外文翻译--可编程逻辑控制器

外文翻译--可编程逻辑控制器 设计巴巴工作室www.88doc88.com PLC Programmable Logic Controllers (PLCs), also referred to as programmable controllers, are in the computer family. They are used in commercial and industrial applications. A PLC monitors inputs, make decisions based on its program, and controls outputs to automate a process or machine. This course is meant to supply you with basic information on the functions and configurations of PLCs. In the 1960s, electromechanical devices were the order of the day as far as control was concerned. These devices commonly known as relays, were being used by the thousands to control many Sequential-type manufacturing processes and Stand-alone machines. Many of these relays were in use in the transportation industry, more specifically, the automothve industry. These relays used hundreds of wires and their interconnections to affect a control solution. The performance of a relay was basically reliable at least as a single device. But the common applications for relay panels called for 300 to 500 or more relays, and the reliability and maintenance issues associated with supposting these penels became a very great challenge. Cost became anther issue, for in spite of the low cost of the relay itself, the installed cost of the panel could be quite high. The total cost indueling purchased parts, wiring, and installation labor, could range from $30-$50 per relay. To make matters worse, the constantly changing needs of a process called for recurring modifications of a constantly changing needs of a process called for recurring modifications of a control panel. With relays, this was a costly prospect, as it was accomplished by a major rewiring effort on the panel. In addition, these changes were sometimes poorly documented, causing a second shift maintencance nightmare months later. In light of this, it was not uncommon to discard an entire control panel in favor of a new one with the appropriate components wired in a manner suited for the new process. Add to this the unpredictable, and potentially hight, cost of maintaining these systems as on high-volume motor vehide production lines, and it became clear that something was needed to improne the control process to make it more reliable, easier to troubleshoot, and more adaptable to changing control needs. That something, in the late 1960s, was the first programmable controller. This first “revollutionary” system was developed as a specific response to the needs of the major automotine manufacturers in the United States. these early controllers, or programmable logic controllers ( PLC ) , represented the first systems that (1) could be used on the factory floor, (2) could have there “ logic ” change without extensive 设计巴巴工作室www.88doc88.com rewiring or component changes, and (3) were easy to diagnost and repair when problems occurred. It is interesting to observe the progress that has been made in the past 15 years in the late 1960s must have been confusing and frightening to a great number of people. For example, what happened to the hardwired and eletromechanical devices that maintenance personnel were used to repairing with hard tools? They were replaced with “ computers ” disquised as electromics designed to replace relays. Even the programming tools were designed to appear as relay equivalent presentations. We have the opportunity now to examine the promise, in retrospect, what