CN111551999A - Long-period magnetotelluric measurement system based on orthogonal vector DLIA - Google Patents
Long-period magnetotelluric measurement system based on orthogonal vector DLIA Download PDFInfo
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- CN111551999A CN111551999A CN202010455415.3A CN202010455415A CN111551999A CN 111551999 A CN111551999 A CN 111551999A CN 202010455415 A CN202010455415 A CN 202010455415A CN 111551999 A CN111551999 A CN 111551999A
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- 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
- G01V3/40—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for measuring magnetic field characteristics of the earth
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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
- G01V3/38—Processing data, e.g. for analysis, for interpretation, for correction
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Abstract
The invention provides a long-period magnetotelluric measurement system based on orthogonal vector DLIA (digital Living interference), which comprises an electromagnetic signal acquisition circuit, a digital demodulation circuit and a control module, wherein the electromagnetic signal acquisition circuit conditions analog signals output by an electric field sensor and a magnetic field sensor, and then converts the electric field analog signals and the magnetic field analog signals after analog conditioning into electric field digital signals and magnetic field digital signals through A/D (analog/digital) conversion; the electric field digital signal and the magnetic field digital signal are isolated by magnetic coupling and then transmitted to a digital demodulation circuit for digital demodulation, demodulated high-frequency components are filtered by a digital low-pass filter, the electromagnetic signal to be detected is obtained by numerical calculation and is transmitted to a control module through a serial port; the control module is used for realizing real-time display and storage of the detected electromagnetic signals and also used for realizing the functions of GPS time service synchronization, function selection, communication with an upper computer, power supply and the like.
Description
Technical Field
The invention relates to the technical field of magnetotelluric detection, in particular to a long-period magnetotelluric measurement system based on an orthogonal vector DLIA (digital Living interference indicator).
Background
The ultra-long period geoelectromagnetic measurement is an effective method for understanding the electrical structure of the continental rock ring, a natural electromagnetic field is used as a field source, the observation cost is reduced, the efficiency is high, the detection depth is large, and the method is one of important methods for understanding the deep structure in recent years. The natural field magnetotelluric signals detected by a long-period magnetotelluric detector (LMT) are very weak, the signal-to-noise ratio is low, and useful signals are often submerged in noise. The effective magnetotelluric signals to be measured are generally low-frequency signals with the acquisition period as low as ten thousand seconds, the lower the frequency is, the larger the noise amplitude is due to the interference of 1/f noise in the low frequency band, and the temperature drift is large in long-time measurement. How to eliminate or reduce low-frequency noise interference such as 1/f noise, drift and the like when acquiring low-frequency electromagnetic signals so as to improve the effective detection depth is always a difficult problem in the research work of long-period magnetotelluric instruments.
Disclosure of Invention
In view of this, the invention provides a long-period magnetotelluric measurement system based on an orthogonal vector type Digital phase-locked amplifier (DLIA), which designs an analog conditioning circuit, converts magnetotelluric analog signals into Digital signals by combining a 32-bit high-precision acquisition technology, and designs the orthogonal vector type Digital phase-locked amplifier aiming at the problem of serious 1/f noise interference in low-frequency electromagnetic signals, so that the interference of 1/f noise can be effectively eliminated, and a data acquisition task with high precision, low noise and low drift can be realized.
The invention provides a long-period magnetotelluric measurement system based on orthogonal vector DLIA, comprising:
the electromagnetic signal acquisition circuit is used for conditioning analog signals output by the electric field sensor and the magnetic field sensor respectively, then converting the analog conditioned electric field analog signals and magnetic field analog signals into electric field digital signals and magnetic field digital signals through A/D conversion, and transmitting the electric field digital signals and the magnetic field digital signals to the digital demodulation circuit after magnetic coupling isolation;
the digital demodulation circuit is used for respectively carrying out digital demodulation on the electric field digital signal and the magnetic field digital signal, filtering out demodulated high-frequency components through a digital low-pass filter, and obtaining a measured electromagnetic signal through numerical calculation;
and the control module is used for displaying and storing the detected electromagnetic signals in real time, and is also used for GPS time service synchronization, function selection, communication with an upper computer and power supply.
