CN113866837B - Electrical source nuclear magnetic resonance and induced polarization combined device and detection method - Google Patents
Electrical source nuclear magnetic resonance and induced polarization combined device and detection method Download PDFInfo
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- CN113866837B CN113866837B CN202111097407.7A CN202111097407A CN113866837B CN 113866837 B CN113866837 B CN 113866837B CN 202111097407 A CN202111097407 A CN 202111097407A CN 113866837 B CN113866837 B CN 113866837B
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- 238000005481 NMR spectroscopy Methods 0.000 title claims abstract description 65
- 230000010287 polarization Effects 0.000 title claims abstract description 65
- 238000001514 detection method Methods 0.000 title claims abstract description 42
- 238000005259 measurement Methods 0.000 claims abstract description 32
- 239000003673 groundwater Substances 0.000 claims abstract description 12
- 238000012937 correction Methods 0.000 claims description 57
- 238000012545 processing Methods 0.000 claims description 24
- 230000005284 excitation Effects 0.000 claims description 21
- 238000000034 method Methods 0.000 claims description 19
- 230000005540 biological transmission Effects 0.000 claims description 16
- 230000000007 visual effect Effects 0.000 claims description 16
- 230000000087 stabilizing effect Effects 0.000 claims description 13
- 230000003321 amplification Effects 0.000 claims description 10
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 10
- 230000003750 conditioning effect Effects 0.000 claims description 8
- 238000012546 transfer Methods 0.000 claims description 8
- 239000003990 capacitor Substances 0.000 claims description 7
- 230000006698 induction Effects 0.000 claims description 7
- 230000015556 catabolic process Effects 0.000 claims description 6
- 238000002955 isolation Methods 0.000 claims description 6
- 238000005516 engineering process Methods 0.000 claims description 3
- 238000012360 testing method Methods 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 11
- 238000004364 calculation method Methods 0.000 abstract description 2
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- 241000238366 Cephalopoda Species 0.000 description 5
- 238000004891 communication Methods 0.000 description 5
- 230000001052 transient effect Effects 0.000 description 5
- 230000005684 electric field Effects 0.000 description 3
- 230000002159 abnormal effect Effects 0.000 description 2
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Classifications
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- G—PHYSICS
- 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
- G01V3/14—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electron or nuclear magnetic resonance
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention belongs to the field of geophysical exploration, and particularly relates to an electric source nuclear magnetic resonance and induced polarization combined device and a detection method. Through the combination of two geophysical prospecting parties, a constraint effect can be achieved for inversion interpretation of geophysical data. During measurement, an induced polarization mode is selected, stable low-frequency alternating voltage is provided for the ground through a transmitting electrode, the potential difference between two receiving electrodes on the ground is collected, and then the polarization rate parameter is obtained through calculation; and switching to a nuclear magnetic resonance detection mode, introducing alternating current pulses with larmor frequency to the transmitting electrode, and receiving nuclear magnetic resonance signals by the receiving electrode after stopping transmitting to obtain the distribution condition of underground water. The device measures the polarizability and groundwater distribution by using a set of equipment, and solves the problem of difficult laying of complex field environment coils.
Description
Technical Field
The invention belongs to the field of geophysical exploration, and particularly relates to an electric source nuclear magnetic resonance and induced polarization combined device and a detection method.
Background
Currently, only magnetic resonance detection techniques are geophysical methods that directly detect the presence of groundwater. Exciting magnetic moment change of hydrogen atoms in underground water by emitting exciting pulses with larmor frequency, and receiving nuclear magnetic resonance signals after stopping the exciting pulses so as to obtain underground water body distribution information; the induced polarization is used for supplying direct current or low-frequency alternating current to the underground through the grounding electrode, the electricity is cut off after a period of time, and the visual polarization rate of the measuring point is obtained by detecting the additional electric field which is generated in the charging and discharging process and changes along with the time, so that the occurrence information and the water content of the underground minerals are obtained.
The nuclear magnetic resonance and transient electromagnetic combined instrument and the working method disclosed in CN104280780A adopt a nuclear magnetic resonance and transient electromagnetic combined detection method, can combine the advantages of accurate nuclear magnetic resonance detection and deep transient electromagnetic detection range, and can realize the exploration of a deeper underground region. During detection, firstly, a transient electromagnetic mode is used for detecting the area for the first time to obtain the underground apparent resistivity distribution condition of the area, then an abnormal apparent resistivity area is found out according to an analysis inversion result, and a nuclear magnetic resonance mode is used for detecting the measuring point with abnormal apparent resistivity for the second time to obtain the underground water content distribution of the area through inversion. Because each measuring point needs to adopt transient electromagnetic mode and nuclear magnetic resonance mode detection, in order to improve detection efficiency, the combined instrument adopts a large fixed source loop mode, and a transmitting loop coverage area is paved. The SQUID sensor is used as a receiving device of nuclear magnetic resonance signals, so that the detection precision of the nuclear magnetic resonance signals is improved, but the SQUID sensor can be used only when the temperature of the SQUID sensor is far lower than the outdoor temperature by using the refrigerant, the workload is increased when the SQUID sensor carries enough refrigerant for field detection, the detection range of the SQUID sensor is small, and the workload is large because the measuring points are required to be moved for a plurality of times if regional measurement is required.
