CN107102363A - A kind of metal object detection device and metal probing method - Google Patents
A kind of metal object detection device and metal probing method Download PDFInfo
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Abstract
The present invention relates to metal detection field, more particularly to a kind of metal object detection device and method based on frequency domain.The metal detection device and detection method that the present invention is provided are based on active electric-field Detection Techniques, and hardware configuration is simple, easily miniaturization, the problem of overcoming other detection method hardware and excessive energy expense；During work, only emission electrode and receiving electrode need to enter in liquid to be detected in device, and emission electrode and receiving electrode can be easily integrated or be arranged on any meet above desired ROV or motion；It is easy to use, it is adaptable in the liquid with conductive characteristic（Such as water）In environment, there is good effect for the wood properly test of the metal object of known volume in liquid environment.
Description
Technical field
The present invention relates to metal detection field, more particularly to a kind of metal object detection device and method based on frequency domain.
Background technology
With the development of society, application of the metal detection technology in modern society's life is more and more extensive.In military, peace
The figure of all visible metal detectors in field such as full field, archaeology, engineer applied, industry.Such as conventional induction gold
Belong to detector, its general principle is exactly that the coil used the power on produces a detection magnetic field, enters detection magnetic field model when there is metal
When enclosing, the change in magnetic field will be caused, metal target is thus determined whether.There is also the detection of various other types simultaneously
Device, such as X-ray detection type, microwave detection type, laser detection type.But on the whole, in existing metal detection technology, no matter
It is which kind of detection principle, which kind of Detection Techniques used, it does not possess the ability for distinguishing different metals target at present.This
Outside, existing metal detection technology is only used for the detection operations in the air ambient of land mostly, and to underwater operation environment simultaneously
It is inapplicable.
At present, main metal detection technical method is such as：Detection Techniques based on current vortex, based on polarization characteristics of lasers
Detection Techniques, based on electromagnetic exploration technology, the Detection Techniques based on the HSV colour spaces, the Detection Techniques based on heat conductivility with
And physical identification method etc..Although in the presence of some metal detection technologies under water, these technologies are not generally to adapt to, very
Cause that it can not be used or Effect on Detecting is undesirable to also many limiting factors.Such as metal material based on current vortex sensor
Matter Detection Techniques, it utilizes the alternating magnetic field that search coil is produced, and is in by metal conductor measured in the magnetic field and causes detection
The change in magnetic field detects metal object.The technology is preferable applied to effect in air ambient, but can not recognize tested metal
The material of object；The Detection Techniques of polarization by reflection characteristic based on Metal object surface laser, by being sweared to reflected light Stokes
The analysis of amount, linearly polarized light or circularly polarized light are changed into elliptically polarized light after metal surface is reflected, according to its ovality and side
The difference of parallactic angle distinguishes detected metal object.Although the technology can recognize underwater hardware body material, such to swash
The effect of some nonlinear opticses inevitably occurs when water transmission for light, so that strong influence metal detection
Effect；Immersed body Detection Techniques based on the HSV colour spaces, it is also a kind of optical recognition of immersed body, utilizes this
The mode that lentor imaging technique and hsv color space are combined, by the object polarization information of same color different materials in HSV
Shown in space.According to the colourity (representing polarization degree information) of HSV color spaces, saturation degree (the polarization side of table reflected light
Azimuth angle information), the difference of brightness testee material is made a distinction, this kind of technology be based on polarization characteristics of lasers with detecting skill
Art is the same, will be carried out the work by the characteristic of reflected light, same restrictive condition is had unavoidably；And based on heat conductivility
Metal detection technology under water, the technology is a kind of contact Detection Techniques, and it has different heat conductivilitys by different materials
Characteristic, the purpose of identification material is can reach by measuring the thermal conductivity of material.But have the disadvantage, it is necessary to contact testee
Its heat conductivility can be detected, for detecting under water, the probe of such detection sensor is exposed in media environment, difficult during detection
Exempt from that the influence that media environment produces thermal conductivity can be brought into；And physical identification method such as sense organ differentiates, Spark Discrimination, spectroscope analysis
Deng should not all be organized work in water.
To sum up, or existing various metal detection technologies can not detect the specific species of metal, or under water
During environment detection, it is vulnerable to such as detection environment, the limitation of detection device itself function and preferable Effect on Detecting can not be reached.
