【正文】 ications will continue to gain popularity. * The ability to network PLC I/O connections with a PC. The same trends that have benefited PLC networking have migrated to the I/O level. Many PLC manufacturers are supporting the most accepted fieldbus networks, allowing PLC I/O to be distributed over large physical distances, or located where it was previously considered nearly impossible. This has opened the door for personal puters to interface with standard PLC I/O subsystems by using interface cards, typically supplied by the PLC manufacturer or a third party developer. Now these challenging locations can be monitored with today a PC. Where industrialgrade control engines are not required, the user can take advantage of more advanced software packages and hardware flexibility at a lower cost. * The ability to use universal programming software for multiple targets/platforms. In the past it was expected that an intelligent controller would be plex to program. That is no longer the case. Users are no longer just trained programmers, such as design engineers or systems integrators, but endusers who expect easiertouse software in more familiar formats. The Windowsbased look and feel that users are familiar with on their personal puters have bee the most accepted graphical user interface. What began as simple relay logic emulation for programming PLCs has evolved into languages that use higher level function blocks that are much more intuitive to configure. PLC manufacturers are also beginning to integrate the programming of diverse functions that allow you to learn only one package in configuring logic, HMI, motion control and other specialized capabilities. Possibly the ultimate wish of the enduser would be for a software package that could seamlessly program many manufacturers PLCs and subsystems. After all, Microsoft Windows operating system and applications work similarly whether installed on a Dell, HP or IBM puter, which makes it easier for the user. Overall, PLC users are satisfied with the products currently available, while keeping their eye on new trends and implementing them where the benefits are obvious. Typically, new installations take advantage of advancing technologies, helping them bee more accepted in the industrial world. PLC的過去、現(xiàn)在與未來眾所周知，科技世界里只有一個永恒真理，那就是變化。電信學(xué)院畢業(yè)設(shè)計任務(wù)書題目 基于PLC的污水池液位控制系統(tǒng)設(shè)計 學(xué)生姓名 班級 學(xué)號 題目類型 工程設(shè)計 指導(dǎo)教師 魏祥林 系主任 一、畢業(yè)設(shè)計（論文）的技術(shù)背景和設(shè)計依據(jù)： 與傳統(tǒng)的人工調(diào)節(jié)液位控制系統(tǒng)相比，變頻液位自動控制系統(tǒng)具有節(jié)能效果顯著、人工勞動強度低，系統(tǒng)工作可靠、自動化程度高等優(yōu)點。t be ignored, such as: * Network speed. * Ease of use when it es to the setup and wiring. * Availability of offtheshelf networking ponents. * Builtin munications setups.Integrated Motion ControlAnother responsibility the PLC has been tasked with is motion control. From simple openloop to multiaxis applications, the trend has been to integrate this feature into PLC hardware and software. There are many applications that require accurate control at a fast pace, but not exact precision at blazing speeds. These are applications where the standalone PLC works well. Many nano and micro PLCs are available with highspeed counting capabilities and highfrequency pulse outputs built into the controller, making them a viable solution for openloop control. The one caveat is that the controller does not know the position of the output device during the control sequence. On the other hand, its main advantage is cost. Even simple motion control had previously required an expensive option module, and at times was restricted to more sophisticated control platforms in order to meet system requirements. More sophisticated motion applications require higherprecision positioning hardware and software, and many PLCs offer highspeed option modules that interface with servo drives. Most drives today can accept traditional mands from host (PLC or PC) controls, or provide their own internal motion control. The trend here is to integrate the motion control configuration into the logic controller programming software package.Programming LanguagesA facet of the PLC that reflects both the past and the future is programming language. The IEC 611313 standard deals with programming languages and defines two graphical and two textual PLC programming language standards: * Ladder logic (graphical). * Function block diagram (graphical). * Structured text (textual).Instruction list (textual). This standard also defines graphical and textual sequential function chart elements to organize programs for sequential and parallel control processing. Based on the standard, many manufacturers offer at least two of these languages as options for programming their PLCs. Ironically, approximately 96 percent of PLC users recently still use ladder diagrams to construct their PLC code. It seems that ladder logic continues to be a top choice given it39。從20世紀80年代到20世紀90年代初，模塊化的PLC逐漸微型化，同時它的容量和性能也得到了提高。在過去的30年里，我們真實地目睹了數(shù)百個專利化協(xié)議和標(biāo)準(zhǔn)化協(xié)議的發(fā)展，每一個協(xié)議都有自己獨特的優(yōu)勢。從簡單的開環(huán)控制到多軸應(yīng)用來看，在PLC的軟件和硬件中集成運動控制已經(jīng)成為一個趨勢。越精密的運動控制系統(tǒng)要求越高精度的定位硬件和軟件，而許多PLC都提供高速選擇模塊接入伺服驅(qū)動。硬件平臺 現(xiàn)代的PLC已經(jīng)在它們的CPU里集成了多種的商業(yè)非定制（COTS）技術(shù)。不只是新協(xié)議在逐漸平面化，許多已經(jīng)使用了許多年的工業(yè)標(biāo)準(zhǔn)化協(xié)議也在逐漸地接入到以太網(wǎng)平臺上，這些協(xié)議包括Modbus (ModbusTCP)、DeviceNet (Ethernet/IP)和Profibus (Profinet)?，F(xiàn)在，這些具挑戰(zhàn)性的廣闊區(qū)域都可以由個人電腦監(jiān)控。畢竟，無論是安裝在Dell、HP電腦上還是安裝在IBM電腦上，微軟的視窗（Windows）操作系統(tǒng)和應(yīng)用程序都是同樣地運行，這就方便了系統(tǒng)用戶。在自動化控制的工業(yè)生產(chǎn)過程中，一個很重要的控制參數(shù)就是液位。一些工廠企業(yè)實現(xiàn)了儀表化和局部自動化。過程控制發(fā)展到現(xiàn)代過程控制的新階段，這是過程控制發(fā)展的第三階段。無錫信捷電子科技有限公司生產(chǎn)的XC系列、上海東屋電氣有限公司生產(chǎn)的CF系列、杭州機床電器廠生產(chǎn)的DKK及D系列、大連組合機床研究所生產(chǎn)的S系列、蘇州電子計算機廠生產(chǎn)的YZ系列等多種產(chǎn)品已具備了一定的規(guī)模并在工業(yè)產(chǎn)品中獲得了應(yīng)用。 20世紀20年代起，人們把各種繼電器。這也是區(qū)別與一般微機控制系統(tǒng)的一個重要特征。第二章 系統(tǒng)控制方案的確定 采用PLC控制液位的優(yōu)點1從定時，計數(shù)上比較：電器控制定時精度不高，易受環(huán)境溫度變化的影響，且無計數(shù)功能；而PLC時鐘脈沖由晶振產(chǎn)生，精度高，定時范圍寬；有計數(shù)功能。37．進行液位控制系統(tǒng)的整體聯(lián)機調(diào)試，調(diào)試中發(fā)現(xiàn)的問題逐一排除，直至調(diào)試成功。那么，如何選購PLC產(chǎn)品呢? 系統(tǒng)規(guī)模首先應(yīng)確定系統(tǒng)用PLC單機控制，還是用PLC形成網(wǎng)絡(luò)，由此計算PLC輸入、輸出點。 編程器的選購PLC編程可采用三種方式：是用一般的手持編程