可编程控制器应用的发展支持软件论文中英文资料对照外文翻译文献综述

中英文资料对照外文翻译文献综述

Support software for the development of

programmable logic

1、Introduction

Programmable Logic Controllers (PLC) class of real-time computers used extensively in industrial control applications. The development of a PLC application requires the configuration of the inputs and outputs of the PLC architecture, that is the selection of the number, type and addresses of the inputs and outputs of the PLC, and the writing and debugging of the application program. Programming these computers is usually done in specific graphical structured text languages [Bekkum93,Hughes 89,Jones 83] and the program debugging is carried out in a development environment. Most of the available environments [Square D 90, Taylor 90] allow program writing in more than one language, running it by step or in segments on the actual PLC and checking whether the assumed logical relationships between the inputs and the outputs at each program step or segment are satisfied. I addition, these environments offer engineering support, such as the preparation of input/output wiring diagrams and the generation of the executable code of the program. Recent versions of commercially available environments are supplied with a software emulator of one or more PLC units. This allows to perform program debugging without having access to the programmable controller itself. Also, the use of emulators makes easier and economically affordable the simulation of a large number of program operating conditions. By making sure that the program operates correcty under all the critical operating conditions, the risk of implementing a

PLC-based system that does not meet the desired requirements is reduced. However, the ultimate goal of a development environment should be to verify the functional properties and behavior of the programs in all the possible states that thes programs and the plants they may enter.

In the literature, various languages and graphical or mathematical formalisms are proposed for writing or specifying real-time programs .The timing and/or functional performance of these programs can be verified at compile time or mathematically. ADA[Ada83],RT-ASLAN[Auemheimer86], EUCLID[Kligerman86], PEARL [Halang 91], FLEX[Lin88] are some of the proposed and most widely known languages. Their graphical or mathematical formalisms are based on the use of finite state automata [Alford 77],Petri-Nets[Fedler 93], dataflow diagrams [Zave 82] and metric temporal logic [Koymans 90]. Although all these formal methods and languages represent significant advances to the problem of real-time program verification, still they have not reached the maturity required to deal with the complexities of large software systems . Until these methods reach a certain level of maturity we must rely on less formal methods, tuned to the needs of specific classes of real-time systems.

In the case of PLC, we may continue to use simulation as a method to reveal logical errors in our programs and assess their behavior under an incomplete set of possible program states. In addition, we may include new facilities in the program development environments, the use of which will reduce the programming and engineering effort of an application. They may be editing and compilation facilities which support application programming in all the languages defined in the IEC 1131-3 standard. By using these languages our programming efficiency will be improved significantly, because each one of them can be used to program the part of the application for which it is appropriate, and yet the whole application can be linked into a single executable program. Other facilities which can reduce engineering effort are those which

can make easier and more meaningful the declaration of the program input conditions. These facilities will allow us to study in a given timing period, a larger number of simulation cases than the ones we might have studied without these facilities. Furthermore, we may expand the scope of the simulation by including a simulator of the plant which interacts with the computer. Also, facilities can be added to assist in the better interpretation of the generated simulation results. Such facilities may allow us to configure the displays of the generated data the way we think appropriate, and animate the simulated operation of the application program.

In this paper an architecture and language constructs are proposed for a software aid which ~an be used to declare input conditions to a PLC program, emulate the PLC operation and configure the display of the emulation results. The core of the architecture is the virtual machine, which is a software module which emulates the operation of a program written for a specific PLC in any application programming language. The virtual machine is linked with executable code generated from two other software modules which interpret instructions defining the input conditions to the application program and the configuration of the output display. Of course, the proposed facilities do not solve the problem of the complete verification of the timing behavior of an application program. However, when they are compared with the facilities offered by various commercially available aids, to our opinion they do significantly reduce the time taken to test the execution of a PLC program under a large number of possible input conditions, on different architectures and interpret the results. A scaled down experimental implementation of facilities for a specific PLC model is used to demonstrate the feasibility of the proposed concepts. The operation of the experimental set-up has been validated with data taken from the execution of sample program on a specific PLC.

1、Principles of PLC Operation.

