An automatic gain control and sensitivity calibration system for a rail flaw detector

Abstract

This invention relates to the field of nondestructive testing technology, specifically to an automatic gain control and sensitivity calibration system for a rail flaw detector, comprising a coupling medium monitoring module, a data processing and calculation module, an automatic gain control module, and a sensitivity calibration module. This invention achieves precise quantification of the coupling state by integrating a humidity sensor and an optical turbidity sensor, combined with an impedance matching algorithm. It uses the density change rate of the coupling medium to predict the fluctuation trend of the coupling layer and dynamically adjusts the fusion weight of the coupling signal and the integral value of the grass wave. Based on the fusion decision, it generates an appropriate gain adjustment command. Combined with coupling medium density compensation and secondary correction of the grass wave level, it achieves graded and segmented adaptive gain adjustment. Simultaneously, damping control achieves overshoot suppression and rapid locking of the gain adjustment, significantly improving the real-time performance, accuracy, and stability of gain control during rail flaw detection.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, specifically to an automatic gain control and sensitivity calibration system for a rail flaw detector. Background Technology

[0002] Rail flaw detectors are instruments used to detect internal defects or small surface cracks in rails. They are mainly divided into two categories: electromagnetic flaw detection and ultrasonic flaw detection. Ultrasonic flaw detectors are widely used in Chinese railways. Their working principle is similar to performing an ultrasound on the rail; sensors convert the minute internal and surface defects detected by ultrasonic waves into waveforms displayed on an electronic screen for analysis. Currently, the main types include single-rail and double-rail rail flaw detectors. In actual rail flaw detection operations, the coupling state between the probe and the rail surface directly affects the ultrasonic wave propagation efficiency, while the gain control and sensitivity level of the flaw detector determine the reliability of defect identification. Existing technologies, such as traditional rail flaw detectors, suffer from problems such as difficulty in accurately quantifying the coupling state, lag in gain adjustment, susceptibility to overshoot and oscillation, weak anti-interference capabilities, and signal distortion and unstable sensitivity under complex operating conditions.

[0003] Based on this, the present invention provides an automatic gain control and sensitivity calibration system for a rail flaw detector to solve the aforementioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide an automatic gain control and sensitivity calibration system for a rail flaw detector. This invention integrates a humidity sensor and an optical turbidity sensor, and combines them with an impedance matching algorithm to achieve precise quantification of the coupling state. It uses the density change rate of the coupling medium to predict the fluctuation trend of the coupling layer and dynamically adjusts the fusion weight of the coupling signal and the integral value of the grass wave. Based on the fusion decision, it generates an appropriate gain adjustment command. Combined with coupling medium density compensation and grass wave level secondary correction, it achieves hierarchical and segmented adaptive gain adjustment. At the same time, it uses damping control to achieve overshoot suppression and rapid locking of gain adjustment, significantly improving the real-time performance, accuracy, and stability of gain control during rail flaw detection. This enables high-fidelity acquisition of flaw detection signals and intelligent, precise, and anti-interference capabilities of gain control under complex working conditions.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides an automatic gain control and sensitivity calibration system for a rail flaw detector, comprising a coupling medium monitoring module, a data processing and calculation module, an automatic gain control module, and a sensitivity calibration module, wherein: The coupling medium monitoring module is used to collect the density parameters of the coupling medium mist in the contact area between the probe and the rail in real time, and convert them into an electrical signal characterizing the coupling efficiency. The data processing and calculation module is used to dynamically adjust the fusion weight of the coupling signal and the grass wave integral value according to the density change rate of the coupling medium, respond in advance when the coupling layer is unstable, restore normal control when it is stable, and output gain control command and sensitivity calibration command. The automatic gain control module is used to receive gain control commands output by the data processing and calculation module, and to call the preset ultrasonic transmittance compensation curve according to the coupling medium density, and to perform graded and segmented adaptive gain adjustment in combination with the integral value of the flaw detection straw wave, and to perform overshoot suppression and fast locking through real-time threshold judgment. The sensitivity calibration module is used to receive calibration instructions output by the data processing and calculation module, and automatically perform sensitivity benchmark calibration and correction of the flaw detector based on the coupling efficiency correction coefficient and the artificial defect reflection wave of the standard test block.

