CN119290046A - A reflectivity-encoded fiber grating sensing system and measurement method - Google Patents
A reflectivity-encoded fiber grating sensing system and measurement method Download PDFInfo
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- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
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Abstract
本发明提供一种反射率编码的光纤光栅传感系统及测量方法，该系统包括宽带光源、环形器、光纤光栅阵列、光纤光栅解调模块和数据处理器；光纤光栅阵列包括串接在一根光纤上的若干光纤光栅传感器；同一根光纤上的光纤光栅传感器的数量小于或等于两倍的宽带光源的解调带宽除以每个光纤光栅传感器所用带宽范围；位于同一根光纤上的光纤光栅传感器按波长大小顺序排列，且按照反射率高低规律间隔排布；数据处理器对光强进行二进制编码，通过分析编码定位到对应的光纤光栅传感器，再换算所述的待测物理量。本发明能够识别光纤光栅阵列里传感器布置过多波长间隔过密而产生的跳峰现象，让相邻传感器可以共用部分带宽，从而实现光纤传感器数量的扩容。
The present invention provides a reflectivity-coded fiber grating sensing system and a measuring method, the system comprising a broadband light source, a circulator, a fiber grating array, a fiber grating demodulation module and a data processor; the fiber grating array comprises a plurality of fiber grating sensors connected in series on an optical fiber; the number of fiber grating sensors on the same optical fiber is less than or equal to twice the demodulation bandwidth of the broadband light source divided by the bandwidth range used by each fiber grating sensor; the fiber grating sensors on the same optical fiber are arranged in order of wavelength size and are arranged at regular intervals according to the reflectivity; the data processor performs binary encoding on the light intensity, locates the corresponding fiber grating sensor by analyzing the encoding, and then converts the physical quantity to be measured. The present invention can identify the peak jumping phenomenon caused by too many sensors arranged in the fiber grating array and too densely spaced wavelengths, so that adjacent sensors can share part of the bandwidth, thereby realizing the expansion of the number of optical fiber sensors.
Description
Technical Field
The invention belongs to the application fields of optical fiber sensing and long-distance measurement, and particularly relates to a reflectivity coded optical fiber grating sensing system and a measuring method.
Background
The multipoint high-temperature or large-strain monitoring system has important application prospect in the field of large-scale structural safety. For example, in the field of large civil engineering safety, concrete is easily cracked due to the influence of temperature and load in the construction process, and the overall safety of engineering is threatened. The multi-point strain monitoring can timely find the strain condition of each key part and predict the health and service life of the structure. And in the fields of oil tanks, tunnels, pipe galleries and the like, fire disaster monitoring and fire source positioning also need a large number of high-temperature sensing points.
The traditional strain and temperature measurement method utilizes an optical fiber grating array to prepare a plurality of optical fiber grating temperature sensors on one optical fiber, so that the multi-point long-distance temperature measurement and strain measurement of one optical fiber can be realized. This multiplexing method is often determined by using the difference in center wavelengths of the reflection spectra of the fiber grating sensors at different locations on the fiber. Since the bandwidth of the demodulator for monitoring the shift of the reflection peak of the fiber grating is limited, each grating sensor needs to occupy a certain bandwidth of the instrument, so that the number of sensors which can be connected in series on one fiber can only be the total bandwidth of the instrument divided by the bandwidth that each sensor needs to occupy at most. In the field of high temperature or large strain monitoring, each grating sensor needs to occupy a large bandwidth, so that the number of sensors which can be connected into a system in series is limited, and the high-density monitoring needs cannot be met. How to effectively increase the number of sensors that can be accommodated by the system under the condition of maintaining the hardware bandwidth of the demodulator is a core technical problem.
In conventional demodulation systems, each grating sensor must occupy a certain bandwidth because its reflectivity is uniform. The reflection spectrum of each grating is the same peak type in the demodulation spectrum. When the spectral shift of the reflection peak of a certain grating is too large to exceed the reflection peak of the grating beside the grating (called a "jump peak" phenomenon), the system cannot recognize the "dislocation" of the two peaks, and the adjacent peaks are taken as the original peaks to store data, so that data recording errors can occur. Therefore, in actual engineering, when the optical fiber sensing system is designed, the difference of the central wavelengths of two gratings, which are possibly subjected to peak jump, is increased actively, and enough bandwidth is reserved, so that the peak jump phenomenon is ensured not to occur. This eliminates the possibility of errors, but significantly reduces the number of gratings multiplexed on one fiber.
Therefore, the peak-jump phenomenon causes a limited number of sensors to be accommodated under a certain bandwidth, so that the fiber bragg grating system is difficult to use in a large scale in actual engineering.
