PLC概述畢業(yè)外文翻譯@中英文翻譯@外文文獻翻譯

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. 譯文： 一、 PLC概述 可編程控制器是 60 年代末在美國首先出現(xiàn)的，當時叫可編程邏輯控制器PLC（ Programmable Logic Controller），目的是用來取代繼電器。以執(zhí)行邏輯判斷、計時、計數(shù)等順序 控制功能。提出 PLC 概念的是美國通用汽車公司。 PLC的基本設計思想是把計算機功能完善、靈活、通用等優(yōu)點和繼電器控制系統(tǒng)的簡單易懂、操作方便、價格便宜等優(yōu)點結合起來，控制器的硬件是標準的、通用的。根據(jù)實際應用對象，將控制內容編成軟件寫入控制器的用戶程序存儲器內 ,使控制器和被控對象連接方便。 70 年代中期以后， PLC 已廣泛地使用微處理器作為中央處理器，輸入輸出模塊和外圍電路也都采用了中、大規(guī)模甚至超大規(guī)模的集成電路，這時的 PLC已不再是僅有邏輯 (Logic)判斷功能，還同時具有數(shù)據(jù)處理、 PID 調節(jié)和數(shù)據(jù)通信功能 。國際電工委員會 (IEC)頒布的可編程控制器標準草案中對可編程控制器作了如下的定義：可編程控制器是一種數(shù)字運算操作的電子系統(tǒng)，專為在工業(yè)環(huán)境下應用而設計。它采用了可編程序的存儲器，用來在其內部存儲執(zhí)行邏輯運算，順序控制、定時、計數(shù)和算術運算等操作的指令，并通過數(shù)字式和模擬式的輸入和輸出，控制各種類型的機械或生產過程。可編程控制器及其有關外圍設備，易于與工業(yè)控制系統(tǒng)聯(lián)成一個整體，易于擴充其功能的設計。 可編程控制器對用戶來說，是一種無觸點設備，改變程序即可改變生產工藝。目前，可編程控制器已成為工廠自動化的強有 力工具，得到了廣泛的普及推廣應用。 可編程控制器是面向用戶的專用工業(yè)控制計算機，具有許多明顯的特點。 可靠性高，抗干擾能力強； 編程直觀、簡單； 適應性好； 功能完善，接口功能強 二、 PLC的歷史 1968 年， Richard E. Morley 創(chuàng)造出了新一代工業(yè)控制裝置可編程邏輯控制器 (PLC),現(xiàn)在， PLC 已經(jīng)被廣泛應用于工業(yè)領域，包括機械制造也、運輸系統(tǒng)、化學過程設備、等許多其他領域。初期可編程控制器只是用一種類似于語言的軟件邏輯于代替繼電器硬件邏輯，并且使開發(fā)時 間由 6 個月縮短到 6 天。 雖然計算機控制技術已經(jīng)產生，但是 PLC 控制因為它的高性能、成本低、并且對惡劣的環(huán)境有很強的適應能力而在工業(yè)控制的廣泛應用中保持優(yōu)勢。而且，盡管硬件的價格在逐漸下跌，據(jù)估計，根據(jù) Frost 和 Sullivan 對 PLC 市場的調查研究表明，每年銷售硬件的價格要比銷售 PLC 的價格（一千五百萬）至少多出八十億美元。 PLC 的創(chuàng)造者 Richard E. Morley 十分肯定的認為目前 PLC市場是一個價值五十億的工業(yè) 雖然 PLC 廣泛應用于工業(yè)控制中， PLC 控制系統(tǒng)的程序依然和語法有關。和軟件過程一樣， PLC 的軟件設計也以同樣的方式會遇到軟件錯誤或危機。Morley 在演講中著重強調了這個方面。 如果房子建造的像軟件過程一樣，那么僅僅一只啄木鳥就可以摧毀文明。特別的， PLC 程序要解決的實際問題是消除軟件錯誤和減少老式梯形邏輯語言的花費。盡管 PLC 的硬件成本在繼續(xù)下降，但是在工業(yè)控制上減少梯形邏輯的掃描時間仍然是一個問題，以至于可以用到低耗時的 PLC。 一般來說，和其他領域相比生產 PLC 的周期要短很多。例如，在實踐中，VISI設計是一種有效的計算機輔助設計。 PLC 不需要使用目前的以軟件設計為基礎軟件工程方法論 ，因為 PLC 程序要求對軟件和硬件搜都要考慮到。因此，軟件設計越來越成為花費動力。在許多的工業(yè)設計工程中，多數(shù)人力分配給了控制系統(tǒng)設計和安裝，并且他們被要求對 PLC 進行程序測試和錯誤排除。 