数控技术专业英语(第2版)：Unit 5 Introduction to PLC

1、Unit Five,Dialogue Text Supplementary Reading Translating Skills 5,Dialogue,Topical Introduction: Tom and Mary are visiting an line of computer integrated manufacturing. They want to get some information about CIM. Mary: Tom I cant understand what the phrase CIM really means. Tom: well did you remem

2、ber that PLC stands for computer integrated manufacturing? Mary: Yes, I did. But I cant grasp the real meaning of “integrated” here,下一页,返回,Dialogue,Tom: to be honest, Im not sure either. You know, many technical terms are too new, too fashionable to understand. But I think, in the phrase “computer-

3、integrated- manufacturing”, “integrated” may be used to mean “all the manufacturing activities are made into a whole system.” That is, all the manufacturing activities, including raw material handing, production planning, production of parts and components, assembly, quality-inspection, and so on, a

4、re controlled and integrated by a computer system. Mary: Tom, Im still not sure if a computer can have so great a power as to control the entire production,下一页,上一页,返回,Dialogue,Tom: No, you are wrong again. Actually, it is not one computer but many computers are working together to form an integrated

5、 system. Mary: Tom, I cant understand the word “inventory” in the text. What does the word really mean? It is very much like “inventor” and “invention”. Tom: Oh, inventory, I believe, has nothing to do with “inventor” or “invention.” While “inventory” means a detailed list of articles, or the amount

6、 of stock which are named in the inventory, the word “inventor” means a person who has invented something, and the word “invention”? the action that an inventor has taken. Mary: Oh, its really amusing,上一页,返回,Text,Introduction to PLC In order to use the advantages of all those controllers and elimina

7、te the difficulties, the programmable logic controllers were invented. A PLC was replacement for relay devices. They are programmed using a ladder diagram, which is standard electric wiring diagram. As PLCs become more flexible, high-level as well as low-level languages are available to PLC programm

8、ers. PLCs have the flexibility of computers as well as a standard and easy interface with processes and other devices. They are widely accepted in industry for controlling from a single device to a complex manufacturing facility,下一页,返回,Text,Programmable logic controllers (PLCs) were first introduced

9、 in 1968 as a substitute for hardwired relay panels. The original intent was to replace a mechanical switching device (relay modules). However, since 1968, the capabilities of the PLCs were to replace relay panels, modern PLCs have many more functions. Their use extends from simple process control t

10、o manufacturing system controls and monitoring. They are used for high-speed digital processing, high-speed digital communication, high-level compute-language support, and, of course, for basic process control1 (Fig.5-1,下一页,上一页,返回,Fig.5-1,返回,Fig.51 Application of PLC( Controls Step/Servo Motor,Text,

11、PLCs vary in size and power. A large PLC can have up to 10000 I/O points and support all the functions discussed earlier. There are also expansion slots to accommodate PC and other communication devices. For many applications, a small PLC is sufficient. Fig.5-2 shows a small PLC. It has 16 I/O point

12、s and a standard RS-232 serial communication port. The speed of PLC is constantly improving, even the low-end PLCs perform at high speed. One to two microsec / kbyte of memory speed is very common,下一页,上一页,返回,Fig.5-2,返回,Fig. 5-2 PLC (FP1 C16 Control Panel,1.CD/DC Power Input 2Mode Select 3Output 4I/O

13、 Expansion Slots 5I/O Status LED 6Label 7Input 8DC Power Output 9Programmer Interface 10Adjustable Input 11PLC Status LED,Text,Programmable controller Architecture In the preceding sections, the basic components in a relay panel circuit and the design of a relay ladder diagram have been discussed. I

14、n the implementation of such a circuit, not only does the logic problem have to be thought out, but also the electrical compatibility and wiring layout have to be considered2. Breadboarding a relay panel circuit is a tedious task; it requires a lot of careful planning and work. The debugging and cha

15、nging of a circuit is even more difficult. Programmable logic controllers replace most of this wiring by software programming,下一页,上一页,返回,Text,Therefore, the task is made much easier, because the wires and the moving mechanical components (relay contacts) are mostly replaced by software, the system i

16、s much more reliable3. Like a general-purpose computer, a programmable controller consists of five major parts: CPU (processor), memory, input/output(I/O), power supply, and peripherals(Fig. 5-3,上一页,返回,Fig. 5-3,返回,Fig.5-3 Programmable Controller Architecture,Notes,1. They are used for high-speed dig

17、ital processing, high-speed digital communication, high-level compute-language support, and, of course, for basic process control. 它们被用于高速数据处理、高速数据通信、高级计算(PLC)机语言支持，当然也用于基本过程控制。 “of course”为插入语，起附加说明的作用，即相当于 “and they are used for basic process control.,返回,Notes,2. In the implementation of such a ci

18、rcuit, not only does the logic problem have to be thought out, but also the electrical compatibility and wiring layout have to be considered. not only 置于句首时需用主谓倒装结构。 在这样的一个电路中，不仅应当考虑逻辑问题，而且电的兼容性和线的布置也应当考虑在内,返回,Notes,3.Therefore, the task is made much easier, because the wires and the moving mechanic