Further, the electromagnetic signal acquisition circuit comprises an electric field analog conditioning circuit, a first analog-to-digital conversion circuit, a first magnetic coupling, a magnetic field analog conditioning circuit, a second analog-to-digital conversion circuit and a second magnetic coupling, wherein the electric field analog conditioning circuit, the first analog-to-digital conversion circuit and the first magnetic coupling process electric field signals output by the electric field sensor, and the magnetic field analog conditioning circuit, the second analog-to-digital conversion circuit and the second magnetic coupling process magnetic field signals output by the magnetic field sensor.
Furthermore, the electric field analog conditioning circuit comprises a voltage follower circuit, a mixing circuit, an alternating current amplifying circuit and a D/A conversion circuit; after impedance matching is carried out on an electric field signal from the electric field sensor by using the voltage follower circuit, the electric field signal is multiplied by a reference signal converted by the D/A conversion circuit through the mixer circuit, and then the signal is amplified by using the alternating current amplification circuit to obtain an electric field analog signal after analog conditioning; the electric field analog signal is converted into an electric field digital signal through the first analog-to-digital conversion circuit, and finally transmitted to the digital demodulation circuit after being magnetically coupled and isolated by the first magnetic coupling.
Furthermore, the magnetic field simulation conditioning circuit comprises a protection circuit and a program-controlled attenuation circuit, wherein the protection circuit consists of a gas discharge tube and a self-recovery fuse and is used for avoiding power on and off, thunder and lightning and various pulse electromagnetic interferences; the program-controlled attenuation circuit is used for ensuring that the output voltage amplitude of the magnetic field sensor is within the input range of the second analog-to-digital conversion circuit.
Further, the digital demodulation circuit includes a first digital demodulation circuit and a second digital demodulation circuit, the first digital demodulation circuit performs correlation demodulation processing on the electric field digital signal from the electromagnetic signal acquisition circuit, and the second digital demodulation circuit performs correlation demodulation processing on the magnetic field digital signal from the electromagnetic signal acquisition circuit.
Further, the first digital demodulation circuit comprises a reference channel circuit, a first PSD operation circuit, a second PSD operation circuit, a first LPF circuit, a second LPF circuit, and a numerical calculation circuit, wherein the reference channel circuit generates two channels of common-frequency and orthogonal reference signals sin (ω t) and cos (ω t) according to the frequency ω of the electric field digital signal from the first magnetic coupling; after the two reference signals sin (ω t) and cos (ω t) are respectively subjected to correlation operation by the first PSD operation circuit and the second PSD operation circuit and an electric field digital signal, filtering is performed by the first LPF circuit and the second LPF circuit respectively to obtain a direct current component I, Q; finally, the amplitude and the phase of the electric field digital signal are obtained by utilizing the numerical calculation circuit; the second digital demodulation circuit has the same structure as the first digital demodulation circuit.
Further, the reference channel circuit generates the internal reference signal by using a table look-up method, wherein 1/4 cycles of sampling are only performed on the sinusoidal signal during sampling.
Further, the first analog-to-digital conversion circuit and the second analog-to-digital conversion circuit both employ a 32-bit high-precision delta-sigma analog-to-digital converter ADS 1262.
Further, the first magnetic coupling and the second magnetic coupling both adopt a digital isolation chip ADuM 1201.
Further, the alternating current amplifying circuit adopts a chopper-stabilized operational amplifier OPA 388.
The technical scheme provided by the invention has the beneficial effects that:
(1) the electromagnetic isolation design is adopted, the wiring is reasonable, the mutual interference among electromagnetic field signals is avoided, and the system noise is reduced;
(2) the analog conditioning circuit is combined with a 32-bit high-precision acquisition technology to convert the magnetotelluric analog signal into a digital signal, low-frequency direct-current noise is effectively inhibited by utilizing alternating-current amplification, and impedance matching and noise matching are carried out according to the characteristics of source impedance; the digital demodulation circuit carries out full digital demodulation based on the orthogonal vector type digital phase-locked amplifier, so that 1/f noise interference is effectively eliminated, the measurement error is reduced, and the influence of operational amplifier temperature drift and offset is avoided;
(3) compared with the traditional digital phase-locked amplifier adopting an external excitation mode, the digital phase-locked amplifier adopting the internal excitation mode is simpler to realize, higher in stability and higher in operation speed;
(4) compared with a magnetotelluric instrument based on a traditional detection mode, the magnetotelluric instrument based on the magnetotelluric detection method has the advantages that the signal-to-noise ratio of data acquisition is improved, and the effective detection depth is greatly increased.
