Distributed temperature, humidity and vibration integrated detection system and method based on optical fiber
By combining fiber optic gratings and humidity-sensitive materials with the Stokes light dynamic calibration method, integrated temperature and humidity detection was achieved, solving the problem that traditional fiber optic sensors cannot measure multiple parameters simultaneously, and providing accurate environmental monitoring and real-time early warning functions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG INST OF COMMERCE & TECH
- Filing Date
- 2023-10-30
- Publication Date
- 2026-05-01
AI Technical Summary
Existing fiber optic sensors cannot simultaneously measure temperature, humidity, and gas concentration, and traditional methods cannot eliminate the influence of light source disturbances, leading to inaccurate measurements.
Temperature is measured using the fiber optic grating (FBG) principle, humidity is measured by coating with a moisture-sensitive material, gas concentration is detected using laser spectral absorption technology, and demodulation is performed using the Stokes light dynamic calibration method, thus realizing integrated detection of temperature, humidity and gas.
It enables simultaneous measurement of temperature, humidity, and gas concentration, reducing measurement errors and providing more accurate environmental parameter monitoring. It also has the advantages of being resistant to electromagnetic interference and requiring no power supply, and supports real-time monitoring and early warning of emergencies.
Smart Images
Figure CN121954262A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of temperature, humidity and gas concentration detection, and more specifically, to a distributed integrated temperature, humidity, gas and vibration detection system and method based on optical fiber. Background Technology
[0002] In agricultural development, especially in the storage and preservation of agricultural products, changes in temperature, humidity, and the composition of gases in the storage environment are crucial factors affecting their development. Measuring these parameters plays a vital role in control and regulation, and developing and using effective devices and technologies is a prerequisite and basis for achieving optimal preservation of agricultural products.
[0003] Currently, most commonly used sensors are electronic sensors, but they are highly susceptible to external factors such as magnetic fields and electrostatic fields, leading to frequent problems such as inaccurate measurement data. Furthermore, the heat generated by the wires used for sensor readings can also affect data measurement. Fiber optic sensing, a new type of sensing technology that has rapidly developed alongside fiber optic communication technology, boasts unparalleled advantages such as long sensing distance, large monitoring area, no power supply required, corrosion resistance, and immunity to electromagnetic interference.
[0004] However, most fiber optic sensors currently on the market only measure one of the parameters: temperature, humidity, or gas concentration. There are no devices that can measure all three parameters simultaneously. Furthermore, traditional distributed fiber optic sensor calibration methods cannot eliminate the effects of light source disturbances, and the calibration conditions are difficult to achieve in practical applications. Summary of the Invention
[0005] The technical problem this invention aims to solve is to provide a distributed integrated temperature, humidity, gas, and vibration detection system and method based on optical fiber, facilitating integrated detection of these factors. Temperature measurement utilizes the principle of fiber optic gratings (FBGs). Any temperature change will cause a wavelength shift in the FBG; by measuring the wavelength... The change in humidity can be used to calculate the ambient temperature; humidity measurement involves uniformly coating a moisture-sensitive material onto the grating portion of the FBG (fiber optic optical fiber) to form the sensitive element of the fiber optic humidity sensor, using a temperature-sensitive fiber as a reference fiber to calculate and measure the relative humidity in the environment; gas concentration detection is mainly based on laser spectral absorption technology, which is based on the spectral consistency between the absorption spectrum of molecular vibration and rotation and the emission spectrum of the light source. When light passes through a medium, its propagation will change even without reflection, refraction, and diffraction. This is because the optical electromagnetic wave interacts with the atoms and molecules that make up the medium, resulting in light absorption and scattering, causing attenuation. Since the scattering of light by gas molecules is very weak, much smaller than the light energy absorbed by the gas, the attenuation is mainly caused by absorption, and scattering can be ignored. Utilizing the characteristic of light attenuation due to light absorption by the medium, it is possible to detect gases using optical fibers; finally, the vibration principle of optical fibers is used to monitor and alarm for sudden situations such as collisions and theft in the detection space. The main principle is to use the refraction and reflection characteristics of optical fibers to convert vibration signals into optical signals, which are then modulated by an optical modulator and finally received and converted into electrical signals by a photodetector.
[0006] The present invention achieves its objective by employing the following technical solution: A distributed temperature, humidity, gas, and vibration integrated detection system and method based on optical fiber, characterized in that it comprises: an intelligent monitoring system, a distributed monitoring host, a Stokes optical dynamic calibration temperature and humidity demodulator, a gas concentration demodulator, an optical fiber vibration alarm system, a gas chamber, and a sensing optical cable; the sensing optical cable is laid in the gas chamber; the sensing optical cable connects the distributed monitoring host and the optical fiber vibration alarm system; the distributed monitoring host connects the Stokes optical dynamic calibration temperature and humidity demodulator, the gas concentration demodulator, and the optical fiber vibration alarm system; the Stokes optical dynamic calibration temperature and humidity demodulator, the gas concentration demodulator, and the optical fiber vibration alarm system are respectively connected to the intelligent monitoring system.
[0007] As a further limitation of this technical solution, the intelligent monitoring system includes a host, a field data acquisition and monitoring system, and a remote monitoring and early warning platform. The field data acquisition and monitoring system and the remote monitoring and early warning platform are respectively connected to the host, and the Stokes optical dynamic calibration temperature and humidity demodulator and the gas concentration demodulator are respectively connected to the field data acquisition and monitoring system.
[0008] As a further limitation of this technical solution, the field data acquisition and monitoring system includes a field data acquisition system and a video monitoring system, which are respectively connected to the host of the intelligent monitoring system. The Stokes optical dynamic calibration temperature and humidity demodulator and the gas concentration demodulator are respectively connected to the field data acquisition system.
[0009] The distributed monitoring host integrates a laser as the light source for the entire detection system. The laser is controlled by the host to turn on and off. The laser's light output end is connected to the sensing optical cable. The data output end of the distributed monitoring host is connected to the gas concentration demodulator and the Stokes light dynamic calibration temperature and humidity demodulator.
