timer timing pulse

例句：

1. 1. The timer goes offevery hour.
   定时器每小时响一次。
2. 2. Thetimer is used to measure the durationof an event.
   定时器用于测量事件的时间长度。
3. 3. The timer was set for10 minutes.
   定时器设置为10分钟。