CN106772642a discloses a "nuclear magnetic resonance water detection system excited by a ground electric field and a field working method", which uses a ground electrode as a transmitting device, and a plurality of coils as receiving devices, and uses the ground electric field to excite nuclear magnetic resonance signals to detect and find water. According to the invention, 12 coils with side length or diameter of 100m are used as receiving sensors, the length of each coil carried by each detection exceeds 3.5 km, the workload of arranging 12 receiving coils at a time is large, the detection complexity is increased, and regional measurement of the position of a measuring point to be moved is inconvenient.
Disclosure of Invention
The invention aims to provide an electric source magnetic resonance and induced polarization combined device, which aims at solving the problems of large work load of field coil laying, inconvenient carrying and insufficient interpretation precision of a single nuclear magnetic resonance signal to an underground water-containing area. The nuclear magnetic resonance signal measurement and the polarizability measurement are carried out by using the same instrument, so that the purposes of reducing the detection workload and improving the interpretation precision are achieved.
The invention further provides a detection method of the combined device of the electric source magnetic resonance and the induced polarization.
An electrical source nuclear magnetic resonance and induced polarization combined device, the device comprising:
a transmitting circuit for converting the energy of the AC generator into a pulse voltage with a certain time sequence and transmitting the pulse voltage through a transmitting electrode pair;
the receiving switching circuit is controlled by the main control unit to acquire the free induction attenuation signal and the voltage attenuation signal in induced polarization respectively by the receiving electrode pair;
the signal conditioning circuit comprises an induced polarization signal processing circuit and a nuclear magnetic resonance signal processing circuit, and is respectively used for processing the induced polarization voltage attenuation signal and the free induction attenuation signal, and controlling the flow direction of the signal by the receiving switching circuit through the main control unit.
Further, the transmitting circuit includes:
the voltage detection circuit is used for collecting the voltage value of the high-power transmitting bridge circuit, comparing and adjusting the voltage value with the voltage value preset in the main control unit, and controlling the on-off of the IGBT to generate an excitation voltage of Larmor frequency and a voltage meeting the excitation polarization transmitting time sequence through a PWM technology;
the correction circuit comprises a correction capacitor and a correction inductor which are connected in series and is connected with the high-power transmitting bridge circuit to correct the transmitting waveform into a sine wave;
the emission control circuit sends an instruction to the emission control circuit after passing through the photoelectric isolation module, the emission control circuit controls the AC-DC converter to supply power to the high-power emission bridge circuit through the power management module and the current stabilizing circuit by the alternating current generator, meanwhile, the emission control circuit sends a control signal to the IGBT driving circuit, and the IGBT switching tube in the high-power emission bridge circuit is controlled to be on-off according to a set time sequence after power amplification, so that energy in the current stabilizing circuit is converted into emission pulses with a certain time sequence;
the current detector reads the current change in the transmitting electrode pair and feeds the current change back to the main control unit;
the LCR tester is used for detecting resistance, capacitance and inductance values of the transmitting circuit and setting correction capacitance values in the correction circuit.
Further, the induced polarization signal processing circuit comprises a filter circuit, an amplifying circuit for instruments and a following amplifying circuit, and the received signals are collected through a signal collecting circuit after sequentially passing through the filter circuit, the amplifying circuit for instruments and the following amplifying circuit; the nuclear magnetic resonance signal processing circuit comprises a pre-amplifier circuit, a program-controlled amplifying circuit and a band-pass filter circuit which are connected, and received signals are collected through a signal collecting circuit after passing through the pre-amplifier circuit, the program-controlled amplifying circuit and the band-pass filter circuit.
Further, the electrode distance of the transmitting electrode is 100-200m, the electrode distance of the receiving electrode is 50-100m, and the receiving electrode is arranged on the same line as the transmitting electrode and the same central point as the transmitting electrode.
Further, the apparatus further comprises: and the computer is used for setting a measurement mode, wherein the measurement mode comprises an induced polarization measurement mode and a ground nuclear magnetic resonance measurement mode, the capacitance value in the correction circuit is configured to be 0 in the induced polarization mode, the emission control circuit sends a control signal to the IGBT driving circuit, the IGBT switching tube in the high-power emission bridge circuit is controlled to be switched on and off according to a set time sequence after power amplification, and then energy in the steady-flow circuit is converted into emission pulses with a certain time sequence and sent to the emission electrode pair through the correction circuit to finish excitation.
