Device for measuring two-dimensional emissivity of object surface

Abstract

The invention discloses a device for measuring the two-dimensional emissivity of the surface of an object, which comprises the following steps: heating an object to be measured, and collecting the response intensity of the object to be measured at different wavebands at the current temperature through a photosensitive micro-unit of a spectrum camera; calculating corresponding radiation intensity according to the response intensity and the response coefficient of the spectrum camera; determining the emissivity of the to-be-measured object at the current temperature based on the radiation intensity; according to the invention, the radiation intensity of the to-be-measured object is reversely calculated through the pre-verified corresponding coefficient of the spectrum camera, and then the emissivity of the to-be-measured object is determined through the obtained radiation intensity, so that the emissivity measurement complexity can be greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the field of radiation temperature measurement and emissivity measurement, and particularly relates to a device for measuring the two-dimensional emissivity of an object surface. Background Art

[0002] Temperature is almost an important indicator of most objects. For an engine, temperature can show the working state and health condition of the engine, and temperature is a parameter that designers must consider in design and control.

[0003] There are many methods for measuring the engine temperature, such as thermocouples and infrared thermometers. Thermocouples belong to contact measurement. On the one hand, they need to be in contact with the object to be measured, which will affect the measurement accuracy. On the other hand, thermocouples can only perform single-point measurement and cannot meet two-dimensional measurement requirements. Compared with thermocouples, devices based on the radiation temperature measurement principle, such as infrared thermometers, do not need to be in contact with the engine, that is, they can perform non-invasive measurement, so that the engine temperature can be measured without affecting it. Although the infrared thermometer can perform two-dimensional temperature field measurement based on the imaging method, it is limited by the revision of the emissivity parameter at a single temperature and can only measure a uniform two-dimensional temperature field, and cannot obtain accurate measurement results of a non-uniformly distributed temperature field.

[0004] The most crucial point of the non-uniform two-dimensional temperature field radiation temperature measurement technology is that accurate two-dimensional emissivity is required for correction to obtain accurate measurement results of non-uniformly distributed temperature. However, the existing emissivity measurement methods can only obtain the emissivity at a single temperature or the average temperature within a single region. Summary of the Invention

[0005] The purpose of the present invention is to provide a device for measuring the two-dimensional emissivity of an object surface to obtain the two-dimensional emissivity of the target at different temperatures.

[0006] The present invention adopts the following technical solutions: A method for measuring the two-dimensional emissivity of an object surface, comprising the following steps:

[0007] Heat the object to be measured, and collect the response intensities of the object to be measured at different wavelength bands at the current temperature through the photosensitive micro-units of the spectral camera;

[0008] Calculate the corresponding radiation intensity according to the response intensity and the response coefficient of the spectral camera;

[0009] Determine the emissivity of the object to be measured at the current temperature based on the radiation intensity.

[0010] Further, the response coefficient of the spectral camera is obtained by the following method:

[0011] Raise the blackbody furnace to a predetermined temperature, and collect the response intensities of the blackbody tubes at different wavelengths in the blackbody furnace at the predetermined temperature through the photosensitive micro-units of the spectral camera;

[0012] Calculate the response coefficients of the spectral camera at different wavelengths at the predetermined temperature based on the response intensities of the blackbody tubes.

[0013] Further, calculating the response coefficients of the spectral camera at different wavelengths at the predetermined temperature based on the response intensities of the blackbody tubes includes:

[0014] Calculate the theoretical radiation intensity of the blackbody tube at the corresponding temperature according to the wavelength band and temperature of the radiation light of the blackbody tube;

[0015] Determine the response coefficient of the photosensitive micro-unit of the spectral camera based on the theoretical radiation intensity and the response intensity of the blackbody tube.

[0016] Further, the method for calculating the theoretical radiation intensity of the blackbody tube at the corresponding temperature according to the wavelength band and temperature of the radiation light of the blackbody tube is:

[0017]

[0018] wherein, E b (λ, T) represents the theoretical radiation intensity when the wavelength band of the radiation light is λ and the temperature of the blackbody tube is T, C 1 and C 2 are the first radiation constant and the second radiation constant respectively.

