CN113567541A - Absolute weak magnetic detection method and detection device - Google Patents
Absolute weak magnetic detection method and detection device Download PDFInfo
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Abstract
本发明公开了一种绝对式弱磁检测方法及检测装置，涉及弱磁检测领域，通过均匀排布若干个弱磁传感器同时采集数据，大大节省了检测时间，提升了效率，使用多个弱磁传感器采集同一时刻的弱磁信号，避免了外界磁场随时间变化而引入的噪声干扰，设置机械结构移动探头架，控制传感器的运动平稳性，对检测分辨率要求不高的场合，无需传感器微动即可实现信号检测；本发明提供了一种绝对式弱磁检测方法及检测装置，采取绝对式检测的方法，使传感器在测量时与检测物保持相对静止，并在传感器移动扫查时进行高效率高精度的数据采集，大大减小因为传感器运动所产生的检测误差。
The invention discloses an absolute weak magnetic detection method and a detection device, which relate to the field of weak magnetic detection. By uniformly arranging several weak magnetic sensors to collect data at the same time, the detection time is greatly saved and the efficiency is improved, and a plurality of weak magnetic sensors are used. The sensor collects the weak magnetic signal at the same time, which avoids the noise interference caused by the change of the external magnetic field over time. The mechanical structure is set to move the probe frame to control the motion stability of the sensor. When the detection resolution is not high, the sensor does not need to move. The signal detection can be realized; the present invention provides an absolute weak magnetic detection method and detection device, which adopts the absolute detection method to keep the sensor relatively stationary with the detection object during measurement, and perform high-precision detection when the sensor moves and scans. Efficient and high-precision data collection greatly reduces detection errors caused by sensor movement.
Description
Technical Field
The invention relates to the technical field of weak magnetic detection, in particular to an absolute weak magnetic detection method and a detection device.
Background
Nondestructive testing refers to a method for inspecting and testing the structure, properties and states of the interior and the surface of a test object by means of modern technology and equipment and by means of physical or chemical methods on the premise of not damaging the test object.
The weak magnetic detection technology belongs to one of electromagnetic detection technology. The nondestructive testing technology is established on the basis of a natural geomagnetic field, scans the surface or the position close to the surface of a test sample through a magnetic signal acquisition instrument, acquires the change of magnetic induction intensity in different directions so as to judge whether a defect exists in the test sample, and judges the position and the size of the defect existing in the test sample through data processing. Due to the requirement of the sampling frequency of the magnetic signal acquisition instrument, the magnetic signal acquisition instrument is required to acquire signals at a constant speed during signal acquisition, so that the change of the amplitude of magnetic induction intensity can be more accurately described, and the region with defects can be further accurately positioned and quantified. For ferromagnetic and paramagnetic materials, the magnetic induction increases with increasing applied magnetic field. When the external magnetic field intensity is constant, the magnetic induction intensity is increased along with the increase of the relative magnetic permeability; for diamagnetic materials, the magnetic induction decreases with increasing applied magnetic field. When the external magnetic field is constant, the magnetic induction intensity is reduced along with the increase of the relative magnetic permeability.
However, the electromagnetic detection method belongs to a comparative measurement method, i.e. the difference between the detection signals of a defect-free part and a defect-free part is observed to judge whether the defect exists or not and the size of the defect, and generally, a sensor is required to move on the surface or near the surface of a detected object to be detected along a certain route for detection. And the sensor is easy to generate the problems of unstable sensor movement, external magnetic signal interference introduced in the movement process and the like in the scanning process of the surface of the detected object.
In order to solve the problems, the application provides an absolute weak magnetic detection method and an absolute weak magnetic detection device, and the absolute weak magnetic detection method is adopted, so that a sensor and a detected object are kept relatively static during measurement, high-efficiency and high-precision data acquisition is carried out during translational micromotion of a sensor group, and detection errors caused by movement of the sensor are greatly reduced.
Disclosure of Invention
The invention aims to provide an absolute weak magnetic detection method and a detection device, which adopt an absolute detection method to ensure that a sensor and a detected object keep relatively static during measurement, and perform high-efficiency and high-precision data acquisition during translational micromotion of a sensor group, thereby greatly reducing detection errors generated by the movement of the sensor.
