A fast detection method for track defects based on signal pulse width capture

Abstract

The present invention discloses a method for rapid detection of track defects based on signal pulse width capture, including: passing a sinusoidal excitation signal to an ACFM detection device, detecting changes in the eddy current field induced by a sensor and outputting a detection signal; passing the sinusoidal excitation signal and the detection signal to a signal conditioning circuit, and converting them into square wave excitation signals and square wave measurement signals with the same frequency and phase as the original signal respectively; capturing the positive and negative pulse width values ​​of the two square waves after conversion, and sending them to a host computer; restoring the originally captured square wave excitation signal and square wave measurement signal; inputting the square wave measurement signal and the square wave excitation signal into a digital phase-locked amplifier to obtain a phase signal with defect information. The present invention can quickly and effectively extract defect phase information, and evaluate defects based on phase signals, providing a track defect detection solution that does not rely on A / D acquisition equipment, has a cheaper detection system cost, a more compact structure, and is more portable.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing, and in particular relates to a method for quickly detecting track defects based on capturing signal pulse width. Background Art

[0002] In ACFM detection, a phase-locked amplifier is often used to extract rail defect signals. The phase-locked amplifier is a device for weak signal detection based on the principle of orthogonal demodulation. Weak signals are often submerged in various noises. The phase-locked amplifier can extract weak signals from the noise and measure them accurately. It uses a reference signal with the same frequency and fixed phase relationship as the detection signal as a reference, filters out noise with different frequencies, and thus extracts useful signal components.

[0003] The lock-in amplifier can be built by hardware circuit or software simulation, but both methods require A / D signal acquisition equipment to convert analog signals into digital signals so that the host computer can evaluate the defect signal. However, most A / D signal acquisition equipment with high sampling accuracy and fast acquisition speed are expensive, and most of them are integrated modules that are not easy to integrate into the existing detection system, which ultimately leads to higher detection equipment costs and loose structure.

[0004] Therefore, a new technical solution is needed to solve the above problems. Summary of the invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the prior art, a method for rapid detection of track defects based on signal pulse width capture is provided, which can quickly and effectively extract defect phase information and evaluate defects based on phase signals, providing a track defect detection solution that does not rely on A / D acquisition equipment, has a cheaper detection system cost, a more compact structure, and is more portable.

[0006] Technical solution: To achieve the above purpose, the present invention provides a method for rapid detection of track defects based on signal pulse width capture, comprising the following steps:

[0007] S1: A sinusoidal excitation signal is applied to the ACFM detection equipment. The ACFM eddy current detection probe generates a uniform eddy current field on the track. The detection sensor senses the change of the eddy current field and outputs a detection signal.

[0008] S2: The sinusoidal excitation signal passed into the ACFM detection device and the detection signal output by the induction are passed into the signal conditioning circuit, and the two signals are converted into a square wave excitation signal and a square wave measurement signal with the same frequency and phase as the original signal respectively;

[0009] S3: Capture the positive and negative pulse width values ​​of the two square waves after conversion, and send the obtained positive and negative pulse width values ​​to the host computer via USB in the capture order;

[0010] S4: The host computer restores the originally captured square wave excitation signal and square wave measurement signal according to the positive and negative pulse width values ​​in the sending order;

[0011] S5: Input the square wave measurement signal and the square wave excitation signal into the digital lock-in amplifier to obtain a phase signal with defect information.

[0012] Furthermore, the step S2 is specifically as follows:

[0013] A1: The sinusoidal excitation signal input into the ACFM detection device is passed into the signal reduction module to be converted into a sinusoidal excitation signal with an amplitude of ±NV, and the detection signal output by the induction is passed into the signal amplification module to be converted into a detection signal with an amplitude of ±NV;

[0014] A2: The converted sinusoidal excitation signal and detection signal are respectively passed into the voltage raising module to change the voltage amplitude of the two signals;

[0015] A3: The two signals after voltage raising are respectively passed into the hysteresis comparator module, and converted into square wave measurement signal and square wave excitation signal with the same frequency and phase as the original signal according to the upper threshold and lower threshold.