The content of the invention
It is an object of the invention to overcome the above-mentioned deficiency in the presence of prior art to be applied there is provided one kind in conducting liquid
The metal object detection device of detection metal object in (such as water)；
In order to realize foregoing invention purpose, the invention provides following technical scheme：
A kind of metal object detection device, including,
Emitter, including at least two emission electrodes, one of emission electrode ground connection；The emitter is used for
Launch the first signal with assigned frequency to target acquisition region under the control of control device, so as to be built in target acquisition region
Vertical detection electric field；
Reception device, including receiving electrode, the reception device are used to gather electric field signal from the detection electric field, and
The electric field signal is processed as after secondary signal to be sent to control device, the control device handles the secondary signal received
For the 3rd signal of different metal materials can be characterized.
Further, the emitter also includes the signal generation apparatus being connected with the emission electrode；The signal
Generating means is used for the signal that assigned frequency is produced according to the instruction of control device.
Further, the reception device includes the first receiving electrode and the second receiving electrode, in addition to simultaneously with described
First receiving electrode and the data sampler of the second receiving electrode connection；
The data sampler is processed as secondary signal for two receiving electrodes to be collected into electric field signal respectively.
It is preferred that, the emission electrode is that distance is 10~90mm between two, two emission electrodes；
The receiving electrode is two, and the distance between two receiving electrodes are 5~80mm.
It is preferred that, at least apart from 5mm between the emission electrode and receiving electrode.
The metal object detection method of metal material can be detected in conducting liquid present invention simultaneously provides a kind of,
Specifically, a kind of metal object detection method, comprises the following steps：
Step 1：Launch the first signal to target acquisition region according to assigned frequency and set up detection electric field；
Step 2：Emission electrode and receiving electrode are moved according to fixed route, from detection electric field collection electric field signal；
Step 3：According to the signal amplitude value of the electric field signal acquisition collected not in the same time, and it is bent to form amplitude versus time
Line；
Step 4：Judged according to amplitude versus time curve, adjust or maintain the assigned frequency, to obtain gold to be detected
The corner frequency of category, and then metal material is judged according to the corner frequency.
The principle that this method can detect different metal materials is：Metal object in different types of conducting liquid (such as water)
Body can form complicated impedance operator change under exchange electric excitation, and then produce electrical potential difference difference in disturbance electric field, specifically,
In detection electric field, tested metal object can cause electric field perturbations due to direct impedance characteristic, and different metal materials under water
Matter can be again because the difference of its complicated impedance operator, causes different electric field perturbations, so as to produce specific corner frequency, passes through
The trend that electrical potential difference changes in detection detection electric field, it is determined that the corner frequency value of detected metal, and then acquisition gold can be compared
Belong to material；Under this principle, even if tested metal object volume very little, as long as its material is different, then the turnover frequency detected
Rate value is also just different, so that the material of tested metal object is distinguished according to the difference of this corner frequency value, meanwhile, according to a large amount of
Metal object test result show, the metal object corner frequency gap that volume is approximate, material is different clearly, using this
Method judges that metal object material accuracy rate is higher.
Further, in the step of gathering electric field signal from detection electric field,
Gather the electric field signal of the detection electric field respectively using at least two receiving electrodes, and obtain two electric field signals
Differential signal.
Further, obtained according to the electric field signal collected in signal amplitude value not in the same time, the difference is believed
Number carry out Fourier transformation, to obtain the signal amplitude value.
Further, judged according to amplitude versus time curve, adjust or maintain the assigned frequency, wait to visit to obtain
In the step of surveying the corner frequency of metal,
Amplitude versus time curve is judged, if range value includes protrusion curve in amplitude versus time curve, then increases
The assigned frequency certain numerical value, and re-start step 1~step 3.
Further, judged according to amplitude versus time curve, adjust or maintain the assigned frequency, wait to visit to obtain
In the step of surveying the corner frequency of metal, if range value includes depression profile in amplitude versus time curve, then reduces the finger
Determine frequency certain numerical value, and re-start step 1~step 3.
Further, judged according to amplitude versus time curve, adjust or maintain the assigned frequency, wait to visit to obtain
In the step of surveying the corner frequency of metal, if amplitude versus time curve is straight line, then now the assigned frequency is to be detected
The corner frequency of metal.
Compared with prior art, beneficial effects of the present invention：Metal detection device and detection method base that the present invention is provided
In active electric-field Detection Techniques, hardware configuration is simple, easily miniaturization, overcomes other detection method hardware and energy expense is excessive
The problem of；During work, only emission electrode and receiving electrode need to enter in liquid to be detected in device, and emission electrode and reception electricity
Extremely can it is easily integrated or be arranged on it is any meet require ROV or motion above；It is easy to use, it is adaptable to
In liquid (such as water) environment with conductive characteristic, have for the wood properly test of the metal object of known volume in liquid environment
Good effect.
Brief description of the drawings：
The structure principle chart for the detection means that Fig. 1 present invention is provided.
