CN101089646A - Metal magnetic memory detection device and method based on magnetic field gradient measuring - Google Patents
Metal magnetic memory detection device and method based on magnetic field gradient measuring Download PDFInfo
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- CN101089646A CN101089646A CN 200710025170 CN200710025170A CN101089646A CN 101089646 A CN101089646 A CN 101089646A CN 200710025170 CN200710025170 CN 200710025170 CN 200710025170 A CN200710025170 A CN 200710025170A CN 101089646 A CN101089646 A CN 101089646A
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Abstract
A method for detecting magnetic memory of metal based on magnetic field gradient measurement includes applying drain magnetic field gradient of component surface as judgment basis of stress and stress concentration, confirming that stress is great when magnetic field gradient is large and so far proving that stress is concentrated. The device used for realizing said method is also disclosed.
Description
Technical field
The present invention relates to a kind of metal magnetic memory pick-up unit, belong to the metal magnetic memory detection range in the Dynamic Non-Destruction Measurement by measurement magnetic field gradient value detection ferromagnetic component inside or the concentrated situation of surface stress.
Technical background
The nondestructive test with metal magnetic memory principle is proposed in the 50th international welding academic conference of san francisco, usa in 1997 by Russian scientist, be that ferromagnetic component is under the carrying situation, directed and the irreversible reorientation of the magnetic domain tissue with magnetostriction character that its stress and distortion concentrated area are taken place by the terrestrial magnetic field excitation, thereby produce own stray field in this zone, this stray field in the component surface distribution characteristics is: tangential component has maximal value, normal component reindexing and have null value.Based on the metal magnetic memory testing instrument of this principle development, great majority are by measurement component surface normal direction magnetic induction density distribution Bn (perhaps magnetic field intensity Hp (y) distributes), seek null value and sign change point, and this position is area of stress concentration or defective locations.The part detector is arranged, increased measurement tangential magnetic field intensity Hp (x) and distributed.
When probe is fixed on the dolly of being with range finding, move by dolly, can obtain the distribution curve of component surface magnetic field normal component Bn along the dolly moving direction.If dolly moves along the x direction of principal axis, by computing that x is differentiated, can obtain the magnetic field gradient profile curve of normal magnetic field component along the x direction, magnetic field gradient is also referred to as change rate of magnetic density.Most magnetic memory detectors all have this function that obtains the change rate of magnetic density curve, do auxiliary judgment but this change rate of magnetic density distribution curve can only be used for the counter stress concentration zones.
Because existing magnetic memory detector all is to calculate change rate of magnetic density by the Distribution of Magnetic Field that measures to distribute, and this calculating is to differentiate, must introduce incremental noise, so the change rate of magnetic density distribution curve that is obtained by these magnetic memory detectors all comprises a large amount of noise signals, can not reflect the real magnetic field gradient profile of component surface, change rate of magnetic density distribution counter stress is concentrated or defective is correctly passed judgment on thus certainly.
Adopt normal direction magnetic field to cross that the null value point methods judges that stress is concentrated or during defective, be subjected to the interference of background magnetic field easily, be difficult to determine the position of normal magnetic field component through zero point.Because background magnetic field is not simple terrestrial magnetic field, stress is concentrated the own stray field that produces not deducted the terrestrial magnetic field by measured magnetic field and is obtained.So, cross the magnetic memory detecting method of zero point based on normal magnetic field component, exist background magnetic field to disturb the shortcoming that easily causes erroneous judgement.
Based on magnetic field intensity or magnetic induction density parameter is the magnetic memory detector of judging basis or measuring object, not only has the shortcoming of above-mentioned easy erroneous judgement, and only depends on normal magnetic field component to cross zero point, can not counter stress and stress concentration degree quantitatively pass judgment on.
Summary of the invention
The objective of the invention is: overcome existing metal magnetic memory testing instrument because of adopt magnetic field intensity be judging basis can not counter stress and stress concentrate the weak point of carrying out quantitative test, providing a kind of is the magnetic memory detection device of judging basis with the magnetic field gradient, the detection that defective or stress are concentrated and can quantitatively be passed judgment on component stress or stress concentration degree more accurately and reliably.This pick-up unit need not to measure the accurate numerical value of magnetic field intensity, does not also produce incremental noise.The present invention can be used for the ferromagnetic component stress intensity is measured indirectly to a certain extent.
