設(shè)計(jì)和開(kāi)發(fā)一種自動(dòng)灌溉系統(tǒng)

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1、 設(shè)計(jì)和開(kāi)發(fā)一個(gè)自動(dòng)灌溉系統(tǒng) 中央土壤含鹽量研究所，Karnal，印度 1996年9月20日 摘要： 在科學(xué)灌溉制度中,水應(yīng)在一個(gè)適當(dāng)?shù)耐寥浪謴埩ο聛?lái)滿(mǎn)足蒸散量來(lái)供給作物。應(yīng)用自動(dòng)控制的水在土壤水分predecided緊張是一種有效的灌溉調(diào)度技術(shù)。這可以通過(guò)一個(gè)本土研制的自動(dòng)灌溉系統(tǒng)來(lái)實(shí)現(xiàn)。 在這個(gè)系統(tǒng)中，土壤水分張力是通過(guò)一種改進(jìn)的電壓表來(lái)測(cè)量的。該方案提供給控制在predecided灌溉土壤水分張力和19,300定時(shí)器。電路能在一個(gè)12V直流蓄電池下工

2、作很長(zhǎng)一段時(shí)間。于1997年，科學(xué)B.V.出版社 關(guān)鍵詞：改造電壓表 閘閥 微灌灌溉表 自動(dòng)抽油機(jī) 自動(dòng)灌溉系統(tǒng) 1.介紹 在發(fā)展中國(guó)家中，大部分可用的水是用于農(nóng)業(yè)。隨著不同領(lǐng)域不斷新增的農(nóng)業(yè)活動(dòng)和競(jìng)爭(zhēng)的需求，節(jié)省水的使用已經(jīng)變得必不可少。這需要利用現(xiàn)有資源最優(yōu)灌溉采用方法的創(chuàng)新的科學(xué)方法的調(diào)度。 壤水分的測(cè)量，蒸散量的估計(jì),葉水勢(shì)、冠層溫度是用于灌溉調(diào)度的各種參數(shù)。為保證基于這些離散參數(shù)的自動(dòng)化在灌溉，一種利用和控制面板是必需的。 1997年0378-3774/97 /B.V. 17.00美元 科學(xué)出版社保留所有權(quán)利。 有價(jià)證券SO378-3774 01292-917

3、0(96) 冠層溫度的方法測(cè)量,由于氣孔關(guān)閉期間的峰值太陽(yáng)輻射，我們可以獲得誤導(dǎo)人的信息。自動(dòng)化領(lǐng)域灌溉的研究主要限于重力系統(tǒng)。典型的是,那些被Haise、Kruse(1969)，F(xiàn)ischbach(1969)和Phene（1973）等人使用了潛在傳感器測(cè)量土壤熱量散失的自動(dòng)化灌溉系統(tǒng)。奧斯汀和羅林斯(1977)敘述了光電探測(cè)器水銀器，并報(bào)道說(shuō)探測(cè)器和控制器使用晶體管電路晶體管邏輯(TTL)被用來(lái)成功地控制了灌溉在29個(gè)情節(jié)。當(dāng)兩個(gè)或兩個(gè)以上的電壓表的示數(shù)達(dá)到或者低于設(shè)置點(diǎn)時(shí)，灌溉會(huì)自動(dòng)進(jìn)行。(Hollis and Dylla, 198

4、0). 在當(dāng)前的課題中，自動(dòng)灌溉制度受到用于實(shí)時(shí)測(cè)量土壤應(yīng)力值的可修改的電壓表的影響。這是一個(gè)特別使用于控制調(diào)度微型灌溉的設(shè)備。汽車(chē)灌溉系統(tǒng)的本土研制可以通過(guò)商業(yè)上可用的部件來(lái)實(shí)現(xiàn)。 1.1原則 電壓表的設(shè)計(jì)是把它改造成，使它可以通過(guò)生成比例電氣信號(hào)值來(lái)測(cè)出土壤水分張力。在一個(gè)預(yù)定值時(shí)的土壤水分張力下，控制電路產(chǎn)生的信號(hào)控制一個(gè)雙向交流電動(dòng)機(jī)控制閥門(mén)開(kāi)始或終止的灌溉。這種交流電機(jī)的最高轉(zhuǎn)速被減速器降低到2 r/min。灌溉的磁力控制調(diào)節(jié)被安放在閥門(mén)的閥體。為防止超調(diào)的馬達(dá)驅(qū)動(dòng)引起的損壞的離合器也被包含在設(shè)計(jì)中。電機(jī)和控制電路工作在12v直流電壓下。該閥的進(jìn)口連接到

