A material level measurement system and method based on FBG temperature sensor array

Abstract

The present invention provides a material level measurement system and method based on an FBG temperature sensor array. The measurement system includes an FBG demodulator, an FBG temperature sensor array, and a control terminal; the FBG demodulator transmits an optical signal to the FBG temperature sensor array through a broadband light source, and the array reflects a characteristic spectrum signal in real time, which is transmitted to a photoelectric conversion module through an optical circulator, and then the spectrum data is processed and plotted at high speed through an FPGA acquisition module, and then the central wavelength of the reflected light of the FBG measuring point is obtained by analyzing the discrete point Gaussian fitting peak search algorithm, and finally converted into a temperature value through a wavelength-temperature function, and then the temperature information is transmitted to the control terminal for information processing, so as to obtain accurate material level information in the raw material tank. The present invention adopts the coupling of laser measurement technology and optical fiber sensing technology, and makes full use of the linearized inversion relationship between the laser direct measurement parameters and the material level measurement value. Through the software algorithm processing flow, accurate material level measurement can be achieved quickly, in real time, and with high precision.

Description

Technical Field

[0001] The invention relates to the field of precision measurement, and in particular to a material level measurement system and method based on an FBG temperature sensor array in a chemical production process. Background Art

[0002] The highly accurate measurement and characterization of the material level in the raw material tank during the chemical production process plays a very important role in the entire production process. The currently commonly used material level measurement technologies mainly include electrode level meters, ultrasonic level meters, weight level meters, microwave level meters and weighing level meters. However, chemical production equipment has the characteristics of high pressure, high temperature and high-density dust / steam, and the internal material level is difficult to directly measure and characterize. It is usually necessary to use manual direct observation through the observation hole. This method is not only labor-intensive, but also difficult to achieve accurate measurement. In order to improve and optimize the accurate monitoring of material levels in the chemical production process, ensure production safety and product quality, it will be very important and necessary to adopt some new technologies and algorithms suitable for production equipment and on-site environment.

[0003] In the prior art, in the invention patent No. CN201911169252.6 "Optical fiber level meter for high temperature and high pressure environment and its manufacturing method", a kind of optical fiber level meter and its manufacturing method which can be used for liquid level tracking of pressurizer and evaporator in water-cooled reactor nuclear power plant, liquid metal level in metal reactor (sodium-cooled, lead-bismuth-cooled reactor), molten salt level in molten salt reactor, and the installation angle is not restricted is proposed, which is mainly for liquid level structure design; Lv Jianfei, a graduate student of control engineering at Beijing University of Chemical Technology, published his master's thesis "Material level measurement based on temperature sensor array" on May 20, 2013. In the article "Development of a Material Level Measuring Instrument", an embedded material level measuring instrument based on a material level model was designed and produced, but it was mainly used for the material level measurement of a flash kettle under feeding state; in the master's thesis "Development of a Material Level Identification System Based on Multi-Temperature Sensors" published by Gao Ming, a control engineering major at Beijing University of Chemical Technology on May 28, 2012, the method mainly used multi-temperature sensors to collect temperature data of various spatial points in the flash kettle, and through the analysis and processing of these data, the material level height in the flash kettle was identified online in real time, but the whole processing method was too complicated, and a large number of temperature sensor measurement points were required, which increased the hardware cost to a certain extent. Summary of the invention

[0004] The invention aims to address the defects of the prior art by providing a material level measurement system and method based on an FBG temperature sensor array. The invention utilizes the characteristics of laser precision measurement and optical fiber sensing to withstand high temperature and high pressure application environments. While achieving accurate measurement and characterization of material levels in high temperature, high pressure and high-density dust / steam environments, it can also realize remote optical fiber transmission and telemetry, and can solve the problem of accurate material level measurement that adapts to the characteristics of production equipment and on-site environments in chemical production processes.

[0005] In order to solve the above technical problems, the present invention provides a material level measurement system based on an FBG temperature sensor array, comprising an FBG demodulator, an FBG temperature sensor array and a control terminal; the FBG temperature sensor array extends into the raw material of the raw material tank, and is connected to the FBG demodulator signal through a conductive optical cable, the FBG temperature sensor array is used to perform distributed measurement of the temperature field in the raw material tank along the array direction, and transmit the temperature measurement signal to the FBG demodulator for temperature signal demodulation;

[0006] The FBG demodulator is equipped with a broadband light source, an optical circulator, a photoelectric conversion module and an FPGA acquisition module; the FBG demodulator transmits an optical signal to the FBG temperature sensor array through the broadband light source, and the FBG temperature sensor array reflects the characteristic spectrum signal in real time, which is transmitted to the photoelectric conversion module through the optical circulator, and then the spectrum data is processed and drawn at high speed through the FPGA acquisition module, and the center wavelength of the reflected light of the FBG measuring point obtained by the discrete point Gaussian fitting peak search algorithm is converted into a temperature value through the wavelength-temperature function, and then connected to the control terminal signal through the signal transmission line, and the temperature information is transmitted to the control terminal for information processing, so as to obtain accurate material level information in the raw material tank;

[0007] The control terminal receives the temperature information sent by the FBG demodulator, stores, analyzes and counts it, and then calculates the average temperature difference ΔT of each FBG measuring point in a certain time period, and obtains the material level value of the time period according to the average temperature difference ΔT and a preset temperature fluctuation threshold.

