毕业论文（设计）外文翻译
题目：可编程逻辑控制器技术
系部名称：信息工程系专业班级：
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2014 年3 月XX 日
译文
可编程逻辑控制器技术
引言
PLC（可编程逻辑控制器）实际是一个工业控制系统（近来我们看到更多的是用处理器来取代微控制器），在软件和硬件都配备的条件下，适合应用于工业环境。PLC 的发明是相当必要的，它代替了传统的依靠由继电接触器电路来控制电机。PLC 的工作原理是根据它的输入信号和工作状态来确定输出。用户通常是通过软件或编程输入一个程序，来输出所需要的结果。
如图 8-1 所示，PLC 是由典型的黑色构件组成。特别需要注意的是它的输入和输出，
因为在这些模块上，工业环境会给 CPU 一个输入线，所以很有必要将 CPU 模块隔离以保护其免遭有害的影响。程序单元通常是用计算机来编写程序（一般是梯形图）。
1.1CPU 的中央处理单元
中央处理单元（CPU）是一个 PLC 的主控制器。一般 CPU 本身是一个微控制器。通常这些都是 8 位微控制器，如 8051 ，现在的这些是 16 位和 32 位微控制器。潜规则是，你会发现用在 PLC 控制器上的微控制器多数是由日本生产的日立和富士通，欧洲的西门子控制器，和美国的摩托罗拉微控制器。CPU 也负责通讯，与 PLC 控制器的其它部分相互联系，如程序执行，内存操作，监督输入和设置输出。PLC 控制器拥有复杂的程序用于内存检查，以确保 PLC 内存不被损坏（内存检查是为了安全原因而作出的）。一般来说，CPU 单元多数用来检查 PLC 控制器本身，所以有可能出现的错误很早就会被发现。你可以简单地看任何 PLC 控制器,查看错误信号在发光二极管上的种种指示形式。
1.2内存
系统内存（今天主要是在 FLASH 技术上实现）用于一台 PLC 的过程控制系统。除了
这个操作系统它还包含用户程序将梯形图翻译成二进制的形式。 FLASH 存储器的内容仅在
用户程序改变下可以改变。PLC 控制器较早被用来代替闪存，EPROM 存储器代替了那些只能依靠紫外线灯等擦除内存并依靠程序员来编程的 FLASH 存储器。在 FLASH 技术的作用下这个过程被大大的缩短了。重组程序内存通过程序中的串行通讯用于应用程序开发。使用内存被划分成多个具有特殊功能的模块。存储器某些部分用来存储输入状态和输出状态。一个
输入信号的实际状态是用 1 或0 存储在一个特定的存储位。每一个输入信号和输出信号在内存里都有一个位与之相对应。内存的其他部分用来存储用户程序中使用的变量以及变量的内容。例如，定时器的值和计数器的值都将被存储在这部分内存里。
1.3PLC 控制器的编程
PLC 控制器可以通过计算机（常用的方式）进行编程，还可以通过手动编程器（控制台）编程。这实际上意味着如果你有需要的编程软件那么每个 PLC 控制器都可以通过计算机进行编程。今天的传输计算机是非常适合在工厂对 PLC 控制器进行编程的。这对工业有着非常重要的意义。一旦系统被刷新，重新读取正确的程序到 PLC 就很重要。还可以定期检查 PLC 中的程序是否改变了。这有助于避免在工厂车间发生危险状况（部分汽车制造商建立了通信网络，定期检查项目中的 PLC 控制器，以确保执行的程序是正确的）。
几乎每一个编程 PLC 控制器的程序都具备各种有用的选项，如：强制开关系统的输入/输出（I / O 线），程序实时跟踪和记录图。这个记录对于理解，检查错误和故障都是很有必要的。程序员可以添加标记，输入或输出设备名称，当发生故障或者系统维护时，注解都很有
帮助。添加注释和标记可以使技术人员（不仅仅是开发人员）马上明白梯形图。如果需
要更换零件，注释和标记甚至可以准确地引用零件号码。这将加快由于损坏零件而引起
的任何问题的修理速度。传统方式中，开发系统的人必须保护这个程序，除了这个人没
有人能理解它是如何完成的，所以正确记录的梯形图可使任何技术人员都能彻底理解系
统的功能。
1.4电源
供电是将电能供给中央处理单元。大部分 PLC 控制器是在 24V 直流或 220V 交流电下
工作。某一些 PLC 控制器，它的电源是作为独立的模块。这些通常是更大的 PLC 控制器，
而中小型系列已经包含电源模块。用户必须确定 I/O 模块需要多大电流，以确保电源提供适当的电流。不同类型的模块使用不同的电流量。该电源一般不用于启动外部输入或输出。用户必须提供独立的电源启动 PLC 控制器的输入或输出，因为这样可以保证所谓的PLC 控
制器“纯”供应。使用纯电源意味着工业环境不会严重影响到它。一些较小的 PLC 控制器，给
它们的输入提供的电压是来自于已经嵌入 PLC 里面的小型电压源。
1.5PLC 控制器的输入
