【正文】 時(shí)，這里還加入了手動(dòng)調(diào)節(jié)方式。當(dāng)前的PLC內(nèi)部都有PID向?qū)Ш妥哉ǖ膮?shù)調(diào)節(jié)方式，這就為我們解決了應(yīng)用PID所面臨的最大問題，所以現(xiàn)在GPRS+PLC的控制方式適用性很強(qiáng)。在本系統(tǒng)里存在的最大的問題就是誤差問題，因?yàn)闇囟瓤刂茖儆诙栊韵到y(tǒng)，它具有很大的慣性，還有就是外部環(huán)境的變化會(huì)對(duì)系統(tǒng)造成影響，這就使系統(tǒng)在控制精度上產(chǎn)生一定的誤差。謝辭這半年的畢業(yè)設(shè)計(jì)過程里，在老師的指導(dǎo)和同學(xué)的幫助下得以順利完成。這段時(shí)間不僅增強(qiáng)了我的實(shí)踐能力，還讓我學(xué)習(xí)到了許多課本上沒有的東西。以前對(duì)這方面的知識(shí)了解的很少，但是通過此次畢業(yè)設(shè)計(jì)對(duì)它有了深刻的認(rèn)識(shí)，雖然達(dá)不到專業(yè)水平，但也覺得有巨大的收獲，也提高了自己自學(xué)的能力。在本次設(shè)計(jì)中首先要感謝我的指導(dǎo)老師馬壯老師。本系統(tǒng)的設(shè)計(jì)和論文的撰寫是在馬老師的悉心指導(dǎo)下才完成的，馬老師知識(shí)淵博，每周不辭辛苦的都為我們指導(dǎo)和講解，尤其是在最后的調(diào)試過程中，更是耐心的指導(dǎo)我們。馬老師為人和善，不僅在學(xué)習(xí)中給了我很大的幫助，在平時(shí)的生活中也教了我們很多的東西。在畢業(yè)之際還要感謝教過我的老師們?cè)趯W(xué)習(xí)過程中給我的幫助和關(guān)心，還有和我朝夕相處的同學(xué)們，對(duì)他們給的幫助送上我最深的祝福。 參考文獻(xiàn)[1] [M].：機(jī)械工業(yè)出版社,2007 [2] [M].北京：電子工業(yè)出版社,2006[3] Jonas Berge. Field buses for process control: engineering operation and maintenance [C].[4] [J].化工自動(dòng)化及儀表，:4648[5] 趙亮,黎峰. GPRS無線網(wǎng)絡(luò)在遠(yuǎn)程數(shù)據(jù)采集中的應(yīng)用[J].計(jì)算機(jī)工程與設(shè)計(jì),2005,26(9):25522554[6] 丁艷華. 熱網(wǎng)遠(yuǎn)程監(jiān)控系統(tǒng)的設(shè)計(jì)與實(shí)現(xiàn)[J]. 城市公用事業(yè), 2005,(02)：3436[7] [M]．北京：機(jī)械工業(yè)出版社,2001[8] 西門子SIMATIC S7200可編程控制器操作與編程指南[M]．四川：重慶鋼鐵設(shè)計(jì)研究所,1998[9] 趙寒濤. 基于GPRS和PLC的集中供熱數(shù)據(jù)采集系統(tǒng)[J]. 黑龍江科技信息, 2010,(03)：5152[10] [M]北京：科學(xué)出版社,2008:172[11] [J].化工自動(dòng)化及儀表,:4648[12] 馬瑩，[J].中國科技信息,:6467[13] 、智能儀表及PLC等組成的工業(yè)控制系統(tǒng)[J].電力自動(dòng)化設(shè)備,:7376[14] 白冰,襲冰. GPRS技術(shù)在熱網(wǎng)監(jiān)控系統(tǒng)中的應(yīng)用[J]. 計(jì)算機(jī)與信息技術(shù), 2007,(12)：911[15] Wei Zhang, Michael S Branicky and Stephen M of network control systems [J].IEEE Control Systems Magazine,2001[16] Lu Weizhong, Wang Yihuai, Xi Xuefeng, Zhang on powerline munication and design of PLC modem[C].ICISE2010. 2010:6823 6826附錄主程序：熱網(wǎng)出水口溫度：流量處理：熱網(wǎng)壓力：補(bǔ)水箱液位：手動(dòng)溫度調(diào)節(jié)：手動(dòng)壓力調(diào)節(jié)：外文資料Introductions to temperature control and PID controllersProcess control systemAutomatic process control is concerned with maintaining process variables temperatures pressures flows positions, and the like at some desired operation value. Processes are dynamic in nature. Changes are always occurring, and if actions are not taken, the important process variablesthose related to safety, product quality, and production rateswill not achieve design conditions.In order to fix ideas, let us consider a heat exchanger in which a process stream is heated by condensing steam. The energy gained by the process fluid is equal to the heat released by the steam, provided there are no heat losses to surroundings, that is, the heat exchanger and piping are well insulated.In this process there are many variables that can change, causing the outlet temperature to deviate from its desired value. If this happens, some action must be taken to correct for this deviation. That is, the objective is to control the outlet process temperature to maintain its desired value. One way to acplish this objective is by first measuring the temperature T(t), then paring it to its desired value, and, based on this parison, deciding what to do to correct for any deviation. The flow of steam can be used to correct for the deviation. This is, if the temperature is above its desired value, then the steam valve can be throttled back to cut the steam (energy) to the heat exchanger. If the temperature is below its desire value, the steam valve could be opened some more to increase the steam flow (energy) to the exchanger. All of these can be done manually by the operator, and since the procedure is fairly straightforward, it should present no problem. However, since in most process plants there are hundreds of variables that must be maintained at some desired value, this correction procedure would like to acplish this control automatically. That is, we want to have equipment control variables with on requiring intervention from the operator. (This is what we mean by automatic process control.)To acplish this objective a control system must be designed and implemented. A possible control system and its basic ponents are shown in .The importance of these ponents is that they perform the three basic operations that must be present in every control system. These operations are(1) Measurement (M): Measuring the variable to be controlled is usually done by the bination of sensor and transmitter.(2) Decision (D): Based on the measurement, the controller must then decide what to do to maintain the variable at its desired value.(3) Action (A): As a result of the controller’s decision, the system must then take an action. This is usually acplished by the final control element.As mentioned, these three operations, M, D, and A, must be present in every control system.PID controllers can be standalone controllers (also called single loop controllers), controllers in PLC, embedded controllers, or software in Visual Basic or C puter programs.PID controllers are process controllers with the following characteristics:Continuous process controlAnalogue input (also known as “measurement” or “Process Variable” or “PV”)Analogue output (referred to simply as “output”)Set point (SP)Proportional (P), Integral (I), and/or Derivative (D) constantsExamples of “continuous process control” are temperature, pressure, flow, and level control. For example, we control the heating of a tank. For simple control, you have two temperature limit sensors (one low and one high) and then switch the heater on when the low temperature limits sensor turns on and then mm the heater off when the temperature rises to the high temperature limit sensor. This is similar to most home air conditioning amp。 heating thermostats.In contrast, the PID controller would receive input as the actual temperature and control a valve that regulates the flow of gas to the heater. The PID controller automatically finds the correct (constant) flow of gas to the heater that keeps the temperature steady at the set point. Instead of the temperature bouncing back and forth between two points, the temperature is held steady. If