Suppose that along the spatial variations amount of component surface x direction be dx, correspondent method is dBn to the variable quantity of magnetic induction density component Bn, the magnetic field gradient of x direction then of the present invention is meant Gx=dBn/dx, and promptly magnetic induction density is to the rate of change of displacement x, and unit commonly used is mT/m (milli tesla/rice).In like manner, the magnetic field gradient of y direction is Gy=dBn/dy.
The present invention is achieved by the following technical solutions: measure apart from the magnetic field gradient value of ferromagnetic component surface less than the 5mm place by the magnetic field gradient measuring instrument, concentrate judging unit to judge component inside or the concentrated situation of surface stress according to the magnetic field gradient size by stress then.Described magnetic field gradient measuring instrument is meant and need not the magnetic field gradient measuring instrument along the magnetic field gradient value of some or a plurality of directions that traverse measurement probe just can be measured the position of popping one's head in that this measuring instrument comprises probe, the amplifying circuit of measuring magnetic field gradient.Described probe is one of following two types structure, and the probe of every kind of structure all comprises the shell that a nonferromugnetic material is made.The array of magnetic sensors of structure A for adopting discrete component to constitute, at least comprise 2 Magnetic Sensors, fixed distance between two sensors that distribute on certain direction, these two sensor output signals send differential amplifier circuit two input ends, through differential amplification, the output signal size is proportional to the difference of the magnetic field intensity of two sensors measurement, the promptly approximate magnetic field gradient along the line direction that is proportional to these two sensor line geometric center positions.Structure B adopts vibratory drilling method to measure magnetic field gradient, probe comprises shell, Magnetic Sensor and makes the oscillating plate of its vibration, oscillating plate is the cantilever beam structure piezoelectric bimorph, Magnetic Sensor is installed in its free end, Magnetic Sensor detection faces normal and tested component surface normal are on same straight line and perpendicular to the sensor direction of vibration, sensor is with fixed frequency and fixed amplitude vibration, become the AC signal of fixed frequency, this signal amplitude to be proportional to the magnetic field gradient along the sensor direction of vibration of probe position the magnetic field modulation of space static distribution.The magnetic field gradient measuring instrument of forming by structure B probe, comprise a low-frequency oscillatory network, be used to produce the low-frequency sine signal, the vibration of driving piezoelectric bimorph, the sensor output terminal is connected to the logical amplifying circuit of source band, the centre frequency of the logical amplifying circuit of band equals the sensor vibration frequency, and the logical amplification circuit output end of band connects sinusoidal wave peak detection circuit, and the peak value of institute's detection signal is represented magnetic field gradient value; It is to preset some kinds of judgment thresholds according to the concrete shape and the material of detected member that described stress is concentrated judging unit, when the magnetic field gradient of tested component surface during greater than corresponding threshold value, show that member has stress to concentrate or defective in this position, realize the nondestructive test with metal magnetic memory purpose.Display unit in the said apparatus is used to receive and show measured magnetic field gradient size, perhaps shows the stress concentration degree or the stress intensity of institute's detection means.
In the said apparatus, the pick-up unit by structure A probe is formed both can be the magnetic field gradient that single channel only detects a direction, also can be the magnetic field gradient that binary channels detects both direction simultaneously; Its each sensor of popping one's head in carries out layout as required, if only measure a magnetic field gradient on the direction, then only need two sensors are placed side by side, can measure along the magnetic field gradient of these two sensor line directions, distance between the center sensor is near, for about 4mm; Measure the magnetic field gradient on two mutually perpendicular direction x and the y direction during if seek common ground, then need 4 sensors to be symmetrically distributed, center probe is true origin and symcenter, 4 sensors are in same plane, two sensors on the x axle be sensor (11) and sensor (12) but magnetic field gradient on the measurement of x direction of principal axis, two sensors on the y axle are that sensor (13) and sensor (14) can be measured the magnetic field gradient on the y direction of principal axis, at this moment need adopt the binary channels differential amplifier circuit, differential amplifier circuit output signal size expression magnetic field gradient value, distance between two center sensors of every passage is 6～10mm, and each sensor performance is identical.