[0008] A further technical solution of the present invention is characterized in that the process of obtaining the center wavelength of the reflected light of the FBG measuring point by the FBG demodulator through the discrete point Gaussian fitting peak finding algorithm is as follows: first, through the intensity threshold judgment, find the positions of all discrete intensity maximum points whose spectral intensity is higher than the threshold, then take each discrete intensity maximum point as the center, select appropriate width data on the left and right, thereby intercepting a discrete point spectrum, and then use the discrete Gaussian fitting algorithm to obtain a continuous point spectrum curve The peak value y of the curve max The corresponding x position is the central wavelength λ of each FBG measurement point FBG .

[0009] A further technical solution of the present invention is as follows: the process of converting the wavelength-temperature function of the FBG demodulator into a temperature value is as follows: Substituting the central wavelength of the reflected light of the FBG measuring point into the wavelength-temperature fitting model to obtain the temperature of each FBG measuring point at the current time t m The wavelength-temperature fitting model is as follows:

[0010]

[0011] where λ 0 is the wavelength value corresponding to the temperature measurement point at the characteristic temperature point, the characteristic temperature point is 0℃ or other temperature reference point value; λ is λ FBG The four variables a, b, c, and d are obtained by calibrating the FBG temperature sensor, that is, the corresponding wavelengths of the FBG at each standard temperature are obtained by fitting the polynomial in the model.

[0012] A further technical solution of the present invention is as follows: the control terminal calculates the average temperature difference ΔT of each FBG measuring point in a certain time period, and obtains the material level value of the time period as follows: an array of temperature changes over time of the mth FBG measuring point in the nth time period is collected [T m,y ], calculate the average temperature difference ΔT of the mth FBG measuring point according to the following formula m :

[0013]

[0014] In the above formula: is the average temperature of the mth FBG measuring point in the n-time period;

[0015] The average temperature difference ΔT of the mth FBG measuring point is calculated m The temperature fluctuation threshold T set in the raw material tank to be tested 0 Compare and satisfy the condition ΔT m ≥T 0 When , the height of the mth FBG measuring point is regarded as the material level value within the n time period.

[0016] A further technical solution of the present invention is as follows: the feed port and discharge port of the raw material tank of the measuring system are respectively provided with flow monitoring interfaces, into which a flow meter can be inserted to monitor the feed flow and discharge flow; and the flow meter transmits the flow information to the control terminal via a connected signal transmission line.

[0017] The preferred technical solution of the present invention is: the FBG temperature sensor array adopts an optical fiber liquid level meter for high temperature and high pressure environment, whose outer shell is a metal armored tube, and two or more temperature measuring optical fibers are attached therein, and the tail end of the temperature measuring optical fiber is connected to the transmission optical cable.

[0018] The present invention also provides a material level measurement method based on an FBG temperature sensor array, characterized in that the specific steps are as follows:

[0019] (1) The broadband light source of the FBG demodulator transmits optical signals to the FBG temperature sensor array. The array reflects the characteristic spectral signals in real time and transmits them back to the optical demodulation module of the FBG demodulator. The spectrum is processed and drawn at high speed through FPGA. Then, the multiple FBG measurement points obtained by discrete point Gaussian fitting peak finding algorithm are analyzed at t m The central wavelength of the reflected light corresponding to the moment FBG ;

[0020] (2) The center wavelength λ of the reflected light from each FBG measurement point in step (1) is FBG Substitute them into the wavelength-temperature fitting model to obtain the value of each FBG measurement point at the current time t m The temperature value T is obtained as t m The FBG measurement point temperature distribution array at time [T x ]; the wavelength-temperature fitting model is as follows:

[0021]

[0022] where λ 0 is the wavelength value corresponding to the temperature measurement point at the characteristic temperature point, the characteristic temperature point is 0℃ or other temperature reference point value; λ is λ FBG ; The four variables a, b, c, and d are obtained by calibrating the FBG temperature sensor, that is, the corresponding wavelength of the FBG at each standard temperature is obtained by fitting the polynomial in the model;

[0023] (3) Take a period of time to sample temperature data and record the sampled temperature values ​​as a two-dimensional temperature array [T x,y ], where x is the FBG measurement point number and y is the acquisition time sequence number; where the two-dimensional array [T x,y ] is the array of temperature variation over time of the mth FBG measuring point [T m,y ], the data in the e-th column is the temperature distribution array of the FBG temperature sensor array space at the e-th sampling moment [T x,e ];

[0024] (4) Calculate the average temperature difference of all FBG measuring points in time period n according to the temperature variation array of the FBG measuring points in step (3), where time period n is a certain period of time within the temperature data collection time period in step (3); the average temperature difference ΔT of the mth FBG measuring point is m is an array of the temperature variation of the mth FBG measuring point over time [T m,y ] is calculated, and the calculation formula is as follows:

[0025]

[0026] In the above formula: is the average temperature of the mth FBG measuring point in the n-time period;

[0027] (5) The average temperature difference ΔT of each FBG measuring point in the n time period calculated in step (4) is compared with the temperature fluctuation threshold T set in the raw material tank to be tested. 0 Compare and determine the material level value of the raw material tank within the time period based on the comparison results; the specific process is as follows:

[0028] If the average temperature difference of the mth FBG measuring point in this time period satisfies the condition ΔT m ≥T 0 When , the height of the mth FBG measuring point is regarded as the material level value;

[0029] If the average temperature difference ΔT of all FBG measuring points in this time period is less than the set temperature fluctuation threshold T 0 , repeatedly calculate the average temperature difference of all FBG measuring points in different time periods before and after the n time period according to the calculation method in step (4) until a temperature difference satisfying ΔT ≥ T is found. 0 The material level value can be obtained by finding the FBG measuring point of the raw material tank, or by looking up the corresponding table between the material level value and the average temperature of the raw material tank.