The invention provides an absolute weak magnetic detection method, which comprises the following steps:
collecting weak magnetic field signals at different positions on the surface of a detected object;
fitting weak magnetic field signals at different positions into a curve in real time;
presetting magnetic conductivity as a threshold range of a fitting curve, and judging whether a detected object has defects in real time;
wherein, the real-time judgement whether the detected object has defects specifically is:
the preset magnetic permeability is mu, the relative magnetic permeability corresponding to the weak magnetic field signal is mu ', and if the mu is equal to mu', no defect exists on the surface of the object to be detected; if mu '> mu or mu' < mu, the magnetic field lines are attracted or repelled to the surface of the object to be detected, and the magnetic field lines generate downward concave or upward convex defects on the surface of the object to be detected.
Further, when the mu 'is greater than mu or the mu' is less than mu, the magnetic induction intensity numerical value of the weak magnetic field signal on the fitting curve is subjected to derivation processing to obtain a corresponding magnetic field gradient value, a threshold range corresponding to the channel of the weak magnetic sensor is calculated, the magnetic field gradient value is compared with the threshold range, and the acquisition position of the weak magnetic field signal corresponding to the magnetic field gradient value exceeding the threshold range is a defect position;
wherein, the threshold range corresponding to the weak magnetic sensor channel is (mu-3 sigma, mu +3 sigma), wherein:
where n is the total number of samples for any sensor channel, μ is the average of the magnetic field gradient for that channel, σ is the standard deviation of the magnetic field gradient for that channel, and Δ B (i) is the magnetic field gradient value for the ith sample point.
Further, the acquiring weak magnetic field signals at different positions of the surface of the object to be detected includes:
and (3) translating the weak magnetic sensor group on the surface of the detected object according to the unit movement standard by taking the space T of the weak magnetic sensors and the diameter D of the weak magnetic sensors as the unit movement standard.
Furthermore, the weak magnetic sensors in the weak magnetic sensor group are arranged in a matrix, the equal spacing between the weak magnetic sensors is 1.5mm, the size of the weak magnetic sensors is phi 14mm 30mm, the detection range is 14mm (N +1), wherein N is the number of the weak magnetic sensors, and the moving distance is 13-15.5 mm.
Further, a detection device applying an absolute weak magnetic detection method comprises:
the probe frame is uniformly provided with a plurality of weak magnetic sensors, and the weak magnetic sensors are connected with an upper computer;
the two supporting arms are arranged outside the probe frame in a transmission manner;
the transmission device is fixed at the tops of the two supporting arms, a control end is arranged in the transmission device, the transmission device is connected with a screw rod motor in a control mode, and the screw rod motor drives the probe frame to move;
and the upper computer sends a control signal to the control end, receives the weak magnetic field signal acquired by the weak magnetic sensor, fits the weak magnetic field signal into a curve, sets the magnetic permeability as a threshold value of the curve, and detects the defects of the detected object.
Furthermore, a plurality of arrangement holes are formed in the surface of the probe frame, and weak magnetic sensors are fixed in the arrangement holes.
Further, still include: the apron, the apron surface sets up the safety cover, the safety cover lock is in support arm tip.
Furthermore, a rotating groove is formed in the surface of the supporting arm, a gear is installed in the rotating groove, and the gear is connected with a screw rod motor.
Further, tooth grooves are formed in the side wall of the probe frame and meshed with the gear.
Compared with the prior art, the invention has the following remarkable advantages:
the invention provides an absolute weak magnetic detection method and a detection device, wherein a plurality of weak magnetic sensors are uniformly distributed to simultaneously acquire data, so that the detection time is greatly saved, the efficiency is improved, a plurality of weak magnetic sensors are used for acquiring weak magnetic signals at the same moment, the noise interference caused by the change of an external magnetic field along with the time is avoided, a mechanical structure is arranged to move a probe frame, the motion stability of the sensors is controlled, and the signal detection can be realized without the micro-motion of the sensors in the occasions with low requirements on the detection resolution; the invention provides an absolute weak magnetic detection method and a detection device, which adopt the absolute detection method to ensure that a sensor and a detected object keep relatively static during measurement, and carry out high-efficiency and high-precision data acquisition during moving scanning of the sensor, thereby greatly reducing the detection error generated by the movement of the sensor.
