CN101995432A - Hall element differential array based ferromagnetic construction member surface crack detector - Google Patents

Abstract

The present invention is a surface crack detector for ferromagnetic components based on the Hall element differential array, which is characterized in that it includes a differential array magnetic flux leakage probe, a displacement detection unit, a signal conditioning circuit, and a data acquisition unit, which are located on the surface of one side of the probe circuit board. The Hall sensors of the probe are arranged in a regular array, and the Hall sensor group of the probe is installed on the upper and lower sides of the circuit board in a differential manner, and the two voltage signals are respectively output to the signal conditioning circuit to form a reflected magnetic flux leakage voltage signal, And input the voltage signal into the data acquisition unit. The invention can conveniently detect the size and position of defects such as cracks, and has the advantages of large detection area, high speed, low rate of missed detection of defects, and the like.

Description

Surface Crack Detector of Ferromagnetic Components Based on Differential Array of Hall Elements

technical field

The invention relates to the field of non-destructive testing, in particular to the non-destructive testing of defects such as surface cracks, air holes, slag inclusions and stress concentration of ferromagnetic components.

Background technique

The existing disclosed ferromagnetic component surface crack detectors have different structures and methods, such as commonly used ultrasonic methods, ray methods, and electromagnetic methods. The ultrasonic method is relatively mature, but it requires high cleanliness on the surface of the workpiece, and it is cumbersome to implement; the ray method is not effective in detecting gradual defects and the radiation pollution is serious; the electromagnetic method includes magnetic particle method, eddy current method, and leakage method. Magnetic method, etc., but magnetic particle method and eddy current method are only suitable for surface or near-surface detection of materials. The degree of automation is low, the process is complicated, and manual observation is inseparable. The requirements for technicians are very high, and it is difficult to achieve quantitative detection. The magnetic flux leakage method can detect both internal and surface defects of the material, and is extremely sensitive to the defects of ferromagnetic materials. It does not need to clean and polish the components during the detection, and does not need to add coupling agent. It can also be used under the pollution conditions such as rust and oil. detection. However, most of the existing crack detectors based on the magnetic flux leakage method are single probes, with a maximum of three probes, which are expensive and can only perform line scanning on the component surface. The one-time detection area is small, the speed is slow, and the detection is not accurate. It is accurate and prone to missed inspections, and it cannot provide the data support required for quantitative analysis of defects such as cracks on the surface of components, which seriously hinders the application of magnetic flux leakage in the field of nondestructive testing.

Contents of the invention

Aiming at the deficiency of the existing ferromagnetic component surface crack detector, the invention proposes a ferromagnetic component surface crack detector based on Hall element differential array.

Technical scheme of the present invention is as follows:

A surface crack detector for ferromagnetic components based on a differential array of Hall elements, including a differential array magnetic flux leakage probe, a displacement detection unit, a signal conditioning circuit, and a data acquisition unit. The differential array magnetic flux leakage probe includes a circuit board and multiple Hall sensor groups, each Hall sensor group is composed of two identical Hall sensors that are symmetrically installed on the upper and lower surfaces of the circuit board and reversely arranged, and the Hall sensors located on the same side surface of the circuit board are arranged to form In an array, all Hall sensors share a ground terminal and a current input terminal, and the voltage signals of the two Hall sensors of each Hall sensor group are respectively output to the signal conditioning circuit, and the signal conditioning circuit includes a differential operational amplifier, filter circuit, etc., the signal conditioning circuit filters out high-frequency noise for the input voltage signal, suppresses common-mode interference signals, and the differential operational amplifier subtracts the two input voltage signals and amplifies the differential-mode signal, and the The differential mode signal corresponds to the crack magnetic flux leakage signal, and the differential mode signal is input into the data acquisition unit; the displacement detection unit is fixedly connected to the differential array magnetic flux leakage probe, and performs synchronous scanning detection with the differential array magnetic flux leakage probe, and Record the displacement signal of the differential array magnetic flux leakage probe moved, and input the displacement signal into the data acquisition unit; the data acquisition unit establishes the displacement signal according to the collected differential mode signal and the displacement signal output by the displacement detection unit There is a one-to-one correspondence relationship between the differential mode signal and the displacement signal.