一个自动化系统的智能化在很大程度上取决于一个 PLC 控制器从不同类型的传感器和输入设备上读取信号的能力。键，键盘和功能开关是人与机器之间关系的基础。另一方面，为了检测工件，在运动观的一种机制，检查压力或液位需要特定的自动设备，如接近传感器，边缘开关，光电传感器，液位传感器。因此，输入信号可以是逻辑（开/关）或模拟量。小型PLC 控制器通常只有数字输入线，而大型的也可以通过特殊的单元将模拟量输入连接到 PLC 控制器。最常见的一个模拟信号是通过各种传感器所产生的 4 到20 毫安的电流信号和毫伏电压信号。传感器通常用作 PLC 的输入。你可以获得不同用途的传感器。他们可以检测到
一些地方存在测量温度，压力，或一些其他的物理量等（如电感式传感器可以计数金属物体）。其他设备也可以作为 PLC 控制器的输入。智能设备如：机器人，视频系统等，它们
往往能够发送信号到 PLC 控制器的输入模块（例如，当机器人完成了将物体从一个地方移动到另一个地方时，可以发送一个信号给 PLC 控制器作为输入信号）。
1.6输入界面调整
调整界面可视为在输入线和 CPU 单元之间放置一个接口。界面调节的目的是为了保
护 CPU 免遭外部环境中不成比例信号的影响。输入调整模块是为了转换一个与 CUP 单元相
合适的标准逻辑（如从传感器输入的 24V 直流必须转换为 DC 5V 信号给 CPU，以便能够对
其进行处理）。这通常是通过光电隔离，这种功能可以查看图 8-2。光电隔离意味着外部
环境和 CPU 单元之间没有电连接。它们是“光学”隔开，或者换句话说，信号通过光传输。其工作原理很简单。外部设备带来了一个信号，传输到 LED 上使其亮，其光又煽动照
片晶体管从而开始导通，这在 CPU 认为是逻辑零（集电极和发射器之间的电源电压
降至低于 1V 以下）。当输入信号停止，LED 二极管熄灭，晶体管停止导通，集电极电压增大，CPU 接收到逻辑 1 的信息。
1.7PLC 控制器的输出
自动化系统如果不与某些输出设备相连接是不完整的。一些最常用的设备如电机，电磁阀，继电器，指示灯，和类似的声音信号。通过启动电机，或继电器，PLC 可管理或控制一个单一的系统，如产品分类系统一直到复杂的系统，数控机床的定位头服务系统。输出类型可以是模拟量或数字。数字输出信号可以作为一个开关，它连接和断开连接线。模拟输出是用来产生模拟信号（例如，电机速度是由对应速度所需的电压控制）。
1.8输出接口调整
输出接口类似于输入接口，如我们看到的图 8-3。 CPU 带来了一个信号使 LED 二极管发光。光煽动光电晶体管开始导电，从而集电极和发射极之间的电压下降到 0.7V，并连接到输出装置，将此视为一个逻辑零。相反地，它意味着一个信号在输出端存在，并且被解释为逻辑 1。光电晶体管没有直接连接到 PLC 控制器的输出端。光电晶体管和输出端之间通常有一个继电器或一个大的晶体管以能确保能够打断更强的信号。
1.9扩展线
每一个 PLC 控制器的输入/输出线数量都是有限的。需要时可以由系统扩展通过扩展线连接的某些额外模块来增加，每个模块可以包含扩展的输入线和输出线。当然，在 PLC 控制器的扩展模块上也可以有不同性质的输入和输出(例如继电器输出控制器和晶体管输出可以在同一个扩展模块中)。
2.1 PLC 运行过程
PLC 的工作就是不断的扫描程序，我们可以把这个扫描周期视为三个重要的步骤，如图8-4 所示。（PLC 的工作过程）通常不止这三个步骤，但我们可以专注这三个重要的部分而不必考虑其它的。一般其他的部分是用来检查系统以及更新当前内部计数器和定时器的值。
关键词：可编程控制器，PLC，控制器
摘自：王伟，张艳丽主编《电气工程与自动化专业英语》，机械工业出版社，第八章（P84-
P88）,Chapter 8 Programmable Logic Controller Technology
Chapter 8 Programmable Logic Controller Technology Introduction
PLC( programmable logic controller ) is actually an industrial microcontroller system (in more recent times we meet processors instead of microcontrollers) where you have hardware and software specifically adapted to industrial environment. It is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/of its outputs. The user enters a program, usually via software or programmer that gives the desired result.
