集散控制系统_毕业论文_英文翻译
集散控制系统
一个典型的DCS控制系统
集散控制系统（Distributed control system）是以微处理器为基础的对生产过程进行集中监视、操作、管理和分散控制的集中分散控制系统，简称DCS系统。该系统将若干台微机分散应用于过程控制，全部信息通过通信网络由上位管理计算机监控，实现最优化控制，整个装置继承了常规仪表分散控制和计算机集中控制的优点，克服了常规仪表功能单一，人-机联系差以及单台微型计算机控制系统危险性高度集中的缺点，既实现了在管理、操作和显示三方面集中，又实现了在功能、负荷和危险性三方面的分散。DCS系统在现代化生产过程控制中起着重要的作用。
集散控制系统一般有以下四部分组成：
现场控制级
又称数据采集装置，主要是将过程非控变量进行数据采集和预处理，而且对实时数据进一步加工处理，供CRT操作站显示和打印，从而实现开环监视，并将采集到的数据传输到监控计算机。输出装置在有上位机的情况下，能以开关量或者模拟量信号的方式，向终端元件输出计算机控制命令。
这一个级别直接面对现场，跟现场过程相连。比如阀门、电机、各类传感器、变送器、执行机构等等。它们都是工业现场的基础设备、同样也是DCS的基础。在DCS系统中，这一级别的功能就是服从上位机发来的命令，同时向上位机反馈执行的情况。拿军队来举例的话，可以形容为最底层的士兵。它们只要能准确地服从命令，并且准确地向上级汇报情况即完成使命。至于它与上位机交流，就是通过模拟信号或者现场总线的数字信号。由于模拟信号在传递的过程或多或少存在一些失真或者受到干扰，所以目前流行的是通过现场总线来进行DCS信号的传递。
过程控制级
又称现场控制单元或基本控制器，是DCS系统中的核心部分。生产工艺的调节都是靠它来实现。比如阀门的开闭调节、顺序控制、连续控制等等。
上面说到现场控制级是“士兵”，那么给它发号施令的就是过程控制级了。它接受现场控制级传来的信号，按照工艺要求进行控制规律运算，然后将结果作为控制信号发给现场控制级的设备。所以，过程控制级要具备聪明的大脑，能将“士兵”反馈的军情进行分析，然后做出命令，以使“士兵”能打赢“战争”。
这个级别不是最高的，相当于军队里的“中尉”。它也一样必须将现场的情况反馈给更高级别的“上校”也就是下面讲的过程管理级。
过程管理级
DCS的人机接口装置，普遍配有高分辨率、大屏幕的色彩CRT、操作者键盘、打印机、大容量存储器等。操作员通过操作站选择各种操作和监视生产情况、这个级别是操作人员跟DCS交换信息的平台。是DCS的核心显示、操作跟管理装置。操作人员通过操作站来监视和控制生产过程，可以通过屏幕了解到生产运行情况，了解每个过程变量的数字跟状态。这一级别在军队中算是很高的“上校”了。它所掌握的“大权”可以根据需要随时进行手动自动切换、修改设定值，调整控制信号、操纵现场设备，以实现对生产过程的控制。
经营管理级
又称上位机，功能强、速度快、容量大。通过专门的通信接口与高速数据通路相连，综合监视系统各单元，管理全系统的所有信息。
这是全厂自动化系统的最高一层。只有大规模的集散控制系统才具备这一级。相当于军队中的“元帅”，他们所面向的使用者是厂长、经理、总工程师等行政管理或运行管理人员。
它的权限很大，可以监视各部门的运行情况，利用历史数据和实时数据预测可能发生的各种情况，从企业全局利益出发，帮助企业管理人员进行决策，帮助企业实现其计划目标。
DCS系统的产生背景
上世纪30年代40年代，工业自动化装置采用的是分散性控制系统。也就是所有设备都是独立运行，不联网控制。操作员根据生产需求进行计算后，将独立设备的特性调节到适合的程度，然后就开始工作。之后采用了气动、电动模拟仪表组成过程控制系统，实现了一定程度上的集中监视、操作和分散控制。较好的适应了工业生产的需求。可是，随着生产规模和复杂程度的不断提高，原有的控制系统显得滞后、笨重、繁冗、因为一台仪表只有一种控制规律，要实现某些复杂的控制就很困难。另外，控制仪表数量越来越多，用原来落后的仪表盘控制的话，控制盘越来越长，看得人眼睛都会花掉。最致命的就是老系统之间不便于实现通信，很难分级控制和综合管理。再一个就是它的系统变更比较麻烦，只有通过更换仪表和变更仪表连线才能实现。
第三次科技革命开始后，随着计算机技术的发展，人们开始尝试将计算机用于过程控制。试图利用计算机所具有的功能特点，来克服常规模拟仪表的局限性。但当时采用的办法是用一台计算机控制几十甚至上百个回路，这样做的危险性很高，如果计算机出现故障，会导致很严重的后果，这就是所谓的“危险集中”。若采用双机双工系统，虽可以提高系统的可靠性，但成本太高，如果工厂的生产规模不大，则经济性很差，用户难以接受。
直到上世纪70年代开始，随着计算机技术的日渐成熟，大规模集成电路及微处理器的诞生后，人们开始思考是否能将“危险分散”。就是原来靠一台大计算机完成的“艰巨”任务，能否用几十台微处理来完成？这样的话，即使某一处理器
坏了，也不至于会“牵一发而动全身”，从而使危险系数大大降低。答案是肯定的。至此DCS就诞生了。
进入九十年代以后，计算机技术突飞猛进，更多新的技术被应用到了DCS 之中。PLC是一种针对顺序逻辑控制发展起来的电子设备，它主要用于代替不灵活而且笨重的继电器逻辑。现场总线技术在进入九十年代中期以后发展十分迅猛，以至于有些人已做出预测：基于现场总线的FCS将取代DCS成为控制系统的主角。
集散控制系统的特点
DCS控制系统与常规模拟仪表及集中型计算机控制系统相比，具有很显著的特点。
1、系统构成灵活。从总体上看，DCS就是由各个工作站通过网络通信系统组网而成的。你可以把他现象成“因特网”。根据生产需求，你可以随时加入或者撤去工作站。系统组态很灵活。
2、操作管理便捷。DCS的人机反馈都是通过CRT跟键盘、鼠标等实现的。你可以想象成在因特网冲浪一样，你可以监视生产装置乃至整个工厂的运行情况。
3、控制功能丰富。原先用模拟控制回路实现的复杂运算，通过高精度的微处理器来实现。难道还有什么算法CPU实现不了的吗？！
4、信息资源共享。你可以把工作站想象成因特网上的各个网站，只要你在DCS系统中，并且限够大，你就能了解到你要的任何参数。
5、安装、调试方便。相比原先的模拟控制系统，那么多的飞线头，一大堆类似头发丝的电线。DCS系统算是很方便了。
DCS系统的硬件结构
DCS的硬件系统主要由集中操作管理装置、分散过程控制装置和通信接口设备等组成。通过通信网络将这些硬件设备连接起来，共同实现数据采集、分散控制和集中监视、操作及管理等功能。
现场控制站
现场控制站中的主要设备是现场控制单元。现场控制单元式DCS直接与生产过程进行信息交互的IO处理系统，它的主要任务是进行数据采集及处理，对被控对象实施闭环反馈控制、顺序控制和批量控制。用户可以根据不同的应用需求，选择配置不同的现场控制单元构成现场控制站。它可以是以面向连续生产的过程控制为主，辅以顺序逻辑控制，构成的一个可以实现多种复杂控制方案的现场控制站；也可以是以顺序控制、连锁控制功能为主的现场控制站；还可以是一个对大批量过程信号进行总体信息采集的现场控制站。
现场控制站是一个可以独立运行的计算机检测控制系统。由于它是专为过程检测、控制而设计的通用型设备，所以其机柜、电源、输入输出通道和控制计算
机等，与一般的计算机系统有所不同。
A typical DCS control system