The Hall sensors on the same side surface of the circuit board are arranged in a regular two-dimensional array, the Hall sensors are neatly arranged in each row, and the Hall sensors in different rows are arranged in a staggered manner.

Two permanent magnets with the same size and magnetism but with opposite polarities are fixed on the displacement detection unit. The permanent magnets provide stable magnetic flux for detection to enhance the magnetic flux leakage signal of the crack, and are symmetrically arranged on the differential The left and right or front and rear sides of the array magnetic flux leakage probe.

It also includes a time-division multiplexing device, the time-division multiplexing device is installed between the differential array magnetic flux leakage probe and the signal conditioning circuit, and the time-division multiplexing device turns on the The voltage output signals of each Hall sensor group on the differential array magnetic flux leakage probe, the two voltage output signals of the Hall sensor group selected each time are differentially amplified and filtered by the signal conditioning circuit and then input to the The data acquisition unit described above.

The displacement detection unit includes a displacement sensor, a motor and a small wheel, the displacement sensor is arranged on the small wheel, the motor is connected to the small wheel, the motor drives the small wheel to move, and the displacement sensor records the motor speed and running time And calculate its displacement, and input the displacement signal into the data acquisition unit.

Another solution of the displacement detection unit may also include a counter and a small wheel, the counter is set on the small wheel, records the number of circles of the small wheel and calculates its displacement, and inputs the displacement signal to the data acquisition unit.

Technical effect of the present invention:

The surface crack detector of the ferromagnetic component based on the Hall element differential array of the present invention reduces the interference signal and improves the sensitivity of detection through the differential array type magnetic flux leakage probe; the unique array type distribution can realize the The area array detection of cracks effectively increases the area and speed of one-time scanning detection and avoids missed detection of defects; with the displacement detection unit and data acquisition unit with high precision, it realizes the real-time detection of magnetic flux leakage signals and displacement signals. Acquisition, the use of software programming can realize the one-to-one correspondence between displacement information and magnetic flux leakage information, which is convenient for the analysis and evaluation of inspectors, and can further realize the graphical reconstruction of component surface defects. Compared with the existing crack detectors, the ferromagnetic component surface crack detector based on the Hall element differential array of the present invention has the advantages of large detection area, fast speed, and low defect missed detection rate, and can form a relatively large price. Competitive advantages, with broad market application prospects.

Description of drawings

Fig. 1 is a layout diagram of a Hall sensor group on a differential array magnetic flux leakage probe.

Fig. 2 is a detection schematic diagram of the detector without an external magnetic field.

Figure 2a is a schematic diagram of the detection of the detector in the case of cracks.

Figure 2b is a schematic diagram of the detection of the detector in the case of no crack.

Figure 2c is the output characteristic of the Hall sensor in the case of cracks.

Figure 2d shows the output characteristics of the Hall sensor without cracks.

Fig. 3 is a detection schematic diagram of the detector under an external magnetic field.

Figure 3a is a schematic diagram of the detection of the detector in the case of cracks.

Figure 3b is a schematic diagram of the detection of the detector in the case of no crack.

Figure 3c shows the output characteristics of the Hall sensor in the case of cracks.

Figure 3d shows the output characteristics of the Hall sensor without cracks.

The reference signs are as follows:

1-The current input terminal of the Hall sensor, 2-The ground terminal of the Hall sensor, 3-The voltage output terminal of the Hall sensor, 4-The common ground wire of the differential array, 5-The common power line of the differential array, 6-The Hall sensor Voltage output line, 7-differential array magnetic flux leakage probe, 8-workpiece surface crack, 9-Hall sensor group, 10-earth magnetic field leakage, 11-earth magnetic field, 12-displacement sensor, 13-displacement detection unit, 14 -small wheel, 15-permanent magnet, 16-leakage field, 17-magnetic flux.