[0010] As a further limitation of this technical solution, the fiber optic vibration alarm system includes a fiber optic coupler, an optical circulator, a photodetector, and an alarm controller. The fiber optic vibration alarm system and the on-site data acquisition and monitoring system share the video monitoring system.
[0011] As a further limitation of this technical solution, the air chamber includes an air chamber shell, a reflector structure, a vent hole located on the air chamber shell, and an optical fiber access hole.
[0012] As a further limitation of this technical solution, after the coating layer is peeled off from the inner grating portion of the sensing optical cable near one end of the gas chamber, a humidity-sensitive material is uniformly coated for humidity detection. The sensing optical cable as a whole is used to lay in the detection space to measure temperature, humidity and gas concentration.
[0013] As a further limitation of this technical solution, the moisture-sensitive material is prepared by mixing lithium chloride and activated carbon into a polyamic acid solution in a mixing ratio of 15:0.5:84.5, stirring at a speed of 200~500 r / min for 15~20 min, and then adding 85 parts of polyamide curing agent at room temperature to form a porous moisture-sensitive material.
[0014] A distributed integrated detection method for temperature, humidity, air, and vibration based on optical fiber, characterized by the following steps: S1: The distributed monitoring host emits the required laser, and the optical fiber in the transmission cable transmits the generated laser to various locations inside the monitoring space. S2: The laser, which is sensitive to different gas concentrations, enters the gas chamber. After multiple reflections by the mirror, it is finally transmitted to the gas concentration demodulator via the laser reflection path and then back to the gas concentration demodulator. The gas concentration demodulator calculates the photochemical signal containing the gas concentration based on the spectral absorption according to the Lambert-Beer law, and finally obtains the concentration of different gases in the detection space. The data is then fed back to the data acquisition system. The primary law relied upon in spectral absorption methods for detecting gas concentration is the Lambert-Beer law. According to this law, when a beam of light has an intensity of... When parallel light passes through a gas chamber containing the gas to be measured, if the spectrum of the light source covers one or more absorption lines of that gas, the transmitted light intensity... With incident light intensity and gas concentration The relationship between them is: (1) in: Wavelength of light, measured in meters (m). The absorption coefficient of the medium; The length of the light-absorbing gas is expressed in cm. The line intensity of the characteristic spectral line of this gas is expressed in cm⁻¹. -2 atm -1 It represents the absorption intensity of a spectral line and is only related to temperature; This represents the total pressure of the gaseous medium, measured in atm. This represents the volume concentration of the gas, expressed in PPM. It is a linear function that represents the shape of the measured absorption spectral line, which is related to temperature, total pressure, and the content of each component in the gas; After performing a logarithmic operation on both sides of Equation 1 and integrating over the entire frequency domain, we obtain: (2) Therefore, the gas concentration can be directly calculated using the following formula: (3) Where, A in equations (2) and (3) is The integral over the entire frequency domain; Given that parameters such as pressure, linear intensity, and length of the light-absorbing gas are known, Substituting the integral value in the frequency domain into Equation 3 yields the gas concentration value; S3: The temperature-sensitive laser is transmitted to the entire detection space via the transmission optical cable and finally back to the Stokes dynamic calibration temperature and humidity demodulator. After receiving the photochemical signal containing temperature and humidity information, the Stokes dynamic calibration temperature and humidity demodulator demodulates the photochemical signal based on the FGB principle. After demodulation, the obtained temperature and humidity values are calibrated according to the Stokes dynamic calibration principle to reduce the error between the measured value and the actual value, and the final temperature and humidity data is fed back to the field data acquisition system. According to coupling theory, when the grating is subjected to external strain and thermal effects, the FBG wavelength shift is: (4) in: It is the effective elastic-optical constant of the optical fiber; It is the longitudinal strain coefficient; Thermo-optic coefficient; It is the coefficient of thermal expansion of optical fiber; The center wavelength of the FBG is in meters. This represents the offset of the FBG wavelength; This represents the change in temperature.
[0015] When both temperature and humidity change simultaneously, the effects of temperature and humidity on the center wavelength of the FBG are independent: (5) in: These are the temperature change and humidity change of the grating, respectively; It is the temperature sensitivity coefficient of the grating; It is the humidity sensitivity coefficient; The center wavelength of the FBG is in meters. This represents the offset of the FBG wavelength.
[0016] For fiber Bragg gratings without moisture-sensitive coating: (6) By measuring the change in wavelength It can calculate the ambient temperature and use it as a temperature reference grating to measure relative humidity using Formula 5.
[0017] When a laser pulse propagates in an optical fiber, Raman scattering occurs, producing anti-Stokes light and Stokes light. The luminous flux can be expressed as: (7) (8) Where: subscript These represent Stokes Raman scattered light, anti-Stokes Raman scattered light, and incident light, respectively. A coefficient related to the fiber scattering cross section; The fiber backscattering factor; The frequency of the scattered photon; The luminous flux of the laser pulse incident on the optical fiber; This represents the average transmission loss of light in the optical fiber. This represents the distance a laser pulse travels within the optical fiber. It is the temperature modulation function of the backscattered light; (9) in: It is Planck's constant. For Raman frequency shift, For Boltzmann constant, The temperature of the environment in which the optical fiber is located; Performing a logarithmic operation on equation 9, we get: (10) in, The back-stokes optical flux in the reference fiber, measured in real time, is represented by curve fitting. Calculate the attenuation coefficient of Stokes light ; Temperature is At that time, the length of the fiber optic head end was The Stokes luminous flux at that location is denoted as By using exponential fitting with the attenuation coefficient, the attenuation coefficient of the remaining optical fibers at a temperature of [insert temperature here]. If the Stokes flux at time t is given, then the Stokes flux at any location in the optical fiber is: (11) in, This represents the length of the optical fiber at that location. Equation 11 is the result of calculating the entire optical fiber at a temperature of [temperature value missing] based on the real-time Stokes flux in the reference fiber. In the environment, the back-Stokes luminous flux in the optical fiber, i.e., the dynamic Stokes luminous flux, is used as the reference light. The real-time measured back-Stokes light is used as the signal light. The temperature is demodulated using the scattered light intensity ratio method. Equation 8 divided by Equation 11 yields: (12) By using a reference fiber to eliminate coefficients related to the fiber scattering cross-section and ignoring the difference in average transmission loss between anti-Stokes and Stokes light, the final demodulation temperature is: (13) S4: The DC monochromatic light wave emitted by the distributed monitoring host will enter the optical fiber in the sensing optical cable through the optical fiber coupler. When theft or collision with the sensing optical cable occurs inside the detection space, the light wave in the optical fiber will undergo a phase change due to these external changes. The resulting phase-modulated sensing signal will be transmitted to the photodetector through the optical fiber coupler and the optical circulator. The photodetector will feed back the signal to the signal processing module based on the detected phase change of the light wave. The signal processing module will report this abnormal situation to the alarm controller of the optical fiber vibration alarm system.