[0016] Furthermore, in step S3, the pulse width capture function of the timer peripheral of the STM32H743 microprocessor is used to capture the positive and negative pulse width values ​​of the two square waves after conversion. The specific process is as follows:

[0017] B1: Connect the square wave excitation signal and the square wave detection signal to the general timer of STM32H743, set the timer to pulse width capture mode, perform double-edge detection on the square wave detection signal, and set the counting mode to upward counting;

[0018] B2: Set the timer to rising edge capture. When the first rising edge of the input square wave detection signal arrives, the CNT counter of the timer is cleared and starts counting. At the same time, the timer is set to falling edge capture.

[0019] B3: When the falling edge arrives, the timer captures the current CNT value, recorded as t1, and the timer is set to capture the rising edge. When the rising edge arrives, the timer captures the current CNT value, recorded as t2, and the counter is cleared and set to capture the falling edge.

[0020] B4: Calculate the positive and negative pulse widths of the square wave within one cycle, that is, the positive pulse width is t1, and the negative pulse width is t2-t1;

[0021] B5: When the detection sensor passes through the defect, the phase difference between the detection signal and the excitation signal will change. When the track rotates, while the detection probe passes through the defect, the timer loops through steps B3 and B4 to capture the positive and negative pulse width values ​​of the detection signal and the excitation signal. This value contains the phase difference information between the detection signal and the detection signal, which is recorded as t1, t2-t1, t3, t4-t3, ..., t 2n-3 ,t 2n-2 -t 2n-3 ,t 2n-1 ,t 2n -t 2n-1 .

[0022] Furthermore, the step S4 is specifically as follows:

[0023] C1: After the upper computer obtains the pulse width values ​​of the square wave excitation signal and the detection signal sent by the lower computer, it arranges them in order: t1, t2-t1, t3, t4-t3, ..., t 2n-3 ,t 2n-2 -t 2n-3 ,t 2n-1 ,t 2n -t 2n-1 According to the positive and negative pulse width values, the positive pulse width of the first square wave cycle is t1, and the negative pulse width is t2-t1. The positive pulse width of the second square wave cycle is t3, and the negative pulse width is t4-t3, ..., the positive pulse width of the n-1th cycle is t 2n-3 , the negative pulse width is t 2n-2 -t 2n-3 , the positive pulse width of the nth cycle is t 2n-1 , the negative pulse width is t 2n -t 2n-1 ;

[0024] C2: According to the arrangement of positive and negative pulse widths in step C1, the amplitude of the positive cycle and the amplitude of the negative cycle of each square wave are set to restore a square wave signal with the same frequency and phase as the originally captured square wave measurement signal and excitation signal.

[0025] Furthermore, the step S5 is specifically as follows:

[0026] D1: Pass the square wave detection signal and the square wave excitation signal into the digital lock-in amplifier to obtain the I-channel and Q-channel signals with defect information;

[0027] D2: The I-channel signal and the Q-channel signal are calculated by the phase formula to obtain a defect phase signal with a phase difference between the detection signal and the excitation signal.

[0028] Furthermore, the process of acquiring the I-path signal and the Q-path signal in step D1 is as follows:

[0029] E1: Multiply the restored square wave excitation signal with the square wave detection signal to obtain the real signal I containing the defect signal and its double frequency signal;

[0030] E2: After the restored square wave excitation signal is phase-shifted by 90°, it is multiplied with the square wave detection signal to obtain the imaginary signal Q containing the defect signal and its double frequency signal;

[0031] E3: Use a digital low-pass filter to filter out the double frequency signal in the I and Q signals, and retain the real signal I and the imaginary signal Q containing only the defect signal.

[0032] Furthermore, the phase formula in step D2 is as follows:

[0033]

[0034] Compared with traditional analog or digital lock-in amplifiers, which require an A / D acquisition system to collect signals to a host computer and have disadvantages such as complex circuit structure and high price, the present invention innovatively uses the input pulse width capture function of the stm32 timer to quickly extract the phase information of the detection signal, thereby getting rid of the dependence on the acquisition system, simplifying the circuit structure, reducing the size of the device, improving the system portability, and reducing the system power consumption.