Further, starting the LCR tester in the ground nuclear magnetic resonance measurement mode, and according to the formulaParameter calculation correction circuit measured by LCR testerAnd calculating the value of the correction inductance according to the amplitude-frequency characteristic of the transfer function, completing the setting of the correction circuit, and controlling the output voltage of the AC-DC converter and the transmission time sequence of the IGBT driving circuit by the transmission control circuit to control the high-power transmission bridge circuit to generate a Larmor frequency variation waveform.
A detection method of an electric source nuclear magnetic resonance and induced polarization combined device comprises the following steps:
the device is placed near the area to be detected, the electrode distance of the transmitting electrode is 200m, the electrode distance of the receiving electrode is 100m, and the receiving electrode is arranged on a test line which is communicated with the transmitting electrode and is the same as the center point of the transmitting electrode;
selecting an induced polarization mode in a computer, and configuring the relative distance between a transmitting electrode and a receiving electrode, transmitting voltage and stepping voltage parameters to be sent to a main control unit so that the device is in the induced polarization working mode;
the computer sends an instruction to the emission control circuit through the main control unit, controls the AC-DC converter to output a specified voltage, simultaneously controls the IGBT driving circuit to generate an emission voltage with a fixed time sequence, and transmits the emission voltage to the emission electrode through the correction circuit, and the voltage detection circuit detects the voltage in the high-power emission bridge circuit in real time in the whole process to prevent the breakdown of the IGBT due to the overhigh voltage;
after the potential difference is received, the potential difference is transmitted to a signal acquisition circuit through an induced polarization signal processing circuit and is transmitted back to a computer, and the visual polarization rate and the visual conductivity are calculated by software;
selecting a nuclear magnetic resonance detection mode in software in a computer, and configuring a transmitting pulse moment sequence to be sent to a main control unit so that an instrument is in a ground nuclear magnetic resonance working mode;
the computer sends an instruction to the main control unit, controls the AC-DC converter to output a designated voltage, and simultaneously controls the IGBT driving circuit to generate a time sequence of Larmor frequency corresponding to the measuring point position, and the time sequence is transmitted to the transmitting electrode through the correction circuit, so that the voltage detection circuit detects the voltage in the high-power transmitting bridge circuit in real time in the whole process, and the breakdown of the IGBT due to the overhigh voltage is prevented;
receiving nuclear magnetic resonance signals generated by excitation of excitation pulse moment, processing the nuclear magnetic resonance signals by a nuclear magnetic resonance signal processing circuit, and transmitting the nuclear magnetic resonance signals to a signal acquisition circuit and a computer;
after the pulse moment sequences are all transmitted, the curve of the groundwater content of the measuring point along with the depth is inverted by combining with the apparent conductivity computer software constraint measured in the induced polarization mode;
and replacing the measuring points, repeating the steps, establishing a visual polarizability and visual conductivity model after the measurement of all the measuring points is completed, inverting the three-dimensional groundwater content model by taking the visual conductivity model as a constraint condition, and finally obtaining the three-dimensional groundwater model in the upper computer software.
Further, the method further comprises: and under the induced polarization mode, the capacitance value in the correction circuit is configured to be 0, the emission control circuit sends a control signal to the IGBT driving circuit, and after power amplification, the IGBT switching tube in the high-power emission bridge circuit is controlled to be switched on and off according to a set time sequence, so that the energy in the current stabilizing circuit is converted into emission pulses with a certain time sequence, and the emission pulses are sent to the emission electrode pair through the correction circuit to finish excitation.
Further, starting the LCR tester in the ground nuclear magnetic resonance measurement mode, and according to the formulaf represents the transmitting frequency, the equivalent inductance L of the transmitting circuit measured by the LCR tester calculates the value of the capacitance in the correcting circuit, and then calculates the value of the correcting inductance according to the amplitude-frequency characteristic of the transfer function, thereby completing the setting of the correcting circuit.
Compared with the prior art, the invention has the beneficial effects that:
the invention is an electric source magnetic resonance and induced polarization combined device, can perform ground nuclear magnetic resonance measurement and induced polarization measurement on the same measuring point under the condition of not changing instruments and equipment, obtains the underground water content condition of the measuring point and the polarization rate of the measuring point, can obtain two-dimensional and three-dimensional underground water content distribution and multi-measuring point polarization rate change curves by combining the results of multiple measuring points, and has important application value.
