Tunnel effect based strip steel magnetic flux leakage detection probe

Abstract

The application provides a strip steel magnetic flux leakage detection probe based on tunnel effect, which comprises a TMR sensor array, a signal processing circuit, a probe main body and a magnetizing coil; the probe main body comprises a horizontal PCB plate and a vertical PCB plate installed on the horizontal PCB plate, the magnetizing coil is arranged on the horizontal PCB plate and is used for generating a uniform magnetic field to magnetize the strip steel; the TMR sensor array is in two groups and is arranged at the bottom edges on both sides of the vertical PCB plate; the signal processing circuit is arranged on the vertical PCB plate and is electrically connected with the TMR sensor array; and the TMR sensor array is used for detecting the magnetic flux leakage and outputting a differential signal. The application generates tunneling effect through the two groups of TMR sensor arrays, improves the detection sensitivity, increases the distance between the strip steel and the probe, avoids collision, and realizes independent detection through the integrated structure design of the probe coil, and does not need the large-size magnetic core and the excitation coil in the traditional magnetic flux leakage detection.

Description

Technical Field

[0001] This invention relates to the field of magnetic flux leakage detection technology for steel strips, and more specifically, to a magnetic flux leakage detection probe for steel strips based on the tunneling effect. Background Technology

[0002] Internal defects in strip steel are one of the main quality defects in cold-rolled thin strip products, especially for special-purpose strip steel products such as DI materials and battery steel. In these types of strip steel products, internal defects can lead to risks such as leakage, causing significant quality disputes and unnecessary trouble for downstream manufacturers. Therefore, in some cold-rolled strip steel production lines, it is essential to inspect for internal quality defects during the production process to prevent defective products from being delivered to users. Because the production of cold-rolled strip steel products is a high-speed and automated process, offline inspection carries sampling risks. Therefore, online internal defect inspection is required.

[0003] Methods for inspecting internal defects include magnetic flux leakage (MFL) and electromagnetic ultrasonic testing. Currently, MFL is the most widely used technique. In MFL detection, sensors typically employ electromagnetic coils, Hall effect elements, or magnetic sensors. During defect detection, multiple sensors are arranged in an array to form an electromagnetic detection probe. The probe examines the magnetized steel plate; if internal defects are present, a magnetic flux leakage field within the steel plate will be detected. In various brands of testing equipment developed based on this method, different sensor probes are used, and different signal processing methods are employed depending on the acquired signal to achieve the goal of detecting weak magnetic flux leakage signals. Existing MFL detection technology has the following problems:

[0004] 1. The Hall effect-based magnetic flux leakage detection probe disclosed in patent document CN205091296U has low sensitivity and the probe will experience contact wear. Even if wear is avoided through mechanical structure design, the detection sensitivity will be further reduced.

[0005] 2. The leakage magnetic field detection probe based on TMR magnetoresistive sensor disclosed in patent document CN112378994A requires a magnetic core during implementation, which accounts for a large volume. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of this invention is to provide a magnetic flux leakage detection probe for strip steel based on the tunneling effect.

[0007] The magnetic flux leakage detection probe for strip steel based on tunneling effect provided by the present invention includes a TMR sensor array, a signal processing circuit, a probe body, and a magnetizing coil.

[0008] The probe body includes a horizontal PCB board and a vertical PCB board mounted on the horizontal PCB board. The magnetizing coil is set on the horizontal PCB board to generate a uniform magnetic field to magnetize the strip steel.

[0009] The TMR sensor array consists of two sets, which are respectively set on the bottom edges of both sides of the vertical PCB board. The signal processing circuit is set on the vertical PCB board and electrically connected to the TMR sensor array. The TMR sensor array is used to detect leakage magnetic field and output differential signal.

[0010] Preferably, there are two magnetizing coils, which are symmetrically arranged on both sides of the vertical PCB board.

[0011] Preferably, the TMR sensor array comprises multiple TMR sensors arranged in parallel.

[0012] Preferably, the signal processing circuit includes a differential amplifier circuit and a filter circuit;

[0013] The two differential input terminals of the differential amplifier circuit are connected to the two output terminals of the TMR sensor, and the output terminal of the differential amplifier circuit is connected to the input terminal of the filter circuit.