[0006] The coupling medium monitoring module includes a multi-dimensional sensing acquisition unit, an environmental differential compensation unit, and a feature signal conversion unit, wherein: The multi-dimensional sensing and acquisition unit integrates a humidity sensor and an optical turbidity sensor to simultaneously acquire the medium humidity value and the optical reflection characteristics of the mist / water film in the contact area. The environmental differential compensation unit is used to collect background environmental temperature and humidity data around the probe, and remove environmental background noise from the total signal to separate the pure coupling layer state data. The feature signal conversion unit is used to convert the separated pure coupling data into a standard electrical signal that characterizes the instantaneous coupling efficiency through an impedance matching algorithm.

[0007] The humidity sensor is used to collect the relative humidity of the coupling medium in the contact area between the probe and the rail; the optical turbidity sensor is used to collect the optical reflection intensity of the mist and water film in the coupling medium, and the sampling frequency of both is consistent with the sampling frequency of the coupling medium density.

[0008] The data processing and computation module includes a dynamic trend analysis unit, an adaptive weighted fusion unit, and an instruction generation and distribution unit, wherein: The dynamic trend analysis unit is used to calculate the differential rate of change of the coupling medium density in real time and predict the upcoming fluctuation trend of the coupling layer. The adaptive weighted fusion unit is used to dynamically adjust the weight ratio of "coupled signal" and "grass wave integral value" in the control algorithm according to the trend analysis results. When the coupling is unstable, sensor data is given priority, and when it is stable, echo data is given priority. The instruction generation and distribution unit generates specific gain adjustment step size instructions and sensitivity calibration trigger instructions based on the fused decision logic, and sends them to the automatic gain control module and sensitivity calibration module, respectively.

[0009] The dynamic trend analysis unit calculates the differential rate of change of the coupling medium density in real time to predict the upcoming fluctuation trend of the coupling layer. The specific operation is as follows: A1: Using the current sampling time as a reference, read the historical coupling medium density data within a preset time window and construct a time series array; A2: Based on the time series array, the first differential rate of change of the coupling medium density at the current moment is calculated using Equation (1). The rate of change characterizes the instantaneous change rate of the coupling layer thickness. ; In the formula, The rate of change is the differential. This represents the coupling medium density value at the current sampling time. This represents the coupling medium density value at the previous sampling time. The time interval between two consecutive samples is d, where d is the differential operator and t is the sampling time. A3: The calculated differential rate of change With the preset stability threshold and fluctuation trigger threshold Compare and predict trends: ①When When the coupling layer is in a stable state, it is determined that the coupling layer is in a stable state. ②When When the coupling layer is in a state of increasing thickness or increasing dielectric density, it is determined that the coupling layer is in a state of increasing thickness or increasing dielectric density. ③When At that time, it is determined that the coupling layer is in a trend of thinning or decreasing dielectric density; ④ When At that time, it is determined that the coupling layer is in a state of flow interruption or probe lifting-off; in, The threshold for determining a stable state. The threshold for triggering fluctuation trends, and .

[0010] The adaptive weighted fusion unit dynamically adjusts the weight ratio of the "coupled signal" and the "grass wave integral value" in the control algorithm based on the trend analysis results. When the coupling is unstable, sensor data is given priority; when it is stable, echo data is given priority. The specific operation is as follows: B1: Let These are the weighting coefficients for the coupled signals. The weighting coefficients for the integral value of the grass wave are given, and they satisfy the normalization condition. ; B2: Weighting coefficient Based on the density change rate of the coupling medium The absolute value is determined according to equation (2): ; B3: Fusion Output Value Calculated according to equation (3) to comprehensively characterize the coupling state and echo features: ; In the formula, These are the normalized characteristic values ​​of the coupled signal. This is the normalized integral value of the grass wave.

[0011] The automatic gain control module includes a transmittance lookup table unit, a segmented adjustment execution unit, and a closed-loop locking unit, wherein: The transmittance lookup unit has a built-in database of the relationship between coupling density and ultrasonic energy loss, which is used to quickly find the corresponding theoretical compensation value based on the current density. The segmented adjustment execution unit is used to perform secondary correction on the compensation value obtained by looking up the table, based on the real-time integral level of the grass wave. The closed-loop locking unit is used to monitor the relationship between the peak value and the threshold value of the output signal and to perform damping control during gain adjustment.