Drawings
FIG. 1 is a schematic diagram of a detecting device according to an embodiment of the present invention;
FIG. 2 is a diagram of a probe holder configuration provided by an embodiment of the present invention;
FIG. 3 is a diagram of a support arm configuration provided by an embodiment of the present invention;
FIG. 4 is a block diagram of a gear mounting arrangement provided in accordance with an embodiment of the present invention;
FIG. 5 is a view of a weak magnetic sensor according to an embodiment of the present invention;
FIG. 6 is a diagram of a cover plate structure according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a detection provided by an embodiment of the present invention;
FIG. 8 is a graph of sensor group displacement provided by an embodiment of the present invention;
FIG. 9 is a schematic diagram of area A detection according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of B-region detection according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of an absolute weak magnetic detection structure according to an embodiment of the present invention;
FIG. 12 is an original curve diagram of a single sensor scanning a pre-crack defect at a certain location according to an embodiment of the present invention;
FIG. 13 is an original graph of a multi-sensor for detecting a pre-crack defect at a location according to an embodiment of the present invention;
FIG. 14 is a graph of a scan of five channel sensors provided by an embodiment of the present invention;
FIG. 15 is a graph of a defect stitching for a five channel sensor according to an embodiment of the present invention;
FIG. 16 is a schematic illustration of a channel splicing scheme provided by an embodiment of the present invention;
FIG. 17 is a diagram illustrating the connection between the curve A and the curve B according to an embodiment of the present invention;
fig. 18 is a five-channel scanning defect stitching differential curve diagram provided in the embodiment of the present invention.
Description of reference numerals: 1-probe frame, 2-supporting arm, 3-transmission device, 4-cover plate, 101 placement hole, 102-weak magnetic sensor, 103-tooth groove, 201-rotation groove, 202-gear, 401-protective cover.
Detailed Description
The technical solutions of the embodiments of the present invention are clearly and completely described below with reference to the drawings in the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
At present, the mainstream nondestructive testing means mainly comprise eddy current testing, ultrasonic testing, magnetic powder testing, penetration testing and ray testing, and other nondestructive testing methods comprise the following steps: acoustic emission detection, thermal image/infrared detection, alternating current electromagnetic field detection, magnetic flux leakage detection, magnetic memory detection and the like.
The eddy current inspection method works on the principle of electromagnetic induction, so that the eddy current inspection method can detect surface defects and near-surface defects of a workpiece. The salient feature of eddy current testing is that it works with conductive materials, not necessarily ferromagnetic materials, but poorly with ferromagnetic materials. Secondly, the smoothness, flatness and boundary of the surface of the workpiece to be detected have great influence on the eddy current, so the eddy current detection method is often used for detecting flaws of non-ferromagnetic workpieces such as copper pipes with regular shapes and smooth surfaces.
Ultrasonic detection refers to a technique in which the acoustic characteristics of a material and the changes of internal tissues have a certain influence on the propagation of ultrasonic waves when the ultrasonic waves propagate through the material to be detected, and the changes of the material performance and structure are known by detecting the influence degree and condition of the ultrasonic waves. The ultrasonic detection method generally includes a transmission method, a pulse reflection method, a tandem method, and the like. The method has the disadvantages that the attenuation of ultrasonic waves in air is fast, and the detection efficiency is low because a sound wave propagation medium such as couplant such as oil or water is generally required during detection. And the ceramic matrix structure is complex, the ultrasonic attenuation is serious, and the debonding detection effect of the ceramic matrix composite material is not good.
The magnetic powder inspection detects the leakage magnetic flux formed at the defect position, is only suitable for ferromagnetic materials, and can form the leakage magnetic flux on the surface of a workpiece only by the defects on the surface and the near surface after the ferromagnetic materials are magnetized. In the magnetic leakage detection, magnetization is a prerequisite for detection, and determines whether a measured object can generate a magnetic field signal to be measured and distinguished, and influences the performance characteristics of the detection signal and the structural characteristics of the measuring device. The leakage flux detection mechanism determines the complexity of the detection device and correspondingly increases the unreliability of the detection system.