[0018] Compared with the prior art, the advantages and positive effects of the present invention are: 1. This invention leverages the advantages of optical fiber to simultaneously detect temperature, humidity, and gas concentration. This device can be applied to cold storage facilities, logistics boxes, and shelves commonly used for fruit and vegetable preservation. Combined with an intelligent monitoring system, it forms a distributed real-time warehouse monitoring system. This system can promptly detect regional temperature differences and gradients caused by uneven storage locations and varying warehouse heights, as well as changes in gas composition within the agricultural product storage environment. This enables comprehensive monitoring of agricultural product storage, preservation, and logistics, allowing for adjustments to storage environment parameters in the shortest possible time to achieve optimal preservation results. Simultaneously, the principle of optical fiber vibration is used to monitor and warn of sudden events within the space, such as cargo collapse, falling, human collisions, and theft, forming real-time monitoring in conjunction with the intelligent monitoring system.
[0019] 2. This invention utilizes a temperature and humidity demodulator based on a Stokes light dynamic calibration principle to read temperature and humidity, thereby improving the negative effects of traditional methods, reducing the error between measured temperature and humidity and actual temperature and humidity, and greatly improving the accuracy of operators in judging whether the temperature of the environment where agricultural products are located is suitable.
[0020] 3. This invention utilizes optical fiber for integrated detection of temperature, humidity, air, and vibration. Compared to traditional electronic sensors, it offers unparalleled advantages such as requiring no power supply, corrosion resistance, and immunity to electromagnetic interference. Employing a distributed deployment, it achieves simultaneous measurement of these three parameters and is equipped with an intelligent monitoring system and an optical fiber vibration alarm system. This enables real-time monitoring, data analysis, and timely early warning of the detection environment and emergencies, providing more reliable data support for the preservation environment of agricultural products, ensuring safety and optimal preservation during storage and transportation, and reducing unnecessary economic losses. Attached Figure Description
[0021] Figure 1 This is a schematic diagram of the system framework of the present invention.
[0022] Figure 2 This invention relates to the principle of fiber optic distributed temperature measurement.
[0023] Figure 3 This is a schematic diagram of the optical fiber vibration principle of the present invention.
[0024] Figure 4 This is a graph showing the real-time temperature measurement within the detection space of the present invention, ranging from 0 to 500 m.
[0025] Figure 5 This invention provides a historical data table query function for the main interface of the system software monitoring system.
[0026] Figure 6 This is a schematic diagram of the air chamber structure of the present invention.
[0027] Figure 7 This is a schematic diagram of the intelligent monitoring system architecture of the present invention.
[0028] Figure 8 This is a schematic diagram of the fiber optic vibration alarm system of the present invention.
[0029] In the diagram: 1. Air chamber, 2. Air chamber shell, 3. Reflector structure, 4. Vent hole, 5. Fiber optic access hole, 6. Sensing optical cable, 7. Laser reflection path. Detailed Implementation
[0030] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.
[0031] This invention includes: an intelligent monitoring system, a distributed monitoring host, a Stokes optical dynamic calibration temperature and humidity demodulator, a gas concentration demodulator, a fiber optic vibration alarm system, a gas chamber, and a sensing optical cable; The sensing optical cable is laid in the air chamber; The sensing optical cable connects the distributed monitoring host and the fiber optic vibration alarm system. The distributed monitoring host is connected to the Stokes optical dynamic calibration temperature and humidity demodulator, the gas concentration demodulator and the fiber optic vibration alarm system. The Stokes optical dynamic calibration temperature and humidity demodulator, the gas concentration demodulator, and the fiber optic vibration alarm system are respectively connected to the intelligent monitoring system.
[0032] The intelligent monitoring system includes a host, a field data acquisition and monitoring system, and a remote monitoring and early warning platform. The field data acquisition and monitoring system and the remote monitoring and early warning platform are respectively connected to the host. The Stokes optical dynamic calibration temperature and humidity demodulator and the gas concentration demodulator are respectively connected to the field data acquisition and monitoring system.
[0033] The host is used for data analysis, monitoring, early warning, data export, etc.
[0034] The functions of the on-site data acquisition system are: to control the temperature measurement system hardware, collect and demodulate on-site data, obtain real-time temperature, gas concentration, etc. of the detection space, upload real-time monitoring data in a standard format, and transmit application layer control commands.
[0035] A video surveillance system mainly consists of cameras, digital hard disk recorders, monitors, and transmission cables. Its primary function is to use digital storage to monitor images within the monitored area, allowing administrators to comprehensively, accurately, and promptly observe the actual situation on-site.
[0036] The remote monitoring and early warning platform displays the cold storage structure and temperature distribution within the warehouse in 3D animation, and displays, records, and analyzes real-time data uploaded by the acquisition system. Functions include, but are not limited to, display, location, alarm, real-time measurement, query, data analysis, report export, comprehensive information display, real-time statistics, and 3D visualization.
[0037] The on-site data acquisition and monitoring system includes an on-site data acquisition system and a video monitoring system. The on-site data acquisition system and the video monitoring system are respectively connected to the host of the intelligent monitoring system. The Stokes optical dynamic calibration temperature and humidity demodulator and the gas concentration demodulator are respectively connected to the on-site data acquisition system.
