Pulsed eddy current array probe and ferromagnetic metal piece thickness detection method

Abstract

The invention discloses a pulsed eddy current array type probe, which is used for detecting the thickness of a detected ferromagnetic metal piece, and comprises two excitation coils with magnetic cores and four detection coils which are arranged in parallel and are used for collecting vertical components of a superposed magnetic field on the surface of the ferromagnetic metal piece, and the two excitation coils are respectively arranged on the inner sides of the two detection coils close to the inner side; the two excitation coils emit excitation magnetic fields, and the four detection coils collect signals. In addition, the invention also discloses a device and a method for detecting the thickness of the ferromagnetic metal piece by using the probe.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing, and in particular provides a pulsed eddy current array probe and a testing method. Background Art

[0002] Pulsed eddy current testing technology is a new type of non-destructive testing technology evolved from traditional eddy current testing technology. It can penetrate the coating layer to detect the wall thickness of metal specimens. By observing the magnetic field distortion caused by defects, the corrosion and thinning position of metal specimens can be determined. Compared with traditional eddy current testing capabilities, pulsed eddy current testing signals have a slow attenuation rate and strong penetration. The sensor can cover a wider scanning area and has higher detection efficiency. There is no need to remove the attachments on the metal surface during testing, which greatly reduces time and labor costs.

[0003] In the development of pulsed eddy current testing technology, there are constant innovations and changes in probe design, signal processing, data acquisition and data processing. Among them, probe design is an important part of the detection process, and the design method of the probe has a significant impact on defect detection. Therefore, how to ensure the detection performance of the probe while meeting the requirements of simple equipment and low energy consumption has become the research and development direction of pulsed eddy current testing technology.

[0004] Traditionally, probes for detecting the thickness of defects in ferromagnetic materials usually use a single sensor. After development, array sensors have been developed to improve detection efficiency. Generally, array sensors have complex structures and are heavy. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a pulsed eddy current array probe. The present invention uses array sensors with different excitation modes for data acquisition, which effectively reduces the weight of the device while ensuring the detection performance, and alleviates the problem of sensor heating. The technical solution adopted by the present invention is as follows:

[0006] A pulsed eddy current array probe is used to detect the thickness of a ferromagnetic metal part to be measured. It is characterized in that it includes two excitation coils with magnetic cores, four detection coils arranged in parallel for collecting the vertical component of the superimposed magnetic field on the surface of the ferromagnetic metal part, and the two excitation coils are respectively placed on the inner side of the two inner detection coils; the two excitation coils emit excitation magnetic fields, and the four detection coils collect signals.

[0007] Furthermore, the magnetic core is a manganese-zinc ferrite magnetic core. The excitation coil is a racetrack-type excitation coil.

[0008] Furthermore, the two excitation coils have an inner diameter of 15 mm, an outer diameter of 40 mm, a straight length of 120 mm, a height of 30 mm, and 1,200 turns; the four runway-type detection coils have an inner diameter of 50 mm, an outer diameter of 80 mm, a straight length of 140 mm, a height of 10 mm, and 1,800 turns; and the interior of the excitation coils is filled with manganese-zinc ferrite cores.

[0009] The present invention also provides a ferromagnetic metal part thickness detection device using the pulse eddy current array probe, including the pulse eddy current array probe, a signal generator and a power amplifier, the signal generator is connected to the excitation coil through the power amplifier, the signal generator is used to generate a low-frequency pulse square wave signal with a set pulse width and periodicity; the two excitation coils emit an excitation magnetic field under the excitation of the power amplifier, the four detection coils are used for signal acquisition, and the acquired signals are used to detect the thickness of the ferromagnetic metal part being measured.

[0010] The present invention also provides a method for detecting the thickness of a ferromagnetic metal part using the detection device, comprising the following steps:

[0011] (5) placing the pulsed eddy current array probe close to the surface of the ferromagnetic metal part to be measured;

[0012] (6) The low-frequency pulse square wave signal generated by the signal generator is amplified by the power amplifier and applied to the two excitation coils to generate an alternating magnetic field;

[0013] (7) When the signals in the two excitation coils undergo a step jump, the four detection coils receive the induced voltage signals of the primary magnetic field from the two excitation coils and the secondary magnetic field generated by the pulse eddy current in the ferromagnetic metal specimen under test, which changes with time. The induced voltage generated at the falling edge of the pulse eddy current excitation is taken, logarithmically transformed, and the late attenuation section of the signal is intercepted for analysis and processing;

[0014] (8) With time as the independent variable and the induced voltage of the attenuation section of the four detection coils as the dependent variable, the slope of the attenuation section of the induced voltage curve of the ferromagnetic metal part under test with different thicknesses is extracted. According to the corresponding relationship between the different thickness values ​​and the slope, a power function relationship is obtained by fitting. The relationship between the characteristic slope and thickness of the probe with and without the excitation coil is calibrated respectively, and the fitting curve of the characteristic slope-wall thickness is obtained, thereby obtaining the wall thickness information of the ferromagnetic metal part under test.

