CN107765316B - Cable path detection multi-frequency emission system and method and cable path detection instrument - Google Patents
Cable path detection multi-frequency emission system and method and cable path detection instrument Download PDFInfo
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- CN107765316B CN107765316B CN201710875457.0A CN201710875457A CN107765316B CN 107765316 B CN107765316 B CN 107765316B CN 201710875457 A CN201710875457 A CN 201710875457A CN 107765316 B CN107765316 B CN 107765316B
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- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
- G01V3/101—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil
Abstract
The invention belongs to the technical field of cable path detection, and discloses a multi-frequency transmission system and method for cable path detection and a cable path detection instrument, which can simultaneously realize the transmission of a plurality of frequency signals; a source coil is added in the resonance transmitting coil, and the current is amplified step by utilizing the coupling relation between the resonance transmitting coil and the source coil; each resonant transmitting module is a resonant cavity formed by an inductance coil and a capacitor, different inductance and capacitance correspond to different resonant frequencies, and when the source coil transmits a multi-frequency signal, different resonant transmitting coils can work under the corresponding resonant frequencies to realize the transmission of a resonant point frequency signal; and the plurality of frequency signals transmitted by the plurality of resonance coils are vector-added in space, so that the propagation of the magnetic fields of the plurality of frequency signals in space is realized. The invention is suitable for various field complex conditions, and the signal generator does not need to be adjusted when the signal frequency is selected, thereby greatly improving the efficiency; the cable may be detected without touching the cable or while the cable is running.
Description
Technical Field
The invention belongs to the technical field of cable path detection, and particularly relates to a cable path detection multi-frequency emission system and method and a cable path detection instrument.
Background
At present, power cable transmission and distribution lines are adopted in urban and rural power grids in China in large quantity, but with social development, power grid transformation, cable relocation and fault cable restoration, original landforms and underground cables are changed greatly, original drawings cannot reflect laying paths and burial depths of the cables correctly, and detection of cable paths and identification of the cables become an extremely important link in cable maintenance work. If the cable path cannot be defined, the incidence rate of accidents of damaging the power supply cable during engineering construction is increased; the fault point of the cable cannot be searched without knowing the specific trend of the cable, so that the rush repair speed and the power supply recovery time are influenced. Therefore, the development of the intelligent cable path detection system has very important social and economic benefits. The signal transmitting system of the cable path detector is very important in the detection of the cable path, and the selection of transmitting signals with different frequencies has great influence on the detection effect. When the frequency transmitted by the transmitter is higher, the iron pipe with the insulating layer at the pipeline joint has a better detection effect, but the signal attenuation is faster, the propagation distance is closer, and the iron pipe is easy to sense on the adjacent pipelines, so that the adjacent pipelines are not distinguished; on the contrary, when the frequency transmitted by the transmitter is lower, the signal attenuation is slow, the detection distance is large, and the signal is not easy to be induced on the adjacent pipelines, which is beneficial to distinguishing the adjacent pipelines, but when the conductivity of the pipelines is poor or the joints are provided with insulating layers, the signal is not easy to be transmitted, and the effect is poor. Early cable path instrumentation stayed predominantly on single frequency probes due to microprocessor performance limitations. The traditional signal transmitting unit consists of a crystal oscillator, a modulation circuit, a transmitting output and the like, and the design of the transmitter of the underground metal pipeline detecting instrument with selectable frequency is that the transmitting unit is designed in a mode of winding a transmitting coil, selecting a matching capacitor according to the working frequency of the instrument and transmitting electromagnetic waves in a resonant mode, so that the measurement of only one fixed frequency can be completed at one time. And the single chip microcomputer is also needed to control the relay to gate the corresponding resonance capacitor, so that the transmitting coil and the resonance capacitor are in a series resonance state, the single chip microcomputer enables the corresponding normally open end of the relay to be attracted, and the capacitor connected with the normally open end and the transmitting coil are connected in series to form a series circuit. The output current of the I/O port of the singlechip is too small to drive the relay, so a triode is required to be added for driving, and a freewheeling diode is added for protecting the relay. As shown in the analysis, the