RU67293U1 - MULTIPROGRAM DIGITAL RECEIVING RECORDING DEVICE FOR GEOPHYSICAL RESEARCH - Google Patents

Abstract

Usage: in the study of the earth's crust, the search for minerals and the forecast of earthquakes. Effect: enhanced functionality. The essence of the utility model: registration of electromagnetic fields and monitoring of the earth's crust, search for minerals and predict the development of tectonic activity leading to earthquakes. 1 ill.

Description

The utility model relates to the field of electro-radio engineering, namely to radio engineering complexes of extremely low frequencies (ELF) and ultra-low frequencies (ELF) and can be used to study the structure of the earth's crust, search for minerals and earthquake prediction by registering electromagnetic fields generated by the ELF-emitting system VLF range.

The known method of seismic exploration - RF patent No. 2029318, MCI 6 σ01V 1/09, 1995. This method consists in exciting a probing signal and multichannel receiving reflected and diffracted waves from an object, working out with the selection of waves in the direction of arrival and displaying the results in the form sizes of parameters on the plotter.

The disadvantage of this method is that the method uses approximate data interpolation, which in some cases leads to low reliability of the sounding results.

Closest to the claimed device according to the technical essence of solving the problem is a device according to the "method of electromagnetic sounding of the earth's crust using normalized field sources" (RF patent No. 2093863, MKI 6 σ 013/12, 1997).

This device contains two sinusoidal current generators, which are loaded on long, low located, horizontally oriented and grounded at the ends of the antenna. The registration of the radiation generated by the UHF radio installation is carried out using a measuring complex of the Borok type.

However, due to the high requirements imposed by geophysics on the accuracy of impedance measurements, it is necessary to study the spatial characteristics of the fields, which can be realized only with the help of a multi-channel digital receiving and recording device, which is not in the prototype.

The purpose of the utility model is to expand the functionality of the prototype by creating a new receiver for ELF and VLF to study the earth's crust, search for minerals and predict earthquakes based on the measurement of electromagnetic fields created by the radiating system of ELF-ELF ranges.

This goal is achieved due to the fact that in the known system the measuring complex is made in the form of two blocks: an analog registration and processing module (MARO) and a personal computer, and the MARO block

contains electric and magnetic antennas, respectively connected to antenna modules of the electric and magnetic channels, each of which is connected to an analog-to-digital converter through analog amplification - filtering and notch filters, the first output of which is connected to the module for generating calibrated signals, and the second through the divider is connected with the module for forming the clock frequency, in addition, the personal computer is connected to the multifunctional module for analog input and digital input-output.

The structural diagram of the proposed device is shown in figure 1.

The structure of the scheme includes:

- module of analog registration and processing (MARO);

- multifunctional input-output board LA-2, inserted into the ISA-slot of a personal computer;

- own V-class personal computer no lower than 486-DX / 66;

- software (software) written in the algorithmic languages Fortran and Assembler.

MARO is designed to equalize the amplitude-frequency characteristics of the electric and magnetic signal amplification and filtering paths, and to coordinate the electrical parameters of antenna devices and an analog-to-digital converter (ADC).

The composition of MARO includes:

- antenna modules of the electric (MA _e ) and magnetic (MA _m ) channels, providing reception of the corresponding horizontal field components, equalization of frequency characteristics in the channels and preliminary amplification of signals;

- analog amplification-filtering modules (UFNF) and notch filters (RF ₅₀ ) and (RF ₁₅₀ ), which carry out low-pass filtering, signal amplification and rejection of the two main harmonics of the network pickup in order to ensure the normal operation of the ADC;

- a module for generating a clock frequency (MFTC) for starting the ADC with a given frequency and temporal stability;

- a module for generating a calibration signal (MFKS), designed for end-to-end simultaneous calibration of electric and magnetic paths.

The antenna module of the magnetic path (MA _m ) contains a remote magnetic antenna made in the form of a two-section coil, the ends of which are connected to the inverting inputs of two operational amplifiers (op amps).

The signal from the input of these amplifiers is fed to the inputs of the third op-amp, the output of which is connected via a cable up to 50 meters to the analog filter amplification module located in the room. The differential inclusion of the magnetic sensor provides effective (up to 60 dB) common-mode interference suppression.

The parameters of the coil are: L = 25 H, r = 105 Ohms. The circuit provides a uniform frequency response in the operating range and preliminary adjustable gain in the path from 10 to 1000, depending on the connection of the corresponding resistance R _s in the feedback circuit of the op-amp. The frame, together with the remote amplifier, is placed in a container at a depth of 1 meter from the ground to reduce vibrational interference to the magnetic field sensor.

The antenna module of the electric path (MA _e ), connected via cable to the analog filtration module, consists of a symmetrical horizontal vibrator and an input differential cascade, almost similar to MA _m . The difference from the latter consists in the presence of diodes at the inputs of the electric path, protecting the inputs from the effects of powerful pulsed noise from powerful radars and close lightning discharges. The gain of the electrical path is 1200.

It is possible to use several types of electric field sensors:

- cable segments, the central veins of which are directly or through matching repeaters connected to a brass or copper electrode rod 50 cm long buried in the ground;

- equal sections of insulated conductors (cables with braided), connected to the differential input of the operational amplifier.

Both the cables themselves and the input repeaters or amplifiers are buried to a certain depth in the ground to eliminate possible interference from the vertical electrical component of the field. The transition resistance of the electrodes R _c , inversely proportional to the conductivity of the soil surrounding them, is subject to significant seasonal variations due to changes in soil moisture or freezing.