Disclosure of Invention
The invention aims to solve the technical problem of providing a reflectivity coded fiber bragg grating sensing system and a measuring method, which can identify the peak jump phenomenon and reduce the bandwidth used by a single fiber bragg grating sensor so as to realize the capacity expansion of the number of the fiber bragg grating sensors.
The invention adopts the technical proposal that the optical fiber grating sensing system with reflectivity coding comprises a broadband light source, a circulator, an optical fiber grating array, an optical fiber grating demodulation module and a data processor, wherein,
The fiber grating array comprises a plurality of fiber grating sensors connected in series on one fiber, the fiber grating sensors are paved in a long-distance object to be measured, and each fiber grating sensor is used for sensing the physical quantity to be measured at the position; the number of the fiber grating sensors on the same fiber is less than or equal to twice the demodulation bandwidth of the broadband light source divided by the bandwidth range used by each fiber grating sensor;
The optical beam emitted by the broadband light source enters an optical fiber grating array through a circulator, each optical fiber grating sensor in the optical fiber grating array returns reflection spectrums with different center wavelengths, the optical fiber grating array demodulation module converts an optical signal into an electric signal according to the reflection spectrums, the data processor carries out binary coding on the electric signal, and the electric signal is positioned to the corresponding optical fiber grating sensor through analysis coding and then converted into the physical quantity to be measured;
the fiber bragg grating sensors are arranged on the optical fibers at intervals according to the respective reflectivity, and meanwhile, the data processor encodes the electric signals according to the corresponding rules.
According to the scheme, the certain ordering rule is that the fiber bragg grating sensors are divided into two types of high-reflection type and low-reflection type according to the reflectivity, and the two types of fiber bragg grating sensors are staggered and set on the same optical fiber;
Setting a certain light intensity threshold according to the two types of fiber bragg grating sensors, so that the highest light intensity of the reflection spectrum center returned by the high-reflection fiber bragg grating sensor is higher than the light intensity threshold, and the highest light intensity of the reflection spectrum center returned by the low-reflection fiber bragg grating sensor is lower than the light intensity threshold;
The data processor sets corresponding rules to code the electric signals specifically that the electric signals comprise wavelengths and light intensities, and the codes are 1 when the received light intensities are higher than a light intensity threshold value, 0 when the received light intensities are lower than the light intensity threshold value, and binary codes are formed according to the light intensities of reflection spectrums returned by all the fiber bragg grating sensors;
in a normal state, the number of bits of the initial binary code is the same as that of the fiber bragg grating sensors, and the binary code values correspond to the position sequences of the fiber bragg grating sensors one by one.
According to the above scheme, the data processor is specifically used for:
The wavelength and the light intensity of each grating are obtained from the fiber grating serial spectrum measured by the fiber grating demodulation module;
The binary codes are obtained according to the light intensity, the state changes of the binary codes are compared in real time, and the position of the fiber bragg grating sensor with the physical quantity change to be detected is determined through analysis of the numerical value changes of the binary codes;
and converting the corresponding physical quantity to be measured according to the peak jump state of the grating and the spectral center wavelength offset.
According to the scheme, the real-time comparison of the binary code state changes, and the determination of the position of the fiber bragg grating sensor with the physical quantity change to be measured through the binary code numerical value change analysis specifically comprises the following steps:
Setting a register for storing the binary subtraction value of the current binary code and the initial binary code;
when the difference value is 0, the peak jumping state is that the peak is not jumped, and the physical quantity to be measured of each fiber bragg grating sensor is determined through the wavelength drift quantity of each fiber bragg grating sensor;
When one bit in the difference value is 1, judging that the peak jump state of the fiber bragg grating sensor corresponding to the bit is the peak jump, exchanging the serial number of the fiber bragg grating sensor with the serial number of the crossed fiber bragg grating sensor, recalculating the wavelength drift amount, and determining the physical quantity to be measured of each fiber bragg grating sensor.
According to the scheme, the physical quantity to be measured is obtained by dividing the wavelength offset of each fiber bragg grating sensor by the sensitivity of the corresponding fiber bragg grating sensor.
According to the scheme, the physical quantity to be measured is the temperature of the long-distance object to be measured at each fiber bragg grating sensor, and the long-distance object to be measured is an oil tank, a tunnel or a pipe gallery.
According to the scheme, the physical quantity to be measured is the strain of the long-distance object to be measured at each fiber bragg grating sensor, and the long-distance object to be measured is a bridge or a building.
