Abstract: This application relates to seismic data gathering devices and to testing the impedances of the geophone channels of such devices. The invention includes impressing a test current on each channel to be tested, said current developing a test voltage indicative of the impedance; generating a high reference voltage which corresponds to the maximum acceptable impedance of the channel; generating a low reference voltage which corresponds to the minimum acceptable impedance of the channel; and comparing the test voltage with the reference voltages.

Abstract: This relates to testing the impedance and common mode rejection characteristics of multi-channel seismic data gathering apparatuses. The apparatus embodying the invention includes a signal recording and computing system with a plurality of input channels; a plurality of geophone channels, each with a high wire and a low wire; a high bus and a low bus; a plurality of reference impedances; and a signal generator with two output terminals. Each geophone channel comprises one or more geophones which are connected by the wires to the input channels of the recording and computing system. Additionally, the high wire of each channel is connected through a reference impedance to the high bus and the low wire of each channel is connected through a reference impedance to the low bus. The apparatus also includes switching means for selectively controlling the connections between the buses, the generator and ground.

Abstract: A system for controlling the force imparted to the ground by a seismic vibrator. A signal is generated which is related to the peak force imparted to the earth and the control signal amplitude is varied in response thereto to achieve the desired force magnitude.

Abstract: A DC signal is generated having a amplitude related to the amplitude of an AC signal, with minimal delay and low sensitivity to noise in the AC signal.