PLC控制器中英对照

PLC(即可编程控制器) 是为了在机械控制中代替必要的继电器时序电路而发明的一种设备。PLC必须考虑它的输入端口并且以他们的状态为依据，来断开和接通它的输出端口。用户通常经过给出理想结果的软件或者上编程其进入程序当中。PLC别用在很多的领域中，人们在从事机械制造，包装，材料加工等不计其数的工业生产中。PLC是必不可少的。如果不用PLC，那么将浪费大量的时间和金钱。几乎任何需要电器控制的设备都需要PLC。例如，在开关闭合时需要一个线圈接通5秒，然后不管开关接通多长时间都将线圈断开。借于此我们可以做一个简单的外部定时器。如果过程中有更多的开关和线圈时，那就需要更的外部定时器。正如人们所见，越大的操作系统就越能应用到PLC。我们可以编写PLC的程序来计算输入量，并且在特定的时候接通线圈。PLC只要由CPU、存储器、和输入/输出端口等组成。我们可以把PLC看成一个里面充满了成千上万的继电器、计数器、定时器和数据存储单元的一个大盒子。2. 1PLC每个元件的作用 输入继电器（接触器）：输入接触器PLC与外界的连接口。输入继电器能接收到开关，传感器等元件发出的信号，并且不仅仅当作继电器使用而且还可以用来做晶体管。计算器：计数器用来计数。有普通计数器和高速计数器两类。普通计数器主要用来对程序中反映的信号进行计数实现。告诉计数器则用来对高于PLC扫描频率的机外脉冲计数。计数器工作中需要一个表示计数器状态的位元件及一个存储计数当前值的字元件，也为位复合元件。定时器：定时器相当于继电接触器系统中的时间继电器，用于时间控制。PLC中的定时对脉冲计数实现。由于定时器以对时基技术的方式计时，在存储器数值的存储单元字长一定时，定时器的计时时间长短就受到分辨率的影响。输出继电器：输出继电器存储程序执行的结果。每个输出继电器在存储区中占一位，每一个输出继电器与一个输出口相对应。输出继电器上通过隔离电路，将程序运算结果到输出口并决定输出口所连接器件的工作状态。正常运行中输出继电器的状态只由程序的执行决定。数据存储单元：数据存储单元用来存放“数字”类数据，占用的存储单元可以是字节、字，也可以是双字。数据存储单元存储数据量大。2. 2PLC工作过程PLC的工作过程是一个持续扫描的过程。通常分为3个阶段。如图1所表示：1) 输出处理：PLC在输入采样阶段，首先扫描所有输入端子，并将个输入状态存入内存中各个对应的输入映像寄存器中。此时，输入映像寄存器被刷新。接着，进入程序执行阶段，在程序执行阶段或输出阶段，输入映像寄存器与外界连接，无论输入信号如何变化，其内容保持不变，直到下一个扫描周期的输入采样阶段，才重新写入输入端的新内容。2) 程序执行阶段：根据PLC梯形图程序扫描原则，当指令中涉及到输入输出状态时，PLC就从输入映像存储器中“读入”上一阶段采入的对应的输入端子状态，从输出映像寄存器“读入”对应元件映像寄存器的当前状态。然后，进行相应的运算，运算结果再存入元件的寄存器中。3) 输出刷新阶段：在所有指令执行完毕后，输出映像寄存器中所有输出继电器的状态(接通/断开)在输出刷新阶段存到输出锁存器中，通过一定方式输出，驱动外部负载。图1 PLC的工作原理Fig.1 The process of the PLCA PLC (Programmable logic Contraller) 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/off its outputs.The user enters a program，usually viasoftware programmer，that gives the desired results.PLC is used in many “real world”applications.If there is industry prerent，chances are good that there is a PLC presrnt.If you are involved in matching，packaging，material handing，automated assembly or countless other industries，you are probably already using them.If you are not，you are wasting money and time.Almost any application that needs some type of electrical control has a need for a PLC.For example，lett assume that that when a switch turns on we want to turn a solenoid on for 5 seconds and then turn it off regardless of how long the switch is on for.We can do this with a simple external timer.But what if the process included 10 switches and solenoids? We would need 10 external timers.But what if the process also needed to count how many times the switches individually turned on，we need a lot of external counters.As we can see，the bigger the process the more of a need we have for a PLC.We can simply program the PLC to count its inputs and turn the solenoids on for the specified time.The PLC mainly consists of a CPU，memory ares，and appropriate circuits to receive input/outputdata，We can actually consider the PLC to be a box full of hundreds or thousands of separate relays，counters，times and data storage locations.1. 1The role of the each part INPUT RELAYS-(contacts)：These are connected to the outside world.They physically exist and receive signals from switchs，sensors，etc.Typically they are not relays but rather they are transistors. COUNTERS： There again do not physically exist.They are simulated counted and they can be programmed to count pulses.Typically these counters can count up，down or both up and down.Since they are simulated，they are limited in their counting speed.Some manufacturers also include high-speed counters that are hardware based.We can think of these as physically existing.Most times these counters can count up，down or up and down.TIMERS：These also do not physically exist.They come in many varieties and increments.The most common type is an on-delay type.Others include off-delay and both retentive and non-retentive types.Increments vary from 1ms through.OUTPUT RELAYS-(coils)：These are connected to the outside world.They physically exist and send on/off signals to solenoids，lights，etc.They can be transistors，relays，or trials depanding upon the model chosen.DATA STORAGE：Typically there are registers assigned to simply store data.They are usually used as temporary storage for math or data manipulation.They can also typically be used to store data when power is removed from the PLC.Upon power-up they will still have the same contents as before power was removed.Very convenient and necessary!1. 2The work process of the PLC A PLC works by continually scanning a program.We can think of this scan cycle as consisting of three important steps，as shown in Figure 1.There are typically the others are checking the system and updating the current internal counter and timer values.Figure 1 the work prcess of PLCStep 1 CHECK INPUT STATUS：First the PLC takes a look at each input to determine if it is on or off.In other words，is the sensor connected to the first input on? How about the second input? How about the third It records this data into its memory to be used during the next step.Step 2 EXEAUTE PROGRAM：Next the PLC executes your program one instruction at a time.Maybe your program said that if the first input was on then it should turn in zhe first out.Since it already kowns which inputs are on/off from the previous step，it will be able to decide whether the first output should be turned on based on the state of the first input.It will store the execution results for use later during the next step.Step 3 UPDATE OUTPUT STATUS：Fially the PLC updates the status of the outputs.It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second step.Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn to the first output when this condition is ture.After the third step PLC goes back to step one and repeats the steps continuously.One scan time is defined as the time id takes to execute the 3 steps list above.Thus a practical system is controlled to perform specified operations as desired.