Research On Control And Data Acquisition Of Borehole Seismometer

Based on the good observation environment in borehole,researchers gradually transferred the seismic observation from the surface to the underground.Seismometer needs to be improved to suit the new application environment.Thus,this paper designed some improvements for the borehole seismometer which was developed by Institute of Seismology,China Earthquake Administration.First of all,the observation hole is not always vertical.That means the instruments may be lie on the hole with a tilt state.Some studies pointed out that the tilt of seismometer has a great influence on performance,especially on sensitivity.When the tilt exceeds a certain angle,it may damage the sophisticated components.Surface seismometer can be manually adjusted by change the height of three legs.But for the downhole seismometer,the original manual adjustment method is no longer applicable.So,researchers put forward some methods to adjust the sensors to accord with the horizontal state.For example,the mechanical method of linkage adjustment of suspension bracket and pull rod;the scheme of use gravity to auto-balance;and the remote-control method of using adjustable tilt control platform by DC motor.In order to solve this problem,this paper promoted a set of automatic control scheme which uses the attitude sensor to obtain the attitude information of the downhole seismometer and controls the angle adjusting platform to adjust the inclination of the sensor.Secondly,the azimuth of the seismometer should be estimated after meeting the requirements of levelness.Many seismological researches depend on the seismograph data’s azimuth consistent with the geographical direction.However,it is difficult to correct the azimuth of downhole seismometers by mechanical adjustment.So,some researches try to design algorithm which can correct the seismometers’ output data by software.This paper briefly introduces several azimuth calculation methods,and then promotes a calculation method by using the projection relationship between the output data of seismometer’s horizontal components,and develops a computer application program based on the algorithm,which is convenient for users to carry out azimuth correction.Finally,the data acquisition of downhole seismometer should be considered.Generally speaking,seismometer includes two relatively independent parts: seismograph and data collector.Such an instrument structure is used in the design of many borehole seismometers.However,with the increase of the depth of the observation hole,such a structure shows some problems such as signal attenuation,increasing of interference and cable overweight.To solve this problem,this paper attempts a scheme of underground integrated data collector which can converting analog signal to digital signal in underground equipment.Also,a long-distance signal transmission scheme based on optical fiber data transceiver module is designed.This paper introduces the theory and method involved in the research,and then discusses the specific scheme of function realization from the perspective of hardware and software design.After the completion of modular design and construction,then design experiments to simulate and verify the actual effect.The results show that the improved scheme can basically meet the design requirements of integrated borehole data acquisition,and can achieve rapid automatic tilt adjustment in the range of ± 5 °.The data azimuth correction speed is fast and stable,and the designed software also has good performance.At the end of this paper,we summarize and prospect this research.