A pulsed eddy current inspection system and method

Abstract

The present application provides a kind of pulsed eddy current testing system and method.A kind of pulsed eddy current testing system includes detection equipment, probe and test piece, probe includes sensor, sensor is by one enameled wire winding excitation coil, four enameled wire winding receiving coil is formed;Excitation coil is outside, after input pulse excitation signal, generates electric eddy current in the inside of the workpiece to be detected;Receiving coil is in excitation coil, two are a pair of cross distribution;Each pair of receiving coil is connected at one end, and a group of differential signal receiving coil pair is formed.The sensor of the present application uses two groups of differential receiving coil, and the amplitude variation ratio of signal is improved using differential signal mode;Using the amplitude width calculation analysis of time base signal, using alarm baseline height, alarm wave width limit gate, confirm wave width limit gate condition, remove the useless interference wave mode formed when detecting the test piece.It is suitable as a kind of pulsed eddy current testing system and method application.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electromagnetic non-destructive testing, in particular to a kind of pulsed eddy current testing system and method. BACKGROUND

[0002] Eddy current testing is to use electromagnetic induction principle, and generates eddy current in the measured workpiece of electrically conductive, when eddy current meets crack or defect, will detour through, thereby causing eddy current distribution disorder, detects by measuring the change of eddy current.Pulsed eddy current testing is a kind of non-destructive testing method, for detecting the surface and near-surface crack, inclusion and other defects of electrically conductive material.It is a kind of detection method without removing paint covering on the surface of workpiece and without coupling medium.It applies the basic theory of electromagnetics as the basis of conductor detection.Eddy current is generated from a phenomenon called electromagnetic induction.When alternating current is applied to a conductor, such as copper wire, a magnetic field will be generated in the conductor and the space around the conductor.Eddy current is the induced current, it flows in a loop.The reason it is called "eddy current" is because it is the same as the form of liquid or gas flowing around obstacles in a loop.If a conductor is placed in the changing magnetic field, eddy current will be generated in that conductor, and the magnetic field generated by eddy current will expand with the increase of alternating current and disappear with the decrease of alternating current.Therefore, when defects appear on the surface or near-surface of the conductor or the properties of the metal material change, it will affect the strength and distribution of eddy current, so we can detect the change of eddy current, and then indirectly know the existence of defects inside the conductor and whether the properties of the metal material have changed.

[0003] At present, the research method of pulsed eddy current testing for defect signal is to use single receiving sensor to observe and calculate the amplitude and zero-crossing time change of signal as shown in Figure 1 The amplitude change ratio of signal is small, and the research method is not intuitive. SUMMARY

[0004] In order to improve the amplitude change ratio of pulsed eddy current testing signal, and facilitate observation and calculation, the present application provides a kind of pulsed eddy current testing system and method.The method calculates the characteristics of pulsed excitation eddy current signal, avoids signal interference caused by the fact that all or part of the detection sensor leaves the surface of the detected workpiece, avoids signal interference caused by the fact that the sensor reaches the edge of the detected workpiece, and solves the technical problem of the amplitude change ratio of pulsed eddy current testing signal.

[0005] The scheme adopted by the present application to solve the technical problem is:

[0006] A kind of pulsed eddy current detection system includes detection equipment, probe and test piece, the probe includes sensor, the sensor includes excitation coil and inductive coil, the excitation coil is used to generate pulsed eddy current excitation signal acting on test piece, the inductive coil is used to receive pulsed eddy current feedback signal from test piece;

[0007] The sensor is composed of an excitation coil wound with enameled wire and four receiving coils wound with enameled wire;The excitation coil is outside, and after inputting a pulsed excitation signal, an eddy current is generated inside the workpiece to be detected;The receiving coils are inside the excitation coil, and two of them are arranged in a 90° cross pattern;One end of each pair of receiving coils is connected to form a differential receiving coil pair.

