Verification method of infrared detection system for defect detection

Abstract

The invention relates to the technical field of nondestructive testing, in particular to a verification method of an infrared detection system for defect detection, which comprises the following steps: determining key parameter requirements related to defect detection; according to key parameter requirements, a thickness step difference of temperature difference sensitivity and a spatial resolution line pair are designed and obtained, and a corresponding test block is manufactured; performing image acquisition on a temperature difference sensitivity test area and a spatial resolution test area in the test block in a standard test environment by adopting an infrared detection system; in the acquired image, selecting a temperature-time curve on a thin step in the temperature difference sensitivity test area, drawing a linear trend line of the temperature-time curve, and finding an X point when the linear trend line intersects with the temperature-time curve; and selecting a time point corresponding to the X point, and carrying out spatial resolution and temperature difference sensitivity analysis on the basis of the instantaneous image of the time point. Through the verification method, the consistency of the spatial resolution and the temperature difference sensitivity of the infrared detection system for defect detection can be quickly and accurately confirmed.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing, and in particular to a calibration method for an infrared testing system for defect detection. Background Art

[0002] As infrared detection systems begin to be gradually applied in the field of defect detection, the original infrared thermal imager measurement method is not suitable for infrared detection systems for defect detection. The original measurement method is mainly based on temperature accuracy, while the infrared detection system for defect detection is mainly based on defect identification, with high requirements for temperature difference sensitivity and spatial resolution, but not high requirements for temperature accuracy.

[0003] However, the temperature difference sensitivity test is extremely difficult at present. First of all, it is very difficult to find two standard temperature black bodies, and the temperature difference between the black bodies needs to reach the temperature sensitivity level of the infrared thermal imager of tens of mK, which is even more difficult to obtain. At the same time, the image spatial resolution is also a key parameter affecting the detection quality, but there is currently no relevant measurement requirement for this parameter.

[0004] In the prior art, a Chinese utility model patent document with publication number CN 216718194A and publication date June 10, 2022 is proposed to solve the above-mentioned technical problems. The technical solution disclosed in the patent document is as follows: A resolution verification test block device based on an infrared detection system for defect detection, comprising a test block base plate, a spatial resolution test card and a thickness resolution test card; one side of the top of the test block base plate is a spatial resolution test area, and one side is a thickness resolution test area, and the height of the thickness resolution test area is higher than the height of the thickness resolution test area; the spatial resolution test card is installed on the spatial resolution test area, and the thickness resolution test card is installed on the thickness resolution test area; the spatial resolution test card is divided into several identification areas, each area is provided with a stripe layer with different line pair density values, and a spatial text mark of the corresponding line value is provided on the stripe layer; the thickness resolution test card is divided into several identification areas, and thin plates of different thicknesses are provided, and thickness text marks of corresponding thicknesses are provided on the thin plates, which are used to verify the resolution verification of the infrared detection system.

[0005] Although the above technical solution proposes the structure of the test block device for calibration, it does not clearly specify the method for specifically identifying the spatial resolution and thickness resolution (i.e., temperature difference sensitivity). Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a calibration method for an infrared detection system for defect detection, which can accurately identify temperature difference sensitivity and spatial resolution.

[0007] The present invention is achieved by adopting the following technical solutions: A method for calibrating an infrared detection system for defect detection comprises the following steps: Step S 1 . According to the needs of the infrared detection system for defect detection, clarify the key parameter requirements related to defect detection; the key parameter requirements include temperature difference sensitivity requirements and spatial resolution requirements; Step S 2 . According to the key parameter requirements, the thickness step difference and spatial resolution line pair of the test block required for temperature difference sensitivity are designed, and the corresponding test blocks are made; Step S 3 . Use an infrared detection system to collect images of the temperature difference sensitivity test area and spatial resolution test area in the test block under a standard test environment; Step S 4 . In the acquired image, select the temperature-time curve on the thin step in the temperature difference sensitivity test area, draw a linear trend line of the temperature-time curve, and find the X point where the linear trend line intersects the temperature-time curve; Step S 5 . Select the time point corresponding to point X, and perform spatial resolution and temperature difference sensitivity analysis based on the instantaneous image at that time point.

[0008] Step S 2 In the process, the thickness step difference and spatial resolution line pairs required for the key temperature difference sensitivity are obtained through infrared simulation or theoretical calculation.

[0009] The test block is made of aluminum alloy, and the test surface of the test block is anodized.

