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1、关于控制系统中的PLC的选型方法YAN AiQing摘要：在设计关于PLC的控制系统时，首先应确定该系统的控制方案，然后下一步工作是为该工程设计选择PLC的型号。该控制系统运行过程中的特点和应用需求是PLC选型的主要依据。PLC和相关设备应该根据综合、标准、以及容易形成一个整体的工业控制系统和易扩展其功能的原则选择器件的类型，所选择的PLC应在相关工业领域的有成功的应用成果、该PLC在控制系统中有成熟和可靠的运用制度，该PLC的硬件、软件配置和功能都可适应安装的规模和控制要求。在设计该系统时知道它所使用的编程控制器，以及它的功能图像及相关的编程语言有利于缩短编程时间，因此，在选择该类型的项目设
2、计和估算时，应先分析该项目的运行过程特点和控制要求，详细地明确该项目的控制任务和范围，根据操作和运动的要求，估算出输入和输出的数量、估计出存储器容量、测定功能的大小以及外部设备性能等，最后选择具有较高的性价比的PLC和相应的控制系统设计。随着PLC在工业控制系统中的普及，PLC的数量和种类越来越多，功能也日趋完善。近年来，刚刚介绍的PLC产品已有自美国、日本和德国以及国内厂家组装或独立发展成型，已有几十种系列，几百种型号。PLC的类型众多，它的结构模型，性能、能力、指令系统和编程方法等各有不同，应用场合也各有不同。因此，在自动控制系统中合理的选择PLC的型号有很重要的作用。随着科技的不断进步，
3、PLC的种类是越来越多，其功能也在逐渐增加强。虽然本文总结了一些选择的方法，以及运用实例说明如何使用PLC，但在实际工作中它还必须做出适当的调整。需要根据实际条件来用PLC设计工业控制系统，满足期望。 关键词：PLC；选型；控制系统1、 介绍PLC的技术随着计算机和微电子技术的发展而得到迅速发展。从开发出第一台PLC后，随着CPU的应用和单片机技术在PLC中的应用,形成现代意义上的第一台PLC。自80年代到20世纪的第一个十年,随着微电子技术的大跃进，出现了大规模集成电路和超级大型微电子技术，16通道和32通道的微处理器的出现PLC得到了惊人的开发,这使得PLC在概念、设计、性价比以及应用上获
4、得了新的突破，不仅控制功能增强,功耗和体积减少,成本下降,可靠性上升,编程和故障检测更加灵活和方便,同时远程通信网络、数据处理以及人机界面(HMI)也得到了快速的发展。现在,PLC不仅可以应用于自动化生产行业,而且可以在连续生产时用于过程控制系统,这些使得它在自动化技术领域成为三大支柱之一,即使总线技术变成了今天的自动化技术应用的热点、但PLC在现场总线系统中仍是不可或缺的控制器。总的来说，随着PLC在自动化工业控制系统中的发展和普及，PLC的种类是越来越多，使用也越来越广泛，因此合理选择PLC，对提高自动控制系统在工作中的运用具有重要的作用。 2、 选择模型我国的市场流行的PLC产品的生产厂
5、家有以下几个公司： 1）施耐德公司，包括引进自Modicon公司由早期天津仪器仪表厂生产的产品，现在的产品有Quantum, Premium 和 Momentum；2）罗克韦尔公司（包括AB公司）PLC产品，现在的产品有SLC、Micro Logix 和 Control Logix等；3）西门子公司的PLC产品，现在的产品有S7 - 400/ 300/ 200等系列；4）通用电气公司PLC产品；5）日本公司的产品如欧姆龙，三菱，富士，松下，其中最受欢迎的是三菱公司的FX系列。PLC选型的基本原理的是:在输入/输出数量满足要求的前提下应选择最可靠、维护和使用最方便以及性价比最优的产品。3、 输入
6、/输出选择PLC是一种工业控制系统,其控制对象是工业生产设备或工业产品生产过程、工作环境是工业生产现场。它连接的工业生产过程是通过I/ O接口模块实现。PLC有很多I / O接口模块包括开关量输入模块、开关量输出模块、模拟量输入模块和模拟量输出模块以及一些特殊的模块,使用时,我们应该根据他们的特征执行选项。1）确定输入/输出数量根据控制系统的需求，确定所需输入/输出的数量，应增加备用量的10% - 20%，为了能在任何时间增加控制功能。2）开关量输入/输出开关量输入/输出接口可以从传感器和开关和控制设备接受信号。典型的交流输入/输出信号24-240V，直流输入/输出信号5-240V。3）模拟量
7、输入/输出模拟量输入/输出接口可以接受由传感器产生的信号。这些接口可以用于测量流动率、温度和压力，并以此来控制由电压或电流的输出设备。这些接口的量程为-10-+ l0v、0-l0v、4-20mA 或10-50mA。有些厂家在PLC上设计了特殊的专用模拟接口，因此它可以接收低电平信号。一般来说，这种接口模块可以用于接收不同类型的热电偶或RTD混合信号。4）特殊功能输入/输出当选择一个PLC，用户可能面临一些特殊类型的输入/输出还有一些因为有限的输入/输出的位置和快速响应以及频率问题造成的非标准的输入 /输出。现在，用户应该考虑是否接受由市场或制造商提供的专用模块，通过专用模块自行处理一部分的数据
8、，从而减少CPU的使用，提高任务处理的效率，以最大限度降低因高温限制造成的控制失灵。5）智能输入/输出目前，PLC厂家制造出了一些智能输入输出连续模块。一般智能输入 /输出模块可以自我处理，它可以对指定的输入或输出信号做出提前处理，并将结果传送到CPU或直接输出，因此可以提高处理速度和节省存储容量。智能输入/输出模块有高速计数器，cam模拟器、凸轮模拟器速度补偿、单回路或者倍增PID调节器、ASCII/BASIC处理器和RS - 232 C / 422接口模块等。PLC的输入/输出模块的一般选择原则：根据设备现场或操作选择的类型和数量来选择I/O模块。4、 选择类型和存储容量PLC所使用的内存
9、的系统主要是有3种：EPROM，ROM和RAM。内存的容量的大小一般与PLC的大小有关，通常小型机的最大的存储能力要小于6kb，中型机器的最大存储能力可以达到64KB，而大型机的最大存储能力可达到兆字节。使用时可以根据程序和数据存储能力选择适合的类型，必要时也可以进行内存扩大设计。PLC中内存的选择方法：根据编程所用的节点数来准确计算实际所需内存的容量。5、 软件选择在系统的实现过程中，PLC的编程问题是非常重要的。用户应该知道PLC产品的软件功能。通常，一个系统的软件是用来处理控制硬件的。但有时一些应用系统除了需要控制硬件部分外还需要软件的一些功能。 一个程序块由可执行代码和注释组成。可执行
10、代码由主程序和若干子程序或者中断服务程序组成。可执行代码被编译并下载到FX2N中，而程序注释不会被下载。您可以使用组织组件（主程序、子程序和中断服务程序）来结构化您的控制程序。主程序主程序中包括控制应用的指令。FX2N在每一个扫描周期中顺序执行这些指令。子程序子程序是应用程序中的可选组件。只有被主程序、中断服务程序或者其它子程序调用时，子程序才会执行。当您希望重复执行某项功能时，子程序是非常有用的。与其在主程序中的不同位置多次使用相同的程序代码，不如将这段程序逻辑写在子程序中，然后在主程序中需要的地方调用。调用子程序有如下优点：(1)用子程序可以减小程序的长度(2)由于将代码从主程序中移出，因
11、而用子程序可以缩短程序扫描周期。FX2N在每个扫描周期中处理主程序中的代码，不管代码是否执行。而子程序只有在被调用时，FX2N才会处理其代码。在不调用子程序时，FX2N不会处理其代码。(3)用子程序创建的程序代码是可传递的。您可以在一个子程序中完成一个独立的功能，然后将它复制到另一个应用程序中而无需作重复工作。中断服务程序中断服务程序是应用程序中的可选组件。当特定的中断事件发生时，中断服务程序执行。您可以为一个预先定义好的中断事件设计一个中断服务程序。当特定的事件发生时，FX2N会执行中断服务程序。中断服务程序不会被主程序调用。只有当中断服务程序与一个中断事件相关联，且在该中断事件发生时，FX
