电缆故障在线测距中高速同步采集卡精确时标获取方法

为减小全球定位系统(GPS)同步时钟误差对双端行波测距的影响,使电缆故障在线测距能达到实用化水平,提出一种能够获取精确时标的高速同步采样方案。利用GPS时钟无累计误差和高精度晶振频率稳定性高的特点,并将高速采样与秒脉冲捕捉有机结合,通过硬件方式无延时地捕捉秒脉冲以获取精确的时间计数值。对秒脉冲间的计数值进行滑动平均处理和最小方差估计,可获得高精度的时间标签,平均误差可达到30ns。设计中采用复杂可编程逻辑器件CPLD(ComplexProgrammableLogicDevice)实现高速时序控制,并考虑了抗干扰和异常处理措施,提高了系统的可靠性和工作性能。

Acquisition of precise time in synchronized high speed sampling unit for on-line cable fault locating

A synchronized high-speed sampling scheme is proposed,which can obtain high precise time to diminish the influence of GPS(Global Position System) clock error on two-terminal traveling wave fault locating for implementing on-line power cable fault locating.Owing to GPS clock,which has no accumulative error,and quartz oscillator,which is very stable,the time counting value is obtained without delay via hardware by combining high speed sampling and PPS(Pulse Per-Second)-snapping.The value between two PPSs snapped is processed using the moving-average method and the least square error algorithm to increase the time precision with an average error of 30 ns.The CPLD(Complex Programmable Logic Device) is used for high-speed sequential control and the anti-interference and abnormality-remediation measures are taken to improve the system reliability and performance.