Distributed Computer Control Systems Research Articles

Automation of a Petroleum Refinery Wastewater Treatment Plant:A Case Study

Abstract Historically, automation was not considered for wastewater treatment plants because it did not significantly affect operating costs, and manual plant operation was considered acceptable. Despite past practices, the BP Oil Refinery at Marcus Hook, Pennsylvania set a new standard when they began upgrading their wastewater facility in 1985. By automating the plant, they ensured safe, reliable operation with minimum labor requirements, process optimization, and long-term reductions in operating costs. Major design features included: a distributed computer control system with monitoring and supervisory capabilities; high-quality control system instruments; control system components; and redundancy and backup to support operation if a component or power failure occurs. In addition, design control philosophies remained consistent from predesign to startup. This advanced wastewater treatment plant can serve as a model for automation of future industrial treatment facilities.

A Distributed Computer Control System of a Chemical Production Complex—Implementation Aspects, Engineering Methodology, and Practical Experience

The paper presents the architecture, functional capabilities, capacity characteristics, information flows, hard- and software solutions as well as design and engineering procedures on the different stages of the practical realization of the Integrated Computer Control System /ICCS/. The first level of the described ICCS is realised on the basis of Honeywell TDC-2000 Basis System with Basis and Multifunctional control lers. The Second /Level 2/ level is realised by TDC-2000 Total and PMX systems, the third- by Honeywell H-4500 and Hungarian ES-1011 computers and the higher functional level- by Soviet-Bulgarian ES-1022 central computer, It is also shown that different digital technologies can operate in an efficient way such that ICCS of the chemical production complex can be realised and important economic, technical and social benefits can be obtained.

Estimating the Feasibility of Communication Network in a Distributed Computer Control System

Distributed computer control systems (DCCS) provide a rather well defined communication environment. In this paper a possibility to estimate the feasibility of a given network for the particular application making use of an automatized design environment is considered. The network load and its behaviour in time is obtained from the formal specification of the DCCS. The feasibility estimation task is stated and a method for its solution is described. The algorithms for solving the feasibility estimation problem are usable in many phases of the distributed computer control system development

Recent Trends in Distributed Process Control Computers

Advances in computer based control systems have closely followed developments in computer technology. The advent of powerful 32 bit microcomputers, high resolution colour graphic displays and local area networks in computer technology will lead to implementation of sophisticated control algorithms for controlling individual control loops, user friendly display systems, menu driven software selection and integration of distributed computer control in global hierarchical plant control. Distributed computer control systems of the future will be easy to specify, design, install and use. Systems will be designed with better reliability and safety. Developments in expert systems will lead to some heuristic rule based control algorithms.

Data acquisition and control using ETHERNET

We have developed a distributed computer control system to monitor and control a linear accelerator. This system consists of two PDP-11s and eight LSI 11 23 s linked together with ETHERNET. The higher level systems (control consoles, etc.) use the RSX11M operating system, whereas the data acquisition and control is performed using the RSX11S operating system downline loaded from a central host computer. Locally written ETHERNET drivers are used to reduce the CPU overhead and therefore improve system response. The ETHERNET system permits remote file access by means of operator or program interaction, as well as supporting downline system loading. Control-system functions supported are supervisory control, closed-loop control, data monitoring, and data recording.

A Language and a Calculus for Distributed Computer Control Systems Description and Analysis

In the paper a language and a calculus based on Gentzen's Sequenzen method is suggested. The application side of the language is obtained as a further abstraction of the Quirk's model, consequently it takes into account timing restrictions on execution and communication of functional tasks of the distributed control system. The paper concludes with an example of deducing a deadlock condition from the description of distributed control system.

Flexible communication structure for distributed embedded systems

The paper describes an extensible communication system for Conic, an architecture for distributed embedded systems. Conic provides a high level programming language with interprocess communication primitives suited to both local and remote communication. These primitives are sufficiently powerful to be used for applications programming yet simple and efficient enough for programming system software. The communication system which supports these primitives is itself implemented in the Conic language. It provides a very simple datagram-like service, over interconnected local area networks. The configuration flexibility of Conic is exploited to allow extension of the basic communication system to give additional services such as virtual circuit or routing. The paper also relates the Conic communication system to the ISO Reference Model and indicates some of the problems of using the model. An earlier version of this paper was presented at the 5th IFAC Workshop on Distributed Computer Control Systems, Sabi Sabi, South Africa, May 1983.