[0038] The distributed monitoring host is equipped with a laser, which serves as the light source for the entire detection system. The laser's on / off state is controlled by the host. The laser's output is connected to the sensing optical cable. The data output of the distributed monitoring host is connected to the gas concentration demodulator and the Stokes light dynamic calibration temperature and humidity demodulator. The laser is an LED light source laser, with a specific wavelength and intensity selected according to actual needs. Multiple LEDs generate light to meet the requirements of different measurement parameters.
[0039] The Stokes optical dynamic calibration temperature and humidity demodulator utilizes the Raman scattering effect and, by referencing the real-time Stokes optical signal attenuation coefficient in the reference fiber, derives the temperature and humidity conditions of the entire fiber. Using the dynamic Stokes flux as the reference demodulation temperature reduces temperature measurement errors caused by the temperature response of Stokes light intensity. Furthermore, it eliminates the need to place the entire fiber at the same temperature to obtain the Stokes light intensity distribution, making the process convenient and quick. Humidity values are calibrated based on the temperature calibration using the same principle. Simultaneously, this demodulator can modulate and demodulate photochemical signals containing temperature and humidity information, and feed the demodulated and calibrated temperature and humidity data back to the field data acquisition system of the intelligent monitoring system.
[0040] The gas concentration demodulator is mainly used to demodulate optical signals containing gas concentration information transmitted through optical fibers, convert them into electrical signals, and then feed the converted electrical signal values back to the field data acquisition system of the intelligent monitoring system.
[0041] The fiber optic vibration alarm system includes a fiber optic coupler, an optical circulator, a photodetector, and an alarm controller. The fiber optic vibration alarm system shares the video monitoring system with the on-site data acquisition and monitoring system. The fiber optic coupler is a single-mode polarization-maintaining fiber optic coupler, using a screw-fastened FC (Ferrule Connector) fiber optic coupler. The optical circulator is a single-mode FC interface, and a fixed-wavelength optical circulator is selected according to actual needs. The photodetector is an APD (Avalanche Photo Diode), which has a fast response and high sensitivity, and can quickly detect weak changes in fiber optic signals. The alarm controller is an audible and visual alarm controller.
[0042] The fiber optic vibration alarm system also includes a signal processing module. The signal processing module is well-known to those skilled in the art and will not be described in detail here.
[0043] When goods fall, collapse, are stolen, or fiber optic cables are accidentally bumped or squeezed, this system will issue an early warning. Combined with the video monitoring system of the intelligent monitoring system, it will display real-time images of the detection space. The alarm controller will use special algorithms and analysis to distinguish between third-party intrusion and normal interference, and feed the data back to the remote early warning platform of the intelligent monitoring system to realize alarm and location functions.
[0044] The gas chamber includes a gas chamber shell, a reflector structure, a vent on the gas chamber shell, and an optical fiber access port. The gas chamber is mainly used to fill the gas to be tested, connect to the optical cable terminal, and reflect and output the incident light.
[0045] The parallel light beam entering the gas chamber is reflected multiple times by the mirror structure before being output, enabling long-path measurements within a relatively small gas chamber and saving manufacturing costs. The output light is then transmitted through an optical fiber to a gas demodulator, where it is demodulated and the gas concentration data is output. For gases that are corrosive, such as ammonia, the reflector is corrosion-resistant.
[0046] After the coating layer is peeled off from the inner grating portion of the sensing optical cable near one end of the gas chamber, a humidity-sensitive material is uniformly coated for humidity detection. The entire sensing optical cable is used to lay in the detection space to measure temperature, humidity and gas concentration.
[0047] The sensing optical cable comprises two independent multimode optical fibers, protected by a hydrophobic filling material, and features a length meter marking. To enhance cable strength, various cable types can be selected based on the application environment, including but not limited to armored and high-temperature resistant types.
[0048] The humidity-sensitive material is prepared by mixing lithium chloride and activated carbon into a polyamic acid solution in a ratio of 15:0.5:84.5, stirring at a speed of 200~500 r / min for 15~20 min, and then adding 85 parts of polyamide curing agent at room temperature to form a porous humidity-sensitive material.
[0049] The air chamber 1 includes an air chamber shell 2, a reflector structure 3, a vent 4 located on the air chamber shell 2, and an optical fiber access hole 5.
[0050] The parallel light beam from the sensing optical cable 6, after multiple reflections by the reflector structure 3, forms a laser reflection path 7 for output. This enables long-path measurements within a relatively small gas chamber, saving manufacturing costs. The output light is then transmitted through the optical fiber to the gas demodulator, where it is demodulated and outputs gas concentration data.
[0051] The reflector structure 3 is designed to be corrosion resistant for some of the gases to be tested that enter the gas chamber, such as ammonia.
[0052] The air chamber 1 is installed inside the detection space according to certain rules. To avoid occupying too much space, it can be installed in a corner or suspended above the space. The sensing optical cable 6 is laid inside the space to be detected according to a certain spatial layout. One end of the optical cable, covered with moisture-sensitive material, is connected to the optical fiber access port 5 of the air chamber 1, and the other end of the sensing optical cable 6 is connected to the distributed temperature measurement host. The camera of the video monitoring system is installed inside the detection space. All other equipment and instruments except for the sensing optical cable 6, air chamber 1, and camera are placed in a monitoring room outside the detection space and operated by designated personnel.