The Programmable Logic Controller is a special purpose digital computer designed to control machine or process operations by means of a stored program and feedback from input/output field devices. It is composed primarily of two basic sections: the Central Processing Unit (PLC) and an Input/Output(I/O) interface. The CPU encompasses all the necessary elements that form the intelligence of the system. It is further subdivided to the Processor, Memory and Power supply. The CPU accepts input data from various input field devices, executes the stored program from the memory, and sends appropriate commands to output field devices. The Input/Output system forms the interface by which the field devices are connected to the controller. Its purpose is to condition the various signals received from or sent to field devices. Through this system the CPU can sense and measure physical quantities regarding a machine or process, such as proximity, position, motion, level temperature, pressure, current and voltage. Based on the status sensed or values measured, the CPU, through this interface system, issues commands that control various devices such as valves, motors, pumps and alarms. The most common type of I/O interface is the discrete one. This interface connects field input or output devices, which provide input signals or receive command signals of the Boolean type.

Pushbuttons, limit switches and selector switches are some of the devices that provide incoming signals of this type,, whereas typical field devices that can be and position valves .The numerical I/O interface is another type of interface, provided in a PLC system. It can allow reading or writing a multi-bit digital or analog device. Multi-bit devices either generate or receive a group of bits which is the digital representation of a decimal number or an analogue quantity. This group of bits is handled as a unit by the CPU and can be in parallel form (BCD inputs or outputs) or in serial form (pulse inputs or outputs). Typical field devices providing multi-bit input to a PLC are thumbwheel switches, bar code readers and encoders ,whereas typical output devices are seven-segment and intelligent displays. The analogue field devices are the various sensors, motor

drives, and process instruments used to monitor arid control physical variables such as temperature, pressure, humidity, flow, etc. The devices which monitor physical variables send to the I/O interface analogue voltages and currents which are converted by the A/D converter of the interface to a multi-bit digital code. On the other hand, an analogue device used to control the value of a physical variable, receives from the interface an analogue voltage or current as a result of the digital to analogue conversion of data produced by the CPU.

The processor of the CPU performs all the mathematical operations, data handling and diagnostic routines by executing a collection , stored in the memory .This collection consists of supervisory programs ,that are permanently stored in the memory, and application programs . The supervisory programs, known as the executive, allow communication with the processor via a programming device or other peripheral memory management, monitoring of field devices, hardware fault diagnosis and execution of the application program written by the user. The memory organization and the way the application program is executed under the control of the executive are two features which distinguish a PLC from any other general purpose computer. In general, all PLC have memory allocated for executive programs, processor work area, data table and application program. The programmed instructions and any data that will be utilized by the processor to perform its control functions are stored in the Application Program Memory Area and Data Table Memory Area respectively. These two areas can be grouped into what is called application memory. Each controller has a maximum amount of application memory which is part of the total memory specified for the controller. The Data Table is functionally divided Into the Input Table, Internal Storage Area and Storage Registers Area. The Input Table is an array of bits that stores the status of the digital inputs which are connected to the I/O interface system.. The Output Table is an array of bits that control the status of the digital output devices, which are also connected. To the I/O system. The Internal Storage Bits Area is the memory area allocated for the

storage of the logic status of flags used by the application program. The Storage Registers Area is allocated for the storage of input registers, holding registers and output registers. The input registers are used to store numerical data received via digital of analogue input interfaces. The holding registers are used to store variable values that are generated by math, timer and counter instructions of a program. The output registers are used to provide storage for numerical or analogue values that control various output devices .

Each virtual machine program is built according to a general computer model applicable to any PLC architecture. This model maps the usual functions performed by a PLC to machine language functions of a simple hypothetical computer. This computer consists of:

(a) a Central Processing Unit (CPU)

(b) a Memory unit(MU) where the application program is stored and

(c) a number of Input and Output modules(I/O)

At system start up, the execution of the executive program is initiated. During this program execution, the processor reads all the inputs, stores their values in the Input Storage Area and runs the application program. The results which are generated during the execution of the application program are saved in the Output Storage Area. The process of reading the inputs, executing the program, and updating the outdate all the outputs of the PLC by suing the data of the Output Storage Area. The process of reading the inputs, executing the program, and updating the outputs is known as scan. The time required to make a single scan is called scan time. A figure for the worst case time is usually provided by the manufacturers. Generally, they specify the maximum scan-time that corresponds to every 1K of programmed memory, i.e. 10msecs/1k. However, since the common method of monitoring the inputs at the end of each scan is inadequate for reading certain extremely fast inputs, some PLC provide software instructions that allow the interruption of the continuous program scan in order to receive an input or update an output immediately. Also, a newer approach in

PLC design, which results to a significant reduction of the total processing time, is to divide the total system load to a number of tasks and assign their execution to several processors.

