Infrared thermal imager measurement angle compensation method
By performing reference temperature measurement and multi-angle compensation calculation on an infrared thermal imager, the problem of insufficient temperature measurement accuracy of infrared thermal imagers at non-vertical angles is solved, and accurate temperature measurement at different angles is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WUHAN GUIDE SENSMART TECH CO LTD
- Filing Date
- 2024-10-17
- Publication Date
- 2026-07-21
Smart Images
Figure CN119394446B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of infrared thermal imager technology, and specifically relates to an infrared thermal imager measurement angle compensation method. Background Technology
[0002] In the field of infrared temperature measurement technology, infrared thermal imagers are widely used in various fields such as industrial inspection, medical diagnosis, and environmental monitoring because they can perform rapid and accurate non-contact temperature measurement. However, the temperature measurement accuracy of infrared thermal imagers is affected by a variety of factors, one of which is the measurement angle.
[0003] Traditional infrared thermometry typically ignores the impact of measurement angle on accuracy or only provides basic calibration functions, which are often insufficient for high-precision measurements. Furthermore, due to the lack of effective measurement angle compensation methods, users often need to rely on experience or complex manual calibration processes when measuring at non-perpendicular angles.
[0004] To improve the temperature measurement accuracy of infrared thermal imagers at non-perpendicular angles, an effective measurement angle compensation method is needed. This method should be able to automatically adjust the temperature reading according to the actual measurement angle to compensate for the temperature measurement error caused by the angle deviation. Summary of the Invention
[0005] To address the aforementioned problems, this invention provides an infrared thermal imager measurement angle compensation method to resolve the issues in the prior art.
[0006] To achieve the aforementioned objective, this invention proposes a method for compensating the measurement angle of an infrared thermal imager, comprising:
[0007] Step S1: Determine the target object for which temperature measurement is required, and measure the temperature of the target object based on the initial measurement angle between the infrared thermal imager and the target object to obtain a reference temperature;
[0008] Step S2: Set the angle range and preset value. Within the angle range, select multiple measurement angles at intervals of the preset value, rotate the target object, and obtain the measured temperature of the target object by the infrared thermal imager at the multiple measurement angles. Define the measured temperature as the first measurement temperature.
[0009] Step S3: Calculate the radiant power by converting the first measured temperature based on Planck's radiation law;
[0010] Step S4: Calculate the compensation coefficient for each measurement angle, compensate the radiation power based on the compensation coefficient to obtain the standard radiation power, and convert the standard radiation power into the compensated target temperature based on the pre-set temperature radiation relationship table.
[0011] Furthermore, obtaining radiated power includes the following steps:
[0012] The radiation power S(T) of the target object is calculated based on the first formula. i The first formula is: Where λ is the wavelength at which the infrared thermal imager measures temperature, λ1 and λ2 are preset upper and lower wavelength limits, c1 and c2 are Planck's constants, and T i The first measured temperature is [temperature].
[0013] Further, calculating the compensation coefficient for the measured angle includes the following steps:
[0014] The compensation coefficient ε(θ) for each measurement angle is obtained by fitting the measurement angle based on the second formula, whereby: Wherein, k1, k2, k3 and k4 are the fitting parameters of the exponential model, and θ is the measurement angle.
[0015] Furthermore, obtaining the standard radiated power includes the following steps:
[0016] The standard radiated power S(T0) is obtained based on the third formula, which is: Among them, S(T) am The target object is located at an ambient temperature T. am The radiated power below.
[0017] Further, obtaining the first measured temperature includes the following steps:
[0018] Multiple measurements are performed at the same measurement angle to obtain various second measurement temperatures, and the average value of the second measurement temperatures is taken as the first measurement temperature corresponding to the measurement angle.
[0019] Furthermore, the number of measurements at the same measurement angle is 3.
[0020] Furthermore, the initial measurement angle is the angle between the thermal imager's normal direction and the surface of the object being measured.
[0021] Furthermore, the angle range is 0-70°.
[0022] Furthermore, the upper wavelength limit and the lower wavelength limit are 8 μm and 14 μm, respectively.
[0023] Furthermore, the preset value is 5 degrees.
[0024] Compared with the prior art, the beneficial effects of the present invention are at least as follows:
[0025] This invention obtains a precise reference temperature by measuring the target object at an initial measurement angle, providing a reference for subsequent angle compensation. By measuring the temperature at multiple preset angles, measurement data at different angles is collected, providing comprehensive information for the compensation algorithm. The temperature data is converted into radiant power, providing a unified comparison standard for measurement results under different conditions. By calculating the compensation coefficient and applying it to the radiant power, errors caused by the measurement angle are accurately corrected. This invention can also correct infrared temperature measurement results at different angles, ensuring accurate and reliable results in various practical scenarios. Attached Figure Description
[0026] Figure 1 This is a flowchart illustrating the steps of an infrared thermal imager angle compensation method according to the present invention.
[0027] Figure 2 This is a diagram showing the variation of the compensation coefficient of the present invention with the angle. Detailed Implementation
[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0029] It is understood that the terms "first," "second," etc., used in this application may be used herein to describe various elements, but unless otherwise specified, these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this application, a first script may be referred to as a second script, and similarly, a second script may be referred to as a first script.
