Calibration method for infrared temperature measuring device

Abstract

The invention relates to the technical field of infrared temperature measurement, in particular to a calibration method for an infrared temperature measurement device, and the method comprises the steps: calculating a first spectral radiation quantity at a reference temperature and a second spectral radiation quantity at an ambient temperature; based on the first spectral radiation quantity and the second spectral radiation quantity, the spectral average emissivity of the target surface of the blackbody calibration source at the reference temperature is obtained, the third spectral radiation quantity of a calibration temperature reference value is obtained through calculation, reverse calculation is conducted on the third spectral radiation quantity, and the calibration temperature reference value is obtained; a response model is constructed based on a calibration temperature reference value, a gain coefficient and a bias coefficient are obtained by solving the response model, a gain value of the infrared temperature measuring device is corrected based on the gain coefficient, and a bias value of the infrared temperature measuring device is corrected based on system bias. The whole calibration process of the method is convenient and easy to operate.

Description

Technical Field

[0001] This invention relates to the field of infrared temperature measurement, and in particular to a calibration method for infrared temperature measurement devices. Background Technology

[0002] Infrared temperature measuring devices are often modified by changing the extended lens, adjusting the aperture, or adding a window to meet different needs. However, such changes can cause the output grayscale value of the infrared temperature measuring device to fail to return to the factory calibration state, resulting in a decrease in temperature measurement accuracy. Therefore, it is necessary to perform temperature measurement calibration on the infrared temperature measuring device.

[0003] A lens replacement temperature compensation test method, disclosed in Chinese Patent Application No. CN202410076931.3, includes: obtaining a first transmittance T1 of a reference lens and a second transmittance T2 of the lens to be compensated; calculating a transmittance compensation coefficient TV; obtaining a first grayscale value G1 of the reference lens after transmittance compensation and a second grayscale value G2 of the lens to be compensated after transmittance compensation; obtaining a third grayscale value G3 of the lens to be compensated after lens compensation; establishing a compensation grayscale value model; obtaining a final grayscale value Gf of the lens to be compensated; obtaining a temperature value calculated from the final grayscale value Gf using a grayscale-to-temperature model; and verifying the temperature of the lens to be compensated based on the temperature value to complete the lens temperature compensation test.

[0004] The above methods have a complex and inefficient calibration process in practical use. They rely on traditional on-site calibration mode, have a single calibration source, lack adaptability to different scenarios, and the calibration results are easily affected by environmental interference, which can cause the calibration results to deviate due to environmental changes. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a calibration method for infrared temperature measurement devices.

[0006] A calibration method for an infrared temperature measuring device according to the present invention includes the following steps:

[0007] Calculate the first spectral radiance at the reference temperature and the second spectral radiance at the preset ambient reflection temperature;

[0008] The average spectral emissivity of the blackbody calibration source target surface in the infrared thermometer is obtained based on the first and second spectral radiance values. The third spectral radiance value of the calibration temperature reference value is calculated based on the actual ambient reflection temperature at the calibration site. The calibration temperature reference value is obtained by reverse calculation of the third spectral radiance value.

[0009] A response model is constructed based on the calibration temperature reference value. The gain coefficient and bias coefficient of the infrared temperature measuring device are obtained by solving the response model. The gain value of the infrared temperature measuring device is corrected based on the gain coefficient, and the bias value of the infrared temperature measuring device is corrected based on the bias coefficient. The infrared temperature measuring device measures the temperature of the blackbody calibration source target surface based on the corrected gain value and the corrected bias value. If the difference between the temperature measurement result of the infrared temperature measuring device and the calibration temperature reference value is within a preset range, the calibration of the infrared temperature measuring device is completed.

[0010] Preferably, a thermoelectric cooler is provided inside the blackbody calibration source, which is used to control the internal temperature of the blackbody calibration source within a preset range.

[0011] Preferably, the spectral radiance for calculating the reference temperature is obtained using Planck's blackbody radiation formula, based on the integrated radiance within the 8-14µm working band.

[0012] Preferably, the number of blackbody calibration source targets is not less than two.

[0013] Preferably, radiation temperature measurement is performed on each of the blackbody calibration source target surfaces at multiple preset angles, and the average value of the temperature measurement results is used as the reference temperature.

[0014] Preferably, the preset angle is in the range of 0-70°.

[0015] Preferably, the blackbody calibration source is provided with multiple target surfaces, and the surface coating of each target surface is deposited with different materials, including Si3N4, zinc oxide, graphite carbon and aluminum.

[0016] Preferably, after correcting the gain value and bias value of the infrared temperature measuring device, a blackbody calibration source with multiple temperatures is set to verify the temperature measurement results. If the measurement accuracy exceeds the preset critical value, the temperature control accuracy of the thermoelectric cooler is corrected.

