Thin film thermocouple dynamic calibration method based on coupling of step starting point and dynamic characteristic curve

Abstract

The invention discloses a thin film thermocouple dynamic calibration method based on coupling of a step starting point and a dynamic characteristic curve, and belongs to the field of surface temperature measurement. The method comprises the following steps: setting the spot size, the pulse width, the laser frequency and the laser energy by using a dynamic calibration device of the thin film thermocouple, and further executing a dynamic characteristic test of the thin film thermocouple; acquiring dynamic characteristic data of the thin film thermocouple by adopting data acquisition equipment; through a curve fitting mode, selecting a step starting point to obtain step starting time t1; acquiring a time point t2 corresponding to a target value of the step value through coupling of the step starting point and the dynamic characteristic curve; taking the difference between t2 and t1 as a time constant; and repeating the dynamic characteristic test, and taking the average value of the plurality of measurement values as the final result of the dynamic characteristic test. The problems that the step starting point of the dynamic characteristic curve of the thin film thermocouple is difficult to determine and the data processing method is not standard are solved, and the measurement accuracy of the dynamic characteristics of the thin film thermocouple is improved.

Description

Technical Field

[0001] This invention belongs to the field of surface temperature measurement technology, and particularly relates to a dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve. Background Technology

[0002] Surface temperature is an important parameter reflecting the state of an object's surface. Thin-film thermocouples, with their advantages of small heat capacity, high sensitivity, fast response time, and minimal interference with the original environment of the measured object, are widely used in the field of transient surface temperature measurement. The working principle of dynamic characteristic calibration of thin-film thermocouples is to generate a pulse signal using a laser, causing an instantaneous temperature rise in the thin-film thermocouple. The response signal of the thermocouple is acquired by a high-speed acquisition device (such as an oscilloscope), and the time constant is used to characterize the thermocouple's response capability to transient temperatures.

[0003] Currently, the traditional method for calculating the time constant is to first determine the starting point of the step in the dynamic characteristic curve, calculate the temperature step using the temperatures corresponding to the starting and ending points, find the time point corresponding to 63.2% of the temperature step, and then subtract the time point corresponding to the step start to obtain the time constant. However, for the dynamic calibration process of thin-film thermocouples using pulsed lasers as heat sources, the step start point in the dynamic characteristic curve is not a stable process, but a set of peak values. This makes it difficult to determine that the highest point is the true step start point. In addition, in actual experiments, a standardized data processing method has not yet been established, which directly affects the measurement accuracy of the dynamic characteristics of thin-film thermocouples. Summary of the Invention

[0004] This invention proposes a dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve. By coupling the step start point with the dynamic characteristic curve, the step start time of the thin-film thermocouple is determined, thereby obtaining the time constant. Furthermore, the method for processing experimental data of thin-film thermocouples is clarified, solving the problems of difficulty in determining the step start point of the dynamic characteristic curve and non-standard data processing methods in current methods, thus improving the measurement accuracy of the dynamic characteristics of thin-film thermocouples.

[0005] A dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve, the method comprising: Step 1, Parameter Setting: Using the dynamic calibration device of the thin-film thermocouple, set the spot size, pulse width, laser frequency, and laser energy to further perform dynamic characteristic tests on the thin-film thermocouple; Step 2, Data Acquisition: Use data acquisition equipment to acquire dynamic characteristic data of the thin-film thermocouple; Step 3, Step start point selection: The step start point is selected by curve fitting to obtain the step start time t1; Step 4: Couple the step start point with the dynamic characteristic curve: By coupling the step start point with the dynamic characteristic curve, obtain the time point t2 corresponding to the target value of the step amount; Step 5: Calculate the time constant: Use the difference between t2 and t1 as the time constant; Step 6: Result Analysis: Repeat the dynamic characteristic test and use the average value of multiple measurements as the final result of the dynamic characteristic test.

[0006] In step 1, the dynamic calibration device of the thin-film thermocouple is used to set the spot size, pulse width, laser frequency, and laser energy to conduct a dynamic characteristic test of the thin-film thermocouple; wherein: the spot completely covers the hot junction of the thin-film thermocouple, the pulse width is at least 10 times the estimated time constant of the thin-film thermocouple, the laser frequency is 1Hz, and the laser energy is the maximum energy without ablation of the thin-film thermocouple.

