【正文】 PLC的外圍硬件連線方面，主要是增加一些保護(hù)設(shè)備。由于輸出都是何接觸器等元件連接，接觸器的突然斷開(kāi)和閉合會(huì)形成突波對(duì)PLC的輸出端子造成損壞，因此需要加裝一些保護(hù)裝置，例如，續(xù)流二極管等，增加觸點(diǎn)的壽命。軟件方面主要問(wèn)題在于程序編寫(xiě)完畢后，需要首先在電腦上對(duì)程序進(jìn)行軟件仿真，主要檢查是否存在各種錯(cuò)誤，可利用西門(mén)子公司配套的仿真軟件。然后通過(guò)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(cuò)誤。調(diào)試時(shí)，可根據(jù)功能模塊分類(lèi)分別調(diào)試，最后進(jìn)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(lái)控制清污機(jī)、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(jì)反饋來(lái)的信息進(jìn)行判斷處理，然后再進(jìn)行輸出控制。謝 詞首先，感謝我的導(dǎo)師蔣飛虎，在這幾個(gè)月里他給了我很多指導(dǎo)性的意見(jiàn)，并且教會(huì)了我很多不懂的知識(shí)。他治學(xué)嚴(yán)謹(jǐn)細(xì)致、一絲不茍。他循循善誘的教導(dǎo)和不拘一格的思路給予我無(wú)盡的啟迪。這篇論文的每個(gè)細(xì)節(jié)和數(shù)據(jù)，都離不開(kāi)他的細(xì)心指導(dǎo)。他嚴(yán)肅的科學(xué)態(tài)度，嚴(yán)謹(jǐn)?shù)闹螌W(xué)精神，精益求精的工作作風(fēng)，深深地感染和激勵(lì)著我。從課題的選擇到項(xiàng)目的最終完成，蔣老師都始終給予我細(xì)心的指導(dǎo)和不懈的支持。四個(gè)多月來(lái)，蔣老師不僅在學(xué)業(yè)上給我以精心指導(dǎo)，同時(shí)還在思想、生活上給我以無(wú)微不至的關(guān)懷，在此謹(jǐn)向朱老師致以誠(chéng)摯的謝意和崇高的敬意。其次，我還要感謝在一塊做設(shè)計(jì)的同學(xué)們，正是由于你們的幫助和支持，我才能克服一個(gè)一個(gè)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(duì)本課題做了不少工作，給予我不少的幫助。感謝同學(xué)對(duì)我的幫助和指點(diǎn)。沒(méi)有他們的幫助和提供資料對(duì)于我一個(gè)對(duì)網(wǎng)絡(luò)知識(shí)一竅不通的人來(lái)說(shuō)要想在短短的幾個(gè)月的時(shí)間里學(xué)習(xí)到網(wǎng)絡(luò)知識(shí)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(wú)法平靜，從開(kāi)始進(jìn)入課題到論文的順利完成，有多少可敬的師長(zhǎng)、同學(xué)、朋友給了我無(wú)言的幫助，在這里請(qǐng)接受我誠(chéng)摯的謝意!最后我還要感謝培養(yǎng)我長(zhǎng)大含辛茹苦的父母，謝謝你們！感謝我的指導(dǎo)老師蔣老師，他嚴(yán)謹(jǐn)細(xì)致、一絲不茍的作風(fēng)一直是我學(xué)習(xí)的榜樣；他循循善誘的教導(dǎo)和不拘一格的思路給予我無(wú)盡的啟迪。 參考文獻(xiàn)[1] [M].北京：機(jī)械工業(yè)出版社，2004. 1.[2]孫振強(qiáng)，王暉， [M].北京：清華大學(xué)出版社，.[3][D].廣州：廣東工業(yè)大學(xué)出版社，2005.[4] [M].北京：機(jī)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(shù)學(xué)院報(bào),2008,6（4）7678.[7][J].湖南冶金職業(yè)技術(shù)學(xué)院學(xué)報(bào)，2004，43（4）：8687.[8]（第3版）[M].北京：機(jī)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(xué)水處理系統(tǒng)的應(yīng)用，工程技術(shù)，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(shè)計(jì)，江西現(xiàn)代職業(yè)技術(shù)學(xué)院學(xué)報(bào)，2008（7）[13]孫衛(wèi)娜，基于PLC的污水處理系統(tǒng)研究,沈陽(yáng)航空工業(yè)學(xué)院學(xué)報(bào)，2007（6）英文文獻(xiàn)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.”P(pán)articularly, 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