再者， PLC 控制系統(tǒng)不適合設計對適應性和重構有越來越多要求的生產系統(tǒng)。一個更深入的問題是在大規(guī)模的工程中軟件越來越復雜，促使要有一個系統(tǒng)化的設計方法論。 主題的客觀性是為 PLC 自動控制系統(tǒng)建立一個系統(tǒng)化的軟件設計方法論。這個設計方法論包括以狀態(tài)轉換模型為基礎的精確的描述，這個轉臺轉換模型是自動控制系統(tǒng)的抽象系統(tǒng)。方法論還包 括一個逐步的設計過程，并且要設置一個設計規(guī)則，這樣才能為一個成功的設計提供導向和方法。這項研究的真正目的是找到一個減少控制軟件發(fā)展過程的不穩(wěn)定性的方法，也就是說，減少程序和調試時間以及他們的變化，以增強自動控制系統(tǒng)的適應性，并且通過調整軟件使得軟件可以再度使用。這樣的目的是為了克服目前程序策略的不足之處，而目前的程序策略是以個人軟件開發(fā)者的經(jīng)驗為基礎的。 三、現(xiàn)今的 PLC 從結構上分， PLC 分為固定式和 模塊 式兩種。固定式 PLC 包括 CPU 板、 I/O板、顯示面板、內存塊、電源等，這些元素組合成一個不可拆卸的整體 。模塊式PLC 包括 CPU 模塊、 I/O 模塊、內存、電源模塊、底板或機架，這些模塊可以按照一定規(guī)則組合配置。 在使用者看來，不必要詳細分析 CPU 的內部電路，但對各部分的工作機制還是應有足夠的理解。 CPU 的控制器控制 CPU 工作，由它讀取指令、解釋指令及執(zhí)行指令。但工作節(jié)奏由震蕩信號控制。 運算器用于進行數(shù)字或邏輯運算，在控制器指揮下工作。寄存器參與運算，并存儲運算的中間結果，它也是在控制器指揮下工作。 CPU 速度和內存容量是PLC 的重要參數(shù)，它們決定著 PLC 的工作速度， IO 數(shù)量及軟件容量等，因此限制著控制規(guī)模。 中 央處理器 (CPU)是 PLC 控制器的大腦。通常 CPU本身 就 是一個微控制器。起先 是 8 位微控制器 例如 8051,現(xiàn)在 發(fā)展為 16 位和 32 位微控制器。你會發(fā)現(xiàn)大部分由日本制造商 制造的 PLC 中 是 日立和 Fujicu的 微控制器 ,西門子 的 微控制器 多應用在 歐洲 的 PLC 中 ,摩托羅拉 生產的 微控制器 則獨占美國市場 。 CPU 同樣關注通信 , PLC 控制器 ,操作程序的執(zhí)行 ,監(jiān)督記憶設置的輸入和輸出 等部分的關聯(lián)性 。 PLC 使用系統(tǒng)存儲器（現(xiàn)在大部分采用閃存技術了）用于過程控制系統(tǒng)。除了這個操作系統(tǒng)之外，它還包括一個由梯形圖翻譯成而進制形式的用 戶程序?？觳列痛鎯ζ鳎?FLASH memory）的內容只有在改變用戶程序的時候可以被改變。 PLC 控制器比快擦型存儲器使用得更早， EPROM 存儲器比快擦型存儲器也更早，快擦型存儲器必須用紫外線（ UV， Ultra-Violet Ray）燈擦除，并在編程器上進行編程。由于快擦型存儲器技術的應用，使得這個過程大大縮短了。在應用程序開發(fā)中，通過一個串行電纜可以對程序存儲器進行重新編程。 用戶存儲器被分成具有特殊功能的塊。一部分存儲器用來存儲輸入和輸出狀態(tài)。一個輸入的實際狀態(tài)存儲狀態(tài)存儲在專用存儲器位上，為 “1”或者 “0”。每一個輸入和輸出在存儲器中都有一個相應的位。另外一部分存儲器用來存儲用戶程序中的變量的內容。例如，定時器值，或者記數(shù)器值存放在存儲器的這個部分。 PLC 控制器可以通過計算機（通常方式）重新編程，但是也可以通過人工編程器 9 控制臺）編程。實際上，這意味著，如果你有編程所需要的軟件，早期PLC 控制器可以通過計算機進行編程。今天的傳輸計算機是工廠自己對 PLC 控制器進行重新編程的理想設備。這對于工業(yè)企業(yè)來說是非常重要的。一旦系統(tǒng)修改結束，將正確的程序重新讀入 PLC 控制器也是非常重要的。定期檢查 PLC 中的程序是否改變是非常好的事情。這有助于避免車間發(fā)生危險情況（一些汽車制造商已經(jīng)建立了通信網(wǎng)絡，可以定期檢查 PLC 中的程序，以保證運行的程序都是正確的）。 