PLC概述毕业外文翻译@中英文翻译@外文文献翻译

外文原文： ONE、 PLC overview Programmable controller is the first in the late 1960s in the United States, then called Plc programmable logic controller (Programmable Logic Controller) is used to replace relays. For the implementation of the logical judgment, timing, sequence number, and other control functions. The concept is presented Plc General Motors Corporation. Plc and the basic design is the computer functional improvements, flexible, generic and other advantages and relay control system simple and easy to operate, such as the advantages of cheap prices combined controller hardware is standard and overall. According to the practical application of target software in order to control the content of the user procedures memory controller, the controller and connecting the accused convenient target. In the mid-1970s, the Plc has been widely used as a central processing unit microprocessor, import export module and the external circuits are used, large-scale integrated circuits even when the Plc is no longer the only logical (IC) judgment functions also have data processing, PID conditioning and data communications functions. International Electro technical Commission (IEC) standards promulgated programmable controller for programmable controller draft made the following definition : programmable controller is a digital electronic computers operating system, specifically for applications in the industrial design environment. It used programmable memory, used to implement logic in their internal storage operations, sequence control, timing, counting and arithmetic operations, such as operating instructions, and through digital and analog input and output, the control of various types of machinery or production processes. Programmable controller and related peripherals, and industrial control systems easily linked to form a whole, to expand its functional design. Programmable controller for the user, is a non-contact equipment, the procedures can be changed to change production processes. The programmable controller has become a powerful tool for factory automation, widely popular replication. Programmable controller is user-oriented industries dedicated control computer, with many distinctive features. First, high reliability, anti-interference capability； Second， programming visual, simple； Third, adaptability good； Fourth functional improvements, strong functional interface. TWO、 History of PLC Programmable Logic Controllers (PLC), a computing device invented by Richard E. Morley in 1968, have been widely used in industry including manufacturing systems, transportation systems, chemical process facilities, and many others. At that time, the PLC replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL), a programming language visually resembling the hardwired logic, and reduced thereby the configuration time from 6 months down to 6 days Moody and Morley, 1999. Although PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in harsh environments. Moreover, according to a study on the PLC market of Frost and Sullivan 1995, an increase of the annual sales volume to 15 million PLCs per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping. The inventor of the PLC, Richard E Morley, fairly considers the PLC market as a 5-billion industry at the present time. Though PLCs are widely used in industrial practice, the programming of PLC based control systems is still very much relying on trial-and-error. Alike software engineering, PLC software design is facing the software dilemma or crisis in a similar way. Morley himself emphasized this aspect most forcefully by indicating If houses were built like software projects, a single woodpecker could destroy civilization.” Particularly, practical problems in PLC programming are to eliminate software bugs and to reduce the maintenance costs of old ladder logic programs. Though the hardware costs of PLCs are dropping continuously, reducing the scan time of the ladder logic is still an issue in industry so that low-cost PLCs can be used. In general, the productivity in generating