Drawings
FIG. 1 is a block diagram of an electrical source nuclear magnetic resonance and induced polarization combined instrument system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the operation of the high-power transmitting bridge circuit when the transmitting current of FIG. 2A flows through the transmitting load in the forward direction, and FIG. 2B is a schematic diagram of the operation of the high-power transmitting bridge circuit when the transmitting current flows through the transmitting load in the reverse direction;
FIG. 3 is a schematic diagram of an emission current correction circuit and a transfer function thereof according to an embodiment of the present invention;
fig. 4 is a waveform diagram of excitation current before and after adding a correction circuit according to an embodiment of the present invention, wherein fig. 4A is a waveform diagram of emission without adding a correction circuit, and fig. 4B is a waveform diagram of emission after adding a correction circuit;
in fig. 1, 1 computer, 2 communication interface, 3 main control unit, 4 optocoupler isolation module, 5 emission control circuit, 6AC-DC converter, 7 current stabilizing circuit, 8IGBT driving circuit, 9 high-power emission bridge circuit, 10 correction circuit, 11 emission electrode pair, 12 alternator, 13 power management module, 14LCR tester, 15 current detector, 16 voltage detection circuit, 17 signal acquisition circuit, 18 band pass filter, 19 program controlled amplifier, 20 preamplifier, 21 follow amplifier circuit, 22 amplifier for instrument, 23 filter circuit, 24 receiving switching circuit, 25 receiving electrode pair, 26 low level reference source, 27 high level reference source, 28 standard frequency source.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, the combination device of electric source nuclear magnetic resonance and induced polarization comprises: the device comprises a computer 1, a communication interface 2, a main control unit 3, an optocoupler isolation module 4, a transmitting control circuit 5, an AC-DC converter 6, a current stabilizing circuit 7, an IGBT driving circuit 8, a high-power transmitting bridge circuit 9, a correcting circuit 10, a transmitting electrode pair 11, an alternating current generator 12, a power supply management module 13, an LCR tester 14, a current detector 15, a voltage detection circuit 16, a signal acquisition circuit 17, a band-pass filter 18, a program-controlled amplifier 19, a preamplifier 20, a follow-up amplifying circuit 21, an amplifier 22 for instruments, a filter circuit 23, a receiving switching circuit 24, a receiving electrode pair 25, a low-level reference source 26, a high-level reference source 27 and a standard frequency source 28.
The device comprises:
a transmitting circuit for converting the energy of the AC generator into a pulse voltage with a certain time sequence and transmitting the pulse voltage through a transmitting electrode pair;
the receiving switching circuit is controlled by the main control unit to acquire the free induction attenuation signal and the voltage attenuation signal in induced polarization respectively by the receiving electrode pair;
the signal conditioning circuit comprises an induced polarization signal processing circuit and a nuclear magnetic resonance signal processing circuit, and is respectively used for processing the induced polarization voltage attenuation signal and the free induction attenuation signal, and controlling the flow direction of the signal by the receiving switching circuit through the main control unit.
Wherein the transmitting circuit includes:
the voltage detection circuit is used for collecting the voltage value of the high-power transmitting bridge circuit, comparing and adjusting the voltage value with the voltage value preset in the main control unit, and controlling the on-off of the IGBT to generate an excitation voltage of Larmor frequency and a voltage meeting the excitation polarization transmitting time sequence through a PWM technology;
the correction circuit comprises a correction capacitor and a correction inductor which are connected in series and is connected with the high-power transmitting bridge circuit to correct the transmitting waveform into a sine wave;
the emission control circuit sends an instruction to the emission control circuit after passing through the photoelectric isolation module, the emission control circuit controls the AC-DC converter to supply power to the high-power emission bridge circuit through the power management module and the current stabilizing circuit by the alternating current generator, meanwhile, the emission control circuit sends a control signal to the IGBT driving circuit, and the IGBT switching tube in the high-power emission bridge circuit is controlled to be on-off according to a set time sequence after power amplification, so that energy in the current stabilizing circuit is converted into emission pulses with a certain time sequence;
the current detector reads the current change in the transmitting electrode pair and feeds the current change back to the main control unit;
the LCR tester is used for detecting resistance, capacitance and inductance values of the transmitting circuit and setting correction capacitance values in the correction circuit.
The emission control circuit provides different emission time sequences by controlling the AC-DC converter and the IGBT driving circuit, and meets the emission sequence and voltage requirements of a nuclear magnetic resonance detection mode and an induced polarization detection mode; the high-power transmitting bridge consists of IGBT switching tubes, and the energy of the alternating-current generator is converted into transmitting pulses with a certain time sequence by controlling the on-off of the IGBT switching tubes.
The signal conditioning circuit comprises 2 signal conditioning circuits, namely an induced polarization signal processing circuit and a nuclear magnetic resonance signal processing circuit, which are respectively used for processing an induced polarization voltage attenuation signal and a free induction attenuation signal, and the main control unit is used for controlling the flow direction of a control signal of the receiving switching circuit;
the main control unit of the invention switches and controls the emission control circuit, the high-power emitter bridge circuit, the receiving switching circuit and the signal conditioning circuit, and is connected with a standard frequency source 28.
