RU1770775C - Geophysical electric survey apparatus - Google Patents

Abstract

Using; in applied geophysics, and more specifically to geophysical electrical exploration for recording weak electric fields. The invention is directed to increasing the sensitivity of a geoelectrical exploration device. SUMMARY OF THE INVENTION: the device comprises a sensing electrode, two varicaps, two RF generators. The invention relates to the field of applied geophysics, and more specifically to geophysical electrical exploration. It can be used to detect weak electric fields caused by electric and electrostatic phenomena in the atmosphere, ionosphere and mechanoelectric phenomena in the bowels of the Earth, for example, during the preparation of earthquakes. A device for measuring electrical signals is known, which comprises sensors made on the basis of varicaps and a mixer, a frequency to voltage converter, a high frequency (HF) phase shifter, a phase detector, and a phase locked loop (PLL) device. The sensing electrode is connected to the varicaps, the outputs of both RF generators are connected to the input of the mixer, and the output of the mixer is connected to the input of the frequency converter to the voltage. The first inputs of the RF phase shifter and the phase detector, the output of which is connected to the modulation input of the second RF generator, are connected in parallel to the output of the first RF generator. The output of the RF phase shifter is connected to the second input of the phase detector, and the frequency to voltage converter has an additional input, which is connected through the PLL to the output of the same converter. The RF phase shifter contains a Q-factor of the oscillatory circuit, to the terminals of which the input and output of the resonant amplifier are connected through the capacitors, and its output through the capacitor is additionally connected to on-parallel diodes. consequently connected generators with frequency-controlled oscillatory systems, an adder and a frequency multiplier, a quadratic detector, and a frequency to voltage converter. The disadvantage of this device is that its sensitivity is limited by the parameters of the natural frequency instability of the generators. The sensitivity of this device with a signal to noise ratio of unity is on the order of 5-8 V / m. - & VJ 3 VI VJ ate

Description

A device for detecting low-frequency electric fields of geophysical origin, adopted as a prototype, comprises a sensing electrode, varicaps, two frequency-controlled oscillators, a mixer and a frequency to voltage converter. The first generator is controlled by the investigated electric field, and the second is controlled by the reference voltage.

The disadvantage of the prototype, in which special measures are taken to increase the frequency stability of the generators, is also1 a relatively low sensitivity, of the order of 1-2 V / m with a signal-to-noise ratio of unity.

The noise floor of the prototype at the output of the frequency to voltage converter is proportional to the total frequency instability of the controlled and reference generators, which can be seen from the following relation;

ish K (b tep + 6 t „),

where Ksc is the level of intrinsic noise at the output of the frequency converter to the voltage;

K is the conversion coefficient;

5 fan, 5 fH - instability of the frequency of the generator controlled by the investigated electric field and the reference generator controlled by voltage.

This noise signal is constantly superimposed on the useful one and prevents the sensitivity of devices of this kind from being increased.

An object of the invention is to increase the sensitivity of a geophysical electrical exploration device. The device provides a sensitivity of about 0.05 V / m with a signal to noise ratio of unity.

The drawing shows a functional diagram of a device for geophysical electrical exploration.

The device comprises a receiving electrode 1, the first and second in series - counter-connected varicaps 2 and 3, the first reference high-frequency generator 4 and the second high-frequency FM generator 5, a mixer 6 and a frequency to voltage converter 7. A distinctive feature of the device is that it also contains a high-frequency phase shifter 8, a phase detector 9, a phase-locked loop (PLL) device 10, while the phase shifter includes an oscillator circuit 11, a multiplier 12 to

brotnosti containing resonant amplifier 13, the reference oscillating circuit 14, the connecting capacitance 15, 16 and 17 and the diode chain of the counter-parallel

5 included diodes 18 and 19.

The receiving electrode 1 is connected to the common point of the series-opposed varicaps 2 and 3, the outputs of the first 4 and second 5 generators are connected to the inputs 10 of the mixer 6, the output of which is connected to the input of the frequency converter 7, and the output of the generator 4 is also connected to the first inputs of the phase shifter 8 and phase detector 9,

15 the output of the phase detector 9 is connected to the modulation input of the second RF generator 5; the output of the high-frequency phase shifter 8 is connected to the second input of the phase detector 9, the converter

20 7 frequencies in voltage with its tuning input the output is connected respectively to the input and output of the PLL 10.

The oscillatory circuit 11 of the phase shifter 25 l is connected to the free terminals of the varicaps 2 and 3, and through the connecting capacitance 15 to the reference oscillating circuit 14 and to the input of the resonant amplifier 13, and through the connecting capacitors 16 and 17 to its output30 and to the parallel-connected diodes 18 and 19.

The device operates as follows.

When exposed to the electrode 1 of the studied signal, the high-frequency oscillations of the generator 4, passing through the oscillating circuit 11, undergo phase modulation with a modulation index p proportional to the instantaneous amplitude

40 value of the electric field strength, Q factor Q of the oscillating circuit 11 and Q factor N.

The output of the phase detector 9 in this

45 case, an analog signal will operate, the value of which is determined by the ratio

50Ua K arctg N Q. (2)

where Ua is the amplitude of the signal at the output of the phase detector 9;

N is the factor of multiplying the quality factor 55; 5;

Q is the quality factor of the oscillatory circuit 11;

Afic - detuning of the oscillatory circuit 11;

fp is the resonant frequency of circuit 11. is equal to the frequency of the RF generator 4.

A comparison of relations (2) and (1) shows that, unlike the prototype, the influence on the sensitivity of the total frequency instability of the generators in the new device is excluded.

From the output of the phase detector, the analog signal is fed to the modulation input of the second RF generator 5, the output of which is the FM signal with a modulation index greater than unity. This signal is then fed to the input of mixer 6, which transfers the spectrum of the FM signal to the lower frequency region. Secondly, the analog signal is restored at the output of the frequency converter 7 to the voltage connected to the PLL 10. In this case, frequency demodulation with high linearity is provided.

Distinctive features of the device made it possible to simultaneously realize the advantages of phase modulation-demodulation, frequency modulation-demodulation of FM signals using PLL, which together ensured the achievement of the goal - increasing sensitivity to a value of the order of 0.05 V / m with a signal ratio / noise equal to one.

The components of the device 2, 3, 4, 5, 6, 7, 10, 13, 14, 15, 16, 17, 18 can be performed on a standard element base.

Claims (2)

1. Device for geophysical electrical exploration containing a receiving electrode, the first and second varicaps, the first and second RF generators. a mixer, a frequency-to-voltage converter, wherein the receiving electrode is connected to a common point of the series-counter-connected varicaps, the outputs of the first and second RF generators are connected to the mixer input, and the mixer output is connected to the input of the frequency converter to voltage, otherwise that, in order to increase the sensitivity, it contains a high-frequency phase shifter, a phase detector and a phase locked loop (PLL), while the output of the first RF generator is connected to by the first inputs of the high-frequency phase shifter and the phase detector, the output of the phase detector is connected to the modulation input of the second RF generator, the output of the high-frequency phase shifter is connected to the second input of the phase detector, and the frequency-to-voltage converter is connected to the output and the PLL by the tuning input and output, respectively. 2. The device according to claim 1, characterized in that the high-frequency phase shifter includes an oscillating circuit and a Q factor containing a resonant amplifier, a reference oscillating circuit, connecting capacitors and a diode chain of counter-parallel connected diodes, while the oscillating circuit is connected to free conclusions varicaps, as well as through connecting capacitance is connected to the input and output of the resonant amplifier, a diode circuit and a reference oscillatory circuit. 2j3