A method for calibrating a thin-walled calorimeter
By using a narrowband laser to provide a single-wave heat flux density signal, the thin-walled calorimeter is calibrated, solving the problem of large errors in traditional methods and achieving high-precision calibration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Chinese People's Liberation Army Cyberspace Force Information Engineering University
- Filing Date
- 2022-07-01
- Publication Date
- 2026-07-21
AI Technical Summary
In traditional thin-walled calorimeter calibration methods, differential operations amplify signal noise, leading to large errors. Long-term constant heat flux density loading causes excessive temperature rise of the thermistor, resulting in inaccurate calibration results.
A narrowband laser is used to provide a single square wave heat flux density signal with a pulse width of 0.2 to 2.5 ms to calibrate a thin-walled calorimeter. By adjusting the laser output energy and position, the static sensitivity, linearity, and repeatability are calculated, the derivative order is reduced, and the temperature rise of the thermistor is lowered.
It reduces the impact of high-frequency noise on calibration results, improves calibration accuracy and reliability, reduces the temperature rise of the thermistor, and ensures the precision of calibration results.
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Figure CN117367626B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a calibration method for a thin-walled calorimeter, belonging to the field of sensor technology. Specifically, it relates to a calibration method for a thin-walled calorimeter based on narrowband laser. This method calibrates the static sensitivity, second-order coefficients, linearity, and repeatability of the calorimeter by applying a single-wave heat flux density signal with known energy and pulse width to the thin-walled calorimeter. Background Technology
[0002] Heat flux density refers to the amount of heat passing through a unit area of a heat acceptor per unit time. This parameter is widely used in many fields such as gas turbine design, wind tunnel testing, and fire thermal damage assessment.
[0003] Thin-walled calorimeters are commonly used devices for measuring heat flux density. The mathematical model of this device can be expressed as:
[0004]
[0005] Where: q u denoted as heat flux density; a1 as the static sensitivity of the calorimeter; a2 as the second-order term coefficient; V(t) as the output voltage of the calorimeter; and t as time.
[0006] During the test, the incident heat flux density measured by the calorimeter can be calculated by combining the output voltage curve of the calorimeter with the above formula.
[0007] Before a thin-walled calorimeter can be put into operation, it needs to be calibrated to obtain the coefficients of the sensor's operating model, namely the static sensitivity a1 and the second-order coefficient a2. The traditional calibration method is to apply a known and constant heat flux density signal to the calorimeter using a quartz lamp or blackbody furnace, then acquire the calorimeter's voltage output, and then calculate the model coefficients a1 and a2, as well as the sensor's linearity and repeatability, based on the first and second derivatives of the voltage signal and the incident heat flux density.
[0008] On the one hand, differential operations greatly amplify high-frequency noise in the signal, resulting in large errors in the calculated a1, a2 and the linearity of the sensor. On the other hand, long-term constant heat flux density loading will cause the temperature of the thermistor of the thin-walled calorimeter to rise too high, which in turn changes the thermophysical parameters of the calorimeter, leading to inaccurate calibration results. Summary of the Invention
[0009] The purpose of this invention is to provide a calibration method for thin-walled calorimeters, which solves the problem of large calibration errors in traditional calibration methods, and can also be used to calibrate thin-walled calorimeters.
[0010] To achieve the above objectives, the present invention includes:
[0011] The technical solution of the thin-walled calorimeter calibration method of the present invention includes the following steps:
[0012] 1) Determine the area of the laser spot formed by the laser at the set position;
[0013] 2) Adjust the position of the calorimeter to be calibrated so that the thermistor of the calorimeter is directly facing the laser spot at the set position;
[0014] 3) Within the range of the quantitative calorimeter to be calibrated, select several calibration points, adjust the output energy of the laser in sequence, obtain the response of the quantitative calorimeter to be calibrated at each calibration point, and complete one round of calibration.
[0015] 4) Perform several rounds of calibration at the same calibration point; calculate the static sensitivity, linearity and repeatability of the calorimeter to be calibrated based on the area of the laser spot and the output energy of the laser at each calibration point in each round and the corresponding response of the calorimeter to be calibrated.
[0016] 5) Calculate the second-order term coefficients of the quantitative calorimeter to be calibrated based on its static sensitivity, and complete the calibration of the quantitative calorimeter to be calibrated.
[0017] The calibration method of this invention calibrates the calorimeter using a laser. When calibrating a thin-walled calorimeter using a narrow-band laser, the output signal of the narrow-band laser is a single-wave heat flux density signal with a pulse width within 0.2 to 2.5 ms. Due to the short pulse duration, this method reduces the loading time of the heat flux density during the calibration process, thereby reducing the temperature rise of the thermistor and solving the problem of the influence of long-term heating on the calibration results such as the linearity of the calorimeter in traditional calibration methods.