[0014] Preferably, the differential amplifier circuit includes an amplification factor adjustment resistor R1 and a differential amplifier U1;

[0015] The inverting and non-inverting input terminals of the differential amplifier U1 are respectively connected to the two output terminals of the TMR sensor. The two ends of the amplification factor adjustment resistor R1 are connected to the amplification factor adjustment pin of the differential amplifier U1. The output terminal of the differential amplifier U1 is connected to the filter circuit.

[0016] Preferably, the differential amplifier circuit further includes an impedance matching resistor R2 and an impedance matching resistor R5;

[0017] The two ends of the impedance matching resistor R2 are respectively connected to the inverting input terminal of the differential amplifier U1 and one output terminal of the TMR sensor, and the two ends of the impedance matching resistor R5 are respectively connected to the non-inverting input terminal of the differential amplifier U1 and the other output terminal of the TMR sensor.

[0018] Preferably, the filter circuit includes resistor R3, resistor R4, capacitor C3, capacitor C1, capacitor C2 and resistor R6;

[0019] The midpoint of the series connection between resistors R3 and R4 is connected to one end of capacitor C3. The midpoint of the series connection between capacitors C1 and C2 is connected to one end of resistor R6. The other end of capacitor C3 is connected to the other end of resistor R6 and grounded. The other end of resistor R4 is connected to the other end of capacitor C2 and connected to the sampling circuit.

[0020] Preferably, the system further includes a sampling circuit, the input of which is connected to the output of the filtering circuit.

[0021] Preferably, the sampling circuit includes a digital-to-analog converter circuit, a controller, and a host computer connected in sequence, and the digital-to-analog converter circuit is connected to the output terminal of the filter circuit.

[0022] Preferably, the TMR sensor includes MTJ resistors R7, R8, R9, and R10.

[0023] The MTJ resistors R7, R8, R9, and R10 are connected to form a Wheatstone bridge. A working voltage VDD is applied to one end of the Wheatstone bridge, and the other end is grounded. The two output terminals of the Wheatstone bridge are connected to the two differential input terminals of the differential amplifier circuit.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention generates a tunneling effect through two sets of TMR sensor arrays, which improves the detection sensitivity, increases the distance between the strip and the probe, avoids collisions, and enables independent detection by adopting an integrated probe coil structure design, eliminating the need for the large-volume magnetic core and excitation coil of traditional magnetic flux leakage detection.

[0026] 2. By employing a Wheatstone bridge structure, this invention enables a single sensor to output a differential signal, thereby suppressing common-mode interference.

[0027] 3. By employing an instrumentation operational amplifier, this invention further increases the signal-to-noise ratio, resulting in higher fidelity of the transmitted signal.

[0028] 4. This invention arranges TMR sensors in an array, and the width of the strip to be measured can be adapted by increasing or decreasing the number of channels. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is a schematic diagram of the probe body in this invention;

[0031] Figure 2 This is a schematic diagram of the circuit model of the signal processing circuit in this invention;

[0032] Figure 3 This is a schematic diagram of the Wheatstone bridge circuit model in the TMR sensor of this invention.

[0033] The diagram shows:

[0034] Signal processing circuit 1, amplifier circuit 5

[0035] TMR sensor array 2 Filter circuit 6

[0036] Magnetizing coil 3 Sampling circuit 7

[0037] TMR sensor 4 Detailed Implementation

[0038] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0039] This invention discloses a strip magnetic flux leakage detection probe based on the tunneling effect. The probe has two rows of tunnel magnetoresistive (TMR) array sensors and its own magnetization excitation coil. It has high detection sensitivity and does not require the large volume magnetic core and excitation coil of traditional magnetic flux leakage detection. It can realize the detection of small defects in high-speed running strip.