PLC is far behind compared to other domains, for instance, VLSI design, where efficient computer aided design tools are in practice. Existent software engineering methodologies are not necessarily applicable to the PLC based software design because PLC-programming requires a simultaneous consideration of hardware and software. The software design becomes, thereby, more and more the major cost driver. In many industrial design projects, more than of the manpower allocated for the control system design and installation is scheduled for testing and debugging PLC programs. In addition, current PLC based control systems are not properly designed to support the growing demand for flexibility and reconfigurability of manufacturing systems. A further problem, impelling the need for a systematic design methodology, is the increasing software complexity in large-scale projects. The objective of this thesis is to develop a systematic software design methodology for PLC operated automation systems. The design methodology involves high-level description based on state transition models that treat automation control systems as discrete event systems, a stepwise design process, and set of design rules providing guidance and measurements to achieve a successful design. The tangible outcome of this research is to find a way to reduce the uncertainty in managing the control software development process, that is, reducing programming and debugging time and their variation, increasing flexibility of the automation systems, and enabling software reusability through modularity. The goal is to overcome shortcomings of current programming strategies that are based on the experience of the individual software developer. Three、 now of PLC From the structure is divided into fixed PLC and Module PLC, the two kinds of PLC including CPU board, I/O board, display panel, memory block, power, these elements into a do not remove overall. Module type PLC including CPU module, I/O modules, memory, the power modules, bottom or a frame, these modules can be according to certain rules combination configuration. In the user view, a detailed analysis of the CPUs internal unnecessary, but working mechanism of every part of the circuit. The CPU control works, by it reads CPU instruction, interprets the instruction and executes instructions. But the pace of work by shock signal control. Unit work under the controller command used in a digital or logic operations.In computing and storage register of computation result, it is also among the controller command and work. CPU speed and memory capacity is the important parameters fot PLC . its determines the PLC speed of work, IO PLC number and software capacity, so limits to control size. Central Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one of the microcontrollers. Aforetime these were 8-bit microcontrollers such as 8051, and now these are 16-and 32-bit microcontrollers. Unspoken rule is that youll find mostly Hitachi and Fujicu microcontrollers in PLC controllers by Japanese makers, Siemens in European controllers, and Motorola microcontrollers in American ones. CPU also takes care of communication, interconnectedness among other parts of PLC controllers, program execution, memory operation, overseeing input and setting up of an output. System memory (today mostly implemented in FLASH technology) is used by a PLC for a process control system. Aside form. this operating system it also contains a user program translated forma ladder diagram to a binary form. FLASH memory contents can be changed only in case where user program is being changed. PLC controllers were used earlier instead of PLASH memory and have had EPROM memory instead of FLASH memory which had to be erased with UV lamp and programmed on programmers. With the use of FLASH technology this process was greatly shortened. Reprogramming a program memory is done through a serial cable in a program for application development. User memory is divided into blocks having special functions. Some parts of a memory are used for storing input and output status. The real