RU2400780C1 - Device for logging electromagnet probing - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: device comprises k three-element probes, consisting of generator and pair of receiving coils, switched generator of working frequencies with power amplifiers, switched generator of heterodyne frequencies, k inlet switches, k high-frequency amplifiers, having inlets of amplification control, track of intermediate frequency, k circuits of automatic amplification control, amplitude metre, switching unit, computer unit, multiplexer of high frequency signals, demultiplexer of signals from metre of k calibration circuits amplitudes. Inlet switches and circuits of calibration alternately connect signals A₂ and A₁ from receiving coils of probes, their difference signal ΔA and calibrating signal to inlets of device, and these signals are converted by amplification-conversion track into digital code and arrive to computer unit. Computer unit corrects signals by calibrating signal and calculates ratios |A₂|/|A₁|, |ΔA|/|A₁|, |ΔA|/|A₂| and phase difference.

EFFECT: enhancement of functional capabilities, increased accuracy of measurements and operational reliability.

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Description

The invention relates to a field-geophysical technique and can be used to measure the electrical resistivity (resistivity) and / or dielectric constant of rocks crossed by a well, as well as to study the distribution of resistivity and / or dielectric constant in the near-wellbore zone in order to isolate permeable sections in wells reservoirs, determining the nature of their saturation and other parameters.

, где

,

- амплитуды напряженностей магнитных компонент поля в первой (ближней) и второй (дальней) приемных катушках зонда.A device is known for electromagnetic well logging (see USSR author's certificate No. 313966, IPC E21B 47/00, publ., September 7, 1971, Bull. No. 27), comprising receiving probe coils, a selective amplifier with an automatic gain control system that sets generator, power supply and ground recording equipment. In order to determine the attenuation of the electromagnetic field in the area between the measurement points and increase the accuracy of its measurement, a dividing system was introduced into the device to measure the ratio of the field strengths at the measurement points, a circuit for switching signals from the receiving coils and a calibration circuit for the receiving path. This device allows you to measure only one relative characteristic of the electromagnetic field, namely, the ratio

where

,

- the amplitudes of the magnetic field components in the first (near) and second (far) receiving coils of the probe.

,

и разность фаз Δφ сигналов в первой и второй приемных катушках (см. Д.С.Даев. Высокочастотные электромагнитные методы исследования скважин. М.: «Недра», 1974, с.37). Здесь

- амплитуда разностного сигнала приемных катушек. Совместная интерпретация результатов измерения этих характеристик позволяет повысить достоверность определения параметров изучаемых горных пород. Данное устройство не обладает возможностью измерения этих характеристик.The magnitude of this relationship is judged by the resistivity of rocks exposed by the well. However, of great practical interest is the joint measurement of other relative characteristics of the electromagnetic field:

,

and the phase difference Δφ of the signals in the first and second receiving coils (see DS Daev. High-frequency electromagnetic methods of well research. M: "Nedra", 1974, p. 37). Here

- the amplitude of the difference signal of the receiving coils. A joint interpretation of the measurement results of these characteristics can improve the reliability of determining the parameters of the studied rocks. This device does not have the ability to measure these characteristics.

A device for logging electromagnetic sounding is also known (see USSR author's certificate No. 1004940, IPC G01V 3/18, Bull. No. 10), containing a generator, three-element probes consisting of a generator and a pair of receiving coils, power amplifiers, intermediate frequency amplifiers converters , phase metering unit, telemetry unit, switching unit. The device also has electronic keys for the generator and measuring circuits of three-element probes, and three-element probes are made geometrically and electrodynamically similar to each other, the generator is made in the form of an operating frequency generator according to the number of generator coils of three-element probes, the number of local oscillator generators corresponds to the number of pairs of receiving coils.

This device allows you to measure only the phase difference Δφ of the signals in the receiving coils of a complex of geometrically and electrodynamically similar probes with different radial depth of study. Using the values of Δφ, the distribution of resistivity in the near-wellbore space is estimated, reservoirs are allocated and their parameters are evaluated.

