Apparatus for recording in a digital form signals detected during magneto-telluric prospection

A recording apparatus for automatically recording digital signals generated from telluric and magnetic detectors during magneto-telluric prospecting, said apparatus comprising:

• an analog input stage comprising a plurality of amplifying cells the number of which is at least equal to the number of said telluric and magnetic detectors, at least one amplifying cell corresponding to each detector;
• a low-pass filtering stage comprising a plurality of filtering cells equal in number to the number of amplifying cells each one of said filtering cells comprising a low-frequency low-pass filter, an intermediate frequency low-pass filter and a high frequency low-pass filter, each one of said filters having a predetermined cut-off frequency, the respective inlets of the low-pass filters of a given filtering cell being sequentially connected to the outlet of the corresponding amplifying cell;
• an analog output stage comprising a plurality of binary gain amplifiers each having an adjustable gain responsive to a binary code, said binary gain amplifiers equal in number to the number of filtering cells, each one of said binary gain amplifiers connected to the outlet of the corresponding filtering cell and producing an amplified analog sample signal and a digital gain signal representing the value of the gain applied to said binary gain amplifiers;
• an analog multiplexer having an adjustable variable sampling sequence and comprising input channels at least equal in number to the number of binary gain amplifiers, the analog sample signal from each one of said binary gain amplifiers being connected to one of said input channels of said multiplexer;
• an analog-to-digital converter the inlet of which is connected to the outlet of the analog multiplexer and producing a first digital signal respresenting the amplitude of the analog sample signal received by the multiplexer, and a second digital signal representing the address of the channel of the multiplexer corresponding to the received sample signal;
• a gain computing module receiving each of the signals produced by the analog-to-digital converter and producing for each of the binary gain amplifiers an optimum gain setting;
• a digital recording system receiving said first and said second digital signals from the analog-to-digital converter;
• and
• a recording selector connected to the analog multiplexer, at least one of said amplifying cells, and to the filtering cells of the filtering stage, said selector being adapted to select for each one of the recording types comprising low-frequency recording, intermediate-frequency recording and high-frequency recording, the sampling frequency of the analog multiplexer, the gain of said at least one amplifying cells, and the appropriate low-pass filter of each filtering cell.