cable path detection transmitting system has a complex circuit, can only realize the transmission of one frequency at a time, has different geological environments where pipelines are located during actual measurement, and needs to manually switch the transmitting frequency for many times when it is unclear which frequency is more suitable for a target pipeline, so that the operation is complicated, and the efficiency is low. A multi-frequency array electric logging resonant emission system is mainly used for obtaining resistivity or dielectric constant information of a stratum and further combining other stratum parameters to calculate and judge oil and gas saturation and distribution conditions of a reservoir. This patent discloses a multi-frequency transmission system, which adopts a time-sharing transmission multi-frequency signal mode. Each transmitting coil in the transmitting coil system works in turn to transmit signals according to the corresponding transmitting frequency, the switching of the coils is controlled by the high-frequency electric control switch assembly to select the currently working transmitting coil, each coil transmits for a period of time, and then the coils are switched to other coils to continue working. Taking 6 kinds of working frequencies as an example, the high-frequency electric control switches G1-G6 control the transmitting coils T1-T6 and the matching capacitors M1-M6 corresponding to the transmitting coils to determine the working state of each path of transmitting coil and matching capacitor. The on-off states of G1-G6 are controlled by a transmitting load control unit of the FPGA main control unit, so that the transmitting coils which participate in the work at present are controlled. Each coil corresponds to a transmitting frequency, the transmitting coil works in a resonance state, participates in resonance as one of resonance loops, and works by realizing the resonance state with the matching capacitor. Although the multi-frequency transmitting system can work in a plurality of frequency states in the same operation time, a plurality of frequency signals are not transmitted at the same time, the transmitting frequency is switched by programming control wheel flow, and a receiver also needs to synchronously receive magnetic field signals, so that the operation implementation structure is complex, the requirement on the control signal time sequence is high, and the realization is difficult.
In summary, the problems of the prior art are as follows: the existing cable path detection method has the defects that a transmitting system circuit is complex, only one frequency can be transmitted at one time, the transmitting frequency needs to be manually switched for many times, the operation is complicated, and the efficiency is low; the multi-frequency transmission system cannot transmit a plurality of frequency signals at the same time, and the operation is complex and difficult to implement.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a cable path detection multi-frequency transmission system and method and a cable path detection instrument.
The cable path detection multi-frequency transmission method can simultaneously realize the transmission of a plurality of frequency signals; the transmitting coil is designed as a resonant transmitting coil, a source coil is added in the resonant transmitting coil, the current is amplified step by utilizing the coupling relation between the resonant transmitting coil and the source coil, and a driving source is utilized to provide smaller current for the source so as to generate larger current gain in the resonant transmitting coil; each resonant transmitting module is a resonant cavity formed by an inductance coil and a capacitor, different inductance and capacitance correspond to different resonant frequencies, and when the source coil transmits a multi-frequency signal, different resonant transmitting coils can work under the corresponding resonant frequencies to realize the transmission of a resonant point frequency signal; and the plurality of frequency signals transmitted by the plurality of resonance coils are vector-added in space, so that the propagation of the magnetic fields of the plurality of frequency signals in space is realized.
Further, the resonance transmitting coil amplifies the current of the source coil step by step, and the current I of the source coil1Induced electromotive force is generated in the resonant transmitting coil, and the voltage balance equation is as follows:
in the formula (I), the compound is shown in the specification,
is mutual inductance; a is a proportionality coefficient of current amplification; and omega is the system working frequency. When the resonant cavity works in a resonant state, the amplification of source-level current is realized, and the emission of signals is realized; in the non-resonant state, the system is detuned, no amplification is generated, and no signal is transmitted.
Further, the source coil and the resonance transmitting coil are both coils containing magnetic cores, and the inductance calculation formula is as follows:
wherein: n is the number of turns of the coil, mu0Is a vacuum permeability, mucFor practical permeability, AcIs the cross-sectional area of the core, l is the length of the coil, lcIs the length of the core;
the actual permeability correlation formula of the cylindrical core:
wherein mucTo a practical permeability, murEffective permeability, and N is a demagnetization coefficient;
wherein DcIs the diameter of the magnetic core, /)cIs the length of the core.