[0035] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0036] 1. Compared with the traditional analog or digital lock-in amplifier which requires an A / D acquisition device to convert the analog signal into a digital signal, the present invention uses the input capture function of the STM32 timer to obtain the phase information of the excitation signal and the detection signal, replacing the A / D acquisition device required by the system, reducing the cost of the detection equipment, and simplifying the system structure.

[0037] 2. The hardware required by the present invention only requires two amplifiers, two comparators and an STM32 chip with a pulse width capture function to form a defect detection system. Compared with the traditional lock-in amplifier, the circuit structure is simpler, the construction difficulty is lower, and the use cost is lower.

[0038] 3. The detection system constructed by the design scheme of the present invention is small in size, low in power consumption, and can adapt to detection environments with narrow spaces.

[0039] 4. In the design of the present invention, after the square wave excitation signal and the detection signal pulse width are captured, the amount of data generated is smaller, which is suitable for detection under conditions of only low-speed data transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic diagram of the structure of a track defect detection system based on square wave demodulation in an embodiment of the present invention;

[0041] Figure 2 is a structural schematic diagram of a turntable rail sample in an embodiment of the present invention;

[0042] Figure 3 is a detailed structural block diagram of a signal conditioning circuit in an embodiment of the present invention;

[0043] Figure 4 Schematic diagram of signal conversion of a signal processing module in an embodiment of the present invention;

[0044] Figure 5 Schematic diagram of the original captured square wave and the restored square wave in an embodiment of the present invention;

[0045] Figure 6 is a defect phase signal diagram obtained based on the pulse width capture method in an embodiment of the present invention;

[0046] Figure 7 3 is a defect phase signal diagram obtained based on a traditional digital lock-in amplifier in an embodiment of the present invention.

[0047] Figure 8 This is a peak comparison and linear fitting diagram of defects No. 4-7 in the embodiment of the present invention;

[0048] Fig. 9 It is a relative error diagram of the actual defect peak values ​​4-7 compared with the theoretical defect peak values ​​in the embodiments of the present invention. DETAILED DESCRIPTION

[0049] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0050] The present invention provides a method for rapid detection of rail defects based on signal pulse width capture. In this embodiment, the method is applied to defect detection of turntable rails. Figure 1 As shown, it includes the following steps:

[0051] 1) A sinusoidal excitation signal with an amplitude of ±10V is introduced into the ACFM detection probe. Figure 2 A uniform eddy current field is generated on the turntable rail sample shown, which senses the change of the eddy current field and outputs a detection signal with an amplitude of about ±100mV;

[0052] like Figure 1 As shown, this embodiment provides a rail defect rapid detection system based on signal pulse width capture, the system includes an ACFM detection probe, a signal generator, a signal conditioning circuit module, an STM32 chip and a host computer;

[0053] When using the ACFM detection probe to detect the turntable rail sample, an AC excitation of 20KHz, 10Vpp is passed into the excitation coil. The sample defects of the turntable rail sample are as follows Figure 2 As shown, the detection probe will generate an eddy current field on the rail sample, and the detection probe senses the change of the eddy current field and outputs a detection signal.

[0054] 2) The sinusoidal excitation signal passed into the ACFM detection device and the detection signal output by the induction are passed into the signal conditioning module, and the two signals are converted into a square wave excitation signal and a square wave measurement signal with the same frequency and phase as the original signal.

