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1、<p><b> 走進(jìn)PLC</b></p><p><b> 1 PLC基礎(chǔ)知識</b></p><p> 1.1 PLC的發(fā)展歷程</p><p> 在工業(yè)生產(chǎn)過程中,大量的開關(guān)量順序控制,它按照邏輯條件進(jìn)行順序動作,并按照邏輯關(guān)系進(jìn)行連鎖保護(hù)動作的控制,及大量離散量的數(shù)據(jù)采集。傳統(tǒng)上,這些功能是通過
2、氣動或電氣控制系統(tǒng)來實(shí)現(xiàn)的。1968年美國GM(通用汽車)公司提出取代繼電氣控制裝置的要求,第二年,美國數(shù)字公司研制出了基于集成電路和電子技術(shù)的控制裝置,首次采用程序化的手段應(yīng)用于電氣控制,這就是第一代可編程序控制器,稱Programmable Controller(PC)。</p><p> 個人計(jì)算機(jī)(簡稱PC)發(fā)展起來后,為了方便,也為了反映可編程控制器的功能特點(diǎn),可編程序控制器定名為Programmab
3、le Logic Controller(PLC)。</p><p> 上世紀(jì)80年代至90年代中期,是PLC發(fā)展最快的時期,年增長率一直保持為30~40%。在這時期,PLC在處理模擬量能力、數(shù)字運(yùn)算能力、人機(jī)接口能力和網(wǎng)絡(luò)能力得到大幅度提高,PLC逐漸進(jìn)入過程控制領(lǐng)域,在某些應(yīng)用上取代了在過程控制領(lǐng)域處于統(tǒng)治地位的DCS系統(tǒng)。</p><p> PLC具有通用性強(qiáng)、使用方便、適應(yīng)面廣、
4、可靠性高、抗干擾能力強(qiáng)、編程簡單等特點(diǎn)。PLC在工業(yè)自動化控制特別是順序控制中的地位,在可預(yù)見的將來,是無法取代的。</p><p> 1.2 PLC的構(gòu)成</p><p> 從結(jié)構(gòu)上分,PLC分為固定式和組合式(模塊式)兩種。固定式PLC包括CPU板、I/O板、顯示面板、內(nèi)存塊、電源等,這些元素組合成一個不可拆卸的整體。模塊式PLC包括CPU模塊、I/O模塊、內(nèi)存、電源模塊、底板或機(jī)
5、架,這些模塊可以按照一定規(guī)則組合配置。</p><p> 1.3 CPU的構(gòu)成</p><p> CPU是PLC的核心,起神經(jīng)中樞的作用,每套PLC至少有一個CPU,它按PLC的系統(tǒng)程序賦予的功能接收并存貯用戶程序和數(shù)據(jù),用掃描的方式采集由現(xiàn)場輸入裝置送來的狀態(tài)或數(shù)據(jù),并存入規(guī)定的寄存器中,同時,診斷電源和PLC內(nèi)部電路的工作狀態(tài)和編程過程中的語法錯誤等。進(jìn)入運(yùn)行后,從用戶程序存貯器中
6、逐條讀取指令,經(jīng)分析后再按指令規(guī)定的任務(wù)產(chǎn)生相應(yīng)的控制信號,去指揮有關(guān)的控制電路。</p><p> CPU主要由運(yùn)算器、控制器、寄存器及實(shí)現(xiàn)它們之間聯(lián)系的數(shù)據(jù)、控制及狀態(tài)總線構(gòu)成,CPU單元還包括外圍芯片、總線接口及有關(guān)電路。內(nèi)存主要用于存儲程序及數(shù)據(jù),是PLC不可缺少的組成單元。</p><p> 在使用者看來,不必要詳細(xì)分析CPU的內(nèi)部電路,但對各部分的工作機(jī)制還是應(yīng)有足夠的理解
7、。CPU的控制器控制CPU工作,由它讀取指令、解釋指令及執(zhí)行指令。但工作節(jié)奏由震蕩信號控制。運(yùn)算器用于進(jìn)行數(shù)字或邏輯運(yùn)算,在控制器指揮下工作。寄存器參與運(yùn)算,并存儲運(yùn)算的中間結(jié)果,它也是在控制器指揮下工作.CPU速度和內(nèi)存容量是PLC的重要參數(shù),它們決定著PLC的工作速度,IO數(shù)量及軟件容量等,因此限制著控制規(guī)模。</p><p><b> 1.4 I/O模塊</b></p>
8、<p> PLC與電氣回路的接口,是通過輸入輸出部分(I/O)完成的。I/O模塊集成了PLC的I/O電路,其輸入暫存器反映輸入信號狀態(tài),輸出點(diǎn)反映輸出鎖存器狀態(tài)。輸入模塊將電信號變換成數(shù)字信號進(jìn)入PLC系統(tǒng),輸出模塊相反。I/O分為開關(guān)量輸入(DI),開關(guān)量輸出(DO),模擬量輸入(AI),模擬量輸出(AO)等模塊。</p><p> 常用的I/O分類如下:</p><p>
9、; 開關(guān)量:按電壓水平分,有220VAC、110VAC、24VDC,按隔離方式分,有繼電器隔離和晶體管隔離。模擬量:按信號類型分,有電流型(4-20mA,0-20mA)、電壓型(0-10V,0-5V,-10-10V)等,按精度分,有12bit,14bit,16bit等。</p><p> 除了上述通用IO外,還有特殊IO模塊,如熱電阻、熱電偶、脈沖等模塊。</p><p> 按I/O
10、點(diǎn)數(shù)確定模塊規(guī)格及數(shù)量,I/O模塊可多可少,但其最大數(shù)受CPU所能管理的基本配置的能力,即受最大的底板或機(jī)架槽數(shù)限制。</p><p><b> 1.5 電源模塊</b></p><p> PLC電源用于為PLC各模塊的集成電路提供工作電源。同時,有的還為輸入電路提供24V的工作電源。電源輸入類型有:交流電源(220VAC或110VAC),直流電源(常用的為24V
11、DC)。</p><p><b> 1.6 底板或機(jī)架</b></p><p> 大多數(shù)模塊式PLC使用底板或機(jī)架,其作用是:電氣上,實(shí)現(xiàn)各模塊間的聯(lián)系,使CPU能訪問底板上的所有模塊,機(jī)械上,實(shí)現(xiàn)各模塊間的連接,使各模塊構(gòu)成一個整體。</p><p> 1.7 PLC系統(tǒng)的其它設(shè)備</p><p> 1.7.1
