frequency of valve operation

例句：

1. 1. Thefrequency of occurrence is increasing.
   发生的频率在增加。
2. 2. The frequency of light waves is measuredin cycles per second.
   光波的频率是以每秒的周期数来衡量的。
3. 3. The frequencyof the signal varies with time.
   信号的频率随时间变化。