status of an input is stored either as “1”or as “0”in a specific memory bit/ each input or output has one corresponding bit in memory. Other parts of memory are used to store variable contents for variables used in used program. For example, time value, or counter value would be stored in this part of the memory. PLC controller can be reprogrammed through a computer (usual way), but also through manual programmers (consoles). This practically means that each PLC controller can programmed through a computer if you have the software needed for programming. Todays transmission computers are ideal for reprogramming a PLC controller in factory itself. This is of great importance to industry. Once the system is corrected, it is also important to read the right program into a PLC again. It is also good to check from time to time whether program in a PLC has not changed. This helps to avoid hazardous situations in factory rooms (some automakers have established communication networks which regularly check programs in PLC controllers to ensure execution only of good programs). Almost every program for programming a PLC controller possesses various useful options such as: forced switching on and off of the system input/outputs (I/O lines), program follow up in real time as well as documenting a diagram. This documenting is necessary to understand and define failures and malfunctions. Programmer can add remarks, names of input or output devices, and comments that can be useful when finding errors, or with system maintenance. Adding comments and remarks enables any technician (and not just a person who developed the system) to understand a ladder diagram right away. Comments and remarks can even quote precisely part numbers if replacements would be needed. This would speed up a repair of any problems that come up due to bad parts. The old way was such that a person who developed a system had protection on the program, so nobody aside from this person could understand how it was done. Correctly documented ladder diagram allows any technician to understand thoroughly how system functions. Electrical supply is used in bringing electrical energy to central processing unit. Most PLC controllers work either at 24 VDC or 220 VAC. On some PLC controllers youll find electrical supply as a separate module. Those are usually bigger PLC controllers, while small and medium series already contain the supply module. User has to determine how much current to take from I/O module to ensure that electrical supply provides appropriate amount of current. Different types of modules use different amounts of electrical current. This electrical supply is usually not used to start external input or output. User has to provide separate supplies in starting PLC controller inputs because then you can ensure so called “pure” supply for the PLC controller. With pure supply we mean supply where industrial environment can not affect it damagingly. Some of the smaller PLC controllers supply their inputs with voltage from a small supply source already incorporated into a PLC. Four、 PLC design criteria A systematic approach to designing PLC software can overcome deficiencies in the traditional way of programming manufacturing control systems, and can have wide ramifications in several industrial applications. Automation control systems are modeled by formal languages or, equivalently, by state machines. Formal representations provide a high-level description of the behavior of the system to be controlled. State machines can be analytically evaluated as to whether or not they meet the desired goals. Secondly, a state machine description provides a structured representation to convey the logical requirements and constraints such as detailed safety rules. Thirdly, well-defined control systems design outcomes are conducive to automatic code generation- An ability to produce control software executable on commercial distinct logic controllers can reduce programming lead-time and labor cost. In particular, the thesis is relevant with respect to the following aspects. In modern manufacturing, systems