Analog amplification - filtration modules, the schemes of which are identical in the electric and magnetic paths, but differ in the magnitude of the gain, contain low-pass filter amplifiers with cut-off frequencies of 200 Hz at 3 dB and asymptotic attenuation of 48 dB per octave and active rejection filters that suppress at 35 dB of the main harmonics of the network 50 and 150 Hz. The maximum gain in the passband of the filters is controlled by the selection of R _S in the feedback loop of the op-amp and can reach 1000 times.

The parameters of the low-pass filter are selected based on the need to ensure effective suppression of specular frequencies outside the operating band of the control panel and ensure the amplification of useful signals to levels approximately corresponding to the first two gradations of the ADC.

The module for generating calibration signals is implemented on the basis of the timer counter 1 of the LA-2 board, operating in the meander generator mode and controlled programmatically by a personal computer. The signal from the output of the board goes to a calibration coil wound on a common frame with a signal coil.

The multifunctional module of the analog output and digital input-output LA-2 performs the most important functions in the central control panel (CPU) and contains:

- An analog-to-digital channel, consisting of an input multiplier, a full instrumentation amplifier with a gain that can be changed from 2 to 100, a 12-bit ADC with a UVX with an input voltage range of up to 10 V.

- three-channel counter timer, digital port with 8 lines to the input and 8 lines to the output. The multiplexer allows you to enter up to 8 signals with a balanced input.

The digital processing module (ICC) is a software module that performs the basic functions in the control unit and contains two main blocks: a block - input routines - filtering and a block - impedance calculation routines.

CPU block software.

Programs that implement the functions of the CPU are contained in the files “FIL2S.ASM”, “IMPEDAS.FOR” and “FILHF.FOR”.

After the analysis time has elapsed, the current information displayed on the monitor screen is output to a file in the root directory of the hard disk with a separate line for the reception time and implementation length in seconds.

Such a construction of the CPU allows it to be used to solve a number of applied geophysical problems, in particular:

- study of the structure of the electrical parameters of the earth's crust according to the registration data of navigation and connected radio stations of the ELF-ELF ranges, signals of natural origin, magnetic telluric fields, noise fields of ELF-ELF ranges of lightning and space origin, broadband electromagnetic pulses from individual powerful lightning discharges;

- search for minerals based on the analysis of the observed local anomalies in the values of the modulus and phase of the reduced surface impedance in the studied areas.

Such a wide range of applied tasks that can be solved with the help of the complex under consideration is determined by the functionality of the digital processing unit of the recorded signals, which are a set of subprograms for implementing various functions that are easily tunable depending on the specific problem being solved. Analog elements of the complex, including antennas of electric and magnetic paths, pre-amplifiers, band-pass and notch filters, highly stable clock generators, analog-to-digital converters - are also selected in accordance with the type of application.

In the existing version, the device can be used for simultaneous multicomponent impedance measurements, since the LA-2 analog-to-digital board included in the kit provides independent signal reception via 16 unbalanced or 8 differential channels.

The possibility of using electromagnetic radiation in the ELF-ELF range in the interests of applied geophysics is based on measuring the reduced surface impedance

D = E _t / (H _t * Z ₀ ), where

E _t and H _t are tangent components of the electric and magnetic fields on the earth's surface;

Z ₀ = 120π Ohm - wave impedance of free space.

In general, the impedance D is a complex quantity.

D = R _E (D) + iI _m (D) = / D / exp [iarg (D)]

Moreover, -π / 2≤arg (D) ≤π / 2

If the source of the ELF-ELF field is located far enough from the observation point, then the field in the vicinity of this point has the properties of a plane wave. In this case, with the known structure of the underlying medium, the impedance can be relatively easily calculated. If the underlying half-space is homogeneous and infinite, then

/ D / = 10 ^-5 - {f / (1,8σ)} ^1/2 ; arg (D) = π / 2, where f is the frequency of Hz,

σ is the specific conductivity of the underlying medium, S / m.

If the underlying medium is heterogeneous, for example, layered, then the impedance argument takes some value from the interval

-π / 2≤arg (D) ≤π / 2.

In practice, they are usually limited to considering a 2-3-layer model of the underlying medium with different conductivities for each

layers that well describe the real characteristics of geological structures. Based on the measured impedance values, the most probable parameters of the studied structures are selected by the method of minimizing residuals. Based on the obtained electrical properties of the layers, a conclusion is drawn about the nature of the geological structure. A priori information about the parameters of the layers is set on the basis of studies by other geophysical methods (seismic, control drilling, etc.). When using ELF-ELF ranges, there are unique opportunities for electromagnetic sounding of depths up to several tens of kilometers.

The positive effect is that the receiving device ELF-ELF frequencies allows you to solve the following tasks:

- to develop new experimental methods for studying the structure of the earth's crust, based on measurements of electromagnetic fields created by emitters of ELF-ELF ranges;

- predict seismic activity in various regions of the globe based on monitoring variations in reduced surface impedance due to changes in the conductivity of individual layers of the earth's crust associated with tectonic activity;

- to search for minerals based on the analysis of the observed anomalies in the values of the modulus and phase of the reduced surface impedance in the studied areas.

Claims (1)

A multi-program digital receiving recording device for geophysical research, containing a measuring complex for recording ELF-ELF emissions, characterized in that the complex is made up of two blocks of an analog diagnostics and processing module (MARO) and a personal electronic computer, and MARO contains an electromagnetic and magnetic antennas, respectively connected to antenna modules of the electric and magnetic channels, each of which through analog amplification modules is a filter AI and notch filters are connected to an analog-to-digital converter, the first output of which is connected to a module for generating calibrated signals, and the second through a divider is connected to a module for generating clock frequencies, in addition, a personal electronic computer is connected to a multifunction module for analog input and digital input - output.