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    FC-E - Design of Industrial Automation Functional Specifications for PLCs, DCSs and SCADA Systems

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    This manual will be useful to both specifiers and implementers providing a theoretical grounding for preparing a control system functional specification for implementation on Industrial control systems consisting of PLC (Programmable Logic Controllers), HMI (Human Machine Interfaces / SCADA devices) or DCS (Distributed Control Systems).

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    Table of Contents

    Design of Industrial Automation Functional Specifications for PLCs, DCSs and SCADA Systems - Function Design Specifications (FDS)

    1         Functional Design Specifications (FDS)

    In this chapter a brief overview of control system FDS is given. The important industrial terms and naming conventions are discussed and the standards are highlighted.

    Learning objectives

    You will learn about:

    • Overview of control system FDS
    • Essential industry terms and abbreviations used in the FDS
    • Naming conventions and standards 
    • Control philosophy needed in guiding the FDS

    1.1      Overview of control system FDS

    Any Supervisory Control and Data Acquisition (SCADA) project will be successful if, and only if, the creating, understanding and execution of the functional specifications are executed perfectly. These technical specifications are important in the overall development and designing of control systems which contain the technical details that lead to the success of the project. These functions are as important as that of the mechanical sections.

    For example, consider piping. The complete description of the valves, pumps, chillers, piping specialties and other components used to construct the piping system are given in piping specifications. Designers will not submit a project without this important information for the piping system. In general, this kind of thorough information is not included for control systems. The lack of proper technical specifications for control systems may lead to difficulty in meeting the project’s design objectives. The design process is said to be successful if it contains descriptions of maintenance, operation and commissioning requirements. This leads to efficient building, and ensures the operation runs smoothly.

    A functional specification defines what the system should do and what functions and facilities are to be provided. It provides a list of design objectives for the system.

    A standard specification of the project should consider what is generally available in the market and what can reasonably be called upon for options. It is of no use to specify aspects which suppliers cannot provide at a reasonable cost and within a sensible time frame. The aim is to match what the manufacturer can offer, within their standard range of equipment. An efficient approach, by the purchaser, is to select standard equipment which is suitable for the manufacturer and then design the power system around the equipment to be purchased. In general, this approach will reduce the amount of time needed to design the power system.

    Functional aspects of the specification should be considered carefully. The function of basic equipment such as generators, motors and switchgear will be understood easily. But, in order to gain an understanding of what is required, it is essential to pay attention to the design and performance details. Functionality implies a more interrelated type of existence, as is the case with systems of equipment rather than individual items of equipment.

    Functional specifications in the area of process control systems cover the following:

    • SCADA systems
    • Power management control system
    • System computer
    • Measuring devices
    • Controller set points
    • Switchgear
    • Rotating machines.

    The entire system should be defined functionally and all the elements should be compatible from the conceptual stage of the specification.

    Control System Engineers analyze the following, to develop the design and functional specifications of automation systems:

    • User requirements
    • Procedures
    • Design process
    • Mechanical equipment
    • Problems to identify the system components.

    The automation system helps the equipment to function in a required manner. The interface between the hardware and software development, for the automation system, is the responsibility of Control System Engineers.

    A FDS is the most important stage in the design of any control system. It provides details of the solution to be implemented, to meet user requirements. It should be accepted by the user and should form the basis of the design for both hardware and software. An excellent FDS clearly specifies the following which are associated with the system:

    • Functions
    • Operator interactions control

    Therefore, before the system is developed, the user must confirm whether the proposed solution fully meets the specified requirements or not. A FDS is considered as the basis for the design of the system. It is used during testing to verify and validate the system, to ensure whether all the required functions are present and that they operate correctly.

    A FDS has all the information associated with the control system including:

    • Details of how each area of the plant operates under automatic control (control philosophy)
    • Details of the SCADA system i.e. screen layouts, navigation charts, alarm handling, trending and reporting
    • Details of the Network architecture
    • Details of any local operator interfaces.

     

    Figure 1.1

    Control system design

    The FDS should cover:

    • Control Modules such as PID Loops, indicators etc
    • HMI Graphic displays
    • Equipment Basic Control
    • Phase Logic
    • Operations
    • Unit Procedures
    • SCADA Recipes
    • The Inputs and Outputs of the systems with cards and channels assigned to them.

    1.1.1    Benefits of using a FDS

    There are numerous benefits provided by a complete and coherent FDS which include time savings of approximately 50% of total time and a saving of resources and money of approximately 25%. These benefits are achieved only after everyone is involved in designing, developing, testing, approving of an application, signing the document containing an ordered list of all design and functional requirements.

    By using a FDS (Functional Design Specification):

    • The manufacturer knows exactly what to develop & deliver
    • The system integrators know exactly what they are working with
    • Quality Assurance knows exactly what to test
    • The client knows exactly what they will be getting.

    1.2       Essential industry terms and abbreviations used in the FDS

    Technical terms and abbreviations are easily understood by professionals in one field whereas they may be confusing to others from another field, and may be misunderstood. Therefore, it is necessary to understand the abbreviations and some of the terms that are used in the text and elsewhere in the industry.