Black schema with typical components, which PLC consists of, is found in Fig .8- 1.Special attention need to be given to input an output, because in these blocks you find protection needed in isolating a CPU blocks from damaging influences that industrial environment can bring to a CPU via input lines. Program unit is usually a computer used for writing a program (often in ladder diagram).
1.1CPU-Central Processing Unit
Central Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one of the microcontrollers. Aforetime these were 8-bit microcontrollers such as 8051, and now these are 16-bit and 32-bit microcontrollers. Unspoken rule is that you’ll find mostly Hitachi and Fujicu microcontrollers in PLC controllers by Japanese makers, Siemens in European controllers, and Motorola microcontrollers in American ones. CPU also takes care of communication, interconnectedness among other parts of PLC controller, program execution, memory operation, overseeing input and setting up of an output. PLC controllers have complex routines for memory checkup in order to ensure that PLC memory was not damaged (memory checkup is done for safety reasons). Generally speaking, CPU unit makes a great number of check-ups of the PLC controller itself so eventual errors would be discovered early. You can simply look at any PLC controller and see that there several indicators in the form of light diodes for error signalization.
1.2Memory
System memory (today mostly implemented in FLASH technology) is used by a PLC for an process control system. Aside from this operation system it also contains a user program translated from a ladder diagram to a binary form. FLASH memory contents can be changed only in case where user program is being changed. PLC controllers were used earlier instead of FLASH memory and have had EPROM memory instead of FLASH memory which had to be erased with UV lamp and programmed on programmers. With the use of FLASH technology this process was greatly shortened. Reprogramming a program memory is done through a serial cable in a program for application development. Use memory is divide into blocks having special functions. Some parts of a memory are used for storing input and output status. The real status of an input is stored either as “1” or as “0” in a specific memory bit. Each input or output has one corresponding bit in memory. Other parts of memory are used to store variable contents for variables used in user program. For example, timer value, or counter value would be stored in this part of the memory.
1.3Programming a PLC Controller
PLC controller can be reprogrammed through a computer (usual way), but also through
manual programmers (consoles). This practically means that each PLC controller can programmed through a computer if you have the software needed for programming. Today’s transmission computers are ideal for reprogramming a PLC controller in factory itself. This is of great importance to industry. Once the system is corrected, it is also important to read the right program into a PLC again. It is also good to check from time to time whether program in a PLC has not changed. This helps to avoid hazardous situation in factory rooms (some automakers have established communication networks which regularly check programs in PLC controllers to ensure execution only of good programs ). Almost every program for programming a PLC controller possesses various useful options such as: forced switching on and off the system inputs/outputs(I/O lines) , program follow up in real time as well as documenting a diagram. This documenting is necessary to understand and define failures and malfunctions. Programmer can add remarks, names of input or output devices, and comments that can be useful when finding errors,or with system maintenance. Adding comments and remarks enables any technician（and not just a person who developed the system）to understand a ladder diagram right away. Comments and remarks can even quote precisely part number if replacements would be needed. This would speed up a repair of any problems that come up due to bad parts. The old way was such that a person who developed a system had protection on the program. So nobody aside from this person could understand how it was done. Correctly documented ladder diagram allows any technician to understand thoroughly how system functions.
