可编程控制器毕业论文外文翻译

1、b：外文文献及译文system block diagrama programmable controller is a specialized computer.since it is a computer, it has all the basic component parts that any other computer has; a central processing unit,memory, input interfacing and output interfacing.a typical programmable controller block diagram is sho

2、wn in figure 1.figure 1 programmable controller block diagramthe central processing unit (cpu) is the control portion of the plc. it interprets the program commands retrieved from memory and acts on those commands.in present day plcs this unit is a microprocessor based system.the cpu is housed in th

3、e processor module of modularized systems.memory in the system is generally of two types; rom and ram.the rom memory contains the program information that allows the cpu to interpret and act on the ladder logic program stored in the ram memory.ram memory is generally kept alive with an on-board batt

4、ery so that ladder programming is not lost when the system power is removed. this battery can be a standard dry cell or rechargeable nickel-cadmium type. newer plc units are now available with electrically erasable programmable read only memory (eeprom) which does not require a battery.memory is als

5、o housed in the processor module in modular systems. input units can be any of several different types depending on input signals expected as described above.when power is applied to a programmable logic controller, the plcs operation consists of two steps: (1) update inputs and outputs and (2) solv

6、e the ladder.the first thing the plc does when it begins to function is update i/o.this means that all discrete input states are recorded from the input unit and all discrete states to be output are transferred to the output unit.register data generally has specific addresses associated with it for

7、both input and output data referred to as input and output registers.these registers are available to the input and output modules requiring them and are updated with the discrete data.since this is input/output updating, it is referred to as i/o . after the i/o update has been accomplished, the plc

8、 begins executing the commands programmed into it.these commands are typically referred to as the ladder diagram.the ladder diagram is basically a representation of the program steps using relay contacts and coils.the ladder is drawn with contacts to the left side of the sheet and coils to the right

9、.after the i/o update, the plc moves to the first rung of ladder logic.it solves the contact configuration to determine if the coil is to be energized or de-energized.it then energizes or de-energizes the coil.after this is accomplished, it moves to the left side of the next rung and repeats the pro

10、cedure.this continues until all rungs have been solved. when this procedure is complete with all rungs solved and all coils in the ladder set up according to the solution of each rung, the plc proceeds to the next step of its sequence, the i/o update.i/o updating occurs, each input point that is on

11、at that time will cause a 1 to be set at the bit address associated with that particular input.if the input is off, a 0 will be set into the bit address.memory in todays plcs is generally configured in 16 bit words.this means that one word of memory can store the states of 16 discrete input points.

12、therefore, there may be a number of words of memory set aside as the input and output image registers.at i/o update, the status of the input image register is set according to the state of all discrete inputs and the status of the output image register is transferred to the output unit. this transfe

13、r of informationtypically only occurs at i/o update.it may be forced to occur at other times in plcs which have an immediate i/o update command.this command will force the plc to update the i/o at other times although this would be a special case.at i/o update, the states of all coils which are desi

14、gnated as outputs are transferred from the output image register to the output unit and the states of all inputs are transferred to the input image register.note that any input changes that occur during the solution of the ladder are ignored because they are only recorded at i/o update time.the stat

15、e of each coil is recorded to the output image register as each rung is solved. however, these states are not transferred to the output unit until i/o update time.figure2 scan cyclethis procedure of i/o update and solving the ladder diagram and i/o update is referred to as scanning and is represente

16、d in figure 2.8. the period between one i/o update and the next is referred to as one scan.the amount of time it takes the plc to get from one i/o update to the next is referred to as scan time.scan time is typically measured in milliseconds and is related to the speed of the cpu and the length of t

17、he ladder diagram that has to be solved. the slower the processor or the longer the ladder diagram, the longer the scan time of the system.the speed atwhich a plc scans memory is referred to as scan rate.scan rate units are usually listed inmsec/k of memory being utilized for the program. as an exam

18、ple, if a particular plc has a rated scan rate of 8 msec/k and the program occupies 6k of memory, it will take the plc 48 msec to complete one scan of the program.译文：系统框图可编程控制器是一种专用的计算机。因为它是一台计算机，它就应该具有其它计算机的基本组成部分：中央处理单元，存储器，输入接口和输出接口。一个典型的可编程控制器框图如图1所示中央处理器输入连续离散寄存器开关、继电接触器等分压器、反馈电压等指轮开关、编码器等输出连续离