By the pick-up unit that structure B probe is formed, the frequency span of the logical amplifying circuit of its band is less than 2Hz, and centre frequency equals the centre frequency of low-frequency oscillatory network, is 30～48Hz; Its peak detection circuit adopts the multiplier synchro detection circuit to realize, multiplier two input signals carry logical amplifying circuit and low-frequency oscillatory network respectively.
In the said apparatus, also comprise the alarm sound Tip element, when measured magnetic field gradient during greater than preset threshold value, produce alarm sound, the prompting member exists defective or stress to concentrate.Magnetic Sensor in the device is integrated linear hall element, and the distance that Hall element detects end face apart from probing shell guarantees that less than 5mm measured magnetic field gradient is apart from the value of component surface less than the 5mm position.Described threshold value can be determined by experiment according to construction material, shape etc., for surface area greater than 0.01m
2Common carbon steel member, as A3 or Q235, the magnetic field gradient threshold value from component surface 3mm position is 10～20mT/m.The display unit display mode of said apparatus both can be the digital demonstration of LCD or LED, also can be the indication of mechanical pointer voltage table gauge outfit.Structure A probe can be improved to integrated morphology, be about to sensor array and be integrated in the chip, differential amplifier circuit also is integrated in the same chip, little when the element apart from score between the sensor, the positional precision of measuring magnetic field gradient is higher, this structure detection principle isostructure A.
The inventor discovers, the own stray field of member is in the distribution of area of stress concentration, not only have component surface normal magnetic field component sign change and cross zero point, the tangential magnetic field branch is measured peaked characteristics, and has normal magnetic field component and get peaked feature along the gradient of certain direction of surface.Obviously, measure magnetic field gradient profile and have more superiority than measuring magnetic field distribution.Because measure the spatial variations amount that magnetic field gradient only need be measured magnetic field, do not need the exact value of magnetic field intensity, component surface among a small circle in the spatial variations amount of background magnetic field very little, the interference of background magnetic field is just very little.Counter stress concentrates the judgement of situation just more accurate.
The intensity of the outer stray field of component surface reduces along with the distance apart from the surface increases, and magnetic field gradient also is to increase with distance to reduce.In order to improve the reliability that the counter stress concentration zones detects, probe should be tried one's best near component surface, so that measure the closely magnetic field gradient profile of position.But because sensor itself has certain thickness, probing shell also has thickness, and for guaranteeing detecting reliability, requiring Hall element is appropriate apart from the distance of probing shell end face less than 5mm, and in fact, this distance is the smaller the better.
Fig. 1 is the block diagram of system of apparatus of the present invention.During actual fabrication, stress concentrates judging unit generally to adopt comparator circuit to realize, according to the factors such as material, structure, shape and environment for use of detected member, set judgment threshold by experiment, magnetic field gradient exists area of stress concentration or defective greater than the position of this threshold value.Display unit generally adopts the needle dc voltmeter indication, also can convert the voltage signal of reflection magnetic field gradient to digital quantity through A/D, by LED or the digital demonstration of LCD.
The inventor is 100mm to gauge length, diameter is that the bar-shaped standard specimen that the mild carbon steel A3 of 10mm makes has carried out a large amount of stretching experiments, discovery was similar between the maximum stress that component surface stray field Gradient distribution and member once be recently and has simple proportional relationship before surrender.In the experiment, stretching is loaded into certain load to test specimen, unloading then, the above-below direction of test specimen when drawing machine takes off and will stretch is changed to along the east-west direction horizontal positioned, measure test specimen surface normal magnetic-field component along the axis magnetic field gradient profile of direction from east to west, calculate the mean value of each measurement point magnetic field gradient in the gauge length scope, suffered magnitude of load had proportional relationship when the mean value of this magnetic field gradient and test specimen were loaded.Measurement to magnetic field gradient is effective property, the inventor is to the measurement of test specimen surface leakage magnetic field gradient, carrying out between 5～10 minutes after the unloading, at this moment the scale-up factor of load and magnetic field gradient is approximately 1.2kN/ (mT/m), and the distance on sensor sensing unit centre distance test specimen surface is 3mm.Placed through 48 hours after the unloading, measure the magnetic field gradient on this mild carbon steel test specimen surface once more, the result is reduced to half of measured value between the unloading back 5～10 minutes.Placed 60 days unloading back, measures its magnetic field gradient once more, and 1/5 of the not enough initial measured value of result illustrates the member stress and the stray field intensity and the magnetic field gradient that produce can slowly weaken in time.Experiment shows that the magnetic memory detection device of measuring based on magnetic field gradient of the present invention not only can concentrate situation to estimate to the stress of ferromagnetic component, and the stress that can once be subjected to the member that carrying unloads is again measured indirectly.Promptly by measurement, extrapolate before this in the certain hour maximum load that member once had been to the magnetic field gradient of component surface.