5、頂上的容器。在頂上的水的水平可以一直被電子傳感器感應(yīng)到。設(shè)計(jì)也提供了自動(dòng)計(jì)量灌溉用水的數(shù)量和比例的措施。滴流灌溉的自動(dòng)測(cè)試單元被安裝放置在Karnal面積0.25公頃的CSSRI地區(qū)。 2.材料和方法 其主要部件的汽車(chē)灌溉系統(tǒng)(圖1),是一種土壤水分傳感器 (經(jīng)過(guò)改裝電壓表),控制電路,閘閥、汽車(chē)抽油機(jī)、定時(shí)器和電源供應(yīng)器。下文簡(jiǎn)要介紹了組件。 2.1經(jīng)改裝的電壓表 在灌溉中引入自動(dòng)化，一個(gè)土壤水分張力傳感器能產(chǎn)生一個(gè)可以表示土壤水分張力（SWT）的適當(dāng)?shù)碾娮有盘?hào)是必要的。改造電壓表的性能已經(jīng)被報(bào)道說(shuō)優(yōu)于壓力表（Trotter，1984）。在現(xiàn)有的設(shè)備中，改裝電壓表

6、已經(jīng)被設(shè)計(jì)出（圖 2），用于自動(dòng)操作閥門(mén)的馬達(dá)并發(fā)展為用于灌溉的調(diào)節(jié)機(jī)體。一個(gè)腈綸管取代了汞杯。大量的等距銅電極已經(jīng)被安裝在并腈綸管上。在飽和條件下(當(dāng)土壤水分張力是零)所有的電極接觸到汞在腈綸管，所以-12V（地）通過(guò)汞供給最低電極并傳到所有的電極。當(dāng)土壤水分張力上升時(shí)，腈綸管中的汞平面開(kāi)始下降，地面也脫離了隨后的電極。這個(gè)斷開(kāi)的信號(hào)在控制電路中被處理后用來(lái)操作閥門(mén)。電極趨于觸到終端帶上的接口。為了啟動(dòng)灌溉，某一特定的土壤水分張力值對(duì)應(yīng)相應(yīng)的插座。 圖 1 自動(dòng)灌溉原理圖 2.2 控制電路 改裝電壓表上產(chǎn)生的控制灌溉啟動(dòng)和終止的信號(hào)在控制電路中處理

7、，并用于控制閥門(mén)的開(kāi)啟和關(guān)閉?？刂齐娐酚蓛煞N智能卡芯片構(gòu)成（圖 3）。土壤水分張力傳感器的輸出被傳送到智能卡IC-4的4腳上。這IC-4智能卡是具有高輸入阻抗的555智能卡。土壤的細(xì)微移動(dòng)通過(guò)10千歐姆的阻抗傳到IC-4的4腳上。另外，如果灌溉的啟動(dòng)是通過(guò)一個(gè)定時(shí)器控制，那么正電壓就通過(guò)定時(shí)器的IC-5387芯片的引腳25傳送到IC-4的引腳4上。IC-4的引腳2與2平方米的地面接觸。當(dāng)正電壓供給IC-4的引腳4上時(shí)，就在引腳8上供給12V電壓。由1M歐姆電阻和5μF電容組成的延時(shí)電路連接到IC-4智能卡芯片的引腳6、7、8上。引腳3上的正電壓輸出驅(qū)動(dòng)“0”復(fù)位。12V電壓通過(guò)繼電器的觸電供給

8、電機(jī)的端口。這個(gè)電機(jī)開(kāi)始以逆時(shí)針?lè)较蜣D(zhuǎn)動(dòng)，而耦合到電機(jī)的閥門(mén)就打開(kāi)了。當(dāng)觸點(diǎn)由M2變到M1時(shí)，磁鐵被替換。因此，M2變?yōu)殚_(kāi)啟而M1關(guān)閉。智能卡芯片IC-4的引腳2也脫離地面，復(fù)位繼電器釋放，觸點(diǎn)01和觸點(diǎn)02是斷開(kāi)的，因此供給電機(jī)的電源是不接通的。當(dāng)提供了足夠的灌溉后，一個(gè)由改裝電壓表產(chǎn)生的負(fù)信號(hào)通過(guò)M1的閉合觸點(diǎn)傳送到智能卡芯片IC-3的引腳2。. 加載在引腳4上的正電壓(通過(guò)改裝電壓表的開(kāi)關(guān)或定時(shí)器),12v電壓在IC-3的引腳3上變得有效。電壓通過(guò)觸點(diǎn)01和地面操作繼電器L。現(xiàn)在的12v通過(guò)操作繼電器L的觸點(diǎn)L1連接到電動(dòng)機(jī)的終端，電動(dòng)機(jī)的其他觸點(diǎn)通過(guò)操作繼電器L的觸點(diǎn)L2連接到地面。當(dāng)