Workflow diagram of the detection means provided in Fig. 2 embodiment of the present invention when being detected.
Detection electrode (emission electrode and receiving electrode) is between signal projector and sampler in Fig. 3 embodiment of the present invention
Connection figure.
Short Time Fourier Transform (STFT) Transformation Graphs of Fig. 4 discrete signals.
When Fig. 5 a are not tested metal, the electric field simulation that detection electrode (emission electrode and receiving electrode) is set up under water
Figure.
When Fig. 5 b have tested metal, the electric field simulation figure that detection electrode (emission electrode and receiving electrode) is set up under water.
It is respectively that aluminium and copper are in caused detection electric field change when in detection electric field that Fig. 6 a, Fig. 6 b, which are tested metal object,
Figure.
Fig. 7 effective scope of detection and different detective path schematic diagrames.
Fig. 8 a are the joint time-frequency distribution collection of illustrative plates example of cylindrical iron when look-in frequency is 10Hz.
Fig. 8 b are the joint time-frequency distribution collection of illustrative plates example that look-in frequency is 12Hz constantly cylindrical irons.
Fig. 9 is detection device embodiment detection exemplary plot.
The flow chart that Figure 10 detectable signals are produced.
The programme diagram that signal is produced in Figure 11 examples.
Figure 12 signal record collection devices be received back to come without metal when detection waveform.
Figure 13 specifically detects signal amplitude change curve exemplary plot in example.
The data illustrated example that Figure 14 data record collection devices are preserved.
When Figure 15 testees are metal cylindrical iron, relation illustrated example of the electrical conductivity with frequency turning point of medium is detected.
Figure 16 testee aluminium cylinder is detected when using less than corner frequency, using corner frequency, higher than corner frequency
Obtained joint time-frequency spectrum contrast schematic diagram.
Figure 17 testee cylindrical irons body is detected when using less than corner frequency, using corner frequency, higher than corner frequency
Obtained joint time-frequency spectrum contrast schematic diagram.
Figure 18 testees bronze cylinders are detected when using less than corner frequency, using corner frequency, higher than corner frequency
Obtained joint time-frequency spectrum contrast schematic diagram.
Marked in figure：1- emitters, 10- multi-function data acquisition cards, 11- emission electrodes, 12- signal generators, 21- data
Sampler, 22- receiving electrodes, 20- is detected conducting liquid 20,3- control devices, 4- motion modules, 5- fixed supports, 6- quilts
Survey metal, 7- signal transmssion lines, 100- sampling windows, 200- effective scope of detection, 400- protrusion curves, the recessed curves of 500-,
600- straight lines, S1, S2, S3- detection route.
Embodiment
Below in conjunction with the accompanying drawings and specific embodiment the present invention is described in further detail.But this should not be interpreted as to this
The scope for inventing above-mentioned theme is only limitted to following embodiment, all to belong to the present invention based on the technology that present invention is realized
Scope.
Embodiment 1：As shown in figure 1, the present embodiment provides a kind of metal object detection device, including, control device 3, hair
Injection device 1 and reception device, wherein, emitter 1 includes two emission electrodes 11, and one of emission electrode 11 is grounded；Institute
Stating emitter 1 is used under the control of control device 3 launch the first signal with assigned frequency to target acquisition region, from
And detection electric field is set up in target acquisition region；Reception device includes receiving electrode 22, and the reception device is used to visit from described
Survey in electric field and gather electric field signal, and the electric field signal is processed as to be sent to control device 3 after secondary signal, the control dress
Put 3 the 3rd signals that the secondary signal received is processed as characterizing to different metal materials.
In the present embodiment, emitter 1 also includes the signal generation apparatus being connected with the emission electrode 11；The signal
Generating means is used for the signal that assigned frequency is produced according to the instruction of control device 3；The reception device includes first and receives electricity
The receiving electrode 22 of pole 22 and second, in addition to the data connected simultaneously with the receiving electrode 22 of the first receiving electrode 22 and second
Sampler；The data sampler is processed as secondary signal for two receiving electrodes 22 to be collected into electric field signal respectively.Tool
Body, the present embodiment realizes signal generation apparatus and data sampler using the multi-function data acquisition card 10 of NI companies.