12、 編程設(shè)備:編程器是PLC開發(fā)應(yīng)用、監(jiān)測運(yùn)行、檢查維護(hù)不可缺少的器件,用于編程、對系統(tǒng)作一些設(shè)定、監(jiān)控PLC及PLC所控制的系統(tǒng)的工作狀況,但它不直接參與現(xiàn)場控制運(yùn)行。小編程器PLC一般有手持型編程器,目前一般由計(jì)算機(jī)(運(yùn)行編程軟件)充當(dāng)編程器。也就是我們系統(tǒng)的上位機(jī)。</p><p> 1.7.2 人機(jī)界面:最簡單的人機(jī)界面是指示燈和按鈕,目前液晶屏(或觸摸屏)式的一體式操作員終端應(yīng)用越來越廣泛,由計(jì)算機(jī)(運(yùn)
13、行組態(tài)軟件)充當(dāng)人機(jī)界面非常普及。</p><p> 1.8 PLC的通信聯(lián)網(wǎng)</p><p> 依靠先進(jìn)的工業(yè)網(wǎng)絡(luò)技術(shù)可以迅速有效地收集、傳送生產(chǎn)和管理數(shù)據(jù)。因此,網(wǎng)絡(luò)在自動化系統(tǒng)集成工程中的重要性越來越顯著,甚至有人提出"網(wǎng)絡(luò)就是控制器"的觀點(diǎn)說法。</p><p> PLC具有通信聯(lián)網(wǎng)的功能,它使PLC與PLC 之間、PLC與上位計(jì)算
14、機(jī)以及其他智能設(shè)備之間能夠交換信息,形成一個統(tǒng)一的整體,實(shí)現(xiàn)分散集中控制。多數(shù)PLC具有RS-232接口,還有一些內(nèi)置有支持各自通信協(xié)議的接口。PLC的通信現(xiàn)在主要采用通過多點(diǎn)接口(MPI)的數(shù)據(jù)通訊、PROFIBUS 或工業(yè)以太網(wǎng)進(jìn)行聯(lián)網(wǎng)。 </p><p> 2 PLC控制系統(tǒng)的設(shè)計(jì)基本原則</p><p> 2.1 最大限度的滿足被控對象的控制要求。</p><
15、;p> 2.2 在滿足控制要求的前提下,力求使控制系統(tǒng)簡單、經(jīng)濟(jì)、使用和維護(hù)方便。</p><p> 2.3 保證控制系統(tǒng)安全可靠。</p><p> 2.4 考慮到生產(chǎn)的發(fā)展和工藝的改進(jìn)在選擇PLC容量時應(yīng)適當(dāng)留有余量。</p><p> 3 PLC軟件系統(tǒng)及常用編程語言</p><p> 3.1 PLC軟件系統(tǒng)由系統(tǒng)程序和
16、用戶程序兩部分組成。系統(tǒng)程序包括監(jiān)控程序、編譯程序、診斷程序等,主要用于管理全機(jī)、將程序語言翻譯成機(jī)器語言,診斷機(jī)器故障。系統(tǒng)軟件由PLC廠家提供并已固化在EPROM中,不能直接存取和干預(yù)。用戶程序是用戶根據(jù)現(xiàn)場控制要求,用PLC的程序語言編制的應(yīng)用程序(也就是邏輯控制)用來實(shí)現(xiàn)各種控制。STEP7是用于SIMATIC可編程邏輯控制器組態(tài)和編程的標(biāo)準(zhǔn)軟件包,也就是用戶程序,我們就是使用STEP7來進(jìn)行硬件組態(tài)和邏輯程序編制,以及邏輯程序
17、執(zhí)行結(jié)果的在線監(jiān)視。</p><p> 3.2 PLC提供的編程語言</p><p> 3.2.1標(biāo)準(zhǔn)語言梯形圖語言也是我們最常用的一種語言,它有以下特點(diǎn) : 它是一種圖形語言,沿用傳統(tǒng)控制圖中的繼電器觸點(diǎn)、線圈、串聯(lián)等術(shù)語和一些圖形符號構(gòu)成,左右的豎線稱為左右母線。</p><p> 3.2.1.2 梯形圖中接點(diǎn)(觸點(diǎn))只有常開和常閉,接點(diǎn)可以是PLC輸入點(diǎn)
18、接的開關(guān)也可以是PLC內(nèi)部繼電器的接點(diǎn)或內(nèi)部寄存器、計(jì)數(shù)器等的狀態(tài)。</p><p> 3.2.1.3 梯形圖中的接點(diǎn)可以任意串、并聯(lián),但線圈只能并聯(lián)不能串聯(lián)。</p><p> 3.2.1.4 內(nèi)部繼電器、計(jì)數(shù)器、寄存器等均不能直接控制外部負(fù)載,只能做中間結(jié)果供CPU內(nèi)部使用。</p><p> 3.2.1.5 PLC是按循環(huán)掃描事件,沿梯形圖先后順序執(zhí)行,
19、在同一掃描周期中的結(jié)果留在輸出狀態(tài)暫存器中所以輸出點(diǎn)的值在用戶程序中可以當(dāng)做條件使用。</p><p> 3.2.2 語句表語言,類似于匯編語言。</p><p> 3.2.3 邏輯功能圖語言,沿用半導(dǎo)體邏輯框圖來表達(dá),一般一個運(yùn)算框表示一個功能左邊畫輸入、右邊畫輸出。</p><p> 4 STEP7程序的使用</p><p> 4
20、.1 創(chuàng)建一個項(xiàng)目結(jié)構(gòu),項(xiàng)目就象一個文件夾,所有數(shù)據(jù)都以分層的結(jié)構(gòu)存在于其中,任何時候你都可以使用。在創(chuàng)建一個項(xiàng)目之后,所有其他任務(wù)都在這個項(xiàng)目下執(zhí)行。</p><p> 4.2 組態(tài)一個站,組態(tài)一個站就是指定你要使用的可編程控制器,例如S7300、S7400等。</p><p> 4.3 組態(tài)硬件,組態(tài)硬件就是在組態(tài)表中指定你的控制方案所要使用的模板以及在用戶程序中以什么樣的地址來訪
21、問這些模板,地址一般不用修改由程序自動生成。模板的特性也可以用參數(shù)進(jìn)行賦值。</p><p> 4.4 組態(tài)網(wǎng)絡(luò)和通訊連接,通訊的基礎(chǔ)是預(yù)先組態(tài)網(wǎng)絡(luò),也就是要創(chuàng)建一個滿足你的控制方案的子網(wǎng),設(shè)置網(wǎng)絡(luò)特性、設(shè)置網(wǎng)絡(luò)連接特性以及任何聯(lián)網(wǎng)的站所需要的連接。</p><p> Come into PLC</p><p> 1 Development course of