9、加載在電動(dòng)機(jī)上的電壓極性顛倒后，電動(dòng)機(jī)以順時(shí)間方向轉(zhuǎn)動(dòng)，同時(shí)關(guān)閉于它耦合的閥門(mén)從而終止灌溉。觸點(diǎn)M1前的磁鐵被替換，觸點(diǎn)M1斷開(kāi)。一個(gè)由10千歐姆電阻和0.1μF電容構(gòu)成的延時(shí)電路提供了幾秒的延時(shí)后，連接到智能卡芯片IC-3的引腳2的-12V電壓被斷開(kāi)。接到智能卡IC-2的引腳3的12V電壓被移除，繼電器L釋放，觸點(diǎn)L1、L2斷開(kāi)。接到電動(dòng)機(jī)終端的12V電壓也被斷開(kāi)。因此，電機(jī)在閥門(mén)關(guān)閉后停止轉(zhuǎn)動(dòng)。 2.3閘閥 閥門(mén)系統(tǒng)是由一個(gè)通過(guò)離合器機(jī)制連接到直流電機(jī)軸的直徑2CM的PVC閥門(mén)（圖 4）。進(jìn)口連接到頂上的容器，而出口連接到主要或者次主要的滴灌系統(tǒng)。這種類(lèi)型的閘閥是商業(yè)上可

10、用在不同的標(biāo)準(zhǔn)，適應(yīng)場(chǎng)上要求尺寸的灌溉系統(tǒng)。閥門(mén)的驅(qū)動(dòng)軸連接到一個(gè)直流電機(jī)。 圖2 改裝電壓表 圖3 控制電路 一個(gè)減速器被用于將電動(dòng)機(jī)的轉(zhuǎn)速降低到2r/min。離合器機(jī)制(圖5)已經(jīng)被設(shè)計(jì)的和納入裝置,以避免從超調(diào)現(xiàn)象的閘閥運(yùn)動(dòng)部件在任一個(gè)方向上引起的損壞。為了閥門(mén)機(jī)制的順利運(yùn)行，閘閥泵軸,軸電機(jī)和離合器齒輪的中心應(yīng)適當(dāng)對(duì)齊的。一個(gè)小環(huán)磁鐵已經(jīng)被嵌入在軸上的閘閥，兩個(gè)觸點(diǎn)M1和M2都安裝外體PVC閥門(mén)上。M1被定位在完全開(kāi)放條件下的磁鐵前面，然而M2直接面向完全關(guān)閉條件下的磁鐵（圖 3）。 2.4

11、汽車(chē)抽水機(jī) 為了頂上容器的水維持一個(gè)predecided水平，一個(gè)汽車(chē)的抽油機(jī)已經(jīng)設(shè)計(jì),開(kāi)發(fā)和安裝(圖6)。汽車(chē)的主要部分是水平抽油機(jī)傳感器、控制線(xiàn)路和一個(gè)三相在線(xiàn)的Starter。當(dāng)頂上容器中的水位低于傳感器L時(shí)，一個(gè)由控制電路產(chǎn)生的電子信號(hào)被傳送到Starter，使三相電機(jī)抽油機(jī)得到供電,它開(kāi)始抽取頂上容器的水。頂上容器中的水位觸到傳感器T時(shí)，一個(gè)由控制電路產(chǎn)生的信號(hào)用于切斷電機(jī)抽油機(jī)。此,在頭頂?shù)乃渌蛔詣?dòng)保持在恒定水位。 圖4 磁控PVC閥門(mén)

12、 圖5 離合器總成(自動(dòng)灌溉閥門(mén)) ①電機(jī)軸 ② 離合器軸 ③ 離合器齒輪 ④ 彈簧 ⑤ 彈簧收緊螺絲 圖6 自動(dòng)抽水機(jī) 2.5微型灌溉表 通過(guò)計(jì)數(shù)頂上容器中水耗盡的次數(shù)，用于滴灌系統(tǒng)的灌溉用水可以被測(cè)量出。（圖 7）。當(dāng)頂上的容器中水位下降到標(biāo)志“L”時(shí)，智能卡芯片IC-7感應(yīng)到這個(gè)條件，并產(chǎn)生一個(gè)由智能卡IC-4的計(jì)算出的脈沖連接到智能卡芯片IC-5。.智能卡IC-7所產(chǎn)生的脈沖數(shù)與頂上容器內(nèi)水位到達(dá)標(biāo)志“L”

