可编程控制器外文文献.doc

2016 届 电子信息工程学院 外文文献及译稿 外文文献题目： Programmable logic controller 姓 名： 梁学文 学 号： 201203024305 专业班级： 自动化B123 院（部）： 电子信息工程学院 指导教师： 尤文强 2016年 6月 1 日 programmable logic controller,?PLC, programmable controller?is a?digital computer?used for?automation?of typically industrial?electromechanical?processes, such as control of machinery on factory?assembly lines,amusement rides, or?light fixtures. PLCs are used in many machines, in many industries. PLCs are designed for multiple arrangements of digital and analog inputs and outputs, extended temperature ranges, immunity toelectrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed-up or?non-volatile memory. A PLC is an example of a hard?real-time?system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was mainly composed of?relays,?cam timers,?drum sequencers, and dedicated closed-loop controllers. Since these could number in the hundreds or even thousands, the process for updating such facilities for the yearly model?change-over?was very time consuming and expensive, as?electricians?needed to individually rewire the relays to change their operational characteristics. Digital computers, being general-purpose programmable devices, were soon applied to control industrial processes. Early computers required specialist programmers, and stringent operating environmental control for temperature, cleanliness, and power quality. Using a general-purpose computer for process control required protecting the computer from the plant floor conditions. An industrial control computer would have several attributes: it would tolerate the shop-floor environment,