An online calibration method for thin film thermal resistors and coaxial thermocouples

Abstract

The present invention discloses an online calibration method for a thin film thermal resistor and a coaxial thermocouple, comprising: utilizing the characteristics of an atomic layer thermopile heat flux sensor, which has a short response time, excellent linearity, and can measure heat for a long time under medium and low heat flux, using the heat flux test result obtained by the calibrated atomic layer thermopile heat flux sensor in a shock wind tunnel or a calibration shock tube test as a calibration heat flux, and using the Cook-Felderman formula to transform the output of the thin film thermal resistor or the coaxial thermocouple, multiplying the thermoelectric coefficient and the thermophysical property parameter of the thin film thermal resistor or the coaxial thermocouple into the sensitivity coefficient of the sensor, and fitting the average value and the calibration heat flux in the effective time period after the sensor output is transformed using the least squares method, so as to obtain the sensitivity coefficient of the thin film thermal resistor or the coaxial thermocouple. The present invention solves the problem of high uncertainty in the heat flux test results obtained when the thin film thermal resistor and the coaxial thermocouple are used for heat flux testing.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal flow sensor calibration, and more specifically, the invention relates to an online calibration method for a thin film thermal resistor and a coaxial thermocouple. Background Art

[0002] At present, pulsed wind tunnels such as shock tunnels mainly use thin film thermal resistors and coaxial thermocouples to carry out heat flow tests. When using thin film thermal resistors or coaxial thermocouples to carry out heat flow tests, the surface temperature obtained by these two sensors is used to obtain the heat flow test results by inversion. The difference is that thin film thermal resistors use the linear dependence between the resistance and temperature of metal films such as platinum to achieve temperature testing, while coaxial thermocouples use the Seebeck effect to obtain surface temperature test results. In a short period of time, the inversion method for obtaining heat flow test results through temperature is often the Cook-Felderman formula. The Cook-Felderman formula is a simplified calculation method derived from the strict heat transfer equation based on the semi-infinite body assumption. In the process of using the Cook-Felderman formula to process the temperature test results to obtain the heat flow test value, the thermophysical parameters of the sensor base material need to be used, such as density, thermoelectric coefficient (for thin film thermal resistors, the thermoelectric coefficient is the resistance-temperature coefficient, and for coaxial thermocouples it is the Seebeck coefficient), specific heat capacity and thermal conductivity. Usually, the two-step method is used to obtain the thermoelectric coefficient and the thermophysical parameter product respectively. In this process, the influence of lateral heat transfer needs to be shielded. The thermoelectric coefficient is mainly obtained by a constant temperature bath to obtain the corresponding relationship between the sensor voltage output and the temperature. For coaxial thermocouples, the thermophysical parameter product is often quickly put into a solution with known temperature and thermophysical parameters, and its effective thermophysical parameter product is obtained by heat transfer calculation; for thin film thermal resistors, the effective thermophysical parameters are mostly determined by pulse radiation method. In fact, the process of obtaining the thermophysical parameter product of the substrate material by pulse heating method is essentially to average the pulse heating amount in a short time into input heat flow in time and space, and then use the Cook-Felderman formula to calculate. Accordingly, the influence of energy averaging is ignored in the uncertainty analysis, that is, there is a lack of direct test of calibration heat flow in the two-step method. As a result, the uncertainty estimate of the thermal measurement results of thin film thermal resistors or coaxial thermocouples calibrated based on the two-step method is low. In addition, when using laser as heat source and water-cooled Gardon meter or atomic layer thermopile (ALTP) heat flow sensor as transfer reference, it is inevitable that in order to obtain consistent, stable and high absorption rate of laser for the thin film thermistor and coaxial thermocouple sensing surface to be calibrated, it is necessary to spray coating on the sensing surface of the thin film thermistor and coaxial thermocouple and strictly control the coating thickness. However, this coating needs to be removed during wind tunnel test. This process is relatively troublesome and may cause sensor damage.The online calibration method provided by the present invention utilizes the characteristics of the ALTP heat flux sensor, which has a short response time, excellent linearity, and can be used for a long time for heat flux testing under medium and low heat flux. The heat measurement results of the calibrated ALTP heat flux sensor in the shock tunnel test are used as the calibration heat flux, and the thermoelectric coefficient and thermophysical property parameters of the thin film thermal resistor or coaxial thermocouple are multiplied to form the sensitivity coefficient of the sensor. The sensitivity coefficient is obtained by fitting the test results under multiple different test conditions or train times. Although the core part of the Cook-Felderman formula is also used when processing the sensor output, the known calibration heat flux plays a correction role in the process of fitting the test data. Summary of the invention