However, the limited amount of information does not always allow us to reliably solve these problems.

A device is known (see the USSR patent for the invention "Method of electromagnetic logging of rocks and a device for its implementation" SU No. 1329630, IPC G01V 3/18, publ. 07.08.1987, Bull. No. 29), close in technical essence and construction to the claimed and taken as a prototype.

. Выход усилителя промежуточной частоты подключен также к входу измерителя разности фаз, содержащего последовательно соединенные схему прямоугольных сигналов, детектор нуля, триггер, интегратор, накопитель и дифференциальный усилитель. Накопитель также содержит две схемы выборки и хранения напряжений, пропорциональных фазам сигналов в приемных катушках относительно опорного сигнала, вырабатываемого формирователем сигналов коммутации. На выходе дифференциального усилителя вырабатывается напряжение, пропорциональное разности фаз Δφ сигналов в приемных катушках зонда. В состав устройства входит также вычислительный блок, расположенный на поверхности и связанный со скважинной частью устройства бронированным кабелем.One of the device variants (see FIG. 12 of the patent description) comprises a generator coil, amplitude and phase detectors made in the form of two pairs of receiving coils remote at predetermined distances from the generator coil (forming three-element probes), a high-frequency generator connected through a power amplifier to the generator coil, a shaper (block) of switching signals, including the first and second frequency dividers, a band-pass filter, a square-wave voltage shaper. There is also a driver (oscillator) of the local oscillator frequency, containing a phase detector, a third frequency divider and a voltage controlled oscillator. The device contains three data processing channels that are similar in structure, each of which includes an input switch that connects signals A ₁ , A ₂ , a high-frequency preamplifier (amplifier) having a gain control input, a mixer, a band-pass filter, an intermediate-frequency amplifier (form a path intermediate frequency), an amplitude meter in the form of a peak detector, the output of which is connected to the automatic gain control circuit, and its output is connected to the control input of the preamplifier as an inverse Noah connection. The output of the amplitude meter is also connected to a drive containing two voltage sampling and storage circuits proportional to the signal amplitudes in the connected receiving coils of the probe. The outputs of the sampling and storage circuits are connected to the division circuit, at the output of which a signal is generated corresponding to the ratio

. The output of the intermediate frequency amplifier is also connected to the input of the phase difference meter, which contains a series-connected circuit of rectangular signals, a zero detector, a trigger, an integrator, a drive and a differential amplifier. The drive also contains two voltage sampling and storage circuits, proportional to the phases of the signals in the receiving coils relative to the reference signal generated by the switching signal generator. The output of the differential amplifier produces a voltage proportional to the phase difference Δφ of the signals in the receiver coils of the probe. The device also includes a computing unit located on the surface and connected to the downhole part of the device with an armored cable.

, так и разность фаз Δφ, что расширяет его функциональные возможности.Thus, this device simultaneously measures both the relative characteristic of the field

, and the phase difference Δφ, which expands its functionality.

и

.However, this device does not allow measuring such informationally significant relative field characteristics as

and

.

Another disadvantage is the low accuracy of measuring the phase difference over a wide range of changes in ambient temperature. This is due to the fact that Δφ is defined as the difference between the phases φ ₁ and φ _{2 of the} signals of the receiving coils relative to the reference signal, which leads to a doubling of the limits of measurement error Δφ in comparison with the phase measurement error. With the achievable accuracy of measuring the phases φ ₁ and φ ₂ ± 1 °, the error in determining Δφ can reach ± 2 °. This leads to significant errors in the determination of the resistivity and permittivity of the medium.

In addition, the division circuit and phase difference meter are located in the downhole part of the device and are exposed to high temperatures, vibration and shock loads, which also reduces the measurement accuracy and operational reliability.

A disadvantage of the device is its relative complexity, which reduces its reliability in harsh downhole operating conditions.