As a second aspect of the present invention, the present invention further provides a measurement method of a fiber grating sensing system based on the reflectivity code, the method comprising:
binary coding is carried out according to the light intensity of the reflection spectrum of the fiber bragg grating sensor;
Positioning the corresponding fiber grating sensor through analysis codes;
And converting the physical quantity to be measured at each fiber bragg grating sensor.
According to the method, an initial binary code is obtained in a normal state;
monitoring the received light intensity in real time to obtain the current binary code;
and judging whether each fiber bragg grating sensor has a peak jump or not by analyzing the difference value between the current binary code and the initial binary code, so that the fiber bragg grating sensor is positioned on the received wavelength, and then the physical quantity to be measured at each fiber bragg grating sensor is converted.
As a third aspect of the invention, the invention also provides an electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the measurement method when executing the computer program.
The invention has the beneficial effects that the fiber bragg grating sensors are arranged according to a certain rule by reflectivity, and the coding rule is formulated according to the rule, so that corresponding codes are obtained according to the coding rule when light intensity is received, the peak jump phenomenon caused by too many wavelength intervals of the sensor arrangement in the fiber bragg grating array is identified through the coding change value, the fiber bragg grating sensors can be accurately positioned when the peak jump exists, and further, adjacent sensors can share partial bandwidth when the fiber bragg grating array is set, so that the expansion of the quantity of the fiber bragg sensors is realized.
Drawings
FIG. 1 is a schematic diagram of a system architecture according to an embodiment of the present invention.
FIG. 2 is a diagram of a normally received fiber grating sensor according to an embodiment of the present invention.
FIG. 3 is a graph showing the spectral change of a fiber grating sensor according to an embodiment of the present invention when the sensor is subjected to high temperature/large strain.
FIG. 4 is a binary code variation diagram of a fiber grating sensor with high temperature according to an embodiment of the present invention.
Fig. 5 is a logic diagram of a method according to an embodiment of the present invention.
In the figure, a 1-broadband light source, a 2-circulator, a 3-fiber bragg grating array, a 4-fiber bragg grating demodulator and a 5-data processor are shown.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention provides a reflectivity coded fiber bragg grating sensing system and a measuring method, which can identify peak jump phenomenon generated by too many sensors arranged in a fiber bragg grating array at too close wavelength intervals, so that adjacent sensors can share part of bandwidth, and the capacity expansion of the number of the fiber bragg sensors is realized. The fiber bragg grating sensing system is mainly used for measuring the physical quantity to be measured of long-distance objects, such as the temperature of an oil tank, a tunnel or a pipe gallery, when the temperature is changed greatly, explosion risks are indicated, and the strain of a bridge or a building is indicated, when the strain is changed greatly, collapse risks are indicated.
As a first aspect of the present invention, the present invention provides a reflectivity coded fiber grating sensing system, as shown in fig. 1, including a broadband light source 1, a circulator 2, a fiber grating array 3, a fiber grating demodulation module 4, and a data processor 5.
The fiber grating array comprises a plurality of fiber grating sensors connected in series on one fiber, the fiber grating sensors are paved in a long-distance object to be measured, and each fiber grating sensor is used for sensing the physical quantity to be measured at the position. The number of the fiber grating sensors on the same fiber is less than or equal to twice the demodulation bandwidth of the broadband light source divided by the bandwidth range used by each fiber grating sensor, and the center wavelengths of the fiber grating sensors on the same fiber are different and are arranged in the order of the center wavelengths, for example, the order of the center wavelengths from small to large or the order of the center wavelengths from large to small. The peak jump phenomenon of the single fiber grating sensor only occurs once, and the maximum central wavelength offset does not exceed the second peak, so that the interval between the central wavelengths of the adjacent fiber grating sensors is generally not required to be constrained, and is generally not more than 3nm in practice.
The optical beam emitted by the broadband light source enters the fiber bragg grating array through the circulator, each fiber bragg grating sensor in the fiber bragg grating array returns to different center wavelengths, the fiber bragg grating array demodulation module converts an optical signal into an electric signal according to a reflection spectrum, the data processor encodes the electric signal, positions the corresponding fiber bragg grating sensor through analysis encoding, and converts the physical quantity to be measured.
The fiber bragg grating sensors are arranged on the optical fibers according to the respective reflectivity and a certain ordering rule, and meanwhile the data processor encodes the electric signals according to the corresponding rule.
