Importance

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Abstract

An apparatus for reducing harmonic distortion and causing a more linear response in a hydraulic vibrator apparatus which generates a seismic signal into the surface of the earth is disclosed. The force developed in the actuator of a hydraulic vibrator is directly related to pressure applied to the hydraulic piston. Conventional vibrators use flow control type servovalves to develop this pressure. Changes in loading due to earth surface conditions reflect back as changes in pressure across the hydraulic piston. Pressure can be better controlled in the actuator such that it varies only as a function of the input signal, and the natural response of a vibrator can be made more linear, and the harmonic distortion can be reduced by using a pressure control type servovalve. Apparatus for changing a flow control type servovalve into what is essentially a pressure control type servovalve includes hydraulic feedback passageways provided from the output ports of the servovalve main stage to the input ports of the servovalve main stage. The passageways are constucted to provide differential negative pressure feedback around the servovalve main stage. Further apparatus damps the servovalve output to increase stability, and further tunes the valve to its load. It consists of a bypass passageway to port hydraulic fluid between the two output ports of the servovalve main stage. Orifices in the pressure feedback and bypass passageways determine the feedback gain and the amount of damping.

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First Claim