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1、精选优质文档-倾情为你奉上Programmable Logic ControllerA programmable logic controller (PLC) or programmable controller is a used for of processes, such as control of machinery on factory , amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the
2、 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 . A PLC is an example of a system since output results must
3、 be produced in response to input conditions within a bounded time, otherwise unintended operation will result.1HistoryThe PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable logic controllers were initially adopted by the automotive industry whe
4、re software revision replaced the re-wiring of hard-wired control panels when production models changed.Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of , , and and dedicated closed-loop controllers. The pro
5、cess for updating such facilities for the yearly model was very time consuming and expensive, as needed to individually rewire each and every relay.In 1968 GM Hydramatic (the automatic transmission division of ) issued a request for proposal for an electronic replacement for hard-wired relay systems
6、. The winning proposal came from Bedford Associates of . 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: Modicon, which
7、 stood for MOdular DIgital CONtroller. One of the people who worked on that project was , who is considered to be the father of the PLC. The Modicon brand was sold in 1977 to , and later acquired by German Company and then by French , the current owner.One of the very first 084 models built is now o
8、n display at Modicons headquarters in . It was presented to Modicon by , 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.The automotive industry is still one of the largest use
9、rs of PLCs.2DevelopmentEarly PLCs were designed to replace relay logic systems. These PLCs were programmed in , which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of progr
10、amming, based on a stack-based logic solver.Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is , a designed to program PLCs based on .Many early PLCs did not have accompanying programming terminals th
11、at were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some version of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more common for ladder logic to be used, for the aforemention
12、ed reasons. Newer formats such as State Logic and Function Block (which is similar to the way logic is depicted when using digital integrated logic circuits) exist, but they are still not as popular as ladder logic. A primary reason for this is that PLCs solve the logic in a predictable and repeatin
13、g sequence, and ladder logic allows the programmer (the person writing the logic) to see any issues with the timing of the logic sequence more easily than would be possible in other formats.3ProgrammingEarly PLCs, up to the mid-1980s, were programmed using proprietary programming panels or special-p
14、urpose programming , 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. The very oldest PLCs used non-volatile
15、 .More recently, PLCs are usually programmed using special application software written for use on desktop computers, and connecting between the desktop computer and the PLC such as via Ethernet or cabling. Such software allows entry and editing of the ladder style logic, and then may provide additi
16、onal functionality to assist debugging and troubleshooting the software, for example by highlights portions of the logic to show current status during operation or via simulation. Finally, the software may allow uploading and downloading of the program between the computer and the PLC, for backup an
17、d restoration purposes. Alternately, specific devices known as are used to hard wire the logic into the controller by the use of a removable chip, such as an , where the program is transferred to the programming board from the workstation via serial or other logic.4FunctionalityThe functionality of
18、the PLC has evolved over the years to include sequential relay control, motion control, , and . The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to . PLC-like programming combined with remote I/O hardware, allow a general-pu
19、rpose desktop computer to overlap some PLCs in certain applications. 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 t
20、han do PLCs, and because the desktop computer hardware is typically not designed to the same levels of tolerance to temperature, humidity, vibration, and longevity as the processors used in PLCs. In addition to the hardware limitations of desktop based logic, operating systems such as Windows do not
21、 lend themselves to deterministic logic execution, with the result that the logic may not always respond to changes in logic state or input status with the extreme consistency in timing as is expected from PLCs. Still, such desktop logic applications find use in less critical situations, such as lab
22、oratory automation and use in small facilities where the application is less demanding and critical, because they are generally much less expensive than PLCs.In more recent years, small products called PLRs (programmable logic relays), and also by similar names, have become more common and accepted.