[0003] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0004] In order to achieve these purposes and other advantages according to the present invention, an online calibration method for a thin film thermal resistor and a coaxial thermocouple is provided, comprising the following steps:

[0005] Taking advantage of the characteristics of the atomic layer thermopile heat flux sensor, such as short response time, excellent linearity, and the ability to measure heat for a long time under medium and low heat fluxes, the heat flux test results obtained by the calibrated atomic layer thermopile heat flux sensor are used as the calibration heat flux in the shock tunnel or calibration shock tube test. At the same time, the Cook-Felderman formula is used to transform the output of the thin film thermal resistor or coaxial thermocouple, and the product of the thermoelectric coefficient and thermophysical property parameters of the thin film thermal resistor or coaxial thermocouple is processed into the sensitivity coefficient of the sensor. The least squares method is used to fit the average value and calibration heat flux in the effective time period after the sensor output is transformed, so as to obtain the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple.

[0006] Preferably, the specific steps of the online calibration method include:

[0007] Step 1: Use a measurement value transfer system consisting of a cryogenic radiometer, a silicon trap detector, and a room temperature electrical substitution radiometer to calibrate a water-cooled Gardon meter using a room temperature electrical substitution radiometer on a laser-based heat flow calibration device;

[0008] Step 2: On a laser-based heat flux calibration device, the water-cooled Gardon meter and the ALTP heat flux sensor are exposed to multiple laser sources with different amplitudes, and the ALTP heat flux sensor is calibrated using the input heat flux measured by the water-cooled Gardon meter.

[0009] Step 3: Install the ALTP heat flow sensor and the thin film thermal resistor or coaxial thermocouple symmetrically on the wind tunnel test model, ensuring that the distance between the ALTP heat flow sensors is as close as possible;

[0010] Step 4: Record the output of the ALTP heat flux sensor and thin film thermal resistor or coaxial thermocouple under the effective driving number of the shock wave wind tunnel, and obtain the calibrated heat flux q under this driving number based on the calibration result of the ALTP heat flux sensor. source ;

[0011] Step 5: Use the Cook-Felderman formula or thermoelectric simulation network to process the output of the thin film thermal resistor or coaxial thermocouple under this trip to obtain V cal ;

[0012] Step 6, repeating steps 4 to 5 under multiple different valid train numbers, to obtain a series of data sets of the ALTP heat flux sensor and the thin film thermal resistor or the coaxial thermocouple under different train numbers;

[0013] Step 7: Use the least square method to fit the series of data sets obtained in step 6 to obtain the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple;

[0014] Step 8. To address the problem of large differences in sensitivity coefficients of thin-film thermal resistors produced in the same batch, the thermoelectric coefficient of each thin-film thermal resistor is obtained using the heat bath method. The corresponding thermoelectric coefficient is divided by the sensitivity coefficient obtained after calibration to obtain a relatively consistent correction coefficient. That is, by calibrating a small number of thin-film thermal resistors online and combining the measurement results of the thermoelectric coefficient, the sensitivity coefficient of each thin-film thermal resistor produced in the same batch can be obtained.

[0015] Preferably, in step one, the measurement value transfer system is not limited to a measurement value transfer system based on comparative calibration and composed of a low-temperature radiometer, a silicon trap detector and a room-temperature electrical substitution radiometer; at the same time, a high-temperature black body based on black body theory can also be used as the primary of the measurement value transfer system, and the absolute calibration of the water-cooled Gardon meter is completed using the high-temperature black body as the basic heat source.