[0030] A further technical solution of the present invention is as follows: in the step (1), the center wavelength λ of the reflected light corresponding to the corresponding FBG measuring point is obtained by analyzing the discrete point Gaussian fitting peak finding algorithm. FBG The specific process is to first judge by the intensity threshold, find the positions of all discrete intensity maximum points with spectral intensity higher than the threshold, and then select appropriate width data on the left and right with each discrete intensity maximum point as the center, so as to intercept a discrete point spectrum, and then use the discrete Gaussian fitting algorithm to obtain the continuous point spectrum curve: The peak value y of the curve max The corresponding x position is the central wavelength λ of each FBG measurement point FBG ; Use the same method to find the central wavelength corresponding to each FBG measurement point and get t m The center wavelength array of the reflected light from the FBG temperature sensor array at the moment.

[0031] A further technical solution of the present invention: the corresponding table of material level value and temperature average value in step (5) is based on the raw material temperature T H The corresponding table of material level value and temperature average value in step (5) is based on the raw material temperature T H and the average tank temperature In the following formula, m represents the number of measurement points of the FBG temperature sensor array, and h 0 ,h 1…h m-1 ,h m They represent the height of each FBG measuring point in the tank, and the specific calculation is as follows:

[0032] A preferred technical solution of the present invention: in the step (5), after the material level value h is preliminarily determined by comparing the temperature fluctuation threshold or the table lookup method, the temperature values ​​of the adjacent FBG measuring points above and below the preliminarily determined material level value h are taken as the difference to determine whether the medium temperature difference T is satisfied. h+1 -T h-1 >ΔT d If it is satisfied, the material level value h is determined to be accurate; where T h+1 Indicates the temperature of the previous measuring point adjacent to the FBG measuring point corresponding to the material level value, T h-1 Indicates the temperature of the next measuring point adjacent to the FBG measuring point corresponding to the material level value, T d Represents the threshold temperature difference, which is smaller than the temperature difference ΔT between the raw material and the air medium 0 , and is greater than the temperature fluctuation threshold T 0 .

[0033] The FBG temperature sensor array in the tank of the present invention can perform distributed measurement of the temperature field in the tank along the array direction; the FBG temperature sensor array outside the tank can transmit the temperature measurement signal to the FBG demodulator through the conductive optical cable for temperature signal demodulation, and then transmit the temperature information to the control terminal through the signal transmission bus for information algorithm processing, so as to obtain accurate material level information in the raw material tank and provide process data for chemical production. The functions of the control terminal also include information alarm, storage, analysis, statistics, and feeding and discharging feedback control functions. The focus of the present invention is the material level measurement algorithm based on the FBG temperature sensor array, which obtains the distribution of the temperature field of the raw material tank through the FBG temperature sensor array, and then obtains the stable material level value through data preprocessing and related software algorithms, so as to provide decision-making for the feeding and discharging of the raw material tank, and the entire process system will quickly measure the material level value in real time.

[0034] The algorithm in the present invention is based on the structure of the fiber optic liquid level meter for high temperature and high pressure environment in the prior invention patent with the patent number CN201911169252.6 applied by the applicant in 2019 and the invention name "Fiber optic liquid level meter for high temperature and high pressure environment and its manufacturing method", and is designed according to the characteristics of the production equipment and the on-site environment in the chemical production process.

[0035] The specific judgment basis of the present invention is: because there is a large temperature difference ΔT between the two medium environments 0 , so the temperature values ​​measured by the sensor measuring points on both sides of the dividing point show a jump state; the average temperature distribution of the FBG temperature sensor array in the stable state is recorded as The value of each measuring point is the temperature of the raw material or the air temperature in the tank. That is, each FBG temperature sensor measures only two types of temperatures, the temperature of the raw material or the temperature of the air. Based on the influence of the multi-sensor network measurement value superimposed on the spatial distribution factor, the temperature value is specifically manifested as a binomial distribution. Due to the temperature difference between the raw material and the air, ΔT 0 The average temperature of the entire FBG temperature sensor array is different when the material level is at different heights. Therefore, the average temperature method can be used to determine the material level value. The average temperature of the entire storage tank in the current state is Pre-calculate the overall average temperature difference caused by the different reference interface sites and summarize it into a temperature level comparison table. The comparison table is shown in the following table. The temperature is determined by the table lookup method in the future. Corresponding to the material level value h, the average temperature value is calculated in real time, and then the material level value is retrieved.

[0036] Because the upper and lower adjacent measuring points of the material level value should be in the air and raw materials respectively, after the material level value is preliminarily determined, the temperature values ​​of the upper and lower adjacent FBG measuring points of the material level value h are taken for difference judgment, which can further determine the accuracy of the material level value; in addition, the material level h determined by this method should be compared with the material level values ​​at the previous and next moments to observe whether the change trend is logical, that is, the change in raw material volume caused by the change in the tank material level within a certain period of time should not obviously exceed the net volume of the raw materials at the inlet and outlet of the material. After all the above are confirmed to be correct, the material level value h determined by this method can be adopted.