[0040] The magnetic flux leakage detection probe based on the tunneling effect provided by the present invention, such as... Figure 1 As shown, the device includes a TMR sensor array 2, a signal processing circuit 1, a probe body, and magnetizing coils 3. The probe body includes a horizontal PCB board and a vertical PCB board mounted on the horizontal PCB board. The magnetizing coils 3 are disposed on the horizontal PCB board and are used to generate a uniform magnetic field to magnetize the strip steel. The TMR sensor array 2 consists of two sets, respectively disposed on the bottom edges of both sides of the vertical PCB board. The signal processing circuit 1 is disposed on the vertical PCB board and electrically connected to the TMR sensor array 2. The TMR sensor array 2 is used to detect leakage magnetic field and output a differential signal. The TMR sensor array 2 is distributed on the bottom edge of the vertical PCB board, on both the front and back sides. The two magnetizing coils 3 on the horizontal board are symmetrically disposed on both sides of the vertical PCB board and can generate a uniform magnetic field.

[0041] The working principle of the probe section is as follows: a uniform magnetic field generated by magnetizing coil 3 magnetizes the strip. If magnetic leakage occurs, it will be detected by the TMR sensors arranged on both sides, and a pair of differential signals will be output at the defect location. Each pair of differential signals constitutes a channel, and multiple channels form an array probe, which can ultimately generate a C-scan image on the host computer. The width of the strip under test can be adapted by increasing or decreasing the number of channels. This invention improves detection sensitivity by using TMR sensors, allowing the distance between the strip and the probe to be increased, avoiding collisions. Furthermore, by adopting an integrated probe-coil structure design, independent detection can be achieved, eliminating the need for the large-volume magnetic core and excitation coil of traditional magnetic leakage detection.

[0042] like Figure 2 As shown, the signal processing circuit 1 includes a TMR sensor 4, a differential amplifier circuit 5, a filter circuit 6, and a sampling circuit 7. The two output terminals of the TMR sensor 4 are connected to the two differential input terminals of the differential amplifier circuit 5, the output terminal of the differential amplifier circuit 5 is connected to the input of the filter circuit 6, and the output terminal of the filter circuit 6 is connected to the input of the sampling circuit 7.

[0043] The differential amplifier circuit 5 includes impedance matching resistors R2 and R5, a gain adjustment resistor R1, and a differential amplifier U1. R2 is connected to the inverting input of differential amplifier U1, R5 is connected to the non-inverting input of differential amplifier U1, and both ends of R1 are connected to the gain adjustment pin of differential amplifier U1. The filter circuit 6 includes a T-type filter composed of resistors R3 and R4 and capacitor C3, and another T-type filter composed of capacitors C1 and C2 and resistor R6. Resistors R3 and R4 are connected in series, with their midpoint connected to capacitor C3. Capacitors C1 and C2 are connected in series, with their midpoint connected to resistor R6. The other end of capacitor C3 is connected to the other end of resistor R6 and grounded. The sampling circuit 7 includes a digital-to-analog converter circuit, a controller, and a host computer.

[0044] The TMR sensor 4 detects the leakage magnetic field inside the strip and outputs a pair of differential signals, which are amplified differentially by the differential amplifier circuit 5. The signals then pass through the notch filter circuit 6 to eliminate the 50Hz power frequency interference. The analog signal is then converted into a digital signal by the ADC, and the controller decodes the digital signal and transmits it to the host computer.

[0045] like Figure 3The diagram shows the Wheatstone bridge, the internal equivalent circuit model of a TMR sensor. R7, R8, R9, and R10 are MTJ resistors, whose resistance changes with the external magnetic field. A full-bridge configuration improves bridge sensitivity and eliminates common-mode interference. The resistance of one half-bridge (R7 and R10) increases with the magnetic field, while the resistance of the other half (R8 and R9) decreases. A working voltage VDD is applied to one end of the bridge, and the other end is grounded. The final output signal of the TMR sensor is calculated by measuring the half-bridge voltages V+ and V... - The calculation formula is as follows:

[0046]

[0047] In this invention, the main sensor for magnetic flux leakage detection is tunneling magnetoresistive (TMR). Two TMR sensor arrays are used to achieve the tunneling effect, which is generated by spin-related tunneling. This effect has the advantages of large magnetoresistive effect and high magnetic field sensitivity. Compared to conventional internal defect detection methods, this invention has the advantage of using TMR tunneling magnetoresistive, resulting in high sensitivity to magnetic flux leakage at defects. Compared to Hall sensors or traditional coils, TMR maintains a high signal-to-noise ratio in complex environments, reducing false alarms. It has low sensitivity to environmental factors such as temperature and vibration, making it suitable for field or industrial applications. Furthermore, it eliminates the need for coupling agents (such as in ultrasonic testing), reducing preparation time and preventing surface damage.

