RU1786459C - Method for measurement of dynamic electromagnetic field and device for its realization - Google Patents

Abstract

Usage: in the field of geophysics for the study of geoelectric section and mapping. SUMMARY OF THE INVENTION: measurement of field components in any area of a source using a low-pass filter in the measurement channel, subsequent digitization of the data with a constant quantization step. The digital signal values for each component are filtered with a time-varying passband, while the filter cut-off frequency of the measuring channel is changed simultaneously with the change of the passband of the filter, the pass-band of the low-pass filter being wider than the pass-band of the digital filter. 2 s.p. f-ly, 4 ill. Sfc

Description

The invention relates to methods and devices for conducting geophysical surveys using an artificial electromagnetic field for studying a geoelectric section and mapping of electrical boundaries.

A known method and device for recording a non-stationary electromagnetic field in any area of a source, including excitation of an electromagnetic field by a supply source in the form of a horizontal electric line 1 AB, or a horizontal ungrounded frame Q and interval measurement of the field at a certain distance from the source or inside the supply О with restriction bandwidth of the measuring channel using analog filters while increasing the sensitivity of the channel. As a field sensor, horizontal

ungrounded frame (s) measuring the derivative of the vertical component of the floor. The floor sensor is connected to the input of the measuring channel of the digital electrical prospecting station.

A prototype of the invention is a method for sensing a field in the near zone of a source by exciting a field with an earthed Q frame and measuring the vertical derivative of the magnetic field EVg / d t in the center of the supply loop with Cycle-2 equipment.

This method is widely used in measuring the signal in the high-frequency region, but has the same drawbacks as the analogue (reducing the accuracy of measurements during interval recording of the signal with limiting the bandwidth of the measuring channel while increasing its sensitivity).

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An electrical exploration complex is also known, which contains a generator set with a master oscillator, autonomous meters including serially connected floor sensors and amplifiers, a switch, as well as an analog-to-digital converter, an arithmetic logic device, random access memory, a synchronization and control system, a telecommand system comprising a transmitter and a decoder, as well as a data transceiver module

The disadvantages of this electrical exploration complex are:

1. A limited number of channels in a stand-alone meter, related to the finite speed of writing data to a magnetic recorder and the limited frequency range for such a system design.

For example, to record data in the range of 10-100 Hz, a minimum quantization frequency of 200 Hz is required.

The data volume per channel, the recording time of 10 s will be 12048 words, with eight-channel construction of the system the speed of receipt - data will be 1600 words / s, or when using a two-byte word 3200 bytes / s. The latter is characteristic of existing types of cassette recorders (for example, type CM 5204). The amount of data required to register one complete measurement with a generator set will be at least 100 arrays per channel with a volume of $ 204 words and a non-channel recording system:. Щ: -№. s:

V 2048x 100x8 1 638400 words: ;;

The indicated amount of data cannot be recorded on a magnetic tape cartridge (NML), while the use of stationary NML is impractical due to the large energy consumption and overall dimensions. Therefore, such a post | 4 Ри of the system limits its ability to use the number of drops used (Yl; reduction of the recorded volume; the formation in the prototype uses digital data filtering, which allows to reduce the amount of recorded information by 6-8 times I v; ... ./ .. v; ..:. r:; -::

2. The signal-to-noise ratio will be determined by the selected bandwidth of the analog path, which especially affects the measurement accuracy of low-frequency signals. In order to obtain acceptable accuracy, it is necessary to significantly increase the accumulation volume.

The aim of the invention is to expand the frequency range and reduce

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the volume of recorded data in romagnetic studies ...

The essence of the method is as follows. It is known that the process of formation of a non-stationary electromagnetic field is a function that varies in time with a large dynamic range (96-120 dB) and a wide range of frequencies from Hz to 105 Hz.The signal parameters (dynamic range, spectral composition) vary over a wide limits depending on the geoelectric section and the distance from the source of the floor.

The duration of the field formation process can vary from the first seconds (regions of Eastern Siberia) to hundreds of seconds (regions of South-West Turkmenistan). This made it necessary to use interval-wise signal acquisition in the known methods, since the limitation on: transmission bandwidths of the measuring channel with an increase in its sensitivity increases the signal-to-noise ratio. Measurement of a signal in a wide frequency range is due to the necessary study of the medium model from the first hundreds of meters to depths of 4-5 and more kilometers. Loss of information about the upper part of the cut (with limited bandwidth of the channel on the high bandwidth) leads to significant errors When interpreting field material, it is painful if there are heterogeneities in the upper part of the section. However, continuous recording of a signal with a constant sampling tag At in a wide frequency range (from 10 kHz to Hz) leads to a sharp increase in the amount of recorded information. Indeed, at At 0.1 ms and a signal duration of 20 s and Bfee, for a single signal, it will be necessary to register 200,000 samples, and taking into account that at 50 ppm, 50-100 signals about $ 2-s are recorded, it will reach 2 10 sA, Tr at 16-bit On the other hand, o4rbe will leave 32 107 bits for one probe. BpNVieV Achieving a reduction in the volume of | information / can be achieved by increasing the accuracy of the measurements by using a discrete change in the procfouling band of the analog channel in the process of signal acquisition. However, it is well known that a little more bandwidth of the measuring channel leads to distortion of the signal in the time domain.