The IGBT driving circuit performs power amplification on PWM pulses output by the emission control circuit to drive the IGBT to work;
a low-level reference source 26 and a high-level reference source 27 are also included for calibrating the receiving loop, the high-level reference source and the low-level reference source are respectively connected to the arranged receiving electrodes and collect signals, and the receiving loop is compared with a standard value and calibrated according to the actually collected values.
The induced polarization signal processing circuit comprises a filter circuit, an amplifying circuit for instruments and a following amplifying circuit, and the received signals are collected through a signal collecting circuit after sequentially passing through the filter circuit, the amplifying circuit for instruments and the following amplifying circuit; the nuclear magnetic resonance signal processing circuit comprises a pre-amplifier circuit, a program-controlled amplifying circuit and a band-pass filter circuit which are connected, and received signals are collected through a signal collecting circuit after passing through the pre-amplifier circuit, the program-controlled amplifying circuit and the band-pass filter circuit.
The computer of the device is used for setting a measurement mode, the measurement mode comprises an induced polarization measurement mode and a ground nuclear magnetic resonance measurement mode, the capacitance value in a correction circuit is configured to be 0 in the induced polarization mode, a transmission control circuit sends a control signal to an IGBT driving circuit, an IGBT switching tube in a high-power transmission bridge circuit is controlled to be on-off according to a set time sequence after power amplification, and then energy in a steady-flow circuit is converted into a transmission pulse with a certain time sequence and sent to a transmission electrode pair through the correction circuit to finish excitation.
Starting an LCR tester in a ground nuclear magnetic resonance measurement mode and according to a formulaThe parameter measured by the LCR tester calculates the value of the capacitor in the correction circuit, then calculates the value of the correction inductance according to the amplitude-frequency characteristic of the transfer function, completes the setting of the correction circuit, and controls the output voltage of the AC-DC converter and the emission time sequence of the IGBT driving circuit through the emission control circuit to control the high-power emission bridge circuit to generate the waveform of Larmor frequency change.
The specific working process of the device comprises the following steps:
first, the positions of the measuring line and each measuring point are determined, and in one embodiment, the distance between the transmitting electrode pair and the receiving electrode pair is 100m, the distance between the receiving electrode pair is 50 m, and the transmitting electrode and the receiving electrode are positioned on the same straight line. The measurement mode is set by the computer 1, and first, the induced polarization measurement mode in which the capacitance value in the configuration correction circuit 10 is 0 is set. The parameters of relative distance between the transmitting electrode and the receiving electrode, transmitting voltage, stepping voltage and the like are set, the parameters are transmitted to the main control unit 3 through the communication interface 2, then the main control unit 3 transmits a control signal, the control signal transmits an instruction to the transmitting control circuit 5 after passing through the photoelectric isolation module 4, the transmitting control circuit 5 controls the AC-DC converter 6 to supply power to the high-power transmitting bridge 9 through the power management module 13 and the current stabilizing circuit 7, meanwhile, the voltage detection circuit 16 detects the voltage of the high-power transmitting bridge 9 in real time, the IGBT is prevented from being broken down due to overhigh voltage, the transmitting control circuit 5 transmits a control signal to the IGBT driving circuit 8, the IGBT switching tube in the high-power transmitting bridge 9 is controlled to be on-off according to a set time sequence after power amplification, energy in the current stabilizing circuit 7 is further converted into transmitting pulses with a certain time sequence, the transmitting pulses are transmitted to the transmitting electrode pair 11 through the correction circuit 10 to complete excitation, and in the process, the current detector 15 reads the current change in the transmitting electrode pair and transmits the current change to the main control unit 3 and displays the current change on the computer 1.
For the receiving loop, after the computer 1 sets the mode to the induced polarization mode, the receiving switching circuit 24 will switch the receiving loop to the induced polarization measurement mode, the signals received by the receiving electrode pair 25 will be processed by the receiving switching circuit 24, the filter circuit 23, the instrumentation amplifier 22 and the follow-up amplifying circuit 21, and then transmitted to the signal acquisition circuit 17, and after being acquired by the A/D sensor therein, transmitted to the main control unit 3, and transmitted back to the computer 1 through the communication interface 2, and the signals are processed by the formulasCalculate the polarizability by the formula +.>The apparent resistivity was calculated.
The computer 1 sets a measurement mode, a ground nuclear magnetic resonance measurement mode and a transmission pulse moment sequence to be sent to the main control unit 3, so that the instrument is in the ground nuclear magnetic resonance working mode. In the nuclear magnetic resonance working mode, the LCR tester is required to be used for carrying out the tuning step, and the specific process is as follows: the LCR tester 14 is activated and the formula is followedThe parameter measured by the LCR tester 14 calculates the value of the capacitance in the correction circuit 10, then calculates the value of the correction inductance according to the amplitude-frequency characteristic of the transfer function, and the main control unit 3 is similar to the induced polarization mode in operation after being connected to the parameter related to the nuclear magnetic resonance detection mode, wherein the difference is that the emission control circuit 5 is different from the emission timing control of the IGBT driving circuit 8 to the output voltage control of the AC-DC converter 6, and the high-power emission bridge 9 needs to be controlled to generate the waveform of larmor frequency change.