[0019] Further, determining the emissivity of the object to be measured at the current temperature based on the radiation intensity includes:

[0020] Generate a radiation intensity relational expression of the object to be measured based on the emissivity calculation model;

[0021] Taking the sum of the squares of the difference between the radiation intensity relational expression of the object to be measured and the radiation intensity as the objective function, optimize the emissivity parameters of the object to be measured at different temperatures;

[0022] Calculate the emissivity of the object to be measured at different temperatures according to the optimized emissivity parameters.

[0023] Further, the radiation intensity relational expression of the object to be measured is:

[0024]

[0025] wherein, E g (λ, T) represents the radiation intensity when the wavelength band of the radiation light of the object to be measured is λ and the temperature of the blackbody tube is T, ε(λ, T) represents the emissivity calculation model of the spectral camera, C 1 and C 2 are the first radiation constant and the second radiation constant respectively.

[0026] Further, the objective function is as follows:

[0027]

[0028] Among them, F(ε,T) represents the objective function when the emissivity is ε and the temperature is T, and I g (λ,T) represents the response intensity of the object to be measured in the wavelength band of λ and at the temperature of T, and k(λ,T) represents the corresponding coefficient of the spectral camera in the wavelength band of λ and at the temperature of T.

[0029] Further, when the spectral camera captures the object to be measured, the first distance between the spectral camera and the object to be measured is equal to the second distance between the spectral camera and the black body tube when the spectral camera captures the black body tube, and the shooting parameters are the same.

[0030] Another technical solution of the present invention: A device for measuring the two-dimensional emissivity of an object surface, which is used to execute the above method.

[0031] Further, it further includes a heating device for heating the object to be measured;

[0032] A spectral camera is arranged at a position corresponding to the observation window of the heating device.

[0033] The beneficial effect of the present invention is that the present invention inversely calculates the radiation intensity of the object to be measured through the pre-calibrated corresponding coefficient of the spectral camera, and then determines the emissivity of the object to be measured through the obtained radiation intensity, which can greatly reduce the complexity of emissivity measurement. Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the temperature region distribution of components during the temperature measurement test in the prior art;

[0035] Figure 2 It is a schematic structural diagram of a device for measuring the two-dimensional emissivity of an object surface in an embodiment of the present invention;

[0036] Figure 3 It is a schematic diagram of the two-dimensional temperature distribution of a blackbody furnace in an embodiment of the present invention;

[0037] Figure 4 It is a schematic diagram of the two-dimensional emissivity distribution of a blackbody furnace in an embodiment of the present invention;

[0038] Figure 5 It is a schematic diagram of the two-dimensional radiation intensity of stainless steel in an embodiment of the present invention;

[0039] Figure 6 It is a schematic diagram of the two-dimensional emissivity distribution of stainless steel in an embodiment of the present invention.

[0040] Among them: 100. Heating control module; 200. Heating device; 300. Spectral camera; 400. Black body tube; 500. Data acquisition unit. Detailed implementation manners

[0041] The present invention will be described in detail below with reference to the accompanying drawings and specific implementation manners.

[0042] An engine is an important power device for human space activities. Different sizes and thrusts can be designed according to different applicable scenarios.

[0043] Generally, non-contact measurement methods, dual-wavelength temperature measurement technology, infrared temperature measurement technology, and other radiation temperature measurement technologies are used for temperature measurement. However, these temperature measurement methods are affected by an important parameter, namely the emissivity. Accurate temperature measurement results require accurate emissivity information.

[0044] In the radiation temperature measurement of an engine nozzle, due to the relatively rapid heating process of the engine nozzle wall surface, in order to obtain detailed transient temperature information that changes with time, high-speed acquisition is required. Generally, a high-speed camera is used to complete it, and then the dual-wavelength temperature measurement method is combined for temperature measurement.

