Calibration method of multi-measuring-point fiber bragg grating temperature measurement sensor

Abstract

The invention discloses a calibration method of a multi-measuring-point fiber grating temperature measurement sensor, and belongs to the technical field of temperature sensor calibration. The calibration method comprises the following steps: firstly, arranging a test environment calibrated by a multi-measuring-point fiber grating temperature measurement sensor, and setting a plurality of calibration temperature points; starting the incubator, keeping the temperature for a set time length when the incubator reaches each calibration temperature point, and recording the temperature indicating value of the thermocouple mounted on each fiber grating temperature measurement sensor and the wavelength value of the connected fiber grating temperature sensor under each calibration temperature line; and the process is cycled for multiple times, and according to the corresponding numerical values of each fiber grating temperature measurement sensor under each calibration temperature line recorded in a certain cycle, a function relation between the thermocouple temperature corresponding to each fiber grating temperature measurement sensor and the wavelength of the fiber grating type temperature sensor is obtained, and the function relation is used as a calibration curve of each fiber grating temperature measurement sensor. According to the invention, errors caused by non-uniformity and instability of the temperature in the calibration temperature box in the calibration process can be reduced.

Description

Technical Field

[0001] The invention relates to a calibration method for a multi-measurement-point optical fiber grating temperature measuring sensor, belonging to the technical field of temperature sensor calibration. Background Art

[0002] Fiber Bragg grating sensors have the advantages of high sensitivity, resistance to electromagnetic interference, small sensor unit size, easy networking, and can be surface-mounted or deployed inside equipment. They have been widely used in power systems, civil engineering, chemical industry, aerospace, medical and other fields.

[0003] The change of fiber Bragg Bragg wavelength is linearly related to the change of temperature under certain conditions. By calibrating the linear fiber Bragg grating sensor, the relationship between the change of fiber Bragg grating wavelength and the change of ambient temperature is determined, and the temperature value can be accurately calculated by wavelength, thus realizing fiber Bragg grating temperature measurement.

[0004] However, in practical applications, the linear fitting curve of the fiber Bragg grating reflection wavelength and temperature has a larger measurement error than the standard temperature sensor. Therefore, it is necessary to add a correction term to the fitting curve to reduce the measurement error and improve the measurement accuracy of the sensor.

[0005] Most of its engineering applications are concentrated in the measurement of temperature range of -20 ~ 80 ° C. In addition to the temperature tolerance restrictions brought by the fiber coating, fiber Bragg grating writing and packaging methods, the wavelength temperature coefficient calibration of multi-measurement point fiber Bragg grating high temperature sensors is also a difficulty that limits its engineering applications. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and propose a calibration method for a multi-measurement-point fiber Bragg grating temperature sensor, which provides accurate and convenient temperature calibration for fiber Bragg grating temperature sensors at several measurement points within the working temperature and design length range of the device.

[0007] The technical solution of the present invention is:

[0008] A calibration method for a multi-measurement-point fiber Bragg grating temperature sensor, comprising:

[0009] S1: Test environment for calibration of fiber Bragg grating temperature sensors with multiple measuring points:

[0010] Select multiple fiber Bragg grating temperature measurement sensors with different central wavelengths and connect them in series to form a string of fiber Bragg grating temperature measurement sensors with multiple measurement points;

[0011] The multi-measurement point fiber Bragg grating temperature sensors are placed in an S shape, and both ends of each fiber Bragg grating temperature sensor are mounted on an anti-static box; a thermocouple is mounted between every two adjacent fiber Bragg grating temperature sensors;

[0012] Put the antistatic box into the temperature box, connect each fiber grating temperature sensor to the fiber wavelength acquisition module, and connect each thermocouple to the thermocouple temperature acquisition module; wherein the fiber wavelength acquisition module is used to record the fiber wavelength;

[0013] S2: Conduct calibration test

[0014] S2.1: Set multiple calibration temperature points according to the measuring range of the fiber Bragg grating temperature sensor;

[0015] S2.2: Start the temperature box, and the temperature in the temperature box rises point by point from low temperature to high temperature. When each calibration temperature point is reached, the insulation time is set. The temperature indication of the thermocouple mounted on each fiber Bragg grating temperature sensor and the wavelength value of the connected fiber Bragg grating temperature sensor under each calibration temperature line are recorded;

[0016] S2.3: Turn off the incubator, wait for the incubator to cool down to room temperature naturally, and then perform S2.2 again; repeat the above process several times;

[0017] S3: According to the thermocouple temperature indications of each fiber Bragg grating temperature sensor under each calibration temperature line and the fiber Bragg grating temperature sensor wavelength value recorded in the pth cycle, p>1, the functional relationship between the thermocouple temperature corresponding to each fiber Bragg grating temperature sensor and the fiber Bragg grating temperature sensor wavelength is obtained as the calibration curve of each fiber Bragg grating temperature sensor.

