文档介绍：毕业设计(论文)外文参考资料及译文
设计(论文)题目:基于PLC的磨板废水自动控制处理系统设计 
学生姓名: 张凤林学号: 0704111019
专业: 自动化
所在学院: 机电工程学院
指导教师: 李志臣
职称: 讲师
2011 年 2月 20 日
Control Devices and PLC
Joseph La Fauci
From Wikipedia, the free encyclopedia
Several types of control devices are used in industry to satisfy the following control needs.
Mechanical Control、Pneumatic Control、Electromechanical Control、Electronic puter Control、Programmable Logic Control (PLC)
Mechanical control includes cams and governors. Although they have been used for the control of plex machines, to be cost effectively, today they are used for simple and fixed-cycle task control. Some automated machines, such as screw machines, still use cam-based control. Mechanical control is difficult to manufacture and is subject to wear.
Pneumatic control is still very popular for certain applications. It pressed air, valves, and switches to construct simple control logic, but is relatively slow. Because ponents are used to construct the logic, it is easier to build than a mechanical control. Pneumatic control parts are subject to wear.
As does a mechanical control, an electromechanical control use switches, relays, timers, counters, and so on, to construct logic. Because electric current is used, it is faster and more flexible. The controllers using electromechanical control are called relay devices.
Electric control is similar to electromechanical control, except that the moving ponents in an electromechanical control device are replaced by electronic switches, which works faster and is more reliable.
Computer control is the most versatile control system. The logic of the control is programmed into puter memory using software. It not only can be for machine and manufacturing system control, but also for munication. plex control strategies with putations can be programmed. The first is the interface with the outside world. Internally, puter uses a low voltage (5 to 12 volts) and a low current (several milliamps). Machine requires