[0045] However, when using a high-speed camera for dual-wavelength temperature measurement, the wavelength range is limited to the visible light and near-infrared wavelength bands (about 300nm - 1000nm range). Therefore, the emissivity needs to be measured in this wavelength band.

[0046] In actual tests, the two-dimensional temperature distribution of the measured position is non-uniform. As Figure 1 shown, the temperatures in regions ①, ②, and ③ in the figure are different. Temperature affects the emissivity. Therefore, the emissivities of these three regions are generally also different, and the emissivity corresponding to the position needs to be used. Therefore, a two-dimensional emissivity measurement method is required to measure the emissivity of the outer wall surface of the engine nozzle in the visible light and near-infrared wavelength bands under the condition that the temperature of the nozzle wall surface is unknown and the temperature distribution is different.

[0047] The present invention discloses a method for measuring the two-dimensional emissivity of an object surface, including the following steps: heating the object to be measured, and collecting the response intensities of the object to be measured at different wavelength bands at the current temperature through the photosensitive micro-units of a spectral camera; calculating the corresponding radiation intensity according to the response intensity and the response coefficient of the spectral camera; and determining the emissivity of the object to be measured at the current temperature based on the radiation intensity.

[0048] The present invention inversely calculates the radiation intensity of the object to be measured through the pre-calibrated response coefficient of the spectral camera, and then determines the emissivity of the object to be measured based on the obtained radiation intensity.

[0049] Specifically, in the present invention, the response coefficient of the spectral camera needs to be calibrated first. The response coefficient of the spectral camera is obtained by the following method: raising the blackbody furnace to a predetermined temperature, collecting the response intensity of the blackbody tube at different bands at the predetermined temperature in the blackbody furnace through the photosensitive micro-units of the spectral camera; calculating the response coefficient of the spectral camera at different bands at the predetermined temperature according to the response intensity of the blackbody tube.

[0050] That is to say, the corresponding coefficient of the spectral camera is calibrated by the blackbody furnace. The blackbody tube is an object with a high emissivity. The characteristics of this kind of object are high emissivity, close to 1, and the emissivity is fixed. The blackbody tube is a tubular object with a special material coated on the inner wall surface and one end closed, generally made of ceramic material and can withstand high temperatures. It can be heated to different temperatures to calibrate the response coefficient of the spectral camera. After the spectral camera is calibrated, the blackbody tube is replaced with the object to be measured before measuring the emissivity of the object to be measured.

[0051] In the embodiment of the present invention, the collected band range is 660nm - 934nm, divided into 24 bands, and the resolution of each band is 407×215. When the spectral camera is calibrated, the distance between the lens and the blackbody furnace cavity opening is 5 - 10 cm. When measuring the two-dimensional emissivity of the object to be measured (such as a nozzle), according to different field of view requirements, the distance between the camera and the nozzle is 50 cm - 200 cm.

[0052] It should be noted that, in order to improve the measurement accuracy, the first distance between the spectral camera and the object to be measured when shooting the object to be measured is equal to the second distance between the spectral camera and the blackbody tube when shooting the blackbody tube, and the shooting parameters are the same (that is, the same lens and the same aperture setting are used).

[0053] In one embodiment, calculating the response coefficient of the spectral camera at different bands at the predetermined temperature according to the response intensity of the blackbody tube includes: calculating the theoretical radiation intensity of the blackbody tube at the corresponding temperature according to the band and temperature of the radiation light of the blackbody tube 400; determining the response coefficient of the photosensitive micro-unit of the spectral camera based on the theoretical radiation intensity and the response intensity of the blackbody tube.