[0018] Further, in step S3, the average value of the thermocouple readings of each fiber Bragg grating temperature sensor at the calibration temperature point in the pth cycle for the last 5 to 10 minutes of heat preservation is taken as the ordinate, and the average value of the wavelength of the fiber Bragg grating temperature sensor is taken as the abscissa, and a polynomial fitting method is used to establish a functional relationship:

[0019] T ′ =a i λ 2 +b i λ+c i

[0020] Where λ is the wavelength of the fiber Bragg grating temperature sensor, T ′ is the thermocouple value, a i 、b i 、c i are respectively the coefficients of the quadratic term, linear term and zero-order term of the function of the i-th fiber Bragg grating temperature sensor.

[0021] Furthermore, the average value of the thermocouple indications of the qth cycle fiber Bragg grating temperature sensor at the calibration temperature point (q>1, q≠p) during the last 5 to 10 minutes of insulation is taken as the standard, and the average value of the wavelength value of the fiber Bragg grating temperature sensor is substituted into the functional relationship of the corresponding fiber Bragg grating temperature sensor to obtain the calculated temperature of the wavelength of the fiber Bragg grating temperature sensor at each calibration temperature point. The calculated temperature is compared with the corresponding standard to obtain the temperature measurement error of each calibration point.

[0022] Furthermore, if the temperature measurement errors of each calibration point are within the allowable range, the obtained calibration curve is the final calibration result; otherwise, the coefficients of the functional relationship are adjusted until the temperature measurement error is within the allowable range.

[0023] Furthermore, according to the temperature measurement range of the fiber grating temperature sensor, a calibration temperature point is selected every 3 to 7 degrees.

[0024] Furthermore, the interval between two adjacent fiber grating temperature sensors is no more than 1.5 cm.

[0025] Furthermore, according to the length of the fiber Bragg grating temperature sensor, 3M double-sided tape is attached to the antistatic box in parallel, and there is no 3M double-sided tape below the grating etching area in the fiber Bragg grating temperature sensor.

[0026] Furthermore, a thermocouple is mounted between every two adjacent fiber grating temperature sensors and is further fixed using 3M 2214 paper tape.

[0027] Furthermore, step 2 is repeated at least 3 times.

[0028] The advantages of the present invention compared with the prior art are:

[0029] (1) The present invention discloses a calibration method based on a fiber Bragg grating temperature sensor, which improves the temperature measurement accuracy of the fiber Bragg grating temperature sensor from the perspective of data algorithm.

[0030] (2) The present invention discloses a calibration method based on a fiber Bragg grating temperature sensor, which uses the obtained calibration curve to perform temperature measurement verification. Compared with the thermocouple indication, the measurement error of the fiber Bragg grating temperature sensor is obtained, and the accuracy of the temperature measurement capability of the fiber Bragg grating temperature sensor is improved by reducing the measurement error. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0032] Figure 1 The calibration test device of the embodiment of the present invention is shown in FIG. (a) is a schematic diagram of a multi-point fiber Bragg grating temperature sensor arranged in an antistatic box, and (b) is a schematic diagram of the connection of the antistatic box;

[0033] Figure 2 This is a flow chart of a calibration method according to an embodiment of the present invention;

[0034] Figure 3 This is a wavelength curve diagram of three calibration tests of the first fiber grating temperature sensor in the second cycle of the embodiment of the present invention;

[0035] Figure 4 This is a temperature curve diagram of three calibration experiments of five thermocouples in the second cycle of the embodiment of the present invention;

[0036] Figure 5 This is a temperature measurement error curve diagram of each calibration point of the first fiber grating sensor in the third cycle of the embodiment of the present invention. DETAILED DESCRIPTION

[0037] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0038] The invention proposes a calibration method for a multi-measurement-point fiber grating temperature sensor, which can reduce the error introduced by the non-uniformity and instability of the temperature in a calibration temperature box during multiple cycle calibration.

[0039] This method is Figure 2 As shown,

[0040] S1: Set up the calibration environment

[0041] like Figure 1 As shown in (a), the fiber Bragg grating temperature sensor 1 is a rectangular parallelepiped with square sides, and its size is 26mm long, 3mm wide and 3mm high. Ten fiber Bragg grating temperature sensors 1 are connected in series to form a series of multi-point fiber Bragg grating temperature sensors. The central wavelength of each fiber Bragg grating temperature sensor 1 is different, and the central wavelength of the first one is 1529.9nm~1530.5nm.

[0042] According to the length of the fiber Bragg grating temperature sensor, the 3M double-sided tape 3 is pasted parallel to the anti-static box 4 with a width of about 20mm to 22mm, so that both ends of the fiber Bragg grating temperature sensor can be pasted on the 3M double-sided tape 3, while ensuring that there is no 3M double-sided tape 3 under the grating etched area in the fiber Bragg grating temperature sensor.