12、2N才会执行中断服务程序。 提示：因为无法预测何时会产生中断，所以应考虑尽量限制中断服务程序和程序中其它部分所共用的变量个数。使用中断服务程序中的局部变量，可以保证中断服务程序只使用临时存储器，并且不会覆盖程序中其它部分使用的数据。为了保证主程序与中断服务程序正确地共享数据，您可以使用许多编程技巧。6、 结论随着科技的不断进步，PLC的种类是越来越多，功能也逐渐增强。在文章中，虽然有总结一些选择的方法，但在实际工作中我们仍然必须做出适当的调整，根据实际情况来设计控制系统以满足期望。The Method Selecting Type of PLC in Controlling SystemYAN
13、 AiQingAbstract: When designing PLC system,first determining control scheme, the work of next step is PLC selecting type of project design. The characteristic of process and application requirement are the major accordance of designing selecting type.PLC and relevant equipments should be integrated、
14、standard 、according to the principle easy to form a whole with industrial control system and easy to expand its function to select type, PLC chosen should have application achievement in related industrial field、the maturation and reliable system,the systematic hardware、software configuration and fu
15、nction of PLC should suit with installation scale and control requirement.Knowing programming controller, function picture and relevant programming language is helpful to shorten programming time. Therefore, selecting type of project design and estimating, it should analyse the characteristic of pro
16、cess and control requirement in detail, definite control task and range, determing operation and movement required,then according to control ask to estimate numbers of inputs and outputs、memory capacity required、determing function of PLC, the external equipment property etc. finally selecting having
17、 higher price performance PLC and desiging the corresponding control system.Along with popularization of PLC in industrial control, quantity and kind of PLC product are more and more and function also becomes perfect day by day. In recent years, the PLC products that introduced from the countries su
18、ch as America、Japan and Germany and the domestic manufacturer assembles or develops independently have had tens of series, hundreds of models. The kind of PLC is numerous, its structural model , performance、capacity、instruction system and programming method etc are different, application occasion ha
19、s also each to stress. Therefore, select PLC reasonably, the application for PLC in control system has important role.Along with the unceasing advance of science and technology, the kind of PLC is increasingly numerous,its function also strengthens gradually. Though the article have sumed up some me
20、thods of choosing PLC and exampled to explain how to use, in practical work it must still make proper adjustment according to practical condition in order to design the industrial control system that satisfies expectation.Key words: PLC; selecting type; controlling systemI. IntroductionPLC technolog
21、y develops promptly along with the development of computer and microelectronics technology, and develops from a initial machine to 8 machines. Along with application of microprocessor CPU and the technical of microcomputer in PLC, it has formed PLC on modern meaning. Since 80 decade of 20 century, a
22、long with microelectronics technology development of the large-scale and super large-scale Integrated circuit etc. microelectronics technology, That the 16 and 32 microprocessor forms microcomputer PLC have gotten astonishing development, these make PLC get new breakthrough in the aspects such as co
23、ncept、design、price performance as well as application. Not only control function strengthens, power consumption and volume reduce, cost drops, reliability rises, programming and fault detection are more flexible and convenient, but also long-range UO and communication network, data handling as well