Another object of the present invention is to provide a cable path detection multi-frequency transmission system of the cable path detection multi-frequency transmission method, the cable path detection multi-frequency transmission system comprising:
the ARM microprocessor is connected with the input end of the waveform generation module and is used for programming and controlling the waveform generation module to generate a required frequency signal;
the ARM microprocessor is used for programming and controlling the waveform generation module to generate required frequency and waveform signals;
the waveform generation module is connected with an SPI bus of the ARM microprocessor and used for generating modulation waves and carrier signals required by PWM modulation;
the PWM module is connected with the output end of the waveform generation module and is used for comparing and outputting the modulation wave and the carrier wave, and the output waveform is a series of square waves with different duty ratios;
the power amplification module is connected with the output end of the PWM module and is used for amplifying the PWM signal output by the PWM module;
the L C low-pass filter circuit is connected with the output of the power amplification module and is used for demodulating the amplified PWM signal, filtering the high-frequency carrier signal and restoring a modulation wave;
the source coil is connected with the output end of the L C low-pass filter circuit and is used for generating current in the source coil;
the resonance transmitting module is connected with the source coil in a magnetic field coupling mode and comprises a resonance transmitting coil and a resonance matching capacitor, the source coil and the resonance transmitting coil are wound on the same magnetic core, the source coil is arranged in the middle, and the resonance transmitting coils are respectively arranged on two sides of the source coil.
Further, the cable path detection multi-frequency emission system emits sine wave signals with any frequency point of 10 kHz-200 kHz.
Further, the resonance transmitting module is an independent resonance loop, the resonance loop comprises a resonance transmitting coil and a resonance matching capacitor, and the resonance transmitting coil works in a resonance state;
the resonant transmission frequency of the resonant circuit is determined by the inductance of the inductance coil and the capacitance of the matching capacitor.
Furthermore, the source coil and the resonance transmitting coil are wound on the same magnetic core, and the magnetic core is made of manganese-zinc ferrite.
Another object of the present invention is to provide a cable path detecting apparatus using the cable path detecting multi-frequency transmission method.
The invention has the advantages that the resonance transmitting coil is adopted to transmit signals, the resonance transmitting coil and the matching capacitor are in a resonance state, the impedance of a resonance loop is minimized, and high-power transmission can be realized, for example, when 10kHz and only a source level transmitting coil exists, a receiver receives a magnetic field signal and carries out fast Fourier transform to obtain the amplitude value of 2.5 × 10 of 10kHz in a frequency spectrum7After the resonant transmitting coil is added, the receiver receives the magnetic field signal and carries out fast Fourier transform to obtain the amplitude value of 1.8 × 10 of 10kHz in the frequency spectrum8(ii) a And can use multiple initiative detection frequency simultaneously, be suitable for multiple on-the-spot complicated situation, need not adjust signal generator when selecting signal frequency, when not knowing which kind of frequency is more suitable for the target pipeline, adopt prior art, need adjust signal generator many times, changeThe transmission frequency is changed until the frequency suitable for the target pipeline is found, and the multi-frequency transmission system can transmit three frequency signals at most simultaneously, so that the efficiency is improved by two to three times compared with the prior art; the cable may be detected without touching the cable or while the cable is running.
Drawings
Fig. 1 is a schematic structural diagram of a cable path detection multi-frequency transmission system provided in an embodiment of the present invention;
FIG. 2 is a schematic diagram of a source coil and resonant coil mutual inductance coupling model provided by an embodiment of the invention;
FIG. 3 is a schematic structural diagram of a source coil and a resonant coil provided in an embodiment of the present invention;
in the figure: 1. an ARM microprocessor; 2. a waveform generation module; 3. a PWM modulation module; 4. a power amplification module; 5. a low-pass filtering module; 6. a source coil; 7. a resonant transmission module; 8. a cylindrical magnetic core.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The multi-frequency cable path detection and transmission system and the method are simple to operate and can transmit multiple frequencies simultaneously.