[0008] To further solve the technical problems to be solved by the present application, in a pulsed eddy current detection method provided by the present application, the sensor of the probe uses two differential receiving coil groups to improve the amplitude variation ratio of the signal using a differential signal method;The amplitude and width of the time-based signal are calculated and analyzed, and the alarm baseline height and alarm wave width limit gate are used to limit the gate conditions and confirm the wave width limit gate to remove the unwanted interference wave patterns formed during the detection of the test piece, so that the detection result is simple and reliable.

[0009] Signal analysis:

[0010] When the test piece has no defects, the differential receiving coil group as the sensor input has no obvious signal waveform.

[0011] When one of the differential receiving coil groups is located at the crack of the test piece, an obvious waveform will appear on the time-based line;The defect waveform appearing at the rising edge of the pulsed excitation signal is defined as a confirmation wave, and the defect waveform appearing at the falling edge of the pulsed excitation signal is defined as an alarm wave, and the vertical line is defined as a confirmation wave width limit gate;If the waveform width exceeds the vertical line, it is considered that it is not a defect waveform;The horizontal line is defined as an alarm wave position limit gate, and if the alarm wave width exceeds the left side of the gate, it is not considered to be a defect waveform.

[0012] Detection equipment calibration:

[0013] Firstly, the position of the differential receiving coil on the front side of the probe is placed on the crack of the test piece, the confirmation wave reaches the highest wave height, the confirmation wave width limit gate is adjusted to the right side of the alarm wave and next to the position of the zero line of the confirmation wave;

[0014] Secondly, move the probe, the alarm wave reaches the maximum wave height, adjust the amplification circuit so that the alarm wave just exceeds the alarm baseline, adjust the alarm wave width limit gate to the outside of the alarm wave and next to the alarm wave, and store the current state in the detection equipment to complete the calibration.

[0015] Detection operation:

[0016] The probe is placed on the surface of the tested piece, no obvious wave pattern appears at the position without cracks, and the dynamic wave pattern is green; when any of the differential receiving coil groups is above the crack, a dynamic wave pattern appears; if any one channel has an alarm wave, the height exceeds the alarm line and the width does not exceed the alarm wave width limit gate position, the detection equipment issues an alarm sound and displays the waveform exceeding the limit as red, at this time, the probe is moved, the other receiving coil in the differential receiving coil group is placed above the crack, a confirmation wave appears, and the width does not exceed the confirmation wave width limit gate position; it can be judged from the above conditions that the tested piece has surface or near-surface cracks;

[0017] Thus, the amplitude variation ratio of the detection signal is improved, which is beneficial for observation and calculation.

[0018] Wherein, when the probe is detecting on the surface of the tested piece, a part or the whole of the probe may be away from the surface of the tested workpiece due to operation reasons, at this time, an interference wave pattern may appear due to the lift-off phenomenon in eddy current flaw detection, which is not conducive to defect judgment; at this time, the alarm wave width exceeds the alarm wave width limit gate, or the confirmation wave width exceeds the confirmation wave width limit gate, at this time, the detection equipment does not alarm, and does not consider this waveform as a crack.

[0019] Active effect, since the sensor adopts two groups of differential receiving coils, the characteristics of the pulse eddy current detection signal are calculated. By calculating the height and width of the signal, signal interference caused by the detection sensor being completely or partially away from the surface of the detected workpiece is avoided; signal interference caused by the sensor reaching the edge of the detected workpiece is avoided. The pulse excitation eddy current has the characteristic that the detection depth is much larger than that of the sinusoidal wave excitation eddy current for ferromagnetic materials. The pulse eddy current flaw detector composed of the above detection system can obtain good detection effect on the tested ferromagnetic material with surface covering or rough surface caused by processing method, reduces false positives caused by the sensor being partially or completely away from the tested piece and the probe reaching the edge of the tested piece, reduces labor intensity, improves the reliability of the detection result, and is suitable for application as a pulse eddy current detection system and method. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The amplitude and zero-crossing time chart of the pulse eddy current signal of the prior art;

[0021] Figure 2 The composition block diagram of the pulse eddy current detection system;