[0015] Furthermore, before executing step (4), a step of removing signal abnormal points is executed.

[0016] Furthermore, the slope of the attenuation section of the induced voltage curve of the ferromagnetic metal part under test with different thicknesses is extracted and the absolute value of the slope is taken; what is obtained is a fitting curve of the absolute value of the slope of the characteristic quantity-wall thickness.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: Different from the self-excitation and self-collection method adopted by the traditional pulsed eddy current array probe, the present invention generates signals for two of the excitation coils and collects signals for four detection coils, which can reduce the weight of the detection equipment while ensuring the detection accuracy and reduce the problem of probe heating and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the thickness detection principle of a ferromagnetic metal part according to the present invention;

[0019] Figure 2 A top view of a pulsed eddy current detection probe of the present invention;

[0020] Figure 3 It is a left side view of the pulsed eddy current detection probe of the present invention;

[0021] Figure 4 It is a single cycle pulse excitation waveform diagram;

[0022] Figure 5 This is the result diagram of the logarithmic transformation of the voltage signal detected for ferromagnetic metal parts of different thicknesses;

[0023] Figure 6 This is a schematic diagram of the fitting curve of the absolute value of the slope of the characteristic quantity of the ferromagnetic metal part-thickness. ;

[0024] Figure 7 The top view of the array probe with one and three excitation coils and the corresponding characteristic quantity slope absolute value-thickness fitting curve.

[0025] In the figure: 1, 2, 7, 12, 13, 14 - racetrack-shaped excitation coils; 3, 4, 5, 6, 8, 9, 10, 11, 15, 16, 17, 18 - racetrack-shaped detection coils; 7 - insulation layer; 8 - ferromagnetic metal specimen to be tested. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. The examples given herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0027] Figure 1 This is a schematic diagram of the thickness detection circuit of a ferromagnetic metal specimen of the present invention. The probe used is a pulse eddy current detection probe, which mainly includes a racetrack-type excitation coil 1, 2 and a racetrack-type detection coil 3, 4, 5, 6, wherein the detection coil 4, 5 has an excitation coil 1, 2 in the center to form a self-excited self-receiving probe. The signal generator is connected to the input end of the power amplifier, the output end of the power amplifier is connected to the racetrack-type excitation coil 1, 2, the racetrack-type detection coil 3, 4, 5, 6 is connected to the input end of the data acquisition card, and the data acquisition card is connected to the computer.

[0028] In this implementation case, Figure 2 is a top view, Figure 3 It is a left view. The probe of the present invention is specifically described below in combination with these two figures.

[0029] The excitation coil and detection coil of the array sensor are perpendicular to the surface of the ferromagnetic metal specimen 7 to be tested. The excitation coil is fixed inside the center of the detection coil, and the inner side of the excitation coil is filled with a manganese-zinc ferrite core.

[0030] The excitation coils 1 and 2 have an inner diameter of 15 mm, an outer diameter of 40 mm, a straight length of 120 mm, a height of 30 mm, and a number of turns of 1200. The detection coils 3, 4, 5, and 6 have an inner diameter of 50 mm, an outer diameter of 80 mm, a straight length of 140 mm, a height of 10 mm, and a number of turns of 1800. The interval between individual sensors is 10 mm.

[0031] The excitation source is pulsed eddy current excitation, and the set voltage is 2V, the frequency is 2Hz, and the duty cycle is a square wave signal of 50%.

[0032] After exciting the excitation coils 1 and 2, the signals received by the four detection coils simultaneously have obvious peak signals in the early stage, and the late signals are consistent with the normal self-excited and self-received signals. The slope of the late signal is extracted as the characteristic value, which does not affect the detection of the thickness of the metal specimen.