[0037] The present invention has the following advantages and beneficial effects:

[0038] The present invention uses the coupling of laser measurement technology and fiber optic sensing technology in hardware devices, which not only utilizes the high precision and high cost performance of laser measurement technology, but also utilizes the characteristics of fiber optic sensing technology, such as full photoelectric passivity, corrosion resistance, high temperature and high pressure resistance, small size for easy integration, high safety, and remote transmission and measurement. In terms of software algorithms, the linearized inversion relationship between laser direct measurement parameters and material level measurement values ​​is fully utilized. Through the software algorithm processing flow, accurate material level measurement can be achieved quickly, in real time, and with high precision. In addition, the structure has good environmental adaptability, mature installation structure, high safety and reliability coefficient, and is far away from the harsh environment on site. It is very suitable for application in the field of material level measurement in extreme environments such as storage tanks in chemical production processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the hardware structure of the present invention;

[0040] In the figure: 1-raw material tank, 2-feeding port, 3-discharging port, 4-sealing interface, 5-raw material surface, 6-conduction optical cable, 7-FBG temperature sensor array, 8-FBG demodulator, 9-signal transmission bus, 10-control terminal. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0042] In the embodiment, a material level measurement system based on an FBG temperature sensor array is provided. Figure 1 As shown, it includes a FBG demodulator 8, a FBG temperature sensor array 7 and a control terminal 10; the FBG temperature sensor array 7 extends into the raw material 5 of the raw material tank 1, and is connected to the FBG demodulator 8 by a transmission optical cable 6. The FBG temperature sensor array 7 is used to perform distributed measurement of the temperature field along the array direction in the raw material tank 1, and transmit the temperature measurement signal to the FBG demodulator 8 for temperature signal demodulation; the FBG demodulator 8 is connected to the control terminal 10 by a signal transmission line 9, and transmits the temperature information to the control terminal 10 for information algorithm processing, so as to obtain accurate material level information in the raw material tank 1; the control terminal 10 is used for information alarm, storage, analysis, and statistics. The feed port 2 and the discharge port 3 of the raw material tank 1 of the measurement system are respectively provided with flow monitoring interfaces, and flow meters are distributedly inserted into the feed port 2 and the discharge port 3 of the raw material tank 1 to monitor the feed flow and the discharge flow, and the flow meters at the two positions transmit the flow information to the control terminal 10 by connecting the signal transmission line 9. The FBG temperature sensor array 7 in the embodiment adopts an optical fiber liquid level meter for high temperature and high pressure environment, whose outer shell is a metal armored tube, and contains two or more temperature measuring optical fibers, and the tail end of the temperature measuring optical fiber is connected to the transmission optical cable 6.

[0043] The FBG temperature sensor array 7 in the embodiment adopts the FBG temperature sensor array disclosed in patent number CN201911169252.6, specifically including a metal armored tube, an insulating thermal conductive core, a high temperature resistant heating wire, one or two or more temperature measuring optical fibers and a tail end cap. The metal armored tube is a hollow metal tube with one end closed and the other end open, and the interior of the tube is filled with an insulating thermal conductive core. The open end is sealed by the tail end cap, and a heating wire and an optical fiber through hole are provided at a corresponding position in the middle of the tail end cap; a central heating wire through hole and one or two or more temperature measuring optical fiber channels surrounding the central heating wire through hole are provided in the insulating thermal conductive core, the high temperature resistant heating wire is located in the central heating wire through hole, and two or more temperature measuring optical fibers are placed in the corresponding temperature measuring optical fiber channels, and the packaged sensor has its connector led out from the tail end cap and connected to the conductive optical cable.

[0044] The FBG demodulator 8 is equipped with a broadband light source, an optical circulator, a photoelectric conversion and an FPGA acquisition module; the FBG demodulator transmits an optical signal to the FBG temperature sensor array through the broadband light source, and the array reflects the characteristic spectrum signal in real time, which is transmitted to the photoelectric conversion module through the optical circulator, and then the spectrum data is processed and drawn at high speed through the FPGA acquisition module, and the center wavelength of the reflected light of the FBG measuring point obtained by the discrete point Gaussian fitting peak search algorithm is converted into a temperature value through the wavelength-temperature function, and then connected to the control terminal 10 through the signal transmission line 9, and the information is transmitted to the control terminal 10 for information processing, so as to obtain accurate material level information in the raw material tank 1; the processing process is as follows:

[0045] The broadband light source of the FBG demodulator transmits the optical signal to the FBG temperature sensor array. The array reflects the characteristic spectrum signal in real time and transmits it back to the optical demodulation module of the FBG demodulator. The spectrum is processed and drawn at high speed through FPGA. Then, the multiple FBG measurement points obtained by discrete point Gaussian fitting peak search algorithm are analyzed at t m The central wavelength of the reflected light corresponding to the moment FBG ; The center wavelength λ of the reflected light from each FBG measurement point FBG Substitute them into the wavelength-temperature fitting model to obtain the value of each FBG measurement point at the current time t m The temperature value T is obtained as t m The FBG measurement point temperature distribution array at time [T x ]; the wavelength-temperature fitting model is as follows:

[0046]

[0047] where λ 0 is the wavelength value corresponding to the temperature measurement point at the characteristic temperature point, the characteristic temperature point is 0℃ or other temperature reference point value; λ is λ FBG The four variables a, b, c, and d are obtained by calibrating the FBG temperature sensor, that is, the corresponding wavelengths of the FBG at each standard temperature are obtained by fitting the polynomial in the model.