[0022] Figure 3 The structure schematic diagram of one excitation coil and four receiving coil sensors;

[0023] Figure 4Fig. 1 is a schematic diagram of a sensor structure with one excitation coil and two receiving coils;

[0024] Figure 5 Fig. 5 is a waveform signal diagram of two sets of differential signals when the test piece is free of defects;

[0025] Figure 6 Fig. 6 is a waveform signal diagram of a defect waveform signal appearing at the rising edge or the falling edge of a square wave excitation signal;

[0026] Figure 7 Fig. 7 is a waveform signal diagram when the front side differential receiving coil of the probe is positioned on a crack of the test piece;

[0027] Figure 8 Fig. 8 is a waveform signal diagram when the alarm wave reaches the maximum wave height and exceeds the alarm baseline;

[0028] Figure 9 Fig. 9 is a waveform signal diagram when the lift-off phenomenon occurs;

[0029] Figure 10 Fig. 10 is a schematic diagram of a detection device;

[0030] Figure 11 Fig. 11 is a schematic diagram of a test piece for calibration;

[0031] Figure 12 Fig. 12 is a schematic diagram of a probe;

[0032] Figure 13 Fig. 13 is a schematic diagram of a defect found during implementation;

[0033] Figure 14 Fig. 14 is a partial schematic diagram of a defect found during implementation. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments of the present application. Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0035] According to Figure 2 the pulse eddy current detection system includes a detection device, a probe and a test piece, and the probe is used to generate a pulse eddy current excitation signal acting on the test piece and receive a pulse eddy current feedback signal from the test piece, which is the same as the prior art;

[0036] The probe comprises a sensor, the sensor comprising an excitation coil for generating a pulsed eddy current excitation signal acting on the tested piece and an induction coil for receiving a pulsed eddy current feedback signal from the tested piece;

[0037] The detection device is used for receiving and analog-digital converting the pulsed eddy current feedback signal to obtain a pulsed eddy current digital signal;

[0038] According to the present application, the sensor is composed of one excitation coil and four receiving coils, which is different from the prior art. Figure 3 The excitation coil is outside and generates an electric eddy current in the tested piece after inputting a pulsed excitation signal; the receiving coils are inside the excitation coil and are cross-distributed in pairs; one end of each pair of receiving coils is connected to form a pair of differential signal receiving coils, as shown in Figure 4 ;

[0039] In order to optimize the structure of the present application, the diameter of the enameled wire of the excitation coil is 0.24-0.51 mm and the number of turns is 100-600.

[0040] In order to further optimize the structure of the present application, the diameter of the enameled wire of the receiving coil is 0.05-0.2 and the number of turns is 200-1200; the center of the receiving coil is a magnetic core, which can enhance the received signal and improve the signal-to-noise ratio.

[0041] In order to further optimize the structure of the present application, the sensor can also be composed of one excitation coil and two receiving coils connected at one end according to the needs.

[0042] A pulsed eddy current detection method, the sensor of the probe adopts two pairs of differential receiving coils to improve the amplitude change ratio of the signal by using a differential signal mode; the amplitude width of a time-based signal is calculated and analyzed, the alarm baseline height, the alarm wave width limit gate and the confirmation wave width limit gate conditions are used to remove the useless interference wave patterns formed during the detection of the tested piece, so that the detection result is simple and reliable.

[0043] Implementation case:

[0044] The present application has been implemented in the railway maintenance system and good results have been achieved, the device model is TZ-WJ, the probe used is PEC-X and the calibration test block used is MW-7-420.

[0045] The detection device is shown in Figure 10 , the tested piece for calibration is shown in Figure 11 , and the probe is shown in Figure 12 . Defects found during implementation are shown in Figure 13 andFigure 14 as shown.