[0016] Preferably, in step 5, the output of the thin film thermal resistor or coaxial thermocouple under this train is processed using the Cook-Felderman formula or the thermoelectric simulation network, and the Cook-Felderman formula used is:

[0017]

[0018] Among them, t i ,t i-1 ,t n is the discrete time, V i 、V i-1 It is the time series output of the collected thin film thermal resistor or coaxial thermocouple.

[0019] Preferably, the least square method used in step seven is as shown below:

[0020]

[0021] Using the above fitting method to process V cal and q source The sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple can be obtained, where β is the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple, and j is the shock tunnel test vehicle number.

[0022] The present invention includes at least the following beneficial effects: the online calibration method provided by the present invention utilizes the characteristics of the ALTP heat flow sensor, which has a short response time, excellent linearity, and can perform heat flow testing for a long time under medium and low heat flows. The heat measurement results of the calibrated ALTP heat flow sensor are used as the calibration heat flow, and the product of the thermoelectric coefficient and thermophysical property parameters of the thin film thermal resistor or coaxial thermocouple is processed into the sensitivity coefficient of the sensor, which is obtained by fitting the test results under multiple different test conditions or train times. Although the core part of the Cook-Felderman formula is also used when processing the sensor output, the known calibration heat flow plays a correction role in the process of fitting the test data. The present invention solves the problem of high uncertainty in the heat flow test results obtained when thin film thermal resistors and coaxial thermocouples are used for heat flow testing.

[0023] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The diagram shows the value transfer chain of the calibration process of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0026] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0027] The invention discloses an online calibration method for a thin film thermal resistor and a coaxial thermocouple, comprising:

[0028] Taking advantage of the characteristics of the atomic layer thermopile heat flux sensor, such as short response time, excellent linearity, and long-term heat measurement under medium and low heat flux, the heat flux test results obtained by the calibrated atomic layer thermopile heat flux sensor are used as the calibration heat flux in the shock tunnel or calibration shock tube test. At the same time, the Cook-Fel derman formula is used to transform the output of the thin film thermal resistor or coaxial thermocouple, and the product of the thermoelectric coefficient and thermophysical parameters of the thin film thermal resistor or coaxial thermocouple is processed into the sensitivity coefficient of the sensor. The least squares method is used to fit the average value and calibration heat flux in the effective time period after the sensor output is transformed, and the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple can be obtained. The equipment used mainly includes: low temperature radiometer, silicon trap detector, room temperature electrical substitution radiometer, water-cooled Gardon meter, ALTP heat flux sensor, thin film thermal resistor or coaxial thermocouple, laser-based heat flux calibration equipment, shock tunnel or calibration shock tube.

[0029] The specific steps of the online calibration method of the thin film thermal resistor and the coaxial thermocouple of the present invention include:

[0030] Step 1: Use a low-temperature radiometer, a silicon trap detector, and a room-temperature electrical substitute radiometer to form a value transfer system. The value transfer chain of the calibration process is as follows: Figure 1 As shown, the value transfer chain composed of a cryogenic radiometer, a silicon trap detector and a room temperature electrical substitution radiometer can effectively ensure that the thermal measurement results of the water-cooled Gardon meter are accurate and reliable. The cryogenic radiometer, the silicon trap detector and the room temperature electrical substitution radiometer are all optical power test equipment, which are used to measure the power of the laser. The cryogenic radiometer is the most accurate equipment among optical power meters. These devices form a value transfer chain to ensure the accuracy of the room temperature electrical substitution radiation test results; the room temperature electrical substitution radiometer is used to complete the calibration of the water-cooled Gardon meter on the laser-based heat flux calibration equipment; the laser-based heat flux calibration equipment provides this series of heat flux sources with different values;

[0031] like Figure 1As shown, the specific calibration method for the water-cooled Gardon meter is: use the cryogenic radiometer with the highest measurement accuracy to measure the laser power P1 emitted by the laser, and then use the silicon trap detector to measure it at the same laser power, and use this method to calibrate the silicon trap detector; use the calibrated silicon trap detector to measure the laser power P2 emitted by the laser, where P1<P2, and then use the room temperature electrical substitution radiometer to measure it at the same laser power, and use this method to calibrate the room temperature electrical substitution radiometer; use the calibrated room temperature electrical substitution radiometer to measure the laser power P3 emitted by the laser, and then use the water-cooled Gardon meter to measure it at the same laser power, thereby completing the calibration of the water-cooled Gardon meter; wherein the cryogenic radiometer is cooled by liquid helium, and the measurement accuracy level is between microwatts and milliwatts, the measurement accuracy level of the silicon trap detector is milliwatts, and the measurement working temperature of the room temperature electrical substitution radiometer is room temperature (generally about 20-25°C); the laser-based heat flow calibration device used here is a laser;