[0010] The spatial resolution analysis specifically refers to: drawing a grayscale amplitude curve for the spatial resolution line pair image, and measuring the image unsharpness of the infrared detection system in this state.

[0011] Measuring the image unsharpness of the infrared detection system in this state specifically refers to: calculating the grayscale difference of the line pair, if the grayscale difference is greater than or equal to the corresponding threshold, the corresponding spatial resolution value is determined as the initial value of the spatial resolution of the infrared detection system.

[0012] The grayscale difference Dip The calculation method is: Where A and E are the grayscale values ​​of the edge areas of the line pairs, B and D are the grayscale values ​​of the lines; C is the grayscale value of the area between the lines.

[0013] When performing spatial resolution analysis, place the block test area at the boundary of the field of view.

[0014] The temperature difference sensitivity analysis refers to: identifying a grayscale amplitude line on two adjacent steps and measuring the thickness resolution of the infrared detection system in this state.

[0015] The temperature difference sensitivity analysis specifically includes: selecting a grayscale amplitude line with uniform image on two adjacent steps of the test image, calculating the grayscale amplitude of the two steps, and when the average grayscale difference of the thick step is greater than 4 times the standard deviation of the grayscale value of the thin step, it is considered that the thickness difference can be identified, and the thickness difference is the initial value of the temperature difference sensitivity of the infrared detection system.

[0016] It also includes using the same area of ​​the test block to test whether the spatial resolution and temperature difference sensitivity of the infrared detection system are consistent with the initial values.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This calibration method can be used to quickly test the spatial resolution of the thermal imager in the infrared detection system at different focal lengths and quickly test the temperature difference sensitivity. After the thermal imager achieves initial measurement, a test block is used for verification. After the minimum step that can be identified by the infrared detection system is determined, the same step can be used for verification during subsequent use to ensure the rapid measurement of the consistency of the temperature difference sensitivity. The calibration process is efficient, low-cost, and operational. It can be used to calibrate the stability of the infrared detection system, quickly monitor the changes in the comprehensive performance of the infrared thermal imager, and monitor the quality stability of the infrared detection system throughout its life cycle.

[0018] Conventional infrared detection generally uses a temperature analysis interval, which may be within the range of point X. If point X is selected in front, its temperature drops too quickly, which will lead to large differences in the selection of point X between different detection systems, which is not conducive to the comparison between different systems; and in subsequent regular system stability tests, the impact of the fluctuation of the temperature drop curve will bring certain disadvantages to stability confirmation. If point X is selected in the back, its temperature drops too slowly, which will lead to a decrease in the recognition rate of thickness resolution (i.e., temperature difference sensitivity) and a decrease in the monitoring ability of this indicator.

[0019] In the present invention, point X can be drawn by a linear trend line standard, the uniformity of selection is high, and it can be found quickly and accurately. The selected point X is a time point at which the temperature drops faster. Based on the instantaneous image of the time point corresponding to point X, the spatial resolution and temperature difference sensitivity analysis are performed, so that the analysis results of the spatial resolution and temperature difference sensitivity are more accurate.

[0020] 2. The aluminum alloy test block used in the present invention has its test surface anodized to avoid the influence of surface finish on the test results.

[0021] 3. When performing spatial resolution testing, place the test block test area at the boundary of the field of view, which can also meet the distortion detection requirements at the boundary.

[0022] 4. The present invention also includes using the same area of ​​the test block to test whether the spatial resolution and temperature difference sensitivity of the infrared detection system are consistent with the initial values, so as to verify the stability of the infrared detection system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 This is a schematic diagram of the spatial resolution and temperature difference sensitivity test block in the present invention; Figure 3 It is a schematic diagram for determining the time point in the present invention; Figure 4 This is a spatial resolution identification curve diagram in the present invention. DETAILED DESCRIPTION

[0024] Example 1 As a basic embodiment of the present invention, the present invention includes a calibration method for an infrared detection system for defect detection, comprising the following steps: Step S 1 . According to the needs of the infrared detection system for defect detection, the key parameter requirements related to defect detection are clarified; the key parameter requirements include temperature difference sensitivity requirements and spatial resolution requirements.

[0025] Step S 2 . According to the key parameter requirements, the thickness step difference and spatial resolution line pair required for temperature difference sensitivity are designed and the corresponding test blocks are made.

[0026] Step S 3 . Use an infrared detection system to collect images of the temperature difference sensitivity test area and spatial resolution test area in the test block under a standard test environment.