The stack register is so designed that the execution of an instruction which reads discrete inputs shifts right by one bit the contents of the stack register and pushes the current state of the O.R flip flop into stack register. When this operation is completed, the O.R flip flop is loaded with the state of a discrete input. Instructions which perform logic operations shift left the contents of the stack register. Then, the leftmost bit of the stack register is loaded into the O.R flip flop. Then, the arithmetic, calculations and numerical handling are using the data registers DROO and DRO1 for byte and word operations respectively.

可编程控制器应用的发展支持软件

1、序

可编程控制器（PLC）构成了工业的控制应用中被广泛地应用的即时计算器的一个类别。PLC应用的发展需要PLC总体的配置，包括输入与输出类型和位置的数目以及书写和应用程序的纠错。通常这些计算机在特定的图解式的结构化语言中被执行[Bekkum93,Hughes89,Jones83]同时程序的纠错在一个发展环境中被实行。大多数运行环境[SquareD90,Taylor90]允许程序用超过一种语言中写，在现行的PLC上通过步进或分段运行，同时检查输入和输出之间假设的逻辑关系在每个程序步或短短是否满意。除此之外，这些环境提供技术支持，例如提供输入\输出线路图和程序运行代码。目前的大规模生产环境由一个plc模拟器支持。这允许运行程序在没有PLC隋况下就可以得到纠错，也使得大量程序的运行显得更容易的和降低成本，通过确定程序在操作条件的所有临界之下操作正确，可以减少PLC基本系统中达不到要求危险条件。然而，最终的发展目标应该是确认作用的特性和程序在所有阶段运行准时，在这些阶段中那些相互间有联系的程序和块都可能进入。

在使用PLC系统过程中，我们可能连续使用模拟这个方法检查程序中逻辑的错误，同时判断在一个不完整的程序状态下它们的动作。此外，我们可以开发包含程序发展环境的新设备，使用这种新设备将会减少一个应用程序的程序规划和工程努力。它们可能是编设备，这种设备支持各种语言以IEC1131-3标准定义的应用程序。使用这些语言我们的程序规划效率将得到很大的改良，因为它们的每一个都可以用来编制合适的应用程序，而且整个的应用程序可以与单个可运行的程序相联系。其他能减少工程耗费的设备是指那些能作更容易和更有意义的程序输入环境的设备，这些设备将会允许我们在一个给定的时间期学习，在不用这些设备时，我们需学习很多模拟情况。此外，我们可以通过与计算机相连的模拟器组来扩展模拟范围，设备之间也可以通过模拟结果二组成更好的联系。这种设备在本文中，一个节结构和语言图形可用来表示一个PLC程序的输入情况，可能允许我们以我们认为合适的方式设定显示和驱动应用程序的模拟结果。

在本文中，一个图和语言结构可能用来解释输入PLC程序，PLC运行要求和模拟结果的输出情况。结构的核心是虚拟机器，它是一个模拟用应用程序写入特定PLC的程序运算的软件模组。虚拟机器可运行的编码相联系，这些编码来自两个解释应用程序输出显示装置的配置和输入条件的定义指令的其他软件模组。当然，计划用的设备并不解决应用程序的正时行为的完全证明的问题。然而当他们用商业效益与所提供的质量相比时，以及在不同的设备和相关的结果所出现的情况的测试时间。安培用

一个特定的PLC模型依比例选择设备的条件下实验，用来证明所设观念可行性。已建立实验的结果与从在特定的PLC上的样本程序的运行所得的数据一样有用。

PLC的工作原理

可编程控制器是一种特殊的数转计算机，它是通过来自输入/输出位装置的一个储存程序和反馈来控制及其或处理运算的。它有两个主要组成部分：中央处理单元（处理器）和输入、输出（I/O）模块。处理器包含所有智能系统所必须的部件，进一步细分为处理机，存储器和电源。处理器接受来自各种不同输入装置的数据，运行来自储存器的储存程序，并且输出正确的指令和输出装置。输入、输出系统通过与控制器相连接的位装置形成控制界面。他的目的是处理接受到的各种不同的讯号或把它输出到位置空间。通过这个处理器系统能够感应和测量机器的物理性能，例如接近，位置，运动，层次，温度，压力，电流和电压。给予检测到的状态或测量到的数值，处理器通过这一模块系统，发出各种不同的装置，如阀，电动机，泵和警报的控制指令。