1.4Power Supply
Electrical supply is used in bringing electrical energy to central processing unit. Most PLC controllers work either as 24V DC or 220V AC. On some PLC controllers you’ll find electrical supply as a separate module. Those are usually bigger PLC controllers, while small and medium series already contain the supply module. User has to determine how much current to take from I/O module to ensure that electrical supply provides appropriate amount of current. Different types of module use different amounts of electrical current. This electrical supply is usually not used to start external inputs or outputs. User has to provide separate supplies in starting PLC controller inputs or outputs because then you can ensure so called “pure” supply for the PLC controller. With pure supply we mean supply where industrial environment can not affect it damagingly. Some of the smaller PLC controllers supply their inputs with voltage from a small supply source already incorporated into a PLC.
1.5PLC Controller Inputs
Intelligence of an automated system depends largely on the ability of a PLC controller to read signal from different types of sensors and input devices. Keys, keyboards and by functional switches are a basis for man versus machine relationship. On the other hand, in order to detect a working piece, view a mechanism in motion, check pressure or fluid level you need specific automatic devices such as proximity sensors, marginal switches, photoelectric sensors, level sensors,etc. Thus, input signals can be logical (on/off) or analogue. Smaller PLC controllers usually have only digital input lines while larger also accept analogue inputs through special units attached to PLC controller. One of the most frequent analogue signals are a current signal of 4 to 20 mA and millivolt voltage signal generated by various sensors.
Sensors are usually used as inputs for PLCs. You can obtain sensors for different purposes. They can sense presence of some parts, measure temperature, pressure,or some other physical dimension, etc.(ex. inductive sensors can register metal object ). Other devices also can serve as inputs to PLC controller. Intelligent devices such as robots, video system, etc. often are capable of sending signals to PLC controller input modules (robot, for instance, can send a signal to PLC controller inputs as information when it has finished moving an object from one place to the other).
1.6Input Adjustment Interface
Adjustment interface also called an interface is placed between input lines and a CPU unit. The purpose of adjustment is to protect a CPU from disproportionate signals from an outside world. Input adjustment module turns a level of real logic to a level that suits CPU unit (ex. Input from a sensor which works on 24V DC must be converted to a signal of 5V DC in order for a CPU to be able to process it ). This is typically done through opto-isolation, and this function you can view in Fig.8-2. Opto-isolation means that there is no electrical connection between external world and CPU unit. They are “optically” separated, or in other words ,signal is transmitted through light. The way this works is simple. External device brings a signal which turns LED on, whose light in turn incites photos transistor which in turn starts conducting, and a CPU sees this as logic zero (supply between collector and transmitter falls under 1V). When input signal stops LED diode turns off, transistor stops conducting, collector voltage increases,and CPU receives logic 1 as information.
1.7PLC Controller Output
Automated system is incomplete if it is not connected with some output devices. Some of the most frequently used devices are motors, solenoids, relays, indicators, sound signalization and similar. By starting a motor, or a relay, PLC can manage or control a simple system such as system for sorting products all the way up to complex systems such as service system for positioning head of CNC machine. Output can be of analogue or digital type. Digital output signal works as a switch and it connects and disconnects line. Analogue output is used to generate the analogue signal (ex. Motor whose speed is controlled by a voltage that corresponds to a desired speed).
1.8Output Adjustment Interface
Output interface is similar to input interface, as we see in Fig.8-3. CPU brings a signal to LED diode and turns it on. Light incites a photo transistor which begins to conduct electricity, and thus the voltage between collector and emitter falls to 0.7V, and a device attached to this output sees this as a logic zero. Inversely it means that a signal at the output exists and is interpreted as logic one. Photo transistor is not directly connected to a PLC controller output. Between photo transistor and an output usually there is a relay or a stronger transistor capable of interrupting stronger signals.
1.9Extension Lines
Every PLC controller has a limited number of input/output line. If needed this number can be increased through certain additional modules by system extension through extension line. Each module can contain extension both of input and output lines. Also, extension modules can have inputs and outputs of a different nature from those on the PLC controller (ex. In case relay
outputs are on a controller, transistor output can be on an extension module).
8.2 PLC Operation Process
A PLC works by continually scanning a program. We can think of this scan cycle as consisting of three important steps, as shown in Fig.8-4. There are typically more than three but we can focus on the important parts and not worry about the others. Typically the others are checking the system and updating the current internal counter and timer values.
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