幾乎所有用于為 PLC 控制器編程的程序都擁有各種不同的選項，例如系統(tǒng)輸入 /輸出（ I/O 線）的強制開關，程序實時跟蹤以及圖表驗證。圖表驗證對于理解、定義失敗和故障非常必要。程序員可以添加標記，書日和輸出設備名稱，以及對于查找錯誤或者對于系統(tǒng)維護很有用的注釋。添加注釋和標記可以使技術人員（不僅僅是開發(fā)人員）很快理解梯形圖。注釋和標記甚至還可以準確地引用零件號，如果需要更換零件的話。這將加快由于損壞零件而引起的任何問題的修理速度。響應的舊方法是這樣的，開發(fā)系統(tǒng)的人必須保護這個程序，他旁邊再沒有人知道系統(tǒng)是怎樣完成的 。正確的、備有證明文件的梯形圖使任何技術人員都能徹底理解系統(tǒng)的功能。 電源是為中央處理單元提供電源的。大部分 PLC 控制器的工作電壓為24VDC 或者 220VAC。在有些 PLC 控制器上，你可以看見作為獨立模塊的電源。用戶必須確定從 I/O 模塊取出多大電流來保證電源提供適當?shù)碾娏?。不同的模塊使用不同的電流量。 該電源一般不用于啟動外部輸入或輸出。用戶必須提供獨立的電源來啟動PLC 控制器的輸入和輸出，因為這樣可以保證 PLC 控制器的所謂 “純電源 ”。使用純電源意味著工業(yè)環(huán)境中的電源不會嚴重影響它。有些較小的 PLC 控制器從與 PLC 控制器集成在一起的小電源為它們的輸入提供電壓源。 四、 PLC的設計標準 一個系統(tǒng)化的設計 PLC 程序的方法可以克服傳統(tǒng)程序生產控制系統(tǒng)的缺點，并且在一些工業(yè)應用總有很大的不同。自動控制系統(tǒng)是狀態(tài)模型用公式語言或等價的語言描述的。公式描述對被控制的系統(tǒng)的行為提供一個精確的描述?？梢酝ㄟ^分析估計看狀態(tài)模型是否達到想要的目標。第二，為狀態(tài)模型的描述提供結構描述，這個結構描述可以說明邏輯要求和如細節(jié)安全規(guī)則的限制。第三，好的控制系統(tǒng)設計是對自動控制代碼生成有益的 一種能夠產生可執(zhí)行的控制軟件的能力， 不同的邏輯控制器可以減少程序掃描時間和執(zhí)行那個時間。特別的，這個主題與隨后的部分的是有關的。 在現(xiàn)代制造業(yè)中，系統(tǒng)是用過程和結果的革新來描述的，并且因此不得不改變系統(tǒng)性能以快速做出反應。因此，一個大的挑戰(zhàn)是提供技術以限制自動控制系統(tǒng)對變化需要和新機會的反應，所以，設計和操作知識可以實時的被再次利用，在工業(yè)實踐中提供了一個重要的競爭面。 研究表明，在自動化系統(tǒng)中，程序實現(xiàn)的方法已經(jīng)與計算機資源應用的急速增長不能匹配。例如，可編程邏輯控制器（）程序仍然依靠一種方便的有邏輯梯形圖的程序實現(xiàn)模式。結果，程序上 的延遲和資源成了生產工業(yè)過程的主要絆腳石。在可編程邏輯控制器程序設計過程中，測試和調試可能會占用超過百分之五十的人力。在發(fā)展和傳播“”已經(jīng)形成標準 IEC 60848, 1999； IEC-61131-3, 1993； IEC 61499, 1998； ISO 15745-1, 1999，但是，基本上這些標準都不能參與有效的程序和系統(tǒng)設計方面知識的革新。 系統(tǒng)的方法通過使用原有的軟件模塊，有助于增加設計自動化的水平，同時也將提供一種可管理的大規(guī)模系統(tǒng)設計的方法。同樣的，它也 將改善軟件的質量的可靠性，以及關系到系統(tǒng)的較高安全標準，尤其是這些對環(huán)境有危害影響的，比如：機場控制、公共鐵路運輸。 軟件工業(yè)被認為是系統(tǒng)性能的破壞者和系統(tǒng)復雜性的產生者。逐漸下降的硬件價格，破壞了對通過優(yōu)化程序獲得的軟件性能的需要。其結果是，一方面造成了大量而低效率的程序代碼，另一方面并沒有獲得高的硬件性能。其次，軟件變得難以掌握其程度的復雜；在現(xiàn)代自動化系統(tǒng)中，軟件設計和保持系統(tǒng)本質幾乎變得不可能。尤其是，可編程邏輯控制器（）程序設計從二十五年前的兩條主線，發(fā)展到現(xiàn)在的