Development of a n alternative control scheme fo r a naval propulsion plant

The control of a gas-turbine powered controllable-pitch propeller ship propulsion plant, of the type found in modern warships is considered. The existing control philosophy is examined, and the development of a gain-scheduled multivariable control system, suitable for implementation in a distributed computer control system, is presented. Some typical non-linear simulation results are presented and a number of potential problem areas of the proposed control system are outlined.

Using Real-Time to Achieve Co-Ordination in Distributed Computer Control Systems

Although a high-speed Local Area Network environment offers great potential for building reliable and flexible real-time distributed computer control systems (DCCS), such communication systems possess undesirable delay and message loss characteristics. In order to overcome these problems, the unique requirements implied by real-time in DCCS are examined and a new protocol based on the inclusion of a validity time as an atomic attribute of every message is proposed as a solution.

Integrated Simulation System for Design and Evaluation of Distributed Computer Control Systems

This paper presents an integrated simulation system to be used for the design and evaluation of distributed computer control systems. The simulation system is comprised of Communication Performance Evaluation Module, System Reliability Evaluation Module and Control Performance Evaluation Module. Different from conventional all-software approaches, dedicated hardware facilities such as a parallel multimicroprocessor system for real-time simulation of controlled system dynamics and a mimic communication system are used advantageously to achieve best overall economy of simulation in conjunction with software simulation modules. The features of the proposed of simulation system as applied to several distributed computer control systems with different system architectures are described.

A software architecture for distributed computer control systems

Distributed computer control systems have a number of potential advantages over centralized systems, especially where the application is itself physically distributed. A computer station can be placed close to the plant being controlled, and a communications network used to enable the stations to communicate to coordinate their actions. However, the software must be carefully designed to exploit the potential advantages of distribution. This paper describes the software architecture of CONIC, a system to support distributed computer control applications. This architecture emphasizes the distinction between the writing of individual software components and the construction and configuration of a system from a set of components. A modular structure is used to separate programming from configuration. Typed entry and exit ports are used to clearly define module interfaces. Ports, analagous to the plugs and sockets of hardware components, permit modules to be interconnected in different ways. On-line modification and extension of the system is supported by permitting the dynamic creation and interconnection of modules. Message passing primitives are provided to permit modules to coordinate and synchronize control actions.

A Memory Intensive Functional Architecture for Distributed Computer Control Systems

A memory-intensive functional architecture for distributed data-acquisition, monitoring, and control systems with large numbers of nodes has been conceptually developed and applied in several large-scale and some smaller systems. This discussion concentrates on (a) the basic architecture; (b) recent expansions of the architecture which now become feasible in view of the rapidly developing component technologies in microprocessors and functional large-scale integration circuits; (c) implementation of some key hardware and software structures and one system implementation which is a system for performing control and data acquisition of a neutron spectrometer at the Brookhaven High Flux Beam Reactor. The spectrometer is equipped with a large-area position-sensitive neutron detector.

Software design methods for distributed computer control

The design of software for distributed computer control systems (DCCS) is a field which has benefited greatly from certain software engineering concepts and methodologies that are used in computer science. This paper aims at reviewing some of the more commonly used software tools that help the control engineer to simplify software design for distributed control. The paper describes the current situation, and the tools which are now available.

Data Consistency in Sensor-Based Distributed Computer Control Systems

The possibility of holding the data collected from the plant in a functionally distributed data base is one of the interesting possibilities offered by distributed computer control systems. In the paper, the concept of state information is clarified and a new definition is given for the validity and consistency of state values in real-time sensor-based systems. A real-time distributed algorithm for establishing a valid and consistent distributed representation of the data collected from sensors by periodic sampling is presented.

Experience with a High Order Programming Language on the Development of the Nova Distributed Control System

Interest in the impact of high order languages (HOL) on real time and process control applications development has intensified recently, due in part to the Ada language development effort sponsored by the U.S. Department of Defense. High order languages, such as Ada, incorporate state-of-the-art features in the areas of modularity, data abstraction, separate module compilation, strong type checking of data, multi-tasking, distributed processing and exception handling. The intent of such languages is to improve programmer productivity, software maintainability, and the effective management of software development in large real time systems.This paper explores the impact of an HOL on the development of the distributed computer control system for a large laser fusion facility called Nova. Nova utilizes fifty microcomputers and four VAX-11/780’s in its distributed process control computer system.Praxis, a high level real time computer language, was designed and implemented for Nova to support the control system development activity. Praxis is similar to Ada in its design goals, has many features comparable to those found in Ada, and has had operational compilers for over two years.The purpose of this paper is to assist readers who are beginning to evaluate the importance of HOL’s in small to medium scale process control applications. It includes a summary of the major design objectives and features of these HOL’s which is followed by a description of our experiences with Praxis. The article concludes with our preliminary expectations and concerns for the use of Ada within process control applications, based upon Praxis experience.