13、的次數(shù)成正比。5個(gè)發(fā)光二極管被均勻的安裝在頂上容器的標(biāo)志“L”和標(biāo)志“T”之間。當(dāng)頭頂上的容器的水位到達(dá)標(biāo)志“T”時(shí)，所有的二極管發(fā)光。當(dāng)頭頂上容器的水位開(kāi)始下降時(shí)，發(fā)光二極管一次熄滅。在兩個(gè)發(fā)光二極管一次熄滅的期間，我們得出灌溉用水的應(yīng)用率。 2.6定時(shí)器 時(shí)器單元由一個(gè)晶振、分頻器（IC-1）和頻率計(jì)數(shù)器組成(圖 3)。另外，定時(shí)器可以用于灌溉控制。這個(gè)定時(shí)器被預(yù)先設(shè)置用于控制灌溉的啟動(dòng)和終止。當(dāng)?shù)竭_(dá)預(yù)設(shè)時(shí)間時(shí)，通過(guò)供給智能卡芯片IC-2的引腳25一個(gè)正電壓，一個(gè)信號(hào)由定時(shí)器發(fā)送到控制電路來(lái)操作閥門(mén)的開(kāi)啟或關(guān)閉。 圖7

14、 微型灌溉表 2.7供電 用于操作直流電動(dòng)機(jī)和電子元器件供電可以從12V蓄電池和12V太陽(yáng)能板獲得。由于自動(dòng)灌溉系統(tǒng)的一個(gè)灌溉周期中直流供電的有限時(shí)間為1到5分鐘，電池的使用壽命很長(zhǎng)而且只需要很少的維護(hù)。保護(hù)設(shè)備,如保險(xiǎn)絲和二極管已納入的電路,以避免由于短路或任何其他的缺陷造成太陽(yáng)能板和電子元件的損壞。 3.自動(dòng)灌溉系統(tǒng)的工作 這個(gè)滴流灌溉系統(tǒng)可以在以下三種模式下操作： 1. 電壓表控制方式 2. 定時(shí)器控制方式 3. 電壓表—定時(shí)控制方式 3.1電壓表控制方式 在電壓表控制方式中，灌溉的啟動(dòng)或者終止所對(duì)應(yīng)的土壤水分張力必須通過(guò)相應(yīng)的接口接到改裝電壓表的終端上。正如前文所

15、解釋的那樣，控制電路經(jīng)過(guò)處理產(chǎn)生于改裝電壓表的信號(hào)，用來(lái)操作灌溉閥門(mén)的開(kāi)啟或關(guān)閉。 3.2定時(shí)器控制方式 在定時(shí)器控制方式中，當(dāng)預(yù)先設(shè)定的灌溉啟動(dòng)時(shí)間到達(dá)以后，定時(shí)器的T1引腳連接到智能卡芯片IC-4的引腳6上，施加了一個(gè)正電壓。由于觸點(diǎn)M1的閉合，智能卡IC-4的引腳2是接地的，即電勢(shì)與地面同為0V。而引腳3的電壓變高。復(fù)位繼電器工作。在電壓表處于這樣的情況下，控制電路打開(kāi)了閥門(mén)。當(dāng)并且當(dāng)達(dá)到預(yù)設(shè)時(shí)間在定時(shí)器T2時(shí)，這個(gè)定時(shí)器給智能卡IC-3的引腳4施加一個(gè)正電壓。在處于閘門(mén)開(kāi)放的條件下，由于位于環(huán)磁鐵前方的觸點(diǎn)M2是閉合的，智能卡IC-4的引腳2是負(fù)電位的。此時(shí)，加在引腳3上的電壓

16、變高，正如上面所描述的電壓表控制方式的設(shè)置，閥門(mén)被控制電路關(guān)閉。 3.3電壓表-定時(shí)器控制方式： 在電壓表-定時(shí)器控制方式中，灌溉是按一定的比率供給植物的，電壓表不能瞬時(shí)響應(yīng)土壤溫濕度的變化（Klute、Gorden-1952）。灌溉的發(fā)起需要一個(gè)預(yù)先設(shè)定的土壤水分張力值。在灌溉開(kāi)始的瞬間，復(fù)位電路將計(jì)時(shí)器重置（圖 3）。通過(guò)操作觸點(diǎn)2,12V電壓被施加到觸點(diǎn)P上。觸點(diǎn)P通過(guò)二極管連接到智能卡IC-1的引腳31、33、34，這個(gè)二極管可以顯示重置到00:00，同時(shí)計(jì)數(shù)器重新啟動(dòng)計(jì)數(shù)。正如更早前所描述的那樣，灌溉的終止受到定時(shí)器的影響。 4.對(duì)改造后的電壓表進(jìn)行校準(zhǔn) 改造后的電壓

