RU2158940C2 - Device for geoelectric reconnaissance - Google Patents

Abstract

FIELD: frequency sounding using magnetic and electric excitation of electromagnetic field. SUBSTANCE: invention preferably may be used for phase-sensitive measurements for investigation of apparent resistance of upper Earth layer in wide frequency range. Device has field excitation source, first, second and third control lines, which are connected to control inputs of first and second frequency synthesizers and digital phase shifter, respectively. Digital phase shifter is inserted between output of second synthesizer and control input of phase-sensitive rectifier, which signal input is connected to field detector, and which output is connected to input of band-pass filter, which output is connected to signal input of phase-sensitive analog-to-digital converter, which is connected to input of indication unit. In addition device has power amplifier, which is connected to output of first frequency synthesizer, which is connected to output of first oscillator. In addition device has second oscillator, which is connected to input of second frequency synthesizer, first and second frequency dividers, commutator, which is inserted between field excitation source and power amplifier. First frequency divider is inserted between output of first frequency synthesizer and control input of commutator. Second frequency divider is inserted between output of second frequency synthesizer and control input of phase- sensitive analog-to-digital converter. First and second control lines are connected to control inputs of first and second frequency synthesizers, respectively. Setting input of second frequency divider is connected to setting input of second frequency synthesizer and fourth control line. EFFECT: increased precision for measuring real and imaginary constituents of electromagnetic field. 1 dwg

Description

 The invention relates to a device for frequency sounding with magnetic and electric excitation of an electromagnetic field. The field of predominant application is phase-sensitive measurements used to study the apparent resistance of the upper layer of the earth in a wide frequency range.

 A device for electrical exploration by the method of induced polarization [1], consisting of an inverter (generator), receiving and supply lines, a selective amplifier, a detector and a pulse voltmeter (measuring device). The generator generates bipolar pulses filled with ripple voltage. These bipolar pulses are fed into the supply line AB. The receiving line is connected to a pulse voltmeter and to a selective amplifier. A selective amplifier extracts a signal from the input voltage with the filling frequency of a polarizing current pulse.

 This signal is detected in the detector and serves to switch the sensitivity of the measuring device that measures the input voltage at certain points in time. The known device has the main advantage in that the measuring device can work offline at a great distance from the generator (generator device).

 However, the known device has a significant drawback, namely, that the synchronization of the measuring device relative to the current in the supply line is accurate to phase, i.e. the sign of the gradient of the transmission potentials and the induced polarization is not determined.

 A device [2] for electrical exploration by the charge method, consisting of a commercially available station type ERS-67 and a portable digital voltmeter PVC-1. The known device allows you to make gradient (phase-sensitive) measurements at infra-low frequencies in large areas under study. However, this device has a significant drawback, which consists in lowering the measurement accuracy with an increase in the operating frequency and with an increase in sensitivity due to spurious radiation of the electromagnetic field of the operating frequency (microphone effect).

 Also known is a device for geoelectrical exploration by frequency sensing [3], comprising a generator device consisting of a first master oscillator, a power amplifier, a power dipole, a frequency synthesizer including a frequency divider and a control circuit, a receiver device consisting of series-connected filter units, a broadband amplifier, a detector with a recorder and a series-connected calibration generator, a calibration voltage divider and a signal receiver. This device is taken by us as a prototype device. In the prototype device, the measurement accuracy is improved by comparing the measured signal with a reference voltage. However, this device has a significant drawback in that it does not allow phase-sensitive measurements, and also with an increase in the frequency of the useful signal and sensitivity, the measurement accuracy is significantly reduced due to spurious radiation of the electromagnetic field of the operating frequency (microphone effect).

 The purpose of the invention is to increase the accuracy of measurements of the real and imaginary components of the electromagnetic field.

 This goal is achieved by the fact that in the device for geoelectrical exploration containing the field exciter, the first, second and third control buses are connected respectively to the control inputs of the first and second frequency synthesizers and a digital phase shifter installed between the output of the second frequency synthesizer and the control input of the phase-sensitive rectifier connected a signal input to the field sensor, and an output to the input of a bandpass filter connected by the output to the signal input of a phase-sensitive analog-digital a converter connected to the input of the display unit, a power amplifier connected to the output of the first frequency synthesizer connected to the output of the first generator, a second generator connected to the input of the second frequency synthesizer, additionally introduced the first and second frequency dividers, a switch installed between the field exciter and the amplifier power, and the first frequency divider is connected between the output of the first frequency synthesizer and the control input of the switch, and the second frequency divider is between the output of the second synthesis torus frequency and phase-sensitive control input of analog-to-digital converter, moreover, the first and second control bus connected respectively with the first and second frequency divider control input and adjusting input of the second frequency divider is connected to the adjusting input of the second frequency synthesizer and a fourth control bus.