Drawings
FIG. 1 is a structural diagram of a long-period magnetotelluric measurement system based on an orthogonal vector DLIA provided by an embodiment of the present invention;
FIG. 2 is a block diagram of an electric field analog conditioning circuit provided by an embodiment of the present invention;
FIG. 3 is a block diagram of a magnetic field analog conditioning circuit provided by an embodiment of the present invention;
fig. 4 is a block diagram of a digital demodulation circuit according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings.
Referring to fig. 1, an embodiment of the invention provides a long-period magnetotelluric measurement system based on an orthogonal vector DLIA, which includes an electromagnetic signal acquisition circuit, a digital demodulation circuit, and a control module. The electromagnetic signal acquisition circuit conditions analog signals output by the electric field sensor and the magnetic field sensor, and then converts the electric field analog signals and the magnetic field analog signals after analog conditioning into electric field digital signals and magnetic field digital signals through A/D conversion; the electric field digital signal and the magnetic field digital signal are isolated by magnetic coupling and then transmitted to a digital demodulation circuit for digital demodulation, demodulated high-frequency components are filtered by a digital low-pass filter, the electromagnetic signal to be detected is obtained by numerical calculation and is transmitted to a control module through a serial port;
the control module comprises a communication interface, an ARM processor, a display module, a data storage module, a matrix keyboard, a GPS module and a system power supply, wherein the communication interface is connected with the digital demodulation circuit through a USART and connected with an upper computer through Bluetooth; the ARM processor is used for processing the detected electromagnetic signals from the digital demodulation circuit, displaying the detected electromagnetic signals in real time by using the display module and storing the detected electromagnetic signals by using the data storage module; the GPS module is used for realizing GPS time service synchronization, the matrix keyboard is used for function selection, and the system power supply is used for supplying power to the whole long-period magnetotelluric measurement system.
The electromagnetic signal acquisition circuit comprises an electric field analog conditioning circuit 101, a first analog-to-digital conversion circuit 102, a first magnetic coupling 103, a magnetic field analog conditioning circuit 201, a second analog-to-digital conversion circuit 202 and a second magnetic coupling 203, wherein the first analog-to-digital conversion circuit 102 and the second analog-to-digital conversion circuit 202 both adopt 32-bit high-precision delta-sigma analog-to-digital converters ADS1262, and the first magnetic coupling 103 and the second magnetic coupling 203 both adopt digital isolation chips ADuM 1201; the electric field analog conditioning circuit 101, the first analog-to-digital conversion circuit 102 and the first magnetic coupler 103 process electric field signals output by the electric field sensor, and the magnetic field analog conditioning circuit 201, the second analog-to-digital conversion circuit 202 and the second magnetic coupler 203 process magnetic field signals output by the magnetic field sensor.
It should be noted that the input signals of the long-period magnetotelluric detection instrument include an electric field signal from the non-polarized electrode and a magnetic field signal from the fluxgate sensor, and the analog conditioning circuit is established, and first, the characteristics of the source impedance need to be known to perform impedance matching and noise matching.
The source resistance of the non-polarized electrode is changed according to the grounding condition, so that a voltage follower circuit needs to be designed to meet the requirement of impedance matching. Referring to fig. 2, the electric field analog conditioning circuit 101 includes a voltage follower circuit, a mixer circuit, an ac amplifier circuit, and a D/a converter circuit; after impedance matching is carried out on electric field signals from the non-polarized electrodes by using a voltage follower circuit, the electric field signals are multiplied by a reference signal subjected to D/A conversion through a mixer circuit, the frequency spectrum of the electric field signals is shifted to high frequency so as to avoid interference of 1/f noise, and then signal amplification is carried out by using a low-noise alternating current amplification circuit to obtain electric field analog signals subjected to analog conditioning; then, the electric field analog signal is converted into an electric field digital signal by the first analog-to-digital conversion circuit 102, and finally transmitted to the digital demodulation circuit after being magnetically coupled and isolated by the first magnetic coupling 103. Preferably, in this embodiment, the ac amplification circuit employs a chopper stabilized operational amplifier OPA388, the offset voltage is ± 0.25 μ V, the temperature drift is ± 0.005 μ V/° c, and there is no 1/f noise.