17、表是相對(duì)標(biāo)準(zhǔn)電壓表進(jìn)行校準(zhǔn)的。經(jīng)過(guò)初始充電后，兩個(gè)電壓表都被安裝在相同的位置和相同的深度。電壓表的安裝校準(zhǔn)如圖 8。.電極通過(guò)個(gè)人的發(fā)光二極管和電位器控制連接到12V電壓上。在這樣的飽和條件下，水銀柱觸到了所有的觸點(diǎn)。因此，所有的噶光二極管都亮了起來(lái)。此時(shí)，通過(guò)發(fā)光二極管的電流受到附加電位器的控制。隨著土壤水分張力的上升，腈綸管中的水銀柱平面會(huì)下降。第一個(gè)發(fā)光二極管的熄滅，表明腈綸管中的水銀柱的平面已經(jīng)下降到了第一個(gè)觸點(diǎn)之下。在這一時(shí)刻，在標(biāo)準(zhǔn)電壓表上會(huì)得到一個(gè)讀數(shù)。隨后，用于改裝電壓表校準(zhǔn)的讀數(shù)，將會(huì)從其他每個(gè)發(fā)光二極管的熄滅時(shí)所對(duì)應(yīng)的標(biāo)準(zhǔn)電壓表讀數(shù)得出。 4.1自動(dòng)灌溉系統(tǒng)的測(cè)試

18、 在Karnal，位于CSSRI的面積0.25公頃的實(shí)驗(yàn)農(nóng)場(chǎng)上，自動(dòng)灌溉系統(tǒng)已經(jīng)在滴灌系統(tǒng)中進(jìn)行測(cè)試（圖 9）。這個(gè)滴灌系統(tǒng)包括了一個(gè)主管道，兩個(gè)次主管道和15個(gè)側(cè)邊。三個(gè)標(biāo)準(zhǔn)壓力補(bǔ)償型的滴管為植物提供灌溉。 為了測(cè)試控制電路和閥門(mén)的設(shè)置，不同土壤的水分張力值被選出用于灌溉的啟動(dòng)。對(duì)于如何終止灌溉，控制電路中的定時(shí)器被預(yù)先編程設(shè)定分出不同持續(xù)時(shí)間的灌溉時(shí)間。 4.2測(cè)試結(jié)果 在田間條件下，控制電路和閥門(mén)已經(jīng)進(jìn)行了測(cè)試。多種土壤水分張力被選擇用來(lái)啟動(dòng)自動(dòng)灌溉。通過(guò)同樣和改裝電壓表一樣被安裝在同一位置和同一深度標(biāo)準(zhǔn)裝電壓表，我們可以獲得即時(shí)灌溉啟動(dòng)的觀察值。預(yù)先程序設(shè)定

19、在計(jì)時(shí)器上的自動(dòng)灌溉持續(xù)時(shí)間值被記錄了下來(lái)。 表格 1：自動(dòng)灌溉系統(tǒng)的測(cè)試結(jié)果 SWTos,預(yù)設(shè)的土壤張力觀察值，單位：毫巴；SWTsi，自動(dòng)灌溉的啟動(dòng)設(shè)定值，單位：毫巴；SWToi，自動(dòng)灌溉瞬間啟動(dòng)的土壤水分張力觀測(cè)值，單位：毫巴；Ts，自動(dòng)灌溉持續(xù)時(shí)間的設(shè)定值，單位：小時(shí)；To，自動(dòng)灌溉持續(xù)時(shí)間的觀測(cè)值，單位：小時(shí)。 表格 1的數(shù)據(jù)表明：土壤水分張力的預(yù)設(shè)值與觀測(cè)值是緊密匹配的，這意味著控制電路和定時(shí)器具有良好的靜動(dòng)態(tài)性能。通過(guò)自動(dòng)控制閥門(mén)的氣量降低值也與手動(dòng)控制想匹配。因此，在完全關(guān)閉和完全開(kāi)啟的狀態(tài)下，閥門(mén)的性能是令人滿(mǎn)意的。 5.總結(jié)和結(jié)論 自動(dòng)灌溉系統(tǒng)可以持

20、續(xù)的監(jiān)控著植物根部的土壤水分壓力，并根據(jù)預(yù)先設(shè)定的土壤水分張力值和灌溉持續(xù)時(shí)間來(lái)控制著灌溉的進(jìn)行。閘閥被電機(jī)控制著，工作在任意一端。用于閘閥結(jié)構(gòu)的磁觸頭和PVC閘門(mén)材料，可以有效的防治腐蝕和氣孔。通過(guò)一個(gè)12V電壓的蓄電池和太陽(yáng)能板，系統(tǒng)所采用的低功率供電系統(tǒng)是很容易取得的。自動(dòng)抽水機(jī)保證了應(yīng)用于滴灌系統(tǒng)的存蓄在頂上容器的灌溉用水存儲(chǔ)量。這個(gè)本土研制的自動(dòng)灌溉系統(tǒng)降低了自動(dòng)灌溉的成本和保證了更好的回報(bào)。印度農(nóng)民可以通過(guò)這個(gè)自動(dòng)灌溉系統(tǒng)極大的節(jié)省勞動(dòng)力和其他的農(nóng)場(chǎng)投入。 來(lái)源： 作者心懷感激的接受來(lái)自于Karnal的C.S.S.R.I的編導(dǎo)的支持和指導(dǎo)。同時(shí)，作者也感謝來(lái)自設(shè)計(jì)和制造了閘

