Research On Capacitance Micrometer System Of Superconducting Gravimeter

The gravitational field of the earth is a basic and important physical field around the itself.Its surroundings and distribution is a reflection of the shape of the earth and the state of the medium inside the earth.The information of the earth's gravity field plays an important role in geodesy,geophysics,resource exploration,marine science,space science and military science.Superconducting gravimeter(SG)is a kind of relative instrument to measure gravity,which was developed in the 1960 s.During long-term using,SG is widely recognized as a best instrument to detect small changes of gravity due to its low noise and high stability.At present,China's related research in SG is blank,and SG mainly depends on import and leasing methods,the technology in this area is relatively limited.This thesis takes the newly developed first-generation superconducting gravimeter as the research object,analyzes the basic principles of superconducting gravimeter,focuses on the introduction and research of the high-precision displacement detection system of superconducting gravimeter,and discusses the influence of gravity The main factors of measurement accuracy and the means to improve accuracy.These studies are of great significance to the development of China's first superconducting gravimeter.The main contents are:The background and research significance of gravity measurement are introduced.At the same time,the current measurement methods and typical gravitymeasurement instruments at home and abroad are elaborated and compared.The basic mechanical structure and working principle of superconducting gravimeter are introduced.The capacitance model of superconducting ball in superconducting gravimeter is analyzed.The principle of the capacitance method for precision displacement measurement is described in detail.The characteristics of different capacitance measurement methods are compared.Due to the capacitance model of superconducting ball,the AC capacitor bridge based on induction voltage divider is selected as a detection device.In-depth research on each module of the capacitance micrometer system,and design a complete capacitance micro-displacement measurement system,which mainly includes the design of high-precision AC capacitor bridge,and the use of phase-locked amplifier to demodulate weak signals The feedback link of constant current source based on analog proportional integral(PI).At the same time,the shielding technology of the measurement device and the key factors affecting the performance of the PCB are studied to improve the reliability of the system.The performance index of each module of the capacitance micrometer system is verified,and the capacitance measurement resolution and linearity of the measurement system are evaluated by simulating the capacitance change.It can be known from the experiment that the capacitance micrometer system can detect a capacitance change signal of 1f F in the range of 2p F,and the measurement non-linearity in the entire range is only 3.45%,so the system can meet the capacitance change measurement caused by the 0.1?Gal gravity change.