基于GPS与恒温晶振的瞬变电磁同步时钟系统

Synchronous clock system of transient electromagnetic based on GPS and OCXO

针对恒温晶振长期稳定性差和GPS易受干扰、短期稳定性差等问题,设计了基于GPS与恒温晶振的瞬变电磁同步时钟系统。该系统采用"ARM+CPLD"的模式作为核心处理单元,以GPS的秒脉冲信号为基准,采用频率偏差测量模块在2个相邻的秒脉冲之间对高频信号的晶振频率进行检测,并采用自适应PID控制器实现对恒温晶振输出频率的调节,有效地解决了因单个频率偏差过大而影响恒温晶振控制电压精度的问题,提高了系统的稳定性;以秒脉冲信号为计时器,定时对分频器进行复位操作,实现了恒温晶振累积误差的自动消除,保证了输出信号相位的同步。测试结果表明,该系统实现了瞬变电磁发射机和接收机的高精度同步,在GPS信号正常的情况下,同步精度约为270ns;在GPS信号丢失的情况下,同步精度约为350ns。目前该系统已成功应用到瞬变电磁探测系统中,大量应用结果表明,该系统稳定性好,同步精度高。

In view of problems of poor long-term stability of OCXO and susceptibility to interference and poor short-term stability of GPS,synchronous clock system of transient electromagnetic based on GPS and OCXO was designed. ＂ ARM＋CPLD＂ mode is used as core processing unit,and frequency deviation measurement module is used to detect crystal frequency of high frequency signal between two adjacent second pulses,taking GPS second pulse signal as benchmark.The self-adaptive PID controller is used to adjust output frequency of crystal oscillator,which effectively solves the problem that accuracy of control voltage of OCXO is affected because single frequency deviation is too large,and improves stability of the system.Second pulse signal is used as a timer to reset divider at regular intervals,which achieves automatic elimination of cumulative error of OCXO and ensures phase synchronization of output signal.The test results show that the system achieves high precision synchronization of transient electromagnetic transmitter and receiver,synchronization precision is about 270 ns when GPS signal is normal,and synchronization precision is about 350 ns when GPS signal is lost.The system has been successfully applied to transient electromagnetic detection system,a large number of practical application results show that the system has good stability and high synchronization accuracy.