 The drawing shows a structural diagram of the proposed device.

 The device comprises a first generator 1, a first frequency synthesizer 2, a power amplifier 3, a switch 4, a field exciter 5, a first frequency divider 6, a first control bus 7, a field sensor 8, a phase-sensitive rectifier 9, a phase-sensitive analog-to-digital converter 11, an indication unit 12 , a digital phase shifter 13, a second generator 14, a second frequency synthesizer 15, a second frequency divider 16, a second control bus 17, a third control bus 18, a fourth control bus 19, a transmission line 20, which is either a two-wire line, or adiokanal not included in the device as the main unit.

 The first frequency synthesizer 2 is installed between the output of the first generator 1 and the inputs of the power amplifier 3 and the first frequency divider 6, the switch 4 is installed between the output of the power amplifier 3 and the field exciter 5. The control input of the switch 4 is connected to the output of the first frequency divider 6. The phase-sensitive rectifier 9 is connected the signal input to the field sensor 8, and the output through the bandpass filter 10 to the signal input of the phase-sensitive analog-to-digital Converter 11. The second frequency synthesizer 15 is installed between the output of the second the generator 14 and the inputs of the digital phase shifter 13 and the second frequency divider 16, connected by the output to the control input of the analog-to-digital converter 11, connected by the output to the input of the display unit 12. The digital phase shifter 13 is connected by the output to the control input of the phase-sensitive rectifier 9. The first control bus 7 is connected to the control inputs of the first frequency synthesizer 2 and the first frequency divider 6, the second control bus 17 to the control inputs of the second frequency synthesizer 15 and the second frequency divider 16, the third bus control 18 to the control input of the digital phase shifter 13, and the fourth control bus 19 to the installation inputs of the second frequency synthesizer 15 and the second frequency divider 16.

The device operates as follows. The first generator 1 generates rectangular pulses with a repetition rate f ₀ . These pulses are fed to the input of the first frequency synthesizer 2. The control code N _y is supplied to the control input of the first frequency synthesizer 2 from the first control bus 7. The first frequency synthesizer 2 generates a sinusoidal voltage U _C1 = U _m1 sin (ω ₀ / N ₀ • t) = U _m1 sinΩ ₀ t, where U _m1 is the amplitude, ω ₀ = 2πf ₀ , N ₀ is an integer defined by the code N _y , Ω ₀ = ω ₀ / N ₀ .
The output voltage U _C1 is supplied to the inputs of the power amplifier 3 and the first frequency divider 6. The first frequency divider 6 generates a rectangular signal U _n1 = U _g • Sign sin (ω ₀ / N ₀ • N _g ) • t = U _g • Sign sinΩ _n t, where U _g is the amplitude, SignSinZ is the sign function of the argument Sin Z, Ω _n = ω ₀ / N ₀ • N _g = Ω ₀ / N _g is the frequency of the low-frequency signal, N _g is the division coefficient specified by the code N _y , from conditions Ω ₀ ≫ Ω _n = const.
The output voltage of the first frequency divider 6 is supplied to the control input of the switch 4, which changes the polarity of the field exciter 5 to the output of the power amplifier 3. As the exciter of field 5, either a magnetic dipole (magnetic excitation) or a supply line AB (electric excitation) can be used .

Let us consider only the magnetic dipole. As a result, an alternating current I _b = I _m Sign sinΩ _n t • sinΩ ₀ t flows in the magnetic dipole, and the magnetic moment created by the dipole is determined by the expression Mg = I _b • S = M _m • Sign sinΩ _n t • sinΩ ₀ t, where M _m = I _m • S is the amplitude, S is the effective area of the magnetic dipole.

At the point of observation (measurement), the magnetic field is determined by the expression B = B _xm Sign sinΩ _n t • sin (Ω ₀ t + φ _b ) + B _nm sin (Ω ₀ t + φ _n ), where B _xm is the amplitude proportional to the amplitude of the magnetic moment M _m , φ _b is the phase shift of the magnetic field relative to the current in the magnetic dipole, B _nm , φ _n are the amplitude and phase of the synchronous interference created by the blocks of the proposed device, respectively.

где S_g - эффективная площадь датчика 8, φ_g - фазовый сдвиг, вносимый датчиком 8. Выходное напряжение датчика 8 поступает на сигнальный вход фазочувствительного выпрямителя 9.From the sensor 8, under the influence of a magnetic field B at the measurement point, the voltage is removed

where S _g is the effective area of the sensor 8, φ _g is the phase shift introduced by the sensor 8. The output voltage of the sensor 8 is supplied to the signal input of the phase-sensitive rectifier 9.