[0012] The segmented adjustment execution unit combines the real-time integral level of the grass wave to perform a secondary correction on the compensation value obtained from the lookup table. The specific operation is as follows: C1: Preset lower threshold for grass wave level and upper limit threshold The real-time integral level is divided into three adjustment regions: undersensitive region, stable region, and oversensitive region; C2: Calculate the correction factor based on the current adjustment zone. ; ① When the real-time integral level is less than When this is detected, it is identified as an undersensitive area, and a correction factor is set. ; ② When the real-time integral level is greater than When the sensitivity is deemed too high, a correction factor is set. ; ③When ≤Real-time integral level≤ When the condition is stable, a correction factor is set. ; C3: Combine theoretical compensation value with correction coefficient Perform the calculation to determine the final gain adjustment.

[0013] The final gain adjustment in step C3 is shown in equation (4): ; In the formula, This is the final gain adjustment amount. This is the theoretical compensation value output by the transmittance lookup table unit. To adjust the gain proportionally, For real-time integrated level, The preset target value for the ideal grass-like wave level.

[0014] The sensitivity calibration module includes a reference reflected wave capture unit, a comprehensive deviation calculation unit, and a reference parameter correction unit, wherein: The reference reflection wave capturing unit is used to accurately identify and lock the highest reflected echo of artificial defects when the flaw detector passes through the standard test block. The comprehensive deviation calculation unit is used to compare the "measured echo amplitude" with the "theoretical standard amplitude" and, in conjunction with the current coupling efficiency correction coefficient, calculate the comprehensive error value caused by instrument drift and coupling loss. The reference parameter correction unit is used to automatically adjust the programmable attenuator or digital gain parameter before the analog-to-digital converter based on the comprehensive error value.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention integrates a humidity sensor and an optical turbidity sensor, and combines them with an impedance matching algorithm to achieve precise quantification of the coupling state. It uses the density change rate of the coupling medium to predict the fluctuation trend of the coupling layer and dynamically adjusts the fusion weight of the coupling signal and the grass wave integral value. Based on the fusion decision, it generates an appropriate gain adjustment command. Combined with coupling medium density compensation and grass wave level secondary correction, it achieves hierarchical and segmented adaptive gain adjustment. At the same time, it uses damping control to achieve overshoot suppression and rapid locking of gain adjustment, which significantly improves the real-time performance, accuracy and stability of gain control in rail flaw detection. Thus, it realizes high-fidelity acquisition of flaw detection signals and intelligent, precise and anti-interference of gain control under complex working conditions. Attached Figure Description

[0016] Figure 1 This is a system diagram of an automatic gain control and sensitivity calibration system for a rail flaw detector according to the present invention.

[0017] Figure 2 This is a flowchart of the dynamic trend analysis unit in the automatic gain control and sensitivity calibration system of a rail flaw detector according to the present invention.

[0018] Figure 3 This is a flowchart of an adaptive weighted fusion unit in an automatic gain control and sensitivity calibration system for a rail flaw detector according to the present invention.

[0019] Figure 4 This is a flowchart of the segmented adjustment execution unit in the automatic gain control and sensitivity calibration system of a rail flaw detector according to the present invention.

[0020] Explanation of icon numbers: 100. Coupled Medium Monitoring Module; 101. Multidimensional Sensing Acquisition Unit; 102. Environmental Differential Compensation Unit; 103. Feature Signal Conversion Unit; 200. Data Processing and Calculation Module; 201. Dynamic Trend Analysis Unit; 202. Adaptive Weighted Fusion Unit; 203. Command Generation and Distribution Unit; 300. Automatic Gain Control Module; 301. Transmittance Lookup Table Unit; 302. Segmented Adjustment Execution Unit; 303. Closed-Loop Locking Unit; 400. Sensitivity Calibration Module; 401. Reference Reflected Wave Capture Unit; 402. Comprehensive Deviation Calculation Unit; 403. Reference Parameter Correction Unit. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example:

[0023] like Figures 1-4 As shown, this embodiment provides an automatic gain control and sensitivity calibration system for a rail flaw detector, including a coupling medium monitoring module 100, a data processing and calculation module 200, an automatic gain control module 300, and a sensitivity calibration module 400. Specifically: the coupling medium monitoring module 100 is used to collect the density parameters of the coupling medium mist in the contact area between the probe and the rail in real time and convert them into an electrical signal characterizing the coupling efficiency; the data processing and calculation module 200 is used to dynamically adjust the fusion weight of the coupling signal and the grass wave integral value according to the rate of change of the coupling medium density, responding in advance when the coupling layer is unstable and restoring normal control when stable, and outputting gain control commands and sensitivity calibration commands; the automatic gain control module 300 is used to receive the gain control commands output by the data processing and calculation module 200, and call a preset ultrasonic transmittance compensation curve according to the coupling medium density, combined with the flaw detection grass wave integral value to perform graded and segmented adaptive gain adjustment, and perform overshoot suppression and rapid locking through real-time threshold judgment; the sensitivity calibration module 400: It is used to receive calibration instructions output by the data processing and calculation module 200, and automatically perform sensitivity benchmark calibration and correction of the flaw detector based on the coupling efficiency correction coefficient and the artificial defect reflection wave of the standard test block.

[0024] It should be noted that the coupling medium monitoring module 100 collects the coupling efficiency signal in real time, and the data processing and calculation module 200 dynamically adjusts the weight strategy according to the density change rate and generates control commands, which in turn drive the automatic gain control module 300 to perform graded and segmented adaptive gain adjustment, and drive the sensitivity calibration module 400 to complete the benchmark calibration in combination with the correction coefficient.

[0025] In this embodiment, it should also be noted that the coupling medium monitoring module 100 includes a multi-dimensional sensing acquisition unit 101, an environmental differential compensation unit 102, and a feature signal conversion unit 103. Specifically: the multi-dimensional sensing acquisition unit 101 integrates a humidity sensor and an optical turbidity sensor to simultaneously acquire the humidity value of the medium in the contact area and the optical reflection characteristics of the mist / water film; the humidity sensor is used to acquire the relative humidity of the coupling medium in the contact area between the probe and the rail; the optical turbidity sensor is used to acquire the optical reflection intensity of the mist and water film in the coupling medium, and the acquisition frequency of both is consistent with the sampling frequency of the coupling medium density. The environmental differential compensation unit 102 is used to acquire the background environmental temperature and humidity data around the probe and remove environmental background noise from the total signal to separate the pure coupling layer state data; the feature signal conversion unit 103 is used to convert the separated pure coupling data into a standard electrical signal characterizing the instantaneous coupling efficiency through an impedance matching algorithm.

[0026] It should be noted that the multi-dimensional sensing acquisition unit 101 simultaneously acquires the medium humidity and optical reflection characteristics of the contact area, and the environmental differential compensation unit 102 removes background environmental noise to separate the pure coupling layer state data. Finally, the feature signal conversion unit 103 uses an impedance matching algorithm to convert the pure data into a standard electrical signal that characterizes the instantaneous coupling efficiency.

[0027] Furthermore, it should be noted that the humidity sensor and optical turbidity sensor in the multi-dimensional sensing acquisition unit 101 are arranged in the circumferential direction of the probe contact surface or in the coupling area at the front end of the flaw detection probe to ensure that the detection area is consistent with the ultrasonic incident area.

[0028] The impedance matching algorithm in the characteristic signal conversion unit 103 specifically includes: calculating the acoustic impedance of the coupling layer using equation (5) based on the relative humidity H collected by the humidity sensor and the reflection intensity T collected by the optical turbidity sensor. : ; Where A and B are experimental fitting constants; subsequently, the instantaneous coupling efficiency is calculated based on the ultrasonic transmittance formula at the interface between the rail and the coupling layer. As shown in equation (6): ; Ultimately Linearly mapped to a standard electrical signal of 0-5V.