[0043] Each string of multi-point fiber Bragg grating temperature sensors is mounted in an antistatic box 4 in an "S" shape, with a spacing of 1.5 cm between two adjacent fiber Bragg grating temperature sensors. A thermocouple 2 is mounted between every two adjacent fiber Bragg grating temperature sensors 1, and 3M 2214 paper tape 5 is used to further fix them as needed.

[0044] The antistatic box will be placed in the incubator, such as Figure 1 As shown in (b), the fiber Bragg grating temperature sensor is connected to the fiber wavelength acquisition module 6 (ie, demodulator) and the computer, and the thermocouple is connected to the thermocouple temperature acquisition module 7. The fiber wavelength acquisition module is used to record the fiber wavelength.

[0045] S2: Conduct calibration test

[0046] S2.1: Check whether the appearance of the fiber Bragg grating temperature sensor is intact; connect the fiber Bragg grating temperature sensor to the demodulation equipment, operate the demodulation software, set the demodulation parameters, and ensure that the tubular fiber Bragg grating temperature sensor is in a stable state; according to the range of the fiber Bragg grating temperature sensor, set the temperature box calibration temperature points to 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃. According to the temperature measurement range, a total of 11 calibration points are required: 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃. Reference Figure 1 , place the thermocouple and the fiber Bragg grating temperature sensor in an antistatic box according to the calibration temperature point, and put it into the temperature box so that the two are on the same isotherm.

[0047] S2.2: Start the temperature box and gradually increase the temperature from low temperature to high temperature. When the indicated value reaches the calibration temperature point, keep the temperature for 60 minutes according to the temperature stability requirements of the temperature box to ensure that the sensor temperature measurement environment reaches thermal equilibrium; record the thermocouple temperature indication t at the calibration temperature point. m The output wavelength value λ of the fiber Bragg grating temperature sensor m .

[0048] S2.3: Calibration temperature point T m After the data is recorded, the sensor and the temperature loading device are cooled down to room temperature naturally;

[0049] S2.4: Repeat steps 2.1 to 2.3 for 3 times.

[0050] S3: Data Processing

[0051] Establish the functional relationship between temperature and wavelength value: in the three calibration tests, the average value of the thermocouple reading in the last 5 minutes of heat preservation at the second cycle calibration temperature point is used as the ordinate, and the average value of the wavelength value in the last 5 minutes of heat preservation of the fiber Bragg grating temperature sensor is used as the abscissa, and the functional relationship is established by using the polynomial fitting method;

[0052]

[0053] T′=aλ 2 +bλ+c

[0054] Where λ is the wavelength of the fiber Bragg grating temperature sensor, t is the temperature in the temperature chamber, and a, b, and c are the coefficients of the quadratic term, linear term, and zero-order term of the function, respectively.

[0055] In this embodiment, the wavelength curves of the three calibration tests of the first fiber grating temperature sensor are as follows: Figure 3 As shown, the temperature curves of 5 thermocouples after 3 calibration tests are as follows Figure 4 As shown, the function corresponding to the first fiber Bragg grating temperature sensor is T′=-5.41968λ 2 +16670.65934λ-12832543.62.

[0056] S4: parameter verification;

[0057] The average value of the thermocouple readings at the third cycle calibration temperature point during the last 5 minutes of heat preservation As a standard, the average wavelength value of the fiber Bragg grating temperature sensor during the last 5 minutes of heating is taken Substitute into the calibration curve in step 2 to obtain the conversion temperature T′ of the wavelength of the fiber Bragg grating temperature sensor at the mth calibration temperature point m :

[0058]

[0059] The measured value T' of the fiber Bragg grating temperature sensor wavelength is compared with the value indicated by the standard temperature sensor. By comparison, the measurement error of the fiber Bragg grating temperature sensor is obtained:

[0060]

[0061] In the formula, Δt 3n In the third cycle, the fiber Bragg grating temperature sensor is at T n The temperature measurement error is ℃; T' is the temperature measurement error of the fiber Bragg grating temperature sensor at the calibration point T in the third cycle. n The measured value at ,℃; In the third cycle, the thermocouple is at the calibration point T n Indication at , ℃.

[0062] The accuracy of the temperature measurement capability of the fiber grating temperature sensor is improved by reducing or eliminating the measurement error.

[0063] In this example, in a series of multi-point fiber Bragg grating temperature sensors, the first fiber Bragg grating temperature sensor is subjected to temperature calibration test and data processing, and the calibration curve obtained is: T′=-5.41968λ 2 +16670.65934λ-12832543.62, the temperature measurement error curve of each calibration point of the first fiber Bragg grating sensor is as follows Figure 5 As shown, the maximum temperature measurement error is 0.191°C.