19、散寄存器继电器、灯等模拟显示、控制电压等数字显示存储器只读存储器随机存储器图1可编程控制器 框图中央处理单元（cpu）是plc的控制部分。它解释来自存储器的程序指令并且按这些指令执行操作。现在plc的中央处理单元是一个基于微处理器的系统，被置于模块化系统的处理器模块中，系统存储器大致分为两类：只读存储器和随机存储器。只读存储器包含程序信息，通过这些程序信息，cpu可以解释和执行存储在随机存储器中的梯形图程序。随机存储器一般都有板上电源维持，这样系统掉电时，梯形图程序不会丢失。这种电源可以是标准的干电池或可充电的镍-镉电池。新型的plc存储单元使用电可擦除可编程只读存储器（eeprom），这就不

20、需要专门的电源维持。内存也设在模块化系统中的处理器模块内。输入单元有若干不同类型，所用类型根据前述输入信号需求选择。输入部件可以接收多种不同电压和电流等级的离散信号或模拟信号。可编程逻辑控制器上电后，其运作包含两个阶段：（1）刷新输入和输出（2）解读梯形图。plc开始运作时的首要操作就是刷新i/o。这就意味着通过输入单元，所有的离散输入状态被记录，而且所有将要输出的离散状态被转移到输出单元。通常有一些特定地址来寄存数据，这些地址与输入和输出数据相关，称为输入和输出寄存器这些寄存器与输入和输出模块相连并且通过离散数据来更新。由于这是输入/输出的更新，因而它被称为i/o刷新。当i/o刷新时，如果输

21、入点输入的是“开”信号，那么与之相联的位地址内容被置“1”。如果输入点输入的是“关”信号，那么相应的位地址内容被置“0”。现在，plc存储器字长大都是16位。这意味着，内存的一个字可存储16个离散输入点的状态信息。因而，内存中可能会有一定数量的字被预留，作为输入和输出映像寄存器。在i/o刷新时，输入映像寄存器的状态根据所有离散输入的状态信息变化，输出映像寄存器的状态被送至输出单元。这种状态信息的转变通常只发生在的i/o刷新阶段。但是，在plc工作的其它时段，当有i/o立即刷新命令时，状态信息的转变也可以被强制进行。作为一种特殊情况，这条命令将会迫使plc在其它任何时候刷新i/o。输入输出刷新完

22、成后，plc开始执行编入的指令。这些指令通常称为梯形图，该梯形图基本上使用继电器触点和线圈编程。输入输出刷新完毕后，plc转向梯形逻辑中的第一个阶梯，处理接点元件，判定线圈将得电或失电，然后使线圈得电或失电。完成此操作后，plc转向下个阶梯，重复前面步骤，这样持续到所有阶梯被处理完毕。当处理所有阶梯的过程完毕，并且梯形图中所有的线圈都已根据处理的每个阶梯设定，那么plc就进入到其下一个阶段i/o刷新。i/o刷新阶段，所有输出线圈的状态从输出映像寄存器转移到输出单元，同时所有输入状态被转移到输入映像寄存器。注意，在处理梯形图期间，输入的任何变化 将被忽略，因为它们只有在i/o刷新阶段才被记录。在

23、处理每一阶梯时，每个线圈的状态将被记录至输出映像寄存器。然而，这些状态直到i/o刷新阶段才被转移至输出单元。这种i/o刷新、处理梯形图再到i/o刷新的过程称为扫描，其描述如图2.8。前一次i/o刷新和下次刷新之间的时段称为一次扫描。plc从前一次i/o刷新到下次刷新所用的时间称为扫描时间。扫描时间通常以毫秒为单位来衡量，而且扫描时间与cpu的运行速度和所要处理的梯形图的长度有关。plc扫描存储器的速度称为扫描速度。扫描速度单位通常为毫秒/k,程序正在使用的内存。例如，如果某一plc扫描速度为8毫秒/k，程序占用8k的内存 ，那么plc将会用48毫秒完成一次程序扫描。图2 循环扫描.附录c：参考

24、文献及内容简介【1】刘裁文.电梯控制系统m.北京:电子工业出版社，1996本文在已有的通用变频器的基础上，采用对电梯进行控制，通过合理的选择和设计，提高了电梯的控制水平，改善了电梯运行的舒适感，使电梯达到较为理想的控制效果【2】唐勇奇，赵葵银，汪超.电梯变频调速plc控制的设计与实现j .湖南工程学院学报.2000年02期.介绍了一种采用和变频器控制的电梯控制系统，阐述了该系统中硬件和软件设计方法，提高了电梯运行的可靠性、舒适性和效率。【3】张燕宾.spwm变频调速应用技术m.机械工业出版社.2005. 本书首先深入浅出地讲解了电力拖动系统的工作要求、异步电动机的主要理论和交直、交变频器的基本原理，而