In this embodiment, the certain ordering rule is that the fiber bragg grating sensors are classified into two types of high-reflection type and low-reflection type according to reflectivity, and the two types of fiber bragg grating sensors are staggered on the same optical fiber. Due to the different reflectivities, the intensity of the reflected light is also different. Setting a certain light intensity threshold according to the two types of fiber bragg grating sensors, so that the highest light intensity of the reflection spectrum center returned by the high-reflection fiber bragg grating sensor is higher than the light intensity threshold, and the highest light intensity of the reflection spectrum center returned by the low-reflection fiber bragg grating sensor is lower than the light intensity threshold;
The data processor sets corresponding rules to code the electric signals specifically that the electric signals comprise wavelengths and light intensities, the codes are 1 when the received light intensities are higher than a light intensity threshold value, the codes are 0 when the received light intensities are lower than the light intensity threshold value, and binary codes are formed according to the light intensities of reflection spectrums returned by all the fiber bragg grating sensors.
Thus, in a normal state, the number of bits of the initial binary code is the same as that of the fiber bragg grating sensors, and the binary code value corresponds to the position sequence of the fiber bragg grating sensors one by one. The normal state means that the physical quantity to be measured is in a normal state, no large change occurs, the reflection spectrum movement amount of the fiber bragg grating sensor is not large, and no peak jump phenomenon occurs. For example, the temperature or strain is the temperature or strain of the long-distance object to be measured in a normal state. When the temperature of the long-distance object to be measured changes greatly (possibly causing explosion) or the strain exceeds a certain threshold (possibly causing structural stability), the object to be measured is abnormal.
The data processor is particularly adapted to:
And acquiring the wavelength and the light intensity of each grating from the fiber grating serial spectrum measured by the fiber grating demodulation module.
And obtaining the binary code according to the light intensity, comparing the state change of the binary code in real time, and analyzing and determining the position of the fiber bragg grating sensor with the change of the physical quantity to be detected through the numerical value change of the binary code. Specifically, a register is set for storing the binary subtraction value of the current binary code and the initial binary code.
And converting the corresponding physical quantity to be measured according to the peak jump state of the grating and the spectral center wavelength offset. Specifically, when the difference is 0, the peak jump state is no peak jump, and the physical quantity to be measured of each fiber bragg grating sensor is determined by the wavelength drift quantity of each fiber bragg grating sensor. When one bit in the difference value is 1, judging that the peak jump state of the fiber bragg grating sensor corresponding to the bit is the peak jump, exchanging the serial number of the fiber bragg grating sensor with the serial number of the crossed fiber bragg grating sensor, recalculating the wavelength drift amount, and determining the physical quantity to be measured of each fiber bragg grating sensor.
Further, the physical quantity to be measured is obtained by dividing the wavelength offset of each fiber bragg grating sensor by the sensitivity of the corresponding fiber bragg grating sensor.
A certain interval is required between the center wavelengths of the adjacent fiber bragg grating sensors on the same fiber.
As a second aspect of the present invention, the present invention further provides a measurement method of a fiber grating sensing system based on the reflectivity code, the method comprising:
S1, coding according to the light intensity of the fiber grating sensor. For ease of computation, the code is preferably binary.
S2, positioning the corresponding fiber bragg grating sensor through analysis codes. And monitoring the received light intensity in real time to obtain the current binary code. And judging whether each fiber bragg grating sensor has a peak jump or not by analyzing the difference value between the current binary code and the initial binary code, so that the fiber bragg grating sensor is positioned on the received wavelength.
S3, converting the physical quantity to be measured at each fiber bragg grating sensor.
The invention will be further described by taking 12 fiber grating sensors as an example. In practice, the number of fiber grating sensors may be much greater than 12.
With continued reference to fig. 1, the fiber bragg grating array 3 includes 12 fiber bragg grating sensors connected in series on one fiber, the reflectivity of the odd-numbered fiber bragg grating sensor is 90%, and the reflectivity of the even-numbered fiber bragg grating sensor is 40%. Since the reflectivity of the fiber bragg grating string is set from left to right in sequence from high to low, the reflection spectrum light intensity is arranged from left to right in sequence from high to low. The fiber grating demodulator converts the spectrum quantization into discrete voltage values, the data processor encodes the collected high voltage into 1, and the low voltage into 0. Therefore, the binary code of the fiber grating string at normal temperature is 101010101010, and the reflection spectrum chart and binary code of the fiber grating at normal temperature need to be recorded to be used as an initial state for identifying the peak jump.
The temperature measurement and positioning conditions of the single-point high-temperature heat source are described below.