[0055] The circuit diagram of the signal conditioning module is as follows: Figure 3 As shown, refer to Figure 3 , the specific process of this step is:

[0056] 2.1) The sinusoidal excitation signal with an amplitude of ±10V is passed into the ACFM detection device, and then it is converted into a sinusoidal excitation signal with an amplitude of ±1V. The detection signal with an amplitude of about ±100mV is passed into the signal amplification module, and then it is also converted into a detection signal of about ±1V. After conditioning, the sinusoidal excitation signal and the detection signal are as follows: Figure 4 As shown in the s1 curve in (a);

[0057] 2.2) The amplified signals are fed into the voltage boost module, and the boost amplitude is 1.65V. Figure 4 As shown in the s2 curve in (b), the amplitudes of the two signals are changed to 0.65V-2.65V. After the voltage is raised, the signal is as follows Figure 4 As shown in the s3 curve in (b);

[0058] 2.3) The two signals after voltage raising are respectively passed into the hysteresis comparator module, and the lower threshold is 1.55V. Figure 4 As shown in the s4 curve in (b), the upper threshold is 1.75V. Figure 4 As shown in the s5 curve in (b), it is converted into a square wave measurement signal and a square wave excitation signal with the same frequency and phase as the original signal, as shown in Figure 4 As shown in the s6 curve in (c).

[0059] 3) Use the input capture function of the timer peripheral of the STM32H743 microprocessor to capture the positive and negative pulse width values ​​of the two square waves after conversion, and send the obtained positive and negative pulse width values ​​to the host computer via USB in the capture order, as follows:

[0060] 3.1) Connect the square wave excitation signal to the first channel of the general timer 1 of the STM32H743, and the square wave measurement signal to the second channel of the general timer 1. Set the timer to input capture mode, perform double-edge detection on the square wave signal, and set the counting mode to up counting;

[0061] 3.2) Set the timer to capture the rising edge. When the first rising edge arrives, the CNT counter of the timer is cleared and starts counting. At the same time, the timer is set to capture the falling edge.

[0062] 3.3) Then when the falling edge arrives, the timer captures the current CNT value, recorded as t1, and the timer is set to rising edge capture. When the rising edge arrives, the timer captures the current CNT value, recorded as t2, and the counter is cleared and set to falling edge capture.

[0063] 3.4) Calculate the positive and negative pulse widths of the square wave within one cycle, that is, the positive pulse width is t1, and the negative pulse width is t2-t1;

[0064] 3.5) The timer loops through steps 3.3) and 3.4), thereby obtaining the positive and negative pulse widths of the two square waves in each cycle, recorded as t1, t2-t1, t3, t4-t3, ..., t 2n-3 ,t 2n-2 -t 2n-3 ,t 2n-1 ,t 2n -t 2n-1 , the square wave signal edge capture time is as follows Figure 5 As shown in s7 in (a);

[0065] 3.6) The positive and negative pulse width values ​​of the obtained square wave excitation signal and square wave detection signal are sent to the host computer via USB.

[0066] 4) The host computer restores the originally captured square wave measurement signal and square wave excitation signal according to the positive and negative pulse width values ​​in the sending order, as follows:

[0067] 4.1) After the upper computer obtains the positive and negative pulse width values ​​of the square wave excitation signal and the square wave detection signal sent by the lower computer, it arranges them in order: t1, t2-t1, t3, t4-t3, ..., t 2n-3 ,t 2n-2 -t 2n-3 ,t 2n-1 ,t 2n -t 2n-1 According to the positive and negative pulse width values, the positive pulse width of the first square wave cycle is t1, and the negative pulse width is t2-t1. The positive pulse width of the second square wave cycle is t3, and the negative pulse width is t4-t3, ..., the positive pulse width of the n-1th cycle is t 2n-3 , the negative pulse width is t2n-2 -t 2n-3 , the positive pulse width of the nth cycle is t 2n-1 , the negative pulse width is t 2n -t 2n-1 ;

[0068] 4.2) According to the arrangement of positive and negative pulse widths described in step 4.1), the amplitude of the positive cycle of each square wave is set to +1V, and the amplitude of the negative cycle is set to -1V, thereby restoring a square wave signal with the same frequency and phase as the original captured square wave measurement signal and the excitation signal. The schematic diagram of restoring the square wave in this embodiment is as follows: Figure 5 As shown in s8 in (b).