Meanwhile, in the present invention, control device 3 can be that all have signal, the controller of data-handling capacity, processing
Device, single-chip microcomputer or PC, control device 3 can by wired or wireless mode with signal generation apparatus and data sampling
Device is connected；And in the present embodiment, control device 3 is PC, meanwhile, PC is connected by data/address bus with multi-function data acquisition card 10
Connect, and as shown in figure 3, in multi-function data acquisition card 10 signal generator module and sampler module respectively by corresponding port with
Two emission electrodes 11, two receiving electrodes 22 are connected, specific as shown in Figure 3；During work, PC signal into multipotency capture card
Generator module sends the signal instruction of band parameter (signal type, signal amplitude, signal frequency etc.), signal generator module root
Detectable signal is produced according to instruction, Figure 11 gives the concrete structure block diagram of signal generator module in the present embodiment, detectable signal
Sent by emission electrode 11 to target acquisition region, the detectable signal can be any common periodic signal, such as square wave is believed
Number, triangular signal, sawtooth signal, pulse signal, sine wave signal, sine wave signal is used in the present embodiment, this be by
In if detectable signal uses nonperiodic signal, what it had been obtained after being deployed using Fourier transformation after detected, which is, one is
The superposition of the different periodic signal of row frequency, so as to cause signal frequency not fix；And the detection device of the invention provided or side
Method operationally requires that detectable signal has fixed detectable signal frequency, therefore detectable signal was required to using week in the present invention
Phase signal, Figure 12 is given when not having metal in region to be detected, after the device that the present embodiment is provided is detected, signal record
The signal waveform example of collection device record.
In the present embodiment, two emission electrodes 11, two receiving electrodes 22 are using same structure, materials, as it can be with
It is the metal electrode or graphite electrode of high conductivity；In the present embodiment, using Titanium silk as detection electrode (including transmitting electricity
Pole 11 and receiving electrode 22).The detection that can ensure to be input in emission electrode 11 using identical structure, the detection electrode of material
The change of signal, only electric charge or voltage influences the regular change that two electrodes of emitter stage are set up without other factors
The detection electric field of change.
Fig. 2 gives the flow chart of present apparatus operation, specifically, during transmission signal, signal generator module is used
Single-end output pattern, as shown in Figure 3, in two emission electrodes 11, a electrodes transmission detectable signal, b electrodes are used for undersea detection
Environment altogether, is realized with publicly for reference point with detection system；Two receiving electrodes 22 gather letter using Differential Input mode
Number, i.e., the electric field information under water detected is transferred to data sampler, data by two receiving electrodes 22 via two paths of signals line
The differential signal that sampler is sampled is potential and d electrode of the c electrodes relative to common ground reference point relative to common ground reference point
Potential between difference signal f (t), be using the advantage of differential signal：Degree of coupling between two signal wires of receiving pole
Very well, when there is interference signal in detection environment, it can almost be coupled to simultaneously in two lines, and receiving terminal (is exactly here
Finger is input to sampler and sampled) what is be concerned about is the difference of two signals, so extraneous interference signal can be offset.
When specifically used, emission electrode 11 and receiving electrode 22 should be fixed according to pre-determined distance and mode, such as at this
In embodiment, when detection electrode is fixed, distance is 10~90mm between two emission electrodes 11；Between two receiving electrodes 22
Distance is 5~80mm.Apart from 30mm between the emission electrode 11 and receiving electrode 22；During concrete application, between detection electrode
Distance can be adjusted according to factors such as volume sizes of specific detected metal, as long as specifically, due to testee place
Detection operations are can be carried out when in the detection electric field, but during actual detection, if it is possible to detected object is allowed in detection electricity
Internal electric field in (allow that piece electric field region of testee through two emitter stages when detecting, be subsequently passed through two
Between receiving electrode) detected, its Effect on Detecting more preferably because in entirely detection electric field in this region electric-field intensity compared with
Greatly, the density of its electric field line is of a relatively high, is more beneficial for collection of the receiving electrode to distortion electric field information under water, therefore either
The distance between two emission electrodes, or during the distance between two receiving electrodes are not steady state value, concrete application, two
The distance between electrode need to only ensure it is preferred that piece electric field that testee passes through between detection electrode can obtain optimal
Effect on Detecting.And emission electrode and the distance between receiving electrode are theoretically more near better, because closer to emission electrode, visiting
The electric field information arrived of regionally detecting of the data that receiving electrode is gathered during survey between use emission electrode, but it is actual
Electrode arrangement when with emission electrode too close on the contrary influence connect detection medium in distortion electric field information collection, thus set
Allow emission electrode with left between receiving electrode any distance (when the distance in instances is set to 30mm Effect on Detecting compared with
It is good).
