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1、如有侵权，请联系网站删除，仅供学习与交流plc外文文献译文【精品文档】第 6 页Programmable logic controllerA programmable logic controller (PLC) is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLC is used in many indu

2、stries and machines. 1.History The PLC was invented in response to the needs of the American automotive manufacturing industry. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum s

3、equencers and dedicated closed-loop controllers. In 1968 GM Hydramatic issued a request for proposal for an electronic replacement for hard-wired relay systems.The first PLC, designated the 084 because it was Bedford Associates eighty-fourth project, was the result. Bedford Associates started a new

4、company dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for MOdular DIgital CONtroller. The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner.One

5、 of the very first 084 models that was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its appearance.2.Development Early PLCs were designed to replace relay logic

6、 systems. These PLCs were programmed in ladder logic, which strongly resembles a schematic diagram of relay logic. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditio

7、nal programming languages such as BASIC and C. Another method is State Logic, a very high-level programming language designed to program PLCs based on state transition diagrams.3.Functionality The functionality of the PLC have sequential relay control, motion control, process control, distributed co

8、ntrol systems and networking.Regarding the practicality of these desktop computer based logic controllers, it is important to note that they have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than do PLCs, and because the desktop com

9、puter hardware is typically not designed to the same levels of tolerance to temperature, In more recent years, small products called PLRs (programmable logic relays), are used in light industry where only a few points of I/O (i.e. a few signals coming in from the real world and a few going out) are

10、involved, and low cost is desired. Popular names include PICO Controller, NANO PLC, and other names implying very small controllers. the PLRs are usually not modular or expandable, but their price can be two orders of magnitude less than a PLC and they still offer robust design and deterministic exe

11、cution of the logic.4.PLC compared with other control systemsPLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and wh

12、ere changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations. PLC application

13、s are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optim

14、ally chosen instead of a generic solution, and where the non-recurring engineering charges are spread over thousands or millions of units. A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies,

15、input/output hardware and necessary testing and certification) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers.

16、However, some specialty vehicles such as transit busses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic.Programmable controllers are widely used in motion control, positioning control and torque control. Some manufac

17、turers produce motion control units to be integrated with PLC so that G-code (involving a CNC machine) can be used to instruct machine movements.PLCs may include logic for single-variable feedback analog control loop, a proportional, integral, derivative or PID controller. A PID loop could be used t

18、o control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. As PLCs have become more powerful, the

19、 boundary between DCS and PLC applications has become less distinct. PLCs have similar functionality as Remote Terminal Units. An RTU, however, usually does not support control algorithms or control loops. As hardware rapidly becomes more powerful and cheaper, RTUs, PLCs and DCSs are increasingly be

20、ginning to overlap in responsibilities, and many vendors sell RTUs with PLC-like features and vice versa. The industry has standardized on the IEC 61131-3 functional block language for creating programs to run on RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and asso

21、ciated development environments.5.The prospects for PLC. 5.1.Features The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements. PLCs read limit switches, analog pro

22、cess variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs. The input/output arrangements may be buil

23、t into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.5.2System scale A small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expansions are available if the base model has insufficient I/O.Modular

24、 PLCs have a chassis (also called a rack) into which are placed modules with different functions. The processor and selection of I/O modules is customised for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special

25、high speed serial I/O link is used so that racks can be distributed away from the processor, reducing the wiring costs for large plants.5.3User interface PLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control. A simple system may use buttons and l

26、ights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use a programming and monitoring software installed on a computer, with the PLC connected via a communication interface.5.4Communications PLCs have built in communications ports, usu

27、ally 9-pin RS-232, but optionally EIA-485 or Ethernet. Modbus, BACnet or DF1 is usually included as one of the communications protocols. Other options include various fieldbuses such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protoc

28、ols. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser. PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of

29、a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI devices such as keypads or PC-type workstations. 可编程逻辑控制器 可编程逻辑控制器（PLC）或可编程序控制器是用于机电过程自动化的数字计算机，例如控制机械厂生产线、游乐设施或照明的装置。可编程控制器可在许

30、多工业和机器中使用。1.历史 PLC发明是针对于美国汽车制造行业的需要。可编程逻辑控制器最初通过了在软件版本更换硬连线的控制板生产模式更改时的汽车工业。在PLC之前，控制、程序化和安全联锁逻辑制造汽车是使用上百或上千的继电器、凸轮计时器、鼓定序仪和专用的闭环控制器来完成的。在1968年 GM Hydramatic发布通用汽车公司的提议，电子替代布线中继系统。第一个PLC选定084，因为它是贝得福得同事的第八十四个项目。贝得福得同事建立了一家新的公司致力开发、生产、销售，和服务这一新产品：Modicon，代表模块化数字控制器。1977年古尔德电子公司当前所有者收购法国施耐德电气公司同德国公司AE

31、G并售予该品牌为Modicon。这是专门为通用汽车服务的，并且经过了近二十多年的不间断服务。直至984出现，Modicon使用的84名字才在其产品范围中结束。2.发展早期的可编程控制器是设计来取代继电器逻辑系统。这些可编程控制器的“阶梯逻辑”是与继电器逻辑示意图非常类似的。其他早期的可编程控制器使用指令列表编程，基于一个堆栈编程逻辑求解器进行求解。 现代可编程控制器在各种各样的方式可以被编程，从梯形逻辑语言到更加传统的编程语言例如BASIC和C语言。另一个方法是状态逻辑，被设计的一种非常高级编程语言根据状态转换图的可编程控制器编程。3.功能PLC的功能包括连续的继电器控制，运动控制，过程控制，