The inventor finds that the size of component surface stray field gradient and the stress intensity on component inside or surface have substantial connection, concentrates if stress appears in member, and the magnetic field gradient around it will significantly increase,
The present invention has compared following beneficial effect with existing magnetic memory detector: simple in structure, with low cost; The magnetic field gradient profile curve of measuring does not have incremental noise, directly passes judgment on defective and the concentrated situation of stress, reliability height by the size of magnetic field gradient; Can carry out quantitative evaluation to the stress and the stress concentration degree of member.
Description of drawings
Fig. 1 is the block diagram of system of the present invention
Fig. 2 is 4 sensor placements according to embodiments of the invention one structure A probe
Fig. 3 is the system architecture synoptic diagram of being made up of structure A probe according to embodiments of the invention one
Fig. 4 is the system architecture synoptic diagram of being made up of structure B probe according to embodiments of the invention two
Fig. 5 is the structure B synoptic diagram of popping one's head in the system that is made up of structure B probe according to embodiments of the invention two
Fig. 6 is the system circuit diagram of being made up of structure A probe according to embodiments of the invention one
Fig. 7 is the system circuit diagram of being made up of structure B probe according to embodiments of the invention two
Embodiment
Below in conjunction with the drawings and specific embodiments the present invention is described in detail, provides 2 embodiment altogether.The present invention is concentrated or defect condition by the magnetic field gradient profile judgement component inside on direct measurement ferromagnetic component surface or surface stress.This magnetic field gradient profile should not calculate by differentiate according to the magnetic field profile that measures, because can produce incremental noise like this.The measurement of magnetic field gradient can adopt following embodiment similar approach to carry out.
Embodiment one: the metal magnetic memory pick-up unit of being made up of structure A probe based on the magnetic field gradient measurement
Present embodiment adopts structure A probe to form detection system, can measure simultaneously along the magnetic field gradient of the orthogonal both direction of component surface, and the magnetic field gradient of any one direction surpasses preset threshold and all can report to the police.Probe adopts the sensor of 4 symmetrical distributions to form, and sensor is an integrated hall element, and layout is seen Fig. 2, and they are encapsulated in the transparent plastic shell.Wherein the distance between sensor 11 and sensor 12 centers is Δ x, the two sensors position is Bn1 and Bn2 along the magnetic induction density component of normal direction, two sensors symcenter then, promptly the magnetic field gradient along the x direction of true origin position is Gx=(Bn2-Bn1)/Δ x; Distance between sensor 13 and sensor 14 centers is Δ y, and their positions are Bn3 and Bn4 along the magnetic induction density component of normal direction, and then the magnetic field gradient along the y direction of true origin position is Gy=(Bn4-Bn3)/Δ y.
Fig. 3 is a present embodiment system architecture synoptic diagram.Fig. 6 is the physical circuit figure of present embodiment.As seen from the figure, two channel architectures are identical, are the example explanation course of work with the x passage.Sensor 11 and 12 is by cable place in circuit socket JP601, and sensor is three end integrated hall elements, and ± 2.5V power supply is after capacitor C 601 filtering, and JP601 powers to sensor by socket.Sensor output signal send the in-phase input end of amplifier U601A and U601B respectively through resistance R 601 and R602.Amplifier U601A, U601B, U601C, resistance R 603, R604, R605, R606, R607, R608, R609, R610, R611, R612, R613, R614, adjustable resistance W603, W604, potentiometer W601, W602 etc. form differential amplifier circuit, its output signal size is proportional to the magnetic field intensity difference that two sensors is measured, and promptly is proportional to magnetic field gradient Gx.Wherein W601 and W602 are a coaxial duplex potentiometer, and slide head current potential increases during rotation, and another slide head current potential reduces, and output potential is different when being used for compensation sensor 11 with zero magnetic field that 12 cause because of performance difference; W603 is used to compensate the difference of two sensors sensitivity.The range of voltage table gauge outfit V601 is ± 2.5V to be used to indicate magnetic field gradient value.W604 is used to be provided with alarm threshold value.Amplifier U601D, resistance R 615, R616, R617, R618 and full-bridge diode D601 form the threshold value comparator circuit, when the absolute value of magnetic field gradient during greater than setting value, amplifier U601D exports electronegative potential, and active hummer LS601 work is reported to the police, and expression x direction magnetic field gradient surpasses threshold value.