22、 PLC</p><p> In the course of industrial production, a large number of switch amount orders are controlled, it carries on order movements according to the logic condition , and carry on the control that the
23、 chain protected movements according to the logic relation, and the data of a large number of dispersed quantity are gathered . Traditionally, these functions were realized through the pneumatic or electric control syste
24、m. The Company put forward and replaced the demand which continued the electric control</p><p> After the personal computer ( abbreviated as PC ) develops, for being convenient, in order to reflect the func
25、tion characteristic of the programmable controller too, can programme controller name Programmable Logic Controller (PLC).</p><p> The eighties of last century is to the middle period of the 1990s, it was P
26、LC the period with the fastest developing speed, the annual growth kept 300%. This period, PLC is improved by a large margin in power to dispose of analog quantity , digital operation ability , man-machine interface abil
27、ity and network ability , PLC enters the course controlled field gradually, has replaced and in DCS system ruling position on the course controlled field in some is used. </p><p> PLC have commonability to
28、be strong easy to use meeting surface wide , dependability high , anti-interference ability strong , programming characteristicking such as being simple. The position in PLC is controlled in the industrial automation esp
29、ecially the order is controlled, in foreseeable future, can replace. </p><p> 1.2 Composition of PLC </p><p> Divide from structure, PLC is divided into a regular type and sectional (module ty
30、pe ) two kinds</p><p> Regular type PLC including CPU board , I/O board , showing the panel , memory lump , power ,etc., these elements are made up into a whole not detachable . Module type PLC includes CPU
31、 module , I/O module , memory , power module , the baseplate or the framework, the module can be made up and disposes according to certain rule. </p><p> 1.3 Composition of CPU </p><p> CPU i
32、s a core of PLC, functions as nerve center, each set of PLC has one CPU at least, it receives and stores user's procedure and data according to the function that the systematic procedure of PLC gives, gathered and in
33、put the state or data that the device sends here live by means of scanning, deposit register that stipulate , meanwhile , diagnose power and working state and grammar mistake ,etc. , programming of course of circuit insi
34、de the PLC. Enter after running, read the order one by one </p><p> CPU and realizes by arithmetic unit , controller , register mainly the data , control and state bus of the connection among them are forme