Therefore, switching the filtering elements (both analog and digital) in the measuring channel must be coordinated with the change in the signal in time and ensure the given accuracy of signal measurement. ...,.

The most easily implemented digital filter is averaging a group of samples. The frequency response of the clock filter can be described by the expression

Ah, f h / Sin KTTf Atx2

AvT Usin; 7rf AtJ

where At is the discretization step of the original function;

K is the number of averaged samples of the original function (K 2);

f is the frequency for which the frequency response is calculated. .; ; :; ;

Taking into account that the field formation signal can be approximated by a piecewise-exponential function, it is easy to show that in the approximation interval

.....:. : .- source signal by function e signal

(y (f)) after averaging with a step t - k A t will be of the form y (f) x (f) j3. The value {3 determines the signal distortion in the approximation interval by the exponential function

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fifteen

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Moreover, the limiting attenuation of the field becoming signal is observed if the conductive cut is underlain by the insulator, then the signal is attenuated as G4. This means that when choosing the limiting exponent, its attenuation during the transition to the next decade in time should be greater than t. Based on this position, in Fig. 1, in the time interval from 0.001 to 10 s, in each decade in time, the limiting exponent with a given value of a is shown. The dashed line in each time interval shows the maximum permissible attenuation of the pbl becoming signal for a model-conducting section above the insulator. Initial recording time (tHaO integer1

frp

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figuratively choose from the condition

;: At must be such as to satisfactorily describe the initial stage of the formation process, gender. Take At 0.1 Tnach.

GO FRP. 1000 Hz, 1 start 0.001 C, A t

HD; OpUT p. As the digital one, we select the most simple one - the averaging filter. Let us set the marginal error not worse than 1% .. Then from condition (2) the value is i - i5 0.5, where i is the number of the current temporary Decade in which the field is measured. The number of averaged samples in each decade can be determined

X-t- 1dec.decade (3)

The analysis of experimental and theoretical signals under various models of the geoelectric section showed that with increasing time the exponent (a) of the approximating exponential function decreases. In connection with this, it is possible, by increasing the averaging interval r, to maintain the constant value of at at a level when / does not exceed a given measurement error.

Figure 1 shows the limiting exponent with a given value of a; figure 2 is a structural diagram of an electrical exploration complex; Fig. 3 is a connection diagram of field modules for organizing work on several profiles; Fig. 4 is a diagram of a synchronization and control system.

Let us consider, as an example, regions of Eastern Siberia, the limiting cases of a ten-day time-varying signal. For simplicity of signal analysis in each decade of time for the most high-frequency signals received in Eastern Siberia, we replace the limiting exponential, where 1 start decad is the initial time of the decade; in which the measurement is performed,

From the given conditions, the number of averagings over decades will be Ki 1, “2 10, KZ - 100, 10) 1000, etc. It follows that the suppression of random interference only due to averaging in each decade will accordingly be 1 time, 3.16 times, 10 times, 31.6 times, etc. For even more active noise suppression in each decade, the analog filter-bandwidth is limited in synchronization with the change in the averaging step. To limit the bandwidth of the analog filter does not lead to even larger errors in the estimation of the signal, its bandwidth should be in the ratio V2 - 2.5, where

.........;. Tf

frp respectively the cutoff frequency (at the level of 0.7) for the analog and digital filters. Then the analog filter bandwidth (frp. 0.4fo) at 0.7 in the corresponding time decades will be limited to the frequencies frp.1 1000 Hz, fYp.2 400 Hz, frp.3 40 Hz, fpp.4 4 Hz, etc. d.

Figure 2 presents a structural diagram of an electrical exploration complex.

The complex includes a generator set, a set of field modules and an on-board module.

Generator set 1 contains a transmitter of telecommands 2 and a receiver of telecommands 3. - - ;; ;; ....

The field module is intended for converting the signals of the electromagnetic field components into a digital equivalent and transmitting data over the communication line. The module includes sensors of electric and magnetic field components 4, 5, amplifiers 6, 7, low-pass filters 8-13, switches 14, 15, 16, ADC - 17, synchronization and control system 18, arithmetic-logic device 19, operational storage device 20, data transmission and reception module 21,:;;: - -., -: -:. .

The on-board module is designed to collect information in digital form, control the parameters of field modules, visualize the recorded information and record it on a magnetic latte,:;. ;

The on-board module includes a data transmitting and receiving module 22, a computer 23, a telecommand decoder 24, a telecommand transmitter 25, an imaging device 26, a tape drive 27 ..- ..; ..