The y channel circuit of forming pick-up unit by socket JP602, capacitor C 602, amplifier U602A, U602B, U602C, U602D, resistance R 621, R622, R623, R624, R625, R626, R627, R628, R629, R630, R631, R632, R633, R634, R635, R636, R637, R638, adjustable resistance W623, W624, duplex gang potentiometer W621, W622, full-bridge diode D621, diode D622, voltage table gauge outfit V602, active hummer LS602 etc.
The present embodiment device is that single range is twin-channel, and the those of skill in the art in the present technique field are to be understood that this just illustrates, and can make change or modification to present embodiment, and not deviate from principle of the present invention and essence.For example, it is single pass at an easy rate this circuit to be changed system into multirange, perhaps makes a little other modifications.
Embodiment two: the metal magnetic memory pick-up unit of being made up of structure B probe based on the magnetic field gradient measurement
Present embodiment adopts structure B probe to form detection system, adopts vibratory drilling method to measure magnetic field gradient.Fig. 4 is the composition synoptic diagram of present embodiment detection system, and Fig. 5 is a kind of sonde configuration synoptic diagram of present embodiment, and Fig. 7 is embodiment physical circuit figure.Probe comprises: integrated linear hall element extension line 1, piezoelectric bimorph lead-in wire 2, stiff end grip block 3, shell 4, piezoelectric bimorph 5, integrated linear hall element fixing circuit board 6, Hall element pin 7, Hall element detection faces 8.
Among Fig. 4 and Fig. 5, low-frequency oscillatory network produces the sine voltage signal of 40Hz, and one the tunnel send booster driving circuit to amplify, and is inserted by piezoelectric bimorph lead-in wire 2 and gives probe, makes piezoelectric bimorph 5 vibrations, drives the sensor vibration; Another road sine wave signal send multiplier an input end as the reference signal, participates in synchronous detection.Hall element detection faces 8 is parallel to detected component surface, if sensor vibrates along the x direction, oscillating region (2 times of amplitudes) is Δ x, is Δ Bn at the variable quantity of this oscillating region magnetic induction density normal component, and then the magnetic field gradient along the x direction is Gx=Δ Bn/ Δ x.Sensor output signal is faint sine wave signal, and the sine wave signal peak value is proportional to magnetic field gradient, and this sine wave signal frequency equals the sensor vibration frequency, also equals 40Hz.Feeble signal send the logical amplifying circuit of band to amplify, and this circuit centre frequency is 40Hz, and bandwidth is 1.5Hz, and centre frequency place voltage amplification factor is 1000, and the signal after the amplification send another input end of multiplier by synchronous detection.Multiplier output signal obtains d. c. voltage signal through low-pass filtering, and this d. c. voltage signal size is proportional to magnetic field gradient, so available this signal indication magnetic field gradient, and shows its size by concentrated the judging whether of stress above threshold value and display unit.
Among Fig. 7, socket JP701 is used for connecting by cable the sensor of probe, and ± 2.5V power supply is powered to sensor after capacitor C 710, C711 filtering.Sensor output signal send the logical amplifying circuit of first order band to carry out the frequency-selecting amplification through adjustable resistance W701, resistance R 701.Circuit comprises the active bandpass amplifier of the unlimited gain in 3 grade of 2 rank altogether, comprises 1 grade of 2 rank active filter that infinitely gains.By amplifier U701B, resistance W701, R701, R702, W702, R703, W703, R704, R705, capacitor C 701, C702 forms first order bandpass amplifier, by amplifier U701A, resistance R 706, R707, W707, R708, R709, W709, R710, capacitor C 703, C704 forms 1 grade of 50Hz wave filter, by amplifier U701C, resistance R 712, W712, R713, W713, R714, W714, capacitor C 705, C706 forms second level bandpass amplifier, by amplifier U701D, resistance R 15, R716, W716, R717, R720, R721, capacitor C 707, C708 forms third level bandpass amplifier.Every grade of bandpass amplifier centre frequency is 40Hz, and is main by regulating adjustable resistance W702, W713, W716 realization; By regulating the gain that adjustable resistance W701, W703, W712, W714 can change this grade, also influential to centre frequency, need to cooperate and adjust each adjustable resistance circuit is met the demands.It is 50Hz that adjusting resistance W707, W709 make the centre frequency of this grade wave filter, and the 50Hz signal is absorbed fully, eliminates power frequency and disturbs.