[0030] like Figure 1 As shown, an infrared thermal imager measurement angle compensation method includes:
[0031] S1: Determine the target object for which temperature measurement is required, and measure the temperature of the target object based on the initial measurement angle between the infrared thermal imager and the target object to obtain the reference temperature.
[0032] Specifically, assuming the target object is a blackbody, a perfect radiator, it emits radiation in a specific manner that depends only on its temperature and is independent of the object's shape, material, color, etc. The radiation characteristics of a blackbody are described by Planck's law of radiation, which states that the radiative exitance (radiative power) of a blackbody is proportional to the fourth power of its temperature and is related to the wavelength of the radiation.
[0033] If the normal direction of the infrared thermal imager is perpendicular to the surface of the target object, record the angle of the infrared thermal imager at this time as the initial measurement angle. Table 1 shows the temperature displayed by the thermal imager at the initial measurement angle before the measurement angle between the infrared thermal imager and the blackbody is corrected.
[0034] Table 1. Temperature displayed by the thermal imager before angle correction.
[0035]
[0036]
[0037] Fix the infrared thermal imager at the initial measurement angle and ensure that its line of sight (normal direction) is perpendicular to the surface of the target object. This means that the thermal imager is directly facing the object surface without any angular tilt, ensuring that the reference temperature T0 is obtained without angular error. The reference temperature will serve as the reference for subsequent measurements and compensation.
[0038] S2: Set the angle range and preset value. Within the angle range, select multiple measurement angles at preset value intervals, rotate the target object, and obtain the measured temperature of the target object by the infrared thermal imager at multiple measurement angles. Define the measured temperature as the first measurement temperature.
[0039] Specifically, the angle range is set to 0-70°, with a preset value of 5 degrees. The target object is placed on a support that can rotate around a central axis. The target object is rotated to adjust the angle between it and the infrared thermal imager. Starting from the initial normal direction (0° angle), the infrared thermal imager or the target object is gradually adjusted to change within the preset angle range. A measurement point is set every 5° to record the first measured temperature of the thermal imager [T1, T2, ..., Tn]. When the infrared thermal imager performs temperature measurement, the change in the measurement angle will cause the emissivity of the object surface to change. This is because the surface area and surface characteristics (such as roughness and shape) of the observed target object may be different at different angles, which will lead to errors in the measured temperature of the infrared thermal imager.
[0040] To reduce the impact of these errors on the measurement results, it is necessary to compensate for the actual measured temperature, i.e., the first measured temperature, in order to obtain a value that is closer to the true temperature of the object, i.e., the target temperature.
[0041] S3: The radiation power is obtained by converting the first measured temperature based on Planck's radiation law.
[0042] Specifically, the temperature measured by the infrared thermal imager is converted into radiation power using Planck's radiation law. This radiation power describes the radiation characteristics of a blackbody in thermal equilibrium. However, since most objects are not ideal blackbodies, a correction factor needs to be introduced to correct the radiation power in order to improve the accuracy of the infrared thermal imager in measuring temperature.
[0043] S4: Calculate the compensation coefficient for each measurement angle, compensate the radiation power based on the compensation coefficient to obtain the standard radiation power, and convert the standard radiation power into the compensated target temperature based on the pre-set temperature radiation relationship table.
[0044] Specifically, a correction factor needs to be introduced before calculating the compensation factor. The correction factor represents the influence of the radiation source size on the infrared thermal imager's temperature measurement; it is the ratio of the difference between the actual measured radiation power and the ambient radiation power to the difference between the normal measured radiation power and the ambient radiation power. The compensation factor for different angles is obtained by fitting the actual measured temperature and the correction factor, such as... Figure 2 The figure shown is a graph illustrating the variation of the compensation coefficient with the angle.
[0045] Through experiments or theoretical calculations, multiple tables relating temperature to radiant power are established. These tables typically contain standard radiant power values at different temperatures within a specific wavelength range. The table is then used to find the value that is closest to the measured standard radiant power, or an interpolation method is used to calculate the target temperature corresponding to the measured radiant power.
[0046] Furthermore, the relationship between angle and emissivity can be obtained through Table 1 and the aforementioned process. Temperature compensation is then performed based on the actual measured angle. Table 2 shows the results of temperature correction for each first point in Table 1 using this correction model.
[0047] Table 2 Results after angle correction
[0048]
[0049] The results show that the corrected target temperature is more accurate and closer to the actual blackbody temperature, meaning that the accuracy of the measurement results of the infrared thermometer is significantly improved after the correction.
[0050] This invention obtains a precise reference temperature by measuring the target object at an initial measurement angle, providing a reference for subsequent angle compensation. By measuring the temperature at multiple preset angles, measurement data at different angles can be collected, providing comprehensive information for the compensation algorithm. The temperature data is converted into radiant power, providing a unified comparison standard for measurement results under different conditions. By calculating the compensation coefficient and applying it to the radiant power, errors caused by the measurement angle can be accurately corrected. This invention can also correct infrared temperature measurement results at different angles, ensuring accurate and reliable results in various practical scenarios.