are characterized by product and process innovation, become customer-driven and thus have to respond quickly to changing system requirements. A major challenge is therefore to provide enabling technologies that can economically reconfigure automation control systems in response to changing needs and new opportunities. Design and operational knowledge can be reused in real-time, therefore, giving a significant competitive edge in industrial practice. Studies have shown that programming methodologies in automation systems have not been able to match rapid increase in use of computing resources. For instance, the programming of PLCs still relies on a conventional programming style with ladder logic diagrams. As a result, the delays and resources in programming are a major stumbling stone for the progress of manufacturing industry. Testing and debugging may consume over 50% of the manpower allocated for the PLC program design. Standards IEC 60848, 1999； IEC-61131-3, 1993； IEC 61499, 1998； ISO 15745-1, 1999 have been formed to fix and disseminate state-of-the-art design methods, but they normally cannot participate in advancing the knowledge of efficient program and system design. A systematic approach will increase the level of design automation through reusing existing software components, and will provide methods to make large-scale system design manageable. Likewise, it will improve software quality and reliability and will be relevant to systems high security standards, especially those having hazardous impact on the environment such as airport control, and public railroads. The software industry is regarded as a performance destructor and complexity generator. Steadily shrinking hardware prices spoils the need for software performance in terms of code optimization and efficiency. The result is that massive and less efficient software code on one hand outpaces the gains in hardware performance on the other hand. Secondly, software proliferates into complexity of unmanageable dimensions； software redesign and maintenance-essential in modern automation systems-becomes nearly impossible. Particularly, PLC programs have evolved from a couple lines of code 25 years ago to thousands of lines of code with a similar number of 1/O points. Increased safety, for instance new policies on fire protection, and the flexibility of modern automation systems add complexity to the program design process. Consequently, the life-cycle cost of software is a permanently growing fraction of the total cost. 80-90% of these costs are going into software maintenance, debugging, adaptation and expansion to meet changing needs. Today, the primary focus of most design research is based on mechanical or electrical products. One of the by-products of this proposed research is to enhance our fundamental understanding of design theory and methodology by extending it to the field of engineering systems design. A system design theory for large-scale and complex system is not yet fully developed. Particularly, the question of how to simplify a complicated or complex design task has not been tackled in a scientific way. Furthermore, building a bridge between design theory and the latest epistemological outcomes of formal representations in computer sciences and operations research, such as discrete event system modeling, can advance future development in engineering design. From a logical perspective, PLC software design is similar to the hardware design of integrated circuits. Modern VLSI designs are extremely complex with several million parts and a product development time of 3 years Whitney, 1996. The design process is normally separated into a component design and a system design stage. At component design stage, single functions are designed and verified. At system design stage, components are aggregated and the whole system behavior and functionality is tested through simulation. In general, a complete verification is impossible. Hence, a systematic approach as exemplified for the PLC program design may impact the logical hardware design. Five、 AK 1703 ACP