On this basis, emission electrode 11 and receiving electrode 22 can be arranged on default fixed support 5, can also be by
According to the requirement of above-mentioned fixed range, it is arranged on other telecontrol equipments or ROV (motion module 4)；Control device 3 can lead to
Cross default instruction control telecontrol equipment or ROV run according to projected route, the route such as can be S1 in Fig. 7,
S2、S3；Wherein, it is effective search coverage 200 to be detected in metal 6 surrounding certain limit, as shown in fig. 7, when emission electrode 11,
When the running route of receiving electrode 22 passes through effective search coverage 200, such as route S2, S3 can then detect detected metal,
And when running route without can by search coverage 200 when, such as route S1, then its can not detect detected metal；When this dress
The relative position for putting each electrode is fixed, and is launched after the detectable signal of assigned frequency, does not have mesh when detecting in electric field region
During standard type, emission electrode 11 is parallel be distributed (as shown in Figure 5 a) with the Electric Field Distribution of the foundation between receiving electrode 22.Work as electricity
In the presence of having an objective body (detected metal) in, then emission electrode 11 with the foundation between receiving electrode 22 Electric Field Distribution by
To influence, specifically as shown in Figure 5 b；It should be noted that the distance of receiving electrode 22 and detected metal will influence receiving electrode 22
On the signal amplitude that detects, and the size of detected metal will also have influence on the distribution situation of this electric field, specifically, tested
Target object is larger by the amplitude formed in its peripheral region the region that changes, and the region of small volume is small.
When by effective search coverage 200, data sampler forms the differential signal collected progress discrete sampling
Secondary signal, and the secondary signal is transmitted to control device 3, control device 3 by the discrete data carry out Fourier transformation with
The signal amplitude value of each position on running route is obtained, amplitude versus time curve is formed, and according to the change of the signal amplitude value
Judge the corner frequency of the whether detected metal object of current demand signal frequency；If amplitude versus time curve exists as shown in Figure 8 a
Curve is protruded, then illustrates that current frequency is less than the corner frequency of detected metal, if amplitude versus time curve is as shown in Figure 8 b,
There is depression profile, then illustrate that current detectable signal frequency is higher than the corner frequency of detected metal, according to amplitude versus time curve
Detectable signal frequency is adjusted, is detected again according to original route, until amplitude versus time curve is a straight line, then it is current to visit
Measured frequency is the corner frequency of detected metal, and preset table is inquired about according to the volume size of detected metal, shape, draw by
Detect the material of metal.
Specifically, the conductance and size, shape and the detected metal of detected metal of detected conducting liquid 20
Material can all there is response to influence on corner frequency, still, constant in detected liquid conduction rate, detected metal size, shape
On the premise of shape is fixed, the corner frequency difference of the detected metal of unlike material substantially, therefore carries out material using this method
The accuracy rate of detection is higher.
Specifically, in order to study influence when detection medium has a different conductances to being tested metal corner frequency, we
Using the water of different conductances as experimental subjects, the influence to conductance to corner frequency is tested, with the cylinder of iron material matter
(size is body：Illustrated exemplified by 20mm*40mm)：It is about in fresh water (running water) electrical conductivity of usually detection test
400us/cm, the electrical conductivity of our water that random arrangement five groups gradually increases by way of iodizedsalt, is surveyed through conductivity meter
Obtain corresponding electrical conductivity and respectively may be about 400us/cm, 5400us/cm, 11000us/cm, 26000us/cm, 40800us/cm.This
In main explanation electrical conductivity when change detection obtain results change (change for being primarily upon corner frequency point).Pass through
In the case that other experimental situation conditions are the same (environment during all with electrical conductivity for 400us/cm is consistent), the electrical conductivity of water is controlled
Change, have in media environment in the case of different electrical conductivity we obtain table 1 such as experimental result.It can be seen that different
Conductivity environments in it is different to the corresponding frequency turning point of the active electric-fields of 20mmx40mm cylindrical iron bodies detection experiment, and
Show also therewith to increase with the corresponding frequency turning point of increase of the electrical conductivity of water, it is specific as shown in figure 15.Therefore, water is being done
, it is necessary to note conductance (the usual fresh water environment of the medium residing for testee at that time during the material differentiation of lower metallic conductor
Electrical conductivity is about that the example in 400us/cm, therefore this patent illustrates to illustrate with the test data under this environment substantially,
Test philosophy under the different media environment of other electrical conductivity is also all consistent).It should be noted that we are with active electric-field experimental ring
The electrical conductivity of border reclaimed water changes, the electric field information changes in distribution received to the active electric-field detection experiment receiving electrode 22 of conductor
Trend can have an impact, can be with the electricity of experimental situation reclaimed water specifically, detecting corresponding frequency turning point to conductor active electric-field
Conductance increases and increased, however, how the size of the electrical conductivity of experimental situation reclaimed water changes, the active electric-field of conductor is detected
During " bumps " phenomenon and corresponding frequency turning point occurs.