[0069] 5) Input the square wave detection signal and the square wave excitation signal into the digital lock-in amplifier to obtain the I-channel and Q-channel signals containing defect information, and perform phase calculation, as follows:

[0070] 5.1) multiplying the square wave excitation signal restored in step 4) with the square wave detection signal to obtain a real signal I including the defect signal and its double frequency signal;

[0071] 5.2) After the square wave excitation signal restored in step 4) is phase-shifted by 90°, it is multiplied with the square wave detection signal to obtain an imaginary signal Q including the defect signal and its double frequency signal;

[0072] 5.3) Use a digital low-pass filter to filter out the double frequency signal in the I and Q signals, and retain the real signal I and the imaginary signal Q containing only the defect signal;

[0073] 5.4) The I-channel signal and the Q-channel signal are calculated by the phase formula (1) to obtain the defect phase signal with the phase difference between the detection signal and the excitation signal. The signal waveform is as follows: Figure 6 As shown, the phase formula is as follows:

[0074]

[0075] In order to verify the effectiveness of the method of the present invention, Figure 7 The defect phase signal diagram obtained by the traditional digital lock-in amplifier is Figure 6 By comparing the defect phase signal diagrams obtained based on the pulse width capture method, it can be found that the defect phase signal waveforms obtained by the two methods are consistent, and both can identify defect samples of different depths, different surface inclination angles, and different internal inclination angles in the rail samples, which can prove the correctness and feasibility of the method of the present invention.

[0076] In order to verify the actual effect of the method of the present invention, a comparative test was conducted between the detection method of the present invention (SQU) and the existing detection method (SIN) in this example, as follows:

[0077] Figure 8 The peak values ​​of defect samples 4-7 in the defect phase signals obtained by the two methods are plotted, and the defect samples represent defects with depths of 4mm, 2mm, 6mm, and 8mm, respectively. It can be found that the defect signals obtained by the two methods show a positive correlation trend for defects of different depths.

[0078] By substituting the defect depth into the two fitting curves, the relative error rate between the actual signal peak and the theoretical signal peak can be obtained as follows: Fig. 9 As shown. It can be found that the relative error rates of the two detection methods are within 10%, which is within the acceptable range in track non-destructive testing. Moreover, the track defect rapid detection method based on signal pulse width capture proposed by the present invention has a lower relative error rate at defect depths of 6mm and 8mm, and has certain advantages in detecting defects at deeper depths.

[0079] Moreover, the detection method of this invention has the advantages of simpler circuit construction, lower use cost, and smaller size, so it has certain applicability in the field of non-destructive testing.