DCS (Distributed control system) is a microprocessor-based centralized onitoring of the production process, operation, management, centralized and decentralized control of distributed control system, called DCS. The system will be used in a number of units distributed process control computer, all information through the communication network by the host management computer monitor, to achieve optimal control, the device inherits the conventional instrument distributed control and the advantages of computer control to overcome the normal function of a single instrument, Human - Machine Contact poor and the single risk of micro-computer control system of a high concentration of defects, both achieved in the management, operation and display of three concentrate, but also realized in functionality, load and risk of spread in three areas. DCS system in the modern production process control plays an important role.
Distributed control systems typically have the following four components:
Field control level
known as data acquisition devices, mainly the non-control variables during data acquisition and preprocessing, and further processing of real-time data for the CRT display and print operation station, in order to achieve open-loop monitoring, and collected data to monitoring computer. Output device in a PC case, or can switch analog signals the way the computer output to the terminal device control commands. This is one level directly to the scene, the process is connected with the site. Such as valves, motors, sensors, transmitters, actuators and so on. They are the basis for industrial field device, it is also the basis of DCS. In the DCS system, this level of function is to obey the commands sent by the host computer, while upward-bit machine feedback implemented. Take for example the armed forces to the case, can be described as the bottom of the soldiers. They just follow orders accurately and precisely report the situation to higher authorities to complete the mission. As for its exchange with the host computer is through the analog signal or fieldbus digital signal. Because analog signals in the transmission process, there are some more or less distortion or interference, so by popular fieldbus for DCS signals.
Process control level
Also known as the basic field control unit or controller, is the core part of the DCS
system. Relied on the regulation of production processes are achieved. Such as regulating the opening and closing valves, sequence control, continuous control and so on.
Speaking of field control level is above the "soldiers", then it is in command of the process control level. It accepts signals coming from field control level, control law in accordance with the requirements of computing technology, and the results sent to the scene as a control signal level control device. Therefore, the process control level to have a smart brain, able to "soldiers" to analyze the feedback of the military, and then make an order to make the "soldiers" can win "war. " his level is not the highest, equivalent to the army's "lieutenant. " It must be the same site feedback to a higher level of "Colonel" is the following about the process management level.