[0033] Combination Figure 1 The thickness detection method for ferromagnetic metal parts is as follows: the detection probe is placed above the ferromagnetic metal specimen 7 to be tested, the signal generator generates a low-frequency pulse square wave signal with a certain pulse width and periodicity, and the pulse square wave signal is transmitted to the power amplifier, and then the power amplifier amplifies the voltage and current and applies them to the two ends of the runway-shaped excitation coils 1 and 2 to generate an alternating magnetic field. When the pulse square wave signal undergoes a step jump, the primary magnetic field from the runway-shaped excitation coils 1 and 2 and the pulse in the ferromagnetic metal specimen 7 to be tested are received by the runway-shaped detection coils 3, 4, 5, and 6. The induced voltage signal of the secondary magnetic field generated by the eddy current that changes with time is collected and processed by a data acquisition card and stored in a computer. The induced voltage of the late attenuation section of the four detection coils is then intercepted by logarithmic transformation, and the abnormal points are removed. The characteristic quantity slope is fitted and solved according to the corresponding functional relationship between the amplitude of the induced voltage signal and time, and the absolute value of the characteristic quantity slope is calculated. Then, the fitting calculation is performed according to the corresponding functional relationship between the thickness of the ferromagnetic metal part and the slope, and the fitting curve of the absolute value of the characteristic quantity slope-wall thickness is obtained, and then the wall thickness information of the test piece is calculated.

[0034] Figure 4 It is a single-cycle pulse excitation waveform diagram; the information contained in the transient response signal generated by the rising and falling edges of the pulse eddy current excitation is symmetrical, and the present invention takes the detection signal within 0.35-0.6s;

[0035] Figure 5 The result diagram of the logarithmic transformation of the voltage signal of ferromagnetic metal pieces with different thicknesses is shown in FIG. The ferromagnetic metal test pieces with thicknesses of 10 mm, 15 mm and 20 mm are selected as the test objects. Under the condition that the probe is 20 mm away from the surface of the test piece, the test is performed according to the following steps:

[0036] The probe is placed above the ferromagnetic metal specimen to be tested, and the signal generator is set to load the pulse excitation square wave signal, set the pulse source duration to 0.5s, the pulse width to 0.25s, the duty cycle to 50%, and the excitation voltage amplitude to 2V. When the pulse square wave signal of the excitation coil jumps in a step, a changing magnetic field will be generated around the excitation coil, and this magnetic field will induce a changing eddy current in the ferromagnetic metal specimen to be tested. The pulse eddy current diffuses and decays inside the ferromagnetic metal specimen to be tested, thereby generating another changing magnetic field. The change of the magnetic field is detected by the detection coil and converted into an induced voltage signal that changes with time. The induced voltages of three different wall thicknesses are collected to the computer through the data acquisition card. In order to effectively distinguish the voltage signals from different detection coils, the detection voltages within the range of 0.5-0.6s in the late decay section of the ferromagnetic metal specimens of each thickness are taken, and logarithm transformation is performed on them respectively. The characteristics of the induced voltage signal are clearly displayed. As the observation delay increases, the induced voltage curve enters the exponential decay stage and tends to a straight line. During this period, the slope has a one-to-one correspondence with the wall thickness of the tested piece.

[0037] Figure 6 The figure is a fitting curve diagram of the absolute value of the characteristic slope of the ferromagnetic metal part-thickness; the attenuation of the induced voltage collected by the detection coils 3, 6 and the detection coils 4, 5 in the later period is roughly the same, so the late signal slopes of the detection coils 3, 6 and the detection coils 4, 5 are calculated respectively. Remove the abnormal signal points, take time as the independent variable, and the detection voltage in the attenuation section of the four detection coils within 0.5-0.6s as the dependent variable. Use the linear equation D=ka+b to obtain the characteristic slope, and then according to the known thickness value D i and the known slope k i Solve the power function D = m|k| n The relationship between the absolute value of the slope of the characteristic quantity and the power function curve corresponding to the thickness of the ferromagnetic metal part being measured is fitted, and then the wall thickness information of the ferromagnetic metal part being measured is calculated. Figure 6In the example shown, the metal test pieces with thicknesses of 10mm, 15mm and 20mm correspond to the induced voltage signals collected by the four detection coils respectively. The voltage signal slopes of detection coil 4 are k1, k2 and k3 respectively. The absolute values ​​of the three data points (10, k1), (15, k2) and (20, k3) are taken and fitted to obtain the power function curve D1. The corresponding slope of the newly measured ferromagnetic metal piece of unknown thickness is k4. The wall thickness information of the ferromagnetic metal test piece corresponding to the slope k4 to be measured can be obtained by calculating the power function expression D1. The calculation method for detection coils 3, 5 and 6 is similar. The absolute value of the characteristic slope of detection coils 4 and 5 and the thickness fitting relationship are the same. The thickness relationship corresponding to the absolute value of the slope of detection coils 4 and 5 is calibrated, and then the wall thickness information of the ferromagnetic metal piece to be measured is calculated. Similarly, the absolute value of the slope of calibration detection coils 3 and 6 corresponds to the thickness of the test piece. In the figure, when the detection coils 4 and 5 measure the slope of the ferromagnetic metal part to be 6.29, the corresponding thickness of the metal part is 13 mm. When the detection coils 3 and 6 measure the slope of the ferromagnetic metal part to be 5.64, the corresponding thickness of the metal part is 13 mm.