当系统开始运行时，运行程序开始运行。在程序运行的过程中，处理机读取所有的输入，存储它们数值到输入存储区域中，同时运行应用程序。把运行应用程序期间产生的结果存储到输出存储区域中。当应用程序运行结束时，处理机使用输出储存区的数据更新PLC的所有输出。读输入，运行程序，而亲更新输出的程序的过程被扫描。对作一次扫描所需的时间叫做扫描周期。在极限条件下的扫描周期的数值通常是由制造业者提供，通常，他们以每1K程序存储容量的反应时间来叙述扫描时间，例如10ms/1k。然而，因为输入的通常方法在每个扫描结束的时候对阅读某些快速的输入是不充分的一些PLC系统提供允许连续的程序扫描中断的软件指令，这是为了能够快速接受输入或更新输出。同时，一种新的能够更大地减少全部处理时间的PLC设计方法，是把总系统负荷分成很多任务和把它们的运行分配到几个处理机。

所有的不连续的或数据输入，内部的标帜，内部的记录器和输出通过它们之间的位置联系在应用程序中相互作用。任何如此的位址可能是一个十进制数或一个在数据表区域中的一个文数符号。PLC系统山使用特征指令或用英语表示的特定程序语言。

以下是四个最通常的类型语言：

梯形线图

布尔体系的存储器

功能模块

模块的功能

通过控制器的尺寸和能力，一种或多种的语言可以被用。在PLC系统中出现的语言最典型的结合是有功能模块的梯形线图。两种语言组成这一

个结合由含继电器，定时器/计数器，算术，数据操作，数据转移，模拟和程序控制运算六个种类指令构成。线圈和接触器是梯形图指令的基本符号。

总的来说，一个梯形图由输入条件和在梯形图末端用线圈表示的输出指令。每个继电器或线圈代表着正在检测的或控制的信号的地址位。取消这些位置数对照着一个输入或输出位数据区。功能模块允许操作者使用梯形图的指令运行更复杂的功能，它们有如定时和计数，运算和数据操作，数据转移，模拟控制运算法则，定义的功能。模块的类型，在模块之内将会有以或较多的控制线和以或较多的数据规格。在图2中，用定时器的梯形图符号举例说明功能模块的特征。在输入端有信号输入事在模块开始定时。记录器X存设定的定时时间，记录器Y存从开始增加的时间。当积累的时间和预先设定的时间相等时，它的输出端为接通状态，梯形图的线圈由输出。

根据我们的想法，PLC程序发展设备需含一个编程器，拟器。编程器要允许用高级语言指令来编写。

给定时间内PLC输入的预期状态变化

PLC硬件的配置编译器和PLC模

结果显示装置的要求形式

PLC的应用程序

编译器的子集一定能够的将高举语言，如C语言，Pascal等的输出文件翻译成程序。二编译器的另外一个子集一定能够编译程序，将PLC应用程序语言写成一般的低级语言，如在一下提到CL，并且能被任何PLC模拟器所运行。

输入编译器将低级的PLC输入的状态变化指令转变为高级语言，如C 语言或Paseal语言。相反地，输出编译器将高级语言程序转化为以PLC 输出的图解式的表示法的指令。因为每种语言都可能用在PLC应用程序中，LANG.1编译器……LANG.N编程器，LANG.N编译器表示出来。用PLC语言编程器写PLC的应用程序，而用PLC编译器将它们转化为在PLC模拟器中运行的低级语言。称虚拟器的软件模组以及输出文件的输入、输出编译器相连接并且生成一个新的可运行的程序。这一个程序接受为输入PLC语言编译器的输出文件并且模拟应用程序的运行输入条件以及在给定的时间以内在定义输入编译器的输出文件。模拟结果以在输出编译器的文件中所定义的动画形式显示。

每个虚拟及其程序都以一般的计算机模型建造的，可以应用在任何的PLC结构。这一个模型把PLC的功能一个简单的虚拟计算机的及其语言相对应。这种计算机有以下结构组成：

中央处理器（CPU）

应用程序储存单元（删）