Process management level
DCS man-machine interface device, generally with a high resolution, large screen color CRT, the operator keyboard, printer, mass storage and so on. Select the operator station through the operation of various operating and monitoring production, This level is the operator with the DCS platform for exchange of information. DCS's core is shown operating with the management device. Operator through the operator station to monitor and control the production process, production can be learned through the operation of the screen to see the number of process variables with each state. This level be high in the armed forces, "Colonel " was. Its possession of "power" as needed to manually switch automatically at any time, modify the settings, adjust the control signals, control field devices to achieve the control of the production process.
Management level
Also known as the host computer, features, speed, large capacity. Through dedicated communication interface and high-speed data path connected, integrated surveillance system unit, and managing all system information.
This is the highest whole plant floor automation systems. Only large-scale distributed control system is qualified for this level. The military equivalent of the "Marshal", they are for the user is a director, manager, chief engineer and other administrative or operational management personnel.
It's a great privilege, you can monitor the operation of various departments, the use of historical data and real-time data to predict the various situations that may occur from
the overall interests of business to help business executives make decisions to help companies achieve their program objectives.
DCS system background
40's 30's last century, industrial automation equipment is used in dispersion control system. All equipment is run independently, not networked control. Operator calculated based on production requirements, will be independent of device characteristics to the appropriate level of regulation, and then began to work. After using a pneumatic, electric analog instrument into the process control system, a certain degree of centralized monitoring, operation and decentralized control. Better adapted to the needs of industrial production. However, with the production scale and complexity of the continuous improvement of the existing control system appears to lag, heavy, cumbersome, because a meter is only one control law to achieve some of the complex control is difficult. In addition, an increasing number of control instruments, using the original control of the instrument panel behind the words, the control panel and longer, to see people's eyes will be spent. The most deadly is the old systems are not easy to implement communication, control and integrated management of difficult classification. Another is that it is too much trouble to change the system only changes through the replacement of meters and meter connections can be achieved.
After the beginning of the third technological revolution, with the development of computer technology, people began to try to computers for process control. Have tried to use the computer features, to overcome the limitations of conventional analog gauges. But then the approach is to use a computer control dozens or even hundreds of loops, a high risk of doing so, if the computer fails, will lead to very serious consequences, and this is the so-called "dangerous concentration." The use of a dual-duplex system, although you can improve system reliability, but the cost is too high, if the factory's production is small, then the economy is poor, the user is difficult to accept.
Until the last century, 70 years, with increasingly sophisticated computer technology, the birth of large scale integrated circuits and microprocessors, people can start thinking about whether the "dangerous spread." NTU is the original by a computer to complete the "arduous" task, can use dozens of micro-processing to complete? In this case, even if a processor is broken, that does not will "affect the situation as a whole", so that greatly reduced the risk coefficient. The answer is yes. Thus was born the DCS. Into the next decade, computer technology advances, more new technology is being
applied to the DCS. PLC is a sequential logic control developed for electronic equipment, which is used instead of inflexible and cumbersome relay logic. Fieldbus Technology in entering developed very rapidly since the mid nineties that some people have to predict: FCS based on field bus control system will replace the DCS as the protagonist.
The characteristics of distributed control system
DCS control system with conventional analog gauges and centralized computer control system, compared with a very significant features.
1, the system constitutes a flexible. Overall, DCS is the workstations through the network by the network communications system formed. You can put him into the phenomenon of "Internet. " Based on production needs, you can join at any time or removed workstations. System configuration is very flexible.
2, operation and management easy. DCS through human-machine feedback CRT with keyboard, mouse, etc. to achieve. You can imagine the same as surfing the Internet, you can monitor the production device and the whole plant operation.
3, the control feature-rich. The original analog control loop with the complex operations realized by the microprocessor to achieve high accuracy. Is there any method to achieve CPU can not it? !
4, information resource sharing. You can imagine the station each site on the Internet, as long as you are in the DCS system, and permission is large enough, you can understand that any parameters you want.
5, installation and debugging. Compared to the original analog control system, so many flying thread, a lot of hair like wires. DCS system be very convenient.
DCS system hardware structure
DCS hardware system mainly from centralized operations management device, distributed process control devices and communications interface devices and other components. Through the communication network will connect these hardware devices, and common data acquisition, distributed control and centralized monitoring, operation and management.
Field control station
The main equipment in the field control station is the site control unit. DCS-site control unit type of information directly with the production process IO interactive processing system, its main task is to carry out data acquisition and processing, the implementation of the controlled object closed-loop feedback control, sequence
control and batch control. Users according to different application requirements, choose to configure a different site constitutes a site controller control unit. It is a process for continuous production control, supplemented by logic control in order to form a complex control scheme can achieve a variety of field control station; also be based on sequential control, field-based chain control control Station; also can be a signal of large quantities of the overall process of information collection on-site control station.
Site controller is a computer that can run independently of the detection and control system. Because it is designed for process measurement and control equipment designed for general-purpose, so its enclosure, power supply, input and output channels and control of computers, computer systems in general be different.