Detailed ways

Embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

Refer to Figure 1 and Figure 2 for the structure and working principle of the ferromagnetic component surface crack detector based on the differential array of Hall elements. The surface crack detector of the ferromagnetic component based on the Hall element differential array includes a differential array magnetic flux leakage probe 7, a displacement detection unit 13, a signal conditioning circuit, and a data acquisition unit. The differential array magnetic flux leakage probe 7 includes a circuit board and a plurality of Hall sensor groups 9, and each Hall sensor group 9 is composed of two identical Hall sensor groups that are symmetrically installed on the upper and lower surfaces of the circuit board and reversely arranged. Hall sensors, the installation method can be welding; the Hall sensors located on the same side surface of the circuit board are arranged in a regular two-dimensional array, wherein the Hall sensors are neatly arranged in each row, and the Hall sensors of different rows Seoul sensor dislocation arrangement, as shown in Figure 1. Wire and solder the Hall sensors in the array void. The Hall sensors on the same side surface of the circuit board are misplaced because this two-dimensional array can arrange Hall sensors densely and regularly on each horizontal row and oblique row, so it can compensate for the limited sensitive area of the device in the detection direction. And the detection gap caused by the installation gap to avoid missed detection of defects. The size of the Hall sensor used in the present invention is 3mm × 3mm × 1mm. At present, there can be 20 Hall sensors in each row of the array. After measuring and calculating, the array of 3 rows can basically achieve the detection of the differential array type drain. A complete scan of the surface of the ferromagnetic material to be inspected covered by a magnetic probe.

It can be seen from Figure 1 that the ground terminals 2 of all Hall sensors are connected to the common ground wire 4 of the differential array, and the current input terminals 1 of all Hall sensors are connected to the common power line 5 of the differential array. The voltage signal of the Hall sensor is output to the signal conditioning circuit through the voltage output terminal 3 of the Hall sensor through the voltage output line 6 of the Hall sensor. The signal conditioning circuit includes a differential operational amplifier, a filter circuit, etc., and the signal conditioning circuit Filter out high-frequency noise on the input voltage signal, suppress common-mode interference signals, and perform subtraction operations on the two input voltage signals by the differential operational amplifier, and amplify the differential-mode signal, which corresponds to the crack magnetic flux leakage signal , and input the differential mode signal into the data acquisition unit. It can be seen from Fig. 2 that when the Hall sensor group 9 scans and detects the surface crack 8 of the workpiece, due to the change of the magnetic permeability of the geomagnetic field 11 at the crack 8, a geomagnetic leakage magnetic field 10 is formed outward, and its magnetic field component perpendicular to the detection plane It will enter the Hall sensor group 9. Since the above-mentioned reverse symmetry is fixed on the upper and lower sides of the circuit board, the output voltage of the same group of sensors is a differential output, and the change is opposite, that is, the output voltage always increases in a positive direction. , and the other increases in the opposite direction. Theoretically speaking, the absolute value of the two changes is not much different. The signal is sent to the differential operational amplifier (such as INA129) of the signal conditioning circuit through the voltage output line 6 of the Hall sensor. On the one hand, most of the common mode signals can be eliminated. , on the other hand, the detection signal will be doubled due to the differential effect, which increases the sensitivity of the measurement and reduces the error. This differential voltage signal can reduce interference signals caused by temperature effects, ambient interference magnetic fields, and the like. If there is no leakage field on the surface of the component, the differential output signal is zero. If there is a leakage field on the surface of the component, the differential output mode has a more obvious signal peak-to-peak value than the single-ended output. The wired connection between the detector and the secondary instrument is convenient for the reliable transmission of sensor power supply and signal.

The displacement detection unit 13 is fixedly connected to the differential array magnetic flux leakage probe 7, and performs synchronous scanning detection with the differential array magnetic flux leakage probe, and records the displacement signal of the differential array magnetic flux leakage probe moved, Input it into the data acquisition unit; the data acquisition unit simultaneously collects the magnetic flux leakage signal and the displacement signal output by the displacement detection unit 13, and establishes a one-to-one correspondence between the magnetic flux leakage signal and the displacement signal.