[0032] Step 2: On a laser-based heat flux calibration device, the water-cooled Gardon meter and the ALTP heat flux sensor are exposed to multiple laser sources with different amplitudes, and the ALTP heat flux sensor is calibrated using the input heat flux measured by the water-cooled Gardon meter.

[0033] Step 3: Install the ALTP heat flow sensor and the thin film thermal resistor or coaxial thermocouple symmetrically on the wind tunnel test model, ensuring that the distance between the ALTP heat flow sensors is as close as possible;

[0034] Step 4: Record the output of the ALTP heat flux sensor and thin film thermal resistor or coaxial thermocouple under the effective driving number of the shock wave wind tunnel, and obtain the calibrated heat flux q under this driving number based on the calibration result of the ALTP heat flux sensor. source ;

[0035] Step 5: Use the Cook-Felderman formula or thermoelectric simulation network to process the output of the thin film thermal resistor or coaxial thermocouple under this trip to obtain V cal ;

[0036] Step 6, repeating steps 4 to 5 under multiple different valid train numbers, to obtain a series of data sets of the ALTP heat flux sensor and the thin film thermal resistor or the coaxial thermocouple under different train numbers;

[0037] Step 7: Use the least square method to fit the series of data sets obtained in step 6 to obtain the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple;

[0038] Step 8. To address the problem of large differences in sensitivity coefficients of thin-film thermal resistors produced in the same batch, the thermoelectric coefficient of each thin-film thermal resistor is obtained using the heat bath method. The corresponding thermoelectric coefficient is divided by the sensitivity coefficient obtained after calibration to obtain a relatively consistent correction coefficient. That is, by calibrating a small number of thin-film thermal resistors online and combining the measurement results of the thermoelectric coefficient, the sensitivity coefficient of each thin-film thermal resistor produced in the same batch can be obtained.

[0039] In the above technical solution, in the step one, the measurement value transfer system is not limited to the measurement value transfer system composed of a low-temperature radiometer, a silicon trap detector and a room-temperature electrical substitution radiometer based on comparative calibration; at the same time, a high-temperature black body based on the black body theory can also be used as the primary of the measurement value transfer system, and the high-temperature black body is used as the basic heat source to complete the absolute calibration of the water-cooled Gardon meter.

[0040] In the above technical solution, the Cook-Felderman formula or the thermoelectric simulation network is used in step 5 to process the output of the thin film thermal resistor or the coaxial thermocouple under this train trip, and the Cook-Felderman formula used is:

[0041]

[0042] Among them, t i ,t i-1 ,t n is the discrete time, V i 、V i-1 It is the time series output of the collected thin film thermal resistor or coaxial thermocouple.

[0043] In the above technical solution, the least square method used in step seven is as follows:

[0044]

[0045] Using the above fitting method to process V cal and q source The sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple can be obtained, where β is the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple, and j is the shock tunnel test vehicle number.

[0046] The results obtained by using the online calibration method provided by the present invention are shown in Table 1 and Table 2, respectively, wherein Table 1 is the calibration results of five thin film thermal resistors, and Table 2 is the calibration results of four coaxial thermocouples.

[0047] Table 1 Calibration results of five thin film thermal resistors

[0048]

[0049] Table 2 Calibration results of four coaxial thermocouples

[0050]

[0051] It can be seen from Table 1 and Table 2 that the correction coefficients of thin-film thermal resistors produced in the same batch are consistent, and the sensitivity coefficients of coaxial thermocouples are consistent, that is, a small number of calibration results can be used to obtain the performance parameters of a large number of thin-film thermal resistors or coaxial thermocouples produced in the same batch.

[0052] Applications, modifications and variations of the present invention will be apparent to those skilled in the art.

