机电工程专业英语 教学课件 ppt 作者 朱晓玲 Lesson 13

Lesson 13 Programmable Logic Controller 可编程逻辑控制器,Section I Words and Phrases Section II Text and Translation Section III Exercises and Answers,词,英,汉,练,End,Next,答,Section I Words and Phrases,actuator 执行机构 pneumatic nju(:)5mAtikadj.气动的，气力的 n.气胎 hydraulichai5drC:likadj. 水力的, 水压的，液压的 n.液压传动装置 relay5ri:lein. 电工继电器 solenoid5sEulinCidn. 电螺线管 proprietary prE5praiEtEriadj. 所有人的：属于一个所有人或作为群体的所有人的，或与之有关的： camkAmn.凸轮 automate 5C:tEmeitv.使自动化, 自动操作 initially I5nIFElIadv.最初, 开头,Topic,Above,Next,End,Section I Words and Phrases,ladder 5lAdE(r)n.梯子，梯形 inspire in5spaiEvt. 作为原因或根源；引起；激励，鼓励：激发行动，促动 trace out描绘出 apprehension 7Apri5henFEnn. 担心，忧虑 circuit 5sE:kitn.电路 load lEudn.负荷, 重担,负载 power supply电源 module 5mCdju:ln.模数, 模块, flexibility 7fleksE5bilitin.弹性, 适应性,柔韧性,Topic,Above,Next,End,Section II Text,A programmable logic controller, PLC, or programmable contr-oller is a small computer used for automation of real-world processes, such as control of machinery on factory assembly lines. The PLC usua-lly uses a microprocessor. The program can often control complex seq-uencing and is often written by engineers. The program is stored in battery-backed memory1 and/or EEPROMs2. PLCs have the basic structure, shown in Figure 13-1. From the figure, the PLC has four main units: the Programme memory, the Data memory, the Output devices and the Input devices. The Programme memory is used for storing the instructions for the lo-gical control sequence. The status of switches, interlocks, past values of data and other working data is stored in the Data memory.,Topic,Above,Next,汉,End,Section II Text,The main differences from other computers are the special input/output arrangements. These connect the PLC to sensors3 and actuators4. PLCs read limit switches, temperature indicators and the positions of complex positioning systems. Some even use machine vision.On the ac-tuator side, PLCs drive any kind of electric motor, pneumatic or hydra-ulic cylinders or diaphragms, magnetic relay-s or solenoids. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a proprietary computer network that plugs into the PLC.,Topic,Above,Next,汉,End,Section II Text,PLCs were invented as less expensive replacements for older auto-mated systems that would use hundreds or thousands of relays and cam- timers. Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the auto-motive manufacturing industry, where software revision replaced the rewiring of hard-wired control panels. The functionality of the PLC has evolved over the years to include typical relay control, sophisticated motion control, process control, Distributed Control Systems5 and complex networking.,Topic,Above,Next,汉,End,Section II Text,The earliest PLCs expressed all decision making logic in simple ladder logic inspired from the electrical connection diagrams. The elect-ricians were quite able to trace out circuit problems with schematic dia-grams using ladder logic. This was chosen mainly to reduce the appreh-ension of the existing technicians. Today, the PLC has been proven very reliable, but the program-mable computer still has a ways to go. With the IEC 661131-3 standard, it is now possible to program these devices using structured programmi-ng languages, and logic elementary operations. A graphical programming notation called Sequential Function Charts7 is available on certain programmable controllers.,Topic,Above,Next,汉,End,Section II Text,However, it should be noted that PLCs no longer have a very high cost (often thousands of dollars), typical of a “generic“ solution. Mode- rn PLCs with full capabilities are available for a few hundred USD8. There are other ways for automating machines, such as a custom micro-controller-based design, but there are differences among both: PLCs contain everything needed to handle high power loads right out of the box, while a microcontroller would need an electronics engineer to des-ign power supplies, power modules, etc. Also a microcontroller based design would not have the flexibility of in-field programmability of a PLC. That is why PLCs are used in production lines, for example. The-se typically are highly customized systems so the cost of a PLC is low compared to the cost of contacting a designer for a specific, one-time,Topic,Above,Next,汉,End,Section II Text,only design.On the other hand, in the case of mass-produced goods, customized control systems quickly pay for themsel-ves due to the lower cost of the components.,Topic,Above,Next,汉,End,Section II Translation,可编程逻辑控制器，PLC, 或者称可编程控制器，它是一种小型计算机，用于自动化生产，比如控制工厂的装配机械等。可编程控制器通常使用了微处理器进行控制。其程序可控制复杂的加工工序，并由工程师编写。程序通常存储在随机存储器和（或）电可擦写可编程只读存储器中。 PLC的基本结构 如图13-所示。 从图中可见，PLC有四个主要的部件：程序存储器，数据存储器，输出设备和输入设备。程序存储器用来存储逻辑控制序列指令。开关状态，联锁状态、数据初始值等其它工作数据存储在数据存储器中。,Topic,Above,Next,英,End,Section II Translation,与其它计算机比较，最大的区别是PLC有专用的输入输出装置。这些装置将P