NEW METHODS OK ELECTRICAL EXPLORATION IN SIREIUA 



217 



inaccessible regions, to measure zlt/ there arc two iiorlabic lvSli()-56 cleclron 

 loop oscillographs with cinefihu recording. 



The ESliO-56 electrical exploration loop oscillograpli (Fig. 16) was 

 developed in 1956 at the L'vov Institute of Machines and Automatics at the 

 request of the Electrical Prospecting Laboratory of VNII Geofizika especially 

 for dipole probing in inaccessible country. The oscillograph has an a.c. 

 amplifier with converter, in the form of a VT vibro -converter (Fig. 17). TIk; 

 vibroconverter converts llu' input current into an alU'iiialiug current with 

 a frequency of about 180 c/s and, at the same lime, acts as a mcclumical 

 rectifier for the output of the amplifier. 



In the output stage of the amplifier there is a Tr-2 tiauslormer, in the 

 secondary winding of which there are connected in series a micro -ammeter, 

 a resistance i?26' one of the resistances R^^-R^^^ (depending on the limit 

 of measurement) and the left contact of the P vibro-converter. 



When the armature of the vibro-converter is m()v<'(l lo ihc left, the 

 secondary winding of tlu; output transformer is loaded and enrrent llo\\> 

 in it, moving the pointer of the micro -annneter and the mirror of the galvano- 

 meter G. At the same linu' iIk^ voltage of the feedback inpnt ot lh<; amplifier, 

 with a polarity opposite to that fed to the input signal, is taken Irom one 

 of the resistances R^ — R^^, i.e. in the instrument there is a deep (close to 

 100%) negative feedback with direct current, and the arrangement as a whole 



(i?00 



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S^^"<t"<,' 'ryj- 



Station; 8 — calling device; 9 — block of contactors; 10 — control panel lor engine opera- 

 tion; 11 — D. C. amplifier; 12 — measurement panel; 13 — output panel; 14 — loading 



resistance. 