21、閥的技術(shù)人員Sh.Munish Kumar的幫助。 參考文獻(xiàn)： Austin R.S.，Rawlins S.L，1997.水銀壓力計(jì)光電水平探測(cè)器. 英國(guó)農(nóng)業(yè)（新聞出版社）58:29-30； Fishchbach,P.E，Thompson,L.T，Stetson,L.E.，1970. 可再利用的自動(dòng)化表面灌溉系統(tǒng)的電氣控制. 譯自美國(guó)工程師協(xié)會(huì)，13:286-288； Haise.H.R，Kruse.E.G，1969. 自動(dòng)化表面灌溉系統(tǒng). 譯自美國(guó)土木工程師協(xié)會(huì). 管道灌溉類(lèi)，95:503-516； Hollis.S，Dylla.A.S.，1980. 灌溉自動(dòng)化與張力感應(yīng)系統(tǒng).

22、 譯自美國(guó)工程師協(xié)會(huì)..23:649-656 Klutr.A，Gorden.W.R，1952. 電壓表響應(yīng)時(shí)間. 土壤科學(xué). 93:204-207； Phene.C.J，Hoffman,O.J，Austin.R.S，應(yīng)用潛在傳感器的自動(dòng)化控制灌溉. 譯自美國(guó)工程師協(xié)會(huì). 16:773-776； Trotter.C.M，1984. 讀取電壓表和真空壓力傳感器時(shí)的錯(cuò)誤. 土壤科學(xué) . 138(4):314-316 ELSEVIER Agricultural Water Management 33 ( 1997) 169- 18 1 Design an

23、d development of an auto irrigation system S.K. Luthra * , M.J. Kaledhonkar, O.P. Singh, N.K. Tyagi Central Soil Salinity Reseurch Institute. Karnal, India Accepted 20 September 1996 Abstract In scientific irrigation scheduling water should be applied to a crop at an appropriate soil water tens

24、ion to fulfil its evapotranspiration requirement. Automatic control of water application at predecided soil water tensions is an effective irrigation scheduling technique. This can be achieved through an indigenously developed auto irrigation system. In this system soil water tension is sensed throu

25、gh a modified manometer type tensiometer. The design provides control of irrigation at the predecided soil water tensions and preprogrammed timer. The circuitry can be operated with a 12 V d.c. storage battery for a long period. 0 1997 Elsevier Science B.V. Keywords: Modified tensiometer; Gate v

26、alve; Micro irrigation water meter; Auto pumping unit; Auto irrigation system 1. Introduction In developing countries, most of the available water is used for agriculture. With the increase in agricultural activity and competitive demand from different sectors, it has become essential to economi

27、se on the use of water. This calls for optimal utilisation of available resources by adopting innovative methods of irrigation with scientific methods of scheduling. Soil moisture measurements, evapotranspiration estimates, leaf water potential and canopy temperature are various parameters employed

28、 for irrigation scheduling. For effecting automation in irrigation based on the discrete values of these parameters, a datalogger and control panel are required. In the case of the infrared thermometer Corresponding author. 0378-3774/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII

29、 SO378-3774(96)01292-9170 2. Materials and methods The main components of the auto irrigation system (Fig. 1) are a soil moisture sensor (modified tensiometer), control circuitry , gate valve, auto pumping unit, timer and power supply. The components are described briefly below. 2.1. Modified

30、 tensiometer For introducing automation in irrigation, it is necessary that a soil moisture sensor should generate an appropriate electrical signal for sensed values of soil water tension (SWT). The performance of the manometer type tensiometer has been reported to be better than that of the pressu

31、re gauge type tensiometer (Trotter, 1984). In the present setup, the design of the manometer type tensiometer has been modified (Fig. 2) forautomatic operation of the valve developed for regulation of irrigation. An acrylic tube replaces the mercury cup. A number of equidistant copper electrodes ha

32、ve been installed on the body of the acrylic tube. In saturated condition (when soil water tension is zero) all electrodes are in contact with the mercury in the acrylic tube, so - 12 V (ground) applied to the lowermost electrode extends to all the electrodes through the mercury. With the rise in v