[0007] In step 2, a data acquisition device is used to acquire dynamic characteristic data of the thin-film thermocouple; wherein: the sampling frequency of the data acquisition device is not less than 1MHz, and the acquisition and recording time is more than 10 times the estimated value of the thermocouple time constant τ; if it is found after data processing that the acquisition and recording time is less than 10 times the actual measured value of the time constant τ, the acquisition and recording time is extended to more than 10 times the actual measured value of the time constant τ, and the test is repeated; the sampling interval is less than 0.1% of the estimated value of the time constant τ.

[0008] In step 3, the step start point is selected through curve fitting, and the step start time is obtained. The selection principle for the step start point is to use plotting software to create a line graph of the dynamic characteristic data, and to fit the falling edge of the curve according to a formula. During the fitting process, the fitted curve covers more than 80% of the falling range of the original curve. The highest point of the fitted curve is the step start point. A perpendicular line is drawn from the step start point to the horizontal axis, and the intersection of the perpendicular line and the horizontal axis is the step start time t1. The fitting formula is: Where y0 represents the translation parameter and a0 is the position of the curve's y-intercept on the y-axis.

[0009] In step 4, the time point corresponding to the target value of the step is obtained by coupling the step start point with the dynamic characteristic curve; wherein: taking the step start point as the coupling point, the tangent line of the fitting curve of the dynamic characteristic is drawn, and the intersection of the tangent line with the horizontal axis is the time point t2 corresponding to the target value of the step.

[0010] In step 6, the dynamic characteristic test is repeated, and the average of multiple measurements is taken as the final result of the dynamic characteristic test; wherein: the deviation of the measured value from its arithmetic mean is not greater than 10%, otherwise the operation is repeated until the requirements are met; in, Let be the measured value of the time constant for the i-th time step, and k represent the number of trials.

[0011] In summary, this invention determines the step start time of a thin-film thermocouple by coupling the step start point with the dynamic characteristic curve, thereby obtaining the time constant. Furthermore, by clarifying the experimental data processing method for thin-film thermocouples, it solves the problems of difficulty in determining the step start point of the dynamic characteristic curve of thin-film thermocouples and the lack of standardization in data processing methods, thereby improving the measurement accuracy of the dynamic characteristics of thin-film thermocouples. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 This is a flowchart illustrating a dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve according to an embodiment of the present invention.

[0014] Figure 2 This is a schematic diagram of the dynamic characteristic curve of a thin-film thermocouple dynamic calibration method based on the coupling of a step start point and a dynamic characteristic curve according to an embodiment of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: A dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve includes parameter setting steps, data acquisition steps, step start point selection steps, step start point coupling steps with dynamic characteristic curves, time constant calculation steps, and result analysis steps.

[0017] The parameter setting steps involve using a dynamic calibration device for thin-film thermocouples to perform dynamic characteristic tests on the thin-film thermocouples by setting the spot size, pulse width, laser frequency, and laser energy. The data acquisition step involves using data acquisition equipment to obtain dynamic characteristic data of the thin-film thermocouple; The step start point selection process involves using curve fitting to select the step start point and obtain the step start time t1. The step start point and dynamic characteristic curve coupling step: By coupling the step start point and dynamic characteristic curve, the time point t2 corresponding to 63.2% of the step amount is obtained; The steps for calculating the time constant are as follows: the difference between t2 and t1 is the time constant. The results analysis procedure involves repeating the dynamic characteristic test at least six times, and the average value of the six measurements is the final result of this dynamic characteristic test.

[0018] Preferably, the parameter setting step utilizes a dynamic calibration device for the thin-film thermocouple to conduct dynamic characteristic tests on the thin-film thermocouple by setting the spot size, pulse width, laser frequency, and laser energy. Specifically, the spot must completely cover the hot junction of the thin-film thermocouple, the pulse width must be at least 10 times the estimated time constant of the thin-film thermocouple, the laser frequency must be set to 1Hz, and the laser energy must be the maximum energy possible without ablating the thin-film thermocouple. Preferably, the data acquisition step employs a data acquisition device to acquire dynamic characteristic data of the thin-film thermocouple. The sampling frequency of the data acquisition device is no less than 1MHz, and the acquisition and recording time should be at least 10 times the estimated value of the thermocouple time constant τ. If, after data processing, it is found that the acquisition and recording time is less than 10 times the actual measured value of the time constant τ, the acquisition and recording time needs to be extended to at least 10 times the actual measured value of the time constant τ, and the test needs to be repeated. The sampling interval should be less than 0.1% of the estimated value of the time constant τ. Preferredly, the step start point selection step involves selecting the step start point and obtaining the step start time through curve fitting. The selection principle for the step start point is to use plotting software to create a line graph of the dynamic characteristic data and fit the descending edge of the curve according to a formula. During the fitting process, it is essential to ensure that the fitted curve covers more than 80% of the descending range of the original curve. The highest point of the fitted curve is the step start point. A perpendicular line is drawn from the step start point to the horizontal axis; the intersection of this perpendicular line and the horizontal axis is the step start time t1. The fitting formula is: Where y0 represents the translation parameter and a0 is the position of the curve's y-intercept.