[0017] Preferably, the temperature of the blackbody calibration source includes at least a first temperature and a second temperature, wherein the first temperature is below 100°C and the second temperature is above 100°C;

[0018] Preferably, the gain coefficient and bias coefficient in the response model are solved by the least squares method.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention applies the radiation balance theory and Kirchhoff's thermal radiation law to a specific infrared temperature measurement scenario, establishing a solution model for the average emissivity of the spectrum of each target surface of the blackbody calibration source. This model serves as the sole calibration source on-site, enabling calibration of the infrared temperature measurement device through simple data acquisition. On one hand, the entire calibration process is convenient and easy to operate. On the other hand, this method has high scene adaptability, suitable for various application scenarios such as changing extended lenses, adjusting aperture size, or adding windows, and can achieve temperature measurement calibration under any ambient reflection temperature. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the technical implementation of the present invention. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0023] This invention discloses a calibration method for an infrared temperature measuring device, comprising the following steps:

[0024] S1: Calculate the first spectral radiance at the reference temperature and the second spectral radiance at the preset ambient reflection temperature.

[0025] S2: Based on the first and second spectral radiance, obtain the average spectral emissivity of the blackbody calibration source target surface in the infrared thermometer. Based on the actual ambient reflection temperature at the calibration site, calculate the third spectral radiance to obtain the calibration temperature reference value. Perform reverse calculation on the third spectral radiance to obtain the calibration temperature reference value.

[0026] S3: Construct a response model based on the calibration temperature reference value, obtain the gain coefficient and bias coefficient of the infrared temperature measuring device by solving the response model, correct the gain value of the infrared temperature measuring device based on the gain coefficient, correct the bias value of the infrared temperature measuring device based on the bias coefficient, and measure the temperature of the blackbody calibration source target surface of the infrared temperature measuring device based on the corrected gain value and the corrected bias value. If the difference between the temperature measurement result of the infrared temperature measuring device and the calibration temperature reference value is within a preset range, the calibration of the infrared temperature measuring device is completed.

[0027] The calibration of an infrared thermometer requires the use of a dedicated blackbody calibration source. This source is designed with multiple uniform target surfaces of equal area, each coated with an opaque coating of a material with a different absorptivity. The calibration process is illustrated below with an example. First, before calibration, the first spectral radiance at a reference temperature is calculated based on Planck's blackbody radiation formula. The reference temperature is a pre-set temperature. Planck's blackbody radiation formula is as follows:

[0028]

[0029] Where C1 represents Planck's first constant, C2 represents Planck's second constant, T is the temperature, λ1 and λ2 are the upper and lower limits of the receiving wavelength of the infrared thermometer detector, and M(λ, T) is the spectral radiation value of a blackbody at temperature T and wavelength λ. In actual calculations, the corresponding ambient temperature or reference temperature is substituted as T into Planck's blackbody radiation formula to obtain the corresponding first spectral radiation quantity.

[0030] Specifically, a thermoelectric cooler is installed inside the blackbody calibration source to control the internal temperature of the blackbody calibration source within a preset range. According to the radiation balance theory, electromagnetic waves incident on any medium will undergo absorption, reflection, and transmission. In this embodiment, considering the presence of a thermoelectric cooler inside the blackbody calibration source, the following first formula is established: W(T1)=α·W(T reflect )+ρ·W(T TEC )+τ·W(T2), where T1 is the reference temperature, T reflect To preset the ambient reflection temperature, T TEC T1 is the temperature control temperature of the thermoelectric cooler (TEC) inside the blackbody calibration source, T2 is the temperature of the atmosphere or other heat source, α is the absorptivity, ρ is the reflectivity, ρ is the average emissivity of the spectrum mentioned above, and τ is the transmittance. According to Kirchhoff's thermal radiation theory, the absorptivity, reflectivity, and transmittance of any substance have the following fixed relationship: α + ρ + τ = 1. Since the thermal radiation coating on the blackbody calibration source target surface undergoes special processing, it has extremely low transmittance in the calibrated wavelength band. Its transmittance is negligible compared to its absorptivity and reflectivity; therefore, the value of τ in the formula is set to 0. Furthermore, according to Kirchhoff's thermal radiation theory, the emissivity of any medium is equal to its absorptivity. Therefore, it can be considered that each target surface of the blackbody calibration source only contains the radiation absorbed and emitted by itself and the radiation reflected from the environment. For ease of distinction, the reflectivity ρ in the above formula is redefined as the average emissivity ε1 of the blackbody calibration source target surface. Then, α = 1 - ρ = 1 - ε1. Based on the above analysis, the first formula can be converted into the second formula, which is:

[0031] Where W(T1) is the first spectral radiance introduced above, then W(T reflect The second spectral radiance mentioned above is used to obtain the average spectral emissivity ε1 of the blackbody calibration source target surface in advance through the above steps. This is also the reflectivity of the blackbody calibration source target surface, which is convenient for subsequent calibration of the infrared thermometer.