    The following are the essential industry terms and relevant abbreviations used in functional design specifications:

    Table 1.2

    Industrial terms and their abbreviations

    Industry terms

    Abbreviations

    AGC

    Automatic Generation Control

    API

    Application Programming Interface

    CORBA

    Common Object Request Broker Architecture

    C & I

    Control and Instrumentation

    CPU

    Central Processing Unit

    CRC16

    16-bit Cyclic Redundancy Check

    CSMA/CD

    Carrier Sense Multiple Access/Collision Detection

    CT

    Current Transformer

    DC

    Direct Current

    DCS

    Distributed Control System

    DMS

    Distributed Management System

    DNP

    Distributed Network Protocol

    DOD

    Department of Defense

    DOE

    Department of Energy

    DISCO

    Distribution Company

    DNP/DNP3

    Distributed Network Protocol, version 3.0

    DPI

    Double-Point Information

    EMS

    Energy Management System

    EMC

    Electromagnetic Compatibility

    EMI

    Electromagnetic Interference

    EPROM

    Erasable Programmable Read-Only Memory

    FTP

    File Transfer Protocol

    FDS

    Functional Design Specification

    FS

    Functional Specification

    FAT

    Factory Acceptance test

    FMEA

    Failure Modes and Effect Analysis

    FPGA

    Field Programmable Gate Array

    GUI

    Graphical User Interface

    GAMP

    Good Automated Manufacturing Practice

    GAL

    Generic Array Logic

    GENCO

    Generation Company

    GPR

    Ground Potential Rise

    HMI

    Human Machine Interface

    HDS

    Hardware Design Specifications

    I/O

    Input/Output

    IED

    Intelligent Electronic Devices

    ICCP

    Intercontrol Centre Communications Protocol

    IEEE

    Institute of Electrical and Electronics Engineers

    INEEL

    Idaho National Engineering and Environmental Laboratory

    ISO

    Independent System Operator or International Organization for Standardization

    IRIG-B

    Inter Range Instrumentation Group format B

    ISA

    Instrumentation Systems and Automation Society

    IT

    Information Technology

    ITU

    International Telecommunication Union

    LCD

    Liquid Crystal Display

    LED

    Light Emitting Diode

    LAN

    Local Area Network

    MMI

    Man Machine Interface

    MTBF

    Mean Time Between Failure

    MTTR

    Mean Time To Repair

    NIM

    Network Interface Module

    NISAC

    National Infrastructure Simulation and Analysis Centre

    NRC

    Nuclear Regulatory Commission

    NTP

    Network Time Protocol

    OASIS

    Open Access Same - Time Information System

    ODBC

    Open Database Connectivity

    PID

    Proportional, Integral and derivative controller

    POSIX

    Portable Operating System Interface

    PLC

    Programmable logic Controller

    P & ID

    Process & Instrumentation Diagram

    PSU

    Power Supply Unit

    PCS

    Process Control System

    PROM

    Programmable Read-Only Memory

    PSTN

    Public Switched Telephone Network

    PT

    Potential Transformer

    RTU

    Remote Terminal Unit

    REA

    Rural Electric Association

    RTO

    Regional Transmission Organization

    RAID

    Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks

    ROM

    Read-Only Memory

    SCADA

    Supervisory Control and Data Acquisition

    SAT

    Site acceptance test

    SOE

    Sequence of Events

    SNTP

    Simple Network Time Protocol

    SPI

    Single-Point Information

    SQL

    Structured Query Language

    SWC

    Surge Withstand Capability

    TASE

    Telecontrol Application Service Element

    TRANSCO

    Transmission Company

    TCP/IP

    Transmission Control Protocol/Internet Protocol

    T&D

    Transmission and Distribution

    UHF

    Ultra High Frequency

    UPS

    Uninterruptible Power Supply

    UTP

    Unshielded Twisted Pair

    VDU

    Video Display Unit

    WAN

    Wide Area Network

    1.3       Naming conventions and standards

    The General Design Principles (GDP) defines the number of conventions to be used.

    For example, consider the standard color scheme. In one division of the plant a device is colored red, meaning 'stopped', and in another part of the plant the same type of motor is colored red, meaning 'dangerous condition'. This may lead to disaster, but by following naming conventions, such risks will be reduced.

    Adopting a standardized reliable naming convention for devices controlled by the system, will be favorable for scalable and maintainable systems in the long run. In some cases, the naming conventions used are forced on the system by external influences. Therefore, they should be properly documented in the GDP.

    Examples of tagging and naming conventions are:

    • Graphic symbols
    • Instrumentation naming.

    Naming conventions and standards are explained in further detail in the next chapter.

    1.4       Control philosophy in guiding FDS

    Philosophy is a belief or a system of beliefs, accepted as authoritative by some groups. Control philosophy is a guideline for a FDS which describes the basic dos and don'ts and requirements of a FDS from the point of view of the end user. It should describe the following:

    • Level of process automation
    • Information handling needs
    • Operational requirements
    • Requirement of flexibility
    • Level of control intervention
    • Operators work and skill
    • Management skills for both organization and data communication
    • Level of management needed
    • Extent of manual control required
    • Extent of the physical area the system is covering
    • Type of communication system
    • Level of security needed for communication
    • Type of control processing.

    1.5        Summary

    This chapter summarizes the following:

    • A functional specification defines what the system should do and what functions and facilities are to be provided.
    • An excellent FDS clearly specifies the following associated with the system:
    • Functions
    • Operator interactions control
    • There are numerous benefits provided by a complete and coherent FDS, which include time savings of approximately 50% of total time and a saving of resources and money of approximately 25%.
    • It is necessary to understand the abbreviations and some of the terms that are used in the text and elsewhere in the industry.
    • Technical terms and abbreviations are easily understood by professionals in one field whereas it may be confusing to others and may be misunderstood
    • Adopting a standardized reliable naming convention for devices, controlled by the system, will be favorable for scalable and maintainable systems in the long run
    • Control philosophy is a guideline for a FDS, which describes the basic dos and don'ts and basic requirements of a FDS, from the point of view of the end user.

     

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