[0038] Figure 7 The top view of the array probe with one and three excitation coils and the corresponding characteristic quantity slope absolute value-thickness fitting curve are shown in the figure. The results of the other two methods are given in this embodiment. Method 1 is an array probe composed of one excitation coil and four detection coils. It can be seen from the curve in the figure that the fitting relationship curves of detection coils 8, 9, 10, and 11 are quite different. Therefore, its detection results must be calibrated four times for the characteristic quantity slope corresponding to the thickness, which increases the workload and causes a large detection error. Method 2 uses an array probe composed of three excitation coils and four detection coils. It can be seen from the curve in the figure that the fitting relationship curves of detection coils 15, 16, and 17 overlap and are quite different from detection coil 18. Its detection results must be calibrated twice for the characteristic quantity slope corresponding to the thickness, which is the same as the calibration workload of the present invention, but the weight of the equipment is increased when a detection coil is added. Compared with the first two methods, the advantages of the present invention are more obvious.

[0039] The above embodiments are only detailed descriptions of the present invention and cannot be used to limit the protection scope of the present invention. Any modifications, replacements, improvements, etc. made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A pulsed eddy current array probe, used for detecting the thickness of a ferromagnetic metal part, characterized in that: It includes two excitation coils with magnetic cores and four parallel arranged detection coils for collecting the vertical component of the superimposed magnetic field on the surface of ferromagnetic metal parts, and the two excitation coils are respectively placed on the inner side of the two inner detection coils; the two excitation coils emit the excitation magnetic field, and the four detection coils collect signals.

2. The pulsed eddy current array probe according to claim 1, characterized in that: The magnetic core is a manganese-zinc ferrite core.

3. The pulsed eddy current array probe according to claim 1, characterized in that: The excitation coil is a racetrack-type excitation coil.

4. The probe according to claim 3, characterized in that: The two excitation coils have an inner diameter of 15mm, an outer diameter of 40mm, a straight length of 120mm, a height of 30mm, and 1200 turns; the four runway-type detection coils have an inner diameter of 50mm, an outer diameter of 80mm, a straight length of 140mm, a height of 10mm, and 1800 turns.

5. The probe according to claim 4, characterized in that: The inside of the excitation coil is filled with manganese-zinc ferrite cores.

6. A ferromagnetic metal part thickness detection device using a pulsed eddy current array probe according to any one of claims 1 to 5, characterized in that: It comprises the pulsed eddy current array probe, a signal generator and a power amplifier. The signal generator is connected to the excitation coil through the power amplifier. The signal generator is used to generate a low-frequency pulse square wave signal with a set pulse width and periodicity. The two excitation coils emit an excitation magnetic field under the excitation of the power amplifier. The four detection coils are used for signal collection. The collected signals are used to detect the thickness of the ferromagnetic metal part being tested.

7. A method for detecting thickness of ferromagnetic metal parts using the detection device according to claim 6, characterized in that: The following steps are involved: (1) Place the pulsed eddy current array probe close to the surface of the ferromagnetic metal part to be tested; (2) The low-frequency pulse square wave signal generated by the signal generator is amplified by the power amplifier and applied to the two excitation coils to generate an alternating magnetic field; (3) When the signals in the two excitation coils undergo a step jump, the four detection coils receive the induced voltage signals of the primary magnetic field from the two excitation coils and the secondary magnetic field generated by the pulsed eddy current in the ferromagnetic metal specimen under test, which changes with time. The induced voltage generated at the falling edge of the pulsed eddy current excitation is taken, logarithmically transformed, and the late attenuation section of the signal is intercepted for analysis and processing; (4) With time as the independent variable and the induced voltage of the attenuation section of the four detection coils as the dependent variable, the slope of the attenuation section of the induced voltage curve of the ferromagnetic metal part with different thicknesses under test is extracted. According to the corresponding relationship between the different thickness values ​​and the slope, a power function relationship is obtained by fitting. The relationship between the characteristic slope and thickness of the probe with and without the excitation coil is calibrated respectively, and the fitting curve of the characteristic slope-wall thickness is obtained, thereby obtaining the wall thickness information of the ferromagnetic metal part under test.

8. The method for detecting thickness of ferromagnetic metal parts according to claim 6, characterized in that: Before executing step (4), a step of removing signal abnormal points is performed.

9. The method for detecting thickness of ferromagnetic metal parts according to claim 6, characterized in that: The extraction is to extract the slope of the attenuation section of the induced voltage curve of the ferromagnetic metal part with different thicknesses and take the absolute value of the slope; what is obtained is the fitting curve of the absolute value of the slope of the characteristic quantity-wall thickness.

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