Table 1
Figure 10 is given in the present embodiment, the Booting sequence of multi-function data acquisition card 10, specifically, control device 3 is selected first
The model output channel of multi-function data acquisition card 10 (also known as data collecting card) is selected, and then selects required detectable signal type
(such as sine wave), calls built-in function to produce the control signal of required waveform, the fluted mould of control signal generator 12 as needed
Block exports desired signal；Specifically, the instruction that control device 3 is sent to signal generator 12 include superposition/single signal, partially
One or more of shifting amount, signal type, assigned frequency, amplitude, duty cycle square wave, frequency multiple.And Fig. 9 then gives spy
Survey the exemplary plot in device orientation when being detected, as seen from Figure 9, the present apparatus when in use, Ke Yishi, only by detection electrode
(including emission electrode 11 and receiving electrode 22) is put into water after being fixed by specific fixed support 5 according to pre-determined distance
Detected, and connected between detection electrode and multi-function data acquisition card 10 by signal transmssion line 7.
Embodiment 2：The present embodiment offer is a kind of can to detect the metal object detection side of metal material in conducting liquid
Method, specifically, comprising the following steps：
Step 1：Launch the first signal to target acquisition region according to assigned frequency and set up detection electric field；The assigned frequency can
To be the frequency being arbitrarily designated, as long as containing the transition frequency range of common metal to be detected, therefore, this reality in theory
Apply in example, assigned frequency is 0Hz~2000Hz；This is due to that (such as size is 20mm*40mm left to common micro metal object
Right metal object) when doing detection experiment, all metal object corner frequencies well below this frequency values of 2000HZ, so I
Have selected the frequency of this sections of 0HZ -2000HZ.In fact, as shown in table 2, corresponding volume is in 12cm3The irony material of left and right
Expect for cylinder, its corner frequency is in 5Hz or so, and so, the corner frequency in the range of 0Hz~10Hz can just be detected in fact
Go out volume in 12cm3The ferrous material cylinder of left and right.
Step 2：Emission electrode 11 and receiving electrode 22 are moved according to fixed route, from detection electric field collection electric field signal；
Specifically, gathering the electric field signal of the detection electric field respectively using at least two receiving electrodes 22, and obtain two electric field letters
Number differential signal.Data sampler carries out sampling processing to differential signal f (t) and obtains sampled signal fm(n), wherein, m is
M sampling, n is the centrifugal pump of the run duration t in sampling time section；
Step 3：According to the signal amplitude value of the electric field signal acquisition collected not in the same time, and it is bent to form amplitude versus time
Line；Specifically, Fourier transformation is carried out to the differential signal, to obtain the signal amplitude value.
Specifically, sampling window 100 is set, to the detectable signal f in sampling window 100m(n) Fourier transformation is carried out,
Its Fourier transform function is：
Calculate the range value F after Fourier transformationm(k) detection signal frequency used when, with reference to time n and the sampling of sampling
Rate f, and draw out the distribution spectrogram of the time-frequency combination as shown in Fig. 8 a, Fig. 8 b, Figure 16, Figure 17, Figure 18.Specifically use joint time-frequency
By way of analysis method, energy density of this method when signal is presented in different time and specific frequency, description signal frequency
The situation that rate is changed over time.The main thought for the Short Time Fourier Transform (STFT) mainly used in joint time frequency analysis method
It is when carrying out make it that it is changed into very little after Fourier transformation, windowed function again by the signal after windowed function by signal windowed function
Between on local spectra, window function can be translated on whole time shaft according to the change of time, can be realized using window function
Period frequency spectrum near to optional position realizes that the time localizes, specifically as shown in Figure 4 in Fu in short-term of discrete signal
Leaf transformation (STFT) Transformation Graphs.
According to Short Time Fourier Transform (STFT), we by sliding window to suitable time point and can calculate new
Frequency spectrum set up a complete three-dimensional joint time-frequency spectrogram.In three-dimensional joint time-frequency spectrogram, what X-axis was represented is excitation letter
Number frequency its unit hertz (Hz), Y-axis represents is that its unit of time of the single detection process operation of positioner is the second
(s) what, Z axis was represented be after Fourier transformation amplitude peak (FFT Amplitude Peak abbreviation FAP) size with color color
It has been shown that, its unit is volt (V).Signal after Fourier transformation after amplitude peak size (FAP) and windowed function is in time domain
Point quantity it is relevant.Amplitude peak size (FAP) after Fourier transformation can be calculated with following formula：
Real [FFT (A)] and Imag [FFT (A)] represent the real and imaginary parts of the signal data after Fourier transformation respectively,
N represents the size of input signal.
