In this paper an instrument containing an amplifier and a data acquisition module is presented. The unit has a data interface which enables sending the measured data to a PC. The instrument, built for Széchenyi István Geophysical Observatory of GGRI-HAS, is suitable for measuring telluric currents (i.e. Earth currents). A similar amplifier is in operation at the observatory, but its maximal sampling rate is only 1 sample/second which is too low to measure the higher frequency components. The experiment setup is composed by two pairs of lead sheets (1m2 area each) being placed 2 meters under the soil at a distance of 500 meters from each other. This allows to measure currents of North-South and East-West directions separately. If current is generated in the soil, a certain amount of voltage appears between the lead sheet pairs. The signal is transferred to the measurement room by armoured wires.
According to the requirements the instrument contains 2 amplifiers with identical parameters and a data acquisition module. The smallest amplitude that can appear at the input of the amplifiers is 500µV and the frequency range is 0,00027Hz to 100Hz. The quasi-stationary components (below 0,00027Hz) are compensated by DC level.