The penetration test is a nondestructive testing method for inspecting surface opening defects based on the principle of capillary action. It is often used for surface defect detection, but near-surface defects are difficult to detect. Therefore, the penetration detection is not suitable for the detection of the debonding of the ceramic matrix composite material.
The ray detection is one of five major conventions of nondestructive detection, and the principle is that the position and size of a defect are judged by comparing the change of the ray intensity by utilizing the mechanism that the photon of an X ray can penetrate through an object and generate complex physical and chemical actions. The detection rate is high, and the defect imaging is more visual; however, the X-ray is not sensitive to the air layer, and the method cannot always ensure that the interface is detected in a bonding and debonding state.
An electromagnetic detection method (including eddy current detection, magnetic powder detection, magnetic flux leakage detection, magnetic memory detection, weak magnetic detection and the like) belongs to a comparative measurement method, namely, the difference of detection signals of a defect-free part and a defect part is observed to judge whether the defect exists or not and the size of the defect, and generally, a sensor is required to move on the surface or the near surface of a detected object to be detected along a certain route for detection.
The sensor is easy to generate the problems of unstable sensor movement, external magnetic signal interference introduced in the movement process and the like in the scanning process of the surface of the detected object. The absolute detection method is adopted, so that the sensor and the detected object keep relatively static or only generate a small moving distance, the data acquisition can be realized at high efficiency, and the detection error caused by the movement of the sensor is greatly reduced. If a magnetic sensor is used alone for detection, the path traveled by the sensor is random, and the attitude of the sensor changes during the movement, because the electromagnetic field is a vector field, noise is introduced into the attitude change of the sensor, and the acquired detection data includes noise caused by the attitude change of the sensor, interference of a surrounding magnetic field, vibration during the movement of the sensor, and the like.
The invention provides an absolute weak magnetic detection method, which comprises the following steps:
uniformly arranging a plurality of weak magnetic sensors in a matrix, arranging a weak magnetic sensor group on the surface of a detected object, taking equal intervals among the weak magnetic sensors as a unit moving standard, translating the weak magnetic sensor group on the surface of the detected object according to the unit moving standard, and collecting weak magnetic field signals at different positions on the surface of the detected object;
fitting weak magnetic field signals at different positions acquired by a plurality of weak magnetic sensors into a curve in real time;
presetting magnetic conductivity as a threshold range of a fitting curve, and judging whether a detected object has defects in real time;
wherein, the real-time judgement whether the detected object has defects specifically is:
the preset magnetic permeability is mu, the relative magnetic permeability corresponding to the weak magnetic field signal is mu ', and if the mu is equal to mu', no defect exists on the surface of the object to be detected; if mu '> mu or mu' < mu, the magnetic field lines are attracted or repelled to the surface of the object to be detected, and the magnetic field lines generate downward concave or upward convex defects on the surface of the object to be detected.
Based on the weak magnetic detection technology, the invention collects magnetic field signals simultaneously by uniformly arranging a plurality of weak magnetic sensors, then connects the signals collected by each sensor in the same period of time, and writes software on an upper computer to analyze data and judge defects.