[0046] Analysis of the acquired signal:

[0047] The input differential signal is as shown, the left and right dynamic timing waveforms are two sets of differential signals input, and under the premise that the tested piece has no defects, since a differential coil group is used as a sensor input, no obvious signal waveform appears. Figure 5 When one of the coil groups is located at the crack of the tested piece, an obvious waveform appears on the time base line as shown, the left waveform is a defect waveform appearing at the rising edge of the square wave pulse excitation signal, and the right waveform is a defect waveform appearing at the falling edge of the square wave excitation signal; if one of the receiving coil groups is located above the crack of the tested piece, a waveform as shown appears; the defect waveform appearing at the rising edge of the square wave pulse excitation signal is defined as a confirmation wave, and the defect waveform appearing at the falling edge of the square wave excitation signal is defined as an alarm wave; the vertical line in the figure is a confirmation wave width limiting gate, which judges whether the confirmation wave width exceeds or not, and if the waveform width exceeds the vertical line, it is considered not to be a defect waveform; the short horizontal line in the figure is an alarm wave position limiting gate, and the alarm wave width exceeds the left side of the gate, which is not considered to be a defect waveform.

[0048] Figure 6 The detection equipment is calibrated, the front side differential receiving coil of the probe is positioned on the crack of the tested piece as shown, the position of the probe is adjusted, the confirmation wave reaches the highest wave height, the confirmation wave width limiting gate is adjusted to the right side of the alarm wave and next to the zero line position of the confirmation wave.

[0049] The probe is moved, the alarm wave reaches the maximum wave height, and the alarm wave just exceeds the alarm base line by adjusting the amplification circuit as shown, the alarm wave width limiting gate is adjusted to the outside of the alarm wave and next to the alarm wave, and the detection equipment stores the current state, and the calibration is completed. Figure 7 At this time, the detection operation can be performed.

[0050] Figure 8 The probe is positioned on the surface of the tested piece, and no obvious waveform appears at the position without cracks, and the dynamic waveform is green; when any of the differential receiving coil groups is above the crack, a dynamic waveform appears; if an alarm wave appears in any channel, the height exceeds the alarm line and the width does not exceed the alarm wave width limiting gate position, the detection equipment issues an alarm sound and displays the waveform exceeding the limit as red, at this time, the probe is moved, and the other receiving coil in the differential coil group is positioned above the crack, then a confirmation wave appears and the width does not exceed the confirmation wave width limiting gate; from the above conditions, it can be judged that the tested piece has surface or near-surface cracks.

[0051]

[0052] The probe is positioned on the surface of the tested piece, and no obvious waveform appears at the position without cracks, and the dynamic waveform is green; when any of the differential receiving coil groups is above the crack, a dynamic waveform appears; if an alarm wave appears in any channel, the height exceeds the alarm line and the width does not exceed the alarm wave width limiting gate position, the detection equipment issues an alarm sound and displays the waveform exceeding the limit as red, at this time, the probe is moved, and the other receiving coil in the differential coil group is positioned above the crack, then a confirmation wave appears and the width does not exceed the confirmation wave width limiting gate; from the above conditions, it can be judged that the tested piece has surface or near-surface cracks.

[0053] ​​​Thus, the amplitude variation ratio of the detection signal is improved, and the observation and calculation are facilitated.

[0054] When the probe detects the surface of the tested workpiece, a part or the whole of the probe may be separated from the surface of the tested workpiece due to operation, and at this time, the lift-off phenomenon in the eddy current detection occurs, and the interference wave type appears, which is not conducive to defect determination. Figure 9 As shown in the figure, the alarm wave width exceeds the alarm wave width limit gate, or the confirmation wave width exceeds the confirmation wave width limit gate, at this time, the detection equipment does not alarm, and does not consider the waveform as a crack.

[0055] Through the calculation of the height and width of the signal, the signal interference caused by the whole or part of the detection sensor leaving the surface of the tested workpiece is avoided, and the signal interference caused by the sensor reaching the edge of the tested workpiece is avoided.