The work is carried out as follows. Generator set 1 generates sounding pulses in an electric dipole, -. . . ...., .. -. At the moment of transition of the edges of the current pulses, the data recording system (on-board module) is launched through the telecom unit 2, 3. The reception of the signal is recorded by the computer through the telecom decoder 24. The signals received by the sensors of the electromagnetic field component 4, 5 are amplified by amplifiers b, 7, filtered by filters 8, 9, 10, 11, 12, 13 at the initial time interval and through the switches 14, 15, 16, are fed to an analog digital converter 17. The digital code after the ADC 17 through the arithmetic-logic device 19 zag) are downloaded to RAM 20. At the same time Information from RAM 20 through the first data receiving and transmitting module 21 enters the communication line,

The synchronization and control system generates control commands for blocks 14, 15, 16, 17, 19, 21 ,:; .

The on-board data transceiver module 22 receives information from the communication line from all field modules, this information is pre-processed on a computer 23, presented on the visualization device 26 with simultaneous recording on magnetic tape 27, the mand decryptor 24 provides synchronization d by the generator set , and the transmitter

telecommands 25 provides synchronization and control of the generating set.

A distinctive feature of the system is the ability to implement collection

0 information with a large number of channels (up to 100-200 or more), which allows the implementation of high-density areal observations.

As shown in Fig. 3, the use of switchable filters in such a system5 allows one to significantly reduce the amount of information transmitted over the communication line (by an order of magnitude), which significantly reduces the requirements for the throughput of communication lines and the telemetric power station CES-T .

As shown in Fig. 4, the synchronization and control systems comprise the following elements: reference generator 28,

pulse counter 29 and decoder 30 |, on

5, the output of which forms the necessary time sequence for controlling the blocks of the field module. Timing and control system provides clock pulse and signal

0 of the initial setup of ALU 19, it also generates clock pulses for functioning

.. of switches 14, 15, 16 and ADC 17.

Arithmetic logic can be applied to the microprocessor complexes of the LSI series K 587 and K $ 88, designed for nocf swapping a series of 1 micro-computers Electronics-IC, thanks to the sectional organization, the use of the micromachine can be increased various casting and control systems. Both series are distinguished from all others by significantly lower power consumption,

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promising their use in MHilpo computers and controllers for control systems

 technological equipment

Preferred is the IPC K 588, since LSI series K587

does not allow to carry out some of the ad-hoc requests from the pfey processing command

 byt, p; expansion for arithmetic operations, as well as macro and

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The telecommand system consists of nipe sensors and telecom decoders. The telecommand, which is a multi-bit binary code, is generated by the telecommand transmitter and contains data on the operating modes and parameters of the measuring channels, autonomous meters and the generator set. For example, when performing areal work according to the ES method from a fixed source by telecommands, it is possible to set the parameters of the measuring and recording channels of field modules distributed over the area of work at different distances from the floor source, so that the signals of the formation of the field are measured for each specific channel in an expanded frequency and dynamic ranges, which provides an increase in the information content of research.

The integrated use of analog and digital filtering will significantly reduce the level of external noise, and the use of an averaging filter will reduce the amount of information recorded. With the selected recording mode, the amount of information in the time interval from 0.001 sec to 10 sec will be 400 samples with a good signal processing in all time intervals (100 samples per decade). In the case of a constant sampling step, for example, At 0.001 sec, the amount of information in the time interval from 0.001 sec to 10 sec will be 10,000 samples, while the signal processing in the initial time region will not be satisfactory. SUMMARY OF THE INVENTION 1. A method for measuring a non-stationary electromagnetic field, in which the components of a non-stationary electromagnetic field are measured in any source zone using low-pass filtering in the measuring channel and then sampling the signal with a constant quantization step At, characterized in that, in order to expand the frequency range and reduce the volume of recorded values, convert the values of the samples of the magnitude of the signals of each component by analog filtering, and After analog-to-digital conversion of digital filtering with a time-varying ten-year-long law, the transmission rate is limited, while matching the frequency characteristics of the analog and digital filtering by synchronous switching, setting the digital and analog filtering modes in such a way that the passbands are determined by the ratio fo / frp 2.5, where fo, frp are the cutoff frequencies at the level of 0.7 of the analog and digital filters, respectively.

2. A device for measuring a non-stationary electromagnetic field, comprising a generator set with a master oscillator, a telecom receiver and a first telecomm transmitter, containing field modules, each of which includes serially connected sensors of the electromagnetic field component and amplifiers that form the receiving channels, a switch, an output which is connected to the information input of an analog-to-digital converter (ADC), the output of which is connected to the first input of an arithmetic logic device (ALU), the first output of which is connected to random access memory (RAM), and the second output is connected to the input of the first transmit-receive module, the control input of which is connected to the output of the synchronization and control system, also connected to the control inputs of the ADC, ALU, and the switch, the second output the first transmit-receive module is connected to the second transmit-receive module, the output of which is connected to the first computer input, the first output of which is connected to the second telecom transmitter, the second output is connected to the visualization device, and this output is connected to a magnetic tape drive, the second computer input is connected to the output of the telecom decoder, characterized in that each receive channel contains low-pass filters and a switch, and the inputs of low-frequency filters are connected to the output of the receive channel amplifier, and the outputs of the filters are low the frequencies are connected to the information inputs of the switch of the reception channel, the control input, which is connected to the output of the channel switches of the synchronization and control system, while the outputs of the channel switches are connected to channel switch information inputs. .

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