[0018] Further, in step 1), the method for determining the area of the laser spot is to determine the area of the laser spot at the set position using photographic paper: first, place the photographic paper in the optical path of the laser output, adjust the output of the laser, so that the laser burns a circular spot on the photographic paper, the position of the circular spot is the set position, and the area of the circular spot is the area of the laser spot.
[0019] Furthermore, the diameter of the circular spot is measured multiple times in different radial directions using vernier calipers. The average diameter of the measured circular spot is taken as the diameter of the laser spot, and the area of the laser spot is calculated according to the formula for the area of a circle.
[0020] By ablating photographic paper, the area and corresponding position of the laser spot were accurately, quickly, and cost-effectively determined.
[0021] Furthermore, in order to improve the calibration accuracy, in step 2), the center of the laser spot is made to coincide with the center of the calorimeter thermistor, the thermistor is perpendicular to the laser beam path, and the laser spot completely covers the calorimeter thermistor.
[0022] Furthermore, in order to improve the calibration accuracy, in step 2), after the position of the calorimeter to be calibrated is adjusted to the correct position, a clamp is used to fix the calorimeter to be calibrated to ensure that the position of the calorimeter does not change during the entire calibration process.
[0023] Furthermore, in step 4), the static sensitivity of the calorimeter to be calibrated is obtained by the following method to obtain the calibration points. The value and the peak voltage of the quantitative calorimeter to be calibrated, In the values, k0 is a fixed parameter of the calorimeter, S is the laser spot area, and Q is the laser output energy; the values at each calibration point... The static sensitivity of the quantitative calorimeter to be calibrated is obtained by fitting the value with the voltage peak value of the quantitative calorimeter to be calibrated, and the slope of the fitted working curve is the static sensitivity of the quantitative calorimeter to be calibrated.
[0024] Furthermore, each calibration point The value and the peak voltage of the quantitative calorimeter to be calibrated are obtained by averaging the output energy of the laser and the corresponding peak voltage of the quantitative calorimeter to be calibrated in each calibration round.
[0025] Further, in step 5), the second-order term coefficient a2 of the calorimeter to be calibrated is calculated according to the following formula:
[0026]
[0027] Where a1 is the static sensitivity of the quantitative calorimeter to be calibrated, and V δ (t) represents the output voltage value of the calorimeter to be calibrated as a function of time t.
[0028] Furthermore, in step 4), the linearity δ of the calorimeter to be calibrated is further determined based on the fitted working curve. L :
[0029]
[0030] Where, ΔY max y is the maximum absolute value of the calibration point residual. FS y represents the full-scale output voltage value of the quantitative calorimeter to be calibrated; FS The maximum excitation of the calorimeter to be calibrated is substituted into the reference working curve to obtain the result.
[0031] Furthermore, in step 4), the repeatability δ of the calorimeter to be calibrated is further determined. R :
[0032]
[0033] Where K is the confidence factor, σ is the mean square value of the standard deviation of the calibration points, and n is the number of calibration points; n ranges from 5 to 7.
[0034] According to the mathematical model, under the action of single-wave heat flux density, the static sensitivity (i.e., a1) and second-order coefficient (i.e., a2) of the calorimeter can be obtained by reducing the differential order. Therefore, compared with the traditional constant heat flux density loading method, this calibration method can reduce the differential order in the back calculation process of a1 and a2, thereby reducing the influence of high-frequency noise on the calibration results. Attached Figure Description
[0035] Figure 1 This is a system schematic diagram of the thin-walled calorimeter calibration method applicable to the present invention;
[0036] Figure 2 This is a schematic diagram of the working curve obtained by fitting in the thin-walled calorimeter calibration method of the present invention in the embodiment. Detailed Implementation
[0037] The present invention will now be described in further detail with reference to the accompanying drawings.
[0038] The thin-walled calorimeter calibration method of the present invention is applicable to, for example, Figure 1 The thin-walled calorimeter calibration system shown includes a laser, a calorimeter to be calibrated, and a data sampling system (hereinafter referred to as the data acquisition system). The thin-walled calorimeter to be calibrated receives the excitation signal emitted by the laser and converts it into a voltage signal. The voltage signal output by the calorimeter to be calibrated is finally acquired by the data acquisition system.