[0056] Finally, it should be pointed out that: the above only for the preferred embodiments of the present application, and is not used to limit the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified to the technical scheme recorded in the foregoing each embodiment, or equivalent replacement to part of the technical features, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A method of pulsed eddy current testing, characterized by: applying a pulsed eddy current testing system, A kind of pulse eddy current detection system includes detection equipment, probe and test piece;The probe includes sensor, the sensor includes excitation coil and inductive coil, the excitation coil is used to generate the pulse eddy current excitation signal acting on test piece, the inductive coil is used to receive the pulse eddy current feedback signal from test piece; The sensor is composed of an excitation coil wound with enameled wire and four receiving coils wound with enameled wire;The excitation coil is outside, and after inputting the pulse excitation signal, it generates eddy current inside the workpiece to be detected;The receiving coils are inside the excitation coil, and two of them are cross-distributed as a pair;One end of each pair of receiving coils is connected to form a pair of differential signal receiving coils. The method comprises the following steps: The sensor of the probe uses two pairs of differential receiving coils to improve the amplitude variation ratio of the signal by using differential signal mode;The amplitude width of the time-based signal is calculated and analyzed, and the alarm baseline height, alarm wave width limit gate and confirmation wave width limit gate conditions are used to remove the useless interference wave patterns formed during the detection of the test piece, so that the detection result is simple and reliable; Signal analysis: When the test piece has no defects, the differential receiving coil group as the sensor input has no obvious signal waveform; When one of the differential receiving coil groups is located at the crack of the test piece, there will be obvious waveform on the time-based line;The defect waveform appearing at the rising edge of the pulse excitation signal is defined as the confirmation wave, and the defect waveform appearing at the falling edge of the pulse excitation signal is defined as the alarm wave, and the vertical line is defined as the confirmation wave width limit gate;If the waveform width exceeds the vertical line, it is considered that it is not a defect waveform;The horizontal line is defined as the alarm wave position limit gate, and if the alarm wave width exceeds the left side of the gate, it is not considered as a defect waveform; Detection operation: The probe is placed on the surface of the test piece, and no obvious waveform will appear at the position without cracks, and the dynamic waveform is green;When any of the differential receiving coil groups is above the crack, a dynamic waveform will appear;If there is an alarm wave in any channel, the height exceeds the alarm line and the width does not exceed the alarm wave width limit gate position, the detection equipment will issue an alarm sound and display the waveform exceeding the limit as red, and at this time, the probe is moved, and the other receiving coil in the differential coil group is placed above the crack, and a confirmation wave will appear;According to the above conditions, it can be judged that there is a surface or near-surface crack in the test piece; When the probe is detected on the surface of the test piece, part or all of the probe may be away from the surface of the test piece due to operation reasons, which may cause lift-off phenomenon in eddy current testing, and interference wave patterns may appear, which is not conducive to defect judgment;At this time, the alarm wave width exceeds the alarm wave width limit gate, or the confirmation wave width exceeds the confirmation wave width limit gate, and the detection equipment does not alarm, and the waveform is not considered as a crack; Thus, the amplitude variation ratio of the detection signal is improved, which is beneficial for observation and calculation.

2. The pulse eddy current detection method according to claim 1, wherein: The sensor is composed of an excitation coil and two receiving coils connected at one end.

3. The method of claim 1, wherein the diameter of the enameled wire of the excitation coil is 0.24-0.51 mm, and the number of turns of the excitation coil is 100-600.

4. The method of claim 1, wherein the diameter of the enameled wire of the receiving coil is 0.05-0.2 mm, and the number of turns of the receiving coil is 200-1200, and the center of the receiving coil is the magnetic core. The method of claim 1 further comprises calibrating the detection device: First, the position of the differential receiving coil on the front side of the probe is placed on the crack of the test piece, the confirmation wave reaches the highest wave height, and the confirmation wave width limiting gate is adjusted to the right side of the alarm wave and next to the position of the zero line of the confirmation wave; 5. A method of pulsed eddy current testing according to claim 1, characterised in that ： Second, the probe is moved, the alarm wave reaches the maximum wave height, and the alarm wave width limiting gate is adjusted to the outside of the alarm wave and next to the alarm wave, and the detection device stores the current state, and the calibration is completed. ​ ​

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