35、d , unit CPU still includes peripheral chip , interface of the bus and relevant circuit. The memory is used for storing the procedure and data mainly, is indispensable composition unit PLC. </p><p> In user
36、's view , it is unnecessary to analyse the inside circuit of CPU in detail, but there should be enough understanding to the working mechnism of every part. The controller of CPU controls CPU and works, is read the or
37、der, explained the order and executed instruction by it. But working rhythm is controlled from the signal of shaking . The arithmetic unit is used for carrying on figures or logic operation, work under the circumstances
38、that the controller is commanded. The register is partici</p><p> CPU speed and capacity of memory are important parameters of PLC, they are determining the working speed of PLC, IO quantity and capacity of
39、 software,etc., so is exercising restraint in controlling the scale . </p><p> 1.4 I/O module</p><p> The interface of PLC and electric return circuit , finished through inputting the output (
40、I/O ). I/O circuit of I/O module integrated PLC, it is input temporarily the storing device reflects the state of the input signal, export and click and reflect that exports the state of the latch. Input module vary elec
41、tric signal digital signal enter PLC system , output module to be opposite. I/O is divided and imported (DI) for the switch amount, the switch amount is exported (DO), analog quantity is inp</p><p> Commonl
42、y used I/O is classified as follows: </p><p> Switch amount: Divide according to the voltage level, there are 220VAC , 110VAC , 24VDC , divide according to the way of isolating, there are relays that are is
43、olated and isolated with the transistor. Analog quantity: Divide according to the signal type, the electric current type (4-20mA , 0-20mA ) , voltage having type (0-10V, 0-5V,- 10-10V),etc.,it is according to precision f
44、en, there is 12bit , 14bit, 16bit ,etc.. </p><p> Besides above-mentioned IO in common use , there is special IO module , for instance such module as thermal resistance , electric thermocouple , pulse ,etc.
45、. Is it confirm module specification and quantity to count according to I/O, I/O module but many and very little, its great number receive CPU can basic ability of disposition of management most, namely is counted the re
46、striction by the biggest baseplate or the framework trough . </p><p> 1.5 Power module </p><p> PLC power is used for offering the working power for integrated circuit of every module of PLC.
47、Meanwhile, some still offer the working power of 24V for inputting the circuit. The type is as follows, that the power imports Exchange the power (220VAC or 110VAC ), direct current power (a commonly used one is 24VDC).