Following the principle of our product development, AK 1703 ACP has high functionality and flexibility, through the implementation of innovative and reliable technologies, on the stable basis of a reliable product platform. For this, the system concept ACP (Automation, Control and Protection) creates the technological preconditions. Balanced functionality permits the flexible combination of automation, telecontrol and communication tasks. Complemented with the scalable performance and various redundancy configurations, an optimal adaptation to the respective requirements of the process is achieved. AK 1703 ACP is thus perfectly suitable for automation with integrated telecontrol technology as: Telecontrol substation or central device Automation unit with autonomous functional groups Data node, station control device, front-end or gateway With local or remote peripherals For rear panel installation or 19 inch assembly Branch-neutral product, therefore versatile fields of application and high product stability Versatile communication Easy engineering Plug & play for spare parts Open system architecture Scalable redundancy The intelligent terminal - TM 1703 The Base Unit AK 1703 ACP with Peripheral Elements has one basic system element CP-2010/CPC25 (Master control element) and CP-2012/PCCE25 (Processing and communication element) ,one bus line with max. 16 peripheral elements can be connected. CP-2010/CPC25 Features and Functions System Functions: Central element,coordinating all system services Central hub function for all connected basic system elements Time management Central clock of the automation unit Setting anf keeping the own clocks time with a resolution of 10ms Synchronization via serid communication via LAN or local Redundancy Voting and change-over for redundant processing and communication elements of the own automation unit Supports voting and change-over by an external SCA-RS redundancy switch Supports applicational voting and change-over by an exterual system,e.g.a control system SAT TOLLBOX| connection Storing firmware and parameters on a Flash Card Communication: Communication via installable protocol elements to any superior or subordinate automation unit Automatic data flow routing Priority based data transmission (priority control) Own circular buffer and process image for each connected station(data keeping) Redundant communication routes Communication with redundant remote stations Special application specific functions for dial-up traffic Test if stations are reachable Process Peripherals: Tansmission of spontaneous information objects from and to peripheral elements, via the serial Ax 1703 peripheral bus Functions for Automatoin: Open-/closed-loop control function for the execution of freely definable user programs which are created with CAEX plus according to IEC 61131-3,e.g.using function diagram technology 512KB for user program Approx 50.000 variables and signals,2.000 of them retained Cycle of 10ms or a multiphe thereof Online test Loadable without service interruption Redundant open-/closed-loop control functions Synchronization via redundancy link Transmission of periodic process information between the open-/closed-loop control function and the peripheral elements,via the serial Ax 1703 peripheral bus SIX、 SIEMENS PLC SIMATIC S7-300 series PLC applied to all walks of life and various occasions in the detection, monitoring and control of automation, its power to both the independent operation of, or connected to a network able to achieve complex control. The photoelectric products with isolation, high electromagnetic compatibility； have high industrial applicability, allowing the ambient temperature of 60 ； has strong anti-jamming and anti-vibration and impact resistance, so in a harsh working environment has been widely Applications. I also mean freedom of communication S7-300 type PLC s a very unique feature, which allows S7-300-PLC can deal openly with any other communications equipment, communications controller, or PLC S7-300 type can be defined by the users own Communications protocol (of the agreement