Integrated circuit U702A is 4 quadrant analog multipliers, and model is MLT04.Resistance R 722, capacitor C 709 formed low-pass filters, and range is used to indicate magnetic field gradient value for the voltage table gauge outfit V701 of ± 2.5V.Form low-frequency oscillatory network by amplifier U703A, resistance R 731, R732, R733, R734, W731, capacitor C 731, C732, diode D731, D732, adjusting resistance W731 can change the amplitude of oscillatory circuit output signal, then by resistance R 731, R732 and capacitor C 731, C732 decision, the present embodiment oscillation frequency is 40Hz to the frequency of oscillatory circuit.The 40Hz sine wave signal one tunnel that produces send multiplier an input end through resistance R 735, participates in synchronous detection, and another road oscillator signal send booster driving circuit through resistance W732.Form booster driving circuit by amplifier amplifier U703C, U703D, resistance R 737 and step-up transformer T731, it is 30V that sine wave signal voltage is elevated to peak-to-peak value, realizes by regulating resistance W732.Voltage after will raising by socket JP702 is drawn and is added on the piezoelectric bimorph, makes it do mechanical vibration.Form the stress threshold concentration by amplifier U703B, resistance W733, R736, R738, R739, R740, diode D733, D734 and active hummer LS731 and judge warning circuit.Threshold setting is realized by regulating resistance W733.
The present embodiment device is that single range is single pass, and the those of skill in the art in the present technique field are to be understood that this just illustrates, and can make change or modification to present embodiment, and not deviate from principle of the present invention and essence.For example, it is multichannel at an easy rate this circuit to be changed system into multirange, or makes a little other modifications.
More than among two embodiment, integrated linear hall element model is 3503, amplifier is LM324, the piezoelectric bimorph overall dimensions are 60mm * 20mm * 0.6mm among the embodiment two.
More than in two embodiments, display unit all adopts the simplest mechanical pointer voltage table, utilizes existing known technology can easily they be changed into LED or LCD and shows, and do not deviate from essence of the present invention.Core essence of the present invention is to pass judgment in the member or the stress and the stress concentration degree on surface by the magnetic field gradient of measuring component surface.All employings are equal to the technical scheme that form obtained of replacement or equivalent transformation, all drop within protection scope of the present invention.
Claims (8)
1, a kind of metal magnetic memory pick-up unit of measuring based on magnetic field gradient, concentrate judging unit and display unit to constitute by magnetic field gradient measuring instrument, stress, it is characterized in that, described device is to measure apart from the magnetic field gradient value of ferromagnetic component surface less than the 5mm place by the magnetic field gradient measuring instrument, concentrates judging unit to judge component inside or the concentrated situation of surface stress according to the magnetic field gradient size by stress then; Described magnetic field gradient measuring instrument is meant and need not the magnetic field gradient measuring instrument along the magnetic field gradient value of some or a plurality of directions that traverse measurement probe just can be measured the position of popping one's head in that this measuring instrument comprises probe, the amplifying circuit of measuring magnetic field gradient; Described probe is one of following two types structure, the probe of every kind of structure all comprises the shell that a nonferromugnetic material is made, the array of magnetic sensors of structure A for adopting discrete component to constitute, at least comprise 2 Magnetic Sensors, fixed distance between two sensors that distribute on certain direction, these two sensor output signals send differential amplifier circuit two input ends, through differential amplification, the output signal size is proportional to the difference of the magnetic field intensity of two sensors measurement, the promptly approximate magnetic field gradient along the line direction that is proportional to these two sensor line geometric center positions; Structure B adopts vibratory drilling method to measure magnetic field gradient, probe comprises shell, Magnetic Sensor and makes the oscillating plate of its vibration, oscillating plate is the cantilever beam structure piezoelectric bimorph, Magnetic Sensor is installed in its free end, Magnetic Sensor detection faces normal and tested component surface normal are on same straight line and perpendicular to the sensor direction of vibration, sensor is with fixed frequency and fixed amplitude vibration, become the AC signal of fixed frequency, this signal amplitude to