Assuming that the fiber grating is characterized by a center wavelength shift to the right of 1pm for every 1 ℃ increase in temperature. At normal temperature, the center wavelength of each fiber grating is 3nm different from that of the adjacent fiber gratings, as shown in fig. 2. Assuming that the x-th fiber grating sensor senses the stimulation of the high-temperature heat source, fig. 3 is a spectrum change diagram of the high-temperature heat source of the x-th fiber grating sensor of the fiber grating string. As can be seen from fig. 3, the center wavelength of the x-th fiber grating is shifted to the position of the x+2-th fiber grating in the whole temperature variation range, so that only 3 bits, x-th bit, x+1-th bit and x+2-th bit of the binary code value need to be considered. FIG. 4 is a graph of the change in binary code of the high temperature heat source occurring at the x-th sensor of the fiber grating string, corresponding to different spectral diagrams and different binary code values according to specific temperature changes and parity of x. When the temperature of the high-temperature heat source detected by the x-number sensor is at normal temperature, the code value corresponding to the odd number is 101, and the code value corresponding to the even number is 010. When the temperature of the detected high-temperature heat source is between 0 and 300 ℃, the reflection spectrum of the X-number fiber grating shifts toNumber position. The code value corresponding to the odd number is 101, the code value corresponding to the even number is 010, and the code value is unchanged. When the temperature is 300 ℃, the reflection spectrum shifts toIn the number position, the code value corresponding to the odd number is 11, and the code value corresponding to the even number is 10. The reason for the one less than the one bit is that the center wavelength of the reflection spectrum of the x-sensor coincides with the center wavelength of the reflection spectrum of the x+1-sensor, and the data processor encodes the voltage value corresponding to the coincidence spectrum as 1. When the temperature is 300-600 ℃, the reflection spectrum shifts toNumber position. The code value corresponding to the odd number is 011, and the code value corresponding to the even number is 100.
The absolute value of the difference between the initial state binary value m 0 and the changed state binary code value m 1 is recorded as an absolute state change value m c. The formula is as follows:
|m0-m1| = mc
And recording the reflection center wavelength value of the spectrum grating at each position, and comparing the reflection center wavelength value with the reflection center wavelength value of the spectrum grating at normal temperature one by one, wherein the fiber grating with the changed center wavelength is the position where the high-temperature heat source appears. And (3) obtaining the wavelength offset by making a difference between the changed central wavelength value and the central wavelength value at normal temperature, thereby converting the measured temperature. This method is referred to as a wavelength-by-wavelength comparison method. When the temperature of the xth sensor is in the interval of 0-300 ℃, the absolute state change value obtained by the register is 000, and the state is in a non-jump peak state. It is therefore necessary to further perform a wavelength-by-wavelength comparison to obtain the measured temperature. When the temperature of the xth sensor is in the interval of 300-600 ℃, x is smaller than 12, the absolute state change value obtained by the register is 010, and the state is in a peak jump state. Because there are a total of 12 bits of binary, the remaining nine bits are 0, the location of the high temperature heat source can be determined by the location of the 1's present in the 12 bits of binary. The x-th sensor has high temperature, and then 1 is at the x+1 bit of the binary system. Then, a wavelength-by-wavelength comparison method is performed, and the temperature value obtained by the conversion is added with 300 ℃ to obtain the measured temperature. In the case where x is equal to 12, the wavelength-by-wavelength comparison method is directly performed. When the temperature of the xth sensor is 300 ℃, the two central wavelengths of the spectrum are overlapped, the obtained 12-bit binary code value is reduced to 11 bits, and the corresponding peaks are in a superposition state. In this case, the central wavelength value of each position is calculated, and when x is greater than 1, the central wavelength of the reflection spectrum of the x-th fiber grating sensor differs from the x+1st position by 6nm, so that the position of the high-temperature heat source can be positioned only by judging that the difference between adjacent wavelengths is 6 nm. Based on the above analysis, a software logic diagram is made as shown in fig. 5.
The invention also provides an electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, which processor implements the steps of the measuring method when executing the computer program. The electronic device is a smart phone, a tablet computer, a notebook computer, a desktop computer, a rack-mounted server, a blade server, a tower server or a cabinet server (comprising an independent server or a server cluster formed by a plurality of servers) and the like which can execute programs.
The invention provides a high-temperature/large-strain measurement fiber grating array capacity expansion method and a system for binary coding of reflectivity, which aim to doubly improve the number of fiber grating sensors accommodated on one fiber under the condition of not reducing a measurement range, and effectively improve the utilization rate of a system by solving the problem of recording errors caused by peak jump.
It should be noted that, how much bandwidth is used by one fiber bragg grating sensor is not standard, and the bandwidth can be selected according to actual conditions. The invention aims to increase the usage amount of the fiber bragg grating sensor by one time under the condition that the original bandwidth is unchanged.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.
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