The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.
As shown in fig. 1, a cable path detection multi-frequency transmission system provided by an embodiment of the present invention includes: the device comprises an ARM microprocessor 1, a waveform generation module 2, a PWM (pulse-width modulation) module 3, a power amplification module 4, a low-pass filtering module 5, a source coil 6 and a resonance transmitting module 7.
The ARM microprocessor 1 is used for programming and controlling the waveform generation module to generate required frequency and waveform signals;
the waveform generation module 2 is connected with an SPI bus of the ARM microprocessor 1 and used for generating modulation waves and carrier signals required by PWM modulation;
the PWM module 3 is connected with the output end of the waveform generation module 2 and used for comparing and outputting the modulation wave and the carrier wave, and the output waveform is a series of square waves with different duty ratios;
the power amplification module 4 is connected with the output end of the PWM module 3 and is used for amplifying the PWM signal output by the PWM module;
l C low-pass filter circuit 5 connected with the output of power amplification module 4 for demodulating amplified PWM signal, filtering high-frequency carrier signal, and restoring modulated wave;
a source coil 6 connected to an output terminal of the L C low-pass filter circuit 5 for generating a current in the source coil;
and the resonance transmitting module 7 is in magnetic field coupling connection with the source coil 6 and comprises a resonance transmitting coil and a resonance matching capacitor, the source coil and the resonance transmitting coil are wound on the same magnetic core, the source coil is arranged in the middle, and the resonance transmitting coils are respectively arranged on two sides of the source coil.
In a preferred embodiment of the invention: the waveform generation module 2 is realized based on an ARM microprocessor and a direct digital frequency synthesis technology DDS, and the specific realization method is as follows: the waveform generator selected by the DDS digital frequency synthesis technology is AD9833, the ARM microprocessor is connected with the AD9833 and communicates with the AD9833 through the SPI, the ARM microprocessor compiles a corresponding program and sends frequency information, phase information and control information to the AD9833 so as to control the AD9833 to generate a required frequency signal; the AD9833 device has 4 devices, and generates signals with different frequencies respectively. The output frequency of the AD9833 is given by equation (1):
fout＝FREQREG×fMCLK/228(1)
in the formula (f)outTo output frequency, fMCLKFor the system reference clock frequency, take fMCLKFREQREG is the input frequency control word at 25 MHz. And respectively calculating corresponding frequency control words according to different frequency signals, and outputting the required frequency signals through software programming.
The mutual inductance coupling model of the source coil 6 and the resonant coil is shown in FIG. 2, and FIG. 2 shows the source coil 6 and the resonant transmitting coilMutual inductive coupling model, wherein VsIs an equivalent signal source at the output of the low pass filter module, L1、L2Self-inductance of the source and transmitter coils, L1、L2Has a coupling coefficient of k12。C2And a transmitting stage coil L2Forming a tuned loop having a resonant frequency, r1、r2Respectively the coil internal resistances. The schematic diagram shows only one resonant transmitting module, and a plurality of resonant transmitting modules are similar to the resonant transmitting module, and a plurality of resonant transmitting modules can be added on the secondary side.
The invention can realize the emission of a plurality of frequency signals simultaneously, designs the emitting coil as a resonance emitting coil, adds a source coil in the emitting coil, realizes the gradual amplification of current by utilizing the coupling relation between the emitting coil and the source coil, can provide a smaller current for the source by utilizing a driving source, can generate larger current gain in the resonance emitting coil, and improves the energy transmission power. Each resonant transmitting coil is a resonant cavity formed by an inductance coil and a capacitor, different inductance and capacitance correspond to different resonant frequencies, when the source coil transmits a multi-frequency signal, different resonant transmitting coils can work under the corresponding resonant frequency to transmit the frequency signal, and a plurality of frequency signals transmitted by the plurality of resonant coils are added in a space vector mode to realize the transmission of a plurality of frequency signal magnetic fields in the space.
