【正文】 PLC的外圍硬件連線方面，主要是增加一些保護設備。由于輸出都是何接觸器等元件連接，接觸器的突然斷開和閉合會形成突波對PLC的輸出端子造成損壞，因此需要加裝一些保護裝置，例如，續(xù)流二極管等，增加觸點的壽命。軟件方面主要問題在于程序編寫完畢后，需要首先在電腦上對程序進行軟件仿真，主要檢查是否存在各種錯誤，可利用西門子公司配套的仿真軟件。然后通過模擬硬件的方式檢查程序，主要檢查程序是否存在邏輯上的錯誤。調(diào)試時，可根據(jù)功能模塊分類分別調(diào)試，最后進行總體調(diào)試。在該控制程序中，需要根據(jù)外界輸入的狀態(tài)來控制清污機、潛水泵，以及污泥回流泵的啟停，因此需要按照液位傳感器和液位差計反饋來的信息進行判斷處理，然后再進行輸出控制。謝 詞首先，感謝我的導師蔣飛虎，在這幾個月里他給了我很多指導性的意見，并且教會了我很多不懂的知識。他治學嚴謹細致、一絲不茍。他循循善誘的教導和不拘一格的思路給予我無盡的啟迪。這篇論文的每個細節(jié)和數(shù)據(jù)，都離不開他的細心指導。他嚴肅的科學態(tài)度，嚴謹?shù)闹螌W精神，精益求精的工作作風，深深地感染和激勵著我。從課題的選擇到項目的最終完成，蔣老師都始終給予我細心的指導和不懈的支持。四個多月來，蔣老師不僅在學業(yè)上給我以精心指導，同時還在思想、生活上給我以無微不至的關懷，在此謹向朱老師致以誠摯的謝意和崇高的敬意。其次，我還要感謝在一塊做設計的同學們，正是由于你們的幫助和支持，我才能克服一個一個的困難和疑惑，直至本文的順利完成。特別感謝我的舍友，他們對本課題做了不少工作，給予我不少的幫助。感謝同學對我的幫助和指點。沒有他們的幫助和提供資料對于我一個對網(wǎng)絡知識一竅不通的人來說要想在短短的幾個月的時間里學習到網(wǎng)絡知識并完成畢業(yè)論文是幾乎不可能的事情。正是由于他們的幫助，才使我的論文日趨完善。 在論文即將完成之際，我的心情無法平靜，從開始進入課題到論文的順利完成，有多少可敬的師長、同學、朋友給了我無言的幫助，在這里請接受我誠摯的謝意!最后我還要感謝培養(yǎng)我長大含辛茹苦的父母，謝謝你們！感謝我的指導老師蔣老師，他嚴謹細致、一絲不茍的作風一直是我學習的榜樣；他循循善誘的教導和不拘一格的思路給予我無盡的啟迪。 參考文獻[1] [M].北京：機械工業(yè)出版社，2004. 1.[2]孫振強，王暉， [M].北京：清華大學出版社，.[3][D].廣州：廣東工業(yè)大學出版社，2005.[4] [M].北京：機械工業(yè)出版社，.[5]張培山，[J].控制系統(tǒng),2006,5（1）：8283.[6]李英輝，趙豫龍，[J].石家莊職業(yè)技術學院報,2008,6（4）7678.[7][J].湖南冶金職業(yè)技術學院學報，2004，43（4）：8687.[8]（第3版）[M].北京：機械工業(yè)出版社，.[9] [M].北京：電子工業(yè)出版社，.[10]陶權(quán)， [M].廣州：.[11]劉建雄，PLC控制系統(tǒng)在化學水處理系統(tǒng)的應用，工程技術，2008（5）[12]陳慕君、吳軼、文方，基于PLC的污水處理模糊控制系統(tǒng)設計，江西現(xiàn)代職業(yè)技術學院學報，2008（7）[13]孫衛(wèi)娜，基于PLC的污水處理系統(tǒng)研究,沈陽航空工業(yè)學院學報，2007（6）英文文獻及譯文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 puter functional improvements, flexible, generic and other advantages and relay control system simple and easy to operate, such as the advantages of cheap prices bined 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.First, high reliability, antiinterference capability。Second，programming visual, simple。Third, adaptability good。Fourth functional improvements, strong functional interface.TWO、History of PLCProgrammable Logic Controllers (PLC), a puting 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 softwired logic or socalled 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 e 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 puting hardware is steadily dropping. The inventor of the PLC, Richard E Morley, fairly considers the PLC market as a 5billion 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 trialanderror. 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 lowcost PLCs can be used.In general, the productivity in generating PLC is far behind pared to other domains, for instance, VLSI design, where efficient puter aided design tools are in practice. Existent software engineering methodologies are not necessarily applicable to the PLC based software design because PLCprogramming requires a simultaneous consideration of hardware and software. The software design bees, 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 plexity in largescale projects.The objective of this thesis is to develop a systematic software design methodology for PLC operated automation systems. The design methodology involves highlevel 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 oute 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 overe shortings of current programming strategies that are based on the experience of the i