Because the earth's magnetic field is weak, in order to increase the measurement accuracy and the height that the probe is lifted away from the surface of the member to be inspected, two permanent magnets 15 with the same size and magnetic properties but with opposite polarities can also be fixed on the displacement detection unit 13. The permanent magnet 15 provides stable magnetic flux for detection to enhance the magnetic flux leakage signal of the crack, and is symmetrically arranged on the left, right or front and rear sides of the differential array type magnetic flux leakage probe. In contrast, their magnetic fluxes are smooth and stable magnetic fluxes 17 in a smooth and crack-free plane. When there is a crack in the detection plane, the differential array magnetic leakage probe 7 can detect the leakage magnetic field 16 more easily. Permanent magnets can adopt rubber magnetic strips.

Since the data acquisition unit has a limited number of channels for acquiring the data of the special two-dimensional array of the Hall sensor array, the data acquisition is in a scanning manner. If there are many Hall sensor groups included on the differential array magnetic flux leakage probe 7, it is also necessary to configure a relevant time-division multiplexing device, which is installed on the differential array magnetic flux leakage probe and signal conditioning Between the circuits, the time-division multiplexing device turns on the voltage output signals of each Hall sensor group on the differential array magnetic flux leakage probe according to the set time interval, so that the Hall sensor group 9 The voltage signal plays a control role, so that in a very short time interval, only two voltage signal inputs of the same group of Hall sensor groups are allowed, which avoids signal channel congestion and signal confusion. The two voltage output signals of the Hall sensor group selected each time are conditioned by the signal conditioning circuit and input to the data acquisition unit.

Described displacement detection unit 13 comprises small wheel 14, displacement sensor 12 or counter, and a kind of scheme is: drive small wheel 14 by uniform speed motor, measure running speed v by displacement sensor 12, record running time t simultaneously, then displacement signal S= v×t; Another solution is: use a counter to count the number of turns N of the small wheel 14 to obtain a displacement signal S=N×L, where L is the circumference of the small wheel. Output the obtained displacement signal to the data acquisition unit.

In terms of data acquisition method design, the array pre-sets the local relative coordinates of the sensor, and together with the overall displacement of the recording bit during scanning detection, the leakage field voltage signal can be matched with the accurate spatial position, and the location of the defect can be known. The position can be clearly displayed on the secondary instrument, or you can further use MATLAB to draw these data as the x-axis and y-axis in the two dimensions of the scanning plane, corresponding to the leakage of each position on the scanning plane. The magnetic field voltage signal is a three-dimensional "topographic map" of the z-axis. In this map, the defect must have ups and downs. In this way, the position and size of the defect can be seen at a glance.

The data acquisition unit is implemented by a single-chip microcomputer, which has the characteristics of small size, fast speed, and low cost. It can provide multiple analog input and output, multiple digital input and output operations, and is very suitable for designing a handheld differential array based on Hall elements. Surface Crack Detector of Ferromagnetic Components. The data acquisition unit includes NI USB-6215 data acquisition card and strobe circuit. The USB-6215 data acquisition card is a M series multifunctional DAQ module with bus power supply and isolation, which can maintain high precision even at high sampling rates. Provides 16 analog inputs; 250kS/s single channel sampling rate, 2 analog outputs, 4 digital input lines, 4 digital output lines, each channel has 4 programmable input ranges (±0.2V-±10V), Digital trigger, 2 counters/timers, the magnetic flux leakage signal on the ferromagnetic component is a low-frequency signal, and the sampling rate and resolution of the USB-6215 data acquisition card are also sufficient to meet our requirements for magnetic flux leakage signal acquisition.

It should be pointed out that the specific embodiments described above can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. Therefore, although the present description has described the present invention in detail with reference to the accompanying drawings and embodiments, those skilled in the art should understand that the present invention can still be modified or equivalently replaced without departing from the spirit and scope of the present invention. The technical solutions and their improvements shall be covered by the scope of protection of the patent for the present invention.