the programmable controller brought manufacturing? All programmale controllers consist of the basic functional blocks. We will examine each block to understand the relathonship to the control system. First we looked at the center, as it is the heard of the system. It consists of a microprocessor, logic memory for the storage of the actual control logic, storage or variable memory for use with data that will ordimarily change as a function of the control propram execution, and a power supply to provide electrical power for the processor and memory. Next comes the I/O block. This function takes the conrtol level signals for the CPU and converts them to voltage and current levels suitable. The I/O type can range from digital, analog, or a variety of special purpose “ smart ” I/O which are dedicated to a certain application task. The programming is normally used only to initially configure and program a system and is not required for the system to operate. It is also used in troubleshooting a system, and can prove to be a valuable tool in pinpointing the exact cause of a problem. The field devices shown here represent the various sensors and actuators connected to the I/O. These are the arms, legs, eyes, and ears of the system, including pushbuttons, limit switches, proximity suitches, photosensors, thermocouple, position sensing devices, and bar code reader as input; and pildt light, display devices, motor starters, DC and AC drivers, solenlids, and printers as outputs. 1. Basic PLC Operation PLCs consist of input modules, a Central Processing Unit (CPU), and output modules or points. An input accepts a variety of digital or analog signals from various field devices (sensors) and converts them into a logic signal that can be used by the CPU. The CPU makes decisions and executes control instructions based on program instructions in memory. Output modules convert control instructions from the CPU into a digital or analog signal that can be used to control various field devices 设计巴巴工作室www.88doc88.com (actuators). A programming device is used to input the desired instructions. These instructions determine what the PLC will do for a specific input. An operator interface device allows process information to be displayed and new control parameters to be entered. Pushbuttons (sensors), in this simple example, connected to PLC inputs, can be used to start and stop a motor connected to a PLC through a motor starter (actuator). 2. Hard-Wired Control Prior to PLCs, many of these control tasks were solved by contactors or relay controls. This is often referred to as hardwired control. Circuit diagrams had to be designed, electrical components specified and installed, and wiring lists created. Electrical components necessary to perform a specific task. If an error was made the wires had to be reconnected correctly. A change in function or system expansion required extensive component changes and rewiring. 3. Advantages of PLCs The same, as well as more complex tasks, can be done with a PLC. Wiring between devices and relay contacts is done in the PLC program. Hard-wiring, though still required to connect field devices, is less intensive. Modifying the application and correcting errors are easier to handle. It is easier to create and change a program in a PLC than it is to wire and rewire a circuit. Following are just a few of the advantages of PLCs: (1) Smaller physical size than hard-wire solutions. (2) Easier and faster to make changes. (3) PLCs have integrated diagnostics and override functions. (4) Applications can be immediately documented. (5) Applications can be duplicated faster and less expensively. 