19、al components (relay contacts)are mostly replaced by software, the system is much more reliable. 由于线路和可动机械零件(延时触点)大部分被软件所代替，因此(PLC)执行某项任务更容易、系统更可靠,返回,Supplementary Reading,Types of Control Devices Several types of control devices are use in industry to satisfy the following control needs: l Mechanic

20、al Control l Pneumatic Control l Electromechanical Control l Electronic Control l Computer Control l Programmable Logic Control (PLC,下一页,返回,Supplementary Reading,Mechanical control includes cams and governors. Although they have been used for the control of very complex machines, to be cost effectiv

21、ely, 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 cert, valves, and switches to construct s

22、imple control logic, but is relatively slow. Because standard components are used to construct the logic, it is easier to build than a mechanical control. Pneumatic control parts are subject to wear,下一页,上一页,返回,Supplementary Reading,As does a mechanical control, an electromechanical control uses swit

23、ches, 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 mechanical compo

24、nents in an electromechanical control device are replaced by electronic switches, which works faster and is more reliable,下一页,上一页,返回,Supplementary Reading,Computer control is the most versatile control system. The logic of the control is programmed into the computer memory using software. It not onl

25、y can be for machine and manufacturing system control, but also for data communication. Very complex control strategies with extensive computations can be programmed. The first is the interface with the outside world. Internally, the computer uses a low voltage (5 to 12 volts) and a low current (sev

26、eral milliamps). Machine requires much higher voltages (24,110, or 220 voltages) and currents (measured in amps). The interface not only has to convert the voltage difference, but also must filter out the electric noise usually found in the shop. The interface thus must be custom-built for each appl

27、ication,上一页,返回,Translating Skills 5,常见多词功能词的用法(1) 英语中有些词，如as, it, that, what等，在句子里可以有不同的功能。以as为例，可作为介词引导主语或宾语的补足语、状语、同位语；可作为关系代词引导定语从句；可作为连词引导时间、原因、比较、让步、方式等状语从句。又如that, 可作为限定词、指示代词、关系代词、连词等。一个词在句中的功能不同，译法也随之而异,下一页,返回,Translating Skills 5,多功能词as, it, that, what 在科技文章中广泛使用，出现的频率很高，有必要提出来重点讨论。然而这并不意味着

28、多功能词仅此四个词，例如，but可以作连词、介词、副词及关系代词，但相对来说，易于判断，翻译不难，因而不予以讨论。此外，所列入讨论的多功能词也不面面俱到，如what可作为限定词，构成感叹句，但由于这种用法在科技英语中很少出现，故而省去。 现将as, it, that, what的用法及译法分述如下,下一页,上一页,返回,Translating Skills 5,I. As 的用法 1 As作为介词的译法 as 作为介词可引导主语补足语、宾语补足语、状语、同位语等，可译为“作为”、“为”“以”“是”“当作” 等。 We take steel as the leading engineering

29、material. (宾语补足语) 我们把钢作为主要的工程材料。 Engineering is considered as an applied science. (主语补足语) 工程学被认为是一门应用科学。 It is well known that water can also exist as a gas or a solid.(状语) 众所周知，水还能以气态或固态存在,下一页,上一页,返回,Translating Skills 5,Electricity is especially convenient as a source of mechanical power. (同位语) 电是

30、机械的一种特别方便的动力源。 2As作为关系代词的译法 As作为关系代词可以单独使用，也可以与such, the same等词搭配使用，引导定语从句，其译法分述如下。 (1) as单独引导定语从句或省略定语从句时，可译成“正如”“如”或“这”“这样”等，有时as 也可略去不译。 As is known us, inertia is an absolute quality possessed by all bodies. 正如我们所知，惯性是所有物体都具有的一种必备属性,下一页,上一页,返回,Translating Skills 5,This machine, as might be expec

31、ted, has stopped operating. 正如所料，这台机器已停止运转。 The density of saturated vapor also increases when the temperature becomes higher, as shown in Table 3. 如表3所示，温度升高时，饱和水蒸气的密度也随之增加。 As described above, the laser beam is much more powerful than other light beams. 如上所述，激光束比其他光束的威力要大得多。 As is often the case i

32、n nature, the commonest things are the complicated. 最普通的东西就是最复杂的，自然界的情况经常就是这样,下一页,上一页,返回,Translating Skills 5,As has been found there are more than a hundred elements. 已经发现，元素有一百多种。(如译成“正如已经发现”，反而显得累赘。 (2) such as和such as引导的定语从句可译成“像这(那)样的”“那样(种)的”“像之类的”等。 Such light as is produced by an incandescen

33、t lamp is called incoherent light. 像白炽灯发出的那种光叫做非相干光。 Such power cables as we need must be strong and yet conduct electricity easily. 我们需要的那种电缆必须具有高强度和良好的导电性,下一页,上一页,返回,Translating Skills 5,Mechanics deals with such ideas as inertia, motion, force and energy. 力学研究诸如惯性、运动、力和能量之类的概念。 (3) the sameas和the

