【正文】 隨著農(nóng)業(yè)、化工生產(chǎn)的需要，這種自動化智能化的控制系統(tǒng)定會被廣泛應(yīng)用，且發(fā)展前景不可估量。 EM235 模擬量輸入電路 本系統(tǒng)使用的西門子 S7200 CPU226 PLC 自身沒有模擬量輸入通道，而經(jīng)溫度變送器送來的溫度信號是模擬信號，為了使 PLC 準(zhǔn)確識別溫度信號，必須擴展模擬量輸入模塊。 （ 1） 溫度傳感器 熱電偶 把兩者不同金屬連接成閉合回路，如果將他們的兩個連接點中的一個進行加熱使其溫度為 T，而另一端置于另一溫度 T0，則在回路中就會產(chǎn)生電動勢，這種效應(yīng)稱作 塞貝克效應(yīng) ，利用 該 效應(yīng) 設(shè)計的溫度傳感器稱作熱電偶溫度傳感器。 溫度 表 征 了 物體冷熱程度，是工農(nóng)業(yè)生產(chǎn)過程中一個很重要而普遍的測量參數(shù)。在整個運行期間，可以看做可編程邏輯控制器的 CPU 不間斷地，循環(huán)往復(fù)的執(zhí)行著三個過程。PLC分為小型、中型和大型 3 類。 PLC 發(fā)出調(diào)節(jié) 命令的同時，計算調(diào)節(jié)時間，若調(diào)節(jié)時間太長，超過三分鐘進行聲光報警（紅燈亮，同時揚聲器工作），以此表示溫度失控，提醒工作人員，進行人工干預(yù)；若調(diào)節(jié)時間未到 3 分鐘，則準(zhǔn)備下次繼續(xù)采樣及調(diào)節(jié)。 該系統(tǒng)以 51 單片機為控制器，并作為下位機，可以實現(xiàn)溫濕度的自動控制，且在一百天之內(nèi)無需人工干預(yù)。 關(guān)鍵字 ： PLC，溫度傳感器，檢測 ,控制 Design of detection and control system of greenhouse temperature based on PLC Abstract: Temperature measurement and control plays an extremely important role in human daily life, including industrial production, weather forecast, material storage, etc.. In many cases, it is very important to acquire the timely and accurate information of the temperature of the targets. Recently, along with the development of digital technology, the rapid development of temperature measurement and control has been widely used in various industrial agricultural fields, meanwhile, the chips of measurement and control the temperature have been on the historical stage. This system, by collecting temperature data through the temperature sensor, with the application of PLC control system based on the theoretical knowledge about temperature measurement and control, intends to analyze the potential causes of the breakdowns in their automatic operation. At the same time, starting from the circuits of actual hardware, and via analyzing operating principles of these electric circuits, this system is aiming at putting forward the revising proposasl and solutions according to the specific situations. The temperature sensor used by the author is XPTPAV010D, which is distinguished with small size, high precision and low power consumption. The temperature data collected by the temperature sensor is an analog signal. Therefore, in the system, an analog extended module of will be added to the PLC so that temperature signal collected by 皖西學(xué)院本科論文（設(shè)計） the module can be directly input to PLC, and PLC will analyze, process the data, and control the temperature through regulating the ponents. This kind of automatic and intelligent disposure will be definitely in infinite application and tremendous development in the temperature controlling system in the greenhouse. Keyword: PLC, Temperature sensors, Detection, Control 皖西學(xué)院本科論文（設(shè)計） 目錄 ............................................................. 1 ................................................. 2 ................................................... 2 ............................................. 4 （ PLC） ............................................ 5 的定義 .................................................. 5 的分類 .................................................. 5 的基本結(jié)構(gòu) .............................................. 5 .PLC 的工作原理 ............................................. 6 . PLC 主要廠家及西門子 S7— 200 ............................... 7 ....................................................... 9 ........................................... 9 .................................................11 ....