The flux gate sensor is usually subjected to analog conditioning, and its output characteristic can be understood as the output of the operational amplifier, and the output resistance is relatively small and stable. Referring to fig. 3, the magnetic field analog conditioning circuit 201 includes a protection circuit and a program-controlled attenuation circuit, and since the instrument needs to work in the field for a long time, and power on/off, lightning and various pulse electromagnetic interferences of large-scale equipment can affect the stability of the instrument, and can seriously cause permanent damage to the instrument, an anti-surge protection circuit composed of a gas discharge tube and a self-recovery fuse is adopted; meanwhile, considering that the output voltage amplitude of the magnetic sensor may exceed the input range of the analog-to-digital converter, the programmable attenuation circuit is designed, the programmable attenuation circuit adopts a high-precision instrument amplifier PGA281 of the company TI, and utilizes an auto-zero technology, has extremely low offset voltage and almost no 1/f noise, and changes the feedback coefficient by changing the high and low levels of the control pin thereof, thereby achieving the effect of dynamically changing the gain of the amplification circuit. Subsequently, the second analog-to-digital conversion circuit 202 converts the analog conditioned magnetic field analog signal into a magnetic field digital signal, and then transmits the magnetic field digital signal to the digital demodulation circuit after performing magnetic coupling isolation by the second magnetic coupling 203.
The digital demodulation circuit comprises a first digital demodulation circuit 104 and a second digital demodulation circuit 204, which respectively perform relevant demodulation processing on the electric field digital signal and the magnetic field digital signal from the electromagnetic signal acquisition circuit, and the structures of the two are the same, taking the first digital demodulation circuit 104 as an example; referring to fig. 4, the first digital demodulation circuit 104 based on the quadrature vector digital phase-locked amplification technology includes a reference channel circuit 1041, a first PSD computing circuit 1042, a second PSD computing circuit 1043, a first LPF (low pass filter) circuit 1044, a second LPF circuit 1045, and a numerical computing circuit 1046, wherein the reference channel circuit 1041 generates two channels of common-frequency and orthogonal reference signals sin (ω t) and cos (ω t) according to a frequency ω of an electric field digital signal x (t) from the first magnetic coupler 103; after the two reference signals sin (ω t) and cos (ω t) are respectively subjected to correlation operation by using the first PSD operation circuit 1042 and the second PSD operation circuit 1043 and the electric field digital signal x (t), filtering is respectively performed through the first LPF circuit 1044 and the second LPF circuit 1045 to obtain a direct current component I, Q in the calculated signal; finally, the amplitude and phase of the electric field digital signal x (t) are obtained through a numerical calculation circuit 1046.
The reference channel circuit 1042 generates an internal reference signal by using an improved table lookup method, and the precision of a sinusoidal signal generated by using the table lookup method is mainly determined by the word length of a sampling value and the table length of a lookup table during sampling. The larger the word length is, the smaller the rounding error of the sampling value of the obtained sinusoidal signal is, and the higher the precision of the sinusoidal signal generated by a table look-up method is finally; the longer the table is, the smaller the error and the smaller the harmonic distortion caused by the method of rounding down to determine the position of the sinusoidal signal in the look-up table, but the longer the table is, the larger the overhead of the memory space is caused. By utilizing the symmetry of the sinusoidal signals in the period, the sinusoidal signals are only required to be subjected to 1/4-period sampling during sampling, and then the sinusoidal signals in the complete period can be output through the output control of the digital demodulation circuit, so that the storage space can be saved by 75%.
The long-period magnetotelluric instrument based on the orthogonal vector DLIA provided by this embodiment adopts an electromagnetic isolation design, and performs layered layout on a top layer, a bottom layer, a power supply layer and a ground layer through four layers of PCB boards, wherein the top layer and the bottom layer are used for signal wiring, the power supply layer is used for digital power supply and analog power supply wiring, and the ground layer is used for wiring of a digital ground and an analog ground, so that an analog device and a digital device are separated during typesetting and wiring, and mutual interference between a digital signal and an analog signal is avoided.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. The long-period magnetotelluric measurement system based on the orthogonal vector DLIA is characterized by comprising the following components:
the electromagnetic signal acquisition circuit is used for conditioning analog signals output by the electric field sensor and the magnetic field sensor respectively, then converting the analog conditioned electric field analog signals and magnetic field analog signals into electric field digital signals and magnetic field digital signals through A/D conversion, and transmitting the electric field digital signals and the magnetic field digital signals to the digital demodulation circuit after magnetic coupling isolation;
the digital demodulation circuit is used for respectively carrying out digital demodulation on the electric field digital signal and the magnetic field digital signal, filtering out demodulated high-frequency components through a digital low-pass filter, and obtaining a measured electromagnetic signal through numerical calculation;
and the control module is used for displaying and storing the detected electromagnetic signals in real time, and is also used for GPS time service synchronization, function selection, communication with an upper computer and power supply.