The objectives of the present invention are to further expand the functionality, improve the accuracy of measurements, simplify the design and increase the operational reliability of the device.

The tasks are solved in that in a known device for electromagnetic well logging, containing k three-element probes, consisting of a generator and a pair of receiving coils, a switched operating frequency generator with k power amplifiers, a switched oscillator of heterodyne frequencies, k input switches, k high-frequency amplifiers, having an gain control input, intermediate frequency path, k automatic gain control circuits, amplitude meter, switching unit, telemetry unit, computing unit, volume 1 ... k the outputs of the switched operating frequency generator are connected to the inputs of the same power amplifiers, the outputs of which are connected to the same-name generator coils of three-element probes, 1 ... k pairs of receiving coils of the three-element probes are connected to the inputs of the same input switches, the first input of the intermediate frequency path is connected to the output of the switched heterodyne frequency generator, and the output of the intermediate frequency path is connected to the input of the amplitude meter, the first output of which is connected to the input of the unit by the body three, 1 ... k the outputs of the automatic gain control circuits are connected to the gain control inputs of the high-frequency amplifiers of the same name, the outputs of the switching unit are electrically connected to the control inputs of the switched oscillators of the working and heterodyne frequencies and the control inputs of the input switches, the output of the telemetry unit is connected via the communication line to the input of the computing unit, additionally introduced a multiplexer of high-frequency signals, a demultiplexer of signals of the amplitude meter and k calibration circuits, and input the switches are made with the additional function of connecting the differential signal of the pairs of receiving coils, while the outputs of the input switches are connected to the inputs of the calibration circuits, and their outputs are connected to the inputs of the high-frequency amplifiers, the inputs of the high-frequency signal multiplexer are connected to the outputs of the high-frequency amplifiers, and the output is connected to the second input, the path of the intermediate frequency, the input of the demultiplexer of the signals of the amplitude meter is connected to the second output of the amplitude meter, and its outputs are connected to the inputs of the automatic circuits eskoy adjustment gain control inputs of the multiplexer high frequency signals, the demultiplexer signal amplitude meter and calibration circuits are electrically connected to the switching unit.

As three-element probes, it is possible to use probes that meet the conditions of geometric and electrodynamic similarity, for which the following relations are true:

where α is the coefficient of geometric similarity; L _i and L _{i + 1} - the distance between any of the same elements of the probes; i = 1; 2; ... k is the serial number of the probe and L _i <L _{i + 1} .

where f _i , f _{i + 1} is the cyclic frequency of field excitation by probes with L _i and L _{i + 1} ,

where β is the coefficient of electrodynamic similarity.

Probe lengths from 0.5 to 2.5 m, operating frequencies from 10 to 0.4 MHz.

The amplitude meter can be made on the basis of a linear peak detector with the subsequent conversion of an analog DC signal into a digital code using an analog-to-digital converter (ADC).

An embodiment of the amplitude meter is also possible using a high-speed ADC that directly converts the amplitude of the variable intermediate frequency signal into a digital code.

The switching unit can be built on the basis of microcontrollers or programmable logic integrated circuits.

The computing unit may be performed using a computer.

Figure 1 presents a functional diagram of the device, figure 2 is an embodiment of an input switch, figure 3 is an embodiment of a calibration circuit, figure 4 is a vector diagram of the signals in the receiving coils of a three-element probe.

A device for logging electromagnetic soundings contains (see Fig. 1) k three-element probes, including generator 1 ₁ , 1 _k and pairs 2 ₁ , 2 _k receiving coils, a switched generator 3 of working frequencies with amplifiers 4 ₁ , ..., 4 _k power, switchable oscillator 5 local oscillation frequencies, input switches 6 ₁ , ..., 6 _k , high-frequency amplifiers 7 ₁ , ..., 7 _k , having a gain control input, intermediate frequency path 8, automatic gain control circuits 9 ₁ , ..., 9 _k , meter 10 amplitudes, switching unit 11, telemetry unit 12, computing unit 13 , multiplexer 14 high-frequency signals, demultiplexer 15 signals of the amplitude meter, calibration circuit 16 ₁ , ..., 16 _k .