[0053] A distributed integrated detection method for temperature, humidity, air, and vibration based on optical fiber, characterized by the following steps: S1: The distributed monitoring host emits the required laser, and the optical fiber in the transmission cable transmits the generated laser to various locations inside the monitoring space. S2: The laser, which is sensitive to different gas concentrations, enters the gas chamber. After multiple reflections by the mirror, it is finally transmitted to the gas concentration demodulator via the laser reflection path and then back to the gas concentration demodulator. The gas concentration demodulator calculates the photochemical signal containing the gas concentration based on the spectral absorption according to the Lambert-Beer law, and finally obtains the concentration of different gases in the detection space. The data is then fed back to the data acquisition system. The primary law relied upon in spectral absorption methods for detecting gas concentration is the Lambert-Beer law. According to this law, when a beam of light has an intensity of... When parallel light passes through a gas chamber containing the gas to be measured, if the spectrum of the light source covers one or more absorption lines of that gas, the transmitted light intensity... With incident light intensity and gas concentration The relationship between them is: (1) in: Wavelength of light, measured in meters (m). The absorption coefficient of the medium; The length of the light-absorbing gas is expressed in cm. The line intensity of the characteristic spectral line of this gas is expressed in cm⁻¹. -2 atm -1 It represents the absorption intensity of a spectral line and is only related to temperature; This represents the total pressure of the gaseous medium, measured in atm. This represents the volume concentration of the gas, expressed in PPM. It is a linear function that represents the shape of the measured absorption spectral line, which is related to temperature, total pressure, and the content of each component in the gas; After performing a logarithmic operation on both sides of Equation 1 and integrating over the entire frequency domain, we obtain: (2) Therefore, the gas concentration can be directly calculated using the following formula: (3) Where, A in equations (2) and (3) is The integral over the entire frequency domain; Given that parameters such as pressure, linear intensity, and length of the light-absorbing gas are known, Substituting the integral value in the frequency domain into Equation 3 yields the gas concentration value. Typically, the spectral absorbance signal is not directly integrated; instead, a corresponding linear function is used for fitting, and the integral value is accurately obtained from the linear fitting result, thus reducing the influence of measurement error during direct integration.
[0054] S3: The temperature-sensitive laser is transmitted to the entire detection space via the transmission optical cable and finally back to the Stokes dynamic calibration temperature and humidity demodulator. After receiving the photochemical signal containing temperature and humidity information, the Stokes dynamic calibration temperature and humidity demodulator demodulates the photochemical signal based on the FGB principle. After demodulation, the obtained temperature and humidity values are calibrated according to the Stokes dynamic calibration principle to reduce the error between the measured value and the actual value. The final temperature and humidity data is fed back to the field data acquisition system to facilitate timely detection of regional temperature differences, temperature gradients, and humidity changes in the detection space caused by uneven cargo positions and different heights. According to coupling theory, when the grating is subjected to external strain and thermal effects, the FBG wavelength shift is: (4) in: It is the effective elastic-optical constant of the optical fiber; It is the longitudinal strain coefficient; Thermo-optic coefficient; It is the coefficient of thermal expansion of optical fiber; The center wavelength of the FBG is in meters. This represents the offset of the FBG wavelength; This represents the change in temperature.
[0055] When both temperature and humidity change simultaneously, the effects of temperature and humidity on the center wavelength of the FBG are independent: (5) in: These are the temperature change and humidity change of the grating, respectively; It is the temperature sensitivity coefficient of the grating; It is the humidity sensitivity coefficient; The center wavelength of the FBG is in meters. This represents the offset of the FBG wavelength.
[0056] For fiber Bragg gratings without moisture-sensitive coating: (6) By measuring the change in wavelength It can calculate the ambient temperature and use it as a temperature reference grating to measure relative humidity using Formula 5.
[0057] The principle of distributed temperature measurement using optical fibers is based on the backscattering Raman effect, as shown in the diagram below. Figure 2 As shown, a laser pulse enters from one end of an optical fiber. During its forward propagation, the fiber molecules interact, resulting in various types of scattering. Raman scattering is caused by the thermal vibrations of fiber molecules, producing light with a wavelength longer than the light source (called Stokes light) and light with a wavelength shorter than the light source (called anti-Stokes light). The intensity of the anti-Stokes light signal is highly sensitive to temperature. The temperature information at any point within the optical waveguide can be obtained from the ratio of the anti-Stokes light signal intensity to the Stokes light signal intensity. These hot spots can be located using the principle of optical time-domain reflectometry (OTDR), which involves measuring the propagation speed of light in the fiber and the time of the backlight echo. Using these principles, distributed measurement of the temperature field along the optical fiber can be achieved.
[0058] To address the shortcomings of traditional temperature demodulation methods, this invention utilizes a Stokes optical dynamic calibration temperature and humidity demodulator to reduce temperature and humidity errors and provide more accurate temperature and humidity values. Its basic principle is as follows: When a laser pulse propagates in an optical fiber, Raman scattering occurs, producing anti-Stokes light and Stokes light. The luminous flux can be expressed as: (7) (8) Where: subscript These represent Stokes Raman scattered light, anti-Stokes Raman scattered light, and incident light, respectively. A coefficient related to the fiber scattering cross section; The fiber backscattering factor; The frequency of the scattered photon; The luminous flux of the laser pulse incident on the optical fiber; This represents the average transmission loss of light in the optical fiber. This represents the distance a laser pulse travels within the optical fiber. It is the temperature modulation function of the backscattered light; In a uniform, unbroken optical fiber, the Raman scattered light signal attenuates exponentially with increasing fiber length. When a distributed optical fiber temperature sensing system measures temperature, the length of the fiber tip is taken as... The optical fiber is used as a reference optical fiber and placed at a temperature of In the environment, the real-time distribution of Stokes flux in the reference fiber is shown in Equation 7.
[0059] (9) in: It is Planck's constant. For Raman frequency shift, For Boltzmann constant, The temperature of the environment in which the optical fiber is located; Performing a logarithmic operation on equation 9, we get: (10) in, The back-stokes optical flux in the reference fiber, measured in real time, is represented by curve fitting. Calculate the attenuation coefficient of Stokes light ; Temperature is At that time, the length of the fiber optic head end was The Stokes luminous flux at that location is denoted as By using exponential fitting with the attenuation coefficient, the attenuation coefficient of the remaining optical fibers at a temperature of [insert temperature here]. If the Stokes flux at time t is given, then the Stokes flux at any location in the optical fiber is: (11) in, This represents the length of the optical fiber at that location. Equation 11 is the result of calculating the entire optical fiber at a temperature of [temperature value missing] based on the real-time Stokes flux in the reference fiber. In the environment, the back-Stokes luminous flux in the optical fiber, i.e., the dynamic Stokes luminous flux, is used as the reference light. The real-time measured back-Stokes light is used as the signal light. The temperature is demodulated using the scattered light intensity ratio method. Equation 8 divided by Equation 11 yields: (12) By using a reference fiber to eliminate coefficients related to the fiber scattering cross-section and ignoring the difference in average transmission loss between anti-Stokes and Stokes light, the final demodulation temperature is: (13) By referencing the real-time Stokes light signal attenuation coefficient in the optical fiber, the Stokes flux of the entire fiber at a given temperature can be derived. Using the dynamic Stokes light flux as the reference demodulation temperature reduces temperature measurement errors caused by the temperature response of Stokes light intensity. Furthermore, it eliminates the need to place the entire fiber at the same temperature to obtain the Stokes light intensity distribution, making the process convenient and quick. Humidity values are calibrated based on the above principles, building upon temperature calibration.