где U_xm = (-K_BΩ₀B_xmS_g)/2 - амплитуда полезного сигнала, К_B - коэффициент передачи фазочувствительного выпрямителя 9, U_nb = (-K_BΩ₀B_nmS_g)/2 - величина, пропорциональная амплитуде B_nm помехи.The second generator 14 generates rectangular pulses with a repetition frequency ω ₀ . These pulses are fed to the input of the second frequency synthesizer 15. The second frequency synthesizer 15 generates a sinusoidal voltage U _c2 = U _m2 sin (ω ₀ / N ₀ • t + φ _c2 ) = U _m2 sin (Ω ₀ t + φ _c2 ), where U _m2 is the amplitude, Ω ₀ = ω ₀ / N ₀ , φ _c2 is the initial phase, N ₀ is the integer determined by the code N _y supplied to the control input from the second control bus 17. The output voltage of the second frequency synthesizer 15 is supplied to the digital inputs the phase shifter 13 and the second frequency divider 16. In the digital phase shifter 13, the voltage U _c2 is shifted in phase by the amount (φ _c + α), where φ _c - I compensate phase shift, α is the initial phase equal to 0 or π / 2.
The output low-frequency signal U _B phase-sensitive rectifier 9 is determined by the expression:

where U _xm = (-K _B Ω ₀ B _xm S _g ) / 2 is the amplitude of the useful signal, K _B is the transfer coefficient of the phase-sensitive rectifier 9, U _nb = (-K _B Ω ₀ B _nm S _g ) / 2 is the value, proportional to the amplitude B _{nm of the} interference.

The installation pulses received through the communication line 20 to the installation input, the second frequency synthesizer 15 is set to a state in which φ _c2 = 0, and the control code supplied to the control input of the digital phase shifter 13 is set φ _c = -φ _g . Then the output voltage of the phase-sensitive rectifier is determined by the expression:
U _B = U _xm sin (φ _b + α) Sign sinΩ _n t + U _nb • sin (φ _n + α).
The output signal U _{B of the} phase-sensitive rectifier 9 is fed to the input of the bandpass filter 10, in which the frequency selection of the useful signal with a frequency of Ω _{n is} carried out, and then to the input of the phase-sensitive ADC 11, the control voltage of which is supplied with the reference voltage U _o = U _om Sign sinΩ _n t from the second frequency divider 16. In the ADC 11, the analog signal is converted to the digital equivalent N, determined from the expression:
N = S • K _f • U _xm sin (φ _b + α) = K ₀ B _xm sin (φ _n + α),
where K ₀ is the product of the transmission coefficients of blocks 8-11, S is the slope (coefficient) of the conversion of the ADC 11, K _f is the transmission coefficient of the band-pass filter.

 From the expressions for N it can be seen that the output code is independent of the interference received at the input of the phase-sensitive rectifier 9.

For α = 0, the output code N _Jm = K _o B _xm • sinφ _{b is} proportional to the imaginary component of the useful signal, and for α = π / 2, the output code N _Re = K _o B _xm • cosφ _{b is} proportional to the real component of the magnetic field. The output code N _{Jm, Re is} indicated in display unit 12.

 The proposed device works in a similar way when measuring electrical signals from a receiving earthed line used as a field sensor 8.

From the expressions for N _Re and N _Jm it can be seen that the output code does not depend on the amount of interference of the operating frequency induced in the field sensor by 8 blocks of the proposed device due to the microphone effect, thereby increasing the accuracy with increasing frequency Ω _{0 of the} useful signal, as well as sensitivity increase, i.e. when measuring small quantities of signals.

 The proposed device was taken as the basis for the development of phase-sensitive equipment ФЧ-1, made for conducting experiments on a subject supported by the Russian Foundation for Basic Research (project N 96-05-64252).

Claims (1)

 A device for geoelectrical exploration, containing a field exciter, first, second and third control buses connected respectively to the control inputs of the first and second frequency synthesizers and a digital phase shifter installed between the output of the second frequency synthesizer and the control input of a phase-sensitive rectifier connected by a signal input to the field sensor, and an output to the input of a bandpass filter connected by the output to the signal input of a phase-sensitive analog-to-digital converter connected to the input display indicator, a power amplifier connected to the output of the first frequency synthesizer connected to the input of the first generator, a second generator connected to the input of the second frequency synthesizer, characterized in that it additionally introduces the first and second frequency dividers, a switch installed between the field exciter and a power amplifier, and the first frequency divider is connected between the input of the first frequency synthesizer and the control input of the switch, and the second frequency divider is between the output of the second frequency synthesizer and Odom control phase-sensitive analog-to-digital converter, moreover, the first and second control bus connected respectively with the first and second frequency divider control input and adjusting input of the second frequency divider is connected to the adjusting input of the second frequency synthesizer and a fourth control bus.