In the nuclear magnetic resonance mode, the receiving switching circuit is connected with a nuclear magnetic resonance receiving loop, signals are transmitted to the signal acquisition circuit 17 through the receiving electrode pair 25, the receiving switching circuit 24, the preamplifier 20, the program-controlled amplifier 19 and the band-pass filter 18, acquired by the A/D sensor in the signal acquisition circuit and transmitted to the main control unit 3, and transmitted back to the computer 1 through the communication interface 2, and software in the computer 1 calculates the groundwater content and distribution of the measuring points according to the corresponding FID signals under different pulse moments.
And after the measurement of the current measuring point is finished, repeating the process to finish the test of all preset measuring points. And calculating by software in the computer 1 to obtain two-dimensional and three-dimensional underground water distribution and polarizability change curves.
As shown in fig. 2, fig. 2A is a schematic diagram of the operation of the high-power transmission bridge when the transmission current flows through the transmission load in the forward direction, and fig. 2B is a schematic diagram of the operation of the high-power transmission bridge when the transmission current flows through the transmission load in the reverse direction. The high-power transmitting bridge consists of 8IGBT switching tubes, and each bridge arm of the H bridge consists of 2 IGBT switching tubes which are connected in series. E1 is a voltage source. C and L2 form a correction circuit, L1 represents a ground parasitic inductance, R1 represents a ground resistance, and F1 and F2 represent a transmitting electrode pair.
The working principle is as follows: when the output current flows through the emission load in the forward direction, the IGBT switch tube A1, the IGBT switch tube A2, the IGBT switch tube D1 and the IGBT switch tube D2 are conducted, the flow direction of the exciting current flows out from the E1+ end and flows through the IGBT switch tube A1, the IGBT switch tube A2, L, C1, the IGBT switch tube F2, the ground, the F1, the IGBT switch tube D1 and the IGBT switch tube D2 and E1-. When the output current reversely flows through the emission load, the IGBT switch tube B1, the IGBT switch tube B2, the IGBT switch tube C1 and the IGBT switch tube C2 are conducted, the flow direction of the exciting current is that the exciting current flows out from the E1+ end, and the exciting current respectively flows through the IGBT switch tube B1, the IGBT switch tube B2, the IGBT switch tube F1, the earth, the F2, the C1 and the L, IGBT switch tube C1 and the IGBT switch tube C2 and E1-.
As shown in FIG. 3, the electrical model of the earth can be simplified into a series connection of a resistor and an inductor, and the resistor of the earth model after good grounding treatment is about 10Ω -30Ω and the inductor is about 70 uH. In the magnetic resonance detection operation process, a sine wave current with larmor frequency needs to be emitted, but as the grounding resistance is larger than the coil resistance and the equivalent inductance after grounding is smaller than the coil inductance, the harmonic wave of the emitted current is increased, and therefore, the output voltage of the IGBT bridge circuit is directly applied to the grounding electrode to generate a quasi-square wave.
In order to solve the problems, the invention designs a correction circuit for eliminating the harmonic component of the emission current, which is formed by connecting an inductor and a capacitor in series, and the correction circuit is connected in series in a circuit between two grounding electrodes to play a role in inhibiting the harmonic. In the actual working process, firstly, a proper capacitor C value is selected, and then, the value of the correction inductance L2 is calculated according to the amplitude-frequency characteristic of the transfer function, so that the design of the correction circuit parameters is completed.
As shown in fig. 4, the transmission waveforms of fig. 3 after the correction circuit is introduced are compared. Fig. 4A is a diagram of a transmit waveform without the addition of a correction circuit, which results in a complex harmonic component of the transmit current due to the large resistance and small inductance of the ground equivalent circuit model. After the correction circuit is added, the emission waveform is as shown in fig. 4B, the harmonic component is suppressed, and the sinusoidal waveform is emitted.
The invention also provides a detection method of the electric source nuclear magnetic resonance and induced polarization combined device, which comprises the following steps:
a. placing an electric source nuclear magnetic resonance and induced polarization combined instrument near a region to be detected, arranging a transmitting electrode at a distance of 200m and a receiving electrode at a polar distance of 100m, and arranging the transmitting electrode and the receiving electrode on a line which is communicated with the transmitting electrode and is the same as the central point of the transmitting electrode;
b. the transmitting electrode is connected to the transmitter, the receiving electrode is connected to the receiver, the transmitter is connected with the computer through a serial port-to-USB line, and the receiver is connected with the computer through another USB line. The computer runs the pre-installed control software of the nuclear magnetic resonance and induced polarization combined instrument to carry out self-checking on the instrument, so that the instrument is ensured to be in good state.