[0029] In this embodiment, it should also be noted that the data processing and operation module 200 includes a dynamic trend analysis unit 201, an adaptive weighted fusion unit 202, and an instruction generation and distribution unit 203, wherein: the dynamic trend analysis unit 201 is used to calculate the differential rate of change of the coupling medium density in real time and predict the fluctuation trend of the coupling layer; the specific operation is as follows: A1: Based on the current sampling time, read the historical coupling medium density data within the preset time window and construct a time series array; A2: Based on the time series array, use formula (1) to calculate the first-order differential rate of change of the coupling medium density at the current time, the rate of change characterizes the instantaneous change speed of the coupling layer thickness; ; In the formula, The rate of change is the differential. This represents the coupling medium density value at the current sampling time. This represents the coupling medium density value at the previous sampling time. A1: The time interval between two adjacent samples, d is the differential operator, and t is the sampling time; A2: The calculated differential rate of change With the preset stability threshold and fluctuation trigger threshold Compare and predict trends: ① When When the coupling layer is in a stable state, it is determined that the coupling layer is in a stable state; ② When When the coupling layer is in a state of increasing thickness or increasing dielectric density, it is determined that the coupling layer is in a state of increasing thickness or increasing dielectric density; ③ When When, it is determined that the coupling layer is in a thinning or dielectric density decreasing trend; ④ When At that time, it is determined that the coupling layer is in a state of flow interruption or probe lifting-off; among which, The threshold for determining a stable state. The threshold for triggering fluctuation trends, and Adaptive weighted fusion unit 202: Used to dynamically adjust the weight ratio of the "coupled signal" and the "grass wave integral value" in the control algorithm based on trend analysis results. When coupling is unstable, sensor data is prioritized; when stable, echo data is prioritized. Specific operation is as follows: B1: Set... These are the weighting coefficients for the coupled signals. The weighting coefficients for the integral value of the grass wave are given, and they satisfy the normalization condition. B2: Weighting coefficient Based on the density change rate of the coupling medium The absolute value is determined according to equation (2): ; B3: Fusion Output Value Calculated according to equation (3) to comprehensively characterize the coupling state and echo features: ; In the formula, These are the normalized characteristic values ​​of the coupled signal. This is the normalized integral value of the grass wave. Instruction generation and distribution unit 203: Based on the fused decision logic, it generates specific gain adjustment step size instructions and sensitivity calibration trigger instructions, and sends them to the automatic gain control module 300 and the sensitivity calibration module 400, respectively.

[0030] It should be noted that the dynamic trend analysis unit 201 calculates the differential rate of change of the coupling medium density based on historical data to predict the fluctuation trend, thereby driving the adaptive weighted fusion unit 202 to dynamically adjust the fusion weight of the coupling signal and the grass wave integral value according to the trend analysis results and calculate the fusion output value. Finally, the instruction generation and distribution unit 203 generates the gain adjustment step size and sensitivity calibration trigger instruction based on the fusion decision logic and distributes them to the automatic gain control module 300 and the sensitivity calibration module 400.

[0031] Furthermore, it should be noted that the preset time window in A1 contains a fixed window of 5-20 consecutive sampling points. The window length can be flexibly adjusted according to the actual flaw detection conditions. The purpose is to smooth the measurement noise of a single sampling point through the accumulation of multiple frames of historical data, avoid misjudgment of trends caused by instantaneous sampling errors, and ensure that the constructed time series array can truly reflect the continuous change law of the coupling medium density.

[0032] The value range is 0.01-0.05 kg / (m³・s). The value range is 0.1-0.5 kg / (m³・s).

[0033] The instruction generation and distribution unit 203's instruction generation decision logic is based on a preset... Mapping relationship with gain adjustment step size: I. When When the gain is ≥0.8, it is determined to be a severe coupling anomaly, and a gain adjustment command with a maximum step size is generated, with the preset step size being 0.5-1dB; II. When 0.2 < When the gain is less than 0.8, it is determined to be a slight coupling anomaly or stability, and a gain adjustment command with a corresponding step size is generated, with the preset step size being 0.1-0.5dB; Ⅲ, when When the value is ≤0.2, the coupling state is considered to be excellent, and a gain adjustment command with the minimum step size is generated or no adjustment command is generated.

