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Research on Micro Astrogeodetic Timer

Author: YangYuFei
Tutor: ZhengYong
School: PLA Information Engineering University
Course: Astrometry and celestial mechanics
Keywords: astronomic geodesy timer crystal oscillator embedded systems time synchro nization clock error prediction GPS timeservice
CLC: P128.1
Type: Master's thesis
Year: 2013
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Abstract

Astronomical positioning and orientation is carried out by observation of celestial bodies onthe celestial sphere. Due to earth’s rotation movement and the continuous changes of the celestialbody position, accurate time should be recorded at the same time when observation. The newastrogeodetic system take the computer internal quartz crystal for time-keeping. But the stability ofcomputer internal quartz crystal is poor, it can only be used to short-term time-keeping. Highprecision UTC time must be received before each observation using GPS receiver. Once GPSsatellite signal can not be received, observation can not be accomplished. This greatly inlfuences theindependence and reliability of astronomical geodesy.To resolve the problem of long-term astrogeodetic time-keeping, a micro astrogeodetic timerwas developed in this dissertation. The timer takes high stability digital temperature compensatedcrystal oscillator as the frequency source and embedded system as platform. The structure andworking process of the timer was designed. The key technologies about astrogeodetic timer weresolved, and two prototypes were developed. Long-term astrogeodetic time-keeping was realized.The automatic measure of temperature, humidity and pressure was realized, the timesynchronization theory was presented, and the time comparison platform based on computer wasdesigned.20days time comparison experiment was carried out, and the accuracy and stability of thetimer were analyzed. Main contents of the thesis were as follows:1.The development of time-keeping science and technology was presented. The developmentof astrogeodetic time acquisition and time reference maintenance was presented. The meaning ofresearch on the micro astrogeodetic timer was analysed.2.The time system related to astronomical geodesy and transformation relationship betweenthem was presented. The calculation steps of time and different application of different time inastronomical geodesy was researched.3.A micro astrogeodetic timer for long-term time-keeping was developed. The structure,working process, different characteristics and application of different kinds of crystal oscillatorswere researched. The micro astrogeodetic timer solution which take high stability digitaltemperature compensated crystal oscillator as the frequency source and embedded system asplatform was developed. The structure, circuit connection and workflow were designed. The controlprogram used in timer microprocessor was compiled.4.The key technologies about astronomical timer were solved, such as microprocessorcounter set method, serial communication, temperature and humidity sensor, pressure sensor andpower protection module. Printed Circuit Board was designed，and two timer prototypes weredeveloped. The long-term independent maintenance of astrogeodetic time was realized. The automatic measurement and output of temperature, humidity and pressure were realized. Timeprotection and recovery after unexpected power-off were realized, and its accuracy were tested andanalyzed.5.The development of time synchronization theory was presented. The time comparisonplatform between GPS time and the timer based on computer was designed，and High accuracy timewas acquired. The computer internal time acquisition was researched. GPS time and coordinateinformation acquisition was researched. The performance of multiple serial card was tested. Timeextrapolation algorithms were researched.6.The accuracy and stability of computer internal time were analyzed. The performance ofpower protection module were analyzed. The acquisition accuracy, clock speed stability andtime-keeping accuracy of timer were analyzed. The timer extrapolation accuracy are analyzed.7.Through the thesis research, two micro astrogeodetic timer prototypes were developed. Therelated programs were compiled. The accuracy and stability of timer were given though experiment.

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