[0051] As a preferred embodiment of the present invention, obtaining radiated power includes the following steps:
[0052] The radiated power S(T) of the target object is calculated based on the first formula. i The first formula is: Where λ is the wavelength used by the infrared thermal imager to measure temperature, λ1 and λ2 are the preset upper and lower wavelength limits, c1 and c2 are Planck's constants, and T i The first temperature to be measured.
[0053] Specifically, the upper and lower wavelength limits are 8 μm and 14 μm, respectively, and Planck's constant is c1 = 2πhc. 2 c² = hc / k, where c is the speed of light, h is Planck's coefficient, and k is Boltzmann's constant. Using Planck's radiation law, the radiant power of a target object at multiple measurement temperatures can be calculated more accurately because it takes into account the relationship between temperature and wavelength.
[0054] Calculating the compensation coefficient for the measured angle includes the following steps:
[0055] The compensation coefficient ε(θ) for each measurement angle is obtained by fitting the measurement angle based on the second formula, which is: Where k1, k2, k3, and k4 are the fitting parameters of the exponential model, and θ is the measurement angle.
[0056] Specifically, this invention selects an exponential model as the fitting model for the compensation coefficients because the exponential relationship can well describe the relationship between the measurement angle and the radiation intensity. Using the least squares method or other optimization algorithms, the model parameters k1, k2, k3 and k4 are determined based on the collected data to minimize the error between the compensation coefficients predicted by the model and the actual measured values. The fitted compensation coefficients are then applied to the measurement results of the infrared thermal imager to correct the errors under different measurement angles.
[0057] Obtaining standard radiated power involves the following steps:
[0058] The standard radiated power S(T0) is obtained based on the third formula, which is: Among them, S(T) am ) represents the ambient temperature T of the target object. am The radiated power below.
[0059] Specifically, the ambient temperature of the target object can usually be obtained through a temperature sensor. The corrected radiant power is then calculated based on the measurement angle and the displayed temperature according to the third formula. This formula takes into account the change in radiant power caused by the measurement angle deviating from the normal direction and the influence of ambient temperature changes on radiant power, and incorporates these into the compensation calculation. The compensation process helps to reduce errors caused by non-perpendicular measurement angles, making the measurement results more reliable.
[0060] Obtaining the first measured temperature includes the following steps:
[0061] Multiple measurements are taken at the same measurement angle to obtain various second measurement temperatures, and the average value of the second measurement temperatures is used as the first measurement temperature for the corresponding measurement angle.
[0062] Specifically, the target temperature is the temperature value obtained after angle compensation processing, and the number of measurements at the same measurement angle is 3.
[0063] It should be understood that although the steps in the flowcharts of the various embodiments of the present invention are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the various embodiments may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least a portion of the sub-steps or stages of other steps.
[0064] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.
[0065] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0066] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.
[0067] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for compensating the measurement angle of an infrared thermal imager, characterized in that, The method includes the following steps: Step S1: Determine the target object for which temperature measurement is required, and measure the temperature of the target object based on the initial measurement angle between the infrared thermal imager and the target object to obtain a reference temperature; Step S2: Set the angle range and preset value, select multiple measurement angles within the angle range with the preset value as the interval, rotate the target object, obtain the measured temperature of the target object by the infrared thermal imager at the multiple measurement angles, and define the measured temperature as the first measurement temperature; Step S3: Calculate the radiant power by converting the first measured temperature based on Planck's radiation law; Obtaining the radiated power includes the following steps: calculating the radiated power of the target object based on the first formula. The first formula is: ,in, The wavelength used for temperature measurement by the infrared thermal imager. and The preset upper and lower wavelength limits, and Let be Planck's constant. The first measured temperature is given; Step S4: Calculate the compensation coefficient for each measured angle, compensate the radiant power based on the compensation coefficient to obtain the standard radiant power, and convert the standard radiant power into the compensated target temperature based on a pre-set temperature-radiant power relationship table; wherein, calculating the compensation coefficient for each measured angle includes the following steps: fitting the measured angle based on the second formula to obtain the compensation coefficient for each measured angle. The second formula is: ,in, and These are the fitting parameters for the exponential model. The measured angle; Obtaining the standard radiated power includes the following steps: obtaining the standard radiated power based on the third formula. The third formula is: ,in, The target object's ambient temperature The radiated power below.
2. The method according to claim 1, characterized in that, Obtaining the first measured temperature includes the following steps: Multiple measurements are performed at the same measurement angle to obtain various second measurement temperatures, and the average value of the second measurement temperatures is taken as the first measurement temperature corresponding to the measurement angle.
3. The method according to claim 2, characterized in that, The number of measurements at the same measurement angle is 3.
4. The method according to claim 1, characterized in that, The initial measurement angle is the angle between the thermal imager's normal direction and the surface of the target object.
5. The method according to claim 1, characterized in that, The angle range is 0-70°.
6. The method according to claim 1, characterized in that, The upper and lower wavelength limits are 8 μm and 14 μm, respectively.
7. The method according to claim 1, characterized in that, The preset value is 5 degrees.