[0048] Compared with ultrasonic testing methods, this invention does not require coupling agent, is not affected by material grain noise, and is suitable for rough surfaces or defects under coatings.

[0049] Compared with eddy current detection methods, this invention can detect deeper defects (eddy current is limited to the surface / near surface) and is not affected by changes in conductivity.

[0050] Compared with traditional magnetic flux leakage (MFL) detection methods, this invention has higher sensitivity and can detect smaller defects and low-intensity magnetic flux leakage fields.

[0051] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0052] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A magnetic flux leakage detection probe for steel strip based on the tunneling effect, characterized in that, Includes a TMR sensor array (2), a signal processing circuit (1), a probe body, and a magnetizing coil (3); The probe body includes a horizontal PCB board and a vertical PCB board mounted on the horizontal PCB board. The magnetizing coil (3) is set on the horizontal PCB board to generate a uniform magnetic field to magnetize the strip steel. The TMR sensor array (2) consists of two groups, which are respectively set on the bottom edges of both sides of the vertical PCB board. The signal processing circuit (1) is set on the vertical PCB board and electrically connected to the TMR sensor array (2). The TMR sensor array (2) is used to detect leakage magnetic field and output differential signal.

2. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 1, characterized in that, There are two magnetizing coils (3), which are symmetrically arranged on both sides of the vertical PCB board.

3. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 1, characterized in that, The TMR sensor array (2) includes multiple TMR sensors (4) arranged in parallel.

4. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 3, characterized in that, The signal processing circuit (1) includes a differential amplifier circuit (5) and a filter circuit (6); The two differential input terminals of the differential amplifier circuit (5) are connected to the two output terminals of the TMR sensor (4), and the output terminal of the differential amplifier circuit (5) is connected to the input terminal of the filter circuit (6).

5. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 4, characterized in that, The differential amplifier circuit (5) includes an amplification factor adjustment resistor R1 and a differential amplifier U1; The inverting input and non-inverting input of the differential amplifier U1 are respectively connected to the two output terminals of the TMR sensor (4), the two ends of the amplification factor adjustment resistor R1 are connected to the amplification factor adjustment pin of the differential amplifier U1, and the output terminal of the differential amplifier U1 is connected to the filter circuit (6).

6. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 5, characterized in that, The differential amplifier circuit (5) also includes impedance matching resistors R2 and R5; The two ends of the impedance matching resistor R2 are respectively connected to the inverting input terminal of the differential amplifier U1 and one output terminal of the TMR sensor (4), and the two ends of the impedance matching resistor R5 are respectively connected to the non-inverting input terminal of the differential amplifier U1 and the other output terminal of the TMR sensor (4).

7. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 4, characterized in that, The filter circuit (6) includes resistor R3, resistor R4, capacitor C3, capacitor C1, capacitor C2 and resistor R6. The midpoint of the series connection of resistor R3 and resistor R4 is connected to one end of capacitor C3. The midpoint of the series connection of capacitor C1 and capacitor C2 is connected to one end of resistor R6. The other end of capacitor C3 is connected to the other end of resistor R6 and grounded. The other end of resistor R4 is connected to the other end of capacitor C2 and connected to sampling circuit (7).

8. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 4, characterized in that, It also includes a sampling circuit (7), the input of which is connected to the output of the filter circuit (6).

9. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 8, characterized in that, The sampling circuit (7) includes a digital-to-analog converter circuit, a controller and a host computer connected in sequence, and the digital-to-analog converter circuit is connected to the output terminal of the filter circuit (6).

10. The strip magnetic flux leakage detection probe based on the tunneling effect according to claim 4, characterized in that, The TMR sensor (4) includes MTJ resistors R7, R8, R9, and R10. The MTJ resistors R7, R8, R9, and R10 are connected to form a Wheatstone bridge. One end of the Wheatstone bridge is supplied with a working voltage VDD, and the other end is grounded. The two outputs of the Wheatstone bridge are connected to the two differential inputs of the differential amplifier circuit (5).

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