33、alue of soil water tension, the level of the mercury in the acrylic tube starts to fall and ground is progressively disconnected from subsequent electrodes. This disconnection signal is processed in the control circuitry for operation of the valve. Electrodes are extended to sockets on a terminal st

34、rip. For initiation of irrigation, a particular value of soil water tension is selected by plugging the corresponding socket. Fig. 1. Schematic diagram of the auto irrigation system 2.2. Control circuitry The signal generated from the modified tensiometer for initiation and term

35、ination of irrigation is processed in the control circuitry for opening and closing of the valve. The control circuitry consists of two I.C. chips (Fig. 3). The output of the soil moisture sensor is fed to pin-4 of IC-4. The IC-4 is 555 I.C. having high input impedance. The removal of the earth at p

36、in-4 extends the supply to pin-4 through a resistance of 10 kR. Alternatively, if initiation of irrigation is to be controlled through a timer, then positive voltage is applied to pin-4 of IC4 through pin-25 of IC-5387 of the timer. The pin-2 of IC-4 is connected to the ground through magnetic con

37、tact M2. On the application of positive supply at pin-4, 12 V is applied on pin-8. The delay circuit, consisting of 1 MR resistance and 5 p_F condenser is connected at pin-6, pin-7 and pin-8 of IC-4. The positive output at pin-3 drives the ‘0’ relay. The 12 V is extended to the port of the motor thr

38、ough operated contact 02 of relay ‘0’. The motor starts to move in an anticlockwise direction. The valve which is coupled to the motor is thus opened. The magnet is displaced from the front of magnetic contact M2 to the front of magnet contact Ml. Thus, M2 becomes open and Ml is closed. The ground o

39、n pin-2 of IC-4 gets disconnected. ‘0’ relay releases, contacts 01 and 02 become open. Thus, supply is disconnected to the motor. When sufficient amount of irrigation has been applied, a negative signal generated from the modified tensiometer is applied to the pin-2 of IC-3, through closed magnetic

40、contact Ml Fig. 2. Modified manometer type tensiometer. On application of positive voltage at pin-4 (through tensiometer switch or timer), 12 V becomes available at pin-3 of IC-3. This voltage operates ‘L’ relay through contact 01 and ground. Now 12 V is connected to the opposite terminal of th

41、e motor through operated contact Ll of ‘L’ relay. The ground is connected to the other motor terminal through operated contact L2 of L relay. As the voltage on the motor terminal is reversed, the motor moves in a clockwise direction, closing the valve coupled to it and terminating the irrigation. Th

42、e magnet in front of contact Ml is displaced and contact Ml opens, - 12 V is disconnected from pin-2 of IC-3 after a delay of a few seconds provided by resistance of 10 kfl and a condenser of 0.1 ~.LF. The 12 V at pin-3 of IC-2 is removed, ‘L’ relay releases, Ll and L2 become open, 12 V supply to t

43、he motor terminal is disconnected. Thus, the motor stops after closing the valve. 2.3. Gate valve The valve system consists of a 2” diameter PVC gate coupled to the shaft of the d.c. motor through the clutch mechanism (Fig. 4). The inlet port is connected to an overhead tank through a PVC pipe a

44、nd the outlet port is connected to the main or submain drip irrigation system. This type of gate valve is commercially available in different standard dimensions to suit the on-field requirements of the irrigation system. The drive shaft of the valve is connected to a d.c. motor. A reduction gear m

45、echanism is used to reduce the speed of the motor to 2 rev min.‘. A clutch mechanism (Fig. 5) has been designed and incorporated in the device to avoid damage to the gate valve from the overshoot of moving parts in either direction. For smooth functioning of the valve mechanism, the shaft of the gat

46、e valve, the shaft of the motor and the centre of the clutch gear should be properly aligned. A small ring magnet has been embedded on the shaft of the gate valve and two reed contacts, Ml and M2, have been installed on the outer body of the PVC valve. Ml is positioned in front of the magnet in the

47、completely open condition of the valve, while contact M2 faces the magnet in the completely closed condition (Fig. 3). 2.4. Auto pumping unit To maintain a predecided level of water in the overhead tank, an auto pumping unit has been designed, developed and installed (Fig. 6). The main component

48、s of the auto pumping unit are level sensors, control circuitry and a three phase on-line starter. When the water level in the overhead tank falls below the lower sensor ‘L’, an electrical signal is generated by the control circuitry to energise the starter to connect three phase supply to the moto

49、r pumping unit, which starts to pump water to the overhead tank. As the level of water touches the upper sensor ‘T’, a signal is generated by the control circuitry to switch off the motor pumping unit. Thus, the water level in the overhead tank is maintained at a constant level automatically. 2.