32、分布式控制系统和网络。在重工业中PLC被认为没有这些桌面计算机为主的逻辑控制器的实际性强，因为PLC在台式计算机系统中运行不是很稳定，并且，因为台式计算机硬件没有被设计成耐温度、湿气、振动和耐用作为可编程控制器的处理器。在近些年，小产品称为PLR（可编程逻辑继电器）已经应用于轻工业，它只有少部分的输入/输出（例如一些真实的输入输出信号）参与，低成本，很理想。俗名包括PICO控制器、纳米PLC和其他的小控制器。PLR通常是模块化，大大扩展,控制器通常不会取模块化并且不是可扩展的，但是他们提供稳健设计的确定性和执行逻辑的价值比PLC少。4.PLC相比其它控制系统可编程控制器是可适应一系列自动化任务

33、。这些都是自动化的在制造中通常工业过程开发和维护自动化系统的成本在哪里高，相对于总成本和其寿命期间预计将对系统更改。可编程控制器包含输入和输出设备兼容工业试验设备和管制，小电气的设计问题对预期操作是必要的。PLC应用程序通常是高度定制系统，因此成本包装可编程序控制器（PLC）的费用比一个具体定制设计的小控制器要高。另外一方面在批量生产货物的情况下自定义的控制系统是组成、成本较低的最佳选择，而不是一个非反复出现工程费用“普通”的解决方案。 一种基于微控制器的设计是需要成百上千个单位（设计电源供应器，输入/输出硬件和必要的检测和认证）和开发成本可以分散到很多的销售，最终用户不需要更改该控件。汽车应

34、用程序就是一个例子：数以百万计的内置单位每一年需要建造，很少最终用户更改这些控制器的编程。然而，一些其他车辆如交通公共汽车经常定制设计的控制,而不是用PLC，因为数量很低,发展成本会赚不到钱的。 可编程序控制器广泛用于运动控制、定位控制和转矩控制。一些制造商生产运动控制单元与PLC集成、G-code（涉及数控机床）可以用于指导机器运作。可编程控制器可能包括一个“比例，积分，微分”的单变量反馈模拟控制循环的逻辑或“控制器”。以PID回路可用于控制温度为例。历史上PLC通常配置只有少数模拟控制回路，通常配置可编程控制器将使用分布式的控制系统（DCS）的过程成百上千的循环。可编程控制器功能已经很强大

35、了，可编程序控制器（PLC）与集散控制系统之间的边界应用已经不是很明显了。可编程控制器具有类似于远程终端设备的功能。RTU，然而通常不支持或控制回路的控制算法。随着硬件迅速变得更强大和更便宜，RTU、PLC和DCS正在越来越多地开始有重叠，职责，并与PLC卖许多供应商的特点类似，RTU反之亦然。业界基于IEC61131-3创建程序上运行的RTU和PLC功能块语言规范，尽管几乎所有供应商还提供专有的替代方案及相关的开发环境。5. PLC的展望5.1未来发展从其他计算机来看，主要区别是可编程控制器具有特殊条件（例如，灰尘、湿、热、冷）和具有广泛的输入/输出（I/O）安排的设施。这些是连接PLC的传

36、感器和执行器。可编程控制器是读取限制开关、模拟过程变量（如温度和压力）以及位置复杂的定位系统。执行器使可编程控制器操作电子电机、气动或液压缸、磁继电器、电磁线圈的模拟输出。输入/输出的安排可以建立一个简单的可编程控制器、或可编程序控制器可以用外部的I/O模块连接插入的计算机网络。5.2系统规模 一个小的PLC是固定数量的输入和输出生成的连接。 模块化可编程控制器有一个机箱（也称为机架）在其中放置具有不同的功能模块。处理器和I/O模块的选择被定制为特定的应用程序。几个机架可以有一个单个的处理器，可能会有成千上万的输入和输出。一种特殊的高速串行I/O环节是机架减少多个线路使用分布式离散处理器。5.

37、3使用界面可编程控制器的配置、报警报告或日常控件可能需要与人进行交互。一个简单的系统可能使用按钮和指示灯与用户进行交互。可以用图形触摸屏文本显示。更复杂的系统使用PLC通过通信接口连接到一台计算机上安装的编程和监测软件来使用。5.4通信方面 可编程控制器被建于通常的9针RS-232，也可以选择485或以太网的通信端口由环境影响评估。协议、BACnet或东方是通常作为通信协议之一包含其中。其它选项包括各项如构架或现场总线。在自动化协议的列表中列出了其他可能使用的通信协议。最现代的可编程控制器可以通过一个网络，以一些其它的系统（例如，运行监控、监测控制与数据采集 系统）或网络浏览器的计算机进行通信。可编程控制器在较大的I/O系统中使用可能会有处理器之间的对等，这允许独立的部分是一个复杂的过程,同时让独立的控制子系统的沟通联系协调。这些通信链接也经常用于人机界面设备（例如键盘或PC型工作站）。