48、</p><p> 1.6 The baseplate or the framework</p><p> Most module type PLCs use the baseplate or the framework, its function is: Have electrically, realize the connection among every module , en
49、able CPU to visit all module on the baseplate, on machinery , realize the connection among every module , make every module form a whole . </p><p> 1.7 Other equipment of PLC system </p><p> 1
50、. 7.A programming equipment: The programmable device is that PLC develops and adopts, monitors operating, checks and maintains the indispensable device, used in programming , do some settlement , working state controllin
51、g the system that PLC and PLC control to the system, but it does not participate in directly and control and run live . The small programmable device PLC generally has holding type programmable device, generally the comp
52、uter (operates the programming software ) makes programmabl</p><p> 1.7.B Man-machine interface: The simplest man-machine interface is indicator lamp and button, the liquid crystal reject (or the touch-sens
53、itive screen ) an organic whole type operator's terminal station of the type and use more and more extensive at present, it is popularized very much that the computer (operation configuration software ) makes man-mac
54、hine interface.</p><p> 1.8 The communication of PLC is networked </p><p> May collect , convey producing and manage the data promptly and efficiently while relying on the advanced industrial
55、network technology. So, the importance of the network in the automatic system integration project is more and more remarkable, even someone proposes the view statement that " the network is the controller " .&l
56、t;/p><p> PLC have function that communication network, it make PLC and between the PLC , PLC with go to location computer and other intellectual equipment can exchange information , form a unified whole, real
57、ize dispersing centralized control. Most PLC has RS-232 interface, puts and supports the interface of each communication protocol when there is some. Communication of PLC adopt through some data communication , PROFIBUS
58、or industry's Ethernet of interface (MPI ) network more mainly now. </p><p> 2. Design basic principle of PLC control system</p><p> 2.1 Meet the control request which is accused of the ta
59、rget maximumly. </p><p> 2.2 On the premise of meeting control request , is it make control system simple , economy , use and maintain convenient to make every effort. </p><p> 2.3 Guarantee t
60、he control system is safe and reliable. </p><p> 2.4 Consider the development of production and improvement of the craft should leave the surplus properly while choosing PLC capacity. </p><p>
61、 3. PLC software system and daily programming language </p><p> 3.1 PLC software system is made up of systematic procedure and user's procedure . The systematic procedure includes controlling procedure
62、, compiler , diagnostic program ,etc., used for manage the whole machine , translate the procedure language into a machine languaging mainly, diagnose the mechanical disorder. Systems soft ware offer by PLC producer and
63、solidification among EPROM, can't direct access interfere from already. User procedure whether user according to on-the-spot control request, </p><p> 3.2 Programming language that PLC offers </p>
64、<p> 3.2.1The ladder-shaped picture language of standard language is a kind of most frequently used languages of ours too, it has the following characteristic </p><p> 3.2.1.1 It is a kind of figur
65、e language, term of continuing to use relay contact , coil that the tradition controls in pictures , contacting etc. and some graphical symbols are formed , the vertical line of left and right sides is called and control
66、led the bus bar. </p><p> 3.2.1.2 The contact (contact ) only often opens and often closes in the ladder-shaped picture, the contact can be that can be a state of contact or inside register , counter of the
67、 relay ,etc. within PLC too that PLC input and click the switch connected . </p><p> 3.2.1.3 Contact of ladder-shaped picture can wanton bunch, connect in parallel, the coil can only be connected in paralle
68、l and can contact . </p><p> 3.2.1.4 Inside relay , counter , register ,etc. can't directly control outside load , can only make middle result to use while supporting CPU . </p><p> 3.2.1.
69、5 PLC scans the incident according to circulation, carry out along the priority order of the ladder-shaped picture, result of the cycle stay in state of outputting temporarily in the person who deposit so value ordered t
70、o output can regard as terms use among the procedure in user in the same scanning. </p><p> 3.2.2 Sentence predicative speech , is similar to the assembler language . </p><p> 3.2.3 Logic func
71、tional diagram language, continue to use semiconductor logic block diagram is it express to come, one operation frame generally show one function on the left draw introduction , on the right paint and export. </p>
72、<p> 4 Use the programe of STEP7</p><p> 4.1 Establishing a project structure, the project is just like a file, all data exist among them with the structure of dividing floor, you can use at any time
73、. After establishing a project, all other tasks are carried out under this project. </p><p> 4.2 Configuration one station, configuration one station to appoint you want programmable controller that use, su
74、ch as S7300 , S7400 ,etc.. </p><p> 4.3 Configuration hardware, configuration hardware appoint control scheme of you want template that use and with what kind of address visit these template among the proce
75、dure in user among the form in configuration, the address needn't generally be revised and produced automatically by the procedure. The characteristic of the template can carry on assignment with the parameter too.
76、 </p><p> 4.4 Configuration network and communication connect, the foundation of the communication is the configuration network in advance , is it is it establish one meet control sub network of scheme of y
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