【正文】 High Level switch is on (up), the PLC will shut the inlet to stop the water from overflowing. This rung is an example of seal in logic. The output is sealed in until some condition breaks the circuit. | | | Low Level High Level Fill Valve | |[/]|[/](OUT)| | | | | | | | | | | Fill Valve | | |[ ]| | | | | | An analog system might use a water pressure sensor or a load cell, and an adjustable (throttling) dripping out of the tank, the valve adjusts to slowly drip water back into the tank. In this system, to avoid 39。s headquarters in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its automotive industry is still one of the largest users of PLCs. Development Early PLCs were designed to replace relay logic systems. These PLCs were programmed in ladder logic, which strongly resembles a schematic diagram of relay logic. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a Very High Level Programming Language designed to program PLCs based on State Transition Diagrams. Many of the earliest PLCs expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stackbased logic solver. Programming Early PLCs, up to the mid1980s, were programmed using proprietary programming panels or specialpurpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. The very oldest PLCs used nonvolatile magic core memory. Functionality The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and working. The data handling, storage, processing power and munication capabilities of some modern PLCs are approximately equivalent to desktop puters. PLClike programming bined with remote I/O hardware, allow a generalpurpose desktop puter to overlap some PLCs in certain applications. 可編程邏輯控制器 可編程邏輯控制器（ PLC）或可編程控制器是一種數(shù)字化的用于機(jī)電自動化進(jìn)程的計(jì)算機(jī)，如控制工廠機(jī)器的組裝生產(chǎn)線，機(jī)動游戲機(jī)，或照明裝置。 PLC 是一個(gè)時(shí)間系統(tǒng)的例子，因?yàn)樵谝欢ǖ臅r(shí)間范圍內(nèi) , 顯示針的輸出結(jié)果必須輸入系統(tǒng)，否則會導(dǎo)致意想不到的結(jié)果。一些使用機(jī)器視覺。通常情況下，如果基礎(chǔ)模板沒有足夠的輸入 /輸出系統(tǒng) ,模板可以 得到擴(kuò)展。把一系列特殊的高速的輸入 /輸出系統(tǒng)連結(jié)起來使用，可以使機(jī)架分散并遠(yuǎn)離處理器，從而降低了大型工廠的布線成本。人機(jī)界面又被稱為多媒體資訊系統(tǒng)（人機(jī)界面）和 GUI（圖形用戶界面） 。 Modbus 協(xié)議， BAC 或 DF1 通常包含在一個(gè)通信協(xié)議內(nèi)。 PLC 在較大輸入 /輸出系統(tǒng)的應(yīng)用需要有處理器之間點(diǎn)對點(diǎn)（ P2P）的通訊。 可編程序邏輯控制器與其它控制系統(tǒng)的比較 PLC 能很好地適應(yīng)各種自動化任務(wù)。 為了達(dá)到高容量和非常固定的簡單自動化任務(wù)，需要使用不同的技術(shù)。數(shù)以百萬計(jì)的單位都要建立，每年只有極少數(shù)最終用戶需要改變這些控制器的編程。 可編程控制器被廣泛應(yīng)用于機(jī)動控制，定位控制和轉(zhuǎn)矩控制。它的運(yùn)行需要數(shù)百或數(shù)千個(gè)循環(huán)，這樣就使得分布式控制系統(tǒng)（ DCS）代替了它。語言功能塊程序編寫使用遠(yuǎn)程終端單元和 PLC 的國際電工委員會行業(yè)標(biāo)準(zhǔn) 611313，但幾乎所有的供應(yīng)商也提供專有的替代品和相關(guān)的軟件開發(fā)環(huán)境。例如， PLC 會使用高于 22A 直流電的 24A 直流電輸出開的信號 ，低于 2A 的輸出關(guān)，但它的中間值未定義。由于 PLC 通常使用 16 個(gè)符號的二進(jìn)制處理器，整數(shù)值在 32,768 和 32767 之間是有限。 對于電氣噪聲（即從焊工或電動馬達(dá)啟動）來說，電流的輸入沒有電壓輸入敏感。當(dāng)水位高于開關(guān)時(shí)， PLC 結(jié)束工作，并傳遞一個(gè)輸入信號。信號不斷輸出，直到這條環(huán)路的尾端才停止。這樣反過來又將最大限度地減少閥門的運(yùn)動，并減少其磨損。該程序是儲存在 PLC 的電池備份 RAM 或其他一些非揮發(fā)快閃記憶體。 最近，國際標(biāo)準(zhǔn) IEC 611313 已得到普遍使用。即使在單一制造商的同一產(chǎn)品線，不同的 PLC 模型可能無法直接兼容。每年的模 型轉(zhuǎn)換設(shè)施更新過程是非常耗時(shí)和昂貴的，因?yàn)槔^電系統(tǒng)需要熟練技工重鋪電線。貝德福德協(xié)會開辦了一個(gè)新的公司，致力于開發(fā)，制造，銷售和服務(wù)這一新的產(chǎn)品：象征著模塊化數(shù)字控制器的莫迪康。莫迪康在其產(chǎn)品系列的最后還是使用 84 綽號，直到 984 被發(fā)明?，F(xiàn)代 PLC 可以用不同的各種方式編程，這些方式可以是從梯形邏輯到更傳統(tǒng)的編程語言，如 BASIC 語言和 C 語言。在更早的時(shí)候， PLC 使用基于邏輯解算器的某種形式指令表。古老的 PLC 用非揮發(fā)性磁芯存儲器。