畢業(yè)設(shè)計(jì)英文翻譯Programmable_logic.doc

附錄Programmable logic controllerCynthia CooperFrom Wikipedia, the free encyclopediaA programmable logic controller or simply programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.FeaturesControl panel with PLC (grey elements in the center). The unit consists of separate elements, from left to right; power supply, controller, relay units for input and output.The main difference from other computers is that PLCs are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.PLCs were invented as replacements for automated systems that would use hundreds or thousands of relays, cam timers, and drum sequencers. Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the re-wiring of hard-wired control panels when production models changed.Many of the earliest PLCs expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. The electricians were quite able to trace out circuit problems with schematic diagrams using ladder logic. 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 stack-based logic solver.The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications.Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers.PLC compared with other control systemsPLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation.PLCs contain input and output devices compatible with industrial pilot devices and controls.PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a generic solution。 For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities.A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies and input/output hardware) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such as transit busses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic.Very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls.PLCs may include logic for single-variable feedback analog control loop, a proportional, integral, derivative or PID controller. A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. However, as PLCs have become more powerful, the boundary between DCS and PLC applications has become less clear-cut.Digital and analog signalsDigital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Push buttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate values undefined. Initially, PLCs had only discrete I/O.Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data. As PLCs typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog 4-20 mA or 0 - 10V input would be converted into an integer value of 0 - 32767.ExampleAs an example, say a facility needs to store water in a tank. The water is drawn from the tank by another system, as needed, and our example system must manage the water level in the tank.Using only digital signals, the PLC has two digital inputs from float switches (tank empty and tank full). The PLC uses a digital output to open and close the inlet valve into the tank.When the water level drops enough so that the tank empty float switch is off (down), the PLC will open the valve to let more water in. Once the water level raises enough so that the tank full switch is on (up), the PLC will shut the inlet to stop the water from overflowing.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 flutter adjustments that can wear out the valve, many PLCs incorporate hysteresis which essentially creates a deadband of activity. A technician adjusts this deadband so the valve moves only for a significant change in rate. This will in turn minimize the motion of the valve, and reduce its wear.A real system might combine both approaches, using float switches and simple valves to prevent spills, and a rate sensor and rate valve to optimize refill rates and prevent water hammer. Backup and maintenance methods can make a real system very complicated.System scaleA small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expansions are available if the base model does not have enough I/O.PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI (Human-Machine Interface) devices such as