[0034] In this embodiment, it should also be noted that the automatic gain control module 300 includes a transmittance lookup table unit 301, a segmented adjustment execution unit 302, and a closed-loop locking unit 303. Specifically: the transmittance lookup table unit 301 has a built-in database of the relationship between coupling density and ultrasonic energy loss, used to quickly find the corresponding theoretical compensation value based on the current density; the segmented adjustment execution unit 302 is used to perform a secondary correction on the compensation value obtained from the lookup table, based on the real-time integrated level of the grass wave; the specific operation is as follows: C1: preset lower threshold value for the grass wave level. and upper limit threshold The real-time integral level is divided into three adjustment regions: undersensitive region, stable region, and oversensitive region; C2: Calculate the correction coefficient based on the current adjustment region. ① When the real-time integration level is less than When this is detected, it is identified as an undersensitive area, and a correction factor is set. ② When the real-time integration level is greater than When the sensitivity is deemed too high, a correction factor is set. ;③ When ≤Real-time integral level≤ When the condition is stable, a correction factor is set. C3: Combine the theoretical compensation value with the correction coefficient. Perform the calculation to determine the final gain adjustment. The final gain adjustment is shown in equation (4): ; In the formula, This is the final gain adjustment amount. This is the theoretical compensation value output by the transmittance lookup table unit 301. To adjust the gain proportionally, For real-time integrated level, The preset ideal grass-like wave level target value. Closed-loop locking unit 303: used to monitor the peak value and threshold relationship of the output signal and perform damping control during gain adjustment.

[0035] It should be noted that the transmittance lookup unit 301 looks up the theoretical compensation value based on the current coupling density, and then the segmented adjustment execution unit 302 calculates the correction coefficient in combination with the adjustment region where the real-time integral level of the grass wave is located, and performs a second correction on the theoretical compensation value to obtain the final gain adjustment amount. Finally, the closed-loop locking unit 303 monitors the output peak value and performs damping control during the adjustment process to achieve rapid locking.

[0036] Furthermore, it should be noted that the specific operation of the damping control in the closed-loop locking unit 303 is as follows: Ⅰ. Real-time monitoring of the peak value of the output signal of the automatic gain control module 300. Compared with the preset target threshold The difference II. Calculate the gain adjustment step size and damping coefficient using a proportional-integral-derivative control algorithm with a damping term. and Inversely proportional: when When the error exceeds the first error threshold, Take the smaller value to achieve a fast response; when When it is less than the second error threshold, Take a larger value to suppress overshoot; III. When If the gain is less than the lock threshold for three consecutive sampling periods, the gain is determined to be locked, and a lock completion flag is output.

[0037] C3 proportional adjustment gain The value ranges from 0.1 to 0.5, and the specific value is dynamically selected based on the current surface roughness grade of the rail: the rougher the surface, the higher the roughness grade. The smaller the value, the lower the sensitivity to grass wave noise.

[0038] In this embodiment, it should also be noted that the sensitivity calibration module 400 includes a reference reflected wave capture unit 401, a comprehensive deviation calculation unit 402, and a reference parameter correction unit 403, wherein: the reference reflected wave capture unit 401 is used to accurately identify and lock the highest reflected echo of the artificial defect when the flaw detector passes through the standard test block; the comprehensive deviation calculation unit 402 is used to compare the "measured echo amplitude" with the "theoretical standard amplitude" and, in combination with the current coupling efficiency correction coefficient, calculate the comprehensive error value caused by instrument drift and coupling loss; the reference parameter correction unit 403 is used to automatically adjust the programmable attenuator or digital gain parameter before the analog-to-digital converter according to the comprehensive error value.

[0039] It should be noted that the reference reflection wave capture unit 401 accurately locks the highest reflected echo of the artificial defect when the flaw detector passes through the standard test block, and hands it over to the comprehensive deviation calculation unit 402 to compare the measured and theoretical standard amplitudes and calculate the comprehensive error value in combination with the current coupling efficiency correction coefficient. Finally, the reference parameter correction unit 403 automatically adjusts the programmable attenuator or digital gain parameter according to the error value to complete the reference calibration.

[0040] Furthermore, it should be noted that the identification in the reference reflected wave capture unit 401 is achieved by setting a time window [T1, T2] corresponding to the location of the artificial defect in the standard test block, and searching for the maximum amplitude value of the echo signal within this time window.

[0041] Locking steps: Take the time corresponding to the maximum amplitude value identified as the reference point and record the echo amplitude at that point. Simultaneously, store the coupling efficiency correction coefficient at that moment. .