24、as man-machine interface (HMI) also have got rapid development. Now, PLC can not only apply in the automation of manufacturing industry but also can still apply in the course control system in serial production, these have made it become one of 3 pillar in automation technical field, even if the tec
25、hnology of bus line becomes today of automation technical application hot point, PLC is still the indispensable controller in the control system on-the-spot of bus line.Synthesized, along with the development of PLC and its popularize in automation industrial control, the kind of PLC product is more
26、 and more and use is also more and more extensive, therefore, selecting PLC reasonably for raising the application of PLC in control system has important role.II. Selecting machine modelThe market of our country has the popular PLC product that has following few company:1) Schneider company, include
27、 early Tianjin instrument and meter plant transfer the product of Modicon company, now, there is the products such as Quantum, Premium and Momentum;2) Rockwell company (include AB company) PLC product, now, there is the products such as SLC、Micro Logix and Control Logix;3) Siemens company product, n
28、ow, there is S7-400/300/200 series products;4) GE company product;5) Japan companys products such as Omron,Mitsubishi, Fuji and Panasonic, in which used more is FX series of Mitsubishi company.The basic principle of PLC type option is: under function satisfies the prerequisite of requirement to sele
29、ct type of most reliable, maintenance and use most facilitate as well as the price performance optimization.III. Selecting I/OPLC is a kind of industrial control system, its control object is industrial production equipment or industrial production course, working environment is industrial productio
30、n scene. Its connections with industrial production course realize through the I/O interface module. PLC has a lot of I/O interface module including switch quantity input module、switch quantity export module, simulated quantity input module and simulated quantity export module as well as some specia
31、l module, when using, we should carry out option according to their characteristic.1) Determine I/O numbersAccording to control systematic requirement to determine I/O numbers needed, it should increase the spare quantity of 10%-20%, in order to increase control function at any time.2) Switch quanti
32、ty I/OThe switch quantity I/O interface can take over signal from sensor and switch and control equipment.Typical AC I/O signal is 24-240V, the DC I/O signal is 5-240V.3) Simulated quantity I/OThe simulated quantity I/O interface normally perceives the signal that sensor produces. These interfaces c
33、an be used to measure rate of flow、temperature and pressure, and used in controlling voltage or current export equipment. the typical span of these interfaces is-10-+ l0V、0-+l0V、4-20mA or 10-50mA.Some manufacturers in PLC design special simulated interface, thus it can take over low level signal. Ge
34、nerally speaking, this kind of interface module can be used to take over the different type of thermocouple or RTD mix signal.4) Special function I/OWhen selecting a PLC, user may faced some special types and cant be realized by standard I/O as the limited position I/O, fast input and frequency etc.