Claims

1. A method for rapid detection of track defects based on signal pulse width capture, characterized in that: The steps include: S1: A sinusoidal excitation signal is applied to the ACFM detection equipment. The ACFM eddy current detection probe generates a uniform eddy current field on the track. The detection sensor senses the change of the eddy current field and outputs a detection signal. S2: The sinusoidal excitation signal passed into the ACFM detection device and the detection signal output by the induction are passed into the signal conditioning circuit, and the two signals are converted into a square wave excitation signal and a square wave measurement signal with the same frequency and phase as the original signal respectively; S3: Capture the positive and negative pulse width values ​​of the two square waves after conversion, and send the obtained positive and negative pulse width values ​​to the host computer in sequence according to the capture order; S4: The host computer restores the originally captured square wave excitation signal and square wave measurement signal according to the positive and negative pulse width values ​​in the sending order; S5: inputting the square wave measurement signal and the square wave excitation signal into the digital lock-in amplifier to obtain a phase signal with defect information; In step S3, the pulse width capture function of the timer peripheral of the STM32H743 microprocessor is used to capture the positive and negative pulse width values ​​of the two square waves after conversion. The specific process is as follows: B1: Connect the square wave excitation signal and the square wave detection signal to the general timer of STM32H743, set the timer to pulse width capture mode, perform double-edge detection on the square wave detection signal, and set the counting mode to upward counting; B2: Set the timer to rising edge capture. When the first rising edge of the input square wave detection signal arrives, the CNT counter of the timer is cleared and starts counting. At the same time, the timer is set to falling edge capture. B3: When the falling edge arrives, the timer captures the current CNT value, recorded as t1, and the timer is set to capture the rising edge. When the rising edge arrives, the timer captures the current CNT value, recorded as t2, and the counter is cleared and set to capture the falling edge. B4: Calculate the positive and negative pulse widths of the square wave within one cycle, that is, the positive pulse width is t1, and the negative pulse width is t2-t1; B5: When the detection sensor passes through the defect, the phase difference between the detection signal and the excitation signal will change. When the track rotates, while the detection probe passes through the defect, the timer loops through steps B3 and B4 to capture the positive and negative pulse width values ​​of the detection signal and the excitation signal. This value contains the phase difference information between the detection signal and the detection signal, which is recorded as t1, t2-t1, t3, t4-t3, ..., t 2n-3 ,t 2n-2 -t 2n-3 ,t 2n-1 ,t 2n -t 2n-1 ; Step S4 is specifically as follows: C1: After the upper computer obtains the pulse width values ​​of the square wave excitation signal and the detection signal sent by the lower computer, it arranges them in order: t1, t2-t1, t3, t4-t3, ..., t 2n-3 ,t 2n-2 -t 2n-3 ,t 2n-1 ,t 2n -t 2n-1 According to the positive and negative pulse width values, the positive pulse width of the first square wave cycle is t1, and the negative pulse width is t2-t1. The positive pulse width of the second square wave cycle is t3, and the negative pulse width is t4-t3, ..., the positive pulse width of the n-1th cycle is t 2n-3 , the negative pulse width is t 2n-2 -t 2n-3 , the positive pulse width of the nth cycle is t 2n-1 , the negative pulse width is t 2n -t 2n-1 ; C2: According to the arrangement of positive and negative pulse widths in step C1, the amplitude of the positive cycle and the amplitude of the negative cycle of each square wave are set to restore a square wave signal with the same frequency and phase as the originally captured square wave measurement signal and excitation signal.

2. A method for rapid detection of track defects based on signal pulse width capture according to claim 1, characterized in that: The step S2 is specifically as follows: A1: The sinusoidal excitation signal input into the ACFM detection device is passed into the signal reduction module to be converted into a sinusoidal excitation signal with an amplitude of ±NV, and the detection signal output by the induction is passed into the signal amplification module to be converted into a detection signal with an amplitude of ±NV; A2: The converted sinusoidal excitation signal and detection signal are respectively passed into the voltage raising module to change the voltage amplitude of the two signals; A3: The two signals after voltage raising are respectively passed into the hysteresis comparator module, and converted into square wave measurement signal and square wave excitation signal with the same frequency and phase as the original signal according to the upper threshold and lower threshold.

3. The method for rapid detection of track defects based on signal pulse width capture according to claim 1, characterized in that: The step S5 is specifically as follows: D1: Pass the square wave detection signal and the square wave excitation signal into the digital lock-in amplifier to obtain the I-channel and Q-channel signals with defect information; D2: The I-channel signal and the Q-channel signal are calculated by the phase formula to obtain a defect phase signal with a phase difference between the detection signal and the excitation signal.

4. A method for rapid detection of track defects based on signal pulse width capture according to claim 3, characterized in that: The phase formula in step D2 is as follows:

5. The method for rapid detection of track defects based on signal pulse width capture according to claim 3 is characterized in that: The process of acquiring the I-path signal and the Q-path signal in step D1 is as follows: E1: Multiply the restored square wave excitation signal with the square wave detection signal to obtain the real signal I containing the defect signal and its double frequency signal; E2: After the restored square wave excitation signal is phase-shifted by 90°, it is multiplied with the square wave detection signal to obtain the imaginary signal Q containing the defect signal and its double frequency signal; E3: Use a digital low-pass filter to filter out the double frequency signal in the I and Q signals, and retain the real signal I and the imaginary signal Q containing only the defect signal.

Images