4. Siemens PLCs Siemens makes several PLC product lines in the SIMATIC S7 family. They are: S7-200, S7-300, and S7-400. (1) S7-200 The S7-200 is referred to as a micro-PLC because of its small size. The S7-200 has a brick design which means that the power supply and I/O terminal are on-board. The S7-200 can be used on smaller, stand-alone applications such as elevators, car 设计巴巴工作室www.88doc88.com washes, or mixing machines. It can also be used on more complex industrial applications such as bottling and packaging machines. (2) S7-300 and S7-400 The S7-300 and S7-400 PLCs are used in more complex applications that support a greater of I/O points. Both PLCs are modular and expandable. The power supply and I/O consist of separate modules connected to the CPU. Choosing either the S7-300 or S7-400 depends on the complexity of the task and possible future expansion. Your Siemens sales representative can provide you with additional information on any of the Siemens PLCs. 5. CPU CPU is a microprocessor system that contains the system memory and is the PLC decision-making unit. The CPU monitors the inputs and makes decisions based on instructions held in the program memory. The CPU performs relay, counting timing ,data comparison, and sequential operations. 6. Programming Devices The program is created in a programming device (PG) and then transferred to the PLC. The program for the S7-200 can be created using a dedicated Siemens SIMATIC S7 programming device, such as a PG 720 or PG 740, if STEP 7 Micro/WIN software is installed. A personal computer (PC), with STEP 7 Micro/WIN installed, can also be used as a programming device with the S7-200. 7. Software A software program is required in order to tell the PLC what instructions it must follow. Programming software is typically PLC specific. A software package for one PLC, or one family of PLCs, such as the S7 family, would not be useful on other PLCs. The S7-200 uses a Windows-based software program called STEP 7-Micro/WIN32. The PG 720 and PG 740 have STEP 7-Micro/WIN32 software pre-installed. Micro/WIN32 is installed on a personal computer in a similar manner to any other computer software. 8. Connector Cables PPI (Point-to-Point Interface) Connector cables are required to transfer data from the programming device to 设计巴巴工作室www.88doc88.com the PLC. Communication can only take place when the two devices speak the same language or protocol. Communication between a Siemens programming device and the S7-200 is referred to as PPI protocol. An appropriate cable is required for a programming device such as a PG 720 or PG 740. The S7-200 uses a 9-pin, D-connector, This is a straight-through serial device that is compatible with Simens programming devices (MPI port) and is a standard connector for other serial interfaces. A special cable, referred to as a PC/PPI cable, is needed when a personal computer is used as a programming device. This cable allows the serial interface of the PLC to communicate with the RS-232 serial interface of a personal computer. DIP switches on the PC/PPI cable are used to select an appropriate speed (bit rate) at which information is passed between the PLC and the computer. 