Force-feedback seismometer

Abstract

A broadband weak-motion seismometer includes: a frame, a mass, a suspension means for movably connecting the mass to the frame, a sensing transducer for measuring displacement of the mass with respect to the frame and for generating a sensing transducer output signal, which is a function of the measured displacement, a forcing transducer for applying a feedback force in a predetermined direction to the mass, and a control circuit. The control circuit receives the sensing transducer output signal and generates a forcing transducer input signal that includes a self-noise component. The forcing transducer input signal is processed by the forcing transducer to apply the feedback force to maintain the mass at rest with respect to the frame. The feedback force is sufficient to counterbalance a constant acceleration of the frame of at least 0.2 m / s2 in the predetermined direction of the feedback force. The self-noise component of the forcing transducer input signal, when processed by the forcing transducer, produces variable acceleration of the mass with spectral density less than -150 dB with respect to 1 m2 / s3 at 0.01 Hz.

Description

technical field [0001] The present invention relates to the field of geophones, and more particularly, to systems and methods for force feedback control in geophones. Background technique [0002] There are two broad classes of geophones known as short period geophones and broadband geophones. Broadband geophones can measure weak ground motions at low frequencies, while short-period geophones cannot. The magnitude of seismic ground motion tends to decrease rapidly at frequencies below 1 Hz, while the self-noise level of geophones tends to increase, so it is easier to achieve at frequencies above 1 Hz (short period) than at lower frequencies Good signal-to-noise ratio. [0003] Most broadband and some short period geophones are force feedback type. All force feedback geophones include electronics for applying a force to hold a movable inertial mass in a predetermined zero position relative to a frame stationary on the ground. In short-period geophones with electronic forc...

AI Technical Summary

Problems solved by technology

This mass centering adjustment mechanism increases the size and cost of the geophone and impairs reliability

Also, it is inconvenient to adjust the internal mechanics every time a geophone is installed in a new location, and it is also inconvenient to readjust from time to time as the installation tilts or the temperature changes

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