[0032] When performing calibration at the calibration site, the ambient reflected temperature is obtained. Combined with the previously calculated average spectral emissivity of the blackbody calibration source target, the spectral radiance of the calibration temperature reference value can be calculated using the following formula:

[0033] W(T * 1)=ε1·W(T TEC )+(1-ε1)·W(T * reflect ),

[0034] Among them, T * reflect To calibrate the ambient reflected temperature at the site, T * 1 represents the calibration temperature reference value for a target surface with an average spectral emissivity of ε1. The spectral radiance W(T) at the calibration temperature reference value is obtained using this formula. * 1) Then, based on the previous Planck blackbody radiation formula, the calibration temperature reference value T is obtained by inverse calculation. * 1.

[0035] The response model of the external temperature measurement device circuit system can be expressed by the following formula:

[0036] V=α·gain·W(T)+β·offset,

[0037] Where V is the output grayscale value after photoelectric conversion, gain is the response gain value, W(T) is the spectral radiance corresponding to a blackbody at temperature T, and offset is the response bias value. Since changing the lens, adjusting the aperture, and adding a window to the infrared temperature measuring device will change the gain value and the bias value of the infrared temperature measuring device, the least squares method is used to solve for the gain coefficient α and the bias coefficient β. By solving for the gain coefficient α and the bias coefficient β, the gain value and the bias value are corrected respectively. Then, the corrected infrared temperature measuring device is used to measure the temperature of the target surface of the blackbody calibration source. If the difference between the temperature measurement result and the calibration temperature reference value is within the preset range, the temperature measurement calibration work is completed.

[0038] The following is an example calibration process. Based on an infrared thermometer, the average emissivity of the spectrum of each target surface of a small blackbody calibration source was calibrated in an indoor environment with an ambient temperature of 20℃. After temperature measurement calibration, the infrared thermometer can accurately measure the temperature. Its detector operates at a wavelength of 8-14µm. The small blackbody calibration source has a dual-target structure, with both the substrate and structural units made of graphite. The internal TEC temperature control unit maintains a stable temperature of 80℃. One side is coated with a Si3N4 coating, and the other side is coated with a zinc oxide coating. The calibration results of the average emissivity of the spectrum of the two target surfaces are shown in Table 1.

[0039] <![CDATA[Si3N4 target surface]]> Zinc oxide target Temperature measurement result (°C) 78.2 31.2 Spectral average emissivity 0.9634 0.1523

[0040] Table 1

[0041] Based on the calibration results of the average emissivity of the two target surfaces, the calibration temperature reference values ​​of the two target surfaces of the small blackbody calibration source were calculated at the calibration site. The temperature of the TEC temperature control unit inside the blackbody was kept stable at 80℃, and the ambient temperature was 10℃. The calculation results are shown in Table 2.

[0042]

[0043] Table 2

[0044] Based on the infrared temperature measuring device to be calibrated, the system gain correction coefficient and system bias correction coefficient are solved by the least squares method. After automatically adjusting the system grayscale output value, the calibration work is completed. The infrared temperature measuring device to be calibrated has only changed the aperture size compared to its calibration state.

[0045] To verify the temperature measurement accuracy of the infrared thermometer after calibration, four blackbodies with temperatures of 20℃, 50℃, 100℃ and 200℃ were set up and their temperatures were measured using the infrared thermometer. The measurement results and absolute errors are shown in Table 3. The temperature measurement accuracy is within ±2℃.

[0046]

[0047] Table 3

[0048] This invention studies the fundamental theory of infrared radiation, applies the radiation balance theory and Kirchhoff's thermal radiation law to a specific infrared temperature measurement scenario, and establishes a solution model for the average emissivity of the spectrum of each target surface of the blackbody calibration source. This model serves as the sole calibration source on-site, and the infrared temperature measurement device can be calibrated through simple data acquisition operations. The calibrated temperature measurement accuracy can reach ±2℃.

[0049] In this embodiment, the spectral radiance at the reference temperature is calculated using Planck's blackbody radiation formula, based on the integrated radiance within the 8-14µm working band.

[0050] The 8-14µm band falls within the "atmospheric window" range for infrared thermometry, where atmospheric attenuation is low, making it suitable for practical industrial applications. Furthermore, this band corresponds to the peak wavelength of thermal radiation from objects at room temperature, effectively capturing the radiation energy of the target and ensuring calibration sensitivity.