[0039] The method of the present invention uses a narrowband laser to calibrate a thin-walled calorimeter. During the calibration process, the excitation of the laser is adjusted sequentially according to the range of the thin-walled calorimeter, and the response of the calorimeter is recorded. Then, the two are substituted into the corresponding mathematical formulas to calculate the linearity, repeatability, static sensitivity and second-order term coefficient of the calorimeter.
[0040] In this embodiment, a Meler-50 laser is used to calibrate the thin-walled calorimeter. The laser output signal is a single square-wave pulse signal, and the laser spot shape is circular. The laser output pulse width is adjustable from 0.5ms to 2.5ms, the output energy is adjustable from 0 to 50J, and the laser spectrum range is between 1.6 and 2.5μm.
[0041] First, it is necessary to obtain the position and corresponding area of the laser spot. This embodiment provides the following method: Fix the photographic paper as close as possible to the laser, adjust the laser output so that the laser burns a circular spot on the photographic paper, and measure the area of this circular spot to obtain the laser spot area. The corresponding position of the circular spot is the position of the laser spot. After determining the spot position and area, remove the photographic paper.
[0042] The diameter of the laser spot on the photographic paper was measured using vernier calipers in different radial directions. The average value of the measurements was taken as the laser spot diameter D, and then calculated according to the formula... Calculate the area of the laser spot.
[0043] Given the known position and area of the laser spot, adjust the position of the thin-walled calorimeter to be calibrated so that the thermistor of the thin-walled calorimeter is directly facing the laser spot, and the center of the spot coincides with the center of the thermistor. The laser spot can completely cover the thermistor of the calorimeter. Use a clamp to fix the thin-walled calorimeter to be calibrated to ensure that the position of the thin-walled calorimeter to be calibrated does not change during the entire calibration process.
[0044] Within the measurement range of the thin-walled calorimeter to be calibrated, 5 to 7 calibration points are selected sequentially from low to high input excitation of the calorimeter. A single-pulse laser signal of 0–50 J is used to calibrate the thin-walled calorimeter. The single-pulse laser is a known excitation; the input excitation of the calorimeter is changed by adjusting the laser output power. The peak output of the measurement system under calibration is the response. After more than three rounds of calibration, the static sensitivity a1 and linearity δ of the thin-walled calorimeter measurement system under calibration are determined. L Repeatability δ R Static characteristic indicators are obtained, and then the second-order term coefficient a2 is obtained based on the static sensitivity a1.
[0045] Before each calibration point, the output of the calorimeter must be near zero. During the calibration process, the ambient temperature must be constant and there must be no wind.
[0046] The peak voltage output V of the calorimeter during the calibration experiment max With the y-axis, With the x-axis as the reference axis (Q is the laser output energy, s is the laser spot area, and k0 is the average absorptivity of the calorimeter in the 1.6–2.5 μm spectral range, provided by the calorimeter manufacturer), the reference working curve of the thin-walled calorimeter to be calibrated can be obtained using the least squares method. The slope of this working curve is the static sensitivity a1 of the calorimeter.
[0047] The linearity δ of the thin-walled calorimeter to be calibrated L The solution formula is as follows (ΔY max y is the maximum absolute value of the calibration point residual. FS To obtain the full-scale output, substitute the reference operating curve into the maximum excitation.
[0048] Repeatability δ of the thin-walled calorimeter to be calibrated R The solution formula is as follows (K is the confidence factor, σ is the mean square value of the standard deviation of the calibration points, and n is the number of calibration points).
[0049] The formula for solving the second-order axial coefficient a2 is as follows: (V δ (t) represents the calorimeter output, and t represents time.
[0050] The calibration method of the present invention can also be used to calibrate the calibration results of a calibrated thin-walled calorimeter.
[0051] Specific embodiments of the calibration method for thin-walled calorimeters:
[0052] The thin-walled calorimeter was calibrated using a Meler-50 laser. During the calibration process, the sensor was always directly facing the laser generator at a constant distance of 1m. The room temperature was kept constant and there was no wind. The laser pulse width was fixed at 0.5ms. The laser output energy was adjusted, and the maximum voltage output by the test system was recorded. The next experiment was conducted after the thermistor cooled to room temperature. The maximum output voltage obtained in each experiment is shown in Table 1.
[0053] Table 1. Calibration data for infrared heat flux density sensor
[0054]
[0055] The sensor output voltage was averaged three times to obtain the sensor output voltage values under different excitations. The sensor input and voltage output were then fitted using the least squares method, and the fitting results are shown below. Figure 2 As shown.
[0056] The obtained least squares fitting formula is:
[0057]
[0058] The system calibration data shows that the system's linearity is 0.09% and its repeatability is 0.62%.