[0054] Since the parameters of the blackbody tube are known and the temperature when the blackbody furnace heats it is also known, the method for obtaining the theoretical radiation intensity of the blackbody tube at different bands and temperatures by calculation is:

[0055]

[0056] Among them, E b (λ, T) represents the theoretical radiation intensity when the band of the radiation light is λ and the temperature of the blackbody tube is T, with the unit of W·m -2 , C 1 and C 2 are the first radiation constant and the second radiation constant respectively, and C 1= 3.7419*10 -16 W·m -2 , C 2 = 1.4388*10 -2 m·K。

[0057] In addition, it should be noted that since the photosensitive array of the spectral camera contains multiple photosensitive micro-units, it is necessary to calculate the theoretical radiation intensity of each photosensitive micro-unit. However, the same parameters are used in the above calculation process, so the theoretical radiation intensity corresponding to each photosensitive micro-unit is substantially the same. For example, the lens is a lens with the same 16 mm focal length, and the same lens setting parameters, such as the aperture is F1.6 for all, and then the integration time is adjusted to ensure a high signal-to-noise ratio of the image and no overexposure, and then start shooting.

[0058] The response intensity of an object obtained by a photosensitive micro-unit in the spectral camera is That is, the response intensity of the x i th row and y j th column in the photosensitive array. In the spectral camera, the photosensitive element converts the radiation intensity into the response intensity, and there is a certain conversion relationship I(λ, T) = k(λ, T)·E(λ, T) between the two. This relationship can be obtained through calibration to obtain the response coefficient k of each photosensitive micro-unit of the spectral camera at different wavelengths and different temperatures.

[0059] In the embodiment of the present invention, when calibrating and shooting the nozzle with the spectral camera, in order to improve the signal-to-noise ratio and control overexposure, at different temperatures, the integration time used (i.e., the exposure time of the spectral camera) is different. In the calculation, finally, the response intensity needs to be divided by the integration time to unify the response intensities with different integration times to the unit integration time.

[0060] In the present invention, determining the emissivity of the object to be measured at the current temperature based on the radiation intensity includes: generating a radiation intensity relationship formula of the object to be measured based on the emissivity calculation model; using the sum of squares of the difference between the radiation intensity relationship formula of the object to be measured and the radiation intensity as the objective function to optimize the emissivity parameters of the object to be measured at different temperatures; calculating the emissivity of the object to be measured at different temperatures according to the optimized emissivity parameters.

[0061] Specifically, the radiation intensity relationship formula of the object to be measured is:

[0062]

[0063] Among them, E g (λ, T) represents the radiation intensity when the radiation band of the object to be measured is λ and the temperature of the blackbody tube is T, ε(λ, T) represents the emissivity calculation model of the spectral camera, C 1 and C 2They are the first radiation constant and the second radiation constant respectively.

[0064] In the above formula, the emissivity calculation model is expressed as a function of the wavelength band λ and can be selected as needed. For example, ε(λ) = a 0 + a 1 ·λ + a 2 ·λ 2 +... + a n ·λ n , where a 0 , a 1 , a 2 , …, a n and n are all parameters to be optimized; another example is where K is the absorption coefficient, L is the flame thickness along the line of sight, a is an empirical coefficient, and K and L are empirical coefficients to be optimized.

[0065] More specifically, the objective function is:

[0066]

[0067] where F(ε, T) represents the objective function when the emissivity is ε and the temperature is T, I g (λ, T) represents the response intensity of the object to be measured at the wavelength band λ and the temperature T, and k(λ, T) represents the corresponding coefficient of the spectral camera at the wavelength band λ and the temperature T.

[0068] It should be noted that in the present invention, for each photosensitive micro-unit, the emissivity at different wavelength bands and different temperatures is obtained, so as to generate a two-dimensional emissivity within the shooting range of the spectral camera. That is to say, the emissivity is related not only to the temperature and the wavelength band, but also to the spatial position. Finally, a two-dimensional emissivity distribution image with a size of 407×215 is obtained, and the emissivity is

[0069] In a specific embodiment, the accuracy of the temperature and emissivity analysis method by the radiation spectroscopy method is verified. In the range of 1064 - 1169K, different temperatures are set for the blackbody furnace, which are respectively marked as the 1st - 3rd groups of experiments. The response intensity curves measured at different temperatures are obtained by using the spectral camera. After the correction of the response coefficient, the spectral data of a certain micro-unit in the spectral image are extracted. The radiation spectra of the full wavelength band and the 660 - 934nm wavelength band are analyzed respectively to obtain the measurement results of the temperature and the emissivity at this micro-unit, and the relative errors between the measurement results and the theoretical values are analyzed. As shown in Table 1 and Table 2, the theoretical emissivity of the blackbody furnace is 0.99.