50、5. Micro irrigation water meter Irrigation water supplied to the drip irrigation system can be measured by counting the number of times the overhead tank is emptied (Fig. 7). When the level of water in the overhead tank falls below mark ‘L’, the IC-7 senses this condition and generates a pulse in c

51、onjunction with IC-5 which is counted by the set of ICs (l-4). The number of pulses generated by IC-7 is in direct proportion to the number of times water in overhead tank reaches the mark ‘L’. Five light emitting diodes (LEDs) with sensors have been fixed on the overhead tank, between marks T and L

52、 equidistantly. When the water in the overhead tank reaches mark T all LEDs glow. As the water level starts to fall, the LEDs go off sequentially. The period between the ‘glowing off’ of two consecutive LEDs gives the rate of application of water. 2.6. Timer The timer unit consists of a crysta

53、l, frequency divider (IC-1) and frequency counter (Fig. 3). Alternatively, the timer can be used for control of irrigation. The timer is preprogrammed for initiation and termination of irrigation. When the preset time is attained, a signal is extended from the timer to control circuitry for opening

54、or closing of the gate valve by applying a positive supply on pin-25 of IC-2. Fig. 3. Control circuitry. Fig. 4. PVC valve with magnetic control. Fig. 5. Clutch assembly (auto irrigation valve) 2.7. Power supply The power

55、supply for operation of the d.c. motor and electronic components is obtained from a 12 V storage battery in float with 12 V solar panel. Since the d.c. power requirement of the auto irrigation system is limited to 5 min duration for an irrigation cycle, the life of the battery is quite long and requ

56、ires minimum maintenance. Protective devices like fuses and diodes have been incorporated into the circuit to avoid damage to the solar panel and electronic components due to a short circuit or any other defect. Fig. 6. Auto pumping unit. 3. Working of auto irrigation s

57、ystem The drip irrigation system can be operated in three modes: 1.tensiometer controlled; 2.timer controlled; 3.tensio-timer controlled. Fig. 7. Micro irrigation water meter. 3.1. Tensiometer controlled In the tensiometer controlled mode, the soil water tension at whi

58、ch irrigation has to be initiated or terminated is selected by plugging the corresponding socket on the terminal strip of the modified tensiometer. The control circuitry processes the signal generated by the modified tensiometer for opening and closing of the valve for initiation and termination of

59、irrigation as explained earlier. 3.2. Timer controlled In timer controlled irrigation, timer Tl extends positive voltage to pin-4 of IC-4 when the preset time for initiation of irrigation has been reached. Pin-2 of IC-4 is already on earth voltage due to closed Ml contact. Pin-3 becomes high. ‘0’

60、relay is operated. Control circuitry opens the gate valve as in the case of the tensiometer. As and when the preset time in timer T2 is attained, the timer extends positive supply to pin-4 of IC-3. Pin-2 of IC-4 is already negative because of closed M2 contact, which is in front of the ring magnet d

61、uring the open condition of the valve. Pin-3 becomes high and the valve is closed by the control circuitry as described in tensiometer control setup. 3.3. Tensio-timer controlled In this mode of control, irrigation is provided to the plants at a certain rate and the tensiometer does not respond in

62、stantaneously to the changing moisture conditions (Klute and Gorden, 1952). Irrigation is initiated with respect to a preset value of soil water tension. At the instant of initiation of irrigation, the timer is reset by the resetting circuit (Fig. 3) 12 V is extended to point ‘P’ through operated 02

63、 contact. The point ‘P’ is connected to pin-32, 33, 34 of IC-1 through diodes which reset the display to 0O:OO and the counter restarts counting. The termination of irrigation is effected through timer control as described earlier. 4. Calibration of modified tensiometer Fig. 8. Calibr

64、ation arrangements for modified tensiometer The modified tensiometer was calibrated with respect to standard manometer type tensiometer. After initial charging both tensiometers were installed at similar locations and the same depth. The calibration setup is shown in Fig. 8. Electrodes are connec

65、ted to 12 V through individual LEDs and potentiometer control. In the saturated condition, mercury touches all the electrodes. Therefore, all the LEDS light up. The current through an LED is controlled by an attached potentiometer. With a rise in soil water tension, the level of mercury in the acry

66、lic tube falls. The fall in the level of mercury from the first electrode is indicated by the ‘glowing off’ of the first LED. At this instant, a reading is taken on a standard manometer type tensiometer. Subsequent readings were taken at the ‘glowing off’ of the other LEDs for the calibration of the modified tensiometer. Fig. 9. Layout of the drip irrigation system 4.1. Testing of auto irrigation system The auto irrigation setup was tested in a drip system laid out in a 0.25