SU379902A1 - - Google Patents

Description

METHOD OF PHASE MEASUREMENTS IN GEO-ELECTRIC EXPLORATION

one

The invention relates to methods of geoelectromagnetic exploration based on phase measurements of parameters of an electromagnetic field, namely to methods of compensatory phase measurements.

Methods are known for compensating phase measurements in geoelectromagnetic exploration, in which the compensation of measured phase angles is performed in measuring devices by changing the ratio between the initial phases of the reference and operating signals.

However, using well-known methods for compensation in measuring devices, calibrated phase shifters of sinusoidal signals are installed, which are complex, have low accuracy and are not stable over time, which causes insufficient accuracy of phase measurements.

The proposed method allows to simplify measuring devices, improve accuracy and resolution. This is achieved by compensating for the measured phase angles by changing the ratio between the initial phases of the first harmonics of the supply currents of several frequencies or by changing the initial shift of the first harmonics of the supply current with single-frequency measurements.

The use of this operation makes it possible to exclude from the known method of compensatory measurements the main operation contributing to the error in the measurement results, the compensation of phase angles by changing the ratios between the initial phases of the reference and operating signals in the receiving device.

The essence of the proposed method is as follows.

When measuring the phase angles of signals received from the earth, or the relationship between the initial phases of signals of several frequencies received from the earth, it is proposed to compensate the phase angles to be measured by changing the phase of the pulses driving the generator. A change in the phase of the generator-controlled pulses leads to a change in the initial phase of the first harmonic of the supply current (with single-frequency measurements) or to a change in the ratio between the initial phases of the first harmonics of the currents that excite the electromagnetic field (with two-frequency or three-frequency measurements). The change in the initial phase of the first harmonic of the supply current is carried out until it compensates for the phase shifts that occur during the propagation of the electromagnetic field in the earth and are the subject of geoelectric research. In this case, the measuring devices are greatly simplified, their role is limited

only by indicating the moment of commanding, i.e., the measuring device becomes a null indicator of phase shifts.

In the regenerator device, it is possible to use not ordinary sinusoidal voltage phase shifters, but pulse phase shifters. It is known that pulsed phase shifters (for example, of fadron type) have stability and accuracy by one to two orders of magnitude higher than ordinary ones. In addition, there are much more possibilities in the generator device to ensure high stability of power sources: a recorder can be installed that automatically records the change in the phase of the control of the pulse generator.

The proposed method can be implemented using a device containing a current and measuring circuit.

FIG. 1 shows a block diagram of the generator circuit of the device; FIG. 2 is a block diagram of a receiving-measuring circuit.

The current circuit, or generator device (Fig. 1), consists of a series-connected master oscillator /; binary frequency divider 2; a two-channel driver, each channel of which contains frequency dividers 5 and 4, respectively, any number of times, differentiators 5 and 6, pulse phase shifters 7 and 8, diodes 9 and 10; adder 11; frequency divider 12 twice; unit 13 run; the inverter 14 and the control unit 15 pulsed phase shifter.

The measuring device (Fig. 2) consists of input terminals 16, amplifiers 17 and 18, drivers 19 and 20, adder 21 and numeric indicator 22.

The generator device operates as follows. Master oscillator / produces the voltage of a given frequency / o- The signal from master oscillator 1 is fed to binary frequency divider 2. From the output of the binary frequency divider, the signal is fed to the inputs of two parallel-connected formation channels, in which are the frequency divider 3 y (4. Next, the square wave signals arrive at differentiators 5 and 6, where they transform the B sequence of short polarized impulses corresponding to the front and rear edges of rectangular voltages. A pulse of phase shifters 7 and 8 delay these pulses for the time Tri var by phase shifter 7 and T2 const by phase shifter 8. The positive polarity delayed relative to the initial ones by time TI and T2 comes through diodes P and 70 to two inputs of the adder 11. From the output of the adder 11 the input of the binary frequency divider 12 receives a sequence of unipolar pulses corresponding to the sum of the sequences of pulses fed to the two inputs of the adder 11. The binary frequency divider 12 restores the rectangular shape for example Yeni. The output voltage of the frequency divider is fed to the input of the starting unit 13, where it is converted into pulses of sufficient amplitude and duration to control the operation of the inverter 14. In the output current of the inverter 14, there are components with the frequencies W and W.

At the input 16 of the measuring device, the signals of the two frequencies sleep and O) B come from the earth. With the help of amplifiers 17 and 18, the first harmonics of these frequencies are extracted, and with the help of shapers 19 and 20, the sinusoidal signals are converted into a sequence of short pulses as well as the conversion of one frequency into another. Signals of equal frequency with a phase shift of one relative to another are fed to the adder 21, where the phase shift is converted into a time interval. The indicator indicator 22 generates a tuning signal for

the generator unit arrives at the control unit 15 of the pulse phase shifter 7. With the help of the control unit, the delay time of the pulse phase shifter 7 is changed until the tuning signal from the null indicator 22 becomes zero. At this moment, the phase angle is taken from the scale of the pulsed phase shifter 7. Change the phase of the generator control

pulse, the ratio between the initial phase shifts of the main harmonics of the supply current is changed by the same amount. Indeed, let the original total signal be written as:

/ 7v (t) - sin WH -f sin (+ cfr) zr

r 2 sin I - (3 * +) I cos 4 (H + B) L L

Hence, by solving the equation Uv (t) 0, it can be found that the sum signal can have zero values when

about, -, 4t / J GE {, And - GK

i (o - -

3

BGS -o „

If a total voltage is formed from a total voltage, then its spectrum is easily determined: 502.

a, -l -, (i) d (., f),

 (V,) o TOS

about

B „U (t) sinnMt-d (wf) -

 .}

J Icos OT - fe) + COS

r.n i

)

(2r. -Cfn

- COSCOS

or

U () - + V 4 COS (t + „),

Zts

lgp n l

where А „} al + bl; tg -f „

g :; 10.Then

Let (p ,,

18

B, -;

0.52 a, 0; , 90

; ,18; Wed.

B.

about-,

The spectrum of the generated voltage can be represented in

 .-. i +

U, (f}

27

four- . siQ (2i) „g; +

+ ...

18 /

379902

6

This shows that when the phase of the control pulses changes by

5, the transition between the initial phases of the fundamental harmonics in the spectrum of the output current of the generator device also changes by an angle

18

The application of the proposed method also makes it possible to carry out compensation phase measurements with the continuous movement of the measuring device.

Subject invention

The method of phase measurements in geoelectromagnetic, based on the excitation in the earth of electromagnetic fields by one or several frequencies and compensatory measurements of phase, characterized in that, in order to simplify measuring devices, improve the accuracy and resolution of the measurement, change the ratio between the initial phases of the first harmonics supply currents to zero total phase shift between received signals.