35、 Right now, user should consider whether supply and market manufacturer offers the special module that is helpful for high limit to reduce control role, some special interface modules selves can handle a part of field data and make CPU free from the consuming task handling.5) Intelligent I/OCurrentl
36、y, PLC manufacturers protrude some intelligent I/O modules in succession. Generally the intelligent I/O module self has with processor, it can assigned handling for inputting or exporting signal in advance, and will send result to CPU or output directly, so this can raise the handling speed of PLC a
37、nd save the capacity of memory.Intelligent I/O has the high speed counter, cam simulator、the cam simulator with speed compensation、single loop or multiply loop PID regulator、the ASCI1/BASIC processor and RS-232C/422 interface module etc.The general principle of selecting the I/O module is: According
38、 to equipment on-the-spot or the operating to select the type and count of the 1l0 module.IV. Selecting type and capacity of memoryThe memory used by PLC system basically is composed from 3 kinds of type as PROM, EPROM and RAM, memory capacity changes with the size of machine, normally the biggest s
39、tore ability of small-sized machine is lower than 6KB, the biggest store ability of medium-sized machine can reach 64KB, the biggest store ability of large scale machine can reach MB. When using we can choose suitable type according to program and data store capacity and can also carry out memory ex
40、pand design especially necessarily.The option method of memory capacity: According to the node that programming uses to calculate accurately the actual use capacity of memory.V. Selecting softwareIn the course of systematic realizing, the programming problem of PLC is very important. User should kno
41、w as software function of PLC product. Usually, a systematic software is used in handling the control hardware that controller has always. But some application systems need also the software function besides controlling hardware parts.A program block is composed of executable code and comments. The
42、executable code consists of a main program and any subroutines or interrupts routines. The code is compiled and downloaded to the FX2N; the program comments are not. You can use the organizational elements (main program, subroutines, and interrupt routines) to structure your control program.Main Pro
43、gramThe main body of the program contains the instructions that control your application. The FX2N executes these instructions sequentially, once per scan cycle.SubroutinesThese optional elements of your program are executed only when called: by the main program, by an interrupt routine, or by anoth
44、er subroutine. Subroutines are useful in cases where you want to execute a function repeatedly. Rather than rewriting the logic for each place in the main program where you want the function to occur, you can write the logic once in a subroutine and call the subroutine as many times as needed during
45、 the main program. Subroutines provide several benefits:(1)Using subroutines reduces the overall size of your program.(2)Using subroutines decreases your scan time because you have moved the code out of the main program. The FX2N evaluates the code in the main program every scan cycle, whether the c
46、ode is executed or not, but the FX2N evaluates the code in the subroutine only when you call the subroutine, and does not evaluate the code during the scans in which the subroutine is not called.(3)Using subroutines creates code that is portable. You can isolate the code for a function in a subrouti
47、ne, and then copy that subroutine into other programs with little or no rework.Interrupt RoutinesThese optional elements of your program react to specific interrupt events. You design an interrupt routine to handle a pre-defined interrupt event. Whenever the specified event occurs, the FX2N executes
48、 the interrupt routine. The interrupt routines are not called by your main program. You associate an interrupt routine with an interrupt event, and the FX2N executes the instructions in the interrupt routine only on each occurrence of the interrupt event.TipBecause it is not possible to predict when
49、 the FX2N might generate an interrupt, it is desirable to limit the number of variables that are used both by the interrupt routine and elsewhere in the program. Use the local variable table of the interrupt routine to ensure that your interrupt routine uses only the temporary memory and does not overwrite data used somewhere else in your program.