1 ... k - the outputs of a switched generator of 3 operating frequencies are connected to the inputs of the same name amplifiers 4 ₁ , ..., 4 _k power, the outputs of which are connected to the same generator coils 1 ₁ , ..., 1 _k three-element probes, pairs 2 ₁ , ..., 2 _k receiving the coils of three-element probes are connected to the inputs of the same input switches 6 ₁ , 6 _k , the first input of the intermediate frequency path 8 is connected to the output of the switching oscillator 5 heterodyne frequencies, the output of the intermediate frequency path 8 is connected to the input of the amplitude meter 10, the first output of which is connected with the input of the telemetry unit 12, 1 ... k the outputs of the automatic gain control circuits 9 ₁ , ..., 9 _{k are} connected to the high-frequency amplifiers 7 ₁ , ..., 7 _k gain control inputs, the outputs of the switching unit 11 are electrically connected to the control inputs of the switched generators 3 and 5 operating and heterodyne frequencies, respectively, and the control inputs of the input switches 6 ₁ , 6 _{k the} output of the telemetry unit 12 is connected via the communication line to the input of the computing unit 13, the outputs of the input switches 6 ₁ , 6 _{k are} connected to the inputs of the circuits 16 ₁ , ..., 16 _k calibration, and their outputs with the inputs of the amplifiers 7 ₁ , ..., 7 _k high frequency, the inputs of the multiplexer 14 high-frequency signals are connected to the outputs of the amplifiers 7 ₁ , ..., 7 _k high frequency, and its output is connected to the second input of the intermediate frequency path 8, the input of the demultiplexer 15 signals measuring amplitudes is connected to the second output meter 10, the amplitudes and outputs of the demultiplexer 15 are connected to the inputs of circuits 9 _1, 9 _k automatic gain control, the control inputs of the multiplexer 14 high-frequency signals, the demultiplexer 15 meter amplitude signals and circuits 16 _1, 16 _k calibration electrically connected to switching unit 11.

The input switches 6 ₁ , ..., 6 _{k are} made with the additional function of connecting the differential signal of pairs 2 ₁ , ..., 2 _{k of the} receiving coils to the inputs of the device.

Figure 2 shows one of the embodiments of the input switches, in particular, 6 ₁ . The input switch contains electronic keys 16, 17, 18 and an inductor 19. The electronic key 16 is connected parallel to the inductor 19, and the electronic keys 17, 18 are parallel to the receiving coils, connected counterclockwise in series. The inductor 19 and the receiving coils are connected in series. The electrical parameters of the inductor 19 and the receiving coils are chosen the same, which is necessary to maintain the constancy of the output impedance.

An embodiment of input switches with opposite parallel connection of receiving coils is also possible.

Figure 3 presents an embodiment of a calibration circuit (16 ₁ ). It contains electronic switches 20, 21 and precision resistors 22, 23, forming a calibrated input voltage divider.

The inputs of the keys 22 and 23 are connected to the upper and lower shoulders of the voltage divider, respectively, and the outputs are interconnected and are the output of the calibration circuit.

The device operates as follows.