And in certain limit be effective scope of detection 200 generally around it for object to be detected, as shown in fig. 7,
In certain limit near detected metal 6, such as scope is probably 30cm*30cm*30cm three-dimensional sense, it is also possible to its
His Typical ranges, the specific size of the effective scope of detection 200 is unimportant, this is because, when detection electrode (including transmitting
Electrode 11, receiving electrode 22) mobile route as route S1 not in effective scope of detection 200 when, detecting electric field will not
Occur disturbed phenomenon, at this moment any change will not occur for detectable signal, and only detection electrode movement route such as route S2 and
When as route S3 by effective scope of detection 200, detectable signal just can produce interference due to detected metal to detection electric field, enter
And the range value of detectable signal is impacted；Specifically, respectively with an equal amount of cylindrical aluminium metal and cylindrical, copper gold
Exemplified by category, we are acquired under the detectable signal of 100Hz frequencies, uniformly in the range of detected metallic perimeter 30cm*30cm
400 discrete datas, specifically as shown in Fig. 6 a, Fig. 6 b, the Z axis in figure is expressed as signal at the collection point and passes through Fourier transformation
Range value afterwards, unit is V；The data points for the direction that x, y-axis are represented.Amplitude peak or minimum point are exactly thing in figure
(when look-in frequency is more than the corner frequency of object, minimum point is the central point of object, conversely, then peak for the center of body
For the central point of object).Wherein Fig. 6 a are the detectable signal amplitudes of cylindrical aluminium metal, and Fig. 6 b believe for cylindrical, copper metal detection
Number range value, it is found that on the premise of detectable signal frequency is not the tested corner frequency of metal 6, detection electrode is by having
When imitating search coverage 200, no matter whether route by the tested place center of metal 6, its amplitude be bound to occur upwards or
The change of person downwards, the testing result of single route can be as shown in figure 13, and signal record collection device preserves data
As shown in figure 14.And during actual detection, amplitude is upward or is bent downwardly, it is more than detected metal with the frequency of detectable signal
Corner frequency be also less than that corner frequency is directly related, thus, this method also has step 4, specifically.
Step 4：Judged according to the amplitude versus time curve as shown in Fig. 8 a, Fig. 8 b, adjust or maintain the specified frequency
Rate, to obtain the corner frequency of metal to be detected, specifically, judging amplitude versus time curve, if amplitude versus time is bent
Range value includes protrusion curve 400 in line, then illustrates that the assigned frequency of current detectable signal is less than the turnover frequency of detected metal
Rate, now, increases the assigned frequency certain numerical value, and re-start step 1~step 3；If, in amplitude versus time curve
Range value includes depression profile, then illustrates that currently assigned frequency is more than corner frequency, now, reduces the fixed number of assigned frequency one
Value, and re-start step 1~step 3；If amplitude versus time curve, which becomes, to be in line, then now the assigned frequency is to wait to visit
Survey the corner frequency of metal；And then metal material is judged according to the corner frequency.Certainly, in some cases, amplitude versus time is bent
Line is that straight line is also likely to be that running route does not enter into effective search coverage, therefore, during actual detection, should at least ensure the route
Under, occur once protruding curve 400 or a depression profile 500 occur, and then just can prove that current detection route is by having
Imitate search coverage.
The principle that this method can detect different metal materials is：Different types of underwater hardware body ac-excited
The lower complicated impedance operator of its display is different, and then different in disturbance electric field generation electrical potential difference, specifically, in detection electric field, quilt
Electric field perturbations can be caused due to direct impedance characteristic by surveying the object of metal 6 under water, and different metal materials can be because impedance
The difference of characteristic, causes different electric field perturbations, the trend changed by electrical potential difference in detection electric field, it is determined that detected gold
The corner frequency value of category, and then acquisition metal material can be compared；Under this principle, even if the tested object volume very little of metal 6,
As long as its material is different, then the corner frequency value detected is also just different, so that according to the difference of this corner frequency value come area
Divide the material of the tested object of metal 6, meanwhile, shown according to substantial amounts of metal object test result, volume is approximate, material is different
Metal object corner frequency gap clearly, judges that metal object material accuracy rate is higher using this method.
Figure 16 is the joint time-frequency spectrogram that testee aluminium cylinder is obtained using different look-in frequencies in one direction,
X-axis represents frequency (Hz) in figure, and Y-axis represents the time (S), and Z axis represents the amplitude peak after FFT, and unit is volt (V).