[0027] Step S 4 . In the acquired image, select the temperature-time curve on the thin step in the temperature difference sensitivity test area, draw the linear trend line of the temperature-time curve, and find the X point where the linear trend line intersects the temperature-time curve. Among them, thin is relative. Since the temperature difference sensitivity test area includes at least two steps of different thicknesses, the thin step at this time refers to the thinner step of the two steps.

[0028] Step S 5. Select the image time data corresponding to point X, that is, select the time point corresponding to point X, and perform spatial resolution and temperature difference sensitivity analysis based on the instantaneous image at this time point.

[0029] Example 2 As a preferred embodiment of the present invention, the present invention includes a calibration method for an infrared detection system for defect detection, comprising the following steps: Step S 1 . According to the needs of the infrared detection system for defect detection, the key parameter requirements related to defect detection are clarified; the key parameter requirements include temperature difference sensitivity and spatial resolution requirements.

[0030] Step S 2 . According to the key parameter requirements, through infrared simulation or theoretical calculation, the thickness step difference and spatial resolution line pair of temperature difference sensitivity are designed and the corresponding test blocks are made.

[0031] Step S 3 . Use an infrared detection system to collect images of the temperature difference sensitivity test area and spatial resolution test area in the test block under a standard test environment.

[0032] Step S 4 . In the acquired image, select the temperature-time curve on the thin step in the temperature difference sensitivity test area, draw a linear trend line of the temperature-time curve, and find the X point where the linear trend line intersects the temperature-time curve.

[0033] Step S 5 . Select the time point corresponding to point X, and perform spatial resolution and temperature difference sensitivity analysis based on the instantaneous image at this time point. Specifically, the spatial resolution analysis specifically refers to: drawing a grayscale amplitude curve for the spatial resolution line pair image, and measuring the image unsharpness of the infrared detection system in this state. The temperature difference sensitivity analysis specifically refers to: identifying a grayscale amplitude line on two adjacent steps, and measuring the temperature difference sensitivity (i.e., thickness resolution) of the infrared detection system in this state.

[0034] Example 3 As another preferred embodiment of the present invention, the present invention includes a calibration method for an infrared detection system for defect detection, comprising the following steps: Step S 1 . According to the needs of the infrared detection system for defect detection, the key parameter requirements related to defect detection are clarified; the key parameter requirements include temperature difference sensitivity requirements and spatial resolution requirements.

[0035] Step S 2. According to the key parameter requirements, the thickness step difference and spatial resolution line pair of the temperature difference sensitivity are designed, and the corresponding test block is made. Among them, the test block can be made of aluminum alloy, and the test surface of the test block is anodized to avoid the influence of surface finish on the test results. More specifically, the specific structure of the test block can adopt the existing technology, such as the technical solution disclosed in the utility model patent document with publication number CN216718194U and publication date June 10, 2022.

[0036] Step S 3 . Use an infrared detection system to collect images of the temperature difference sensitivity test area and spatial resolution test area in the test block under a standard test environment.

[0037] Step S 4 . In the acquired image, select the temperature-time curve on the thin step in the temperature difference sensitivity test area, draw a linear trend line of the temperature-time curve, and find the X point where the linear trend line intersects the temperature-time curve.

[0038] Step S 5 . Select the time point corresponding to point X, and based on the instantaneous image at that time point, perform spatial resolution and temperature difference sensitivity analysis to obtain the initial values ​​of the spatial resolution and temperature difference sensitivity (i.e., thickness resolution) of the infrared detection system.

[0039] Step S 6 Repeat the test and directly use the time point data corresponding to point X, and use the same area of ​​the test block to test whether the spatial resolution and temperature difference sensitivity of the infrared detection system are consistent with the initial values.

[0040] Example 4 As the best embodiment of the present invention, refer to the attached specification Figure 1 The present invention includes a method for verifying an infrared detection system for defect detection, comprising the following steps: Step S 1 . According to the needs of the infrared detection system for defect detection, the key parameter requirements related to defect detection are clarified. The key parameter requirements include temperature difference sensitivity requirements (i.e., thickness difference requirements of adjacent steps) and spatial resolution requirements. For example, the temperature difference sensitivity of the infrared thermal imager is verified based on the factory value for sensitivity change trend, and the temperature difference sensitivity (i.e., thickness resolution) requirement can be ≤60mk. By analyzing the defect size and pixel conditions to be detected, the spatial resolution required by the infrared detection system can be calculated. Generally, the defects to be found require at least 3 pixels to cover any length, and the spatial resolution requirement can be, for example, 2LP / mm.