[0048] The control terminal 10 in the embodiment receives the temperature information sent by the FBG demodulator 8 for information alarm, storage, analysis and statistics; according to the above two-dimensional temperature array [T x,y ] and the material level value in each time period obtained by the calculation method, that is, the temperature data of the FBG temperature sensor array is obtained in real time through the FBG demodulator, and the material level value and material level change in the raw material tank can be obtained in real time. The specific process is as follows: take a period of time to sample temperature data, and record the sampled temperature values ​​as a two-dimensional temperature array [T x,y], where x is the FBG measurement point number and y is the acquisition time sequence number; where the two-dimensional array [T x,y ] is the array of temperature variation over time of the mth FBG measuring point [T m,y ], the data in the e-th column is the temperature distribution array of the FBG temperature sensor array space at the e-th sampling moment [T x,e ]; According to the temperature change array of the measuring point [T m,y ], calculate the average temperature difference of the mth FBG measuring point in the n time period in is the average temperature of the mth FBG measuring point in the n-time period; the average temperature difference ΔT of the mth FBG measuring point is calculated m The temperature fluctuation threshold T set in the raw material tank to be tested 0 For comparison; temperature fluctuation threshold T 0 It is a system parameter. The setting of this parameter is closely related to the inlet and outlet material temperatures and the thermal insulation characteristics of the raw material tank. Generally, if the thermal insulation characteristics of the raw material tank are good, the fluctuation threshold is small. This value is usually measured by the temperature during the trial operation of the material system.

[0049] If the average temperature difference of the mth FBG measuring point satisfies the condition ΔT m <T 0 When , it means that the measuring point is in a stable temperature state during this period of time, that is, the measuring point is located in the material or in the air, that is, the FBG temperature measuring point is below or above the material level value; then by comparing its average temperature If the temperature difference between the material and the actual temperature is less than the system parameter T 0 , it means that the FBG temperature measurement point is below the material level value; if it is greater than the system parameter T 0 , it means that the FBG temperature measurement point is above the material level value;

[0050] If the average temperature difference of the mth FBG measuring point satisfies the condition ΔT m ≥T 0 When , it means that the measuring point is in a temperature change state during the n time period, and it can be determined that the current measuring point is located at the interface between the material and the air. The height of the current measuring point can be regarded as the material level value.

[0051] The same method is used to calculate the average temperature difference of all FBG measuring points in the n time period and compare it with the system parameter T 0By comparison, the position of the FBG measuring point where the material is located in the n time period is obtained; if the average temperature difference of all FBG measuring points in the n time period is less than the set temperature fluctuation threshold, it means that the material level value has not changed in the time period. At this time, the material level change moment can be found by calculating the different time periods before and after the n time period, so as to obtain the material level value, or the material level value can be obtained by looking up the corresponding table between the material level value and the temperature average value of the raw material tank to be measured; if the average temperature difference of a certain FBG measuring point in the n time period is greater than the set temperature fluctuation threshold, it means that the material level value in the n time period is at the measuring point position, and only one FBG measuring point has a temperature average difference greater than the system temperature fluctuation threshold, that is, the critical point of the interface between the material and the air is the only determined value.

[0052] The material level value and temperature average value correspondence table is based on the raw material temperature T H and air temperature T L The average temperature of the raw material in the tank at each FBG measuring point is obtained in advance by simulation calculation, that is, the corresponding table of material level value and temperature average value is obtained. In actual testing, it is only necessary to calculate the temperature of the FBG temperature sensor array in real time to obtain the average temperature of the tank. Then, the corresponding table can be retrieved to obtain the material level value h in real time; the material level value h is related to the average temperature of the tank. The calculation of the corresponding table is as follows:

[0053] Average tank temperature (T) Material level height (h) <![CDATA[T L ]]> <![CDATA[h 0 ]]> <![CDATA[(T L *(m-1)+T H ) / m]]> <![CDATA[h 1 ]]> <![CDATA[(T L *(m-2)+T H *2) / m]]> <![CDATA[h 2 ]]> … <![CDATA[(T L +T H *(m-1)) / m]]> <![CDATA[h m-1 ]]> <![CDATA[T H ]]> <![CDATA[h m ]]>

[0054] The specific judgment basis is: because there is a large temperature difference ΔT between the two medium environments 0 , so the temperature values ​​measured by the sensor measuring points on both sides of the dividing point show a jump state; the average temperature distribution of the FBG temperature sensor array in the stable state is recorded as The value of each measuring point is the temperature of the raw material or the air temperature in the tank. That is, each FBG temperature sensor measures only two types of temperatures, the temperature of the raw material or the temperature of the air. Based on the influence of the multi-sensor network measurement value superimposed on the spatial distribution factor, the temperature value is specifically manifested as a binomial distribution. Due to the temperature difference between the raw material and the air, ΔT 0 The average temperature of the tank measured by the entire FBG temperature sensor array is different when the material level is at different heights. Therefore, the average temperature method can be used to determine the material level value. The average temperature of the entire storage tank in the current state is Pre-calculate the overall average temperature difference caused by the different reference interface sites and summarize it into a temperature level comparison table. The comparison table is shown in the following table. The temperature is determined by the table lookup method in the future. Corresponding to the material level value h, the average temperature value is calculated in real time, and then the material level value is retrieved.