[0060] S4: The DC monochromatic light wave emitted by the distributed monitoring host will enter the optical fiber within the sensing optical cable through the optical fiber coupler. When theft or collision with the sensing optical cable occurs within the detection space, the light wave in the optical fiber undergoes a phase change due to these external changes. The resulting phase-modulated sensing signal is transmitted to the photodetector through the optical fiber coupler and the optical circulator. The photodetector feeds back the detected phase change to the signal processing module of the optical fiber vibration alarm system. The signal processing module reports this abnormal situation to the alarm controller of the optical fiber vibration alarm system. The alarm control system, in conjunction with the video monitoring system, will determine whether the sudden situation is a negative event such as theft requiring an alarm or a negligible event such as an accidental collision based on real-time footage, and feeds back the final judgment result to the host of the intelligent control system. The host of the intelligent monitoring system can access the data and footage from the signal processing module, alarm controller, and video monitoring system at any time for manual verification.
[0061] The principle of fiber optic vibration alarm is as follows: Figure 3As shown, the basic principle is that the laser emits a DC monochromatic light wave, which is coupled into the two sensing optical fibers in the forward and reverse directions through the fiber coupler, forming forward and reverse loop Mach-Zehnder interference optical signals. When the optical fiber is subjected to external vibration interference along the line, such as vibration, collision, or compression, it will cause a change in the phase of the light wave during transmission in the optical fiber, forming a phase-modulated sensing signal based on double-loop Mach-Zehnder interference. This signal is transmitted to the photodetector through the fiber coupler and optical circulator to detect the change in the intensity of the interference light signal, thereby realizing optical fiber vibration alarm.
[0062] S5: The field data acquisition system collects data from various demodulation instruments and the fiber optic vibration alarm system in real time, packages the data, and sends it to the host via a wide area network through a data transmission service. This, combined with the video surveillance system, forms a complete field data acquisition and monitoring system, providing the host with more comprehensive data support and alarm analysis. For example, real-time data on temperature, humidity, and gas concentration in the monitored space can be displayed on the host of the intelligent monitoring system. Figure 4 As shown; the length indicator on the temperature-sensing optical cable can be correlated with the internal structural dimensions of the detection space, enabling accurate location of monitored temperature anomalies, cable damage points, etc.; historical data can be queried and displayed or printed; equipment information, operating parameters, statistical information, etc., can be directly queried on the system diagram, such as... Figure 5 As shown. Furthermore, the host computer's analysis and calculations can also achieve functions including, but not limited to, real-time analysis, reporting, and partitioning.
[0063] S6: The on-site data acquisition system connects to a remote monitoring and early warning platform via a network. This platform, combined with a video surveillance system, enables interactive monitoring of the real scene and the 3D environment. It features online analysis of monitoring data, detailed data statistics and queries, and in-depth analysis of temperature and multi-parameter gas concentration changes within the monitored space. When the system detects abnormal temperature, humidity, or gas concentration changes in a warehouse, or when the fiber optic vibration alarm system detects an anomaly, it reports to the host computer. The host computer then controls the on-site data acquisition and monitoring system and the remote alarm platform to analyze and determine the center location of the anomaly, locate the cameras installed in the warehouse, and automatically adjust the camera pan-tilt-zoom (PTZ) to point at that location, storing the video content during the anomaly in real time. The remote alarm system analyzes the anomaly and feeds back the real-time situation to the host computer, issuing an alarm. The entire intelligent monitoring system works collaboratively to establish a model of the relationship between cargo stacking and temperature, humidity, and gas concentration within the warehouse. By monitoring relevant data, it analyzes and predicts the temperature, humidity, and gas concentration distribution in various areas of the monitored space. For example, if a potential overheating issue is detected in a cargo storage area, the system issues an early warning, and, in conjunction with the fiber optic vibration alarm system, corrects improper stacking practices by operators.
[0064] The workflow of this invention is as follows: When the system of this invention is running, the distributed monitoring host emits the required laser. The optical fiber within the transmission cable 6 transmits the generated laser to various locations within the monitoring space. Specifically, the laser, sensitive to different gas concentrations, enters the gas chamber 1, undergoes multiple reflections by the reflector structure 3 within the gas chamber 1, and is ultimately transmitted to and from the gas concentration demodulator via the laser reflection path 7. The gas concentration demodulator then performs calculations based on the spectral absorption of the photochemical signal containing gas concentrations, applying the Lambert-Beer law to obtain the concentrations of different gases within the detection space, and feeds the data back to the data acquisition system.
[0065] The temperature-sensitive laser generated by the distributed monitoring host is transmitted via optical fiber optic cable 6 to the entire detection space and finally back to the Stokes dynamic calibration temperature and humidity demodulator. Upon receiving the photochemical signal containing temperature and humidity information, the Stokes dynamic calibration temperature and humidity demodulator demodulates the signal based on the FGB principle. After demodulation, the obtained temperature and humidity values are calibrated according to the Stokes dynamic calibration principle to reduce the error between the measured and actual values. The final temperature and humidity data is then fed back to the on-site data acquisition system, facilitating the timely detection of regional temperature differences, temperature gradients, and humidity changes within the detection space caused by uneven cargo placement and varying elevations.
