arquitectura de la comunicacion

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Merlin Gerin Modicon Square D Telemecanique WHAT YOU HAVE TO REMEMBER A monitoring and control system can be broken down into 3 main components: the physical inputs-outputs; the data processing tools; the monitoring and control panels, to interface with the operators. Two fundamentally opposite architecture approaches can be used: the “top-wise approach” or the “global approach”; the “bottom-wise approach” or the “building block approach”. The chosen architecture will be a compromise between costs and technical constraints relative to a global monitoring and control system performance objective. Monitoring and control system architecture date 10/97 - C•1•6 - revised 10/97 Process Data processing Man-machine interface

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Arquitectura de La Comunicacion

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  • n Merlin Gerin n Modicon n Square D n Telemecanique

    WHAT YOU HAVE TO REMEMBERA monitoring and control systemcan be broken down into 3 maincomponents:n the physical inputs-outputs;n the data processing tools;n the monitoring and control panels,to interface with the operators.

    Two fundamentally oppositearchitecture approaches can be used:n the top-wise approach or the global approach;n the bottom-wise approach or the building block approach.

    The chosen architecture will be a compromise between costs andtechnical constraints relative to a global monitoring and controlsystem performance objective.

    Monitoring and control system architecture

    date

    10/97

    - C16 -

    revised

    10/97

    Process

    Dataprocessing

    Man-machineinterface

  • THE 3 COMPONENTS OFA MONITORING ANDCONTROL SYSTEM

    The process system provides the main installation function such as for examplean assembly line, an electrical distribution system, a heating installation, etc. The monitoring and control system provides either local or remote monitoringand control of a process together with an automatic reaction capability(regulation, automatic control).The monitoring and control system enables the process to function betterby providing easier and more reliable operation and maintenance, by optimizing economic resources and by reducing the number of failures and their impact.

    A system is intended to perform a global function through the juxtapositionof several components. Alone these components are not sufficient, they mustbe arranged, meaning that the relations between them must be organized so that the system performs its given function.Example: the juxtaposition of circuit boards in a computer is not sufficient to make it function. It is also necessary to use a DOS to set up and managethe relations between them.In all monitoring and control systems, there are three main components:the inputs-outputs, the displays, and the controls.n the physical inputs-outputs which are in contact with the process system;n the display and control of the installation through the surveillance andcontrol screen panels and man-machine interfaces.

    The architecture of a monitoring and control system is thearrangement of the systems components so as to providethe global function.

    The process system and the monitoring and controlsystem are complementary in an installation.

    Monitoring and control system architecture

    page 2

    date

    10/97

    - C16 -

    revised

    10/97

    Man-machineinterface

    Inputs-outputs and local dataprocessingInputs-outputs

    Dataprocessing

  • FROM WIRED TO DIGITAL SOLUTIONS

    Monitoring and control system architecture

    page 3

    date

    10/97

    - C16 -

    revised

    10/97

    Processcontrol station Programmable logical controllersAutomatic control relays

    Monitoring and control systems have moved from cumbersome solutionsinvolving a lot of wiring and using automatic control relay switchboards to current solutions using digital and computer technology.The initial monitoring and control systems appeared in process industries,power stations and railroads. These systems were based on automatic control relaying cabinets withwired connections to the inputs-outputs and with wired connections to a displayand control wall board (mimic diagram).An initial development was the replacement of the automatic control relaysby PLCs (programmable logical controllers). These logical controllers werealways centralized in cabinets with wired connections to the inputs-outputs.

    Current technology enables:n wired connections to the inputs-outputs to be reduced or eliminated throughthe use of off-set input-output terminal boxes or communicating sensorstogether with systems to communicate with the processing equipment(example: Sepam, etc.); n certain system sub-assemblies to be made independent, by carrying outdata processing in the sensors themselves, as near as possible to the process(example: Sepam, etc.);n wired connections to the surveillance and control panel to be reduced or eliminated using computer monitors and communication systems(example: ES1000 software).

    Technological developments have had a dramatic impacton monitoring and control system architecture.

  • Monitoring and control system architecture

    page 4

    date

    10/97

    - C16 -

    revised

    10/97

    TWO OPPOSINGARCHITECTUREAPPROACHES

    The global approach involves defining and organizing the components of the monitoring and control system, based on the need to be satisfied. This approach offers the advantage of defining the ideal system for a customers needs. However, engineering design and development lead times are a lot longer.It is a utopian approach because it assumes a steady and consistent stateof the system components and complete system control (computers, networks,processing components, sensors, etc.). Upgrading will be possible but difficult.This approach is used within a contracting or large project framework(example: extra high voltage substation monitoring and control).

    The lego block approach is based on defining or using standardizedinterface connections between system components. These components canbe individually designed and for a particular need (an independent function).The system designer constructs the system using lego block components,adding the links needed to achieve the required system function.

    This approach offers the advantages of enabling quick response to component developments, of providing good system upgradability, and of being open-ended for the integration of third-party components(from various manufacturers).The engineering design and development lead time is greatly reduced and the solutions are tried and tested. This approach is typically that used with Isis 1000.

    The architecture of a monitoring and control system canbe designed according to two fundamentally oppositeapproaches:n a global, descending or proprietary approach;n a lego block, ascending and open-ended approach.

  • TWO TECHNOLOGICALFIELDS BECOMINGCLOSER

    COSTS

    TYPES OFCOMMUNICATIONNETWORKS

    In real terms, the system components appear to be divided into two categoriesbased on different technological fields:

    n the components physically connected to the process system (intelligentsensors, off-set inputs/outputs) performing local functions and based ondigital technology (hardware and soft).(example: metering units, protection units like Sepam, LV release mechanisms, etc.).

    n the centralized processing and display components performing global functionsand based on systems designers software technology.(example: PC computer, Windows operating system, Ethernet system, J-Bus).

    The growth of monitoring and control activities in the market is bringingthese different technologies closer together. Software tools in particular are becoming increasingly adapted to process users.(example: electricians, in the case of Isis 1000).

    Monitoring and control system architecture

    page 5

    date

    10/97

    - C16 -

    revised

    10/97

    Low cost communications systems (terrestrial networks) have limitedperformance levels (throughput) which make it necessary to use networkswitching components (batibus to J-Bus) either to increase the throughputto the PC (like a country road joining a freeway), or to solve problems ofgeographical distance.

    It is advisable to adapt communication network performance, and thereforecosts, to the actual requirements in order not to penalize the costs of acommunicating unit (example: Sepam).

    Optimizing the costs of hardware/communication components often leadsto the use of an architecture that transfers the critical processing features(e.g. short response time) closer to the input-output components using logicalcontrollers as near as possible to the process. Non-critical processing thentakes place in the computer used for the man-machine interface.

    System architecture depends on the compromise betweentechnical constraints and costs.

    To communicate between components, the standard inputs-outputs/logicalcontroller terrestrial networks used today are: ASI, Batibus, ElBus, CAN,Echelon with unit connection costs of a few tens of francs.

    High throughput networks commonly encountered are J-Bus and Profibus, as well as Ethernet, Modbus+. These networks are used to provideexchanges between system components (example: Sepam, ES1000).