[0070] Table 1 Temperature measurement results

[0071]

[0072]

[0073] Table 2 Emissivity measurement results

[0074]

[0075] The results show that: the relative deviation between the measured temperature and the set temperature is less than 2%, and the relative deviation between the measured emissivity and the theoretical value is less than 3%. The repeatability is ±0.03. Compared with the results of full-band measurement, the measurement results in the optimal band greatly improve the accuracy of temperature and emissivity analysis by the radiation spectroscopy method, verifying the accuracy of the measurement of temperature and emissivity parameters based on the radiation spectroscopy method.

[0076] Process the measurement data of each photosensitive micro-unit of the spectral camera to obtain the two-dimensional temperature distribution of the blackbody furnace Figure 3 and emissivity distribution Figure 4 .

[0077] In another embodiment, the emissivity of stainless steel is measured at 800 degrees Celsius using the device according to the above process. The spectral camera captures information in 24 bands. In this embodiment, the effective information of 20 bands (i.e., 706nm, 722nm, 733nm, 747nm, 761nm, 775nmnm, 782nm, 797nm, 807nm, 820nm, 836,nm 845nm, 857nm, 872nm, 884,nm 893,nm 906nm, 914nm, 924nm, 934nm) is extracted, and illustrations of 8 bands (i.e., 761nm, 775nm, 807nm, 820nm, 845nm, 857nm, 872nm, 893nm) in this embodiment are given. Although the bands are recorded as fixed values here, their band ranges are actually determined by the sensitivity of each band. For example, the band range corresponding to 722nm is 722±5nm. The illustrations of the 8 bands are as Figure 5 (a) to Figure 5 (h) shown. The greater the brightness in the middle circle of the figure, the greater the radiation intensity; the two-dimensional emissivity results are as Figure 6 (a) to Figure 6 (h) shown.

[0078] By looking up the table, it is known that at 800 degrees Celsius, the total normal emissivity of the oxidized stainless steel surface is 0.731. The average value of the normal emissivity of the measured stainless steel is 0.717, and the relative error is 1.91%, which is less than 2%, proving the accuracy of the method of the present invention.

[0079] In summary, the method of the present invention does not require prior knowledge of temperature, so it can measure the emissivity of an object with a temperature gradient and non-uniform temperature distribution. By using a multi-spectral camera, the emissivity of the material can be obtained in different bands, and through imaging, two-dimensional emissivity information can be obtained, so that it is clear which part of the object the measured emissivity corresponds to. It is also possible to measure objects of different materials simultaneously, without being affected by whether the material is single. When there are different materials, such as ① and ②, due to different emissivities and temperatures, their brightnesses are different, and different regions are distinguished to measure the emissivity separately.

[0080] The present invention also discloses a device for measuring the two-dimensional emissivity of an object surface, which is used to execute the above method. As Figure 2 shown, the device further includes a heating device 200 for heating the object to be measured. The heating device 200 is connected to a heating control module 100 to control the heating temperature of the heating device 200; a spectral camera 300 is arranged at a position corresponding to the observation window of the heating device. The spectral camera 300 is also connected to a data acquisition unit 500, which is used to collect and save the response intensity of the spectral camera 300, and at the same time supply power to the spectral camera 300.

[0081] It should be noted that the position corresponding to the heating device 200 and the spectral camera 300 has light-transmitting ability, so that the radiated light can be collected.

[0082] The data acquisition unit is a computer, which is connected to the spectral camera 300 through a USB cable and a data line. The spectral camera 300 is set, controlled, and the data collected by the spectral camera 200 is received, stored, and processed through software to obtain the emissivity of the object to be measured.

[0083] In one embodiment, the heating device 200 is a muffle furnace. There is a circular observation window on the furnace door, and a colorless light-transmitting glass is equipped on the window. The glass can transmit light in the visible and near-infrared bands, and the heated object can be observed and photographed through the observation window.