[0066] The DC monochromatic light wave generated by the distributed monitoring host enters the optical fiber within the sensing optical cable 6 through an optical fiber coupler. When theft or collision with the sensing optical cable 6 occurs within the detection space, the light wave in the optical fiber undergoes a phase change due to these external changes. The resulting phase-modulated sensing signal is transmitted to the photodetector through the optical fiber coupler and optical circulator. The photodetector feeds back the detected phase change to the signal processing module. The signal processing module reports this anomaly to the alarm controller. The alarm control system, in conjunction with the video monitoring system, determines whether the emergency is a serious incident requiring an alarm, such as theft, or a negligible event like an accidental collision, based on real-time footage, and feeds back the final judgment to the host of the intelligent control system. The host of the intelligent monitoring system can access data and footage from the signal processing module, alarm controller, and video monitoring system at any time for manual verification.
[0067] The on-site data acquisition system collects data in real time from various demodulation instruments and fiber optic vibration alarm systems, packages the data, and sends it to the host of the intelligent monitoring system via a wide area network through a data transmission service. This, combined with the video surveillance system, forms a complete on-site data acquisition and monitoring system, providing the host with more comprehensive data support and alarm analysis. For example, real-time data on temperature, humidity, and gas concentration in the monitored space can be displayed on the host of the intelligent monitoring system. Figure 4As shown; the length indicator on the temperature-sensing optical cable can be correlated with the internal structural dimensions of the detection space, enabling accurate location of monitored temperature anomalies, cable damage points, etc.; historical data can be queried and displayed or printed; equipment information, operating parameters, statistical information, etc., can be directly queried on the system diagram, such as... Figure 5 As shown. Furthermore, the host computer's analysis and calculations can also achieve functions including, but not limited to, real-time analysis, reporting, and partitioning.
[0068] The on-site data acquisition system connects to a remote monitoring and early warning platform via a network. This platform, combined with a video surveillance system, enables interactive monitoring of the real scene and the 3D environment. It features online analysis of monitoring data, detailed data statistics and queries, and in-depth analysis of temperature and multi-parameter gas concentration changes within the monitored space. When the system detects abnormal temperature, humidity, or gas concentration changes in a warehouse, or when the fiber optic vibration alarm system detects an anomaly, it reports to the main unit of the intelligent monitoring system. The main unit then controls the on-site data acquisition and monitoring system and the remote alarm platform to analyze and determine the center location of the anomaly, locate the cameras installed in the warehouse, and automatically adjust the camera pan-tilt-zoom (PTZ) to point at that location, storing the video content during the anomaly in real time. The remote alarm system analyzes the anomaly and feeds back the real-time situation to the main unit, issuing an alarm. The entire intelligent monitoring system works collaboratively to establish a model of the relationship between cargo stacking and temperature, humidity, and gas concentration within the warehouse. By monitoring relevant data, it analyzes and predicts the distribution of temperature, humidity, and gas concentration in different areas of the monitored space. For example, if a potential overheating issue is detected in a cargo storage area, the system issues an early warning, and, in conjunction with the fiber optic vibration alarm system, corrects improper stacking practices by operators.
[0069] The above-disclosed embodiments are merely specific examples of the present invention. However, the present invention is not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.
Claims
1. A distributed temperature, humidity, gas, and vibration integrated detection system based on optical fiber, characterized in that, include: Intelligent monitoring system, distributed monitoring host, Stokes optical dynamic calibration temperature and humidity demodulator, gas concentration demodulator, fiber optic vibration alarm system, gas chamber, and sensing optical cable; The sensing optical cable is laid in the air chamber; The sensing optical cable connects the distributed monitoring host and the fiber optic vibration alarm system. The distributed monitoring host is connected to the Stokes optical dynamic calibration temperature and humidity demodulator, the gas concentration demodulator and the fiber optic vibration alarm system. The Stokes optical dynamic calibration temperature and humidity demodulator, the gas concentration demodulator, and the fiber optic vibration alarm system are respectively connected to the intelligent monitoring system.
2. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 1, characterized in that: The intelligent monitoring system includes a computer host, an on-site data acquisition and monitoring system, and a remote monitoring and early warning platform. The on-site data acquisition and monitoring system and the remote monitoring and early warning platform are respectively connected to the host. The Stokes optical dynamic calibration temperature and humidity demodulator and the gas concentration demodulator are respectively connected to the on-site data acquisition and monitoring system.
3. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 2, characterized in that: The on-site data acquisition and monitoring system includes an on-site data acquisition system and a video monitoring system. The on-site data acquisition system and the video monitoring system are respectively connected to the host of the intelligent monitoring system. The Stokes optical dynamic calibration temperature and humidity demodulator and the gas concentration demodulator are respectively connected to the on-site data acquisition system.
4. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 3, characterized in that: The distributed monitoring host integrates a laser as the light source for the entire detection system. The laser is controlled by the host to turn on and off. The laser's light source output is connected to the sensing optical cable. The data output of the distributed monitoring host is connected to the gas concentration demodulator and the Stokes light dynamic calibration temperature and humidity demodulator.
5. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 4, characterized in that: The fiber optic vibration alarm system includes a fiber optic coupler, an optical circulator, a photodetector, and an alarm controller. The fiber optic vibration alarm system and the on-site data acquisition and monitoring system share the video monitoring system.
6. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 5, characterized in that: The air chamber includes an air chamber shell, a reflector structure, a vent on the air chamber shell, and an optical fiber access hole.
7. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 6, characterized in that: After the coating layer is peeled off from the inner grating portion of the sensing optical cable near one end of the gas chamber, a humidity-sensitive material is uniformly coated for humidity detection. The entire sensing optical cable is used to lay in the detection space to measure temperature, humidity and gas concentration.
8. The fiber-optic-based distributed temperature, humidity, gas, and vibration integrated detection system according to claim 7, characterized in that: The humidity-sensitive material is prepared by mixing lithium chloride and activated carbon into a polyamic acid solution in a ratio of 15:0.5:84.5, stirring at a speed of 200~500 r / min for 15~20 min, and then adding 85 parts of polyamide curing agent at room temperature to form a porous humidity-sensitive material.