. При измерении первым трехэлементным зондом блок 11 коммутации устанавливает переключаемый генератор 3 рабочих частот в состояние генерации сигнала рабочей частоты f₁ первого трехэлементного зонда, который усиливается усилителем 4₁ мощности до необходимого уровня и подается на генераторную катушку 1₁ первого трехэлементного зонда. Ток в этой катушке возбуждает в горных породах электромагнитное поле, индуцирующее сигналы в приемных катушках зонда. Блок 11 коммутации устанавливает также переключаемый генератор 5 гетеродинных частот в состояние генерации сигнала гетеродинной частоты f_г1 первого трехэлементного зонда, который подается на первый вход тракта 8 промежуточной частоты. Разность частот Δf=f_г1-f₁ является промежуточной частотой. Гетеродинные частоты выбраны так, что промежуточная частота Δf=f_гi-f_i одинакова при измерении всеми k трехэлементными зондами. Δf выбирается в пределах 10-100 кГц.Consistently, with time separation, the characteristics of the excited electromagnetic field k are measured using three-element probes, forming a complete cycle T, the duration of which can be selected within 100-200 ms. The measurement time Δt by one probe is respectively equal

. When measured by the first three-element probe, the switching unit 11 sets the switchable operating frequency generator 3 to the state of generating the working frequency signal f _{1 of the} first three-element probe, which is amplified by the power amplifier 4 ₁ to the required level and is supplied to the generator coil 1 _{1 of the} first three-element probe. The current in this coil excites an electromagnetic field in the rocks, inducing signals in the receiving coils of the probe. The switching unit 11 also sets the switched oscillator of the local oscillator frequency 5 in the state of generation of the local oscillator frequency signal f _{g1 of the} first three-element probe, which is fed to the first input of the intermediate frequency path 8. The frequency difference Δf = f _g1 -f ₁ is an intermediate frequency. The heterodyne frequencies are chosen so that the intermediate frequency Δf = f _gi -f _{i is the} same when measured with all k three-element probes. Δf is selected in the range of 10-100 kHz.

At the command of the switching unit 11, the multiplexer 14 connects the output _{of the} high-frequency amplifier 7 ₁ to the second input of the intermediate frequency path 8, and the demultiplexer 15 connects the second output of the amplitude meter 10 with the input _{of the} automatic gain control circuit 9 ₁ . Further, after the end of transient processes, four measurement steps are performed.

In the first cycle, the switching unit 11 sets the input switch 6 ₁ to the connection position of the signal A _{2 of the} second (far) receiving coil in pair 2 ₁ , while in the input switch 6 ₁ (see figure 2) the keys 16, 18 are open, and the key 17 closed.

In the calibration circuit 16 ₁ (see FIG. 3), the switching unit 11 sets the key 20 to the closed state, and the key 21 to the open state. Thus, in the first measurement step, the first (near) coil of pair 2 ₁ turns out to be closed by key 17, and the second (distant) is connected together with inductance coil 19 to the input _of calibration circuit 16 ₁ and through its closed key 20 to the input _of high-frequency amplifier 7 ₁ signal A _{2 of the} second coil of pair 2 _{1 of the} three-element probe is supplied. The amplified signal A ₂ with a frequency f ₁ through a multiplexer 14 is fed to the second input of the intermediate frequency path 8, where, after mixing with the local oscillation frequency f _g1 , a differential intermediate frequency Δf is formed. An amplified intermediate frequency signal proportional to A ₂ is supplied to the input of the amplitude meter 10. The amplitude meter 10 converts an alternating signal A ₂ with a frequency Δf into a digital code equivalent to its amplitude. This digital code is supplied from the first output of the amplitude meter 10 to the input of the telemetry unit 12, where it is converted into a form convenient for transmission via a communication line, transmitted to the computing unit 13, and recorded in its memory.

In the second measurement step, the switching unit 11 sets the input switch 6 ₁ to the connection position of the differential signal ΔA of the pair 2 _{1 of the} receiving coils, while in the input switch 6 _{1, the} key 16 closes, the key 17 opens, and the key 18 remains in the open state.

In the circuit 16 ₁ calibration of the state of the keys 20, 21 remain the same. This cycle of measurement to the input amplifier _{1 July} high frequency circuit through calibration January ₁₆ are connected oppositely included receiver coils couple 2 ₁ and at the input of the amplifier 7, the difference signal ΔA acts. This signal undergoes the same transformations as the signal A ₂ and in the form of a digital equivalent of its amplitude is recorded in the memory of the computing unit 13.

