time reference signal

例句：

1. 1.The satellite transmits a time reference signal to the ground station.
   卫星向地面站发送一个时间参考信号。
2. 2. This device uses a time reference signal to measure the distance between two points.
   这个设备使用一个时间参考信号来测量两点之间的距离。
3. 3.The clock's time reference signal is accurate to within a few seconds.
   这个时钟的时间参考信号准确到几秒内。