer, 40 - main grating, 50 - reference grating, 60 - isolation layer, 70 - elastic buffer layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The following further describes in detail the embodiments of the present invention in conjunction with the drawings and embodiments. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0018] Please refer to Figure 1 In this application, Embodiment 1 is disclosed: An optical fiber grating sensor for a boiler heating surface with temperature compensation, comprising: A packaging shell 20, which is composed of an inner layer, a middle layer, and an outer layer. The inner layer is made of a zirconia ceramic tube, the middle layer is a titanium alloy elastic support for buffering the mechanical stress caused by boiler vibration, and the outer layer is made of a 316L stainless steel shell with an A12O3 anti-corrosion coating sprayed on its surface, resistant to acid-base corrosion and high-pressure steam scouring; A packaging cavity, which is arranged inside the packaging shell 20; A main grating 40, which is fixedly arranged inside the packaging cavity for sensing the closing temperature and thermal collision strain; A reference grating 50, which is suspended inside the packaging cavity and is in the same temperature field as the main grating 40 but isolates the strain for corresponding to the ambient temperature; Among them, the main grating 40 and the reference grating 50 are on the same axis, and an isolation layer 60 is provided between the reference grating 50 and the main grating 40, so that the temperature difference between the environments where the two gratings are located is ≤ 0.1 °C, avoiding errors introduced by local temperature drift; The optical fiber 10, which is electrically connected to the main grating 40 and the reference grating 50, is used for signal transmission.

[0019] In the above, the main grating 40 senses temperature + strain, and the reference grating 50 only senses temperature, directly eliminating the errors caused by the thermal expansion of the boiler heating surface or environmental temperature fluctuations, achieving a temperature compensation accuracy of ±0.3 °C. At the same time, the filling of the isolation layer 60 ensures that the temperature difference between the two gratings is ≤ 0.1 °C, avoiding measurement deviations caused by uneven internal heat distribution in the encapsulation cavity, and is especially suitable for high-temperature and high-pressure scenarios such as thermal power generation and chemical reactors.

[0020] Furthermore, the isolation layer 60 is thermal conductive silicone grease or aerogel, and nano-aerogel (thermal conductivity ≤ 0.016 W / m·K) is preferably selected, which is superior to silicone grease (prone to carbonization at high temperatures for a long time).

[0021] Furthermore, an isolation adhesive layer 30 is filled between the encapsulation cavity and the encapsulation housing 20, and the material of the isolation adhesive layer 30 is aerogel or high-temperature silicone grease (thermal conductivity ≤ 0.02 W / m·K).

[0022] Furthermore, for the reference optical fiber 90, an elastic buffer layer 70 is provided at one end thereof. The elastic buffer layer 70 adopts a combined design of a titanium alloy bellows + a disc spring. The bellows absorbs axial vibration, and the disc spring buffers radial impact, and the multi-directional vibration attenuation rate ≥ 90%.

[0023] This application also discloses Embodiment 2: This embodiment discloses a temperature compensation method for an optical fiber sensor, including: 1. Additionally attach a temperature sensor beside the optical fiber grating sensor, and use the temperature signal monitored by it as the measured reference temperature. Since the temperature changes very slowly over time and appears as a signal with a very low frequency in the frequency domain, approximately below 0.01 Hz. Therefore, it is considered that the frequency value of the reference temperature is equal to the temperature frequency value of the optical fiber strain sensor.

[0024] 2. In the frequency domain, the measured signal of the optical fiber grating sensor contains both the true signal and also the interference component caused by temperature fluctuations Therefore, there is: (1) k Ts —Cross-sensitivity coefficient. The true strain signal can be obtained by eliminating the interference caused by temperature changes in the frequency domain.

[0025] 3. Design the passband frequency Ω and stopband frequency Ω of a high-pass filter adapted to the energy distribution range of the measured temperature signal in the frequency domain to ensure that the interference caused by temperature changes in the frequency domain can be filtered out while the true strain signal is retained. ph and the stopband frequency Ω sh , so as to ensure that the interference caused by temperature changes in the frequency domain can be filtered out while the true strain signal is retained.

[0026] (2) (3) 4. In the frequency domain, the temperature signal is an absolute low-frequency component compared to the strain signal; based on this, design a high-pass filter adapted to the energy distribution range of the measured temperature signal in the frequency domain, which can eliminate the interference caused by temperature changes in the measured signal, thereby obtaining the true strain signal.

[0027] The present invention effectively solves the problem of temperature detection of the boiler heating surface and effectively improves the safety of the boiler.

[0028] The embodiments of the present invention are given for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A fiber Bragg grating sensor for boiler heating surface with temperature compensation, characterized in that: including an encapsulation housing (20) composed of an inner layer, a middle layer, and an outer layer. The inner layer is made of a zirconia ceramic tube, the middle layer is a titanium alloy elastic support for buffering mechanical stress caused by boiler vibration, and the outer layer is made of a 316L stainless steel shell with an Al2O3 anti-corrosion coating on its surface, resistant to acid and alkali corrosion and high-pressure steam scouring; an encapsulation cavity provided inside the encapsulation housing (20); a main grating (40) fixedly provided inside the encapsulation cavity for sensing the closing temperature and thermal collision strain; a reference grating (50) suspended inside the encapsulation cavity, which is in the same temperature field as the main grating (40) but isolated from strain for corresponding to the ambient temperature; wherein the main grating (40) and the reference grating (50) are on the same axis, and an isolation layer (60) is provided between the reference grating (50) and the main grating (40) to make the ambient temperature difference between the two gratings ≤ 0.1 °C, avoiding errors introduced by local temperature drift; an optical fiber (10) electrically connected to the main grating (40) and the reference grating (50) for signal transmission.

2. The fiber Bragg grating sensor for the boiler heating surface with temperature compensation according to claim 1, wherein: The isolation layer (60) is nano-aerogel.

3. The fiber Bragg grating sensor for the boiler heating surface with temperature compensation according to claim 1, characterized in that: An isolation adhesive layer (30) is filled between the encapsulation cavity and the encapsulation housing (20), and the material of the isolation adhesive layer (30) is aerogel or high-temperature silicone grease.

4. A fiber Bragg grating sensor for a boiler heating surface with temperature compensation according to claim 1, characterized in that: A reference optical fiber (90) has an elastic buffer layer (70) provided at one end, and the elastic buffer layer (70) adopts a combination design of a titanium alloy bellows + a disc spring.

5. The fiber optic grating sensor for a boiler heating surface with temperature compensation according to claim 1, characterized in that: In the frequency domain, the measured signal of the fiber Bragg grating sensor contains both the true signal and the interference component caused by temperature fluctuations Therefore, we have: (1) k Ts — Cross-sensitivity coefficient; Another temperature sensor is additionally attached to the side adjacent to the fiber optic grating sensor. In the frequency domain, the temperature signal is an absolute low-frequency component compared to the strain signal. Therefore, the monitored temperature signal is used as the reference temperature signal of the measured signal. The temperature signal monitored by the reference temperature sensor is used to design a high-pass filter adapted to the energy distribution range of the measured temperature signal in the frequency domain. The passband and stopband frequencies are respectively: （2） （3） Ωsh is the stopband frequency; Ωph is the passband frequency; A(fi ) is the amplitude of the temperature signal monitored by the temperature sensor at the frequency fi; E is the energy of the temperature signal monitored by the temperature sensor.

6. The fiber Bragg grating sensor for the boiler heating surface with temperature compensation according to claim 5, characterized in that: The high-pass filter adopts a Butterworth filter or a Chebyshev filter.

Images