23、 These are very much like PLCs, and 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 involved, and low cost is desired. These small devices are typically made in a common physical size and shape by several manufactur
24、ers, and branded by the makers of larger PLCs to fill out their low end product range. Popular names include PICO Controller, NANO PLC, and other names implying very small controllers. Most of these have between 8 and 12 digital inputs, 4 and 8 digital outputs, and up to 2 analog inputs. Size is usu
25、ally about 4 wide, 3 high, and 3 deep. Most such devices include a tiny postage stamp sized LCD screen for viewing simplified ladder logic (only a very small portion of the program being visible at a given time) and status of I/O points, and typically these screens are accompanied by a 4-way rocker
26、push-button plus four more separate push-buttons, similar to the key buttons on a VCR remote control, and used to navigate and edit the logic. Most have a small plug for connecting via RS-232 to a personal computer so that programmers can use simple Windows applications for programming instead of be
27、ing forced to use the tiny LCD and push-button set for this purpose. Unlike regular PLCs that are usually modular and greatly expandable, 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 deterministi
28、c execution of the logic.5FeaturesThe 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 (I/O) arrangements. These connect the PLC to and . PLCs read limit , analog process variables (such as te
29、mperature and pressure), and the positions of complex positioning systems. Some use . On the actuator side, PLCs operate , or cylinders, magnetic , , 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 netwo
30、rk that plugs into the PLC.6System styleA 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 PLCs have a chassis (also called a rack) into which are placed modules with different functi
31、ons. 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 high speed serial I/O link is used so that racks can be distributed away from the processor,
32、reducing the wiring costs for large plants.7PLC compared with other control systemsPLCs are well-adapted to a range of 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 automat
33、ion, and where 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
34、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 c
35、an be optimally chosen instead of a generic solution, and where the non-recurring engineering charges are spread over thousands or millions of units.For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer would be controlled by an electromechanic
36、al costing only a few dollars in production quantities.A -based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies, input/output hardware and necessary testing and certification) can be spread over many sales, and w
37、here 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 PLCs instead of custom-des
38、igned 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 PLCs. Very high-speed or precision controls may also req