[0041] Step S2 . Refer to the instruction manual Figure 2 According to the key parameter requirements, through infrared simulation or theoretical calculation, the thickness step difference of the spatial resolution line pair and the temperature difference sensitivity is designed, and the corresponding test block is made. Specifically, 25°C and 60% (easier to achieve conditions) are used as the simulation environment input, and for different excitation methods, such as halogen lamp and flash lamp excitation, a thickness step that will produce the initial temperature difference sensitivity of the thermal imager, such as a temperature difference of 60mk, is designed. When in use, this step can be used as the center to expand several steps up and down, so as to improve the versatility of a test block in different infrared detection systems. This embodiment uses 1mm aluminum alloy as the thinnest thickness and 2mm as the maximum thickness. The step difference starts at 0.02, and the subsequent step difference is 1.5 times the previous step difference.

[0042] The spatial resolution determines the theoretical blur according to the pixel and focal length of the thermal imager. The required spatial resolution line pair card is designed based on the theoretical blur. For example, if the pixel pitch is 17um, the lens focal length is 6.5mm, and the angular resolution is 1.48°, based on the angular resolution and the spatial resolution at the required distance, it can be calculated that the focal length should not exceed 92.09mm, and the spatial resolution at this point is 2LP / mm, which can meet the requirements.

[0043] Step S 3 . An infrared detection system is used to collect images of the temperature difference sensitivity test area and the spatial resolution test area in the test block under a standard test environment. In this embodiment, the standard test environment can be: the test distance is 90mm. Among them, the test block is made of aluminum alloy. Due to the high requirements for temperature difference sensitivity, 2024 aluminum alloy with low cost, easy processing and high thermal conductivity is used as the test block matrix. At the same time, since the metal has a large interference with infrared reflection, after a large number of experiments, the aluminum alloy test surface is anodized (temperature 13~25℃, voltage 18~20V, time 40~60 minutes) to obtain a more ideal infrared detection surface quality, greatly reducing infrared reflection, making the test results more accurate and less interfering. For spatial resolution, laser etching method is used for processing. The spatial resolution of 1LP / mm means that there is 1 black line and 1 white line within a width of 1mm. Mechanical processing is used for temperature difference sensitivity (i.e. thickness resolution).

[0044] Step S 4 . In the acquired image, select a point on the thin step or a pixel area in the temperature difference sensitivity test area, and draw a linear trend line of the temperature time curve. Figure 3 , find the point X where the linear trend line intersects the temperature-time curve. After the X point is confirmed for the first time, the time point data at that point (such as the 50th frame) can be used directly in subsequent repeated tests without reconfirmation.

[0045] Step S 5 . Select the time point corresponding to point X, and perform spatial resolution and temperature difference sensitivity analysis based on the instantaneous image at that time point.

[0046] The spatial resolution analysis specifically refers to: drawing the grayscale amplitude curve of the spatial resolution line pair image, and measuring the image unsharpness of the infrared detection system in this state. Specifically, when analyzing the spatial resolution, the test block test area should be placed at the boundary of the field of view, and at the same time, the distortion detection of the boundary can be met. Figure 4 , draw a grayscale amplitude curve for the spatial resolution line pair image of a grayscale amplitude line (or a line with a certain pixel width) on the test image, calculate the grayscale difference of the line pair, measure the grayscale difference of different spatial resolution areas, if the grayscale difference is greater than or equal to the corresponding threshold, in this embodiment, the threshold may be 19%, that is, when the lowest grayscale value is less than 0.81 of the highest grayscale value, then it can be considered that the two lines are distinguishable, and the corresponding spatial resolution value is identified as the initial value of the spatial resolution of the thermal imager in the infrared detection system at this focal length.

[0047] Among them, the grayscale difference Dip The calculation method is: Where A and E are the grayscale values ​​of the edge areas of the line pairs, B and D are the grayscale values ​​of the lines; C is the grayscale value of the area between the lines.