[0055] After the material level value h is preliminarily determined by comparing the temperature fluctuation threshold or looking up the table, the temperature values ​​of the adjacent FBG measuring points above and below the preliminarily determined material level value h should be taken to determine whether the medium temperature difference T is satisfied. h+1 -T h >ΔT d , where the threshold T d The value is smaller than the temperature difference ΔT between the material temperature and the air 0 , and is greater than the temperature fluctuation threshold T 0 In addition, the material level h determined by this method should be compared with the material level values ​​before and after to observe whether the change trend is logical, that is, the change in raw material volume caused by the change in tank material level within a certain period of time should not obviously exceed the net volume of raw materials at the inlet and outlet of the material. After the above are confirmed to be correct, the material level value h determined by this method can be used.

[0056] The present invention is further described below in conjunction with a specific embodiment. In the embodiment, the fiber Bragg grating temperature sensor 7 uses a fiber Bragg grating temperature sensor array with 6 FBG measuring points and is vertically installed in the tank body. Each FBG measuring point is 50mm apart, and the heights of each FBG measuring point in the tank body are 50mm, 100mm, 150mm, 200mm, 250mm, and 300mm respectively; the FBG is made using femtosecond laser point-by-point direct writing technology; the fiber Bragg grating high temperature sensor 2 is packaged in a stainless steel tube with an outer diameter of 0.8mm, which is filled with protective gas, and the stainless steel tube packaging length is 2.5m; the fiber Bragg grating demodulator uses a fiber Bragg grating demodulator with a spectral sampling range of 1510-1595nm and a wavelength accuracy of ±2pm, which can perform real-time measurement of the wavelength signal of the fiber Bragg grating high temperature sensor 7 with 6 measuring points. The material level measurement method of the embodiment mainly includes the following steps:

[0057] Step 1: The broadband light source of the FBG demodulator 8 transmits an optical signal to the FBG temperature sensor array 7. The array reflects the characteristic spectral signal in real time and transmits it back to the FBG demodulator 8 to draw the spectrum. The spectrum peak search algorithm of the instrument is then used to analyze and obtain the reflected light center wavelengths of 1520nm, 1530nm, 1540nm, 1550nm, 1560nm, and 1570nm corresponding to the six temperature measurement points.

[0058] Step 2: Substitute the central wavelength λ of the reflected light of the measuring point in step 1 into the wavelength-temperature fitting model to obtain the temperature value T of the measuring point at the current moment; the specific model is as follows: where λ 0 is the wavelength value corresponding to the temperature measurement point at 20°C, and the four variables a, b, c, and d are obtained by fitting a cubic polynomial. Thus, the temperature values ​​of the six temperature measurement points are [80, 80, 80, 30, 30, 30].

[0059] Step 3: Repeat the measurement of the central wavelength λ of the six temperature measurement points and convert them into temperature values ​​to form a two-dimensional temperature array as shown below:

[0060] [80,80,80,80,80,80,80,80,80,80;

[0061] 80,80,80,80,80,80,80,80,80,80,80;

[0062] 80,80,80,80,80,80,80,80,80,80,80;

[0063] 30,30,30,30,30,30,30,30,30,30,30;

[0064] 30,30,30,30,30,30,30,30,30,30,30;

[0065] 30,30,30,30,30,30,30,30,30,30,30,30]

[0066] Step 4: Based on the two-dimensional temperature array in step 3, it can be seen that the temperature of each measuring point is relatively stable, and through the formula Calculate the sample mean difference, in order:

[0067] (|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|) / 10=0

[0068] (|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|) / 10=0

[0069] (|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|+|80-80|) / 10=0

[0070] (|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|) / 10=0

[0071] (|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|) / 10=0

[0072] (|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|+|30-30|) / 10=0

[0073] Set the temperature fluctuation threshold T 0 is 5℃. The average temperature difference of all FBG measuring points calculated 6 times above is less than 5℃. It can be seen that the tank material level value has not changed. Therefore, it is necessary to calculate the temperature average value of the FBG temperature sensor array, and then retrieve the corresponding table of material level value and temperature average value to determine the position of the interface between the material level and the air.

[0074] Based on the raw material temperature of 80°C and the air temperature of 30°C, the average temperature of the raw material in the tank at each FBG measuring point is obtained in advance through simulation calculation, that is, the corresponding table of material level value and temperature average value is obtained, as follows:

[0075] Average tank temperature (℃) Material level height (mm) 30*6 / 6＝30 0 (30*5+80) / 6＝38.3 50 (30*4+80*2) / 6＝46.7 100 (30*3+80*3) / 6＝55 150 (30*2+80*4) / 6＝63.3 200 (30+80*5) / 6＝71.7 250 80*6 / 6＝80 300

[0076] Step 5: According to the two-dimensional temperature array distribution, the tank temperature distribution from bottom to top is [80, 80, 80, 30, 30, 30]; at this moment, the measured average tank temperature is 55. From the table, it can be seen that the current material level height value corresponds to 150mm, that is, at measuring point 3.