In the third measurement step, the switching unit 11 sets the input switch 6 ₁ to the connection position of the signal A _{1 of the} first (near) receiving coil in pair 2 ₁ , while in the input switch 6 _{1, the} key 16 is opened, the key 17 remains in the open state, and the key 18 closes. In the circuit 16 ₁ calibration of the state of the keys 20, 21 also remain the same. To the input amplifier 7 ₁ through the high frequency circuit 16 is connected _one calibration coil 19 together with the first receiving coil inductance Pairs 2 and _1, the input amplifier 7 receives the signal A _{1 1.}

The signal A _{1 is} converted in the same way as the signals A ₂ and ΔA, after which it is recorded in the memory of the computing unit 13 in the form of a digital equivalent of its amplitude.

In the fourth measurement cycle, the input switch 6 ₁ remains in the position of signal A ₁ connection, and in the calibration circuit 16 ₁ , the key 20 opens, the key 21 closes. In this case, only part of the signal A ₁ , determined by the division coefficient m of the divider on the resistors 22, 23, is fed to the input _{of the} high-frequency amplifier 7 ₁ , i.e.

where R ₂₂ , R ₂₃ - resistance of the resistors 22 and 23.

The division coefficient m is selected in the range of 0.03-0.08.

The signal mA ₁ passes through the same amplification-conversion path and in the form of a digital equivalent of its amplitude is recorded in the memory of the computing unit 13.

In the measurement process in the circuit 9 ₁ automatic gain control connected to the second output of the amplitude meter 10 through the demultiplexer 15, a signal is generated that controls the amplification _{of the} high-frequency amplifier 7 ₁ and is supplied to its gain control input. As a result of the operation _{of the} automatic gain control circuit 9 ₁ at the input of the amplitude meter 10, signal levels are maintained that are little dependent on the electrical parameters of the environment of the probe.

;

;

.At the end of the fourth measurement cycle, in the computing unit 13, the measured signal values are corrected according to the measurement results of the known calibration signal mA ₁ and the amplitude relative field characteristics are calculated as ratios

;

;

.

,

и

.The method for determining the phase difference Δφ is illustrated by the vector diagram shown in Fig.4. On it, in the form of complex quantities in the coordinates of the real ReA and imaginary ImA parts, the signal vectors are shown

,

and

.

и

относительно тока в генераторной катушке - φ₁ и φ₂ соответственно.Phase Vectors

and

relative to the current in the generator coil - φ ₁ and φ _2, respectively.

и

Разностный сигнал ΔА приемных катушек это вектор

, соединяющий концы векторов

и

Векторы

и

и

образуют треугольник.The phase difference Δφ = φ ₂ -φ ₁ is the angle between the vectors

and

The difference signal ΔA of the receiving coils is a vector

connecting the ends of vectors

and

Vectors

and

and

form a triangle.

From the cosine theorem we have:

,

,

whence follows:

Computing unit 13 performs these calculations.

,

,

и Δφ₁ запоминаются вычислительным блоком 13.The measurement results of the first three-element probe

,

,

and Δφ _{1 are} stored by the computing unit 13.

At the end of the first three-element probe, the switching unit 11 sets the switched oscillator 3 of the operating frequency to the state of generating the signal of the operating frequency f _{2 of the} second three-element probe, and the switched generator 5 of the heterodyne frequencies to the state of generating the signal of the local oscillation frequency f _{g2 of the} second three-element probe, multiplexer 14 connects the amplifier output _{2 July} high frequency path to the second input 8 of the intermediate frequency, and a second demultiplexer 15 connects output amplitude meter 10 to an input circuit ₉ February automated eskoy gain.

Further, the measurement process proceeds as described for the first three-element probe. As a result of the second three-element probe, relative field characteristics are measured:

,

,

и Δφ₂, которые фиксируются в памяти вычислительного блока 13.