c. The induced polarization mode is selected in the software in the computer, and parameters such as the relative distance between the transmitting electrode and the receiving electrode, the transmitting voltage, the stepping voltage and the like are configured and sent to the main control unit, so that the instrument is in the induced polarization working mode.
d. The computer sends an instruction to the emission control circuit through the main control unit, controls the AC-DC converter to output a specified voltage, simultaneously controls the IGBT driving circuit to generate an emission voltage with a fixed time sequence, and transmits the emission voltage to the emission electrode through the correction circuit, and the voltage detection circuit detects the voltage in the high-power emission bridge circuit in real time in the whole process to prevent the breakdown of the IGBT due to the overhigh voltage;
e. after the receiving electrode receives the potential difference, the potential difference is processed by the signal conditioning circuit and then transmitted to the signal acquisition circuit to be transmitted back to the computer, and the visual polarization rate and the visual conductivity are calculated by software.
f. And selecting a nuclear magnetic resonance detection mode in software in the computer, and configuring a transmitting pulse moment sequence to be sent to the main control unit so that the instrument is in a ground nuclear magnetic resonance working mode.
g. The computer sends an instruction to the main control unit, controls the AC-DC converter to output specified voltage, and simultaneously controls the IGBT driving circuit to generate a time sequence of larmor frequency corresponding to the measuring point position, and the time sequence is transmitted to the transmitting electrode through the correction circuit, so that the voltage detection circuit detects the voltage in the high-power transmitting bridge circuit in real time in the whole process, and the breakdown of the IGBT due to the overhigh voltage is prevented.
h. The receiving electrode receives nuclear magnetic resonance signals generated by excitation of the excitation pulse moment, and the nuclear magnetic resonance signals are transmitted to the acquisition card and the computer after being processed by the signal conditioning circuit.
i. And after all excitation pulse moment sequences are transmitted, inverting the change curve of the groundwater content of the measuring point along with the depth by combining the apparent conductivity computer software constraint measured in the excitation polarization mode.
And (3) replacing the measuring point, and repeating the step c-i. And after the measurement of all the measuring points is completed, establishing a visual polarizability and visual conductivity model, inverting the three-dimensional groundwater content model by taking the visual conductivity model as a constraint condition, and finally obtaining the three-dimensional groundwater model in the upper computer software.
Claims (5)
1. An electrical source nuclear magnetic resonance and induced polarization combined device, comprising:
a transmitting circuit for converting the energy of the AC generator into a pulse voltage with a certain time sequence and transmitting the pulse voltage through a transmitting electrode pair;
the receiving switching circuit is controlled by the main control unit to acquire the free induction attenuation signal and the voltage attenuation signal in induced polarization respectively by the receiving electrode pair;
the signal conditioning circuit comprises an induced polarization signal processing circuit and a nuclear magnetic resonance signal processing circuit, and is used for processing the induced polarization voltage attenuation signal and the free induction attenuation signal respectively and controlling the flow direction of the signals of the receiving switching circuit through the main control unit;
the transmitting circuit includes:
the voltage detection circuit is used for collecting the voltage value of the high-power transmitting bridge circuit, comparing and adjusting the voltage value with the voltage value preset in the main control unit, and controlling the on-off of the IGBT to generate an excitation voltage of Larmor frequency and a voltage meeting the excitation polarization transmitting time sequence through a PWM technology;
the correction circuit comprises a correction capacitor and a correction inductor which are connected in series and is connected with the high-power transmitting bridge circuit to correct the transmitting waveform into a sine wave;
the emission control circuit sends an instruction to the emission control circuit after passing through the photoelectric isolation module, the emission control circuit controls the AC-DC converter to supply power to the high-power emission bridge circuit through the power management module and the current stabilizing circuit by the alternating current generator, meanwhile, the emission control circuit sends a control signal to the IGBT driving circuit, and the IGBT switching tube in the high-power emission bridge circuit is controlled to be on-off according to a set time sequence after power amplification, so that energy in the current stabilizing circuit is converted into emission pulses with a certain time sequence;
the current detector reads the current change in the transmitting electrode pair and feeds the current change back to the main control unit;
the LCR tester is used for detecting resistance, capacitance and inductance values of the transmitting circuit and setting a correction capacitance value in the correction circuit;
the electrode distance of the transmitting electrode is 100-200m, the electrode distance of the receiving electrode is 50-100m, and the receiving electrode is arranged on the same measuring line as the transmitting electrode and is the same as the central point of the transmitting electrode;
the apparatus further comprises: a computer for setting a measurement mode including an induced polarization measurement mode in which a capacitance value in the correction circuit is configured to be 0 and a ground nuclear magnetic resonance measurement mode, a transmission control circuit transmitting a control signal to the IGBT driving circuit, after power amplification, the IGBT switching tube in the high-power transmitting bridge circuit is controlled to be switched on and off according to a set time sequence, so that energy in the current stabilizing circuit is converted into transmitting pulses with a certain time sequence, and the transmitting pulses are sent to the transmitting electrode pair through the correction circuit to finish excitation;
starting an LCR tester in the ground nuclear magnetic resonance measurement mode and according to a formulaThe parameter measured by the LCR tester calculates the value of the capacitor in the correction circuit, then calculates the value of the correction inductance according to the amplitude-frequency characteristic of the transfer function, completes the setting of the correction circuit, and controls the output voltage of the AC-DC converter and the emission time sequence of the IGBT driving circuit through the emission control circuit to control the high-power emission bridge circuit to generate the waveform of Larmor frequency change.