CONIC: an integrated approach to distributed computer control systems

Distributed computer control systems (DCCS) have a number of potential advantages over centralised systems, especially where the application is itself physically distributed. A computer station can be placed close to the plant being controlled, and a communications network used to enable the stations to communicate to co-ordinate their actions. However, the software must be carefully designed to exploit the potential advantages of distribution. In the paper, the CONIC architecture for DCCS is described, concentrating on the software structure but also briefly describing the physical architecture designed to support a CONIC system. The software structure emphasises the distinction between the writing of individual software components and the construction and configuration of a system from a set of components. A modular structure is used to separate programming from configuration. Typed entry and exit ports clearly define a module interface which, like the plugs and sockets of hardware components, permit modules to be interconnected in different ways. On-line modification and extension of the system is supported by permitting the dynamic creation and interconnection of modules. Message-passing primitives are provided to permit modules to co-ordinate and synchronise control actions.

Computer control of decentralized process systems

All processes, such as oil refineries, chemical plants, steel mills, etc. are distributed in the sense that the process equipment, measurement sensors and final control elements are distributed over a significant geographical area. Historically, process control systems have changed from the original, fully-distributed, manual systems, to centralized control rooms, to what are now called distributed computer control systems. This paper presents a board overview of process-computer systems from the point of view of the user, or process engineer. The major conclusions are that process computer systems are evolving from first-level process control functions to higher-level plant supervisory and management functions; that it is time to change from bottom-up development to top-down design; that process computer systems are becoming less of a separate specialty, and more of an inter-disciplinary area; and that there is a real need for an organized, international group of process and computer-oriented people to develop a high-level functional specification and statement of requirements for plant-wide process control and management systems. The design and implementation of such systems should be done by computer specialists, not process personnel. Interdisciplinary cooperation will lead to better process systems.

Development and Quantitative Evaluation of Distributed Sensor Base Management System

The sensor-base-management-system (abbr. SBMS) is a standard software package, designed to perform the control data aquisition and the control output data initiation, in place of application software. Furthermore, the distributed SBMS was newly developed to support distributed system architectures, upon success of the conventional SBMS. This distributed SBMS is assumed to be constituted on a distributed computer control system, where remote process input/output subsystems together with front-end-processors will be installed as local stations on the plant floor.In order to give the practical aspects of this distributed SBMS, the model system applied to a hot-strip-mill control system is outlined. The quantitative evaluation studies on this distributed SBMS, focussing the interests on data communication cost, data processing cost and system performance loss are done with reference to the above-mentioned model. The objectives of these studies are to give the system designers adequate suggestions on where is the balancing point between a distributed and a non-distributed architecture, what is the optimal number of the local stations, and hopefully more.

Standardization Work for Communication Among Distributed Computer Control Systems

The current position of some standardization groups working in local area communications are discussed and compared with the needs of Distributed Computer Control Systems in industry. The standards groups are International Electrotechnical Commission (IEC), International Standards Organization (ISO) and Institute of Electrical and Electronic Engineers (IEEE).The paper then introduces the following issues which may affect further evolution of the work on these standards:-(1)The need and direction for services and protocols in the higher levels.(2)The impact of fibre optics which favour a change from the passive "T bus" to a network of point-to-point links for communication.(3)The economic arguments for the application areas with numerically small markets to adopt subsets of the standards developed for large markets.

The Challenge of Standards for Plant Communication

Publisher Summary This chapter discusses the challenge of standards for plant communication. A distributed computer control system offers two important features for a user organization. The features include small, modular control units, which allow partitioning of a process into separate local areas, each with a dedicated local unit control system, and the multimaster communication systems used within local areas can also provide connection to other plant areas. The result is a complete plant wide integrated control structure. Some benefits from the small modular approach includes low initial cost to try out the control structure, faster payback when plants are commissioned in stages, paying for each stage when it is built, gives better cash flow. The benefits from multimaster communication across the complete plant includes a common message structure throughout the plant simplifies fault monitoring and reduces maintenance costs. All stations can readily obtain data from other stations. The system supports great control flexibility.