可编程序控制器--外文文献翻译大学论文.doc

英语原文：Programmable logic controllerA programmable logic controller (PLC) or simply programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.FeaturesThe main difference from other computers is that PLC are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLC read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some even use machine vision. On the actuator side, PLC operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.PLC were invented as replacements for automated systems that would use hundreds or thousands of relays, cam timers, and drum sequencers. Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the re-wiring of hard-wired control panels when production models changed.Many of the earliest PLC expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. The electricians were quite able to trace out circuit problems with schematic diagrams using ladder logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLC used a form of instruction list programming, based on a stack-based logic solver.The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLC are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLC in certain applications.PLC compared with other control systemsPLC 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 where changes to the system would be expected during its operational life. PLC 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 in ladder logic notation. PLC applications 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 optimally chosen instead of a "generic" solution, and where the non-recurring engineering charges are spread over thousands of places.For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities.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 and input/output hardware) 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. However, some specialty vehicles such as transit busses economically use PLC instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic.Very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLC. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls.PLC may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller." A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLC 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. However, as PLC have become more powerful, the boundary between DCS and PLC applications has become less clear-cut.Digital and analog signalsDigital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Push buttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate values undefined. Initially, PLC had only discrete I/O.Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data. As PLC typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog 4-20 m or 0 - 10 V input would be converted into an integer value of 0-32767.Current inputs are less sensitive to electrical noise (i.e. from welders or electric motor starts) than voltage inputs.System scaleA small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expansions are available if the base model does not have enough I/O.Modular PLC have a chassis (also called a rack) into which is placed modules with different functions. The processor and selection of I/O modules is custom for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special 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.PLC used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of 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 (Human-Machine Interface) devices such as keypads or PC-type workstations. Some of today's PLC can communicate over a wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at network speeds up to 100m.ProgrammingEarly PLC, up to the mid-1980s, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. More recently, PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The very oldest PLC used non-volatile magnetic core memory but now the program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory.Early PLC were designed to replace relay logic systems. These PLC were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. Modern PLC can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a Very High Level Programming Language designed to program PLC based on State Transition Diagrams.Recently, the International standard IEC 61131-3 has