9. The fiber-optic-based distributed integrated temperature, humidity, gas, and vibration detection method according to claim 6, characterized in that, Includes the following steps: S1: The distributed monitoring host emits the required laser, and the optical fiber in the transmission cable transmits the generated laser to various locations inside the monitoring space. S2: The laser, which is sensitive to different gas concentrations, enters the gas chamber. After multiple reflections by the mirror, it is finally transmitted to the gas concentration demodulator via the laser reflection path and then back to the gas concentration demodulator. The gas concentration demodulator calculates the photochemical signal containing the gas concentration based on the spectral absorption according to the Lambert-Beer law, and finally obtains the concentration of different gases in the detection space. The data is then fed back to the data acquisition system. The primary law relied upon in spectral absorption methods for detecting gas concentration is the Lambert-Beer law. According to this law, when a beam of light has an intensity of... When parallel light passes through a gas chamber containing the gas to be measured, if the spectrum of the light source covers one or more absorption lines of that gas, the transmitted light intensity... With incident light intensity and gas concentration The relationship between them is: （1） in: Wavelength of light, measured in meters (m). The absorption coefficient of the medium; The length of the light-absorbing gas is expressed in centimeters. The line intensity of the characteristic spectral line of this gas is expressed in cm⁻¹. -2 atm -1 It represents the absorption intensity of a spectral line and is only related to temperature; This represents the total pressure of the gaseous medium, measured in atm. This represents the volume concentration of the gas, expressed in PPM. It is a linear function that represents the shape of the measured absorption spectral line, which is related to temperature, total pressure, and the content of each component in the gas.
10. After performing a logarithmic operation on both sides of Equation 1 and integrating over the entire frequency domain, we obtain: （2） Therefore, the gas concentration can be directly calculated using the following formula: （3） in, In equations (2) and (3), A is... The integral over the entire frequency domain; Given that parameters such as pressure, linear intensity, and length of the light-absorbing gas are known, Substituting the integral value in the frequency domain into Equation 3 yields the gas concentration value; S3: The temperature-sensitive laser is transmitted to the entire detection space via the transmission optical cable and finally back to the Stokes dynamic calibration temperature and humidity demodulator. After receiving the photochemical signal containing temperature and humidity information, the Stokes dynamic calibration temperature and humidity demodulator demodulates the photochemical signal based on the FGB principle. After demodulation, the obtained temperature and humidity values are calibrated according to the Stokes dynamic calibration principle to reduce the error between the measured value and the actual value, and the final temperature and humidity data is fed back to the field data acquisition system. According to coupling theory, when the grating is subjected to external strain and thermal effects, the wavelength shift of the FBG can be expressed as: （4） in: It is the effective optical elastic constant of the optical fiber; It is the longitudinal strain coefficient; Thermo-optic coefficient; It is the coefficient of thermal expansion of optical fiber; The center wavelength of the FBG is in meters. This represents the offset of the FBG wavelength; This represents the change in temperature.
11. When both temperature and humidity change simultaneously, the effects of temperature and humidity on the center wavelength of the FBG are independent of each other: （5） in: These are the temperature change and humidity change of the grating, respectively; It is the temperature sensitivity coefficient of the grating; It is the humidity sensitivity coefficient; The center wavelength of the FBG is in meters. This represents the offset of the FBG wavelength.
12. For fiber Bragg gratings without moisture-sensitive coating: （6） By measuring the change in wavelength It can calculate the ambient temperature and use it as a temperature reference grating. Relative humidity can be measured using Formula 5. When a laser pulse propagates in an optical fiber, Raman scattering occurs, producing anti-Stokes light and Stokes light. The luminous flux can be expressed as: （7） （8） Where: subscript These represent Stokes Raman scattered light, anti-Stokes Raman scattered light, and incident light, respectively. A coefficient related to the fiber scattering cross section; The fiber backscattering factor; The frequency of the scattered photon; The luminous flux of the laser pulse incident on the optical fiber; This represents the average transmission loss of light in the optical fiber. This represents the distance a laser pulse travels within the optical fiber. It is the temperature modulation function of the backscattered light; （9） in: It is Planck's constant. For Raman frequency shift, For Boltzmann constant, The temperature of the environment in which the optical fiber is located; Performing a logarithmic operation on equation 9, we get: （10） in, The back-stokes optical flux in the reference fiber, measured in real time, is represented by curve fitting. Calculate the attenuation coefficient of Stokes light ; Temperature is At that time, the length of the fiber optic head end was The Stokes luminous flux at that location is denoted as By using exponential fitting with the attenuation coefficient, the attenuation coefficient of the remaining optical fibers at a temperature of [insert temperature here]. If the Stokes flux at time t is given, then the Stokes flux at any location in the optical fiber is: （11） in, This represents the length of the optical fiber at that location. Equation 11 is the result of calculating the entire optical fiber at a temperature of [temperature value missing] based on the real-time Stokes flux in the reference fiber. In the environment, the back-Stokes luminous flux in the optical fiber, i.e., the dynamic Stokes luminous flux, is used as the reference light. The real-time measured back-Stokes light is used as the signal light. The temperature is demodulated using the scattered light intensity ratio method. Equation 8 divided by Equation 11 yields: （12） By using a reference fiber to eliminate coefficients related to the fiber scattering cross-section and ignoring the difference in average transmission loss between anti-Stokes and Stokes light, the final demodulation temperature is: （13） S4: The DC monochromatic light wave emitted by the distributed monitoring host will enter the optical fiber in the sensing optical cable through the optical fiber coupler. When theft or collision with the sensing optical cable occurs inside the detection space, the light wave in the optical fiber will undergo a phase change due to these external changes. The resulting phase-modulated sensing signal will be transmitted to the photodetector through the optical fiber coupler and the optical circulator. The photodetector will feed back the signal to the signal processing module of the optical fiber vibration alarm system based on the detected phase change of the light wave. The signal processing module will report this abnormal situation to the alarm controller of the optical fiber vibration alarm system.