Example 1
Referring to fig. 1 to 6, a detecting apparatus applying an absolute weak magnetic detecting method includes:
the probe frame 1 is provided with a plurality of placing holes 101 uniformly on the surface, weak magnetic sensors 102 are fixed in the placing holes 101, the placing holes 101 are consistent with the sensors in size, the intervals among round holes are 1.5mm, and the weak magnetic sensors 102 are connected with an upper computer and used for sending weak magnetic data to the upper computer;
the two supporting arms 2 are installed outside the probe frame 1 in a transmission mode, a rotating groove 201 is formed in the surface of each supporting arm 2, a gear 202 is installed in each rotating groove 201, the gear 202 is connected with a screw rod motor, a tooth groove 103 is formed in the side wall of the probe frame 1, the tooth groove 103 is meshed with the gear 202, the screw rod motor drives the gear 202 to rotate and rotates in the tooth groove 103, and therefore the probe frame 1 moves relative to the supporting arms 1, and the sensor group moves smoothly;
and the transmission device 3 is fixed at the tops of the two supporting arms 2, is internally provided with a control end and is in control connection with a screw motor, and the screw motor drives the probe frame 1 to move. The rotating speed and the starting and stopping of the screw rod motor are used for controlling the moving speed and the moving distance of the probe frame 1. The noise interference caused by vibration and attitude change caused by large-range movement of the sensor is avoided. An adjusting switch is arranged on the surface of the transmission device 3 and used for controlling the rotating speed and the rotating direction of the screw rod motor;
and the upper computer sends a control signal to the control end, receives the weak magnetic field signal acquired by the weak magnetic sensor 102, fits the weak magnetic field signal into a curve, sets the magnetic permeability as a threshold value of the curve, and detects the defect of the detected object.
Set up apron 4, apron 4 surface sets up safety cover 401, safety cover 401 lock is in 2 tip of support arm. For protecting the sensor group in the non-operative state.
When a defect exists in the object to be detected, namely, mu '> mu or mu' < mu, the defect generates attraction or repulsion action on the magnetic force lines, and the magnetic force lines generate an abnormality of sinking downwards or bulging upwards at the defect. When a defect such as a crack exists on the surface of the test object, a dishing-down abnormality is generally generated due to the attraction of the test object material to the magnetic field lines.
The working principle is as follows: when an object to be detected is placed in the earth magnetic field, as shown in fig. 7, the relative permeability of the object is μ, the relative permeability of the defect is μ', and the arrow indicates the magnetic induction component in a certain direction passing through the object to be detected, as shown in B. When a defect exists in the object to be detected, namely, mu '> mu or mu' < mu, the defect generates attraction or repulsion action on the magnetic force lines, and the magnetic force lines generate an abnormality of sinking downwards or bulging upwards at the defect. When a defect such as a crack exists on the surface of the test object, a dishing-down abnormality is generally generated due to the attraction of the test object material to the magnetic field lines.
Example 2
A plurality of sensors are uniformly arranged on the probe frame, and the micro-motion of the sensors is controlled by the transmission device. The 12 sensors are uniformly arranged, so that corresponding 12 groups of detection data can be obtained, the detection range is expanded by 12 times compared with that of the plurality of sensors, and the detection data covers the detection range of 14mm (12+1) to 182 mm. When other areas need to be detected, the tool is lifted, detection is carried out again according to the surface of the detected object to be detected, and the defect detection work of the workpiece to be detected can be completed efficiently. The whole detection process is like 'stamping', the tool is pressed at a certain position to complete detection, and then the next position is detected.
As shown in fig. 8, the solid line is the initial position of the sensor group, the dashed line is the position after the sensors have moved, and the general movement distance is the diameter of one sensor plus the gap between the sensors. The arrow is the direction of movement. If the size of the sensor is phi 14mm 30mm, the sensor generally needs to move 13-15.5 mm (with a gap between the sensors), and if the size of the sensor is phi 2.5mm 7mm, the sensor generally needs to move 0-2.5 mm (without a gap between the sensors). When the diameter of the sensor is larger, a mounting hole needs to be arranged; when the diameter of the sensor is small, the sensor can be directly and tightly installed without arranging a separate installation hole.
As shown in fig. 9-10, if the inspector needs to inspect area a, the sensor can be placed in area a for inspection, and the inspection tool can be placed in area B for inspection. The region a and the region B may or may not overlap each other. In the subsequent data processing process, the detection data of a plurality of sensors are fitted to the same curve by means of a software algorithm, and the defect positions are judged by setting appropriate upper and lower threshold limits according to the detection objects.
The method greatly shortens the detection time, and because a plurality of sensors detect simultaneously, if N sensors exist, compared with the situation that only one sensor detects, the detection time is approximate to 1/N of the original detection time when the same length is detected, thereby greatly saving the detection time and improving the efficiency.