[0019] Preferably, the step start point and dynamic characteristic curve coupling step obtains the time point corresponding to 63.2% of the step amount by coupling the step start point and the dynamic characteristic curve. Taking the step start point as the coupling point, the tangent line of the fitting curve of the dynamic characteristic is drawn, and the intersection of the tangent line and the horizontal axis is the time point t2 corresponding to 63.2% of the step amount.

[0020] Preferably, in the time constant calculation step, the difference between t2 and t1 is the time constant; Preferably, the result analysis step involves repeating the dynamic characteristic test at least six times, and the average of the six measurements is the final result τ of this dynamic characteristic test. The deviation of each of the six measurements from its arithmetic mean must not exceed 10%; otherwise, the operation needs to be repeated until the requirement is met.

[0021] in Let be the measured value of the time constant for the i-th time step.

[0022] Example 2: A dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve is provided, such as... Figure 1-2 As shown ( Figure 2 In the figure, 1 is the original dynamic characteristic curve, 2 is the fitted curve, 3 is the step start point, and 4 is the tangent line between the step start point and the dynamic characteristic curve. The dynamic calibration method of thin film thermocouple coupled with the step start point and the dynamic characteristic curve in this embodiment includes steps 1-6.

[0023] Step 1 is the parameter setting step. In this step, the thermocouple is fixed on the vibration-damping platform, and the positive and negative leads of the thin-film thermocouple are connected to the data acquisition device. The size of the laser spot is adjusted by using a focusing lens, and the position of the thermocouple is adjusted so that the focused spot completely covers the thermal junction of the thermocouple. The laser and data acquisition device are turned on, and the energy of the pulsed laser is adjusted. The laser parameters are set as follows: pulse width of 8 ns, laser frequency of 1 Hz, and single-pulse output energy of 40 mJ. In this embodiment, the thin-film thermocouple substrate is 0.1 mm polyimide, the positive electrode of the sensitive layer is Nicr, the negative electrode is Nisi, the thickness of the sensitive layer is 200 nm, and the protective layer is polyimide.

[0024] Step 2 is the data acquisition step. In this step, the data acquisition device first starts collecting data, then the start button on the laser is clicked, causing the thermocouple to experience a momentary temperature rise. The data and curves showing the change in the thermocouple's thermoelectric potential over time are recorded. The acquisition and recording time should be at least 10 times the estimated value of the thermocouple time constant τ. If, after data processing, it is found that the acquisition and recording time is less than 10 times the actual measured value of the time constant τ, the acquisition and recording time needs to be extended to at least 10 times the actual measured value of the time constant τ, and the test needs to be repeated. The sampling interval should be less than 0.1% of the estimated value of the time constant τ.

[0025] Step 3 is the step start point selection step. In this step, after obtaining the dynamic characteristic data of the thin-film thermocouple, a line graph of the dynamic characteristic data is drawn using plotting software, and the falling edge of the curve is fitted according to a formula. During the fitting process, the coverage area of ​​the original curve to be fitted is selected, ensuring that the fitted curve covers more than 80% of the falling range of the original curve. The highest point of the fitted curve is the step start point. A perpendicular line is drawn from the step start point to the horizontal axis, and the intersection of the perpendicular line and the horizontal axis is the step start time t1. The fitting formula is: Where y0 represents the translation parameter and a0 is the position of the curve's y-intercept.

[0026] Step 4 is the coupling step between the step start point and the dynamic characteristic curve. In this step, the tangent line of the dynamic characteristic fitting curve is drawn with the step start point as the coupling point. The intersection of the tangent line and the horizontal axis is the time point t2 corresponding to 63.2% of the step amount.

[0027] Step 5 is the time constant calculation step, where the difference between t2 and t1 is the time constant.