ASCII), the baud rate to 1.5 Mbit / s (adjustable). So that can greatly increase the scope of communications so that the control system configuration more flexible and convenient. Of any kind with a serial interface peripherals, such as: printers or bar code readers, Drives, a modem (Modem), the top PC-connected, and so can be used. Users can program to develop communication protocols, the exchange of data (for example: ASCII character code), RS232 interfaces with the equipment can also be used PC / PPI cable linking the free communication communications. When the PC offline, under the control of the next crew, the whole system can operate normally. PC that is by control centre, mainly by the PC and laser printer components, using SIMATIC WINCC software platform, the all-Chinese interface, friendly man-machine dialogue. Managers and operators can be observed through a PC, shown in the various kinds of information to understand the present and past the ice-storage operation of the automatic control system and all the parameters, and through the mouse to print equipment management and implementation tasks. WINCC software in the field of automation can be used for all the operators control and monitoring tasks. Can be controlled in the process of the events clearly show, and shows the current status and order records, the recorded data can show all or select summary form, or may be required for editing, printing and output statements and trends . WINCC able to control the critical situation in the early stages of the report, and the signal can be displayed on the screen, can also use sound to be felt. It supported by online help and operational guidelines to eliminate failure. WINCC a workstation can be devoted to the process control to the process so that important information not is shielded. Software-assisted operation strategy ensures that the process was not illegal to visit and to provide for non-industrial environment in the wrong operation. WINCC is MICRSOFT WINDOWS98 or WINDOWS NT4.0 operating system, running on a PC object-oriented class 32-bit applications, OLE through the window and ODBC standard mechanism, as an ideal partner to enter the communications world WINDOWS, it can be easily WINCC To integrate a company-wide data processing system. Seven、 Communications Communications are vital to an individual automation cell and to the automated factory as a whole. Weve heard a lot about MAP in the last few years, and a lot of companies have jumped on the band wagon. Many, however were disappointed when a fully-defined and completed MAP specification didn t appear immediately. Says Larry Kumara:” Right now , MAP is still a moving target for the manufacturers specification that is not final. Presently, for example, people are introducing products to meet the MAP 2.1standard.Yet 2.1-based products will be obsolete when the new standard for MAP,3.0is introduced.” Because of this, many PLC vendors are holding off on full MAP implementations. Omron, for example , has an ongoing MAP-compatibility program, but Frank Newborn, vice president of Omron s Industrial Division, reports that because of the lack of a firm definition, Omrons PLCs dont yet talk to MAP. Since it s unlikely that an individual PLC would talk to broadband MAP anyway, makers are concentrating n proprietary networks. According to Sal Provanzano, users fear that if they do get on board and vendors withdraw from MAP, they ll pulse width modulation control system be the ones left holding a communications structure that s not supported. 译文： 一、 PLC概述 可编程控制器是 60 年代末在美国首先出现的，当时叫可编程逻辑控制器PLC（ Programmable Logic Controller），目的是用来取代继电器。以执行逻辑判断、计时、计数等顺序 控制功能。提出 PLC 概念的是美国通用汽车公司。 PLC的基本设计思想是把计算机功能完善、灵活、通用等优点和继电器控制系统的简单易懂、操作方便、价格便宜等优点结合起来，控制器的硬件是标准的、通用的。根据实际应用对象，将控制内容编成软件写入控制器的用户程序存储器内 ,使控制器和被控对象连接方便。 70 年代中期以后， PLC 已广泛地使用微处理器作为中央处理器，输入输出模块和外围电路也都采用了中、大规模甚至超大规模的集成电路，这时的 PLC已不再是仅有逻辑 (Logic)判断功能，还同时具有数据处理、 PID 调节和数据通信功能 。国际电工委员会 (IEC)颁布的可编程控制器标准草案中对可编程控制器作了如下的定义：可编程控制器是一种数字运算操作的电子系统，专为在工业环境下应用而设计。它采用了可编程序的存储器，用来在其内部存储执行逻辑运算，顺序控制、定时、计数和算术运算等操作的指令，并通过数字式和模拟式的输入和输出，控制各种类型的机械或生产过程。