机电工程英语省公开课一等奖全国示范课微课金奖PPT课件.pptx

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Section I Words and Phrases
Section II Text and Translation
Section III Exercises and Answers
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第1页
Section I Words and Phrases
actuator 执行机构
pneumatic ［nju(:)5mAtik］，气力　
hydraulic［hai5drC:lik］adj. 水力, 水压，液压　　
relay［5ri:lei］n. [电工]继电器
solenoid［5sEulinCid］n. [电]螺线管
proprietary ［prE5praiEtEri］adj. 全部些人：属于一个全部些人或作为群体全部些人，或与之相关：
cam［kAm］
automate [5C:tEmeit], 自动操作
initially [I5nIFElI], 开头
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Section I Words and Phrases
ladder [5lAdE(r)]，梯形
inspire [in5spaiE]vt. 作为…原因或根源；引发；激励，勉励：激发行动，促动
trace out描绘出
apprehension [7Apri5henFEn]n. 担心，忧虑
circuit [5sE:kit]
load [lEud], 重担,负载
power supply电源
module [5mCdju:l], 模块,
flexibility [7fleksE5biliti], 适应性,柔韧性
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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.
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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 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.
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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.
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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.
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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
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Section II Text
only 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.
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Section II Translation
可编程逻辑控制器，PLC, 或者称可编程控制器，它是一个小型计算机，用于自动化生产，比如控制工厂装配机械等。可编程控制器通常使用了微处理器进行控制。其程序可控制复杂加工工序，并由工程师编写。程序通常存放在随机存放器和（或）电可擦写可编程只读存放器中。
PLC基本结构 如图13-１所表示。
从图中可见，PLC有四个主要部件：程序存放器，数据存放器，输出设备和输入设备。程序存放器用来存放逻辑控制序列指令。开关状态，联锁状态、数据初始值等其它工作数据存放在数据存放器中。
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