Research On Tilt Feedback Control System For Superconducting Gravimeter

Superconducting gravimeter is a precision relative gravity measuring instrument constructed with superconductivity.It has the characteristics of low inherent noise and good stability of the instrument.It is the best time-varying gravity measuring instrument at present and has been widely used in geodynamic research,Major natural disasters and early warning.One of the key points in gravity measurement is to ensure that the direction of the sensitive axis of the gravimeter is consistent with the direction of the local gravity acceleration g.Due to the influence of various external factors,the basic platform installed on the superconducting gravimeter will tilt to varying degrees,thereby affecting the accuracy of gravity observation.Therefore,in order to reduce the measurement error caused by the tilt of the basic platform,a tilt feedback control system must be used to compensate the impact of the tilt change on the measurement accuracy of the gravimeter.The main task of this subject is to develop a tilt feedback control system for superconducting gravimeters,establish a tilt error model,and propose tilt control indicators.The tilt feedback control system of superconducting gravimeter mainly includes four parts: actuator,inclinometer,support frame and control circuit.The first is the selection and design of the actuator: after the investigation and selection of the electro-thermal drive type,it has been independently designed and packaged,which can achieve manual large-range coarse adjustment and automatic small-range precision fine-tuning.Then,the plan of the inclinometer and support frame is determined: the support frame structure and the installation method of the inclinometer are selected under the premise of investigating the current research situation at home and abroad.The cross symmetry distribution is conducive to the implementation of feedback control.Finally,the control circuit: the PID feedback control method based on Lab VIEW is established,and the corresponding control software is written.The use of virtual instruments to build control circuits is easy to operate and has the advantages of strong data processing capabilities and independent function definition.After completing the design of each part of the tilt feedback control system,for the characteristics of high control accuracy and long-term stability requirements for the superconducting gravimeter tilt feedback control system,a long-term tilt control experiment was carried out.The 80 h stable time domain data shows that the control level of the two sensitive axes of the inclinometer is ±0.3μrad at the working point,which reaches the time domain control index proposed by the tilt error model,that is,the long-term stability is ±2.5μrad.