keypads or PC-type workstations. Some of todays PLCs can communicate over a wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at network speeds up to 100 Mbit/s.ProgrammingEarly PLCs, up to the mid-1980s, were programmed using proprietary programming panels or special-purpose programming terminals. they 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.Recently, the International standard IEC 61131-3 has become popular. IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations.While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.User interfacePLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control. A Human-Machine Interface (HMI) is employed for this purpose. HMIs are also referred to as MMIs (Man Machine Interface) and GUI (Graphical User Interface).A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser.CommunicationsPLCs usually have built in communications ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. Modbus or DF1 is usually included as one of the communications protocols. Others options include various fieldbuses such as DeviceNet or Profibus. HistoryThe PLC was invented in response to the needs of the American automotive industry. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using relays, timers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as the relay systems needed to be rewired by skilled electricians. In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems.The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates eighty-fourth project, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for MOdular DIgital CONtroller. One of the people who worked on that project was Dick Morley, who is considered to be the father of the PLC. The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner.The automotive industry is still one of the largest users of PLCs, and Modicon still numbers some of its controller models. PLCs are used in many different industries and machines such as packaging and semiconductor machines. Well known PLC brands are Toshiba, Siemens, Allen-Bradley, ABB, Mitsubishi, Omron, and General Electric.附錄B 中文翻譯可編程邏輯控制器辛西婭.庫珀維基自由百科全書可編程邏輯控制器或者簡易可編程控制器是一種數(shù)字化的計(jì)算機(jī)，它應(yīng)用于工業(yè)自動(dòng)化的生產(chǎn)過程中，比如工廠裝配生產(chǎn)線中機(jī)械的控制。不同于普通用途的計(jì)算機(jī)，可編程邏輯控制器是專為安排多輸入和多輸出而設(shè)計(jì)的，它拓展了工作溫度范圍，可抑制電氣噪聲，抗振動(dòng)和干擾。Programs to control machine operation are typically stored in battery-backed or non-volatile memory.程序控制機(jī)器操作指令通常存儲在備用電池或非易失性存儲器中。A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will resulPLC要求實(shí)時(shí)系統(tǒng)的輸出結(jié)果在一個(gè)時(shí)間范圍內(nèi)必須對輸入條件做出響應(yīng)，否則會導(dǎo)致意想不到的結(jié)果。特征PLC的 Control panel with PLC (grey elements in the center).控制面板（灰色元素的中心），它的每個(gè)The unit consists of separate elements, from left to right; power supply , controller, relay units for in- and output單位都是由單獨(dú)的元素組成的，由左向右分別是：電源供應(yīng)器，控制器，繼電器單元的輸入輸出。PLC和其他計(jì)算機(jī)的The main difference from other computers is that PLCs are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements.主要區(qū)別是它適用于各種惡劣環(huán)境條件下（如灰塵，潮濕，高溫，低溫等），并配備了適合于各種輸入/輸出端口的設(shè)備。 These connect the PLC to sensors and actuators .這些設(shè)備將PLC連接到相應(yīng)的傳感器和信號發(fā)生器上。PLCs read limit switches , analog process variables (such as temperature and pressure), and the positions of complex positioning sPLC可以定義各種開關(guān)量，模擬量（如溫度和壓力等）用來配置各種復(fù)雜系統(tǒng)的各種變量，一些PLC甚至還需要使用機(jī)器視覺。在On the actuator side, PLCs operate electric motors , pneumatic or hydraulic cylinders, magnetic relays or solenoids , or analog outputs.在在信號發(fā)生器方面，PLC可以控制的設(shè)備有電動(dòng)機(jī)，氣壓缸或液壓缸，電磁繼電器或螺線管繼電器，以及一些模擬輸出設(shè)備。通過The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.輸入/輸出模塊的配置，可以構(gòu)建一個(gè)簡單的PLC系統(tǒng)。這個(gè)PLC系統(tǒng)可以通過外部I/O模塊連接到一個(gè)計(jì)算機(jī)網(wǎng)絡(luò)上。PLC的出現(xiàn)改變了過去使用成百上千的繼電器，凸輪定時(shí)器，鼓音序器來構(gòu)建一個(gè)自動(dòng)化系統(tǒng)的時(shí)代。Often, a single PLC can be programmed to replace thousands of relays .通常，一個(gè)簡單可編程控制器通過編程，以取代成千上萬的繼電器。 Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the re-wiring of hard-wired control panels when production models changed.可編程控制器最初應(yīng)用于汽車制造業(yè)中，軟件修改取代了硬連線控制面板的重新布線，這標(biāo)志著生產(chǎn)模式發(fā)生了徹底的改變。許多早期的PLC設(shè)計(jì)表明，在簡單的梯形邏輯的決策中，已經(jīng)出現(xiàn)了類似梯形圖的電氣原理圖。The electricians were quite able to trace out circuit problems with schematic diagrams using ladder logic.電工們通過使用梯形邏輯能夠很方便的查找出電路示意圖的問題。This program notation was chosen to reduce training demands for the existing technicians.這項(xiàng)計(jì)劃符號的選擇使用可以降低培訓(xùn)其現(xiàn)有的技術(shù)人員的要求。而Other early PLCs used a form of instruction list programming, based on a stack-based logic solver.其他早期的PLC則使用一種基于堆棧的邏輯解決方法指令表編程的方式。 PLC的功能經(jīng)過多年的發(fā)展，已經(jīng)包括順序控制，運(yùn)動(dòng)控制，過程控制，分布式控制系統(tǒng)和網(wǎng)絡(luò)控制系統(tǒng)等多個(gè)方面。一些現(xiàn)代的PLC的The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers .數(shù)據(jù)處理，儲存，整理能力和通信能力，已大約相當(dāng)于臺式電腦了。PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain application可編程控制器的編程結(jié)合遠(yuǎn)程I/O硬件，允許通用臺式電腦進(jìn)行一些PLC方面的特定應(yīng)用。根據(jù)國際電工委員會61131-3標(biāo)準(zhǔn)，PLC的編程可以使用基于標(biāo)準(zhǔn)的編程語言。所謂順序功能圖的圖形符號編程適用于某些特定的可編程控制器。可編程控制器與其他控制系統(tǒng)PLC可以很好的適應(yīng)各種自動(dòng)化任務(wù)。這些都是典型的工業(yè)機(jī)械生產(chǎn)，在這些部門自動(dòng)控制系統(tǒng)的高額費(fèi)用是與其昂貴的的制造維護(hù)費(fèi)用分不開的。PLC能控制輸入輸出設(shè)備并兼容工業(yè)試驗(yàn)裝置和控制。通常PLC應(yīng)用于高度定制的系統(tǒng),以便使組裝PLC的成本低于設(shè)計(jì)控制器的成本。另外，在大規(guī)模生產(chǎn)產(chǎn)品方面，自定義的控制系統(tǒng)是經(jīng)濟(jì)的，由于他的組成部分成本較低。這是代替通用解決方案的最佳選擇。為大批量或者簡單的固定自動(dòng)化任務(wù)，不同的技術(shù)被采用。例如：消費(fèi)者洗碗機(jī)被成本只有幾美元的機(jī)電凸輪計(jì)時(shí)器控制。微處理器的設(shè)計(jì)要考慮成百上千的組成單元，以便開發(fā)成本（電源供應(yīng)器和輸入輸出硬件的設(shè)計(jì)）能遍布到很多銷售領(lǐng)域，并且最終用戶不需要改變控制。汽車應(yīng)用是一個(gè)例子，每年有數(shù)以百萬輛汽車被制造，只有極少數(shù)最終用戶改變控制程序。然而，一些特殊車輛，如使用PLC系統(tǒng)代替定制設(shè)計(jì)控制的過境巴士因?yàn)槭褂昧可偎蚤_發(fā)費(fèi)用不夠經(jīng)濟(jì)。復(fù)雜的過程控制，如用于化學(xué)工業(yè)的過程控制要求的算法和性能甚至超過了高性能的PLC控制。高速度和精度的控制也可能需要量身定制的解決方案，如飛機(jī)的飛行控制。PLC系統(tǒng)包括邏輯單變量反饋模擬控制回路，一個(gè)“比例、積分、導(dǎo)數(shù)”或“控制器”。PID回路可用于控制制造過程的溫度，例如歷史上的PLC通常只用于少數(shù)模擬控制回路這個(gè)過程需要成百上千的循環(huán)、分布式控制系統(tǒng)（DCS）將代替使用。然而，由于PLC的功能越來越強(qiáng)大，DCS與PLC的界定越發(fā)的不明確。數(shù)字和模擬信號數(shù)字或離散信號表現(xiàn)為二進(jìn)制開關(guān)信號，收益率只是一個(gè)閉合或關(guān)斷信號。按鈕、限位開關(guān)、光電傳感器能提供了一個(gè)離散信號。離散信號以電壓或電流的形式傳送，它在一個(gè)特定的范圍內(nèi)被設(shè)置成開和關(guān)。例如：PLC必須使用24伏直流電壓的I/O口，高于22伏直流電壓代表開，低于2伏直流電壓代表關(guān)，中間值不確定。最初，PLC只有離散的I/O接口。模擬信號和音量控制一樣，在零和滿量程之間有一系列的值。這些常常被定義為PLC中的整數(shù)，它的范圍取決于設(shè)備中可用來存儲比特?cái)?shù)據(jù)的存儲單元的數(shù)量。由于PLC通常使用16位有符號二進(jìn)制處理器，整數(shù)值被限定在-32768+32767之間。壓力、溫度、流量、重量往往代表的模擬信號。模擬型號可以使用與原信號成正比的電壓或電流信號。例如：一個(gè)4-20mA的電流信號或者0-10V的電壓信號將被轉(zhuǎn)化成一個(gè)0-32767之間的整型值。事例水箱可以作為一個(gè)例子。一個(gè)設(shè)備用于向水箱中注水，另一個(gè)設(shè)備用于從水箱中取水，根據(jù)需要，我們必須建立一個(gè)系統(tǒng)去控制水箱的水位。若只用數(shù)字信號，PLC有兩個(gè)數(shù)字輸入開關(guān)量（水箱空和水箱滿）。PLC有一個(gè)數(shù)字輸出量去控制水箱閥門的開關(guān)。當(dāng)水位下降使得水箱空箱開關(guān)關(guān)閉時(shí)，PLC將會打開閥門使更多的水進(jìn)入。一旦水位升高到一定高度使得滿箱開關(guān)閉合，PLC將會臨時(shí)關(guān)閉進(jìn)水閥門防止水的溢出。一個(gè)模擬系統(tǒng)可能會使用水位的壓力傳感器、可調(diào)（節(jié)流）出水閥和調(diào)節(jié)閥來逐漸提高水箱水位。在這一系統(tǒng)中，為了避免損壞閥的擾動(dòng)調(diào)節(jié)器，很多的PLC加入“滯后”環(huán)節(jié)，基本上實(shí)現(xiàn)了“死區(qū)”的活動(dòng)。 A technician adjusts this deadband so the valve moves only for a significant change in rate.技術(shù)員通過調(diào)整死區(qū)，使閥只在有一個(gè)顯著變化率的時(shí)刻動(dòng)作。This will in turn minimize the motion of the valve, and reduce its wear.這將依次把閥門的動(dòng)作減到最少，從而減少其磨損。一個(gè)真正的系統(tǒng)可能把這兩種做法結(jié)合起來，使用浮動(dòng)開關(guān)和簡單閥門來防止泄漏，使用速率傳感器和速度閥來優(yōu)化水位上升速率并防止水錐的發(fā)生?？紤]到Backup and maintenance methods can make a real system very complicated.支持性的維護(hù)方法，一個(gè)實(shí)際的系統(tǒng)將會非常復(fù)雜。系統(tǒng)規(guī)模A small PLC will have a fixed number of connections built in for inputs and outputs.一個(gè)小型PLC將有固定數(shù)量的I/O接口。Typically, expansions are available if the base model does not have enough I/O.通常情況下，如果相應(yīng)的模型并沒有足夠的I/O接口，則需要擴(kuò)展I/O口。在較大的I/O系統(tǒng)中，PLC可能使用點(diǎn)對點(diǎn)（P2P）的處理器通信。This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link.這使得一個(gè)復(fù)雜過程的單獨(dú)部分有各自的控制，同時(shí)又允許各子系統(tǒng)同級之間進(jìn)行通信聯(lián)系。These communication links are also often u