可编程控制器及其有关外围设备，易于与工业控制系统联成一个整体，易于扩充其功能的设计。 可编程控制器对用户来说，是一种无触点设备，改变程序即可改变生产工艺。目前，可编程控制器已成为工厂自动化的强有 力工具，得到了广泛的普及推广应用。 可编程控制器是面向用户的专用工业控制计算机，具有许多明显的特点。 可靠性高，抗干扰能力强； 编程直观、简单； 适应性好； 功能完善，接口功能强 二、 PLC的历史 1968 年， Richard E. Morley 创造出了新一代工业控制装置可编程逻辑控制器 (PLC),现在， PLC 已经被广泛应用于工业领域，包括机械制造也、运输系统、化学过程设备、等许多其他领域。初期可编程控制器只是用一种类似于语言的软件逻辑于代替继电器硬件逻辑，并且使开发时 间由 6 个月缩短到 6 天。 虽然计算机控制技术已经产生，但是 PLC 控制因为它的高性能、成本低、并且对恶劣的环境有很强的适应能力而在工业控制的广泛应用中保持优势。而且，尽管硬件的价格在逐渐下跌，据估计，根据 Frost 和 Sullivan 对 PLC 市场的调查研究表明，每年销售硬件的价格要比销售 PLC 的价格（一千五百万）至少多出八十亿美元。 PLC 的创造者 Richard E. Morley 十分肯定的认为目前 PLC市场是一个价值五十亿的工业 虽然 PLC 广泛应用于工业控制中， PLC 控制系统的程序依然和语法有关。和软件过程一样， PLC 的软件设计也以同样的方式会遇到软件错误或危机。Morley 在演讲中着重强调了这个方面。 如果房子建造的像软件过程一样，那么仅仅一只啄木鸟就可以摧毁文明。特别的， PLC 程序要解决的实际问题是消除软件错误和减少老式梯形逻辑语言的花费。尽管 PLC 的硬件成本在继续下降，但是在工业控制上减少梯形逻辑的扫描时间仍然是一个问题，以至于可以用到低耗时的 PLC。 一般来说，和其他领域相比生产 PLC 的周期要短很多。例如，在实践中，VISI设计是一种有效的计算机辅助设计。 PLC 不需要使用目前的以软件设计为基础软件工程方法论 ，因为 PLC 程序要求对软件和硬件搜都要考虑到。因此，软件设计越来越成为花费动力。在许多的工业设计工程中，多数人力分配给了控制系统设计和安装，并且他们被要求对 PLC 进行程序测试和错误排除。 再者， PLC 控制系统不适合设计对适应性和重构有越来越多要求的生产系统。一个更深入的问题是在大规模的工程中软件越来越复杂，促使要有一个系统化的设计方法论。 主题的客观性是为 PLC 自动控制系统建立一个系统化的软件设计方法论。这个设计方法论包括以状态转换模型为基础的精确的描述，这个转台转换模型是自动控制系统的抽象系统。方法论还包 括一个逐步的设计过程，并且要设置一个设计规则，这样才能为一个成功的设计提供导向和方法。这项研究的真正目的是找到一个减少控制软件发展过程的不稳定性的方法，也就是说，减少程序和调试时间以及他们的变化，以增强自动控制系统的适应性，并且通过调整软件使得软件可以再度使用。这样的目的是为了克服目前程序策略的不足之处，而目前的程序策略是以个人软件开发者的经验为基础的。 三、现今的 PLC 从结构上分， PLC 分为固定式和 模块 式两种。固定式 PLC 包括 CPU 板、 I/O板、显示面板、内存块、电源等，这些元素组合成一个不可拆卸的整体 。模块式PLC 包括 CPU 模块、 I/O 模块、内存、电源模块、底板或机架，这些模块可以按照一定规则组合配置。 在使用者看来，不必要详细分析 CPU 的内部电路，但对各部分的工作机制还是应有足够的理解。 CPU 的控制器控制 CPU 工作，由它读取指令、解释指令及执行指令。但工作节奏由震荡信号控制。 运算器用于进行数字或逻辑运算，在控制器指挥下工作。寄存器参与运算，并存储运算的中间结果，它也是在控制器指挥下工作。 CPU 速度和内存容量是PLC 的重要参数，它们决定着 PLC 的工作速度， IO 数量及软件容量等，因此限制着控制规模。 中 央处理器 (CPU)是 PLC 控制器的大脑。通常 CPU本身 就 是一个微控制器。起先 是 8 位微控制器 例如 8051,现在 发展为 16 位和 32 位微控制器。你会发现大部分由日本制造商 制造的 PLC 中 是 日立和 Fujicu的 微控制器 ,西门子 的 微控制器 多应用在 欧洲 的 PLC 中 ,摩托罗拉 生产的 微控制器 则独占美国市场 。 CPU 同样关注通信 , PLC 控制器 ,操作程序的执行 ,监督记忆设置的输入和输出 等部分的关联性 。 PLC 使用系统存储器（现在大部分采用闪存技术了）用于过程控制系统。除了这个操作系统之外，它还包括一个由梯形图翻译成而进制形式的用 户程序。快擦型存储器（ FLASH memory）的内容只有在改变用户程序的时候可以被改变。 PLC 控制器比快擦型存储器使用得更早， EPROM 存储器比快擦型存储器也更早，快擦型存储器必须用紫外线（ UV， Ultra-Violet Ray）灯擦除，并在编程器上进行编程。由于快擦型存储器技术的应用，使得这个过程大大缩短了。在应用程序开发中，通过一个串行电缆可以对程序存储器进行重新编程。 用户存储器被分成具有特殊功能的块。一部分存储器用来存储输入和输出状态。一个输入的实际状态存储状态存储在专用存储器位上，为 “1”或者 “0”。每一个输入和输出在存储器中都有一个相应的位。另外一部分存储器用来存储用户程序中的变量的内容。例如，定时器值，或者记数器值存放在存储器的这个部分。 PLC 控制器可以通过计算机（通常方式）重新编程，但是也可以通过人工编程器 9 控制台）编程。实际上，这意味着，如果你有编程所需要的软件，早期PLC 控制器可以通过计算机进行编程。今天的传输计算机是工厂自己对 PLC 控制器进行重新编程的理想设备。这对于工业企业来说是非常重要的。一旦系统修改结束，将正确的程序重新读入 PLC 控制器也是非常重要的。定期检查 PLC 中的程序是否改变是非常好的事情。这有助于避免车间发生危险情况（一些汽车制造商已经建立了通信网络，可以定期检查 PLC 中的程序，以保证运行的程序都是正确的）。 几乎所有用于为 PLC 控制器编程的程序都拥有各种不同的选项，例如系统输入 /输出（ I/O 线）的强制开关，程序实时跟踪以及图表验证。图表验证对于理解、定义失败和故障非常必要。程序员可以添加标记，书日和输出设备名称，以及对于查找错误或者对于系统维护很有用的注释。添加注释和标记可以使技术人员（不仅仅是开发人员）很快理解梯形图。注释和标记甚至还可以准确地引用零件号，如果需要更换零件的话。这将加快由于损坏零件而引起的任何问题的修理速度。响应的旧方法是这样的，开发系统的人必须保护这个程序，他旁边再没有人知道系统是怎样完成的 。正确的、备有证明文件的梯形图使任何技术人员都能彻底理解系统的功能。 电源是为中央处理单元提供电源的。大部分 PLC 控制器的工作电压为24VDC 或者 220VAC。在有些 PLC 控制器上，你可以看见作为独立模块的电源。用户必须确定从 I/O 模块取出多大电流来保证电源提供适当的电流。不同的模块使用不同的电流量。 该电源一般不用于启动外部输入或输出。用户必须提供独立的电源来启动PLC 控制器的输入和输出，因为这样可以保证 PLC 控制器的所谓 “纯电源 ”。使用纯电源意味着工业环境中的电源不会严重影响它。有些较小的 PLC 控制器从与 PLC 控制器集成在一起的小电源为它们的输入提供电压源。 四、 PLC的设计标准 一个系统化的设计 PLC 程序的方法可以克服传统程序生产控制系统的缺点，并且在一些工业应用总有很大的不同。自动控制系统是状态模型用公式语言或等价的语言描述的。公式描述对被控制的系统的行为提供一个精确的描述。可以通过分析估计看状态模型是否达到想要的目标。第二，为状态模型的描述提供结构描述，这个结构描述可以说明逻辑要求和如细节安全规则的限制。第三，好的控制系统设计是对自动控制代码生成有益的 一种能够产生可执行的控制软件的能力， 不同的逻辑控制器可以减少程序扫描时间和执行那个时间。特别的，这个主题与随后的部分的是有关的。 在现代制造业中，系统是用过程和结果的革新来描述的，并且因此不得不改变系统性能以快速做出反应。因此，一个大的挑战是提供技术以限制自动控制系统对变化需要和新机会的反应，所以，设计和操作知识可以实时的被再次利用，在工业实践中提供了一个重要的竞争面。 研究表明，在自动化系统中，程序实现的方法已经与计算机资源应用的急速增长不能匹配。例如，可编程逻辑控制器（）程序仍然依靠一种方便的有逻辑梯形图的程序实现模式。结果，程序上 的延迟和资源成了生产工业过程的主要绊脚石。在可编程逻辑控制器程序设计过程中，测试和调试可能会占用超过百分之五十的人力。在发展和传播“”已经形成标准 IEC 60848, 1999； IEC-61131-3, 1993； IEC 61499, 1998； ISO 15745-1, 1999，但是，基本上这些标准都不能参与有效的程序和系统设计方面知识的革新。 系统的方法通过使用原有的软件模块，有助于增加设计自动化的水平，同时也将提供一种可管理的大规模系统设计的方法。同样的，它也 将改善软件的质量的可靠性，以及关系到系统的较高安全标准，尤其是这些对环境有危害影响的，比如：机场控制、公共铁路运输。 软件工业被认为是系统性能的破坏者和系统复杂性的产生者。逐渐下降的硬件价格，破坏了对通过优化程序获得的软件性能的需要。其结果是，一方面造成了大量而低效率的程序代码，另一方面并没有获得高的硬件性能。其次，软件变得难以掌握其程度的复杂；在现代自动化系统中，软件设计和保持系统本质几乎变得不可能。尤其是，可编程逻辑控制器（）程序设计从二十五年前的两条主线，发展到现在的