2. The device according to claim 1, wherein the induced polarization signal processing circuit comprises a filter circuit, an amplifying circuit for an instrument and a following amplifying circuit, and the received signals are collected by a signal collecting circuit after passing through the filter circuit, the amplifying circuit for an instrument and the following amplifying circuit in sequence; the nuclear magnetic resonance signal processing circuit comprises a pre-amplifier circuit, a program-controlled amplifying circuit and a band-pass filter circuit which are connected, and received signals are collected through a signal collecting circuit after passing through the pre-amplifier circuit, the program-controlled amplifying circuit and the band-pass filter circuit.
3. A detection method using the device of any one of claims 1-2, comprising the steps of:
the device is placed near the area to be detected, the electrode distance of the transmitting electrode is 200m, the electrode distance of the receiving electrode is 100m, and the receiving electrode is arranged on a test line which is communicated with the transmitting electrode and is the same as the center point of the transmitting electrode;
selecting an induced polarization mode in a computer, and configuring the relative distance between a transmitting electrode and a receiving electrode, transmitting voltage and stepping voltage parameters to be sent to a main control unit so that the device is in the induced polarization working mode;
the computer sends an instruction to the emission control circuit through the main control unit, controls the AC-DC converter to output a specified voltage, simultaneously controls the IGBT driving circuit to generate an emission voltage with a fixed time sequence, and transmits the emission voltage to the emission electrode through the correction circuit, and the voltage detection circuit detects the voltage in the high-power emission bridge circuit in real time in the whole process to prevent the breakdown of the IGBT due to the overhigh voltage;
after the potential difference is received, the potential difference is transmitted to a signal acquisition circuit through an induced polarization signal processing circuit and is transmitted back to a computer, and the visual polarization rate and the visual conductivity are calculated by software;
selecting a nuclear magnetic resonance detection mode in software in a computer, and configuring a transmitting pulse moment sequence to be sent to a main control unit so that an instrument is in a ground nuclear magnetic resonance working mode;
the computer sends an instruction to the main control unit, controls the AC-DC converter to output a designated voltage, and simultaneously controls the IGBT driving circuit to generate a time sequence of Larmor frequency corresponding to the measuring point position, and the time sequence is transmitted to the transmitting electrode through the correction circuit, so that the voltage detection circuit detects the voltage in the high-power transmitting bridge circuit in real time in the whole process, and the breakdown of the IGBT due to the overhigh voltage is prevented;
receiving nuclear magnetic resonance signals generated by excitation of excitation pulse moment, processing the nuclear magnetic resonance signals by a nuclear magnetic resonance signal processing circuit, and transmitting the nuclear magnetic resonance signals to a signal acquisition circuit and a computer;
after the pulse moment sequences are all transmitted, the curve of the groundwater content of the measuring point along with the depth is inverted by combining with the apparent conductivity computer software constraint measured in the induced polarization mode;
and replacing the measuring points, repeating the steps, establishing a visual polarizability and visual conductivity model after the measurement of all the measuring points is completed, inverting the three-dimensional groundwater content model by taking the visual conductivity model as a constraint condition, and finally obtaining the three-dimensional groundwater model in the upper computer software.
4. A method of probing as claimed in claim 3, further comprising: and under the induced polarization mode, the capacitance value in the correction circuit is configured to be 0, the emission control circuit sends a control signal to the IGBT driving circuit, and after power amplification, the IGBT switching tube in the high-power emission bridge circuit is controlled to be switched on and off according to a set time sequence, so that the energy in the current stabilizing circuit is converted into emission pulses with a certain time sequence, and the emission pulses are sent to the emission electrode pair through the correction circuit to finish excitation.
5. A method of probing as claimed in claim 3 wherein the LCR tester is activated in a ground nuclear magnetic resonance measurement mode and is formulated as followsf represents the transmitting frequency, the equivalent inductance L of the transmitting circuit measured by the LCR tester calculates the value of the capacitance in the correcting circuit, and then calculates the value of the correcting inductance according to the amplitude-frequency characteristic of the transfer function, thereby completing the setting of the correcting circuit.
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