Claims

1. A method for measuring the two-dimensional emissivity of an object surface, characterized in that: The following steps are involved: The object to be tested is heated, and the response intensity of the object to be tested in different bands at the current temperature is collected by the photosensitive micro-unit of the spectral camera; Calculating the corresponding radiation intensity according to the response intensity and the response coefficient of the spectral camera; The emissivity of the object to be measured at a current temperature is determined based on the radiation intensity.

2. A method for measuring two-dimensional emissivity of an object surface as claimed in claim 1, characterized in that: The response coefficient of the spectral camera is obtained by the following method: The blackbody furnace is raised to a predetermined temperature, and the response intensity of the blackbody tubes in different wavelength bands in the blackbody furnace at the predetermined temperature is collected by the photosensitive micro-unit of the spectral camera; The response coefficients of the spectral cameras in different wavebands at a predetermined temperature are calculated according to the response intensity of the blackbody tube.

3. A method for measuring two-dimensional emissivity of an object surface as claimed in claim 2, characterized in that: Calculating the response coefficient of the spectral camera in different bands at a predetermined temperature according to the response intensity of the blackbody tube includes: Calculating the theoretical radiation intensity of the black body tube at the corresponding temperature according to the wavelength band and temperature of the radiation light of the black body tube; The response coefficient of the photosensitive micro-unit of the spectral camera is determined based on the theoretical radiation intensity and the black body tube response intensity.

4. A method for measuring two-dimensional emissivity of an object surface as claimed in claim 3, characterized in that: The method for calculating the theoretical radiation intensity of the black body tube at the corresponding temperature according to the wavelength band and temperature of the radiation light of the black body tube is: Among them, E b (λ, T) represents the theoretical radiation intensity when the wavelength of the radiation light is λ and the temperature of the black body tube is T, and C1 and C2 are the first radiation constant and the second radiation constant respectively.

5. A method for measuring two-dimensional emissivity of an object surface as claimed in any one of claims 2 to 4, characterized in that: Determining the emissivity of the object to be measured at the current temperature based on the radiation intensity includes: Generate the radiation intensity relationship of the object to be tested based on the emissivity calculation model; Taking minimizing the square sum of the difference between the radiation intensity relationship of the object to be tested and the radiation intensity as the objective function, optimizing the emissivity parameters of the object to be tested at different temperatures; The emissivity of the object to be tested at different temperatures is calculated according to the optimized emissivity parameters.

6. A method for measuring two-dimensional emissivity of an object surface as claimed in claim 5, characterized in that: The radiation intensity relation of the object to be measured is: Among them, E g (λ,T) represents the radiation intensity when the wavelength band of the radiation light of the object to be measured is λ and the temperature of the black body tube is T, ε(λ,T) represents the emissivity calculation model of the spectral camera, and C1 and C2 are the first radiation constant and the second radiation constant, respectively.

7. A method for measuring two-dimensional emissivity of an object surface as claimed in claim 6, characterized in that: The objective function is: Where F(ε,T) represents the objective function when the emissivity is ε and the temperature is T, I g (λ,T) represents the response intensity of the object under test when the wavelength is λ and the temperature is T, and k(λ,T) represents the corresponding coefficient of the spectral camera when the wavelength is λ and the temperature is T.

8. A method for measuring two-dimensional emissivity of an object surface as claimed in claim 2, characterized in that: The first distance between the spectral camera and the object to be measured when photographing the object to be measured is equal to the second distance between the spectral camera and the black body tube when photographing the black body tube, and the photographing parameters are the same.

9. A device for measuring the two-dimensional emissivity of an object surface, characterized in that: Used to perform the method according to any one of claims 1 to 8.

10. The device for measuring two-dimensional emissivity of an object surface as claimed in claim 9, characterized in that: Also included is a heating device (200) for heating the object to be tested; A spectral camera (300) is arranged at a position corresponding to the observation window of the heating device (200).

Images