Claims (10)

1. ferromagnetic component surface crack detector based on the Hall element difference array, it is characterized in that, comprise difference array formula leakage field probe, the displacement detecting unit, signal conditioning circuit, data acquisition unit, described difference array formula leakage field probe comprises circuit board and a plurality of Hall element group, each Hall element group is installed in described circuit board upper and lower surface by two symmetries and forms through the identical Hall element that oppositely is provided with, the Hall element that is positioned at surface, described circuit board the same side is arranged in array, all Hall element shared grounding end and current input terminals, the voltage signal of two Hall elements of each described Hall element group exports described signal conditioning circuit respectively to, described signal conditioning circuit comprises differential operational amplifier, filtering circuit etc., described signal conditioning circuit is to the voltage signal filter away high frequency noise of input, suppress common mode interference signal, described differential operational amplifier is done the two-way voltage signal of input and is subtracted computing, and amplification difference mode signal, described difference mode signal is corresponding with the crackle magnetic leakage signal, and difference mode signal is imported data acquisition unit; Fixedly connected with described difference array formula leakage field probe in described displacement detecting unit, carrying out synchronous scanning with described difference array formula leakage field probe detects, and write down the displacement signal that described difference array formula leakage field probe moved, with this displacement signal input data acquisition unit; Data acquisition unit is set up described difference mode signal and described displacement signal one-to-one relationship according to the displacement signal of described difference mode signal that collects and the output of described displacement detecting unit.

2. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 1, it is characterized in that, Hall element on surface, described circuit board the same side is arranged in the two-dimensional array of rule, described Hall element is proper alignment in each row, and the Hall element dislocation of different rows is arranged.

3. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 1 and 2, it is characterized in that, identical but the polarity of two sizes and magnetic is fixed on the described displacement detecting unit towards opposite permanent magnet, described permanent magnet provides stable magnetic flux for detection, to strengthen the crackle magnetic leakage signal, be arranged symmetrically in the left and right sides or the both sides, front and back of described difference array formula leakage field probe.

4. according to claim 1 or 2 one of any described ferromagnetic component surface crack detectors based on the Hall element difference array, it is characterized in that, also comprise time sharing multiplex device, described time sharing multiplex device is installed between described difference array formula leakage field probe and the signal conditioning circuit, described time sharing multiplex device is connected the described voltage output signal of each the Hall element group on the described difference array formula leakage field probe in turn according to the time interval of setting, two voltage output signals of each selecteed described Hall element group amplify by described signal conditioning circuit difference and filtering after import described data acquisition unit.

5. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 3, it is characterized in that, also comprise time sharing multiplex device, described time sharing multiplex device is installed between described difference array formula leakage field probe and the signal conditioning circuit, described time sharing multiplex device is connected the described voltage output signal of each the Hall element group on the described difference array formula leakage field probe in turn according to the time interval of setting, two voltage output signals of each selecteed described Hall element group amplify by described signal conditioning circuit difference and filtering after import described data acquisition unit.

6. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 1 and 2, it is characterized in that, described displacement detecting unit comprises displacement transducer, motor and steamboat, described displacement transducer is arranged on the steamboat, and described motor links to each other with steamboat, and described motor drives the steamboat motion, described displacement transducer recording pen motor speed and working time are also calculated its displacement, and displacement signal is imported described data acquisition unit.

7. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 3, it is characterized in that, described displacement detecting unit comprises displacement transducer, motor and steamboat, described displacement transducer is arranged on the steamboat, and described motor links to each other with steamboat, and described motor drives the steamboat motion, described displacement transducer recording pen motor speed and working time are also calculated its displacement, and displacement signal is imported described data acquisition unit.

8. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 4, it is characterized in that, described displacement detecting unit comprises displacement transducer, motor and steamboat, described displacement transducer is arranged on the steamboat, and described motor links to each other with steamboat, and described motor drives the steamboat motion, described displacement transducer recording pen motor speed and working time are also calculated its displacement, and displacement signal is imported described data acquisition unit.

9. the ferromagnetic component surface crack detector based on the Hall element difference array according to claim 5, it is characterized in that, described displacement detecting unit comprises displacement transducer, motor and steamboat, described displacement transducer is arranged on the steamboat, and described motor links to each other with steamboat, and described motor drives the steamboat motion, described displacement transducer recording pen motor speed and working time are also calculated its displacement, and displacement signal is imported described data acquisition unit.

10. according to one of any described ferromagnetic component surface crack detector of claim 1 to 5 based on the Hall element difference array, it is characterized in that, described displacement detecting unit comprises counter and steamboat, described counter is arranged on the steamboat, all numbers of record steamboat motion also calculate its displacement, and displacement signal is imported described data acquisition unit.

Images