become popular. IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations.While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.User interfacePLC may need to interact with people for the purpose of configuration, alarm reporting or everyday control. A Human-Machine Interface (HMI) is employed for this purpose. HMI' are also referred to as MMI' (Man Machine Interface) and GUI (Graphical User Interface).A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. Most modern PLC 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.CommunicationsPLC usually have built in communications ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. DF1 is usually included as one of the communications protocols. Other communications protocols that may be used are listed in the List of automation protocols.HistoryThe PLC was invented in response to the needs of the American automotive industry. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using relays, timers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as the relay systems needed to be rewired by skilled electricians. In 1968 GM Hydra (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems.The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: Mod, which stood for One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC. The 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 of the very first 084 models built is now on display at headquarters in North Andover, Massachusetts. It was presented to by GM, when the unit was retired after nearly twenty years of uninterrupted service.The automotive industry is still one of the largest users of PLC, and still numbers some of its controller models such that they end with eighty-four. PLC are used in many different industries and machines such as packaging and semiconductor machines. Well known PLC brands are Toshiba, Siemens, Allen-Bradley, ABB, Mitsubishi, Omron, and General Electri.附录 B英语翻译：可编程序控制器可编程逻辑控制器(PLC)或干脆可编程序控制器是一个数字化的计算机用于自动化的工业生产过程，如控制机械的工厂装配生产线。不同于一般用途的电脑，临立会是专为多重输入和输出的安排，延长工作温度范围，免疫力电气噪声，抗振动和影响。程式控制机器操作通常存储在备用电池或非挥发性记忆体。PLC的便是一个例子，一个实时系统的输出结果，因为必须出示在回应输入条件，在一个范围内的时间，否则意想不到的行动将导致.特征 主要区别从其他电脑上是PLC的是装甲严重条件(灰尘，潮湿，热源，冷等)，并有设施，广泛的输入/输出(I/O)的安排。这些连接PLC在传感器和致动器。PLC的阅读限位开关，模拟过程变量(如温度和压力)，以及立场复杂的定位系统。有的甚至使用机器视觉。对致动器方面，PLC的运作，电机，气动或液压缸，磁继电器或螺线管，或模拟输出。输入/输出的安排，可能建成一个简单的PLC，或临立会可能有外部I/O模块连接到一个计算机网络，插入PLC。 PLC的发明替代的自动化系统将使用数百或数千继电器，凸轮定时器，和鼓时序。很多时候，一个单一的可编程控制器可以编程，以取代数以千计的继电器。可编程控制器最初所通过的汽车制造业，软件修订取代了重新布线的硬连线控制面板，当生产模式改变。 很多最早的PLC表示，所有的决策逻辑，在简单逻辑的阶梯，出现类似的电气示意图。该电工是相当能追查出电路的问题与示意图使用阶梯逻辑。这个程式符号选择，以减少培训的要求，对于现有的技术人才。其他早期的PLC使用的一种形式，教学名单编程的基础上，堆栈为基础的逻辑求解。 功能的PLC已多年的发展，包括序贯继电器控制，运动控制，过程控制，分布式控制系统和网络。数据处理，储存，加工能力和通信能力，一些现代的PLC是约相当于台式电脑。PLC的编程一样，结合远程I/O的硬件，让一般用途的台式电脑相重叠的一些PLC在某些应用。PLC的比较，与其他控制系统PLC的良好适应了一系列自动化的任务。这些都是典型的工业工序，在哪里制造的开发成本和维护自动化系统是高相对的总成本的自动化，并在变化，该系统预计将在其运行寿命。PLC的控制输入和输出设备兼容的工业试验装置和控制;很少电气设计要求，并设计问题为中心的表达理想序列的行动在阶梯逻辑符号。PLC的应用通常是高度客制化的系统，使成本包装的PLC是比较低的成本，一个具体的自订内建控制器的设计。在另一方面，在如此大规模生产的货物，自定义的控制系统是经济，由于成本较低的元件，而最佳的选择而不是一个“通用”的解决方案，并在非经常性工程费用遍布数以千计的地方。 高音量或很简单的固定自动化的任务，不同的技术使用。举例来说，消费者洗碗机将控制机电凸轮计时器的成本只有几块钱，在生产数量。 1基于微控制器的设计将是适当的情况下数百或数千单位将制作等，开发成本(设计电源供应器及输入/输出硬件)，可以传播很多的销售，并在最终用户不会需要改变控制。汽车应用的一个例子;百万计的单位，每年兴建，只有极少数的最终用户改变编程这些控制器。然而，一些专业车辆，如过境客，在经济上使用的PLC不是定制设计的控制，因为量低，开发成本将是不经济。非常复杂的过程控制，如用在化学工业中，可能需要算法和性能超越的能力，甚至性能高的PLC。非常高的速度和精确度的控制可能还需要定制的解决方案;举例来说，飞机的飞行管制。 临立会可能包括逻辑单变量反馈的模拟控制回路，“比例，积分，导数”或“ PID控制”。1PID控制回路可用于控制温度的制造过程，例如。历史上的PLC通常配置，只有少数的模拟控制回路;何处过程中所需的数百或数千循环，分布式控制系统(DCS)反而会使用。不过，由于临立会已成为更强大，边界之间的DCS与PLC的应用已成为少，旗帜鲜明。数字和模拟信号 数字或离散信号的表现，作为二进制开关，收益率只是一个或关闭的信号(1或0，真或假，分别)。按键，限位开关，光电传感器的例子装置提供了一个离散信号。离散信号发送使用的电压或电流，在特定范围指定为就和另一个作为小康。举例来说，一个PLC可能使用24伏直流电的I/O，价值观，上述22伏直流电代表对，价值观下面2vdc代表起飞，中间值未定义。最初，PLC的只有离散的I/O。 模拟信号一样，音量控制，与一系列的价值观之间的零和满标。这些都是典型的解释为整数的值(计数)由临立会，与各范围的准确性，根据设备和双边投资协定的数量可用来储存数据。作为PLC的通常使用的16位二进制签署的处理器，整数的价值是有限的之间-32768和32767。压力，温度，流量，和重量，往往所代表的模拟信号。模拟信号可以使用的电压或电流与规模成比例的价值的过程中的信号。举例来说，一个充满模拟信号的4-20米或0-10V的输入电压会转化为一个整数，值为0-32767。目前的投入是不太敏感的电气噪声(即由焊工或电动马达启动)，比电压输入。编程早期的PLC ，直至20世纪80年代中期，它当初的程序使用专有的编程小组或特殊用途的编程终端，往往有专门的功能键代表不同的逻辑要素的PLC程序。程序存储在盒式磁带匣。设施，为印刷及文件很小由于缺乏内存容量。最近，PLC程序通常是书面处于一个特殊的应用对一台个人电脑，然后下载一个直接连接电缆或通过网络向临立会。非常最古老的PLC用于非挥发性记忆体磁芯，但现在该程序是储存在临立会无论是在备用电池的后续RAM或其他一些非挥发性快闪记忆体。 早期的PLC设计，以取代继电器逻辑系统。这些PLC的编程人在“阶梯式的逻辑”，这强烈类似于示意图继电器逻辑。现代的PLC可以编程在以各种方式，从阶梯的逻辑来更传统的编程语言，如基本和C另一种方法是国家的逻辑，一个很高的水平编程语言设计程序基于PLC的关