[0064] The calibration device in the present invention has a simple structure and is easy to build. The calibration method is simple to operate and has high positioning accuracy. It can provide accurate and convenient wavelength temperature coefficient calibration for the fiber grating temperature measurement sensor at several measuring points within the working temperature and design length range of the temperature chamber, thereby improving the measurement accuracy of the sensor.

[0065] The above-described embodiments are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A calibration method for a multi-point fiber Bragg grating temperature sensor, characterized in that: include: S1: Test environment for calibration of fiber Bragg grating temperature sensors with multiple measuring points: Select multiple fiber Bragg grating temperature measurement sensors with different central wavelengths and connect them in series to form a string of fiber Bragg grating temperature measurement sensors with multiple measurement points; The multi-measurement point fiber Bragg grating temperature sensors are placed in an S shape, and both ends of each fiber Bragg grating temperature sensor are mounted on an anti-static box; a thermocouple is mounted between every two adjacent fiber Bragg grating temperature sensors; Put the antistatic box into the temperature box, connect each fiber grating temperature sensor to the fiber wavelength acquisition module, and connect each thermocouple to the thermocouple temperature acquisition module; wherein the fiber wavelength acquisition module is used to record the fiber wavelength; S2: Conduct calibration test S2.1: Set multiple calibration temperature points according to the measuring range of the fiber Bragg grating temperature sensor; S2.2: Start the temperature box, and the temperature in the temperature box rises point by point from low temperature to high temperature. When each calibration temperature point is reached, the insulation time is set. The temperature indication of the thermocouple mounted on each fiber Bragg grating temperature sensor and the wavelength value of the connected fiber Bragg grating temperature sensor under each calibration temperature line are recorded; S2.3: Turn off the incubator, wait for the incubator to cool down to room temperature naturally, and then perform S2.2 again; repeat the above process several times; S3: According to the thermocouple temperature indications of each fiber Bragg grating temperature sensor under each calibration temperature line and the fiber Bragg grating temperature sensor wavelength value recorded in the pth cycle, p>1, the functional relationship between the thermocouple temperature corresponding to each fiber Bragg grating temperature sensor and the fiber Bragg grating temperature sensor wavelength is obtained as the calibration curve of each fiber Bragg grating temperature sensor.

2. The calibration method of the multi-measurement-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: In step S3, the functional relationship corresponding to each fiber Bragg grating temperature sensor is established by using the polynomial fitting method, with the average value of the thermocouple readings of the last 5 to 10 minutes of insulation of each fiber Bragg grating temperature sensor at the calibration temperature point in the pth cycle as the ordinate and the average value of the wavelength of the fiber Bragg grating temperature sensor as the abscissa: T ′ =a i l 2 +b i λ+c i Where λ is the wavelength of the fiber Bragg grating temperature sensor, T ′ is the thermocouple value, a i 、b i 、c i are respectively the coefficients of the quadratic term, linear term and zero-order term of the function of the i-th fiber Bragg grating temperature sensor.

3. The calibration method of the multi-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: The average value of the thermocouple readings of the qth cycle fiber Bragg grating temperature sensor at the calibration temperature point (q>1, q≠p) during the last 5 to 10 minutes of insulation is taken as the standard, and the average value of the wavelength value of the fiber Bragg grating temperature sensor is substituted into the functional relationship of the corresponding fiber Bragg grating temperature sensor to obtain the calculated temperature of the fiber Bragg grating temperature sensor wavelength at each calibration temperature point. The calculated temperature is compared with the corresponding standard to obtain the temperature measurement error of each calibration point.

4. The calibration method of the multi-measurement-point fiber Bragg grating temperature sensor according to claim 3, characterized in that: If the temperature measurement error of each calibration point is within the allowable range, the obtained calibration curve is the final calibration result; otherwise, adjust the coefficient of the functional relationship until the temperature measurement error is within the allowable range.

5. The calibration method of the multi-measurement-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: According to the temperature measurement range of the fiber grating temperature sensor, a calibration temperature point is selected every 3 to 7 degrees.

6. The calibration method of the multi-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: The distance between two adjacent fiber grating temperature sensors is no more than 1.5 cm.

7. The calibration method of the multi-measurement-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: According to the length of the fiber Bragg grating temperature sensor, 3M double-sided tape is attached parallel to the anti-static box, and there is no 3M double-sided tape under the grating etching area in the fiber Bragg grating temperature sensor.

8. The calibration method of the multi-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: A thermocouple is mounted between every two adjacent fiber grating temperature sensors and further fixed using 3M 2214 paper tape.

9. The calibration method of the multi-measurement-point fiber Bragg grating temperature sensor according to claim 1, characterized in that: Perform step 2 at least 3 times.

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