be proportional to the magnetic field gradient along the sensor direction of vibration of probe position the magnetic field modulation of space static distribution; The magnetic field gradient measuring instrument of forming by structure B probe, comprise a low-frequency oscillatory network, be used to produce the low-frequency sine signal, the vibration of driving piezoelectric bimorph, the sensor output terminal is connected to the logical amplifying circuit of source band, the centre frequency of the logical amplifying circuit of band equals the sensor vibration frequency, and the logical amplification circuit output end of band connects sinusoidal wave peak detection circuit, and the peak value of institute's detection signal is represented magnetic field gradient value; It is to preset some kinds of judgment thresholds according to the concrete shape and the material of detected member that described stress is concentrated judging unit, when the magnetic field gradient of tested component surface during greater than corresponding threshold value, show that member has stress to concentrate or defective in this position, realize the nondestructive test with metal magnetic memory purpose; Described display unit is used to receive and show measured magnetic field gradient size, perhaps shows the stress concentration degree or the stress intensity of institute's detection means.
2, pick-up unit according to claim 1 is characterized in that, the pick-up unit by structure A probe is formed both can be the magnetic field gradient that single channel only detects a direction, also can be the magnetic field gradient that binary channels detects both direction simultaneously; Its each sensor of popping one's head in carries out layout as required, if only measure a magnetic field gradient on the direction, then only need two sensors are placed side by side, can measure along the magnetic field gradient of these two sensor line directions, distance between the center sensor is near, be 3～5mm if measure magnetic field gradient on two mutually perpendicular direction x and the y direction when seeking common ground, then need 4 sensors to be symmetrically distributed, center probe is true origin and symcenter, 4 sensors are in same plane, two sensors on the x axle be sensor (11) and sensor (12) but magnetic field gradient on the measurement of x direction of principal axis, two sensors on the y axle are that sensor (13) and sensor (14) can be measured the magnetic field gradient on the y direction of principal axis, at this moment need adopt the binary channels differential amplifier circuit, differential amplifier circuit output signal size expression magnetic field gradient value, distance between two center sensors of every passage is 6～10mm, and each sensor performance is identical.
3, pick-up unit according to claim 1 is characterized in that, by the pick-up unit that structure B probe is formed, the frequency span of the logical amplifying circuit of its band is less than 2Hz, and centre frequency equals the centre frequency of low-frequency oscillatory network, is 30～48Hz; Its peak detection circuit adopts the multiplier synchro detection circuit to realize, multiplier two input signals carry logical amplifying circuit and low-frequency oscillatory network respectively.
4, pick-up unit according to claim 1 is characterized in that, described pick-up unit also comprises the alarm sound Tip element, when measured magnetic field gradient during greater than preset threshold value, produces alarm sound, and the prompting member exists defective or stress to concentrate.
5, pick-up unit according to claim 1, it is characterized in that, described Magnetic Sensor is integrated linear hall element, and the distance that Hall element detects end face apart from probing shell guarantees that less than 5mm measured magnetic field gradient is apart from the value of component surface less than the 5mm position.
6, pick-up unit according to claim 1 is characterized in that, described threshold value should be determined by experiment according to construction material, shape etc., for surface area greater than 0.01m
2Common carbon steel member, as A3 or Q235, the magnetic field gradient threshold value from component surface 3mm position is 10～20mT/m.
7, pick-up unit according to claim 1 is characterized in that, described display unit display mode both can be the digital demonstration of LCD or LED, also can be the indication of mechanical pointer voltage table gauge outfit.
8, pick-up unit according to claim 1, it is characterized in that, structure A probe is improved to integrated morphology, being about to sensor array is integrated in the chip, differential amplifier circuit also is integrated in the same chip, little when the element apart from score between the sensor, the positional precision of measuring magnetic field gradient is higher, this structure detection principle isostructure A.
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