后向通道是在控制系统中，后向通道指系统的输出信号通道，例如控制信号输出等；前向通道似乎就是指信号的输入通道，例如人机接口的键盘、传感器信号输入等。
电控系统由设定器（上位机）、数字控制器、输入通道（位置检测）和后向通道（执行机构）构成。
The control system is composed of setting unit(host computer ), digital controller , input channel (position detector)and output channel (actuating mechanism).
他走了几步，然后向上爬到上一层的通道，然后不断向上直到看到屋顶的入口。
He walks a few steps, and then pushes his way up to the catwalk above him. He keeps climbing until he sees the roof access.
随着一声叹息和滴答一声，一块石头向前移动了一段距离然后向外打开，露出一条秘密通向外面的通道。
With a sigh and a click, a section of stone moved forward and then swung out, revealing a secret passage beyond.
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