[0042] Comprehensive deviation calculation unit 402 Comprehensive error value The calculation is shown in equation (7): ; In the formula, To measure the echo amplitude, For the theoretical standard amplitude, This is the current coupling efficiency correction coefficient, with a value ranging from 0 to 1. A time value indicates no overall error; otherwise, the baseline parameters need to be adjusted.

[0043] The reference parameter correction unit 403 calculates the corrected programmable attenuator value according to equation (8). : ; Alternatively, the digital gain correction value can be calculated according to equation (9). : ; in, The comprehensive error value output by the comprehensive deviation calculation unit 402. This is the conversion coefficient between the attenuator step size and the error value.

[0044] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An automatic gain control and sensitivity calibration system for a rail flaw detector, characterized in that, It includes a coupling medium monitoring module (100), a data processing and calculation module (200), an automatic gain control module (300), and a sensitivity calibration module (400), wherein: The coupling medium monitoring module (100) is used to collect the density parameters of the coupling medium mist in the contact area between the probe and the rail in real time, and convert them into an electrical signal characterizing the coupling efficiency. The data processing and operation module (200) is used to dynamically adjust the fusion weight of the coupling signal and the grass wave integral value according to the density change rate of the coupling medium, respond in advance when the coupling layer is unstable, restore normal control when it is stable, and output gain control command and sensitivity calibration command. The automatic gain control module (300) is used to receive the gain control command output by the data processing and calculation module (200), and call the preset ultrasonic transmittance compensation curve according to the coupling medium density, and perform graded and segmented adaptive gain adjustment in combination with the integral value of the flaw detection grass wave, and perform overshoot suppression and fast locking through real-time threshold judgment. The sensitivity calibration module (400) is used to receive the calibration instructions output by the data processing and calculation module (200), and automatically perform the sensitivity benchmark calibration and correction of the flaw detector according to the coupling efficiency correction coefficient and the artificial defect reflection wave of the standard test block.

2. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 1, characterized in that, The coupling medium monitoring module (100) includes a multi-dimensional sensing acquisition unit (101), an environmental differential compensation unit (102), and a feature signal conversion unit (103), wherein: The multi-dimensional sensing and acquisition unit (101) integrates a humidity sensor and an optical turbidity sensor to simultaneously acquire the medium humidity value and the optical reflection characteristics of the mist / water film in the contact area. The environmental differential compensation unit (102) is used to collect background environmental temperature and humidity data around the probe, and remove environmental background noise from the total signal to separate pure coupling layer state data. The feature signal conversion unit (103) is used to convert the separated pure coupling data into a standard electrical signal that characterizes the instantaneous coupling efficiency through an impedance matching algorithm.

3. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 2, characterized in that, The humidity sensor is used to collect the relative humidity of the coupling medium in the contact area between the probe and the rail; the optical turbidity sensor is used to collect the optical reflection intensity of the mist and water film in the coupling medium, and the sampling frequency of both is consistent with the sampling frequency of the coupling medium density.

4. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 1, characterized in that, The data processing and operation module (200) includes a dynamic trend analysis unit (201), an adaptive weighted fusion unit (202), and an instruction generation and distribution unit (203), wherein: The dynamic trend analysis unit (201) is used to calculate the differential rate of change of the coupling medium density in real time and predict the fluctuation trend of the coupling layer. The adaptive weighted fusion unit (202) is used to dynamically adjust the weight ratio of "coupled signal" and "grass wave integral value" in the control algorithm according to the trend analysis results. When the coupling is unstable, the sensor data is trusted first, and when it is stable, the echo data is trusted first. The instruction generation and distribution unit (203) generates specific gain adjustment step size instructions and sensitivity calibration trigger instructions based on the fused decision logic, and sends them to the automatic gain control module (300) and sensitivity calibration module (400) respectively.

5. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 4, characterized in that, The dynamic trend analysis unit (201) calculates the differential rate of change of the coupling medium density in real time to predict the upcoming fluctuation trend of the coupling layer. The specific operation is as follows: A1: Using the current sampling time as a reference, read the historical coupling medium density data within a preset time window and construct a time series array; A2: Based on the time series array, the first differential rate of change of the coupling medium density at the current moment is calculated using Equation (1). The rate of change characterizes the instantaneous change rate of the coupling layer thickness. ； In the formula, The rate of change is the differential. This represents the coupling medium density value at the current sampling time. This represents the coupling medium density value at the previous sampling time. The time interval between two consecutive samples is d, where d is the differential operator and t is the sampling time. A3: The calculated differential rate of change With the preset stability threshold and fluctuation trigger threshold Compare and predict trends: ①When When the coupling layer is in a stable state, it is determined that the coupling layer is in a stable state. ②When When the coupling layer is in a state of increasing thickness or increasing dielectric density, it is determined that the coupling layer is in a state of increasing thickness or increasing dielectric density. ③When At that time, it is determined that the coupling layer is in a trend of thinning or decreasing dielectric density; ④ When At that time, it is determined that the coupling layer is in a state of flow interruption or probe lifting-off; in, The threshold for determining a stable state. The threshold for triggering fluctuation trends, and .

6. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 5, characterized in that, The adaptive weighted fusion unit (202) dynamically adjusts the weight ratio of "coupled signal" and "grass wave integral value" in the control algorithm based on the trend analysis results. When the coupling is unstable, sensor data is given priority; when it is stable, echo data is given priority. The specific operation is as follows: B1: Let These are the weighting coefficients for the coupled signals. The weighting coefficients for the integral value of the grass wave are and they satisfy normalization. ; B2: Weighting coefficient Based on the rate of change of the coupling medium density The absolute value is determined according to equation (2): ； B3: Fusion Output Value Calculated according to equation (3) to comprehensively characterize the coupling state and echo features: ； In the formula, These are the normalized characteristic values ​​of the coupled signal. This is the normalized integral value of the grass wave.

7. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 1, characterized in that, The automatic gain control module (300) includes a transmittance lookup table unit (301), a segmented adjustment execution unit (302), and a closed-loop locking unit (303), wherein: The transmittance lookup unit (301) has a built-in database of the relationship between coupling density and ultrasonic energy loss, which is used to quickly find the corresponding theoretical compensation value based on the current density. The segmented adjustment execution unit (302) is used to perform secondary correction on the compensation value obtained by looking up the table, based on the real-time integral level of the grass wave. The closed-loop locking unit (303) is used to monitor the relationship between the peak value and the threshold value of the output signal and to perform damping control during the gain adjustment process.

8. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 7, characterized in that, The segmented adjustment execution unit (302) combines the real-time integral level of the grass wave to perform a secondary correction on the compensation value obtained by looking up the table. The specific operation is as follows: C1: Preset lower threshold for grass wave level and upper limit threshold The real-time integral level is divided into three adjustment regions: undersensitive region, stable region, and oversensitive region; C2: Calculate the correction factor based on the current adjustment zone. ; ① When the real-time integral level is less than When this is detected, it is identified as an undersensitive area, and a correction factor is set. ; ② When the real-time integral level is greater than When the sensitivity is deemed too high, a correction factor is set. ; ③When ≤Real-time integral level≤ When the condition is stable, a correction factor is set. ; C3: Combine theoretical compensation value with correction coefficient Perform the calculation to determine the final gain adjustment.

9. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 8, characterized in that, The final gain adjustment in step C3 is shown in equation (4): ； In the formula, This is the final gain adjustment amount. The theoretical compensation value output by the transmittance lookup table unit (301) is... To adjust the gain proportionally, For real-time integrated level, The preset target value for the ideal grass-like wave level.

10. The automatic gain control and sensitivity calibration system for a rail flaw detector according to claim 1, characterized in that, The sensitivity calibration module (400) includes a reference reflected wave capture unit (401), a comprehensive deviation calculation unit (402), and a reference parameter correction unit (403), wherein: The reference reflection wave capturing unit (401) is used to accurately identify and lock the highest reflected echo of the artificial defect when the flaw detector passes through the standard test block; The comprehensive deviation calculation unit (402) is used to compare the "measured echo amplitude" with the "theoretical standard amplitude" and, in conjunction with the current coupling efficiency correction coefficient, calculate the comprehensive error value caused by instrument drift and coupling loss. The reference parameter correction unit (403) is used to automatically adjust the programmable attenuator or digital gain parameter before the analog-to-digital converter based on the comprehensive error value.

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