As shown in fig. 2, the source current I1Induced electromotive force is generated in the resonant transmitting coil, and the voltage balance equation is shown in the formulas (2) and (3):
in the formula (I), the compound is shown in the specification,
is mutual inductance; a is a proportionality coefficient of current amplification; and omega is the system working frequency.
The resonant circuit is a resonant cavity consisting of a resonant transmitting coil and a resonant matching capacitor, and when the resonant cavity works in a resonant state, the amplification of source-level current can be realized, the transmission of signals is realized, and the magnetic field enhancement function of the system is realized; in the non-resonant state, the system is detuned, no amplification is generated, and no signal is transmitted.
Fig. 3 shows a schematic structural diagram of the source coil 6 and the resonant coil, and fig. 3 shows a schematic structural diagram of the source coil 6 and the resonant transmitting module. The source coil 6 and the resonance transmitting coil are wound on the same magnetic core, the source coil 6 is arranged in the middle, and the resonance transmitting coils are respectively arranged on two sides of the source coil. 1 is a cylindrical magnetic core, 2 is a source coil, and is connected with the output end of the low-pass filtering module; and 3 and 4 are resonance transmitting modules, which are composed of resonance transmitting coils and resonance matching capacitors and respectively correspond to different resonance frequencies so as to correspond to different signal transmitting frequencies. The resonant emission frequency is:
where f is the resonant frequency, L is the resonant transmit coil inductance, and C is the matching capacitance.
The coil adopts a mode of closely winding a ring cylinder, the source coil and the resonance transmitting coil are wound on the same magnetic core, and the magnetic core is made of manganese-zinc ferrite. The magnetic core is added into the hollow area of the coil framework, so that the intensity of the emission magnetic field can be obviously increased. The magnetic core is a cylindrical magnetic core, and the outer diameter of the magnetic core is consistent with the inner diameter of the coil. The coil adopts a sectional winding method, so that the influence of distributed capacitance on the performance of the coil is reduced.
The inductance value calculation formula of the coil with the magnetic core is as follows:
wherein: n is the number of turns of the coil, mu0Is a vacuum permeability, mucFor practical permeability, AcIs the cross-sectional area of the core, l is the length of the coil, lcIs the length of the core.
The actual permeability of the core is much less than the effective permeability of the core material. This is related to the demagnetization factor, which is related to the geometry of the core. The actual permeability of the cylindrical core is related by the following formula:
wherein mucTo a practical permeability, murEffective permeability, and N is a demagnetization coefficient;
wherein DcIs the diameter of the magnetic core, /)cIs the length of the core.
And the effective permeability of the magnetic core is different according to the position of the magnetic core, so that the inductance value of the coil is in direct proportion to the effective permeability of the position of the magnetic core. If the width of the coil is wide, the inductance is proportional to the average value of the actual magnetic permeability of the magnetic core within the width of the coil. Along with the change of the position from the center of the magnetic core, the actual magnetic conductivity is decreased according to a certain rule. Therefore, when winding the coil on the bobbin, the coil winding should be wound at the center of the core.