According to the method and the device, if a micro sensor is adopted or the requirement on the detection resolution is not high, the detection can be realized without the need of micro-motion of the sensor, and the absolute detection is really realized. Resolution here refers to the resolution in terms of size, if the diameter of the sensor is Φ 14mm, then there is one sample every 14mm if the sensor position is stationary, and there is one sample every 2.5mm if the diameter of the sensor is Φ 2.5 mm. If the sensor is able to move, the sampling point on a straight line will increase significantly.
As shown in fig. 11, the detection structure of the absolute detection method based on the weak magnetic principle mainly uses a notebook computer as an upper computer for running software, a detection device as a lower computer for receiving and transmitting signals, and a weak magnetic detection instrument uses a fluxgate sensor as a magnetic field detection sensor, and the detection resolution of the sensor can reach 1nT, so that a defect signal can be effectively extracted.
Example 3
Through N array sensor evenly distributed, remove the specified distance (sensor interval T + sensor diameter D), rely on the dynamic curve of software real-time N sensors that obtains, after data processing, can splice N curve and generate same figure window, then through removing a distance, just can obtain the effect that single sensor removed longer distance and reach, enlarge detection range, improve detection efficiency.
Taking the detection of the prefabricated crack defect of a certain nickel-based superalloy material test plate as an example, the surface of a workpiece to be detected is regarded as a flat surface, 5 sensors are selected and uniformly arranged in a straight line and are fixed by a probe frame. The sensor frame is connected with the transmission device through the supporting arm, and the movement of the sensor frame is controlled by the transmission device. The lift-off of the sensor from the workpiece is a fixed value.
Before detection, the normal connection of the lines is confirmed, and the initialization of software is normal. In the process of acquiring signals in real time, each magnetic induction intensity signal corresponds to one sampling point on a detected workpiece, and a software interface can present a weak magnetic signal intensity curve in real time and simultaneously store corresponding data.
After the multi-sensor tool is adopted for detection, 5 groups of detection data of corresponding 5 sensors are stored in the system, an original curve with the collection points as an X axis and the magnetic induction intensity as a Y axis is generated by relying on upper computer software, and the defects are judged by utilizing the original curve. And carrying out differential processing on the basis of the original data to generate a differential curve reflecting the intensity mutation of the weak magnetic signal, setting a proper threshold line, and judging that the defect exists in a sampling point area corresponding to the spatial magnetic field gradient value beyond the threshold range.
Fig. 12 shows a curve obtained by scanning the surface of the object to be detected using a single sensor. The number of the collection points is 100 points, the moving distance is 90mm, and the detection time is approximately 15.5 seconds. As shown in fig. 13, the results obtained by connecting five sensors to form a single detection curve by using a micro-motion method are as follows. The data points collected by each sensor were 21 points, some of which were merged to form a total of 100 data points, with a detection time of approximately 3.5 seconds. Comparing fig. 12 with fig. 13, the detection curves of the two methods are in agreement. The former is the detection data of a single sensor scanning the length of 90mm, and the latter is the detection data of five sensors detecting the length of 90 mm. The splicing of the detection curves of the five sensors is realized by using C # software, so that detection personnel can conveniently and quickly check the detection result after the detection operation is finished.
As can be seen from fig. 14, the detection curves of the five channel sensors (each channel represents one sensor) are sequentially displayed, because each sensor detects only a small distance, and therefore, the data of the five channel sensors need to be concatenated together for defect detection. By the principle of curve head-to-tail splicing, five channel curves arranged in sequence are spliced to obtain the same curve, as shown in fig. 15.
The processing process of the detection curve is shown in fig. 16, and the five-channel sensor detects the prefabricated crack defects of a certain nickel-based superalloy material test plate to obtain A, B, C, D, E total five groups of detection curves. The A curve consists of n points of A1, A2, a, Ak, a, An, the B curve consists of n points of B1, B2, a, Bk, B, n, the C curve consists of n points of C1, C2, a, Ck, a, Cn, the D curve consists of n points of D1, D2, D, E, E1, E2, E, k, E, n, wherein n is the number of sampling points. If the 5 sets of curves are connected end to end into one detection curve, the problem of curve discontinuity can occur without any processing. If the curve a is connected to the curve B, the following curve form is connected without any processing, as shown in fig. 17.