39、uire customized solutions; for example, aircraft flight controls.Programmable controllers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC so that (involving a machine) can be used to instruct machine
40、 movements.PLCs may include logic for single-variable feedback analog control loop, a proportional, integral, derivative or . A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; w
41、here processes required hundreds or thousands of loops, a (DCS) would instead be used. As PLCs have become more powerful, the boundary between DCS and PLC applications has become less distinct.PLCs have similar functionality as . An RTU, however, usually does not support control algorithms or contro
42、l loops. As hardware rapidly becomes more powerful and cheaper, , PLCs and are increasingly beginning 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
43、run on RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and associated development environments.可编程控制器可编程逻辑控制器（PLC）或可编程控制器是一种数字化的计算机，机电流程自动化应用，如机械控制的工厂流水线，机动游戏，或照明装置。可编程控制器可用于许多工业和机器。不同于通用计算机，PLC是专为多输入和输出的安排，扩展温度范围，免疫电气噪声，振动和阻力和影响。方案，以控制机床操作通常是在电池供电或非易失性内存中存储。可编程控制器是一个实
44、时系统的例子，因为产生输出结果必须输入条件响应时间范围内，否则将导致错误操作。1历史发明的PLC回应美国汽车制造业的需要。可编程逻辑控制器，最初通过的汽车工业调整软件取代了重新硬有线控制面板布线时，改变生产模式。 前PLC，控制测序，汽车制造和安全联锁逻辑实现使用数百或数千继电器，凸轮计时器和鼓音序器和专用的闭环控制器。在每年更新的模型等设施交接是非常耗时和昂贵的过程，需要单独电工ReWire的每一个接力。 1968年，通用汽车Hydramatic（即通用汽车自动变速器分公司）发出了一个硬有线中继系统的电子替代方案的要求。获奖的建议来自贝德福德的贝德福德，马萨诸塞州协会。第一个可编程控制器，指
45、定的084，因为它是贝德福德Associates的第八十四项目，也是结果。贝德福德协会开始一个新的公司，致力于开发，生产，销售和服务这一新产品：莫迪康，其中模块化数字控制器站着。谁的人在该项目的工作之一是迪克莫利，谁是被认为是“父亲的临立会”。该莫迪康品牌是在1977年出售给古尔德电子，后来由德国AEG公司收购公司和法国施耐德电气公司，目前的所有者，然后。 在建的第一个084模式之一，现已在莫迪康在北安多佛，马萨诸塞州总部展出。它是由通用汽车介绍，以莫迪康在部队退役后，近20年的不间断服务。莫迪康使用在其产品范围的结束的84个名字，直到984于是出现。 汽车行业仍是PLC的最大用户之一。 2发
46、展早期的PLC的目的是取代继电器逻辑系统。 PLC的程序，这些都在“阶梯逻辑”，它类似于一个强烈的继电器逻辑示意图。这一方案被选中符号，以减少对现有技术人员的培训需求。其他早期的PLC用编程的指令表的形式，在一个基于堆栈的逻辑解算器的基础。 现代PLC的编程可以在各种不同的方式，从梯子逻辑如BASIC和C的另一种方法，以更传统的编程语言是国家的逻辑，一个非常高层次的编程语言PLC的设计方案基于状态转换图。 许多早期的PLC没有人陪同的编程终端的图形表示的逻辑能力，所以逻辑，而不是表现为一个逻辑布尔表达式中的一些格式，类似于布尔代数版本系列。作为编程终端的演变，变得更常见的梯形逻辑的使用，为上述
47、原因。如国家和逻辑功能块（新格式，类似的描述方法的逻辑是在使用数字集成逻辑电路）存在，但他们仍然不如梯形逻辑受欢迎。一个原因是PLC的解决可预见和重复序列的逻辑，梯形逻辑允许程序员（写作的人的逻辑）来查看与时间序列的逻辑更容易比任何问题都可以在其他的主要原因格式。3程序设计早期的PLC，到80年代中期，都是用专有的编程板或特殊用途的编程终端，其中往往有专门的功能键代表不同的PLC程序逻辑元素。方案存储在盒式磁带。打印和文件的设施被很小的，由于内存容量不足。很古老的PLC使用非挥发性磁芯存储器。 最近，PLC的编程通常是使用特殊的应用软件在台式电脑上使用书面和桌面计算机之间的连接，并通过可编程控
48、制器，如以太网或RS - 232电缆。这种软件允许进入和阶梯式逻辑编辑，然后可能会提供额外的功能，以协助调试和故障排除的软件，例如突出的逻辑部分，以显示在操作过程中或通过模拟的现状。最后，该软件可允许上传和之间的计算机和可编程控制器的备份和恢复的目的，程序下载。或者，特定的设备称为编程板是用硬线将控制器由一个可移动芯片的使用，如EEPROM的，该方案是通过转移或其他串行总线逻辑工作站的编程板，逻辑。4功能临立会的功能已多年形成的包括继电器顺序控制，运动控制，过程控制，分布式控制系统和网络。数据处理，存储，处理能力和一些现代的PLC通信能力大约相当于台式电脑。 PLC的编程等结合远程I / O硬
49、件，允许通用台式电脑重叠在某些特定的应用PLC的。关于这些桌面电脑为基础的逻辑控制器的实用性，重要的是要注意，他们have没有得到普遍接受，因为重industry桌面电脑操作系统上less stable systems做比PLC的run，and hardware因为桌面电脑通常是不designed以容忍的水平相同的温度，湿度，振动，寿命在可编程控制器使用的处理器。除了桌面基础逻辑的硬件限制，操作系统，如Windows不适合自己的确定性逻辑的执行，其结果是可能的逻辑并不总是以回应逻辑状态或输入状态的变化与极端的一致性，在时间预计从PLC的。不过，这种台式逻辑应用在更短的危急情况下找到，例如在实验室自动化和应用程序不要求和重要小型设施，使用，因为它们通常比PLC的便宜得多。 最近几年，小产品称为PLRs（可编程逻辑继电器），并以类似的名称，已变得越来越普遍接受。这些都是非常喜欢的PLC多，而且在轻