The transmitter transmits a sine wave signal, and the proximity effect and the skin effect cause the AC resistance to increase, so that the proper coil wire size needs to be selected according to the Dowell curve. The Dowlell curve represents a sinusoidal current excitation FR(ac/dc resistance) with Q (effective wire thickness/skin depth) and the number of layers p. The wire dimensions are typically selected so that
The right and left are the best.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (3)
1. A cable path detection multi-frequency transmission method is characterized in that the cable path detection multi-frequency transmission method can simultaneously realize the transmission of a plurality of frequency signals; a source coil is added in the resonance transmitting coil, and the current is amplified step by utilizing the coupling relation between the resonance transmitting coil and the source coil; each resonant transmitting module is a resonant cavity formed by an inductance coil and a capacitor, different inductance and capacitance correspond to different resonant frequencies, and when the source coil transmits a multi-frequency signal, different resonant transmitting coils can work under the corresponding resonant frequencies to realize the transmission of a resonant point frequency signal; the multiple frequency signals transmitted by the multiple resonance coils are vector-added in space, so that the propagation of the magnetic fields of the multiple frequency signals in space is realized;
the resonance transmitting coil amplifies the current of the source coil step by step, and the current of the source coil I1Induced electromotive force is generated in the resonant transmitting coil, and the voltage balance equation is as follows:
in the formula (I), the compound is shown in the specification,
is mutual inductance; a is a proportionality coefficient of current amplification; omega is the system working frequency; when the resonant cavity works in a resonant state, the amplification of source-level current is realized, and the emission of signals is realized; in a non-resonant state, the system is detuned, amplification cannot be generated, and signals are not transmitted;
the source coil and the resonance transmitting coil are both coils containing magnetic cores, and the inductance calculation formula is as follows:
wherein: n is the number of turns of the coil, mu0Is a vacuum permeability, mucFor practical permeability, AcIs the cross-sectional area of the core, l is the length of the coil, lcIs the length of the core;
the actual permeability correlation formula of the cylindrical core:
wherein mucTo a practical permeability, murEffective permeability, and N is a demagnetization coefficient;
wherein DcIs the diameter of the magnetic core, /)cIs the length of the core;
the cable path detection multi-frequency transmission system includes:
the ARM microprocessor is used for programming and controlling the waveform generation module to generate required frequency and waveform signals;
the waveform generation module is connected with the ARM microprocessor through an SPI bus and used for generating modulation waves and carrier signals required by PWM modulation;
the PWM module is connected with the output end of the waveform generation module and is used for comparing and outputting the modulation wave and the carrier wave, and the output waveform is a series of square waves with different duty ratios;
the power amplification module is connected with the output end of the PWM module and is used for amplifying the PWM signal output by the PWM module;
the L C low-pass filter circuit is connected with the output of the power amplification module and is used for demodulating the amplified PWM signal, filtering the high-frequency carrier signal and restoring a modulation wave;
the source coil is connected with the output end of the L C low-pass filter circuit and is used for generating current in the source coil;
the resonant transmitting module is in magnetic field coupling connection with the source coil and comprises a resonant transmitting coil and a resonant matching capacitor, the source coil and the resonant transmitting coil are wound on the same magnetic core, the source coil is arranged in the middle, and the resonant transmitting coils are respectively arranged on two sides of the source coil;
the cable path detection multi-frequency emission system emits sine wave signals with any frequency point of 10 kHz-200 kHz.
2. The cable path detection multi-frequency transmission method as claimed in claim 1, wherein said resonant transmission module is a separate resonant tank, said resonant tank including a resonant transmission coil and a resonant matching capacitor, said resonant transmission coil operating in a resonant state;
the resonant transmission frequency of the resonant circuit is determined by the inductance of the inductance coil and the capacitance of the matching capacitor.
3. The method of claim 1, wherein the source coil and the resonant transmitting coil are wound on a same core, and the core is made of Mn-Zn ferrite.
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| CN1961222A (en) * | 2004-06-04 | 2007-05-09 | 安立产业机械株式会社 | Metal detection device |
| CN102520452A (en) * | 2011-11-23 | 2012-06-27 | 刘德军 | Inductance type metal detector |
| CN103412340A (en) * | 2013-08-29 | 2013-11-27 | 高玉琴 | Metal detector |
| CN104297805A (en) * | 2014-11-07 | 2015-01-21 | 吴建堂 | Metal detection device |
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| KR102458770B1 (en) * | 2015-07-17 | 2022-10-26 | 한국전자통신연구원 | Apparatus and method for reducing an electromagnetic wave in wireless power transfer devices |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1961222A (en) * | 2004-06-04 | 2007-05-09 | 安立产业机械株式会社 | Metal detection device |
| CN102520452A (en) * | 2011-11-23 | 2012-06-27 | 刘德军 | Inductance type metal detector |
| CN103412340A (en) * | 2013-08-29 | 2013-11-27 | 高玉琴 | Metal detector |
| CN104297805A (en) * | 2014-11-07 | 2015-01-21 | 吴建堂 | Metal detection device |
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