2. The orthogonal vector DLIA-based long-period magnetotelluric measurement system of claim 1, wherein the electromagnetic signal acquisition circuit comprises an electric field analog conditioning circuit, a first analog-to-digital conversion circuit, a first magnetic coupling, a magnetic field analog conditioning circuit, a second analog-to-digital conversion circuit and a second magnetic coupling, wherein the electric field analog conditioning circuit, the first analog-to-digital conversion circuit and the first magnetic coupling process the electric field signal output by the electric field sensor, and the magnetic field analog conditioning circuit, the second analog-to-digital conversion circuit and the second magnetic coupling process the magnetic field signal output by the magnetic field sensor.
3. The orthogonal vector DLIA-based long-period magnetotelluric measurement system of claim 2, wherein the electric field analog conditioning circuit comprises a voltage follower circuit, a mixer circuit, an AC amplifier circuit, a D/A converter circuit; after impedance matching is carried out on an electric field signal from the electric field sensor by using the voltage follower circuit, the electric field signal is multiplied by a reference signal converted by the D/A conversion circuit through the mixer circuit, and then the signal is amplified by using the alternating current amplification circuit to obtain an electric field analog signal after analog conditioning; the electric field analog signal is converted into an electric field digital signal through the first analog-to-digital conversion circuit, and finally transmitted to the digital demodulation circuit after being magnetically coupled and isolated by the first magnetic coupling.
4. The orthogonal vector DLIA-based long-period magnetotelluric measurement system of claim 2, wherein the magnetic field analog conditioning circuit comprises a protection circuit and a program-controlled attenuation circuit, the protection circuit is composed of a gas discharge tube and a self-recovery fuse, and is used for avoiding power failure, thunder and various pulse electromagnetic interferences; the program-controlled attenuation circuit is used for ensuring that the output voltage amplitude of the magnetic field sensor is within the input range of the second analog-to-digital conversion circuit.
5. The quadrature vector type DLIA-based long-period magnetotelluric measurement system of claim 4, wherein the digital demodulation circuit comprises a first digital demodulation circuit and a second digital demodulation circuit, the first digital demodulation circuit performs correlation demodulation processing on the electric field digital signal from the electromagnetic signal acquisition circuit, and the second digital demodulation circuit performs correlation demodulation processing on the magnetic field digital signal from the electromagnetic signal acquisition circuit.
6. The orthogonal vector DLIA-based long-period magnetotelluric measurement system of claim 5, wherein the first digital demodulation circuit comprises a reference channel circuit, a first PSD operation circuit, a second PSD operation circuit, a first LPF circuit, a second LPF circuit and a numerical calculation circuit, wherein the reference channel circuit generates two co-frequency and orthogonal reference signals sin (ω t) and cos (ω t) according to the frequency ω of the electric field digital signal from the first magnetic coupling; after the two reference signals sin (ω t) and cos (ω t) are respectively subjected to correlation operation by the first PSD operation circuit and the second PSD operation circuit and an electric field digital signal, filtering is performed by the first LPF circuit and the second LPF circuit respectively to obtain a direct current component I, Q; finally, the amplitude and the phase of the electric field digital signal are obtained by utilizing the numerical calculation circuit; the second digital demodulation circuit has the same structure as the first digital demodulation circuit.
7. The quadrature vector type DLIA-based long period magnetotelluric measurement system of claim 6, wherein the reference channel circuit uses a look-up table to generate the internal reference signal, wherein the sinusoidal signal is sampled for 1/4 periods only.
8. The quadrature vector type DLIA-based long-period magnetotelluric measurement system of claim 2, wherein the first and second analog-to-digital conversion circuits each employ a 32-bit high-precision delta-sigma analog-to-digital converter ADS 1262.
9. The orthogonal vector type DLIA-based long-period magnetotelluric measurement system of claim 2, wherein the first magnetic coupling and the second magnetic coupling both use a digital isolation chip ADuM 1201.
10. The quadrature vector DLIA-based long-period magnetotelluric measurement system of claim 2, wherein the ac amplification circuit employs a chopper-stabilized operational amplifier OPA 388.
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Application publication date: 20200818 |