34、 same as引导的定语从句可译成“和一样”“与同”、“和相等”。 After transformation the energy has the same amount as it has before the transformation. 能量在转换后和转换前一样大。 The current is in the same direction as the motion of the positive particles. 电流的方向与带正电粒子的运动方向相同,下一页,上一页,返回,Translating Skills 5,The weight of the neutron is abo

35、ut the same as a proton, but it has no electrical charge. 中子的重量和质子差不多相等，但中子不带电荷。 3 As作为关系副词的译法 As作为关系副词，引导定语从句的译法与作为关系代词引导定语从句的译法基本相同。 Molecular weights are expressed in the same unit as atomic weights. 分子量用与原子量相同的单位来表示,下一页,上一页,返回,Translating Skills 5,A vector multiplied by a scalar quantity is a ve

36、ctor in the same direction as the original vector. 乘以标量的矢量是一个与原向量同向的矢量。 4 As 作为连词的译法 As作连词可引导时间、原因、比较、让步、方式等状语从句。不同的状语从句中as有不同的译法，分述如下。 (1) as 引导时间状语从句时可译为“(当)时”、“随着”等。 As the steam expands, the temperature fails. 当水蒸气膨胀时，温度就下降。 :Light waves weaken as they spread out from a source. 光波光源扩散时，强度减弱,下一页,

37、上一页,返回,Translating Skills 5,2) as引导原因状语从句时可译为“由于”“因为所以”等。 As liquids and gases flow, they are called fluids. 由于液体和气体能流动，因此称为流体。 As water is good solvent, pure water is never met with in nature. 因为水是一种很好的溶剂，所以在自然界中从来见不到纯水,下一页,上一页,返回,Translating Skills 5,3) as 引导比较状语从句的译法。 as+形容词或副词+as可译为“与一样(同样) not+

38、so+形容词或副词+as可译为“不如(没有)(那样)” Heat is another form of energy, which is as important as other kinds of energy. 热是能量的另一种形式，与其他形式的能量同样重要。 The melting point of copper is not so high as that of iron. 铜的熔点没有铁高。 在as+形容词或副词+as的结构中，形容词或副词往往转译成名词，再按照“与一样(相同)”的译法处理,下一页,上一页,返回,Translating Skills 5,In vacuum, ligh

39、t bodies will fall as fast as heavy ones. 真空中轻物体下落的速度与重物体下落的速度相同。 Zirconium is almost as strong as steel. 锆的强度几乎与钢一样。 One proton is almost as heavy as an entire atom of hydrogen. 在一个质子几乎与整个氢原子的重量相等。 在asas结构中，往往将asas译成“多多；as many (much) as 可译为“多少多少”，as long as 可译成“多久”等。 In such a system of a computer

40、 as many circuits are required as there are numerous in the word. 在这种计算机系统中，词里有多少位数字，就需要有多少条线路,下一页,上一页,返回,Translating Skills 5,The development stage lasts as long as it needs to. 研制阶段需要持续多久，就持续多久。 在as+形容词或副词+as+形容词或副词的结构中，前后的形容词或副词表示同一事物的两种不同性质的比较，asas可译成“又又”。 This method is as simple as practical.

41、这种方法又简单又实用。 The wheel turns as fast as stably. 这只轮子旋转得又快又稳,下一页,上一页,返回,Translating Skills 5,4) as引导让步状语从句(倒装句)，可译为“虽然”、“尽管”等。 Small as atoms are, they contain vast amounts of energy. 原子虽小，但具有很大的能量。 Complicated as the problem is, it can be worked out in a few minutes by an electronic computer. 尽管那个问题很

42、复杂，电子计算机能在几分钟内将它解出,下一页,上一页,返回,Translating Skills 5,5) as引导方式状语从句时可译为“像那样”“正如”“正如”等。 Solids expand and contract as liquids and gases do. 固体会像液体和气体那样膨胀和收缩。 Friction, as the term is understood in mechanics, is the resistance to relative motion between two bodies in contact. 正如大家在力学中所知，摩擦就是两个相接触的物体产生相对运

43、动的阻力。 A digital computer employs numbers, as we usually do in paper and pencil calculations. 数字计算机使用数字，正如我们通常用纸和铅笔计算时使用数字一样,下一页,上一页,返回,Translating Skills 5,IIIt 的译法 1 在下列句型结构中，It略去不译 (1) it用作无人称主语(impersonal subject)，表示天气、时间、距离等。 It is very cold and often snows here in winter. 此地冬天很冷，常常下雪。 It is jus

44、t six oclock. 现在正好六点钟,下一页,上一页,返回,Translating Skills 5,2) it用作先行主语(anticipatory subject) It is easier to roll something over a surface than to slide it. 在任一表面上滚动一个物体比滑动它容易。 It seems that the result of this test will be very important to the oil industry. 看来，这个试验的结果对石油工业非常重要,下一页,上一页,返回,Translating Skills 5,3) it用作先行宾语(anticipatory object) The development of integrated circuits made i