[0028] Step 6 is the result analysis step. In this step, the dynamic characteristic test is repeated no less than six times, and the average of the six measurements is the final result of this dynamic characteristic test. The deviation of the six measurements from its arithmetic mean must not exceed 10%; otherwise, the operation needs to be repeated until the requirement is met.

[0029] in, Let be the measured value of the time constant for the i-th time step.

[0030] The test results of this embodiment are shown in Table 1.

[0031] Table 1: Test Results of This Example Therefore, the time constant of this embodiment is 129.9µs.

[0032] This embodiment of a dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve has the following advantages: by coupling the step start point with the dynamic characteristic curve, the step start time of the thin-film thermocouple is determined, and the time constant is obtained; in addition, by clarifying the experimental data processing method for thin-film thermocouples, the problems of difficulty in determining the step start point of the dynamic characteristic curve of thin-film thermocouples and the lack of standardization of data processing methods are solved, thereby improving the measurement accuracy of the dynamic characteristics of thin-film thermocouples.

[0033] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A dynamic calibration method for thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve, characterized in that, The method includes: Step 1, Parameter Setting: Using the dynamic calibration device of the thin-film thermocouple, set the spot size, pulse width, laser frequency, and laser energy to further perform dynamic characteristic tests on the thin-film thermocouple; Step 2, Data Acquisition: Use data acquisition equipment to acquire dynamic characteristic data of the thin-film thermocouple; Step 3, Step start point selection: The step start point is selected by curve fitting to obtain the step start time t1; Step 4: Couple the step start point with the dynamic characteristic curve: By coupling the step start point with the dynamic characteristic curve, obtain the time point t2 corresponding to the target value of the step amount; Step 5: Calculate the time constant: Use the difference between t2 and t1 as the time constant; Step 6: Result Analysis: Repeat the dynamic characteristic test and use the average value of multiple measurements as the final result of the dynamic characteristic test.

2. The method for dynamic calibration of thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve according to claim 1, characterized in that, In step 1, the dynamic calibration device of the thin-film thermocouple is used to set the spot size, pulse width, laser frequency, and laser energy to conduct a dynamic characteristic test of the thin-film thermocouple; wherein: the spot completely covers the hot junction of the thin-film thermocouple, the pulse width is at least 10 times the estimated time constant of the thin-film thermocouple, the laser frequency is 1Hz, and the laser energy is the maximum energy without ablation of the thin-film thermocouple.

3. The method for dynamic calibration of thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve according to claim 2, characterized in that, In step 2, a data acquisition device is used to acquire dynamic characteristic data of the thin-film thermocouple; wherein: the sampling frequency of the data acquisition device is not less than 1MHz, and the acquisition and recording time is more than 10 times the estimated value of the thermocouple time constant τ; if it is found after data processing that the acquisition and recording time is less than 10 times the actual measured value of the time constant τ, the acquisition and recording time is extended to more than 10 times the actual measured value of the time constant τ, and the test is repeated; the sampling interval is less than 0.1% of the estimated value of the time constant τ.

4. The method for dynamic calibration of thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve according to claim 3, characterized in that, In step 3, the step start point is selected through curve fitting, and the step start time is obtained. The selection principle for the step start point is to use plotting software to create a line graph of the dynamic characteristic data, and to fit the falling edge of the curve according to a formula. During the fitting process, the fitted curve covers more than 80% of the falling range of the original curve. The highest point of the fitted curve is the step start point. A perpendicular line is drawn from the step start point to the horizontal axis, and the intersection of the perpendicular line and the horizontal axis is the step start time t1. The fitting formula is: Where y0 represents the translation parameter and a0 is the position of the curve's y-intercept on the y-axis.

5. The method for dynamic calibration of thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve according to claim 4, characterized in that, In step 4, the time point corresponding to the target value of the step is obtained by coupling the step start point with the dynamic characteristic curve; wherein: taking the step start point as the coupling point, the tangent line of the fitting curve of the dynamic characteristic is drawn, and the intersection of the tangent line with the horizontal axis is the time point t2 corresponding to the target value of the step.

6. The method for dynamic calibration of thin-film thermocouples based on the coupling of a step start point and a dynamic characteristic curve according to claim 5, characterized in that, In step 6, the dynamic characteristic test is repeated, and the average of multiple measurements is taken as the final result of the dynamic characteristic test; wherein: the deviation of the measured value from its arithmetic mean is not greater than 10%, otherwise the operation is repeated until the requirements are met; in, Let be the measured value of the time constant for the i-th time step, and k represent the number of trials.

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