[0077] Step 6: Repeat steps 1 to 5 to confirm whether the material level height value is connected to measuring point 3. If so, it complies with the data fluctuation logic and can be adopted. Otherwise, the measurement data will not be adopted.

[0078] The present invention discloses a material level measurement algorithm based on an FBG temperature sensor array. The principle is to couple laser measurement technology and optical fiber sensing technology based on the temperature value change trend and overall distribution of each measuring point in the tank. It not only utilizes the high-precision and cost-effective characteristics of laser measurement technology, but also utilizes the characteristics of optical fiber sensing technology, such as full photoelectric passivity, corrosion resistance, high temperature and high pressure resistance, small size for easy integration, high safety, and remote transmission and measurement. In terms of software algorithm, it fully utilizes the linearized inversion relationship between laser direct measurement parameters and material level measurement values. Through the software algorithm processing flow, accurate material level measurement can be achieved quickly, in real time, and with high precision. In addition, the structure has good environmental adaptability, mature installation structure, high safety and reliability coefficient, and is far away from the harsh environment on site. It is very suitable for application in the field of material level measurement in extreme environments such as storage tanks in chemical production processes.

[0079] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A material level measurement system based on FBG temperature sensor array, characterized in that: The measurement system comprises an FBG demodulator (8), an FBG temperature sensor array (7) and a control terminal (10); the FBG temperature sensor array (7) extends into the raw material (5) of the raw material tank (1) and is connected to the FBG demodulator (8) through a transmission optical cable (6) for signal transmission; the FBG temperature sensor array (7) is used to perform distributed measurement of the temperature field in the raw material tank (1) along the array direction, and transmit the temperature measurement signal to the FBG demodulator (8) for temperature signal demodulation; The FBG demodulator (8) is equipped with a broadband light source, an optical circulator, a photoelectric conversion and an FPGA acquisition module; the FBG demodulator transmits an optical signal to the FBG temperature sensor array through the broadband light source, and the array reflects a characteristic spectrum signal in real time, which is transmitted to the photoelectric conversion module through the optical circulator, and then the spectrum data is processed and plotted at high speed through the FPGA acquisition module, and the center wavelength of the reflected light of the FBG measuring point obtained by the discrete point Gaussian fitting peak search algorithm is converted into a temperature value through a wavelength-temperature function, and then connected to the control terminal (10) through a signal transmission line (9), and the temperature information is transmitted to the control terminal (10) for information processing, so as to obtain accurate material level information in the raw material tank (1); The control terminal (10) receives the temperature information sent by the FBG demodulator (8), stores, analyzes and counts the temperature information, and then calculates the average temperature difference ΔT of each FBG measuring point in a certain time period, and obtains the material level value in the time period based on the average temperature difference ΔT and a preset temperature fluctuation threshold.

2. A material level measurement system based on FBG temperature sensor array according to claim 1, characterized in that The process of obtaining the center wavelength of the reflected light of the FBG measuring point by the FBG demodulator (8) through the discrete point Gaussian fitting peak finding algorithm is as follows: first, through the intensity threshold judgment, the positions of all discrete intensity maximum points whose spectrum intensity is higher than the threshold are found, and then, with each discrete intensity maximum point as the center, appropriate width data is selected on the left and right to intercept a discrete point spectrum, and then the discrete Gaussian fitting algorithm is used to obtain a continuous point spectrum curve. The peak value y of the curve max The corresponding x position is the central wavelength λ of each FBG measurement point FBG .

3. A material level measurement system based on FBG temperature sensor array according to claim 1, characterized in that The process of converting the wavelength-temperature function into a temperature value by the FBG demodulator (8) is as follows: Substituting the central wavelength of the reflected light of the FBG measuring point into the wavelength-temperature fitting model to obtain the temperature of each FBG measuring point at the current time t m The wavelength-temperature fitting model is as follows: Where λ0 is the wavelength value corresponding to the temperature measurement point at the characteristic temperature point, and the characteristic temperature point is 0℃ or other temperature reference point value; λ is λ FBG The four variables a, b, c, and d are obtained by calibrating the FBG temperature sensor, that is, the corresponding wavelengths of the FBG at each standard temperature are obtained by fitting the polynomial in the model.

4. A material level measurement system based on FBG temperature sensor array according to claim 1, characterized in that The control terminal (10) calculates the average temperature difference ΔT of each FBG measuring point in a certain time period to obtain the material level value in the time period as follows: an array [T m,y ], calculate the average temperature difference ΔT of the mth FBG measuring point according to the following formula m : In the above formula: is the average temperature of the mth FBG measuring point in the n-time period; The average temperature difference ΔT of the mth FBG measuring point is calculated m Compare with the temperature fluctuation threshold T0 set in the raw material tank to be tested, and meet the condition ΔT m When ≥T0, the height of the mth FBG measuring point is regarded as the material level value within the n time period.

5. The material level measurement system based on the FBG temperature sensor array according to claim 1, characterized in that: The feed port (2) and discharge port (3) of the raw material tank (1) of the measurement system are respectively provided with flow monitoring interfaces, into which a flow meter can be inserted to monitor the feed flow rate and the discharge flow rate; and the flow meter transmits the flow information to the control terminal (10) via a connected signal transmission line (9).