[0059] From the above equation, the static sensitivity a1 = 1 / 0.2223 is 4.4984 kJ·m. -2 ·V -1 Further calculations yielded that the coefficient a² of the second-order term is 0.004 kJ·m. -2 ·V -1 .
Claims
1. A calibration method for a thin-walled calorimeter, characterized in that, Includes the following steps: 1) Determine the area of the laser spot formed by the laser at the set position; 2) Adjust the position of the calorimeter to be calibrated so that the thermistor of the calorimeter is directly facing the laser spot at the set position; 3) Within the range of the quantitative calorimeter to be calibrated, select several calibration points, adjust the output energy of the laser in sequence, obtain the response of the quantitative calorimeter to be calibrated at each calibration point, and complete one round of calibration; 4) Perform several rounds of calibration at the same calibration point; calculate the static sensitivity, linearity and repeatability of the calorimeter to be calibrated based on the area of the laser spot and the output energy of the laser at each calibration point in each round and the corresponding response of the calorimeter to be calibrated. 5) Calculate the second-order term coefficients of the quantitative calorimeter to be calibrated based on its static sensitivity, and complete the calibration of the quantitative calorimeter to be calibrated; The second-order coefficients of the quantitative calorimeter to be calibrated Calculate using the following formula: in, To determine the static sensitivity of the quantitative calorimeter to be calibrated, The output voltage value of the calorimeter to be calibrated as a function of time t. Here, S is the fixed parameter of the calorimeter, S is the laser spot area, and Q is the output energy of the laser.
2. The calibration method for a thin-walled calorimeter according to claim 1, characterized in that, In step 1), the method for determining the area of the laser spot is as follows: the area of the laser spot at the set position is determined by the photographic paper: first, the photographic paper is placed in the optical path of the laser output, and the output of the laser is adjusted so that the laser burns a circular spot on the photographic paper. The position of the circular spot is the set position, and the area of the circular spot is the area of the laser spot.
3. The calibration method for a thin-walled calorimeter according to claim 2, characterized in that, The diameter of the circular spot is measured multiple times in different radial directions using vernier calipers. The average diameter of the measured circular spot diameter is taken as the diameter of the laser spot. The area of the laser spot is then calculated using the formula for the area of a circle.
4. The calibration method for a thin-walled calorimeter according to claim 1, characterized in that, In step 2), the center of the laser spot is aligned with the center of the calorimeter thermistor, the thermistor is perpendicular to the laser path, and the laser spot completely covers the calorimeter thermistor.
5. The calibration method for a thin-walled calorimeter according to claim 4, characterized in that, In step 2), after the position of the calorimeter to be calibrated is adjusted to the correct position, a clamp is used to fix the calorimeter to be calibrated to ensure that the position of the calorimeter does not change during the entire calibration process.
6. The calibration method for a thin-walled calorimeter according to claim 1, characterized in that, In step 4), the static sensitivity of the calorimeter to be calibrated is obtained as follows, obtaining the values at each calibration point. The value and the peak voltage of the quantitative calorimeter to be calibrated, In the value, For the calorimeter's fixed parameters, S is the laser spot area, and Q is the laser's output energy; the values at each calibration point... The static sensitivity of the quantitative calorimeter to be calibrated is obtained by fitting the value with the voltage peak value of the quantitative calorimeter to be calibrated, and the slope of the fitted working curve is the static sensitivity of the quantitative calorimeter to be calibrated.
7. The calibration method for a thin-walled calorimeter according to claim 6, characterized in that, Each calibration point The value and the peak voltage of the quantitative calorimeter to be calibrated are obtained by averaging the output energy of the laser and the corresponding peak voltage of the quantitative calorimeter to be calibrated in each calibration round.
8. The calibration method for a thin-walled calorimeter according to claim 1, characterized in that, Before each calibration point, the calorimeter output must be near zero. During the calibration process, the ambient temperature must be constant and there must be no wind.
9. The calibration method for a thin-walled calorimeter according to claim 6, characterized in that, In step 4), the linearity of the calorimeter to be calibrated is further determined based on the fitted working curve. : in, The maximum absolute value of the calibration point residual. This is the full-scale output voltage value of the quantitative calorimeter to be calibrated; The working curve is obtained by substituting the maximum excitation of the calorimeter to be calibrated into the curve.
10. The calibration method for a thin-walled calorimeter according to claim 9, characterized in that, In step 4), the repeatability of the calorimeter to be calibrated is further determined. : Where K is the confidence factor, σ is the mean square value of the standard deviation of the calibration points, and n is the number of calibration points; n ranges from 5 to 7.