,

,

and Δφ ₂ , which are fixed in the memory of the computing unit 13.

The full measurement cycle ends with the work of the k-th three-element probe and obtaining the relative characteristics of the field:

,

,

и Δφ_k.

,

,

and Δφ _k .

The described measurement cycle is repeated over time many times. The measurement results are converted by the computing unit 13 in accordance with the calibration dependencies in the corresponding values of the apparent resistivities and / or dielectric constants, which can be written in the form of well logs as a function of well depth.

If the device contains, for example, five three-element probes, twenty relative field characteristics can be obtained. Such a volume of information received significantly increases the functionality of the device and allows a more reliable study of rock parameters.

In the proposed device, the measurements of the signals of the three-element probe are made by one amplification-conversion path, therefore, changes in the transmission coefficient, for example, when exposed to temperature, equally affect the measurement results of signals A ₁ , A ₂ , ΔA, and since the final results are the ratio of the amplitudes of these signals, changes in the transmission coefficient of the path do not affect their value. The phase difference Δφ here is determined directly and as a function of the signal ratio, which also eliminates the influence of changes in the transmission coefficient on the measurement accuracy and does not require the use of a reference signal.

The use of a calibration scheme makes it possible to take into account the zero-level drift of the amplification-conversion path and to correct the measured signals for its influence.

In the downhole part of the device, unlike the prototype, there are no such blocks as a division circuit and phase difference meter that largely determine the metrological characteristics of the device.

The operations of determining the ratio of the amplitudes and the phase difference are performed with high accuracy by a ground computing unit located in normal conditions.

The described measures have significantly improved the accuracy of measuring relative amplitude and phase characteristics.

Thanks to the use of a single conversion path for all three-element probes, elimination of the division circuit from the borehole part, as well as a phase difference meter, the device was significantly simplified and, therefore, its operational reliability increased.

Working drawings of the device were developed and prototypes were made, tests of which confirmed the effectiveness of the proposed technical solutions.

Claims (1)

An electromagnetic logging device comprising k three-element probes consisting of a generator and a pair of receiving coils, a switchable operating frequency generator with k power amplifiers, a switchable heterodyne frequency generator, k input switches, k high-frequency amplifiers having a gain control input, an intermediate frequency path , k circuits for automatic gain control, amplitude meter, switching unit, telemetry unit, computing unit, while outputs 1 ... k of the switched oscillator frequencies are connected to the inputs of the same name power amplifiers, the outputs of which are connected to the same-name generator coils of three-element probes, l ... k from a pair of receiving coils of three-element probes are connected to the inputs of the same input switches, the first input of the intermediate frequency path is connected to the output of the switching oscillator of heterodyne frequencies, and the output the intermediate frequency path is connected to the input of the amplitude meter, the first output of which is connected to the input of the telemetry unit, 1 ... k outputs of automatic control circuits gain coils are connected to the gain control inputs of high-frequency amplifiers of the same name, the outputs of the switching unit are electrically connected to the control inputs of switched oscillators of working and heterodyne frequencies and the control inputs of input switches, the output of the telemetry unit is connected via the communication line to the input of the computing unit, characterized in that it is additionally introduced a multiplexer of high-frequency signals, a demultiplexer of the signals of the amplitude meter and k calibration circuits, and the input switches are made s with the additional function of connecting a differential signal of pairs of receiving coils, while the outputs of the input switches are connected to the inputs of the calibration circuits, and their outputs are connected to the inputs of the high-frequency amplifiers, the inputs of the high-frequency signal multiplexer are connected to the outputs of the high-frequency amplifiers, and the output is connected to the second input of the path intermediate frequency, the input of the demultiplexer of the signals of the amplitude meter is connected to the second output of the amplitude meter, and its outputs are connected to the inputs of the automatic control circuits eniya, the control inputs of multiplexer high frequency signals, the demultiplexer signal amplitude meter and calibration circuits are electrically connected to the switching unit.

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