Its corresponding look-in frequency is respectively 50Hz, 150Hz, 170Hz, when look-in frequency is less than corner frequency 150Hz time-frequency spectrums
In show as the phenomenon of " convex ", that is, there is protrusion curve 400, be now expressed as detection electrode by away from testee to connecing
Its amplitude gradually increases during nearly object is crossed, and when electrode is in directly over object, its amplitude reaches maximum.Then in detection
Its amplitude is tapered into again when electrode is gradually distance from object.For obtaining situation less than this turnover frequency value 150HZ, look-in frequency is got over
Small, its " convex " shows the more obvious of performance.When look-in frequency for more than this value when show as " it is recessed " and phenomenon, that is, go out
Existing depression profile 500, and look-in frequency bigger " recessed " shows also more obvious.In the joint that repeatedly adjustment look-in frequency is obtained
In spectrogram, when frequency is 150Hz, the performance of its FFT amplitude occurs in constant value phenomenon, i.e. figure, and amplitude is straight line 600, is now said
The corner frequency of the bright cylinder is near 150Hz.And Figure 17, Figure 18 then sets forth cylindrical iron body, bronze cylinders and adopt
The joint time-frequency spectrogram obtained with different look-in frequencies, table 2 then gives turning under common different metal materials different shape
Roll over frequency values.
Table 2
Claims (10)
1. a kind of metal object detection device, it is characterised in that including,
Emitter, including at least two emission electrodes, one of emission electrode ground connection；The emitter is used for target
First signal of the search coverage transmitting with assigned frequency, so as to set up detection electric field in target acquisition region；
Reception device, including receiving electrode, the reception device are used to gather electric field signal from the detection electric field, and should
Electric field signal is processed as after secondary signal being sent to control device, and the secondary signal received is processed as by the control device can
To characterize the 3rd signal of different metal materials.
2. metal object detection device as claimed in claim 1, it is characterised in that the emitter also includes and the hair
The signal generation apparatus of radio pole connection；The signal generation apparatus is used to produce assigned frequency according to the instruction of control device
Signal.
3. metal object detection device as claimed in claim 1, it is characterised in that the reception device includes first and receives electricity
Pole and the second receiving electrode, in addition to the data sampler connected simultaneously with first receiving electrode and the second receiving electrode；
The data sampler is processed as secondary signal for two receiving electrodes to be collected into electric field signal respectively.
4. metal object detection device as claimed in claim 1, it is characterised in that the emission electrode is two, two hairs
Distance is 10 ~ 90mm between radio pole；
The receiving electrode is two, and the distance between two receiving electrodes are 5 ~ 80mm；
At least apart from 5mm between the emission electrode and receiving electrode.
5. a kind of metal object detection method, it is characterised in that comprise the following steps：
Step 1：Launch the first signal to target acquisition region according to assigned frequency and set up detection electric field；
Step 2：Emission electrode and receiving electrode are moved according to fixed route, from detection electric field collection electric field signal；
Step 3：According to the signal amplitude value of the electric field signal acquisition collected not in the same time, and form amplitude versus time curve；
Step 4：Judged according to amplitude versus time curve, adjust or maintain the assigned frequency, to obtain metal to be detected
Corner frequency, and then metal material is judged according to the corner frequency.
6. metal object detection method as claimed in claim 5, it is characterised in that the step of electric field signal is gathered from detection electric field
In rapid,
Gather the electric field signal of the detection electric field respectively using at least two receiving electrodes, and obtain the difference of two electric field signals
Sub-signal.
7. metal object detection method as claimed in claim 6, it is characterised in that obtained not according to the electric field signal collected
In signal amplitude value in the same time, Fourier transformation is carried out to the differential signal, to obtain the signal amplitude value.
8. metal object detection method as claimed in claim 5, it is characterised in that judged according to amplitude versus time curve,
Adjust or maintain the assigned frequency, the step of corner frequency to obtain metal to be detected in,
Amplitude versus time curve is judged, if range value includes protrusion curve in amplitude versus time curve, then increases described
Assigned frequency certain numerical value, and re-start step 1 ~ step 3.
9. metal object detection method as claimed in claim 5, it is characterised in that judged according to amplitude versus time curve,
Adjust or maintain the assigned frequency, the step of corner frequency to obtain metal to be detected in, if, amplitude versus time curve
Middle range value includes depression profile, then reduces the assigned frequency certain numerical value, and re-start step 1 ~ step 3.
10. metal object detection method as claimed in claim 5, it is characterised in that sentenced according to amplitude versus time curve
It is disconnected, adjust or maintain the assigned frequency, the step of corner frequency to obtain metal to be detected in, if amplitude versus time is bent
Line is straight line, then now the assigned frequency is the corner frequency of metal to be detected.
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| CN112596108A (en) * | 2020-11-24 | 2021-04-02 | 中国地质科学院地球物理地球化学勘查研究所 | AMT (automated mechanical Transmission) profile detection method, device and equipment |
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