An amplifier and recording system for seismic crustal refraction work

Abstract

Abstract For successful seismic crustal refraction work, a reliable, robust, and portable recording system capable of detecting ground movements of 10−3 m sec−1 at 1 Hz is necessary. The miniature preamplifier described in this paper, accepts microvolt signals directly from the seismometer and by using integrated circuits it has been made small enough to fit within the seismometer case. The preamplifier has a low impedance and differential output. The signal is fed via a shielded landline to the main amplifier which also has a differential input. The use of differential output for the preamplifier and differential input for the main amplifier, interconnected by a shielded line, assures a high degree of noise immunity for the system. The main amplifier also has differential output for feeding a suitable recorder such as the Brush 220 or San'ei Visigrsph. Integrated circuits are also used in the construction of the main amplifiers. Accurate standard time is vital for the success of crustal refraction work and the circuit of a digital clock (1 Hz-1 MHz) with direct drive capability and an accuracy of better than 1 sec/day is given. Power for the entire system is supplied by a 12 V accumulator; the total current drain is 8 mA for the amplifier and 300 mA for the clock. A feature of the design is that the shielded pair of wires from the preamplifier serves both to supply the power for the preamplifier and to carry the signal from the preamplifier to the main amplifier.