[0053] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. An online calibration method for thin film thermal resistors and coaxial thermocouples, characterized in that: include: Taking advantage of the characteristics of the atomic layer thermopile heat flow sensor, such as short response time, excellent linearity, and the ability to measure heat for a long time under medium and low heat flows, the heat flow test results obtained by the calibrated atomic layer thermopile heat flow sensor are used as the calibration heat flow in the shock tunnel or calibration shock tube test. At the same time, the Cook-Felderman formula is used to transform the output of the thin film thermal resistor or coaxial thermocouple, and the product of the thermoelectric coefficient and the thermophysical property parameter of the thin film thermal resistor or coaxial thermocouple is processed into the sensitivity coefficient of the sensor. The least square method is used to fit the average value and the calibration heat flow in the effective time period after the sensor output is transformed, so as to obtain the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple. The specific steps of the online calibration method include: Step 1: Use a measurement value transfer system consisting of a cryogenic radiometer, a silicon trap detector, and a room temperature electrical substitution radiometer to calibrate a water-cooled Gardon meter using a room temperature electrical substitution radiometer on a laser-based heat flow calibration device; Step 2: On a laser-based heat flux calibration device, the water-cooled Gardon meter and the ALTP heat flux sensor are exposed to multiple laser sources with different amplitudes, and the ALTP heat flux sensor is calibrated using the input heat flux measured by the water-cooled Gardon meter. Step 3: Install the ALTP heat flow sensor and the thin film thermal resistor or coaxial thermocouple symmetrically on the wind tunnel test model, ensuring that the distance between the ALTP heat flow sensors is as close as possible; Step 4: Record the output of the ALTP heat flux sensor and thin film thermal resistor or coaxial thermocouple under the effective driving number of the shock wave wind tunnel, and obtain the calibration heat flux under this driving number based on the calibration result of the ALTP heat flux sensor. q source ; Step 5: Use the Cook-Felderman formula or thermoelectric simulation network to process the output of the thin film thermal resistor or coaxial thermocouple under this train trip to obtain V cal ; Step 6: Repeat steps 4 to 5 under multiple different valid train numbers to obtain a series of data sets of ALTP heat flux sensor and thin film thermal resistor or coaxial thermocouple under different train numbers; Step 7: Use the least square method to fit the series of data sets obtained in step 6 to obtain the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple; Step 8. To address the problem of large differences in sensitivity coefficients of thin-film thermal resistors produced in the same batch, the thermoelectric coefficient of each thin-film thermal resistor is obtained using the heat bath method. The corresponding thermoelectric coefficient is divided by the sensitivity coefficient obtained after calibration to obtain a relatively consistent correction coefficient. That is, by calibrating a small number of thin-film thermal resistors online and combining the measurement results of the thermoelectric coefficient, the sensitivity coefficient of each thin-film thermal resistor produced in the same batch can be obtained.

2. The online calibration method of thin film thermal resistor and coaxial thermocouple as claimed in claim 1, characterized in that: In the step one, the measurement value transfer system is not limited to the measurement value transfer system composed of a low-temperature radiometer, a silicon trap detector and a room-temperature electrical substitution radiometer based on comparative calibration; a high-temperature black body based on black body theory is used as the primary of the measurement value transfer system, and the high-temperature black body is used as the basic heat source to complete the absolute calibration of the water-cooled Gardon meter.

3. The online calibration method of thin film thermal resistor and coaxial thermocouple as claimed in claim 1, characterized in that: In step 5, the output of the thin film thermal resistor or coaxial thermocouple under this train is processed using the Cook-Felderman formula or the thermoelectric simulation network. The Cook-Felderman formula used is: in, t i , t i-1 , t n is a discrete time, V i , V i-1 It is the time series output of the collected thin film thermal resistor or coaxial thermocouple.

4. The online calibration method of thin film thermal resistor and coaxial thermocouple as claimed in claim 1, characterized in that: The least square method used in step seven is shown below: Using the above fitting method V cal and q source The sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple can be obtained, where β is the sensitivity coefficient of the thin film thermal resistor or coaxial thermocouple, j It is the vehicle serial number for the shock tunnel test.

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