[0048] The temperature difference sensitivity analysis refers to: identifying a grayscale amplitude line on two steps, and measuring the temperature difference sensitivity (i.e., thickness resolution) of the infrared detection system in this state. Specifically, when analyzing the temperature difference sensitivity, select steps with adjacent thicknesses on the temperature difference sensitivity test block, select a grayscale amplitude line or a certain pixel area with uniform images on two adjacent steps of the test image, such as a square box with pixels not less than 10*10, calculate the grayscale amplitude of the two steps, and perform statistics on the average value and standard deviation of the data on the thin steps. When the average grayscale difference of the thick step is greater than 4 times the standard deviation of the grayscale value of the thin step, it is considered that the thickness difference can be identified, and the thickness difference is the initial value of the temperature difference sensitivity (i.e., thickness resolution) of the infrared detection system. Generally, the minimum identifiable thickness difference should be selected for initial state confirmation and recording. After the thickness difference sensitivity is obtained for the first time, the instantaneous data at that time point can be directly selected for direct analysis during subsequent repeated tests, without having to reconfirm all of them.

[0049] The above steps can be quickly repeated later, and the same area of ​​the test block can be used to test whether the spatial resolution and temperature difference sensitivity of the system are consistent with the initial values, so as to verify the stability of the infrared detection system.

[0050] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical scheme and technical concept of the present invention without creative mental labor, which all fall within the scope of protection of the present invention.

Claims

1. A method for calibrating an infrared detection system for defect detection, characterized in that: The following steps are involved: Step S1. According to the needs of the infrared detection system for defect detection, clarify the key parameter requirements related to defect detection; the key parameter requirements include temperature difference sensitivity requirements and spatial resolution requirements; Step S2. According to the key parameter requirements, the thickness step difference and spatial resolution line pair of the temperature difference sensitivity are designed and the corresponding test blocks are made; Step S3. Using an infrared detection system to collect images of the temperature difference sensitivity test area and the spatial resolution test area in the test block under a standard test environment; Step S4. In the acquired image, select the temperature-time curve on the thin step in the temperature difference sensitivity test area, draw a linear trend line of the temperature-time curve, and find the X point where the linear trend line intersects the temperature-time curve; Step S5: Select the time point corresponding to point X, and perform spatial resolution and temperature difference sensitivity analysis based on the instantaneous image at this time point.

2. The method for verifying an infrared detection system for defect detection according to claim 1, characterized in that: In step S2, the thickness step difference and spatial resolution line pair of the key temperature difference sensitivity are obtained through infrared simulation or theoretical calculation.

3. The method for verifying an infrared detection system for defect detection according to claim 1, characterized in that: The test block is made of aluminum alloy, and the test surface of the test block is anodized.

4. A method for calibrating an infrared detection system for defect detection according to any one of claims 1 to 3, characterized in that: The spatial resolution analysis specifically refers to: drawing a grayscale amplitude curve for the spatial resolution line pair image, and measuring the image unsharpness of the infrared detection system in this state.

5. The method for calibrating an infrared detection system for defect detection according to claim 4, characterized in that: Measuring the image unsharpness of the infrared detection system in this state specifically refers to: calculating the grayscale difference of the line pair, if the grayscale difference is greater than or equal to the corresponding threshold, the corresponding spatial resolution value is determined as the initial value of the spatial resolution of the infrared detection system.

6. The method for calibrating an infrared detection system for defect detection according to claim 5, characterized in that: The grayscale difference Dip The calculation method is: Where A and E are the grayscale values ​​of the edge areas of the line pairs, B and D are the grayscale values ​​of the lines; C is the grayscale value of the area between the lines.

7. The method for calibrating an infrared detection system for defect detection according to claim 4, characterized in that: When performing spatial resolution analysis, place the block test area at the boundary of the field of view.

8. The method for calibrating an infrared detection system for defect detection according to claim 5, characterized in that: The temperature difference sensitivity analysis refers to: identifying a grayscale amplitude line on two steps and measuring the temperature difference sensitivity of the infrared detection system in this state.

9. The method for calibrating an infrared detection system for defect detection according to claim 8, characterized in that: The temperature difference sensitivity analysis specifically includes: selecting a grayscale amplitude line with uniform image on two adjacent steps of the test image, calculating the grayscale amplitude of the two steps, and when the average grayscale difference of the thick step is greater than 4 times the standard deviation of the grayscale value of the thin step, it is considered that the thickness difference can be identified, and the thickness difference is the initial value of the temperature difference sensitivity of the infrared detection system.

10. The method for calibrating an infrared detection system for defect detection according to claim 9, characterized in that: It also includes using the same area of ​​the test block to test whether the spatial resolution and temperature difference sensitivity of the infrared detection system are consistent with the initial values.

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