SU729543A1 - Electric geosurvey apparatus - Google Patents

Description

The invention relates to devices for geoelectromagnetic and a transient method for electrical prospecting. The known equipment for geo-electric prospecting by the method of transient processes of the type MPSP-2. This equipment has a measuring device containing a magneto-induction measuring transducer (receiving frame), an attenuator, an amplifier, a synchronous filter, a DC amplifier, a measuring device and a control circuit from time delay blocks 1. However, such equipment has a limited time range of measurements . It is also known a device containing a magneto receiver, an input gate key, a load resistance, a measuring channel having a pulse amplifier, a accumulator, a DC amplifier with a converter, a recorder, as well as a time delay circuit, a strobe pulse multivibrator, and qo conductor capacitor connected between drive and a constant current amplifier connected to the time delay circuit 2. The disadvantage of this device is the loss of information due to the inability to measure in the early stages X transient, due to the low fast action of the magneto-induction measuring transducer. To increase the speed of the device without reducing the sensitivity of the measuring path, a broadband amplifier can be used connected to the output of the measuring transducer. However, the limitation of this method of increasing the speed of the converter is the noise level of the wideband preamplifier. In accordance with the invention, the goal is achieved by turning on the measuring channel to the output of the magnetic induction converter and performing the amplifier resonant. This device structure allows you to replace the measurement of the instantaneous amplitude value.

strobe pulse measurement of the amplitude of a damped sinusoidal signal, the amplitude of which is proportional to the instantaneous value of the transient emf at the time of measurement, and the phase corresponds to the polarity of the measured signal.

Fig, 1 is given a block diagram of the proposed device; FIG. 2 is a time chart of his work.

The device contains a magnetic inductance measuring transducer PI 1 connected to a switch 2 for switching the load resistance 3 and a measuring channel consisting of a narrowband amplifier 4, a phase-sensitive rectifier 5, a synchronous accumulator b, a DC amplifier 7 of the recorder

8 and control unit with unit

9 time delays.

The device works as follows.

When measuring the instantaneous value of the EMF of the transient process for time (see Fig. 2) relative to the moment of switching off the current in the generator circuit, switch 2 opens, disconnecting the load 3 from the PI converter 1. In this case, the converter switches from critical mode to oscillatory mode. At the output of the converter, damped sinusoidal oscillations occur, the initial amplitude of which is proportional to the EMF value at the output of the measuring converter at the moment of the opening of the switch .2, and its polarity corresponds to the polarity of the measured signal. The decrement of attenuation of sinusoidal oscillations at the output of the converter is determined by its Q-factor when the key is open 2. After the time tf (see Fig.2), after opening the key 2, oscillations in the circuit formed by the inductance of the converter PI and capacity (parasitic capacitance of the converter coil or the sum of the parasitic capacitance external capacitance decays and the key is closed. After time tg. (see FIG. 2) after the key 2 is closed in the converter, transient processes are terminated due to its transfer from the oscillatory mode to the critical one, and then the output voltage corresponds to the output voltage of the converter operating in the critical mode. If, during each pause, a measurement is made only for a time to, the next closure of switch 2 is observed at a time t o the current drop in the generator circuit in the next period of current pulses, although it is possible to measure the indicated circuit at several times during one period. Formed by the proposed

In this way, the sinusoid attenuation is fed to the input of the resonant amplifier 4, rectified by the phase-sensitive rectifier 5, converted into a constant voltage by the synchronous drive 6, amplified by the amplifier - direct current 7 and fed to the measuring device 8. The opening time of key 2 is determined by the control unit 9 regarding the current decay in the generator circuit and can

О be installed at will within the working time range of the device.

The device allows to increase the speed of the magnetic induction converter by reducing the number of: turns without loss of sensitivity compared with the converter operating in the critical mode; significantly increase

0 speed of the magnetic induction converter without losing the sensitivity of the measuring path (which is achieved by further reducing the number of turns of the converter, which is possible due to a significant decrease in the noise level of the narrowband amplifier compared to the broadband one); reduce the size and mass of the magnetic induction converter by reducing

0 volume of ferrite (permalloy) rod without reducing the sensitivity of the measuring path; to increase the initial amplitude of the output signal of the measuring transducer in comparison with the output signal of the transducer operating in the critical mode and gating in a known manner by converting the energy of the magnetic field stored by the coil of the transducer at time tQ to the energy of the electric field stored capacitance measuring transducer. Device made by

5 this scheme has 20-30 times

faster performance compared with serial types of equipment for electrical prospecting by the transient process method (MPSD-2 and MFP-3) without loss of the threshold sensitivity or increasing the initial amplitude of the output signal of the measuring converter 3 times without increasing speed.

Claims (2)

1. USSR author's certificate No. 406177, cl. G 01 V 3/10, 1973. 2.Sb. Geophysical instrumentsNedra 1971  51, L., 40 (prototype).