This is because the magnetic induction intensity values detected by the sensors cannot be completely the same when the sensors are in the same magnetic field strength environment due to the differences of the manufacturing process, the performance of the parts, the calibration accuracy and the like of the sensors, and a certain deviation exists.
In weak magnetic detection, the calculation method for judging defects mainly inspects the relative change of a curve, but rarely explores the absolute detection value of the detection curve, so that the detection curve can be translated along the Y axis at the position, and the continuity of a splicing curve is ensured. The translation difference T1-An-B1, the translation difference T2-Bn-C1 + T1, the translation difference T3-Cn-D1 + T2 and the translation difference T4-Dn-E1 + T3 are recorded. The A curve and the B curve are smoothly connected, and only the longitudinal coordinate value of the A curve is required to be unchanged, and the T1 value is added to the numerical values of B1, B2, B3. The specific formula is Bk '═ Bk + T1, where Bk is the magnitude of any point on the B curve, Bk' is a new value obtained by calculation of any point on the B curve, and k is 1 to n. After the above operations are performed, the points on the B curve are all increased by T1 at the same time in value, which is equivalent to moving the whole B curve by a distance of T1 along the Y axis at the same time, so that the B1 point coincides with the An point, and the purpose of smoothing the connected detection curve is achieved. Similarly, the C curve is moved by the distance of T2 at the same time in a similar way, so that the C1 point is coincided with the Bn point; simultaneously moving the D curves by a distance T3 to make the D1 point coincide with the Cn point; the E curve is simultaneously shifted by a distance T4 such that the E1 point coincides with the Dn point. Finally, the five curves are stitched together as shown in fig. 16.
Example 4
According to the weak magnetic detection principle, if the detected object has a defect, the corresponding magnetic anomaly phenomenon exists on the detection curve of the sensor. As shown in fig. 12 and 13, the defect position can be clearly displayed, but if the defect is automatically determined by the computer, the corresponding algorithm calculation is required.
When the curve is abnormal, the difference value will change greatly. The difference curve is obtained by performing derivation processing once on the magnetic induction intensity value of each point on the original curve on the basis of the original curve to obtain a corresponding magnetic field gradient value. When mu 'is greater than mu or mu' is less than mu, carrying out derivation processing on the magnetic induction intensity numerical value of the weak magnetic field signal on the fitting curve to obtain a corresponding magnetic field gradient value, calculating a threshold range corresponding to the channel of the weak magnetic sensor, comparing the magnetic field gradient value with the threshold range, and setting the acquisition position of the weak magnetic field signal corresponding to the magnetic field gradient value exceeding the threshold range as a defect position; where μ is the average of the magnetic field gradient values obtained and σ is the standard deviation of the magnetic field gradient values obtained. The specific μ and σ calculation methods are as follows:
where n is the total number of samples of any sensor channel, μ is the average of the magnetic field gradient of that channel, σ is the standard deviation of the magnetic field gradient of that channel, and Δ b (i) is the magnetic field gradient value of the ith sample point.
And according to the formula and the principle, after data processing is carried out, a differential curve of the spliced detection curve is obtained, and the differential curve is formed by connecting the magnetic field gradient values corresponding to each sampling point. And comparing the magnetic field gradient value corresponding to each sampling point with a threshold value line (namely the upper limit and the lower limit of the threshold value range), and judging the position of the sampling point corresponding to the magnetic field gradient value exceeding the threshold value range as the defect position.
As can be seen from fig. 18, the gradient values of the magnetic field exceeding the upper and lower threshold lines are mainly concentrated in the range of the number of acquisition points 44 to 56, and the number of acquisition points corresponding to the defect position indicated by the stitching curve in fig. 13 is 50, and the two are matched with each other, thereby determining that the defect exists in the region. The crack defect prefabricated by the nickel-based superalloy material test plate is a crack with the width of 0.3mm, and the detection result is reasonable because the influence of the defect on a magnetic field exists in a large range far exceeding the size of the defect in electromagnetic detection.
The above disclosure is only for a few specific embodiments of the present invention, however, the present invention is not limited to the above embodiments, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.
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