6. A material level measurement system based on FBG temperature sensor array according to claim 1 or 2, characterized in that: The FBG temperature sensor array (7) uses an optical fiber liquid level meter for high temperature and high pressure environments, the outer shell of which is a metal armored tube, and contains two or more temperature measuring optical fibers, the tail ends of which are connected to the transmission optical cable (6).

7. A material level measurement method based on FBG temperature sensor array, characterized in that: The specific steps are as follows: (1) The broadband light source of the FBG demodulator transmits optical signals to the FBG temperature sensor array. The array reflects the characteristic spectral signals in real time and transmits them back to the optical demodulation module of the FBG demodulator. The spectrum is processed and drawn at high speed through FPGA. Then, the multiple FBG measurement points obtained by discrete point Gaussian fitting peak finding algorithm are analyzed at t m The central wavelength of the reflected light corresponding to the moment FBG ; (2) The center wavelength λ of the reflected light from each FBG measurement point in step (1) is FBG Substitute them into the wavelength-temperature fitting model to obtain the value of each FBG measurement point at the current time t m The temperature value T is obtained as t m The FBG measurement point temperature distribution array at time [T x ]; the wavelength-temperature fitting model is as follows: Where λ0 is the wavelength value corresponding to the temperature measurement point at the characteristic temperature point, and the characteristic temperature point is 0℃ or other temperature reference point value; λ is λ FBG ; The four variables a, b, c, and d are obtained by calibrating the FBG temperature sensor, that is, the corresponding wavelength of the FBG at each standard temperature is obtained by fitting the polynomial in the model; (3) Take a period of time to sample temperature data and record the sampled temperature values ​​as a two-dimensional temperature array [T x,y ], where x is the FBG measurement point number and y is the acquisition time sequence number; where the two-dimensional array [T x,y ] is the array of temperature variation over time of the mth FBG measuring point [T m,y ], the data in the e-th column is the temperature distribution array of the FBG temperature sensor array space at the e-th sampling moment [T x,e ]; (4) Calculate the average temperature difference of all FBG measuring points in time period n according to the temperature variation array of the FBG measuring points in step (3), where time period n is a certain period of time within the temperature data collection time period in step (3); the average temperature difference ΔT of the mth FBG measuring point is m is an array of the temperature variation of the mth FBG measuring point over time [T m,y ] is calculated, and the calculation formula is as follows: In the above formula: is the average temperature of the mth FBG measuring point in the n-time period; (5) Compare the average temperature difference ΔT of each FBG measuring point in the n time period calculated in step (4) with the temperature fluctuation threshold T0 set in the raw material tank to be tested, and determine the material level value of the raw material tank in the time period according to the comparison result; the specific process is as follows: If the average temperature difference of the mth FBG measuring point in this time period satisfies the condition ΔT m When ≥T0, the height of the mth FBG measuring point is regarded as the material level value; If the average temperature difference ΔT of all FBG measuring points in the time period is less than the set temperature fluctuation threshold T0, the average temperature difference of all FBG measuring points in different time periods before and after the n time period is repeatedly calculated according to the calculation method in step (4) until the FBG measuring point satisfying ΔT≥T0 is found, thereby obtaining the material level value, or the material level value is obtained according to the corresponding table of the material level value and the temperature average value of the raw material tank.

8. The material level measurement method based on the FBG temperature sensor array according to claim 7, characterized in that: In the step (1), the center wavelength λ of the reflected light corresponding to the corresponding FBG measuring point is obtained by analyzing the discrete point Gaussian fitting peak finding algorithm. FBG The specific process is to first judge by the intensity threshold, find the positions of all discrete intensity maximum points with spectral intensity higher than the threshold, and then select appropriate width data on the left and right with each discrete intensity maximum point as the center, so as to intercept a discrete point spectrum, and then use the discrete Gaussian fitting algorithm to obtain the continuous point spectrum curve: The peak value y of the curve max The corresponding x position is the central wavelength λ of each FBG measurement point FBG ; Use the same method to find the central wavelength corresponding to each FBG measurement point and get t m The center wavelength array of the reflected light from the FBG temperature sensor array at the moment.

9. The material level measurement method based on the FBG temperature sensor array according to claim 7, characterized in that: The corresponding table of material level value and temperature average value in step (5) is based on the raw material temperature T H and the average tank temperature In the following formula, m represents the number of measurement points of the FBG temperature sensor array, h0,h1…h m-1 ,h m They represent the height of each FBG measuring point in the tank, and the specific calculation is as follows:

10. The material level measurement method based on the FBG temperature sensor array according to claim 7, characterized in that: In step (5), after the material level value h is preliminarily determined by comparing the temperature fluctuation threshold or the table lookup method, the temperature values ​​of the adjacent FBG measuring points above and below the preliminarily determined material level value h are taken as the difference to determine whether the medium temperature difference |T h+1 -T h-1 |>ΔT d If it is satisfied, the material level value h is determined to be accurate; where T h+1 Indicates the temperature of the previous measuring point adjacent to the FBG measuring point corresponding to the material level value, T h-1 Indicates the temperature of the next measuring point adjacent to the FBG measuring point corresponding to the material level value, T d It represents the threshold temperature difference, which is smaller than the temperature difference ΔT0 between the raw material and the air, and larger than the temperature fluctuation threshold T0.

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