[0051] In this embodiment, the number of blackbody calibration source targets is no less than two.

[0052] Multiple target surfaces provide calibration references with different emissivity, covering scenarios from low to high emissivity. Furthermore, multi-point calibration can eliminate material inhomogeneity errors that may exist on a single target surface, thus improving the robustness of calibration.

[0053] In this embodiment, radiation temperature measurement is performed on each blackbody calibration source target surface at multiple preset angles, and the average value of the temperature measurement results is used as the reference temperature.

[0054] In this embodiment, the preset angle range is between 0 and 70°.

[0055] By compensating for edge radiation distortion or coating anisotropy of the lens through angle averaging, the reliability of calibration data is improved. Furthermore, the 70° angle limit avoids significant attenuation of radiated energy or reflection interference caused by large tilt angles.

[0056] In this embodiment, the blackbody calibration source is provided with multiple target surfaces, and the surface coating of each target surface is deposited with different materials.

[0057] By using a variety of different materials, the adaptability of the calibration model under extreme emissivity conditions can be verified.

[0058] In this embodiment, after correcting the gain value and bias value of the infrared temperature measuring device, a blackbody calibration source with multiple temperatures is set to verify the temperature measurement results. If the measurement accuracy exceeds the preset critical value, the temperature control accuracy of the thermoelectric cooler is corrected.

[0059] In this embodiment, the temperature of the blackbody calibration source includes at least a first temperature and a second temperature, wherein the first temperature is below 100°C and the second temperature is above 100°C.

[0060] For example, a blackbody is set at four temperatures: 20℃, 50℃, 100℃, and 200℃. Verification is performed at multiple temperature points, with values ​​taken both below and above 100℃, covering the entire performance range to ensure that linearity meets standards after calibration.

[0061] In this embodiment, the gain coefficient and bias coefficient in the response model are solved by the least squares method.

[0062] All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A calibration method for an infrared temperature measuring device, characterized in that, Includes the following steps: Calculate the first spectral radiance at the reference temperature and the second spectral radiance at the preset ambient reflection temperature; The average spectral emissivity of the blackbody calibration source target surface in the infrared thermometer is obtained based on the first and second spectral radiance values. The third spectral radiance value of the calibration temperature reference value is calculated based on the actual ambient reflection temperature at the calibration site. The calibration temperature reference value is obtained by reverse calculation of the third spectral radiance value. A response model is constructed based on the calibration temperature reference value. The gain coefficient and bias coefficient of the infrared temperature measuring device are obtained by solving the response model. The gain value of the infrared temperature measuring device is corrected based on the gain coefficient, and the bias value of the infrared temperature measuring device is corrected based on the bias coefficient. The infrared temperature measuring device measures the temperature of the blackbody calibration source target surface based on the corrected gain value and the corrected bias value. If the difference between the temperature measurement result of the infrared temperature measuring device and the calibration temperature reference value is within a preset range, the calibration of the infrared temperature measuring device is completed.

2. The calibration method as described in claim 1, characterized in that, The blackbody calibration source is equipped with a thermoelectric cooler, which is used to control the internal temperature of the blackbody calibration source within a preset range.

3. The calibration method as described in claim 1, characterized in that, The spectral radiance for calculating the reference temperature is obtained using Planck's blackbody radiation formula, based on the integrated radiance within the 8-14µm working band.

4. The calibration method as described in claim 1, characterized in that, The number of blackbody calibration source targets shall not be less than two.

5. The calibration method as described in claim 4, characterized in that, Radiation temperature measurement is performed on each of the blackbody calibration source target surfaces at multiple preset angles, and the average value of the temperature measurement results is used as the reference temperature.

6. The calibration method as described in claim 5, characterized in that, The preset angle range is 0-70°.

7. The calibration method as described in claim 1, characterized in that, The blackbody calibration source has multiple target surfaces, and the surface coating of each target surface is deposited with different materials, including Si3N4, zinc oxide, graphite carbon, and aluminum.

8. The calibration method as described in claim 1, characterized in that, After correcting the gain and bias values ​​of the infrared temperature measuring device, blackbody calibration sources at various temperatures are set to verify the temperature measurement results. If the measurement accuracy exceeds the preset critical value, the temperature control accuracy of the thermoelectric cooler is corrected.

9. The calibration method as described in claim 8, characterized in that, The temperature of the blackbody calibration source includes at least a first temperature and a second temperature, wherein the first temperature is below 100°C and the second temperature is above 100°C.

10. The calibration method as described in claim 1, characterized in that, The gain coefficient and the bias coefficient in the response model are solved by the least squares method.

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