设计巴巴工作室www.88doc88.com 可编程逻辑控制器 可编程逻辑控制器,PLC,～也就是可编程控制器～是计算机家族的一员。它们被应用于商业和工业领域。可编程控制器通过监视输入～根据程序得到的结果～控制输出自动控制过程或机器。这一课程在给你提供基本的PLC的功能和配置信息。 20世纪60年代～在控制器受到关注以前～机电装置一直是这个年代的流行产品。这些通常被称为继电器的装置被数以千计的系统用来控制许多制造过程和单独的机器。许多这样的继电器被应用于运输工业～更明确地说～应用于汽车工业。这些继电器使用成百上千的金属导线～他们的相互联系将影响控制的解决 方案 气瓶 现场处置方案 .pdf气瓶 现场处置方案 .doc见习基地管理方案.doc关于群访事件的化解方案建筑工地扬尘治理专项方案下载 。至少作为一个单独的装置～继电器的性能使基本稳定的。但是～继电器盒通常需要安装三百到五百甚至更多的继电器～于是可靠性及维修和保养问题就不可避免地摆到了我们面前。成本问题成为另以问题～尽管继电器本身成本很低,但是继电器盒的安装成本很高～每个继电器总的成本～其中包括购买零件、配线和安装工作的成本～大体在30美元到50美元之间不等。更糟糕的事情是～控制面板需要经常不断地更改。对于继电器来说～这是一个昂贵的事实。因为这一更改过程需要大量的劳动在控制面板上重新接线。此外～这些变化有时很少备有证明文件的。这就使得以后的再次维护成为很头痛的事。按照这样的考虑～丢弃整个旧的控制面板～同意使用一个适合的新的控制过程方式的相匹配的接线元件的控制面板～也是常见的事情。这就给这些系统的维护成本增加了不可预制的～潜在的高成本。正如在昂贵的电动车辆生产线上一样。越来越清楚地认识到要使系统更可靠～更容易排除故障～更适合不断变化的控制过程需要～就必须改进控制过程。 在20世纪60年代～出现了第一个可编程控制器。这是第一个“革命性”的系统～这个系统是按照美国汽车制造工业的特点要求开发研制出来的。这些早期的控制器～即可编程逻辑控制器,PLC,是能应用于工厂车间的最早系统。这些控制器在不需要在量重新接线或改变大件的情况下能够作“逻辑”变化～一旦出现问题～它能够很轻易地诊断和修补。观察可编程控制器在最近15年取得的进步使很有趣的事情～在20世纪60年代末早期的产品或许会使很多人感到惊恐或迷惑不解～例如～维修人员习惯了手动工具～那么对于电子仪器的部件和机电设备将会发生什么呢,改装过的计算机代替这些设备～正如电子器件代替继电器～甚至设计出了工具来作为继电器的替代品。我们现在有机会来审视一下前景～回顾过去～可编程控制器带给制造业使什么, 可编程控制器都包含了基本的功能模块。为了理解控制系统的关系～我们将检查一下每个模块。首先～我们看一下中心～它是系统的心脏。中心包括微处理设计巴巴工作室www.88doc88.com 器、存储当前控制逻辑的逻辑存储器、存储常变量数据的变量存储器～中心部分具有控制程序执行和微处理器与存储器提供电力的功能。接着是I/O模块～它的功能是为CPU提供控制水平信号～并把它们转化为适合连接工厂级别的传感器和调节器的标准电压和电流。I/O类型可以是数字信号～模拟信号或是应用于某一特定应用的“智能”I/O。程序员通常仅需编写程序～而不需要考虑程序在系统中的运行。它可以用来发现并修理系统故障的确切原因方面是个很有用的设备。在这里提到的设备代表了与I/O连接的各种传感器和调节器～它们是系统的手臂、腿、眼睛和耳朵～其中包括按钮、行程开关、光敏元件、热电偶、位置传感器～作为输入的读卡机～标灯～显示设备～发动机～DC和AC驱动器～螺线管和作为输出的打印机。 1、PLC的基本操作 PLC包括输入或输入点、一个中央处理单元,CPU,以及输出模块或输出点。输入单元可以接收来自不同现场设备,传感器,的各种数字或模拟信号～然后将它们转换为CPU可以使用的逻辑信号。CPU根据存储器中的程序指令做出判断～然后执行指令。输出模块将来自CPU的控制指令转换为现场控制的各个设备,执行机构,所能使用的数字或逻辑信号。编程设备用于输入期望指令～由这些指令来决定对于特定的输入PLC做什么。操作界面能够显示过程信息及输入新的控制参数。在这个简单的例子里～连接到PLC输入端的按钮,传感器,～通过电动机的启动器,执行机构,可以启动和停止与PLC连接的电动机。 2、硬接线控制 使用PLC之前～许多控制任务是通过接触器和继电器来完成的。这就是经常所说的硬接线控制。必须先设计电路图～确定元件～并且进行安装以及建立接线表～电工再连接需要执行特定任务的元件。如果接线中有一个错误～就必须重新连接来纠正。如果改变功能或扩充系统～元件就需要大量变化～并且线路要重接。 3、PLC的优势 同样或更加复杂的任务～可以用PLC来做。设备同继电器触点之间的连线由PLC中的程序完成。硬接线虽然依然需要连接到现场设备～但这一要求已很少了。修改应用软件或纠正错误要容易些。在PLC中建立或修改程序比起连接或重新连接电路要容易。 下面列出的只是PLC的一小部分优点: ,1, 比通过硬接线方式的物理尺寸小。 设计巴巴工作室www.88doc88.com ,2, 修改时更简单且更快速。 ,3, PLC有综合诊断和忽略功能。 ,4, 应用软件能被立即生成文件。 ,5, 应用程序能够被更快并且费用更低复制。 4、西门子PLC 西门子制造了几种属于SIMATIC S7产品系列的PLC。它们是S7-200～S7-300和S7-400。 ,1, S7-200 S7-200由于尺寸小～被称为微型PLC。S7-200是块状设计结构～即它的电源和I/O都在一块板上。S7-200可以被使用在小型的、独立的应用设备中～比如:电梯、汽车冲洗器或搅拌机。它也能被使用到更复杂的工业应用中～比如:装瓶机和打包机。 ,2, S7-300和S7-400 S7-300和S7-400型的PLC被使用到更复杂的应用中～它们支持更多数量的I/O点。这两种PLC都是模块化的和可扩展的。由分离模块组成的电源和I/O都与CPU连接。根据应用的复杂性及以后的扩展需要来选择S7-300和S7-400。西门子销售代表可以提供给你任何型号的西门子PLC的附加信息。 5、CPU CPU是包括系统存储的微处理器系统～是PLC的决策单元。CPU监控输入～并根据保存在程序存储器中的指令做出决策。然后CPU执行继电器、计数器、计时器、数据比较和顺序操作等功能。 6、编程设备 程序是在一个编程设备,PG,中建立的～然后被传送到PLC中。S7-200的程序可以使用西门子SIMATIC S7编程设备来建立～如已经安装了STEP 7 Micro/WIN软件～就可以使用PG 720或PG 740。 安装了STEP 7 Micro/WIN软件的个人计算机,PC,也可以用作S7-200的编程设备。 7、软件 必须要有一个软件程序告诉PLC应服从哪一条指令。编程软件具有PLC的特点。一个软件包针对一个PLC或一个PLC系列～比如S7系列～不能应用到其他PLC上。基于Windows平台的S7-200的编程软件称为STEP 7-Micro/WIN32。设计巴巴工作室www.88doc88.com PG 720 和PG 740使用前必须先安装Micro/WIN32软件。在个人计算机上安装STEP 7-Micro/WIN32的方法同安装其他计算机软件的方法类似。 8、连接电缆PPI ,点对点接口, 连接电缆被用来将编程设备的数据传送到PLC。只有当两个设备使用相同的语言或协议时才能够进行通讯。西门子编程设备同S7-200之间的通讯采用PPI协议。对于PG 720或PG 740的编程设备～需要一个合适的连接电缆。S7-200使用9针的D型连接器。这是一个直插串行接口设备～与西门子编程设备,MPI接口,兼容～对于其他串行接口它是一个标准接口。 当个人计算机用作编程设备时也需要一个专用电缆～也就是PC/PPI电缆。这根电缆能够使PLC的串行口与个人计算机的RS-232串口进行通讯。PC/PPI上的DIP开关用来设置PLC同个人计算机之间信息传输的合适速度,比特率,。 设计巴巴工作室www.88doc88.com